AU2012211347B9 - Polypeptides and antibodies derived from chronic lymphocytic leukemia cells and uses thereof - Google Patents

Description

- 1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: Alexion Pharmaceuticals, Inc. Actual Inventors: Katherine S. Bowdish and Anke Kretz-Rommel and John McWhirter Address for Service is: SHELSTON IP 60 Margaret Street Telephone No: (02) 9777 1111 SYDNEY NSW 2000 Facsimile No. (02) 9241 4666 CCN: 3710000352 Attorney Code: SW Invention Title: Polypeptides and antibodies derived from chronic lymphocytic leukemia cells and uses thereof Details of Original Application No. 2005274785 dated 19 Jul 2005 The following statement is a full description of this invention, including the best method of performing it known to me/us: File: 52958AUP01 POLYPEPTIDES AND ANTIBODIES DERIVED FROM CHRONIC LYMPHOCYTIC LEUKEMIA CELLS AND USES THEREOF The present application is a divisional application of Australian Application No. 2005274785, which is incorporated in its entirety herein by reference. 5 RELATED APPLICATIONS This application claims priority to U.S. Application Serial No. 11/171,567 filed June 30, 2005 which is a continuation in part of U.S. Application Serial No. 10/996,316 filed November 23, 2004 which is a continuation in part of U.S. Application Serial No. 10/894,672 filed July 20, 2004 which is a continuation in part of U.S. Application Serial 10 No. 10/736,188 filed December 15, 2003 which is a continuation in part of U.S. Application Serial No. 10/379,151 filed on March 4, 2003 which, in turn, is a continuation in part of PCT/US01/47931 filed on December 10, 2001, which is an international application that claims priority to U.S. Provisional Application No. 60/254,113 filed December 8, 2000. The entire disclosures of the aforementioned U.S., 15 international and provisional applications are incorporated herein by reference. TECHNICAL FIELD Cancer treatments using a therapy that provides a combination of two mechanisms are disclosed. More specifically, this disclosure relates to treating cancer using a therapy that: 1) interferes with the interaction between CD200 and its receptor to 20 block immune suppression thereby promoting eradication of the cancer cells; and 2) directly kills the cancer cells either by a) complement-mediated or antibody-dependent cellular cytotoxicity or b) by targeting cells using a fusion molecule that includes a CD200-targeting portion. BACKGROUND 25 Chronic Lymphocytic Leukemia (CLL) is a disease of the white blood cells and is the most common form of leukemia in the Western Hemisphere. CLL represents a diverse group of diseases relating to the growth of malignant lymphocytes that grow slowly but have an extended life span. CLL is classified in various categories that include, for example, B-cell chronic lymphocytic leukemia (B-CLL) of classical and 30 mixed types, B 1a cell and T-cell prolymphocytic leukemia, hairy cell leukemia, and large granular lymphocytic leukemia. Of all the different types of CLL, B-CLL accounts for approximately 30 percent of all leukemias. Although it occurs more frequently in individuals over 50 years of age, 5 it is increasingly seen in younger people. B-CLL is characterized by accumulation of B lymphocytes that are morphologically normal but biologically immature, leading to a loss of function. Lymphocytes normally function to fight infection. In B-CLL, however, lymphocytes accumulate in the blood and bone marrow and cause swelling of the lymph nodes. The production of normal bone marrow and blood cells is reduced and patients 10 often experience severe anemia as well as low platelet counts. This can pose the risk of life-threatening bleeding and the development of serious infections because of reduced numbers of white blood cells. To further understand diseases such as leukemia it is important to have suitable cell lines that can be used as tools for research on their etiology, pathogenesis and 15 biology. Examples of malignant human B-lymphoid cell lines include pre-B acute lymphoblasticleukemia (Reh), diffuse large cell lymphoma (WSU-DLCL2), and Waldenstrom's macroglobulinemia (WSU- WM). Unfortunately, many of the existing cell lines do not represent the clinically most common types of leukemia and lymphoma. The use of Epstein Barr Virus (EBV) infection in vitro has resulted in some CLL 20 derived cell lines, in particular B-CLL cells lines, that are representative of the malignant cells. The phenotype of these cell lines is different than that of the in vivo tumors and instead the features of B-CLL lines tend to be similar to those of lymphoblastoid cell lines. Attempts to immortalize B-CLL cells with the aid of EBV infection have had little success. The reasons for this are unclear but it is known that it is not due to a lack of EBV 25 receptor expression, binding or uptake. Wells et al. found that B-CLL cells were arrested in the Gl/S phase of the cell cycle and that transformation associated EBV DNA was not expressed, This suggests that the interaction of EBV with B-CLL cells is different from that with normal B cells. ES V-transformed CLL cell lines moreover appear to differentiate, possessing a morphology more similar to lymphoblastoid cell lines (LCL) 30 immortalized by EBV. An EBV-negative CLL cell line, WSU-CLL, has been established previously (Mohammad et al., (1996) Leukemia 10(1):130-7). However, no other such cell lines are known. 2 Various mechanisms play a role in the body's response to a disease state, including cancer and CLL. For example, CD4* T helper cells play a crucial role in an effective immune response against various malignancies by providing stimulatory factors to effector cells. Cytotoxic T cells are believed to be the most effective cells to 5 eliminate cancer cells, and T helper cells prime cytotoxic T cells by secreting ThI cytokines such as IL-2 and IFN-y. In various malignancies, T helper cells have been shown to have an altered phenotype compared to cells found in healthy individuals. One of the prominent altered features is decreased Th 1 cytokine production and a shift to the production of Th2 cytokines. (See, e.g., Kiani, et al., Haematologica 88:754-761 (2003); 10 Maggio, et al., Ann Oncol 13 Suppl 1:52-56 (2002); Ito, et al., Cancer 85:2359-2367 (1999); Podhorecka, et al., Leuk Res 26:657-660 (2002); Tatsumi, et al., J Exp Med 196:619-628 (2002); Agarwal, et al., Immunol Invest 32:17-30 (2003); Smyth, et al., Ann Surg Oncol 10:455-462 (2003); Contasta, et al., Cancer Biother Radiopharm 18:549-557 (2003); Lauerova, et al., Neoplasma 49:159-166(2002)). Reversing that 15 cytokine shift to a ThI profile has been demonstrated to augment anti-tumor effects of T cells. (See Winter, et al., Immunology 108:409-419 (2003); Inagawa, et al., Anticancer Res 18:3957-3964 (1998)). Mechanisms underlying the capacity of tumor cells to drive the cytokine expression of T helper cells from Thl to Th2 include the secretion of cytokines such as 20 IL-10 or TGF-# as well as the expression of surface molecules interacting with cells of the immune system. OX-2/CD200, a molecule expressed on the surface of dendritic cells which possesses a high degree of homology to molecules of the immunoglobulin gene family, has been implicated in immune suppression (Gorczynski et al., Transplantation 65:1106-1114 (1998)) and evidence that OX-2/CD200-expressing cells can inhibit the 25 stimulation ofThl cytokine production has been provided. Gorczynski et al. demonstrated in a mouse model that infusion of OX-2/CD200 Fc suppresses the rejection of tumor cells in an animal model using leukaemic tumor cells (Clin Exp Immunol 126:220-229 (2001)). Improved methods for treating individuals suffering from cancer or CLL are 30 desirable, especially to the extent they can enhance the activity of T cells 3 Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. It is an object of the present invention to overcome or ameliorate at least one of 5 the disadvantages of the prior art, or to provide a useful alternative. SUMMARY According to a first aspect, the present invention provides an isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDR1 having the sequence set forth in residues 26-36 of SEQ 10 NO:209; a light chain CDR2 having the 10 sequence set forth in residues 52-58 of SEQ ID NO:209; a light chain CDR3 having the sequence set forth in residues 91-99 of SEQ ID NO:209; a heavy chain CDR1 having the sequence set forth in SEQ ID NO: 149; a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 174; and a heavy chain CDR1 having the sequence set forth in SEQ ID NO: 195. 15 According to a second aspect, the present invention provides an isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDRI having the sequence set forth in residues 26-36 of SEQ ID NO:208, a light chain CDR2 having the sequence set forth in residues 52-58 of SEQ ID NO:208, a light chain CDR3 having the sequence set forth in residues 91-99 of SEQ ID NO:208, a heavy chain CDR1 having 20 the sequence set forth in SEQ ID NO: 114. a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 165, and a heavy chain CDR3 Ihaving the sequence set forth in SEQ ID NO: 189. According to a third aspect, the present invention provides an isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDRI having the 25 sequence set forth in residues 26-35 of SEQ ID NO:207; a light chain CDR2 having the sequence set forth in residues 51-57 of SEQ ID NO:207; a light chain CDR3 having the sequence set forth in residues 90-98 of SEQ ID NO:207; a heavy chain CDR] having the sequence set forth in SEQ ID NO: 111; a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 118; and a heavy chain CDR3 having the sequence set forth in 30 residues 100-112 of SEQ ID NO:201. According to a fourth aspect, the present invention provides an isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDR] having the 3a sequence set forth in residues 26-41 of SEQ ID NO:210; a light chain CDR2 having the sequence set forth in residues 57-63 of SEQ ID NO:2 10; a light chain CDR3 having the sequence set forth in residues 96-104 of SEQ ID NO:2 10; a heavy chain CDRI having the sequence set forth in SEQ I) NO: 140; a heavy chain CDR2 having the sequence set 5 forth in SEQ ID NO: 162; and a heavy chain CDR3 having the sequence set forth in SEQ ID NO: 187. According to a fifth aspect, the present invention provides a pharmaceutical composition comprising a pharmaceutically acceptable carrier and the isolated antibody, or CD200-binding fragment thereof, according to the first aspect. 10 According to a sixth aspect, the present invention provides a method for treating a patient afflicted with cancer, the method comprising administering to the patient the isolated antibody, or CD200-binding fragment thereof, according to the first aspect to thereby treat the cancer. According to a seventh aspect, the present invention provides a method for 15 treating a patient afflicted with cancer, the method comprising administering to the patient the pharmaceutical composition according to the fifth aspect to thereby treat the cancer. Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an 20 inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". In one embodiment a CLL cell line of malignant origin is provided that is not established by immortalisation with EBV. The cell line was derived from primary CLL cells and is deposited under ATCC accession no. PTA-3920. In a preferred embodiment, 25 3b the cell line is CLL-AAT. CLL-AAT is a B-CLL cell line, derived from a 3-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 5 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 10 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 15 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 20 expressed in CLL cells employing the CLL-AAT cell line, by methods well known to those skilled in the 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 25 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. 30 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. 4 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 5 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. 10 The present disclosure further is directed to methods wherein a determination is made as to whether OX-2/CD200 is upregulated in a subject and, if so, administering to the subject a therapy that enhances immune response. Upregulation of OX2/CD200 can be determined by measuring OX2/CD200 levels directly, or by monitoring the level of any marker that correlates with OX2/CD200. Suitable immunomodulatory therapies 15 include the administration of agents that block negative regulation of T cells or antigen presenting cells, administration of agents that enhance positive co-stimulation of T cells, cancer vaccines, general adjuvants stimulating the immune system or treatment with cytokines such as IL-2, GM-CSF and IFN-gamma. In particularly useful embodiments, the therapy that enhances immune response includes the administration of a polypeptide 20 that binds to OX-2/CD200, optionally in combination with one or more other immunomodulatory therapies. In another embodiment, the polypeptide binds to an OX 2/CD200 receptor. In another aspect, methods in accordance with this disclosure are used to treat a disease state in which OX-2/CD200 is upregulated In a subject by administering a 25 polypeptide that binds to OX-2/CD200 or an OX-2/CD200 receptor to the subject afflicted with the disease state. In one embodiment, the disease state treated by these methods includes cancer, specifically, in other embodiments, CLL. In a particularly useful embodiment, a cancer therapy in accordance with this disclosure includes i) administering an antibody that interferes with the interaction 30 between CD200 and its receptor to block immune suppression, thereby promoting eradication of the cancer cells; and ii) administering a fusion molecule that includes a CD200-targeting portion to directly kill cancer cells. Alternatively, the antibody directly kills the cancer cells through complement-mediated or antibody-dependent cellular cytotoxicity. 5 In another embodiment in accordance with the present disclosure, methods are provided for monitoring the progress of a therapeutic treatment. The method involves administering an immunomodulatory therapy and determining OX-2/CD200 levels in a subject at least twice to determine the effectiveness of the therapy. 5 In another aspect, the present disclosure provides methods for assessing the immunomodulatory effect of molecules expressed by cancer cells. In these methods a molecule that is expressed or upregulated by a cancer cell is identified (e.g., experimentally or from a database). Cancer cells, lymphocytes and the molecule that is expressed or upregulated by a cancer cell are administered to a subject and the rate of 10 growth of the cancer cells is monitored. The number of lymphocytes administered is predetermined to be either a) sufficient to slow the growth of the cancer cells or b) insufficient to slow the growth of cancer cells. The molecule that is expressed or upregulated by a cancer cell can be administered as the molecule or the active portion of the molecule itself, or by administering cells that produce or express the molecule or 15 portions thereof naturally, or by administering cells that have been engineered to produce or express the molecule or portions thereof. If any change in the growth rate of the cancer cells is observed compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the molecule is deemed to have an immunomodulatory effect. For example, if the number of lymphocytes administered is 20 sufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is higher compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the molecule that is expressed or upregulated by a cancer cell is considered immunosuppressive. As another example, if the number of lymphocytes administered is insufficient to slow the growth of the cancer cells and the 25 rate of growth of the tumor cells observed is lowered compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is considered immune enhancing. Once the immunomodulatory effect of the molecule is established, compounds that either enhance or inhibit the activity of the molecule can be identified in accordance with embodiments described herein. The enhancing or inhibiting 30 effect can be the result of direct interaction with the molecule expressed or upregulated by the cancer cell or may be the result of an interaction with other molecules in the metabolic pathway of the compound expressed or upregulated by the cancer cell. In another aspect, the present disclosure provides methods for assessing the immunomodulatory effect of a compound. In these methods cancer cells, lymphocytes 6 and the compound to be assessed are administered to a subject and the rate of growth of the cancer cells is monitored. The number of lymphocytes administered is predetermined to be either a) sufficient to slow the growth of the cancer cells or b) insufficient to slow the growth of cancer cells. The compound to be assessed can be administered as the 5 compound itself, or by administering cells that produce the compound naturally, or by administering cells that have been engineered to produce the compound. If any change in the growth rate of the cancer cells is observed compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is deemed to have an immunomodulatory effect. For example, if the number of lymphocytes 10 administered is sufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is higher compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is considered immunosuppressive. As another example, if the number of lymphocytes administered is insufficient to slow the growth of the cancer cells and the rate of growth of the tumor 15 cells observed is lowered compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is considered immune enhancing. BRJEF DESCRIPTION OF THE FIGURES Fig. 1 schematically illustrates typical steps involved in cell surface panning of 20 antibody libraries by magnetically-activated cell sorting (MACS). Fig. 2 is a graph showing the results of whole cell ELISA demonstrating binding of selected scFv clones to primary B-CLL cells and absence of binding to normal human PBMC. The designation 2*+3* in this and other figures refers to negative control wells stained with Mouse Anti-HA and detecting antimouse antibodies alone. The designation 25 RSC-S Library in this and other figures refers to soluble antibodies prepared from original rabbit scFv unpanned library. The designation R3/RSC-S Pool in this and other figures refers to soluble antibodies prepared from the entire pool of scFv antibodies from round 3 of panning. Anti-CD5 antibody was used as a positive control to verify that equal numbers of B-CLL and PBMC cells were plated in each well. 30 Figs. 3a and 3b show the results of whole cell ELISA comparing binding of selected scFv antibodies to primary B-CLL cells and normal primary human B cells. Anti-CD19 antibody was used as a positive control to verify that equal numbers of B CLL and normal B cells were plated in each well. Other controls were as described in the legend to Fig. 2. 7 Figs. 4a and 4b show the results of whole cell ELISA used to determine if scFv clones bind to patient-specific (i.e. idiotype) or blood type-specific (i.e. HLA) antigens. Each clone was tested for binding to PBMC isolated from 3 different B-CLL patients. Clones that bound to only one patient sample were considered to be patient or blood type 5 specific. Figs. 5a and 5b show the results of whole cell ELISA comparing binding of scFv clones to primary B-CLL cells and three human leukemia cell lines. Ramos is a mature B cell line derived from a Burkitt's lymphoma. RL is a mature B cell line derived from a non-Hodgkin's lymphoma. TF-1 is an erythroblastoid cell line derived from an 10 erythroleukemia. Figs. 6a, 6b and 6c show the results of whole cell ELISA comparing binding of scFv clones to primary B-CLL cells and CLL-AAT, a cell line derived from a B-CLL patient. TF-l cells were included as a negative control. Fig. 7 shows the binding specificity of scFv antibodies in accordance with this 15 disclosure as analyzed by 3-color flow cytometry. In normal peripheral blood mononuclear cells, the antigen recognized by scFv-9 is moderately expressed on B lymphocytes and weakly expressed on a subpopulation of T lymphocytes. PBMC from a normal donor were analyzed by 3-color flow cytomctry using anti-CD5-FITC, anti CD19-PerCP, and scFv-9/Anti-HA-biotin/streptavidin-PE. 20 Figs. 8a, 8b and 8e show the expression levels of antigens recognized by scFv antibodies in accordance with this disclosure. The antigens recognized by scFv-3 and scFv-9 are overexpressed on the primary CLL tumor from which the CLL-AAT cell line was derived. Primary PBMC from the CLL patient used to establish the CLL-AAT cell line or PBMC from a normal donor were stained with scFv antibody and analyzed by 25 flow cytometry. ScFv-3 and scFv-9 stain the CLL cells rom brightly than the normal PBMC as measured by the mean fluorescent intensities. Figs. 9A - 9C provide a summary of CDR sequences and binding specificities of selected scFv antibodies. Fig. 10 is Table 2 which shows a summary of flow cytometry results comparing 30 expression levels of scFv antigens on primary CLL cells vs. normal PBMC as described in Figs 8a-8c. Fig. 11 is a Table showing a summary of flow cytometry results comparing expression levels of scFv-9 antigen with the percentage of CD38* cells in peripheral blood mononuclear cells isolated from ten CLL patients. 8 Fig. 12 shows the identification of scFv antigens by immunoprecipitation and rnass spectrometry. CLL-AAT cells were labeled with a solution of 0.5mg/mi sulfo NHS-LC-biotin (Pierce) in PBS, pH8.0 for 30'. After extensive washing with PBS to remove unreacted biotin, the cells were disrupted by nitrogen cavitation and the 5 microsomal fraction was isolated by differential centrifugation. The microsomal fraction was resuspended in NP40 Lysis Buffer and extensively precleared with normal rabbit serum and protein A Sepharose. Antigens were immunoprecipitated with HA-tagged scFv antibodies coupled to Rat Anti-HA agarose beads (Roche). Following immunoprecipitation, antigens were separated by SDS-PAGE and detected by Western 10 blot using streptavidin-alkaline phosphatase (AP) or by Coomassie G-250 staining. ScFv 7, an antibody which doesn't bind to CLL-AAT cells, was used as a negative control. Antigen bands were excised from the Coomassie-stained gel and identified by mass spectrometry (MS). MALDI-MS was performed at the Proteomics Core Facility of The Scripps Research Institute (La Jolla, CA). pLC/MS/MS was performed at the Harvard 15 Microchemistry Facility (Cambridge, MA). Fig. 13 shows that three scFv antibodies bind specifically to 293-EBNA cells transiently transfected with a human OX-2/CD200 cDNA clone. An OX-2/CD200 cDNA was cloned from CLL cells by RT-PCR and inserted into the mammalian expression vector pCEP4 (Invitrogen). PCEP4-CD200 plasmid or the corresponding empty vector 20 pCBP4 was transfected into 293-EBNA cells using Polyfect reagent (QIAGEN). Two days after transfection, the cells were analyzed for binding to scFv antibodies by flow cytometry. Fig. 14 shows that the presence of OX-2/CD200 transfected cells resulted in down-regulation of Th1 cytokines such as IL-2 and IFN-y. Addition of the anti-OX 25 2/CD200 antibody at 30 pg/ml fully restored the Thi response. Fig. 15 shows that the presence of CLL cells in a mixed lymphocyte reaction resulted in down-regulation of the Thl response for IL-2. Fig. 16 shows that the presence of CLL cells in a mixed lymphocyte reaction resulted in down-regulation of the Th1 response for IFN-y. 30 Figs. 17A and B show the mean +/-SD of tumor volumes for all groups of NOD/SCID mice were injected subcutaneously with 4x10 6 RAJI cells either in the presence or absence of human PBL cells. Fig. 18 shows the results of statistical analyses performed using 2 parametric tests (Student's t-test and Welch's test) and one non-parametric test (the Wilcox test). 9 Fig. 19A shows ELISA results of representative IgG1 kappa clones after round 3 panning on CD200-Fc captured on goat anti-mouse IgG Fe antibody. Fig. 19B shows ELISA results of representative IgG2a kappa clones after round 3 panning on CD200-Fc captured on goat anti-mouse IgG Fc antibody. 5 Fig. 19C shows ELISA results of representative IgG1 kappa clones after round 3 panning on CD200-Fc directly coated on. microtiter wells. Fig. 19D shows ELISA results of representative IgG2a kappa clones after round 3 panning on CD200-Fc directly coated on microtiter wells. Fig. 20A shows flow cytometry results of representative IgGI clones selected on 10 CD200-Fc captured with goat anti-mouse IgG Fc. Fig. 20B shows flow cytometry results of representative IgG2a clones selected on CD200-Fc captured with goat anti-mouse IgG Fc. Fig. 20C shows flow cytometry results of representative IgG1 clones selected on directly coated CD200-Fc. 15 Fig. 20D shows flow cytometry results of representative IgG2a clones selected on directly coated CD200-Fc. Fig. 21A shows deduced amino acid sequence of heavy chain complementarity regions of CD200-specific clones. Fig. 21B shows deduced amino acid sequence of heavy chain complementarity 20 regions of CD200-specific clones. Fig. 22 shows ability of selected clones to block the interaction of CD200 with its receptor (CD200R) in a fluorescent bead assay. Fig. 23 shows deduced amino acid sequences of selected CD200 Fabs for chimerization. 25 Fig. 24 shows ELISA results of chimeric IgG obtained from the culture supernatant of a small-scale transient transfection. Fig. 25 shows bead inhibition assay results on purified IgG showing that all antibodies directed against CD200 blocked the receptor ligand interaction very well. Figs. 26A and 26B show that the presence of CLL cells completely abrogated 30 IFN-gamma and most of IL-2 production observed in the mixed lymphocyte reaction but that the presence of any of the antibodies allowed for production of these Th1 cytokines. Fig. 26C shows that IL-10 production was downregulated in the presence of the antibodies. 10 Fig. 27 shows the ability to kill CD200 expressing tumor cells in an antibody dependent cell-mediated cytotoxicity assay (ADCC). All of the mouse chineric CD200 antibodies produced similar levels of lysis when cultured with CD200 positive cells. Fig. 28 shows a representative example of 10 experiments using different PBL 5 donors compared to a group that received tumor cells only, analyzed by a 2-tailed unpaired Student's t-test. Significant differences were observed in the groups that received 5 or 10 million PBLs, but not in the group that received I million PBLs from Day 32 on. Fig. 29 shows a representative example of 10 experiments using different PBL 10 donors compared to a group that received tumor cells only, analyzed by 2-tailed unpaired Student's t-test. Significant differences were observed in the groups that received 10 million PBLs for both donors, but not in the group that received 2 million PBLs from Day 8 on. Fig. 30(a) shows RAI cells infected with CD200 expressing tumor cells 15 transduced from a lentivirus vector appeared to grow somewhat more slowly than its parental RAIl cells. The growth difference between the transduced and parental cells did not reach statistical significance. Fig. 30(b) shows the presence of PBLs reduced tumor growth in the RAJI cells transduced with the reversed CD200 (non functional CD200) by up to 84% when 5 or 20 10x10' PBLs were injected indicating that this particular donor rejects RAJI tumor cells very strongly. Fig. 30(c) shows results indicating that CD200 expression on tumor cells does indeed prevent the immune system from slowing tumor growth. Also this study demonstrates the usefulness of the RAJI/PBL model to assess immunosuppressive 25 compounds or molecules. Figs. 31 (a)-(d) show whether the effects seen in the RAJ/PBL model can also be observed with other tumor cell models. Fig. 31(a) shows Namalwa tumor cells resulted in rapid tumor growth with no significant difference between transduced and parental cells. 30 Fig. 31(b) shows the presence of PBLs slowed tumor growth by about 50%. The 2-tailed Student's t-test results showed that the differences between the PBL treated group versus groups that received only tumor cells were statistically significant. Figs. 31(c) and (d) show tumor growth in the groups that received CD200 expressing Namalwa cells and PBLs was similar to the tumor growth in the group that 11 received Namalwa cells. These data confirm that CD200 expression on tumor cells prevents slowing of tumor growth by the human immune system. Fig. 32 shows results demonstrating that the RAJI PBL model is an efficient way to assess efficacy of immune-enhancing compounds. 5 Figure 33 shows that CD200 expression on the tumor cells prevented the immune cells from reducing tumor growth. Figure 34 shows that CD200 expression on the tumor cells prevented the immune cells from reducing tumor growth. 10 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In accordance with the present disclosure, methods are provided for determining whether OX-2/CD200 is upregulated in a subject and, if so, administering to the subject a therapy that enhances immune response. Illustrative examples of suitable immunomodulatory therapies include the administration of agents that block negative 15 regulation of T cells or antigen presenting cells (e.g., anti-CTLA4 antibodies, anti-PD-LI antibodies, anti-PDL-2 antibodies, anti-PD-1 antibodies and the like) or the administration of agents that enhance positive co-stimulation of T cells (e.g., anti-CD40 antibodies or anti 4-1BB antibodies) or administration of agents that increase NK cell number or T-cell activity (e.g., anti-CD200 antibodies alone or in combination with 20 inhibitors such as IEDs, thalidomide, or thalidomide analogs). Furthermore, immunomodulatory therapy could be cancer vaccines such as dendritic cells loaded with tumor cells, tumor RNA or tumor DNA, tumor protein or tumor peptides, patient derived heat-shocked proteins (hsp's) or general adjuvants stimulating the imnmune system at various levels such as CpG, Luivac, Biostim, Ribominyl, Imudon, Bronchovaxom or any 25 other compound activating receptors of the innate immune system (e.g., toll like receptors). Also, immunomodulatory therapy could include treatment with cytokines such as L-2, GM-CSF and IFN-gamma. In particularly useful embodiments, the therapy that enhances immune response is the administration of a polypeptide that binds to OX-2/CD200, alone or in combination 30 with one of the previously mentioned immunomodulatory therapies. In general, the polypeptides utilized in the present disclosure can be constructed using different techniques which are known to those skilled in the art. In one embodiment, the polypeptides are obtained by chemical synthesis. In other embodiments, the polypeptides 12 are antibodies or constructed from a fragment or several fragments of one or more antibodies. Preferably, the polypeptides utilized in the methods of the present disclosure are obtained from a CLL cell line. "CLL", as used herein, refers to chronic lymphocytic 5 leukemia involving any lymphocyte including, but not limited to, various developmental stages of B cells and T cells including, but not limited to, B cell CLL ("B-CLL"). B-CLL, as used herein, refers to leukemia with a mature B cell phenotype which is CD5 4 , CD23* CD20"*, sIg " and arrested in G0/G1 of the cell cycle. In a further aspect, the CLL cell line is used to generate polypeptides, including antibodies, useful in the diagnosis 10 and/or treatment of a disease state in which OX-2/CD200 is upregulated, including cancer and CLL. As used herein, the term "antibodies" refers to complete antibodies or antibody fragments capable of binding to a selected target. Included are Fab, Fv, scFv, Fab' and F(ab')2, monoclonal and polyclonal antibodies, engineered antibodies (including chimeric, 15 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 as Fv and soFy, possess advantageous properties for diagnostic and therapeutic applications on account of their small size and consequent superior tissue distribution. 20 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 25 on the sequence of the monoclonal antibodies, as well as polypeptides capable of binding to OX-2/CD200. 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 or polypeptides on the basis of target specificity. 30 In a still further aspect, antibodies or polypeptides 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 or 13 polypeptide specific for CLL is provided, which includes assessing the binding of the antibody or polypeptide to a CLL cell line. Preparation of Cell Lines 5 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. 10 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 types) 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 15 thereby, and will be identified by increased growth in culture. In one embodiment a CLL cell line of malignant origin is provided that is not established by immortalization with EBV. "Malignant origin" refers to the derivation of the cell line from malignant CLL primary cells, as opposed to non-proliferating cells which are transformed, for example, with EBV. Cell lines useful according to this 20 disclosure may be themselves malignant in phenotype, or not. A CLL cell having a "malignant" phenotype encompasses cell growth unattached from substrate media characterized by repeated cycles of cell growth and exhibits resistance to apoptosis. The cell line, which was derived from primary CLL cells, is deposited under ATCC accession no. PTA-3920. In a preferred embodiment, the cell line is CLL-AAT. CLL-AAT is a B 25 CLL cell line, derived from a B-CLL primary cell. In one embodiment, proteins uniquely expressed in CLL cells are identified employing the CLL-AAT cell line by methods well known to those skilled in the 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 30 patients. Small molecule libraries (many available commercially) may be screened using the CL-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 14 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., 5 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 one embodiment, the CLL-AAT cell line may be used to identify internalizing antibodies, which bind to cell surface components and are then internalized by the cell. 10 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. Preparation of Monoclonal Antibodies 15 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. Patent No. 5,225,539, the 20 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 25 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 30 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. 15 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 scrum), or trace elements 5 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, 10 NZCYM, NZYM, NZM, Terrific Broth, SOB, SOC, 2 x YT, or M9 Minimal Medium. For yeast, suitable culture media include medium YPD, YBPD, 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, 15 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 20 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 25 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/O 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. 30 The foregoing, and other, techniques are discussed in, for example, Kohler and Milstein, (1975) Nature 256:495-497; U.S. Patent 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 are described in the above references and also in, for example 16 W097/08320; U.S. Patent No. 5,427,908; U.S. Patent 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. PatentNo. 5,403,484; U.S. Patent No. 5223409; W088/06630; W092/15679; U.S. Patent No. 5 5780279; U.S. Patent No, 5571698; U.S. Patent No. 6040136; Davis et al., 1999, Cancer Metastasis Rev., 18(4):421-5; Taylor, et al., Nucleic Acids Research 20 (1992): 6287 6295; Tomizuka et al., Proc. Natl. 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 10 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 15 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 one or more surface polypeptides derived from a CLL cell line according to this disclosure, or with Protein-A or G. 20 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 25 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 recloning. 30 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 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 17 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 5 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 10 between 106 and 10e 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 15 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. 20 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 25 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 30 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 18 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 degenerate sequence. Degenerate sequences are degenerate within the meaning of the genetic code in 5 that an unlimited number of nucleotides are replaced by other nucleotides without resulting in a change of the amino acid sequence originally encoded. Such degenerate 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 10 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 15 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 20 domain g, for example yl, y2, y3 or 14, preferably yl or 1 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 x or ) preferably ; are also provided Another embodiment pertains to recombinant DNAs coding for a recombinant 25 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. 30 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 19 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. Uses of the Present Antibodies/Polypeptides 5 The polypeytides and/or antibodies utilized herein are especially indicated for diagnostic and therapeutic applications. The present antibodies can be administered as a therapeutic to cancer patients, especially, but not limited to CLL patients. In some embodiments, the antibodies are capable of interfering with the interaction of CD200 and its receptors. This interference 10 can block the immune suppressing effect of CD200. By improving the immune response in this manner, such antibodies can promote the eradication of cancer cells. The anti-CD200 antibody can also be administered in combination with other immunomodulatory compounds, vaccines or chemotherapy. For example, elimination of existing regulatory T cells with reagents such as anti-CD25 or cyclophosphamide is 15 achieved in one particularly useful embodiment before starting anti-CD200 treatment. Also, therapeutic efficacy of myeloablative therapies followed by bone marrow transplantation or adoptive transfer of T cells reactive with CLL cells is enhanced by anti CD200 therapy. Furthermore, anti-CD200 treatment can substantially enhance efficacy of cancer vaccines such as dendritic cells loaded with CLL cells or proteins, peptides or 20 RNA derived from such cells, patient-derived heat-shocked proteins (hsp's), tumor peptides or protein. In other embodiments, an anti-CD200 antibody is used in combination with an immuno-stimulatory compound, such as CpG, toll-like receptor agonists or any other adjuvant, anti-CTLA-4 antibodies, and the like. In yet other embodiments, efficacy of anti-CD200 treatment is improved by blocking of 25 immunosuppressive mechanisms such as anti-PDLI and/or 2 antibodies, anti-IL-1 0 antibodies, anti-IL-6 antibodies, and the like. In yet other embodiments, efficacy of anti CD200 treatment is improved by administration of agents that increase NK cell number or T-cell such as the small molecule inhibitor IMiDs, thalidomide, or thalidomide analogs). 30 Anti-CD200 antibodies in accordance with the present disclosure can also be used as a diagnostic tool. For example, using blood obtained from patients with hematopoietic cancers, expression of CD200 can be evaluated on cancer cells by FACS analysis using anti-CD200 antibodies in combination with the appropriate cancer cell markers such as, e.g., CD38 and CD1 9 on CLL cells. Patients with CD200 levels at least 1.4-fold above 20 the levels found on normal B cells can be selected for treatment with anti-CD200 antibodies. In another example of using the present anti-CD200 antibodies as a diagnostic tool, biopsies from patients with malignancies are obtained and expression of CD200 is 5 determined by FACS analysis using anti-CD200 antibodies. If tumor cells express CD200 at levels that are at least 1.4-fold higher compared to corresponding normal tissue, cancer patients are selected for immunomodulatory therapy. Immunornodulatory therapy can be anti-CD200 therapy, but can also be any other therapy affecting the patient's immune system. Examples of suitable immunomodulatory therapies include the 10 administration of agents that block negative regulation-of T cells or antigen presenting cells (e.g., anti-CTLA4, anti-PD-L1, anti-PDL-2, anti-PD-1) or the administration of agents that enhance positive co-stimulation of T cells (e.g., anti-CD40 or anti 4-IBB). Furthermore, immunomodulatory therapy could be the administration of agents that increase NK cell number or T-cell activity (e.g., anti-CD200 antibodies alone or in 15 combination with inhibitors such as IMiDs, thalidomide, or thalidomide analogs) or the administration of agents that deplete regulatory T cells (e.g. anti-CD200 antibodies alone or in combination with ONTAK). Furthermore, immunomodulatory therapy could be cancer vaccines such as dendritic cells loaded with tumor cells, tumor RNA or tumor DNA, tumor protein or tumor peptides, patient derived heat-shocked proteins (hsp's) or 20 general adjuvants stimulating the immune system at various levels such as CpG, Luivac, Biostim, Ribominyl, Imudon, Bronchovaxom or any other compound activating receptors of the innate immune system (e.g., toll like receptors). Also, therapy could include treatment with cylokines such as TL-2, GM-CSF and IFN-gamma. In another embodiment in accordance with the present disclosure, methods are 25 provided for monitoring the progress and/or effectiveness of a therapeutic treatment. The method involves administering an immunomodulatory therapy and determining OX 2/CD200 levels in a subject at least twice to determine the effectiveness of the therapy. For example, pre-treatment levels of OX-2/CD200 can be ascertained and, after at least one administration of the therapy, levels of OX-2/CD200 can again be determined. A 30 decrease in OX-21CD200 levels is indicative of an effective treatment Measurement of OX-2/CD200 levels can be used by the practitioner as a guide for increasing dosage amount or frequency of the therapy. It should of course be understood that OX-2/CD200 levels can be directly monitored or, alternatively, any marker that correlates with OX 2/CD200 can be monitored. 21 The present antibodies also may be utilized to detect cancerous cells in vivo. This is achieved by labeling the antibody, administering the labeled antibody to a subject, and then imaging the subject Examples of labels useful for diagnostic imaging in accordance with the present disclosure are radiolabels such as 1311, 1m in, 123, "mTc, 3p, 251, 3 H, 14c, 5 and 'mRh, fluorescent labels such as fluorescein and rhodamine, nuclear magnetic resonance active labels, positron emitting isotopes detectable by a positron emission tomography ("PET") scanner, chemiluminescers such as luciferin, and enzymatic markers such as peroxidaso or phosphatase. Short-range radiation emitters, such as isotopes detectable by short-range detector probes, such as a transrectal probe, can also be 10 employed. The antibody can be labeled with such reagents using techniques known in the art. For example, see Wensel and Meares, Radioimmunoimaging and Radioimmunotherapy, Elsevier, N.Y. (1983), which is hereby incorporated by reference, for techniques relating to the radiolabeling of antibodies. See also, D. Colcher et al., "Use of Monoclonal Antibodies as Radiopharmaceuticals for the Localization of Human 15 Carcinoma Xcnografts in Athymic Mice", Meth. Enzymol. 121: 802-816 (1986), which is hereby incorporated by reference. A radiolabeled antibody in accordance with this disclosure can be used for in vitro diagnostic tests. The specific activity of an antibody, binding portion thereof probe, or ligand, depends upon the half-life, the isotopic purity of the radioactive label, and how the 20 label is incorporated into the biological agent In immunoassay tests, the higher the specific activity, in general, the better the sensitivity. Procedures for labeling antibodies with the radioactive isotopes are generally known in the art. The radiolabeled antibody can be administered to a patient where it is localized to cancer cells bearing the antigen with which the antibody reacts, and is detected or 25 "imaged" in vivo using known techniques such as radionuclear scanning using e.g., a gamma camera or emission tomography. See e.g., A. R. Bradwell et al., "Developments in Antibody Imaging", Monoclonal Antibodies for Cancer Detection and Therapy, R. W. Baldwin et al., (eds.), pp. 65-85 (Academic Press 1985), which is hereby incorporated by reference. Alternatively, a positron emission transaxial tomography scanner, such as 30 designated Pet VI located at Brookhaven National Laboratory, can be used where the radiolabel emits positrons (e.g., "Ic, 1 8 F, 15, and 3N). 22 Fluorophore and chromophore labeled biological agents can be prepared from standard moieties known in the art. Since antibodies and other proteins absorb light having wavelengths up to about 310 n, the fluorescent moieties should be selected to have substantial absorption at wavelengths above 310 nm and preferably above 400 n. 5 A variety of suitable fluorescers and chromophores am described by Stryer, Science, 162:526 (1968) and Brand, L. et al., Annual Review of Biochemistry, 41:843-868 (1972), which are hereby incorporated by reference. The antibodies can be labeled with fluorescent chromophore groups by conventional procedures such as those disclosed in U.S. Patent Nos. 3,940,475, 4,289,747, and 4,376,110, which are hereby incorporated by 10 reference. In other embodiments, bispecific antibodies are contemplated. Bispecific antibodies are monoclonal, preferably human or humanized, antibodies that have binding specificities for at least two different antigens. In the present case, one of the binding specificities is for the CD200 antigen on a cancer cell, the other one is for any other 15 antigen, and preferably for a cell-surface protein or receptor or receptor subunit. Methods for making bispocific antibodies are within the purview of those skilled in the art. Traditionally, the recombinant production of bispecific antibodies is based on the co-expression of two immunoglobulin heavy-chain/light-chain pairs, where the two heavy chains have different specificities (Milstein and Cuello, Nature, 305:537-539 20 (1983)). Antibody variable domains with the desired binding specificities (antibody antigen combining sites) can be fused to immunoglobulin constant domain sequences. The fusion preferably is with an immunoglobulin heavy-chain constant domain, including at least part of the hinge, CH2, and CH3 regions. DNAs encoding the immunoglobulin heavy-chain fusions and, if desired, the immunoglobulin light chain, are inserted into 25 separate expression vectors, and are co-transfected into a suitable host organism. For further details of illustrative currently known methods for generating bispecific antibodies see, for example, Suresh et al., Methods in Enzymology, 121:210 (1986); WO 96/27011; Brennan et al., Science 229:81 (1985); Shalaby et al., J. Exp. Med. 175:217-225 (1992); Kostelny et al., J. Immunol. 148(5):1547-1553 (1992); Hollinger et al., Proc. Nati. Acad. 30 Sci. USA 90:6444-6448 (1993); and Gruber et al., J. Immunol. 152:5368 (1994); and Tutt et al., J. Immunol. 147:60 (1991). 23 The present antibodies can also be utilized to directly kill or ablate cancerous colls in vivo. This involves administering the antibodies (which are optionally fused to a cytotoxic drug) to a subject requiring such treatment. Since the antibodies recognize CD200 on cancer cells, any such cells to which the antibodies bind are destroyed. 5 Where the antibodies are used alone to kill or ablate cancer cells, such killing or ablation can be effected by initiating endogenous host immune functions, such as complement-mediated or antibody-dependent cellular cytotoxicity. Assays for determining whether an antibody kills cells in this manner are within the purview of those skilled in the art. 10 The antibodies of the present disclosure may be used to deliver a variety of cytotoxic compounds. Any cytotoxic compound can be fused to the present antibodies. The fusion can be achieved chemically or genetically (e.g., via expression as a single, fused molecule). The cytotoxic compound can be a biological, such as a polypeptide, or a small molecule. As those skilled in the art will appreciate, for small molecules, chemical 15 fusion is used, while for biological compounds, either chemical or genetic fusion can be employed. Non-limiting examples of cytotoxic compounds include therapeutic drugs, a compound emitting radiation, molecules of plants, fungal, or bacterial origin, biological proteins, and mixtures thereof. The cytotoxic drugs can be intracellularly acting cytotoxic 20 drugs, such as short-range radiation emitters, including, for example, short-range, high energy a-emitters. Enzymatically active toxins and fragments thereof are exemplified by diphtheria toxin A fragment, nonbinding active fragments of diphtheria toxin, exotoxin A (from Pseudomonas aeruginosa), ricin A chain, abrin A chain, modcccin A chain, .alpha.

sacrin, certain Aleurites fordif proteins, certain Dianthin proteins, Phytolacca americana 25 proteins (PAP, PAPII and PAP-S), Morodica charantia inhibitor, curcin, crotin, Saponaria officinalis inhibitor, gelonin, mitogillin, restrictocin, phenomycin, and enomycin, for example. Procedures for preparing enzymatically active polypeptides of the immunotoxins are described in W084/03508 and WO85/03508, which are hereby incorporated by reference. Certain cytotoxic moieties are derived from adriamycin, 30 chlorambuclt, daunomycin, methotrexate, neocarzinostatin, and platinum, for example. Procedures for conjugating the antibodies with the cytotoxic agents have been previously described and are within the purview of one skilled in the art. Alternatively, the antibody can be coupled to high energy radiation emitters, for example, a radioisotope, such as 1m , a y-emitter, which, when localized at the tumor site, 24 results in a killing of several cell diameters. See, e.g., S. B. Order, "Analysis, Results, and Future Prospective of the Therapeutic Use of Radiolabeled Antibody in Cancer Therapy", Monoclonal Antibodies for Cancer Detection and Therapy, R. W. Baldwin et al. (eds.), pp 303-316 (Academic Press 1985), which is hereby incorporated by reference. Other 5 suitable radioisotopes include a-emitters, such as 21 2 Bi, 21 ,Bi and 211 At, and p-emitters, such as lS&Re and 90 Y. The route of antibody administration of the present antibodies (whether the pure antibody, a labeled antibody, an antibody fused to a toxin, etc.) is in accord with known methods, e.g., injection or infusion by intravenous, intraperitoneal, intracerebral, 10 intramuscular, subcutaneous, intraocular, intraarterial, intrathecal, inhalation or intralesional routes, or by sustained release systems. The antibody is preferably administered continuously by infusion or by bolus injection. One may administer the antibodies in a local or systemic manner. The present antibodies may be prepared in a mixture with a pharmaceutically 15 acceptable carrier. Techniques for formulation and administration of the compounds of the instant application may be found in "Remington's Pharmaceutical Sciences," Mack Publishing Co., Easton, PA, latest edition. This therapeutic composition can be administered intravenously or through the nose or lung, preferably as a liquid or powder aerosol (lyophilized). The composition may also be administered parenterally or 20 subcutaneously as desired. When administered systemically, the therapeutic composition should be sterile, pyrogen-free and in a parenterally acceptable solution having due regard for pH, isotonicity, and stability. These conditions are known to those skilled in the art. Pharmaceutical compositions suitable for use include compositions wherein one or more of the present antibodies are contained in an amount effective to achieve their 25 intended purpose. More specifically, a therapeutically effective amount means an amount of antibody effective to prevent, alleviate or ameliorate symptoms of disease or prolong the survival of the subject being treated. Determination of a therapeutically effective amount is well within the capability of those skilled in the art, especially in light of the detailed disclosure provided herein. Therapeutically effective dosages may be determined 30 by using in vitro and in vivo methods. In some embodiments, present CD200 binding antibodies provide the benefit of blocking immune suppression in CLL by targeting the leukemic cells directly through CD200. Specifically, stimulating the immune system can allow the eradication of CLL cells from the spleen and lymph nodes. Applicants are unaware of any successful 25 eradication of CLL cells from these microenvironments having been achieved with agents that simply target B cells (such as alemtuzumab). In contrast, CLL reactive T cells can have better access to these organs than antibodies. In other embodiments, direct cell killing is achieved by tagging the CLL cells with anti-CD200 Abs. 5 In particularly useful embodiments, the combination of direct cell killing and driving the immune response towards a Thl profile provides a particularly powerful approach to cancer treatment Thus, in one embodiment, a cancer treatment is provided wherein an antibody or antibody fragmcnt, which binds to CD200 and both a) blocks the interaction between CD200 and its receptor and b) directly kills the cancer cells 10 expressing CD200, is administered to a cancer patient. The mechanism by which the cancer cells are killed can include, but are not limited to antibody-dependent cellular cytotoxicity (ADCC) or complement dependent cytotoxicity (CDC); fusion with a toxin; fusion with a radiolabel; fusion with a biological agent involved in cell killing, such as granzyme B or perforin; fusion with a cytotoxic virus; fusion with a cytokine such as 15 TNF-% or IFN-u. In an alternative embodiment, a cancer treatment involves administering an antibody that both a) blocks the interaction between CD200 and its receptor and b) enhances cytotoxic T cell or NK cell activity against the tumor. Such enhancement of the cytotoxic T cell or NK cell activity may, for example, be combined by fusing the antibody with cytokines such as e.g. 11-2, IL-12, IL-18, IL-13, and IL-5. In 20 addition, such enhancement may be achieved by administration an anti-CD200 antibody in combination with inlibitors such as IMiDs, thalidomide, or thalidomide analogs. In yet another embodiment, the cancer treatment involves administering an antibody that both a) blocks the interaction between CD200 and its receptor and b) attracts T cells to the tumor cells. T cell attraction can be achieved by fusing the Ab with 25 chemokines such as MIG, IP-10, I-TAC, CCL21, CCL5 or LIGHT. The combined action of blocking immune suppression and killing directly through antibody targeting of the tumor cells is a unique approach that provides increased efficacy. While the above disclosure has been directed to antibodies, in some embodiments polypeptides derived from such antibodies can be utilized in accordance with the present 30 disclosure. 26 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, cancer, and other disease states characterized by upregulated levels of OX-2/CD200, e.g., melanoma. 5 A cell line according to this disclosure may be used for in vitro studies on the etiology, pathogenesis and biology of CLL and other disease states characterized by upregulated levels of OX-2/CD200. This assists in the identification of suitable agents that are useful in the therapy of these diseases. The cell line may also be used to produce polypeptides and/or monoclonal 10 antibodies for in vitro and In vivo diagnosis of CLL, cancer, and other disease states characterized by upregulated levels of OX-2/CD200 (e.g,, melanoma), 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. 15 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 20 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 25 multiple lymphocyte-specific antigens on lymphocyte tumors. Existing antibody therapies (such as Rituximab", directed against the CD20 antigen, which is expressed on the surface ofB-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 30 (4) (1992) 259-263). The CLL cell line described herein thus permits the development of novel anti CLL antibodies and polypeptides having specificity for one or more antigenic determinants of the present CLL cell line, and their use in the therapy and diagnosis of 27 CLL, cancer, and other disease states characterized by upregulated levels of OX 2/CD200. The antibody or polypeptide may bind to a receptor with which OX-2/CD200 normally interacts, thereby preventing or inhibiting OX-2/CD200 from binding to the 5 receptor. As yet another alternative, the antibody can bind to an antigen that modulates expression of OX-2/CD200, thereby preventing or inhibiting normal or increased expression of OX-2/CD200. 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 10 disease state, such as cancer or CLL, more effectively. In a particularly useful embodiment, the polypeptide binds to OX-2/CD200. In one embodiment, the polypeptide can be an antibody which binds to OX-2/CD200 and prevents or inhibits OX-2/CD200 from interacting with other molecules or receptors. As CLL cells and other cells overexpressing OX-2/CD200 greatly diminish the production of 15 Th1 cytokines, the administration of anti-CD200 antibody or a polypeptide which binds to OX-2/CD200 to a subject having upregulated levels of OX-2/CD200 restores the Thi cytokine profile. Thus, these polypeptides and/or antibodies can be useful therapeutic agents in the treatment of CLL and other cancers or diseases overexpressing OX 2/CD200. 20 Thus, in another embodiment, the method of the present disclosure includes the steps of screening a subject for the presence OX-2/CD200 and administering a polypeptide that binds to OX-2/CD200. It should of course be understood that the presence of OX-2/CD200 can be directly monitored or, alternatively, any marker that correlates with OX-2/CD200 can be detected. In a particularly useful embodiment, a 25 CLL patient is screened for overexpression of OX-2/CD200 and an antibody that binds to OX-2/CD200 is administered to the patient. One such antibody is the commercially available anti-CD200 antibody from Serotec Inc. (3200 Atlantic Ave, Suite 105, Raleigh, NC 27604). As described in detail below, another such antibody is scFv-9 (see Fig. 9B) which binds to OX-2/CD200. 30 In another aspect, the present disclosure provides methods for assessing the immunomodulatory effect of molecules expressed by cancer cells. In these methods a molecule that is expressed or upregulated by a cancer cell is first identified. The molecule can be identified from a database or experimentally. Databases that identify molecules that are expressed or upregulated by cancer cells are known and include, for 28 example, the NCI60 cancer microarray project (http//genome-www.stanford.edu/nci6o) (Ross et al., Nature Genetics 24:227-34, 2000), the Carcinoma classification (http://www.gnf.org/cancer/epican/) (Andrew I. Suet al., "Molecular Classification of Human Carcinomas by Use of Gene Expression Signatures." Cancer Research 61:7388 5 7393, 2001), and the Lymphoma/Leukemia molecular profiling project (http://llmpp.nih.gov/lymphoma/) (Alizadeh et al., Nature 403: 503-11, 2000). Experimental methods useful for identifying molecules that are expressed or upregulated by cancer cells are also known and include, for example microarray experiments, quantitative PCR, FACS, and Northern analysis. 10 Cancer cells, lymphocytes and the previously identified molecule that is expressed by a cancer cell are administered to a subject and the rate of growth of the cancer cells is monitored. Any type of cancer cells can be employed in the present methods. In some embodiments, the cancer cells express an immunosuppressive compound. In particularly useful embodiments, the cancer cells express or even overexpress CD200. Suitable 15 cancer cells include, but are not limited to lymphoma cell lines such as the RAJI or Namalwa cell lines. The amount of cancer cells administered may range from about 1 x 10' to about 20 x 10. Any type of lymphocyte may be employed in the present process. Suitable lymphocytes include, for example, PBLs, T cells, cytotoxic T cells, dendritic cells or NK 20 cells. In particularly useful embodiments, the lymphocytes are human lymphocytes, specifically human PBLs. The number of lymphocytes administered is predetermined to be either a) sufficient to slow the growth of the cancer cells or b) insufficient to slow the growth of cancer cells. The amount of lymphocytes administered may be greater than or equal to the number of cancer cells administered when the number of lymphocytes 25 administered is intended to be sufficient to slow the growth of the cancer cells. In embodiments, the amount of lymphocytes administered may be from about 5 x 106 to about 10 x 106 when the number of lymphocytes administered is intended to be sufficient to slow the growth of the cancer cells. The amount of lymphocytes administered may be less than the number of cancer cells administered when the number of lymphocytes 30 administered is intended to be insufficient to slow the growth of the cancer cells. In embodiments, the amount of lymphocytes administered may range from about 1 x 10' to about 4 x 10'6 when the number of lymphocytes administered is intended to be insufficient to slow the growth of the cancer cells. The foregoing amounts are illustrative and other suitable amounts may be experimentally determined and used in the present methods. 29 The molecule that is expressed or uprgulated by a cancer cell can be administered as the molecule or the active portion thereof itself (either isolated or recombinantly generated), or by administering cells that produce the molecule naturally, or by administering cells that have been engineered to produce the molecule or portions 5 thereof. Methods for engineering cells to express a desired molecule are known to those skilled in the art. The amount of molecule administered can be any amount above the amount found in a healthy individual. For example, the amount of the molecule administered can be from about 1.4-fold above what is found in a healthy individual in the same type of cell to about 10,000-fold above what is found in a healthy individual in 10 the same type of cell. It should be understood that the molecule being assessed may or may not be known to have some degree of immunoinodulatory activity. Thus, the present methods may be used to confirm the immunomodulatory effect of a molecule as well as to determine such activity ab initio. Any small animal may be chosen as the subject to which the cancer cells, 15 lymphocytes and the molecule are administered. The subject may advantageously be immunocompromised. Suitable small animals include, for example, immunodeficient mice, irradiated rats, irradiated guinea pigs and the like. The rate of cancer cell growth can be monitored using conventional techniques, For example, tumor growth can be monitored by measuring length and width with a 20 caliper. Tumor volume can be calculated, for example, based on multiplying the length of the tumor by the width of the tumor and then multiplying by one-half the width of the tumor. The rate of cancer cell growth can be measured periodically, such as, for example, three times a week. The rate of growth of cancer cells when cancer cells and lymphocytes alone have been administered may be determined by administering cancer 25 cells and lymphocytes alone to a control subject and periodically measuring tumor size. Alternatively, cancer cells and lymphocytes alone can be administered initially, and once a baseline growth rate is established, the molecule that is expressed or upregulated by a cancer cell can be subsequently administered to the subject and the rate of growth of the cancer cells after the second administration can be measured. Alternatively, with 30 systemic models the rate of cancer cell growth can be monitored using FACS, survival or other conventional techniques. If any change in the growth rate of the cancer cells is observed compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the molecule is deemed to have an immunomodulatory effect. If the number of lymphocytes 30 administered is sufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is higher compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the molecule that is expressed or upregulated by a cancer cell is considered immunosuppressive. If the number of 5 lymphocytes administered is insufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is lowered compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the molecule is considered immune enhancing. Typically, the rate of cancer cell growth observed may be about 20 to about 1,000% higher than the rate of growth when the tumor cells and donor 10 lymphocytes are administered alone for the immunosuppressing or immune enhancing effect to be statistically significant. Once the immunomodulatory effect of the molecule is established, compounds that either enhance or inhibit the activity of the molecule can be identified in accordance with embodiments described herein. The compound that either enhances or inhibits the 15 activity of the molecule previously found to have immunomodulatory effect can be any compound that alters the protein/protein interaction that provides the immunomodulatory effect. The enhancing or inhibiting effect can be the result of direct interaction with the compound expressed or upregulated by the cancer cell or may be the result of an interaction with other compounds in the metabolic pathway of the compound expressed or 20 upregulated by the cancer cell. For example, antibodies or functional antibody fragments can be identified that interact with the molecule previously found to have an immunomodulatory effect, the receptor with which the molecule interacts, or some other molecule in the metabolic pathway of the molecule responsible for the immunomodulatory effect. Techniques for 25 making antibodies (including antibody libraries) and screening them for an inhibitory or enhancing effect will be apparent to those skilled in the art. As another example, small molecules may be screened for an inhibitory or enhancing effect. Techniques for screening small molecule libraries for an inhibitory or enhancing effect will be apparent to those skilled in the art. 30 In another aspect, methods for assessing the immunomodulatory effect of a compound are contemplated by the present disclosure. Demonstrating immunomodulatory properties of compounds or molecules acting on the human immune system is very challenging in small animal models. Often, the compounds do not act on the immune system of small animals, requiring reconstitution of the human immune 31 system in mice. Reconstitution can be accomplished by grafting of various fetal immune organs into mice or by injection of human lymphocytes, but none of the models described to date has proven to be useful for demonstrating immunomodulatory properties of compounds or molecules. The immune system is believed to play an important role in 5 eradicating cancer cells. Cancer cells have found ways to evade the immune system by upregulation of immunosuppressive receptors. The present methods of assessing the immunomodulatory effect of a compound is accomplished by a model that mimics the graft versus leukemia effect observed in patients with leukemia that are infused with donor lymphocytes (e.g., PBLs) resulting in 10 remission in up to 80% of patients. The method involves administering cancer cells, lymphocytes and the compound to be assessed to a subject and the rate of growth of the cancer cells is monitored. Any type of cancer cells can be employed in the present methods. In some embodiments, the cancer cells express an immunosuppressive compound. In particularly 15 useful embodiments, the cancer cells express or even overexpress CD200. Suitable cancer cells include, but are not limited to lymphoma cell lines such as the RAJI or Namalwa cell lines. The amount of cancer cells administered may range from about 2 x104 to about 20 x 106. Any type of lymphocyte may be employed in the present process. Suitable 20 lymphocytes include, for example, PBLs, dendritic cells, T cells, cytotoxic T cells, NK cells. In particularly useful embodiments, the lymphocytes are human lymphocytes, specifically human PBts. The number of lymphocytes administered is predetermined to be either a) sufficient to slow the growth of the cancer cells or b) insufficient to slow the growth of cancer cells. The amount of lymphocytes administered may be greater than or 25 equal to the number of cancer cells administered when the number of lymphocytes administered is intended to be sufficient to slow the growth of the cancer cells. In embodiments, the amount of lymphocytes administered may be from about 5 x 10' to about 10 x 106 when the number of lymphocytes adminitered is intended to be sufficient to slow the growth of the cancer cells. The amount of lymphocytes administered may be 30 less than the number of cancer cells administered when the number of lymphocytes administered is intended to be insufficient to slow the growth of the cancer cells. In embodiments, the amount of lymphocytes administered may range from about I x 106 to about 4 x 10' when the number of lymphocytes administered is intended to be insufficient 32 to slow the growth of the cancer cells. The foregoing amounts are illustrative and other suitable amounts may be experimentally determined and used in the present methods. The compound being assessed can be any compound whose immunomodulatory effect is sought to be determined. Illustrative examples of compounds include the 5 antibodies and peptides described herein above. The amount of the compound being assessed administered may range from about 1 mg/kg to about 200 mg/kg. The compound to be assessed can be administered as the compound itself, or by administering cells that produce the compound naturally, or by administering cells that have been engineered to produce the compound. It should be understood that the compound being 10 assessed may or may not be known to have some degree of immunomodulatory activity. Thus, the present methods may be used to confirm the immunomodulatory effect of a compound as well as to determine such activity ab initio. Any small animal may be chosen as the subject to which the cancer cells, lymphocytes and the compound are administered. The subject may advantageously be 15 immunocompromised. Suitable small animals include, for example, immunodeficient mice, irradiated rats, irradiated guinea pigs and the like. The rate of cancer cell growth can be monitored using conventional techniques. For example, tumor growth can be monitored by measuring length and width with a caliper. Tumor volume can be calculated, for example, based on multiplying the length of 20 the tumor by the width of the tumor and then multiplying by one-half the width of the tumor. The rate of cancer cell growth can be measured periodically, such as, for example, three times a week. The rate of growth of cancer cells when cancer cells and lymphocytes alone have been administered may be determined by administering cancer cells and lymphocytes alone to a control subject and periodically measuring tumor size. 25 Alternatively, cancer cells and lymphocytes alone can be administered initially, and once a baseline growth rate is established, the compound to be assessed can be subsequently administered to the subject and the rate of growth of the cancer cells after the second administration can be measured. When injecting cancer cells such as the lymphoma cell lines RAJI or Namalwa 30 into immune-deficient mice, administration of five to 10 million PBLs results in significantly slower tumor growth. In contrast, low PBL numbers (1-2 million depending on donor) do not slow tumor growth. If any change in the growth rate of the cancer cells is observed compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the 33 molecule is deemed to have an immunomodulatory effect If the number of lymphocytes administered is sufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is higher compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is considered 5 immunosuppressive. If the number of lymphocytes administered is insufficient to slow the growth of the cancer cells and the rate of growth of the tumor cells observed is lowered compared to the rate of growth when the tumor cells and donor lymphocytes are administered alone, the compound is considered immune enhancing. In order that those skilled in the art may be better able to practice the 10 compositions and methods described herein, the following examples are given for illustration purposes. EXAMPLE I Isolation of Cell Line CLL-AAT Establishment of the cell line 15 Peripheral blood from a patient diagnosed with CLL was obtained. The WBC count was I.6x10 8 /ml. Mononuclear cells were isolated by Histopaque-1077 density gradient centrifugation (Sigma Diagnostics, St. Louis, MO). Cells were washed twice with Iscove's Modified Dulbecco's Medium (IMDM) supplemented with 10% heat inactivated fetal bovine serum (FBS), and resuspended in 5 ml of ice-cold IMDM/10% 20 FBS. Viable cells were counted by staining with trypan blue. Cells were mixed with an equal volume of 85% FBS/I 5% DMSO and frozen in I ml aliquots for storage in liquid nitrogen. Immunophenotyping showed that >90% of the CD45+ lymphocyte population expressed IgD, kappa light chain, CD5, CD19, and CD23. This population also expressed 25 low levels of IgM and CD20. Approximately 50% of the cells expressed high levels of CD38. The cells were negative for lambda light chain, CD10 and CD138 An aliquot of the cells was thawed, washed, and resuspended at a density of 10 7 /mL in IMDM supplemented with 20% heat-inactivated FBS, 2mM L-glutamine, 100 units/ml penicillin, 100 pg/ml streptomycin, 50 pM 2-mercaptoethanol, and 5 ng/ml 30 recombinant human IL-4 (R & D Systems, Minneapolis, MN). The cells were cultured at 37*C in a humidified 5% CO2 atmosphere. The medium was partially replaced every 4 days until steady growth was observed. After 5 weeks, the number of cells in thc culture began to double approximately every 4 days. This cell line was designated CLL-AAT. 34 Characterization of the cell line Immunophenotyping of the cell line by flow cytometry showed high expression of IgM, kappa light chain, CD23, CD38, and CD138, moderate expression of CD19 and CD20, and weak expression of IgD and CD5. The cell line was negative for lambda light chain, CD4, CD8, and CD1O. 5 Immunophenotyping of the cell line was also done by whole cell ELISA using a panel of rabbit soFv antibodies that had been selected for specific binding to primary B CLL cells. All of these CLL-spocific scFv antibodies also recognized the CLL -AAT cell line. In contrast, the majority of the scFvs did not bind to two cell lines derived from B cell lymphomas: Ramos, a Burkitt's lymphoma cell line, and RL, a non-Hodgkin's 10 lymphoma cell line. EXAMPLE 2 Selection of scFv Antibodies for B-CLL-specific Cell Surface Antigens using Antibody Phage Display and Cell Surface Panning Immunizations and scFv antibody library construction Peripheral blood mononuclear cells (PBMC) were isolated from blood drawn from CLL patients at the Scripps Clinic (La Jolla, CA). Two rabbits were immunized with 15 2x10 7 PBMC pooled from 10 different donors with CLL. Three immunizations, two subcutaneous injections followed by one intravenous injection, were done at three week intervals. Serum titers were checked by measuring binding of serum IgG to primary CLL cells using flow cytometry. Five days after the final immunization, spleen, bone marrow, and PBMC were harvested from the animals. Total RNA was isolated from these tissues 20 using Tri-Reagent (Molecular Research Center, Inc). Single-chain Fv (scFv) antibody phage display libraries were constructed as previously described (Barbas et al., (2001) Phage Display: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York). For cell surface panning, phagemid particles from the reamplified library were precipitated with polyethylene glycol (PEG), resuspended in phosphate 25 buffered saline (PBS) containing 1% bovine serum albumin (BSA), and dialysed overnight against PBS. 35 Antibody selection by cell surface panning The libraries were enriched for CLL cell surface-specific antibodies by positive negative selection with a magnetically-activated cell sorter (MACS) as described by Siegel et al. (1997, J. Immunol. Methods 206:73-85). Briefly, phagemid particles from the scFv antibody library were preincubated in MPBS (2% nonfat dry milk, 0.02% 5 sodium azide in PBS, pH 7.4) for I hour at 25*C to block nonspecific binding sites. Approximately I 0 7 primary CLL colls were labeled with mouse anti-CD5 IgG and mouse anti-CD19 IgG conjugated to paramagnetic microbeads (Miltenyi Biotec, Sunnyvale, CA). Unbound microbeads were removed by washing. The labeled CLL cells ("target cells") were mixed with an excess of "antigen-negative absorber cells", pelleted, and 10 resuspended in 0pl ( 10 W4-10" efu) of phage particles. The absorber cells serve to soak up phage that stick non-specifically to cell surfaces as well as phage specific for "common" antigens present on both the target and absorber cells. The absorber cells used were either TF-1 cells (a human erythroleukemia cell line) or normal human B cells isolated from peripheral blood by immunomagnetic negative selection (StemSep system, 15 StemCell Technologies, Vancouver, Canada). The ratio of absorber cells to target cells was approximately 10 fold by volume. After a 30 minute incubation at 25*C, the cell/phage mixture was transferred to a MiniMACS MS+ separation column. The column was washed twice with 0.5 ml of MPBS, and once with 0.5 ml of PBS to remove the unbound phage and absorber cells. The target cells were eluted from the column in 1 ml 20 of PBS and pelleted in a microcentrifuge at maximum speed for 15 seconds. The captured phage particles were eluted by resuspending the target cells in 200 pl of acid elution buffer (0.1 N HCI, pH adjusted to 2.2 with glycine, plus 1 mg/mi BSA). After a 10 minute incubation at 25"C, the buffer was neutralized with 12 jtL of 2M Tris base, pHI 0.5, and the eluted phage were amplified in E. coli for the next round of panning. For 25 each round of panning, the input and output phage titers were determined. The input titer is the number of reamplified phage particles added to the target cell/absorber cell mixture and the output titer is the number of captured phage eluted from the target cells. An enrichment factor (E) is calculated using the formula E=(Rn output/Rn input)/(Ri output/R, input), where R 1 = round 1 and &- round 2, 3, or 4. In most cases, an 30 enrichment factor of 102-103 fold should be attained by the third or fourth round. 36 Analysis of enriched antibody pools following panning After 3-5 rounds of panning, the pools of captured phage were assayed for binding to CLL cells by flow cytometry and/or whole cell ELISA: 1. To produce an entire pool in the form of HA-tagged soluble antibodies, 2m] of a non suppressor strain of E. coli (e.g. TOP1OF') was infected with ipl (109-1014 cfu) of 5 phagemid particles. The original, unpanned library was used as a negative control. Carbenicillin was added to a final concentration of 1OIM and the culture was incubated at 37'C with shaking at 250rpm for 1 hour. Eight ml of SB medium containing 50ig/mI carbenicillin was added and the culture was grown to an OD 600 of-0.8. IPTG was added to a final concentration of ImM to induce scFv expression 10 from the Lac promoter and shaking at 37"C was continued for 4 hours. The culture was centrifuged at 3000xg for 15'. The supernatant containing the soluble antibodies was filtered and stored in 1 ml aliquots at -20"C. 2. Binding of the scFv antibody pools to target cells vs. absorber cells was determined by flow cytometry using high-affinity Rat Anti-HA (clone 3F10, Roche Molecular 15 Biochemicals) as secondary antibody and PE-conjugated Donkey Anti-Rat as tertiary antibody. 3. Binding of the antibody pools to target cells vs. absorber cells was also determined by whole-cell ELISA as described below, Screening individual scFv clones following panning To screen individual scFv clones following panning, TOPIOF' cells were infected 20 with phage pools as described above, spread onto LB plates containing carbenicillin and tetracycline, and incubated overnight at 37"C. Individual colonies were inoculated into deep 96-well plates containing 0.6-1.0 ml of SB-carbenicillin medium per well. The cultures were grown for 6-8 hours in a HiGro shaking incubator (GeneMachines, San Carlos, CA) at 520 rpm and 37*C. At this point, a 90 pl aliquot from each well was 25 transferred to a deep 96-well plate containing 10 pL of DMSO. This replica plate was stored at -80"C. IPTG was added to the original plato to a final concentration of 1 mM and shaking was continued for 3 hours. The plates were centrifuged at 3000xg for 15 minutes. The supernatants containing soluble scFv antibodies were transferred to another deep 96-well plate and stored at -20(C. 37 A sensitive whole-cell ELISA method for screening HA-tagged scFv antibodies was developed: 1. An ELISA plate is coated with concanavalin A (10mg/mi in 0.1 M NaHCO 3 , pH8.6, 0.1 mM CaCI 2 ). 5 2. After washing the plate with PBS, 0.5-1x10 5 target cells or absorber cells in 50p1 of PBS are added to each well, and the plate is centrifuged at 250xg for 10 minutes. 3. 50pl of 0.02% glutaraldehyde in PBS are added and the cells are fixed overnight at 4 0 C. 4. After washing with PBS, non-specific binding sites are blocked with PBS containing 10 4% non-fat dry milk for 3 hours at room temperature. 5. The cells are incubated with 50pil of soluble, HA-tagged scFv or Fab antibody (TOP1OF' supernatant) for 2 hours at room temperature, then washed six times with PBS. 6. Bound antibodies are detected using a Mouse Anti-HA secondary antibody (clone 15 12CA5) and an alkaline phosphatase (AP)-conjugated Anti-Mouse IgG tertiary antibody. An about 10-fold amplification of the signal is obtained by using AMDEX AP-conjugated Sheep Anti-Mouse IgG as the tertiary antibody (Amersham Pharmacia Biotech). The AMDEX antibody is conjugated to multiple AP molecules via a doxtran backbone. Color is developed with the alkaline phosphatase substrate PNPP 20 and measured at 405nm using a microplate reader. Primary screening of the scFv clones was done by ELISA on primary CLL cells versus normal human PBMC. Clones which were positive on CLL cells and negative on normal PBMC were rescreened by ELISA on normal human B cells, human B cell lines, TF-1 cells, and the CLL-AAT cell line. The clones were also rescreened by ELISA on 25 CLL cells isolated from three different patients to eliminate clones that recognized patient-specific or blood type-specific antigens. Results from representative ELISAs are shown in Figures 2-6 and summarized in Figs. 9A - 9C. The number of unique scFv antibody clones obtained was determined by DNA fingerprinting and sequencing. The scFv DNA inserts were amplified from the plasmids 30 by PCR and digested with the restriction enzyme BstNI. The resulting fragments were separated on a 4% agarose gel and stained with ethidium bromide. Clones with different restriction fragment patterns must have different amino acid sequences. Clones with identical patterns probably have similar or identical sequences. Clones with unique BstNI fingerprints were further analyzed by DNA sequencing. Twenty-five different sequences 38 were found, which could be clustered into 16 groups of antibodies with closely related complementarity determining regions (Figs. 9A - 9C). Characterization of scFv antibodies by flow cytometry 5 The binding specificities of several scFv antibodies were analyzed by 3-color flow cytometry (Fig. 7). PBMC isolated from normal donors were stained with F1TC conjugated anti-CD5 and PerCP-conjugated anti-CD19. Staining with scFv antibody was done using biotin-conjugated anti-HA as secondary antibody and PE-conjugated streptavidin. Three antibodies, scFv-2, scFv-3, and scFv-6, were found to specifically 10 recognize the CD19 B lymphocyte population (data not shown). The fourth antibody, scFv-9, recognized two distinct cell populations: the CD19* B lymphocytes and a subset of CD5* T lymphocytes (Fig. 7). Further characterization of the T cell subset showed that it was a subpopulation of the CD4*CD8- TH cells (data not shown). To determine if the antigens recognized by the scFv antibodies were 15 overexpressed on primary CLL cells, PBMC from five CLL patients and five normal donors were stained with scFv and compared by flow cytometry (Fig. 8 and Table 2). By comparing the mean fluorescent intensities of the positive cell populations, the relative expression level of an antigen on CIL cells vs. normal cells could be determined. One antibody, scFv-2, consistently stained CLL cells less intensely than normal PBMC, 20 whereas scFv-3 and soFv-6 both consistently stained CLL cells more brightly than normal PBMC. The fourth antibody, scFv-9, stained two of the five CLL samples much more intensely than normal PBMC, but gave only moderately brighter staining for the other three CLL samples (Fig. 8 and Table 2). This indicates that the antigens for scFv-3 and scFv-6 are overexpressed approximately 1.4 fold on most if not all CLL tumors, whereas 25 scFv-9 is overexpressed 3 to 6-fold on a subset of CLL tumors. CLL patients can be divided into two roughly equal groups: those with a poor prognosis (median survival time of 8 years) and those with a favorable prognosis (median survival time of 26 years). Several unfavorable prognostic indicators have been identified for CLL, most notably the presence of VH genes lacking somatic mutations and the 30 presence of a high percentage of CD38+ B cells. Since scFv-9 recognizes an antigen overexpressed in only a subset of CLL patients, it was sought to determine if scFv-9 antigen overexpression correlated with the percentage of CD38+ cells in blood samples from ten CLL patients (Fig. 11). The results indicate that scFv-9 antigen overexpression and percent CD38* cells are completely independent of one another. 39 Identification of antigens recognized by scFv antibodies by immunoprecipitation (IP) and mass spectrometry (MS) To identify the antigens for these antibodies, scFys were used to immunoprecipitate the antigens from lysates prepared from the microsomal fraction of 5 cell-surface biotinylated CLL-AAT cells (Fig. 12). The ninunoprecipitated antigens were purified by SDS-PAGE and identified by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) or microcapillary reverse-phase HPLC nano electrospray tandem mass spectrometry (sLC/MS/MS) (data not shown). ScFv-2 immunoprecipitated a 110 kd antigen from both RL and CLL-AAT cells (Fig. 12). This 10 antigen was identified by MALDI-MS as the B cell-specific marker CD19. ScFv-3 and scFv-6 both immunoprecipitated a 45 kd antigen from CLL-AAT cels (not shown). This antigen was identified by MALDI-MS as CD23, which is a known marker for CLL and activated B cells. ScFv-9 immunoprecipitated a 50 kd antigen from CLL-AAT cells (Fig. 12). This antigen was identified by pLC/MS/MS as OX-2/CD200, a known marker for B 15 cells, activated CD4+ T cells, and thymocytes. OX-21CD200 is also expressed on some non-lymphoid cells such as neurons and endothelial cells. EXAMPLE 3 The capability of cells overexpressing OX-2/CD200 to shift the cytokine response 20 from a Th1 response (IL-2, IFN-y) to a Th2 response (IL-4, IL-10) was assessed in a mixed lymphocyte reaction using monocyte-derived macrophages/dendritic cells from one donor and blood-derived T cells from a different donor. As a source of OX 2/CD200-expressing cells, either OX-2/CD200 transfected EBNA cells as described below or CLL patient samples were used. 25 Transfection of 293-EBNA cells 293-EBNA cells (Invitrogen) were seeded at 2.5x1 06 per I 00mm dish. 24 hours later the cells were transiently transfected using Polyfect reagent (QIAGEN) according to the manufacturer's instructions. Cells were cotransfected with 7.2ig of OX-2/CD200 30 cDNA In vector pCEP4 (Invitrogen) and 0.8jig of pAdVAntage vector (Promega). As a negative control, cells were cotransfected with empty pCEP4 vector plus pAdVAntage. 48 hours after transfection, approximately 90% of the cells expressed OX-2/CD200 on their surface as determined by flow cytometry with the scFv-9 antibody. 40 Maturation of dendritic cells/macrophages from blood monocytes Buffy coats were obtained from the San Diego Blood Bank and primary blood lymphocytes (PBL) were isolated using Ficoll. Cells were adhered for 1 hour in Eagles Minimal Essential Medium (EMBM) containing 2% human serum followed by vigorous 5 washing with PBS. Cells were cultured for 5 days either in the presence of GM-CSF, ]L 4 and IFN-y or M-CSF with or without the addition of lipopolysaccharide (LPS) after 3 days. Matured cells were harvested and irradiated at 2000 RAD using a 7-irradiator (Shepherd Mark I Model 30 irradiator (Cs137)). 10 Mixed lymphocyte reaction Mixed lymphocyte reactions were set up in 24 well plates using 500,000 dendritic cells/macrophages and 1x10 6 responder cells. Responder cells were T cell enriched lymphocytes purified from peripheral blood using Ficoll. T cells were enriched by incubating the cells for 1 hour in tissue culture flasks and taking the non-adherent cell 15 fraction. 500,000 OX-2/CD200 transfected EBNA cells or CLL cells were added to the macrophages/dendritic cells in the presence or absence of 30 ig/ml anti-CD200 antibody (scFv-9 converted to full IgG) 2-4 hours before the lymphocyte addition. Supernatants were collected after 48 and 68 hours and analyzed for the presence of cytokines. 20 Conversion of scFv-9 to full IgG Light chain and heavy chain V genes of scFv-9 were amplified by overlap PCR with primers that connect the variable region of each gene with human lambda light chain constant region gene, and human IgGI heavy chain constant region CHI gene, respectively. Variable regions of light chain gene and heavy chain gene of scFv-9 were 25 amplified with specific primers and the human lambda light chain constant region gene and the IgGI heavy chain constant region CHI gene were separately amplified with specific primers as follows: R9VL-FI QP: 5' GGC CTC TAG ACA GCC TGT OCT GAC TCA GTC 30 GCC CTC 3' (SEQ ID NO: 103); R9VL/hCL2-rev: 5' CGA OGG GGC AGC CTl' GGG CTG ACC TGT GAC GGT CAG CTG GOT C 3' (SEQ ID NO: 104); 41 R9VL/hCL2-F: 5' GAC CCA GCT GAC CGT CAC AGG TCA GCC CAA GGC TGC CCC CTC G 3' (SEQ ID NO: 105); R9VH-F1: 5' TCT AAT CTC GAG CAG CAG CAG CTG ATG GAG 5 TCC G 3' (SEQ ID NO: 106); R9VH/hCG-rev: 5' GAC CGA TOG GCC CTT GGT GGA GGC TGA GGA GAC GGT GAC CAG GGT GC 3' (SEQ ID NO: 107); 10 R9VH/hCG-F: 5' GCA CCC TGG TCA CCG TCT CCT CAG CCT CCA CCA AGG GCC CAT CGG TC 3' (SEQ ID NO: 108); hCL2-rev: 5' CCA CTG TCA GAG CTC CCG GGT AGA AGT C 3' (SEQ ID NO: 109); 15 hCG-rev: 5' GTC ACC GGT TCG GGG AAG TAG TC 3' (SEQ ID NO: 110). Amplified products were purified and overlap PCR was performed. 20 Final products were digested with Xba I/Sac I (light chain) and Xbo 1/Pin AI (heavy chain) and cloned into a human Fab expression vector, PAX243bGL (see published International Application WO 2004/078937, the disclosure of which is incorporated herein by this reference). DNA clones were analyzed for PCR errors by DNA sequencing. The hCMV IE promoter gene was inserted at Not Il Xho I site (in front 25 of the heavy chain). The vector was digested with Xba I/Pin AI/EcoR I/Nhe I and a 3472 bp fragment containing the light chain plus the hCMV IE promoter and the heavy chain gene was transferred to an IgG 1 expression vector at the Xba I/Pin Al site. Cytokine analysis 30 The effect of the scFv-9 converted to full IgG on the cytokine profile in the mixed lymphocyte reaction was determined. Cytokines such as IL-2, IFN-.y, IL-4, IL-10 and IL-6 found in the tissue culture supernatant were quantified using ELISA. Matched capture and detection antibody pairs for each cytokine were obtained from R+D Systems (Minneapolis, MN), and a standard 42 curve for each cytokine was produced using recombinant human cytokine. Anti-cytokine capture antibody was coated on the plate in PBS at the optimum concentration. After overnight incubation, the plates werc washed and blocked for 1 hour with PBS containing 1 % BSA and 5% sucrose. After 3 washes with PBS containing 0.05% Tween, 5 supernatants were added at dilutions of two-fold or ten-fold in PBS containing 1% BSA. Captured cytokines were detected with the appropriate biotinylated anti-cytolkne antibody followed by the addition of alkaline phosphatase conjugated streptavidin and SigmaS substrate. Color development was assessed with an ELISA plate reader (Molecular Devices). 10 As shown in Figure 14, the presence of OX-2/CD200 transfected but not untransfected cells resulted in down-regulation of ThI cytokines such as IL-2 and IFNy. Addition of the anti-CD200 antibody at 30 pg/ml fully restored the ThI response, indicating that the antibody blocked interaction of OX-2/CD200 with its receptor. As set forth in Figures 15 and 16, the presence of CLL cells in a mixed 15 lymphocyte reaction resulted in down-regulation of the Thl response. (Figure 15 shows the results for IL-2; Figure 16 shows the results for IFN-).. This was not only the case for cells over-expressing OX-2/CD200 (IB, EM, HS, BH), but also for CLL cells that did not overexpress OX-2/CD200 (JR, JG and GB) (the expression levels for these cells are set forth in Figure 11). However, the anti-CD200 antibody only restored the Th1 20 response in cells over-expressing OX-2/CD200, indicating that for patients overexpressing OX-2/CD200, abrogating OX-2/CD200 interaction with its receptor on macrophages was sufficient to restore a TlI response. In patients that did not overexpress OX-2/CD200, other mechanisms appeared to be involved in down-regulating the Thi response. 25 Animal Models To Test An Effect Of Anti-CD200 On Tunor Rejection A model was established in which RAJI lymphoma tumor growth is prevented by the simultaneous injection of PBLs. NOD/SCI D mice were injected subcutaneously with 4x10 6 RAJI cells either in the presence or absence of human PBLs from different donors 30 at 1x10 6 , 5x10 6 or 10x10 6 cells. Tumor length and width as well as body weight was determined 3 times a week. Mean +/-SD of tumor volumes for all groups is shown in Figures 17 A and B. Statistical analysis was performed using 2 parametric tests (Student's t-test and Welch's test) and one non-parametric test (the Wilcox test). Results of the statistical analysis are found in Figure 18. RAJI cells form subcutaneous tumors 43 with acceptable variation. Rejection is dependent on the specific donor and the PBL cell number. lx106 PBLs were insufficient to prevent tumor growth. Donor 2 at 5x105 PBLs from day 22-43 and donor 3 at 5x10 6 or 1x10 7 PBLs starting at day 36 significantly reduced tumor growth. Donor 4 is very close to being significant after day 48. 5 To test for an effect of anti-CD200, RAJI cells are stably transfected with CD200. Animals are injected as described in the previous paragraph. In the presence of CD200 transfected cells, tumors grow even in the presence of human PBLs. Anti-CD200 antibody is administered to evaluate tumor rejection in this model. Also, a liquid tumor model is established. RAJI cells are injected intraperitoneally 10 into NOD/SCID mice. Cells disseminate to bone marrow, spleen, lymph node and other organs resulting in paralysis. Concurrent injection of human PBLs prevents or slows tumor growth. Tumor growth is monitored by assessing the mice for signs of movement impairment and paralysis. Once these signs are observed, mice are sacrificed and the number of tumor cells is assessed in various organs including bone marrow, spleen, 15 lymph nodes and blood by FACS analysis and PCR. Similar to the subcutaneous model, CD200 transfected cells are injected intraperitoneally. They grow even in the presence of human PBLs. Treatment with anti CD200 results in tumor rejection or slower tumor growth. 20 EXAMPLE 4 Library construction A mouse was immunized alternately with baculovirus expressed recombinant CD200 extracellular domain fused to mouse IgG Pc (CD200-Fo) (Orbigen Inc., San Diego, CA) and 293-EBNA cells transiently transfected with a vector containing full 25 length CD200. Total RNA was prepared from mouse spleen using TRI reagent (Molecular Research Center, Inc., Cincinnati, OH) according to the manufacturer's protocol. Messenger RNA (mRNA) was purified using Oligotex (QIAGEN Inc., Valencia, CA) according to the manufacturer's manual. First strand cDNA was synthesized using SuperScript II RTase (Invitrogen Life Technologies, Carlsbad, CA) 30 according to the manufacturer's protocol. First strand eDNA was digested with restriction endonuclease and second strand cDNA was synthesized according to the method fully described in published PCT application W003/025202A2, published March 27, 2003. Second strand cDNA was cleaned up with PCR purification kit (QIAGEN) and single primer amplification was performed according to the method described in published PCT 44 application W003/025202A2, published March 27, 2003. Amplified products were pooled and purified with PCR purification kit. Kappa light chain was digested with Xba I and BspE I, and IgG1 and IgG2a heavy chains were digested with Xho I and Bln I. Digested fragments were purified from the agarose gel using Gel extraction kit 5 (QIAGEN) and cloned into PAX313m/hG vector as described in published PCT application WO/04078937A2 published September 16, 2004. Library panning The libraries (IgGI kappa and IgG2a kappa) were panned on CD200-Fc either 10 directly coated on the microtiter wells (Costar Group, Bethesda, MD) or captured with goat anti-mouse IgG Fc specific antibody (Sigma-Aldrich Corp., St. Louis, MO). For the preparation of library phage, clectrocompetent XL1-Blue cells (Stratagene, La Jolla, CA) were electroporated with library DNA and grown in SOC medium for 1 hour and in SB medium for 2 hours with carbonicillin. Phage production was induced with the addition of 15 VCS M13 helper phage (Amersham Biosciences Corp., Piscataway, NJ) and 1 mM IPTG at 30'C overnight. The culture was spun down and phage were precipitated with 4% polyethylene glycol and 3% NaCI. The phage were spun down and resuspended in 1% BSA/PBS containing unrelated antigen, FLJ32028 that is also baculovirus expressed extracellular domain fused to mouse IgG Fc (FLJ32028-Fo) (Orbigen, San Diego), as a 20 soluble competitor. For the panning on directly coated CD200-Fc, four wells were coated with 100 pl of CD200-Fc (5 gg/ml in 0.1 M NaHCO 3 pH8.6) at 4'C overnight. The wells were washed 5 times with phosphate buffered saline (PBS) pH7.0 and blocked with 1% bovine serum albumin (BSA)/PBS at 3TC for I hr. For the panning on CD200-Fc captured on goat anti-mouse IgG Fc, four microtiter wells were coated with 100 i4 goat 25 anti-mouse IgG Fc (20 pLg/ml in PBS) at 4'C overnight. The wells were washed 5 times with PBS and incubated with 100 sl CD200-Fc (20 pg/ml in PBS) for 1 hour at 37C. The wells were washed 5 times with PBS and blocked with 1% BSA/PBS at 37C for I hour. For both directly-coated and captured methods of panning, the blocker was replaced with the mixture of soluble Fabs obtained from the panning of another library (the library 30 described in Example 3 of PCT application serial No. PCT/USO4/17 118 filed June 2, 2004 (not yet published), the entire disclosure of which is incorporated herein by this reference) on FLJ32028 to mask epitopes on mouse IgG Fe and the wells were incubated for 30 min at 37'C. These masking Fabs were shown to also bind to CD200-Fe. Library 45 phage were added on top of the masking Fabs and the wells were incubated for approximately 1.5 hours at 37C. The unbound phage were washed with PBS with increasing stringency (3 times in the first round, 5 times in the 2'" round and 10 times in the 3 'd and the 4 rounds) with 5 minute incubation and pipetting up and down 5 times for 5 each wash. The bound phage were eluted twice with 100 Pl 0.1 M HCl with 1 mg/ml BSA, pH2.2 and neutralized with 2 M Tris Base pH 11.5. The freshly grown ER2738 cells were infected with eluted phage and titrated onto LB agarose plates containing carbenicillin and glucose. The remaining phage were propagated overnight at 30-37C with the addition of VCS M13 helper phage and 1 mM IPTG for the next round of 10 panning. Library screening Ninety five colonies from round 3 and 4 titration plates were grown In I ml SB containing 12.5 pg/ml tetracycline and 50 pg/ml carbenicillin for approximately 6 hours 15 at 37'C. VCS M13 helper phage were added and the culture was incubated for 2 hours at 3T C. 1 mM EG and 70 pg/mI kanamycin were added and Fab-phage production was induced at 30*C overnight. Microtiter wells were coated with 50 pl of rabbit anti-mouse IgG F(ab')z (4 pg/mI in PBS), CD200-Fe (4 pg/ml in 0.1 M NaHCO 3 pH8.

6 ), or FLJ32028-Fo (4 g/ml in 0.1 M NaHCO 3 pH 8

.

6 ) at 4'C overnight The wells were 20 washed 3 times with PBS and blocked with 100 il 1% BSA/PBS for 1 hour at 37C. The culture was spun down. The blocker was replaced with the culture supernatant containing Fab-phage and the wells were incubated for 1.5-2 hours at 37C. The remaining Fab phage was stored at -80'C for flow cytometry. The plates were washed 3 times with PBS and the binding was detected with 50 pl alkaline phosphatase (AP)-conjugated goat anti 25 mouse IgG F(ab')2 antibody (Pierce)(1:500 in 1% BSA/PBS) for 1 hr at 37C. The plates were washed 3 times with PBS and developed with AP substrate (Sigma-Aldrich) in pNPP buffer. Almost all of the clones from round 3 were already specifically positive to CD200 (Figs. 19A-D). Clones were also screened by high throughput flow cytometry analysis. One hundred microliters of 293 cells transiently transfected with CD200 (1 x 105 30 cells) were aliquotcd into a 96 well plate (Costar). Fifty microliters Fab-phage was added to the cells and mixed by pipetting and incubated on ice for 30 minutes. The cells were washed twice with 1% BSA/PBS containing 0.01% NaN3. The cells were resuspended in 100 p1 PE-conjugated goat anti-mouse IgG antibody (Sigma-Aldrich) in 1% BSA/PBS 46 containing 0.01% NaN 3 and incubated on ice for 30 minutes. The cells were washed twice with 1% BSA/PBS containing 0.01% NaN 3 and resuspended in 200 pl 1% paraformaldehyde in PBS. Representative clones showing positive binding to CD200 expressing cells are shown in Figs. 20A-D. 5 DNA sequences were analyzed and deduced amino acid sequences of the heavy chain were grouped according to the complementarity determining region 3 (CDR3) (Figs. 21A, B). They were divided into 17 groups. Fluorescent bead assay 10 23 clones were selected for further analysis. They were cG2aR3B5, dGIR3A5, cG2aR3A2, dG2aR3B2, dGIR3AI, cG2aR3A1, cG2aR3B, dG1R3B, cG1R3A, cG1R3A, oG1R3A1, dGIR3B, dG1R3B, cGIR3C, dG2aR3C, dG2aR3A1, cG2aR3B, cG2aR3B, dG1R3B, cG2aR3B, cG2aR3C, dG1R3H, and dG2aR3A6. DNA of selected Fabs was digested with Spe I/Nhe I fbr gene IIl removal and soluble Fab expression and 15 purification. The purified Fabs were evaluated for their ability to block the interaction of CD200 with its receptor (CD200R) in a fluorescent bead assay. TransFluoSpheres carboxylate-modified microspheres (488/645) (Molecular Probes Invitrogen Detection Technologies, Eugene, OR) were coated with streptavidin followed by a biotin-labeled anti-human Fe antibody and baculovirus-produced CD200-Fc protein. 293 cells were 20 transiently transfected with CD200R. Cell surface expression was confirmed by FACS analysis. 1 million CD200-coated beads were pre-incubated with various amounts of anti CD200 Fabs or chimeric IgG for 10 minutes before the addition of 50,000 CD200R transfected cells. After a 30 minute incubation at 37'C, the cells were washed in Tris buffer containing 1% BSA and analyzed using a FACS Calibur. Fabs c1A10, c2aB7, and 25 d1A5 showed the best blocking of CD200 and CD200R interaction at 6.7 ig/mI of Fab (Fig. 22). These clones are referred to as cGIR3AIO, cG2aR3B7 and dG1R3A5, respectively in Figs. 21A and/or B. Chimerization and IgG conversion 30 Six antibodies were selected for chimerization and IgG conversion. (See Fig. 23.) They were c1A10 (oG1R3A1O), c2aA10 (cG2aR3A1O), c2aB7 (cG2aR3B7), dIA5 (dG1R3A5), dlB5 (dG1R3BS), and dIB10 (dGIR3B10). For the chimerization, overlap PCR was performed to connect mouse kappa chain variable region and human kappa 47 chain constant region. Mouse heavy chain variable region was amplified with a 3' primer that contains a partial human IgGI constant region and Apa I site for cloning. Amplified kappa chain fragments and heavy chain fragments were cloned into PAX243hGK vector (see published International Application WO 2004/078937) that contains human IgGI 5 constant region at Xba I/Not I for kappa light chain and Xho I/Apa I for heavy chain fragment. Binding of chimeric Fab to CD200 was confirmed by ELISA and flow cytometry. These chimeric Fabs were converted into IgG by insertion of human cytomegalovirus immediate early promoter (hCMV IB Pro) sequence for the heavy chain expression at Not I/Xbo I, then the transfer of the light chain and heavy chain into a 10 human IgGI expression vector at Xba YIPin AI sites. This vector has an additional hCMV IB Pro sequence upstream Xba I site for the light chain expression in mammalian cells. The DNA sequences were confirmed and maxi prep DNA was prepared using HiSpeed Maxi prep columns (QIAGEN) for mammalian cell transfection. Transient transfection was performed in 293-EBNA cells using Effectene (QIAGEN) according to the 15 manufacturer's protocol with the addition of pAdVAntage vector (Promega US, Madison, WI). Stable cell line transfection was performed in NSO cells using Effectene according to the manufacturer's protocol. After a small scale transient transfection, culture supernatant for each antibody was tested by ELISA (Fig. 24). After a large scale transient transfection, each IgG was purified from the culture supernatant by anti-human IgG 20 F(ab')2 affinity column using FPLC (Amersham Biosciences). The purified IgG were tested in a bead inhibition assay as described for the Fabs. All antibodies directed against CD200 blocked the receptor ligand interaction very well as shown below in Fig. 25. 25 Mixed ymphocyte reaction Whether blocking of CD200 interaction with its receptor also prevents the cytokine shift from Th1 to Th2 observed in mixed lymphocytes reactions in the presence of CD200 was evaluated. Buffy coats were obtained from the San Diego Blood Bank and primary blood lymphocytes (PBL) were isolated using Histopaque (Sigma-Aldrich). Cells 30 were adhered for 1 h in EMBM containing 2% human serum followed by vigorous washing with PBS. Cells were cultured for 5 days in the presence of GM-CSF, ILR4 and IFN-y. Matured cells were harvested and irradiated at 2000 RAD using a y-irradiator (University of California San Diego). Mixed lymphocyte reactions were set up in 24 well plates using 500,000 dendritic cells and 1 x 10 responder cells. Responder cells were T 48 cell enriched lymphocytes purified from peripheral blood using Histopaque. T cells were enriched by incubating the cells for 1 hour in tissue culture flasks and taking the non adherent cell fraction. Five hundred thousand CD200 expressing primary irradiated CLL cells were added to the dendritic cells in the presence or absence of various amounts of 5 anti-CD200 antibodies 2-4 hours before the lymphocyte addition. Supernatants were collected after 48 and 68 hours and cytokines such as IL-2, IFN-y, IL-4, IL-10 and IL-6 were quantified using ELISA. Matched capture and detection antibody pairs for each cytokine were obtained from R+D Systems (Minneapolis), and a standard curve for each cytokine was produced using recombinant human cytokine. Anti-cytokine capture 10 antibody was coated on the plate in PBS at the optimum concentration. After overnight incubation, the plates were washed and blocked for 1h with PBS containing 1% BSA and 5% sucrose. After 3 washes with PBS containing 0.05% Tween, supernatants were added at the indicated dilutions in PBS containing 1% BSA. Captured cytokines were detected with the appropriate biotinylated anti-cytokine antibody followed by the addition of 15 alkaline phosphatase conjugated streptavidin and SigmaS substrate. Color development was assessed with an BLISA plate reader (Molecular Devices Corp., Sunnyvale, CA). As shown in Figs. 26A and B, the presence of CLL cells completely abrogated IFN-gamma and most of IL-2 production observed in the mixed lymphocyte reaction. Presence of any of the antibodies allowed for production of these Th1 cytokines (Figs. 26A and B). In 20 contrast, IL-1 0 production was downregulatcd in the presence of the antibodies. (See Fig. 26C.) Antibody-dependent cell-mediated cytotoxicity assay Furthermore, the six chimeric mouse anti-CD200 antibodies were evaluated for their 25 ability to kill CD200 expressing tumor cells in an antibody-dependent cell-mediated cytDtoxicity assay (ADCC). 293-EBNA cells transfected with CD200 were labeled with 100 gCi/million cells in 0.5ml medium for lhr at 37*C. After 3 washes, cells were counted, resuspended in medium (RPMI supplemented with 10% human AB serum) at 02 million/ml and 50 p1 (10,000 cells/well) was dispensed in triplicate into a 96 well 30 round bottom plate. 20 p1 of anti-CD200 antibodies were dispensed into each well so as to achieve a final concentration of 20 pg/ml. Peripheral blood mononuclear cells (cffector cells) were isolated on a Ficoll gradient, red blood cells were lysed with ammonium chloride, washed and resuspended in culture medium and 50 pl of cells were dispensed 49 into each well. The assay plates were spun (1,500 rpm/5 minutes/low brake) and transferred to the cell culture incubator. After 4 hours, assay plates wcre spun as before. 36 pl of the supernatants were transferred to pico plates and mixed with 250 pl microscint-20 cocktail, and placed on the orbital shaker for 2 minutes and read on a Top 5 count. As illustrated in the Fig. 27, all of the mouse chimeric CD200 antibodies produced similar levels of lysis when cultured with CD200 positive cells. No lysis was observed with CD200 negative cells. In addition, the extent of lysis was statistically significant (p < 0.05) when compared to isotype control antibody, d2A6 (anti-FLJ32028 antibody). 10 EXAMPLE 5 Raji/PBL Model NOD.CB17-Prkdc<scid> mice (Jackson Laboratory) were injected with 200t RPMI containing 4x10 6 RAI cells (ATCC) s.c. along with 0, 1, 5 or 10 million PBLs. 15 Nine or ten mice were included per group. PBLs were isolated from 250 ml whole ammonium chloride. Tumor growth was monitored three times a week by measuring length and width with a caliper. Tumor volume was calculated based on length x width x width/2. Differences between the groups that were injected with PBLs compared to the 20 group that received tumor cells only were analyzed by 2-tailed unpaired Student's t-test. Significant differences were observed in the groups that received 5 or 10 million PBLs, but not in the group that received 1 million PBLs from Day 32 on. The data shown in Figure 28 are a representative example of 10 experiments using different PBL donors. 25 Namalwa PBL model NOD.CB1 7-Prkdc<scid> mice (Jackson Laboratory, Bar Harbor, Maine) were injected with 200p RPMI containing 4x106Namalwa cells (ATCC) s.c. along with 0, 2 or 10 million PBLs. 9-10 mice were included per group. PBLs were isolated from 250 ml whole blood on a histopaque gradient followed by red blood cell lysis using 0.90/ 30 ammonium chloride. Tumor growth was monitored three times a week by measuring length and width with a caliper. Tumor volume was calculated based on length x width x width/2. 50 Figure 29 shows differences between the groups that were injected with PBLs compared to the group that received tumor cells only analyzed by 2-tailed unpaired Student's t-test. Significant differences were observed in the groups that received 10 million PBLs for both donors, but not in the group that received 2 million PBLs from day 5 8 on. Creation of stable CD200-expressing cell lines Stable CD200-expressing Raji and Namalwa cell lines were generated using the Virapower Lentiviral Expression System (Invitrogen, Carlsbad, CA). A CD200 cDNA was isolated from primary CLL cells by RT-PCR using forward primer 10 5'-GACAAGCTTGCAAGGATGGAGAGGCTGGTGA-3' (SEQ IDNO: 212) and reverse primer 5'-GACGGATCCGCCCCTITCCTCCTGCTITTCTC-3' (SEQ ID NO: 213). The PCR product was cloned into the Gateway entry vector pCR8/GW/TOPO-TA and individual clones were sequenced. Clones with the correct sequence were recombined in both the sense and antisense orientations into the lentiviral vectors 15 pLenti6/V5/DEST and pLenti6/UbCIVSDEST using Gateway technology (Invitrogen, Carlsbad, CA). The primary difference between these two vectors is the promoter used to drive CD200 expression: pLenti6N5/DEST contains the human CMV immediate early promoter, whereas pLenti6/UbC/VS/DEST contains the human ubiquitin C promoter. High-titer, VSV-G pseudotyped lentiviral stocks were produced by transient 20 cotransfection of 293-FT cells as recommended by the manufacturer. Raji or Namalwa cells were transduced by resuspending 106 cells in Iml of growth medium containing 12pg/m Polybrene and adding Iml of lentiviral stock. After incubating the cells overnight at 37*C, the medium containing virus was removed and replaced with 4ml of fresh medium. Two days later, the infected cells were analyzed for CD200 expression by 25 flow cytometry. In all experiments, 270% of the cells were CD200*, whereas CD200 was undetectable in the parental cell lines and in cells transduced with the negative control (antisense CD200) viruses. To isolate clonal cell lines that overexpress CD200, the infected cells were selected with blasticidin for 13 days. The concentrations of blasticidin used were 6 pig/mI 30 for Raji cells or 2 pg/ml for Namalwa cells. Stable clones were then isolated by limiting dilution of the blasticidin-resistant cells into 96-well plates. Clones were screened in 96 51 well format by flow cytometry using PE-conjugated Mouse Anti-Human CD200 (clone MRC OX104, Serotec) and a BD FACSCalibur equipped with a High Throughput Sampler. After screening a total of 2000 Raji and 2000 Namalwa clones, those clones with the highest CD200 expression were expanded for further characterization using 5 conventional techniques. Immunosunressive effect of CD200 in the RAJIIPBL model In accordance with the methods disclosed, it has been demonstrated that CD200 is upregulated on CLL cells. Upregulation of this molecule might potentially be 10 immunosuppressive. To test whether cancer cells expressing CD200 prevent the immune system from eradicating the cancer cells, RAJI cells, that normally do not express CD200, were infected with a lentivirus vector system encoding for CD20D as described above. RAJI clones stably expressing CD200 were selected. As a control to ensure that there was no effect of vector infection, clones expressing a reversed, nonfunctional form of CD200 15 (CD200rev) were also selected. RAJI cells expressing CD200, CD200REV or the ~ parental RAJI cells were injected subcutaneously into NOD.CB17-Prkde<scid> mice. The following groups were included in the study: group 1: 4 x 106 RAJI s.c.; 9 mice 20 This group was needed to ensure that the lentivirus transduced cells show similar growth as the parent cells. group 2: 4 x 106 RAJICD200 s.c.; 9 mice This group was needed to ensure that the CD200 transduced cells showed similar growth as the parent cells. Also, this group will give the maximum 25 tumor growth. Group 3 and group 4 were compared to this group. group 3: 4 x 106 RAJICD200 + 5x10 6 PBL s.c.; 9 mice This PBL number has been shown to reduce tumor growth in some mice in previous experiments. Rejection is not as strong as with 10 million cells, but in oider to determine whether CD200 can affect only a certain number of cells, 30 and 5x10 6 is the minimum amount of PBLs which can be used to get rejection; rejection should be prevented by the presence of CD200. group 4: 4 x 106 RAJICD200 + 10x10 6 PBL s.c.; 8 mice This is the optimum number of PBLs to see rejection in the RAJTI/PBL model. 52 The design was that CD200 expression would prevent this rejection. group 5: 4x10' RAJICD200rev s.c.; 9 mice This group was needed to ensure that the lentivirus transduced cells show similar growth as the parent cells. 5 group 6: 4x106 RAJICD200rev + 2x10 6 PBL s.c.; 9 mice This number of PBLs should not result in strong rejection or reduction of tumor growth. This is the positive control for group 3 and group 4 (maximum expected tumor growth). If there is no rejection in this group, then the donor PBLs were hyperactivated to start with which could explain lack of an effect by 10 CD200. group 7: 4 x 10' RAJICD200rev + 5x10 6 PBL s.c.; 9 mice Controls that any observed effects in the CD200 group 3 are really related to CD200 and not to lentivirus transduction. group 8: 4 x 106 RAJICD200rev + 1Oxl06 PBL s.c.; 8 mice 15 Controls that any observed effects in the CD200 group 4 are really related to CD200 and not to lentivirus transduction. Animals were sacrificed at day 38 based on tumors reaching a size above acceptable limits. Tumors from 4 animals/group were removed. Two tumors/group were 20 frozen in OCT, the other 2 were used to isolate cells and analyze by FACS for CD200 expression. Figures 30(a-c) demonstrate the results for this study. Although RAJICD200 cells appeared to grow somewhat more slowly, the growth difference between transduced and parental cells did not reach statistical significance as shown in Figure 30(a). 25 The presence of PBLs slowed tumor growth by up to 84% when 5 or 10xl0O PBLs were injected, although generally 1Ox10' PBL resulted in a stronger reduction over time compared to 5x10' PBL. The reduction in growth compared to the parent tumor cells was significant from day 20 on. 2x10' PBL resulted in a significant tumor growth reduction from d22-d29, but that reduction was overcome at later timepoints (Fig. 30(b)). 30 This study indicated that this particular donor rejects RAJI tumor cells very strongly. Tumor growth in the groups that received CD200 expressing RAJI cells and PBLs was not significantly different from the tumor growth in the group that only received RAJI cells although mice that received l0xl0' PBL showed a trend of reduced tumor growth, but the difference reached no statistical significance at any time point 53 after tumors reach 100 mm 3 . Every mouse in the group that received RAJI cells and 5x10 6 PBL developed a second tumor, some mice as early as d7, while this was not observed in any other group. For analysis, the second tumor was added to the first tumor and the combined size is shown in Fig. 30(c). 5 These results indicate that CD200 expression on tumor cells does indeed prevent the immune system from slowing tumor growth. Also, this study demonstrates the usefulness of the RAJI/PBL model to assess immunosuppressive compounds or molecules. 10 Immunosuppressive effect of CD200 in the Namalwa/PBL model To evaluate whether the effects seen in the RAJI/PBL model can also be observed in other tumor models, Namalwa tumor cells were also infected with the lentivirusCD200 system and stable clones selected. As a control to ensure that there is no effect of vector infection, clones expressing a reversed, nonfunctional form of CD200 15 (CD200rev) were also selected. NOD.CB 17-Prkdc<scid> mice were injected according to the following scheme as shown in Figures 3 1(a)-(d): group 1: 4 x 106 Namalwa s.c.; 9 mice This group was needed to ensure that the lentivirus transduced cells show 20 similar growth as the parent cells. group 2: 4 x 106 Namalwa CD200 (ID12Ub) s.c.; 9 mice This group was needed to ensure that the CD200 transduced cells showed similar growth as the parent cells. Also, this group will give the maximum tumor growth. Group 3 and group 4 were compared to this group. 25 group 3:4 x 10 Namalwa CD200 (1D12Ub)+ 5x10 6 PBL s.c.; 9 mice This PBL number has been shown to reduce tumor growth in some mice in previous experiments. Rejection is not as strong as with 10 million cells, but if CD200 can affect only a certain number of cells, and this is the minimum PBL we can use to get rejection; rejection will be prevented by the presence of 30 CD200. group 4: 4 x 106 Namalwa CD200 (ID12Ub) + 1 Ox 106 PBL s.c.; 8 mice This is the optimum number of PBLs to see rejection in the Namalwa /PBL model. This was done to show that CD200 expression prevents this rejection. 54 group 5: 4 x 10 Namalwa CD200rev (C5Ubrev) s.c.; 9 mice This group was needed to ensure that the lentivirus transduccd cells showed similar growth as the parent cells. group 6: 4 x 10 Namalwa CD200rev + 2x10' PBL s.c.; 9 mice 5 This number of PBLs should not result in strong rejection of reduction of tumor growth. This is the positive control for group 3 and group 4 (maximum expected tumor growth). If there is no rejection in this group, then the donor PBLs were hyperactivated to start with which would explain lack of an effect by CD200. 10 group 7: 4 x 106 Namalwa CD200rev + 5x10 6 PBL s.c.; 9 mice This group was needed as a control to detect any effects in the CD200 group 3 that were related to CD200 and not to lentivirus transduction. group 8: 4 x 106 Namalwa CD200rev + 10x10 6 PBL s.c.; 8 mice This group was needed as a control to detect any effects in the CD200 group 4 15 that were related to CD200 and not to lentivirus transduction. Tumor length and width were assessed three times/week. All tumor cells resulted in rapid tumor growth. There was no significant growth difference between transduced and parental cells. The tumor grows more aggressively 20 than previously observed as shown in Figure 3 1(a). Figure 31(b) shows the presence of PBLs slows tumor growth by about 50%. This trend was observed from d12 on. The differences of the PBL treated group versus groups that received only tumor cells are statistically significant (as determined by 2 tailed Student's t-test) at d17 and d19 when 2 million or 10 million PBLs were injected. 25 Injection of 5 million PBLs resulted in tumor growth reduction, but did not reach significance. Tumor growth in the groups that received CD200 expressing Namalwa cells and PBLs was similar to the tumor growth in the group that only received Namalwa cells (Figure 31(c)). 30 These data confirm that CD200 expression on tumor cells prevents slowing of tumor growth by the human immune system. 55 Blockage of the immunosuppressive effect of CD200 in the RAJI/PBL model by anti CD200 antibodies To evaluate whether anti-CD200 antibodies can block the immunosuppressive effect of CD200 expressed on tumor cells, RAJI cells transduced with CD200 were injected s.c. 5 into NOD.CB17-Prkdc<scid> mice, and the ability of PBLs to reduce tumor growth in the presence or absence of chimeric anti-CD200 antibodies d1B5 and c2aB7 or a control antibody that does not bind tumor cells (alxn4100) was assessed. Antibodies were administered initially at 10 mg/kg or 2.5 mg/kg with the tumor cells, and then at concentrations indicated below twice/week i.v.. The following groups were set up: 10 1. 4 x 106 RAJICD200; 10 mice 2. 4 x 106 RAJICD200 + 5 x 106 PBL; 10 mice 3. 4 x 106 RAJICD200 + 5 x 106 PBL+ 100 mg/kg d1B5; 12 mice 4. 4 x 106 RAJICD200 + 5 x 106 PBL + 20 mg/kg dIB5; 9 mice 15 5. 4 x 106 RAJICD200+5 x 106 PBL +100 mg/kg c2aB7; 11 mice 6. 4 x 10' RAJICD200 +5 x 106 PBL +20 mg/kg c2aB7; 9 mice 7. 4 x 106 RAJICD200 + 5 x 106 PBL + 100 mg/kg aIxn4100; 9 mice Tumor length and width was measured 3 times a week, and the tumor volume was 20 calculated by tumor length*width*width/2. Figure 33 shows that as expected, CD200 expression on the tumor cells prevented the immune cells from reducing tumor growth. However, addition of anti-CD200 antibodies reduced the tumor volume by 50-75 %. The reduction in growth by the antibodies was statistically significant as determined by Student's t-test and Mann Whitney test from day 18 on through the end of the study. In 25 contrast, treatment with the control antibody did not reduce the tumor growth. These data demonstrate the uscfulness of anti-CD200 in anti-cancer treatment. Also, this study demonstrates the usefulness of the RAJI/PBL model to assess immunomodulatory therapeutics. 30 Blockage of the immunosuppressive effect of CD200 in the Namalwa/PBL model by anti CD200 antibodies To evaluate whether the effect seen with the anti-CD200 antibodies in the RAJI/PBL model can also be observed in other tumor models, RAI cells transduced with CD200 were injected s.c. into NOD.CB17-Prkdc<scid> mice, and the ability of PBLs to reduce 35 tumor growth in the presence or absence of chimeric anti-CD200 antibodies dIB5 and c2aB7 or a control antibody that does not bind tumor cells (aIxn4lOO) was assessed. Antibodies at concentrations indicated below were administered initially with the tumor 56 cells, and then twice/week s.c. within 0.5 cm of the tumor. The following groups 'were set up (10 mice/group unless indicated otherwise): 1. 4 x 10' NamalwaCD200 5 2. 4 x 10'NamalwaCD200 + 5 x 106 PBL; 12 mice 3. 4 x 10'NamalwaCD200+5 x 10' PBL + 10 mg/kg dlB5; 12 mice 4. 4 x 106 NamalwaCD200 +5 x 10' PBL + 2.5 mg/kg dlBS 5. 4 x 106 NamalwaCD200 + 5 x 10' PBL + 10 mg/kg c2aB7; 12 mice 6. 4 x 10' NamalwaCD200 + 5 x 10' PBL + 2.5 mg/kg c2aB7 10 7. 4 x 106 NamalwaCD200 + 5 x 10' PBL + 10 mg/kg alxn4lOO Tumor length and width was measured 3 times a week, and the tumor volume was calculated by tumor length*width*width/2. Figure 34 shows that as expected, CD200 expression on the tumor cells prevented the immune cells from reducing tumor growth. 15 However, addition of anti-CD200 antibodies reduced the tumor volume by up to 97%. The reduction in growth by the antibodies was statistically significant as determined by Student's t-test and Mann Whitney test from day 12 on through the end of the study. In contrast, treatment with the control antibody did not reduce the tumor growth. These data confirm the usefulness of anti-CD200 In anti-cancer treatment, and the use of the 20 tumor/PBL models in assessing immunomodulatory therapeutics. Detection of a potential immune-enhancing effect of compounds in the RAM/PBL model T cells isolated from PRLs using CD3 columns (Miltenyi) were incubated in vitro with an ascites preparation of AZNDI (anti-DC-SIGN antibody) or an ascites preparation 25 of a control antibody (BB5). NOD.CB17-Prkdc<scid> mice were injected according to the following scheme: Group 6: 8 mice, 4x1 06 RAJ +0.8xl06 AZNDl -potentiated T cells + 2x1 06 PBL s.c. Group 5: 10 mice, 4x106 RAJI s.c. 30 Group 4: 8 mice, 4x106 RAjI + 8X10' PBL s.c. Group 3: 8 mice, 4x106 RAI +0.8x10 6 fresh T cells s.c. Group 2: 8 mice, 4x106 RAJI +O.8x10' AZND 1-potentiated T cells s.c. Group 1: 8 mice, 4x10 6 RAJI +0.8x106 BB5.1-potentiated T cells s.c. 57 Tumor length and width were measured 3 times/week. While T cells incubated with the negative control BB5 did not reduce tumor growth, AZNDI treated T cells did reduce tumor growth significantly (See, Figure 32). These results demonstrate that the RAJI PBL model can be used to assess efficacy 5 of immune-enhancing compounds. EXAMPLE 6 Determination of CD200 Upregulation in CLL Patients Lymphocytes from 15 CLL patients were stained with FITC-conjugated anti-CD5 10 (e-bioscience), APC-conjugated anti-CD19 (e-bioscience) and PB-conjugated anti-CD200 (Serotec). Lymphocytes from healthy donors were stained accordingly. CD200 expression on CD5+CD19+ cells was determined. As shown In the table below, although the level of CD200 expression varied among CLL patient samples, all CLL samples showed elevated levels (1.6-4-fold range) higher CD200 expression compared to CD200 15 expression on normal B cells. The CLL patients showing elevated levels of CD200 expression are selected for anti-CD200 treatment in accordance with the methods described herein. FACS analysis of CD200 expression on B-CLL cells in comparison to normal B cells 20 CLL sample Healthy donor Donor ID B-CLL CD200 Normal B Ratio(CLL/normal B) (GMFI) CD200 (GMFI) RCO1 1731 93 58 1.6 RF020934 659 185 3.6 JA073031 334 64 5.2 GR011846 156 64 2.4 BB101735 420 95 4.4 DM6988172 290 97 2.9 MR8074020 403 97 4.2 CB8267677 300 97 3.1 GB1325248 178 77(7) 2.3 VN7029373 154 77(7) 2.0 DG8942820 146 77(7) 1.9 MM8451869 237 77(7) 3.1 58 JR4539931 215 77(7) 2.8 HS6787771 305 77(7) 4.0 VB040439 123 41 3.0 MEAN= 3.1 SMEV= 1.0 REFERENCES The following references are incorporated herein by reference to more fully describe the state of the art to which the present invention pertains. Any inconsistency between these publications below or those incorporated by reference above and the 5 present disclosure shall be resolved in favor of the present disclosure. 1) Agarwal, et al., (2003). Disregulated expression of the Th2 cytokine gene in patients with intraoral squamous cell carcinoma. Immunol Invest 32:17-30. 2) Almasri, NM et al. (1992). Am J Hemato 140 259-263. 10 3) Contasta, et al., (2003). Passage from normal mucosa to adenoma and colon cancer: alteration of normal sCD30 mechanisms regulating TH1/H2 cell functions. Cancer Biother Radiopharm 18:549-557. 4) Gorczynski, et al., (1998). Increased expression of the novel molecule OX-2 is involved in prolongation of murine renal allograft survival. Transplantation 65:1106 15 1114. 5) Gorczynski, et al., (2001). Evidence of a role for CD200 in regulation of immune rejection of leukaemic tumour cells in C57BU6 mice. Clin Exp Immunol 126:220-229. 6) Hainsworth, JD (2000). Oncologist 2000;5(5):376-84. 7) Inagawa, et al., (1998). Mechanisms by which chemotherapeutic agents augment 20 the antitumor effects of tumor necrosis factor: involvement of the pattern shift of cytokines from Th2 to Th1 in tumor lesions. Anticancer Res 18:3957-3964. 8) Ito, et al., (1999). Lung carcinoma: analysis of T helper type 1 and 2 cells and T cytotoxic type 1 and 2 cells by intracellular cytokine detection with flow cytometry. Cancer 85:2359-2367. 25 9) Kiani, et al., (2003). Normal intrinsic ThlJTh2 balance in patients with chronic phase chronic myeloid leukemia not treated with interferon-alpha or imatinib. Haematologica 88:754-761. 59 10) Lauerova, et al., (2002). Malignant melanoma associates with Th/11h2 imbalance that coincides with disease progression and immunotherapy response. Neoplasma 49:159 166. 11) Maggio, et al., (2002). Chemokines, cytokines and their receptors in Hodgkin's 5 lymphoma cell lines and tissues. Ann Oncol 13 Suppl 1:52-56. 12) Nilsson, K (1992). Burn Cell. 5(1):25-41. 13) Podhorecka, et al., (2002). T type 1/type 2 subsets balance in B-cell chronic lymphocytic leukemia-the three-color flow cytometry analysis. Leuk Res 26:657-660. 14) Pu, QQ and Bezwoda, W (2000). Anticancer Res. 20(4):2569- 78. 10 15) Smyth, et al., (2003). Renal cell carcinoma induces prostaglandin E2 and T-helper type 2 cytokine production in peripheral blood mononuclear cells. Ann Surg Oncol 10:455-462. 16) Tatsumi, et al., (2002). Disease-associated bias in T helper type 1 (Thl)Th2 CD4(+) T cell responses against MAGB-6 in HLA-DRB10401(+) patients with renal cell 15 carcinoma or melanoma. J Exp Med 196:619-628. 17) Walls A Vet al. (1989). Int. J Cancer 44846-853. 18) Winter, et al., (2003). Tumour-induced polarization of tumour vaccine-draining lymph node T cells to a type 1 cytokine profile predicts inherent strong immunogenicity of the tumour and correlates with therapeutic efficacy in adoptive transfer studies. 20 Immunology 108:409-419. It will be understood that various modifications may be made to the embodiments disclosed herein. For example, as those skilled in the art will appreciate, the specific sequences described herein can be altered slightly without necessarily adversely affecting 25 the functionality of the polypeptide, antibody or antibody fragment used in binding OX 2/CD200. For instance, substitutions of single or multiple amino acids in the antibody sequence can frequently be made without destroying the functionality of the antibody or fragment. Thus, it should be understood that polypeptides or antibodies having a degree of identity greater than 70% to the specific antibodies described herein are.within the 30 scope of this disclosure. In particularly useful embodiments, antibodies having an identity greater than about 80% to the specific antibodies described herein are contemplated. In other useful embodiments, antibodies having an identity greater than about 90% to the specific antibodies described herein are contemplated. Therefore, the above description should not be construed as limiting, but merely as exemplifications of 60 preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of this disclosure. 61

Claims (13)

1. An isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDRI having the sequence set forth in residues 26-36 of SEQ 10 NO:209; a light chain CDR2 having the sequence set forth in residues 52-58 of SEQ ID NO:209; a light 5 chain CDR3 having the sequence set forth in residues 91-99 of SEQ I) NO:209; a heavy chain CDRI having the sequence set forth in SEQ ID NO: 149; a heavy chain CDR2 having the sequence set forth in SEQ I) NO: 174; and a heavy chain CDRI having the sequence set forth in SEQ ID NO: 195.

2. An isolated antibody, or CD200-binding fragment thereof, comprising: a light 10 chain CDR I having the sequence set forth in residues 26-36 of SEQ ID NO:208, a light chain CDR2 having the sequence set forth in residues 52-58 of SEQ ID NO:208, a light chain CDR3 having the sequence set forth in residues 91-99 of SEQ ID NO:208, a heavy chain CDRI having the sequence set forth in SEQ ID NO: 114, a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 165, and a heavy chain CDR3 having the 15 sequence set forth in SEQ I) NO: 189.

3. An isolated antibody, or CD200-binding fragment thereof, comprising: a light chain CDR1 having the sequence set forth in residues 26-35 of SEQ ID NO:207; a light chain CDR2 having the sequence set forth in residues 51-57 of SEQ ID NO:207; a light chain CDR3 having the sequence set forth in residues 90-98 of SEQ ID NO:207; a heavy 20 chain CDRI having the sequence set forth in SEQ ID NO: 111; a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 118; and a heavy chain CDR3 having the sequence set forth in residues 100-112 of SEQ ID NO:201.

4. An isolated antibody. or CD200-binding fragment thereof, comprising: a light chain CDRI having the sequence set forth in residues 26-41 of SEQ ID NO:210; a light 25 chain CDR2 having the sequence set forth in residues 57-63 of SEQ ID NO:210; a light chain CDR3 having the sequence set forth in residues 96-104 of SEQ ID NO:210; a heavy chain CDRI having the sequence set forth in SEQ ID NO: 140; a heavy chain CDR2 having the sequence set forth in SEQ ID NO: 162; and a heavy chain CDR3 having the sequence set forth in SEQ I) NO: 187. 62

5. The isolated antibody, or CD200-binding fragment thereof, according to any one of claims 1 to 4, wherein the CD200-binding fragment is selected from the group consisting of an Fv, scFv, Fab' or F(ab') 2 fragment.

6. The isolated antibody, or CD200-binding fragment thereof, according to any one 5 of claims 1-4, wherein the antibody or CD200-binding fragment thereof is a humanized, fully human, or chimeric antibody or CD200-binding fragment thereof.

7. A pharmaceutical composition comprising a pharmaceutically acceptable carrier and the isolated antibody, or CD200-binding fragment thereof, according to any one of claims 1-6. 10

8. A method for treating a patient afflicted with cancer., the method comprising administering to the patient the isolated antibody. or CD200-binding fragment thereof, according to any one of claims 1-6 to thereby treat the cancer.

9. A method for treating a patient afflicted with cancer, the method comprising administering to the patient the pharmaceutical composition according to claim 7 to 15 thereby treat the cancer.

10. The method according to claim 8 or 9, wherein the cancer comprises cancer cells overexpressing CD200.

11. The method according to claim 8 or 9. wherein the cancer is chronic lymphocytic leukemia. 20

12. The method according to claim 11, wherein the chronic lymphocytic leukemia is B cell chronic lymphocytic leukemia.

13. An isolated antibody, or a CD200-binding fragment thereof, according to any one of claims I to 4: or a pharmaceutical composition according to claim 7; or a method according to any one of claims 8 or 9, substantially as herein described with reference to 25 any one of the examples and/or figures but excluding comparative examples. 63