WO2024102190A2 - Affinity agents - Google Patents

Abstract

Provided herein are affinity agents comprising ligands that specifically bind target molecules. The affinity agents are useful for binding, isolation, and/or purifications.

Description

AFFINITY AGENTS

BACKGROUND

[0001] The purity of biologically produced therapeutics is tightly scrutinized and regulated by authorities to ensure safety and efficacy. Thus, there remains a need for means to efficiently purify of biologically produced therapeutics to a high degree of purity.

SUMMARY

[0002] To support clinical efforts for therapeutic proteins, compositions and methods to efficiently purify proteins from recombinant sources are needed. Affinity purification is a means to isolate and/or achieve desired purity of a protein in few steps, or a single step. However, the development of affinity agents (e.g., comprising an affinity ligand) can be a resource intensive and time consuming task. This has resulted in the development of affinity agents for a limited number of proteins. In the absence of an affinity agent, purification typically involves inefficient, labor intensive, and expensive processes, such as a multi-column process.

[0003] Exemplary therapeutic proteins include, but are not limited to, bioactive polypeptides/proteins, fusion proteins, enzymes, hormones, antibodies, and antibody fragments.

[0004] Affinity agents that bind proteins and are useful for isolation and/or affinity purification are described herein. In some embodiments, an affinity agent comprises a solid support and a ligand.

[0005] Human monoclonal antibody therapy is a rapidly growing segment of the biologic pharmaceutical industry with very promising clinical applications in cancer therapy. Traditional methods for recombinant antibody purification utilize affinity chromatography resins based on Protein A ligands. Protein A based affinity resins provide highly efficient, high yield processes for purification of monoclonal antibodies. The utility of Protein A affinity resins in industrial antibody production processes highlights a need for suitable affinity purification devices for other classes of molecules.

[0006] Human serum albumin (HSA) is a therapeutic protein that can either be purified directly from human plasma or produced through recombinant protein expression. This therapeutic protein is commonly used and produced at large rates annually (e.g., tonnes/year). It has also been found that fusion of a therapeutic polypeptide or protein to HSA can be used to extend the serum half-life of the therapeutic polypeptide or protein. Tn fact, some HSA fusion products have even achieved FDA approval (e.g., Idelvion® and Tanzeum® (Albiglutide)) and more are in clinical development. Due to the therapeutic relevance of HSA and its fusion products, there is a need for affinity purification solutions for HSA and fusion products of HSA (e.g., HSA fused to a polypeptide and/or a protein) that possess high binding capacity and an ability to be used more than once after being cleaned, for example, with alkaline conditions (e.g., with sodium hydroxide). Previous efforts to produce affinity purification methods for HSA have been based upon the natural molecule Protein G. The Protein G affinity resins have been demonstrated to be limited by both their low binding capacity and instability towards cleaning with sodium hydroxide (Gulich et al. , “Stability towards alkaline conditions can be engineered into a protein ligand”, Journal of Biotechnology 80 (2000) 169-178 and US6613884). Consequently, a Protein G affinity resin commercial product has not been launched.

[0007] Protein G is derived from Streptococcus sp. G148 protein G and contains 3 albumin binding domains (ABDs) that comprise 3 helical bundle (3HB).The wild type ABDs are each 46 amino acids (Kraulis et al. 1996), flanked by linkers to the remainder of the protein. Binding of Protein G to albumin is mediated by contact points in the 2nd and 3rd helix defined by a known core binding sequence of 25 amino acids (see, for example, US Patent No. 8,937,153). However, the stability of 3HB proteins is influenced by all 3 helices, hence helix 1 as well as the flanking sequences are an integral part of the final molecule.

[0008] The binding affinity of ABDs have been improved to femtomolar concentrations as evidenced by US Patent No. 8,937,153 (the “153 patent”) , US Patent No. 9,156,887 (the “887 patent”) and US Patent No. 10,280,200 ( the “200 patent”)) describing, in part, by fusing proteins comprising ABDs with small protein drug to increase their circulatory half-life. Noticeably the 887 and 200 patents established non-natural ABDs with sequences significantly different from the earlier US Patent No. 8,937,153 patent. US Patent No. 9,156,887 teaches a protein comprising SEQ ID NOs : 1 - 14 or isolated albumin binding domain comprising an amino acid sequence of SEQ ID NO: 1 having substitutions at 1, 2, 3, 4, 5, or 6, residues. Moreover, the substitutions are only allowed at certain positions, indicated by an X in SEQ ID NOs: 2 - 4. The best ligand had an affinity to human albumin (KD ) of 75 pM, with k_oa of 4.04 E x 10⁵ M^-1s^-1 and k_Off of 3.02 x 10^-5 s’¹. [0009] Surprisingly, the inventors discovered that 7 substitutions could be made to SEQ ID NO: 1 and although the affinity was reduced by over 40-fold to 3 nM, the resulting ligand afforded an effective affinity purification tool. Moreover, these substitutions could be made at positions outside of those taught by US Patent No. 9,156 887.

[0010] In some embodiments, provided herein is an affinity agent that comprises the sequence SEQ ID NO: 15, LREAKERAIEELRRAGISSDYYFDLIQKAKTVEGVQALKDEILKA. A comparison of SEQ ID NO: 15 and SEQ ID NOs: 1 - 14 (i.e. the sequences taught by US Patent No. 9,156,887) is shown in the table below:

[0011] US Patent No. 8,937,153 teaches an engineered albumin binding polypeptide comprising an albumin binding motif, wherein the motif consists of the amino acid sequence: GVSDXsYKXgXgl XI IXI2AXI4TVEGVX20ALX23X24X25I (SEQ ID NO: 16) wherein, independently of each other, X5 is selected from Y and F;

Xg is selected from N, R and S ;

X9 is selected from V, I, L, M, F and Y ;

Xu is selected from N, S, E and D;

Xi2is selected from R, K and N;

Xuis selected from K and R;

X2ois selected from D, N, Q, E, H, S, R and K;

X23 is selected from K, I and T ;

X₂₄is selected from A, S, T, G, H, L and D; and

X25 is selected from H, E and D; with the proviso that the amino acid sequence is not GVSDYYKNLI NNAKTVEGVK ALIDEI; or (US8937153, SEQ ID NO: 517) GVSDYYKNLI NNAKTVEGVN ALKAEI (US Patent No. 8,937,153, SEQ ID NO: 541) and the albumin binding polypeptide binding to albumin such that the KD value of the interaction is at most 1 x 10^-9M.

[0012] US Patent No. 10,155,792 teaches an albumin binding polypeptide comprising an albumin binding motif (BM), wherein the motif consists of the amino acid sequence: (SEQ ID NO: 19) GVSDFYKKLI XaKAKTVEGVE ALKXbXcI wherein, independently of each other, Xa is selected from D and E;

Xb is selected from D and E; and

Xc is selected from A and E, wherein the albumin binding motif has enhanced resistance to clostripain cleavage compared to the motif of SEQ ID NO: 19 with position 8 substituted with R, S, or N. The amino acid sequences of SEQ ID NO: 19 correspond to residues 17 - 44 of SEQ ID NO: 15, i.e. SEQ ID NO: 20. A comparison of SEQ ID NO: 20 and SEQ ID NOs : 1 - 14 (i.e. the sequences taught by US Patent No. 8,937,153 and US Patent No. 10,155,792) is shown in the table below and highlights the differences present in SEQ ID NO: 20.

[0013] Affinity agents that bind a HS A and/or a HS A fusion product that are useful for isolation and/or affinity purification are described herein. Tn some embodiments, an affinity agent comprises a solid support and a ligand.

[0014] In some embodiments, provided herein is an affinity agent that comprises a multimer polypeptide comprising at least two subunits, wherein each subunit comprises a polypeptide according to the aforementioned embodiments.

[0015] In some embodiments, provided herein is an affinity agent that comprise a multimer polypeptide wherein the subunits are not all the same.

[0016] In some embodiments, provided herein is an affinity agent used for the purification of HSA and HSA fusion products.

DEFINITIONS

[0017] In order for the present disclosure to be more readily understood, certain terms are defined below. Unless defined otherwise herein, technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art.

[0018] Approximately or about'. As used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0019] Biologically active'. As used herein, the term “biologically active” refers to a characteristic of any agent that has activity in a biological system, and particularly in an organism. For instance, an agent that, when administered to an organism, has a biological effect on that organism, is considered to be biologically active.

[0020] Conservative and non-conservative substitution: A “conservative” amino acid substitution is one in which one amino acid residue is replaced with another amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art, including basic side chains (e.g., lysine (K), arginine (R), histidine (H)); acidic side chains (e.g., aspartic acid (D), glutamic acid (E)); uncharged polar side chains (e.g., glycine (G); asparagine (N), glutamine (Q) , serine (S), threonine (T), tyrosine (Y), cysteine (C)); nonpolar side chains (e.g., alanine (A), valine (V), leucine (L), isoleucine (I), proline (P), phenylalanine (F), methionine (M), tryptophan (W), beta-branched side chains (e.g., threonine (T), valine (V), isoleucine (I)); and aromatic side chains (e.g., tyrosine (Y), phenylalanine (F), tryptophan (W), histidine (H)). For example, substitution of a phenylalanine for a tyrosine is a conservative substitution. In some embodiments, conservative amino acid substitutions in the sequence of a ligand confer or improve specific binding of the ligand a target of interest. In some embodiments, conservative amino acid substitutions in the sequences of a ligand do not reduce or abrogate the binding of the ligand to a target of interest. In some embodiments, conservative amino acid substitutions do not significantly affect specific binding of a ligand to a target of interest. Methods of identifying nucleotide and amino acid conservative substitutions and nonconservative substitutions which confer, alter or maintain selective binding affinity are known in the art (see, e.g., Brummell, Biochem. 32:1180-1187 (1993); Kobayashi, Protein Eng. 12(10):879-884 (1999); and Burks, PNAS 94:412-417 (1997)). In some embodiments, non-conservative amino acid substitutions in the sequence of a ligand confer or improve specific binding of the ligand a target of interest. In some embodiments, non-conservative amino acid substitutions in the sequences of a ligand do not reduce or abrogate the binding of the ligand to a target of interest. In some embodiments, non- conservative amino acid substitutions do not significantly affect specific binding of a iigand to a target of interest.

[0021] Linker: As used herein a “linker” refers to a peptide or other chemical linkage that functions to link otherwise independent functional domains. In some embodiments, a linker is located between a ligand and another polypeptide component containing an otherwise independent functional domain. In some embodiments, a linker is a peptide or other chemical linkage located between a ligand and a surface.

[0022] Naturally occurring: The term “naturally occurring” when used in connection with biological materials such as a nucleic acid molecules, polypeptides, and host cells, refers to those which are found in nature and not modified by a human being. Conversely, “non-natural” or “synthetic” when used in connection with biological materials refers to those which are not found in nature and/or have been modified by a human being. [0023] “Non-natural amino acids, ” “amino acid analogs ” and “non-standard amino acid residues ” are used interchangeably herein. Non-natural amino acids that can be substituted in a ligand as provided herein are known in the art. In some embodiments, a non-natural amino acid is 4- hydroxyproline which can be substituted for proline; 5-hydroxylysine which can be substituted for lysine; 3 -methylhistidine which can be substituted for histidine; homoserine which can be substituted for serine; and ornithine which can be substituted for lysine. Additional examples of non-natural amino acids that can be substituted in a polypeptide ligand include, but are not limited to molecules such as: D-isomers of the common amino acids, 2,4-diaminobutyric acid, alpha-amino isobutyric acid, A-aminobutyric acid, Abu, 2-amino butyric acid, gamma-Abu, epsilon-Ahx, 6-amino hexanoic acid, Aib, 2-amino isobutyric acid, 3-amino propionic acid, ornithine, norleucine, norvaline, hydroxyproline, sarcosine, citrulline, homocitrulline, cysteic acid, t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, beta-alanine, lanthionine, dehydroalanine, y-aminobutyric acid, selenocysteine and pyrrolysine fluoro-amino acids, designer amino acids such as beta-methyl amino acids, C alpha-methyl amino acids, and N alpha-methyl amino acids.

[0024] “Polynucleotide’’ and “nucleic acid molecule”: As used interchangeably herein, polynucleotide and nucleic acid molecule refer to a polymeric form of nucleotides of any length, either ribonucleotides or deoxyribonucleotides. These terms include, but are not limited to, DNA, RNA, cDNA (complementary DNA), mRNA (messenger RNA), rRNA (ribosomal RNA), shRNA (small hairpin RNA), snRNA (small nuclear RNA), snoRNA (short nucleolar RNA), miRNA (microRNA), genomic DNA, synthetic DNA, synthetic RNA, and/or tRNA.

[0025] Operably linked: The term “operably linked,” as used herein, indicates that two molecules are attached so as to each retain functional activity. Two molecules are “operably linked” whether they are attached directly or indirectly.

[0026] Peptide tag: The term “peptide tag” as used herein refers to a peptide sequence that is part of or attached (for instance through genetic engineering) to another protein, to provide a function to the resultant fusion. Peptide tags are usually relatively short in comparison to a protein to which they are fused. In some embodiments, a peptide tag is four or more amino acids in length, such as, 5, 6, 7, 8, 9, 10, 15, 20, or 25 or more amino acids. In some embodiments, a ligand is a protein that contains a peptide tag. Numerous peptide tags that have uses as provided herein are known in the art. Examples of peptide tags that may be a component of a ligand fusion protein or a target bound by a ligand (e.g., a ligand fusion protein) include but are not limited to HA (hemagglutinin), c-myc, the Herpes Simplex virus glycoprotein D (gD), T7, GST, GFP, MBP, Strep-tags, His-tags, Myc-tags, TAP-tags and FLAG tag (Eastman Kodak, Rochester, N.Y.) Likewise, antibodies to the tag epitope allow detection and localization of the fusion protein in, for example, affinity purification, Western blots, ELISA assays, and immunostaining of cells.

[0027] Polypeptide: The term “polypeptide” as used herein refers to a sequential chain of amino acids linked together via peptide bonds. The term is used to refer to an amino acid chain of any length, but one of ordinary skill in the art will understand that the term is not limited to lengthy chains and can refer to a minimal chain comprising two amino acids linked together via a peptide bond. As is known to those skilled in the art, polypeptides may be processed and/or modified.

[0028] Protein: The term “protein” as used herein refers to one or more polypeptides that function as a discrete unit. If a single polypeptide is the discrete functioning unit and does not require permanent or temporary physical association with other polypeptides in order to form the discrete functioning unit, the terms “polypeptide” and “protein” may be used interchangeably. If the discrete functional unit is comprised of more than one polypeptide that physically associate with one another, the term “protein” refers to the multiple polypeptides that are physically coupled and function together as the discrete unit.

[0029] Specifically binds: As used herein in reference to ligands, the term “specifically binds” or “has selective affinity for” means a ligand reacts or associates more frequently, more rapidly, with greater duration, with greater affinity, or combinations of the above to a particular epitope, protein, or target molecule than with alternative substances, including unrelated proteins. Because of the sequence identity between homologous proteins in different species, specific binding can include a binding agent that recognizes a protein or target in more than one species. Likewise, because of homology within certain regions of polypeptide sequences of different proteins, specific binding can include a binding agent that recognizes more than one protein or target. It is understood that, in certain embodiments, a binding agent that specifically binds a first target may or may not specifically bind a second target. As such, “specific binding” does not necessarily require (although it can include) exclusive binding, i.e. binding to a single target. Thus, a ligand or affinity agent may, in certain embodiments, specifically bind more than one target. In certain embodiments, multiple targets may be bound by the same antigen-binding site on an affinity agent. [0030] Substantially: As used herein, the term “substantially” refers to the qualitative condition of exhibiting total or near-total extent or degree of a characteristic or property of interest. One of ordinary skill in the biological arts will understand that biological and chemical phenomena rarely, if ever, go to completion and/or proceed to completeness or achieve or avoid an absolute result. The term “substantially” is therefore used herein to capture the potential lack of completeness inherent in many biological and chemical phenomena.

[0031] HSA fusion product: As used herein, the term “HSA fusion product” refers to a human serum albumin protein fused to one or more polypeptides and/or proteins. The HSA fusion product can be made through any of a variety of means, for example through genetic engineering and expression of a fusion gene or chemical ligation methods commonly known in the art (e.g., native chemical ligation, expressed protein ligation, Staudinger ligation, Ser/Thr ligation, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A shows an exemplary crystal structure of some of the albumin ligands contemplated herein. The binding interface of the albumin ligands is highlighted by the lighter shading.

[0033] Figure IB shows an exemplary crystal structure of some of the albumin ligands contemplated herein. The positions of the mutations made to SEQ ID NO: 1 to make SEQ ID NO: 15 are highlighted by the lighter shading.

[0034] Figure 2 shows the sensorgram for the biotinylated ligand corresponding to SEQ ID NO: 21 challenged with a titration of HS A in solution.

[0035] Figure 3 shows the overlaid chromatograms before and after repeated cycling an affinity resin of the invention.

[0036] Figure 4 shows the residual HCP levels across 5 purification cycles of an affinity resin of the present invention. Between each cycle the resin was exposed to 0.5 M NaOH for 6 hours.

[0037] Figure 5 shows the yield obtained across 5 purification cycles of an affinity resin of the present invention. Between each cycle the resin was exposed to 0.5 M NaOH for 6 hours.

[0038] Figure 6 shows the static binding capacity as a function of pH for an affinity resin of the invention [0039] Figure 7 shows the influence of elution pH for a particular albumin fusion protein. The overlaid chromatograms for the elution peak (at ~ 26 mL) and CTP peaks (at ~36 mL) are shown for elution pH 9 (Dark, full line), pH 8.25 (Dashed line) and pH 7.4 (Gray line).

[0040] Figure 8 shows the SDS-PAGE analysis for the scavenging of albumin from Fraction V paste to isolate the minor components. The samples loaded in each lane are listed in the following table.

[0041] Figure 9 shows the breakthrough curves for resins prepared from ligands corresponding to SEQ ID Nos: 29 and 34-37 when challenged with HSA @ Img/mL and 7 minute residence time.

DETAILED DESCRIPTION

[0042] The present disclosure encompasses, inter alia, the recognition that affinity agents prepared from identified and characterized ligands are shown to generate highly purified preparations of one or more targets of interest, for example, in some embodiments, a HSA and/or a HSA fusion product. In some embodiments, affinity resins described herein are useful for, inter alia, removal of protein product related impurities as well as the host cell derived contaminants.

Ligand binding to targets of interest for use in an affinity agent

[0043] The characteristics of a ligand binding to a target can be determined using known or modified assays, bioassays, and/or animal models known in the art for evaluating such activity.

[0044] As used herein, terms such as “binding affinity for a target”, “binding to a target” and the like refer to a property of a ligand which may be directly measured, for example, through the determination of affinity constants (e.g., the amount of ligand that associates and dissociates at a given antigen concentration). Several methods are available to characterize such molecular interactions, for example, competition analysis, equilibrium analysis and microcalorimetric analysis, and real-time interaction analysis based on surface plasmon resonance interaction (for example using a BIACORE instrument). These methods are well-known to those of skill in the art and are discussed in publications such as Neri D et al. (1996) Tibtech 14:465-470 and Jansson M et al. (1997) J Biol Chem 272:8189- 8197. [0045] Affinity requirements for a given ligand binding event are contingent on a variety of factors including, but not limited to: the composition and complexity of a binding matrix, the valency and density of both a ligand and a target molecule, and the functional application of a ligand. In some embodiments, a ligand binds a target of interest with a dissociation constant (KD) of less than or equal to 5xl0^-3 M, 10^-3 M, SxlO^-4 M, 10^-4 M, 5xl0^-5 M, or 10^-5 M. In some embodiments, a ligand binds a target of interest with a KD of less than or equal to 5xl0^-6 M, 10^-6 M, 5xl0^-7 M, 10^-7M, 5xl0^-8 M, or 10“⁸ M. In some embodiments, a ligand binds a target of interest with a KD more than or equal to IxlO^-9 M. In some embodiments, a ligand generated by methods disclosed herein has a dissociation constant of from about IO^-4 M to about 10’⁵ M, from about 10’⁵ M to about 10’⁶ M, from about 10’⁶ M to about IO ⁷ M, from about 10’⁷ M to about 10’⁸ M, from about 10’⁸ M to about 10’⁹ M.

[0046] Binding experiments to determine KD and off-rates (k_Off) can be performed in a number of conditions. The buffers in which to make these solutions can readily be determined by one of skill in the art, and depend largely on the desired pH of the final solution. Low pH solutions (<pH 5.5) can be made, for example, in citrate buffer, glycine-HCl buffer, or in succinic acid buffer. High pH solutions can be made, for example, in Tris-HCl, phosphate buffers, or sodium bicarbonate buffers. A number of conditions may be used to determine KD and off-rates for the purpose of determining, for example, optimal pH and/or salt concentrations.

[0047] In some embodiments, a ligand specifically binds a target of interest with a koff ranging from 0.1 to IO’⁷ sec ¹, 10’² to IO ⁷ sec ¹, or 0.5 x 10’² to 10’⁷ sec ¹. In some embodiments, a ligand binds a target of interest with a k_Off of less than 5 xlO^-2 sec^-1, 10’² sec^-1, 5 xlO^-3 sec^-1, or 10’³ sec ¹. In some embodiments a ligand binds a target of interest with a koff of less than 5 xlO^-4 sec^-1, 10’⁴ sec^-1, 5 xlO^-5 sec^-1, or 10’⁵ sec ¹, 5 xlO^-6 sec^-1, 10’⁶ sec ¹, 5 xlO^-7 sec^-1, or 10’⁷ sec^-1. In some embodiments, a ligand specifically binds a target of interest with an on rate (k_on) ranging from about 10³ to 10⁷ M ⁴sec ^-1, 10³ to 10⁶ M^-1sec^-1, or 10³ to 10⁵ M^-1sec^-1. In some embodiments, a ligand (e.g., a ligand fusion protein) binds the target of interest with a k_on of greater than 10³ M^-1sec^-1, 5 xlO³ M^-1sec^-1, 10⁴ M^-1sec^-1, or 5 xlO⁴ M ^sec ¹. In an additional embodiment, a ligand, binds a target of interest with a k_on of greater than 10⁵ M^-1sec^-1, 5 xl0⁵M^-1sec^-1, 10⁶ M’¹ sec^-1, 5 xlO⁶ M’¹ sec^-1, or 10⁷ M^-1 sec^-1. Targets of interest

[0048] Tn accordance with various embodiments, a target of interest specifically bound by a ligand can be any molecule for which it is desirable for a ligand of an affinity agent to bind. For example, a target specifically bound by ligand can be any target of purification, manufacturing, formulation, therapeutic, diagnostic, or prognostic relevance or value. Non-limiting uses include therapeutic and diagnostic uses. A number of exemplary targets are provided herein, by way of example, and are intended to be illustrative and not limiting. A target of interest can be naturally occurring or synthetic. In some embodiments, a target comprises a human serum albumin (HSA) protein or fragment thereof, or an HSA fusion protein.

Linkers

[0049] The terms “linker” and “spacer” are used interchangeably herein to refer to a peptide or other chemical linkage that functions to link otherwise independent functional domains. In some embodiments, a linker is located between a ligand and another polypeptide component containing an otherwise independent functional domain. Suitable linkers for coupling two or more linked ligands may generally be any linker used in the art to link peptides, proteins or other organic molecules. In some embodiments, such a linker is suitable for constructing proteins or polypeptides that are intended for pharmaceutical use.

[0050] Suitable linkers for operably linking a ligand and an additional component of a ligand fusion protein in a single-chain amino acid sequence include but are not limited to, polypeptide linkers such as glycine linkers, serine linkers, mixed glycine/serine linkers, glycine- and serine-rich linkers or linkers composed of largely polar polypeptide fragments.

[0051] In some embodiments, a linker comprises a majority of amino acids selected from glycine, alanine, proline, asparagine, glutamine, and lysine. In some embodiments, a linker comprises a majority of amino acids selected from glycine, alanine, proline, asparagine, aspartic acid, threonine, glutamine, and lysine. In some embodiments, a ligand linker is made up of a majority of amino acids that are sterically unhindered. In some embodiments, a linker comprises a majority of amino acids selected from glycine, serine, and/or alanine. In some embodiments, a peptide linker is selected from polyglycines (such as (Gly)s, and (Gly)s, poly(Gly-Ala), and polyalanines. [0052] Linkers can be of any size or composition so long as they are able to operably link a ligand in a manner that permits the ligand to bind a target of interest. Tn some embodiments, linkers are from about 1 to 50 amino acids, from about 1 to 20 amino acids, from about 1 to 15 amino acids, from about 1 to 10 amino acids, from about 1 to 5 amino acids, from about 2 to 20 amino acids, from about 2 to 15 amino acids, from about 2 to 10 amino acids, or from about 2 to 5 amino acids. It should be clear that the length, the degree of flexibility and/or other properties of the linker(s) may influence certain properties of a ligand for use in an affinity agent, such as affinity, specificity or avidity for a target of interest, or for one or more other target proteins of interest, or for proteins not of interest (i.e., nontarget proteins). In some embodiments, two or more linkers are utilized. In some embodiments, two or more linkers are the same. In some embodiments, two or more linkers are different.

[0053] In some embodiments, a linker is a non-peptide linker such as an alkyl linker, or a PEG linker. For example, alkyl linkers such as -NH-(CH2)_s-C(0)-, wherein s = 2-20 can be used. These alkyl linkers may further be substituted by any non-sterically hindering group such as lower alkyl e.g., Ci- Ce) lower acyl, halogen (e.g., Cl, I, Br, F), CN, NH2, phenyl, etc. An exemplary non- peptide linker is a PEG linker. In some embodiments, a PEG linker has a molecular weight of from about 100 to 5000 kDa, or from about 100 to 500 kDa. In some embodiments, a PEG linker has a molecular weight of from about 100 to 500 kDa.

[0054] Linkers can be evaluated using techniques described herein and/or otherwise known in the art. In some embodiments, linkers do not alter (e.g., do not disrupt) the ability of a ligand to bind a target molecule.

Affinity agents comprising conjugated ligands

[0055] Ligands that promote specific binding to targets of interest can be chemically conjugated with a variety of chromatography compositions (e.g., beads, resins, gels, membrane, monoliths, etc.) to prepare an affinity agent. Affinity agents comprising ligands are particularly useful for purification and manufacturing applications.

[0056] In some embodiments, a ligand (e.g., a ligand fusion protein) contains at least one reactive residue. Reactive residues are useful, for example, as sites for the attachment of conjugates such as chemotherapeutic drugs. An exemplary reactive amino acid residue is lysine. A reactive residue (e.g., lysine) can be added to a ligand at either end, or within the ligand sequence and/or can be substituted for another amino acid in the sequence of a ligand. A suitable reactive residue (e.g., lysine, serine, tyrosine, hydroxytryptophan, etc.) can also be located within the sequence of an identified ligand without need for addition or substitution. In some embodiments, an additional exemplary reactive amino acid residue is cysteine. In some embodiments, a reactive amino acid residue is lysine. In some embodiments, a reactive amino acid is serine. In some embodiments, a reactive amino acid residue is tyrosine. In some embodiments, a reactive amino acid residue is hydroxy tryptophan.

Attachment to solid surface

[0057] “Solid surface,” “support,” or “matrix” are used interchangeably herein and refer to, without limitation, any column (or column material), bead, test tube, microtiter dish, solid particle (for example, agarose or sepharose), microchip (for example, silicon, silicon-glass, or gold chip), or membrane (synthetic (e.g. a filter) or biological (e.g. liposome or vesicle) in origin) to which a ligand, affinity agent, antibody, or other protein may be attached (i.e., coupled, linked, or adhered), either directly or indirectly (for example, through other binding partner intermediates such as other antibodies or Protein A), or in which a ligand or antibody may be embedded (for example, through a receptor or channel). Reagents and techniques for attaching polypeptides to solid supports (e.g, matrices, resins, plastic, etc.) are well-known in the ait. Suitable solid supports include, but are not limited to, a chromatographic resin or matrix (e.g., SEPHAROSE-4 FF agarose beads), the wall or floor of a well in a plastic microtiter dish, a silica based biochip, polyacrylamide, agarose, silica, nitrocellulose, paper, plastic, nylon, metal, and combinations thereof. Ligands and other compositions may be attached on a support material by a non-covalent association or by covalent bonding, using reagents and techniques known in the art. In some embodiments, a ligand is coupled to a chromatography material using a linker.

Production of ligands

[0058] The production of a ligand, useful in practicing several embodiments of provided methods, may be carried out using a variety of standard techniques for chemical synthesis, semi-synthetic methods, and recombinant DNA methodologies known in the art. Also provided are methods for producing a ligand, individually or as part of multi-domain fusion protein, as soluble agents and cell associated proteins. In some embodiments, the overall production scheme for a ligand comprises obtaining a reference protein scaffold and identifying a plurality of residues within the scaffold for modification. Depending on the embodiment, the reference scaffold may comprise a protein structure with one or more alpha-helical regions, or other tertiary structure. Once identified, any of a plurality of residues can be modified, for example by substitution of one or more amino acids. In some embodiments, one or more conservative substitutions are made. In some embodiments, one or more non-conservative substitutions are made. In some embodiments a natural amino acid (e.g., one of alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, or valine) is substituted into a reference scaffold at targeted positions for modification. In some embodiments, modifications do not include substituting in either a cysteine or a proline. After modifications have been made at identified positions desired in a particular embodiment, the resulting modified polypeptides (e.g., candidate ligands) can be recombinantly expressed, for example in a plasmid, bacteria, phage, or other vector (e.g. to increase the number of each of the modified polypeptides). The modified polypeptides can then be purified and screened to identify those modified polypeptides that have specific binding to a particular target of interest. Modified polypeptides may show enhanced binding specificity for a target of interest as compared to a reference scaffold, or may exhibit little or no binding to a given target of interest (or to a non-target protein). In some embodiments, depending on the target of interest, the reference scaffold may show some interaction (e.g. nonspecific interaction) with a target of interest, while certain modified polypeptides will exhibit at least about two fold, at least about five fold, at least about 10 fold, at least about 20 fold, at least about 50 fold, or at least about 100 fold (or more) increased binding specificity for the target of interest. Additional details regarding production, selection, and isolation of ligand are provided in more detail below.

Recombinant expression of ligands

[00591 In some embodiments, a ligand such as a ligand fusion protein is “recombinantly produced,” (i.e., produced using recombinant DNA technology). Exemplary recombinant methods available for synthesizing ligand fusion proteins, include, but are not limited to polymerase chain reaction (PCR) based synthesis, concatemerization, seamless cloning, and recursive directional ligation (RDL) (see, e.g., Meyer et ah, Biomacromolecules 3:357-367 (2002), Kurihara et ah, Biotechnol. Lett. 27:665-670 (2005), Haider et al., Mol. Pharm. 2:139-150 (2005); and McMillan et al., Macromolecules 32(1 l ):3643-3646 (1999)).

[0060] Nucleic acids comprising a polynucleotide sequence encoding a ligand are also provided. Such polynucleotides optionally further comprise one or more expression control elements. For example, a polynucleotide can comprise one or more promoters or transcriptional enhancers, ribosomal binding sites, transcription termination signals, and polyadenylation signals, as expression control elements. A polynucleotide can be inserted within any suitable vector, which can be contained within any suitable host cell for expression.

[0061] The expression of nucleic acids encoding ligands is typically achieved by operably linking a nucleic acid encoding the ligand to a promoter in an expression vector. Typical expression vectors contain transcription and translation terminators, initiation sequences, and promoters useful for regulation of the expression of the desired nucleic acid sequence. Exemplary promoters useful for expression in E. coli include, for example, the T7 promoter.

[0062] Methods known in the art can be used to construct expression vectors containing the nucleic acid sequence encoding a ligand along with appropriate transcriptional/ translational control signals. These methods include, but are not limited to in vitro recombinant DNA techniques, synthetic techniques and in vivo recombination/genetic recombination. The expression of the polynucleotide can be performed in any suitable expression host known in the art including, but not limited to, bacterial cells, yeast cells, insect cells, plant cells or mammalian cells. In some embodiments, a nucleic acid sequence encoding a ligand is operably linked to a suitable promoter sequence such that the nucleic acid sequence is transcribed and/or translated into ligand in a host.

[0063] A variety of host-expression vector systems can be utilized to express a nucleic acid encoding a ligand. A vector containing nucleic acids encoding a ligand (e.g., individual ligand subunits or ligand fusions) or portions or fragments thereof, may include a plasmid vector, a single- stranded phage vector, a double-stranded phage vector, a single- stranded RNA or DNA viral vector, or a doublestranded RNA or DNA viral vector. Phage and viral vectors may also be introduced into host cells in the form of packaged or encapsulated virus using known techniques for infection and transduction. Moreover, viral vectors may be replication competent or alternatively, replication defective. Alternatively, cell-free translation systems may also be used to produce a protein and/or a ligand using RNAs derived from the DNA expression constructs (see, e.g., W086/05807 and W089/01036; and U.S. Pat. No. 5,122,464).

[0064] Generally, any type of cell or cultured cell line can be used to express a ligand provided herein. In some embodiments a background cell line used to generate an engineered host cell is a bacterial cell, a yeast cell or a mammalian cell. A variety of host-expression vector systems may be used to express the coding sequence of a ligand fusion protein. A mammalian cell can be used as a host cell system transfected with recombinant plasmid DNA or a cosmid DNA expression vector containing the coding sequence of the target of interest and the coding sequence of the fusion polypeptide. A cell can be a primary isolate from an organism, culture, or cell line of transformed or transgenic nature. [0065] Suitable host cells include, but are not limited to, microorganisms such as bacteria (e.g., E. coli, B. sublilis) transformed with recombinant bacteriophage DNA, plasmid DNA or cosmid DNA expression vectors containing ligand coding sequences; yeast (e.g., Saccharomyces, Pichia) transformed with recombinant yeast expression vectors containing ligand coding sequences; insect cell systems infected with recombinant virus expression vectors (e.g., Baculovirus) containing ligand coding sequences; plant cell systems infected with recombinant virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing ligand coding sequences.

[0066] Prokaryotes useful as host cells in producing a ligand may include gram negative or gram positive organisms such as, E. coli and B. subtilis. Expression vectors for use in prokaryotic host cells generally contain one or more phenotypic selectable marker genes (e.g., genes encoding proteins that confer antibiotic resistance or that supply an autotrophic requirement). Examples of useful prokaryotic host expression vectors include the pKK223-3 (Pharmacia, Uppsala, Sweden), pGEMl (Promega, Wis., USA), pET (Novagen, Wis., USA) and pRSET (Invitrogen, Calif., USA) series of vectors (see, e.g., Studier, J. Mol. Biol. 219:37 (1991) and Schoepfer, Gene 124:83 (1993)). Exemplary promoter sequences frequently used in prokaryotic host cell expression vectors include T7, (Rosenberg et al., Gene 56:125-135 (1987)), beta-lactamase (penicillinase), lactose promoter system (Chang et al., Nature 275:615 (1978)); and Goeddel et al., Nature 281 :544 (1979)), tryptophan (trp) promoter system (Goeddel et al., Nucl. Acids Res. 8:4057 , (1980)), and tac promoter (Sambrook et al., 1990, Molecular Cloning, A Laboratory Manual, 2d Ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.). [0067] In some embodiments, a eukaryotic host cell system is used. In some embodiments, the eukaryotic host cell system is a yeast cell transformed with a recombinant yeast expression vector containing the coding sequence of a ligand. Exemplary yeast that can be used to produce compositions of the invention, include yeast from the genera Saccharomyces, Pichia, Actinomycetes and Kluyveromyces. Yeast vectors typically contain an origin of replication sequence from a 2mu yeast plasmid, an autonomously replicating sequence (ARS), a promoter region, sequences for polyadenylation, sequences for transcription termination, and a selectable marker gene. Examples of promoter sequences in yeast expression constructs include, promoters from metallothionein, 3- phosphoglycerate kinase (Hitzeman, J. Biol. Chem. 255:2073 (1980)) and other glycolytic enzymes, such as, enolase, glyceraldehyde-3 -phosphate dehydrogenase, hexokinase, pyruvate decarboxylase, phosphofructokinase, glucose-6-phosphate isomerase, 3-phospho glycerate mutase, pyruvate kinase, triosephosphate isomerase, phosphoglucose isomerase, and glucokinase. Additional suitable vectors and promoters for use in yeast expression as well as yeast transformation protocols are known in the art. See, e.g., Fleer, Gene 107:285-195 (1991) and Hinnen, PNAS 75:1929 (1978).

[0068] Insect and plant host cell culture systems are also useful for producing the compositions of the invention. Such host cell systems include for example, insect cell systems infected with recombinant virus expression vectors (e.g., baculovirus) containing the coding sequence of a ligand; plant cell systems infected with recombinant virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing the coding sequence of a ligand, including, but not limited to, the expression systems taught in U.S. Pat. No. 6,815,184; U.S. Publ. Nos. 60/365,769, and 60/368,047; and W02004/057002, W02004/024927, and W02003/078614.

[0069] In some embodiments, a host cell system may be used. In some embodiments, the host cell system is an animal cell system infected with recombinant virus expression vectors (e.g., adenoviruses, retroviruses, adeno-associated viruses, herpes viruses, lentiviruses). In some embodiments, the host cell system is a cell line engineered to contain multiple copies of the DNA encoding a ligand either stably amplified (CHO/dhfr) or unstably amplified in double-minute chromosomes (e.g., murine cell lines). In some embodiments, a vector comprising a polynucleotide(s) encoding a ligand is polycistronic. Exemplary mammalian cells useful for producing these compositions include HEK293 cells (e.g., 293T and 293F), CHO cells, BHK cells, NS0 cells, SP2/0 cells, YO myeloma cells, P3X63 mouse myeloma cells, PER cells, PER.C6 (Crucell, Netherlands) cells VERY, HeLa cells, COS cells, MDCK cells, 3T3 cells, W138 cells, BT483 cells, Hs578T cells, HTB2 cells, BT20 cells, T47D cells, CRL7O30 cells, HsS78Bst cells, hybridoma cells, and other mammalian cells. Additional exemplary mammalian host cells that are useful in practicing the invention include but are not limited, to T cells. Exemplary expression systems and selection methods are known in the art and may include those described in the following references and references cited therein: Borth et al., Biotechnol. Bioen. 71(4):266-73 (2000), in Werner et al., Arzneimittelforschung/Drug Res. 48(8):870-80 (1998), Andersen et al., Curr. Op. Biotechnol. 13:117-123 (2002), Chadd et al., Curr. Op, Biotechnol. 12:188- 194 (2001), and Giddings, Curr. Op. Biotechnol. 12:450-454 (2001). Additional examples of expression systems and selection methods are described in Logan et al., PNAS 81:355-359 (1984), Birtner et al. Methods Enzymol. 153:51-544 (1987)). Transcriptional and translational control sequences for mammalian host cell expression vectors are frequently derived from viral genomes. Commonly used promoter sequences and enhancer sequences in mammalian expression vectors include, sequences derived from Polyoma virus, Adenovirus 2, Simian Virus 40 (SV40), and human cytomegalovirus (CMV). Exemplary commercially available expression vectors for use in mammalian host cells include pCEP4 (Invitrogen) and pcDNA3 (Invitrogen).

[0070] Physical methods for introducing a nucleic acid into a host cell (e.g., a mammalian host cell) include, but are not limited to, calcium phosphate precipitation, lipofection, particle bombardment, microinjection, and electroporation. Methods for producing cells comprising vectors and/or exogenous nucleic acids are well-known in the art. See, for example, Sambrook et al. (2001, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York).

[0071] Biological methods for introducing a polynucleotide of interest into a host cell include the use of DNA and RNA vectors. Viral vectors, and especially retroviral vectors, have become the most widely used method for inserting genes into mammalian cells (e.g., human cells). Other viral vectors may be derived from lentivirus, poxviruses, herpes simplex virus I, adenoviruses and adeno-associated viruses. See, for example, U.S. Pat, Nos. 5,350,674 and 5,585,362.

[0072] Methods for introducing a DNA and RNA polynucleotides of interest into a host cell include, but are not limited to, electroporation of a cell, in which an electrical field is applied to a cell in order to increase the permeability of the cell membrane, allowing chemicals, drugs, or polynucleotides to be introduced into the cell. Ligand containing DNA or RNA constructs may be introduced into a mammalian or prokaryotic cell using electroporation.

[0073] In some embodiments, electroporation of cells results in the expression of a ligand-CAR on the surface of T cells, NK cells, NKT cells. Such expression may be transient or stable over the life of the cell. Electroporation may be accomplished with methods known in the art including MaxCyte GT® and STX® Transfection Systems (MaxCyte, Gaithersburg, MD, USA).

[0074] Chemical means for introducing a polynucleotide into a host cell include colloidal dispersion systems, such as macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. An exemplary colloidal system for use as a delivery vehicle in vitro and in vivo is a liposome (e.g., an artificial membrane vesicle). In the case where a non- viral delivery system is utilized, an exemplary delivery vehicle is a liposome. The use of lipid formulations is contemplated for the introduction of the nucleic acids into a host cell (in vitro, ex vivo or in vivo). In some embodiments, the nucleic acid is associated with a lipid. A nucleic acid associated with a lipid may be encapsulated in the aqueous interior of a liposome, interspersed within the lipid bilayer of a liposome, attached to a liposome via a linking molecule that is associated with both the liposome and the oligonucleotide, entrapped in a liposome, complexed with a liposome, dispersed in a solution containing a lipid, mixed with a lipid, combined with a lipid, contained as a suspension in a lipid, contained or complexed with a micelle, or otherwise associated with a lipid. Lipid, lipid/DNA or lipid/expression vector associated compositions are not limited to any particular structure in solution. For example, they may be present in a bilayer structure, as micelles, or with a “collapsed” structure. They may also be interspersed in a solution, possibly forming aggregates that are not uniform in size or shape. Lipids are fatty substances which can be naturally occurring or synthetic lipids. For example, lipids include the fatty droplets that naturally occur in the cytoplasm as well as the class of compounds which contain long-chain aliphatic hydrocarbons and their derivatives, such as fatty acids, alcohols, amines, amino alcohols, and aldehydes.

[0075] Lipids suitable for use can be obtained from commercial sources. For example, dimyristyi phosphatidylcholine (“DMPC”) can be obtained from Sigma (St. Louis, MO); dicetyl phosphate (“DCP”) can be obtained from K & K Laboratories (Plainview, NY); cholesterol (“Choi”) can be obtained from Calbiochem-Behring; dimyristyi phosphatidylglycerol (“DMPG”) and other lipids may be obtained from Avanti Polar Lipids, Inc. (Birmingham, AL). Stock solutions of lipids in chloroform or chloroform/methanol can be stored at about -20°C. Chloroform may be used as the only solvent since it is more readily evaporated than methanol. “Liposome” is a generic term encompassing a variety of single and multilamellar lipid vehicles formed by the generation of enclosed lipid bilayers or aggregates. Liposomes can be characterized as having vesicular structures with a phospholipid bilayer membrane and an inner aqueous medium. Multilamellar liposomes have multiple lipid layers separated by aqueous medium. They form spontaneously when phospholipids are suspended in an excess of aqueous solution. The lipid components undergo self-rearrangement before the formation of closed structures and entrap water and dissolved solutes between the lipid bilayers (Ghosh et al., Glycobiology 5:505-510 (1991)). However, compositions that have different structures in solution than the normal vesicular structure are also encompassed. For example, the lipids can assume a micellar structure or merely exist as non-uniform aggregates of lipid molecules. Also contemplated are lipofectamine-nucleic acid complexes.

[0076] Regardless of the method used to introduce exogenous nucleic acids into a host cell, the presence of the recombinant nucleic acid sequence in the host cell can routinely be confirmed through a variety of assays known in the art. Such assays include, for example, “molecular biological” assays known in the ail, such as Southern and Northern blotting, RT-PCR and PCR; “biochemical” assays, such as detecting the presence or absence of a particular peptide, e.g., by immunological means (ELISAs and Western blots) or by assays described herein to identify agents falling within the scope of the invention.

[0077] Reporter genes are used for identifying potentially transfected cells and for evaluating the functionality of regulatory sequences. In general, a reporter gene is a gene that is not present in or expressed by the recipient organism, tissue, or cell and that encodes a polypeptide whose expression is manifested by some easily detectable property, e.g., enzymatic activity. Expression of the reporter gene is assayed at a suitable time after the DNA has been introduced into the recipient cells. Suitable reporter genes include, but are not limited to, genes encoding luciferase, beta-galactosidase, chloramphenicol acetyl transferase, secreted alkaline phosphatase, or the green fluorescent protein gene (e.g., Ui-Tei et al., FEBS Lett. 479:79-82 (2000)). Suitable expression systems are known in the art and can be prepared using known techniques or obtained commercially. In general, the construct with the minimal 5' flanking region showing the highest level of expression of reporter gene is identified as the promoter. Such promoter regions can routinely be linked to a reporter gene and used to evaluate agents for the ability to modulate promoter-driven transcription.

[0078] A number of selection systems can be used in mammalian host-vector expression systems, including, but not limited to, the herpes simplex virus thymidine kinase, hypoxanthine-guanine phosphoribosyltransferase and adenine phosphoribosyltransferase (Lowy et al., Cell 22:817 (1980)) genes. Additionally, antimetabolite resistance can be used as the basis of selection for e.g., dhfr, gpt, neo, hygro, trpB, hisD, ODC (ornithine decarboxylase), and the glutamine synthase system.

Ligand purification

[0079] Once a ligand or a ligand fusion protein has been produced by recombinant expression, it can be purified by methods known in the art for purification of a recombinant protein, for example, by chromatography (e.g., ion exchange, affinity, and sizing column chromatography), centrifugation, differential solubility, or by any other standard technique for the purification of proteins. In some embodiments, a ligand is optionally fused to heterologous polypeptide sequences specifically disclosed herein or otherwise known in the art to facilitate purification. In some embodiments, ligands (e.g., antibodies and other affinity matrices) for ligand affinity columns for affinity purification and that optionally, the ligand or other components of the ligand fusion composition that are bound by these ligands are removed from the composition prior to final preparation of the ligand using techniques known in the art.

Chemical synthesis of ligand

[0080] In addition to recombinant methods, ligand production may also be carried out using organic chemical synthesis of the desired polypeptide using a variety of liquid and solid phase chemical processes known in the art. Various automatic synthesizers are commercially available and can be used in accordance with known protocols. See, for example, Tam et al., J. Am. Chem. Soc., 105:6442 (1983); Merrifield, Science, 232:341-347 (1986); Barany and Merrifield, The Peptides, Gross and Meienhofer, eds, Academic Press, New York, 1- 284; Barany et al., Int. J. Pep. Protein Res., 30:705 739 (1987); Kelley et al. in Genetic Engineering Principles and Methods, Setlow, J. K., ed. Plenum Press, NY. 1990, vol. 12, pp. 1-19; Stewart et al., Solid-Phase Peptide Synthesis, W.H. Freeman Co., San Francisco, 1989. One advantage of these methodologies is that they allow for the incorporation of non-natural amino acid residues into the sequence of the ligand.

[0081] The ligand that are used in the methods of the present invention may be modified during or after synthesis or translation, e.g., by glycosylation, acetylation, benzylation, phosphorylation, amidation, pegylation, formylation, derivatization by known protecting/blocking groups, proteolytic cleavage, linkage to an antibody molecule, hydroxylation, iodination, methylation, myristoylation, oxidation, pegylation, proteolytic processing, phosphorylation, prenylation, racemization, selenoylation, sulfation, ubiquitination, etc. (See, e.g., Creighton, Proteins: Structures and Molecular Properties, 2d Ed. (W.H. Freeman and Co., N.Y., 1992); Postranslational Covalent Modification of Proteins, Johnson, ed. (Academic Press, New York, 1983), pp. 1-12; Seifter, Meth. Enzymol., 182:626- 646 (1990); Rattan, Ann. NY Acad. Sci., 663:48-62 (1992).) In some embodiments, the peptides are acetylated at the N-terminus and/or amidated at the C-terminus.

[0082] Any of numerous chemical modifications may be carried out by known techniques, including, but not limited to acetylation, formylation, etc. Additionally, derivatives may contain one or more non- classical amino acids.

[0083] In some embodiments cyclization, or macrocyclization of the peptide backbone is achieved by sidechain to sidechain linkage formation. Methods for achieving this are well known in the ail and may involve natural as well as unnatural amino acids. Approaches includes disulfide formation, lanthionine formation or thiol alkylations (e.g. Michael addition), amidation between amino and carboxylate sidechains, click chemistry (e.g. azide - alkyne condensation), peptide stapling, ring closing metathesis and the use of enzymes.

Affinity agents for purification

[0084] In purification based on affinity chromatography, a target of interest (e.g. protein or molecule) is selectively isolated according to its ability to specifically and reversibly bind to a ligand that may be covalently coupled to a chromatographic matrix. In some embodiments, ligands may be used as reagents for affinity purification of targets of interest from either recombinant sources or natural sources such as biological samples (e.g., serum, a cell).

[0085] In some embodiments, a ligand that specifically binds a target of interest is immobilized on beads and then used to affinity purify the target. [0086] Methods of covalently coupling proteins to a surface are known by those of skill in the art. Peptide tags that can be used to attach a ligand to a solid surface are known to those of skill in the art. Further, a ligand may be attached (i.e., coupled, linked, or adhered) to a solid surface using any reagents or techniques known in the art. In some embodiments, a solid support comprises beads, glass, slides, chips and/or gelatin. Thus, a series of ligands can be used to make an array on a solid surface using techniques known in the art. For example, U.S. Publ. No. 2004/0009530 discloses methods for preparing arrays.

[0087] In some embodiments, a ligand is used to isolate a target of interest (e.g., HSA or an HSA fusion protein) by affinity chromatography. In some embodiments, a ligand is immobilized on a solid support. The ligand can be immobilized on the solid support using techniques and reagents described herein or otherwise known in the art. Suitable solid supports are described herein or otherwise known in the art and in specific embodiments are suitable for packing a chromatography column. The immobilized ligand may be loaded or contacted with a solution under conditions favorable to form a complex between the ligand and the target of interest. Non-binding materials may be washed away. Suitable wash conditions can readily be determined by one of skill in the art. Examples of suitable wash conditions are described in Shukla and Hinckley, Biotechnol Prog. 2008 Sep-Oct;24(5):1115- 21. doi: 10.1002/btpr.50.

[0088] In some embodiments, chromatography is carried out by mixing a solution containing a target of interest and a ligand followed by isolation of complexes of a target of interest and a ligand. For example, a ligand is immobilized on a solid support such as beads, then separated from a solution along with a target of interest by filtration. In some embodiments, a ligand is a fusion protein that contains a peptide tag, such as a poly-HIS tail or streptavidin binding region, which can be used to isolate the ligand after complexes have formed using an immobilized metal affinity chromatographic resin or streptavidin-coated substrate. Once separated, a target of interest can be released from the ligand under elution conditions and recovered in a purified form.

[0089] In some embodiments, a ligand is isolated that includes the initiator N-terminal methionine since that is the protein sequence encoded by the DNA. In some embodiments, a ligand is isolated without the N-terminal methionine residue. In some embodiments, a mixture is obtained with only a proportion of the purified ligand containing the N-terminal methionine. It is obvious to those skilled in the art that the presence or absence of the N-terminal methionine does not affect the conclusions herein.

EXAMPLES

Example 1

[0090] Recombinant protein ligands were expressed in E. Coli and/or Pichia Pastoris using standard techniques. Ligands were purified using multi-column chromatography. For HIS-tagged ligands IMAC was used as the primary capture step. The purity and identity of recombinant protein ligands was assessed by a combination of SDS-PAGE, RP UPLC, quadrupole time-of-flight mass spectrometry and SEC. Biotinylated ligands were generated by coupling to Maleimide-PEG2 -biotin. In many instances the ligand is isolated without the N-terminal methionine residue, which is presumed to be cleaved during expression. In many instances a mixture is obtained with only a proportion of the purified ligand containing the N-terminal methionine. One of skill in the art will appreciate that the presence or absence of the N-terminal methionine does not affect the conclusions herein. For clarity, we include the N-terminal methionine.

Example 2

[0091] This example demonstrates the binding of a biotinylated ligand to albumin molecules using biolayer interferometry (ForteBio, Menlo park, CA). The biotinylated ligand corresponding to SEQ ID NO: 21 was immobilized on sensors and incubated with solutions containing albumin protein at various concentrations. An example sensorgram is shown in Figure 2 for the binding to HSA. The binding curves were fitted with a 1:1 binding model using the ForteBio software to determine the affinity and the resulting data is shown in Table 1.

Table 1. Affinity data for binding of albumin and albumin fusion proteins (AFPs) to the ligand corresponding to SEQ ID NO: 21:

Example 3

[0092] This example demonstrates the production and characterization of affinity agents comprising ligands identified and described herein. Affinity resins were prepared by conjugating ligands to either bromoacetyl or epoxy activated Praesto® Jetted A50 beads (Purolite, King of Prussia, PA) or ABT700 (Agarose Bead Technologies, Madrid, Spain) agarose beads.

[0093] Bromoacetyl activated beads were activated with disuccinimidyl carbonate and coupled with excess ethylenediamine. After washing bromoacetate was conjugated to the aminated beads using EDC activation. After washing ligands were conjugated to the beads at room temperature. Epoxy activated beads were either obtained from the vendor or prepared using standard methods well known in the art. Ligands were coupled to epoxy activated beads at 37 - 40 °C. Targeted ligand densities were varied from 5 - 20 g/L. After washing, the beads were deactivated with excess thioglycerol. The actual ligand density for all resins was measured using a subtractive RP-HPLC method according to the following formula:

Actual Ligand Density = (Measured [ligand] in feed - Measured [ligand] in effluent).

Example 4

This example demonstrates the binding characteristics of affinity chromatography resins prepared from affinity ligands described herein. Monomeric and multimeric ligands, including multimers in which the domains are different, were conjugated to bromoacetyl activated resin and the static binding capacity determined according to the following process.

1. Washes (water, 3 x 5 min shaking)

2. 0.1 M NaOH pre-treatment: 5 min with shaking

3. Neutralization and PBS washes: 2 x 5 min shaking 4. Challenge with HSA target at 20 mg/mL with shaking for 1 hour

5. Drain and assay

6. Wash 3x with PBS and assay

Table 2. The static binding capacity of monomer and multimer ligands. A domain containing SEQ ID NO: 15 is designated by a circle (“O”) and an “X” denotes a non-binding domain.

Example 5

[0094] This example demonstrates repeated use of affinity agents comprising binding ligands described herein for affinity purification of an albumin fusion protein and the stability of the resin towards NaOH. Clarified cell culture feed stream (CCCF) from a CHO cell line was spiked with albumin fusion protein at a titer of 1.0 g/L. A resin prepared from the ligand corresponding to SEQ ID NO. 21 was packed into a 0.3 x 10 cm (0.707 mL) column. The column was operated for 5 cycles, with each cycle comprising the procedure shown in the following table.

[0095] The overlaid chromatogram from the first and 5th cycle is shown in Figure 3. The residual HCP content of the purified protein was measured using the Cygnus™ CHO Host Cell Proteins 3^rd Generation assay for all 5 cycles. The results demonstrated high purity was achieved and maintained for all cycles and is shown in Figure 4. Consistent yields were obtained across all 5 cycles and are shown in Figure 5. In summary, the resin performed as well after 30 hours exposure to 0.5 M NaOH as it did on the first cycle.

Example 6

[0096] This example demonstrates the pH of the binding solution can be manipulated to increase binding capacity. A resin prepared from the ligand corresponding to SEQ ID NO. 21 was used in a static binding (Filter plate) experiment. As shown in Figure 6, higher binding capacity was achieved at pH 5 relative to higher pH.

Example 7

[0097] This example demonstrates that affinity resins with high binding capacities can be achieved with ligands of the invention. Affinity resins were prepared with the ligand corresponding to SEQ ID NO: 29 conjugated to either bromoacetyl or epoxy activated Jetted A50 agarose beads and packed into 3 x 50 mm columns to determine the dynamic binding capacities (DBCs) of the resins using HSA as a test substrate.

Example 8

[0098] This example demonstrates the influence of the elution pH for a particular albumin fusion protein. The elution solution comprised 0.5 M Proline, 20% hexanediol at pH 9, 8.25 and 7.4. For pH 9, 50 mM Glycine was included as buffer, 50 mM HEPES for pH 8.25, and phosphate for pH 7.4. The sharpest peak and highest yield was obtained at pH 9, as shown in Figure 7.

Example 9

[0099] This example demonstrates that the resin can be used to selectively remove albumin from protein preparations. The albumin content of Faction V paste from the Cohn process is greater than 95% of the total protein with small amounts of other serum proteins. Fraction V paste (Seraplex, Pasadena, CA) was re-solubilized in 10 mM acetate buffer pH 4.7 and then adjusted to pH 7.4 with 1 M tris and filtered. The solution was applied to a 100 mL column containing resin prepared with the ligand corresponding to SEQ ID NO: 29 conjugated to epoxy activated Jetted A50 agarose beads. The equivalent of approximately 10 g of paste was loaded onto the column and chased with PBS. The flow through was collected and analyzed by SDS PAGE. As shown in Figure 8, the column effectively removed the albumin and afforded a mixture of proteins free of albumin. The lanes of Figure 8 were loaded as follows:

Example 10

[00100] This example demonstrates that the linker influences the binding capacity of the resin. 5 Ligands were conjugated to epoxy activated A50 beads at the ligand density indicated in the example below. The resulting resins were packed into 0.3 x 5 cm columns and DBCs were determined at 7 minute residence time using HSA @ 1 mg/mL . The breakthrough curves shown in Figure 9 and the table below indicate that resins prepared from SEQ ID NOs:34, 36 and 37 had the highest binding capacity.

Table 3. SEQUENCES

Claims

1. An affinity agent comprising a ligand comprising the sequence SEQ ID No: 15 LREAKERAIEELRRAGISSDYYFDLIQKAKTVEGVQALKDEILKA, or an amino acid sequence that differs by no more than three, by no more than two, or by no more than one, substitutions, additions, or deletions, wherein the ligand binds to albumin such that the KD value of the interaction is at most 1 x IO"⁹ M.

2. The affinity agent of claim 1, which binds to serum albumin and/or one or more serum albumin fusion proteins.

3. The affinity agent of claim 1 or claim 2 that binds to human serum albumin and/or one or more human albumin fusion proteins.

4. An affinity agent comprising a ligand that binds human serum albumin and/or human albumin fusion proteins comprising at least one sequence of any one of SEQ ID NOs: 21 - 37, or an amino acid sequence that differs by no more than three, by no more than two, or by no more than one, substitutions, additions, or deletions.

5. The affinity agent of any one of claims 1 - 4, that comprise a multimer polypeptide, wherein the multimer polypeptide comprises at least two subunits; and wherein each subunit comprises or consists of a polypeptide (e.g. ligand) according to any one of claims 1 - 4.

6. The affinity agent of claim 5, wherein the subunits are not all the same.

7. The affinity agent according to any one of claims 1-6, wherein the ligand is attached to a solid surface.

8. The affinity agent of claim 7, wherein the solid surface is a resin or a bead.

9. The affinity agent of claim 7, wherein the solid surface is a membrane.

10. The affinity agent of claim 7, wherein the solid surface is a monolith.

11. The affinity agent of any one of claims 7 to 10, wherein the ligand is conjugated to the solid surface via a linker.

12. An affinity agent of any one of claims 1-11, that is used for purification of a human serum albumin or human albumin fusion proteins.

13. A method of making an affinity agent comprising conjugating a ligand according to any one of claims 1-11 to a solid surface.