WO2023115528A1

WO2023115528A1 - Antibodies against mesothelin and uses thereof

Info

Publication number: WO2023115528A1
Application number: PCT/CN2021/141145
Authority: WO
Inventors: Zuoxiang XIAO; Jiaping PENG; Dongwen ZHOU; Wei Zhou
Original assignee: Zhejiang Shimai Pharmaceutical Co., Ltd.
Priority date: 2021-12-24
Filing date: 2021-12-24
Publication date: 2023-06-29
Also published as: CN114423789B; CN114423789A

Abstract

Disclosed herein are antibodies against mesothelin and uses thereof, specifically monoclonal antibodies against mesothelin, bispecific antibodies against mesothelin and CD3, nucleic acids comprising nucleotide sequences encoding the antibodies, vectors comprising the nucleic acids, and host cell comprising the nucleic acids or the vectors. Also disclosed are pharmaceutical compositions and conjugates comprising the antibodies, and therapeutic methods for using the antibodies.

Description

ANTIBODIES AGAINST MESOTHELIN AND USES THEREOF

FIELD OF THE INVENTION

The present invention is directed to antibodies against mesothelin, and uses of such antibodies, in particular their use in the treatment of cancers.

BACKGROUND OF THE INVENTION

Mesothelin (MSLN) is encoded as a 71-kDa precursor protein which is subsequently processed by the endoprotease furin to yield a 31-kDa shed protein called megakaryocyte potentiating factor (MPF) and a 40-kDa fragment, mesothelin, that is attached to cell membrane by a glycosylphosphatidylinositol (GPI) anchor.

Mesothelin is tumor differentiation antigen, which is normally expressed in mesothelial cells lining the pleura, peritoneum, and pericardium, but is highly expressed in a number of human cancers, including virtually all mesotheliomas and pancreatic adenocarcinomas, and approximately 70%of ovarian cancers and 50%of lung adenocarcinomas.

Studies showed that aberrant expression of mesothelin plays a central role in cancer cell proliferation, invasion and metastasis through activating PI3K, ERK, and MAPK signaling pathways. In the neoplastic setting, mesothelin is known to bind to the ovarian cancer antigen MUC16/CA125, which is a very large cell surface mucin that is shed into the serum and is used for monitoring response to therapy in ovarian cancer. The two proteins are frequently coexpressed, and binding of mesothelin and MUC16 has been shown to induce cell-to-cell adhesion and facilitate the peritoneal spread of ovarian cancer. In addition, signaling mediated by binding of MSLN and MUC16 has been reported to increase cellular resistance to anoikis, upregulate matrix metalloproteinases that are important in cellular invasion and metastasis, and induce secretion of autocrine growth factors by constitutively activating nuclear factor kappa B (NF-kB) .

Given the mesothelin expression pattern in normal tissues and tumors, it has become an attractive target for cancer therapy.

SUMMARY OF THE INVENTION

The present disclosure provides novel antibodies binding to mesothelin or antigen binding fragments thereof, which can be in a form of a monoclonal antibody or bispecific antibody, such as a bispecific T-cell engager (BiTE) . The antibodies disclosed herein are capable of binding to mesothelin and mediating killing of effector cells against target cells expressing mesothelin (such as various cancer cells) .

In an aspect, the present disclosure provides an antibody specifically binding to mesothelin, or an antigen binding fragment thereof, comprising a light chain variable region (VL) and a heavy chain variable region (VH) , wherein the VL comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 1-3 respectively, and the VH comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 6-8 respectively.

In some embodiments of the antibody or the antigen binding fragment thereof disclosed herein, the VL comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 4, and the VH comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 9. In some embodiments, the VL comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH comprises an amino acid sequence as set forth in SEQ ID NO: 9.

In some embodiments, the antibody is of an isotype selected from the group consisting of IgG, IgA, IgM, IgE and IgD. In some embodiments, the antibody is of a subtype selected from the group consisting of IgG1, IgG2, IgG3, and IgG4.

In some embodiments, the antigen binding fragment can be selected from the group consisting of Fab, Fab’, F (ab') ₂, Fv, scFv, and ds-scFv.

In some embodiments, the antibody can be a monoclonal antibody. In some embodiments, the antibody comprises a light chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 5 and a heavy chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 11.

In other embodiments, the antibody can be a bispecific or a multi-specific antibody. In some embodiments, the antibody can be a bispecific antibody which further comprises a second antigen binding region binding to a second antigen. In some embodiments, the second antigen can be a tumor associated antigen or an immune cell antigen. In some embodiments, the second antigen can be a T-cell antigen. In some embodiments, the T-cell antigen can be selected from the group consisting of T cell receptor (TCR) , CD3, CD4, CD8, CD16, CD25, CD28, CD44, CD62L, CD69, ICOS, 41-BB (CD137) , and NKG2D.

In some embodiments, the second antigen is CD3, and the second antigen binding region comprises a VL and a VH, wherein the VL comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 12-14 respectively, and the VH comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 17-19 respectively.

In some embodiments, the second antigen binding region comprises a VL comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 15 and a VH comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 20. In some embodiments, the second antigen binding region comprises a VL comprising an amino acid sequence as set forth in SEQ ID NO: 15 and a VH comprising an amino acid sequence as set forth in SEQ ID NO: 20.

In some embodiments, the VL of the second antigen binding region is linked to the C-terminal of the VL of the antibody specifically binding to mesothelin, optionally via a first linker, and the VH of the second antigen binding region is linked to the C-terminal of the VH of the antibody specifically binding to mesothelin, optionally via a second linker, wherein the first linker and the second linker are the same or different.

In some embodiments, the first linker comprises an amino acid sequence as set forth in SEQ ID NO: 22 (GGGGSGGGGSGGGGS) , and the second linker comprises an amino acid sequence as set forth in SEQ ID NO: 23 (GSSGGGGSGGGGS) .

In some embodiments, the bispecific antibody comprises a light chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 16 and a heavy chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 21.

In some embodiments, the bispecific antibody is a bispecific T-cell engager (BiTE) .

In another aspect, the present disclosure provides a bispecific antibody or an antigen binding fragment thereof, comprising a first antigen binding region binding to mesothelin comprising a VL and a VH and a second antigen binding region binding to CD3 comprising a VL and a VH, wherein the VL of the first antigen binding region comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 1-3 respectively, and the VH of the first antigen binding region comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 6-8 respectively; and the VL of the second antigen binding region comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 12-14 respectively, and the VH of the second antigen binding region comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 17-19 respectively.

In some embodiments of the bispecific antibody or the antigen binding fragment thereof disclosed herein, the VL of the first antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 4 and the VH of the first antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 9; and the VL of the second antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 15 and the VH of the second antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 20.

In some embodiments, the VL of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 9; and the VL of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 15 and the VH of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 20.

In some embodiments, the VL of the second antigen binding region is linked to the C-terminal of the VL of the first antigen binding region, optionally via a first linker, and the VH of the second antigen binding region is linked to the C-terminal of the VH of the first antigen binding region, optionally via a second linker, wherein the first linker and the second linker are the same or different.

In some embodiments, the bispecific antibody can be a bispecific T-cell engager (BiTE) .

In still another aspect, the present disclosure provides a nucleic acid comprising a nucleotide sequence encoding the antibody or the antigen binding fragment thereof disclosed herein or the bispecific antibody or the antigen binding fragment thereof disclosed herein.

In yet another aspect, the present disclosure provides a vector comprising the nucleic acid disclosed herein.

In another aspect, the present disclosure provides a host cell comprising the nucleic acid disclosed herein or the vector disclosed herein.

In still another aspect, the present disclosure provides a pharmaceutical composition comprising (i) the antibody or the antigen binding fragment thereof disclosed herein, or the bispecific antibody or the antigen binding fragment thereof disclosed herein, and (ii) a pharmaceutically acceptable carrier or excipient.

In some embodiments of the pharmaceutical composition disclosed herein, the pharmaceutical composition further comprising a second therapeutic agent. In some embodiments, the second therapeutic agent can be selected from an antibody, a chemotherapeutic agent and a small molecule drug. In some embodiments, the second therapeutic agent can be selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid.

In yet another aspect, the present disclosure provides a conjugate comprising the antibody or the antigen binding fragment thereof disclosed herein or the bispecific antibody or the antigen binding fragment thereof disclosed herein, and a chemical moiety conjugated thereto.

In some embodiments of the conjugate disclosed herein, the chemical moiety can be selected from the group consisting of a therapeutic agent, a detectable moiety, and an immune stimulatory molecule.

In another aspect, the present disclosure provides a method of treating a cancer in a subject comprising administering to the subject an effective amount of the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, the pharmaceutical composition disclosed herein, or the conjugate disclosed herein.

In some embodiments of the method disclosed herein, the cancer is a mesothelin positive cancer. In some embodiments, the cancer can be selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer, lung cancer, gastric cancer, and ovarian cancer. In some embodiments, the cancer is triple negative breast cancer (TNBC) .

In some embodiments, the method further comprises administering to the subject a second therapeutic agent. In some embodiments, the second therapeutic agent can be selected from an antibody, a chemotherapeutic agent and a small molecule drug. In some embodiments, the second therapeutic agent can be selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid.

In another aspect, the present disclosure provides use of the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, the pharmaceutical composition disclosed herein, or the conjugate disclosed herein in the manufacture of a medicament for treating a cancer in a subject. In some embodiments, the cancer is a mesothelin positive cancer. In some embodiments, the cancer can be selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer, lung cancer, gastric cancer, and ovarian cancer. In some embodiments, the cancer is triple negative breast cancer (TNBC) .

In still another aspect, the present disclosure provides the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, the pharmaceutical composition disclosed herein, or the conjugate disclosed herein for use in treating a cancer in a subject. In some embodiments, the cancer is a mesothelin positive cancer. In some embodiments, the cancer can be selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer, lung cancer, gastric cancer, and ovarian cancer. In some embodiments, the cancer is triple negative breast cancer (TNBC) .

BRIEF DESCRIPTION OF THE DRAWINGS

An understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

Figure 1 shows binding of M8, M10 and M38 Fabs against recombinant human mesothelin as measured by ELISA. BSA is used as negative control.

Figure 2 shows binding of M8, M10 and M38 Fabs against mesothelin transient transfected HEK293 cells as measured by flow cytometry. A commercial anti-mesothelin antibody is used as positive control (CTRL) . Color code, black: negative control (without primary antibody) ; pink: CTRL or M8 Fab; green: M10 Fab; cyan: M38 Fab.

Figure 3 shows binding of M10 Fab against cancer cell lines H226 and N87 as measured by flow cytometry. Color code, purple: negative control (without primary antibody) ; green: M10 Fab.

Figure 4 shows binding of M10 mAb against recombinant human mesothelin as measured by ELISA.

Figure 5 shows binding of M10 mAb against cancer cell line H226 as measured by flow cytometry. Color code, purple: negative control (without primary antibody) ; green: M10 mAb.

Figure 6 shows ADCC killing of M10 mAb against H226 cells in the presence of NK cells. An IgG4 isotype antibody is used as negative control.

Figure 7A shows binding of CMD007 against recombinant human CD3 as measured by ELISA.

Figure 7B shows binding of CMD007 against recombinant human mesothelin as measured by ELISA.

Figure 8A shows binding of CMD007 against mesothelin expressing cancer cell line H226 as measured by flow cytometry.

Figure 8B shows binding of CMD007 against CD3 expressing Jurkat cells as measured by flow cytometry.

Figure 8C shows binding of CMD007 against cancer cell LS174T-MSLN (2B6) stably transfected with mesothelin as measured by flow cytometry. Color code, purple: negative control (without primary antibody) ; green: CMD007.

Figure 8D shows binding of CMD007 against mesothelin negative cancer cell line LS174T as measured by flow cytometry. Color code, purple: negative control (without primary antibody) ; green: CMD007.

Figure 9 shows CMD007 induced T cell activation monitored by CD69 expression in the presence of mesothelin expressing cell lines H226 and LS174T-MSLN (2B6) . LS174T is used as negative control of cell line. CMD006-M2 is used as negative control of antibody.

Figure 10 shows CMD007 induced T cell activation monitored by CD25 expression in the presence of mesothelin expressing cell line LS174T-MSLN (2B6) . LS174T is used as negative control of cell line. CMD006-M2 is used as negative control of antibody.

Figure 11 shows killing of CMD007 against N87 cells in the presence of human PBMCs. The ratio of target cells (N87) to effector cells (PBMCs) is 1: 10. An IgG4 isotype antibody is used as negative control.

Figure 12 shows killing of CMD007 against LS174T-MSLN (2B6) cells in the presence of human PBMCs. The ratio of target cells (LS174T-MSLN (2B6) ) to effector cells (PBMCs) is 1: 5.

Figure 13 shows killing of CMD007 against H226 cells in the presence of human PBMCs. The ratio of target cells (H226) to effector cells (PBMCs) is 1: 10. An IgG4 isotype antibody is used as negative control (CTRL-IgG4) .

Figure 14 shows concentration of CMD007 in serum from CMD007-treated mice at 0.25hr, 5hr, 21hr, 49hr and 69hr after treatment.

Figure 15A shows inhibition of tumor growth by CMD007 at 50 μg/kg or 200 μg/kg in mice. 200 μg/kg of IgG4 isotype antibody is used as negative control.

Figure 15B shows body weight of mice in the tumor growth inhibition assay. 200 μg/kg of IgG4 isotype antibody is used as negative control.

Figure 15C shows inhibition rate of tumor growth by CMD007 at 50 μg/kg or 200 μg/kg in mice.

DETAILED DESCRIPTION OF THE INVENTION

The aforementioned features and advantages of the invention as well as additional features and advantages thereof will be more clearly understood hereafter as a result of a detailed description of the following embodiments when taken in conjunction with the drawings.

The embodiments described herein with reference to drawings are explanatory, illustrative, and used to generally understand the present invention. The embodiments shall not be construed to limit the scope of the present invention. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions.

Unless indicated or defined otherwise, all terms used have their usual meaning in the art, which will be clear to the skilled person. Reference is for example made to the standard handbooks, such as Leuenberger, H.G.W, Nagel, B. and Klbl, H. eds., "A multilingual glossary of biotechnological terms: (IUPAC Recommendations) " , Helvetica Chimica Acta (1995) , CH-4010 Basel, Switzerland; Sambrook et al, "Molecular Cloning: A Laboratory Manual" (2nd Ed. ) , Vols. 1-3, Cold Spring Harbor Laboratory Press (1989) ; F. Ausubel et al, eds., "Current protocols in molecular biology" , Green Publishing and Wiley InterScience, New York (1987) ; Roitt et al., "Immunology (6th Ed. ) , Mosby/Elsevier, Edinburgh (2001) ; and Janeway et al., "Immunobiology" (6th Ed. ) , Garland Science Publishing/Churchill Livingstone, New York (2005) , as well as the general background art cited above.

As used herein, singular forms “a” , “and, ” and “the” include plural referents unless the context clearly indicates otherwise. Thus, for example, reference to “an antibody” includes a plurality of antibodies and reference to “an antibody” in some embodiments includes multiple antibodies, and so forth.

Unless indicated or defined otherwise, the term "comprise" , and variations such as "comprises" and "comprising" , should be understood to imply the inclusion of a stated elements or step or group of elements or steps but not the exclusion of any other element or step or group of elements or steps.

As used herein, the term “antibody” refers to an immunoglobulin molecule which has the ability to specifically bind to a specific antigen. An antibody often comprises a variable region and a constant region in each of a heavy chain and a light chain. The variable regions of the heavy and light chains of antibodies contain a binding domain that interacts with an antigen. The constant regions of antibodies may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (such as effector cells) and components of the complement system such as CIq, the first component in the classical pathway of complement activation. Accordingly, most antibodies have a heavy chain variable region (VH) and a light chain variable region (VL) that together form the portion of the antibody that binds to the antigen.

A “light chain variable region” (VL) or “heavy chain variable region” (VH) consists of a “framework” region interrupted by three “complementarity determining regions” or “CDRs” . The framework regions serve to align the CDRs for specific binding to an epitope of an antigen. The CDRs include the amino acid residues of an antibody that are primarily responsible for antigen binding. From amino-terminus to carboxyl-terminus, both VL and VH domains comprise the following framework (FR) and CDR regions: FR1, CDR1, FR2, CDR2, FR3, CDR3, and FR4. CDRs 1, 2, and 3 of a VL domain are also referred to herein, respectively, as LCDR1, LCDR2, and LCDR3; CDRs 1, 2, and 3 of a VH domain are also referred to herein, respectively, as HCDR1, HCDR2, and HCDR3.

The assignment of amino acids to each VL and VH domain is in accordance with any conventional definition of CDRs. Conventional definitions include, the Kabat definition (Kabat, Sequences of Proteins of Immunological Interest (National Institutes of Health, Bethesda, MD, 1987 and 1991) , the Chothia definition (Chothia &Lesk, J. Mol. Biol. 196: 901-917, 1987; Chothia et al., Nature 342: 878-883, 1989) ; a composite of Chothia Kabat CDR in which CDR-H1 is a composite of Chothia and Kabat CDRs; the AbM definition used by Oxford Molecular’s antibody modelling software; and, the contact definition of Martin et al. (world wide web bioinfo. org. uk/abs) . Kabat provides a widely used numbering convention (Kabat numbering system) in which corresponding residues between different heavy chains or between different light chains are assigned the same number. The present disclosure can use CDRs defined according to any of these numbering systems, although preferred embodiments use Kabat defined CDRs.

The term "antibody" as used herein should be understood in its broadest meaning, and includes monoclonal antibodies (including full-length monoclonal antibodies) , polyclonal antibodies, antibody fragments, and multi-specific antibodies containing at least two different antigen binding regions (e.g., bispecific antibodies) . The antibody may contain additional modifications, such as non-naturally occurring amino acids, mutations in Fc regions, and mutations in glycosylation sites. Antibodies also include post-translation modified antibodies, fusion proteins containing the antigenic determinants of the antibody, and immunoglobulin molecules containing any other modifications to antigen recognition sites, as long as these antibodies exhibit desired biological activity.

As used herein, the term “antigen binding fragment” of an antibody refers to one or more fragments of an antibody that retain the ability to specifically bind to an antigen (e.g., a mesothelin protein) . It has been shown that the antigen binding function of an antibody can be performed by fragments of a full-length antibody.

Examples of antigen binding fragments encompassed within the term "antigen binding portion" of an antibody include (i) a Fab fragment, a monovalent fragment consisting of the VL, VH, CL and CH1 domains; (ii) a F (ab') 2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fab'fragment, which is essentially an Fab with part of the hinge region (see, FUNDAMENTALIMMUNOLOGY (Paul ed., 3. sup. rd ed. 1993) ; (iv) a Fd fragment consisting of the VH and CH1 domains; (v) a Fd'fragment having VH and CH1 domains and one or more cysteine residues at the C-terminus of the CH1 domain; (vi) a Fv fragment consisting of the VL and VH domains of a single arm of an antibody, (vii) a dAb fragment (Ward et al., (1989) Nature 341: 544-546) , which consists of a VH domain; (viii) an isolated complementarity determining region (CDR) ; and (ix) a nanobody, a heavy chain variable region containing a single variable domain and two constant domains. Furthermore, although the two domains of the Fv fragment, V Land VH are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VL and VH regions pair to form monovalent molecules (known as single chain Fv (scFv) ; see e.g., Bird et al. (1988) Science 242: 423-426; and Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85: 5879-5883) . Such single chain antibodies are also intended to be encompassed within the term "antigen binding fragment" of an antibody. Furthermore, the term also includes a "linear antibody" comprising a pair of tandem Fd segments (VH-CH1-VH-CH1) , which forms an antigen binding region together with a complementary light chain polypeptide, and a modified version of any of the foregoing fragments, which retains antigen binding activity.

These antigen binding fragments can be obtained using conventional techniques known to those with skill in the art, and the fragments are screened for utility in the same manner as are intact antibodies.

As used herein, the term "binding" or "specifically binding" refers to a non-random binding reaction between two molecules, such as between an antibody and its target antigen. The binding specificity of an antibody can be determined based on affinity and/or avidity. The affinity, represented by the equilibrium constant for the dissociation of an antigen with an antibody (KD) , is a measure for the binding strength between an antigenic determinant and an antigen-binding site on the antibody: the lesser the value of the KD, the stronger the binding strength between an antigenic determinant and the antibody. Alternatively, the affinity can also be expressed as the affinity constant (KA) , which is 1/KD.

Avidity is the measure of the strength of binding between an antibody and the pertinent antigen. Avidity is related to both the affinity between an antigenic determinant and its antigen binding site on the antibody and the number of pertinent binding sites present on the antibody. Typically, an antibody will bind with a dissociation constant (KD) of 10 ^-5 to 10 ^-12 M or less, and preferably 10 ^-7 to 10 ^-12 M or less and more preferably 10 ^-8 to 10 ^-12 M, and/or with a binding affinity of at least 10 ⁷ M ^-1, preferably at least 10 ⁸ M ^-1, more preferably at least 10 ⁹ M ^-1, such as at least 10 ¹² M ^-1. Any K _D value greater than 10 ^-4 M is generally considered to indicate non-specific binding. Specifically binding of an antibody to an antigen or antigenic determinant can be determined in any suitable manner known per se, including, for example, Scatchard analysis and/or competitive binding assays, such as radioimmunoassays (RIA) , enzyme immunoassays (EIA) and sandwich competition assays, and the different variants thereof known per se in the art.

The term “epitope” refers to a site on an antigen to which an antibody binds. An epitope can be formed from contiguous amino acids or noncontiguous amino acids juxtaposed by tertiary folding of one or more proteins. Epitopes formed from contiguous amino acids (also known as linear epitopes) are typically retained on exposure to denaturing solvents whereas epitopes formed by tertiary folding (also known as conformational epitopes) are typically lost on treatment with denaturing solvents. An epitope typically includes at least 3, and more usually, at least 5 or 8-10 amino acids in a unique spatial conformation. The epitope defines the smallest binding site of an antibody and therefore is the specific target of the antibody or antigen binding fragment thereof.

As used herein, the term “sequence identity” refers to the extent to which two sequences (amino acid) have the same residue at the same positions in an alignment. For example, “an amino acid sequence is X%identical to SEQ ID NO: Y” refers to %identity of the amino acid sequence to SEQ ID NO: Y and is elaborated as X%of residues in the amino acid sequence are identical to the residues of sequence disclosed in SEQ ID NO: Y.

Generally, computer programs are employed for such calculations. Exemplary programs that compare and align pairs of sequences, include ALIGN (Myers and Miller, 1988) , FASTA (Pearson and Lipman, 1988; Pearson, 1990) and gapped BLAST (Altschul et al., 1997) , BLASTP, BLASTN, or GCG (Devereux et al., 1984) .

Also, in determining the degree of sequence identity between two amino acid sequences, the skilled person may take into account so-called "conservative" amino acid substitutions, which can generally be described as amino acid substitutions in which an amino acid residue is replaced with another amino acid residue of similar chemical structure and which has little or essentially no influence on the function, activity or other biological properties of the polypeptide. Such conservative amino acid substitutions are well known in the art, for example from WO 04/037999, GB-A-2 357 768, WO 98/49185, WO 00/46383 and WO 01/09300; and (preferred) types and/or combinations of such substitutions may be selected on the basis of the pertinent teachings from WO 04/037999 as well as WO 98/49185 and from the further references cited therein.

Such conservative substitutions preferably are substitutions in which one amino acid within the following groups (a) - (e) is substituted by another amino acid residue within the same group: (a) small aliphatic, nonpolar or slightly polar residues: Ala, Ser, Thr, Pro and Gly; (b) polar, negatively charged residues and their (uncharged) amides: Asp, Asn, Glu and Gln; (c) polar, positively charged residues: His, Arg and Lys; (d) large aliphatic, nonpolar residues: Met, Leu, He, Val and Cys; and (e) aromatic residues: Phe, Tyr and Trp.

Particularly preferred conservative substitutions are as follows: Ala into Gly or into Ser; Arg into Lys; Asn into Gln or into His; Asp into Glu; Cys into Ser; Gln into Asn; Glu into Asp; Gly into Ala or into Pro; His into Asn or into Gln; Ile into Leu or into Val; Leu into Ile or into Val; Lys into Arg, into Gln or into Glu; Met into Leu, into Tyr or into Ile; Phe into Met, into Leu or into Tyr; Ser into Thr; Thr into Ser; Trp into Tyr; Tyr into Trp; and/or Phe into Val, into Ile or into Leu.

Any amino acid substitutions applied to the polypeptides described herein may also be based on the analysis of the frequencies of amino acid variations between homologous proteins of different species developed by Schulz et al., Principles of Protein Structure, Springer-Verlag, 1978, on the analyses of structure forming potentials developed by Chou and Fasman, Biochemistry 13: 211, 1974 and Adv. Enzymol., 47: 45-149, 1978, and on the analysis of hydrophobicity patterns in proteins developed by Eisenberg et al., Proc. Nat. Acad Sci. USA 81: 140-144, 1984; Kyte &Doolittle, J Mol. Biol. 157: 105-132, 198 1, and Goldman et al., Ann. Rev. Biophys. Chem. 15: 321-353, 1986, all incorporated herein in their entirety by reference.

As used herein, the term "monoclonal antibody" refers to an antibody obtained from a substantially homogeneous antibody population. That is, each antibodies constituting the population are the same, except for possible naturally occurring mutations in small amount. Monoclonal antibodies are highly specific and are directed against a single antigen. The term "monoclonal antibody" herein is not limited to antibodies produced by hybridoma technology, and should not be interpreted as requiring production of antibodies by any specific method.

The term “bispecific antibody” is in the context of the present invention to be understood as an antibody having two different antigen-binding regions defined by different antibody sequences. This can be understood as different target binding but includes as well binding to different epitopes in one target.

As used herein, the term "tumor associated antigen" refers to an antigen that is differentially expressed in cancer cells compared to normal cells, and therefore can be used to target cancer cells.

As used herein, the term “CD3” refers to the human CD3 protein complex, which has five peptide chains, γ chain, δ chain, ε chain, ζ chain and η chain, and is associated with the T cell receptor α and β chain to form a TCR-CD3 complex. The term includes any CD3 variants, isoforms and species homologs which are naturally expressed by cells, including T cells, or are expressed on cells transfected with genes or cDNA encoding the aforementioned chains.

As used herein, the term “bispecific T-cell engager” or “BiTE” refers to single polypeptide chain molecules that having two antigen-binding domains, one of which binds to a T-cell antigen and the second of which binds to an antigen present on the surface of a target (See, PCT Publication WO 05/061547; Baeuerle et al., 2008, Drugs of the Future 33: 137-147; Bargou, et al., 2008, Science 321: 974-977, which are incorporated herein by reference in their entireties) . Thus, the BiTE of the disclosure has an antigen binding region that binds to mesothelin and a second antigen binding region that is directed towards a T-cell antigen.

As used herein, the term "vector" is intended to refer to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked.

As used herein, the term "host cell" refers to a cell into which an expression vector has been introduced.

The term “pharmaceutically acceptable” means that the carrier or adjuvant is compatible with the other ingredients of the composition and not substantially deleterious to the recipient thereof and/or that such carrier or adjuvant is approved or approvable for inclusion in a pharmaceutical composition for parenteral administration to humans.

As used herein, the terms "treatment, " "treating, " and the like, refer to administering an agent, or carrying out a procedure, for the purposes of obtaining an effect. The effect may be prophylactic in terms of completely or partially preventing a disease or symptom thereof and/or may be therapeutic in terms of effecting a partial or complete cure for a disease and/or symptoms of the disease. "Treatment, " as used herein, may include treatment of a disease or disorder (e.g. cancer) in a mammal, particularly in a human, and includes: (a) preventing the disease or a symptom of a disease from occurring in a subject which may be predisposed to the disease but has not yet been diagnosed as having it (e.g., including diseases that may be associated with or caused by a primary disease; (b) inhibiting the disease, i.e., arresting its development; and (c) relieving the disease, i.e., causing regression of the disease. Treating may refer to any indicia of success in the treatment or amelioration or prevention of a cancer, including any objective or subjective parameter such as abatement; remission; diminishing of symptoms or making the disease condition more tolerable to the patient; slowing in the rate of degeneration or decline; or making the final point of degeneration less debilitating. The treatment or amelioration of symptoms is based on one or more objective or subjective parameters; including the results of an examination by a physician. Accordingly, the term "treating" includes the administration of the antibodies or compositions or conjugates disclosed herein to prevent or delay, to alleviate, or to arrest or inhibit development of the symptoms or conditions associated with diseases (e.g. cancers) . The term "therapeutic effect" refers to the reduction, elimination, or prevention of the disease, symptoms of the disease, or side effects of the disease in the subject.

The term "effective amount" as used herein means the amount that, when administered to a subject for treating a disease, is sufficient to effect treatment for that disease.

The term “subject” , as used herein, refers to any mammalian subject for whom diagnosis, treatment, or therapy is desired. "Mammal" for purposes of treatment refers to any animal classified as a mammal, including humans, domestic and farm animals, and laboratory, zoo, sports, or pet animals, such as dogs, horses, cats, cows, sheep, goats, pigs, mice, rats, rabbits, guinea pigs, monkeys etc.

In some embodiments, CDR sequences are defined according to Kabat numbering system.

When CDR sequences are defined according to Kabat numbering system, the VL of the antibody disclosed herein comprises LCDR1, LCDR2 and LCDR3 having the amino acid sequences as set forth in SEQ ID NO: 1 (SGDALPKQYAF) , SEQ ID NO: 2 (KDSERPS) and SEQ ID NO: 3 (QSADSSATSVI) respectively, and the VH of the antibody disclosed herein comprises HCDR1, HCDR2 and HCDR3 having the amino acid sequences as set forth in SEQ ID NO: 6 (DYAMH) , SEQ ID NO: 7 (GISWNSGSIGYADSVKG) and SEQ ID NO: 8 (DSGSSGWYGYFQH) respectively.

In some embodiments of the antibody or the antigen binding fragment thereof disclosed herein, the VL comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 4, and the VH comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 9.

In some embodiments, the VL comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 4 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin. In some embodiments, the VH comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 9 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin.

The functional variant comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to the amino acid sequence of the parent polypeptide. For example, the functional variant of SEQ ID NO: 4 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 4. For example, the functional variant of SEQ ID NO: 9 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 9.

In some embodiments, the functional variant of SEQ ID NO: 4 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 4 and formed by insertion, deletion and/or substitution of one or more amino acid (s) in SEQ ID NO: 4. In some embodiments, the functional variant of SEQ ID NO: 9 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 9 and formed by insertion, deletion and/or substitution of one or more amino acid (s) in SEQ ID NO: 9.

In the context of the functional variant, the number of the inserted, deleted and/or substituted amino acid is preferably no more than 40%of the total number of amino acids in the parent amino acid sequence, more preferably no more than 35%, more preferably 1-33%, and more preferably 5-30%, more preferably 10-25%, more preferably 15-20%. For example, the number of the inserted, deleted and/or substituted amino acid can be 1-20, preferably 1-10, more preferably 1-7, still more preferably 1-5, and most preferably 1-2. In a preferred embodiment, the number of the inserted, deleted and/or substituted amino acid is 1, 2, 3, 4, 5, 6, or 7.

In some embodiments, the insertion, deletion and/or substitution can be performed at framework (FR) regions, e.g., at FR1, FR2, FR3, and/or FR4.

In some embodiments, the substitution of one or more amino acid (s) can be conservative substitution of one or more amino acid (s) . Such conservative substitutions preferably are substitutions in which one amino acid within the following groups (a) - (e) is substituted by another amino acid residue within the same group: (a) small aliphatic, nonpolar or slightly polar residues: Ala, Ser, Thr, Pro and Gly; (b) polar, negatively charged residues and their (uncharged) amides: Asp, Asn, Glu and Gln; (c) polar, positively charged residues: His, Arg and Lys; (d) large aliphatic, nonpolar residues: Met, Leu, He, Val and Cys; and (e) aromatic residues: Phe, Tyr and Trp.

In a preferred embodiment, the VL comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH comprises an amino acid sequence as set forth in SEQ ID NO: 9.

Based on the amino acid sequence of heavy chain constant regions of the antibody, a immunoglobulin molecule can be divided into five classes (isotypes) : IgA, IgD, IgE, IgG, and IgM, and can be further divided into different subtypes, such as IgG1, IgG2, IgG3, IgG4, IgA1, IgA2, etc. The light chain of the antibody can be classified as a lambda (λ) chain or a kappa (κ) chain, based on the amino acid sequence of the light chain. The antibodies disclosed herein can be of any classes or subtypes above.

In some embodiments, the antibody can be of an isotype selected from the group consisting of IgG, IgA, IgM, IgE and IgD. In some embodiments, the antibody can be of a subtype selected from the group consisting of IgG1, IgG2, IgG3, and IgG4. In a preferred embodiment, the antibody is an IgG1 antibody.

The antibody disclosed herein can be an intact antibody or the antigen binding fragment thereof. The antigen binding fragment can be any fragments of the antibody that retain the ability to specifically bind to mesothelin. Examples of antigen binding fragments include but are not limited to a Fab fragment; a F (ab') 2 fragment; a Fab'fragment; a Fd fragment; a Fd'fragment; a Fv fragment; a scFv fragment; a dAb fragment; an isolated complementarity determining region (CDR) ; a nanobody; a linear antibody comprising a pair of tandem Fd segments (VH-CH1-VH-CH1) , and a modified version of any of the foregoing fragments, which retains antigen binding activity.

In some embodiments, the antigen binding fragment can be selected from the group consisting of Fab, Fab’ , F (ab') ₂, Fv, scFv, and ds-scFv. In a preferred embodiment, the antigen binding fragment is Fab or scFv. In another preferred embodiment, the antigen binding fragment is Fab, and the Fab comprising a light chain having amino acid as set forth in SEQ ID NO: 5 (SYVLTQPPSVSVSPGQTARITCSGDALPKQYAFWYQQKPGQAPVLVIYKDSERPSGIPER FSGSSSGTTVTLTISGVQAEDEADYYCQSADSSATSVIFGGGTKLTVLGQPKAAPSVTLF PPSSEELQANKATLVCLISDFYPGAVTVAWKADSSPVKAGVETTTPSKQSNNKYAASSY LSLTPEQWKSHKSYSCQVTHEGSTVEKTVAPTECS) and a heavy chain having amino acid as set forth in SEQ ID NO: 10 (QLVETGGGLVQPGRSLRLSCAASGFTFDDYAMHWVRQAPGKGLEWVSGISWNSGSIG YADSVKGRFTISRDNAKNSLYLQMNSLRAEDTAVYYCARDSGSSGWYGYFQHWGQGT LVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFP AVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCGQAGHHHHHH GDYKDDDDKG) .

In some embodiments, the light chain comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 5 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin. In some embodiments, the heavy chain comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 11 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin.

For example, the functional variant of SEQ ID NO: 5 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 5. For example, the functional variant of SEQ ID NO: 11 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 11.

In some embodiments, the number of the inserted, deleted and/or substituted amino acid is preferably no more than 40%of the total number of amino acids in the parent amino acid sequence, more preferably no more than 35%, more preferably 1-33%, and more preferably 5-30%, more preferably 10-25%, more preferably 15-20%. For example, the number of the inserted, deleted and/or substituted amino acid can be 1-50, preferably 1-20, more preferably 1-10, still more preferably 1-5. In a preferred embodiment, the number of the inserted, deleted and/or substituted amino acid is 1, 2, 3, 4, 5, 6, or 7.

In some embodiments, the insertion, deletion and/or substitution can be performed at framework (FR) regions, e.g., at FR1, FR2, FR3 and/or FR4; and/or constant regions, e.g., CL, CH1, CH2 and/or CH3.

In some embodiments, the substitution of one or more amino acid (s) can be conservative substitution of one or more amino acid (s) . Examples of conservative substitutions are as described above.

In a preferred embodiment, the light chain comprises an amino acid sequence as set forth in SEQ ID NO: 5 and the heavy chain comprises an amino acid sequence as set forth in SEQ ID NO: 11.

In other embodiments, the antibody can be a bispecific or a multi-specific antibody. In some embodiments, the antibody is a bispecific antibody which further comprises a second antigen binding region binding to a second antigen. In some embodiments, the second antigen can be a tumor associated antigen or an immune cell antigen.

Many tumor associated antigens associated with specific cancers have been identified in the art. In some embodiments, tumor-associated antigens are antigens that can potentially stimulate an obvious tumor-specific immune response. Some of these antigens are encoded by normal cells, but not necessarily expressed by normal cells. These antigens can be characterized as those that are usually silent (i.e., not expressed) in normal cells, those that are expressed only during certain stages of differentiation, and those that are expressed over time, such as embryonic and fetal antigens. Other cancer antigens are encoded by mutant cell genes such as oncogenes (e.g. activated ras oncogene) , suppressor genes (e.g. mutant p53) , and fusion proteins produced by internal deletions or chromosomal translocations. Other cancer antigens can be encoded by viral genes, such as those carried on RNA and DNA tumor viruses. Many other tumor associated antigens and antibodies against them are known and/or commercially available, and can also be produced by those skilled in the art.

Examples of tumor associated antigens include but are not limited to 5T4, alphafetoprotein, CA-125, carcinoembryonic antigen, CD19, CD20, CD22, CD23, CD30, CD33, CD40, CD56, CD79, CD78, CD123, CD138, c-Met, CSPG4, IgM, C-type lectin-like molecule 1 (CLL-1) , EGFR, EGFRvIII, epithelial tumor antigen, ERBB2, FLT3, folate binding protein, GD2, GD3, HIV-1 envelope glycoprotein gp41, HIV-1 envelope glycoprotein gpl20, melanoma-associated antigen, MUC-1, mutated p53, mutated ras, ROR1, GPC3, VEGFR2, and combinations thereof.

In some embodiments, the second antigen can be a T-cell antigen. In some embodiments, the T-cell antigen can be selected from the group consisting of T cell receptor (TCR) , CD3, CD4, CD8, CD16, CD25, CD28, CD44, CD62L, CD69, ICOS, 41-BB (CD137) , and NKG2D or any combination thereof. In some embodiments, the T-cell antigen is CD3, and the second antigen binding region binds to any of γ chain, δ chain, ε chain, ζ chain and η chain of CD3.

In some embodiments, CDR sequences are defined according to Kabat numbering system. When using Kabat defined CDR sequences, the VL of the second antigen binding region disclosed herein comprises LCDR1, LCDR2 and LCDR3 having the amino acid sequences as shown in SEQ ID NO: 12 (RSSTGAVTTSNYAN) , SEQ ID NO: 13 (GANKRAP) and SEQ ID NO: 14 (ALWYSNLWV) respectively, and the VH of the second antigen binding region disclosed herein comprises HCDR1, HCDR2 and HCDR3 having the amino acid sequences as shown in SEQ ID NO:17 (GFTFNTY) , SEQ ID NO: 18 (RSKYNNYA) and SEQ ID NO: 19 (HGNFGSSYVSYFAY) respectively.

In some embodiments, the second antigen binding region comprises a VL comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 15 and a VH comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 20.

In some embodiments, the VL comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 15 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to CD3. In some embodiments, the VH comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 20 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to CD3.

For example, the functional variant of SEQ ID NO: 15 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 15. For example, the functional variant of SEQ ID NO: 20 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 20.

In some embodiments, the number of the inserted, deleted and/or substituted amino acid is preferably no more than 40%of the total number of amino acids in the parent amino acid sequence, more preferably no more than 35%, more preferably 1-33%, and more preferably 5-30%, more preferably 10-25%, more preferably 15-20%. For example, the number of the inserted, deleted and/or substituted amino acid can be 1-20, preferably 1-10, more preferably 1-7, still more preferably 1-5, and most preferably 1-2. In a preferred embodiment, the number of the inserted, deleted and/or substituted amino acid is 1, 2, 3, 4, 5, 6, or 7.

In a preferred embodiment, the second antigen binding region comprises a VL comprising an amino acid sequence as set forth in SEQ ID NO: 15 and a VH comprising an amino acid sequence as set forth in SEQ ID NO: 20.

In some embodiments, the light chain comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 16 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin and CD3. In some embodiments, the heavy chain comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 21 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin and CD3.

For example, the functional variant of SEQ ID NO: 16 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 16. For example, the functional variant of SEQ ID NO: 21 comprises or consists of an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9%sequence identity to SEQ ID NO: 21.

In a preferred embodiment, the light chain comprises an amino acid sequence as set forth in SEQ ID NO: 16 and the heavy chain comprises an amino acid sequence as set forth in SEQ ID NO: 21.

In some embodiments, the bispecific antibody can be a bispecific T-cell engager (BiTE) . In some embodiments of the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody is in form of an HBiTE as described in PCT application No. PCT/US2018/016524 (which is incorporated herein by reference in its entirety) . In the HBiTE, the light chain, from N-terminus to C-terminus, comprises an anti-target VL domain, an anti-CD3 VL-CL and a monomeric human IgG1 Fc (e.g., mFc7.2) ; and the heavy chain, from N-terminus to C-terminus, comprises an anti-target VH domain, an anti-CD3 VH-CH1 and a monomeric human IgG1 Fc (e.g., mFc7.2) . Monomeric Fc7.2 contains two amino acid mutations (T366L and Y407H) capable of inhibiting Fc homodimerization.

In some embodiments, the VL of the first antigen binding region comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 4 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin. In some embodiments, the VH of the first antigen binding region comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 9 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to mesothelin. In some embodiments, the VL of the second antigen binding region comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 15 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to CD3. In some embodiments, the VH of the second antigen binding region comprises a functional variant of the amino acid sequence as set forth in SEQ ID NO: 20 formed by insertion, deletion and/or substitution of one or more amino acid (s) therein, provided that the functional variant retains the ability of binding to CD3.

The functional variants of SEQ ID NOs: 4, 9, 15 and 20 can be those as described above.

In a preferred embodiment, the VL of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 9; and the VL of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 15 and the VH of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 20.

In some embodiments, the VL of the second antigen binding region is linked to the C-terminal of the VL of the first antigen binding region, optionally via a first linker, and the VH of the second antigen binding region is linked to the C-terminal of the VH of the first antigen binding region, optionally via a second linker, wherein the first linker and the second linker are the same or different. In some embodiments, the first linker comprises an amino acid sequence as set forth in SEQ ID NO: 22 (GGGGSGGGGSGGGGS) , and the second linker comprises an amino acid sequence as set forth in SEQ ID NO: 23 (GSSGGGGSGGGGS) .

In some embodiments, the bispecific antibody comprises a single polypeptide chain comprising the first antigen binding region and the second antigen binding region, and optionally an Fc region.

The Fc region may be of any isotype, including, but not limited to, IgG1, IgG2, IgG3 and IgG4, and may comprise one or more mutations or modifications. In one embodiment, the Fc region is of IgG1 isotype or derived therefrom, optionally with one or more mutations or modifications. In one embodiment, the Fc region is human IgG1 Fc.

In one embodiment, the Fc region is effector-function-deficient. For example, the Fc region may be of an IgG1 isotype, or a non-IgG1 type, e.g. IgG2, IgG3 or IgG4, which has been mutated such that the ability to mediate effector functions, such as ADCC, has been reduced or even eliminated. Such mutations have e.g. been described in Dall'A cqua WF et al., J Immunol. 177 (2) : 1129-1138 (2006) and Hezareh M, J Virol.; 75 (24) : 12161-12168 (2001) .

In one embodiment, the Fc region comprises a mutation removing the acceptor site for Asn-linked glycosylation or is otherwise manipulated to change the glycosylation properties. For example, in an IgG1 Fc region, an N297Q mutation can be used to remove an Asn-linked glycosylation site. Accordingly, in a specific embodiment, Fc region comprise an IgG1 wildtype sequence with an N297Q mutation.

In a further embodiment, the Fc region is glyco-engineered to reduce fucose and thus enhance ADCC, e.g. by addition of compounds to the culture media during antibody production as described in US2009317869 or as described in van Berkel et al. (2010) Biotechnol. Bioeng. 105: 350 or by using FUT8 knockout cells, e.g. as described in Yamane-Ohnuki et al. (2004) Biotechnol. Bioeng 87: 614. ADCC may alternatively be optimized using the method described by

et al. (1999) Nature Biotech 17: 176. In a further embodiment, the Fc region has been engineered to enhance complement activation, e.g. as described in Natsume et al. (2009) Cancer Sci. 100: 2411.

In some embodiments, the Fc region comprises modifications or mutations that can inhibit Fc homodimerization. In some embodiments, the Fc region comprises a variant of a human IgG1 Fc wildtype sequence. The variant can comprise amino acid substitutions at positions T366 and Y407 of human IgG1 (Kabat numbering) . Preferably, T366 is substituted with L (Leucine) . Preferably, Y407 is substituted with I (Isoleucine) , F (Phenylalanine) , L (Leucine) , M (Methionine) , H (Histidine) , K (Lysine) , S (Serine) , Q (Glutamine) , T (Threonine) , W (Tryptophan) , A (Alanine) , G (Glycine) or N (Asparagine) . More preferably, Y407 is substituted with H. In one embodiment, T366 is substituted with L, and Y407 is substituted with H.

In some embodiments, the Fc region can be a monomeric human IgG1 Fc (e.g., mFc7.2) as described in PCT application No. PCT/US2018/016524, which is incorporated herein by reference in its entirety.

In some embodiments, the bispecific antibody comprises a first polypeptide chain comprising the VL of the first antigen binding region and the VL of the second antigen binding region, and optionally an Fc region; and a second polypeptide chain comprising the VH of the first antigen binding region and the VH of the second antigen binding region, and optionally an Fc region. The Fc region can be those as describe above.

In some embodiments, the first polypeptide chain further comprises a light chain constant region (CL) . In some embodiments, the first polypeptide chain comprises a monomeric human IgG1 Fc (e.g., mFc7.2) as described above. In some embodiments, the first polypeptide chain comprises, from N-terminal to C-terminal: the VL of the first antigen binding region, the VL of the second antigen binding region, CL and mFc7.2.

In some embodiments, the second polypeptide chain further comprises a heavy chain constant region (CH) , e.g., CH1. In some embodiments, the first polypeptide chain comprises a monomeric human IgG1 Fc (e.g., mFc7.2) as described above. In some embodiments, the second polypeptide chain comprises, from N-terminal to C-terminal: the VH of the first antigen binding region, the VH of the second antigen binding region, CH1 and mFc7.2.

The functional variants of SEQ ID NOs: 16 and 21 can be those as described above.

In some embodiments, the bispecific antibody can be a bispecific T-cell engager (BiTE) , preferably an HBiTE as described above.

Any vector may be suitable for the present disclosure. In some embodiments, the vector is a viral vector. In some embodiments, the vector is a retroviral vector, a DNA vector, a murine leukemia virus vector, an SFG vector, a plasmid, a RNA vector, an adenoviral vector, a baculoviral vector, an Epstein Barr viral vector, a papovaviral vector, a vaccinia viral vector, a herpes simplex viral vector, an adenovirus associated vector (AAV) , a lentiviral vector, or any combination thereof. Suitable exemplary vectors include e.g., pGAR, pBABE-puro, pBABE-neo largeTcDNA, pBABE-hygro-hTERT, pMKO. 1 GFP, MSCV-IRES-GFP, pMSCV PIG (Puro IRES GFP empty plasmid) , pMSCV-loxp-dsRed-loxp-eGFP-Puro-WPRE, MSCV IRES Luciferase, pMIG, MDH1-PGK-GFP_2.0, TtRMPVIR, pMSCV-IRES-mCherry FP, pRetroX GFP T2A Cre, pRXTN, pLncEXP, and pLXIN-Luc.

A recombinant expression vector may be any suitable recombinant expression vector. Suitable vectors comprise those designed for propagation and expansion or for expression or both, such as plasmids and viruses. For example, a vector may be selected from the pUC series (Fermentas Life Sciences, Glen Burnie, Md. ) , the pBluescript series (Stratagene, LaJolla, Calif. ) , the pET series (Novagen, Madison, Wis. ) , the pGEX series (Pharmacia Biotech, Uppsala, Sweden) , and the pEX series (Clontech, Palo Alto, Calif. ) . Bacteriophage vectors, such as λGT10, λGT11, λZapII (Stratagene) , λEMBL4, and λNM1149, also may be used. Examples of plant expression vectors useful in the context of the disclosure comprise pBI01, pBI101.2, pBI101.3, pBI121 and pBIN19 (Clontech) . Examples of animal expression vectors useful in the context of the disclosure comprise pcDNA, pEUK-Cl, pMAM, and pMAMneo (Clontech) .

Recombinant expression vectors may be prepared using standard recombinant DNA techniques described in, for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., Cold Spring Harbor Press, Cold Spring Harbor, N. Y. 2001; and Ausubel et al., Current Protocols in Molecular Biology, Greene Publishing Associates and John Wiley &Sons, NY, 1994. Constructs of expression vectors, which are circular or linear, may be prepared to contain a replication system functional in a prokaryotic or eukaryotic host cell. Replication systems may be derived, e.g., from ColEl, 2μ plasmid, λ, SV40, bovine papilloma virus, and the like.

Any cell may be used as a host cell for the nucleic acids or the vectors of the present disclosure. In some embodiments, the cell can be a prokaryotic cell, fungal cell, yeast cell, or higher eukaryotic cells such as a mammalian cell. Suitable prokaryotic cells include, without limitation, eubacteria, such as Gram-negative or Gram-positive organisms, for example, Enterobactehaceae such as Escherichia, e.g., E. coli; Enterobacter; Erwinia; Klebsiella; Proteus; Salmonella, e.g., Salmonella typhimurium; Serratia, e.g., Serratia marcescans, and Shigella; Bacilli such as B. subtilis and B. licheniformis; Pseudomonas such as P. aeruginosa; and Streptomyces. In some embodiments, the cell is a human cell. In some embodiments, the cell is an immune cell. In some embodiments, host cells include, for example, CHO cells, such as CHOS cells and CHO-K1 cells, or HEK293 cells, such as HEK293A, HEK293T and HEK293FS.

In still another aspect, the present disclosure provides a pharmaceutical composition comprising (i) the antibody or the antigen binding fragment thereof disclosed herein, or the bispecific antibody or the antigen binding fragment thereof disclosed herein; and (ii) a pharmaceutically acceptable carrier or excipient.

In some embodiments, the carrier or excipient for use with the composition disclosed herein includes but is not limited to maleic acid, tartaric acid, lactic acid, citric acid, acetic acid, sodium bicarbonate, sodium phosphate, histidine, glycine, sodium chloride, potassium chloride, calcium chloride, zinc chloride, water, dextrose, N-methylpyrrolidone, dimethyl sulfoxide, N, N- dimethylacetamide, ethanol, propylene glycol, polyethylene glycol, diethylene glycol monoethyl ether, and surfactant polyoxyethylene-sorbitan monooleate.

In some embodiments of the pharmaceutical composition disclosed herein, the pharmaceutical composition further comprises a second therapeutic agent. In some embodiments, the second therapeutic agent can be selected from an antibody, a chemotherapeutic agent and a small molecule drug. In some embodiments, the second therapeutic agent can be selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid, or any combination thereof.

In some embodiments, the therapeutic agent is a chemotherapeutic agent. The chemotherapeutic agents can include, for example, cytotoxic agents, anti-metabolite agents (e.g., folate antagonists, purine analogs, pyrimidine analogs, etc. ) , topoisomerase inhibitors (e.g., camptothecin derivatives, anthracenedione, anthracyclines, epipodophyllotoxins, quinoline alkaloids, etc. ) , anti-microtubule agents (e.g., taxanes, vinca alkaloids) , protein synthesis inhibitors (e.g., cephalotaxine, camptothecin derivatives, quinoline alkaloids) , alkylating agents (e.g., alkyl sulfonates, ethylenimines, nitrogen mustards, nitrosoureas, platinum derivatives, triazenes, etc. ) , alkaloids, terpenoids, and kinase inhibitors.

In some embodiments of the conjugate disclosed herein, the chemical moiety is selected from the group consisting of a therapeutic agent, a detectable moiety, and an immunostimulatory molecule.

In some embodiments, the therapeutic agent includes but is not limited to immunomodulators, radioactive compounds, enzymes (for example perforin) , chemotherapeutic agents (for example cis-platin) , or a toxin. In some embodiments, the therapeutic agent can be such as maytansine, geldanamycin, tubulin inhibitors such as tubulin binding agents (e.g., auristatins) , or minor groove binding agents such as calicheamicin.

Other suitable therapeutic agents include such as, small molecule cytotoxic agents, i.e. compounds with the ability to kill mammalian cells having a molecular weight of less than 700 Daltons. Such compounds could also contain toxic metals capable of having a cytotoxic effect. Furthermore, it is to be understood that these small molecule cytotoxic agents also include pro-drugs, i.e. compounds that decay or are converted under physiological conditions to release cytotoxic agents. Examples of such agents include cis-platin, maytansine derivatives, rachelmycin, calicheamicin, docetaxel, etoposide, gemcitabine, ifosfamide, irinotecan, melphalan, mitoxantrone, sorfimer sodiumphotofrin II, temozolomide, topotecan, trimetreate glucuronate, auristatin E vincristine and doxorubicin; peptide cytotoxins, i.e. proteins or fragments thereof with the ability to kill mammalian cells, for example, ricin, diphtheria toxin, pseudomonas bacterial exotoxin A, DNase and RNase; radio-nuclides, i.e. unstable isotopes of elements which decay with the concurrent emission of one or more of a or β particles, or γ rays, for example, iodine-131 , rhenium-186, indium-111, yttrium-90, bismuth-210, bismuth-213, actinium-225 and astatine-213; chelating agents may be used to facilitate the association of these radionuclides to the molecules, or multimers thereof.

In some embodiments, the detectable moiety can be selected from the group consisting of biotin, streptavidin, an enzyme or catalytically active fragment thereof, a radionuclide, a nanoparticle, a paramagnetic metal ion, or a fluorescent, phosphorescent, or chemiluminescent molecule. A detectable moiety for diagnostic purposes include for instance, fluorescent labels, radiolabels, enzymes, nucleic acid probes and contrast reagents.

In some embodiments, the immunostimulatory molecule is an immune effector molecules which stimulate immune response. For example, the immunostimulatory molecule can be cytokines such as IL-2 and IFN-γ, chemokines such as IL-8, platelet factor 4, melanoma growth stimulatory protein, complement activators; viral/bacterial protein domains, or viral/bacterial peptides.

In some embodiments of the method disclosed herein, the cancer is a mesothelin positive cancer. In some embodiments, the cancer can be selected from the group consisting of mesothelioma, liver cancer, colon cancer, pancreatic cancer, breast cancer, lung cancer, ovarian cancer, esophageal cancer, bladder cancer, prostate cancer, colorectal cancer, uterine cancer, cervical cancer, brain cancer, cervical cancer, gastric cancer, cholangiocarcinoma, chondrosarcoma, kidney cancer, thyroid cancer, skin cancer, melanoma, glioma, neuroblastoma, lymphoma and myeloma. Preferably, the cancer is selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer (pancreatic adenocarcinomas) , lung cancer (such as lung mesothelioma, lung adenocarcinomas and lung squamous cell carcinoma) , gastric cancer, and ovarian cancer. In a preferred embodiment, the cancer is triple negative breast cancer (TNBC) .

In some embodiments, dosage administered to a subject may vary with the embodiment, the medicament employed, the method of administration, and the site and subject being treated. However, a dose should be sufficient to provide a therapeutic response. A clinician may determine the effective amount to be administered to a human or other subject in order to treat a medical condition. The precise amount required to be therapeutically effective may depend upon numerous factors, e.g., such as the activity of the antibody, and the route of administration.

A dose of the antibodies, compositions or conjugates described herein may be administered to a mammal at one time or in a series of sub-doses administered over a suitable period of time, e.g., on a daily, semi-weekly, weekly, bi-weekly, semi-monthly, bi-monthly, semi-annual, or annual basis, as needed. A dosage unit comprising an effective amount of antibodies, compositions or conjugates may be administered in a single daily dose, or the total daily dosage may be administered in two, three, four, or more divided doses administered daily, as needed.

A suitable means of administration may be selected by a medical practitioner. Route of administration may be parenteral, for example, administration by injection, transnasal administration, transpulmonary administration, or transcutaneous administration. Administration may be systemic or local by intravenous injection, intramuscular injection, intraperitoneal injection, subcutaneous injection. In some embodiments, the antibodies, compositions or conjugates are selected for parenteral delivery, for inhalation, or for delivery through the digestive tract, such as orally. Dose and method of administration may vary depending on the weight, age, condition, and the like of the subject, and may be suitably selected.

In some embodiments, the method further comprises administering to the subject a second therapeutic agent. In certain embodiments, a binding agent is administered prior to, substantially simultaneously with, or after the administration of the second therapeutic agent.

In some embodiments, the second therapeutic agent is selected from an antibody, a chemotherapeutic agent and a small molecule drug. In some preferred embodiments, the second therapeutic agent can be selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid, or any combination thereof.

In some embodiments, the second therapeutic agent is a chemotherapeutic agent. The chemotherapeutic agents can include, for example, cytotoxic agents, anti-metabolite agents (e.g., folate antagonists, purine analogs, pyrimidine analogs, etc. ) , topoisomerase inhibitors (e.g., camptothecin derivatives, anthracenedione, anthracyclines, epipodophyllotoxins, quinoline alkaloids, etc. ) , anti-microtubule agents (e.g., taxanes, vinca alkaloids) , protein synthesis inhibitors (e.g., cephalotaxine, camptothecin derivatives, quinoline alkaloids) , alkylating agents (e.g., alkyl sulfonates, ethylenimines, nitrogen mustards, nitrosoureas, platinum derivatives, triazenes, etc. ) , alkaloids, terpenoids, and kinase inhibitors.

In still another aspect, the present disclosure provides a method of detecting mesothelin positive cancer in a subject comprising (i) contacting a sample obtained from the subject with the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, or the conjugate disclosed herein; and (ii) detecting binding of the antibody or the antigen binding fragment thereof to mesothelin in the sample.

In some embodiments, the antibody or the antigen binding fragment thereof is linked to a detectable moiety. The detectable moiety can be selected from the group consisting of biotin, streptavidin, an enzyme or catalytically active fragment thereof, a radionuclide, a nanoparticle, a paramagnetic metal ion, or a fluorescent, phosphorescent, or chemiluminescent molecule. A detectable moiety for diagnostic purposes include for instance, fluorescent labels, radiolabels, enzymes, nucleic acid probes and contrast reagents.

In some embodiments, the cancer is a mesothelin positive cancer. Preferably, the cancer is selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer (pancreatic adenocarcinomas) , lung cancer (such as lung mesothelioma, lung adenocarcinomas and lung squamous cell carcinoma) , gastric cancer, and ovarian cancer. In a preferred embodiment, the cancer is triple negative breast cancer (TNBC) .

In yet another aspect, the present disclosure provides 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 the antibodies or the antigen binding fragment disclosed 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.

In a specific embodiment, the kit comprises a first container containing the antibodies or the antigen binding fragment disclosed herein. In a specific embodiment, the kit comprises a first container that is a vial containing the antibodies or the antigen binding fragment as a lyophilized sterile powder under vacuum, and the kit further comprises a second container comprising a pharmaceutically acceptable fluid.

In a specific embodiment, provided herein is an injection device containing the antibodies or the antigen binding fragment disclosed herein. In a specific embodiment, the injection device comprises the antibody in sterile solution. In a specific embodiment, the injection device is a syringe.

In still another aspect, the present disclosure provides a kit for detecting the presence of a mesothelin antigen in a sample comprising the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, or the conjugate disclosed herein. Preferably, the antibody or the antigen binding fragment thereof is linked to a detectable moiety. The detectable moiety can be selected from the group consisting of biotin, streptavidin, an enzyme or catalytically active fragment thereof, a radionuclide, a nanoparticle, a paramagnetic metal ion, or a fluorescent, phosphorescent, or chemiluminescent molecule. A detectable moiety for diagnostic purposes include for instance, fluorescent labels, radiolabels, enzymes, nucleic acid probes and contrast reagents.

In another aspect, the present disclosure provides use of the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, the pharmaceutical composition disclosed herein, or the conjugate disclosed herein in the manufacture of a medicament for treating a cancer in a subject. In some embodiments, the cancer is a mesothelin positive cancer.

In still another aspect, the present disclosure provides the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, the pharmaceutical composition disclosed herein, or the conjugate disclosed herein for use in treating a cancer in a subject. In some embodiments, the cancer is a mesothelin positive cancer.

In yet another aspect, the present disclosure provides use of the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, or the conjugate disclosed herein in the manufacture of a kit for detecting mesothelin positive cancer in a subject.

In still another aspect, the present disclosure provides the antibody or the antigen binding fragment thereof disclosed herein, the bispecific antibody or the antigen binding fragment thereof disclosed herein, or the conjugate disclosed herein for use in detecting mesothelin positive cancer in a subject.

In some embodiments of the use disclosed herein, the mesothelin positive cancer is preferably selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer (pancreatic adenocarcinomas) , lung cancer (such as lung mesothelioma, lung adenocarcinomas and lung squamous cell carcinoma) , gastric cancer, and ovarian cancer. In a preferred embodiment, the cancer is triple negative breast cancer (TNBC) .

EXAMPLES

The following examples are given for the purpose of illustrating various embodiments of the invention and are not meant to limit the present invention in any fashion. The present examples, along with the methods described herein are presently representative of preferred embodiments, are exemplary, and are not intended as limitations on the scope of the invention. Changes therein and other uses which are encompassed within the spirit of the invention as defined by the scope of the claims will occur to those skilled in the art.

Cell lines including H226 (human lung squamous cell carcinoma cell line) , N87 (human gastric carcinoma cell line) , and LS174T (human colorectal cancer cell line) were purchased from National Collection of Authenticated Cell Cultures.

A tumor cell line stably expressing mesothelin, LS174T-MSLN (2B6) , was generated by transient transfection of the commercial MSLN recombinant plasmid pCMV-MSLN (Sino Biological) into LS174T cells using the agent Lipofectamine ^TM LTX Reagent with PLUS ^TM Reagent (Thermo) and transfection-specific media Opti-MEM ^TM I (Gibco) . Cell culture was supplemented with hygromycin B and positive clones were selected. After 2-3 weeks, single positive clones were gradually separated and verified with flow-cytometry.

Human mesothelin (MSLN) protein and cynomolgus mesothelin (MSLN) (296-580) protein were purchased from ACROBiosystems. Anti-human IgG (γ-chain specific) -R-PE antibody, anti-human IgG (Fc-specific) -peroxidase antibody and monoclonal

M2-peroxidase were purchased from Sigma. M13KO7 helper phage purchased from Invitrogen. Dynabeads ^TM Myone ^TM Streptavidin T1 was purchased from ThermoFisher Scientific. PE anti-His tag antibody was purchased from BioLegend.

Example 1. Panning and screening of a phage-display naive human Fab library for identification of mesothelin antibodies

Two large (size, 10 ¹¹) phage-display naive human Fab libraries with peripheral blood B cells from about 30 healthy individuals were used for selection of antibodies against recombinant human mesothelin conjugated to magnetic beads (Dynabeads ^TM Myone ^TM Streptavidin T1; ThermoFisher Scientific) as described previously (Zhu et al., J Virol 2006, 80: 891-899) with minor modification that 5, 1 and 0.2 mg of antigen was used in the first, second and third round of panning, respectively. After 3 rounds of biopanning, strong positive signals were observed by using polyclonal phage ELISA. The 3 ^th round phage was subsequently subjected to test for its specific binding. By soluble expression-based monoclonal enzyme-linked immunosorbent assay (SemELISA) and DNA sequencing analysis, three specific Fab clone, designated as M8, M10, and M38 respectively, were identified. Three Fab clones all have a λ light chain.

The hexahistidine-tagged M8, M10 and M38 Fabs were expressed in E. coli strain HB2151 and purified from the soluble fraction of periplasm by using the Ni-NTA resin. Then ELISA was performed by using standard protocols to measure binding affinity to recombinant human mesothelin (full-length extracellular domain) . Briefly, the recombinant human mesothelin (ACROBiosystems) was coated on Corning EIA/RIA high-binding 96-well plates (Corning Inc. ) at 50 ng per well overnight at 4℃ and blocked with 3%nonfat milk in PBS (pH7.4) . Fivefold serially diluted antibodies were added and incubated at room temperature for 2 h. The plates were washed with PBS containing 0.05%Tween 20. Bound antibodies were detected by HRP-conjugated anti-FLAG tag antibody (Sino Biological) . The assay was developed at room temperature with TMB substrate (Solarbio) and OD value was measured at 450 nm with a microplate reader. The results showed that M8, M10, and M38 Fabs have an affinity with EC ₅₀ of 127nM, 21nM and 15.7nM, respectively (Figure 1) .

To measure the binding of M8, M10, and M38 Fabs against cell surface-associated mesothelin, flow cytometry was carried out with mesothelin transient transfected HEK293 cells. A commercial anti-mesothelin antibody (anti-mesothelin-FITC, Miltenyi, Cat#: 130-118-167) was used as positive control. The results indicated that only M10 Fab has the ability of binding to the cell surface-associated mesothelin (Figure 2) .

Then, M10 Fab was further tested for binding to cell surface-associated mesothelin with cancer cell lines including H226 and N87. Each cell line (5 x 10 ⁵ cells) was incubated with Fab antibody (10 μg/ml) on ice for 60 min. The cells were washed once with PBS containing 0.1%bovine serum albumin (PBSA) and resuspended in 200 ml PBSA. Then 2 μl anti-His-PE conjugates (BioLegend) were added and incubated for 60 min. The cells were washed once with PBSA and then used for flow cytometry analysis. The results are shown in Figure 3.

As can be seen from Figure 3, M10 Fab binds well to H226 and N87 cells, suggesting that M10 Fab can bind well to cancer cell lines expressing mesothelin.

Example 2. Construction and initial characterization of anti-mesothelin monoclonal antibody

Fab clone M10 was used to construct an intact form of monoclonal antibody IgG1 against human mesothelin (M10 mAb) . Briefly, the heavy chain Fd fragment of M10 Fab was fused to the N-terminus of human IgG1 Fc fragment. Both light chain and heavy chain were constructed into the vector pDin1, which was modified from pDR12 by the inventors to comprise two molecular cloning sites (MCS) . Construction and initial characterization of the M10 mAb were performed as follow.

Cloning of anti-mesothelin monoclonal antibody

To generate the construct of anti-mesothelin monoclonal antibody, following primers were used:

bnIgG20L1, 5’ GTGTAAGCTTACCATGGGTGTGCCCACTCAGGTCCTGGGGT 3’ (sense) (SEQ ID NO: 24) ;

MSLN-IgG1-VL-Forward, 5’ CTTACAGATGCCAGATGTTCCTATGTGCTGACTCAG 3’ (sense) (SEQ ID NO: 25) ;

MSLN-IgG1-VL-Reverse, 5’ CGGAATTCTTATGAACATTCTGTAGGGGCCAC 3’ (antisense) (SEQ ID NO: 26) ;

MSLN-IgG1-VH-FP-Xba1, 5’ TGTTCTAGAGCCACCATGGAATGGAGCTGGGTCTTT CTCTTCTTCCTGTCAGTAACTACAGGTGTCCACTCCCAGCTGGTGGAGA 3’ (sense) (SE Q ID NO: 27) ;

MSLN-IgG1-VH-RP-OL, 5’A TGTGTGAGTTTTGTCACAAGATTTGGGCTCAACT 3’ (antisense) (SEQ ID NO: 28) ;

MSLN-IgG1-FC-FP-OL, 5’ GACAAAACTCACACATGCCCACCGT 3’ (sense) (SEQ ID NO: 29) ;

MSLN-IgG1-FC-RP-Sal1, 5’ CTGAGTCGACTTATTTACCCGGGGACAGGGAGA 3’ (antisense) (SEQ ID NO: 30) .

For the generation of light chain, the VL gene fragment was amplified from anti-mesothelin M10 Fab with the primer pair MSLN-IgG1-VL-Forward/MSLN-IgG1-VL-Reverse. The leader L peptide was fused to the 5’ end of VL PCR fragment by overlapping PCR by using the primer pair bnIgG20L1/MSLN-IgG1-VL-Reverse. The PCR product was cloned into the MCS of pDin1 vector containing CL and Fc fragments of IgG1 light chain, by using restriction enzymes EcoR I/Hind III.

For the generation of heavy chain, the VH-CH1 gene fragment was amplified from anti-mesothelin M10 Fab with the primer pair MSLN-IgG1-VH-FP-Xba1/MSLN-IgG1-VH-RP-OL. The Fc domain was amplified from an irrelevant IgG1 with the primer pair MSLN-IgG1-FC-FP-OL/MSLN-IgG1-FC-RP-Sal1. To obtain the full-length heavy chain, these two gene fragments were fused together by overlapping PCR using the primer pair MSLN-IgG1-VH-FP-Xba1/MSLN-IgG1-FC-RP-Sal1. The full-length heavy chain gene fragment was then cloned into the recombinant plasmid containing the anti-mesothelin light chain insert via the XbaI and SalI restriction sites.

Protein expression, purification and initial characterization

Anti-mesothelin M10 mAb was expressed in either 293FS or CHO-Scells. The plasmids and transfection agent PEI were mixed at ratio 1: 3 and then dropwise added into 293FS or CHO-Scell culture. The cells were continued to grow for 5-7 days after transfection. The cell culture was harvested by centrifugation at 8000rpm for 20 min. The culture supernatant containing target proteins were loaded onto Protein A Sepharose 4 Fast Flow column chromatography (GE Healthcare) , and purified according to the manufacturer’s instructions.

The purified proteins were subjected to SDS-PAGE. On a non-reducing SDS-PAGE, M10 mAb displays an apparent molecular weight (aMW) of approximately 150 kDa. On a reducing SDS-PAGE, the heavy chain and light chain have apparent molecular weight of approximately 55 kDa and 30kDa, respectively (data not shown) . The CDR sequences of M10 mAb according to the Kabat numbering system are shown in Table 1. The amino acid sequences of light chain variable region (VL) and heavy chain variable region (VH) are shown in Table 2. The whole light chain and heavy chain sequences of M10 mAb are shown in Table 3.

Table 1. CDR sequences of M10 mAb

LCDR1	SGDALPKQYAF (SEQ ID NO: 1)
LCDR2	KDSERPS (SEQ ID NO: 2)
LCDR3	QSADSSATSVI (SEQ ID NO: 3)
HCDR1	DYAMH (SEQ ID NO: 6)
HCDR2	GISWNSGSIGYADSVKG (SEQ ID NO: 7)
HCDR3	DSGSSGWYGYFQH (SEQ ID NO: 8)

Table 2. VL and VH sequences of M10 mAb

Table 3. Light chain and heavy chain sequences of M10 mAb

Example 3. Binding of the anti-mesothelin monoclonal antibody to mesothelin

ELISA was performed according to standard protocols, to determine binding affinity of anti-mesothelin M10 mAb to recombinant human mesothelin (AcroBiosystems) . Briefly, recombinant human mesothelin was coated on Corning EIA/RIA high-binding 96-well plates (Corning Inc. ) at 50 ng per well overnight at 4℃ and blocked with 3%nonfat milk in PBS (pH7.4) . Fivefold serially diluted antibodies were added and incubated at room temperature for 2 h. The plates were washed with PBS containing 0.05%Tween 20. Bound antibodies were detected by HRP-conjugated streptavidin (Sino Biological) . The assay was developed at room temperature with TMB substrate (Solarbio) and monitored at 450 nm with a microplate reader. The half-maximal binding (EC ₅₀) was calculated by fitting the data to the Langmuir adsorption isotherm. The results are shown in Figure 4.

The results indicate that the M10 mAb can bind to recombinant human mesothelin with EC ₅₀ of 0.2 nM, suggesting that the M10 mAb has high binding affinity to human mesothelin.

Example 4. Binding of the anti-mesothelin monoclonal antibody to cancer cell line

To measure binding ability of the anti-mesothelin M10 mAb to cell surface-associated mesothelin, flow cytometry was carried out with a mesothelin positive cancer cell line H226. About 5 × 10 ⁵ cells were incubated with the antibody (10μg/ml) on ice for 1 h. The cells were washed once with PBS containing 0.1%bovine serum albumin (PBSA) and resuspended in 100 μl PBSA. Then 1 μl anti-human IgG (Fc-specific) -FITC conjugate (Sigma) was added and incubated for 30 min. The cells were washed once with PBSA and then used for flow cytometry analysis. The results are shown in Figure 5.

The results indicate that M10 mAb binds well to H226, suggesting that M10 mAb have good binding ability to mesothelin positive tumor cell lines.

Example 5. Anti-mesothelin monoclonal antibody mediated ADCC killing against human cancer cell line

To evaluate ADCC killing of M10 mAb, H226 cells were used as target cells and NK cells were used as effector cells. Frozen NK cells (

Biotechnologies, cat#: PB56-N-1CW) were revived and cultured in RPMI1640 complete medium containing 20%FBS, 1%penicillin/streptomycin, and 50 IU of IL-2 in 5%CO ₂ incubator at 37℃ overnight. H226 cells were prepared to a concentration of 1×10 ⁵ cells/mL with the complete medium, and added to a 96-well plate at 100 μL/well, and incubated in a 37℃ incubator supplied with 5%CO ₂ overnight. At the second day, a serial of concentration (400μg/mL, 40μg/mL, and 0μg/mL) of M10 mAbs were prepared with the complete medium, and an IgG4 isotype antibody was used as negative control. 50μL of antibody solutions were added into the 96-well plate containing H226 cells. The NK cells were harvested and diluted to 3×10 ⁵ cells/mL, and then added to the 96-well plate at 50μL/well. The plate was incubated in 5%CO ₂ incubator at 37℃ for 72 hours. The final concentration of antibodies are 100μg/mL, 10μg/mL, and 0μg/mL, respectively. After 72h incubation, the culture media was removed and replaced with fresh complete medium containing 10%CCK8 at 100μL/well, and the plate was incubated at 37℃ for 30 minutes. The OD value at 450nm was measured with an ELISA reader. Killing efficiency was calculated according to the equation:

(OD _{Tumor+NK+0 μg/mL mab}-OD _{Tumor+NK+x μg/mL mab}) /OD _{Tumor+NK+0 μg/mL mab}×100%,

in which x represents 10 or 100.

The ADCC killing of M10 mAb against H226 cells was shown in Figure 6. The result showed that M10 mAb induced less than 10%killing against tumor cells at 10μg/mL, and over 30%killing against tumor cells at 100μg/mL, while the control antibody IgG4 isotype did not induce any ADCC at the highest concentration of 100μg/mL, suggesting that ADCC is triggered by specific binding of M10 mAb to mesothelin positive tumor cells H226 and recruiting of NK cells through the Fc portion of the mAb. This demonstrates that the M10 mAb possesses substantial capability of inducing ADCC killing against mesothelin positive tumor cells.

Example 6. Construction and initial characterization of anti-mesothelin bispecific antibody

Bispecific T cell engager (BiTE) is a novel class of bispecific antibodies which can guide cytotoxic T cells to kill cancer cells by simultaneously binding to a tumor antigen and a T cell antigen, such as CD3 molecule on T cell surface. HBiTE as described in PCT application No. PCT/US2018/016524 (which is incorporated herein by reference in its entirety) is a specific form of BiTE. HBiTE has a light chain and a heavy chain forming a heterodimer. The light chain, from N-terminus to C-terminus, comprises an anti-target (e.g. tumor antigen) VL domain, an anti-CD3 VL-CL and a monomeric human IgG1 Fc (e.g., mFc7.2) . The heavy chain, from N-terminus to C-terminus, comprises an anti-target VH domain, an anti-CD3 VH-CH1 and a monomeric human IgG1 Fc (e.g., mFc7.2) . Monomeric Fc7.2 contains two amino acid mutations (T366L and Y407H) capable of inhibiting Fc homodimerization. To generate MSLN×CD3 HBiTE, the VL and VH domains of the above anti-mesothelin antibody were fused to the N-terminus of VL and VH domains of anti-CD3 Fab via linkers GGGGSGGGGSGGGGS (SEQ ID NO: 22) and GSSGGGGSGGGGS (SEQ ID NO: 23) , respectively. The anti-CD3 Fab is further fused to the N terminus of mFc7.2. The light chain and heavy chain were constructed into a single vector pDin1 for expression in mammalian cells. Construction and initial characterization of the bispecific antibody targeting mesothelin and CD3 (M10-based MSLN×CD3 HBiTE) , were performed as follow.

Cloning of the bispecific antibody targeting mesothelin and CD3

To generate constructs of the bispecific antibody M10-based MSLN×CD3 HBiTE, following primers were used:

MSLN-VL-forward, 5’A CTACAGGTGTCCACTCCTCCTATGTGCTGACTCAGC 3’ (sense) (SEQ ID NO: 31) ;

MSLN-VL-reverse, 5’ GTAGGATCCTAGGACGGTCAGCTTGGTC 3’ (antisense) (SEQ ID NO: 32) ;

bnIgG20H1, 5’ GTGTTCTAGAGCCGCCACCATGGAATGGAGCTGGGTCTTTC 3’ (sense) (SEQ ID NO: 33) ;

MSLN-VH-forward, 5’ GGCTTACAGATGCCAGATGTCAGCTGGTGGAGACCGG 3’ (sense) (SEQ ID NO: 34) ;

MSLN-VH-reverse, 5’ GATAGAGCTCCCTCCACCTGAGGAGACGGTGACC 3’ (antisense) (SEQ ID NO: 35) .

For the generation of the bispecific antibody, the gene fragments of VL and VH domains were amplified from M10 Fab with primer pairs MSLN-VL-forward/MSLN-VL-reverse and MSLN-VH-forward/MSLN-VH-reverse, respectively. The PCR products were fused to the 3’ end of H leader and L leader by overlapping PCR using the primer pairs bnIgG20H1/MSLN-VL-reverse and bnIgG20L1/MSLN-VH-reverse, respectively. The H leader-VL gene fragment was digested with XbaI and BamHI and cloned into HBiTE derived pDin1 vector containing an anti-CD3 hSP34 Fab and a complete Fc fragment. The L leader-VH gene fragment was then further cloned into the recombinant plasmid containing the H leader-VL insert via the HindIII and SacI restriction sites. The M10-based MSLN×CD3 HBiTE was designated as CMD007.

Protein expression, purification and initial characterization

CMD007 was expressed in either 293FS or CHO-Scells. The plasmids and transfection agent PEI were mixed at ratio 1: 3 and then added into 293FS or CHO-Scell culture. The cells were continued to grow for 5-7 days after transfection. The cell culture was harvested by centrifugation at 8000rpm for 20 min. The culture supernatant containing target proteins were loaded onto Protein A Sepharose 4 Fast Flow column chromatography (GE Healthcare) , and purified according to the manufacturer’s instructions.

The purified proteins were subjected to SDS-PAGE. On a non-reducing SDS-PAGE, CMD007 displays an apparent molecular weight (aMW) of approximately 120 kDa. On a reducing SDS-PAGE, the heavy chain and light chain are close to each other with an apparent molecular weight of approximately 62 kDa (data not shown) . The CDR sequences of CMD007 according to the Kabat numbering system are shown in Table 4. The amino acid sequences of light chain variable region (VL) and heavy chain variable region (VH) are shown in Table 5. The light chain and heavy chain sequences of CMD007 are shown in Table 6.

Table 4. CDR sequences of CMD007

LCDR1 against mesothelin	SGDALPKQYAF (SEQ ID NO: 1)
LCDR2 against mesothelin	KDSERPS (SEQ ID NO: 2)
LCDR3 against mesothelin	QSADSSATSVI (SEQ ID NO: 3)
HCDR1 against mesothelin	DYAMH (SEQ ID NO: 6)
HCDR2 against mesothelin	GISWNSGSIGYADSVKG (SEQ ID NO: 7)
HCDR3 against mesothelin	DSGSSGWYGYFQH (SEQ ID NO: 8)
LCDR1 against CD3	RSSTGAVTTSNYAN (SEQ ID NO: 12)
LCDR2 against CD3	GANKRAP (SEQ ID NO: 13)
LCDR3 against CD3	ALWYSNLWV (SEQ ID NO: 14)
HCDR1 against CD3	GFTFNTY (SEQ ID NO: 17)
HCDR2 against CD3	RSKYNNYA (SEQ ID NO: 18)
HCDR3 against CD3	HGNFGSSYVSYFAY (SEQ ID NO: 19)

Table 5. VL and VH sequences of CMD007

Table 6. Light chain and heavy chain sequences of CMD007

Example 7. Binding of the bispecific antibody to mesothelin and CD3

To determine binding affinity of the bispecific antibody CMD007 to both mesothelin and CD3, ELISA experiments were performed as described in Example 3, with the coating proteins of human mesothelin or human CD3. The results are shown in Figures 7A-7B.

The results indicate that CMD007 binds to human CD3 with EC ₅₀ of 12.1 nM (Figure 7A) , and binds to human mesothelin with EC ₅₀ of 8.3 nM (Figure 7B) . These results suggested that CMD007 can bind to both mesothelin and CD3 proteins, with affinity suitable for been used as BiTE to trigger tumor cell killing by T cells.

Example 8. Binding of the bispecific antibody targeting mesothelin and CD3 to cancer cell lines

To determine binding affinity of the bispecific antibody CMD007 to mesothelin and CD3 expressed on cell surface, flow cytometry was carried out with mesothelin positive cancer cell line H226, CD3 positive Jurkat cell line, mesothelin negative cancer cell LS174T (negative control) and LS174T-MSLN (2B6) stably transfected with mesothelin. The procedures were similar to those described in Example 4. The results were shown in Figures 8A-8D.

The results indicate that CMD007 binds well to H226, Jurkat and LS174T-MSLN (2B6) cells, and does not bind to mesothelin negative LS174T cells. This suggests that CMD007 can bind to both cancer cells expressing mesothelin and cells expressing CD3.

Example 9. Bispecific antibody mediated T cell activation

To evaluate ability and specificity of CMD007 to activate human T cells in the presence of mesothelin-expressing tumor cells, target cells (one mesothelin negative cell LS174T and two mesothelin positive cells LS174T-MSLN (2B6) and H226) were plated on 96-well plates at a density of 1 × 10 ⁴ (for H226) or 2 × 10 ⁴ (for LS174T and LS174T-MSLN (2B6) ) cells in 100 μl RMPI1640 complete medium per well. 50 μl of 5-fold serially diluted CMD007 was added into each well, and a bispecific antibody CMD006-M2 (containing an anti-CD3 Fab, an irrelevant TAA antibody variable fragment, and mFc7.2) was used as a negative control. Then effector cells (Jurkat cells) were added at a density of 1 × 10 ⁵ cells in 50 μl RMPI1640 complete medium per well, with a target : effector cell ratio of 1: 10 (H226 : Jurkat) or 1: 5 (LS174T : Jurkat, and LS174T-MSLN (2B6) : Jurkat) . After 24h incubation, the assay was developed by using the BD FACS Calibur with CD3 monoclonal antibody (17A2) , human CD69 monoclonal antibody (FN50) , anti-CD25/IL2RA antibody (APC) , and mouse monoclonal antibody following manufacturer’s instruction.

First, the expression of the early activation marker CD69 was determined with H226, LS174T-MSLN (2B6) and LS174T cells. In the presence of mesothelin positive H226 cells, human Jurkat cells were efficiently activated (63%) by CMD007. For LS174T-MSLN (2B6) cells, human T cells were also efficiently activated (65%) by CMD007. For negative control groups in which CMD007 was incubated with Jurkat cells alone, or CMD007 was incubated with mesothelin negative cells LS174T and Jurkat cells, or a control antibody CMD006-M2 was incubated with Jurkat and LS174T-MSLN (2B6) cells, no expression of CD69 was detected (Figure 9) . The results indicate that T cells can be activated only when CMD007 simultaneously binds to CD3 antigen of Jurkat cells and mesothelin antigen of tumor cells.

Next, the expression of T cell activation marker CD25 was determined with LS174T-MSLN (2B6) and LS174T cells. When CMD007 was incubated with both mesothelin positive LS174T-MSLN (2B6) cells and Jurkat cells, around 45%Jurkat cells were observed to express CD25. For negative control groups in which CMD007 was incubated with mesothelin negative LS174T cells and Jurkat cells or the control antibody CMD006-M2 was incubated with LS174T-MSLN (2B6) and Jurkat cells, no expression of CD25 was detected (Figure 10) . These results demonstrate that T cell can be activated only when CMD007 binds to both CD3 expressing Jurkat cells and mesothelin expressing tumor cells, suggesting that T cell activation is specific target tumor antigen dependent.

Example 10. Bispecific antibody mediated killing of human cancer cell lines

Bispecific T cell engager can simultaneously bind to a tumor antigen and a T cell antigen (e.g., CD3 molecular on T cell surface) causing aggregation and activation of T cells, eventually leading to the killing of tumor cells. To evaluate killing efficiency of the bispecific antibody CMD007, CCK8 assay was performed using three mesothelin expressing tumor cell lines H226, N87, and LS174T-MSLN (2B6) as target cells.

Target cells (1×10 ⁴ for H226, 3×10 ⁴ for N87, and 2×10 ⁴ for LS174T-MSLN (2B6)) were seeded in 100 μl RPMI 1640 complete medium overnight. Meanwhile, frozen PBMCs were revived and inoculated in 30 mL RPMI 1640 complete medium overnight. At the second day, PBMCs (1×10 ⁵ for H226 and LS174T-MSLN (2B6) , and 3×10 ⁵ for N87) in 50 μl RPMI 1640 complete medium were added. Then, 50 μl antibodies (5-fold serially diluted from 4 μg/ml for H226 and N87, and 5-fold serially diluted from 3.2 μg/ml for LS174T-MSLN (2B6) ) were added into each well, and an IgG4 isotype antibody was used as a negative control. 48 h after incubation, the medium was removed and 100 μl RPMI 1640 complete medium containing 20%CCK8 was added and incubated 30 minutes in a CO ₂ incubator. Cell killing activity was measured by using microplate reader according to the manufacturer’s instructions. The results were shown in Figures 11-13.

The results indicated that nearly 100%tumor cells N87 and LS174T-MSLN (2B6) were killed in the presence of CMD007 and PBMCs. The EC ₅₀ of N87 killing by CMD007 was 1.381 ng/ml (Figure 11) , and the EC ₅₀ of LS174T-MSLN (2B6) killing by CMD007 was 1.685 ng/ml (Figure 12) . For H226 cells, CMD007 showed moderate killing efficiency with around 50%tumor cells being killed in the presence of PBMCs, and the EC ₅₀ of H226 killing by CMD007was 0.812 ng/ml (Figure 13) .

In summary, the results have demonstrated that CMD007 possesses potent killing capability against multiple cancer cell lines expressing mesothelin.

Example 11. Bispecific antibody mediated inhibition of tumor growth in mice

Pharmacokinetic measurement

Three NOD/SCID mice were administered intravenously with 300 μg CMD007 on day 0. Plasma samples were collected at time points 0.25hr, 5hr, 21hr, 49hr and 69hr after treatment and used for measurement of antibody serum concentration by ELISA.

The result indicated that the serum concentration of CMD007 was gradually decreased but still maintained a relatively high level until the end point, and the calculated serum half-life (t _1/2) was around 57.3 hours (Figure 14) .

In-vivo tumor growth inhibition

The effector cells PBMCs (100μl, 1×10 ⁶) and mesothelin expressing tumor cells LS174T-MSLN (2B6) (100μl, 1×10 ⁶) were mixed in 100μl matrigel and inoculated subcutaneously into the right side of abdomen of B-NDG mice. In experiment groups, 50 μg/kg or 200 μg/kg of CMD007 was injected intravenously into mice. 200 μg/kg of IgG4 isotype antibody was used as negative control. These mice were dosed twice a week. After three weeks of treatment, mice were sacrificed and tumor volume and body weight of mice were measured. Tumor growth inhibition rate was calculated by using the following formula:

(Average weight of control group -average weight of experiment group) /average weight of control group.

The results indicate that CMD007 exhibits potent inhibition of tumor growth in a dose-dependent manner (Figure 15A) . The body weight of mice in all groups only has minor variation (Figure 15B) . 200μg/kg of CMD007 exhibits 95%inhibition of tumor growth, and 50μg/kg of CMD007 exhibits 61%inhibition of tumor growth (Figure 15C) .

In summary, the results have demonstrated that CMD007 has a long serum half-life, and can specifically and potently inhibit growth of the tumor cells expressing mesothelin, suggesting its potential for treating mesothelin positive cancers.

While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments described herein may be employed. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

An antibody specifically binding to mesothelin, or an antigen binding fragment thereof, comprising a light chain variable region (VL) and a heavy chain variable region (VH) , wherein the VL comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 1-3 respectively, and the VH comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 6-8 respectively.
The antibody or the antigen binding fragment thereof according to claim 1, wherein the VL comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 4, and the VH comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 9.
The antibody or the antigen binding fragment thereof according to claim 2, wherein the VL comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH comprises an amino acid sequence as set forth in SEQ ID NO: 9.
The antibody or the antigen binding fragment thereof according to any one of claims 1-3, wherein the antibody is of an isotype selected from the group consisting of IgG, IgA, IgM, IgE and IgD.
The antibody or the antigen binding fragment thereof according to any one of claims 1-3, wherein the antibody is of a subtype selected from the group consisting of IgG1, IgG2, IgG3, and IgG4.
The antibody or the antigen binding fragment thereof according to any one of claims 1-5, wherein the antigen binding fragment is selected from the group consisting of Fab, Fab’, F (ab') ₂, Fv, scFv, and ds-scFv.
The antibody or the antigen binding fragment thereof according to any one of claims 1-6, wherein the antibody is a monoclonal antibody.
The antibody or the antigen binding fragment thereof according to claim 7, wherein the antibody comprises a light chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 5 and a heavy chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 11.
The antibody or the antigen binding fragment thereof according to any one of claims 1-6, wherein the antibody is a bispecific or a multi-specific antibody.
The antibody or the antigen binding fragment thereof according to claim 9, wherein the antibody is a bispecific antibody which further comprises a second antigen binding region binding to a second antigen.
The antibody or the antigen binding fragment thereof of according to claim 10, wherein the second antigen is a tumor associated antigen or an immune cell antigen.
The antibody or the antigen binding fragment thereof according to claim 11, wherein the second antigen is a T-cell antigen.
The antibody or the antigen binding fragment thereof according to claim 12, wherein the T-cell antigen is selected from the group consisting of T cell receptor (TCR) , CD3, CD4, CD8, CD16, CD25, CD28, CD44, CD62L, CD69, ICOS, 41-BB (CD137) , and NKG2D.
The antibody or the antigen binding fragment thereof according to claim 10, wherein the second antigen is CD3, and the second antigen binding region comprises a VL and a VH, wherein the VL comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 12-14 respectively, and the VH comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 17-19 respectively.
The antibody or the antigen binding fragment thereof according to claim 14, wherein the second antigen binding region comprises a VL comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 15 and a VH comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 20.
The antibody or the antigen binding fragment thereof according to claim 15, wherein the second antigen binding region comprises a VL comprising an amino acid sequence as set forth in SEQ ID NO: 15 and a VH comprising an amino acid sequence as set forth in SEQ ID NO: 20.
The antibody or the antigen binding fragment thereof according to any one of claims 14-16, wherein the VL of the second antigen binding region is linked to the C-terminal of the VL of the antibody specifically binding to mesothelin, optionally via a first linker, and the VH of the second antigen binding region is linked to the C-terminal of the VH of the antibody specifically binding to mesothelin, optionally via a second linker, wherein the first linker and the second linker are the same or different.
The antibody or the antigen binding fragment thereof according to claim 17, wherein the first linker comprises an amino acid sequence as set forth in SEQ ID NO: 22, and the second linker comprises an amino acid sequence as set forth in SEQ ID NO: 23.
The antibody or the antigen binding fragment thereof according to any one of claims 14-18, wherein the bispecific antibody comprises a light chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 16 and a heavy chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 21.
The antibody or the antigen binding fragment thereof according to any of claims 10-19, wherein the bispecific antibody is a bispecific T-cell engager (BiTE) .
A bispecific antibody or an antigen binding fragment thereof, comprising a first antigen binding region binding to mesothelin comprising a VL and a VH and a second antigen binding region binding to CD3 comprising a VL and a VH, wherein

the VL of the first antigen binding region comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 1-3 respectively, and the VH of the first antigen binding region comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 6-8 respectively; and

the VL of the second antigen binding region comprises LCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 12-14 respectively, and the VH of the second antigen binding region comprises HCDRs 1-3 having the amino acid sequences as set forth in SEQ ID NOs: 17-19 respectively.
The bispecific antibody or the antigen binding fragment thereof according to claim 21, wherein the VL of the first antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 4 and the VH of the first antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 9; and

the VL of the second antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 15 and the VH of the second antigen binding region comprises an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 20.
The bispecific antibody or the antigen binding fragment thereof according to claim 22, wherein the VL of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 4 and the VH of the first antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 9; and

the VL of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 15 and the VH of the second antigen binding region comprises an amino acid sequence as set forth in SEQ ID NO: 20.
The bispecific antibody or the antigen binding fragment thereof according to any one of claim 21-23, wherein the VL of the second antigen binding region is linked to the C-terminal of the VL of the first antigen binding region, optionally via a first linker, and the VH of the second antigen binding region is linked to the C-terminal of the VH of the first antigen binding region, optionally via a second linker, wherein the first linker and the second linker are the same or different.
The bispecific antibody or the antigen binding fragment thereof according to claim 24, wherein the first linker comprises an amino acid sequence as set forth in SEQ ID NO: 22, and the second linker comprises an amino acid sequence as set forth in SEQ ID NO: 23.
The bispecific antibody or the antigen binding fragment thereof according to any one of claims 21-25, wherein the bispecific antibody comprises a light chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 16 and a heavy chain comprising an amino acid sequence having at least 80%, at least 85%, at least 90%, at least 95%, at least 98%, at least 99%, or 100%sequence identity to SEQ ID NO: 21.
The bispecific antibody or the antigen binding fragment thereof according to any of claims 21-26, wherein the bispecific antibody is a bispecific T-cell engager (BiTE) .
A nucleic acid comprising a nucleotide sequence encoding the antibody or the antigen binding fragment thereof according to any one of claims 1-20 or the bispecific antibody or the antigen binding fragment thereof according to any one of claims 21-27.
A vector comprising the nucleic acid according to claim 28.
A host cell comprising the nucleic acid according to claim 28 or the vector according to claim 29.
A pharmaceutical composition comprising (i) the antibody or the antigen binding fragment thereof according to any one of claims 1-20, or the bispecific antibody or the antigen binding fragment thereof according to any one of claims 21-27; and (ii) a pharmaceutically acceptable carrier or excipient.
The pharmaceutical composition according to claim 31, further comprising a second therapeutic agent.
The pharmaceutical composition according to claim 32, wherein the second therapeutic agent is selected from an antibody, a chemotherapeutic agent and a small molecule drug.
The pharmaceutical composition according to claim 32 or 33, wherein the second therapeutic agent is selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid.
A conjugate, comprising the antibody or the antigen binding fragment thereof according to any one of claims 1-20 or the bispecific antibody or the antigen binding fragment thereof according to any one of claims 21-27, and a chemical moiety conjugated thereto.
The conjugate according to claim 35, wherein the chemical moiety is selected from the group consisting of a therapeutic agent, a detectable moiety, and an immune stimulatory molecule.
A method of treating a cancer in a subject, comprising administering to the subject an effective amount of the antibody or the antigen binding fragment thereof according to any one of claims 1-20, the bispecific antibody or the antigen binding fragment thereof according to any one of claims 21-27, the pharmaceutical composition according to any one of claims 31-34, or the conjugate according to claim 35 or 36.
The method according to claim 37, wherein the cancer is a mesothelin positive cancer.
The method according to claim 38, wherein the cancer is selected from the group consisting of mesothelioma, breast cancer, pancreatic cancer, lung cancer, gastric cancer, and ovarian cancer.
The method according to claim 38, wherein the cancer is triple negative breast cancer (TNBC) .
The method according to any one of claims 37-40, further comprising administering to the subject a second therapeutic agent.
The method according to claim 41, wherein the second therapeutic agent is selected from an antibody, a chemotherapeutic agent and a small molecule drug.
The method according to claim 41 or 42, wherein the second therapeutic agent is selected from a Bruton’s tyrosine kinase (BTK) inhibitor, a PI3K inhibitor, a HDAC inhibitor, a PD-1/PD-L1 inhibitor, a LAG3 inhibitor, an ERK inhibitor, a MAPK inhibitor, a TIGIT inhibitor, a TIM3 inhibitor, and glucocorticoid.