WO2020106461A2

WO2020106461A2 - Anti-mertk antibodies and methods of use thereof

Info

Publication number: WO2020106461A2
Application number: PCT/US2019/060223
Authority: WO
Inventors: Tibor Keler; Joel Goldstein; Diego ALVARADO; Richard W. GEDRICH; Laura Vitale; Tom O'NEILL; Andrea CROCKER; Michael B. Murphy
Original assignee: Celldex Therapeutics, Inc.
Priority date: 2018-11-08
Filing date: 2019-11-07
Publication date: 2020-05-28
Also published as: WO2020106461A3

Abstract

Provided herein are compositions, methods and uses involving antibodies that specifically bind to MerTK, a receptor tyrosine kinase, and modulate the expression and/or activity of MerTK. Also provided are uses and methods for managing, treating, or preventing disorders, such as cancer.

Description

ANTI-MERTK ANTIBODIES AND METHODS OF USE THEREOF

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Application No. 62/757,651, filed November 8, 2018, and U.S. Provisional Application No. 62/826,301, filed March 29, 2019, the entire contents of each of which is incorporated herein by reference in its entirety.

SEQUENCE LISTING

[0002] This application incorporates by reference a Sequence Listing submitted with this application as an ASCII text file, entitled 12638-160-228_SEQ_LISTING.txt created on

November 3, 2019 and having a size of 45,668 bytes.

1. FIELD

[0003] Provided herein are compositions, methods and uses involving antibodies that specifically bind to MerTK, a receptor tyrosine kinase, and modulate the expression and/or activity of MerTK for managing, treating, or preventing disorders, such as cancer.

2. BACKGROUND

[0004] MerTK, a transmembrane receptor, belongs to the TAM (Tyro3, Axl and MerTK) family of receptor tyrosine kinases. The extracellular domain of MerTK has two

immunoglobulin (Ig) and two fibronectin (FN) type III motifs (Graham et al. (2014) Nat Rev Cancer. ;14: 769-785; Rothlin et al. (2015) Annu Rev Immunol. ;33: 355-391; Lemke G. (2013) Cold Spring Harb. Perspect Biol. 5).

[0005] Two closely related ligands, Protein S (PROS1) and Growth arrest specific gene 6 (Gas6) bind and activate MerTK. Activation of PI3K and its downstream target, serine/threonine protein kinase Akt, is an important aspect of MerTK-dependent signal transduction. MerTK stimulation of the PI3K/Akt pathway in dendritic cells and macrophages leads to deactivation of NFKB, thus decreasing TNF-a production. Thus, MerTK plays an essential role in attenuation of proinflammatory cytokine responses.

[0006] The TAM family of receptor tyrosine kinases also display ectopic or overexpression in numerous cancers. In tumors, activation of TAM signaling cascades appears to promote an anti-inflammatory and immunosuppressive microenvironment, in turn driving tumor growth. Overexpression and activation of MerTK has been implicated in lymphoid leukemia, lymphoma, adenoma, melanoma, gastric, prostate and breast cancers. [0007] There is a need for therapies modulating MerTK to manage, treat or prevent conditions involving MerTK and/or abnormal MerTK signaling or abnormal MerTK expression.

3. SUMMARY

[0008] In one aspect, provided herein are antibodies, including antigen-binding fragments, which specifically bind to MerTK, for example, the extracellular domain (ECD) of MerTK. In one embodiment, antibodies and antigen binding fragments presented herein specifically bind the ECD of human MerTK. Also provided herein are polynucleotides and vectors comprising sequences encoding such antibodies, cells comprising such polynucleotides and vectors, and compositions, reagents and kits comprising such antibodies. In another aspect, provided herein are methods for modulating MerTK activity, e.g ., inhibiting MerTK activity, diagnostic methods and uses, and therapeutic methods and uses of such anti-MerTK antibodies.

[0009] In a particular embodiment, provided herein is an isolated antibody, or an antigen binding fragment thereof, which specifically binds to human MerTK, comprising: (i) a light chain variable region (VL) comprising SEQ ID NO: 2; and/or (ii) a heavy chain variable region (VEl) comprising SEQ ID NO: 1.

[0010] In another particular embodiment, provided here is an isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising: (i) a light chain variable region (VL) comprising SEQ ID NO: 2; and (ii) a heavy chain variable region (VET) comprising SEQ ID NO: 1.

[0011] In one embodiment, provided herein is antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises SEQ ID NO: 2 or sequences having at least 80%, 85%, 90%, 95% or 98% amino acid sequence identity to SEQ ID NO: 2.

[0012] In a certain embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises a VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3 that comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8, respectively, or conservative sequence modifications thereof. In a specific embodiment, the VL that comprises VL CDR1, VL CDR2, and VL CDR3 (that comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8,

respectively, or conservative sequence modifications thereof) comprises at least 80%, 85%, 90%. 95%, or 98% identity to SEQ ID NO: 2. [0013] In another certain embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises a VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3 that comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8, respectively. In a specific embodiment, the VL that comprises VL CDR1, VL CDR2, and VL CDR3 (that comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8, respectively) comprises at least 80%, 85%, 90%. 95%, or 98% identity to SEQ ID NO: 2.

[0014] In one embodiment with respect to an antibody described herein or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VH that comprises SEQ ID NO: 1 or sequences having at least 80%, 85%, 90%, 95% or 98% amino acid sequence identity to SEQ ID NO: 1.

[0015] In a certain embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VH that comprises a VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3 that comprise the amino acid sequences of SEQ ID NOS: 3, 4, and 5, respectively, or conservative sequence modifications thereof. In a specific embodiment, the VH that comprises VH CDR1 VH CDR2, and VH CDR3 (that comprise the amino acid sequences of SEQ ID NOS: 3, 4, and 5,

respectively, or conservative sequence modifications thereof) comprises at least 80%, 85%, 90%. 95%, or 98% identity to SEQ ID NO: 1 comprises at least 80%, 85, 90%, 95%, 98% amino acid sequence identity to SEQ ID NO: 1.

[0016] In a certain embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VH that comprises a VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3 that comprise the amino acid sequences of SEQ ID NOS: 3, 4, and 5, respectively, or conservative sequence modifications thereof. In a specific embodiment, the VH comprises at least 80% amino acid sequence identity to SEQ ID NO: 1, the VH comprises at least 85% amino acid sequence identity to SEQ ID NO: 1; the VH comprises at least 90% amino acid sequence identity to SEQ ID NO:

1; the VH comprises at least 95% amino acid sequence identity to SEQ ID NO: 1; or at least 98% amino acid sequence identity to SEQ ID NO: 1.

[0017] In another embodiment, provide herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises SEQ ID NO: 2 or sequences having at least 80%, 85%, 90%, 95% or 98% amino acid sequence identity to SEQ ID NO: 2, and a VH that comprises SEQ ID NO: 1 or sequences having at least 80%, 85%, 90%, 95% or 98% amino acid sequence identity to SEQ ID NO: 1.

[0018] In a particular embodiment, provided herein is an isolated antibody ( e.g ., monoclonal antibody), or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7 and 8, respectively or conservative sequence modifications thereof; and/or

(ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 3, 4 and 5 respectively or conservative sequence modifications thereof.

[0019] In one embodiment, presented herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8, respectively or sequences having at least 80% amino acid sequence identity thereto.

[0020] In a certain embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VH CDR1, VH CDR2, and VH CDR3 that comprises the amino acid sequences of SEQ ID NOS: 3, 4, and 5, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0021] In a particular embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7, and 8, respectively, or sequences having at least 80% amino acid sequence identity thereto, and the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 3, 4, and 5, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0022] In a particular embodiment, provided herein is an isolated antibody (e.g., monoclonal antibody), or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising: (i) a light chain variable region (VL) comprising VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 16, 17 and 18, respectively or conservative sequence modifications thereof; and/or

(ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 13, 14 and 15 respectively or conservative sequence modifications thereof.

[0023] In one embodiment provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises VL CDR1, VL CDR2, and VL CDR3 that comprise the amino acid sequences of SEQ ID NOS: 16, 17, and 18, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0024] In a certain embodiment provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 13, 14, and 15, respectively or sequences having at least 80% amino acid sequence identity thereto.

[0025] In a particular embodiment presented herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises a VL CDR1, VL CDR2, and VL CDR3 comprising the amino acid sequences of SEQ ID NOS: 16, 17, and 18, respectively, or sequences having at least 80% amino acid sequence identity thereto, and comprises a VH that comprises VH CDR1, VH CDR2, and VH CDR3 comprising the amino acid sequences of SEQ ID NOS: 13, 14, and 15, respectively or sequences having at least 80% amino acid sequence identity thereto.

[0026] In a particular embodiment, provided herein is an isolated antibody ( e.g ., monoclonal antibody), or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 22, 23 and 24, respectively or conservative sequence modifications thereof; and/or (ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 19, 20 and 21 respectively or conservative sequence modifications thereof.

[0027] In one embodiment provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprises a VL CDR1, VL CDR2, and VL CDR3 comprising the amino acid sequences of SEQ ID NOS: 22, 23, and 24, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0028] In a certain embodiment provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VH that comprises a VH CDR1, VH CDR2, and VH CDR3 comprising the amino acid sequences of SEQ ID NOS: 19, 20, and 21, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0029] In a particular embodiment provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, comprising a VL that comprise a VL CDR1, VL CDR2, and VL CDR3 comprising the amino acid sequences of SEQ ID NOS: 22, 23, and 24, respectively, or sequences having at least 80% amino acid sequence identity thereto, and comprise a VH that comprises a VH CDR1, VH CDR2, and VH CDR3 comprising the amino acid sequences of SEQ ID NOS: 19, 20, and 21, respectively, or sequences having at least 80% amino acid sequence identity thereto.

[0030] In one embodiment, provided herein is an antibody or an antigen binding fragment thereof that specifically binds to human MerTK, that comprises a VL CDR1, VL CDR2, and VL CDR3 present in one polypeptide, and a comprises a VH CDR1, VH CDR2, and VH CDR3 on a second polypeptide. In a specific embodiment, an antibody or antigen binding fragment described herein which specifically binds to human MerTK comprises a VL and a VH, wherein the VL and VH are present in the same polypeptide.

[0031] In another embodiment, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which specifically binds to Domain 2 (D2) of human MerTK. In a certain embodiment, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which binds to the same epitope of human MerTK as an antibody described herein or antigen binding fragment thereof. In another embodiment, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which competes for binding to human MerTK with an antibody described herein or antigen-binding fragment thereof. In another embodiment, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which binds to Domain 2 (D2) of human MerTK and inhibits binding of Gas6 to MerTK and/or inhibits MerTK phosphorylation. However, the antibodies and antigen-binding fragments described herein are not limited to antagonist antibodies or antigen-binding fragments. In yet another embodiment, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which binds to Domain 2 (D2) of human MerTK and does not inhibit binding of Gas6 to cell-surface MerTK, e.g., does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit phosphorylation of cell-surface MerTK, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%. As a non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, provided herein does not inhibit binding of Gas6 to MerTK expressed on cells (e.g, L cells or macrophages). In some embodiments, provided herein is an isolated antibody, or an antigen-binding fragment thereof that does not inhibit binding of Gas6 to MerTK expressed on fibroblasts, e.g . L cells. In some embodiments, an isolated antibody, or an antigen-binding fragment thereof that does not inhibit binding of Gas6 to MerTK on fibroblasts, e.g, L cells, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40%. In some embodiments, provided herein is an isolated antibody, or an antigen-binding fragment thereof that does not inhibit binding of Gas6 to MerTK expressed on L cells or macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40%. In another non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, provided herein does not inhibit

phosphorylation of MerTK in cells (e.g, macrophages) , e.g, does not inhibit such

phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%. In one embodiment the antibody acts substantially independently of MerTK kinase activity.

[0032] In one embodiment, an antibody or antigen binding fragment presented herein is a MerTK receptor antagonist.

[0033] In one embodiment, an antibody or antigen binding fragment described herein, which specifically binds to human MerTK, comprises a human heavy chain constant region. In a specific embodiment, an antibody or antigen-binding fragment described herein, which specifically binds to human MerTK, comprises a human heavy chain comprising a VH and a human heavy chain constant region.

[0034] In another embodiment, an antibody or antigen binding fragment described herein, which specifically binds to human MerTK, comprises a human light chain constant region. In a specific embodiment, an antibody or antigen-binding fragment described herein, which specifically binds to human MerTK, comprises a human light chain comprising a VL and a human light chain constant region.

[0035] In yet another embodiment, an antibody or antigen binding fragment described herein which specifically binds to human MerTK comprises a human heavy chain constant region and a human light chain constant region. In a specific embodiment, such an antibody or antigen binding fragment comprises a human heavy chain comprising a VH and a human heavy chain constant region and a human light chain comprising a VL and a human light chain constant region.

[0036] In a certain embodiment, an antibody or antigen binding fragment described herein, which specifically binds to human MerTK, is an IgGl antibody. In a specific embodiment, an antibody or antigen binding fragment described herein, which specifically binds to human MerTK, is a human IgGl antibody.

[0037] In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain constant region or a light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a heavy chain constant region and a light chain constant region. In certain embodiments, the antibody or antigen-binding fragment comprises a human heavy chain constant region or a human light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human heavy chain constant region and a human light chain constant region.

[0038] In certain embodiments, the antibody or antigen-binding fragment is an IgGl antibody or antigen-binding fragment. In certain embodiments, the antibody or antigen-binding fragment is an IgG2 antibody or antigen-binding fragment. In some embodiments, the antibody or antigen-binding fragment is a human IgGl antibody or antigen-binding fragment or a human IgG2 antibody or antigen-binding fragment. In some embodiments, the antibody or antigen binding fragment comprises a kappa light chain constant region or a lambda light chain constant region. In some embodiments, the antibody or antigen-binding fragment comprises a human kappa light chain constant region or a human lambda light chain constant region.

[0039] In certain embodiments, the antibody or antigen-binding fragment comprises the amino acid sequence of SEQ ID NO: 31 or the amino acid sequence of SEQ ID NO: 32. In some embodiments, the antibody or antigen-binding fragment comprises the amino acid sequence of SEQ ID NO: 31 and the amino acid sequence of SEQ ID NO: 32.

[0040] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises the amino acid sequence of SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, or SEQ ID NO: 36.

[0041] In some embodiments, the antibody or antigen-binding fragment disclosed herein comprises the amino acid sequence of SEQ ID NO: 31 and the amino acid sequence of SEQ ID NO: 32; the amino acid sequence of SEQ ID NO: 31 and the amino acid sequence of SEQ ID NO: 33; the amino acid sequence of SEQ ID NO: 36 and the amino acid sequence of SEQ ID NO: 34; or the amino acid sequence of SEQ ID NO: 36 and the amino acid sequence of SEQ ID NO: 35.

[0042] In a certain embodiment, an antibody or antigen binding fragment described herein which specifically binds to human MerTK comprises a human kappa light chain constant region or a human gamma heavy chain constant region.

[0043] In a certain embodiment, an isolated antibody described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a monoclonal antibody.

[0044] In a certain embodiment, an antibody ( e.g ., monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a human antibody.

[0045] In a certain embodiment, an antibody (e.g., monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a chimeric antibody.

[0046] In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a humanized antibody. [0047] In a certain embodiment, an isolated antibody ( e.g ., monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a single chain antibody.

[0048] In a certain embodiment, an isolated antibody (e.g., monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a multispecific, e.g, bispecific, antibody.

[0049] In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is a monovalent antibody.

[0050] In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is fused to a heterologous polypeptide.

[0051] In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is conjugated to an agent. In a particular embodiment, the agent is a toxin. In one embodiment, the toxin is abrin, ricin A, pseudomonas exotoxin, cholera toxin, or diphtheria toxin.

[0052] In some embodiments, an antibody, or an antigen-binding fragment thereof, that binds to human MerTK has a mutated IgG Fc domain which binds to Fc gamma receptors with a greater affinity than the corresponding native IgG Fc domain.

[0053] In certain embodiments, provided herein is a human or humanized monoclonal antibody, or an antigen-binding fragment thereof that binds to Domain 2 (D2) of human MerTK. As a non-limiting example, in some embodiments, an antigen-binding fragment thereof that binds to Domain 2 (D2) of human MerTK can exhibit one or more of the following properties: i) binds to human MerTK with an affinity constant (equilibrium dissociation constant) KD of lOnM or less, preferably InM or less or preferably 0.5nM or less as determined by bio-layer interferometry; ii) does not inhibit binding of Gas6 to MerTK in human macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in human macrophages, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40% ; iii) when tested in vitro increases IL-1RA secretion from human dendritic cells, PBMCs and/or macrophages by at least 100% as determined by ELISA when compared to isotype control; iv) when tested in vitro increases TNF-alpha secretion from human dendritic cells upon stimulation with LPS by at least 50% as determined by ELISA when compared to isotype control; v) when tested in vitro increases IL-6 secretion from human dendritic cells by at least 50% as determined by ELISA when compared to isotype control; and/or vi) when tested in vitro increases IL-8, MIP-la and MIP-Ib secretion from human dendritic cells by at least 100% as determined by ELISA when compared to isotype control.

[0054] In a certain embodiment, provided herein is a composition comprising a

therapeutically effective amount of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0055] In a certain embodiment, provided herein is a pharmaceutical composition comprising an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK and a pharmaceutically acceptable carrier.

[0056] In a certain embodiment, provided herein is a polynucleotide comprising nucleotide sequences encoding a VH, a VL, or both a VL and a VH, of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0057] In a certain embodiment, provided herein is a polynucleotide comprising nucleotide sequences encoding a heavy chain, a light chain, or both heavy chain and a light chain of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0058] In a certain embodiment, provided herein is a population of polynucleotides comprising (i) a first polynucleotide comprising nucleotide sequences encoding a VH or a heavy chain of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK, and (ii) a second polypeptide comprising nucleotide sequences encoding a VL or a light chain of the antibody.

[0059] In a certain embodiment, provided herein is a vector comprising a polynucleotide described herein comprising nucleotide sequences encoding a VH, or a VL, or a VH and VL of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0060] In a certain embodiment, provided herein is a vector comprising a polynucleotide described herein comprising nucleotide sequences encoding a heavy chain, a light chain, or both heavy chain and a light chain of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0061] In a certain embodiment, provided herein is a population of vectors comprising (i) a first vector comprising nucleotide sequences encoding a VH or a heavy chain of an anti-MerTK antibody or antigen-binding fragment described herein, and (ii) a second vector comprising nucleotide sequences encoding a VL or a light chain of an anti-MerTK antibody or antigen binding fragment described herein.

[0062] In a certain embodiment, provided herein is an isolated cell comprising a

polynucleotide comprising nucleotide sequences encoding a VH, a VL, or both a VH and a VL of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0063] In a certain embodiment, provided herein is an isolated cell comprising a

polynucleotide comprising nucleotide sequences encoding a heavy chain, a light chain, or both heavy chain and a light chain of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0064] In a certain embodiment, provided herein is an isolated cell comprising a population of polynucleotides described herein.

[0065] In a certain embodiment, provided herein is a population of cells comprising (i) a first host cell comprising a polynucleotide described herein comprising nucleotide sequences encoding a VH or a heavy chain an anti-MerTK antibody or antigen-binding fragment described herein, and (ii) a second host cell comprising a polynucleotide comprising nucleotide sequences encoding a VL or a light chain of an anti-MerTK antibody or antigen-binding fragment described herein.

[0066] In a certain embodiment, provided herein is an isolated cell producing an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0067] In a certain embodiment, provided herein is a kit comprising an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0068] In a particular aspect, provided herein is a method of managing, protecting against, or treating cancer, for example, breast cancer, prostate cancer, gastric cancer, lung cancer, e.g ., non small cell lung cancer, adenoma, melanoma, lymphoma, or leukemia, or infection, for example, bacterial, e.g. , gram -negative or gram-positive bacteria, fungal, viral, or parasitic infection in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody or antigen binding fragment described herein, for example, Ab3000, or antigen binding fragment thereof, which specifically binds to human MerTK.

[0069] In a certain embodiment, provided herein is a method of modulating an immune response, e.g ., enhancing an immune response, in a subject, comprising administering to a subject in need thereof an effective amount of an antibody described herein, for example, Ab3000, or antigen-binding fragment thereof, which specifically binds to human MerTK. In a particular embodiment, the subject is a subject suffering from an infection, a subject having cancer, or an immunocompromised subject such as, for example, a subject who is undergoing, or had undergone treatment with, an anti-cancer therapy, is HIV positive, or who has AIDS or SCID, has diabetes, or has had a transplant and is taking an immunosuppressant. In a particular embodiment, the subject has been treated with an immunosuppressant.

[0070] In a certain embodiment, provided herein is a method of enhancing a

proinflammatory response in a subject, comprising administering to a subject in need thereof an effective amount of an antibody described herein, for example, Ab3000, or antigen-binding fragment thereof, which specifically binds to human MerTK. In a particular embodiment, such a method of enhancing a proinflammatory response in a subject results in an increase in TNF-a secretion.

[0071] In a specific embodiment, provided herein is a method of enhancing an immune response to a vaccine in a subject, comprising administering to a subject in need thereof, who is or has been administered the vaccine, an effective amount of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK. In a certain embodiment, the vaccine is a cancer or tumor vaccine

[0072] In one embodiment, provided herein is a vaccine antigen that can also be targeted, for example, to particular cell types or to particular tissues. In a specific embodiment, the vaccine antigen can be targeted to Antigen Presenting Cells (APCs), for example by use of agents such as antibodies targeted to APC-surface receptors such as DEC-205, for example as discussed in WO 2009/061996 (Celldex Therapeutics, Inc.), or the Mannose Receptor (CD206) for example as discussed in WO 03040169 (Medarex, Inc.).

[0073] In one embodiment, provided herein is a method of managing, preventing, protecting against, or treating metastasis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK.

[0074] In a certain embodiment, provided herein is a method for activating or

increasing/enhancing an innate immune response in a subject, comprising administering to a subject in need thereof an effective amount of an antibody described herein or antigen-binding fragment thereof, which specifically binds to human MerTK. In a particular embodiment, the subject has cancer and the method is effective in treating or managing the subject’s cancer.

[0075] In a certain embodiment, provided herein is a method for stimulating cytotoxicity of NK cells in a subject, comprising administering to a subject in need thereof an effective amount of an antibody described herein, for example, Ab3000, or antigen-binding fragment thereof, which specifically binds to human MerTK. In one embodiment, the subject has cancer, or is being treated for cancer with an anti-cancer therapeutic, or the subject has an infection.

[0076] In a specific embodiment, provided herein is a method of making an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, comprising culturing a cell, host cell, or population of cells described herein to express an anti-MerTK antibody or antigen-binding fragment thereof.

[0077] In a certain embodiment, provided herein is a method of making an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, comprising expressing a polynucleotide described herein or a population of polynucleotides described herein.

[0078] In another embodiment, presented herein is a method of increasing proinflammatory cytokine production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK such that the cytokine production is increased. For example, the cytokine secretion can be increase by about 5%, about 10%, about 15%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90% or more relative to secretion in the absence of the antibody.

In a specific embodiment, the proinflammatory cytokine is TNFa (tumor necrosis factor a). In yet another embodiment, the antibody or antigen-binding fragment does not substantially induce phosphorylation of MerTK. For example, the antibody or antigen-binding fragment induces phosphorylation of MerTK at least 50%, 60%, 70%, 80%, 90% or less than the phosphorylation induced by Gas6 binding to MerTK. In a particular embodiment, the antibody or antigen- binding fragment is one that specifically binds to Domain 2 (D2) of human MerTK. In some embodiments, the antibody or antigen-binding fragment is one of the antibodies or antigen binding fragments described herein.

[0079] In yet another embodiment, the antibody or antigen-binding fragment is one that specifically binds to Domain 2 (D2) of human MerTK and does not inhibit binding of Gas6 to cell-surface MerTK, e.g., does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit phosphorylation of cell-surface MerTK, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%.

[0080] In a certain aspect, further provided herein is a method of increasing proinflammatory cytokine production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof disclosed herein such that the production of one or more cytokines is increased. In some embodiments, the production of proinflammatory cytokine TNFa (tumor necrosis factor a) is increased. In certain embodiments, the production of proinflammatory cytokine IL-1RA (interleukin- 1 receptor antagonist) is increased. In some embodiments, provided herein is a method wherein the production of proinflammatory cytokines TNFa and IL-IRA are increased.

[0081] In a certain embodiment, provided herein is a method of increasing proinflammatory secretory factor production and/or secretion in a subject in need thereof, comprising

administering to the subject an antibody or an antigen-binding fragment thereof disclosed herein such that the production and/or secretion of about 1 or more, about 2 or more, about 3 or more, about 4 or more, about 5 or more, about 10 or more, about 15 or more, or about 20 or more proinflammatory secretory factors is increased. In a certain embodiment, the production and/or secretion of one or more proinflammatory factors can be increase by about 5%, about 10%, about 15%, about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90% or more relative to secretion in the absence of the antibody.

[0082] In a specific embodiment, the one or more proinflammatory secretory factor cytokine can be any 1, 2, 3, 4 or 5 of TNFa (tumor necrosis factor a)is IL-IRA (interleukin- 1 receptor antagonist), interleukin-6 (IL-6), macrophage inflammatory protein (MIP-la) and interferon g- induced protein 10 (IP- 10). [0083] In some embodiments, provided herein is a method of increasing proinflammatory secretory factor production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof disclosed herein such that the production of one or more secretory factor is increased. In some embodiments, the production of

proinflammatory secretory factor TNFa (tumor necrosis factor a) is increased. In certain embodiments, the production of proinflammatory secretory factor IL-1RA (interleukin- 1 receptor antagonist) is increased. In some embodiments, provided herein is a method wherein the production of proinflammatory secretory factor TNFa and IL-1RA are increased. In a specific embodiment, the proinflammatory secretory factor is interleukin-6 (IL-6). In a specific embodiment, the proinflammatory secretory factor is macrophage inflammatory protein (MIP- la). In a specific embodiment, the proinflammatory secretory factor is interferon g-induced protein 10 (IP- 10).

[0084] In one aspect, provided herein is a method of increasing proinflammatory secretory factor production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof disclosed herein such that the production of any 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, or more proinflammatory secretory factors is increased. As a non-limiting example, in certain embodiments, provided herein are methods wherein the production of one or more of proinflammatory secretory factors TNFa, IL-IRA, fibroblast growth factor 2 (FGF-2), eotaxin-1 (CCL11), transforming growth factor alpha (TGF-a) granulocyte-colony stimulating factor (G-CSF), Fms-related tyrosine kinase 3 ligand (Flt-3L), granulocyte macrophage-colony stimulating factor (GM-CSF), fractalkine (CX3CL1), interferon alpha-2 (IFN-a2), interferon-gamma (IFN-g), growth-regulated oncogene alpha (GRO alpha), interleukin- 10 (IL-10), monocyte chemotactic protein 3 (MCP-3), interleukin- 12 p40 (IL- 12P40), macrophage-derived chemokine (MDC), platelet-derived growth factor AA homodimer (PDGF-AA), interleukin- 13 (IL-13), platelet-derived growth factor BB homodimer (PDGF-BB), soluble CD40 ligand (sCD40L), interleukin- IB (IL-1B), interleukin-4 (IL-4), interleukin-6 (IL- 6), interleukin-8 (IL-8), interferon g-induced protein 10 (IP- 10), macrophage inflammatory protein (MIR)-Ia, MIR-Ib, Regulated on Activation Normal T cell Expressed and Secreted (RANTES), vascular endothelial growth factor A (VEGF-A) or IL-18 is increased.

[0085] In some embodiments of methods provided herein for increasing proinflammatory secretory factor production in a subject in need thereof, such methods comprise administering to the subject an antibody or an antigen-binding fragment thereof disclosed herein such that the production of any 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, or more proinflammatory secretory factors is increased, wherein the production of one or more of such proinflammatory secretory factors is NFKB-dependent. In certain embodiments of the methods provided herein, one or more co stimulatory molecules is upregulated and/or activated. In particular embodiments, such upregulation and/or activation occurs in PBMCs. In other particular embodiments, such upregulation and/or activation occurs in dendritic cells. As a non-limiting example, in certain embodiments, the co-stimulatory molecules are CD86 and/or CD54.

[0086] In certain embodiments, an antibody or antigen-binding fragment thereof disclosed herein does not substantially induce phosphorylation of MerTK, for example, does not substantially induce phosphorylation of MerTK as, e.g.,, detected by Western blot. Any method known in the art can be used to assay the phosphorylation of proteins. As a non-limiting example, Western blot, ELISA, flow cytometry, immunohistochemistry/immunofluorescence or membrane-based sandwich immunoassay can be employed to assay the phosphorylation of one or more proteins. In certain embodiments, an antibody or antigen-binding fragment disclosed herein does not substantially induce phosphorylation of Syk, for example, as detected by Western blot. In certain embodiments, an antibody or antigen-binding fragment disclosed herein does not substantially induce phosphorylation of SHP-1, for example as detected by western blot.

4. BRIEF DESCRIPTION OF THE FIGURES

[0087] FIG. 1 depicts the binding curve of Ab3000-IgGl, Ab3000-IgG2, and isotype controls to human MerTK (hMerTK) as determined by ELISA. The absorbance at OD450 is plotted as a function of antibody concentration.

[0088] FIG. 2 depicts the binding of Ab3000-IgGl and isotype control to human and cynomolgus MerTK as determined by ELISA.

[0089] FIG. 3A depicts the binding of anti -MerTK antibody Ab3000-IgGl, Ab3000-IgG2, and isotype controls to full length human MerTK (hMerTK) expressed on MerTK-L cells as determined by flow cytometry. FIG. 3B depicts the binding of anti-MerTK antibody Ab3000- IgGl and isotype control to full length human MerTK (hMerTK) expressed on SK-mel-5 cells as determined by flow cytometry. Mean fluorescence intensity (MFI) is plotted as a function of antibody concentration (pg/mL).

[0090] FIG. 4 shows the binding of Ab3000-IgGl to MerTK extracellular domains Dl, D2, D3 and D4. Ab3000 bound to domain D2 and a protein comprising domains Dl and D2.

Ab3000 also bound to full-length human and cynomalgous MerTK (huMerTK-ECD and cynoMerTK-ECD, respectively) but not human Axl extracellular domain (huAxl-ECD).

[0091] FIG. 5 depicts inhibition of binding of human MerTK extracellular domain

(huMerTK-ECD) to immobilized biotinylated Gas6 by Ab3000-IgGl as determined by ELISA. Binding was compared to horseradish peroxidase (HRP), PBS and antibody isotype controls.

[0092] FIG. 6 depicts the effect of Ab3000-IgGl on total MerTK levels in human macrophages. Percent total MerTK is indicated in response to a 24 hour treatment with Ab3000- IgGl antibody or Gas6.

[0093] FIG. 7 shows that treatment of human PBMCs with Ab3000-IgGl inhibits phosphorylation of ITIM-bearing immunoreceptors. Percent change over isotype control is plotted.

[0094] FIG. 8A depicts an increase in IL-IRA (pg/mL) secretion from dendritic cells in response to Ab3000-IgGl and Ab3000-IgG2 as determined by ELISA. FIG. 8B depicts an increase in TNF-a secretion from dendritic cells upon stimulation with LPS in response to Ab3000-IgGl, Ab3000-IgG2.

[0095] FIG. 9 depicts multiplex analysis of production of 30 different cytokines, chemokines and growth factors in response to Ab3000-IgGl in human dendritic cells. Fold increase in protein production in response to Ab3000 over isotype control is plotted.

[0096] FIG. 10 depicts multiplex analysis of production of 30 different cytokines, chemokines and growth factors in response to Ab3000-IgGl in human PBMCs. Fold increase in protein production in response to Ab3000 over isotype control is plotted.

[0097] FIG. 11A shows IL-IRA production by macrophages in response to Ab3000-IgGl antibody. FIG. 11B shows TNF-a production by macrophages in response to Ab3000-IgGl antibody. Fold increase over isotype control (huIgGl) is plotted.

[0098] FIG. 12 depicts secretion of TNF-a, IL-IRA and IL-6 (pg/ml) by CD14⁺-enriched PBMCs. Results from two different donors are shown (top panels and bottom panels). [0099] FIG. 13 depicts expression of MerTK in indicated immune cells as analyzed by flow cytometry.

[00100] FIG. 14 depicts tumor growth in the CT26 mouse tumor model in response to treatment. Tumor volume (cm³) is plotted as a function of days post-injection. Mice were treated with saline, murine anti -MerTK antibody (3C), anti -PD 1 antibody (RMP1-14), or a combination of both antibodies. Mean survival for each treatment group is shown with p-values. (top right).

[00101] FIG. 15A depicts activation of CD86 in dendritic cells as analyzed by FACS. FIG. 15B depicts activation of CD54 in dendritic cells as analyzed by FACS. The fold mean fluorescence intensity (MFI) over media is plotted.

[00102] FIG. 16A depicts activation of CD86 in PBMC as analyzed by Quantitative Real Time PCR. FIG. 16B depicts activation of CD54 in PBMC as analyzed by Quantitative Real Time PCR.

[00103] FIG. 17 depicts IFNy secretion in a mixed leukocyte reaction as evaluated by ELISA.

[00104] FIG. 18 depicts induction of IL-1RA in human PBMCs as analyzed by ELISA.

PBMCs were incubated with IgGl, Ab3000-IgGl or LPS in the presence or absence of IKK1/2 inihibtor as indicated.

[00105] FIG. 19 depicts western blot analysis of proteins from human PBMCs following incubation with PBS, huIgGl, X-linked huIgGl or Ab3000-IgGl. Phospho-Syk, Total Syk, Phospho-SHP-1, and Total SHP-1 were detected.

[00106] FIG. 20 depicts Gas6 binding to human MerTK-expressing L cells as analyzed by flow cytometry.

[00107] FIG. 21 depicts western blot analysis of proteins from human PBMCs following incubation with PBS, huIgGl, or Ab3000-IgGl in the presence or absence of Gas6. Phospho- MerTK, MerTK, and b-Tubulin were detected.

[00108] FIG. 22A depicts secretion of IL-1RA in human PBMCs as analyzed by ELISA.

FIG. 22B depicts secretion of MIP-la in human PBMCs as analyzed by ELISA. PBMCs were incubated in the presence or absence of the MerTK kinase inhibitor UNC-2025. 5. DETAILED DESCRIPTION

[00109] MerTK is a receptor tyrosine kinase of the TAM group (which includes Tyro-3, Axl, and MerTK) (Graham et al. (2014) Nat Rev Cancer ;14: 769-785; Lemke G. (2013) Cold Spring Harb Perspect Biol.; 5). In a specific embodiment, MerTK is human MerTK. UniProKB accession number Q 12866 provides an exemplary human MerTK amino acid sequence. Native MerTK comprises two extracellular immunoglobulin (Ig)-like domains, two extracellular fibronectin (FN) type III motifs, and a intracellular tyrosine kinase domain (see, e.g ., Lemke G. (2013) Cold Spring Harb Perspect Biol.; 5). GenBank™ accession number NM 006343.2 provides an exemplary human MerTK nucleic acid coding sequence.

5.1 Antibodies

[00110] In a specific aspect, provided herein are antibodies and antigen-binding fragments thereof that specifically bind to human MerTK, for example, an extracellular domain (ECD) of human MerTK, and modulate MerTK expression and/or MerTK activity.

[00111] In certain embodiments, an antibody or antigen-binding fragment disclosed herein can bind to one or more domains of the extracellular domain of human MerTK. In certain embodiments, an antibody or antigen-binding fragment disclosed herein can bind to one or more purified domains of the extracellular domain of human MerTK. As a non-limiting example, in certain embodiments, an antibody or antigen-binding fragment disclosed herein can bind to domain D2 of the extracellular domain of human MerTK. In some embodiments, an antibody or antigen-binding fragment disclosed herein can have diminished binding to one or more purified domains of the extracellular domain of human MerTK (e.g, Domain D3 and/or Domain D4). In some embodiments, an antibody or antigen-binding fragment disclosed herein can bind to a purified domain D2 of the extracellular domain of human MerTK but does not bind to, or exhibits reduced binding to, a purified domain D2/D3 portion of the extracellular domain of human MerTK.

[00112] An antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein that specifically binds to MerTK (e.g, human MerTK) can, for example, i) bind Domain 2 of human MerTK, ii) does not inhibit binding of Gas6 to MerTK in human macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in human macrophages, e.g., does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40% , iii) bind to human MerTK with a KD of lOnM or less (e.g, InM or less, or 0.5nM or less), as determined, for example, by bio layer interferometry, and/or iv) increase production of proinflammatory secretory factors, e.g, increase IL-1RA secretion from human dendritic cells, PBMCs and/or macrophages when compared to isotype control, increase TNF-alpha secretion from human dendritic cells upon stimulation with LPS when compared to isotype control, increase IL-6 secretion from human dendritic cells when compared to isotype control, and/or increase IL-8, MIP-la and/or MPMb secretion from human dendritic cells when compared to isotype control.

[00113] An antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein that specifically binds to MerTK (e.g, human MerTK) can, for example, bind Domain 2 of human MerTK, and i) does not inhibit binding of Gas6 to MerTK in human macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in human macrophages, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%, ii) can bind to human MerTK with a KD of lOnM or less (e.g., InM or less, or 0.5nM or less), as determined, for example, by bio layer interferometry, and/or iii) can increase production of proinflammatory secretory factors, e.g, increase IL-IRA secretion from human dendritic cells, PBMCs and/or macrophages when compared to isotype control, increase TNF-alpha secretion from human dendritic cells upon stimulation with LPS when compared to isotype control, increase IL-6 secretion from human dendritic cells when compared to isotype control, and/or increase IL-8, MIP-la and/or MPMb secretion from human dendritic cells when compared to isotype control.

[00114] An antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein that specifically binds to MerTK (e.g, human MerTK) can, for example, bind Domain 2 of human MerTK, does not inhibit binding of Gas6 to MerTK in human macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK

phosphorylation in human macrophages, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%, and can i) bind to human MerTK with a KD of lOnM or less (e.g, InM or less, or 0.5nM or less), as determined, for example, by bio-layer interferometry, and/or ii) increase production of proinflammatory secretory factors, e.g ., increase IL-IRA secretion from human dendritic cells, PBMCs and/or macrophages when compared to isotype control, increase TNF-alpha secretion from human dendritic cells upon stimulation with LPS when compared to isotype control, increase IL-6 secretion from human dendritic cells when compared to isotype control, and/or increase IL-8, MIP-la and/or MPMb secretion from human dendritic cells when compared to isotype control. In some embodiments, wherein an antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein specifically binds to MerTK (e.g, human MerTK) and increases the production of proinflammatory secretory factors (e.g, IL-IRA and MIP-la), treatment with an inhibitor of MerTK kinase activity does not reduce the increased production of these factors. In some embodiments, wherein an antibody or antigen-binding fragment presented herein specifically binds to MerTK (e.g, human MerTK) and increases the production of proinflammatory secretory factors, the increase in the production of proinflammatory secretory factors is independent of MerTK kinase activity.

[00115] An antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein that specifically binds to MerTK (e.g, human MerTK) can, for example, bind Domain 2 of human MerTK, does not inhibit binding of Gas6 to MerTK in human macrophages, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK

phosphorylation in human macrophages, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%, can bind to human MerTK with a KD of lOnM or less (e.g, InM or less, or 0.5nM or less), as determined, for example, by bio layer interferometry, and can i) increase production of IL-IRA secretion from human dendritic cells, PBMCs and/or macrophages when compared to isotype control, ii) increase TNF-alpha secretion from human dendritic cells upon stimulation with LPS when compared to isotype control, iii) increase IL-6 secretion from human dendritic cells when compared to isotype control, and/or iv) increase IL-8, MIP-la and/or MIP-Ib secretion from human dendritic cells when compared to isotype control.

[00116] An antibody or antigen-binding fragment (for example, a human or humanized antibody or antigen-binding fragment) presented herein that specifically binds to MerTK (e.g, human MerTK) can, for example, bind Domain 2 of human MerTK, can bind to human MerTK with a KD of lOnM or less ( e.g ., InM or less, or 0.5nM or less), as determined, for example, by bio-layer interferometry, does not inhibit binding of Gas6 to MerTK human macrophages, e.g., does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in human macrophages, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%, iii) can bind to human MerTK with a KD of lOnM or less (e.g, InM or less, or 0.5nM or less), as determined, for example, by bio-layer interferometry, iv) can increase IL-1RA secretion from human dendritic cells, PBMCs and/or macrophages by at least 100%, in vitro, as determined by ELISA when compared to isotype control; v) can increase TNF-alpha secretion from human dendritic cells upon stimulation with LPS by at least 50%, in vitro, as determined by ELISA when compared to isotype control; vi) can increase IL-6 secretion from human dendritic cells by at least 50%, in vitro, as determined by ELISA when compared to isotype control; and/or vii) can increase IL-8, MIP-la and MPMb secretion from human dendritic cells by at least 100%, in vitro, as determined by ELISA when compared to isotype control.

[00117] In some embodiments, provided herein is an isolated antibody, or an antigen-binding fragment thereof, which binds to Domain 2 (D2) of human MerTK and does not inhibit binding of Gas6 to cell-surface MerTK, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit phosphorylation of cell-surface MerTK, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%. As a non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, provided herein does not inhibit binding of Gas6 to MerTK expressed on cells (e.g, L cells or human macrophage), e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40%. In another non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, provided herein does not inhibit phosphorylation of MerTK in cells (e.g, macrophages) , e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%.

[00118] An antibody or antigen-binding fragment presented herein can, for example, be antibody Ab3000 or an antigen-binding fragment thereof. An antibody or antigen-binding fragment presented herein can comprise CDRs of any of Table 1, Table 3, Table 4 or Table 5.

An antibody or an antibody or antigen-binding fragment presented herein can comprise a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6.

[00119] As used herein, the terms“antibody” and“immunoglobulin” and“Ig” are terms of art and can be used interchangeably herein and refer to a molecule with an antigen binding site that specifically binds an antigen.

[00120] Antibodies can include, for example, monoclonal antibodies, recombinantly produced antibodies, monospecific antibodies, multispecific antibodies (including bispecific antibodies), human antibodies, humanized antibodies, chimeric antibodies, synthetic antibodies, tetrameric antibodies comprising two heavy chain and two light chain molecules, an antibody light chain monomer, an antibody heavy chain monomer, an antibody light chain dimer, an antibody heavy chain dimer, an antibody light chain/antibody heavy chain pair, an antibody with two light chain/heavy chain pairs ( e.g ., identical pairs), intrabodies, heteroconjugate antibodies, single domain antibodies, monovalent antibodies, bivalent antibodies (including monospecific or bispecific bivalent antibodies), single chain antibodies, or single-chain Fvs (scFv), camelized antibodies, affybodies, Fab fragments, F(ab’) fragments, F(ab’)2 fragments, disulfide-linked Fvs (sdFv), anti -idiotypic (anti-id) antibodies (including, e.g., anti-anti-Id antibodies), and epitope binding fragments of any of the above. In certain embodiments, antibodies described herein refer to polyclonal antibody populations.

[00121] In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is fused to a heterologous polypeptide. In a certain embodiment, an isolated antibody (e.g, monoclonal antibody) described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, is conjugated to an agent. In a particular embodiment, the agent is a toxin. In one embodiment, the toxin is abrin, ricin A, pseudomonas exotoxin, cholera toxin, or diphtheria toxin.

[00122] Antibodies can be of any type (e.g, IgG, IgE, IgM, IgD, IgA or IgY), any class, (e.g, IgGl, IgG2, IgG3, IgG4, IgAl or IgA2), or any subclass (e.g, IgG2a or IgG2b) of

immunoglobulin molecule. In certain embodiments, antibodies described herein are IgG antibodies (e.g, human IgG), or a class (e.g, human IgGl, IgG2, IgG3 or IgG4) or subclass thereof. For example, in certain embodiments, an Ab3000 antibody as described herein is an Ab3000-IgGl antibody. [00123] In a particular embodiment, an antibody is a 4-chain antibody unit comprising two heavy (H) chain / light (L) chain pairs, wherein the amino acid sequences of the H chains are identical and the amino acid sequences of the L chains are identical. In a specific embodiment, the H and L chains comprise constant regions, for example, human constant regions. In a yet more specific embodiment, the L chain constant region of such antibodies is a kappa or lambda light chain constant region, for example, a human kappa or lambda light chain constant region.

In another specific embodiment, the H chain constant region of such antibodies comprise a gamma heavy chain constant region, for example, a human gamma heavy chain constant region. In a particular embodiment, such antibodies comprise IgG constant regions, for example, human IgG constant regions.

[00124] As used herein, an“antigen” is a moiety or molecule that contains an epitope to which an antibody can specifically bind. As such, an antigen is also is specifically bound by an antibody. In a specific embodiment, the antigen, to which an antibody described herein binds is MerTK (e.g, human MerTK), or a fragment thereof, for example, an extracellular domain of MerTK (e.g, human MerTK).

[00125] As used herein, an“epitope” is a term in the art and refers to a localized region of an antigen to which an antibody can specifically bind. An epitope can be a linear epitope or a conformational, non-linear, or discontinuous, epitope. In the case of a polypeptide antigen, for example, an epitope can be contiguous amino acids of the polypeptide (a“linear” epitope) or an epitope can comprise amino acids from two or more non-contiguous regions of the polypeptide (a“conformational,”“non-linear” or“discontinuous” epitope). It will be appreciated by one of skill in the art that, in general, a linear epitope may or may not be dependent on secondary, tertiary, or quaternary structure. For example, in some embodiments, an antibody binds to a group of amino acids regardless of whether they are folded in a natural three dimensional protein structure. In other embodiments, an antibody requires amino acid residues making up the epitope to exhibit a particular conformation (e.g, bend, twist, turn or fold) in order to recognize and bind the epitope.

[00126] As used herein, the terms“specifically binds,”“specifically recognizes,”

“immunospecifically binds,”“immunospecifically recognizes” and“immunospecific” are analogous terms in the context of antibodies and refer to molecules that bind to an antigen (e.g, epitope) as such binding is understood by one skilled in the art. For example, a molecule that specifically binds to an antigen may bind to other peptides or polypeptides, generally with lower affinity as determined by, e.g ., immunoassays, Biacore™, KinExA 3000 instrument (Sapidyne Instruments, Boise, ID), or other assays known in the art. In a specific embodiment, molecules that specifically bind to an antigen bind to the antigen with a K_a that is at least 2 logs, 2.5 logs, 3 logs, 4 logs or greater than the K_a when the molecules bind to another antigen. In another specific embodiment, molecules that specifically bind to an antigen do not cross react with other proteins. In another specific embodiment, molecules that specifically bind to an antigen do not cross react with other non-MerTK proteins.

[00127] As used herein, the term“constant region” or“constant domain” is a well-known antibody term of art (sometimes referred to as“Fc”), and refers to an antibody portion, e.g. , a carboxyl terminal portion of a light and/or heavy chain which is not directly involved in binding of an antibody to antigen but which can exhibit various effector functions, such as interaction with the Fc receptor. The terms refer to a portion of an immunoglobulin molecule having a generally more conserved amino acid sequence relative to an immunoglobulin variable domain.

[00128] As used herein, the term“heavy chain” when used in reference to an antibody can refer to any distinct types, e.g. , alpha (a), delta (d), epsilon (e), gamma (g) and mu (m), based on the amino acid sequence of the constant domain, which give rise to IgA, IgD, IgE, IgG and IgM classes of antibodies, respectively, including subclasses of IgG, e.g. , IgGi, IgG2, IgG3 and IgG4.

[00129] As used herein, an“isolated” or“purified” antibody or antigen binding fragment is substantially free of cellular material or other contaminating proteins from the cell or tissue source from which the antibody or antigen binding fragment is derived, or substantially free of chemical precursors or other chemicals when the antibody or antigen binding fragment is chemically synthesized.

[00130] As used herein, the term“light chain” when used in reference to an antibody can refer to any distinct types, e.g. , kappa (K) of lambda (l) based on the amino acid sequence of the constant domains. Light chain amino acid sequences are well known in the art. In specific embodiment is a human light chain.

[00131] The term“monoclonal antibody” is a well-known term of art that refers to an antibody obtained from a population of homogenous or substantially homogeneous antibodies. The term“monoclonal” is not limited to any particular method for making the antibody.

Generally, a population of monoclonal antibodies can be generated by cells, a population of cells, or a cell line. In specific embodiments, a“monoclonal antibody,” as used herein, is an antibody produced by a single cell ( e.g ., hybridoma or host cell producing a recombinant antibody), wherein the antibody specifically binds to a MerTK epitope (e.g., an epitope of the extracellular domain of human MerTK) as determined, e.g, by ELISA or other antigen-binding or competitive binding assay known in the art or in the Examples provided herein. In particular embodiments, a monoclonal antibody can be a chimeric antibody or a humanized antibody. In certain embodiments, a monoclonal antibody is a monovalent antibody or multivalent (e.g, bivalent) antibody. In particular embodiments, a monoclonal antibody is a monospecific or multispecific antibody (e.g, bispecific antibody).

[00132] As used herein, the term“polyclonal antibodies” refers to an antibody population that includes a variety of different antibodies that specifically to the same and/or to different epitopes within an antigen or antigens.

[00133] As used herein, the terms“variable region” or“variable domain” refer to a portion of an antibody, generally, a portion of a light or heavy chain, typically about the amino-terminal 110 to 120 amino acids in the mature heavy chain and about 90 to 100 amino acids in the mature light chain. Variable regions comprise complementarity determining regions (CDRs) flanked by framework regions (FRs). Generally, the spatial orientation of CDRs and FRs are as follows, in an N-terminal to C-terminal direction: FR1-CDR1-FR2-CDR2-FR3-CDR3-FR4. Without wishing to be bound by any particular mechanism or theory, it is believed that the CDRs of the light and heavy chains are primarily responsible for the interaction of the antibody with antigen and for the specificity of the antibody for an epitope. In a specific embodiment, numbering of amino acid positions of antibodies described herein is according to the EU Index, as in Rabat et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242. In certain embodiments, the variable region is a human variable region.

[00134] In certain aspects, the CDRs of an antibody can be determined according to (i) the Rabat numbering system (Rabat et al. (1971) Ann. NY Acad. Sci. 190:382-391 and, Rabat et al. (1991) Sequences of Proteins of Immunological Interest Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242); or (ii) the Chothia numbering scheme, which will be referred to herein as the“Chothia CDRs” (see, e.g, Chothia and Lesk, 1987, J. Mol. Biol., 196:901-917; Al-Lazikani et al., 1997, J. Mol. Biol., 273:927-948; Chothia et al., 1992, J. Mol. Biol., 227:799-817; Tramontano A et al., 1990, J. Mol. Biol. 215(1): 175-82; and U.S. Patent No. 7,709,226); or (iii) the ImMunoGeneTics (IMGT) numbering system, for example, as described in Lefranc, M.-P., 1999, The Immunologist, 7: 132-136 and Lefranc, M.-P. et al., 1999, Nucleic Acids Res., 27:209-212 (“IMGT CDRs”); or (iv) the AbM numbering system, which will be referred to herein as the“AbM CDRs”, for example as described in MacCallum et al., 1996, J. Mol. Biol., 262:732-745. See also, e.g ., Martin, A.,“Protein

Sequence and Structure Analysis of Antibody Variable Domains,” in Antibody Engineering, Kontermann and Diibel, eds., Chapter 31, pp. 422-439, Springer-Verlag, Berlin (2001).

[00135] In certain embodiments, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK comprises VL and VH CDR as set forth in Table 1, which utilizes standard one letter amino acid abbreviations. In a particular embodiment, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, and comprises VL CDR1 (SEQ ID NO: 6), VL CDR2 (SEQ ID NO: 7), and VL CDR3 (SEQ ID NO: 8), and VH CDR1 (SEQ ID NO: 3), VH CDR2 (SEQ ID NO: 4), and VH CDR3 (SEQ ID NO: 5).

Table 1. VL and VH CDR Amino Acid Sequences (Kabat)

[00136] In certain embodiments, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK and comprises a VL and/or a VH as set forth in Table 2, which utilizes standard one letter amino acid abbreviations. In a particular embodiment, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, and comprises VL (SEQ ID NO: 2) and VH (SEQ ID NO:

1). For ease of description, an antibody that comprises the VL and VH amino acid sequences of Table 2 is referred to herein as“Ab3000” In one embodiment, such an antibody or antigen- binding fragment comprises a separate light chain comprising the VL amino acid sequence and a separate heavy chain comprising the VH amino acid sequence. In another embodiment, such an antibody or antigen-binding fragment comprises a single chain comprising the VL amino acid sequence and the VH amino acid sequence.

Table 2: Ab3000 VL and VH Amino Acid Sequences

[00137] In a particular embodiment, an antibody or an antigen-binding fragment described herein, comprises the VL CDR1, VL CDR2, and VL CDR3 of Ab3000. In a specific embodiment, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 1 (SEQ ID NOS: 6_, 7, and 8, respectively). In another embodiment, the antibody or antigen-binding fragment further comprises a VH as set forth in Table 2.

[00138] In a particular embodiment, an antibody or an antigen-binding fragment described herein, which specifically binds to human MerTK, comprises a VL as set forth in Table 2. In another embodiment, the antibody or antigen-binding fragment further comprises VH CDR1, VH CDR2 and/or VH CDR3 as set forth in Table 1.

[00139] In a particular embodiment, an antibody described herein, or an antigen-binding fragment thereof, comprises the VH CDR1, VH CDR2, and VH CDR3 of Ab3000. In a specific embodiment, the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 1. In another embodiment, the antibody or antigen-binding fragment further comprises a VL as set forth in Table 2.

[00140] In a particular embodiment, an antibody described herein, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprises a VH as set forth in Table 2. In another embodiment, the antibody or antigen-binding fragment further comprises VL CDR1, VL CDR2 and/or VL CDR3 as set forth in Table 1.

[00141] In a particular embodiment, an antibody described herein, or an antigen-binding fragment thereof, comprises the VL CDR1, VL CDR2, and VL CDR3 of Ab3000, and the VH CDR1, VH CDR2, and VH CDR3 of Ab3000. In a particular embodiment, for example, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 1 (SEQ ID NOS: 6, 7, and 8, respectively), and the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table (SEQ ID NOS: 3, 4, and 5, respectively).

[00142] In certain embodiments, an MerTK-binding antibody, or antigen-binding fragment thereof, described herein comprises CDRs of antibody Ab3000, as determined by the IMGT (Immunogenetics) numbering system; see, e.g ., Lefranc, M.-P., 1999, The Immunologist, 7: 132- 136 and Lefranc, M.-P. et al., 1999, Nucleic Acids Res., 27:209-212), both of which are incorporated herein by reference in their entirety.

[00143] In certain aspects, the CDRs of an antibody described herein are Chothia CDRs (see, e.g, Chothia and Lesk, 1987, J. Mol. Biol., 196:901-917; and U.S. Patent No. 7,709,226 and Martin, A.,“Protein Sequence and Structure Analysis of Antibody Variable Domains,” in Antibody Engineering, Kontermann and Diibel, eds., Chapter 31, pp. 422-439, Springer-Verlag, Berlin (2001)). The term“Chothia CDRs,” and like terms are recognized in the art and refer to antibody CDR sequences as determined according to the method of Chothia and Lesk, 1987, J. Mol. Biol., 196:901-917, which will be referred to herein as the“Chothia CDRs” (see also, e.g., U.S. Patent No. 7,709,226 and Martin, A.,“Protein Sequence and Structure Analysis of

Antibody Variable Domains,” in Antibody Engineering, Kontermann and Diibel, eds., Chapter 31, pp. 422-439, Springer-Verlag, Berlin (2001)). In certain embodiments, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK comprises VL and VH CDR as set forth in Table 3. In a particular embodiment, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, and comprises VL CDR1 (SEQ ID NO: 16), VL CDR2 (SEQ ID NO: 17), and VL CDR3 (SEQ ID NO: 18), and VH CDR1 (SEQ ID NO: 13), VH CDR2 (SEQ ID NO: 14), and VH CDR3 (SEQ ID NO: 15).

Table 3. VL and VH CDR Amino Acid Sequences (Chothia)

[00144] In a specific embodiment, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 3 (SEQ ID NOS: 16, 17, and 18, respectively).

[00145] In a specific embodiment, the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 3 (SEQ ID NOS: 13, 14, and 15, respectively).

[00146] In a particular embodiment, for example, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 3 (SEQ ID NOS: 16, 17, and 18, respectively), and the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 3 (SEQ ID NOS: 13, 14, and 15, respectively).

In certain aspects, the CDRs of an antibody described herein are AbM CDRs. In certain embodiments, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK comprises VL and VH CDR as set forth in Table 4. In a particular embodiment, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, and comprises VL CDR1 (SEQ ID NO: 22), VL CDR2 (SEQ ID NO: 23), and VL CDR3 (SEQ ID NO: 24), and VH CDR1 (SEQ ID NO: 19), VH CDR2 (SEQ ID NO: 20), and VH CDR3 (SEQ ID NO: 21).

Table 4. VL and VH CDR Amino Acid Sequences (AbM)

[00147] In a specific embodiment, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 4 (SEQ ID NOS: 22, 23, and 24, respectively).

[00148] In a specific embodiment, the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 4 (SEQ ID NOS: 19, 20, and 21, respectively). [00149] In a particular embodiment, for example, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 4 (SEQ ID NOS: 22, 23, and 24, respectively), and the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 4 (SEQ ID NOS: 19, 20, and 21, respectively).

Table 5. VL and VH CDR Amino Acid Sequences (Contact)

[00150] In certain aspects, the CDRs of an antibody described herein are Contact CDRs. In certain embodiments, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK comprises VL and VH CDR as set forth in Table 5. In a particular embodiment, provided herein is an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, and comprises VL CDR1 (SEQ ID NO: 28), VL CDR2 (SEQ ID NO: 29), and VL CDR3 (SEQ ID NO: 30), and VH CDR1 (SEQ ID NO: 25), VH CDR2 (SEQ ID NO: 26), and VH CDR3 (SEQ ID NO: 27).

[00151] In a specific embodiment, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 5 (SEQ ID NOS: 28, 29, and 30 respectively).

[00152] In a specific embodiment, the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 5 (SEQ ID NOS: 25, 26, and 27, respectively).

[00153] In a particular embodiment, for example, the VL CDR1, VL CDR2, and VL CDR3 are as set forth in Table 5 (SEQ ID NOS: 28, 29, and 30, respectively), and the VH CDR1, VH CDR2, and VH CDR3 are as set forth in Table 5 (SEQ ID NOS: 25, 26, and 27, respectively).

[00154] In certain aspects, an antibody described herein may be described by its VL alone, or its VH alone, or by its 3 VL CDRs alone, or its 3 VH CDRs alone. See, for example, Rader et al., 1998, Proc. Natl. Acad. Sci. USA, 95: 8910-8915, which is incorporated herein by reference in its entirety, describing the humanization of the mouse anti-avP3 antibody by identifying a complementing light chain or heavy chain, respectively, from a human light chain or heavy chain library, resulting in humanized antibody variants having affinities as high or higher than the affinity of the original antibody. See also, Clackson et al., 1991, Nature 352:624-628, which is incorporated herein by reference in its entirety, describing methods of producing antibodies that bind a specific antigen by using a specific VL domain (or VH domain) and screening a library for the complementary variable domains. The screen produced 14 new partners for a specific VH domain and 13 new partners for a specific VL domain, which were strong binders, as determined by ELISA. See also, Kim & Hong, 2007, J. Microbiol. 45:572-577, which is incorporated herein by reference in its entirety, describing methods of producing antibodies that bind a specific antigen by using a specific VH domain and screening a library ( e.g ., human VL library) for complementary VL domains; the selected VL domains in turn could be used to guide selection of additional complementary (e.g., human) VH domains.

[00155] In another embodiment, affinity maturation techniques can be used to alter one or more CDR region(s), followed by screening of the resultant binding molecules for the desired change in binding. Any affinity maturation techniques known in the art can be used. See also, Holland et al., 2013, J. Immun. Methods 394:55-61, which is incorporated herein by reference in its entirety, describing methods of producing libraries for directed evolution of proteins (e.g, affinity matured antibodies). In certain embodiments, a CDR region altered (e.g, by affinity maturation) can result in changes in binding affinity (e.g, on-rate of binding and/or off-rate of binding). In some embodiments, methods known in the art can be used to analyze binding affinity and immunogenicity of affinity matured antibodies. Any method known in the art can be used to ascertain immunospecific binding to MerTK (e.g, human MerTK ECD), for example, the binding assays and conditions described in the“Examples” section (Section 6) provided herein.

[00156] In a specific embodiment, the position of one or more CDRs along the VH (e.g, CDR1, CDR2, or CDR3) and/or VL (e.g, CDR1, CDR2, or CDR3) region of an antibody described herein may vary by one, two, three, four, five, or six amino acid positions so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). For example, in one embodiment, the position defining a CDR of any of Table 1, Table 3, Table 4 or Table 5 may vary by shifting the N-terminal and/or C-terminal boundary of the CDR by one, two, three, four, five, or six amino acids, relative to the current CDR position, so long as immunospecific binding to MerTK (e.g., human MerTK) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In another embodiment, the length of one or more CDRs along the VH (e.g, CDR1, CDR2, or CDR3) and/or VL (e.g, CDR1, CDR2, or CDR3) region of an antibody described herein may vary (e.g, be shorter or longer) by one, two, three, four, five, or more amino acids, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). For example, in one embodiment, a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be one, two, three, four, five or more amino acids shorter than one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In another embodiment, a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be one, two, three, four, five or more amino acids longer than one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In another embodiment, the amino terminus of a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In another embodiment, the carboxy terminus of a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be extended by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In another embodiment, the amino terminus of a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). In one embodiment, the carboxy terminus of a VH and/or VL CDR1, CDR2, and/or CDR3 described herein may be shortened by one, two, three, four, five or more amino acids compared to one or more of the CDRs described by SEQ ID NOS: 3-8, so long as immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained (e.g, substantially maintained, for example, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%). Any method known in the art can be used to ascertain whether immunospecific binding to MerTK (e.g, human MerTK ECD) is maintained, for example, the binding assays and conditions described in the“Examples” section (Section 6) provided herein. For example, Section 6.2 provided herein describes an assay for measuring binding to an ECD of human MerTK.

[00157] In specific aspects, provided herein is an antibody comprising an antibody light chain and heavy chain, e.g, a separate light chain and heavy chain. With respect to the light chain, in a specific embodiment, the light chain of an antibody described herein is a kappa light chain. In another specific embodiment, the light chain of an antibody described herein is a lambda light chain. In yet another specific embodiment, the light chain of an antibody described herein is a human kappa light chain or a human lambda light chain. In a particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK) comprises a light chain wherein the amino acid sequence of the VL chain region comprises any amino acid sequence described herein (e.g, SEQ ID NO: 2), and wherein the constant region of the light chain comprises the amino acid sequence of a human kappa light chain constant region. In another particular embodiment, an antibody described herein, which specifically binds a MerTK polypeptide (e.g, human MerTK) comprises a light chain wherein the amino acid sequence of the VL chain region can comprise any amino acid sequence described herein (e.g, SEQ ID NO: 2), and wherein the constant region of the light chain comprises the amino acid sequence of a human lambda light chain constant region. Non-limiting examples of human constant region sequences have been described in the art, e.g, see U.S.

Patent No. 5,693,780 and Kabat et al. (1991) Sequences of Proteins of Immunological Interest Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242.

With respect to the heavy chain, in a specific embodiment, the heavy chain of an antibody described herein can be an alpha (a), delta (d), epsilon (e), gamma (g) or mu (m) heavy chain. In another specific embodiment, the heavy chain of an antibody described can comprise a human alpha (a), delta (d), epsilon (e), gamma (g) or mu (m) heavy chain. In a particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide e.g ., human MerTK), comprises a heavy chain wherein the amino acid sequence of the VH chain region can comprise any amino acid sequence described herein (e.g., any of SEQ ID NO: 1), and wherein the constant region of the heavy chain comprises the amino acid sequence of a human gamma (g) heavy chain constant region. Non-limiting examples of human constant region sequences have been described in the art, e.g, see U.S. Patent No. 5,693,780 and Kabat et al. (1991) Sequences of Proteins of Immunological Interest Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242.

[00158] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a constant region amino acid sequence as shown in Table 6. In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain constant region comprising the amino acid sequence of SEQ ID NO: 31. In certain embodiments, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 32. In certain

embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain constant region comprising the amino acid sequence of SEQ ID NO: 31 and a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 32.

[00159] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 33. In certain

embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain constant region comprising the amino acid sequence of SEQ ID NO: 31 and a heavy chain constant region comprising the amino acid sequence of SEQ ID NO: 33.

[00160] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a heavy chain and/or a light chain comprising an amino acid sequence shown in Table 6. In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 34.

[00161] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 35.

[00162] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain comprising the amino acid sequence of SEQ ID NO: 36.

[00163] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain comprising the amino acid sequence of SEQ ID NO: 36 and a heavy chain comprising the amino acid sequence of SEQ ID NO: 34. In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain comprising the amino acid sequence of SEQ ID NO: 36 and a heavy chain comprising the amino acid sequence of SEQ ID NO: 35.

Table 6. Heavy Chain, Light Chain and Constant Region Amino Acid Sequences

[00164] In a specific embodiment, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK) comprises a VL chain region and a VH chain region comprising any amino acid sequences described herein, and wherein the constant regions comprise the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, or a human IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule. In another specific embodiment, an antibody or antigen binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK) comprises a VL chain region and a VH chain region comprising any amino acid sequences described herein, and wherein the constant regions comprise the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, any class (e.g, IgGl, IgG2, IgG3, IgG4, IgAl and IgA2), or any subclass (e.g, IgG2a and IgG2b) of immunoglobulin molecule. In a particular embodiment, the constant regions comprise the amino acid sequences of the constant regions of a human IgG, IgE, IgM, IgD, IgA or IgY

immunoglobulin molecule, any class (e.g, IgGl, IgG2, IgG3, IgG4, IgAl and IgA2), or any subclass (e.g, IgG2a and IgG2b) of immunoglobulin molecule.

[00165] In yet another specific embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a VL chain region and a VH chain region comprising any amino acid sequences described herein, and wherein the constant regions comprise the amino acid sequences of the constant regions of a human IgGl (e.g, isotype a, z, or f), human IgG2, or human IgG4. Non-limiting examples of human constant regions are described in the art, e.g, see Kabat et al. (1991) Sequences of Proteins of

Immunological Interest Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242.

[00166] In another specific embodiment, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK) comprises a VL chain region and a VH chain region comprising any amino acid sequences described herein, and further comprises one or more modifications to the amino acid sequences of the constant regions, wherein the constant regions comprise the amino acid sequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, any class (e.g, IgGl, IgG2, IgG3, IgG4, IgAl and IgA2), or any subclass (e.g, IgG2a and IgG2b) of immunoglobulin molecule. In some embodiments, modifications refer to at most 1, 2, 3, 4, 5, or 6 amino acid substitutions. As a non-limiting example, in certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide comprises a heavy chain constant region comprising an amino acid sequence with 1, 2, 3, 4, or 5 modifications to the amino acid sequence of SEQ ID NO: 32.

[00167] In certain embodiments the constant region can be deglycosylated (e.g, via mutation at the glycosylation consensus sequence).

[00168] The constant region can mediate several effector functions. For example, binding of the Cl component of complement to the Fc region of IgG or IgM antibodies (bound to antigen) activates the complement system. Activation of complement is important in the opsonization and lysis of cell pathogens. The activation of complement also stimulates the inflammatory response and can also be involved in autoimmune hypersensitivity. In addition, the Fc region of an antibody can bind a cell expressing a Fc receptor (FcR). There are a number of Fc receptors which are specific for different classes of antibody, including IgG (gamma receptors), IgE (epsilon receptors), IgA (alpha receptors) and IgM (mu receptors). Binding of antibody to Fc receptors on cell surfaces triggers a number of important and diverse biological responses including engulfment and destruction of antibody-coated particles, clearance of immune complexes, lysis of antibody-coated target cells by killer cells (called antibody-dependent cell cytotoxicity or ADCC), release of inflammatory mediators, and control of immunoglobulin production.

[00169] In certain embodiments, the constant region does not have effector function or has a diminished effector function. For example, in certain embodiments, a MerTK antibody or antigen-binding fragment thereof described herein can comprise an Fc region in which a portion of the Fc region has been deleted or otherwise altered so as to provide desired biochemical characteristics, such as increased localization in an inflamed tissue, increased tissue penetration, reduced serum half-life, or increased serum half-life, when compared with a fusion protein of approximately the same immunogenicity comprising an unaltered Fc region. In some embodiments, a MerTK antibody or antigen-binding fragment thereof comprises an Fc region with altered binding affinity to one or more Fc receptors (FcR).

[00170] Those skilled in the art will appreciate that Fc of an antibody or antigen-binding fragment thereof may interact with both activating and inhibitory Fey receptors, which may yield vastly different clinical outcomes. In some embodiments, a MerTK antibody or antigen-binding fragment thereof comprises an Fc region with altered binding affinity to an activating Fc gamma receptor (FcyR). In some embodiments, a MerTK antibody or antigen-binding fragment thereof comprises an Fc region with enhanced binding affinity to an activating Fc gamma receptor (FcyR).

[00171] In some embodiments, such a modified antibody may have only a partial deletion of a constant domain or substitution of a few or even a single amino acid. For example, the mutation of 1, 2, 3, 4 or 5 amino acids in selected areas of the CH2 domain may be enough to substantially alter Fc binding. Similarly, it may be desirable to simply delete the part of one or more constant region domains that control a specific effector function to be modulated. Such partial deletions of the constant regions may improve selected characteristics of the antibody while leaving other desirable functions associated with the subject constant region domain intact. Moreover, the constant regions of the disclosed antibodies may be modified through the mutation or

substitution of one or more amino acids that enhances the profile of the resulting construct. In this respect it may be possible to alter the activity provided by a conserved binding site ( e.g ., FcyR binding) while substantially maintaining the configuration and immunogenic profile of the modified antibody. In certain embodiments, the modified antibodies comprise the addition of one or more amino acids to the constant region to enhance desirable characteristics such as decreasing effector function or to eliminate carbohydrate attachment sites.

[00172] In certain embodiments, an antibody or antigen-binding fragment thereof disclosed herein can be modified such that it can provide for altered effector functions that, in turn, affect the biological profile of the administered antibody. For example, in some embodiments, the deletion or modification (through point mutations or other means) of a constant region domain may alter Fc receptor binding of the circulating modified antibody. In other embodiments, the constant region modifications increase the serum half-life of the antibody. In other embodiments, the constant region modifications reduce the serum half-life of the antibody. In some embodiments, the constant region is modified to eliminate disulfide linkages or oligosaccharide moieties.

[00173] In certain embodiments, an antibody or antigen-binding fragment disclosed herein can be modified such that it does not have one or more effector functions. In some embodiments, the antibody or antigen-binding fragment disclosed herein can be modified such that it has altered ADCC activity, and/or altered complement-dependent cytotoxicity (CDC) activity. In certain embodiments, an antibody or antigen-binding fragment disclosed herein can be modified such that it does not bind an Fc receptor, and/or complement factors. For example, in certain embodiments, an antibody or antigen-binding fragment disclosed herein can be modified such that it preferentially binds to an Fc receptor (e.g,. an activating FcyR).

[00174] In certain alternative embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide can be bispecific or multispecific and comprise at least two antigen-binding sites with differing specificities. In certain embodiments, the bispecific binding molecule can alter effector function, or enhance or diminish affinity of antibody to FcR. For example, in certain embodiments, an antibody or antigen-binding fragment disclosed herein can be bispecific such that it preferentially binds to an Fc receptor (e.g,. an activating FcyR).

[00175] In another embodiment, a polypeptide making up antibody or antigen-binding fragment described herein further comprises a signal sequence, for example, an N-terminal signal sequence. In certain instances, such a polypeptide may contain such a signal sequence when initially produced, e.g., translated, but may have the signal sequence removed prior to or during assembly of the final antibody or antigen-binding fragment. In alternative embodiments, the antibody polypeptide or antigen-binding fragment does not comprise a signal sequence.

[00176] In some embodiments, a polypeptide described herein further comprises a signal sequence comprising an amino acid sequence of SEQ ID NO: 46, e.g, comprises, at its N- terminus the amino acid sequence of SEQ ID NO: 46, wherein SEQ ID NO: 46 has the amino acid sequence of MEFGLSWVFLVALLRGVQC. As a non-limiting example, in certain embodiments, a polypeptide described herein comprises an amino acid sequence of SEQ ID NO:

1 and an amino acid sequence of SEQ ID NO: 46, e.g, the polypeptide comprises the amino acid sequence of SEQ ID NO: 46 at its N-terminus. In some embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO: 48. As another non-limiting example, in certain embodiments, a polypeptide described herein comprises an amino acid sequence of SEQ ID NO: 2 and an amino acid sequence of SEQ ID NO: 46, e.g., the polypeptide comprises the amino acid sequence of SEQ ID NO: 46 at its N-terminus. As another non-limiting example, in certain embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO: 37 (see Table 6). In yet another non-limiting example, in certain embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO: 38 (see Table 6)·

[00177] In some embodiments, a polypeptide described herein further comprises a signal sequence comprising the amino acid sequence of SEQ ID NO: 47, e.g, comprises, at its N- terminus, the amino acid sequence of SEQ ID NO: 47, wherein SEQ ID NO: 47 has the amino acid sequence of MRVPAQLLGLLLLWLPGARC. As a non-limiting example, in certain embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO:

1 and the amino acid sequence of SEQ ID NO: 47, e.g, the polypeptide comprises the amino acid sequence of SEQ ID NO: 47 at its N-terminus. As another non-limiting example, in certain embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO:

2 and the amino acid sequence of SEQ ID NO: 47 e.g, the polypeptide comprises at its N- terminus the amino acid sequence of SEQ ID NO: 47. In some embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO: 49. As another non limiting example, in certain embodiments, a polypeptide described herein comprises the amino acid sequence of SEQ ID NO: 39 (see Table 6).

[00178] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising a VL CDR1, VL CDR2, and VL CDR3 of Ab3000; (ii) the heavy chain comprises a VH chain region comprising a VH CDR1, VH CDR2, and VH CDR3 of Ab3000; (iii) the light chain further comprises a constant light chain domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant heavy chain domain comprising the amino acid sequence of the constant domain of a human IgG, e.g, IgGl, heavy chain.

[00179] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising a VL CDR1, VL CDR2, and VL CDR3 of Table 1; (ii) the heavy chain comprises a VH chain region comprising a VH CDR1, VH CDR2, and VH CDR3 of Table 1; (iii) the light chain further comprises a constant light chain domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant heavy chain domain comprising the amino acid sequence of the constant domain of a human IgG, e.g ., IgGl, heavy chain.

[00180] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g., human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising a VL CDR1, VL CDR2, and VL CDR3 of Table 3; (ii) the heavy chain comprises a VH chain region comprising a VH CDR1, VH CDR2, and VH CDR3 of Table 3; (iii) the light chain further comprises a constant light chain domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant heavy chain domain comprising the amino acid sequence of the constant domain of a human IgG, e.g, IgGl, heavy chain.

[00181] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising a VL CDR1, VL CDR2, and VL CDR3 of Table 4; (ii) the heavy chain comprises a VH chain region comprising a VH CDR1, VH CDR2, and VH CDR3 of Table 4; (iii) the light chain further comprises a constant light chain domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant heavy chain domain comprising the amino acid sequence of the constant domain of a human IgG, e.g, IgGl, heavy chain.

[00182] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising a VL CDR1, VL CDR2, and VL CDR3 of Table 5; (ii) the heavy chain comprises a VH chain region comprising a VH CDR1, VH CDR2, and VH CDR3 of Table 5; (iii) the light chain further comprises a constant light chain domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant heavy chain domain comprising the amino acid sequence of the constant domain of a human IgG, e.g ., IgGl, heavy chain.

[00183] In another particular embodiment, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), comprises a light chain and a heavy chain, wherein (i) the light chain comprises a VL chain region comprising the amino acid sequence of SEQ ID NO: 2; (ii) the heavy chain comprises a VH chain region comprising the amino acid sequence of SEQ ID NO: 1; (iii) the light chain further comprises a constant domain comprising the amino acid sequence of the constant domain of a human kappa or lambda light chain; and (iv) the heavy chain further comprises a constant domain comprising the amino acid sequence of the constant domain of a human IgGl, e.g. , IgGl, heavy chain.

[00184] In certain embodiments, one or more modifications can be made to the Fc region of an antibody or antigen-binding fragment thereof described herein. Generally, such a

modification or modifications can be introduced to alter one or more functional properties of the antibody or antigen-binding fragment, such as serum half-life, complement fixation, Fc receptor binding, and/or antibody-dependent cellular cytotoxicity. Exemplary modifications are described, for example, in International Patent Application Publication No. WO 2008/153926 A2.

[00185] In specific embodiments, an antibody described herein, which specifically binds to MerTK, e.g., human MerTK ECD, comprises framework regions (e.g, framework regions of the VL domain and/or VH domain) that are human framework regions or derived from human framework regions. Non-limiting examples of human framework regions are described in the art, e.g, see Kabat et al. (1991) Sequences of Proteins of Immunological Interest Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242).

[00186] In certain embodiments, an antibody described herein comprises framework regions (e.g, framework regions of the VL domain and/or VH domain) that are primate (e.g, non-human primate) framework regions or derived from primate (e.g, non-human primate) framework regions.

[00187] In certain embodiments, an antibody described herein comprises a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, wherein the antibody specifically binds to MerTK, e.g, human MerTK ECD.

[00188] In certain embodiments, an antibody described herein comprises a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, wherein the antibody specifically binds to MerTK, e.g. , human MerTK ECD, and wherein the antibody comprises VL CDRs that are identical to the VL CDRs of antibody Ab3000.

[00189] In certain embodiments, an antibody described herein comprises a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, wherein the antibody specifically binds to MerTK, e.g. , human MerTK ECD, and wherein the antibody comprises VL CDRs that are identical to the VL CDRs of Table 1.

[00190] In certain embodiments, an antibody described herein comprises a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1, wherein the antibody specifically binds to MerTK, e.g. , human MerTK ECD.

[00191] In certain embodiments, an antibody described herein comprises a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1, wherein the antibody specifically binds to MerTK, e.g. , human MerTK ECD, and wherein the antibody comprises VH CDRs that are identical to the VH CDRs of antibody Ab3000.

[00192] In certain embodiments, an antibody described herein comprises a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1, wherein the antibody specifically binds to MerTK, e.g. , human MerTK ECD, and wherein the antibody comprises VH CDRs that are identical to the VH CDRs of Table 1.

[00193] In other embodiments, the antibodies and antigen binding fragments thereof presented herein that specifically bind to human MerTK comprise conservative sequence modifications as described herein. With respect to polypeptides such as antibodies or antigen binding fragment thereof, conservative sequence modifications include conservative amino acid substitutions that include ones in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains ( e.g ., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g, glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta- branched side chains (e.g, threonine, valine, isoleucine) and aromatic side chains (e.g, tyrosine, phenylalanine, tryptophan, histidine). Thus, in a particular embodiment, a predicted nonessential amino acid residue in a human anti-MerTK antibody is replaced with another amino acid residue from the same side chain family. Methods of identifying nucleotide and amino acid conservative substitutions which do not eliminate antigen binding are well-known in the art (see, e.g,

Brummell et al., Biochem. 32: 1180-1187 (1993); Kobayashi et al. Protein Eng. 12(10):879-884 (1999); and Burks et al. Proc. Natl. Acad. Sci. USA 94:412-417 (1997)). In particular embodiments, the conservative sequence modifications described herein modify the amino acid sequences of the MerTK antibodies or antigen binding fragments thereof by 50%, or 55%, or 60%, or 65%, or 70%, or 75%, or 80%, or 85%, or 90%, or 95%, or 98%, or 99%. In certain embodiments, the nucleotide and amino acid sequence modifications refer to at most 1, 2, 3, 4, 5, or 6 amino acid substitutions to the CDRs described in any of Table 1, Table 3, Table 4 or Table 5. Thus, for example, each such CDR may contain up to 5 conservative amino acid substitutions, for example up to (not more than) 4 conservative amino acid substitutions, for example up to (not more than) 3 conservative amino acid substitutions, for example up to (not more than) 2 conservative amino acid substitutions, or no more than 1 conservative amino acid substitution.

[00194] In certain embodiments, an antibody or antigen-binding fragment thereof that specifically binds to MerTK, e.g, human MerTK ECD described herein comprises: i) a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, ii) a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, and wherein the antibody comprises VL CDRs that are identical to the VL CDRs of antibody Ab3000, or iii) a VL domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 2, and wherein the antibody comprises VL CDRs that are identical to the VL CDRs of Table 1; and iv) a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1, v) a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1 and wherein the antibody comprises VH CDRs that are identical to the VH CDRs of antibody Ab3000, or vi) a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, or at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1 and wherein the antibody comprises VH CDRs that are identical to the VH CDRs of Table 1.

[00195] The determination of percent identity between two sequences ( e.g ., amino acid sequences or nucleic acid sequences) can also be accomplished using a mathematical algorithm. A preferred, non-limiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul, 1990, Proc. Natl. Acad. Sci. U.S.A. 87:2264 2268, modified as in Karlin and Altschul, 1993, Proc. Natl. Acad. Sci. U.S.A. 90:5873 5877. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al., 1990, J. Mol. Biol. 215:403. BLAST nucleotide searches can be performed with the NBLAST nucleotide program parameters set, e.g., for score=100, word length=12 to obtain nucleotide sequences homologous to a nucleic acid molecules described herein. BLAST protein searches can be performed with the XBLAST program parameters set, e.g, to score 50, wordlength=3 to obtain amino acid sequences homologous to a protein molecule described herein. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., 1997, Nucleic Acids Res. 25:3389 3402. Alternatively, PSI BLAST can be used to perform an iterated search which detects distant relationships between molecules (Id.). When utilizing BLAST, Gapped BLAST, and PSI Blast programs, the default parameters of the respective programs (e.g, of XBLAST and NBLAST) can be used (see, e.g, National Center for Biotechnology Information (NCBI) on the worldwide web,

ncbi.nlm.nih.gov). Another preferred, non limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller, 1988, CABIOS 4: 11 17. Such an algorithm is incorporated in the ALIGN program (version 2.0) which is part of the GCG sequence alignment software package. When utilizing the ALIGN program for comparing amino acid sequences, a PAM 120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used. [00196] The percent identity between two sequences can be determined using techniques similar to those described above, with or without allowing gaps. In calculating percent identity, typically only exact matches are counted.

[00197] Provided herein are antibodies that specifically bind to MerTK and that can modulate MerTK activity and/or expression (e.g, inhibit MerTK activity and/or expression). In certain embodiments, a MerTK antibody or antigen-binding fragment thereof provided herein specifically binds to a MerTK polypeptide, e.g. , an ECD of human MerTK, and that inhibits (e.g, partially inhibits) a MerTK activity. In yet another embodiment, a MerTK antibody or antigen-binding fragment thereof provided herein specifically binds to a MerTK polypeptide, e.g, an ECD of human MerTK, and does not inhibit binding of Gas6 to cell-surface MerTK, e.g, does not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit phosphorylation of cell-surface MerTK, e.g, does not inhibit such phosphorylation by more than 10%, more than 20%, more than 30% or more than 40%.

[00198] MerTK activity can relate to any activity of MerTK such as those known or described in the art. Non-limiting examples of MerTK activity include: MerTK receptor dimerization, MerTK receptor phosphorylation (e.g., tyrosine phosphorylation or autophosphorylation in the cytoplasmic domain), signaling downstream of the MerTK receptor (e.g, P13K, PLC, GRB2, RAC1, SOCS-1, AKT, STAT1, or MAPK/ERK signaling), MerTK ligand (e.g, Gas6 and PROS1) induced enhancement of cell proliferation, or cell survival (e.g, natural killer (NK) cells), modulation of NK cells, dendritic cells or macrophages, phagocytosis, inhibition of proinflammatory cytokine production (e.g, inhibition of TLR-induced production of

proinflammatory cytokines (e.g, TNF, IL-6, IL-12 and type I interferons)).

[00199] In specific embodiments, antibodies described herein specifically bind to human MerTK and block or inhibit (e.g, partially inhibit) binding of MerTK ligand (e.g, Gas6 and PROS1) to MerTK by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or 100% as assessed by methods described herein or known to one of skill in the art, e.g, ELISA assay, flow cytometry, or competition assay.

[00200] In specific embodiments, antibodies described herein specifically bind to human MerTK and do not block or inhibit binding of MerTK ligand (e.g, Gas6) to cell-surface MerTK, e.g., do not inhibit such binding by more than 10%, more than 20%, more than 30% or more than 40% as assessed by cell-based methods described herein or known to one of skill in the art.

[00201] In certain aspects, inhibition by anti-MerTK antibodies described herein (e.g, monoclonal antibody) of MerTK ligand (e.g, Gas6 and PROS1) binding to MerTK can be characterized by ICso values, which reflects the concentration of anti-MerTK antibodies achieving 50% inhibition of binding of MerTK ligand to MerTK. Thus, in specific

embodiments, an anti-MerTK antibody described herein (e.g, antibody Ab3000 or an antigen binding fragment thereof, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody comprising a VH and/or VL of Table 2, or an antibody comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) inhibits binding of MerTK ligand to MerTK with an ICso of at most about 10,000 nM, 1,000 nM, 900 nM, 800 nM, 700 nM, 600 nM, 500 nM, 400 nM, 300 nM, 200 nM, 100 nM, 90 nM, 80 nM, 70 nM, 60 nM, 50 nM, 40 nM, 30 nM, 20 nM, 10 nM, 5 nM, 1 nM, 0.75 nM, 0.5 nM, 0.1 nM, 0.05 nM, 0.01 nM, 0.005 nM, or 0.001 nM, as assessed by methods described herein and/or known to one of skill in the art, (e.g, ELISA assay or flow cytometry). In particular embodiments, an anti-MerTK antibody described herein inhibits binding of MerTK ligand to MerTK with an ICso in the range of about 0.01 nM to 10,000 nM, 0.01 nM to 1,000 nM, 0.05 nM to 500 nM, 0.05 nM to 100 nM, or 0.05 nM to 50 nM, 0.1 nM to 50 nM as assessed by methods described herein and/or known to one of skill in the art, (e.g, ELISA assay or flow cytometry).

[00202] In certain embodiments, an anti-MerTK antibody described herein can inhibit (e.g, partially inhibit) MerTK activity by at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, or 100% as assessed by methods described herein and/or known to one of skill in the art, relative to MerTK activity in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody (e.g, an antibody that does not specifically bind to MerTK). In certain embodiments, an anti- MerTK antibody described herein can inhibit (e.g, partially inhibit) MerTK activity by at least about 25% to about 65% as assessed by methods described herein and/or known to one of skill in the art, relative to MerTK activity in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody (e.g, an antibody that does not specifically bind to MerTK). Non-limiting examples of MerTK activity can include MerTK receptor

phosphorylation, MerTK receptor signaling, MerTK ligand (e.g, Gas6 and PROS I) mediated cell proliferation, and MerTK ligand (e.g., Gas6 and PROS1) mediated cell survival (e.g, natural killer (NK) cells), modulation of maturation of NK cells, dendritic cells or macrophages, phagocytosis, inhibition of proinflammatory cytokine production (e.g, inhibition of TLR- induced production of proinflammatory cytokines (e.g, TNF, IL-6, IL-12 and type I

interferons)).

[00203] In one embodiment, an antibody can block (e.g, partially block) or inhibit (e.g, partially inhibit) (e.g, human MerTK), specifically tyrosine phosphorylation of one or more residues in the cytoplasmic domain of MerTK.

[00204] Thus, in specific embodiments, antibodies described herein (e.g, antibody Ab3000 or an antigen-binding fragment thereof, or an antibody comprising CDRs of an of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) specifically bind to human MerTK and block, inhibit, or reduce tyrosine (e.g, human MerTK) by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%,

45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, or 100% as assessed by methods described herein or known to one of skill in the art, e.g, as described in Section 6, relative to phosphorylation in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody (e.g, an antibody that does not specifically bind to MerTK). In particular embodiments, antibodies described herein specifically bind to MerTK and block or inhibit tyrosine phosphorylation in the cytoplasmic domain of MerTK by at least about 25%, optionally to about 65%, 75%, 80% or 85%, as assessed by methods described herein or known to one of skill in the art, e.g, as described in Section 6, below. In certain embodiments, antibodies described herein specifically bind to MerTK and block or inhibit tyrosine

phosphorylation of MerTK by at least about 25% to about 80% as assessed by methods described herein or known to one of skill in the art, e.g, as described in Section 6, below. In certain embodiments, antibodies described herein (e.g, antibody Ab3000 or an antigen-binding fragment thereof, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) specifically bind to MerTK and block or inhibit tyrosine (e.g, human MerTK) by at least about 50% to about 100% as assessed by methods described herein or known to one of skill in the art, e.g ., as described in Section 6, below.

[00205] In specific embodiments, antibodies described herein specifically bind to MerTK and block or inhibit tyrosine phosphorylation of MerTK with an ICso of less than about 10 nM, about 1 nM, about 500 pM, about 400 pM, about 200 pM, or about 100 pM, as assessed by methods described herein in Section 6 below or known to one of skill in the art. In specific embodiments, antibodies described herein specifically bind to MerTK and block or inhibit tyrosine

phosphorylation of MerTK with an ICso in the range of about 10 nM to about 100 pM, about 1 nM to 100 pM, or about 500 pM to about 100 pM. For example, an ICso for inhibition of tyrosine phosphorylation can be determined by assaying lysates from cells, recombinantly expressing MerTK, in ELISA which detects tyrosine phosphorylation, for example, as described in Section 6 below. In certain embodiments, cells, recombinantly expressing MerTK, are sorted, e.g. , sorted to select for cells highly expressing MerTK, prior to use in the phosphorylation inhibition assays. In some embodiments, the cells are not sorted prior to use in the

phosphorylation inhibition assays.

[00206] In specific embodiments, antibodies described herein (e.g, antibody Ab3000 or an antigen-binding fragment thereof, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) specifically bind to MerTK and block or inhibit phosphorylation of one or more tyrosine residues in the cytoplasmic domain of MerTK by at least about 5%,

10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%,

90%, 95%, 98%, 99%, or 100% as assessed by methods described herein or known to one of skill in the art, e.g, immunoblotting assay, relative to phosphorylation in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody (e.g, an antibody that does not specifically bind to MerTK). In specific embodiments, blocking or inhibition (e.g, partial inhibition) of phosphorylation of MerTK by antibodies described herein can be assessed upon MerTK ligand stimulation.

[00207] Signaling events downstream of MerTK receptor phosphorylation can serve as indicators of MerTK activity. For example, MerTK ligand (e.g, Gas6 and PROS1) binding to its receptor MerTK stimulates several distinct signaling pathways, including for example members of phosphatidylinositol (PI) 3 -kinases, and mitogen-activated protein kinase (MAPK) (see Korshunov, Clin. Sci. (Lond.), 2012, 122(8):361-368).

[00208] Thus, in certain aspects, anti-MerTK antibodies described herein which act as inhibitors of MerTK activity (e.g., antibody Ab3000 or an antigen-binding fragment thereof, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) can inhibit signaling of a member of the PI 3-kinases or MAPK. In particular embodiments, anti- MerTK antibodies described herein which act as inhibitors of MerTK activity can inhibit binding (or inhibit interaction), to the cytoplasmic domain of MerTK, of one or more of PI3K, PLC, and Grb2. In certain embodiments, anti-MerTK antibodies described herein which act as inhibitors of MerTK activity can inhibit activation by MerTK of one or more of PI3K, PLC, and Grb2.

[00209] In particular embodiments, anti-MerTK antibodies described herein which act as inhibitors of MerTK activity (e.g, antibody Ab3000 or an antigen-binding fragment thereof, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) can inhibit downstream signaling such as phosphorylation of MAPK, phosphorylation of P13K, or phosphorylation of AKT. Thus, in certain embodiments, an anti-MerTK antibody described herein can inhibit or reduce phosphorylation of MAPK (e.g, MerTK ligand (e.g, Gas6 and PROS1) induced phosphorylation of MAPK) by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or 99% as assessed by methods described herein or known to one of skill in the art, e.g, Western blot or ELISA assay as described in Section 6 or immunoblotting assay, relative to phosphorylation in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody (e.g, an antibody that does not specifically bind to MerTK). In certain embodiments, an anti- MerTK antibody described herein can inhibit or reduce phosphorylation of AKT (e.g, MerTK ligand (e.g, Gas6 and PROS1) induced phosphorylation of AKT) by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, or 99% as assessed by methods described herein or known to one of skill in the art, e.g, as described in Section 6, relative to phosphorylation in the presence of MerTK ligand stimulation without any antibody or with an unrelated antibody ( e.g ., an antibody that does not specifically bind to MerTK).

[00210] Cells and cell lines which are appropriate for use in the assays described herein relating to MerTK activity are readily available (e.g., ATCC) or can be readily identified using methods known in the art. For example, cells and/or cell lines that express MerTK endogenously or that possess MerTK signaling or activity are known to one of skill in the art. In certain embodiments, cells or cell lines that are appropriate for use in the assays described herein can express MerTK, either endogenously or recombinantly.

[00211] Non-limiting examples of cells that can be used in the methods and assays described herein include primary cells, transformed cells, stem cells, mast cells, primordial germ cells, oocytes, spermatocytes, embryonic stem cells, hematopoietic cells, erythroleukemia cells (e.g, F36P and TF-1 cell lines), human monocytic cell lines, e.g, acute monocytic leukemia cell lines, human myeloid leukemia cell lines, such as M07E cells; gastrointestinal stromal tumor cell lines such as ST-882, GIST430, and GIST882; neuroblastoma cell lines such as SK-N-SH, SK-SY5Y, H-EP1, SK-N-BE(2), SK-N-BE(ZkM17), SK-N-BE(2)C, LA-N-1, or LA-N-l-5s; small cell lung carcinoma cell lines such as H526, ECC12, TMK1, MKN7, GCIY, and HGC27; and melanoma cell lines such as SKMEL3, SKMEL5, G361, MALME-3M, HMCB. In particular embodiments, cells that can be used in the methods and assays described herein include immune cells, such as macrophages, dendritic cells, and natural killer (NK) cells. In particular embodiments, cells that can be used in the methods and assay described herein include THP1 cells.

[00212] Alternatively, cells and cell lines that express MerTK, e.g, human MerTK, can routinely be generated recombinantly. Non-limiting examples of cells that can be engineered to express MerTK recombinantly include COS cells, HEK 293 cells, CHO cells, H1299 cells, fibroblasts (e.g, human fibroblasts) such as NIH3T3 cells, and MEFS. In a specific

embodiment, cells for use in the methods described herein are HEK 293 cells expressing human MerTK ECD.

5.2 Antibody Production

[00213] Antibodies described herein (or an antigen-binding fragment thereof) that specifically bind to MerTK (e.g, ECD of human MerTK) can be produced by any method known in the art for the synthesis of antibodies, for example, by chemical synthesis or by recombinant expression techniques. The methods described herein employs, unless otherwise indicated, conventional techniques in molecular biology, microbiology, genetic analysis, recombinant DNA, organic chemistry, biochemistry, PCR, oligonucleotide synthesis and modification, nucleic acid hybridization, and related fields within the skill of the art. These techniques are described, for example, in the references cited herein and are fully explained in the literature. See, e.g ., Maniatis et al. (1982) Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory Press; Sambrook et al. (1989), Molecular Cloning: A Laboratory Manual Second Edition, Cold Spring Harbor Laboratory Press; Sambrook et al. (2001) Molecular Cloning: A Laboratory Manual Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Ausubel et al, Current Protocols in Molecular Biology John Wiley & Sons (1987 and annual updates); Current Protocols in Immunology John Wiley & Sons (1987 and annual updates) Gait (ed.) (1984) Oligonucleotide Synthesis: A Practical Approach. IRL Press; Eckstein (ed.) (1991)

Oligonucleotides and Analogues: A Practical Approach. IRL Press; Birren et al. (eds.) (1999) Genome Analysis: A Laboratory Manual Cold Spring Harbor Laboratory Press.

[00214] In a specific embodiment, an antibody described herein is an antibody (e.g., recombinant antibody) prepared, expressed, created or isolated by any means that involves creation, e.g, via synthesis, genetic engineering of DNA sequences. In certain embodiments, such antibody comprise sequences (e.g, DNA sequences or amino acid sequences) that do not naturally exist within the antibody germline repertoire of an animal or mammal (e.g, human) in vivo.

[00215] In a certain aspect, provided herein is a method of making an antibody or an antigen binding fragment thereof that specifically binds to human MerTK comprising culturing a cell or host cell described herein. In a certain aspect, provided herein is a method of making an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK comprising expressing (e.g, recombinantly expressing) the antibody or antigen-binding fragment thereof using a cell or host cell described herein (e.g, a cell or a host cell comprising

polynucleotides encoding an antibody described herein). In a particular embodiment, the cell is an isolated cell. In a particular embodiment, the exogenous polynucleotides have been introduced into the cell. In a particular embodiment, the method further comprises the step of purifying the antibody or antigen-binding fragment thereof obtained from the cell or host cell. [00216] Monoclonal antibodies can be prepared using a wide variety of techniques known in the art including the use of hybridoma, recombinant, and phage display technologies, or a combination thereof. For example, monoclonal antibodies can be produced using hybridoma techniques including those known in the art and taught, for example, in Harlow et ah,

Antibodies: A Laboratory Manual (Cold Spring Harbor Laboratory Press, 2nd ed. 1988);

Hammerling et ah, in: Monoclonal Antibodies and T-Cell Hybridomas 563 681 (Elsevier, N.Y., 1981). The term“monoclonal antibody” as used herein is not limited to antibodies produced through hybridoma technology. For example, monoclonal antibodies can be produced recombinantly from host cells exogenously expressing an antibody described herein ( e.g ., anti- MerTK antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or a fragment thereof, for example, light chain and/or heavy chain of such antibody.

[00217] Methods for producing and screening for specific antibodies using hybridoma technology are routine and well known in the art. For example, in the hybridoma method, a mouse or other appropriate host animal, such as a sheep, goat, rabbit, rat, hamster or macaque monkey, is immunized to elicit lymphocytes that produce or are capable of producing antibodies that will specifically bind to the protein (e.g., ECD of human MerTK) used for immunization. Alternatively, lymphocytes may be immunized in vitro. Lymphocytes then are fused with myeloma cells using a suitable fusing agent, such as polyethylene glycol, to form a hybridoma cell (Goding, Monoclonal Antibodies: Principles and Practice, pp. 59-103 (Academic Press, 1986)). Additionally, a RIMMS (repetitive immunization multiple sites) technique can be used to immunize an animal (Kilptrack et ak, 1997 Hybridoma 16:381-9, incorporated by reference in its entirety).

[00218] In some embodiments, mice (or other animals, such as rats, monkeys, donkeys, pigs, sheep, hamster, or dogs) can be immunized with an antigen (e.g, MerTK, for example human MerTK) and once an immune response is detected, e.g, antibodies specific for the antigen are detected in the mouse serum, the mouse spleen is harvested and splenocytes isolated. The splenocytes are then fused by well known techniques to any suitable myeloma cells, for example cells from cell line SP20 available from the American Type Culture Collection (ATCC®) (Manassas, VA), to form hybridomas. Hybridomas are selected and cloned by limited dilution. In certain embodiments, lymph nodes of the immunized mice are harvested and fused with NSO myeloma cells.

[00219] The hybridoma cells thus prepared are seeded and grown in a suitable culture medium that preferably contains one or more substances that inhibit the growth or survival of the unfused, parental myeloma cells. For example, if the parental myeloma cells lack the enzyme

hypoxanthine guanine phosphoribosyl transferase (HGPRT or HPRT), the culture medium for the hybridomas typically will include hypoxanthine, aminopterin, and thymidine (HAT medium), which substances prevent the growth of HGPRT-deficient cells.

[00220] Specific embodiments employ myeloma cells that fuse efficiently, support stable high-level production of antibody by the selected antibody-producing cells, and are sensitive to a medium such as HAT medium. Among these myeloma cell lines are murine myeloma lines, such as NSO cell line or those derived from MOPC-21 and MPC-11 mouse tumors available from the Salk Institute Cell Distribution Center, San Diego, CA, USA, and SP-2 or X63-Ag8.653 cells available from the American Type Culture Collection, Rockville, MD, USA. Human myeloma and mouse-human heteromyeloma cell lines also have been described for the production of human monoclonal antibodies (Kozbor, J. Immunol., 133:3001 (1984); Brodeur et ah, Monoclonal Antibody Production Techniques and Applications, pp. 51-63 (Marcel Dekker, Inc., New York, 1987)).

[00221] Culture medium in which hybridoma cells are growing is assayed for production of monoclonal antibodies directed against human MerTK antigen (e.g, ECD of human MerTK).

The binding specificity of monoclonal antibodies produced by hybridoma cells is determined by methods known in the art, for example, immunoprecipitation or by an in vitro binding assay, such as radioimmunoassay (RIA) or enzyme-linked immunoabsorbent assay (ELISA).

[00222] After hybridoma cells are identified that produce antibodies of the desired specificity, affinity, and/or activity, the clones may be subcloned by limiting dilution procedures and grown by standard methods (Goding, Monoclonal Antibodies: Principles and Practice, pp. 59-103 (Academic Press, 1986)). Suitable culture media for this purpose include, for example, D-MEM or RPMI 1640 medium. In addition, the hybridoma cells may be grown in vivo as ascites tumors in an animal.

[00223] The monoclonal antibodies secreted by the subclones are suitably separated from the culture medium, ascites fluid, or serum by conventional immunoglobulin purification procedures such as, for example, protein A-Sepharose, hydroxylapatite chromatography, gel electrophoresis, dialysis, or affinity chromatography.

[00224] In some embodiments, antibody variants having an improved property such as affinity, stability, and/or expression level as compared to a parent antibody may be prepared by affinity maturation. Affinity maturation techniques that are known in the art and/or described herein can be used to alter the CDR region(s), followed by screening of the resultant binding molecules for the desired change in binding. Without being bound by theory, libraries of antibodies can be displayed on the surface of an organism ( e.g ., phage, bacteria, yeast, or mammalian cell) or in association with their encoding mRNA or DNA (e.g., covalently or non- covalently). Affinity selection of the displayed antibodies allows isolation of organisms or complexes carrying the genetic information encoding the antibodies. Two or three rounds of mutation and selection using display methods such as phage display usually results in antibody fragments with improved affinities (e.g, in the low nanomolar or picomolar range). Further methods that can be used to generate antibody libraries and/or antibody affinity maturation are disclosed in Holland et al., 2013, J. of Immunol. Methods 394:55-61, incorporated herein by reference in its entirety.

[00225] Antibodies described herein include antibody fragments which recognize specific MerTK antigens (e.g, ECD of MerTK) and can be generated by any technique known to those of skill in the art. For example, Fab and F(ab’)2 fragments described herein can be produced by proteolytic cleavage of immunoglobulin molecules, using enzymes such as papain (to produce Fab fragments) or pepsin (to produce F(ab’)2 fragments). A Fab fragment corresponds to one of the two identical arms of an antibody molecule and contains the complete light chain paired with the VH and CHI domains of the heavy chain. A F(ab’)2 fragment contains the two antigen binding arms of an antibody molecule linked by disulfide bonds in the hinge region.

[00226] Further, the antibodies described herein or antigen-binding fragments thereof can also be generated using various phage display methods known in the art. In phage display methods, functional antibody domains are displayed on the surface of phage particles which carry the polynucleotide sequences encoding them. In particular, DNA sequences encoding VH and VL domains are amplified from animal cDNA libraries (e.g., human or murine cDNA libraries of affected tissues). The DNA encoding the VH and VL domains are recombined together with an scFv linker by PCR and cloned into a phagemid vector. The vector is electroporated in E. coli and the E. coli is infected with helper phage. Phage used in these methods are typically filamentous phage including fd and Ml 3, and the VH and VL domains are usually recombinantly fused to either the phage gene III or gene VIII. Phage expressing an antigen binding domain that binds to a particular antigen can be selected or identified with antigen, e.g ., using labeled antigen or antigen bound or captured to a solid surface or bead. Examples of phage display methods that can be used to make the antibodies described herein include those disclosed in Brinkman et ah, 1995, J. Immunol. Methods 182:41-50; Ames et ah, 1995, J. Immunol. Methods 184: 177-186; Kettleborough et ah, 1994, Eur. J. Immunol. 24:952-958; Persic et ah, 1997, Gene 187:9-18; Burton et ah, 1994, Advances in Immunology 57: 191-280; PCT Application No. PCT/GB91/01 134; International Publication Nos. WO 90/02809, WO 91/10737, WO 92/01047, WO 92/18619, WO 93/1 1236, WO 95/15982, WO 95/20401, and W097/13844; and U.S. Patent Nos.

5,698,426, 5,223,409, 5,403,484, 5,580,717, 5,427,908, 5,750,753, 5,821,047, 5,571,698, 5,427,908, 5,516,637, 5,780,225, 5,658,727, 5,733,743 and 5,969,108.

[00227] As described in the above references, after phage selection, the antibody coding regions from the phage can be isolated and used to generate whole antibodies, including human antibodies, or any other desired antigen binding fragment, and expressed in any desired host, including mammalian cells, insect cells, plant cells, yeast, and bacteria, e.g. , as described below. Techniques to recombinantly produce antibody fragments such as Fab, Fab’ and F(ab’)2 fragments can also be employed using methods known in the art such as those disclosed in PCT publication No. WO 92/22324; Mullinax et ak, 1992, BioTechniques 12(6):864-869; Sawai et ah, 1995, AJRI 34:26-34; and Better et ak, 1988, Science 240: 1041-1043.

[00228] In one aspect, to generate whole antibodies, PCR primers including VH or VL nucleotide sequences, a restriction site, and a flanking sequence to protect the restriction site can be used to amplify the VH or VL sequences from a template, e.g. , scFv clones. Utilizing cloning techniques known to those of skill in the art, the PCR amplified VH domains can be cloned into vectors expressing a VH constant region, and the PCR amplified VL domains can be cloned into vectors expressing a VL constant region, e.g. , human kappa or lambda constant regions. The VH and VL domains can also be cloned into one vector expressing the necessary constant regions. The heavy chain conversion vectors and light chain conversion vectors are then co-transfected into cell lines to generate stable or transient cell lines that express full-length antibodies, e.g. ,

IgG, using techniques known to those of skill in the art. [00229] A chimeric antibody is a molecule in which different portions of the antibody are derived from different immunoglobulin molecules. For example, a chimeric antibody can contain a variable region of a mouse or rat monoclonal antibody fused to a constant region of a human antibody. Methods for producing chimeric antibodies are known in the art. See, e.g ., Morrison, 1985, Science 229: 1202; Oi et al., 1986, BioTechniques 4:214; Gillies et al., 1989, J. Immunol. Methods 125: 191-202; and U.S. Patent Nos. 5,807,715, 4,816,567, 4,816,397, and 6,331,415.

[00230] A humanized antibody is capable of binding to a predetermined antigen and which comprises a framework region having substantially the amino acid sequence of a human immunoglobulin and CDRs having substantially the amino acid sequence of a non-human immunoglobulin (e.g, a murine immunoglobulin). In particular embodiments, a humanized antibody also comprises at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin. The antibody also can include the CHI, hinge, CH2, CH3, and CH4 regions of the heavy chain. A humanized antibody can be selected from any class of immunoglobulins, including IgM, IgG, IgD, IgA and IgE, and any isotype, including IgGi, IgG2, IgG3 and IgG4. Humanized antibodies can be produced using a variety of techniques known in the art, including but not limited to, CDR-grafting (European Patent No. EP 239,400;

International publication No. WO 91/09967; and U.S. Patent Nos. 5,225,539, 5,530,101, and 5,585,089), veneering or resurfacing (European Patent Nos. EP 592,106 and EP 519,596; Padlan, 1991, Molecular Immunology 28(4/5):489-498; Studnicka et al., 1994, Protein Engineering 7(6):805-814; and Roguska et al., 1994, PNAS 91 :969-973), chain shuffling (U.S. Patent No. 5,565,332), and techniques disclosed in, e.g, U.S. Pat. No. 6,407,213, U.S. Pat. No. 5,766,886, WO 9317105, Tan et al., J. Immunol. 169: 1119 25 (2002), Caldas et al., Protein Eng. 13(5):353- 60 (2000), Morea et al., Methods 20(3):267 79 (2000), Baca et al., J. Biol. Chem.

272(16): 10678-84 (1997), Roguska et al., Protein Eng. 9(10):895 904 (1996), Couto et al.,

Cancer Res. 55 (23 Supp):5973s- 5977s (1995), Couto et al., Cancer Res. 55(8): 1717-22 (1995), Sandhu JS, Gene 150(2):409-10 (1994), and Pedersen et al., J. Mol. Biol. 235(3):959-73 (1994). See also U.S. Patent Pub. No. US 2005/0042664 Al (Feb. 24, 2005), which is incorporated by reference herein in its entirety. [00231] Methods for making multispecific (e.g, bispecific antibodies) have been described, see, for example, U.S. Patent Nos. 7951917, 7183076, 8227577, 5837242, 5989830, 5869620, 6132992, and 8586713.

[00232] Single domain antibodies, for example, antibodies lacking the light chains, can be produced by methods well-known in the art. See Riechmann et ak, 1999, J. Immunol. 231 :25- 38; Nuttall et ak, 2000, Curr. Pharm. Biotechnok l(3):253-263; Muylderman, 2001, J.

Biotechnok 74(4):277302; U.S. Patent No. 6,005,079; and International Publication Nos. WO 94/04678, WO 94/25591, and WO 01/44301.

[00233] Further, antibodies that specifically bind to a MerTK antigen can, in turn, be utilized to generate anti-idiotype antibodies that“mimic” an antigen using techniques well known to those skilled in the art. (See, e.g., Greenspan & Bona, 1989, FASEB J. 7(5):437-444; and Nissinoff, 1991, J. Immunol. 147(8):2429-2438).

[00234] Human antibodies which specifically bind to an ECD of human MerTK can be made by a variety of methods known in the art including phage display methods described above using antibody libraries derived from human immunoglobulin sequences. See also U.S. Patent NOs. 4,444,887 and 4,716,111; and International Publication Nos. WO 98/46645, WO 98/50433, WO 98/24893, WO 98/16654, WO 96/34096, WO 96/33735, and WO 91/10741.

[00235] In some embodiments, human antibodies can be produced using mouse-human hybridomas. For example, human peripheral blood lymphocytes transformed with Epstein-Barr virus (EBV) can be fused with mouse myeloma cells to produce mouse-human hybridomas secreting human monoclonal antibodies, and these mouse-human hybridomas can be screened to determine ones which secrete human monoclonal antibodies that specifically bind to a target antigen (e.g, ECD of human MerTK). Such methods are known and are described in the art, see, e.g, Shinmoto et ak, Cytotechnology, 2004, 46: 19-23; Naganawa et ak, Human Antibodies, 2005, 14:27-31.

5.2.1 Polynucleotides

[00236] In certain aspects, provided herein are polynucleotides comprising a nucleotide sequence encoding an antibody described herein or a fragment thereof (e.g., a variable light chain region and/or variable heavy chain region) that specifically binds to a MerTK antigen, and vectors, e.g, vectors comprising such polynucleotides for recombinant expression in host cells (e.g., E. coli and mammalian cells). Provided herein are polynucleotides comprising nucleotide sequences encoding any of the antibodies provided herein, as well as vectors comprising such polynucleotide sequences, e.g. , expression vectors for their efficient expression in host cells, e.g, mammalian cells.

[00237] As used herein, an“isolated” polynucleotide or nucleic acid molecule is one which is separated from other nucleic acid molecules which are present in the natural source (e.g, in a mouse or a human) of the nucleic acid molecule. Moreover, an“isolated” nucleic acid molecule, such as a cDNA molecule, can be substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. For example, the language“substantially free” includes preparations of polynucleotide or nucleic acid molecule having less than about 15%, 10%, 5%, 2%, 1%, 0.5%, or 0.1% (in particular less than about 10%) of other material, e.g, cellular material, culture medium, other nucleic acid molecules, chemical precursors and/or other chemicals. In a specific embodiment, a nucleic acid molecule(s) encoding an antibody described herein is isolated or purified.

[00238] In particular aspects, provided herein are polynucleotides comprising nucleotide sequences encoding antibodies or antigen-binding fragments thereof, which specifically bind to a MerTK polypeptide (e.g, human MerTK, for example, human MerTK) and comprises an amino acid sequence as described herein, as well as antibodies which compete with such antibodies for binding to a MerTK polypeptide (e.g, in a dose-dependent manner), or which binds to the same epitope as that of such antibodies.

[00239] In certain aspects, provided herein are polynucleotides comprising a nucleotide sequence encoding the light chain or heavy chain of an antibody described herein. The polynucleotides can comprise nucleotide sequences encoding a light chain comprising the VL of antibodies described herein (see, e.g, Table 2). The polynucleotides can comprise nucleotide sequences encoding a heavy chain comprising the VH of antibodies described herein (see, e.g, Table 2). In specific embodiments, a polynucleotide described herein encodes a VL chain region comprising the amino acid sequence of SEQ ID NO: 2. In specific embodiments, a

polynucleotide described herein encodes a VH chain region comprising the amino acid sequence of SEQ ID NO: 1. [00240] In particular embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g. , containing VL CDR1, VL CDR2, and VL CDR3 of Table 1. In specific embodiments, provided herein are polynucleotides comprising three VH chain CDRs, e.g. , containing VH CDR1, VH CDR2, and VH CDR3 of Table 1. In specific embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g., containing VL CDR1, VL CDR2, and VL CDR3 of Table 1 and three VH chain CDRs, e.g, containing VH CDR1, VH CDR2, and VH CDR3 of Table 1.

[00241] In particular embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g, containing VL CDR1, VL CDR2, and VL CDR3 of Table 3. In specific embodiments, provided herein are polynucleotides comprising three VH chain CDRs, e.g, containing VH CDR1, VH CDR2, and VH CDR3 of Table 3. In specific embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g., containing VL CDR1, VL CDR2, and VL CDR3 of Table 3 and three VH chain CDRs, e.g, containing VH CDR1, VH CDR2, and VH CDR3 of Table 3.

[00242] In particular embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g, containing VL CDR1, VL CDR2, and VL CDR3 of Table 4. In specific embodiments, provided herein are polynucleotides comprising three VH chain CDRs, e.g, containing VH CDR1, VH CDR2, and VH CDR3 of Table 4. In specific embodiments, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody comprising three VL chain CDRs, e.g., containing VL CDR1, VL CDR2, and VL CDR3 of Table 4 and three VH chain CDRs, e.g, containing VH CDR1, VH CDR2, and VH CDR3 of Table 4.

[00243] In certain embodiments, a polynucleotide described herein comprises a nucleotide sequence encoding an antibody provided herein comprising a variable light (VL) chain region comprising an amino acid described herein, wherein the antibody specifically binds to a MerTK polypeptide, e.g, a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK).

[00244] In certain embodiments, a polynucleotide described herein comprises a nucleotide sequence encoding an antibody provided herein comprising a variable heavy (VH) chain region comprising an amino acid sequence described herein, wherein the antibody specifically binds to a MerTK polypeptide, e.g. , a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK).

[00245] In specific embodiments, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein comprising: framework regions (e.g, framework regions of the VL domain and VH domain) that are human framework regions, wherein the antibody specifically binds a MerTK polypeptide, e.g, a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK).

[00246] In specific aspects, provided herein is a polynucleotide comprising a nucleotide sequence encoding an antibody comprising a light chain and a heavy chain, e.g, a separate light chain and heavy chain. With respect to the light chain, in a specific embodiment, a

polynucleotide provided herein comprises a nucleotide sequence encoding a kappa light chain.

In another specific embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding a lambda light chain. In yet another specific embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein comprising a human kappa light chain or a human lambda light chain. In a particular

embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein, which specifically binds to a MerTK polypeptide, e.g, a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK), wherein the antibody comprises a light chain, and wherein the amino acid sequence of the VL chain region can comprise any amino acid sequence described herein (e.g, SEQ ID NO: 1), and wherein the constant region of the light chain comprises the amino acid sequence of a human kappa light chain constant region. In another particular embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein, which specifically binds to a MerTK polypeptide, e.g, a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK), and comprises a light chain, wherein the amino acid sequence of the VL chain region can comprises any amino acid sequence described herein (e.g, SEQ ID NO: 2), and wherein the constant region of the light chain comprises the amino acid sequence of a human lambda light chain constant region. For example, human constant region sequences can be those described in U.S. Patent No. 5,693,780. In some embodiments, human constant region sequences can comprise the amino acid sequence of SEQ ID NO: 31. In some embodiments, human constant region sequences can comprise the amino acid sequence of SEQ ID NO: 32. In some embodiments, human constant region sequences can comprise the amino acid sequence of SEQ ID NO: 33.

[00247] In a particular embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein, which specifically binds to a MerTK polypeptide, e.g ., a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK), wherein the antibody comprises a heavy chain, wherein the amino acid sequence of the VEl chain region can comprise any amino acid sequence described herein (e.g, SEQ ID NO: 1), and wherein the constant region of the heavy chain comprises the amino acid sequence of a human gamma (g) heavy chain constant region.

[00248] In yet another specific embodiment, a polynucleotide provided herein comprises a nucleotide sequence encoding an antibody described herein (or an antigen-binding fragment thereof), which specifically binds a MerTK polypeptide, e.g, a human MerTK polypeptide, for example, human MerTK (e.g, human MerTK), wherein the antibody comprises a VL chain region and a VH chain region comprising any amino acid sequences described herein, and wherein the constant regions comprise the amino acid sequences of the constant regions of a human IgGl (e.g, isotype a, z, or f), human IgG2, or human IgG4.

[00249] In a specific embodiment, provided herein are polynucleotides comprising a nucleotide sequence encoding an anti-MerTK antibody, or an antigen-binding fragment or domain thereof, designated herein.

[00250] As a non-limiting example, in some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprises nucleotide sequence of SEQ ID NO: 42, wherein the nucleotide sequence for SEQ ID NO: 42 is

C AGGT GC AGCTGGTGGAGTCTGGGGGAGGCGT GGTCC AGCCTGGGAGGTCCCTGAG

ACTCTCCTGTGCAGCGTCTGGATTCACCTTCAGGAGTTATGGCATGCACTGGGTCCG

CCAGGCTCCAGGCAAGGGGCTGGAGTGGGTGGCAGTTATATGGAATGATGGAAGTA

ATAAATACTCTGCAGACTCCGTGAAGGGCCGATTCACCATCTCCAGAGACAATTCCA

AGAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCTGTGTAC

TACTGTGCGAGAGTGGGGTATAGTGGGACCTACTACTACTACTACGGTATGGACGTC

TGGGGCCAAGGGACCACGGTCACCGTCTCCTCA. [00251] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that further comprises a signal sequence. As a non-limiting example, in some embodiments, in certain embodiments, the signal sequence can comprise the nucleotide sequence of SEQ ID NO: 44, wherein the nucleotide sequence for SEQ ID NO: 44 comprises

ATGGAGTTTGGGCTGAGCTGGGTTTTCCTCGTTGCTCTTTTAAGAGGTGTCCAGTGT.

[00252] In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprises nucleotide sequence of SEQ ID NO: 40, wherein the nucleotide sequence for SEQ ID NO: 40 is

ATGGAGTTTGGGCTGAGCTGGGTTTTCCTCGTTGCTCTTTTAAGAGGTGTCCAGTGTC

AGGTGCAGCTGGTGGAGTCTGGGGGAGGCGTGGTCCAGCCTGGGAGGTCCCTGAGA

CTCTCCTGTGCAGCGTCTGGATTCACCTTCAGGAGTTATGGCATGCACTGGGTCCGC

C AGGCTCC AGGC A AGGGGC T GGAGT GGGT GGC AGTT AT AT GGA AT GAT GG A AGT A A

TAAATACTCTGCAGACTCCGTGAAGGGCCGATTCACCATCTCCAGAGACAATTCCAA

GAACACGCTGTATCTGCAAATGAACAGCCTGAGAGCCGAGGACACGGCTGTGTACT

ACTGTGCGAGAGTGGGGTATAGTGGGACCTACTACTACTACTACGGTATGGACGTCT

GGGGCCAAGGGACCACGGTCACCGTCTCCTCA.

[00253] In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprises nucleotide sequence of SEQ ID NO: 43, wherein the nucleotide sequence for SEQ ID NO: 43 is

GACATCCAGTTGACCCAGTCTCCATCCTTCCTGTCTGCATCTGTAGGAGACAGAGTC

ACCATCACTTGCCGGGCCAGTCAGGGCATTAGTAATTATTTAGCCTGGTATCAGCAA

AAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCACTTTGCAAAGTGGG

GTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGAATTCACTCTCACAATCAGC

AGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAACAACTTAATCGTTTATTCA

CTTTCGGCCCTGGGACCAAAGTGGATATCAAA.

[00254] In certain embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that further comprises a signal sequence. As a non-limiting example, in some embodiments, in certain embodiments, the signal sequence can comprise the nucleotide sequence of SEQ ID NO: 45, wherein the nucleotide sequence for SEQ ID NO: 45 comprises

ATGAGGGTCCCCGCTCAGCTCCTGGGGCTCCTGCTGCTCTGGCTCCCAGGTGCCAGA TGT.

[00255] In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprises nucleotide sequence of SEQ ID NO: 41, wherein the nucleotide sequence for SEQ ID NO: 41 is

ATGAGGGTCCCCGCTCAGCTCCTGGGGCTCCTGCTGCTCTGGCTCCCAGGTGCCAGA

TGTGACATCCAGTTGACCCAGTCTCCATCCTTCCTGTCTGCATCTGTAGGAGACAGA

GTCACCATCACTTGCCGGGCCAGTCAGGGCATTAGTAATTATTTAGCCTGGTATCAG

CAAAAACCAGGGAAAGCCCCTAAGCTCCTGATCTATGCTGCATCCACTTTGCAAAGT

GGGGTCCCATCAAGGTTCAGCGGCAGTGGATCTGGGACAGAATTCACTCTCACAATC

AGCAGCCTGCAGCCTGAAGATTTTGCAACTTATTACTGTCAACAACTTAATCGTTTA

TTCACTTTCGGCCCTGGGACCAAAGTGGATATCAAA.

[00256] In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprising a nucleotide sequence having at least 80%, at least 85%, at least 90%, at least 95%, or more sequence identity to SEQ ID NO: 42. In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprising a nucleotide sequence having at least 80%, at least 85%, at least 90%, at least 95%, or more sequence identity to SEQ ID NO: 43. In certain embodiments, an antibody described herein, which specifically binds to a MerTK polypeptide (e.g, human MerTK), can be encoded by a nucleotide that comprising a nucleotide sequence having at least 80%, at least 85%, at least 90%, at least 95%, or more sequence identity to SEQ ID NO: 42 and a nucleotide that comprising a nucleotide sequence having at least 80%, at least 85%, at least 90%, at least 95%, or more sequence identity to SEQ ID NO: 43.

[00257] Also provided herein are polynucleotides encoding an anti-MerTK antibody or a fragment thereof that are optimized, e.g, by codon/RNA optimization, replacement with heterologous signal sequences, and elimination of mRNA instability elements. Methods to generate optimized nucleic acids encoding an anti-MerTK antibody or a fragment thereof (e.g., light chain, heavy chain, VH domain, or VL domain) for recombinant expression by introducing codon changes and/or eliminating inhibitory regions in the mRNA can be carried out by adapting the optimization methods described in, e.g., U.S. Patent Nos. 5,965,726; 6,174,666; 6,291,664; 6,414,132; and 6,794,498, accordingly. For example, potential splice sites and instability elements (e.g., A/T or A/U rich elements) within the RNA can be mutated without altering the amino acids encoded by the nucleic acid sequences to increase stability of the RNA for recombinant expression. The alterations utilize the degeneracy of the genetic code, e.g, using an alternative codon for an identical amino acid. In some embodiments, it can be desirable to alter one or more codons to encode a conservative mutation, e.g, a similar amino acid with similar chemical structure and properties and/or function as the original amino acid. Such methods can increase expression of an anti-MerTK antibody or fragment thereof by at least 1 fold, 2 fold, 3 fold, 4 fold, 5 fold, 10 fold, 20 fold, 30 fold, 40 fold, 50 fold, 60 fold, 70 fold, 80 fold, 90 fold, or 100 fold or more relative to the expression of an anti-MerTK antibody encoded by

polynucleotides that have not been optimized.

[00258] In certain embodiments, an optimized polynucleotide sequence encoding an anti- MerTK antibody described herein or a fragment thereof (e.g, VL domain and/or VH domain) can hybridize to an antisense (e.g, complementary) polynucleotide of an unoptimized polynucleotide sequence encoding an anti-MerTK antibody described herein or a fragment thereof (e.g, VL domain and/or VH domain). In specific embodiments, an optimized nucleotide sequence encoding an anti-MerTK antibody described herein or a fragment hybridizes under high stringency conditions to antisense polynucleotide of an unoptimized polynucleotide sequence encoding an anti-MerTK antibody described herein or a fragment thereof. In a specific embodiment, an optimized nucleotide sequence encoding an anti-MerTK antibody described herein or a fragment thereof hybridizes under high stringency, intermediate or lower stringency hybridization conditions to an antisense polynucleotide of an unoptimized nucleotide sequence encoding an anti-MerTK antibody described herein or a fragment thereof. Information regarding hybridization conditions have been described, see, e.g, U.S. Patent Application Publication No. US 2005/0048549 (e.g, paragraphs 72-73), which is incorporated herein by reference.

[00259] The polynucleotides can be obtained, and the nucleotide sequence of the

polynucleotides determined, by any method known in the art. Nucleotide sequences encoding antibodies described herein and modified versions of these antibodies can be determined using methods well known in the art, i.e., nucleotide codons known to encode particular amino acids are assembled in such a way to generate a nucleic acid that encodes the antibody. Such a polynucleotide encoding the antibody can be assembled from chemically synthesized

oligonucleotides ( e.g ., as described in Kutmeier et ah, 1994, BioTechniques 17:242), which, briefly, involves the synthesis of overlapping oligonucleotides containing portions of the sequence encoding the antibody, annealing and ligating of those oligonucleotides, and then amplification of the ligated oligonucleotides by PCR.

[00260] Alternatively, a polynucleotide encoding an antibody described herein can be generated from nucleic acid from a suitable source (e.g., a hybridoma) using methods well known in the art (e.g, PCR and other molecular cloning methods). For example, PCR amplification using synthetic primers hybridizable to the 3’ and 5’ ends of a known sequence can be performed using genomic DNA obtained from hybridoma cells producing the antibody of interest. Such PCR amplification methods can be used to obtain nucleic acids comprising the sequence encoding the light chain and/or heavy chain of an antibody. Such PCR amplification methods can be used to obtain nucleic acids comprising the sequence encoding the variable light chain region and/or the variable heavy chain region of an antibody. The amplified nucleic acids can be cloned into vectors for expression in host cells and for further cloning, for example, to generate chimeric and humanized antibodies.

[00261] If a clone containing a nucleic acid encoding a particular antibody is not available, but the sequence of the antibody molecule is known, a nucleic acid encoding the

immunoglobulin can be chemically synthesized or obtained from a suitable source (e.g, an antibody cDNA library or a cDNA library generated from, or nucleic acid, preferably poly A+ RNA, isolated from, any tissue or cells expressing the antibody, such as hybridoma cells selected to express an antibody described herein) by PCR amplification using synthetic primers hybridizable to the 3’ and 5’ ends of the sequence or by cloning using an oligonucleotide probe specific for the particular gene sequence to identify, e.g, a cDNA clone from a cDNA library that encodes the antibody. Amplified nucleic acids generated by PCR can then be cloned into replicable cloning vectors using any method well known in the art.

[00262] DNA encoding anti-MerTK antibodies described herein can be readily isolated and sequenced using conventional procedures (e.g, by using oligonucleotide probes that are capable of binding specifically to genes encoding the heavy and light chains of the anti-MerTK antibodies). Hybridoma cells can serve as a source of such DNA. Once isolated, the DNA can be placed into expression vectors, which are then transfected into host cells such as E. coli cells, simian COS cells, Chinese hamster ovary (CHO) cells ( e.g ., CHO cells from the CHO GS System™ (Lonza)), or myeloma cells that do not otherwise produce immunoglobulin protein, to obtain the synthesis of anti-MerTK antibodies in the recombinant host cells.

[00263] To generate whole antibodies, PCR primers including VH or VL nucleotide sequences, a restriction site, and a flanking sequence to protect the restriction site can be used to amplify the VH or VL sequences in scFv clones. Utilizing cloning techniques known to those of skill in the art, the PCR amplified VH domains can be cloned into vectors expressing a heavy chain constant region, e.g., the human gamma 4 constant region, and the PCR amplified VL domains can be cloned into vectors expressing a light chain constant region, e.g, human kappa or lambda constant regions. In certain embodiments, the vectors for expressing the VH or VL domains comprise an EF-la promoter, a secretion signal, a cloning site for the variable domain, constant domains, and a selection marker such as neomycin. The VH and VL domains can also be cloned into one vector expressing the necessary constant regions. The heavy chain conversion vectors and light chain conversion vectors are then co-transfected into cell lines to generate stable or transient cell lines that express full-length antibodies, e.g, IgG, using techniques known to those of skill in the art.

[00264] The DNA also can be modified, for example, by substituting the coding sequence for human heavy and light chain constant domains in place of the murine sequences, or by covalently joining to the immunoglobulin coding sequence all or part of the coding sequence for a non-immunoglobulin polypeptide.

[00265] Also provided are polynucleotides that hybridize under high stringency, intermediate or lower stringency hybridization conditions to polynucleotides that encode an antibody described herein. In specific embodiments, polynucleotides described herein hybridize under high stringency, intermediate or lower stringency hybridization conditions to polynucleotides encoding a VH chain region and/or VL chain region provided herein.

[00266] Hybridization conditions have been described in the art and are known to one of skill in the art. For example, hybridization under stringent conditions can involve hybridization to filter-bound DNA in 6x sodium chloride/sodium citrate (SSC) at about 45° C followed by one or more washes in 0.2xSSC/0.1% SDS at about 50-65° C; hybridization under highly stringent conditions can involve hybridization to filter-bound nucleic acid in 6xSSC at about 45° C followed by one or more washes in O.lxSSC/O.2% SDS at about 68° C. Hybridization under other stringent hybridization conditions are known to those of skill in the art and have been described, see, for example, Ausubel, F.M. et ah, eds., 1989, Current Protocols in Molecular Biology, Vol. I, Green Publishing Associates, Inc. and John Wiley & Sons, Inc., New York at pages 6.3.1-6.3.6 and 2.10.3.

5.2.2 Cells and Vectors

[00267] In certain aspects, provided herein are cells ( e.g ., host cells) expressing ( e.g ., recombinantly) antibodies described herein (or an antigen-binding fragment thereof) which specifically bind to an ECD of human MerTK and related polynucleotides and expression vectors. Provided herein are vectors (e.g., expression vectors) comprising polynucleotides comprising nucleotide sequences encoding anti-MerTK antibodies or a fragment for recombinant expression in host cells, preferably in mammalian cells. Also provided herein are host cells comprising such vectors for recombinantly expressing anti-MerTK antibodies described herein (e.g, human or humanized antibody). In a particular aspect, provided herein are methods for producing an antibody described herein, comprising expressing such antibody from a host cell.

[00268] Recombinant expression of an antibody described herein (e.g, a full-length antibody, heavy and/or light chain of an antibody, or a single chain antibody described herein) that specifically binds to human MerTK involves construction of an expression vector containing a polynucleotide that encodes the antibody. Once a polynucleotide encoding an antibody molecule, heavy and/or light chain of an antibody, or a fragment thereof (e.g, heavy and/or light chain variable domains) described herein has been obtained, the vector for the production of the antibody molecule can be produced by recombinant DNA technology using techniques well- known in the art. Thus, methods for preparing a protein by expressing a polynucleotide containing an antibody or antibody fragment (e.g, light chain or heavy chain) encoding nucleotide sequence are described herein. Methods which are well known to those skilled in the art can be used to construct expression vectors containing antibody or antibody fragment (e.g, light chain or heavy chain) coding sequences and appropriate transcriptional and translational control signals. These methods include, for example, in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination. Also provided are replicable vectors comprising a nucleotide sequence encoding an antibody molecule described herein, a heavy or light chain of an antibody, a heavy or light chain variable domain of an antibody or a fragment thereof, or a heavy or light chain CDR, operably linked to a promoter. Such vectors can, for example, include the nucleotide sequence encoding the constant region of the antibody molecule (see, e.g ., International Publication Nos. WO 86/05807 and WO 89/01036; and U.S. Patent No. 5,122,464) and variable domains of the antibody can be cloned into such a vector for expression of the entire heavy, the entire light chain, or both the entire heavy and light chains.

[00269] An expression vector can be transferred to a cell (e.g, host cell) by conventional techniques and the resulting cells can then be cultured by conventional techniques to produce an antibody described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or a fragment thereof. Thus, provided herein are host cells containing a polynucleotide encoding an antibody described herein or fragments thereof, or a heavy or light chain thereof, or fragment thereof, or a single chain antibody described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), operably linked to a promoter for expression of such sequences in the host cell. In certain embodiments, for the expression of double-chained antibodies, vectors encoding both the heavy and light chains, individually, can be co-expressed in the host cell for expression of the entire immunoglobulin molecule, as detailed below. In certain embodiments, a host cell contains a vector comprising a polynucleotide encoding both the heavy chain and light chain of an antibody described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), or a fragment thereof. In specific embodiments, a host cell contains two different vectors, a first vector comprising a polynucleotide encoding a heavy chain or a heavy chain variable region of an antibody described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), or a fragment thereof, and a second vector comprising a polynucleotide encoding a light chain or a light chain variable region of an antibody described herein ( e.g ., an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), or a fragment thereof. In other embodiments, a first host cell comprises a first vector comprising a polynucleotide encoding a heavy chain or a heavy chain variable region of an antibody described herein (e.g., an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), or a fragment thereof, and a second host cell comprises a second vector comprising a polynucleotide encoding a light chain or a light chain variable region of an antibody described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6). In specific embodiments, a heavy chain/heavy chain variable region expressed by a first cell associated with a light chain/light chain variable region of a second cell to form an anti-MerTK antibody described herein (e.g, antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen binding fragment thereof. In certain embodiments, provided herein is a population of host cells comprising such first host cell and such second host cell.

[00270] In a particular embodiment, provided herein is a population of vectors comprising a first vector comprising a polynucleotide encoding a light chain/light chain variable region of an anti-MerTK antibody described herein (e.g, antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6), and a second vector comprising a polynucleotide encoding a heavy chain/heavy chain variable region of an anti-MerTK antibody described herein (e.g., antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6)·

[00271] A variety of host-expression vector systems can be utilized to express antibody molecules described herein ( e.g. , an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) (see, e.g, U.S. Patent No. 5,807,715). Such host-expression systems represent vehicles by which the coding sequences of interest can be produced and subsequently purified, but also represent cells which can, when transformed or transfected with the appropriate nucleotide coding sequences, express an antibody molecule described herein in situ. These include but are not limited to microorganisms such as bacteria (e.g, E. coli and B. subtilis) transformed with recombinant bacteriophage DNA, plasmid DNA or cosmid DNA expression vectors containing antibody coding sequences; yeast (e.g, Saccharomyces Pichia) transformed with recombinant yeast expression vectors containing antibody coding sequences; insect cell systems infected with recombinant virus expression vectors (e.g, baculovirus) containing antibody coding sequences; plant cell systems (e.g, green algae such as

Chlamydomonas reinhardtii) infected with recombinant virus expression vectors (e.g, cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g, Ti plasmid) containing antibody coding sequences; or mammalian cell systems (e.g, COS, CHO, BHK, MDCK, HEK 293, NS0, PER.C6, VERO, CRL7030, HsS78Bst, HeLa, and NIH 3T3 cells) harboring recombinant expression constructs containing promoters derived from the genome of mammalian cells (e.g, metallothionein promoter) or from mammalian viruses (e.g, the adenovirus late promoter; the vaccinia virus 7.5K promoter). In a specific embodiment, cells for expressing antibodies described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof are CHO cells, for example CHO cells from the CHO GS System™ (Lonza). In a specific embodiment, a mammalian expression vector is pOptiVEC™ or pcDNA3.3. In a particular embodiment, bacterial cells such as Escherichia coli, or eukaryotic cells ( e.g ., mammalian cells), especially for the expression of whole recombinant antibody molecule, are used for the expression of a recombinant antibody molecule. For example, mammalian cells such as Chinese hamster ovary (CHO) cells, in conjunction with a vector such as the major intermediate early gene promoter element from human cytomegalovirus is an effective expression system for antibodies (Foecking et ak, 1986, Gene 45: 101; and Cockett et ah, 1990, Bio/Technology 8:2). In certain embodiments, antibodies described herein are produced by CHO cells or NS0 cells. In a specific embodiment, the expression of nucleotide sequences encoding antibodies described herein which specifically bind to human MerTK is regulated by a constitutive promoter, inducible promoter or tissue specific promoter.

[00272] In bacterial systems, a number of expression vectors can be advantageously selected depending upon the use intended for the antibody molecule being expressed. For example, when a large quantity of such an antibody is to be produced, for the generation of pharmaceutical compositions of an antibody molecule, vectors which direct the expression of high levels of fusion protein products that are readily purified can be desirable. Such vectors include, but are not limited to, the E. coli expression vector pUR278 (Ruther et ak, 1983, EMBO 12: 1791), in which the antibody coding sequence can be ligated individually into the vector in frame with the lac Z coding region so that a fusion protein is produced; pIN vectors (Inouye & Inouye, 1985, Nucleic Acids Res. 13:3101-3109; Van Heeke & Schuster, 1989, J. Biol. Chem. 24:5503-5509); and the like. For example, pGEX vectors can also be used to express foreign polypeptides as fusion proteins with glutathione 5-transferase (GST). In general, such fusion proteins are soluble and can easily be purified from lysed cells by adsorption and binding to matrix glutathione agarose beads followed by elution in the presence of free glutathione. The pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned target gene product can be released from the GST moiety.

[00273] In an insect system, Autographa califomica nuclear polyhedrosis virus (AcNPV), for example, can be used as a vector to express foreign genes. The virus grows in Spodoptera frugiperda cells. The antibody coding sequence can be cloned individually into non-essential regions (for example the polyhedrin gene) of the virus and placed under control of an AcNPV promoter (for example the polyhedrin promoter). [00274] In mammalian host cells, a number of viral-based expression systems can be utilized. In cases where an adenovirus is used as an expression vector, the antibody coding sequence of interest can be ligated to an adenovirus transcription/translation control complex, e.g ., the late promoter and tripartite leader sequence. This chimeric gene can then be inserted in the adenovirus genome by in vitro or in vivo recombination. Insertion in a non-essential region of the viral genome (e.g, region El or E3) will result in a recombinant virus that is viable and capable of expressing the antibody molecule in infected hosts (e.g, see Logan & Shenk, 1984, Proc. Natl. Acad. Sci. USA 8 1 :355-359). Specific initiation signals can also be required for efficient translation of inserted antibody coding sequences. These signals include the ATG initiation codon and adjacent sequences. Furthermore, the initiation codon must be in phase with the reading frame of the desired coding sequence to ensure translation of the entire insert. These exogenous translational control signals and initiation codons can be of a variety of origins, both natural and synthetic. The efficiency of expression can be enhanced by the inclusion of appropriate transcription enhancer elements, transcription terminators, etc. (see, e.g, Bittner et al., 1987, Methods in Enzymol. 153:51-544).

[00275] In addition, a host cell strain can be chosen which modulates the expression of the inserted sequences, or modifies and processes the gene product in the specific fashion desired. Such modifications (e.g, glycosylation) and processing (e.g, cleavage) of protein products can be important for the function of the protein. Different host cells have characteristic and specific mechanisms for the post-translational processing and modification of proteins and gene products. Appropriate cell lines or host systems can be chosen to ensure the correct modification and processing of the foreign protein expressed. To this end, eukaryotic host cells which possess the cellular machinery for proper processing of the primary transcript, glycosylation, and

phosphorylation of the gene product can be used. Such mammalian host cells include but are not limited to CHO, VERO, BHK, Hela, COS, MDCK, HEK 293, NIH 3T3, W138, BT483,

Hs578T, HTB2, BT20 and T47D, NS0 (a murine myeloma cell line that does not endogenously produce any immunoglobulin chains), CRL7030 and HsS78Bst cells. In certain embodiments, anti-MerTK antibodies described herein (e.g, an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) are produced in mammalian cells, such as CHO cells.

[00276] For long-term, high-yield production of recombinant proteins, stable expression cells can be generated. For example, cell lines which stably express an anti-MerTK antibody described herein ( e.g ., an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof can be engineered. In specific embodiments, a cell provided herein stably expresses a light chain/light chain variable domain and a heavy chain/heavy chain variable domain which associate to form an antibody described herein (e.g., an antibody comprising the CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof.

[00277] In certain aspects, rather than using expression vectors which contain viral origins of replication, host cells can be transformed with DNA controlled by appropriate expression control elements (e.g., promoter, enhancer, sequences, transcription terminators, polyadenylation sites, etc.), and a selectable marker. Following the introduction of the foreign DNA/polynucleotide, engineered cells can be allowed to grow for 1-2 days in an enriched media, and then are switched to a selective media. The selectable marker in the recombinant plasmid confers resistance to the selection and allows cells to stably integrate the plasmid into their chromosomes and grow to form foci which in turn can be cloned and expanded into cell lines. This method can

advantageously be used to engineer cell lines which express an anti-MerTK antibody described herein or a fragment thereof. Such engineered cell lines can be particularly useful in screening and evaluation of compositions that interact directly or indirectly with the antibody molecule.

[00278] A number of selection systems can be used, including but not limited to, the herpes simplex virus thymidine kinase (Wigler et al., 1977, Cell 11 :223), hypoxanthineguanine phosphoribosyltransferase (Szybalska & Szybalski, 1992, Proc. Natl. Acad. Sci. USA 48:202), and adenine phosphoribosyltransferase (Lowy et al., 1980, Cell 22:8-17) genes can be employed in tk-, hgprt- or aprt-cells, respectively. Also, antimetabolite resistance can be used as the basis of selection for the following genes: dhfr, which confers resistance to methotrexate (Wigler et al., 1980, Natl. Acad. Sci. USA 77:357; O’Hare et al., 1981, Proc. Natl. Acad. Sci. USA

78: 1527); gpt, which confers resistance to mycophenolic acid (Mulligan & Berg, 1981, Proc. Natl. Acad. Sci. USA 78:2072); neo, which confers resistance to the aminoglycoside G-418 (Wu and Wu, 1991, Biotherapy 3:87-95; Tolstoshev, 1993, Ann. Rev. Pharmacol. Toxicol. 32:573- 596; Mulligan, 1993, Science 260:926-932; and Morgan and Anderson, 1993, Ann. Rev.

Biochem. 62: 191-217; May, 1993, TIB TECH 11 (5):155-2 15); and hygro, which confers resistance to hygromycin (Santerre et al., 1984, Gene 30: 147). Methods commonly known in the art of recombinant DNA technology can be routinely applied to select the desired recombinant clone, and such methods are described, for example, in Ausubel et al. (eds.), Current Protocols in Molecular Biology John Wiley & Sons, NY (1993); Kriegler, Gene Transfer and Expression. A Laboratory Manual, Stockton Press, NY (1990); and in Chapters 12 and 13, Dracopoli et al. (eds.), Current Protocols in Human Genetics. John Wiley & Sons, NY (1994); Colberre-Garapin et al., 1981, J. Mol. Biol. 150: 1, which are incorporated by reference herein in their entireties.

[00279] The expression levels of an antibody molecule can be increased by vector

amplification (for a review, see Bebbington and Hentschel, The use of vectors based on gene amplification for the expression of cloned genes in mammalian cells in DNA cloning, Vol. 3 (Academic Press, New York, 1987)). When a marker in the vector system expressing antibody is amplifiable, increase in the level of inhibitor present in culture of host cell will increase the number of copies of the marker gene. Since the amplified region is associated with the antibody gene, production of the antibody will also increase (Crouse et al., 1983, Mol. Cell. Biol. 3:257).

[00280] The host cell can be co-transfected with two or more expression vectors described herein, the first vector encoding a heavy chain derived polypeptide and the second vector encoding a light chain derived polypeptide. The two vectors can contain identical selectable markers which enable equal expression of heavy and light chain polypeptides. The host cells can be co-transfected with different amounts of the two or more expression vectors. For example, host cells can be transfected with any one of the following ratios of a first expression vector and a second expression vector: 1 :1, 1 :2, 1 :3, 1 :4, 1 :5, 1 :6, 1 :7, 1 :8, 1 :9, 1 :10, 1 : 12, 1 : 15, 1 :20, 1 :25, 1 :30, 1 :35, 1 :40, 1 :45, or 1 :50.

[00281] Alternatively, a single vector can be used which encodes, and is capable of expressing, both heavy and light chain polypeptides. In such situations, the light chain should be placed before the heavy chain to avoid an excess of toxic free heavy chain (Proudfoot, 1986, Nature 322:52; and Kohler, 1980, Proc. Natl. Acad. Sci. USA 77:2197-2199). The coding sequences for the heavy and light chains can comprise cDNA or genomic DNA. The expression vector can be monocistronic or multi cistronic. A multi cistronic nucleic acid construct can encode 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, or in the range of 2-5, 5-10 or 10-20 genes/nucleotide sequences. For example, a bicistronic nucleic acid construct can comprise in the following order a promoter, a first gene ( e.g ., heavy chain of an antibody described herein), and a second gene and (e.g., light chain of an antibody described herein). In such an expression vector, the transcription of both genes can be driven by the promoter, whereas the translation of the mRNA from the first gene can be by a cap-dependent scanning mechanism and the translation of the mRNA from the second gene can be by a cap-independent mechanism, e.g, by an IRES.

[00282] Once an antibody molecule described herein has been produced by recombinant expression, it can be purified by any method known in the art for purification of an

immunoglobulin molecule, for example, by chromatography (e.g, ion exchange, affinity, particularly by affinity for the specific antigen after Protein A, and sizing column

chromatography), centrifugation, differential solubility, or by any other standard technique for the purification of proteins. Further, the antibodies described herein can be fused to heterologous polypeptide sequences described herein or otherwise known in the art to facilitate purification.

[00283] In specific embodiments, an antibody described herein is isolated or purified.

Generally, an isolated antibody is one that is substantially free of other antibodies with different antigenic specificities than the isolated antibody. For example, in a particular embodiment, a preparation of an antibody described herein is substantially free of cellular material and/or chemical precursors. The language“substantially free of cellular material” includes preparations of an antibody in which the antibody is separated from cellular components of the cells from which it is isolated or recombinantly produced. Thus, an antibody that is substantially free of cellular material includes preparations of antibody having less than about 30%, 20%, 10%, 5%, 2%, 1%, 0.5%, or 0.1% (by dry weight) of heterologous protein (also referred to herein as a “contaminating protein”) and/or variants of an antibody, for example, different post-translational modified forms of an antibody or other different versions of an antibody (e.g, antibody fragments). When the antibody is recombinantly produced, it is also generally substantially free of culture medium, i.e., culture medium represents less than about 20%, 10%, 2%, 1%, 0.5%, or 0.1% of the volume of the protein preparation. When the antibody is produced by chemical synthesis, it is generally substantially free of chemical precursors or other chemicals, i.e., it is separated from chemical precursors or other chemicals which are involved in the synthesis of the protein. Accordingly, such preparations of the antibody have less than about 30%, 20%, 10%, or 5% (by dry weight) of chemical precursors or compounds other than the antibody of interest. In a specific embodiment, antibodies described herein are isolated or purified.

5.3 Pharmaceutical Compositions and Kits

[00284] Provided herein are compositions, pharmaceutical compositions, and kits comprising one or more antibodies ( e.g ., anti-MerTK antibodies comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) described herein, or antigen-binding fragments thereof, or conjugates thereof. In particular aspects, compositions (e.g., pharmaceutical compositions) described herein can be for in vitro, in vivo, or ex vivo uses. Non-limiting examples of uses include uses to modulate (e.g, inhibit) MerTK activity and uses to manage or treat a disorder, for example, cancer. In specific embodiments, provided herein is a pharmaceutical composition comprising an antibody (e.g, a humanized antibody) described herein (or an antigen-binding fragment thereof) and a pharmaceutically acceptable carrier or excipient.

[00285] As used herein, the term“pharmaceutically acceptable” means being approved by a regulatory agency of the Federal or a state government, or listed in the U.S. Pharmacopeia, European Pharmacopeia or other generally recognized Pharmacopeia for use in animals, and more particularly in humans.

[00286] Therapeutic formulations containing one or more antibodies provided herein (e.g, antibodies comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof can be prepared for storage by mixing the antibody having the desired degree of purity with optional physiologically acceptable carriers, excipients or stabilizers (Remington’s Pharmaceutical Sciences (1990) Mack Publishing Co., Easton, PA; Remington: The Science and Practice of Pharmacy 21st ed. (2006) Lippincott Williams & Wilkins, Baltimore, MD), in the form of lyophilized formulations or aqueous solutions. Acceptable carriers, excipients, or stabilizers are nontoxic to recipients at the dosages and concentrations employed, and include buffers such as phosphate, citrate, and other organic acids; and/or non-ionic surfactants such as TWEEN™, PLEIRONICS™ or polyethylene glycol (PEG).

[00287] Formulations, such as those described herein, can also contain more than one active compounds (for example, molecules, e.g ., antibody or antibodies described herein) as necessary for the particular indication being treated. In certain embodiments, formulations comprise an antibody provided herein and one or more active compounds with complementary activities that do not adversely affect each other. Such molecules are suitably present in combination in amounts that are effective for the purpose intended. For example, an antibody described herein can be combined with one or more other therapeutic agents (e.g, a tyrosine kinase inhibitor such as imatinib mesylated or sunitinib, a checkpoint inhibitor such as PD-1 or PD-L1 antibody, or a histone deacetylase inhibitor such as vorinostat). Such combination therapy can be administered to the patient serially or simultaneously or in sequence.

[00288] The formulations to be used for in vivo administration can be sterile. This is readily accomplished by filtration through, e.g, sterile filtration membranes.

[00289] In specific aspects, the pharmaceutical compositions provided herein contain therapeutically effective amounts of one or more of the antibodies provided herein, and optionally one or more additional prophylactic of therapeutic agents, in a pharmaceutically acceptable carrier. Such pharmaceutical compositions are useful in the prevention, treatment, management or amelioration of a condition or disorder described herein or one or more symptoms thereof.

[00290] Pharmaceutical carriers suitable for administration of the antibodies provided herein include any such carriers known to those skilled in the art to be suitable for the particular mode of administration.

[00291] In addition, the antibodies described herein can be formulated as the sole

pharmaceutically active ingredient in the composition or can be combined with other active ingredients (such as one or more other prophylactic or therapeutic agents).

[00292] Compositions provided herein can contain one or more antibodies provided herein (e.g, antibodies comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof. In one embodiment, the antibodies are formulated into suitable pharmaceutical preparations, such as solutions, suspensions, powders, sustained release formulations or elixirs in sterile solutions or suspensions for parenteral administration, or as transdermal patch preparation and dry powder inhalers.

[00293] In compositions provided herein, one or more antibodies described herein is (are) mixed with a suitable pharmaceutical carrier. The concentrations of the antibody or antibodies in the compositions can, for example, be effective for delivery of an amount, upon administration, that treats, prevents, or ameliorates a condition or disorder described herein or a symptom thereof.

[00294] In one embodiment, compositions provided herein are formulated for single dosage administration. To formulate a composition, the weight fraction of compound is dissolved, suspended, dispersed or otherwise mixed in a selected carrier at an effective concentration such that the treated condition is relieved, prevented, or one or more symptoms are ameliorated.

[00295] In certain aspects, an antibody provided herein ( e.g ., antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) is included in the pharmaceutically acceptable carrier in an effective amount sufficient to exert a therapeutically useful effect in the absence of, or with minimal or negligible, undesirable side effects on the patient treated.

[00296] Concentrations of anti-MerTK antibody in a pharmaceutical composition provided herein will depend on, e.g., the physicochemical characteristics of the antibody, the dosage schedule, and amount administered as well as other factors known to those of skill in the art.

[00297] The pharmaceutical compositions, in another embodiment, provide a dosage of about 50 mg of antibody per kilogram of body weight for administration over a period of time, e.g, every day or few days, every week, every 2 weeks, or every 3 weeks. Pharmaceutical dosage unit forms can be prepared to provide from about 500 mg.

[00298] Pharmaceutical compositions described herein are provided for administration to humans or animals (e.g, mammals) in unit dosage forms, such as sterile parenteral (e.g, intravenous) solutions or suspensions containing suitable quantities of the compounds or pharmaceutically acceptable derivatives thereof. Pharmaceutical compositions are also provided for administration to humans and animals in unit dosage form, such as tablets, capsules, pills, powders, granules, and oral or nasal solutions or suspensions, and oil-water emulsions containing suitable quantities of an anti-MerTK antibody or pharmaceutically acceptable derivatives thereof. The antibody is, in one embodiment, formulated and administered in unit-dosage forms or multiple-dosage forms. Unit-dose forms as used herein refers to physically discrete units suitable for human or animal ( e.g ., mammal) subjects and packaged individually as is known in the art. Each unit-dose contains a predetermined quantity of an anti-MerTK antibody sufficient to produce the desired therapeutic effect, in association with the required pharmaceutical carrier, vehicle or diluent. Examples of unit-dose forms include ampoules and syringes and individually packaged tablets or capsules. Unit-dose forms can be administered in fractions or multiples thereof. A multiple-dose form is a plurality of identical unit-dosage forms packaged in a single container to be administered in segregated unit-dose form. Examples of multiple-dose forms include vials, bottles of tablets or capsules or bottles. Hence, in specific aspects, multiple dose form is a multiple of unit-doses which are not segregated in packaging.

[00299] In certain embodiments, one or more anti-MerTK antibodies described herein (e.g., antibodies comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or an antigen-binding fragment thereof are in a liquid pharmaceutical formulation. Liquid

pharmaceutically administrable compositions can, for example, be prepared by dissolving, dispersing, or otherwise mixing an antibody and optional pharmaceutical adjuvants in a carrier, such as, for example, water, saline, aqueous dextrose, glycerol, glycols, and the like, to thereby form a solution or suspension. In certain embodiments, a pharmaceutical composition provided herein to be administered can also contain minor amounts of nontoxic auxiliary substances such as wetting agents, emulsifying agents, solubilizing agents, and pH buffering agents and the like.

[00300] Actual methods of preparing such dosage forms are known, or will be apparent, to those skilled in this art; for example, see, e.g, Remington’s Pharmaceutical Sciences (1990) Mack Publishing Co., Easton, PA; Remington: The Science and Practice of Pharmacy 21st ed. (2006) Lippincott Williams & Wilkins, Baltimore, MD. Dosage forms or compositions containing antibody in the range of 0.005% to 100% with the balance made up from non-toxic carrier can be prepared. [00301] Parenteral administration, in one embodiment, is characterized by injection, either subcutaneously, intramuscularly or intravenously is also contemplated herein. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions. The injectables, solutions and emulsions also contain one or more excipients. Suitable excipients are, for example, water, saline, dextrose, glycerol or ethanol. Other routes of administration may include, enteric administration, intracerebral administration, nasal administration, intraarterial administration, intracardiac administration, intraosseous infusion, intrathecal administration, and intraperitoneal administration.

[00302] Preparations for parenteral administration include sterile solutions ready for injection, sterile dry soluble products, such as lyophilized powders, ready to be combined with a solvent just prior to use, including hypodermic tablets, sterile suspensions ready for injection, sterile dry insoluble products ready to be combined with a vehicle just prior to use and sterile emulsions. The solutions can be either aqueous or nonaqueous.

[00303] If administered intravenously, suitable carriers include physiological saline or phosphate buffered saline (PBS), and solutions containing thickening and solubilizing agents, such as glucose, polyethylene glycol, and polypropylene glycol and mixtures thereof.

[00304] Pharmaceutically acceptable carriers used in parenteral preparations include aqueous vehicles, nonaqueous vehicles, antimicrobial agents, isotonic agents, buffers, antioxidants, local anesthetics, suspending and dispersing agents, emulsifying agents, sequestering or chelating agents and other pharmaceutically acceptable substances.

[00305] Pharmaceutical carriers also include ethyl alcohol, polyethylene glycol and propylene glycol for water miscible vehicles; and sodium hydroxide, hydrochloric acid, citric acid or lactic acid for pH adjustment.

[00306] In certain embodiments, intravenous or intraarterial infusion of a sterile aqueous solution containing an anti-MerTK antibody described herein is an effective mode of

administration. Another embodiment is a sterile aqueous or oily solution or suspension containing an anti-MerTK antibody described herein injected as necessary to produce the desired pharmacological effect.

[00307] In specific embodiments, an anti-MerTK antibody described herein can be suspended in micronized or other suitable form. The form of the resulting mixture depends upon a number of factors, including the intended mode of administration and the solubility of the compound in the selected carrier or vehicle.

[00308] In other embodiments, the pharmaceutical formulations are lyophilized powders, which can be reconstituted for administration as solutions, emulsions and other mixtures. They can also be reconstituted and formulated as solids or gels.

[00309] The lyophilized powder is prepared by dissolving an anti-MerTK antibody provided herein, in a suitable solvent. In some embodiments, the lyophilized powder is sterile. Suitable solvents can contain an excipient which improves the stability or other pharmacological component of the powder or reconstituted solution, prepared from the powder. Excipients that can be used include, but are not limited to, dextrose, sorbital, fructose, corn syrup, xylitol, glycerin, glucose, sucrose or other suitable agent. A suitable solvent can also contain a buffer, such as citrate, sodium or potassium phosphate or other such buffer known to those of skill in the art at, in one embodiment, about neutral pH. Subsequent sterile filtration of the solution followed by lyophilization under standard conditions known to those of skill in the art provides an example of a formulation. In one embodiment, the resulting solution will be apportioned into vials for lyophilization. Lyophilized powder can be stored under appropriate conditions, such as at about 4 °C to room temperature.

[00310] Reconstitution of this lyophilized powder with water for injection provides a formulation for use in parenteral administration. For reconstitution, the lyophilized powder is added to sterile water or other suitable carrier.

[00311] In certain aspects, anti-MerTK antibodies provided herein can be formulated for local administration or topical application, such as for topical application to the skin and mucous membranes, such as in the eye, in the form of gels, creams, and lotions and for application to the eye or for intraci sternal or intraspinal application. Topical administration is contemplated for transdermal delivery and also for administration to the eyes or mucosa, or for inhalation therapies. Nasal solutions of the active compound alone or in combination with other pharmaceutically acceptable excipients can also be administered.

[00312] Anti-MerTK antibodies and other compositions provided herein can also be formulated to be targeted to a particular tissue, receptor, or other area of the body of the subject to be treated. Many such targeting methods are well known to those of skill in the art. All such targeting methods are contemplated herein for use in the instant compositions. For non-limiting examples of targeting methods, see, e.g, U.S. Patent Nos. 6,316,652, 6,274,552, 6,271,359,

6,253,872, 6,139,865, 6,131,570, 6,120,751, 6,071,495, 6,060,082, 6,048,736, 6,039,975,

6,004,534, 5,985,307, 5,972,366, 5,900,252, 5,840,674, 5,759,542 and 5,709,874. In some embodiments, anti-MerTK antibodies described herein are targeted (or otherwise administered) to the visual organs, bone marrow, gastrointestinal tract, lungs, brain, or joints. In specific embodiments, an anti-MerTK antibody described herein is capable of crossing the blood-brain barrier.

[00313] Provided herein is a pharmaceutical pack or kit comprising one or more containers filled with one or more of the ingredients of the pharmaceutical compositions described herein, such as one or more anti-MerTK antibodies provided herein. Optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration.

[00314] Also provided herein are kits that can be used in the above methods. In one embodiment, a kit comprises an antibody described herein, preferably a purified antibody, in one or more containers. In a specific embodiment, kits described herein contain a substantially isolated MerTK antigen (e.g, ECD of human MerTK) as a control. In another specific embodiment, the kits described herein further comprise a control antibody which does not react with a MerTK antigen. In another specific embodiment, kits described herein contain one or more elements for detecting the binding of a modified antibody to a MerTK antigen (e.g, the antibody can be conjugated to a detectable substrate such as a fluorescent compound, an enzymatic substrate, a radioactive compound or a luminescent compound, or a second antibody which recognizes the first antibody can be conjugated to a detectable substrate). In specific embodiments, a kit provided herein can include a recombinantly produced or chemically synthesized MerTK antigen. The MerTK antigen provided in the kit can also be attached to a solid support. In a more specific embodiment, the detecting means of the above described kit includes a solid support to which a MerTK antigen is attached. Such a kit can also include a non-attached reporter-labeled anti-human antibody or anti-mouse/rat antibody. In this embodiment, binding of the antibody to the MerTK antigen can be detected by binding of the said reporter-labeled antibody. 5.4 Uses and Methods

[00315] In particular aspects, provided herein are methods of modulating MerTK activity with an anti-MerTK antibody (e.g, antibody Ab3000 or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) described herein or an antigen-binding fragment thereof. In certain embodiments, the anti-MerTK antibody or antigen-binding fragment may be a MerTK antagonist.

[00316] In specific embodiments, provided herein are methods of inhibiting (e.g, partially inhibiting) MerTK activity with an anti-MerTK antibody described herein which may be a MerTK antagonist. In certain embodiments, provided herein are methods of managing or treating a condition or disorder using an anti-MerTK antibody described herein which may be a MerTK antagonist or inhibitor.

[00317] Provided herein are methods of managing or treating a condition by inhibiting an activity of MerTK with an anti-MerTK antibody (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) described herein. In certain embodiments, an antibody or antigen-binding fragment disclosed herein may be a MerTK antagonist. Non-limiting examples of a condition which can be treated or managed with a MerTK antibody or antigen-binding fragement thereof disclosed herein include cancer, sepsis, and infection, described in more detail below.

[00318] In certain embodiments, a condition which can be treated or managed with a MerTK antagonist is one which can be managed or treated by enhancing an immune response.

[00319] An anti-MerTK antibody described herein or an antigen-binding fragment thereof, which may be a MerTK antagonist, for use in the methods provided herein is capable of inhibiting (e.g, partially inhibiting) or decreasing/reducing MerTK expression and/or a MerTK activity. Activities of MerTK are known in the art. In specific embodiments, an anti-MerTK antibody described herein inhibits (e.g, partially inhibits) one or more of the following MerTK activities: phosphorylation (e.g, autophosphorylation) of MerTK receptor (e.g, cytoplasmic domain of MerTK, such as cytoplasmic kinase domain of MerTK), promotion of phagocytosis, modulation of maturation of NK cells, dendritic cells or macrophages, inhibition of toll-like receptor (TLR) activation of dendritic cells, inhibition or decrease in TLR-induced

proinflammatory cytokine (e.g, TNF, IL-6, IL-12 and type I interferon production, increase in SOCS1 expression, association with interleukin- 15 (IL-15) to protect cells against TNF-induced cell death (e.g, fibroblasts and DCs), and activation of Statl in dendritic cells. Methods for measuring these activities are known in the art.

[00320] In specific embodiments, an anti-MerTK antibody described herein which may be a MerTK antagonist inhibits (e.g, partially inhibits), by at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 97%, 98%, 99%, or 100%, one or more such MerTK activities.

[00321] However, the antibodies and antigen-binding fragments described herein are not limited to antagonist antibodies or antigen-binding fragments. In certain embodiments, an isolated antibody, or an antigen-binding fragment thereof, which binds to human MerTK does not inhibit one or more MerTK activities. As a non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, does not inhibit binding of Gas6 to MerTK expressed on cells (e.g, L cells or macrophages) , e.g, does not inhibit such binding by more, for example, than 10%, more than 20%, more than 30% or more than 40%. In another non-limiting example, in some embodiments, an isolated antibody, or an antigen-binding fragment thereof, does not inhibit phosphorylation of MerTK in cells (e.g, macrophages) , e.g, does not inhibit such phosphorylation by more, for example, than 10%, more than 20%, more than 30% or more than 40%.

[00322] In particular aspects, provided herein is a method of enhancing an immune response in a subject comprising administering to a subject in need thereof an effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits MerTK.

[00323] In specific embodiments, a subject (e.g, human subject) in need of enhancing an immune response include an immunocompromised subject, for example a subject suffering from an infection (e.g, bacterial, viral, fungal, or protozoan). In certain embodiments, an

immunocompromised subject has cancer and is undergoing, or had undergone treatment with, anti-cancer therapy, such as, chemotherapy. Other non-limiting examples of

immunocompromised subjects include, but are not limited to, subjects who are HIV positive, subjects with AIDS or SCID, subjects with diabetes, and subjects who have undergone transplants and are taking immunosuppressants. In certain embodiments, an

immunocompromised subject is taking immunosuppressants ( e.g ., steroids) to manage or treat asthma, arthritis (e.g., rheumatoid arthritis), or allergy or an allergic condition.

[00324] In a particular embodiment, provided herein is a method of enhancing an immune response to a vaccine in a subject, comprising administering to a subject in need thereof, who is or has been administered the vaccine, an effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits MerTK. In specific embodiments, the antibody is administered before, concurrently, or after administration of the vaccine.

[00325] An example of vaccines in the methods provides herein include cancer/tumor vaccines, such as vaccines comprising tumor cells or tumor cell lysates and vaccines comprising dendritic cells or dendritic cell lysates activated against a tumor.

[00326] Provided herein is a method of managing, preventing, protecting against, or treating cancer in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression. In particular embodiments, such a method involves inhibition of tumor growth, cancer cell proliferation, cancer cell migration, inhibition of tumor- associated macrophage activity (e.g, tumor-promoting activity such as production of cytokines), and modulating stromal cells such as macrophages or dendritic cells

[00327] Non-limiting examples of cancers to be managed, prevented, protected against, or treated in the methods provided herein include breast cancer, pancreatic cancer, leukemia, lung cancer such as non-small cell lung cancer, glioblastoma, melanoma, prostate cancer, colon cancer, gastric cancer, pituitary adenomas, ovarian cancer, renal cancer, bladder cancer, and sarcomas, including rhabdomyosarcomas.

[00328] In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide described herein is capable of inhibiting tumor growth at a site of local administration. In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide described herein is capable of inhibiting tumor growth in vivo (e.g, in a mouse model and/or in a human having cancer) at a site of local administration. In some embodiments, an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide described herein administered to a patient using the methods described herein has one or more of the following non-limiting effects at a site of local administration: inhibit proliferation of tumor cells, inhibit tumor growth, reduce the tumorigenicity of a tumor, trigger cell death of tumor cells, increase cell contact-dependent growth inhibition, increase tumor cell apoptosis, decrease survival of tumor cells, reduce the number of tumor cells, decrease tumorigenic frequency, reduce the number or frequency of cancer stem cells, reduce the tumor size, reduce the cancer cell population; inhibit or stop cancer cell infiltration into peripheral organs including, inhibit metastasis, inhibit tumor growth.

[00329] In some embodiments, an antibody or antigen-binding fragment described herein relieves one or more of the symptoms associated with cancer, reduces morbidity and mortality, and/or improves quality of life.

[00330] In a specific embodiment, provided herein is a method of treating cancer in a subject comprising administering to a subject in need thereof an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits MerTK, in an effective amount to enhancing an immune response to the cancer.

[00331] In one aspect, provided herein is a method of managing, preventing, protecting against, or treating metastasis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression.

[00332] In a certain aspect, provided herein is a method of inhibiting MerTK expression and/or activity of a tumor-associated macrophage comprising contacting a tumor-associated macrophage with an effective amount of an antibody described herein ( e.g ., antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression. In a specific embodiment, such a method disrupts tumor-macrophage cross talk and inhibits the ability of tumor-associated macrophages to promote cancer cell proliferation.

[00333] In a certain aspect, provided herein is a method of modulating (e.g., inhibiting) stromal cell (e.g, macrophage or dendritic cell) activity, comprising contacting a stromal cell with an effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression in the stromal cell. In a specific embodiment, such method is for modulating stromal cell activity in a subject with cancer.

[00334] In a certain aspect, provided herein is a method of modulating (e.g, inhibiting) natural killer (NK) cell activity, comprising contacting an NK cell with an effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression in the NK cell. In a specific embodiment, such method is for modulating NK cell activity in a subject with cancer.

[00335] In another aspect, provided herein is a method of modulating ( e.g ., inhibiting) T cell activity, comprising contacting a T cell with an effective amount of an antibody described herein (e.g., antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression in the T cell. In a specific embodiment, such method is for modulating stromal cell activity in a subject with cancer.

[00336] In a particular embodiment, provided herein is a method of inhibiting or reducing tumor growth or cancer cell proliferation in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity or inhibits or reduces MerTK expression.

[00337] In a specific embodiment, provided herein is a method of treating cancer in a subject comprising administering (e.g, administering concurrently or sequentially) to a subject in need thereof (i) an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits MerTK, and (ii) another anti-cancer agent.

[00338] In one embodiment, provided herein is a method of managing, preventing, protecting against, or treating an infection in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity.

[00339] In a specific embodiment, the infection is an infection caused by bacteria (gram negative bacteria or gram-positive bacteria), fungi, viruses, or parasites.

[00340] In a particular embodiment, provided herein is a method of managing or treating sepsis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein ( e.g ., antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity.

[00341] Sepsis (a systemic inflammatory response syndrome or SIRS) is an immunological condition characterized by whole-body inflammation caused by infection, such as infection by bacteria (gram-negative bacteria or gram-positive bacteria), fungi, viruses, or parasites. Stages of sepsis include, but are not limited to, onset of sepsis, severe sepsis, and septic shock. Severe sepsis can be accompanied by organ dysfunction.

[00342] In certain embodiments, the sepsis is advanced sepsis. In a particular embodiment, the sepsis is characterized with increased expression of SOCS, for example during the stage of severe sepsis. In a particular embodiment, the sepsis is characterized with elevated levels of circulating Gas6 in a subject with sepsis. Levels or concentrations of circulating Gas6 can be measured from blood samples using conventional methods, such as ELISAs. Levels or concentrations of Gas6 can be compared with a reference value to determine whether Gas6 levels or concentrations are elevated in a subject with sepsis. For example, the reference values can be a set standard range of levels and concentrations of Gas6 accepted in the art as correlating with those of a population of healthy subjects not suffering from sepsis. As another example, the reference values can be levels of concentrations of Gas6 in a subject prior to the onset of sepsis or at the early stages of sepsis. Symptoms of sepsis include, but are not limited to, high fevers, hot, flushed skin, elevated heart rate, hyperventilation, altered mental status, swelling, and low blood pressure. [00343] In a particular embodiment, provided herein is a method of managing, alleviating or treating one or more symptoms of sepsis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of an antibody described herein ( e.g ., antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity.

[00344] In certain embodiments, the method of managing or treating sepsis provided herein further comprises the step of administering an antibiotic to a subject in need thereof, for example, prior to, concurrently with, or subsequent to administering an anti-MerTK antibody described herein.

[00345] In certain aspects, provided herein are methods for managing, treating, preventing, or protecting against infection in a subject, comprising administering to a subject in need thereof an effective amount of an antibody described herein (e.g., antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity.

[00346] In certain embodiments, the infection is caused by microbes, e.g, bacteria, viruses or parasites. In certain embodiments, the viral infection is HIV, herpes, shingles, influenza, common cold, and encephalitis.

[00347] In certain embodiments, provided herein are methods for prevent or inhibit entry of a viruses by contacting a cell to an effective amount of an antibody described herein (e.g, antibody Ab3000, or an antibody comprising CDRs of any of Table 1, Table 3, Table 4 or Table 5, or an antibody or antigen-binding fragment comprising a VH and/or VL of Table 2, or an antibody or antigen-binding fragment comprising Ab3000 heavy chain and/or Ab3000 light chain of Table 6) or antigen-binding fragment thereof that specifically binds to human MerTK and inhibits a MerTK activity. In particular embodiments, the method provided herein prevents or inhibits entry of lymphocytic choriomeningitis virus, HIV, herpes virus (e.g, herpes simplex virus or herpes zoster), influenza virus, or common cold virus. [00348] In certain embodiments, the anti-MerTK antibody or antigen-binding fragment thereof for use in the methods provided herein is an antibody ( e.g ., monoclonal antibody, such as a humanized monoclonal antibody) comprising CDRs of Table 1, Table 3, Table 4 or Table 5. In particular embodiments, the anti-MerTK antibody inhibits a MerTK activity.

[00349] In other aspects, provided herein are methods of enhancing a type I interferon (IFN) response against a pathogen in a subject, comprising administering to a subject in need thereof an effective amount of an anti-MerTK antibody described herein, such as a MerTK antagonist antibody.

[00350] As used herein,“administer” or“administration” refers to the act of injecting or otherwise physically delivering a substance (e.g., a humanized anti-MerTK antibody provided herein or an antigen-binding fragment thereof) to a subject or a patient (e.g, human), such as by mucosal, topical, intradermal, parenteral, intravenous, intramuscular delivery and/or any other method of physical delivery described herein or known in the art.

[00351] As used herein, the terms“effective amount” or“therapeutically effective amount” refer to an amount of a therapy (e.g, an antibody or pharmaceutical composition provided herein) which is sufficient to reduce and/or ameliorate the severity and/or duration of a given condition, disorder or disease and/or a symptom related thereto. These terms also encompass an amount necessary for the reduction, slowing, or amelioration of the advancement or progression of a given disease, reduction, slowing, or amelioration of the recurrence, development or onset of a given disease, and/or to improve or enhance the prophylactic or therapeutic effect(s) of another therapy (e.g, a therapy other than an anti-MerTK antibody provided herein). In some embodiments,“effective amount” as used herein also refers to the amount of an antibody described herein to achieve a specified result.

[00352] As used herein, the term“in combination” in the context of the administration of other therapies refers to the use of more than one therapy. The use of the term“in combination” does not restrict the order in which therapies are administered. The therapies may be

administered, e.g, serially, sequentially, concurrently, or concomitantly.

[00353] As used herein, the terms“manage,”“managing,” and“management” refer to the beneficial effects that a subject derives from a therapy (e.g, a prophylactic or therapeutic agent), which does not result in a cure of a condition associated with MerTK. In certain embodiments, a subject is administered one or more therapies (e.g, prophylactic or therapeutic agents, such as an antibody described herein) to“manage” a condition or disorder described herein, one or more symptoms thereof, so as to prevent the progression or worsening of the condition or disorder.

[00354] As used herein, the terms“impede” or“impeding” in the context of a condition or disorder provided herein refer to the total or partial inhibition (e.g, less than 100%, 95%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, or 5%) or blockage of the development, recurrence, onset or spread of a condition or disorder provided herein and/or symptom related thereto, resulting from the administration of a therapy or combination of therapies provided herein (e.g, a combination of prophylactic or therapeutic agents, such as an antibody described herein).

[00355] As used herein, the term“prophylactic agent” refers to any agent that can totally or partially inhibit the development, recurrence, onset or spread of a condition or disorder provided herein, and/or symptom related thereto in a subject. In certain embodiments, the term “prophylactic agent” refers to an antibody described herein. In certain other embodiments, the term“prophylactic agent” refers to an agent other than an antibody described herein. Generally, a prophylactic agent is an agent which is known to be useful to or has been or is currently being used to prevent a condition or disorder provided herein, and/or a symptom related thereto or impede the onset, development, progression and/or severity of a condition or disorder provided herein, and/or a symptom related thereto. In specific embodiments, the prophylactic agent is an anti-MerTK antibody, as described herein.

[00356] As used herein, the terms“subject” and“patient” are used interchangeably. As used herein, a subject is a mammal such as a non-primate (e.g, cows, pigs, horses, cats, dogs, goats, rabbits, rats, mice, etc.) or a primate (e.g, monkey and human), for example a human. In one embodiment, the subject is a mammal, e.g, a human, diagnosed with a condition or disorder provided herein. In another embodiment, the subject is a mammal, e.g, a human, at risk of developing a condition or disorder provided herein. In another embodiment, the subject is human.

[00357] As used herein, the terms“therapies” and“therapy” can refer to any protocol(s), method(s), compositions, formulations, and/or agent(s) that can be used in the prevention, treatment, management, or amelioration of a condition or disorder or symptom thereof (e.g, a condition or disorder provided herein or one or more symptoms or condition associated therewith). In certain embodiments, the terms“therapies” and“therapy” refer to drug therapy, adjuvant therapy, radiation, surgery, biological therapy, supportive therapy, and/or other therapies useful in treatment, management, prevention, or amelioration of a condition or disorder or one or more symptoms thereof. In certain embodiments, the term“therapy” refers to a therapy other than an anti-MerTK antibody described herein or pharmaceutical composition thereof. In specific embodiments, an“additional therapy” and“additional therapies” refer to a therapy other than a treatment using an anti-MerTK antibody described herein or pharmaceutical composition thereof. In a specific embodiment, a therapy includes the use of an anti-MerTK antibody described herein as an adjuvant therapy. For example, using an anti-MerTK antibody described herein in conjunction with a drug therapy, biological therapy, surgery, and/or supportive therapy.

[00358] As used herein, the term“therapeutic agent” refers to any agent that can be used in the treatment, management or amelioration of a condition or disorder or symptom thereof. In certain embodiments, the term“therapeutic agent” refers to an anti-MerTK antibody described herein or an antigen-binding fragment thereof. In certain other embodiments, the term

“therapeutic agent” refers to an agent other than an antibody described herein. In specific embodiments, a therapeutic agent is an agent which is known to be useful for, or has been or is currently being used for the treatment, management or amelioration of a condition or disorder provided herein or one or more symptoms or condition associated therewith or one or more symptoms related thereto.

[00359] In one embodiment, for example, an antibody or antigen-binding fragment thereof that specifically binds to human MerTK as described herein can be administered in combination with another therapeutic agent for addressing one or more of the indications described herein. In a specific embodiment, such a therapeutic agent can be a stimulator of T cell responses

[00360] In some embodiments, an antibody or antigen-binding fragment thereof that specifically binds to human MerTK as described herein can be administered in combination with another therapeutic agent, wherein the therapeutic agent is an immune checkpoint modulator. As a non-limiting example, the immune checkpoint modulator can be a modulator of Cytotoxic T- lymphocyte antigen-4 (CTLA-4), CD80, CD86, Programmed cell death 1 (PD-1), Programmed cell death ligand 1 (PD-L1), Programmed cell death ligand 2 (PD-L2), 0X40, CD27, CD28, CD40, CD137 (4-1BB), CGEN-15001T, CGEN-15022, CGEN-15027, CGEN-15049, CGEN- 15052, CGEN-15092, Lymphocyte activation gene-3 (LAG-3), Galectin-3, B and T lymphocyte attenuator (BTLA), T-cell membrane protein 3 (TIM3), Galectin-9 (GAL9), B7-H1, B7-H3, B7- H4, T-Cell immunoreceptor with Ig and ITIM domains (TIGIT/Vstm3/WUCAM/VSIG9), V- domain Ig suppressor of T-Cell activation (VISTA), Glucocorticoid-induced tumor necrosis factor receptor-related (GITR) protein, or Herpes Virus Entry Mediator (HVEM).

[00361] In certain embodiments, a method for treating a disease in a patient disclosed herein comprises administering to the patient a therapeutically effective amount of an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide ( e.g ., human MerTK) and one or more other therapeutic agents, wherein a therapeutic agent is a checkpoint inhibitor (e.g., PD1 inhibitor or PD-L1 inhibitor). In some embodiments, provided herein are methods for treating a neoplastic disease in a subject by administering in combination with an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide, an immune checkpoint inhibitor that inhibits, decreases or interferes with the activity of a negative checkpoint regulator. In some embodiments, the negative checkpoint regulator is selected from the group consisting of PD-1, PD-L1, and PD-L2.

[00362] In specific embodiments, a therapeutic agent can be an immune checkpoint inhibitor, e.g, a PD-1, PD-L1, or CTLA-4 inhibitor. Such exemplary agents can include, e.g, Yervoy™ (ipilimumab) or tremelimumab (to CTLA-4), BMS-936558/nivolumab (to PD-1), MK- 3475/pembrolizumab (to PD-1). In additional embodiments, such a therapeutic agent can be, for example, CDX-1127 (to CD27), CP-870893 (to CD40), lucatumumab (to CD40), or

dacetuzumab (to CD40).

[00363] In some embodiments, a method of treating cancer in a subject comprises

administering to the subject a therapeutically effective amount of an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide. In some embodiments, a method of treating cancer in a subject comprises administering to the subject a therapeutically effective amount of antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide in combination with a checkpoint inhibitor. In some embodiments, the checkpoint inhibitor is an anti-PD-1 antibody (e.g, MEDI0680, REGN2810, BGB-A317, or PDR001). In some embodiments, the checkpoint inhibitor is an anti-PD-1 antibody (e.g,. nivolumab (OPDIVO), pembrolizumab (KEYTRUDA), or

pidilzumab). In some embodiments, the checkpoint inhibitor is an anti-PD-Ll antibody (e.g,. BMS935559 (MDX-1105), atezolizumab (TECENTRIQ), durvalumab (MEDI4736; IMFINZI), avelumab (MSB0010718C), or LY3300Q54). [00364] It will be appreciated that the combination of an antibody or antigen-binding fragment described herein, which specifically binds to a MerTK polypeptide and one additional therapeutic agent can be administered in any order or concurrently.

[00365] In some embodiments, combined administration can include co-administration, either in a single pharmaceutical formulation or using separate formulations, or consecutive

administration in either order but generally within a time period such that all active agents can exert their biological activities simultaneously. In some embodiments, an antibody or antigen binding fragment described herein, which specifically binds to a MerTK polypeptide and at least one additional therapeutic agent can be administered using the same methods or can be administered using different methods known in the art.

5.4.1 Diagnostic Uses

[00366] In one aspect, anti-MerTK antibodies described herein and antigen-binding fragments thereof, which specifically bind to an ECD of human MerTK can be used for diagnostic purposes to detect, diagnose, or monitor a condition described herein ( e.g ., a condition involving MerTK and/or abnormal MerTK signaling and/or abnormal MerTK expression). In specific

embodiments, anti-MerTK antibodies described herein or an antigen-binding fragment thereof for use in diagnostic purposes are labeled.

[00367] In certain embodiments, provided herein are methods for the detection of a condition described herein comprising: (a) assaying the expression of MerTK in cells or a tissue sample of a subject using one or more antibodies described herein or an antigen-binding fragment thereof; and (b) comparing the level of MerTK expression with a control level, e.g., levels in normal tissue samples (e.g, from a patient not having a condition described herein, or from the same patient before onset of the condition), whereby an increase or decrease in the assayed level of MerTK expression compared to the control level of MerTK expression is indicative of a condition described herein.

[00368] Antibodies described herein can be used to assay MerTK levels in a biological sample using classical immunohistological methods as described herein or as known to those of skill in the art (e.g, see Jalkanen et al., 1985, J. Cell. Biol. 101 :976-985; and Jalkanen et al., 1987, J.

Cell. Biol. 105:3087-3096). Other antibody-based methods useful for detecting protein gene expression include immunoassays, such as the enzyme linked immunosorbent assay (ELISA) and the radioimmunoassay (RIA). Suitable antibody assay labels are known in the art and include enzyme labels, such as, glucose oxidase; radioisotopes, such as iodine (1251, 1211), carbon (14C), sulfur (35S), tritium (3H), indium (121In), and technetium (99Tc); luminescent labels, such as luminol; and fluorescent labels, such as fluorescein and rhodamine, and biotin.

[00369] In one embodiment, monitoring of a condition described herein is carried out by repeating the method for diagnosing for a period of time after initial diagnosis.

[00370] Presence of the labeled molecule can be detected in the subject using methods known in the art for in vivo scanning. Skilled artisans will be able to determine the appropriate method for detecting a particular label. Methods and devices that may be used in the diagnostic methods include, but are not limited to, computed tomography (CT), whole body scan such as position emission tomography (PET), magnetic resonance imaging (MRI), and sonography.

6. EXAMPLES

[00371] The examples in this section (z.e., Section 6) are offered by way of illustration, and not by way of limitation.

6.1 Example 1: Generation of anti-MerTK Human Monoclonal Antibodies

[00372] Human anti-MerTK monoclonal antibodies were generated by immunizing the H2L2 strain of Harbour® transgenic mice (Harbour BioMed) with the purified human MerTK extracellular domain antigen fused to a mouse Fc Tag (huMerTK- msFc). Harbour® transgenic mice have had the endogenous mouse heavy chain (HC) and kappa light chain (k-chain) DNA sequences knocked out and have had sequences for the human variable (V) regions and rat constant (C) regions stably incorporated into the mouse genome.

[00373] Antigen and Immunization: Mice were immunized with the soluble MerTK protein in MPL plus TDM adjuvant system (Sigma). 10-20 micrograms soluble recombinant MerTK antigen in PBS was mixed 1 :1 with the adjuvant. Mice were injected with 200 microliters of the prepared antigen into the peritoneal cavity every 14 days. Animals that developed anti- MerTK titers were given an iv injection of 10 micrograms soluble recombinant MerTK antigen three to four days prior to fusion. Mouse spleens were harvested, and the isolated splenocytes used for hybridoma preparation.

[00374] Hybridoma Preparation: The P3x63Ag8.653 murine myeloma cell line (ATCC CRL 1580) was used for the fusions. RPMI 1640 (Invitrogen) containing 10% FBS was used to culture the myeloma cells. Additional media supplements were added to the Hybridoma growth media, which included: up to 10% BM Condimed HI Hybridoma Cloning Supplement (Sigma), 10% FBS (Sigma), L-glutamine (Gibco) 0.1% gentamycin (Gibco), 2-mercaptoethanol (Gibco), with HAT (Sigma; 1.0 x 10⁴ M hypoxanthine, 4.0 x 10 ⁷ M aminopterin, 1.6 x 10 ⁵ M thymidine media.

[00375] Spleen cells were mixed with the P3x63 Ag8.653myeloma cells in a 6: 1 ratio and pelleted by centrifugation. Polyethylene glycol was added dropwise with careful mixing to facilitate fusion. Hybridomas were allowed to grow out for one to two weeks until visible colonies become established. Supernatant was harvested and used for initial screening for rat IgG via ELISA using a human soluble MerTK fusion protein and a rat Fc specific detection. IgG positive supernatants were then assayed for MerTK binding specificity via flow cytometry. The hybridomas were also screened for cross-reactivity with cynomolgus macaque MerTK and all were positive for binding.

[00376] Hybridoma cells were expanded and cell pellets were frozen for RNA isolation and sequencing. The VH and VL coding regions of human mAbs were identified using RNA from the corresponding hybridomas. RNA was reverse-transcribed to cDNA and the variable coding regions were amplified by PCR. The PCR product was sequenced, inserted into human IgGl vector, transiently expressed and purified by protein A column chromatography, which led to the isolation of antibody Ab3000.

6.2 Example 2: Binding to human MerTK

[00377] Microtiter plates were coated with either recombinant human MerTK-msFc, recombinant mouse MerTK-msFc, or recombinant cynomolgus MerTK-Flag-HIS in PBS, and then blocked with 5% bovine serum albumin in PBS. Protein A purified human mAbs and an isotype control were added at various concentrations and incubated at 37°C. The plates were washed with PBS/Tween and then incubated with a goat-anti-human IgG Fc-specific polyclonal reagent conjugated to horseradish peroxidase at 37°C. After washing, the plates were developed with HRP substrate, and analyzed at OD 450-650 using a microtiter plate reader. Representative binding curves and reactivity results are shown on Figures 1 and 2.

6.3 Example 3: Binding to MerTK expressing cells

[00378] The ability of anti-MerTK human mAbs to bind to MerTK on cells expressing human MerTK on their surface was investigated by flow cytometry as follows: [00379] Antibodies were tested for binding to human cell lines expressing human MerTK on their surface. Protein A-purified human mAbs were incubated with MerTK-L cells or SK-mel-5 cells at room temperature on a plate shaker. After 20 minutes, the cells were washed with PBS containing 0.1% BSA and 0.05% NaN3 (PBA) and the bound antibodies were detected by incubating the cells with a PE labeled goat anti-human IgG Fc-specific probe. The excess probe was washed from the cells with PBA and the cell associated fluorescence was determined by analysis using a FACSCanto II™ instrument (BD Biosciences, NJ, USA) according to the manufacturer’s directions.

[00380] As shown in Figures 3 A and 3B, the human mAbs demonstrated high level binding to cells expressing human MerTK as a function of antibody concentration.

6.4 Example 4: Determination of Affinity and Rate Constants of Human mAbs by Bio-Layer Interferometry (BLI)

[00381] Binding affinity and binding kinetics of various human anti-MerTK antibodies were examined by bio-layer interferometry (BLI) using an Octet™ QK^e instrument (Pall ForteBio, Menlo Park, CA) according to the manufacturer’s guidelines.

[00382] Purified antibodies were captured on Anti -Human Fc Capture (AHC) biosensors (Fortebio Product No. 18-5060). Each antibody was prepared in dilution buffer (10mMPO4, 150mM NaCl, lmg/mL BSA, 0.05%Tween 20, pH 7.2) to 1 pg/mL and loaded on freshly hydrated and conditioned AHC biosensors for 180 seconds at 30°C and 1000 rpm plate shake speed to achieve a target response of 1.0 nM. For one assay, eight biosensors were loaded with the same antibody.

[00383] Binding was determined by exposing six of the antibody loaded biosensors to analyte: soluble human MerTK-CD4-Biotin-HIS (Celldex, 77.5kD by SDS-PAGE). Affinity measurements were determined using 2-fold serial dilutions of analyte ranging from 25 to 0.78nM in dilution buffer at 30°C and 1000 rpm plate shake speed. Association of the antibody loaded biosensors in analyte wells was carried out for 180 seconds, the biosensors were then moved to dilution buffer wells for 900 seconds for dissociation measurements.

[00384] Corresponding controls were conducted in each case by keeping the two remaining biosensors with captured antibody in dilution buffer wells for association and dissociation steps. The data for the control biosensors was used to subtract background and account for biosensor drift and antibody dissociation from the biosensors. [00385] Fortebio’s Data Analysis Software version 11.0.0.4 (Pall ForteBio, Menlo Park, CA) was used in each case to derive kinetic parameters from the concentration series of analyte in dilution buffer binding to captured antibody. The association and dissociation curves were fitted to a 1 : 1 binding model using the data analysis software according to the manufacturer’s guidelines.

[00386] The affinity and kinetic parameters (with background subtracted) as determined are shown in Table 7, where kon = rate of association, kdis = rate of dissociation, and KD = affinity constant (equilibrium dissociation constant), determined by the ratio kdis/kon.

Table 7: Amino acid sequences of the proteins encoding each of the 4 domains that

comprise the human MerTK extracellular domain

6.5 Example 5: Domain Binding Analysis

[00387] An ELISA-based method was utilized to determine to which of the four MerTK domains Ab3000 binds.

6.5.1 Domain construction and purification

[00388] The MerTK extracellular domain (ECD) contains two N-terminal immunoglobulin like domains (here named D1 and D2, respectively) followed by two Fibronectin-III domains (here named D3 and D4, respectively). Table 8, utilizing standard one letter amino acid codes, shows the amino acid sequences of the proteins encoding each of the 4 domains that comprise the human MerTK extracellular domain.

Table 8: Amino acid sequences of the proteins encoding each of the domains that comprise the human MerTK extracellular domain

[00389] Proteins encoding each of the 4 domains that comprise the human MerTK extracellular domain (ECD) were fused in frame to a rat CD4 domain, followed by a biotinylation (Avi) tag and a hexahistidine tag. The IL-2 signal sequence for secretion into the culture media was engineered at the 5’ end of each construct. Expression vectors encoding these constructs were transfected in Expi293 cells, and conditioned media containing each fusion protein was purified by nickel-affinity chromatography and buffer exchanged to phosphate buffer saline (PBS).

6.5.2 Domain binding analysis and Results

[00390] Purified domains and ECDs were coated on Nickel-coated 96 well plates (Thermo Scientific) at 100 ng/well in borate buffer. Plates were washed and incubated with 50 nM of each mAh at room temperature for 1 hour, followed by washing and incubation with an HRP- conjugated anti-human secondary antibody for 1 hour at room temperature. Plates were washed and developed using a TMB substrate as described by the manufacturer (Thermo Scientific). A BioTek plate reader was used to quantitate the TMB signal at A450.

[00391] Data are shown in Figure 4. Results show that Ab3000 binds to recombinantly purified MerTK D2 alone, and a protein comprising D1 and D2. Ab3000 did not bind to recombinantly purified MerTK Dl, D3, or D4 alone. Moreover, Ab3000 binds to the intact human and cynomolgus MerTK extracellular domain (ECD) and did not bind to the Axl ECD. 6.6 Example 6: Ligand Blocking Assay

6.6.1 ELISA-based Method [00392] To characterize the effect of anti-MerTK antibody Ab3000 on MerTK activity, specifically, a plate-based assay was developed to establish whether a given antibody blocks binding of Gas6 to human MerTK (hMerTK).

[00393] Biotinylated human Gas6 (R&D Systems) was captured to a streptavidin microtiter plate (Pierce) at 5 pg/mL The anti-MerTK antibodies ([final] = 20 pg/mL, or a titration thereof) were mixed with soluble recombinant human MerTK-msFc ([final] = 0.05 pg/mL), incubated for 10 minutes at room temperature then added to the plate. Goat anti-mouse IgG (Fc specific) antibody was added. MerTK binding was then detected with a horseradish peroxidase conjugated donkey anti -goat IgG (H&L) antibody and TMB substrate (KPL).

[00394] As shown in Figure 5, Ab3000 partially inhibited Gas6 binding to hMerTK as evaluated by ELISA plate assay.

6.7 Example 7: MerTK turnover assay

6.7.1 Human Macrophage Cell Culture

[00395] PBMCs were added to a T175 cm² flasks and monocytes allowed to adhere for ~2 hours at 37°C, 6%C02. The non-adherent cells were removed and the monocytes cultured for 6 days in RPMI containing 10% FBS and 100 ng/mL MCSF (R&D Systems).

[00396] On the day of the assay, growth medium is removed from the wells and replaced with medium containing Ab3000-IgGl or Gas6 (100 nM). Cells are then incubated at 37°C for 24 hours. Data is shown in Figure 6. Results indicate that Ab3000 induces a significant decrease in total MerTK levels in human macrophages after prolonged treatment.

6.8 Example 8: Immunoreceptor phosphorylation assay

[00397] 4xl0⁷ human PBMCs were treated with 100 nM Ab3000 or a control human IgGl monoclonal antibody for 1 hour in the presence of serum. PBMCs were lysed, and 0.2-0.4 mg of lysate was applied to Proteome Profiler Human Phospho-Immunoreceptor array membranes (R&D Systems) and developed according to manufacturer’s instructions with the following modification. Anti-phosphotyrosine-biotin conjugated antibody (R&D HAM1676) was added as a probing antibody, followed by incubation with IR Dye 800 streptavidin (LI-COR) for imaging on a LI-COR® Odyssey instrument. Imaged data were quantified and normalized to control antibody-treated samples. [00398] Data are shown in Figure 7 and reflect the mean and S.E.M of 5 independent PBMC donors. It can be seen that Ab3000 induces a decrease in the activation of immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing immunoreceptors expressed in human PBMCs.

6.9 Example 9: Cytokine Production in Human Dendritic Cells

6.9.1 Cytokine Production in Human Dendritic Cells

[00399] Dendritic cells were derived from human monocytes as follows:

[00400] PBMC’s were added to a T175cm² flasks and monocytes allowed to adhere for approximately 2 hours at 37°C, 6% CO2. The non-adherent cells were removed and the monocytes cultured for 7 days in RPMI containing 10% FBS, lOng/mL IL-4 (R&D Systems) and lOOng/mL GM-CSF (R&D Systems). The cells were harvested and frozen for future use.

[00401] On the day of the experiment, the cells were thawed, washed twice in RPMI and counted. The cells were then incubated in the presence of anti-MerTK antibody or appropriate isotype control overnight at 37°C, 6%C02, with or without 5ng/mL LPS (Invivogen). All reagents were prepared in RPMI (no serum). The supernatant was collected, clarified and either used immediately or stored frozen for cytokine analysis. Production of IL-IRA and TNF-alpha was evaluated by ELISA (R&D Systems). Multiplex analysis was performed by Eve

Technologies (Alberta, CA). Representative data are shown in Figures 8A and 8B and Figure 9.

6.10 Example 10: Cytokine Production in Human PBMCs

[00402] Human PBMCs were treated with 100 nM of mAbs for 24 hours in the absence of serum. Conditioned media was subjected to cytokine analysis, performed by Eve Technologies (Alberta, CA). Cytokine data were normalized to human IgGl control-treated samples and are shown in Figure 10.

6.11 Example 11: Cytokine Production in Human Macrophages

[00403] Macrophages were derived from human monocytes as follows:

[00404] PBMCs were added to a T175cm² flasks and monocytes allowed to adhere for ~2 hours at 37°C, 6%CC>2. The non-adherent cells were removed and the monocytes cultured for 7 days in RPMI containing 10% FBS and 50ng/mL MCSF (R&D Systems). The cells were harvested and frozen for future use.

[00405] On the day of the experiment, the cells were thawed, washed twice in RPMI and counted. The cells were then incubated in the presence of anti-MerTK antibody or appropriate isotype control overnight at 37°C, 6%C02. All reagents were prepared in RPMI (no serum).

The supernatant was collected, clarified and either used immediately or stored frozen for cytokine analysis. Production of IL-IRA and TNF-alpha was evaluated by ELISA (R&D Systems). Representative data are shown in Figures 11 A and 1 IB.

6.12 Example 12: CD14⁺ Cell Enrichment or Depletion from human PBMCs

[00406] Peripheral blood mononuclear cells (PBMCs) were isolated from donor whole blood following manufacturer’s protocol (StemCell Technologies). Purified PBMCs were plated at l .QxTO⁶ ceils/well in a 24-well plate and treated with lOOnM monoclonal antibody for 24 hours. Following 24 hour treatment, cell-free supernatants were collected and stored at -80°C prior to assessing cytokine secretion by ELISA (IL-IRA R&D Systems).

[00407] CD14+ monocytes were enriched from purified PBMCs using CD56, CD3, and CD19 microbeads following manufacturer’s protocol (Miltenyi Biotec). These microbeads were used to deplete the PBMC culture of NK/T/B cells, in turn, enriching the culture for CD14⁺ monocytes. PBMCs enriched for CD14⁺ monocytes were plated and treated as stated above. TNF-a, IL-6, and IL-IRA levels were measured by ELISA (R&D Systems). Results from two different donors are shown in the top panels and bottom panels of Figure 12.

6.13 Example 13: MerTK expression in Immune Cell Populations

[00408] Human MerTK expression from two donors was monitored in immune cell populations using flow cytometry using CD14, CD20, CD56 and CD3 markers (Figure 13, top and bottom panels). MerTK is highly expressed in CD14⁺ monocytes, moderately expressed in Cd20⁺ cells and CD56⁺ NK cells, and not detectable in CD3⁺ T cells.

6.14 Example 14: A Surrogate Anti-MerTK Mouse mAh Demonstrates Antitumor Activity Alone and in Combination with a PD-1 Inhibitor

[00409] CT26 Tumor Model. To generate the CT26 tumor model, mice were implanted subcutaneously with 30,000 cells of a mouse colon carcinoma cell line (CT26.WT).

[00410] The CT26 tumor model was dosed with saline, anti-mouse MerTK monoclonal antibody (3C6 at 300 pg intraperitoneally twice per week xl, once per week x3), anti-mouse PD1 monoclonal antibody (RMPl-14, ThermoFisher) at 100 pg intraperitoneally twice per week x2), or a combination of anti-MerTK and anti-PD-1. Ten mice in each treatment group were monitored for tumor growth and tumor volumes (cm³) were measured at indicated days post- tumor injection (Figure 14). Both anti-PDl and anti-MerTK resulted in anti-tumor activity compared to the saline control.

[00411] Survival post-injection was also monitored (Figure 14, top right panel). Mice treated with anti-PDl and anti-MerTK showed an improved survival compared to control mice, while mice administered combination therapy indicated an additive or synergetic effect.

6.15 Example 15: Activation of Co-Stimulatory Molecules in Dendritic Cells

[00412] Dendritic cells were derived from human monocytes as follows: PMBCs were added to a T175cm² flasks and monocytes were allowed to adhere for approximately 2 hours at 37°C, 6% CO2. The non-adherent cells were removed and the monocytes cultured for 7 days in RPMI containing 10% FBS, lOng/mL IL-4 (R&D Systems) and lOOng/mL GM-CSF (R&D Systems). The cells were harvested and frozen.

[00413] The cells were then incubated in the presence of Ab3000-IgGl antibody or indicated controls at 37°C, 6% CO2. After 24 hours, the cells were harvested and the supernatant was collected and stored for cytokine analysis. The cells were stained with the following labeled antibodies for 20 minutes at room temperature, shaking: fluorochrome-conjugated CD54 and CD86 (both from Becton Dickinson (BD) Biosciences). (CD54 was conjugated to R- phycoerythrin (PE) and CD86 was conjugated to PharRed (APC-Cy7).) Cells were then washed twice and analyzed on a FACSCanto II™ instrument (BD Biosciences, NJ, USA).

[00414] Incubation of dendritic cells with Ab3000-IgGl antibody resulted in an

approximately 3.8-fold increase in co-stimulatory molecule CD86-positive cells compared to isotype control (huIgGl) (Figure 15 A) and an approximately 2-fold increase in co-stimulatory molevule CD54-positive cells over media control (Figure 15B). As a positive control, dendritic cells were incubated with anti-CD40 antibody (a-CD-40), resulting in a 4.5-fold increase in CD54-positive cells (Figure 15B). Results indicate that Ab3000 antibody promotes upregulation of co-stimulatory CD54 and CD86 molecules in dendritic cells.

6.16 Example 16: Activation of Co-Stimulatory Molecules in PBMCs

[00415] Human PBMCs were enriched for CD14+ monocytes by depleting the full PBMC population of CD3+, CD19+, and CD56+ cells, using Miltenyi Biotech positive selection kits. CD 14+ enriched PBMCs were treated with serum-free medium containing 100 nM of Ab3000- IgGl or IgGl human isotype control. Cells were then incubated at 37°C for 24 hours. After treatment, supernatants were removed, CD14+ enriched cells were lysed and total RNA was extracted per manufacturer’s guidelines (RNEasy, Qiagen). Total RNA (0.5 pg) was used for input for cDNA synthesis, using Superscript III First-Strand Synthesis System (per

manufacturer’s protocol). CD86, and CD54 expression was examined by Quantitative Real Time PCR using the Applied Biosystems 7900HT platform. DDOT (fold change) was calculated as previously described (Livak and Schmittgen (2001) Methods; 25(4): 402-8).

[00416] Results indicate the Ab3000-IgGl promotes upregulation of co-stimulatory molecules CD86 and CD54 in human donor PBMCs (Figure 16A and 16B, respectively).

6.17 Example 17: T-cell Activation in Mixed Lymphocyte Reactions

[00417] T cells were incubated with allogeneic dendritic cells (DCs) and Ab3000-IgGl or isotype control for 72 hours. The supernatant was collected, clarified and either used

immediately or stored frozen for cytokine analysis. Production of IFN-gamma was evaluated by ELISA (R&D Systems). Ab3000-IgGl promotes an increase in IFN-gamma secretion in mixed T cell and dendritic cell culture (Figure 17).

6.18 Example 18: NF-KB Inhibition in Human PBMCs

[00418] Human PBMCs were treated with 100 nM of Ab3000-IgGl, IgGl human isotype control or 100 ng/ml of LPS (Invivogen) in serum-free medium in the presence or absence of 10 pM IKKl/2 inhibitor BMS-345541 (Selleck Chemicals), which blocks NF-KB-dependent transcription. IKKl/2 inhibitor-treated cells were pretreated with the inhibitor for 60 minutes. Cells were then incubated at 37°C for 24 hours. After treatment, cell-free supernatants were isolated and IL-IRA cytokine secretion was analyzed using Human IL-lra/IL-lF3 DuoSet ELISA (R&D Systems), per manufacturer’s protocol. Results indicate that Ab3000-IgGl- induced cytokine release is NF-KB-dependent (Figure 18).

6.19 Example 19: Ab3000-IgGl Does not Promote Phosphorylation of Upstream FcyR Signaling molecules

[00419] Human PBMCs were added to a T175 cm² flasks and monocytes were allowed to adhere for approximately 2 hours at 37°C in 5% CO2. The non-adherent cells were removed and the monocytes were cultured for 6 days in RPMI containing 10% FBS and 100 ng/mL MCSF (R&D Systems).

[00420] On the day of the assay, growth medium was removed from the wells and replaced with medium containing PBS, IgGl, Ab3000 or X-linked huIgGl at lOOnM. Cells were then incubated at 37°C for 10 minutes, before addition of 100 nM of each indicated mAh. Human IgGl (huIgGl) was chemically cross-linked (X-linked huIgGl) using Sulfo-EGS

(ThermoFisher) according to manufacturer’s instructions, and aggregation was verified by SEC- HPLC and SDS-PAGE.

[00421] After treatment, plates were washed with cold PBS, lysed, subjected to SDS-PAGE and transferred to nitrocellulose membranes for immunoblotting. Membranes were blocked with Odyssey blocking buffer (LI-COR Biosciences) and subsequently analyzed by western blot for phosphorylated and total Syk and SHP-1 (Cell Signaling). Primary antibodies were prepared in antibody dilution buffer and incubated with membranes for 1 hour at room temperature. After washing, membranes were incubated for 1 hour at room temperature with LI-COR secondary antibodies diluted 1 :20,000 in antibody dilution buffer. Blots were scanned using a LI-COR Odyssey Imaging System.

[00422] Ab3000-IgGl incubation did not result in an increase in phosphorylation of Syk or SHP-1 (Figure 19). Results indicate that Ab3000-IgGl promotes FcyR activation through modulation of MerTK activity rather than through the phosphorylation of upstream signaling molecules Syk and SHP-1.

6.20 Example 20: Ab3000 Does Not Block Binding of Gas6 to MerTK Expressed on Cells

[00423] Recombinantly-expressed Gas6 was fluorescently labeled with Alexa-647 according to manufacturer’s instructions (Thermofisher). Human MerTK was stably expressed in L cells (fibroblasts, ATCC CRL-2648). Cells were incubated in DMEM (10% serum) in the presence of 100 nM of indicated antibodies or 1 uM of excess unlabeled Gas6 at 4°C for 45 minutes, followed by incubation with 50 nM of Alexa647-labeled Gas6 for 30 minutes. Cells were washed, fixed using Cytofix./Cytoperm (BD Biosciences), washed again and analyzed in an Accuri C6 flow cytometer (BD Biosciences). Data are presented as mean fluorescent values (MFI).

[00424] Incubation of cells with Ab3000 did not increase binding of Gas6 to human MerTK expressed on L cells compared to the binding in the presence of IgGl control or no antibody (Figure 20). Binding was reduced in cells incubated with excess unlabeled Gas6 or an anti- MerTK control antibody that blocks ligand binding but does not induce cytokines. The results presented herein indicate that Ab3000 does not block binding of Gas6 to MerTK expressed on cells. 6.21 Example 21: Ab3000 Does Not Inhibit Gas6-Dependent MerTK Phosphorylation in Human Macrophages

[00425] PBMCs were added to a T175 cm² flasks and monocytes were allowed to adhere for approximately 2 hours at 37°C, 6% CO2. The non-adherent cells were removed and the monocytes were cultured for 6 days in RPMI containing 10% FBS and 100 ng/mL MCSF (R&D Systems).

[00426] On the day of the assay, growth medium was removed from the wells and replaced with medium containing Ab3000 or a control human IgGl at 100 nM. Cells were then incubated at 37°C for 1 hour, before addition of 100 nM Gas6 for an additional 10 minutes as indicated. After treatment, plates were washed with cold PBS, lysed, subjected to SDS-PAGE

electrophoresis and transferred to nitrocellulose membranes for immunoblotting. Membranes were blocked with Odyssey blocking buffer and subsequently analyzed by western blot for human MerTK or phospho-MerTK (R&D Systems), and b-tubulin (Cell Signaling). Membranes were washed and incubated for 1 hour at room temperature with secondary antibodies (LI-COR Biosciences), diluted 1 :20,000 in antibody dilution buffer. Blots were scanned using a LI-COR® Odyssey Imaging System (LI-COR Biosciences).

[00427] Incubation of cells with indicated concentrations of Ab3000-IgGl did not inhibit of Gas6-dependent MerTK phosphorylation (Figure 21).

6.22 Example 22: Inhibition of MerTK Kinase does not Reduce Ab3000-IgGl- Dependent Increase in IL-1RA and MIP-la Secretion

[00428] Human donor PBMCs were isolated from whole blood using Lymphoprep™

(Stemcell Technologies) following manufacturer’s protocol. Human IgGl isotype control or Ab3000-IgGl was wet-coated onto a 96-well plate by diluting monoclonal antibodies in lx PBS to a final concentration of 100 nM and 50 pL was added to a 96-well plate. Monoclonal antibodies were incubated at room-temperature for one hour and then washed three times with lx PBS. The plate was then blocked by adding lx PBS + 10% FBS and incubating at 37°C for one hour. The plate was washed three times with lx PBS.

[00429] Next, l.OxlO⁵ human donor PBMCs were added to each well in 100 pL of serum -free RPMI. Then, the MerTK small molecule inhibitor UNC-2025 (Selleck Chemicals), was diluted to 1600 nM in serum-free RPMI and 100 pL was added to appropriate wells for a final concentration of 800 nM. Human donor PBMCs and UNC-2025 were incubated at 37°C for 24 hours and conditioned supernatants were harvested. Human IL-IRA ELISA and MIP-la ELISA was performed following manufacturer’s protocol using Human IL-IRA Duoset ELISA kit (R&D Systems).

[00430] Treatment of human PBMCs with MerTK mAh Ab3000-IgGl elicited secretion of IL-IRA and MIP-la (Figure 22A and 22B, respectively). By contrast, WNiC-2025, which inhibits MerTK kinase activity, did not induce secretion of these cytokines. Moreover, inhibition of MerTK kinase activity did not reduce Ab3000-IgGl -dependent increase in IL-IRA and MIP- la secretion.

Claims

WHAT IS CLAIMED:

1. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising an amino acid sequence having at least 80% sequence identity to SEQ ID NO: 2; and/or

(ii) a heavy chain variable region (VH) comprising an amino acid sequence having at least 80% sequence identity to SEQ ID NO: 1.

2. The antibody or an antigen-binding fragment of claim 1, comprising:

(i) a light chain variable region (VL) comprising an amino acid sequence having at least 80% sequence identity to SEQ ID NO: 2; and

3. The antibody or antigen-binding fragment of claim 1 or 2, wherein the VL comprises a VL complementarity determining region 1 (CDR1), VL CDR2, and VL CDR3, comprising the amino acid sequences of SEQ ID NOS: 6, 7 and 8, respectively, or conservative sequence modifications thereof.

4. The antibody or antigen-binding fragment of any one of claims 1 to 3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7 and 8, respectively.

5. The antibody or antigen-binding fragment of any one of claims 1 to 4, wherein the VL comprises at least 80% amino acid sequence identity to SEQ ID NO: 2.

6. The antibody or antigen-binding fragment of any one of claims 1 to 4, wherein the VL comprises at least 85% amino acid sequence identity to SEQ ID NO: 2.

7. The antibody or antigen-binding fragment of any one of claims 1 to 4, wherein the VL comprises at least 90% amino acid sequence identity to SEQ ID NO: 2.

8. The antibody or antigen-binding fragment of any one of claims 1 to 4, wherein the VL comprises at least 95% amino acid sequence identity to SEQ ID NO: 2.

9. The antibody or antigen-binding fragment of any one of claims 1 to 4, wherein the VL comprises at least 98% amino acid sequence identity to SEQ ID NO: 2.

10. The antibody or antigen-binding fragment of claim 1 or 2, wherein the VL comprises SEQ ID NO: 2.

11. The antibody or antigen-binding fragment of any one of claims 1 to 10, wherein the VH comprises a VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, comprising the amino acid sequences of SEQ ID NOS: 3, 4 and 5, respectively, or conservative sequence modifications thereof.

12. The antibody or antigen-binding fragment of claim 11, wherein the VH CDR1,

VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 3, 4 and 5, respectively.

13. The antibody or antigen-binding fragment of any one of claims 1 to 12, wherein the VH comprises at least 80% amino acid sequence identity to SEQ ID NO: 1.

14. The antibody or antigen-binding fragment of any one of claims 1 to 12, wherein the VH comprises at least 85% amino acid sequence identity to SEQ ID NO: 1.

15. The antibody or antigen-binding fragment of any one of claims 1 to 12, wherein the VH comprises at least 90% amino acid sequence identity to SEQ ID NO: 1.

16. The antibody or antigen-binding fragment of any one of claims 1 to 12, wherein the VH comprises at least 95% amino acid sequence identity to SEQ ID NO: 1.

17. The antibody or antigen-binding fragment of any one of claims 1 to 3, wherein the VH comprises at least 98% amino acid sequence identity to SEQ ID NO: 1.

18. The antibody or antigen-binding fragment of claim 1 or 2, wherein the VH comprises SEQ ID NO: 1.

19. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

20. The antibody antigen-binding fragment of claim 19, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7 and 8, respectively or conservative sequence modifications thereof; and

21. The antibody or antigen-binding fragment of claim 19, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7 and 8; and/or

(ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 3, 4 and 5 respectively.

22. The antibody or antigen-binding fragment of claim 20, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 6, 7 and 8; respectively, and

23. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 16, 17 and 18, respectively or conservative sequence modifications thereof; and/or

24. The antibody or antigen-binding fragment of claim 23, wherein the VL CDR1,

VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 16, 17, and 18, respectively or sequences having at least 80% amino acid sequence identity thereto.

25. The antibody or antigen-binding fragment of claim 23, wherein the VH CDR1,

VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 13, 14, and 15, respectively or sequences having at least 80% amino acid sequence identity thereto.

26. The antibody or an antigen-binding fragment of claim 23, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 16, 17, and 18, respectively or sequences having at least 80% amino acid sequence identity thereto, and the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 13, 14, and 15, respectively or sequences having at least 80% amino acid sequence identity thereto.

27. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 22, 23 and 24, respectively or conservative sequence modifications thereof; and/or

(ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 19, 20 and 21 respectively or conservative sequence modifications thereof.

28. The antibody or antigen-binding fragment of claim 27, wherein the VL CDR1,

VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 22, 23 and 24, respectively or sequences having at least 80% amino acid sequence identity thereto.

29. The antibody or antigen-binding fragment of claim 27, wherein the VH CDR1,

VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 19, 20, and 21, respectively or sequences having at least 80% amino acid sequence identity thereto.

30. The antibody or antigen-binding fragment of claim 27, wherein the VL CDR1,

VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 22, 23 and 24, respectively or sequences having at least 80% amino acid sequence identity thereto, and the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 19, 21, and 22, respectively or sequences having at least 80% amino acid sequence identity thereto.

31. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to human MerTK, comprising:

(i) a light chain variable region (VL) comprising VL complementarity

determining region 1 (CDR1), VL CDR2, and VL CDR3, wherein the VL CDR1, VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 28, 29 and 30, respectively or conservative sequence modifications thereof; and/or

(ii) a heavy chain variable region (VH) comprising VH complementarity determining region 1 (CDR1), VH CDR2, and VH CDR3, wherein the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 25, 26 and 27 respectively or conservative sequence modifications thereof.

32. The antibody or antigen-binding fragment of claim 31, wherein the VL CDR1,

VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 28, 29 and 30, respectively or sequences having at least 80% amino acid sequence identity thereto.

33. The antibody or antigen-binding fragment of claim 31, wherein the VH CDR1,

VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 25, 26 and 27, respectively or sequences having at least 80% amino acid sequence identity thereto.

34. The antibody or antigen-binding fragment of claim 31, wherein the VL CDR1,

VL CDR2, and VL CDR3 comprise the amino acid sequences of SEQ ID NOS: 28, 29 and 30, respectively or sequences having at least 80% amino acid sequence identity thereto, and the VH CDR1, VH CDR2, and VH CDR3 comprise the amino acid sequences of SEQ ID NOS: 25, 26 and 27, respectively or sequences having at least 80% amino acid sequence identity thereto.

35. An isolated antibody, or an antigen-binding fragment thereof, which specifically binds to Domain 2 of human MerTK.

36. An isolated antibody, or an antigen-binding fragment thereof, which binds to the same epitope of human MerTK as the antibody of any of claims 1 to 35.

37. An isolated antibody, or an antigen-binding fragment thereof, which competes for binding to human MerTK with the antibody of any of claims 1 to 35.

38. An isolated antibody, or an antigen-binding fragment thereof, which binds to Domain 2 of human MerTK, and does not inhibit binding of Gas6 to cell-surface MerTK and/or does not inhibit MerTK phosphorylation in human macrophages.

39. The antibody or antigen-binding fragment of any one of claims 1 to 38, wherein the antibody comprises a heavy chain constant region or a light chain constant region.

40. The antibody or antigen-binding fragment of claim 39, wherein the antibody comprises a heavy chain constant region and a light chain constant region.

41. The antibody or antigen-binding fragment of claim 39, wherein the antibody comprises a human heavy chain constant region or a human light chain constant region.

42. The antibody or antigen-binding fragment of claim 41, wherein the antibody comprises a human heavy chain constant region and a human light chain constant region.

43. The antibody or antigen-binding fragment of any one of claims 39 to 42, wherein the antibody or antigen-binding fragment is an IgGl antibody or antigen-binding fragment or a human IgG2 antibody or antigen-binding fragment.

44. The antibody or antigen-binding fragment of claim 43, wherein the antibody or antigen-binding fragment is an IgGl antibody or antigen-binding fragment.

45. The antibody or antigen-binding fragment of any one of claims 39 to 44, wherein the antibody comprises a kappa light chain constant region or a lambda light chain constant region.

46. The antibody or antigen-binding fragment of any one of claims 39 to 44, wherein the antibody comprises a human kappa light chain constant region or a human lambda light chain constant region.

47. The antibody or antigen-binding fragment of any one of claims 39 to 46, wherein the antibody comprises the amino acid sequence of SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, or SEQ ID NO: 36.

48. The antibody or antigen-binding fragment of claim 47, wherein the antibody comprises the amino acid sequence of SEQ ID NO: 31 and the amino acid sequence of SEQ ID NO: 32; the amino acid sequence of SEQ ID NO: 31 and the amino acid sequence of SEQ ID NO: 33; the amino acid sequence of SEQ ID NO: 36 and the amino acid sequence of SEQ ID NO: 34; or the amino acid sequence of SEQ ID NO: 36 and the amino acid sequence of SEQ ID NO: 35.

49. The antibody or antigen-binding fragment of any one of claims 1 to 48, which is a monoclonal antibody.

50. The antibody or antigen-binding fragment of any one of claims 1 to 49, which is a bispecific antibody.

51. The antibody or antigen-binding fragment of any one of claims 1 to 50, which is fused to a heterologous polypeptide.

52. The antibody or antigen-binding fragment of any one of claims 1 to 50, which is conjugated to an agent.

53. The antibody or antigen-binding fragment of claim 52, wherein the agent is a toxin.

54. An antibody, or an antigen-binding fragment thereof, that binds to human MerTK which antibody or fragment has a mutated IgG Fc domain which binds to Fc gamma receptors with a greater affinity than the corresponding native IgG Fc domain.

55. A human or humanized monoclonal antibody, or an antigen-binding fragment thereof, that binds to Domain 2 (D2) of human MerTK and which exhibits one or more of the following properties:

i) binds to human MerTK with an affinity constant (equilibrium dissociation constant) KD of lOnM or less, preferably InM or less or preferably 0.5nM or less as determined by bio-layer interferometry;

ii) and does not inhibit binding of Gas6 to MerTK in cells;

iii) when tested in vitro increases IL-1RA secretion from human dendritic cells, PBMCs and/or macrophages by at least 100% as determined by ELISA when compared to isotype control;

iv) when tested in vitro increases TNF-a secretion from human dendritic cells upon stimulation with LPS by at least 50% as determined by ELISA when compared to isotype control;

v) when tested in vitro increases IL-6 secretion from human dendritic cells by at least 50% as determined by ELISA when compared to isotype control;

vi) when tested in vitro increases IL-8, MIP-la and MIP-Ib secretion from human dendritic cells by at least 100% as determined by ELISA when compared to isotype control; and/or vii) acts substantially independently of MerTK kinase activity.

56. A composition comprising a therapeutically effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

57. A pharmaceutical composition comprising the antibody or antigen-binding fragment of any one of claims 1 to 55 and a pharmaceutically acceptable carrier.

58. A polynucleotide comprising nucleotide sequences encoding a VH chain region, a VL chain region, or both a VL chain region and a VH chain region, of an antibody or antigen binding fragment of any one of claims 1 to 55

59. A polynucleotide comprising nucleotide sequences encoding a heavy chain, a light chain, or both heavy chain and a light chain of an antibody or antigen-binding fragment of any one of claims 1 to 55.

60. A population of polynucleotides comprising (i) a first polynucleotide comprising nucleotide sequences encoding a VH or a heavy chain of the antibody or antigen-binding fragment of any one of claims 1 to 55 and (ii) a second polypeptide comprising nucleotide sequences encoding a VL or a light chain of the antibody or antigen-binding fragment of any one of claims 1 to 55.

61. A vector comprising the polynucleotide of claim 58 or 59.

62. A population of vectors comprising (i) a first vector comprising nucleotide sequences encoding a VH or a heavy chain of the antibody or antigen-binding fragment of any one of claims 1 to 55, and (ii) a second vector comprising nucleotide sequences encoding a VL or a light chain of the antibody or antigen-binding fragment of any one of claims 1 to 55.

63. An isolated cell comprising the polynucleotide of claim 58 or 59.

64. An isolated cell comprising the population of polynucleotides of claim 60.

65. A population of cells comprising (i) a first host cell comprising a polynucleotide comprising nucleotide sequences encoding a VH or a heavy chain of the antibody or antigen binding fragment of any one of claims 1 to 55, and (ii) a second host cell comprising a polynucleotide comprising nucleotide sequences encoding a VL or a light chain of the antibody or antigen-binding fragment of any one of claims 1 to 55.

66. An isolated cell producing the antibody or antigen-binding fragment of any one of claims 1 to 55.

67. A kit comprising the antibody or antigen-binding fragment of any one of claims 1 to 55.

68. A method of managing, protecting against, or treating cancer in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

69. A method of enhancing an immune response in a subject comprising

administering to a subject in need thereof an effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

70. The method of claim 69, wherein the subject is an immunocompromised subject.

71. The method of claim 70, wherein the immunocompromised subject is suffering from an infection, has cancer, is undergoing, or had undergone treatment with, an anti-cancer therapy, is HIV positive, or has AIDS or SCID, or diabetes, or has had a transplant and is taking immunosuppressants.

72. The method of claim 71, wherein the subject has been treated with an

immunosuppressant.

73. A method of enhancing an immune response to a vaccine in a subject, comprising administering to a subject in need thereof, who is or has been administered the vaccine, an effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

74. The method of claim 73, wherein the vaccine is a cancer or tumor vaccine.

75. A method of managing, preventing, protecting against, or treating metastasis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

76. A method of managing or treating sepsis in a subject, comprising administering to a subject in need thereof a therapeutically effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

77. A method for activating or enhancing an innate immune response in a subject, comprising administering to a subject in need thereof an effective amount of the antibody or antigen-binding fragment of any one of claims 1 to 55.

78. The method of claim 77, wherein the subject has cancer, or is being treated for cancer with an anti-cancer therapeutic agent, or the subject has an infection.

79. A method of making an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, comprising culturing the cell or population of cells of any one of claims 63 to 66 to express the antibody or antigen-binding fragment.

80. A method of making an antibody or an antigen-binding fragment thereof that specifically binds to human MerTK, comprising expressing the polynucleotide or population of polynucleotides of any one of claims 58 to 60.

81. A method of increasing proinflammatory cytokine production in a subject in need thereof, comprising administering to the subject an antibody or antigen-binding fragment thereof that specifically binds to human MerTK such that the cytokine production is increased.

82. The method of claim 80, wherein the proinflammatory cytokine is TNFa (tumor necrosis factor a) or IL-1RA (interleukin- 1 receptor antagonist).

83. A method of increasing proinflammatory cytokine production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof of any one of claims 1 to 55 such that the production of one or more cytokines is increased.

84. The method of claim 83, wherein the production of proinflammatory cytokine TNFa (tumor necrosis factor a) is increased.

85. The method of claim 84, wherein the production of proinflammatory cytokine IL- 1RA (interleukin- 1 receptor antagonist) is increased.

86. The method of claim 84, wherein the production of one or more proinflammatory cytokines TNFa and IL-1RA, interleukin-6 (IL-6), macrophage inflammatory protein (MIP-la) and interferon g-induced protein 10 (IP- 10) are increased.

87. A method of increasing proinflammatory secretory factor production in a subject in need thereof, comprising administering to the subject an antibody or an antigen-binding fragment thereof of any one of claims 1 to 55 such that the production of one or more proinflammatory secretory factors is increased.

88. The method of claim 87, wherein the production of one or more of

proinflammatory secretory factors TNFa, IL-1RA, fibroblast growth factor 2 (FGF-2), eotaxin-1 (CCL11), transforming growth factor alpha (TGF-a) granulocyte-colony stimulating factor (G- CSF), Fms-related tyrosine kinase 3 ligand (Flt-3L), granulocyte macrophage-colony stimulating factor (GM-CSF), fractalkine (CX3CL1), interferon alpha-2 (IFN-a2), interferon-gamma (IFN- g), growth-regulated oncogene alpha (GRO alpha), interleukin- 10 (IL-10), monocyte chemotactic protein 3 (MCP-3), interleukin- 12 p40 (IL-12P40), macrophage-derived chemokine (MDC), platelet-derived growth factor AA homodimer (PDGF-AA), interleukin- 13 (IL-13), platelet- derived growth factor BB homodimer (PDGF-BB), soluble CD40 ligand (sCD40L), interleukin- 1B (IL-IB), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-8 (IL-8), interferon g-induced protein 10 (IP- 10), macrophage inflammatory protein (MIR)-Ia, MIR-Ib, Regulated on

Activation Normal T cell Expressed and Secreted (RANTES), vascular endothelial growth factor A (VEGF-A) or IL-18 is increased.

89. The method of claim 88, wherein the increase in production of one or more proinflammatory secretory factors is not dependent on MerTK kinase activity.

90. The method of any one of claims 68 to 89, wherein the antibody does not substantially induce phosphorylation of MerTK.

91. The method of any one of claims 68 to 90, wherein the antibody specifically binds to Domain 2 of human MerTK.

92. The method of any one of claims 68 to 91, wherein the antibody or antigen binding fragment thereof is an antibody or antigen-binding fragment thereof of any one of claims 1 to 55.

93. The method of any one of claims 68 to 92, wherein the antibody does not substantially induce phosphorylation of Syk.

94. The method of any one of claims 68 to 93, wherein the antibody does not substantially induce phosphorylation of SHP-1.

95. The method of any one of claims 68 to 94, wherein the production of one or more of proinflammatory secretory factors is NFrcB-dependent.

96. The method of any one of claims 68 to 95, wherein the activation of one or more co-stimulatory molecules is increased in PBMCs.

97. The method of any one of claims 68 to 96, wherein the activation of one or more co-stimulatory molecules is increased in dendritic cells.

98. The method of claims 96 or 97, wherein the activation of one or more co stimulatory molecules CD86 and CD54 is increased.

99. The isolated antibody, or antigen-binding fragment thereof, of claim 38, wherein the antibody, or antigen-binding fragment thereof, does not inhibit binding of Gas6 to MerTK in L cells or macrophages by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in macrophages by more than 10%, more than 20%, more than 30% or more than 40%.

100. The human or humanized monoclonal antibody, or antigen-binding fragment thereof, of claim 55, wherein the human or humanized monoclonal antibody, or antigen-binding fragment thereof, does not inhibit binding of Gas6 to MerTK in L cells by more than 10%, more than 20%, more than 30% or more than 40% and/or does not inhibit MerTK phosphorylation in macrophages by more than 10%, more than 20%, more than 30% or more than 40%.