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  Pharmaceutical Patents  

 

Title:  Chronic lymphocytic leukemia cell line
United States Patent: 
7,435,412
Issued: 
October 14, 2008

Inventors:
 Bowdish; Katherine S. (Del Mar, CA), McWhirter; John (San Diego, CA)
Assignee:
  Alexion Pharmaceuticals, Inc. (Chesire, CT)
Appl. No.:
 10/379,151
Filed:
 March 4, 2003


 

Executive MBA in Pharmaceutical Management, U. Colorado


Abstract

The preparation and characterization of antibodies that bind to antigens on CLL or other cancer cells, especially to antigens upregulated in the cancer cells, and the identification and characterization of antigens present on or upregulated by cancer cells are useful in studying and treating cancer.

Description of the Invention

SUMMARY

In one embodiment an CLL cell line of malignant origin is provided that is not established by immortalisation with EBV. The cell line, which was derived from primary CLL cells, and is deposited under ATCC accession no. PTA-3920. In a preferred embodiment, the cell line is CLL-AAT. CLL-MT is B-CLL cell line, derived from a B-CLL primary cell.

In a further aspect, the CLL-AAT cell line is used to generate monoclonal antibodies useful in the diagnosis and/or treatment of CLL. Antibodies may be generated by using the cells as disclosed herein as immunogens, thus raising an immune response in animals from which monoclonal antibodies may be isolated. The sequence of such antibodies may be determined and the antibodies or variants thereof produced by recombinant techniques. In this aspect, "variants" includes chimeric, CDR-grafted, humanized and fully human antibodies based on the sequence of the monoclonal antibodies.

Moreover, antibodies derived from recombinant libraries ("phage antibodies") may be selected using the cells described herein, or polypeptides derived therefrom, as bait to isolate the antibodies on the basis of target specificity.

In a still further aspect, antibodies may be generated by panning antibody libraries using primary CLL cells, or antigens derived therefrom, and further screened and/or characterized using a CLL cell line, such as, for example, the CLL cell line described herein. Accordingly, a method for characterizing an antibody specific for CLL is provided, which includes assessing the binding of the antibody to a CLL cell line.

In a further aspect, there is provided a method for identifying proteins uniquely expressed in CLL cells employing the CLL-AAT cell line, by methods well known to those, skilled with art, such as by immunoprecipitation followed by mass spectroscopy analyses. Such proteins may be uniquely expressed in the CLL-AAT cell line, or in primary cells derived from CLL patients.

Small molecule libraries (many available commercially) may be screened using the CLL-AAT cell line in a cell-based assay to identify agents capable of modulating the growth characteristics of the cells. For example, the agents may be identified which modulate apoptosis in the CLL-AAT cell line, or which inhibit growth and/or proliferation thereof. Such agents are candidates for the development of therapeutic compounds.

Nucleic acids isolated from CLL-AAT cell lines may be used in subtractive hybridization experiments to identify CLL-specific genes or in micro array analyses (e.g., gene chip experiments). Genes whose transcription is modulated in CLL cells may be identified. Polypeptide or nucleic acid gene products identified in this manner are useful as leads for the development of antibody or small molecule therapies for CLL.

In a preferred aspect, the CLL-AAT cell line may be used to identify internalizing antibodies, which bind to cell surface components which are internalized by the cell. Such antibodies are candidates for therapeutic use. In particular, single-chain antibodies, which remain stable in the cytoplasm and which retain intracellular binding activity, may be screened in this manner.

In yet another aspect, a therapeutic treatment is described in which a patient is screened for the presence of a polypeptide that is upregulated by a malignant cancer cell and an antibody that interferes with the metabolic pathway of the upregulated polypeptide is administered to the patient.

DETAILED DESCRIPTION

Preparation of Cell Lines

Cell lines may be produced according to established methodologies known to those skilled in the art. In general, cell lines are produced by culturing primary cells derived from a patient until immortalized cells are spontaneously generated in culture. These cells are then isolated and further cultured, to produce clonal cell populations or cells exhibiting resistance to apoptosis.

For example, CLL cells may be isolated from peripheral blood drawn from a patient suffering from CLL. The cells may be washed, and optionally immunotyped in order to determine the type(s) of cells present. Subsequently, the cells may be cultured in a medium, such as a medium containing IL-4. Advantageously, all or part of the medium is replaced one or more times during the culture process. Cell lines may be isolated thereby, and will be identified by increased growth in culture.

Preparation of Monoclonal Antibodies

Antibodies, as used herein, refers to complete antibodies or antibody fragments capable of binding to a selected target. Included are Fv, ScFv, Fab' and F(ab')2, monoclonal and polyclonal antibodies, engineered antibodies (including chimeric, CDR-grafted and humanized, fully human antibodies, and artificially selected antibodies), and synthetic or semi synthetic antibodies produced using phage display or alternative techniques. Small fragments, such Fv and ScFv, possess advantageous properties for diagnostic and therapeutic applications on account of their small size and consequent superior tissue distribution.

The antibodies are especially indicated for diagnostic and therapeutic applications. Accordingly, they may be altered antibodies comprising an effector protein such as a toxin or a label. Especially preferred are labels which allow the imaging of the distribution of the antibody in vivo. Such labels may be radioactive labels or radiopaque labels, such as metal particles, which are readily visualisable within the body of a patient. Moreover, the labels may be fluorescent labels or other labels which are visualisable on tissue samples removed from patients.

Recombinant DNA technology may be used to improve the antibodies produced in accordance with this disclosure. Thus, chimeric antibodies may be constructed in order to decrease the immunogenicity thereof in diagnostic or therapeutic applications. Moreover, immunogenicity may be minimized by humanizing the antibodies by CDR grafting and, optionally, framework modification. See, U.S. Pat. No. 5,225,539, the contents of which are incorporated herein by reference.

Antibodies may be obtained from animal serum, or, in the case of monoclonal antibodies or fragments thereof produced in cell culture. Recombinant DNA technology may be used to produce the antibodies according to established procedure, in bacterial or preferably mammalian cell culture. The selected cell culture system preferably secretes the antibody product.

In another embodiment, a process for the production of an antibody disclosed herein includes culturing a host, e.g. E. coli or a mammalian cell, which has been transformed with a hybrid vector. The vector includes one or more expression cassettes containing a promoter operably linked to a first DNA sequence encoding a signal peptide linked in the proper reading frame to a second DNA sequence encoding the antibody protein. The antibody protein is then collected and isolated. Optionally, the expression cassette may include a promoter operably linked to polycistronic, for example bicistronic, DNA sequences encoding antibody proteins each individually operably linked to a signal peptide in the proper reading frame.

Multiplication of hybridoma cells or mammalian host cells in vitro is carried out in suitable culture media, which include the customary standard culture media (such as, for example Dulbecco's Modified Eagle Medium (DMEM) or RPMI 1640 medium), optionally replenished by a mammalian serum (e.g. fetal calf serum), or trace elements and growth sustaining supplements (e.g. feeder cells such as normal mouse peritoneal exudate cells, spleen cells, bone marrow macrophages, 2-aminoethanol, insulin, transferrin, low density lipoprotein, oleic acid, or the like). Multiplication of host cells which are bacterial cells or yeast cells is likewise carried out in suitable culture media known in the art. For example, for bacteria suitable culture media include medium LE, NZCYM, NZYM, NZM, Terrific Broth, SOB, SOC, 2.times.YT, or M9 Minimal Medium. For yeast, suitable culture media include medium YPD, YEPD, Minimal Medium, or Complete Minimal Dropout Medium.

In vitro production provides relatively pure antibody preparations and allows scale-up to give large amounts of the desired antibodies. Techniques for bacterial cell, yeast, plant, or mammalian cell cultivation are known in the art and include homogeneous suspension culture (e.g. in an airlift reactor or in a continuous stirrer reactor), and immobilized or entrapped cell culture (e.g. in hollow fibres, microcapsules, on agarose microbeads or ceramic cartridges).

Large quantities of the desired antibodies can also be obtained by multiplying mammalian cells in vivo. For this purpose, hybridoma cells producing the desired antibodies are injected into histocompatible mammals to cause growth of antibody-producing tumors. Optionally, the animals are primed with a hydrocarbon, especially mineral oils such as pristane (tetramethyl-pentadecane), prior to the injection. After one to three weeks, the antibodies are isolated from the body fluids of those mammals. For example, hybridoma cells obtained by fusion of suitable myeloma cells with antibody-producing spleen cells from Balb/c mice, or transfected cells derived from hybridoma cell line Sp2/0 that produce the desired antibodies are injected intraperitoneally into Balb/c mice optionally pre-treated with pristine. After one to two weeks, ascitic fluid is taken from the animals.

The foregoing, and other, techniques are discussed in, for example, Kohler and Milstein, (1975) Nature 256:495-497; U.S. Pat. No. 4,376,110; Harlow and Lane, Antibodies: a Laboratory Manual, (1988) Cold Spring Harbor, the disclosures of which are all incorporated herein by reference. Techniques for the preparation of recombinant antibody molecules is described in the above references and also in, for example WO97/08320; U.S. Pat. No. 5,427,908; U.S. Pat. No. 5,508,717; Smith, 1985, Science, Vol. 225, pp 1315-1317; Parmley and Smith 1988, Gene 73, pp 305-318; De La Cruz et al, 1988, Journal of Biological Chemistry, 263 pp 4318-4322; U.S. Pat. No. 5,403,484; U.S. Pat. No. 5,223,409; WO88/06630; WO92/15679; U.S. Pat. No. 5,780,279; U.S. Pat. No. 5,571,698; U.S. Pat. No. 6,040,136; Davis et al., Cancer Metastasis Rev.,1999;18(4):421-5; Taylor, et al., Nucleic Acids Research 20 (1992): 6287-6295; Tomizuka et al., Proc. Nat. Academy of Sciences USA 97(2) (2000): 722-727. The contents of all these references are incorporated herein by reference.

The cell culture supernatants are screened for the desired antibodies, preferentially by immunofluorescent staining of CLL cells, by immunoblotting, by an enzyme immunoassay, e.g. a sandwich assay or a dot-assay, or a radioimmunoassay

For isolation of the antibodies, the immunoglobulins in the culture supernatants or in the ascitic fluid may be concentrated, e.g. by precipitation with ammonium sulfate, dialysis against hygroscopic material such as polyethylene glycol, filtration through selective membranes, or the like. If necessary and/or desired, the antibodies are purified by the customary chromatography methods, for example gel filtration, ion-exchange chromatography, chromatography over DEAE-cellulose and/or (immuno-) affinity chromatography, e.g. affinity chromatography with a one or more surface polypeptides derived from a CLL cell line according to this disclosure, or with Protein-A or G.

Another embodiment provides a process for the preparation of a bacterial cell line secreting antibodies directed against the cell line characterized in that a suitable mammal, for example a rabbit, is immunized with pooled CLL patient samples. A phage display library produced from the immunized rabbit is constructed and panned for the desired antibodies in accordance with methods well known in the art (such as, for example, the methods disclosed in the various references incorporated herein by reference).

Hybridoma cells secreting the monoclonal antibodies are also contemplated. The preferred hybridoma cells are genetically stable, secrete monoclonal antibodies described herein of the desired specificity and can be activated from deep-frozen cultures by thawing and reckoning.

In another embodiment, a process is provided for the preparation of a hybridoma cell line secreting monoclonal antibodies directed to the CLL cell line is described herein. In that process, a suitable mammal, for example a Balb/c mouse, is immunized with a one or more polypeptides or antigenic fragments thereof derived from a cell described in this disclosure, the cell line itself, or an antigenic carrier containing a purified polypeptide as described. Antibody-producing cells of the immunized mammal are grown briefly in culture or fused with cells of a suitable myeloma cell line. The hybrid cells obtained in the fusion are cloned, and cell clones secreting the desired antibodies are selected. For example, spleen cells of Balb/c mice immunized with the present cell line are fused with cells of the myeloma cell line PAI or the myeloma cell line Sp2/0-Ag 14, the obtained hybrid cells are screened for secretion of the desired antibodies, and positive hybridoma cells are cloned.

Preferred is a process for the preparation of a hybridoma cell line, characterized in that Balb/c mice are immunized by injecting subcutaneously and/or intraperitoneally between 10.sup.6 and 10.sup.7 cells of a cell line in accordance with this disclosure several times, e.g. four to six times, over several months, e.g. between two and four months. Spleen cells from the immunized mice are taken two to four days after the last injection and fused with cells of the myeloma cell line PAI in the presence of a fusion promoter, preferably polyethylene glycol. Preferably, the myeloma cells are fused with a three- to twenty-fold excess of spleen cells from the immunized mice in a solution containing about 30% to about 50% polyethylene glycol of a molecular weight around 4000. After the fusion, the cells are expanded in suitable culture media as described hereinbefore, supplemented with a selection medium, for example HAT medium, at regular intervals in order to prevent normal myeloma cells from overgrowing the desired hybridoma cells.

In a further embodiment, recombinant DNA comprising an insert coding for a heavy chain variable domain and/or for a light chain variable domain of antibodies directed to the cell line described hereinbefore are produced. The term DNA includes coding single stranded DNAs, double stranded DNAs consisting of said coding DNAs and of complementary DNAs thereto, or these complementary (single stranded) DNAs themselves.

Furthermore, DNA encoding a heavy chain variable domain and/or a light chain variable domain of antibodies directed to the cell line disclosed herein can be enzymatically or chemically synthesized DNA having the authentic DNA sequence coding for a heavy chain variable domain and/or for the light chain variable domain, or a mutant thereof. A mutant of the authentic DNA is a DNA encoding a heavy chain variable domain and/or a light chain variable domain of the above-mentioned antibodies in which one or more amino acids are deleted or exchanged with one or more other amino acids. Preferably said modification(s) are outside the CDRs of the heavy chain variable domain and/or of the light chain variable domain of the antibody in humanization and expression optimization applications. The term mutant DNA also embraces silent mutants wherein one or more nucleotides are replaced by other nucleotides with the new codons coding for the same amino acid(s). The term mutant sequence also includes a degenerated sequence. Degenerated sequences are degenerated within the meaning of the genetic code in that an unlimited number of nucleotides are replaced by other nucleotides without resulting in a change of the amino acid sequence originally encoded. Such degenerated sequences may be useful due to their different restriction sites and/or frequency of particular codons which are preferred by the specific host, particularly E. coli, to obtain an optimal expression of the heavy chain murine variable domain and/or a light chain murine variable domain.

The term mutant is intended to include a DNA mutant obtained by in vitro mutagenesis of the authentic DNA according to methods known in the art.

For the assembly of complete tetrameric immunoglobulin molecules and the expression of chimeric antibodies, the recombinant DNA inserts coding for heavy and light chain variable domains are fused with the corresponding DNAs coding for heavy and light chain constant domains, then transferred into appropriate host cells, for example after incorporation into hybrid vectors.

Recombinant DNAs including an insert coding for a heavy chain murine variable domain of an antibody directed to the cell line disclosed herein fused to a human constant domain g, for example .gamma.1, .gamma.2, .gamma.3 or .gamma.4, preferably .gamma.1 or .gamma.4 are also provided. Recombinant DNAs including an insert coding for a light chain murine variable domain of an antibody directed to the cell line disclosed herein fused to a human constant domain .kappa.or .lamda., preferably .kappa. are also provided

Another embodiment pertains to recombinant DNAs coding for a recombinant polypeptide wherein the heavy chain variable domain and the light chain variable domain are linked by way of a spacer group, optionally comprising a signal sequence facilitating the processing of the antibody in the host cell and/or a DNA coding for a peptide facilitating the purification of the antibody and/or a cleavage site and/or a peptide spacer and/or an effector molecule.

The DNA coding for an effector molecule is intended to be a DNA coding for the effector molecules useful in diagnostic or therapeutic applications. Thus, effector molecules which are toxins or enzymes, especially enzymes capable of catalyzing the activation of prodrugs, are particularly indicated. The DNA encoding such an effector molecule has the sequence of a naturally occurring enzyme or toxin encoding DNA, or a mutant thereof, and can be prepared by methods well known in the art.

Antibodies and antibody fragments disclosed herein are useful in diagnosis and therapy. Accordingly, a composition for therapy or diagnosis comprising an antibody disclosed herein is provided.

In the case of a diagnostic composition, the antibody is preferably provided together with means for detecting the antibody, which may be enzymatic, fluorescent, radioisotopic or other means. The antibody and the detection means may be provided for simultaneous, separate or sequential use, in a diagnostic kit intended for diagnosis.

Uses of the CLL Cell Line

There are many advantages to the development of a CLL cell line, as it provides an important tool for the development of diagnostics and treatments for CLL.

A cell line according to this disclosure may be used for in vitro studies on the etiology, pathogenesis and biology of CLL. This assists in the identification of suitable agents that are useful in the therapy of CLL disease.

The cell line may also be used to produce monoclonal antibodies for in vitro and in vivo diagnosis of CLL, as referred to above, and for the screening and/or characterization of antibodies produced by other methods, such as by panning antibody libraries with primary cells and/or antigens derived from CLL patients.

The cell line may be used as such, or antigens may be derived therefrom. Advantageously, such antigens are cell-surface antigens specific for CLL. They may be isolated directly from cell lines according to this disclosure. Alternatively, a cDNA expression library made from a cell line described herein may be used to express CLL-specific antigens, useful for the selection and characterization of anti-CLL antibodies and the identification of novel CLL-specific antigens.

Treatment of CLL using monoclonal antibody therapy has been proposed in the art. Recently, Hainsworth (Oncologist 5 (5) (2000) 376-384) has described the current therapies derived from monoclonal antibodies. Lymphocytic leukemia in particular is considered to be a good candidate for this therapeutic approach due to the presence of multiple lymphocyte-specific antigens on lymphocyte tumors.

Existing antibody therapies (such as Rituximab.TM., directed against the CD20-antigen, which is expressed on the surface of B-lymphocytes) have been used successfully against certain lymphocytic disease. However, a lower density CD20 antigen is expressed on the surface of B-lymphocytes in CLL (Almasri et al., Am. J. Hematol., 40 (4) (1992) 259-263).

The CLL cell line described herein thus permits the development of novel anti-CLL antibodies having specificity for one or more antigenic determinants of the present CLL cell line, and their use in the therapy and diagnosis of CLL.

In a particularly useful embodiment, the antibody binds to or otherwise interferes with the metabolic pathway of a polypeptide that is upregulated by a malignant cancer cell. For instance, the antibody can bind to the upregulated polypeptide and in this manner prevent or inhibit the polypeptide from interacting with other molecules or receptors. Alternatively, the antibody may bind to a receptor with which the upregulated polypeptide normally interacts, thereby preventing or inhibiting the polypeptide from binding to the receptor. As yet another alternative, the antibody can bind to an antigen that modulates expression of the polypeptide, thereby preventing or inhibiting normal or increased expression of the polypeptide. For example, the peptide OX-2/CD200 is upregulated in a portion of CLL patients. Because the presence of OX-2/CD200 has been associated with reduced immune response, it would be desirable to interfere with the metabolic pathway of OX-2/CD200 so that the patient's immune system can defend against the cancer more effectively.

Thus, in another embodiment, a method for treating a cancer patient in accordance with this disclosure includes the steps of screening a cancer patient for the presence of a polypeptide that is upregulated by a malignant cancer cell and administering an antibody that interferes with the metabolic pathway of the upregulated polypeptide. In a particularly useful embodiment, a CLL patient is screened for overexpression of OX-2/CD200 and an antibody that interferes with the metabolic pathway of OX-2/CD200 is administered to the patient. As described in detail below, one such antibody is scFv9 (see FIG. 9B, see Original Patent) which binds to OX-2/CD200.
 

Claim 1 of 15 Claims

1. A method of treating chronic lymphocytic leukemia (CLL) comprising administering to a patient suffering from CLL an antibody or antigen-binding fragment thereof that specifically binds to OX-2/CD200, wherein said antibody or antigen-binding fragment thereof comprises a light chain CDR1 having the sequence set forth in SEQ ID NO: 5; a light chain CDR2 having the sequence set forth in SEQ ID NO: 21; a light chain CDR3 having the sequence set forth in SEQ ID NO: 29; a heavy chain CDR1 having the sequence set forth in SEQ ID NO: 50; a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 69; and a heavy chain CDR3 having the sequence set forth in SEQ ID NO: 88.

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If you want to learn more about this patent, please go directly to the U.S. Patent and Trademark Office Web site to access the full patent.

 

 

     
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