US 20050112698 A1
The present invention provides human antibodies specific for stem cell factor that contain at least one CDR derived from a combinatorial antibody library. The invention also provides pharmaceutical compositions comprising the antibodies and methods of treating asthma. The invention further provides methods of detecting stem cell factor using the antibodies.
1. A purified human antibody which binds to stem cell factor protein, said antibody comprising
a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 19-24 or
a heavy chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS:13-18,
said antibody being optionally bound to a cytotoxic molecule or detectable label.
2. The antibody of
3. The antibody of
4. The antibody of
5. The antibody of
6. The antibody of
7. The antibody of
8. The antibody of
9. The antibody of
10. The antibody of
11. The antibody of
12. The antibody of
13. A preparation comprising the antibody of
14. A pharmaceutical composition comprising the antibody of
15. An isolated polynucleotide or nucleotides encoding the antibody of
16. An expression vector comprising the polynucleotide or polynucleotides of
17. A host cell comprising the expression vector of
18. A method of producing a human antibody, comprising the steps of: culturing a host cell of
19. A method of treating asthma comprising the steps of administering to a human in need of such treatment an effective amount of a Human Stem Cell Factor antibody of
20. A method of treating a human disorder in which stem cell factor protein is expressed in certain cells, comprising the steps of administering to a human in need of such treatment an effective amount of a human stem cell factor antibody of
21. A method for identifying a disorder in which stem cell factor protein level is elevated, comprising the steps of: contacting a sample from a patient suspected of having the disorder with an antibody of
22. The method of
23. A purified human antibody which binds to stem cell factor protein, said antibody comprising a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 86-92, said antibody being optionally bound to a cytotoxic molecule or detectable label.
24. The antibody of
25. The antibody of
26. The antibody of
27. The antibody of
28. The antibody of
29. The antibody of
30. The antibody of
31. The antibody of
32. The antibody of
33. The antibody of
34. A preparation comprising the antibody of
35. A pharmaceutical composition comprising the antibody of
36. An isolated polynucleotide or nucleotides encoding the antibody of
37. An expression vector comprising the polynucleotide or polynucleotides of
38. A host cell comprising the expression vector of
39. A method of producing a human antibody, comprising the steps of: culturing a host cell of
40. A method of treating asthma comprising the steps of administering to a human in need of such treatment an effective amount of a Human Stem Cell Factor antibody of
41. A method of treating a human disorder in which stem cell factor protein is expressed in certain cells, comprising the steps of administering to a human in need of such treatment an effective amount of a human stem cell factor antibody of
42. A method for identifying a disorder in which stem cell factor protein level is elevated, comprising the steps of: contacting a sample from a patient suspected of having the disorder with an antibody of
43. The method of
This is a continuation-in-part of U.S. application Ser. No. 10/320,231 filed Dec. 16, 2002, which claims the benefit of U.S. Provisional Application 60/342,174 filed Dec. 17, 2001, which is hereby incorporated herein in its entirety by reference.
The present invention relates to antibodies and treatments for asthma and other disorders in which stem cell factor protein is expressed in certain cells. More specifically, the present invention relates to human antibodies that inhibit stem cell factor activity, polynucleotide sequences encoding the antibodies, and use of the antibodies in the treatment of asthma and other disorders in which stem cell factor is expressed in certain cells.
Allergic asthma is characterized by variable reversible airway obstruction, and airway hyperresponsiveness associated with airway inflammation. The inflammation is itself characterized by the presence of activated mast cells and eosinophils, which through the generation of proinflammatory mediators and cytokines play a fundamental role in the pathogenesis of the disease. The eosinophil is thought to be a major effector cell in the development of airway hyperresponsiveness, through the release of cytotoxic granule proteins. However, the initial induction of IgE-mediated mast cell activation/degranulation constitutes the primary mechanism that drives the allergic airway response and changes in airway physiology. Activation of mast cells by cross linking of IgE leads to the release of histamine and generation of leukotrienes that appear to contribute to the early bronchoconstriction occurring within minutes of allergen exposure. Moreover, the production of cytokines (TNF, IL-4, IL-5), angiogenic and fibrotic factors, and the release of chemokines (RANTES, eotaxin, MCP-1, TARC) which favor the infiltration of the airway tissues with eosinophils and lymphocytes, drive/enhance the maintenance and progression of the disease. The relationship between mast cell activation and eosinophil recruitment has substantial consequences on tie pathogenesis of asthma.
Stem Cell Factor (SCF; also known as Mast Cell Growth Factor, Steel Factor or c-kit ligand) is an important hematopoietic factor that drives the differentiation of mast cells in the bone marrow. SCF as a result of alternate splicing exists as a membrane bound and soluble form and is produced by bone marrow stromal cells. SCF is also produced by several cell types found in peripheral tissues including fibroblasts, endothelial cells, epithelial cells, mast cells and eosinophils, and is thought to be the primary cytokine regulating the survival, activation, and degranulation of mature mast cells in the lung microenvironment. In addition to IgE mediated activation of mast cells, SCF can directly induce mast cell activation and degranulation resulting in the release of inflammatory mediators, cytokines and chemokines as discussed above. Moreover, SCF strongly augments the IgE-mediated activation of mast cells. The prolonged activation of local airway mast cell populations by SCF after initial IgE-mediated activation may play a significant role in persistent activation leading to prolonged impairment of lung function. SCF also induces mast cell adhesion to extra cellular matrix proteins as well as their chemotaxis. SCF has also demonstrated a direct role on eosinophil adhesion by altering avidity of VLA-4 on the surface of eosinophils which has significant consequences for eosinophil migration to the lung.
In vivo administration of SCF to the airways has been shown to be a potent inducer of airway hyperreactivity and inflammation in mice (Lukacs et al., J. Immunol., 156: 3945 (1996); Campbell et al., Am. J. Pathol., 154:1259 (1999). Recently, published studies have demonstrated therapeutic benefit of inhibitors of SCF, either antibodies or antisense RNA, in treating antigen-induced asthma in rodent models (Campbell et al., Am. J. Pathol., 154:1259 (1999); Finotto et al., J. Allergy Clin. Immunol., 107:279 (2001)).
It is an object of the invention to provide reagents and methods of inhibiting stem cell factor activity.
The invention provides human antibodies that bind to stem cell factor. These antibodies are useful for a variety of therapeutic and diagnostic purposes, including the treatment of asthma.
The invention provides a purified human antibody which binds to stem cell factor protein, the antibody comprising a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 19-24 or a heavy chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 13-18, the antibody being optionally bound to a cytotoxic molecule or detectable label. In other embodiments, the antibody comprises heavy and light chain variable regions comprising a pair of amino acid sequences selected from the group consisting of SEQ ID NOS: 13 and 19, SEQ ID NOS: 14 and 20, SEQ ID NOS: 15 and 24, SEQ ID NOS: 16 and 21, SEQ ID NOS: 17 and 22 and SEQ ID NOS: 18 and 23.
In a preferred embodiment of the invention the antibody comprises heavy and light chain variable regions comprising SEQ ID NOS: 14 and 20. The antibody can also comprise a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 57, 59, 61, 63 and 65 and a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 67, 69, 71, 73 and 75. More preferably the antibody comprises a heavy chain variable region comprising SEQ ID NO: 14, a light chain variable region comprising SEQ ID NO: 20, a light chain variable region comprising SEQ ID NO: 59, and a light chain variable region comprising SEQ ID NO: 69.
In another preferred embodiment of the invention, the antibody comprises a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 86-92, the antibody being optionally bound to a cytotoxic molecule or detectable label. More preferably, the light chain variable region further comprises SEQ ID NO: 59 and SEQ ID NO: 69. Preferably, the antibody comprises a heavy chain variable region comprising SEQ ID NO: 14. More preferably, the antibody comprises a heavy chain variable region comprising SEQ ID NO: 14, a light chain variable region comprising SEQ ID NO: 59, a light chain variable region comprising SEQ ID NO: 69, and a light chain variable region selected from the group consisting of SEQ ID NO: 86-92. Most preferably, the antibody comprises heavy chain variable and constant regions having the amino acid sequence of SEQ ID NO: 79, and light chain variable and constant regions having the amino acid sequence of SEQ ID NO: 77 wherein the amino acid subsequence at residues 87-94 is replaced with a sequence selected from the group consisting of SEQ ID NO: 86-92.
The heavy and light chain variable regions of the antibody can comprise framework residues from native human antibodies, but preferably the heavy and light chain variable region framework are comprised of consensus framework residues. More preferably, the heavy chain variable region comprises human VH3 consensus framework residues. The light chain variable region can comprise either human Vκ1 consensus framework residues or human Vλ1 consensus framework residues.
The invention also provides a preparation comprising the antibodies of the invention. The purified preparations can contain one or more different antibodies of the invention.
Another aspect of the invention provides a pharmaceutical composition comprising the antibody of the invention and a pharmaceutically acceptable carrier.
A further aspect of the invention provides an isolated polynucleotide or nucleotides encoding the antibodies. The antibodies of the invention typically contain light and heavy chains, and the sequences encoding the light and heavy chains can be contained in one polynucleotide or in two or more polynucleotides.
An additional aspect of the invention provides an expression vector comprising the purified polynucleotide or polynucleotides encoding the antibodies, and host cells comprising the expression vector. The invention further provides a method of producing a human antibody, comprising the steps of: culturing a host cell comprising an expression vector of the invention under conditions whereby the antibody is expressed; and purifying the antibody from the host cell or host cell culture medium.
Yet another aspect of the invention provides a method of treating a human disorder in which stem cell factor protein is expressed in certain cells, preferably asthma, comprising the steps of administering to a mammal, preferably a human, in need of such treatment an effective amount of a human stem cell factor antibody of the invention wherein the antibody is bound to a cytotoxic molecule, which cytotoxic molecule is capable of inducing apoptosis in the stem cell factor expressing cells.
A further aspect of the invention provides a method of treating a human disorder in which stem cell factor protein is expressed in certain cells, preferably asthma comprising the steps of administering to a mammal, preferably a human, in need of such treatment an effective amount of a human stem cell factor antibody of the invention.
These and other aspects of the invention are set out the appended claims and in the following detailed description.
It is an object of the invention to provide reagents and methods of inhibiting stem cell factor activity. This and other objects of the invention are provided by one or more of the embodiments set out below.
Naturally occurring antibodies (immunoglobulins) comprise two heavy chains linked together by disulfide bonds and two light chains, one light chain being linked to each of the heavy chains by disulfide bonds. Each heavy chain has at one end a variable domain (VH) followed by a number of constant domains. Each light chain has a variable domain (VL) at one end and a constant domain at its other end, the constant domain of the light chain is aligned with the first constant domain of the heavy chain, and the light chain variable domain is aligned with the variable domain of the heavy chain. Particular amino acid residues are believed to form an interface between the light and heavy chain variable domains, see e.g. Chothia et al., J. Mol. Biol. 186:651-663 (1985); Novotny and Haber, Proc. Natl. Acad. Sci. USA 82:4592-4596 (1985).
The constant domains are not involved directly in binding the antibody to an antigen, but are involved in various effector functions, such as participation of the antibody in antibody-dependent cellular cytotoxicity. The variable domains of each pair of light and heavy chains are involved directly in binding the antibody to the antigen. The domains of natural light and heavy chains have the same general structure, and each domain comprises four framework (FR) regions, whose sequences are somewhat conserved, connected by three hyper-variable or complementarity determining regions (CDRs) (see Kabat, E. A. et a., Sequences of Proteins of Immunological Interest, National Institutes of Health, Bethesda, Md., (1987)). The four framework regions largely adopt a beta-sheet conformation and the CDRs form loops connecting, and in some cases forming part of, the beta-sheet structure. The CDRs in each chain are held in close proximity by the framework regions and, with the CDRs from the other chain, contribute to the formation of the antigen binding site.
“Antibody” as used herein includes intact immunoglobulin molecules (e.g., IgG1, IgG2a, IgG2b, IgG3, IgM, IgD, IgE, IgA), as well as fragments thereof, such as Fab, F(ab′)2, scFv, and Fv, which are capable of specific binding to an epitope of a human Stem Cell Factor protein. “Antibody fragments” comprise a portion of a full length antibody, generally the antigen binding or variable region thereof. Examples of antibody fragments include Fab, Fab′, F(ab′)2, and Fv fragments; diabodies; linear antibodies; single-chain antibody molecules; and multispecific antibodies formed from antibody fragments. Antibodies that specifically bind to Stem Cell Factor provide a detection signal at least 5-,10-, or 20-fold higher than a detection signal provided with other proteins when used in an immunochemical assay. Preferably, antibodies that specifically bind to human Stem Cell Factor do not detect other proteins in immunochemical assays and can immunoprecipitate the Stem Cell Factor from solution.
In general, the antibodies of the invention will comprise substantially all of at least one, and typically two, variable domains (such as Fab, Fab′, F(ab′).sub.2, Fabc, Fv) in which one or more of the CDR regions are synthetic amino acid sequences that bind with Stem Cell Factor, and all or substantially all of the framework regions are those of a human immunoglobulin consensus sequence. The framework regions can also be those of a native human immunoglobulin sequence. Other CDR regions in the antibody can be selected to have human immunoglobulin consensus sequences for such CDRs or the sequence of a native human antibody. The antibody optimally also will comprise at least a portion of an immunoglobulin constant region (Fc) of a human immunoglobulin. Ordinarily, the antibody will contain both the light chain as well as at least the variable domain of a heavy chain. The antibody also may include the CH1, hinge, CH2, CH3, and CH4 regions of the heavy chain.
The antibody will be selected from any class of immunoglobulins, including IgM, IgG, IgD, IgA and IgE, and any isotype, including IgG1, IgG2, IgG3 and IgG4. Usually the constant domain is a complement fixing constant domain where it is desired that the antibody exhibit cytotoxic activity, and the class is typically IgG1. Where such cytotoxic activity is not desirable, the constant domain may be of the IgG2 class. The antibody may comprise sequences from more than one class or isotype, and selecting particular constant domains to optimize desired effector functions is within the ordinary skill in the art. The sequences of human immunoglobulin heavy and light chains are known in the art. The variable regions can also be selected from human immunoglobulin consensus sequences known in the art, such as the sequences disclosed in Knappik et al., J. Mol. Biol. 296, 57-86 (2000) and U.S. Pat. No. 6,300,064.
The dissociation constant (Kd) of human antibody binding to Stem Cell Factor can be assayed using any method known in the art, including technologies such as real-time Bimolecular Interaction Analysis (BIA) (Sjolander & Urbaniczky, Anal. Chem. 63, 2338-2345, 1991, and Szabo et al., Curr. Opin. Struct. Biol. 5, 699-705, 1995). BIA is a technology for studying biospecific interactions in real time, without labeling any of the interactants (e.g., BIAcore™). Changes in the optical phenomenon surface plasmon resonance (SPR) can be used as an indication of real-time reactions between biological molecules.
In a BIAcore™ assay as described above in Sjolander & Urbaniczky (1991) and Szabo et al. (1995) human antibodies of the present invention specifically bind to human Stem Cell Factor with a Kd in the range from about 1 nM (1×10−9 M) to about 70 nM (70×10−8 M). More preferred human antibodies of the present invention specifically bind to human Stem Cell Factor with a Kd of approximately 4 nM to about 50 nM, with the most preferred antibodies of this invention binding human Stem Cell Factor protein with a Kd of approximately 1 nM. Other preferred human antibodies of the present invention specifically bind to human Stem Cell Factor with a Kd of approximately 0.8-1.7 nM (1×10−9M).
Additionally, human antibodies of this invention will preferably bind Stem Cell Factor and neutralize its biological activity with an IC50 ranging from about 10 μg/ml to 30 μg/ml. More preferred human antibodies bind Stem Cell Factor and neutralize its biological activity with an IC50 ranging from approximately 1 μg/ml to 3 μg/ml, with the most preferred antibodies of this invention neutralizing activity of human Stem Cell Factor protein with an IC50 of approximately 0.1 μg/ml to 0.3 μg/ml. IC50 is the dose that effectively neutralizes 50% of the biological response induced by human stem cell factor. (IC50 can also refer to the inhibitory or effective concentration causing 50% of the maximum response induced by stem cell factor.)
This invention uses Morphosys phage-antibody technology to generate fully human antibodies against the Stem Cell Factor protein in accordance with the method of Knappik et al., J. Mol. Biol. 296, 57-86 (2000) and U.S. Pat. No. 6,300,064; 6,696,242; and 6,706,248. Briefly, a fully synthetic human combinatorial antibody library (HuCAL) based on modular consensus frameworks and CDRs randomized with trinucleotides is screened to identify antibodies that bind to stem cell factor. The library is based upon human backbones, greatly reducing the probability of immunogenicity. A number of human antibodies having the Stem Cell Factor binding characteristics described above have been identified by screening the MorphoSys HuCAL Fab library. The randomized CDR cassettes assembled for the HuCAL library were designed to achieve a length distribution ranging from 5 to 28 amino acid residues, covering the stretch from position 95 to 102. A number of human antibodies having the Stem Cell Factor binding characteristics described above have been identified by screening the MorphoSys HuCAL Fab library. Generally, the CDR3 region is first randomized, and antibodies identified as specific for the test protein are then optimized by randomizing the CDR1 and/or CDR2 regions of such antibodies to identify additional antibodies with more desirable binding profiles.
Human antibodies with the Stem Cell Factor binding activity described above can be identified from the MorphoSys HuCAL library as follows. Human Stem Cell Factor is coated on a microtiter plate and incubated with the MorphoSys HuCAL-Fab phage library (see Example 1). Those phage-linked Fabs not binding to Stem Cell Factor can be washed away from the plate, leaving only phage that tightly bind to Stem Cell Factor. The bound phage can be eluted by a change in pH and amplified by infection of E. coli hosts. This panning process can be repeated once or twice to enrich for a population of phage-linked antibodies that tightly bind to Stem Cell Factor. The Fabs from the enriched pool are then expressed, purified, and screened in an ELISA assay. The identified hits are then tested for binding using a BIAcore™ assay, and these hits can be further screened in the cell adhesion assay as described above.
The initial panning of the HuCAL-Fab library also can be performed with Stem Cell Factor as the antigen in round one, followed in round 2 by Stem Cell Factor peptides fused to carrier proteins, such as BSA or transferrin, and in round 3 by Stem Cell Factor antigen again. Human Stem Cell Factor peptides that can be used for panning include the amino acid shown in SEQ I.D. NO: 25.
Details of the screening process are described in the Examples 2, 3 and 4. Other selection methods for highly active specific antibodies or antibody fragments can be envisioned by those skilled in the art and used to identify human Stem Cell Factor antibodies.
In some embodiments of the invention, the CDR3 of the heavy chain, which heavy chain preferably comprises a VH3 consensus heavy chain, has an amino acid sequence shown in SEQ ID NOS: 13-18. In other embodiments of the invention, the CDR3 region of the light chain has an amino acid sequence shown in SEQ ID NOS: 19-23. In such embodiments the light chain variable region preferably comprises a VLκ1 consensus variable region. In additional embodiments of the invention, the CDR3 region of the light chain has the amino acid sequence shown in SEQ ID NO: 24, and the light chain is preferably comprised of a VLλ1 consensus variable region. Human antibodies that have Stem Cell Factor binding activity are as shown in Table 3. The consensus variable regions for antibodies with Stem Cell Factor binding activity are shown in Tables 1 and 2.
In other embodiments of the invention, the antibody comprises heavy and light chain variable regions comprising a pair of amino acid sequences selected from the group consisting of SEQ ID NOS: 13 and 19, SEQ ID NOS: 14 and 20, SEQ ID NOS: 15 and 24, SEQ ID NOS: 16 and 21, SEQ ID NOS: 17 and 22 and SEQ ID NOS: 18 and 23. In each pair of sequences, the first sequence is preferably in the heavy chain CDR3 region and the second sequence is preferably in the light chain CDR3 region.
In preferred embodiments, the antibody comprises heavy and light chain variable regions comprising the pair of amino acid sequences SEQ ID NOS: 14 and 20, wherein SEQ ID NO: 14 is in the heavy chain CDR3 region and SEQ ID NO: 20 is in the light chain CDR3 region. Such preferred antibodies can also contain a light chain variable region, corresponding to the CDR1 region, comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 57, 59, 61, 63 or 65, and a light chain variable region, corresponding to the CDR2 region, comprising an amino acid sequence selected from the group consisting of SEQ ID NOS: 67, 69, 71, 73 and 75.
More preferably, the antibody comprises a heavy chain variable region comprising SEQ ID NO: 14, a light chain variable region comprising SEQ ID NO: 20, a light chain variable region comprising SEQ ID NO: 59, and a light chain variable region comprising SEQ ID NO: 69. A preferred antibody of the invention comprises light chain variable and constant regions as shown in SEQ ID NO: 77, and heavy chain variable and constant regions as shown in SEQ ID NO: 79.
In other preferred embodiments the antibodies of the invention comprise a light chain variable region comprising a sequence selected from the group consisting of SEQ ID NO: 86-92, and a heavy chain variable region comprising SEQ ID NO: 14. In such embodiments the light chain variable region preferably comprises a VLκ1 consensus variable region, and the heavy chain variable region preferably comprises a VH3 consensus heavy chain. More preferably, the antibodies comprise a light chain variable region comprising SEQ ID NO: 59, SEQ ID NO: 69 and a sequence selected from the group consisting of SEQ ID NO: 86-92, and a heavy chain variable region comprising SEQ ID NO: 14. Preferably, SEQ ID NO: 59 is in the CDR1 position of the light chain variable region, SEQ ID NO: 69 is in the CDR2 position of the light chain variable region and the sequence selected from the group consisting of SEQ ID NO: 86-92 is in the CDR3 position of the light chain variable region. Most preferably the antibodies comprise a heavy chain having the sequence of SEQ ID NO: 79 and a light chain having the sequence of SEQ ID NO: 77 wherein the amino acid subsequence at residues 87-94 is replaced with a sequence selected from the group consisting of SEQ ID NO: 86-92.
Human antibodies with the characteristics described above also can be purified from any cell that expresses the antibodies, including host cells that have been transfected with antibody-encoding expression constructs. The host cells are cultured under conditions whereby the human antibodies are expressed. The antibodies can then be purified from the host cells or cell culture medium. Suitable methods include, but are not limited to, size exclusion chromatography, ammonium sulfate fractionation, ion exchange chromatography, affinity chromatography, and preparative gel electrophoresis.
A purified antibody is one which has been separated from other compounds that normally associate with the antibody in the cell, such as certain proteins, carbohydrates, or lipids or separated from reagents used for chemical synthesis of the antibody, using methods well known in the art. Such methods include, but are not limited to, size exclusion chromatography, ammonium sulfate fractionation, ion exchange chromatography, affinity chromatography, and preparative gel electrophoresis. In preferred embodiments, the antibody will be purified (1) to at least 70% by weight of antibody as determined by the Lowry method, more preferably 80%, 90%, 95% or 99% by weight, (2) to a degree sufficient to obtain at least 15 residues of N-terminal or internal amino acid sequence by use of a spinning cup sequenator, or (3) to homogeneity by SDS-PAGE under reducing or nonreducing conditions using Coomassie blue or, preferably, silver stain.
A preparation of the antibodies comprises at least one type of antibody of the invention in a purified form, wherein the antibodies preferably comprise at least 70% by weight of the total protein in the preparation, more preferably, 80%, 90%, 95% or 99% by weight of the total protein in the preparation. Purity of the preparations can be assessed by any means known in the art, such as SDS-polyacrylamide gel electrophoresis. A preparation of purified human antibodies of the invention can contain more than one type of human antibody with the Stem Cell Factor binding and neutralizing characteristics described above.
Alternatively, human antibodies can be produced using chemical methods to synthesize its amino acid sequence, such as by direct peptide synthesis using solid-phase techniques (Merrifield, J. Am. Chem. Soc. 85, 2149-2154, 1963; Roberge et al., Science 269, 202-204, 1995). Protein synthesis can be performed using manual techniques or by automation. Automated synthesis can be achieved, for example, using Applied Biosystems 431A Peptide Synthesizer (Perkin Elmer). Optionally, fragments of human antibodies can be separately synthesized and combined using chemical methods to produce a full-length molecule.
The newly synthesized molecules can be substantially purified by preparative high performance liquid chromatography (e.g., Creighton, PROTEINS: STRUCTURES AND MOLECULAR PRINCIPLES, WH Freeman and Co., New York, N.Y., 1983) or other methods known in the art. The composition of a synthetic polypeptide can be confirmed by amino acid analysis or sequencing (e.g., using Edman degradation).
The invention also provides polynucleotides encoding human stem cell factor antibodies. These polynucleotides can be used, for example, to produce quantities of the antibodies for therapeutic or diagnostic use. The antibodies of the invention typically contain light and heavy chains, and the sequences encoding the light and heavy chains can be contained in one polynucleotide or in two or more polynucleotides. The polynucleotides can be DNA or RNA.
Polynucleotides that can be used to encode the CDR3 regions of SEQ ID NOS: 13-24, and SEQ ID NOS: 86-92 are shown in SEQ ID NOS: 1-13 and SEQ ID NO: 93-99, respectively. Polynucleotides that encode consensus heavy chains and light chains of human antibodies that have been isolated from the Morphosys HuCAL library are shown in Table 1 (SEQ ID NOS: 26-39). Polynucleotides that can be used to encode the CDR1 and CDR2 regions are shown in Table 5. Polynucleotides encoding human immunoglobulin light and heavy chains are known in the art. Any combination of native human immunoglobulin light and heavy chains or consensus sequences can be used in the production of the antibodies of the invention.
Polynucleotides of the invention present in a host cell can be isolated from other cellular components such as membrane components, proteins, and lipids. The polynucleotides can be made by a cell and isolated using standard nucleic acid purification techniques, or synthesized using an amplification technique, such as the polymerase chain reaction (PCR), or by using an automatic synthesizer. Methods for isolating polynucleotides are routine and are known in the art. Any such technique for obtaining a polynucleotide can be used to obtain isolated polynucleotides encoding antibodies of the invention. For example, restriction enzymes and probes can be used to isolate polynucleotides which encode the antibodies. Isolated polynucleotides are in preparations that are free or at least 70, 80, or 90% free of other molecules.
Human antibody-encoding cDNA molecules of the invention can be made with standard molecular biology techniques, using mRNA as a template. Thereafter, cDNA molecules can be replicated using molecular biology techniques known in the art and disclosed in manuals such as Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, USA (1989). An amplification technique, such as PCR, can be used to obtain additional copies of the polynucleotides.
Alternatively, synthetic chemistry techniques can be used to synthesize polynucleotides encoding antibodies of the invention. The degeneracy of the genetic code allows alternate nucleotide sequences to those depicted in SEQ ID NOS: 1-6, 7-11, 12, or 93-99 to be synthesized that will encode an antibody having, for example, one of the VH3-CDR3, VLκ-CDR3, VLλ-CDR3 amino acid sequences shown in SEQ ID NOS: 13-18, 19-23, 24 or 86-92, respectively.
A polynucleotide encoding an antibody of the invention can comprise all or a portion of the antibody. For example, the polynucleotide can encode the light chain or heavy chain or both, or any portion of the light chain or heavy chain, or any portion of the light and heavy chains.
To express a polynucleotide encoding a human antibody of the invention, the polynucleotide can be inserted into an expression vector that contains the necessary elements for the transcription and translation of the inserted coding sequence. Expression vectors of the invention thus comprise a polynucleotide or polynucleotides encoding the antibody or portion thereof and at least one element necessary for the transcription and translation of the coding sequence, such as a promoter operably linked to the coding sequence. Methods that are well known to those skilled in the art can be used to construct expression vectors containing sequences encoding human antibodies and appropriate transcriptional and translational control elements. These methods include in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination. Such techniques are described, for example, in Sambrook et al. (1989) supra and in Ausubel et al., CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, John Wiley & Sons, New York, N.Y., 1995. See also Examples 1-3, below.
A variety of expression vector/host systems can be utilized to contain and express sequences encoding a human antibody of the invention. These include, but are not limited to, microorganisms, such as bacteria transformed with recombinant bacteriophage, plasmid, or cosmid DNA expression vectors; yeast transformed with yeast expression vectors, insect cell systems infected with virus expression vectors (e.g., baculovirus), plant cell systems transformed with virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or with bacterial expression vectors (e.g., Ti or pBR322 plasmids), or animal cell systems, such as CHO-K1 cells or HKB11 cells described in U.S. Pat. No. 6,136,599 and the vectors described therein. HKB11 cells and vectors described in U.S. Pat. No. 6,136,599 are a preferred expression vector/host cell system.
The control elements or regulatory sequences are those non-translated regions of the vector, including enhancers, promoters, and 5′ and 3′ untranslated regions, which interact with host cellular proteins to carry out transcription and translation. Such elements can vary in their strength and specificity. Depending on the vector system and host utilized, any number of suitable transcription and translation elements, including constitutive and inducible promoters, can be used. For example, when cloning in bacterial systems, inducible promoters such as the hybrid lacZ promoter of the BLUESCRIPT phagemid (Stratagene, LaJolla, Calif.) or pSPORT1 plasmid (Life Technologies) and the like can be used. The baculovirus polyhedrin promoter can be used in insect cells. Promoters or enhancers derived from the genomes of plant cells (e.g., heat shock, RUBISCO, and storage protein genes) or from plant viruses (e.g., viral promoters or leader sequences) can be cloned into the vector. In mammalian cell systems, promoters from mammalian genes or from mammalian viruses are preferable. If it is necessary to generate a cell line that contains multiple copies of a nucleotide sequence encoding a human antibody, vectors based on SV40 or EBV can be used with an appropriate selectable marker.
To assess the efficacy of a particular antibody in allergic asthma therapy, the antibody can be tested in vitro in TF-1 proliferation and eosoniphil survival assays as detailed in Examples 7 & 8, respectively. In addition, the ability of Stem Cell Factor antibodies to inhibit Stem Cell Factor activity can be measured in vivo with a cynomologous monkey model.
Any of the human Stem Cell Factor antibodies described above can be provided in a pharmaceutical composition comprising a pharmaceutically acceptable carrier. The pharmaceutically acceptable carrier preferably is non-pyrogenic. The compositions can be administered alone or in combination with at least one other agent, such as stabilizing compound, which can be administered in any sterile, biocompatible pharmaceutical carrier, including, but not limited to, saline, buffered saline, dextrose, and water. A variety of aqueous carriers may be employed, e.g., 0.4% saline, 0.3% glycine, and the like. These solutions are sterile and generally free of particulate matter. These solutions may be sterilized by conventional, well-known sterilization techniques (e.g., filtration). The compositions may contain pharmaceutically acceptable auxiliary substances as required to approximate physiological conditions such as pH adjusting and buffering agents, etc. The concentration of the antibody of the invention in such pharmaceutical formulation can vary widely, i.e., from less than about 0.5%, usually at or at least about 1% to as much as 15 or 20% by weight and will be selected primarily based on fluid volumes, viscosities, etc., according to the particular mode of administration selected. See U.S. Pat. No. 5,851,525. If desired, more than one type of human antibody, for example with different Kd for Stem Cell Factor binding, can be included in a pharmaceutical composition.
The compositions can be administered to a patient alone, or in combination with other agents, drugs or hormones. In addition to the active ingredients, these pharmaceutical compositions can contain suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries that facilitate processing of the active compounds into preparations which can be used pharmaceutically. Pharmaceutical compositions of the invention can be administered by any number of routes including, but not limited to, oral, intravenous, intratracheal, inhalation, intramuscular, intra-arterial, intramedullary, intrathecal, intraventricular, transdermal, subcutaneous, intraperitoneal, intranasal, parenteral, topical, sublingual, or rectal means.
After pharmaceutical compositions have been prepared, they can be placed in an appropriate container and labeled for treatment of an indicated condition. Such labeling would include amount, frequency, and method of administration.
The invention also provides methods of ameliorating symptoms of a disorder in which Stem Cell Factor is elevated. These disorders include, without limitation, asthma and other immunological or allergic disorders. In one embodiment of the invention, a therapeutically effective dose of a human antibody of the invention is administered to a patient having a disorder in which Stem Cell Factor activity is elevated, such as those disorders above.
The determination of a therapeutically effective dose is well within the capability of those skilled in the art. A therapeutically effective dose refers to the amount of human antibody that is used to effectively treat asthma or other disorder in which stem cell factor is elevated compared with the efficacy that is evident in the absence of the therapeutically effective dose.
The therapeutically effective dose can be estimated initially in animal models, usually rats, mice, rabbits, dogs, pigs or non-human primates. The animal model also can be used to determine the appropriate concentration range and route of administration. Such information can then be used to determine useful doses and routes for administration in humans. An experimental mouse model of allergic asthma is described in Example 9.
Therapeutic efficacy and toxicity, e.g., ED50 (the dose therapeutically effective in 50% of the population) and LD50 (the dose lethal to 50% of the population) of a human antibody, can be determined by standard pharmaceutical procedures in cell cultures or experimental animals. The dose ratio of toxic to therapeutic effects is the therapeutic index, and it can be expressed as the ratio, LD50/ED50.
Pharmaceutical compositions that exhibit large therapeutic indices are preferred. The data obtained from animal studies is used in formulating a range of dosage for human use. The dosage contained in such compositions is preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage varies within this range depending upon the dosage form employed, sensitivity of the patient, and the route of administration.
The exact dosage will be determined by the practitioner, in light of factors related to the patient who requires treatment. Dosage and administration are adjusted to provide sufficient levels of the human antibody or to maintain the desired effect. Factors that can be taken into account include the severity of the disease state, general health of the subject, age, weight, and gender of the subject, diet, time and frequency of administration, drug combination(s), reaction sensitivities, and tolerance/response to therapy. Long-acting pharmaceutical compositions can be administered every 3 to 4 days, every week, or once every two weeks depending on the half-life and clearance rate of the particular formulation.
Polynucleotides encoding human antibodies of the invention can be constructed and introduced into a cell either ex vivo or in vivo using well-established techniques including, but not limited to, transferrin-polycation-mediated DNA transfer, transfection with naked or encapsulated nucleic acids, liposome-mediated cellular fusion, intracellular transportation of DNA-coated latex beads, protoplast fusion, viral infection, electroporation, “gene gun,” and DEAE- or calcium phosphate-mediated transfection.
Effective in vivo dosages of an antibody are in the range of about 5 μg to about 50 μg/kg, about 50 μg to about 5 mg/kg, about 100 μg to about 500 μg/kg of patient body weight, and about 200 to about 250 μg/kg of patient body weight. For administration of polynucleotides encoding the antibodies, effective in vivo dosages are in the range of about 100 ng to about 200 ng, 500 ng to about 50 mg, about 1 μg to about 2 mg, about 5 μg to about 500 μg, and about 20 μg to about 100 μg of DNA.
The mode of administration of human antibody-containing pharmaceutical compositions of the invention can be any suitable route which delivers the antibody to the host. Pharmaceutical compositions of the invention are particularly useful for parenteral administration, i.e., subcutaneous, intramuscular, intravenous, or intranasal administration.
The antibodies of the invention can also be bound to a cytotoxic molecule such as a chemotherapeutic agent, a toxin (such as an enzymatically active toxin of bacterial, fungal, plant or animal origin, or fragments thereof), or a radioactive isotope (i.e., a radioconjugate). Preferably, the cytotoxic molecule is capable of inducing apoptosis in stem cell factor expressing cells upon administration of the antibody with bound cytotoxic molecule. Antibodies of the invention bound to a cytotoxic molecule can be used in the same manner as antibodies without a bound cytotoxic molecule, with adjustments to the dose, route of administration and dosing regimen depending on the type of cytotoxic molecule employed.
Suitable chemotherapeutic agents include adriamycin, doxorubicin, 5-fluorouracil, cytosine arabinoside (“Ara-C“), cyclophosphamide, thiotepa, taxotere (docetaxel), busulfan, cytoxin, taxol, methotrexate, cisplatin, melphalan, vinblastine, bleomycin, etoposide, ifosfamide, mitomycin C, mitoxantrone, vincreistine, vinorelbine, carboplatin, teniposide, daunomycin, carminomycin, aminopterin, dactinomycin, mitomycins, esperamicins, taxane and maytansin derivatives. Enzymatically active toxins and fragments thereof which can be used include diphtheria A chain, nonbinding active fragments of diphtheria toxin, exotoxin A chain (from Pseudomonas aeruginosa), ricin A chain, abrin A chain, modeccin A chain, alpha-sarcin, Aleurites fordii proteins, dianthin proteins, Phytolaca americana proteins (PAPI, PAPII, and PAP-S), momordica charantia inhibitor, curcin, crotin, sapaonaria officinalis inhibitor, gelonin, mitogellin, restrictocin, phenomycin, enomycin and the tricothecenes. A variety of radionuclides are available for the production of radioconjugated antibodies including 212Bi, 131I, 131In, 90Y and 186Re.
Conjugates of the antibody and cytotoxic agent are made using a variety of bifunctional protein coupling agents such as N-succinimidyl-3-(2-pyridyldithiol)propionate (SPDP), iminothiolane (IT), bifinctional derivatives of imidoesters (such as dimethyl adipimidate HCL), active esters (such as disuccinimidyl suberate), aldehydes (such as glutareldehyde), bis-azido compounds (such as bis(p-azidobenzoyl)hexanediamine), bis-diazonium derivatives (such as bis-(p-diazoniumbenzoyl)-ethylenediamine), diisocyanates (such as tolyene 2,6-diisocyanate), and bis-active fluorine compounds (such as 1,5-difluoro-2,4-dinitrobenzene). For example, a ricin immunotoxin can be prepared as described in Vitetta et al., Science 238: 1098 (1987). Carbon-14-labeled 1-isothiocyanatobenzyl-3-methyldiethylene triaminepentaacetic acid (MX-DTPA) is an exemplary chelating agent for conjugation of radionucleotide to the antibody. See WO94/11026.
The invention also provides diagnostic methods, with which human Stem Cell Factor can be detected in a test preparation, including without limitation a sample of serum, broncheoalveolar lavage fluid, lung, a cell culture system, or a cell-free system (e.g., a tissue homogenate). Such diagnostic methods can be used, for example, to diagnose disorders in which Stem Cell Factor is altered. When used for diagnosis, detection of an amount of the antibody-Stem Cell Factor complex in a test sample from a patient which varied with that of an amount of the complex in a normal sample identifies the patient as likely to have the disorder. The test preparation is contacted with a human antibody of the invention, and the test preparation is then assayed for the presence of an antibody-Stem Cell Factor complex. Suitable assay formats include those described herein for detecting Stem Cell Factor or antibodies of the invention.
The invention also provides methods for detecting Stem Cell Factor or antibodies to Stem Cell Factor. The methods comprise the steps of adding an antibody of the invention to a test sample suspected of containing Stem Cell Factor and detecting antibody bound to Stem Cell Factor, whereby the presence of bound antibody indicates the presence of Stem Cell Factor in the test sample. Alternatively, the invention provides methods for detecting antibodies of the invention comprising adding Stem Cell Factor to a test sample suspected of containing antibodies of the invention and detecting Stem Cell Factor bound to antibodies of the invention, whereby the presence of bound Stem Cell Factor indicates the presence of antibodies of the invention in the test sample.
Numerous formats for immunoassays are known in the art, including, for example, competitive binding assays, direct and indirect sandwich assays, and immuno-precipitation assays.
If desired, the human antibody can comprise a detectable label, such as a fluorescent, radioisotopic, chemiluminescent, or enzymatic label, such as horseradish peroxidase, alkaline phosphatase, or luciferase.
Optionally, the antibody can be bound to a solid support, which can accommodate automation of the assay. Suitable solid supports include, but are not limited to, glass or plastic slides, tissue culture plates, microtiter wells, tubes, silicon chips, or particles such as beads (including, but not limited to, latex, polystyrene, or glass beads). Any method known in the art can be used to attach the antibody to the solid support, including use of covalent and non-covalent linkages, passive absorption, or pairs of binding moieties attached to the antibody and the solid support. Binding of Stem Cell Factor and the antibody can be accomplished in any vessel suitable for containing the reactants. Examples of such vessels include microtiter plates, test tubes, and microcentrifuge tubes.
Suitable radioisotopic labels include radioisotopes, such as 35S, 14C, 125I, 3H, and 131I. The antibody can be labeled with the radioisotope using the techniques described in Current Protocols in Immunology, Volumes 1 and 2, Coligen et al., Ed. Wiley-Interscience, New York, N.Y., Pubs. (1991) for example and radioactivity can be measured using scintillation counting.
Suitable fluorescent labels include rare earth chelates (europium chelates) or fluorescein and its derivatives, rhodamine and its derivatives, dansyl, Lissamine, phycoerythrin and Texas Red are available. The fluorescent labels can be conjugated to the antibody using the techniques disclosed in Current Protocols in Immunology, supra, for example. Fluorescence can be quantified using a fluorimeter.
Suitable enzymatic labels include luciferases (e.g., firefly luciferase and bacterial luciferase, luciferin, 2,3-dihydrophthalazinediones, malate dehydrogenase, urease, peroxidase such as horseradish peroxidase (HRPO), alkaline phosphatase, .beta.-galactosidase, glucoamylase, lysozyme, saccharide oxidases (e.g., glucose oxidase, galactose oxidase, and glucose-6-phosphate dehydrogenase), heterocydic oxidases (such as uricase and xanthine oxidase), lactoperoxidase, microperoxidase, and the like. Techniques for conjugating enzymes to antibodies are described in O'Sullivan et al., Methods for the Preparation of Enzyme-Antibody Conjugates for use in Enzyme Immunoassay, in Methods in Enzym. (ed J. Langone & H. Van Vunakis), Academic press, N.Y., 73: 147-166 (1981). Examples of enzyme-substrate combinations include, for example: Horseradish peroxidase (HRPO) with hydrogen peroxidase as a substrate, wherein the hydrogen peroxidase oxidizes a dye precursor (e.g., orthophenylene diamine (OPD) or 3,3′,5,5′-tetramethyl benzidine hydrochloride (TMB)); alkaline phosphatase (AP) with para-Nitrophenyl phosphate as chromogenic substrate; and beta.-D-galactosidase (.beta.-D-Gal) with a chromogenic substrate (e.g., p-nitrophenyl-.beta.-D-galactosidase) or fluorogenic substrate 4-methylumberlliferyl-.beta.-D-galactosidase.
The detectable label can be indirectly conjugated with the antibody. For example, the antibody can be conjugated with biotin and any of the three broad categories of labels mentioned above can be conjugated with avidin, or vice versa. Biotin binds selectively to avidin and thus, the label can be conjugated with the antibody in this indirect manner. Alternatively, to achieve indirect conjugation of the label with the antibody, the antibody is conjugated with a small hapten (e.g., digoxin) and one of the different types of labels mentioned above is conjugated with an anti-hapten antibody (e.g., anti-digoxin antibody). Thus, indirect conjugation of the label with the antibody can be achieved.
Additionally, the antibody of the invention need not be labeled, and the presence thereof can be detected using a labeled antibody which binds to the antibody of the invention.
For immunohistochemistry, a tissue sample may be fresh or frozen or may be embedded in paraffin and fixed with a preservative such as formalin.
The antibodies may also be used for in vivo diagnostic assays. Generally, the antibody is labeled with a radio nuclide (such as 111In, 99Tc, 14C, 131I, 125I, 3H, 32P or 35S) so that the Stem Cell Factor can be localized using immunoscintiography.
The antibodies of the invention may be used as affinity purification agents. In this process, the antibodies are immobilized on a solid phase such as glass or plastic slides, tissue culture plates, microtiter wells, tubes, silicon chips, or particles such as beads, using methods well known in the art. The immobilized antibody is contacted with a sample containing the Stem Cell Factor to be purified, and thereafter the support is washed with a suitable solvent that will remove substantially all the material in the sample except Stem Cell Factor protein, which is bound to the immobilized antibody. Finally, the support is washed with another suitable solvent, such as a buffer at a pH that will release the Stem Cell Factor protein from the antibody.
As a matter of convenience, the antibody of the present invention can be provided in a kit, i.e., a packaged combination of reagents in predetermined amounts with instructions for performing the diagnostic assay. Where the antibody is labeled with an enzyme, the kit will include substrates and cofactors required by the enzyme (e.g., a substrate precursor which provides the detectable chromophore or fluorophore). In addition, other additives may be included such as stabilizers, buffers (e.g., a block buffer or lysis buffer) and the like. The relative amounts of the various reagents may be varied widely to provide for concentrations in solution of the reagents which substantially optimize the sensitivity of the assay. Particularly, the reagents may be provided as dry powders, usually lyophilized, including excipients which on dissolution will provide a reagent solution having the appropriate concentration.
All patents and patent applications cited in this disclosure are expressly incorporated herein by reference. The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific examples, which are provided for purposes of illustration only and are not intended to limit the scope of the invention.
1.1 Cloning of HuCAL-Fab 1.
HuCAL-Fab 1 is a fully synthetic, modular human antibody library in the Fab antibody fragment format. HuCAL-Fab 1 was assembled starting from an antibody library in the single-chain format (HuCAL-scFv) in accordance with the method of Knappik et al., J. Mol. Biol. 296: 55-86 (2000)). The heavy and light chain variable region sequences in the library are shown in Tables 1 and 2.
The sequence identification numbers for Tables 1 and 2 are as follows:
HuCAL-Fab 1 was cloned into a phagemid expression vector pMORPH18 Fab1 (
First, the Vλ and Vκ libraries were isolated from HuCAL-scFv by restriction digest using EcoRV/DraIII and EcoRV/BsiWI, respectively. These Vλ and Vκ libraries were cloned into pMORPH18 Fab1 cut with EcoRV/DraIII and EcoRV/BsiWI, respectively. After ligation and transformation in E. coli TG-1, library sizes of 4.14×108 and 1.6×108, respectively, were obtained, in both cases exceeding the VL diversity of HuCAL-scFv.
Similarly, the VH library was isolated from HuCAL-scFv by restriction digest using StyI/MunI. This VH library was cloned into the pMORPH18-Vλ and Vκ libraries cut with StyI/MunI. After ligation and transformation in E. coli TG-1, a total library size of 2.09×1010 was obtained, with 67% correct clones (as identified by sequencing of 207 clones).
1.2 Phagemid rescue, phage amplification and purification.
HuCAL-Fab was amplified in 2×TY medium containing 34 μg/ml chloramphenicol and 1% glucose (2×TY-CG). After helper phage infection (VCSM13) at 37° C. at an OD600 of about 0.5, centrifugation and resuspension in 2×TY/34 μg/ml chloramphenicol/50 μg/ml kanamycin, cells were grown overnight at 30° C. Phage were PEG-precipitated from the supernatant (Ausubel et al., 1998), resuspended in PBS/20% glycerol, and stored at −80° C. Phage amplification between two panning rounds was conducted as follows: mid-log phase TG1-cells were infected with eluted phage and plated onto LB-agar supplemented with 1% of glucose and 34 μg/ml of chloramphenicol. After overnight incubation at 30° C., colonies were scraped off and adjusted to an OD600 of 0.5. Helper phage were added as described above.
Design of the CDR3 Libraries VA Positions 1 and 2.
The original HuCAL master genes (Knappik et al. J. Mol. Biol. 296: 55 (2000)) were constructed with their authentic N-termini: VLλ1: QS (CAGAGC), VLλ2: QS (CAGAGC), and VLλ3: SY (AGCTAT). Sequences containing these amino acids are shown in WO 97/08320. During HuCAL library construction, the first two amino acids were changed to DI to facilitate library cloning (EcoRI site). All HuCAL libraries contain VLλ genes with the EcoRV site GATATC (DI) at the 5′-end. All HuCAL kappa genes (master genes and all genes in the library) contain DI at the 5′-end.
VH Position 1.
The original HuCAL master genes were constructed with their authentic N-termini: VH1A, VH1B, VH2, VH4, and VH6 with Q (=CAG) as the first amino acid and VH3 and VH5 with E (=GAA) as the first amino acid. Sequences containing these amino acids are shown in WO 97/08320. In the HuCAL Fab 1 library, all VH chains contain Q (=CAG) at the first position.
Vκ1/Vκ3 Position 85.
Because of the cassette mutagenesis procedure used to introduce the CDR3 library (Knappik et al., J. Mol. Biol. 296, 57-86, 2000), position 85 of Vκ1 and Vκ3 can be either T or V. Thus, during HuCAL scFv 1 library construction, position 85 of Vκ1 and Vκ3 was varied as follows: Vk1 original, 85T (codon ACC); Vκ1 library, 85T or 85V (TRIM codons ACT or GTT); Vκ3 original, 85V (codon GTG); Vκ3 library, 85T or 85V (TRIM codons ACT or GTT); the same applies to HuCAL Fab1.
All CDR3 residues which were kept constant are indicated in TABLE 1.
The designed CDR3 length distribution is as follows. Residues which were varied are shown in brackets (x) in TABLE 1. Vκ CDR3, 8 amino acid residues (position 89 to 96) (occasionally 7 residues), with Q90 fixed; V lambda CDR3, 8 to 10 amino acid residues (position 89 to 96) (occasionally 7-10 residues), with Q89, S90, and D92 fixed; and VH CDR3, 5 to 28 amino acid residues (position 95 to 102) (occasionally 4-28), with D101 fixed.
Solid Phase Panning
Wells of MaxiSorpTM microtiter plates (Nunc, Wiesbaden, Germany) were coated with rat- or human TIMP protein dissolved in PBS (2 μg/well). After blocking with 5% non-fat dried milk in PBS, 1-5×1012 HuCAL-Fab phage purified as above were added for 1 h at 20° C. After several washing steps, bound phage were eluted by pH-elution with 100 mM triethylamine and subsequent neutralization with 1M TRIS-Cl pH 7.0. Three rounds of panning were performed with phage amplification conducted between each round as described in Example 1.
Subcloning of Selected Fab Fragments for Expression
The Fab-encoding inserts of the selected HuCAL Fab fragments were subcloned into the expression vector pMORPHx7_FS to facilitate rapid expression of soluble Fab. The DNA preparation of the selected HuCAL Fab clones was digested with XbaI/EcoRI, thus cutting out the Fab encoding insert (ompA-VL and phoA-Fd). Subcloning of the purified inserts into the XbaI/EcoRI cut vector pMORPHx7, previously carrying a scFv insert, leads to a Fab expression vector designated pMORPHx9_Fab1_FS which is shown in
Identification of Stem Cell Factor-Binding Fab Fragments by ELISA
The wells of a Maxisorp ELISA plates were coated with 100 μl/well solutions of rat Stem Cell Factor or human Stem Cell Factor at a concentration of 5 μg/ml diluted in coating buffer. Expression of individual Fab was induced with 0.5 mM IPTG for 12 h at 30° C. Soluble Fab was extracted from the periplasm by osmotic shock (Ausubel et al., 1998) and used in an ELISA. The Fab fragment was detected with an anti-Fab antibody (Dianova, Hamburg, Germany). Values at 370 nm were read out after addition of horseradish peroxidase-conjugated anti-mouse IgG antibody and POD soluble substrate (Roche Diagnostics, Pleasanton, Calif., USA).
Kappa light chain constant region (DNA sequence):
Kappa light chain constant region (protein sequence):
Lambda light chain constant region (DNA sequence):
Lambda light chain constant region (protein sequence):
Construction of HuCAL Immunoglobulin Expression Vectors
Heavy Chain Cloning.
The multiple cloning site of pcDNA3.1+ (Invitrogen, Carlsbad, Calif., USA) was removed (NheI/ApaI), and a stuffer compatible with the restriction sites used for HuCAL design was inserted for the ligation of the leader sequences (NheI/EcoRI), VH-domains (EcoRI/BlpI), and the immunoglobulin constant regions (BlpI/ApaI). The leader sequence (EMBL M83133) was equipped with a Kozak sequence (Kozak, 1987). The constant regions of human IgG1 (PIR J00228), IgG4 (EMBL K01316), and serum IgA1 (EMBL J00220) were dissected into overlapping oligonucleotides with lengths of about 70 bases. Silent mutations were introduced to remove restriction sites non-compatible with the HuCAL design. The oligonucleotides were spliced by overlap extension-PCR.
Light Chain Cloning.
The multiple cloning site of pcDNA3.1/Zeo+ (Invitrogen, Carlsbad, Calif., USA) was replaced by two different stuffers. The κ-stuffer provided restriction sites for insertion of a κ-leader (NheI/EcoRV), HuCAL-scFv Vk-domains (EcoRV/BsiWI,) and the κ-chain constant region (BsiWI/ApaI). The corresponding restriction sites in the λ-stuffer were NheI/EcoRV (1-leader), EcoRV/HpaI (V1-domains), and HpaI/ApaI (λ-chain constant region). The κ-leader (EMBL Z00022) as well as the λ-leader (EMBL L27692) were both equipped with Kozak sequences. The constant regions of the human κ-(EMBL J00241) and λ-chain (EMBL M18645) were assembled by overlap extension-PCR as described above.
Generation of IgG-Expressing CHO-Cells.
CHO-K1 cells were co-transfected with an equimolar mixture of IgG heavy and light chain expression vectors. Double-resistant transfectants were selected with 600 μg/ml G418 and 300 μg/ml Zeocin (Invitrogen) followed by limiting dilution. The supernatant of single clones was assessed for IgG expression by capture-ELISA (see below). Positive clones were expanded in RPMI-1640 medium supplemented with 10% ultra-low IgG-FCS (Life Technologies, Rockville, Md., USA). After adjusting the pH of the supernatant to 8.0 and sterile filtration, the solution was subjected to standard protein A column chromatography (Poros 20 A, PE Biosystems, Foster City, Calif., USA)
All five of the Fabs that showed anti-SCF activity in the TF-1 assay were converted to IgG (A1, A2, A8, D5 and E6). There was insufficient material to test A1 and E6 but the other 3 IgG clones were assayed. At a concentration of 10 ug/ml, A2 and D5 inhibited TF-1 proliferation to the greatest extent and were therefore chosen for affinity optimization.
The capacity of stem cell factor antibodies to inhibit Stem Cell Factor growth factor activity was measured utilizing a TF1 human hematopoietic cell proliferation assay. In this assay, TF1 cells (American Type Culture Collection, Rockville, Md., USA) were cultured for 4 days in 96 well plates (1×104/well, 100 μl volume) in RPMI+10% serum with Stem Cell Factor (human from R&D Systems, rat and cyno from Bayer) with or without anti-human Stem Cell Factor murine polyclonal antibody (R&D Systems, catalog #AF-255-NA, Minneapolis, Minn., USA). GM-CSF(R&D Systems) treatment was used as a positive control. Twenty four hours before the final reading, 10 μl Alamar Blue (10% vol, BioSource, Camarillo, Calif., USA) is added to each well. Fluorescence is determined at 530/590 nm using a WALLAC Victor 2 fluorometer (Wallac Oy, Turku, Finland).
This assay was used to measure the bioactivity of the Fabs and IgGs, species cross-reactivity of the Fabs and IgGs, and for other preformulation activities.
Stem cell factor was shown to stimulate TF-1 cell proliferation with an IC50 of 2 ng/ml while the addition of polyclonal Stem Cell Factor antibodies neutralized this activity with an IC50 of 8 μg/ml.
Treatment of TF-1 cells with Fab clones A1, A2, A8, D5 and E6 resulted in inhibition of human, cyno and rat SCF-induced proliferation. All the Fabs inhibited >100% at 200 ug/ml (D5 was only tested up to 120 ug/ml due to limited protein availability). The greater than 100% inhibition could not be accounted for by cytotoxicity (as determined by GM-CSF stimulation of TF-1 proliferation in the presence of 200 ug/ml Fab) or PBS dilution effects. A dose titration of Fabs A1, A2 and E6 indicated very similar dose/response characteristics among the three Fabs. The IC50 values for inhibition of cyno SCF were between 20 and 60 ug/ml for all three Fabs tested. The IC50 values for inhibition of rat SCF were between 20 and 60 ug/ml for A1 and A2 and between 6.1 and 20 ug/ml for E6. The observation that rat SCF could be inhibited by any of the Fabs was unexpected due to the lack of strong binding between the Fabs and rat SCF as determined by BIAcore assay. The reason for an inhibitory effect in the TF-1 proliferation assays is still unclear but may be due to low affinity binding of the Fabs to rat SCF that is adequate enough to block its interaction with c-kit on the TF-1 cells.
Six anti-SCF Fab clones (A2, E6-1, D5, A1, A8, F8) generated using Morphosys technology were screened for bioactivity in the TF-1 proliferation assay. TF-1 cells were stimulated with 10 ng/ml SCF with or without pretreatment with Fab. At 100 ug/ml, 5 out of 6 of the clones (A2, E6-1, D5, A1, A8) inhibited TF-1 proliferation 40% or greater. F8 failed to inhibit any SCF effect at that concentration. A dose titration was done for A1, A8 and F8 (100, 50, 25 and 12.5 ug/ml). There was not enough E6-1 and D5 protein for a full dose titration of those two clones. A1 and A8 both appeared to show some titration of the Fab effect. In a repeat assay, A1 and A8 were titrated (200, 100, 50 and 25 ug/ml) and again showed a dose-dependent effect on SCF-induced proliferation of TF-1 cells. A GM-CSF-stimulated control indicated that the Fabs (A1, A8, F8) were not cytotoxic and did not inhibit the proliferation of the TF-1 cells non-specifically.
More of the Fab protein was expressed for all 5 Fab clones. A side-by-side comparison of the 5 Fab clones (A1, A2, A8, D5, and E6), that inhibited TF-1 proliferation 40% or greater at 100 ug/ml, was performed in a full dose response study (200, 66, 20, 6.6 ug/ml). The five Fab clones were assayed for their ability to inhibit TF-1 proliferation with 10 ng/ml SCF or GM-CSF. All five clones were capable of inhibiting SCF-induced TF-1 proliferation up to 96.6-139.7% at 200 ug/ml. D5 and E6 had the most favorable IC50 values (10-12 ug/ml) compared to the other clones, which had IC50s of 29-30 ug/ml. None of the clones had an effect on GM-CSF-induced TF-1 proliferation at up to 200 ug/ml suggesting little to no non-specific or cytotoxic effects of the Fab clones on the TF-1 cells. PBS dilution controls indicated no significant effect on proliferation compared to SCF alone. However, there was a trend to lower proliferation with the 1:5 dilution (that used for the 200 ug/ml Fab clone treatment) which may have contributed to the greater than 100% inhibition that was calculated at the highest concentration of 3 of the 5 Fab clones.
In Vitro Testing of Cross Reactivity of the Fabs with Rat and Cyno SCF
In an effort to predict in vivo cross-reactivity of the anti-SCF antibodies, TF-1 cells were stimulated with recombinant SCF from rat and cynomologous monkeys. It was determined that both recombinant cyno and rat SCF were capable of stimulating human TF-1 proliferation in a dose responsive manner. The approximate IC50 for human, cyno and rat SCF in the assay were 2, 25 and 17 ng/ml, respectively
The human primary eosinophil survival and activation assays involved isolation of peripheral blood eosinophils and long term culture (i.e. up to 3 days) with or without growth and survival factors such as IL-5 or SCF. These assays were performed to confirm the bioactivity of Fabs and IgGs and evaluate species cross-reactivity in primary cells.
The capacity of stem cell factor antibodies to inhibit Stem Cell Factor-mediated eosinophil survival and activation was determined in cells harvested from human and cynomolgus monkey blood. First, eosinophils are isolated from peripheral blood by negative selection of CD16 using a steel VarioMacs column protocol (Miltenyi Biotec, Auburn, Calif.). This protocol typically returns eosinophils at >95% purity and works equally well for human and cynomolgus monkey blood. Purified eosinophils are then plated at 1×105 cells/well in a 96 well plate with varying concentrations of Stem Cell Factor (R&D Systems) or anti-Stem Cell Factor antibodies.
Supernatants from eosinophils incubated with activation factors such as Stem Cell Factor are assayed for the presence of eosinophil peroxidase, a marker of activation, by the addition of the peroxidase substrate OPD.
The results demonstrated that Stem Cell Factor promotes eosinophil survival in a dose-dependent manner while survival can be inhibited by Stem Cell Factor antibodies, also in a dose-dependent manner.
Activation of eosinophils by Stem Cell Factor can also be inhibited by anti-Stem Cell Factor antibodies. Results demonstrated that anti-Stem Cell Factor antibodies dose dependently decreased the Stem Cell Factor-mediated eosinophil activation.
SCF promotes eosinophil survival in a dose dependent manner and that survival can be inhibited by anti-SCF (10 ug/ml). The anti-apoptotic effect of anti-SCF was also dose dependent.
Cockroach Allergen Test Model
The effect of anti-mouse Stem Cell Factor polyclonal antibody (20 mg/kg) in a mouse model of asthma was assessed. The mice were immunized intraperitoneally (i.p.) with cockroach allergen (CRA) in phosphate buffered saline (PBS) on day 0. On day 14 an intranasal challenge of CRA to localize the response to the airway was given. Mice were then rechallenged on day 20 and 22 by intratracheal (i.t.) administration of CRA. The second i.t. challenge is given at a time when there is a considerable amount of inflammation found within and around the airway, including eosinophils. Anti-mouse Stem Cell Factor polyclonal antibody (20 mg/kg) was administered in saline buffer at the time of i.t. CRA challenge. Airway responsiveness to methacholine (AHR) was measured 24 hours after the last CRA challenge with a mouse plethysmograph (Buxco, Trot N.Y.). Airway eosinophil counts were determined 24 h after the last CRA challenge. Anti-mouse Stem Cell Factor polyclonal antibody yielded a 6-fold reduction in the development of AHR versus animals receiving no antibodies. Anti-mouse Stem Cell Factor polyclonal antibody also produced a 2-fold reduction in airway tissue eosinophilia.
The effect of an anti-mouse Stem Cell Factor monoclonal antibody (R&D Systems) was assessed in a CRA mouse model of asthma. Monoclonal antibody (400 ug/kg, 2 mg/kg, or 4 mg/kg) was administered i.t. with CRA on both days of antigen challenge (days 20, 22). Airway responsiveness to methacholine (AHR) and lung cytokine levels were measured as before 6 h after the final CRA challenge. Almost complete inhibition of airway hyperresponsiveness was observed with the lowest dose (400 ug/kg) of antibody tested. Assessment of baseline airway resistance prior to methacholine challenge revealed that the highest dose of monoclonal antibody (4 mg/kg) caused a slight increase in baseline airway resistance. The effect of the monoclonal antibody on various pro-inflammatory chemokines and cytokines was also assessed in this model. A dose-dependent reduction in IL-4, IL-5, tumor necrosis factor (TNF), RANTES and TARC was observed.
Optimization of Fab Activity
10.1 Fab Affinity Optimization
Fabs A2 and D5 were optimized for higher affinity binding to human SCF. The CDR3 loops from A2 and D5 were maintained, while the CDR1 and CDR2 loops from both the light and heavy chain were randomized and approximately ten million A2 variants and ten million D5 variants were expressed on the surface of M13 bacteriophage (Morphosys). The CDR1 and CDR2 loops were simultaneously excised from the A2 and D5 kappa light chain variable region with the restriction enzymes PstI and SanDI. Randomized cassettes prepared according to the method in Knappik et al. (2000) containing randomized CDR1 and CDR2 with the intervening Framework 2 region were then inserted to provide A2 and D5 kappa light chain variable regions with randomized CDR1 and CDR2.
The CDR1 region of the A2 and D5 heavy chain variable region VH3 was excised using BspE1 and BssHII and randomized using cassettes prepared according to the method in Knappik et al. (2000). The CDR2 region of the A2 and D5 heavy chain variable region H3 was excised with XhoI and BssHII and randomized using the same type of cassettes.
Three Fab phage libraries were thus created for each of A2 and D5: 1) light chain having randomized CDR1 and CDR2; 2) heavy chain having a randomized CDR1; and 3) heavy chain having a randomized CDR2.
The phagemid expression vector pMORPH18 Fab1 containing the CDR1 and CDR2 libraries was amplified as described in Example 1. The Fab phage libraries were panned for three rounds against human SCF as described in Example 3.
The Fab-encoding inserts of selected HuCAL Fab 1 clones were subcloned into the expression vector pMORPHx7_FS as described in Example 4 to create the Fab expression vector designated pMORPHx9_Fab1_FS. The clones were expressed in E. coli and purified using StrepTagII via StrepTactin affinity chromatography (Sigma-Genosys, Woodland, Tex.). The “Strep-tagged” proteins readily bind StrepTactin with high specificity and the protein was eluted from the column upon competition with desthiobiotin. A 1 L culture typically yielded 1-3 mg of purified Fab. The expressed Fabs were tested in BiaCORE assays (Uppsala, Sweden). The Fabs with the highest affinity were selected for testing in the TF-1 proliferation assay.
For transient expression, immunoglobulin expression vectors were constructed in accordance with the method of Example 6. The scFv portion of the Fab heavy chain was inserted into the expression vector pcDNA3.1+ with IgG1 heavy chain constant regions. The scFv portion of the Fab light chain was inserted into the vector pcDNA3.1/Zeo+ with kappa light chain constant regions.
For selection expression, an expression vector containing both heavy and light chains was constructed. The scFv portions of the Fab heavy and light chains were inserted into an expression vector of the type described in U.S. Pat. No. 6,136,599 that contains heavy and light IgG chains. The expression vector also contained the drug resistance gene hph.
The DNA sequence of the light chain variable region of antibody A2-G8:
The sequence of the CDR1 region is AGAGCGAGCCAGGGCATTCGGGGGTA CCTGGGG. The sequence of the CDR2 region is TCGGCCAGCAGCTTGCAAAGC. The sequence of the CDR3 region is CAGCAGTATTCTGGTATGCCTTAT.
SCF antibody A2-G8 light chain variable and constant region (protein sequence):
The sequence of the CDR1 region is RASQGIRGYLG. The sequence of the CDR2 region is SASSLQS. The sequence of the CDR3 region is QQYSGMPY.
SCF antibody A2-G8 heavy chain variable region (DNA sequence):
The sequence of the CDR1 region is GGATTTACCTTTAGCAGCTATG CGATGAGC. The sequence of the CDR2 region is GCGATTAGCGGTAGCGGCGGC AGCACCTATTATGCGGATAGCGTGAAAGGC. The sequence of the CDR3 region is CGTGATTTTTTTGCTCACTTTGATGTT.
SCF antibody A2-G8 heavy chain variable and constant region (protein sequence):
The sequence of the CDR1 region is GFTFSSYAMS. The sequence of the CDR2 region is AISGSGGSTYYADSVKG. The sequence of the CDR3 region is RDFFAHFDV.
SCF antibody A2-G8 heavy chain constant region (DNA sequence):
SCF antibody A2-G8 heavy chain constant region (protein sequence):
SCF antibody A2-G8 light chain constant region (DNA sequence) is SEQ ID NO: 82.
SCF antibody A2-G8 light chain constant region (protein sequence) is SEQ ID NO: 83.
Expression of IgG from HKB11 Cells:
For transient expression HKB11 cells (as described in U.S. Pat. No. 6,136,599) were co-transfected with an equimolar mixture of IgG heavy and light chain expression vectors. The antibody was expressed without selection.
For expression with selection, IgG-heavy and light chain were cloned in a single expression vector also possessing a drug resistant gene (e.g. hph). Three days post transfection of HKB11 cells (200×106 cells) with the expression vector DNA (200 μg), cells were selected with Hygromycin B (50 μg/ml). By feeding the cells twice a week with fresh media, HygB-resistant cells were obtained ˜3 weeks post transfection. When stable levels of IgG expression were obtained (5-6 weeks post transfection), cells were scaled up (7 weeks post transfection) and large volume of cells (10 liters) were utilized for production of IgG on a weekly-basis using a Wave Bioreactor to produce smaller amounts of IgG until the required amount of IgG (˜100 mg) was obtained. To obtain larger (gram) quantities of IgG, the scaled-up culture had to be inoculated in a fermentor to produce larger volumes of material which took ˜4 weeks. An additional three weeks were required for affinity purification.
10.2 In Vitro Screening Cascade for Anti-SCF Fabs and IgGs
The first screen was a cell-free binding assay using the BIAcore system to identify Fabs that bound purified SCF. Antibodies showing such activity proceeded to cell-based assays. The second screen was a TF-1 human hematopoietic cell line proliferation assay. SCF stimulates TF-1 cells to proliferate with an IC50 of approximately 1 ng/ml. Antibodies that were capable of inhibiting SCF-induced TF-1 proliferation with an IC50 of 100 ug/ml or less were tested on primary eosinophils and mast cells in vitro. In vitro survival of eosinophils harvested from either human or Cynomologus monkey peripheral blood can be prolonged by treatment with SCF. Antibodies capable of inhibiting this prolonged survival with an IC50 of 100 ug/ml or better proceeded to in vivo screening.
Soluble human, cynomologous (also referred to as “cyno”), and rat SCF were immobilized on a BIAcore sensor chip through amine coupling. Binding to all three forms of SCF was measured for Fabs that were shown to bind to SCF to a level that was at least two-fold over background in a direct ELISA assay. Those antibodies that showed binding to human SCF were scaled up, purified, and decontaminated of endotoxins. These antibodies were further studied in cell-based assays described below.
Biacore Screening Results
Fabs were expressed at small scale and tested for binding using the BIAcore. Six anti-SCF Fabs with binding to human SCF were expressed and tested in the TF-1 proliferation assay. The lead candidates from this assay were Fabs A2 and D5. The affinity of Fabs A2 and D5 were further optimized for higher affinity binding methods through randomization of the CDR1 and CDR2 loops of the heavy and light chains of the Fabs. Fabs derived from this optimization process were screened using BIAcore for binding to SCF. The optimization of the A2 Fabs were most successful, and of these Fabs A2-G8 and Fabs A2-EI were identified as the highest affinity anti-SCF antibodies. These results correlated well with the cell assays described below.
Seven optimized Fabs (A2-A1, A2-D12, A2-E2, A2-E8, A2-G8, A2-H8, D5-F9) were tested in the TF-1 proliferation assay disclosed in Example 7. Clones A2-E8 and A2-G8 had the best inhibitory activity of all the clones and were chosen for conversion into IgG.
Optimized IgG clones A2-E8 and A2-G8 inhibited TF-1 proliferation equally well with an IC50 of 1-6 ug/ml. Likewise, SCF-stimulated human and cyno eosinophil survival was equally affected by pre-treatment with either IgG clone (IC50=1.1-8 ug/ml). A summary of the results is shown in Table 8.
To address concerns about the stability of the anti-SCF antibody following nebulization, a comparison of pre-nebulized material to nebulized material was done in the TF-1 proliferation assay. There was no difference between stock A2-G8 IgG and those samples that were nebulized in SCF blocking ability over a range of doses.
Library Construction and Cloning
The gene encoding the anti-SCF Fab A2-G8 was cloned into the pMORPH18 phagemid vector (Morphosys, Munich, Germany) (
The amplified PCR product was gel purified and digested with BbsI and XhoI. The pMORPH18 phagemid vector with the Fab A2-G8 insert was similarly digested with BbsI/XhoI and gel purified to obtain the remaining fragment of the A2-G8 Fab. The purified PCR product was ligated into the BbsI/XhoI digested vector and electroporated into electrocompetent TG1 E. coli cells. The resultant library contained 5×105 clones.
Library Selection/Selection of High Affinity Mabs
Cynomolgus Monkey SCF (cSCF) was expressed in HKB11 cells and purified using a NiNTA affinity resin (Process Sciences, Berkeley Calif.). The randomized CDR3 phage library was panned for three rounds against cSCF using 4 different panning strategies. All panning strategies were performed with 300 μl of 10 μg/ml cSCF, in PBS, coated in triplicate to wells of Maxisorp ELISA plates (Corning) in the first round of panning. The second strategy used 10 μg/ml cSCF in the second round of panning followed by 2 μg/ml cSCF in the third round, both coated to a single well. Strategy 3 used 2 μg/ml cSCF coated to a single well of an ELISA plate in the second round of panning and 0.2 μg/ml cSCF in the third round. The fourth strategy used 2 μg/ml cSCF in the second round and 0.05 μg/ml in the third.
The extracts containing Fab were also tested for the ability to inhibit SCF binding to the SCF receptor. ELISA plates were coated overnight with 2 μg/ml human SCFR (R&D Systems, Minneapolis, Minn.) in PBS at 4° C. After washing with TBS-T, the plate was blocked with 5 mg/ml BSA in PBS. The extract was diluted 1/5 in PBS buffer containing 12.5 ng/ml cSCF and 1 mg/ml BSA. After a 1 hr incubation at room temperature, 100 μl was added to the blocked ELISA plate and incubated an additional hour. The plate was washed 5 times with TBS-T, and 100 μl of a 0.4 μg/ml solution of anti-SCF (R&D Systems) in 1 mg/ml BSA in PBS was added. After 1 hour the plate was washed and incubated with anti-Mouse-HRP (Sigma, St. Louis, Mo.). The plate was developed with BM Blue POD substrate (Roche Diagnostics, Chicago, Ill.) and read at 370 nm.
Selection of High Affinity Fabs
Panning was performed for three rounds with decreasing concentration of antigen for each subsequent round. In this process, high affinity phage antibodies can be enriched by competition for limiting amounts of antigen (Hawkins et al. J. Mol. Biol. 226: 889-896, (1992)). To test this, four panning strategies were performed. Fabs were picked from each panning (46 each) and the dissociation constants were measured using BIAcore with immobilized SCF. The Fabs showing similar dissociation constants were grouped and data panning strategy (Table 10).
The data shows a trend that a decrease in the antigen concentration during panning led to an increase in the percentage of Fabs possessing lower dissociation constants. Panning with either 0.2 or 0.05 μg/ml cSCF in the final round resulted in 3 Fabs with a dissociation constant of 2.5×10−4 sec−1. This represented a 24-fold improvement over the original A2-G8 clone. The Fabs were further selected by the ability to block SCF binding to SCF receptor which had been immobilized to an ELISA plate. The panning strategies using higher antigen concentrations (strategies 1 and 2), resulted in 35% and 33% of clones able to inhibit over 40% of SCF binding to its receptor when tested at a single Fab concentration. Panning strategies 3 and 4, using less antigen during panning, resulted in 58% and 59% of clones able to inhibit over 40% of SCF receptor binding, respectively. The original clone A2-G8 was able to inhibit only 10% of receptor binding when tested at the same dilution (data not shown).
The resulting Fab DNA sequences were subcloned into the pMORPHx9_Fab1_FS (Morphosys) (
Fab Expression and Screening
The above transformed cells were plated onto agar plates containing 2YT/1% glucose/34 μg/ml chloramphenicol. A total of 188 clones were picked and expressed in 96-well deep well blocks containing 1.5 ml 2YT/0.1% glucose/34 μg/ml chloramphenicol. The cells were centrifuged and resuspended in BBS buffer (0.2 M boric acid, pH 8.0, 0.15 M NaCl, 2.5 mM EDTA ) containing 2.5 mg/ml lysozyme. After 1 hr at RT, the solution was centrifuged and filtered using a 96 well 0.45 μm plate (Millipore, Bedford, Mass.).
Analysis of Fab binding to cSCF was performed by surface plasmon resonance using a BIAcore 2000 (Biacore, Piscataway, N.J.), according to the manufacturer's instructions and a CM5 chip (Biacore) coated with cSCF. For amine coupling, a research grade CM5 chip was activated using the standard NHS/EDC procedure. Cynomologus monkey SCF was diluted to 20 μg/ml in 10 mM NaAcetate, pH 5.0, and a total of 5000 RU's were coupled to channel 2 of the sensor surface. The remaining active sites were quenched by the addition of 1M ethanolamine, pH 8.0. Channel 1 was subjected to the coupling procedure in the absence of protein and was used as a reference surface. Extracts were diluted 1/5 in HBS-EP running buffer and injected for 2 min using a flow rate of 20 μl/min. The surface was regenerated by two consecutive injections of 25 μl, 10 mM glycine, pH 2.5, using a flow rate of 100 μl/min. The koff was calculated from a single concentration of Fab using BIAevaluation software (Biacore).
Fab Purification using StrepTactin Sepharose
Selected Fabs from BIAcore and ELISA screening were sequenced (Agencourt, Beverly, Mass.) and unique clones identified. Fabs were transformed into TG1 F− E. coli and expressed by inoculating a single fresh colony in 10 ml of 2YT media containing 1.0% glucose and 34 μg/ml chloramphenicol and growing overnight at 30° C. Seven ml of the overnight culture was used to inoculate 1 L of 2YT media containing 0.1% glucose, and 34 μg/ml chloramphenicol. After reaching an OD600 nm of 0.5 (30 ° C.), the cells were induced by addition of IPTG to a final concentration of 0.6 mM. Growth continued at 30° C. overnight. Cells were harvested by centrifugation (15 min at 5000 RPM in GS3 rotor) and periplasmic extracts prepared. Cells were resuspended in 40 ml buffer containing 30 mM Tris, pH 8.0, 1 mM EDTA, 20% sucrose, and protease inhibitor cocktail. After incubation for 1 hr at 4° C., the solution was centrifuged for 10 min at 5000×g. The supernatant was kept at 4° C. and the remaining pellet resuspended in 40 ml buffer containing 0.2 M boric acid, pH 8.0, 0.15 M NaCl, 2.5 mM EDTA, and a protease inhibitor cocktail. The solution was left overnight at 4° C.
After centrifugation for 10 min at 5000×g, the two supernatants were combined, and centrifuged for 30 min at 10,000×g. The supernatant was filtered through at 0.2 μm filter and preincubated with 40 μl of a 10 mg/ml avidin stock for 30 min at 4° C. to block biotinylated proteins. A 20 ml disposable column (Biorad) was packed with 1 ml StrepTactin Sepharose (Sigma Genosys, The Woodlands, Tex.) and equilibrated in running buffer (100 mM Tris, pH 8.0, 250 mM NaCl, 1 mM EDTA). The periplasmic extract was applied to the column, washed with 20 mls running buffer and Fab eluted with 5 mls of 5 mM desthiobiotin in running buffer. Elutions were concentrated 10-fold using a Millipore Ultrafree Biomax 5K NMWL centrifugal devise.
To remove endotoxin contamination, the concentrated Fab was loaded onto a Vivapure Mini Q High Load spin column (Vivascience, Carlsbad, Calif.), which had been equilibrated in running buffer. The column was centrifuged for 5 min at 5000 rpm and flow through collected. The spin column was rinsed with 100 μl of running buffer, combined with original flow thru, and applied to an additional column. The resultant solution was dialyzed into RPMI media, sterile filtered, and stored at 4° C. until needed. Protein concentration was determined using Coomassie Plus Protein Assay Reagent (Pierce, Rockford, Ill.) using BSA as standard. Endotoxin levels were determined using QCL1000 assay kit (Biowhittaker, Walkersville, Md.).
Eight Fabs were selected for large scale purification based on BIAcore koff ranking and the ability to inhibit receptor binding (Table 12). Affinity purification using StrepTactin Sepharose yielded between 0.5 and 2.0 mg of Fab from a 1 L of culture. The endotoxin in the preparations was removed using ion-exchange chromatography with a Vivascience Mini Q High Load spin column in flow through mode. The endotoxin load was reduced from approximately 1 million EU/ml to 50 EU/ml in the final product.
Fab Purification using Protein L
Fabs A12 and F5L were chosen to test the feasibility of purifying untagged versions using Protein L chromatography. Expression in E. coli TG1 F− cells and preparation of periplasmic extracts were performed as described above. The extracts were dialyzed overnight in binding buffer containing 0.1 M NaPhosphate, pH 7.2, and 0.15 M NaCl. After equilibrating a 1 ml Protein L Plus column (Pierce, Rockford, Ill.) in binding buffer, the dialyzed extract was loaded at a flow rate of approximately 3 ml/min. The column was washed with 20 column volumes of binding buffer and eluted with low pH elution buffer (Pierce, Rockford, Ill.). Fractions (1 ml) were collected in tubes containing 100 μl of 1 M Tris, pH 7.5. Protein concentration was determined using Coomassie Plus Protein Assay Reagent using BSA as standard.
Protein L is an immunoglobulin-binding protein that came originally from the bacteria Peptostreptococcus magnus. Unlike Protein A and G, Protein L has the ability to bind immunoglobulins through the kappa light chain and hence has the unique ability to bind both ScFv and Fab fragments. Affinity purification using Protein L yielded 1.9 and 3.7 mg of the Fabs A12 and F5L, respectively, from a 1 L culture. This yield was 24 fold higher than the same clones purified via StrepTactin Sepharose. The activity of the Fab F5L purified via Protein L was comparable to that purified via StrepTactin Sepharose (data not shown), as judged by affinity characterization. Therefore, the acid elution employed during purification was not detrimental to the protein activity. The purity of the material was similar for both purification schemes. Fab F5L did have a few lower molecular weight contaminants that should be easily removed via a second chromatography step. The utility of Protein L will become important in the scale-up procedure for an untagged Fab.
TF-1 Proliferation Assay
The TF1 cell proliferation assay was used to measure the ability of anti-SCF Fab's and IgG to inhibit the proliferative effect of SCF on TF1 cells. TF1 cells (American Type Culture Collection, Rockville, Md.) were cultured for 34 days in 96 well plates (1×104/well, 100 μl volume) in RPMI+10% serum with or without 10 ng/ml human (R&D systems) or cynomologus SCF and anti-SCF. GM-CSF (R&D Systems) was used as a positive control. Twenty-four hours prior to the final reading, 10 μl alamarBlue (10% volume, BioSource, Camarillo, Calif.) was added to each well. Fluorescence was determined at 530/590 nm using a WALLAC Victor 2 (Wallac Oy, Turku, Finland). The resultant RFU's were plotted vs. concentration of antibody and IC50's calculated using GraphPad Prism V.3.0.
Seven of the Fabs were more potent at inhibiting the proliferation of TF-1 cells than the parent A2-G8 clone in either the Fab or IgG construct. Fabs D6L, F5L, D5, B1, and A12 had at least 6-fold lower IC50's than the A2-G8 Mab (Table 12). These Fabs were equal in potency when inhibiting the TF-1 proliferation response to either human or cyno SCF (Table 12).
Affinity Measurements using Surface Plasmon Resonance
Affinity measurements were carried out on a BIAcore 2000 (Biacore) at 25° C. For measuring the affinity constants of Fab, A BIAcore CM5 chip (Biacore) was used to amine couple 185 RU's of cSCF and 150 RU's of hSCF as described above. Purified Fab's were diluted in HBS-EP running buffer at concentrations ranging from 1.95 to 125 nM. A volume of 100 μl was injected using a flow rate of 50 μl/min in Kinject mode. After a 10 min dissociation, 50 μl of 10 mM Glycine, pH 2.5 and 25 μl of 10 mM Glycine, pH 2.0 was injected using a flow rate of 100 μl/min. All samples were run in duplicate. For measuring the affinity constant of cSCF to A2-G8-IgG, a total of 550 RUs of IgG were immobilized to the surface of a CM5 chip. Cynomologus monkey SCF was diluted in HBS-EP running buffer at concentrations ranging from 15.6 to 500 nM and 150 μl injected at a flow rate of 50 μl/min. After a 15 min dissociation, 50 μl of 10 mM Glycine, pH 2.5, and 25 μl of 10 mM Glycine, pH 1.5 was injected using a flow rate of 100 μl/min. All samples were run in duplicate. The data was globally fit to the 1 to 1 binding model using BIAevaluation software. The raw experimental data were corrected for instrumental and bulk solvent artifacts by double referencing using both activated and blocked surfaces as controls.
Affinity Characterization of Selected Anti-SCF Fabs
To evaluate the binding properties of anti-SCF Fabs selected from affinity optimization of the CDR3 loop with SCF, the real time interaction was measured using surface plasmon resonance with the BIAcore 2000. Using immobilized cSCF and hSCF, the derived equilibrium dissociation constants (Kd) for CDR3 optimized Fabs are in the low nanomolar range, thus demonstrating improved binding affinity compared to the parent Fab A2-G8 (Table 13). The improvement in Kd's are primarily governed by a substantial reduction in the off-rate (koff). However, the corresponding kon values were also reduced by 2-4 fold, yielding an overall improvement in the affinity for SCF of 5-10 fold. The affinity constants for Fab binding to human SCF were slightly lower than those Kd's for cynomologus monkey SCF. The panning design, with lower antigen concentrations and extensive washing steps, favors off-rate selection. The affinity of the A2-G8 clone in an IgG vector was measured using the IgG immobilized to the surface of the CM5 chip. In this orientation, the avidity affects of the antibody are not factored into the Kd calculation and therefore represents a true measure of the affinity for the binding site. The Kd value, was approximately equal to the A2-G8 in the Fab vector. An improvement in the koff was offset by a reduction in the on-rate.
The koffrates determined using kinetic conditions (low RU's of immobilized antigen and high flow rates) on the BIAcore gave higher values than those koff's determined under non-kinetic conditions used during the initial screening procedure (high RU's of immobilized antigen and low flow rates). This is especially apparent for the A2-G8 Fab, where a koff of 6×10−3 sec−1 was measured during the initial screening process, compared to a koff value of 1×10−2 sec−1 measured using kinetic parameters. The low flow rate and high immobilized antigen used in the original determination would favor rebinding events that would lead to a lower apparent koff. This is especially true of binding events that have fast on-rates. The koff rates determined in the initial screening process, therefore, should not be considered absolute values but a ranking with other Fabs.