WO2007044887A2 - Method for producing a population of homogenous tetravalent bispecific antibodies - Google Patents

Method for producing a population of homogenous tetravalent bispecific antibodies Download PDF

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WO2007044887A2
WO2007044887A2 PCT/US2006/040029 US2006040029W WO2007044887A2 WO 2007044887 A2 WO2007044887 A2 WO 2007044887A2 US 2006040029 W US2006040029 W US 2006040029W WO 2007044887 A2 WO2007044887 A2 WO 2007044887A2
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antibody
immunoglobulin
fab
engineered
method
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WO2007044887A3 (en
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James Larrick
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Transtarget, Inc.
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    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K16/00Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/46Hybrid immunoglobulins
    • C07K16/468Immunoglobulins having two or more different antigen binding sites, e.g. multifunctional antibodies
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL, OR TOILET PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6849Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a receptor, a cell surface antigen or a cell surface determinant
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL, OR TOILET PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6851Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell
    • A61K47/6855Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody targeting a determinant of a tumour cell the tumour determinant being from breast cancer cell
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61KPREPARATIONS FOR MEDICAL, DENTAL, OR TOILET PURPOSES
    • A61K47/00Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient
    • A61K47/50Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates
    • A61K47/51Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent
    • A61K47/68Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment
    • A61K47/6835Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site
    • A61K47/6875Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody being a hybrid immunoglobulin
    • A61K47/6879Medicinal preparations characterised by the non-active ingredients used, e.g. carriers or inert additives; Targeting or modifying agents chemically bound to the active ingredient the non-active ingredient being chemically bound to the active ingredient, e.g. polymer-drug conjugates the non-active ingredient being a modifying agent the modifying agent being an antibody, an immunoglobulin or a fragment thereof, e.g. an Fc-fragment the modifying agent being an antibody or an immunoglobulin bearing at least one antigen-binding site the antibody being a hybrid immunoglobulin the immunoglobulin having two or more different antigen-binding sites, e.g. bispecific or multispecific immunoglobulin
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K16/00Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/28Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants
    • C07K16/2803Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants against the immunoglobulin superfamily
    • C07K16/2809Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against receptors, cell surface antigens or cell surface determinants against the immunoglobulin superfamily against the T-cell receptor (TcR)-CD3 complex
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K16/00Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies
    • C07K16/18Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans
    • C07K16/32Immunoglobulins [IGs], e.g. monoclonal or polyclonal antibodies against material from animals or humans against translation products of oncogenes
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/20Immunoglobulins specific features characterized by taxonomic origin
    • C07K2317/21Immunoglobulins specific features characterized by taxonomic origin from primates, e.g. man
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/50Immunoglobulins specific features characterized by immunoglobulin fragments
    • C07K2317/52Constant or Fc region; Isotype
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/50Immunoglobulins specific features characterized by immunoglobulin fragments
    • C07K2317/55Fab or Fab'
    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07KPEPTIDES
    • C07K2317/00Immunoglobulins specific features
    • C07K2317/60Immunoglobulins specific features characterized by non-natural combinations of immunoglobulin fragments
    • C07K2317/62Immunoglobulins specific features characterized by non-natural combinations of immunoglobulin fragments comprising only variable region components
    • C07K2317/626Diabody or triabody

Abstract

The present invention is directed toward methods and compositions for generating a homogenous population of tetravalent bispecific antibodies.

Description

METHOD FOR PRODUCING A POPULATION OF HOMOGENOUS TETRAVALENT BISPECIFIC ANTIBODIES

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application claims priority to United States Provisional Patent Application number 60/725,714 filed October 11, 2005, which is herein incorporated by reference in its entirety.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] NOT APPLICABLE

REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER

PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK. [0003] NOT APPLICABLE

BACKGROUND OF THE INVENTION

[0004] An antibody binds with high affinity and specificity to a single antigen and can therefore be used to target cells, protein, etc. Bispecific antibodies, on the other hand, are engineered molecules that have two distinct specificities. They can be used to bring two different entities into proximity. One non-limiting example is the use of a bispecific antibody in which one specificity is for binding to a cancer cell and the other specificity is for binding to an activated T-cell. Such a bispecific molecule can be used therapeutically, since it can cause a T-cell to come into close contact with a cancer cell, and this can lead to selective destruction of the latter. Another non-limiting example is to use a bispecific antibody to recruit stem cells into a particular tissue (e.g. cardiac tissue). One of the specificities of such bispecific antibodies could be towards the target tissue, and the other specificity towards the stem cell that is being targeted.

[0005] Because antibodies consist of two heavy chains and two light chains, it has been difficult to produce homogeneous populations of bispecific antibodies. The present application addresses this need by providing methods for producing homogenous populations of tetravalent bispecific antibodies.

[0006] Several approaches have been used in the antibody engineering community to create homogeneous bispecific antibodies (BiMabs), but each of these suffers from drawbacks. Most methods rely on co-expressing two antibodies in the same cell. This solves the size heterogeneity issue, since all species have two heavy and two light chains (H2L2), but there are still 9 different compositions of such species (Millstein and Cuello, (1983) Nature 305:537-540). This can be alleviated by engineering the interchain interaction surfaces, but this method has variable success (Carter, (2001) J. Immunol. Methods 248:7-15). Other methods (reviewed in Peipp and Valerius, (2002) Biochem. Soc. Transactions 30:507-5111), such as the creation of diabodies, (two scFv's tethered together), heterospecific F(ab)'2, etc, suffer from being monovalent with respect to each type of target cell. Because bivalency can increase the avidity towards target cells by orders of magnitude, preferred formats retain the bivalency with respect to each specificity.

[0007] The method of this invention is superior to other methods that have been described in the literature because the products are bivalent with respect to both binding specificities, therefore increasing the avidity for both targets, and are produced with greater homogeneity because the method does not rely on stochastic coupling reactions or light chain-heavy chain associations.

BRIEF SUMMARY OF THE INVENTION

[0008] The present invention provides methods for producing homogenous populations of tetravalent bispecific antibodies, hi general, the method involves obtaining a population of Fab fragments recombinantly engineered to have a cysteine residue in the constant region of either the heavy or light chain; obtaining a population of immunoglobulin molecules with a cysteine residue recombinantly engineered into the constant region of the heavy chain; reacting the Fab fragments with a molar excess of a bifunctional crosslinking reagent having thiol reactive moieties able to form a stable disulfide linkage with the engineered cysteine residue; removing the unreacted bifunctional crosslinking reagents; and contacting the Fab fragments joined to the bifunctional crosslinking agent with the immunoglobulins such that the crosslinking reagent forms a disulfide bond with the engineered cysteine residue in the heavy chain of the constant region of the immunoglobulin. [0009] In some embodiments the cysteine residue, engineered into the Fab fragment and the immunoglobulin, is located within the 10 most C-terminal amino acid residues of the Fab fragment or immunoglobulin. In other embodiments, the cysteine residue is located within the 20 most C-terminal amino acid residues of the Fab fragment or immunoglobulin. In some embodiments the cysteine residue is introduced into the constant region of the light chain of the Fab. In other embodiments the cysteine residue is introduced into the constant region of the heavy chain of the Fab. In other embodiments, the cysteine is engineered into the CH3 domain of the immunoglobulin heavy chain, and in still other embodiments, the cysteine residue is located within the 50 most C-terminal amino acid residues of the heavy chain constant region. In yet other embodiments, the cysteine is located within the most 40, 35, 30, or 25 C-terminal amino acid residues of the immunoglobulin heavy chain. In still other embodiments, the engineered cysteine residue is a mutation of serine 415 of an IgG subclass (e.g. human IgGl or IgG4, mouse IgGl, or Guinea pig IgG2). With respect to the human IgGl and IgG4, serine 415 is the sixth serine from the C-terminal end of the heavy chain constant region. With respect to the mouse IgGl , serine 415 is the fifth serine from the C- termini, and in the Guinea pig IgG2, serine 415 is the fourth serine from the C-terminal end of the heavy chain constant region.

[0010] In some embodiments, the immunoglobulin is an IgG, while in other embodiments the immunoglobulin is an IgA. In other embodiments, the immunoglobulin is a member of an immunoglobulin subclass, e.g. IgGl, or IgG4. In still other embodiments, the immunoglobulin can be an IgD, IgE, or IgM. In still other embodiments of the invention, the Fab fragment is produced via proteolytic cleavage using proteolytic enzymes known in the art (e.g. papain or pepsin).

[0011] In some embodiments the bifunctional crosslinking reagent is homobifunctional. In alternative embodiments the crosslinking reagent can be heterobifunctional. In some embodiments, the crosslinking agent is between 10 and 50 angstroms in length. In other embodiments, the crosslinker is less than 50 angstroms in length.

[0012] In yet another embodiment, the linker between the thiol reactive groups of the bifunctional crosslinking agent is a polyether ester. In some embodiments the bifunctional cross linking agent is 1,8-bis-maleimidodiethyleneglycol, while in other embodiments the bifunctional cross linking agent is 1,11-bis-maleimidotriethyleneglycol. [0013] In yet another embodiment of the invention the tetravalent bispecific antibody comprises an intact immunoglobulin with two heavy chains and two light chains, each heavy chain of which, is conjugated to a Fab through a linker of 10 to 50 angstroms via cysteines engineered into the constant region of the immunoglobulin heavy chains and the constant region of either the heavy or light chain of the Fab, and the two immunoglobulin heavy chains linked to each other by disulfide bonds.

[0014] In some embodiments, one part of the tetravalent bispecific antibody binds to a protein on the surface of a stem cell. In other embodiments one part of the tetravalent bispecific antibody binds to a protein on a cardiac cell. In still other embodiments, one part of the tetravalent bispecific antibody binds to a protein associated to diseased tissue, e.g. , bone marrow, atherosclerotic lesions, brain, heart or kidney. In still yet another embodiment, one part of the tetravalent bispecific antibody binds to a protein associated with a pathogen.

BRIEF DESCRIPTION OF THE DRAWINGS [0015] Figure 1 shows the method for creating a bispecific tetravalent antibody. Figure IA shows the general method where the Fab fragment (antibody 1) is first joined to the bifunctional crosslinking agent before reacting with the immunoglobulin (antibody 2) in the second step to create the tetravalent bispecific antibody. Figure IB shows the general method where the immunoglobulin (antibody 2) is first joined to the bifunctional crosslinking agent before reacting with the Fab fragment (antibody 1) in the second step to create the tetravalent bispecific antibody.

[0016] Figure 2 shows the successful expression of mutant IgG. Both the wild type and S415C mutant IgG proteins were produced in mammalian cells and identified by Western blot probed with an anti-human Fc antibody.

[0017] Figure 3 shows the nucleotide (SEQ ID NO 1) and amino acid (SEQ ID NO 2) for a CHl heavy chain wildtype followed by His and myc tags and the nucleotide (SEQ ID NO 3) and amino acid (SEQ ID NO 4) for the Fab heavy chain containing the engineered cysteine residue.

[0018] Figure 4 shows the purification of Fab protein containing an additional cysteine residue in the C-terminus. The Fab-cys expression vector was used to transform E coli. Proteins from the total cell lysate were run over a nickel column (N), a protein L column (L), or sequentially over nickel and protein L columns (NL) or protein L and nickel columns (LN). Elution fractions (E) were collected and samples analyzed in a non-reducing SDS PAGE gel. Protein was detected by Western blot using an anti-Ig kappa chain antibody. LCD = light chain dimer. LCM = light chain monomer.

[0019] Figure 5 shows an amino acid sequence alignment of the CH3 domain of the heavy chain for guinea pig IgGl (SEQ ID NO 5) guinea pig IgG2 (SEQ ID NO 6) mouse IgGl (SEQ ID NO 7) mouse IgG2a (SEQ ID NO 8) human IgGl (SEQ ID NO 9) and human IgG4 (SEQ ID NO 10). The serine at position 415 is suitable for mutation to a cysteine for producing a tetravalent bispecifϊc antibody as described herein.

DETAILED DESCRIPTION OF THE INVENTION Definitions [0020] The term "Fab fragment" as used herein refers to a light chain (comprised of both the variable (VL) and constant (CL) regions) dimerized to a variable heavy chain-constant heavy chain 1(VH-CHI). Although the methods disclosed herein rely in general on Fab fragments generated through recombinant means, the present invention is also intended to include the use of proteolytically produced Fab fragments.

[0021] Originally, Fab fragments were produced through proteolytic cleavage using papain or other proteases to digest the immunoglobulin. Generally, papain digestion of an immunoglobulin produces Fab fragments by cleavage N-terminal to the cysteine residues in the hinge region. By contrast, pepsin digestion typically cleaves the immunoglobulin C- terminal to the cysteines in the hinge region, yielding the F(ab')2 fragments, consisting of two Fab' fragments covalently joined by disulfide bonds from the hinge region. As used herein, the term "Fab fragment" is meant to encompass the classical papain-produced Fab fragment as well as the pepsin-produced Fab' fragment, as well as any recombinant Fab or Fab' fragments, including those with recombinantly attached affinity or detection tags, polypeptide linkers, and other conservative modifications known to persons of skill in the art.

[0022] An "antibody" as used herein is a polypeptide that is encoded by an immunoglobulin gene or a functional fragment thereof that specifically binds to and recognizes an antigen (e.g. an antigen expressed on a T-cell such as CD3). The antibody is comprised of at least one binding domain formed from the folding of variable domains of an antibody molecule to form three-dimensional binding spaces with a surface shape and charge distribution complementary to the features of an antigenic determinant of an antigen which allows for an immunological reaction with the antigen. The term "antigenic determinant" refers to that portion of an antigen molecule that determines the specificity of the antigen- antibody reaction.

[0023] The term "immunoglobulin" as used herein refers to a polypeptide encoded by an immunoglobulin gene. The recognized immunoglobulin genes include kappa, lambda, alpha, gamma, delta, epsilon, and mu constant region genes, as well as the myriad of immunoglobulin variable region genes. "Light chains" (about 25 IdDa) are classified as either kappa or lambda. "Heavy chains" (about 50-70 IcDa) are classified as gamma, mu, alpha, delta, or epsilon, which in turn define the immunoglobulin classes IgG, IgM, IgA, IgD, and IgE, respectively.

[0024] In view of all of the possible modifications that can be introduced in making an immunoglobulin suitable for use with the present invention, we define an immunoglobulin to have as a minimum at least the following characteristics. At a minimum, the immunoglobulin for the purposes described herein comprises a two chain antigen-specific protein having either complementary determining regions (CDRs) from a naturally generated antibody or framework sequences having originated from an animal.

[0025] An exemplary immunoglobulin structural unit comprises a tetramer. Each tetramer, (i.e., holo-antibody) is composed of two identical pairs of polypeptide chains, each pair having one light chain and one heavy chain. The N-terminus of each chain defines a variable region of about 100-110 or more amino acids that is primarily responsible for antigen recognition.

[0026] The term "bispecific tetravalent antibody" as used herein refers to a bispecific antibody that is bivalent for each specificity. For example, a first holo-antibody having two binding domains recognizing a first specificity (i.e. bivalent specificity for the first epitope) is conjugated to two Fab fragments, each of which has a binding domain recognizing a second specificity (i.e. bivalent specificity for the second epitope). The resultant bispecific antibody has a total of four binding domains (i.e. tetravalent) with two binding domains (i.e. bivalent) directed toward each of the two specificities.

[0027] The term "cysteine" as used herein refers to one of the naturally occurring nonessential amino acids. The chemical name for cysteine is 2-amino-3-mercaptopropanoic acid. Cysteine is unique in that it contains a thiol group (-SH) bonded to a carbon atom. [0028] The term "thiol reactive moiety" as used herein refers to any compound that reacts with a thiol group, which is a sulfhydral (-SH) group attached to a carbon atom. An exemplary thiol reactive moiety is maleimide, which reacts with -SH groups to form stable thioether linkages. Additional non-limiting exemplary thiol reactive groups that are suitable for use with the present invention may include pyridyl disulfides and -haloacetyls.

[0029] The term "homobifunctional crosslinking agent" as used herein refers to a cross- linking agent where the reactive moieties on each end are the same. For example two reactive maleimide groups joined by a variable length water-soluble spacer such as 1,8-bis- maleimidodiethyleneglycol. Typically the spacer separating the reactive moieties is between about 10 to about 50 angstroms. The spacers may be comprised of a variety of molecules, including alkanes -(CH2)n- where n is from about 3 to about 12 and polyether esters (e.g. PEG/PEO) where the PEO bridge is from about 4 to about 15.

Introduction

[0030] The present invention allows for construction of homogeneous bispecific antibodies that are bivalent with respect to each specificity. In one aspect of the present invention, a first antibody is produced as a recombinant Fab fragment with a natural or engineered single cysteine residue at or near the C-terminus of the heavy chain or the light chain. La a preferred embodiment, the cysteine is at the C-terminus of the naturally occurring sequence of the heavy chain of the Fab fragment. Such recombinant Fab fragments are produced and purified using methods known in the art and as described in more detail below. In parallel, a second antibody is produced and consists of an immunoglobulin with an engineered heavy chain, such that a single engineered cysteine residue is present at or near the C-terminus of the heavy chain, preferably in the Fc domain, still more preferably in the CH3 domain, and still more preferably at a position in the CH3 domain that faces away from the heavy chain-heavy chain dimer interface, such that the two engineered cysteines, one on each heavy chain, are at least 25 angstroms apart from each other in the three dimensional Fc structure, and are positioned in a sterically unhindered region (e.g. in a particular embodiment, the native side- chain of the engineered cysteine is at least 50% solvent exposed) allowing for conjugation to the Fab fragments. This second antibody is produced and purified using methods known in the art and described in more detail below. In order to conjugate the Fab fragment and the immunoglobulin together, in a first step the recombinant Fab fragment is reacted with a large excess of a homobifunctional crosslinking reagent in which each reactive moiety is thiol- reactive and therefore reacts with the unique cysteine residue on the C-tenninus of the recombinant Fab fragment. Since the cross-linking compound is in vast excess over the Fab stoichiometrically, the formation of doubly reacted crosslinker to form dimeric Fab fragments is minimized. After this reaction, the unreacted crosslinldng agent is then removed. Next, the crosslinker-conjugated Fab fragments are then mixed with the cysteine-containing immunoglobulin allowing for the formation of the immunoglobulin crosslinked to the Fab fragment. These resulting molecules are tetravalent, consisting of two binding sites from the Fab fragments and two binding sites from the immunoglobulin. Alternatively, the homobifunctional crosslinking agent may be added first to the holoantibody, followed by removal of the unreacted crosslinldng agent. The cross-linker conjugated holoantibody is then mixed with the cysteine-containing Fab fragments allowing formation of the immunoglobulin crosslinked to the Fab fragment. The general methodology is illustrated in Figure IA and IB and described in more detail below.

Obtaining a population of Fab fragments having an engineered cysteine residue [0031] In one embodiment of the invention, the first step in generating the tetravalent bispecific antibodies is obtaining a population of Fab fragments engineered to contain a single cysteine residue in the constant region of either the heavy or light chain. Typically, the engineered Fab fragment will be produced using recombinant DNA methodologies well known to a person of skill in the art. In cases where the DNA sequence for the antibody is not known, it may be sequenced from the genome of the hybridoma from which the antibody is derived. Once the DNA sequence for the antibody is known, the variable regions may be constructed by gene assembly (Stemmer et al., Gene 16:49-53 (1995)) using overlapping oligonucleotides and confirmed by DNA sequencing. A point mutation can then be introduced into the sequence of the light or heavy chain constant region at or near (within 10 amino acids) the C-termini of the Fab fragment using standard molecular biology techniques, such as PCR.

[0032] The DNA sequences encoding the variable heavy and light chains (VH and VL) along with the constant heavy and light chains (CHI and CL) having the engineered cysteine residue are near the C-termini of one of the constant regions are cloned into an expression vector for expressing the Fab fragments. The vector, under the control of an inducible promoter, may have a single bicistronic message encoding both the heavy chain (VH + CRI) as well as the entire light chain (VL + CL ) followed by myc and his tags for identification and purification of the Fab fragments. In certain embodiments, the use of an internal ribosome entry site (IRES) sequence may be used to create the bicistronic message (see, U.S. pat. Nos. 5925,565 and 5,935,819).

[0033] Expression systems utilized in the generation of the Fab fragments of the invention are commercially available and may be either prokaryotic and/or eukaryotic expression systems. Exemplary non-limiting expression systems may include the insect cell/baculovirus system described in U.S. Pat Nos. 5,871,986 and 4,879,236. These systems are also commercially available under the name MAXBAC™ baculovirus expression system from INVITROGEN (Carlsbad, CA), and BACP ACK™ baculovirus expression system from CLONTECH (Mountain View, CA). Other commercially available expression systems may include COMPLETE CONTROL™ inducible mammalian expression system from STRATAGENE (La Jolla, CA) which uses a synthetic ecdysone-inducible receptor, or its pET expression system which is an E. coli expression system. Another inducible expression system from INVITROGEN is T-REX™, which is a tetracycline regulated expression system. Yeast expression systems are also available for the high-level production of recombinant proteins in the methyltrophic yeast Pichia methanolica, available from INVITROGEN. The expressed engineered Fab fragments are then purified using methods known to persons of skill in the art. Such methods may include but are not limited to column chromatography, affinity chromatography, or size exclusion filtration. The binding components of the Fab fragment may also be prepared as a single-chain Fv (scFv) and the cysteine residue added to the C-terminus using methods known to persons of skill in the art.

[0034] As an alternative approach to generating the population of Fab fragments having the engineered cysteine residue can be accomplished by introducing the point mutation into the desired location of the constant region for either the heavy or light chain, and then expressing the entire antibody sequence to produce intact immunoglobulins having the engineered cysteine residue. The Fab fragments are then produced by digesting the engineered antibody with a protease (e.g., papain or pepsin) resulting in Fab fragments and Fc regions. The Fab fragments can then be purified using methods known to persons of skill in the art for example, size filtration, column chromatography, or affinity chromatography.

[0035] A non-limiting exemplary protease useful for digesting an immunoglobulin in the methods of the present invention is pepsin. Digestion of an immunoglobulin with pepsin typically cleaves the immunoglobulin C-terminal to the cysteines in the hinge region, yielding the F(ab')2 fragments, which consist of two Fab' fragments covalently joined by disulfide bonds from the hinge region. Mild reduction of such F(ab')2 fragments with fnercaptoethylamine or other mild reducing agents yields Fab' fragments, which contain the Fab domain and a C-terminal tail consisting of a portion of the hinge region, which contains at least one reduced cysteine. This cysteine can be used for conjugation to, for example, thiol-reactive homobifunctional crosslinking agents.

[0036] As another alternative, the light and/or heavy chain sequences containing the engineered cysteine reside can be synthesized from commercial vendors such as Blue Heron Biotechnology (Bothell, WA).

Engineering a population of immunoglobulins having a cysteine residue in the constant region of the heavy chain.

[0037] The second step in generating the tetravalent bispecific antibodies of the present invention is obtaining a population of intact immunoglobulins having a cysteine residue engineered into the heavy chain of the constant region, preferably in the C-terminal most domain, e.g., the CH3 domain of an IgG. For each immunoglobulin class (e.g. IgG, IgA, etc) the three dimensional structure of the Fc domain is analyzed using coordinates available in the protein databank and several amino acid residues that would be appropriate for engineering in the cysteine residue are identified. For example, as shown in Figure 5, in the case of human IgGl or IgG4, an exemplary amino acid suitable for mutating to a Cys residue is Ser 415 (according to the numbering system in Brunhouse, (1979) Molecular Immunology 16:907-917). The 50 most C-terminal amino acid residues of the CH3 domain for IgGl and IgG4 are shown below as SEQ ID NO 11 and SEQ ID NO 12 respectively:

397-VLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG-446 397-VLDSDGSFFLYSRLTVDKSRWZZGBVFSCSVMHZALHBHYTQKSLSLSLG-446. [0038] As shown above, serine 415 (underlined in SEQ ID NO 11 and 12 above) is the sixth serine from the C-terminal end of the heavy chain in the CH3 domain of human IgGl or IgG4 respectively (can also be seen in SEQ ID NO 9 and 10 in Figure 5). Furthermore, it should be noted that IgGl and IgG4 have a conserved motif (shown in bold) 411- TVDKSRW-417 (SEQ ID NO 13) which surrounds the serine at position 415 in IgGl and IgG4. This motif and the conserved serine (underlined) is also present within the 50 most C- terminal amino acid residues of other human immunoglobulin subclasses (e.g. IgG2 and IgG3). As can also be seen in Figure 5, position 415 of the CH3 domain is a serine in the guinea pig IgG2 (SEQ ID NO 6) (S er 415 is the fourth serine from the C-terminal end) and mouse IgGl (SEQ ID NO 7) (serine 415 is the fifth serine from the C-terminal end of the sequence). In the event that the selected residue results in folding or solubility problems, additional residues are also identified.

[0039] Methods for introducing the point mutation into the antibody sequence are known to persons of skill in the art. An exemplary method includes the use of PCR to introduce the mutation into the constant region, as detailed in Example 2. Briefly, starting with the hybridoma, total RNA is extracted and first strand cDNA synthesized. PCR is then used to amplify the heavy and light chains, and add restrictions sites for cloning into expression vectors. Myeloma cells are then transfected with the expression vector and stable tranfectants selected using a selectable drug (e.g. G418). Clones expressing high levels of secreted immunoglobulin are identified and characterized via western blot using anti-human immunoglobulin antibodies under both oxidizing and reducing conditions to verify expected molecular weights. Such methods are well known to persons of skill in the art and detailed in the Examples.

[0040] Once the desired stable transfectant has been identified large-scale production of the holo-antibody is achieved using standard methods known in the art. Generally, the stable transfectants are grown in serum-free media in roller bottles. Immunoglobulins are isolated using ultrafiltration of the crude supernatant with a 100 kDa cut-off followed by filtration through a 0.45 μm filter. Further purification can be achieved using a Protein A and/or

Protein G column, or Jacalin ((a -D-galactose binding lectin extracted from jack-fruit seeds) for the purification of IgA) PIERCE (Rockford, IL). Purified immunoglobulin is typically then dialyzed against PBS containing a reducing agent (e.g. 100 mM mercaptoethylamine) to keep the engineered, but not the native, cysteines in a reduced state. These methods will be well known to a person of skill in the art.

Determining the Binding Constants for the engineered Fab Fragments and the Engineered Immunoglobulins

[0041] In selecting the pairs (Fab fragment and Immunoglobulin) to be conjugated in the present invention, it is important that they will have high affinity for their targets, with dissociation constants typically less than about 107 M"1, preferably less than 108 M"1 , and even more preferably less than 109 M"1. A variety of assays are known to persons of skill in the art for determining the binding affinity and specificity for antibodies. For example, Friguet et al., discloses a general procedure for determining the dissociation constant (Kd) of antigen-antibody equilibria in solution with a sensitivity in the 109 M"1 range (Friguet et α/.,(1985) J. Immunol Meth. 77(2):305-319). Briefly, the method involves incubating the antibody in solution with a large excess of antigen until equilibrium is reached. The proportion of antibody which remains unsaturated at equilibrium is then measured using indirect ELISA. Alternative assays for determining binding affinity that will be known to persons of skill in the art may include immunopercipitation of radiolabeled antigen and fluorescence transfer methods.

Reacting the Fab fragments with a thiol reactive bi-functional cross-linking agent

[0042] The next step in the generation of the tetravalent bispecific antibodies of the present invention reacting the expressed and purified Fab fragments with the thiol reactive bi- functional crosslinking agent. Bifunctional cross-linking agents suitable for use with the present invention may include any crosslinking agent that reacts with sulfhydral groups (-SH) under conditions which will not result in the denaturation of the proteins (Fab and immunoglobulin) or interfere with the binding specificity of the tetravalent bispecific antibody. Further desired properties include linkers that are soluble, non-toxic and non- immunogenic. Exemplary bifunctional cross linking agents may include maleimide (which is highly reactive to thiol groups) connected via a polyether ester.

[0043] The reaction of a maleimide group to a sulfhydral group results in the formation of a stable thioether linkage which cannot be cleaved by reducing agents or physiological buffer conditions. The reaction between a maleimide and a sulfhydral is very specific at pH 6.5 to 7.5. At pH values greater than 7.5, reactivity toward primary amines and hydrolysis of the maleimide group can occur. At a pH of 7, the maleimide group is approximately 1,000 times more reactive toward a sulfhydral than toward an amine. Unlike other thiol reactive moieties such as iodoacetamide, maleimide does not react with tyrosine, histidine or methionine residues.

[0044] Two exemplary bifunctional cross-linking agents having thiol reactive moieties that are suitable for use with the present invention are 1,8-bis-maleeimidodiethyleneglycol (BM[PEO]2) and 1,11-bis-maleimidotriethyleneglycol (BM[PEO]3). These particular crosslinkers have a spacer length of 14.7 and 17.8 angstroms, respectively. These and other bifunctional cross-linking agents having thiol reactive moieties suitable for use with the present invention are available from commercial suppliers, for example, PIERCE (Rockford, IL) and are used according to the manufacturers instructions. Other crosslinking agents that are suitable for use with the present invention will be known to persons of skill in the art, (e.g. pyridyl disulfides and haloacetyls) and are widely available from commercial suppliers such as Genotech (St. Louis, MO).

[0045] The general conditions for cross-linking using the bismaleimide moieties require that the molecules to be reacted must have free (reduced) sulfhydral groups. Furthermore extraneous sulfhydral containing components in the reaction buffers during conjugation (e.g. DTT) should be avoided. Typically, the reaction requires a two to three fold molar excess of the cross-linker to the sulfhydral containing proteins. The proteins are dissolved in a conjugation buffer (Phosphate Buffered Saline pH 7.2) or other sulfhydral free buffer (pH6.5- 7.5) at a concentration of 0. ImM (5mg per ml for a 50 kDa protein). The cross-linker stock solution is comprised of the cross-linker dissolved in DMSO or DMF at a concentration of 5- 20 mM. The reaction is then carried out by adding 2-3 or more fold molar excess of the cross linker stock solution to the protein dissolved in conjugation buffer. The exact amount of molar excess is determined for the specific Fab fragment, and may be as much as 25 fold molar excess as detailed in Example 2. The reaction then proceeds for 1-2 hours depending on the temperature (typical temperatures can range between 40C and 370C). The reaction is then quenched with the addition of a molar excess of cysteine, DTT or other thiol-containing reducing agent.

Removing the unreacted bi-functional cross-linking agent

[0046] The next step is the removal of any unreacted bi-functional cross-linking agent. In an exemplary embodiment, the unreacted bifunctional cross-linking agent is removed via dialysis using a suitable biological buffer (e.g. conjugation buffer). Other methods that are suitable for the removal of the unreacted cross-linking agent may include but are not limited to column chromatography (e.g. desalting columns), HPLC, size exclusion filtration, and affinity chromatography. Additional methods and buffers will be known to persons of skill in the art.

Reacting the Fab fragments attached to the bi-functional cross-linking agents with Immunoglobulin

[0047] The final step in generating the tetravalent bispecific antibodies of the present invention is reacting the engineered Fab fragments joined to the bifunctional cross-linking agents to the engineered immunoglobulins. Here, the Fab fragment is added in a 2 to 3 fold, or more, stoichiometric excess to that of the immunoglobulins (to obtain the most efficient crosslinking) and incubated for 1-2 hours as described previously. The unreacted or partially reacted Fab and immunoglobulins are then removed using methodologies known to persons of skill in the art. Typical methodologies may include but are not limited to gel filtration, HPLC, affinity chromatography and size exclusion filtration. Other suitable methodologies will be well known to persons of skill in the art.

Purifying the tetravalent bispecific antibodies to generate a homogenous population

[0048] Once the tetravalent bispecific antibodies of the present invention have been generated, homogenous populations can then be purified using techniques well known to persons of skill in the art. Non-limiting exemplary methods may include for example, size exclusion filtration, or size exclusion chromatography, HPLC, or affinity chromatography. Additional methods for purifying the homogenous tetravalent bispecific antibodies will be known to persons of skill in the art.

EXAMPLES [0049] The examples below are intended to describe certain aspects and embodiments of the present invention and not to limit the invention.

Example 1

[0050] General Method: First, a recombinant Fab fragment of monoclonal antibody 1 (antibody 1), retaining a single cysteine residue in the linker region, is produced using recombinant methods (Figure IA). The single cysteine is ideally positioned at the opposite end of the Fab fragment from the antigen-combining site. This Fab fragment is then reacted with a homobifunctional crosslinking agent, having thiol reactive moieties, added in large excess to prevent formation of chemically crosslinked Fab dimers. In this way, a Fab fragment with a single cysteine-reactive group is created. In parallel, a holo-antibody (antibody 2) is point mutated so as to contain a single cysteine on its Fc region, near the C- terminus. Because IgG' s contains two heavy chains, thus mutated antibody 2 will contain two cysteines, distanced from each other by about 30 angstroms. This minimally modified IgG is then reacted with the cysteine-reactive antibody 1 Fab fragment to produce the bispecific antibody containing two combining regions from each antibody and a single Fc domain. This construct has all of the desirable properties for a bispecific antibody: it is bivalent for each target; it is homogeneous; it contains an intact, human immunoglobulin Fc region, thus conferring favorable pharmacokinetics. Alternatively, as shown in Figure IB, the conjugation process may be performed by first reacting the crosslinking agent to the holo- antibody and then mixing the cysteine-reactive holo-antibody with the Fab fragments containing the unreacted cysteine residue.

Example 2. Production of Immunoglobulin and Fab with Engineered Cysteines.

[0051] Construction of Human Immunoglobulin G Heavy Chain Mutant. The human immunoglobulin G (IgG) heavy chain carrying a serine to cysteine mutation at amino acid position 415 (S415C) in the CH3 region was constructed using recombinant PCR. To generate the mutant, the pVS JG-A-Fc plasmid, which encodes the human IgG heavy chain, was used as the template for the initial two PCR reactions. The first PCR amplified a region upstream the site of mutation using a forward primer with wAflffl. site and a reverse primer containing the desired mutation. The second PCR amplified a region downstream the site of mutation using a forward primer which was complementary to the reverse primer of the first PCR and a reverse primer with a Notl site. Both of these PCR products were gel extracted and used as templates for a third PCR, which used the forward primer of the first PCR and the reverse primer of the second PCR. The final recombinant PCR product was gel extracted, ligated into AβUl and Notl sites of the plasmid, and confirmed by sequencing.

[0052] Expression of Human Immunoglobulin G in Mammalian Cells. To express the human IgG in mammalian cells, the expression plasmid that encodes the human IgG light chain was cotransfected with either wild-type (WT) heavy chain Fc or mutant heavy chain FcCys (S415C) in Chinese Hamster Ovary suspension (CHOS) cells using DIMRIE-C transfection reagent (Invitrogen). The size, identity and yield of WT or S415C IgG were monitored by western blotting probed with an anti-human Fc antibody (Figure 2). After 3 days of transient transfection, the expression of WT and S415C IgG was comparable, generating approximately 180 ng/ml and 125 ng/ml, respectively.

[0053] Construction of human Fab heavy chain mutant. A Fab cys modification was performed by substituting the penultimate C-terminal alanine (GCC) at the end of a c-Myc Tag with a cysteine (TGC). The mutation was done as follows: A Notl/Clal fragment containing a cysteine (TGC) insertion was generated by PCR as shown in Figure 2. Overlapping PCR reactions were used to introduce the mutant cysteine residue at the position indicated in the figure. The PCR fragment was subcloned into TOPO TA cloning vector and sequence confirmed. The mutated Notl/Clal fragment was then subcloned to replace the original Notl/Clal fragment in a pBR322 Fab expression vector.

[0054] Expression of Human Fab-cys in E. coli. The Fab-cys expression vector was used to transform E. coli cells and grown in broth culture followed by induction of the inducible promoter. The cell pellet was resuspended (per 500ml culture) in 10ml TE extraction buffer (10 mM Tris, pH 6.8, 5 mM EDTA, 1 mini tablet/10ml protease inhibitor cocktail, ImM PMSF) and subjected to three cycles of freezing and thawing. Freshly prepared hen egg lysozyme was added at 10mg/500ml culture (0.2 mg/mL), and freshly prepared iodacetic acid was added to a final concentration of 5-10 mM (10OuI IM IAA/lOml broth sample). After incubating on ice for 5- 10 minutes, the sample was sonicated for 3x10 pulses followed by centrifugation at 40C at 14,000 rpm for 20 minutes. The supernatant was collected as the soluble fraction.

[0055] Purification of Human Fab-cys. The supernatant containing the human Fab-cys was processed using either a nickel column (Ni-NTA Agarose, nickel-charged resign, Qiagen, catalog # 30210) or protein L column (ImmunoPure(L) Immunoglobulin Purification Kit, Pierce catalog #20550) per manufacturer's instructions. Material obtained from either method alone contained the complete Fab-cys fragment as well as lesser amounts of light chain dimers (LCD) and light chain monomers (LCM) (Figure 3). When the samples were treated sequentially with the nickel column followed by the protein L column, the sample was enriched for the Fab-cys fragment, with some residual (LCM) present. When the samples were treated sequentially with the protein L column followed by the nickel column, the Fab- cys was again the most prominent fraction. However small amounts of the LCM and (LCD) were also present. The sample obtained from the nickel column followed by the protein L column will be used for conjugating with the Ig-cys antibody.

[0056] Conjugation to Form Bispecific Antibody. The human Fab, with the single cysteine at the C-terminus, will be reacted with the homobifunctional thiol-reactive crosslinker 1,11-bis-maleimidotriethyleneglycol (BM[PEO]3; Pierce, Rockford II) in crosslinking buffer (phosphate buffered saline, ImM EDTA, pH 6.5) at Fab concentration of ~ 2mg/mL with a 25-fold molar excess BM[PEO]3, for 1 hour at 370C in the dark. The addition of excess crosslinker ensures that minimal amounts of chemically crosslinked Fab dimers will be formed. The reaction will then be dialyzed to remove unreacted BM[PEO]3. The activated Fabs will then be mixed with the IgG-Ser415Cys (previously dialyzed into Crosslinking Buffer) at a 3:1 (Fab:IgG) ratio and incubated for 1 hour at 370C in the dark. Gel filtration will then be used to remove unreacted or partially reacted IgG and Fab fragments. The resulting bispecific antibody, with a molecular weight of ~250,000, will be detected by Western blot using anti-Ig light chain or anti-Ig heavy chain antibodies to show that the tetravalent bispecific antibody conjugate is obtained and migrates at the predicted size range in a non-reducing SDS PAGE gel.

Example 3. Detailed Method for making a bispecific anti-CD3 x anti-HER2 antibody

[0057] Production of Recombinant Fab Fragments of Anti-Her2 Antibody. The sequence of the humanized anti-HER2 antibody (Herceptin) variable regions have been published (U.S. Pat. No. 6,800,738). These may be constructed by gene assembly (Stemmer, et at, (1995) Gene 16:49-53) using overlapping oligonucleotides, and confirmed by DNA sequencing. These sequence-confirmed variable regions can then be cloned into an expression vector for expressing Fab fragments. Such a vector may co-express the heavy chain variable region + constant heavy chain 1 (CHl) region, and the entire light chain (VL + CL region), followed by myc and his tags for protein detection and purification. The vector may have a single bicistronic message under control of an inducible promoter. Restriction maybe designed for convenient cloning of VH and VL regions, without alteration of the natural human sequences at the junction between the Variable and Constant regions of the heavy and light chains. Signal peptides at the N-termini of the heavy and light chains can allow for periplasmic expression in E coli. Fab fragment expression can be performed in E coli grown in L-B media with antibiotic at 260C, until reaching OD500 = 0.5, at which point the inducer for the proprietary promoter system can be added, and induction will continue for 2-16 hours. Cells can then be spun down at 6000 rpm for 30 minutes. The pellet can then be resuspended and lysed in BugBuster™ HT (Pierce, Rockford, IL). The lysed cell extract may be re-centrifuged at 14,000 rpm for 10 minutes and the soluble fraction then purified using Ni-NTA beads (Qiagen, Emeryville, CA) followed by anti-FLAG tag beads. The majority (>90%) of the Fab fragments expressed in this system should not oxidize to Fab dimers in the periplasm and will therefore be ready for conjugation to a cysteine-reactive anti-CD3 antibody (see below).

[0058] Generation of Anti-CD3 Antibody with Engineered Cysteines. We examined the three-dimensional structure of the human IgGl Fc domain using protein coordinates in the protein data bank (e.g. 1T83), and identified several amino acid positions that would be appropriate for engineering in a cysteine residue for coupling to Fab fragments. Our first choice is to mutate Ser415 to Cys. The cysteine thus introduced will be at the opposite end of the Fc domain from the region where the natural hinge region (and therefore natural position of the Fabs) is attached. The side chain of the serine normally present at that location is facing into the solvent and does not make any contacts with the antibody, so the single atom change (oxygen to sulfur) is not expected to disrupt the structure (Radaev et al, (2001) J. Biol. Chem. 276:16469-16477). Since there are two heavy chains per IgG, this single point mutation will introduce 2 cysteines per IgG, spaced by about 30 angstroms apart. There is ample room to attach one Fab to each of the introduced cysteines without steric hindrance.

[0059] The Ser415Cys IgG will be produced using myeloma expression vectors. Cells will be adapted to serum-free medium and the antibody can be purified using a BIO-CAD M protein G column (Perceptive Biosystems, ).

[0060] The variable regions of a murine CD3 antibody will be cloned using PCR. Starting with the hybridoma, total RNA will be extracted and first strand cDNA synthesized. The heavy chain DNA is then amplified using PCR with a set of degenerate 5' primers specific for mouse heavy chains and an IgG constant region-specific 3' primer of the appropriate isotype (as determined using an isotyping kit). The light chain will be amplified using a set of degenerate 5' primers specific for mouse kappa light chains and a kappa-specific 3! primer. The PCR reactions will also add 5' and 3' restriction sites for cloning into expression vectors for making a chimeric IgGl/kappa holo-antibody with engineered single cysteine near the C- terminus of the Fc domain.

[0061] After introducing the Ser415Cys point mutation, the expression vector will be called p VS JG-A-FcCys. The light chain vector, pVSJG-CL, contains human C kappa constant region-encoding sequence. For the present work, the murine anti-CD3 heavy and light chain V region cDNAs will be linked to the human IgGl heavy chain (CHl) or kappa light chain constant regions for expression in these vectors. The IgGl isotype has been selected to maximize Fc receptor-binding and recycling and is commonly used for therapeutic antibodies with long serum half-lives (e.g. Herceptin, which has a 25 day half-life in human serum).

[0062] Experience indicates that different myeloma cells produce different levels of different antibodies. Therefore, to select the best producers, we will transfect myeloma cells P3X63.Ag8.653, Sp2/0 or NSO/1. Electroporation is routinely used in our laboratory to introduce DNA into these cells. Stable transfectomas will be isolated using G418 as a selectable drag. Culture supernatants will be screened by ganima-1 chain specific ELISA to identify clones secreting high levels of the antibody. Cytoplasmic and secreted proteins will be examined by Western blots using anti-human antibodies, under oxidizing and reducing conditions, to verify expected molecular weights.

[0063] Transfectants may be grown in roller bottles or in a CellMax hollow fiber system for large-scale production of humanized anti-CD3-Ser415Cys. Most transfectomas can be adapted to grow in serum-free medium. Antibodies in serum free medium can be easily concentrated and dialyzed using Millipore Ultrafree-4 Centrifugal Filter Units (Millipore Corp., Bedford, MA). A standard procedure involves ultrafiltration and diafiltration of the crude extract with a 100 kD molecular weight cut-off tangential flow device, followed by filtration through 0.45 micron filter and direct application to a Protein G column. The purified anti-CD3 antibody, eluted with 3 M potassium thiocyanate, pH 7.5, will be dialyzed extensively against PBS with 100 μM mercaptoethylamine (which will keep the introduced cysteines, but not the native cysteines in the antibody, reduced).

[0064] The concentration of proteins will be determined with a combination of the bicinchoninic acid assay (Pierce, Rockford, IL) and comparison with a standard of known concentration following SDS-PAGE and staining with Coomassie blue. The binding of the purified antibodies will be confirmed using the assays described above.

[0065] Conjugation to Form Bispecific Antibody. The humanized anti-Her2 Fab, with the single cysteine at the C-terminus, will be reacted with the homobifunctional thiol-reactive crosslinker 1,11-bis-maleirnidotriethyleneglycol (BM[PEO]3; Pierce, Rockford II) in Crosslinking Buffer (phosphate buffered saline, ImM EDTA, pH 6.5) at Fab concentration of ~ 2mg/mL with a 25-fold molar excess BM[PEO]3, incubated for 1 hour at 370C in the dark. The addition of excess crosslinker ensures that minimal amounts of chemically crosslinked Fab dimers will be formed. The reaction will then be dialyzed to remove unreacted BM[PEO]3. The activated Fabs will then be mixed with the anti-CD3 IgG-Ser415Cys (previously dialyzed into Crosslinking Buffer) at a 3:1 (Fab:IgG) ratio and incubated for 1 hour at 370C in the dark. Gel filtration will then be used to remove unreacted or partially reacted IgG and Fab fragments. The resulting bispecific antibody, with a molecular weight of 250,000, will be tested for binding to CD3 and HER2 by ELISA.

[0066] With respect to the Ser to Cys mutation in the IgG heavy chain, in case any folding/solubility issues are caused by this single atom change in the antibody, alternative positions are tested where cysteines could be introduced. Occasionally, transfectants do not produce well in serum-free medium. As an alternative, we will grow cells in 1% fetal bovine serum. As a further alternative, we will modify our mammalian expression vectors to produce the Fab fragments.

[0067] All publications, patents and patent applications cited in this specification are herein incorporated by reference as if each individual publication patent or patent application were specifically and individually indicated to be incorporated by reference to the extent that it is consistent with the teachings herein.

[0068] Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to one of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

Claims

WHAT IS CLAIMED IS:
1. A method for obtaining a population of bispecific tetravalent antibodies comprising the steps of:
i. obtaining a first antibody population comprised of Fab fragments with a cysteine engineered into the constant region of either the heavy chain or the light chain;
ii. obtaining a second antibody population comprised of immunoglobulin with a cysteine engineered into the constant heavy chain;
iii. reacting either the first antibody population or the second antibody population with a molar excess of a bifunctional crosslinking agent having thiol reactive moieties able to join to the engineered cysteine in the antibody population with which it is reacted;
iv. removing unreacted bifunctional crosslinking reagent; and,
v. contacting the antibody population joined to the crosslinking agent with the unjoined antibody population under conditions that allow the antibody population joined to the crosslinking agent to crosslink with the engineered cysteine residues of the unreacted antibody population to yield the population of bispecific tetravalent antibodies.
2. The method of claim 1 where the bifunctional crosslinking agent is a homo-bifunctional crosslinking agent.
3. The method of claim 1 wherein the bifunctional crosslinking agent is between 10 and 50 angstroms in length.
4. The method of claim 1 where the cysteines are engineered within the last 10 C-terminal amino acid residues of both the Fab fragment and the immunoglobulin.
5. The method of claim 1 where removal of the crosslinking reagent is by dialysis.
6. The method of claim 1 , wherein the bifunctional crosslinking reagent is a polyether ester.
7. The method of claim 6 where the bifunctional crosslinking reagent is 1 ,8-bis,-maleimidodiethyleneglycol.
8. The method of claim 6 where the bifunctional crosslinking reagent is 1,11 -bis-maleimidotriethyleneglycol.
9. The method of claim 1 , wherein the immunoglobulin is an IgG.
10. The method of claim 1 , wherein the immunoglobulin is an IgA.
11. A tetravalent bispecific antibody comprising an intact immunoglobulin with two heavy chains and two light chains, with each heavy chain conjugated to a Fab linked through a linker of 10-50 angstroms via cysteines engineered into the constant region of the immunoglobulin heavy chains and the constant region of either the heavy or light chain of the Fab and the two immunoglobulin heavy chains linked to each other by disulfide bonds.
12. The tetravalent bispecific antibody of claim 11, where the cysteines are engineered within the last 10 C-terminal amino acid residues of both the immunoglobulin heavy chain and either the heavy or light chain of the Fab.
13. The tetravalent bispecific antibody of claim 11 , wherein the immunoglobulin is IgG.
14. The tetravalent bispecific antibody of claim 11 , wherein the immunoglobulin is IgA.
15. The tetravalent bispecific antibody of claim 13 , wherein the cysteine residue engineered into an IgG is a Ser 415 Cys heavy chain mutation.
16. The tetravalent bispecific antibody of claim 11 , wherein one part of the antibody binds to a protein on the surface of a stem cell.
17. The tetravalent bispecific antibody of claim 11 , wherein one part of the antibody binds to a protein associated with diseased tissue.
18. The tetravalent bispecific antibody of claim 11 , wherein one part of the antibody binds to a protein on the surface of a pathogen.
19. The tetravalent bispecific antibody of claim 11 , wherein one part of the antibody binds to a protein on the surface of a cardiac cell.
20. The tetravalent bispecific antibody of claim 11 , wherein the cysteines are engineered into one of the 20 most C-terminal amino acids of the immunoglobulin and Fab fragment.
21. The tetravalent bispecific antibody of claim 11 , wherein the linker is less than 50 angstroms in length.
PCT/US2006/040029 2005-10-11 2006-10-10 Method for producing a population of homogenous tetravalent bispecific antibodies WO2007044887A2 (en)

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