COMPOSITIONS AND METHODS FOR WT1 SPECIFIC IMMUNOTHERAPY

Abstract: Compositions and methods for the therapy of malignant diseases, such as leukemia and cancer, are disclosed. The compositions comprise one or more of a WT1 polynucleotide, a WT1 polypeptide, an antigen-presenting cell presenting a WT1 polypeptide, an antibody that specifically binds to a WT1 polypeptide; or a T cell that specifically reacts with a WT1 polypeptide. Such compositions may be used, for example, for the prevention and treatment of metastatic diseases.

Description: COMPOSITIONS AND METHODS FOR WTl SPECIFIC IMMUNOTHERAPY TECHNICAL FIELD The present invention relates generally to the immunotherapy of malignant diseases such as leukemia and cancers. The invention is more specifically related to compositions for generating or enhancing an immune response to WTl, and to the use of such compositions for preventing and/or treating malignant diseases. BACKGROUND OF THE INVENTION Cancer and leukemia are significant health problems in the United States and throughout the world. Although advances have been made in detection and treatment of such diseases, no vaccine or other universally successful method for prevention or treatment of cancer and leukemia is currently available. Management of the diseases currently relies on a combination of early diagnosis and aggressive treatment, which may include one or more of a variety of treatments such as surgery, radiotherapy, chemotherapy and hormone therapy. The course of treatment for a particular cancer is often selected based on a variety of prognostic parameters, including an analysis of specific tumor markers. However, the use of established markers often leads to a result that is difficult to interpret, and the high mortality continues to be observed in many cancer patients. Immunotherapies have the potential to substantially improve cancer and leukemia treatment and survival. Recent data demonstrate that leukemia can be cured by immunotherapy in the context of bone marrow transplantation (e.g., donor lymphocyte infusions). Such therapies may involve the generation or enhancement of an immune response to a tumor-associated antigen (TAA). However, to date, relatively few TAAs are known and the generation of an immune response against such antigens has, with rare exceptions, not been shown to be therapeutically beneficial. Accordingly, there is a need in the art for improved methods for leukemia and cancer prevention and therapy. The present invention fulfills these needs and further provides other related advantages. SUMMARY OF THE INVENTION Briefly stated, this invention provides compositions and methods for the diagnosis and therapy of diseases such as leukemia and cancer. In one aspect, the present invention provides polypeptides comprising an immunogenic portion of a native WTl, or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished. Within certain embodiments, the polypeptide comprises no more than 16 consecutive amino acid residues of a native WTl polypeptide. Within other embodiments, the polypeptide comprises an immunogenic portion of amino acid residues 1 - 174 of a native WTl polypeptide or a variant thereof, wherein the polypeptide comprises no more than 16 consecutive amino acid residues present within amino acids 175 to 449 of the native WTl polypeptide. The immunogenic portion preferably binds to an MHC class I and/or class II molecule. Within certain embodiments, the polypeptide comprises a sequence selected from the group consisting of (a) sequences recited in any one or more of Tables II - XLVI, (b) variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished and (c) mimetics of the polypeptides recited above, such that the ability of the mimetic to react with antigen-specific antisera and/or T cell lines or clones is not substantially diminished. Within other embodiments, the polypeptide comprises a sequence selected from the group consisting of (a) ALLPAVPSL (SEQ ID NO:34), GATLKGVAA (SEQ ID NO:88), CMTWNQMNL (SEQ ID NOs: 49 and 258), SCLESQPTI (SEQ ID NOs: 199 and 296), SCLESQPAI (SEQ ID NO: 198), NLYQMTSQL (SEQ ID NOs: 147 and 284), ALLPAVSSL (SEQ ID NOs: 35 and 255), RMFPNAPYL (SEQ ID NOs: 185 and 293), (b) variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished and (c) mimetics of the polypeptides recited above, such that the ability of the mimetic to react with antigen-specific antisera and/or T cell lines or clones is not substantially diminished. Mimetics may comprises amino acids in combination with one or more amino acid mimetics or may be entirely nonpeptide mimetics. Within further aspects, the present invention provides polypeptides comprising a variant of an immunogenic portion of a WTl protein, wherein the variant differs from the immunogenic portion due to substitutions at between 1 and 3 amino acid positions within the immunogenic portion such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is enhanced relative to a native WTl protein. The present invention further provides WTl polynucleotides that encode a WTl polypeptide as described above. Within other aspects, the present invention provides pharmaceutical compositions and vaccines. Pharmaceutical compositions may comprise a polypeptide or mimetic as described above and/or one or more of (i) a WTl polynucleotide; (ii) an antibody or antigen-binding fragment thereof that specifically binds to a WTl polypeptide; (iii) a T cell that specifically reacts with a WTl polypeptide or (iv) an antigen-presenting cell that expresses a WTl polypeptide, in combination with a pharmaceutically acceptable carrier or excipient. Vaccines comprise a polypeptide as described above and/or one or more of (i) a WTl polynucleotide, (ii) an antigen- presenting cell that expresses a WTl polypeptide or (iii) an anti-idiotypic antibody, and a non-specific immune response enhancer. Within certain embodiments, less than 23 consecutive amino acid residues, preferably less than 17 amino acid residues, of a native WTl polypeptide are present within a WTl polypeptide employed within such pharmaceutical compositions and vaccines. The immune response enhancer may be an adjuvant. Preferably, an immune response enhancer enhances a T cell response. The present invention further provides methods for enhancing or inducing an immune response in a patient, comprising administering to a patient a pharmaceutical composition or vaccine as described above. In certain embodiments, the patient is a human. The present invention further provides methods for inhibiting the development of a malignant disease in a patient, comprising administering to a patient a pharmaceutical composition or vaccine as described above. Malignant diseases include, but are not limited to leukemias (e.g., acute myeloid, acute lymphocytic and chronic myeloid) and cancers (e.g., breast, lung, thyroid or gastrointestinal cancer or a melanoma). The patient may, but need not, be afflicted with the malignant disease, and the administration of the pharmaceutical composition or vaccine may inhibit the onset of such a disease, or may inhibit progression and/or metastasis of an existing disease. The present invention further provides, within other aspects, methods for removing cells expressing WTl from bone marrow and/or peripheral blood or fractions thereof, comprising contacting bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood with T cells that specifically react with a WTl polypeptide, wherein the step of contacting is performed under conditions and for a time sufficient to permit the removal of WTl positive cells to less than 10%, preferably less than 5% and more preferably less than 1%, of the number of myeloid or lymphatic cells in the bone marrow, peripheral blood or fraction. Bone marrow, peripheral blood and fractions may be obtained from a patient afflicted with a disease associated with WTl expression, or may be obtained from a human or non-human mammal not afflicted with such a disease. Within related aspects, the present invention provides methods for inhibiting the development of a malignant disease in a patient, comprising administering to a patient bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood prepared as described above. Such bone marrow, peripheral blood or fractions may be autologous, or may be derived from a related or unrelated human or non-human animal (e.g., syngeneic or allogeneic). In other aspects, the present invention provides methods for stimulating (or priming) and/or expanding T cells, comprising contacting T cells with a WTl polypeptide under conditions and for a time sufficient to permit the stimulation and/or expansion of T cells. Such T cells may be autologous, allogeneic, syngeneic or unrelated WTl -specific T cells, and may be stimulated in vitro or in vivo. Expanded T cells may, within certain embodiments, be present within bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood, and may (but need not) be clonal. Within certain embodiments, T cells may be present in a mammal during stimulation and/or expansion. WTl -specific T cells may be used, for example, within donor lymphocyte infusions. Within related aspects, methods are provided for inhibiting the development of a malignant disease in a patient, comprising administering to a patient T cells prepared as described above. Such T cells may, within certain embodiments, be autologous, syngeneic or allogeneic. The present invention further provides, within other aspects, methods for monitoring the effectiveness of an immunization or therapy for a malignant disease associated with WTl expression in a patient. Such methods are based on monitoring antibody, CD4+ T cell and/or CD8+ T cell responses in the patient. Within certain such aspects, a method may comprise the steps of: (a) incubating a first biological sample with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide, wherein the first biological sample is obtained from a patient prior to a therapy or immunization, and wherein the incubation is performed under conditions and for a time sufficient to allow immunocomplexes to form; (b) detecting immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide; (c) repeating steps (a) and (b) using a second biological sample obtained from the same patient following therapy or immunization; and (d) comparing the number of immunocomplexes detected in the first and second biological samples, and therefrom monitoring the effectiveness of the therapy or immunization in the patient. Within certain embodiments of the above methods, the step of detecting comprises (a) incubating the immunocomplexes with a detection reagent that is capable of binding to the immunocomplexes, wherein the detection reagent comprises a reporter group, (b) removing unbound detection reagent, and (c) detecting the presence or absence of the reporter group. The detection reagent may comprise, for example, a second antibody, or antigen-binding fragment thereof, capable of binding to the antibodies that specifically bind to the WTl polypeptide or a molecule such as Protein A. Within other embodiments, a reporter group is bound to the WTl polypeptide, and the step of detecting comprises removing unbound WTl polypeptide and subsequently detecting the presence or absence of the reporter group. Within further aspects, methods for monitoring the effectiveness of an immunization or therapy for a malignant disease associated with WTl expression in a patient may comprise the steps of: (a) incubating a first biological sample with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide, wherein the biological sample comprises CD4+ and/or CD8+ T cells and is obtained from a patient prior to a therapy or immunization, and wherein the incubation is performed under conditions and for a time sufficient to allow specific activation, proliferation and/or lysis of T cells; (b) detecting an amount of activation, proliferation and/or lysis of the T cells; (c) repeating steps (a) and (b) using a second biological sample comprising CD4+ and/or CD8+ T cells, wherein the second biological sample is obtained from the same patient following therapy or immunization; and (d) comparing the amount of activation, proliferation and/or lysis of T cells in the first and second biological samples, and therefrom monitoring the effectiveness of the therapy or immunization in the patient. The present invention further provides methods for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + and/or CD8+ T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide, such that the T cells proliferate; and (b) administering to the patient an effective amount of the proliferated T cells, and therefrom inhibiting the development of a malignant disease in the patient. Within certain embodiments, the step of incubating the T cells may be repeated one or more times. Within other aspects, the present invention provides methods for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + and/or CD8+ T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide, such that the T cells proliferate; (b) cloning one or more cells that proliferated; and (c) administering to the patient an effective amount of the cloned T cells. Within other aspects, methods are provided for determining the presence or absence of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + and/or CD8+ T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; and (b) detecting the presence or absence of specific activation of the T cells, therefrom determining the presence or absence of a malignant disease associated with WTl expression. Within certain embodiments, the step of detecting comprises detecting the presence or absence of proliferation of the T cells. Within further aspects, the present invention provides methods for determining the presence or absence of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating a biological sample obtained from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide, wherein the incubation is performed under conditions and for a time sufficient to allow immunocomplexes to form; and (b) detecting immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide; and therefrom determining the presence or absence of a malignant disease associated with WTl expression. These and other aspects of the present invention will become apparent upon reference to the following detailed description and attached drawings. All references disclosed herein are hereby incorporated by reference in their entirety as if each was incorporated individually. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 depicts a comparison of the mouse (MO) and human (HU) WTl protein sequences (SEQ ID NOS: 320 and 319 respectively). Figure 2 is a Western blot illustrating the detection of WTl specific antibodies in patients with hematological malignancy (AML). Lane 1 shows molecular weight markers; lane 2 shows a positive control (WTl positive human leukemia cell line immunoprecipitated with a WTl specific antibody); lane 3 shows a negative control (WTl positive cell line immunoprecipitated with mouse sera); and lane 4 shows a WTl positive cell line immunoprecipitated with sera of a patient with AML. For lanes 2-4, the immunoprecipitate was separated by gel electrophoresis and probed with a WTl specific antibody. Figure 3 is a Western blot illustrating the detection of a WTl specific antibody response in B6 mice immunized with TRAMP-C, a WTl positive tumor cell line. Lanes 1 , 3 and 5 show molecular weight markers, and lanes 2, 4 and 6 show a WTl specific positive control (N180, Santa Cruz Biotechnology, polypeptide spanning 180 amino acids of the N-terminal region of the WTl protein, migrating on the Western blot at 52 kD). The primary antibody used was WTl 80 in lane 2, sera of non- immunized B6 mice in lane 4 and sera of the immunized B6 mice in lane 6. Figure 4 is a Western blot illustrating the detection of WTl specific antibodies in mice immunized with representative WTl peptides. Lanes 1, 3 and 5 show molecular weight markers and lanes 2, 4 and 6 show a WTl specific positive control (N180, Santa Cruz Biotechnology, polypeptide spanning 180 amino acids of the N-terminal region of the WTl protein, migrating on the Western blot at 52 kD). The primary antibody used was WTl 80 in lane 2, sera of non-immunized B6 mice in lane 4 and sera of the immunized B6 mice in lane 6. Figures 5 A to 5C are graphs illustrating the stimulation of proliferative T cell responses in mice immunized with representative WTl peptides. Thymidine incorporation assays were performed using one T cell line and two different clones, as indicated, and results were expressed as cpm. Controls indicated on the x axis were no antigen (No Ag) and B6/media; antigens used were p6-22 human (pi), pi 17-139 (p2) or p244-262 human (p3). Figure 6A and 6B are histograms illustrating the stimulation of proliferative T cell responses in mice immunized with representative WTl peptides. Three weeks after the third immunization, spleen cells of mice that had been inoculated with Vaccine A or Vaccine B were cultured with medium alone (medium) or spleen cells and medium (B6/no antigen), B6 spleen cells pulsed with the peptides p6-22 (p6), pi 17-139 (pi 17), p244-262 (p244) (Vaccine A; Figure 6A) or p287-301 (p287), p299- 313 (p299), p421-435 (p421) (Vaccine B; Figure 6B) and spleen cells pulsed with an irrelevant control peptide (irrelevant peptide) at 25ug/ml and were assayed after 96hr for proliferation by ( 3 H) thymidine incoφoration. Bars represent the stimulation index (SI), which is calculated as the mean of the experimental wells divided by the mean of the control (B6 spleen cells with no antigen). Figures 7A-7D are histograms illustrating the generation of proliferative T-cell lines and clones specific for pi 17-139 and p6-22. Following in vivo immunization, the initial three in vitro stimulations (IVS) were carried out using all three peptides of Vaccine A or B, respectively. Subsequent IVS were carried out as single peptide stimulations using only the two relevant peptides pi 17-139 and p6-22. Clones were derived from both the p6-22 and pi 17-139 specific T cell lines, as indicated. T cells were cultured with medium alone (medium) or spleen cells and medium (B6/no antigen), B6 spleen cells pulsed with the peptides p6-22 (p6), pi 17-139 (pi 17) or an irrelevant control peptide (irrelevant peptide) at 25ug/ml and were assayed after 96hr for proliferation by ( 3 H) thymidine incoφoration. Bars represent the stimulation index (SI), which is calculated as the mean of the experimental wells divided by the mean of the control (B6 spleen cells with no antigen). Figures 8A and 8B present the results of TSITES Analysis of human WTl (SEQ ID NO:319) for peptides that have the potential to elicit Th responses. Regions indicated by "A" are AMPHI midpoints of blocks, "R" indicates residues matching the Rothbard/'Taylor motif, "D" indicates residues matching the IAd motif, and 'd' indicates residues matching the IEd motif. Figures 9 A and 9B are graphs illustrating the elicitation of WTl peptide- specific CTL in mice immunized with WTl peptides. Figure 9 A illustrates the lysis of target cells by allogeneic cell lines and Figure 9B shows the lysis of peptide coated cell lines. In each case, the % lysis (as determined by standard chromium release assays) is shown at three indicated effectoπtarget ratios. Results are provided for lymphoma cells (LSTRA and ElO), as well as ElO + p235-243 (E10+P235). ElO cells are also referred to herein as EL-4 cells. Figures 10A-10D are graphs illustrating the elicitation of WTl specific CTL, which kill WTl positive tumor cell lines but do not kill WTl negative cell lines, following vaccination of B6 mice with WTl peptide PI 17. Figure 10A illustrates that T-cells of non-immunized B6 mice do not kill WTl positive tumor cell lines. Figure 10B illustrates the lysis of the target cells by allogeneic cell lines. Figures IOC and 10D demonstrate the lysis of WTl positive tumor cell lines, as compared to WTl negative cell lines in two different experiments. In addition, Figures 10C and 10D show the lysis of peptide-coated cell lines (WTl negative cell line ElO coated with the relevant WTl peptide PI 17) In each case, the % lysis (as determined by standard chromium release assays) is shown at three indicated effector:target ratios. Results are provided for lymphoma cells (ElO), prostate cancer cells (TRAMP-C), a transformed fibroblast cell line (BLK-SV40), as well as ElO+pl 17. Figures 11A and 1 IB are histograms illustrating the ability of representative peptide PI 17-139 specific CTL to lyse WTl positive tumor cells. Three weeks after the third immunization, spleen cells of mice that had been inoculated with the peptides p235-243 or pi 17-139 were stimulated in vitro with the relevant peptide and tested for ability to lyse targets incubated with WTl peptides as well as WTl positive and negative tumor cells. The bars represent the mean % specific lysis in chromium release assays performed in triplicate with an E:T ratio of 25:1. Figure 11A shows the cytotoxic activity of the p235-243 specific T cell line against the WTl negative cell line EL-4 (EL-4, WTl negative); EL-4 pulsed with the relevant (used for immunization as well as for restimulation) peptide p235-243 (EL-4+p235); EL-4 pulsed with the irrelevant peptides pi 17-139 (EL-4+pl l7), pl26-134 (EL-4+pl26) or pl30- 138 (EL-4+pl30) and the WTl positive tumor cells BLK-SV40 (BLK-SV40, WTl positive) and TRAMP-C (TRAMP-C, WTl positive), as indicated. Figure 11B shows cytotoxic activity of the pi 17-139 specific T cell line against EL-4; EL-4 pulsed with the relevant peptide PI 17-139 (EL-4+pl l7) and EL-4 pulsed with the irrelevant peptides pl23-131 (EL-4+pl23), or pl28-136 (EL-4+pl28); BLK-SV40 and TRAMP- C, as indicated. Figures 12A and 12B are histograms illustrating the specificity of lysis of WTl positive tumor cells, as demonstrated by cold target inhibition. The bars represent the mean % specific lysis in chromium release assays performed in triplicate with an E:T ratio of 25:1. Figure 12A shows the cytotoxic activity of the pi 17-139 specific T cell line against the WTl negative cell line EL-4 (EL-4, WTl negative); the WTl positive tumor cell line TRAMP-C (TRAMP-C, WTl positive); TRAMP-C cells incubated with a ten-fold excess (compared to the hot target) of EL-4 cells pulsed with the relevant peptide pi 17-139 (TRAMP-C + pi 17 cold target) without 51 Cr labeling and TRAMP-C cells incubated with EL-4 pulsed with an irrelevant peptide without 51 Cr labeling (TRAMP-C + irrelevant cold target), as indicated. Figure 12B shows the cytotoxic activity of the pi 17-139 specific T cell line against the WTl negative cell line EL-4 (EL-4, WTl negative); the WTl positive tumor cell line BLK-SV40 (BLK-SV40, WTl positive); BLK-SV40 cells incubated with the relevant cold target (BLK-SV40 + pi 17 cold target) and BLK-SV40 cells incubated with the irrelevant cold target (BLK- SV40 + irrelevant cold target), as indicated. Figures 13A-13C are histograms depicting an evaluation of the 9mer CTL epitope within pi 17-139. The pi 17-139 tumor specific CTL line was tested against peptides within aal 17-139 containing or lacking an appropriate H-2 b class I binding motif and following restimulation with pl26-134 or pl30-138. The bars represent the mean % specific lysis in chromium release assays performed in triplicate with an E:T ratio of 25:1. Figure 13A shows the cytotoxic activity of the pi 17-139 specific T cell line against the WTl negative cell line EL-4 (EL-4, WTl negative) and EL-4 cells pulsed with the peptides pi 17-139 (EL-4 + pi 17), pi 19-127 (EL-4 + pi 19), pl20-128 (EL-4 + pl20), pl23-131 (EL-4 + pl23), pl26-134 (EL-4 + pl26), pl28-136 (EL-4 + pl28), and pl30-138 (EL-4 + pl30). Figure 13B shows the cytotoxic activity of the CTL line after restimulation with pl26-134 against the WTl negative cell line EL-4, EL-4 cells pulsed with pi 17-139 (EL-4 + pi 17), pl26-134 (EL-4 + pl26) and the WTl positive tumor cell line TRAMP-C. Figure 13C shows the cytotoxic activity of the CTL line after restimulation with pi 30-138 against EL-4, EL-4 cells pulsed with pi 17-139 (EL-4 + pi 17), pl30-138 (EL-4 + pl30) and the WTl positive tumor cell line TRAMP-C. DETAILED DESCRIPTION OF THE INVENTION As noted above, the present invention is generally directed to compositions and methods for the immunotherapy and diagnosis of malignant diseases. The compositions described herein may include WTl polypeptides, WTl polynucleotides, antigen-presenting cells (APC, e.g., dendritic cells) that express a WTl polypeptide, agents such as antibodies that bind to a WTl polypeptide and/or immune system cells (e.g., T cells) specific for WTl. WTl Polypeptides of the present invention generally comprise at least a portion of a Wilms Tumor gene product (WTl) or a variant thereof. Nucleic acid sequences of the subject invention generally comprise a DNA or RNA sequence that encodes all or a portion of such a polypeptide, or that is complementary to such a sequence. Antibodies are generally immune system proteins, or antigen-binding fragments thereof, that are capable of binding to a portion of a WTl polypeptide. T cells that may be employed within such compositions are generally T cells (e.g., CD4 ~ and/or CD8 + ) that are specific for a WTl polypeptide. Certain methods described herein further employ antigen-presenting cells that express a WTl polypeptide as provided herein. The present invention is based on the discovery that an immune response raised against a Wilms Tumor (WT) gene product (e.g., WTl) can provide prophylactic and/or therapeutic benefit for patients afflicted with malignant diseases characterized by increased WTl gene expression. Such diseases include, but are not limited to^ leukemias (e.g., acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphocytic leukemia (ALL) and childhood ALL), as well as many cancers such as lung, breast, thyroid and gastrointestinal cancers and melanomas. The WTl gene was originally identified and isolated on the basis of a cytogenetic deletion at chromosome l lpl3 in patients with Wilms' tumor (see Call et al., U.S. Patent No. 5,350,840). The gene consists of 10 exons and encodes a zinc finger transcription factor, and sequences of mouse and human WTl proteins are provided in Figure 1 and SEQ ID NOs: 319 and 320. WTl POLYPEPTIDES Within the context of the present invention, a WTl polypeptide is a polypeptide that comprises at least an immunogenic portion of a native WTl (i.e., a WTl protein expressed by an organism that is not genetically modified), or a variant thereof, as described herein. A WTl polypeptide may be of any length, provided that it comprises at least an immunogenic portion of a native protein or a variant thereof. In other words, a WTl polypeptide may be an oligopeptide (i.e., consisting of a relatively small number of amino acid residues, such as 8-10 residues, joined by peptide bonds), a full length WTl protein (e.g., present within a human or non-human animal, such as a mouse) or a polypeptide of intermediate size. Within certain embodiments, the use of WTl polypeptides that contain a small number of consecutive amino acid residues of a native WTl polypeptide is preferred. Such polypeptides are preferred for certain uses in which the generation of a T cell response is desired. For example, such a WTl polypeptide may contain less than 23, preferably no more than 18, and more preferably no more than 15 consecutive amino acid residues, of a native WTl polypeptide. Polypeptides comprising nine consecutive amino acid residues of a native WTl polypeptide are generally suitable for such puφoses. Additional sequences derived from the native protein and/or heterologous sequences may be present within any WTl polypeptide, and such sequences may (but need not) possess further immunogenic or antigenic properties. Polypeptides as provided herein may further be associated (covalently or noncovalently) with other polypeptide or non-polypeptide compounds. An "immunogenic portion," as used herein is a portion of a polypeptide that is recognized (i.e., specifically bound) by a B-cell and/or T-cell surface antigen receptor. Certain preferred immunogenic portions bind to an MHC class I or class II molecule. As used herein, an immunogenic portion is said to "bind to" an MHC class I or class II molecule if such binding is detectable using any assay known in the art. For example, the ability of a polypeptide to bind to MHC class I may be evaluated indirectly by monitoring the ability to promote incoφoration of 125 I labeled β2- microglobulin (β2m) into MHC class I/β2m/peptide heterotrimeric complexes (see Parker et al., J. Immunol. 152:163, 1994). Alternatively, functional peptide competition assays that are known in the art may be employed. Certain immunogenic portions have one or more of the sequences recited within one or more of Tables II - XIV. Representative immunogenic portions include, but are not limited to, RDLNALLPAVPSLGGGG (human WTl residues 6-22; SEQ ID NO:l), PSQASSGQARMFPNAPYLPSCLE (human and mouse WTl residues 117-139; SEQ ID NOs: 2 and 3 respectively), GATLKGVAAGSSSSVKWTE (human WTl residues 244-262; SEQ ID NO:4), GATLKGVAA (human WTl residues 244-252; SEQ ID NO:88), CMTWNQMNL (human and mouse WTl residues 235-243; SEQ ID NOs: 49 and 258 respectively), SCLESQPTI (mouse WTl residues 136-144; SEQ ID NO:296), SCLESQPAI (human WTl residues 136-144; SEQ ID NO:198), NLYQMTSQL (human and mouse WTl residues 225-233; SEQ ID NOs: 147 and 284 respectively); ALLPAVSSL (mouse WTl residues 10-18; SEQ ID NO:255); or RMFPNAPYL (human and mouse WTl residues 126-134; SEQ ID NOs: 185 and 293 respectively). Further immunogenic portions are provided herein, and others may generally be identified using well known techniques, such as those summarized in Paul, Fundamental Immunology, 3rd ed., 243-247 (Raven Press, 1993) and references cited therein. Representative techniques for identifying immunogenic portions include screening polypeptides for the ability to react with antigen-specific antisera and/or T- cell lines or clones. An immunogenic portion of a native WTl polypeptide is a portion that reacts with such antisera and/or T-cells at a level that is not substantially less than the reactivity of the full length WTl (e.g., in an ELISA and/or T-cell reactivity assay). In other words, an immunogenic portion may react within such assays at a level that is similar to or greater than the reactivity of the full length polypeptide. Such screens may generally be performed using methods well known to those of ordinary skill in the art, such as those described in Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988. Alternatively, immunogenic portions may be identified using computer analysis, such as the Tsites program (see Rothbard and Taylor, EMBO J. 7:93-100, 1988; Deavin et al, Mol. Immunol. 33:145-155, 1996), which searches for peptide motifs that have the potential to elicit Th responses. CTL peptides with motifs appropriate for binding to murine and human class I or class II MHC may be identified according to BIMAS (Parker et al., J. Immunol. 152:163, 1994) and other HLA peptide binding prediction analyses. To confirm immunogenicity, a peptide may be tested using an HLA A2 transgenic mouse model and/or an in vitro stimulation assay using dendritic cells, fibroblasts or peripheral blood cells. As noted above, a composition may comprise a variant of a native WTl protein. A polypeptide "variant," as used herein, is a polypeptide that differs from a native polypeptide in one or more substitutions, deletions, additions and/or insertions, such that the immunogenicity of the polypeptide is retained (i.e., the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished relative to the native polypeptide). In other words, the ability of a variant to react with antigen-specific antisera and/or T-cell lines or clones may be enhanced or unchanged, relative to the native polypeptide, or may be diminished by less than 50%, and preferably less than 20%, relative to the native polypeptide. Such variants may generally be identified by modifying one of the above polypeptide sequences and evaluating the reactivity of the modified polypeptide with antisera and/or T-cells as described herein. It has been found, within the context of the present invention, that a relatively small number of substitutions (e.g., 1 to 3) within an immunogenic portion of a WTl polypeptide may serve to enhance the ability of the polypeptide to elicit an immune response. Suitable substitutions may generally be identified by using computer programs, as described above, and the effect confirmed based on the reactivity of the modified polypeptide with antisera and/or T-cells as described herein. Accordingly, within certain preferred embodiments, a WTl polypeptide comprises a variant in which 1 to 3 amino acid resides within an immunogenic portion are substituted such that the ability to react with antigen-specific antisera and/or T-cell lines or clones is statistically greater than that for the unmodified polypeptide. Such substitutions are preferably located within an MHC binding site of the polypeptide, which may be identified as described above. Preferred substitutions allow increased binding to MHC class I or class II molecules. Certain variants contain conservative substitutions. A "conservative substitution" is one in which an amino acid is substituted for another amino acid that has similar properties, such that one skilled in the art of peptide chemistry would expect the secondary structure and hydropathic nature of the polypeptide to be substantially unchanged. Amino acid substitutions may generally be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity and/or the amphipathic nature of the residues. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; and amino acids with uncharged polar head groups having similar hydrophilicity values include leucine, isoleucine and valine; glycine and alanine; asparagine and glutamine; and serine, threonine, phenylalanine and tyrosine. Other groups of amino acids that may represent conservative changes include: (1) ala, pro, gly, glu, asp, gin, asn, ser, thr; (2) cys, ser, tyr, thr; (3) val, ile, leu, met, ala, phe; (4) lys, arg, his; and (5) phe, tyr, tφ, his. A variant may also, or alternatively, contain nonconservative changes. Variants may also (or alternatively) be modified by, for example, the deletion or addition of amino acids that have minimal influence on the immunogenicity, secondary structure and hydropathic nature of the polypeptide. As noted above, WTl polypeptides may be conjugated to a signal (or leader) sequence at the N-terminal end of the protein which co-translationally or post- translationally directs transfer of the protein. A polypeptide may also, or alternatively, be conjugated to a linker or other sequence for ease of synthesis, purification or identification of the polypeptide (e.g., poly-His), or to enhance binding of the polypeptide to a solid support. For example, a polypeptide may be conjugated to an immunoglobulin Fc region. WTl polypeptides may be prepared using any of a variety of well known techniques. Recombinant polypeptides encoded by a WTl polynucleotide as described herein may be readily prepared from the polynucleotide. In general, any of a variety of expression vectors known to those of ordinary skill in the art may be employed to express recombinant WTl polypeptides. Expression may be achieved in any appropriate host cell that has been transformed or transfected with an expression vector containing a DNA molecule that encodes a recombinant polypeptide. Suitable host cells include prokaryotes, yeast and higher eukaryotic cells. Preferably, the host cells employed are E. coli, yeast or a mammalian cell line such as COS or CHO. Supernatants from suitable host/vector systems which secrete recombinant protein or polypeptide into culture media may be first concentrated using a commercially available filter. The concentrate may then be applied to a suitable purification matrix such as an affinity matrix or an ion exchange resin. Finally, one or more reverse phase HPLC steps can be employed to further purify a recombinant polypeptide. Such techniques may be used to prepare native polypeptides or variants thereof. For example, polynucleotides that encode a variant of a native polypeptide may generally be prepared using standard mutagenesis techniques, such as oligonucleotide-directed site-specific mutagenesis, and sections of the DNA sequence may be removed to permit preparation of truncated polypeptides. Certain portions and other variants may also be generated by synthetic means, using techniques well known to those of ordinary skill in the art. For example, polypeptides having fewer than about 500 amino acids, preferably fewer than about 100 amino acids, and more preferably fewer than about 50 amino acids, may be synthesized. Polypeptides may be synthesized using any of the commercially available solid-phase techniques, such as the Merrifield solid-phase synthesis method, where amino acids are sequentially added to a growing amino acid chain. See Merrifield, J. Am. Chem. Soc. 55:2149-2146, 1963. Equipment for automated synthesis of polypeptides is commercially available from suppliers such as Applied BioSystems, Inc. (Foster City, CA), and may be operated according to the manufacturer's instructions. In general, polypeptides and polynucleotides as described herein are isolated. An "isolated" polypeptide or polynucleotide is one that is removed from its original environment. For example, a naturally-occurring protein is isolated if it is separated from some or all of the coexisting materials in the natural system. Preferably, such polypeptides are at least about 90% pure, more preferably at least about 95% pure and most preferably at least about 99% pure. A polynucleotide is considered to be isolated if, for example, it is cloned into a vector that is not a part of the natural environment. Within further aspects, the present invention provides mimetics of WTl polypeptides. Such mimetics may comprise amino acids linked to one or more amino acid mimetics (i.e., one or more amino acids within the WTl protein may be replaced by an amino acid mimetic) or may be entirely nonpeptide mimetics. An amino acid mimetic is a compound that is conformationally similar to an amino acid such that it can be substituted for an amino acid within a WTl polypeptide without substantially diminishing the ability to react with antigen-specific antisera and/or T cell lines or clones. A nonpeptide mimetic is a compound that does not contain amino acids, and that has an overall conformation that is similar to a WTl polypeptide such that the ability of the mimetic to react with WTl -specific antisera and/or T cell lines or clones is not substantially diminished relative to the ability of a WTl polypeptide. Such mimetics may be designed based on standard techniques (e.g., nuclear magnetic resonance and computational techniques) that evaluate the three dimensional structure of a peptide sequence. Mimetics may be designed where one or more of the side chain functionalities of the WTl polypeptide are replaced by groups that do not necessarily have the same size or volume, but have similar chemical and/or physical properties which produce similar biological responses. It should be understood that, within embodiments described herein, a mimetic may be substituted for a WTl polypeptide. WTl POLYNUCLEOTIDES Any polynucleotide that encodes a WTl polypeptide as described herein is a WTl polynucleotide encompassed by the present invention. Such polynucleotides may be single-stranded (coding or antisense) or double-stranded, and may be DNA (genomic, cDNA or synthetic) or RNA molecules. Additional coding or non-coding sequences may, but need not, be present within a polynucleotide of the present invention, and a polynucleotide may, but need not, be linked to other molecules and/or support materials. WTl polynucleotides may encode a native WTl protein, or may encode a variant of WTl as described herein. Polynucleotide variants may contain one or more substitutions, additions, deletions and/or insertions such that the immunogenicity of the encoded polypeptide is not diminished, relative to a native WTl protein. The effect on the immunogenicity of the encoded polypeptide may generally be assessed as described herein. Preferred variants contain nucleotide substitutions, deletions, insertions and/or additions at no more than 20%, preferably at no more than 10%, of the nucleotide positions that encode an immunogenic portion of a native WTl sequence. Certain variants are substantially homologous to a native gene, or a portion thereof. Such polynucleotide variants are capable of hybridizing under moderately stringent conditions to a naturally occurring DNA sequence encoding a WTl polypeptide (or a complementary sequence). Suitable moderately stringent conditions include prewashing in a solution of 5 X SSC, 0.5% SDS, 1.0 mM EDTA (pH 8.0); hybridizing at 50°C-65°C, 5 X SSC, overnight; followed by washing twice at 65°C for 20 minutes with each of 2X, 0.5X and 0.2X SSC containing 0.1% SDS). Such hybridizing DNA sequences are also within the scope of this invention. It will be appreciated by those of ordinary skill in the art that, as a result of the degeneracy of the genetic code, there are many nucleotide sequences that encode a WTl polypeptide. Some of these polynucleotides bear minimal homology to the nucleotide sequence of any native gene. Nonetheless, polynucleotides that vary due to differences in codon usage are specifically contemplated by the present invention. Once an immunogenic portion of WTl is identified, as described above, a WTl polynucleotide may be prepared using any of a variety of techniques. For example, a WTl polynucleotide may be amplified from cDNA prepared from cells that express WTl . Such polynucleotides may be amplified via polymerase chain reaction (PCR). For this approach, sequence-specific primers may be designed based on the sequence of the immunogenic portion and may be purchased or synthesized. For example, suitable primers for PCR amplification of a human WTl gene include: first step - PI 18: 1434-1414: 5' GAG AGT CAG ACT TGA AAG CAGT 3' (SEQ ID NO:5) and P135: 5' CTG AGC CTC AGC AAA TGG GC 3' (SEQ ID NO:6); second step - P136: 5' GAG CAT GCA TGG GCT CCG ACG TGC GGG 3' (SEQ ID NO:7) and P137: 5' GGG GTA CCC ACT GAA CGG TCC CCG A 3' (SEQ ID NO:8). Primers for PCR amplification of a mouse WTl gene include: first step - PI 38: 5' TCC GAG CCG CAC CTC ATG 3' (SEQ ID NO:9) and P139: 5' GCC TGG GAT GCT GGA CTG 3' (SEQ ID NO:10), second step - P140: 5' GAG CAT GCG ATG GGT TCC GAC GTG CGG 3' (SEQ ID NO:l l) and P141 : 5' GGG GTA CCT CAA AGC GCC ACG TGG AGT TT 3' (SEQ ID NO: 12). An amplified portion may then be used to isolate a full length gene from a human genomic DNA library or from a suitable cDNA library, using well known techniques. Alternatively, a full length gene can be constructed from multiple PCR fragments. WTl polynucleotides may also be prepared by synthesizing oligonucleotide components, and ligating components together to generate the complete polynucleotide. WTl polynucleotides may also be synthesized by any method known in the art, including chemical synthesis (e.g., solid phase phosphoramidite chemical synthesis). Modifications in a polynucleotide sequence may also be introduced using standard mutagenesis techniques, such as oligonucleotide-directed site-specific mutagenesis (see Adelman et al., DNA 2:183, 1983). Alternatively, RNA molecules may be generated by in vitro or in vivo transcription of DNA sequences encoding a WTl polypeptide, provided that the DNA is incoφorated into a vector with a suitable RNA polymerase promoter (such as T7 or SP6). Certain portions may be used to prepare an encoded polypeptide, as described herein. In addition, or alternatively, a portion may be administered to a patient such that the encoded polypeptide is generated in vivo (e.g., by transfecting antigen-presenting cells such as dendritic cells with a cDNA construct encoding a WTl polypeptide, and administering the transfected cells to the patient). Polynucleotides that encode a WTl polypeptide may generally be used for production of the polypeptide, in vitro or in vivo. WTl polynucleotides that are complementary to a coding sequence (i.e., antisense polynucleotides) may also be used as a probe or to inhibit WTl expression. cDNA constructs that can be transcribed into antisense RNA may also be introduced into cells of tissues to facilitate the production of antisense RNA. Any polynucleotide may be further modified to increase stability in vivo. Possible modifications include, but are not limited to, the addition of flanking sequences at the 5' and/or 3' ends; the use of phosphorothioate or 2' O-methyl rather than phosphodiesterase linkages in the backbone; and/or the inclusion of nontraditional bases such as inosine, queosine and wybutosine, as well as acetyl- methyl-, thio- and other modified forms of adenine, cytidine, guanine, thymine and uridine. Nucleotide sequences as described herein may be joined to a variety of other nucleotide sequences using established recombinant DNA techniques. For example, a polynucleotide may be cloned into any of a variety of cloning vectors, including plasmids, phagemids, lambda phage derivatives and cosmids. Vectors of particular interest include expression vectors, replication vectors, probe generation vectors and sequencing vectors. In general, a vector will contain an origin of replication functional in at least one organism, convenient restriction endonuclease sites and one or more selectable markers. Other elements will depend upon the desired use, and will be apparent to those of ordinary skill in the art. Within certain embodiments, polynucleotides may be formulated so as to permit entry into a cell of a mammal, and expression therein. Such formulations are particularly useful for therapeutic puφoses, as described below. Those of ordinary skill in the art will appreciate that there are many ways to achieve expression of a polynucleotide in a target cell, and any suitable method may be employed. For example, a polynucleotide may be incoφorated into a viral vector such as, but not limited to, adenovirus, adeno-associated virus, retrovirus, or vaccinia or other pox virus (e.g., avian pox virus). Techniques for incoφorating DNA into such vectors are well known to those of ordinary skill in the art. A retroviral vector may additionally transfer or incoφorate a gene for a selectable marker (to aid in the identification or selection of transduced cells) and/or a targeting moiety, such as a gene that encodes a ligand for a receptor on a specific target cell, to render the vector target specific. Targeting may also be accomplished using an antibody, by methods known to those of ordinary skill in the art. cDNA constructs within such a vector may be used, for example, to transfect human or animal cell lines for use in establishing WTl positive tumor models which may be used to perform tumor protection and adoptive immunotherapy experiments to demonstrate tumor or leukemia-growth inhibition or lysis of such cells. Other therapeutic formulations for polynucleotides include colloidal dispersion systems, such as macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. A preferred colloidal system for use as a delivery vehicle in vitro and in vivo is a liposome (i.e., an artificial membrane vesicle). The preparation and use of such systems is well known in the art. ANTIBODIES AND FRAGMENTS THEREOF The present invention further provides binding agents, such as antibodies and antigen-binding fragments thereof, that specifically bind to a WTl polypeptide. As used herein, an agent is said to "specifically bind" to a WTl polypeptide if it reacts at a detectable level (within, for example, an ELISA) with a WTl polypeptide, and does not react detectably with unrelated proteins under similar conditions. As used herein, "binding" refers to a noncovalent association between two separate molecules such that a "complex" is formed. The ability to bind may be evaluated by, for example, determining a binding constant for the formation of the complex. The binding constant is the value obtained when the concentration of the complex is divided by the product of the component concentrations. In general, two compounds are said to "bind," in the context of the present invention, when the binding constant for complex formation exceeds about 10 3 L/mol. The binding constant maybe determined using methods well known in the art. Any agent that satisfies the above requirements may be a binding agent. In a preferred embodiment, a binding agent is an antibody or an antigen-binding fragment thereof. Certain antibodies are commercially available from, for example, Santa Cruz Biotechnology (Santa Cruz, CA). Alternatively, antibodies may be prepared by any of a variety of techniques known to those of ordinary skill in the art. See, e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988. In general, antibodies can be produced by cell culture techniques, including the generation of monoclonal antibodies as described herein, or via transfection of antibody genes into suitable bacterial or mammalian cell hosts, in order to allow for the production of recombinant antibodies. In one technique, an immunogen comprising the polypeptide is initially injected into any of a wide variety of mammals (e.g., mice, rats, rabbits, sheep or goats). In this step, the polypeptides of this invention may serve as the immunogen without modification. Alternatively, particularly for relatively short polypeptides, a superior immune response may be elicited if the polypeptide is joined to a carrier protein, such as bovine serum albumin or keyhole limpet hemocyanin. The immunogen is injected into the animal host, preferably according to a predetermined schedule incoφorating one or more booster immunizations, and the animals are bled periodically. Polyclonal antibodies specific for the polypeptide may then be purified from such antisera by, for example, affinity chromatography using the polypeptide coupled to a suitable solid support. Monoclonal antibodies specific for the antigenic polypeptide of interest may be prepared, for example, using the technique of Kohler and Milstein, Eur. J. Immunol 6:511-519, 1976, and improvements thereto. Briefly, these methods involve the preparation of immortal cell lines capable of producing antibodies having the desired specificity (i.e., reactivity with the polypeptide of interest). Such cell lines may be produced, for example, from spleen cells obtained from an animal immunized as described above. The spleen cells are then immortalized by, for example, fusion with a myeloma cell fusion partner, preferably one that is syngeneic with the immunized animal. A variety of fusion techniques may be employed. For example, the spleen cells and myeloma cells may be combined with a nonionic detergent for a few minutes and then plated at low density on a selective medium that supports the growth of hybrid cells, but not myeloma cells. A preferred selection technique uses HAT (hypoxanthine, aminopterin, thymidine) selection. After a sufficient time, usually about 1 to 2 weeks, colonies of hybrids are observed. Single colonies are selected and their culture supematants tested for binding activity against the polypeptide. Hybridomas having high reactivity and specificity are preferred. Monoclonal antibodies may be isolated from the supematants of growing hybridoma colonies. In addition, various techniques may be employed to enhance the yield, such as injection of the hybridoma cell line into the peritoneal cavity of a suitable vertebrate host, such as a mouse. Monoclonal antibodies may then be harvested from the ascites fluid or the blood. Contaminants may be removed from the antibodies by conventional techniques, such as chromatography, gel filtration, precipitation, and extraction. The polypeptides of this invention may be used in the purification process in, for example, an affinity chromatography step. Within certain embodiments, the use of antigen-binding fragments of antibodies may be preferred. Such fragments include Fab fragments, which may be prepared using standard techniques. Briefly, immunoglobulins may be purified from rabbit serum by affinity chromatography on Protein A bead columns (Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988) and digested by papain to yield Fab and Fc fragments. The Fab and Fc fragments may be separated by affinity chromatography on protein A bead columns. Monoclonal antibodies and fragments thereof may be coupled to one or more therapeutic agents. Suitable agents in this regard include radioactive tracers and chemotherapeutic agents, which may be used, for example, to purge autologous bone marrow in vitro). Representative therapeutic agents include radionuclides, differentiation inducers, drugs, toxins, and derivatives thereof. Preferred radionuclides include 90 Y, 123 I, 125 I, 131 I, ,86 Re, ,88 Re, 2, 1 At, and 2I2 Bi. Preferred drugs include methotrexate, and pyrimidine and purine analogs. Preferred differentiation inducers include phorbol esters and butyric acid. Preferred toxins include ricin, abrin, diptheria toxin, cholera toxin, gelonin, Pseudomonas exotoxin, Shigella toxin, and pokeweed antiviral protein. For diagnostic puφoses, coupling of radioactive agents may be used to facilitate tracing of metastases or to determine the location of WTl -positive tumors. A therapeutic agent may be coupled (e.g., covalently bonded) to a suitable monoclonal antibody either directly or indirectly (e.g., via a linker group). A direct reaction between an agent and an antibody is possible when each possesses a substituent capable of reacting with the other. For example, a nucleophilic group, such as an amino or sulfhydryl group, on one may be capable of reacting with a carbonyl- containing group, such as an anhydride or an acid halide, or with an alkyl group containing a good leaving group (e.g., a halide) on the other. Alternatively, it may be desirable to couple a therapeutic agent and an antibody via a linker group. A linker group can function as a spacer to distance an antibody from an agent in order to avoid interference with binding capabilities. A linker group can also serve to increase the chemical reactivity of a substituent on an agent or an antibody, and thus increase the coupling efficiency. An increase in chemical reactivity may also facilitate the use of agents, or functional groups on agents, which otherwise would not be possible. It will be evident to those skilled in the art that a variety of bifunctional or polyfunctional reagents, both homo- and hetero-functional (such as those described in the catalog of the Pierce Chemical Co., Rockford, IL), may be employed as the linker group. Coupling may be effected, for example, through amino groups, carboxyl groups, sulfhydryl groups or oxidized carbohydrate residues. There are numerous references describing such methodology, e.g., U.S. Patent No. 4,671,958, to Rodwell et al. Where a therapeutic agent is more potent when free from the antibody portion of the immunoconjugates of the present invention, it may be desirable to use a linker group which is cleavable during or upon internalization into a cell. A number of different cleavable linker groups have been described. The mechanisms for the intracellular release of an agent from these linker groups include cleavage by reduction of a disulfide bond (e.g., U.S. Patent No. 4,489,710, to Spitler), by irradiation of a photolabile bond (e.g., U.S. Patent No. 4,625,014, to Senter et al.), by hydrolysis of derivatized amino acid side chains (e.g., U.S. Patent No. 4,638,045, to Kohn et al.), by serum complement-mediated hydrolysis (e.g., U.S. Patent No. 4,671,958, to Rodwell et al.), and acid-catalyzed hydrolysis (e.g., U.S. Patent No. 4,569,789, to Blattler et al.). It may be desirable to couple more than one agent to an antibody. In one embodiment, multiple molecules of an agent are coupled to one antibody molecule. In another embodiment, more than one type of agent may be coupled to one antibody. Regardless of the particular embodiment, immunoconjugates with more than one agent may be prepared in a variety of ways. For example, more than one agent may be coupled directly to an antibody molecule, or linkers which provide multiple sites for attachment can be used. Alternatively, a carrier can be used. A carrier may bear the agents in a variety of ways, including covalent bonding either directly or via a linker group. Suitable carriers include proteins such as albumins (e.g., U.S. Patent No. 4,507,234, to Kato et al.), peptides and polysaccharides such as aminodextran (e.g., U.S. Patent No. 4,699,784, to Shih et al.). A carrier may also bear an agent by noncovalent bonding or by encapsulation, such as within a liposome vesicle (e.g., U.S. Patent Nos. 4,429,008 and 4,873,088). Carriers specific for radionuclide agents include radiohalogenated small molecules and chelating compounds. For example, U.S. Patent No. 4,735,792 discloses representative radiohalogenated small molecules and their synthesis. A radionuclide chelate may be formed from chelating compounds that include those containing nitrogen and sulfur atoms as the donor atoms for binding the metal, or metal oxide, radionuclide. For example, U.S. Patent No. 4,673,562, to Davison et al. discloses representative chelating compounds and their synthesis. A variety of routes of administration for the antibodies and immunoconjugates may be used. Typically, administration will be intravenous, intramuscular, subcutaneous or in the bed of a resected tumor. It will be evident that the precise dose of the antibody/immunoconjugate will vary depending upon the antibody used, the antigen density on the tumor, and the rate of clearance of the antibody. Also provided herein are anti-idiotypic antibodies that mimic an immunogenic portion of WTl . Such antibodies may be raised against an antibody, or antigen-binding fragment thereof, that specifically binds to an immunogenic portion of WTl, using well known techniques. Anti-idiotypic antibodies that mimic an immunogenic portion of WTl are those antibodies that bind to an antibody, or antigen- binding fragment thereof, that specifically binds to an immunogenic portion of WTl, as described herein. T CELLS Immunotherapeutic compositions may also, or alternatively, comprise T cells specific for WTl. Such cells may generally be prepared in vitro or ex vivo, using standard procedures. For example, T cells may be present within (or isolated from) bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood of a mammal, such as a patient, using a commercially available cell separation system, such as the CEPRATE™ system, available from CellPro Inc., Bothell WA (see also U.S. Patent No. 5,240,856; U.S. Patent No. 5,215,926; WO 89/06280; WO 91/16116 and WO 92/07243). Alternatively, T cells may be derived from related or unrelated humans, non-human animals, cell lines or cultures. T cells may be stimulated with WTl polypeptide, polynucleotide encoding a WTl polypeptide and/or an antigen presenting cell (APC) that expresses a WTl polypeptide. Such stimulation is performed under conditions and for a time sufficient to permit the generation of T cells that are specific for the WTl polypeptide. Preferably, a WTl polypeptide or polynucleotide is present within a delivery vehicle, such as a microsphere, to facilitate the generation of antigen-specific T cells. Briefly, T cells, which may be isolated from a patient or a related or unrelated donor by routine techniques (such as by Ficoll/Hypaque density gradient centrifugation of peripheral blood lymphocytes), are incubated with WTl polypeptide. For example, T cells may be incubated in vitro for 2-9 days (typically 4 days) at 37°C with WTl polypeptide (e.g., 5 to 25 μg/ml) or cells synthesizing a comparable amount of WTl polypeptide. It may be desirable to incubate a separate aliquot of a T cell sample in the absence of WTl polypeptide to serve as a control. T cells are considered to be specific for a WTl polypeptide if the T cells kill target cells coated with a WTl polypeptide or expressing a gene encoding such a polypeptide. T cell specificity may be evaluated using any of a variety of standard techniques. For example, within a chromium release assay or proliferation assay, a stimulation index of more than two fold increase in lysis and/or proliferation, compared to negative controls, indicates T cell specificity. Such assays may be performed, for example, as described in Chen et al., Cancer Res. 54:1065-1070, 1994. Alternatively, detection of the proliferation of T cells may be accomplished by a variety of known techniques. For example, T cell proliferation can be detected by measuring an increased rate of DNA synthesis (e.g., by pulse-labeling cultures of T cells with tritiated thymidine and measuring the amount of tritiated thymidine incoφorated into DNA). Other ways to detect T cell proliferation include measuring increases in interleukin-2 (IL-2) production, Cε + flux, or dye uptake, such as 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyl-tetrazolium. Alternatively, synthesis of lymphokines (such as interferon- gamma) can be measured or the relative number of T cells that can respond to a WTl polypeptide may be quantified. Contact with a WTl polypeptide (200 ng/ml - 100 μg/ml, preferably 100 ng/ml - 25 μg/ml) for 3 - 7 days should result in at least a two fold increase in proliferation of the T cells and/or contact as described above for 2-3 hours should result in activation of the T cells, as measured using standard cytokine assays in which a two fold increase in the level of cytokine release (e.g., TNF or IFN-γ) is indicative of T cell activation (see Coligan et al., Current Protocols in Immunology, vol. 1, Wiley Interscience (Greene 1998). WTl specific T cells may be expanded using standard techniques. Within preferred embodiments, the T cells are derived from a patient or a related or unrelated donor and are administered to the patient following stimulation and expansion. T cells that have been activated in response to a WTl polypeptide, polynucleotide or WTl -expressing APC may be CD4 + and/or CD8 + . Specific activation of CD4 + or CD8 + T cells may be detected in a variety of ways. Methods for detecting specific T cell activation include detecting the proliferation of T cells, the production of cytokines (e.g., lymphokines), or the generation of cytolytic activity (i.e., generation of cytotoxic T cells specific for WTl). For CD4 + T cells, a preferred method for detecting specific T cell activation is the detection of the proliferation of T cells. For CD8 + T cells, a preferred method for detecting specific T cell activation is the detection of the generation of cytolytic activity. For therapeutic puφoses, CD4 + or CD8 + T cells that proliferate in response to the WTl polypeptide, polynucleotide or APC can be expanded in number either in vitro or in vivo. Proliferation of such T cells in vitro may be accomplished in a variety of ways. For example, the T cells can be re-exposed to WTl polypeptide, with or without the addition of T cell growth factors, such as interleukin-2, and/or stimulator cells that synthesize a WTl polypeptide. The addition of stimulator cells is preferred where generating CD8 + T cell responses. T cells can be grown to large numbers in vitro with retention of specificity in response to intermittent restimulation with WTl polypeptide. Briefly, for the primary in vitro stimulation (IVS), large numbers of lymphocytes (e.g., greater than 4 x 10?) may be placed in flasks with media containing human serum. WTl polypeptide (e.g., peptide at 10 μg/ml) may be added directly, along with tetanus toxoid (e.g., 5 μg/ml). The flasks may then be incubated (e.g., 37°C for 7 days). For a second IVS, T cells are then harvested and placed in new flasks with 2-3 x 10^ irradiated peripheral blood mononuclear cells. WTl polypeptide (e.g., 10 μg/ml) is added directly. The flasks are incubated at 37°C for 7 days. On day 2 and day 4 after the second IVS, 2-5 units of interleukin-2 (IL-2) may be added. For a third IVS, the T cells may be placed in wells and stimulated with the individual's own EBV transformed B cells coated with the peptide. IL-2 may be added on days 2 and 4 of each cycle. As soon as the cells are shown to be specific cytotoxic T cells, they may be expanded using a 10 day stimulation cycle with higher IL-2 (20 units) on days 2, 4 and 6. Alternatively, one or more T cells that proliferate in the presence of WTl polypeptide can be expanded in number by cloning. Methods for cloning cells are well known in the art, and include limiting dilution. Responder T cells may be purified from the peripheral blood of sensitized patients by density gradient centrifugation and sheep red cell rosetting and established in culture by stimulating with the nominal antigen in the presence of irradiated autologous filler cells. In order to generate CD4 + T cell lines, WTl polypeptide is used as the antigenic stimulus and autologous peripheral blood lymphocytes (PBL) or lymphoblastoid cell lines (LCL) immortalized by infection with Epstein Barr virus are used as antigen presenting cells. In order to generate CD8 + T cell lines, autologous antigen-presenting cells transfected with an expression vector which produces WTl polypeptide may be used as stimulator cells. Established T cell lines may be cloned 2-4 days following antigen stimulation by plating stimulated T cells at a frequency of 0.5 cells per well in 96-well flat-bottom plates with 1 x 10^ irradiated PBL or LCL cells and recombinant interleukin-2 (rIL2) (50 U/ml). Wells with established clonal growth may be identified at approximately 2-3 weeks after initial plating and restimulated with appropriate antigen in the presence of autologous antigen-presenting cells, then subsequently expanded by the addition of low doses of rIL2 (10 U/ml) 2-3 days following antigen stimulation. T cell clones may be maintained in 24-well plates by periodic restimulation with antigen and rIL2 approximately every two weeks. Within certain embodiments, allogeneic T-cells may be primed (i.e., sensitized to WTl) in vivo and/or in vitro. Such priming may be achieved by contacting T cells with a WTl polypeptide, a polynucleotide encoding such a polypeptide or a cell producing such a polypeptide under conditions and for a time sufficient to permit the priming of T cells. In general, T cells are considered to be primed if, for example, contact with a WTl polypeptide results in proliferation and/or activation of the T cells, as measured by standard proliferation, chromium release and/or cytokine release assays as described herein. A stimulation index of more than two fold increase in proliferation or lysis, and more than three fold increase in the level of cytokine, compared to negative controls, indicates T-cell specificity. Cells primed in vitro may be employed, for example, within a bone marrow transplantation or as donor lymphocyte infusion. PHARMACEUTICAL COMPOSITIONS AND VACCINES Within certain aspects, polypeptides, polynucleotides, antibodies and/or T cells may be incoφorated into pharmaceutical compositions or vaccines. Alternatively, a pharmaceutical composition may comprise an antigen-presenting cell_ (e.g., a dendritic cell) transfected with a WTl polynucleotide such that the antigen presenting cell expresses a WTl polypeptide. Pharmaceutical compositions comprise one or more such compounds or cells and a physiologically acceptable carrier or excipient. Certain vaccines may comprise one or more such compounds or cells and a non-specific immune response enhancer, such as an adjuvant or a liposome (into which the compound is incoφorated). Pharmaceutical compositions and vaccines may additionally contain a delivery system, such as biodegradable microspheres which are disclosed, for example, in U.S. Patent Nos. 4,897,268 and 5,075,109. Pharmaceutical compositions and vaccines within the scope of the present invention may also contain other compounds, which may be biologically active or inactive. Within certain embodiments, pharmaceutical compositions and vaccines are designed to elicit T cell responses specific for a WTl polypeptide in a patient, such as a human. In general, T cell responses may be favored through the use of relatively short polypeptides (e.g., comprising less than 23 consecutive amino acid residues of a native WTl polypeptide, preferably 4-16 consecutive residues, more preferably 8-16 consecutive residues and still more preferably 8-10 consecutive residues. Alternatively, or in addition, a vaccine may comprise a non-specific immune response enhancer that preferentially enhances a T cell response. In other words, the immune response enhancer may enhance the level of a T cell response to a WTl polypeptide by an amount that is proportionally greater than the amount by which an antibody response is enhanced. For example, when compared to a standard oil based adjuvant, such as CFA, an immune response enhancer that preferentially enhances a T cell response may enhance a proliferative T cell response by at least two fold, a lytic response by at least 10%>, and/or T cell activation by at least two fold compared to WTl-megative control cell lines, while not detectably enhancing an antibody response. The amount by which a T cell or antibody response to a WTl polypeptide is enhanced may generally be determined using any representative technique known in the art, such as the techniques provided herein. A pharmaceutical composition or vaccine may contain DNA encoding one or more of the polypeptides as described above, such that the polypeptide is_ generated in situ. As noted above, the DNA may be present within any of a variety of delivery systems known to those of ordinary skill in the art, including nucleic acid expression systems, bacterial and viral expression systems and mammalian expression systems. Appropriate nucleic acid expression systems contain the necessary DNA, cDNA or RNA sequences for expression in the patient (such as a suitable promoter and terminating signal). Bacterial delivery systems involve the administration of a bacterium (such as Bacillus-Calmette-Guerri ) that expresses an immunogenic portion of the polypeptide on its cell surface. In a preferred embodiment, the DNA may be introduced using a viral expression system (e.g., vaccinia or other pox vims, retrovims, or adenovirus), which may involve the use of a non-pathogenic (defective), replication competent vims. Techniques for incoφorating DNA into such expression systems are well known to those of ordinary skill in the art. The DNA may also be "naked," as described, for example, in Ulmer et al., Science 259: 1745-1749, 1993 and reviewed by Cohen, Science 259:1691-1692, 1993. The uptake of naked DNA may be increased by coating the DNA onto biodegradable beads, which are efficiently transported into the cells. As noted above, a pharmaceutical composition or vaccine may comprise an antigen-presenting cell that expresses a WTl polypeptide. For therapeutic puφoses, as described herein, the antigen presenting cell is preferably an autologous dendritic cell. Such cells may be prepared and transfected using standard techniques, such as those described by Reeves et al., Cancer Res. 56:5612-5611, 1996; Tuting et al., J. Immunol 7(50:1139-1147, 1998; and Nair et al., Nature Biotechnol 7(5:364-369, 1998). Expression of a WTl polypeptide on the surface of an antigen-presenting cell may be confirmed by in vitro stimulation and standard proliferation as well as chromium release assays, as described herein. While any suitable carrier known to those of ordinary skill in the art may be employed in the pharmaceutical compositions of this invention, the type of carrier will vary depending on the mode of administration. Compositions of the present invention may be formulated for any appropriate manner of administration, including for example, topical, oral, nasal, intravenous, intracranial, intraperitoneal, subcutaneous or intramuscular administration. For parenteral administration, such as subcutaneous injection, the carrier preferably comprises water, saline, alcohol, a fat, a wax or a buffer. For oral administration, any of the above carriers or a solid carrier, such as mannitol, lactose, starch, magnesium stearate, sodium saccharine, talcum, cellulose, glucose, sucrose, and magnesium carbonate, may be employed. Biodegradable microspheres (e.g., polylactate polyglycolate) may also be employed as carriers for the pharmaceutical compositions of this invention. For certain topical applications, formulation as a cream or lotion, using well known components, is preferred. Such compositions may also comprise buffers (e.g., neutral buffered saline or phosphate buffered saline), carbohydrates (e.g., glucose, mannose, sucrose or dextrans), mannitol, proteins, polypeptides or amino acids such as glycine, antioxidants, chelating agents such as EDTA or glutathione, adjuvants (e.g., aluminum hydroxide) and/or preservatives. Alternatively, compositions of the present invention may be formulated as a lyophilizate. Compounds may also be encapsulated within liposomes using well known technology. Any of a variety of non-specific immune response enhancers, such as adjuvants, may be employed in the vaccines of this invention. Most adjuvants contain a substance designed to protect the antigen from rapid catabolism, such as aluminum hydroxide or mineral oil, and a stimulator of immune responses, such as lipid A, Bortadella pertussis or Mycobacterium tuberculosis derived proteins. Suitable nonspecific immune response enhancers include alum-based adjuvants (e.g., Alhydrogel, Rehydragel, aluminum phosphate, Algammulin, aluminum hydroxide); oil based adjuvants (Freund's adjuvant (FA), Specol, RIBI, TiterMax, Montanide ISA50 or Seppic MONTANIDE ISA 720; cytokines (e.g., GM-CSF or Flat3 -ligand); microspheres; nonionic block copolymer-based adjuvants; dimethyl dioctadecyl ammoniumbromide (DDA) based adjuvants AS-1, AS-2 (Smith Kline Beecham); Ribi Adjuvant system based adjuvants; QS21 (Aquila); saponin based adjuvants (cmde saponin, the saponin Quil A ); muramyl dipeptide (MDP) based adjuvants such as SAF (Syntex adjuvant in its microfluidized form (SAF-m)); dimethyl-dioctadecyl ammonium bromide (DDA); human complement based adjuvants m. vaccae and derivatives; immune stimulating complex (iscom) based adjuvants; inactivated toxins; and attenuated infectious agents (such as M. tuberculosis). As noted above, within certain embodiments, immune response enhancers are chosen for their ability to preferentially elicit or enhance a T cell response (e.g., CD4 + and/or CD8 + ) to a WTl polypeptide. Such immune response enhancers are well known in the art, and include (but are not limited to) Montanide ISA50, Seppic MONTANIDE ISA 720, cytokines (e.g., GM-CSF, Flat3 -ligand), microspheres, dimethyl dioctadecyl ammoniumbromide (DDA) based adjuvants, AS-1 (Smith Kline Beecham), AS-2 (Smith Kline Beecham), Ribi Adjuvant system based adjuvants, QS21 (Aquila), saponin based adjuvants (crude saponin, the saponin Quil A), Syntex adjuvant in its microfluidized form (SAF-m), MV, ddMV (Genesis), immune stimulating complex (iscom) based adjuvants and inactivated toxins. The compositions and vaccines described herein may be administered as part of a sustained release formulation (i.e., a formulation such as a capsule or sponge that effects a slow release of compound following administration). Such formulations may generally be prepared using well known technology and administered by, for example, oral, rectal or subcutaneous implantation, or by implantation at the desired target site. Sustained-release formulations may contain a polypeptide, polynucleotide, antibody or cell dispersed in a carrier matrix and/or contained within a reservoir surrounded by a rate controlling membrane. Carriers for use within such formulations are biocompatible, and may also be biodegradable; preferably the formulation provides a relatively constant level of active component release. The amount of active compound contained within a sustained release formulation depends upon the site of implantation, the rate and expected duration of release and the nature of the condition to be treated or prevented. THERAPY OF MALIGNANT DISEASES In further aspects of the present invention, the compositions and vaccines described herein may be used to inhibit the development of malignant diseases (e.g., progressive or metastatic diseases or diseases characterized by small tumor burden such as minimal residual disease). In general, such methods may be used to prevent, delay or treat a disease associated with WTl expression. In other words, therapeutic methods provided herein may be used to treat an existing WTl -associated disease, or may be used to prevent or delay the onset of such a disease in a patient who is free of disease or who is afflicted with a disease that is not yet associated with WTl expression. As used herein, a disease is "associated with WTl expression" if diseased cells (e.g., tumor cells) at some time during the course of the disease generate detectably higher levels of a WTl polypeptide than normal cells of the same tissue. Association of WTl expression with a malignant disease does not require that WTl be present on a tumor. For example, overexpression of WTl may be involved with initiation of a tumor, but the protein expression may subsequently be lost. Alternatively, a malignant disease that is not characterized by an increase in WTl expression may, at a later time, progress to a disease that is characterized by increased WTl expression. Accordingly, any malignant disease in which diseased cells formerly expressed, currently express or are expected to subsequently express increased levels of WTl is considered to be "associated with WTl expression." Immunotherapy may be performed using any of a variety of techniques, in which compounds or cells provided herein function to remove WTl -expressing cells from a patient. Such removal may take place as a result of enhancing or inducing an immune response in a patient specific for WTl or a cell expressing WTl . Alternatively, WTl -expressing cells may be removed ex vivo (e.g., by treatment of autologous bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood). Fractions of bone marrow or peripheral blood may be obtained using any standard technique in the art. Within such methods, pharmaceutical compositions and vaccines may be administered to a patient. As used herein, a "patient" refers to any warm-blooded animal, preferably a human. A patient may or may not be afflicted with a malignant disease. Accordingly, the above pharmaceutical compositions and vaccines may be used to prevent the onset of a disease ( . e., prophylactically) or to treat a patient afflicted with a disease (e.g., to prevent or delay progression and/or metastasis of an existing disease). A patient afflicted with a disease may have a minimal residual disease (e.g., a low tumor burden in a leukemia patient in complete or partial remission or a cancer patient following reduction of the tumor burden after surgery radiotherapy and/or chemotherapy). Such a patient may be immunized to inhibit a relapse (i.e., prevent or delay the relapse, or decrease the severity of a relapse). Within certain preferred embodiments, the patient is afflicted with a leukemia (e.g., AML, CML, ALL or childhood ALL), a myelodysplastic syndrome (MDS) or a cancer (e.g., gastrointestinal, lung, thyroid or breast cancer or a melanoma), where the cancer or leukemia is WTl positive (i.e., reacts detectably with an anti-WTl antibody, as provided herein or expresses WTl mRNA at a level detectable by RT-PCR, as described herein) or suffers from an autoimmune disease directed against WTl -expressing cells. The compositions provided herein may be used alone or in combination with conventional therapeutic regimens such as surgery, irradiation, chemotherapy and/or bone marrow transplantation (autologous, syngeneic, allogeneic or unrelated). As discussed in greater detail below, binding agents and T cells as provided herein may be used for purging of autologous stem cells. Such purging may be beneficial prior to, for example, bone marrow transplantation or transfusion of blood or components thereof. Binding agents, T cells, antigen presenting cells (APC) and compositions provided herein may further be used for expanding and stimulating (or priming) autologous, allogeneic, syngeneic or unrelated WTl -specific T-cells in vitro and/or in vivo. Such WTl -specific T cells may be used, for example, within donor lymphocyte infusions. Routes and frequency of administration, as well as dosage, will vary from individual to individual, and may be readily established using standard techniques. In general, the pharmaceutical compositions and vaccines may be administered by injection (e.g., intracutaneous, intramuscular, intravenous or subcutaneous), intranasally (e.g., by aspiration) or orally. In some tumors, pharmaceutical compositions or vaccines may be administered locally (by, for example, rectocoloscopy, gastroscopy, videoendoscopy, angiography or other methods known in the art). Preferably, between 1 and 10 doses may be administered over a 52 week period. Preferably, 6 doses are administered, at intervals of 1 month, and booster vaccinations may be given periodically thereafter. Alternate protocols may be appropriate for individual patients. A suitable dose is an amount of a compound that, when administered as described above, is capable of promoting an anti-tumor immune response that is at least 10-50%) above the basal (i.e., untreated) level. Such response can be monitored by measuring the anti-tumor antibodies in a patient or by vaccine-dependent generation of cytolytic effector cells capable of killing the patient's tumor cells in vitro. Such vaccines should also be capable of causing an immune response that leads to an improved clinical outcome (e.g., more frequent complete or partial remissions, or longer disease-free and/or overall survival) in vaccinated patients as compared to non- vaccinated patients. In general, for pharmaceutical compositions and vaccines comprising one or more polypeptides, the amount of each polypeptide present in a dose ranges from about 100 μg to 5 mg. Suitable dose sizes will vary with the size of the patient, but will typically range from about 0.1 mL to about 5 mL. In general, an appropriate dosage and treatment regimen provides the active compound(s) in an amount sufficient to provide therapeutic and/or prophylactic benefit. Such a response can be monitored by establishing an improved clinical outcome (e.g., more frequent complete or partial remissions, or longer disease-free and/or overall survival) in treated patients as compared to non-treated patients. Increases in preexisting immune responses to WTl generally correlate with an improved clinical outcome. Such immune responses may generally be evaluated using standard proliferation, cytotoxicity or cytokine assays, which may be performed using samples obtained from a patient before and after treatment. Within further aspects, methods for inhibiting the development of a malignant disease associated with WTl expression involve the administration of autologous T cells that have been activated in response to a WTl polypeptide or WT1- expressing APC, as described above. Such T cells may be CD4 + and/or CD8 + , and may be proliferated as described above. The T cells may be administered to the individual in an amount effective to inhibit the development of a malignant disease. Typically, about 9 11 2 1 x 10 to 1 x 10 T cells/M are administered intravenously, intracavitary or in the bed of a resected tumor. It will be evident to those skilled in the art that the number of cells and the frequency of administration will be dependent upon the response of the patient. Within certain embodiments, T cells may be stimulated prior to an autologous bone marrow transplantation. Such stimulation may take place in vivo or in vitro. For in vitro stimulation, bone marrow and/or peripheral blood (or a fraction of bone marrow or peripheral blood) obtained from a patient may be contacted with a WTl polypeptide, a polynucleotide encoding a WTl polypeptide and/or an APC that expresses a WTl polypeptide under conditions and for a time sufficient to permit the stimulation of T cells as described above. Bone marrow, peripheral blood stem cells and/or WTl -specific T cells may then be administered to a patient using standard techniques. Within related embodiments, T cells of a related or unrelated donor may be stimulated prior to a syngeneic or allogeneic (related or unrelated) bone marrow transplantation. Such stimulation may take place in vivo or in vitro. For in vitro stimulation, bone marrow and/or peripheral blood (or a fraction of bone marrow or peripheral blood) obtained from a related or unrelated donor may be contacted with a WTl polypeptide, WTl polynucleotide and/or APC that expresses a WTl polypeptide under conditions and for a time sufficient to permit the stimulation of T cells as described above. Bone marrow, peripheral blood stem cells and/or WTl -specific T cells may then be administered to a patient using standard techniques. Within other embodiments, WTl -specific T cells as described herein may be used to remove cells expressing WTl from autologous bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood (e.g., CD34 + enriched peripheral blood (PB) prior to administration to a patient). Such methods may be performed by contacting bone marrow or PB with such T cells under conditions and for a time sufficient to permit the reduction of WTl expressing cells to less than 10%>, preferably less than 5% and more preferably less than 1%, of the total number of myeloid or lymphatic cells in the bone marrow or peripheral blood. The extent to which such cells have been removed may be readily determined by standard methods such as, for example, qualitative and quantitative PCR analysis, moφhology, immunohistochemistry and FACS analysis. Bone marrow or PB (or a fraction thereof) may then be administered to a patient using standard techniques. DIAGNOSTIC METHODS The present invention further provides methods for detecting a malignant disease associated with WTl expression, and for monitoring the effectiveness of an immunization or therapy for such a disease. Such methods are based on the discovery, within the present invention, that an immune response specific for WTl protein can be detected in patients afflicted with such diseases, and that methods which enhance such immune responses may provide a preventive or therapeutic benefit. To determine the presence or absence of a malignant disease associated with WTl expression, a patient may be tested for the level of T cells specific for WTl. Within certain methods, a biological sample comprising CD4 + and/or CD8 + T cells isolated from a patient is incubated with a WTl polypeptide, a polynucleotide encoding a WTl polypeptide and/or an APC that expresses a WTl polypeptide, and the presence or absence of specific activation of the T cells is detected, as described herein. Suitable biological samples include, but are not limited to, isolated T cells. For example, T cells may be isolated from a patient by routine techniques (such as by Ficoll/Hypaque density gradient centrifugation of peripheral blood lymphocytes). T cells may be incubated in vitro for 2-9 days (typically 4 days) at 37°C with WTl polypeptide (e.g., 5 - 25 μg/ml). It may be desirable to incubate another aliquot of a T cell sample in the absence of WTl polypeptide to serve as a control. For CD4" T cells, activation is preferably detected by evaluating proliferation of the T cells. For CD8 + T cells, activation is preferably detected by evaluating cytolytic activity. A level of proliferation that is at least two fold greater and/or a level of cytolytic activity that is at least 20% greater than in disease- free patients indicates the presence of a malignant disease associated with WTl expression. Further correlation may be made, using methods well known in the art, between the level of proliferation and/or cytolytic activity and the predicted response to therapy. In particular, patients that display a higher antibody, proliferative and/or lytic response may be expected to show a greater response to therapy. Within other methods, a biological sample obtained from a patient is tested for the level of antibody specific for WTl. The biological sample is incubated with a WTl polypeptide, a polynucleotide encoding a WTl polypeptide and/or an APC that expresses a WTl polypeptide under conditions and for a time sufficient to allow immunocomplexes to form. Immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide are then detected. A biological sample for use within such methods may be any sample obtained from a patient that would be expected to contain antibodies. Suitable biological samples include blood, sera, ascites, bone marrow, pleural effusion, and cerebrospinal fluid. The biological sample is incubated with the WTl polypeptide in a reaction mixture under conditions and for a time sufficient to permit immunocomplexes to form between the polypeptide and antibodies specific for WTl. For example, a biological sample and WTl polypeptide may be incubated at 4°C for 24-48 hours. Following the incubation, the reaction mixture is tested for the presence of immunocomplexes. Detection of immunocomplexes formed between the WTl polypeptide and antibodies present in the biological sample may be accomplished by a variety of known techniques, such as radioimmunoassays (RIA) and enzyme linked immunosorbent assays (ELISA). Suitable assays are well known in the art and are amply described in the scientific and patent literature (e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988). Assays that may be used include, but are not limited to, the double monoclonal antibody sandwich immunoassay technique of David et al. (U.S. Patent 4,376.110); monoclonal-polyclonal antibody sandwich assays (Wide et al., in Kirkham and Hunter, eds., Radioimmunoassay Methods, E. and S. Livingstone, Edinburgh, 1970); the "western blot" method of Gordon et al. (U.S. Patent 4,452,901); immunoprecipitation of labeled ligand (Brown et al, J. Biol. Chem. 255:4980-4983, 1980); enzyme-linked immunosorbent assays as described by, for example, Raines and Ross (J. Biol. Chem. 257:5154-5160, 1982); immunocytochemical techniques, including the use of fluorochromes (Brooks et al, Clin. Exp. Immunol. 39: 477, 1980); and neutralization of activity (Bowen-Pope et al., Proc. Natl Acad. Sci. USA 81:2396-2400, 1984). Other immunoassays include, but are not limited to, those described in U.S. Patent Nos.: 3,817,827; 3,850,752; 3,901,654; 3,935,074; 3,984,533; 3,996,345; 4,034,074; and 4,098,876. For detection puφoses, WTl polypeptide may either be labeled or unlabeled. Unlabeled WTl polypeptide may be used in agglutination assays or in combination with labeled detection reagents that bind to the immunocomplexes (e.g., anti-immunoglobulin, protein G, protein A or a lectin and secondary antibodies, or antigen-binding fragments thereof, capable of binding to the antibodies that specifically bind to the WTl polypeptide). If the WTl polypeptide is labeled, the reporter group may be any suitable reporter group known in the art, including radioisotopes, fluorescent groups, luminescent groups, enzymes, biotin and dye particles. Within certain assays, unlabeled WTl polypeptide is immobilized on a solid support. The solid support may be any material known to those of ordinary skill in the art to which the polypeptide may be attached. For example, the solid support may be a test well in a microtiter plate or a nitrocellulose or other suitable membrane. Alternatively, the support may be a bead or disc, such as glass, fiberglass, latex or a plastic material such as polystyrene or polyvinylchloride. The support may also be a magnetic particle or a fiber optic sensor, such as those disclosed, for example, in U.S. Patent No. 5,359,681. The polypeptide may be immobilized on the solid support using a variety of techniques known to those of skill in the art, which are amply described in the patent and scientific literature. In the context of the present invention, the term "immobilization" refers to both noncovalent association, such as adsoφtion, and covalent attachment (which may be a direct linkage between the antigen and functional groups on the support or may be a linkage by way of a cross-linking agent). Immobilization by adsoφtion to a well in a microtiter plate or to a membrane is preferred. In such cases, adsoφtion may be achieved by contacting the WTl polypeptide, in a suitable buffer, with the solid support for a suitable amount of time. The contact time varies with temperature, but is typically between about 1 hour and about 1 day. In general, contacting a well of a plastic microtiter plate (such as polystyrene or polyvinylchloride) with an amount of polypeptide ranging from about 10 ng to about 10 μg, and preferably about 100 ng to about 1 μg, is sufficient to immobilize an adequate amount of polypeptide. Following immobilization, the remaining protein binding sites on the support are typically blocked. Any suitable blocking agent known to those of ordinary skill in the art, such as bovine semm albumin, Tween 20™ (Sigma Chemical Co., St. Louis, MO), heat-inactivated normal goat semm (NGS), or BLOTTO (buffered solution of nonfat dry milk which also contains a preservative, salts, and an antifoaming agent). The support is then incubated with a biological sample suspected of containing specific antibody. The sample can be applied neat, or, more often, it can be diluted, usually in a buffered solution which contains a small amount (0.1%>-5.0%> by weight) of protein, such as BSA, NGS, or BLOTTO. In general, an appropriate contact time (i.e., incubation time) is a period of time that is sufficient to detect the presence of antibody that specifically binds WTl within a sample containing such an antibody. Preferably, the contact time is sufficient to achieve a level of binding that is at least about 95%> of that achieved at equilibrium between bound and unbound antibody. Those of ordinary skill in the art will recognize that the time necessary to achieve equilibrium may be readily determined by assaying the level of binding that occurs over a period of time. At room temperature, an incubation time of about 30 minutes is generally sufficient. Unbound sample may then be removed by washing the solid support with an appropriate buffer, such as PBS containing 0.1%) Tween 20™. A detection reagent that binds to the immunocomplexes and that comprises a reporter group may then be added. The detection reagent is incubated with the immunocomplex for an amount of time sufficient to detect the bound antibody. An appropriate amount of time may generally be determined by assaying the level of binding that occurs over a period of time. Unbound detection reagent is then removed and bound detection reagent is detected using the reporter group. The method employed for detecting the reporter group depends upon the nature of the reporter group. For radioactive groups, scintillation counting or autoradiographic methods are generally appropriate. Spectroscopic methods may be used to detect dyes, luminescent groups and fluorescent groups. Biotin may be detected using avidin, coupled to a different reporter group (commonly a radioactive or fluorescent group or an enzyme). Enzyme reporter groups (e.g., horseradish peroxidase, beta-galactosidase, alkaline phosphatase and glucose oxidase) may generally be detected by the addition of substrate (generally for a specific period of time), followed by spectroscopic or other analysis of the reaction products. Regardless of the specific method employed, a level of bound detection reagent that is at least two fold greater than background (i.e., the level observed for a biological sample obtained from a disease-free individual) indicates the presence of a malignant disease associated with WTl expression. In general, methods for monitoring the effectiveness of an immunization or therapy involve monitoring changes in the level of antibodies or T cells specific for WTl in the patient. Methods in which antibody levels are monitored may comprise the steps of: (a) incubating a first biological sample, obtained from a patient prior to a therapy or immunization, with a WTl polypeptide, wherein the incubation is performed under conditions and for a time sufficient to allow immunocomplexes to form; (b) detecting immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide; (c) repeating steps (a) and (b) using a second biological sample taken from the patient following therapy or immunization; and (d) comparing the number of immunocomplexes detected in the first and second biological samples. Alternatively, a polynucleotide encoding a WTl polypeptide, or an APC expressing a WTl polypeptide may be employed in place of the WTl polypeptide. Within such methods, immunocomplexes between the WTl polypeptide encoded by the polynucleotide, or expressed by the APC, and antibodies in the biological sample are detected. Methods in which T cell activation and/or the number of WTl specific precursors are monitored may comprise the steps of: (a) incubating a first biological sample comprising CD4+ and/or CD8+ cells (e.g., bone marrow, peripheral blood or a fraction thereof), obtained from a patient prior to a therapy or immunization, with a WTl polypeptide, wherein the incubation is performed under conditions and for a time sufficient to allow specific activation, proliferation and/or lysis of T cells; (b) detecting an amount of activation, proliferation and/or lysis of the T cells; (c) repeating steps (a) and (b) using a second biological sample comprising CD4+ and/or CD8+ T cells, and taken from the same patient following therapy or immunization; and (d) comparing the amount of activation, proliferation and/or lysis of T cells in the first and second biological samples. Alternatively, a polynucleotide encoding a WTl polypeptide, or an APC expressing a WTl polypeptide may be employed in place of the WTl polypeptide. A biological sample for use within such methods may be any sample obtained from a patient that would be expected to contain antibodies, CD4+ T cells and/or CD8+ T cells. Suitable biological samples include blood, sera, ascites, bone marrow, pleural effusion and cerebrospinal fluid. A first biological sample may be obtained prior to initiation of therapy or immunization or part way through a therapy or vaccination regime. The second biological sample should be obtained in a similar manner, but at a time following additional therapy or immunization. The second biological sample may be obtained at the completion of, or part way through, therapy or immunization, provided that at least a portion of therapy or immunization takes place between the isolation of the first and second biological samples. Incubation and detection steps for both samples may generally be performed as described above. A statistically significant increase in the number of immunocomplexes in the second sample relative to the first sample reflects successful therapy or immunization. The following Examples are offered by way of illustration and not by way of limitation. EXAMPLES Example 1 Identification of an Immune Response to WTl in Patients with Hematological Malignancies This Example illustrates the identification of an existent immune response in patients with a hematological malignancy. To evaluate the presence of preexisting WTl specific antibody responses in patients, sera of patients with AML, ALL, CML and severe aplastic anemia were analyzed using Western blot analysis. Sera were tested for the ability to immunoprecipitate WTl from the human leukemic cell line K562 (American Type Culture Collection, Manassas, VA). In each case, immunoprecipitates were separated by gel electrophoresis, transferred to membrane and probed with the anti WT-1 antibody WTl 80 (Santa Cruz Biotechnology, Inc., Santa C z, CA). This Western blot analysis identified potential WTl specific antibodies in patients with hematological malignancy. A representative Western blot showing the results for a patient with AML is shown in Figure 2. A 52 kD protein in the immunoprecipitate generated using the patient sera was recognized by the WTl specific antibody. The 52 kD protein migrated at the same size as the positive control. Example 2 Induction of Antibodies to WTl in Mice Immunized with Cell Lines Expressing WTl This Example illustrates the use of cells expressing WTl to induce a WTl specific antibody response in vivo. Detection of existent antibodies to WTl in patients with leukemia strongly implied that it is possible to immunize to WTl protein to elicit immunity to WTl. To test whether immunity to WTl can be generated by vaccination, mice were injected with TRAMP-C, a WTl positive tumor cell line of B6 origin. Briefly, male B6 mice were immunized with 5 x 10 6 TRAMP-C cells subcutaneously and boosted twice with 5 x 10 6 cells at three week intervals. Three weeks after the final immunization, sera were obtained and single cell suspensions of spleens were prepared in RPMI 1640 medium (GIBCO) with 25μM β-2-mercaptoethanol, 200 units of penicillin per ml, lOmM L-glutamine, and 10%> fetal bovine semm. Following immunization to TRAMP-C, a WTl specific antibody response in the immunized animals was detectable. A representative Western blot is shown in Figure 3. These results show that immunization to WTl protein can elicit an immune response to WTl protein. Example 3 Induction of Th and Antibody Responses in Mice Immunized with WTl Peptides This Example illustrates the ability of immunization with WTl peptides to elicit an immune response specific for WTl . Peptides suitable for eliciting Ab and proliferative T cell responses were identified according to the Tsites program (Rothbard and Taylor, EMBO J. 7:93-100, 1988; Deavin et al., Mol. Immunol. 33:145-155, 1996), which searches for peptide motifs that have the potential to elicit Th responses. Peptides shown in Table I were synthesized and sequenced. Table I WTl Peptides For immunization, peptides were grouped as follows: Group A: p6-22 human: 10.9mg in 1ml (lOμl - lOOμg) pi 17-139 human/mouse: 7.6mg in 1ml (14μl = lOOμg) p244-262 human: 4.6.mg in 1ml (22μl = lOOμg) Group B: p287-301 human/mouse: 7.2mg in 1ml (14μl = lOOμg) mouse p299-313: 6.6.mg in 1ml (15μl = lOOμg) p421-435 human/mouse: 3.3mg in 1ml (30μl = lOOμg) Control: (FBL peptide 1 OOμg) + CFA/IFA Control: (CD45 peptide 1 OOμg) + CFA/IFA Group A contained peptides present within the amino terminus portion of WTl (exon 1) and Group B contained peptides present within the carboxy terminus, which contains a four zinc finger region with sequence homology to other DNA-binding proteins. Within group B, p287-301 and p299-313 were derived from exon 7, zinc finger 1, and p421-435 was derived from exon 10, zinc finger IV. B6 mice were immunized with a group of WTl peptides or with a control peptide. Peptides were dissolved in 1ml sterile water for injection, and B6 mice were immunized 3 times at time intervals of three weeks. Adjuvants used were CFA/IFA, GM-CSF, and Montinide. The presence of antibodies specific for WTl was then determined as described in Examples 1 and 2, and proliferative T cell responses were evaluated using a standard thymidine incoφoration assay, in which cells were cultured in the presence of antigen and proliferation was evaluated by measuring incoφorated radioactivity (Chen et al., Cancer Res. 54:1065-1070, 1994). In particular, lymphocytes were cultured in 96-well plates at 2x10 5 cells per well with 4x10 5 irradiated (3000 rads) syngeneic spleen cells and the designated peptide. Immunization of mice with the group of peptides designated as Group A elicited an antibody response to WTl (Figure 4). No antibodies were detected following immunization to Vaccine B, which is consistent with a lack of helper T cell response from immunization with Vaccine B. PI 17-139 elicited proliferative T cell responses (Figures 5A-5C). The stimulation indices (SI) varied between 8 and 72. Other peptides (P6-22 and P299-313) also were shown to elicit proliferative T cell responses. Immunization with P6-22 resulted in a stimulation index (SI) of 2.3 and immunization with P299-313 resulted in a SI of 3.3. Positive controls included ConA stimulated T cells, as well as T cells stimulated with known antigens, such as CD45 and FBL, and allogeneic T cell lines (DeBruijn et al., Eur. J. Immunol. 27:2963-2970, 1991). Figures 6A and 6B show the proliferative response observed for each of the three peptides within vaccine A (Figure 6 A) and vaccine B (Figure 6B). Vaccine A elicited proliferative T cell responses to the immunizing peptides p6-22 and pi 17-139, with stimulation indices (SI) varying between 3 and 8 (bulk lines). No proliferative response to p244-262 was detected (Figure 6A). Subsequent in vitro stimulations were carried out as single peptide stimulations using only p6-22 and pi 17-139. Stimulation of the Vaccine A specific T cell line with pi 17-139 resulted in proliferation to pi 17-139 with no response to p6-22 (Figure7A). Clones derived from the line were specific for pi 17-139 (Figure 7B). By contrast, stimulation of the Vaccine A specific T cell line with p6-22 resulted in proliferation to p6-22 with no response to pi 17-139 (Figure 7C). Clones derived from the line were specific for p6-22 (Figure 7D). These results show that vaccination with WTl peptides can elicit antibody responses to WTl protein and proliferative T cell responses to the immunizing peptides. Example 4 Induction of CTL Responses in Mice Immunized with WTl Peptides This Example illustrates the ability of WTl peptides to elicit CTL immunity. Peptides (9-mers) with motifs appropriate for binding to class I MHC were identified using a BIMAS HLA peptide binding prediction analysis (Parker et al., J. Immunol. 752:163, 1994). Peptides identified within such analyses are shown in Tables II - XLIV. In each of these tables, the score reflects the theoretical binding affinity (half-time of dissociation) of the peptide to the MHC molecule indicated. Peptides identified using the Tsites program (Rothbard and Taylor, EMBO J. 7:93-100, 1988; Deavin et al., Mol. Immunol. 33:145-155, 1996), which searches for peptide motifs that have the potential to elicit Th responses are further shown in Figures 8A and 8B, and Table XLV. Table II Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA Al Table III Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A 0201 Table IV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A 0205 Table V Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A24 Table VI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A3 Table VII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A68.1 Table VIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A 1101 Table IX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A 3101 Table X Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA A 3302 Table XI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B14 Table XII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B40 Table XIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B60 Table XIV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B61 Table XV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B62 Table XVI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B7 Table XVII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B8 Table XVIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 2702 Table XIX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 2705 Table XX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 3501 Table XXI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 3701 Table XXII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 3801 Table XXIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 3901 Table XXIV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 3902 Table XXV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 4403 Table XXVI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 5101 Table XXVII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 5102 Table XXVIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 5201 Table XXIX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA B 5801 Table XXX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA CW0301 Table XXXI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA CW0401 Table XXXII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA CW0602 Table XXXIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Human HLA CW0702 Table XXXIV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Db Table XXXV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Dd Table XXXVI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Kb Table XXXVII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Kd Table XXXVIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Kk Table XXXIX Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Mouse MHC Class I Ld Table XL Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Human WTl Peptides to Cattle HLA A20 Table XLI Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Mouse WTl Peptides to Mouse MHC Class I A 0201 Table XLII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Mouse WTl Peptides to Mouse MHC Class I Db Table XLIII Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Mouse WTl Peptides to Mouse MHC Class I Kb Table XLIV Results of BIMAS HLA Peptide Binding Prediction Analysis for Binding of Mouse WTl Peptides to Mouse MHC Class I Kd Table XLV Results of TSites Peptide Binding Prediction Analysis for Human WTl Peptides Capable of Eliciting a Helper T cell Response p91-105 AFTVHFSGQFTGTAG (SEQ ID NO:311) pl l7-139 PSQASSGQARMFPNAPYLPSCLE (SEQ ID NO:2) pl67-171 HAAQF (SEQ ID NO:312) p202-233 CHTPTDSCTGSQALLLRTPYSSDNLYQMTSQL (SEQ ID NO:313) p244-262 GATLKGVAAGSSSSVKWTE (SEQ ID NO:4) p287-318 RIHTHGVFRGIQDVRRVPGVAPTLVRSASETS (SEQ ID NO:314) p333-336 RYFK (SEQ ID NO:315) p361-374 ERRFSRSDQLKRHQ (SEQ ID NO:316) p389-410 QRKFSRSDHLKTHTRTHTGKTS (SEQ ID NO:317) p421-441 CQKKFARSDELVRHHNMHQRN (SEQ ID NO:318) Certain CTL peptides (shown in Table XL VI) were selected for further study. For each peptide in Table XL VI, scores obtained using BIMAS HLA peptide binding prediction analysis are provided. Table XLVI WTl Peptide Sequences and HLA Peptide Binding Predictions Peptide binding to C57B1/6 murine MHC was confirmed using the leukemia cell line RMA-S, as described by Ljunggren et al., Nature 346:476-480, 1990. In brief, RMA-S cells were cultured for 7 hours at 26°C in complete medium supplemented with 1%> FCS. A total of 10 6 RMA-S cells were added into each well of a 24-well plate and incubated either alone or with the designated peptide (25ug/ml) for 16 hours at 26°C and additional 3 hours at 37°C in complete medium. Cells were then washed three times and stained with fluorescein isothiocyanate-conjugated anti D b or anti-K b antibody (PharMingen, San Diego, CA). Labeled cells were washed twice, resuspended and fixed in 500ul of PBS with 1% paraformaldehyde and analyzed for fluorescence intensity in a flow cytometer (Becton-Dickinson FACSCalibur®). The percentage of increase of D b or K b molecules on the surface of the RMA-S cells was measured by increased mean fluorescent intensity of cells incubated with peptide compared with that of cells incubated in medium alone. Mice were immunized with the peptides capable of binding to murine class I MHC. Following immunization, spleen cells were stimulated in vitro and tested for the ability to lyse targets incubated with WTl peptides. CTL were evaluated with a standard chromium release assay (Chen et al., Cancer Res. 54:1065-1070, 1994). 10 6 target cells were incubated at 37°C with 150μCi of sodium 51 Cr for 90 minutes, in the presence or absence of specific peptides. Cells were washed three times and resuspended in RPMI with 5%> fetal bovine serum. For the assay, 10 4 51 Cr-labeled target cells were incubated with different concentrations of effector cells in a final volume of 200μl in U-bottomed 96-well plates. Supematants were removed after 4 to 7 hours at 37°C, and the percentage specific lysis was determined by the formula: %> specific lysis = 100 x (experimental release - spontaneous release)/(maximum release-spontaneous release). The results, presented in Table XL VII, show that some WTl peptides can bind to class I MHC molecules, which is essential for generating CTL. Moreover, several of the peptides were able to elicit peptide specific CTL (Figures 9A and 9B), as determined using chromium release assays. Following immunization to CTL peptides pl0-18 human, pl36-144 human, pl36-144 mouse and p235-243, peptide specific CTL lines were generated and clones were established. These results indicate that peptide specific CTL can kill malignant cells expressing WTl . Table XLVII Binding of WTl CTL Peptides to mouse B6 class I antigens Example 5 Use of a WTl Polypeptide to Elicit WTl Specific CTL in Mice This Example illustrates the ability of a representative WTl polypeptide to elicit CTL immunity capable of killing WTl positive tumor cell lines. PI 17-139, a peptide with motifs appropriate for binding to class I and class II MHC, was identified as described above using TSITES and BIMAS HLA peptide binding prediction analyses. Mice were immunized as described in Example 3. Following immunization, spleen cells were stimulated in vitro and tested for the ability to lyse targets incubated with WTl peptides, as well as WTl positive and negative tumor cells. CTL were evaluated with a standard chromium release assay. The results, presented in Figures 10A-10D, show that PI 17 can elicit WTl specific CTL capable of killing WTl positive tumor cells, whereas no killing of WTl negative cells was observed. These results demonstrate that peptide specific CTL in fact kill malignant cells expressing WTl and that vaccine and T cell therapy are effective against malignancies that express WTl. Similar immunizations were performed using the 9-mer class I MHC binding peptides pl36-144, p225-233, p235-243 as well as the 23-mer peptide pi 17- 139. Following immunization, spleen cells were stimulated in vitro with each of the 4 peptides and tested for ability to lyse targets incubated with WTl peptides. CTL were generated specific for pl36-144, p235-243 and pi 17-139, but not for p225-233. CTL data for p235-243 and pi 17-139 are presented in Figures 11A and 11B. Data for peptides pl36-144 and p225-233 are not depicted. CTL lysis demands that the target WTl peptides are endogenously processed and presented in association with tumor cell class I MHC molecules. The above WTl peptide specific CTL were tested for ability to lyse WTl positive versus negative tumor cell lines. CTL specific for p235-243 lysed targets incubated with the p235-243 peptides, but failed to lyse cell lines that expressed WTl proteins (Figure 11 A). By marked contrast, CTL specific for pi 17-139 lysed targets incubated with pi 17-139 peptides and also lysed malignant cells expressing WTl (Figure 11B). As a negative control, CTL specific for pi 17-139 did not lyse WTl negative EL-4 (also referred to herein as ElO). Specificity of WTl specific lysis was confirmed by cold target inhibition (Figures 12A-12B). Effector cells were plated for various effector: target ratios in 96- well U-bottom plates. A ten-fold excess (compared to hot target) of the indicated peptide-coated target without 51 Cr labeling was added. Finally, 10 4 51 Cr-labeled target cells per well were added and the plates incubated at 37°C for 4 hours. The total volume per well was 200μl. Lysis of TRAMP-C by pi 17-139 specific CTL was blocked from 58% to 36%o by EL-4 incubated with the relevant peptide pi 17-139, but not with EL-4 incubated with an irrelevant peptide (Figure 12A). Similarly, lysis of BLK-SV40 was blocked from 18% to 0% by EL-4 incubated with the relevant peptide pi 17-139 (Figure 12B). Results validate that WTl peptide specific CTL specifically kill malignant cells by recognition of processed WTl. Several segments with putative CTL motifs are contained within pi 17- 139. To determine the precise sequence of the CTL epitope all potential 9-mer peptides within pi 17-139 were synthesized (Table XL VIII). Two of these peptides (pl26-134 and pi 30- 138) were shown to bind to H-2 b class I molecules (Table XLVIII). CTL generated by immunization with pi 17-139 lysed targets incubated with pl26-134 and pl30-138, but not the other 9-mer peptides within pi 17-139 (Figure 13A). The pi 17-139 specific CTL line was restimulated with either pl26-134 or pl30-138. Following restimulation with pl26-134 or pl30-138, both T cell lines demonstrated peptide specific lysis, but only pi 30- 138 specific CTL showed lysis of a WTl positive tumor cell line (Figures 13B and 13C). Thus, pl30-138 appears to be the naturally processed epitope. Table XLVIII Binding of WTl CTL 9mer Peptides within pi 17-139 to mouse B6 class I antigens Peptide Binding Affinity to Mouse MHC Class I PI 17-125 PSQASSGQA (SEQ ID 2% NO:221) PI 18-126 SQASSGQAR (SEQ ID 2% NO:216) PI 19-127 QASSGQARM (SEQ ID 2% NOs: 161 and 288) P120-128 ASSGQARMF (SEQ ID 1% NO:40 P121-129 SSGQARMFP (SEQ ID 1% NO:222) P122-130 SGQARMFPN (SEQ ID 1% NO:212) PI 23-131 GQARMFPNA (SEQ ID 1% NOs: 98 and 269) PI 24- 132 QARMFPNAP (SEQ ID 1% NO:223) P125-133 ARMFPNAPY (SEQ ID 1% NO:38) PI 26- 134 RMFPNAPYL (SEQ ID 79% NOs: 185 and 293) P127-135 MFPNAPYLP (SEQ ID 2% NO:224) PI 28- 136 FPNAPYLPS (SEQ ID 1% NOs: 79 and 267) P129-137 PNAPYLPSC (SEQ ID 1% NO:225) P130-138 NAPYLPSCL (SEQ ID 79% NOs: 144 and 282) P131-139 APYLPSCLE (SEQ ID 1% NO:226) Example 6 Identification of WTl Specific mRNA in Mouse Tumor Cell Lines This Example illustrates the use of RT-PCR to detect WTl specific mRNA in cells and cell lines. Mononuclear cells were isolated by density gradient centrifugation, and were immediately frozen and stored at -80°C until analyzed by RT-PCR for the presence of WTl specific mRNA. RT-PCR was generally performed as described by Fraizer et al., Blood 5(5:4704-4706, 1995. Total RNA was extracted from 10 7 cells according to standard procedures. RNA pellets were resuspended in 25 μL diethylpyrocarbonate treated water and used directly for reverse transcription. The zinc- finger region (exons 7 to 10) was amplified by PCR as a 330 bp mouse cDNA. Amplification was performed in a thermocycler during one or, when necessary, two sequential rounds of PCR. AmpliTaq DNA Polymerase (Perkin Elmer Cetus, Norwalk, CT), 2.5 mM MgCl 2 and 20 pmol of each primer in a total reaction volume of 50μl were used. Twenty μL aliquots of the PCR products were electrophoresed on 2% agarose gels stained with ethidium bromide. The gels were photographed with Polaroid film (Polaroid 667, Polaroid Ltd., Hertfordshire, England). Precautions against cross contamination were taken following the recommendations of Kwok and Higuchi, Nature 339:237-238, 1989. Negative controls included the cDNA- and PCR-reagent mixes with water instead of cDNA in each experiment. To avoid false negatives, the presence of intact RNA and adequate cDNA generation was evaluated for each sample by a control PCR using β-actin primers. Samples that did not amplify with these primers were excluded from analysis. Primers for amplification of WTl in mouse cell lines were: PI 15: 1458- 1478: 5' CCC AGG CTG CAA TAA GAG ATA 3' (forward primer; SEQ ID NO:21); and PI 16: 1767-1787: 5' ATG TTG TGA TGG CGG ACC AAT 3' (reverse primer; SEQ ID NO:22) (see Inoue et al, Blood 88:2267-2218, 1996; Fraizer et al., Blood S6 ' :4704-4706, 1995). Beta Actin primers used in the control reactions were: 5' GTG GGG CGC CCC AGG CAC CA 3' (sense primer; SEQ ID NO:23); and 5' GTC CTT AAT GTC ACG CAC GAT TTC 3' (antisense primer; SEQ ID NO:24) Primers for use in amplifying human WTl include: PI 17: 954-974: 5' GGC ATC TGA GAC CAG TGA GAA 3' (SEQ ID NO:25); and PI 18: 1434-1414: 5' GAG AGT CAG ACT TGA AAG CAGT 3' (SEQ ID NO:5). For nested RT-PCR, primers may be: PI 19: 1023-1043: 5' GCT GTC CCA CTT ACA GAT GCA 3' (SEQ ID NO:26); and P120: 1345-1365: 5' TCA AAG CGC CAG CTG GAG TTT 3' (SEQ ID NO:27). Table XLVIII shows the results of WTl PCR analysis of mouse tumor cell lines. Within Table IV, (+++) indicates a strong WTl PCR amplification product in the first step RT PCR, (++) indicates a WTl amplification product that is detectable by first step WTl RT PCR, (+) indicates a product that is detectable only in the second step of WTl RT PCR, and (-) indicates WTl PCR negative. Table XLIX Detection of WTl mRNA in Mouse Tumor Cell Lines From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for puφoses of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims: CLAIMS 1. A polypeptide comprising an immunogenic portion of a native WTl , or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with WTl -specific antisera and/or T-cell lines or clones is not substantially diminished, wherein the polypeptide comprises no more than 16 consecutive amino acid residues present within a native WTl polypeptide. 2. A polypeptide according to claim 1, wherein the immunogenic portion binds to an MHC class I molecule. 3. A polypeptide according to claim 1, wherein the immunogenic portion binds to an MHC class II molecule. 4. A polypeptide according to claim 1, wherein the polypeptide comprises a sequence selected from the group consisting of: (a) sequences recited in one or more of Tables II - XL VI: (b) variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished; and (c) mimetics of the foregoing sequences, wherein the ability of the mimetic to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished. 5. A polypeptide according to claim 1, wherein the polypeptide comprises a sequence selected from the group consisting of: (a) ALLPAVPSL (SEQ ID NO:34), GATLKGVAA (SEQ ID NO:88), CMTWNQMNL (SEQ ID NOs: 49 and 258), SCLESQPTI (SEQ ID NOs: 199 and 296), SCLESQPAI (SEQ ID NO: 198), NLYQMTSQL (SEQ ID NOs: 147 and 284); ALLPAVSSL ( SEQ ID NOs: 35 and 255), RMFPNAPYL (SEQ ID NOs: 185 and 293); (b) variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished; and (c) mimetics of the foregoing sequences, wherein the ability of the mimetic to react with antigen-specific antisera and/or T-cell lines or clones is not substantially diminished. 6. A polypeptide according to claim 1, wherein the polypeptide comprises 4-16 consecutive amino acids of a native WTl polypeptide. 7. A polypeptide according to claim 1, wherein the polypeptide comprises 8-10 consecutive amino acids of a native WTl polypeptide. 8. A polypeptide comprising an immunogenic portion of amino acid residues 1 - 174 of a native WTl polypeptide, or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with WTl -specific T-cell lines or clones is not substantially diminished, wherein the polypeptide comprises no more than 16 consecutive amino acid residues present within amino acids 175 to 449 of the native WTl polypeptide. 9. A polypeptide comprising a variant of an immunogenic portion of WTl that differs in substitutions at between 1 and 3 amino acid positions within the immunogenic portion, such that the ability of the variant to react with WTl -specific antisera and/or T-cell lines or clones is enhanced relative to a native WTl. 10. A mimetic of an immunogenic portion of a WTl polypeptide, wherein at least one amino acid residue is replaced by a compound that is not an amino acid, such that the ability of the mimetic to react with antigen-specific antisera and or T-cell lines or clones is not diminished. 11. A pharmaceutical composition comprising a polypeptide according to claim 1, in combination with a pharmaceutically acceptable carrier or excipient. 12. A pharmaceutical composition according to claim 11, wherein- the polypeptide comprises 4-16 consecutive amino acids of a native WTl polypeptide. 13. A pharmaceutical composition according to claim 11, wherein the polypeptide comprises 8-16 consecutive amino acids of a native WTl polypeptide. 14. A pharmaceutical composition comprising a polypeptide according to claim 8, in combination with a pharmaceutically acceptable carrier or excipient. 15. A vaccine comprising a polypeptide according to claim 1, in combination with a non-specific immune response enhancer. 16. A vaccine according to claim 15, wherein the polypeptide comprises 4- 16 consecutive amino acids of a native WTl polypeptide. 17. A vaccine according to claim 15, wherein the polypeptide comprises 8- 10 consecutive amino acids of a native WTl polypeptide. 18. A vaccine according to claim 15, wherein the immune response enhancer is an adjuvant. 19. A vaccine comprising a polypeptide according to claim 8, in combination with a non-specific immune response enhancer. 20. A vaccine according to claim 19. wherein the immune response enhancer is an adjuvant. 21. A vaccine comprising : (a) a WTl polypeptide, wherein the polypeptide comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to eact with antigen-specific T cell lines or clones is not substantially diminished; and (b) a non-specific immune response enhancer that preferentially enhances a T cell response in a patient. 22. A vaccine according to claim 21, wherein the immune response enhancer is selected from the group consisting of Montanide ISA50, Seppic MONTANIDE ISA 720, cytokines (e.g., GM-CSF, Flat3 -ligand), microspheres, dimethyl dioctadecyl ammoniumbromide (DDA) based adjuvants, AS-1, AS-2, Ribi Adjuvant system based adjuvants, QS21, saponin based adjuvants, Syntex adjuvant in its microfluidized form, MV, ddMV, immune stimulating complex (iscom) based adjuvants and inactivated toxins. 23. A pharmaceutical composition comprising a mimetic according to claim 10, in combination with a pharmaceutically acceptable carrier or excipient. 24. A vaccine comprising a mimetic according to claim 10, in combination with a non-specific immune response enhancer. 25. A polynucleotide encoding a polypeptide according to claim 1 or claim 8. 26. A pharmaceutical composition, comprising: (a) a polynucleotide encoding a WTl polypeptide, wherein the polypeptide comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a pharmaceutically acceptable carrier or excipient. 27. A pharmaceutical composition, comprising: (a) an antibody or antigen-binding fragment thereof that specifically binds to a WTl polypeptide; and (b) a pharmaceutically acceptable carrier or excipient. 28. A pharmaceutical composition, comprising: (a) a T cell that specifically reacts with a WTl polypeptide; and (b) a pharmaceutically acceptable carrier or excipient. 29. A pharmaceutical composition, comprising: (a) an antigen presenting cell that expresses (i) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a pharmaceutically acceptable carrier or excipient. 30. A vaccine, comprising: (a) a polynucleotide encoding a WTl polypeptide, wherein the polypeptide comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and or T cell lines or clones is not substantially diminished; and (b) a non-specific immune response enhancer. 31. A vaccine, comprising: (a) an antigen presenting cell that expresses: (i) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a non-specific immune response enhancer. 32. A vaccine comprising: (a) an anti-idiotypic antibody or antigen-binding fragment thereof that is specifically bound by an antibody that specifically binds to an immunogenic portion of WTl; and (b) non-specific immune response enhancer. 33. A vaccine according to any one of claims 30-32, wherein the immune response enhancer is an adjuvant. 34. A vaccine according to any one of claims 30-32, wherein the immune response enhancer preferentially enhances a T cell response in a patient. 35. A method for enhancing or inducing an immune response in a human patient, comprising administering to a patient a pharmaceutical composition comprising: (a) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a physiologically acceptable carrier or excipient; and thereby enhancing or inducing an immune response specific for WTl or a cell expressing WTl in the human patient. 36. A method for enhancing or inducing an immune response in a patient, comprising administering to a patient a pharmaceutical composition according to any one of claims 11, 14, 23 or 26-29. 37. A method for enhancing or inducing an immune response in a human patient, comprising administering to a patient a vaccine comprising: (a) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a non-specific immune response enhancer; and thereby enhancing or inducing an immune response specific for WTl or a cell expressing WTl in the human patient. 38. A method for enhancing or inducing an immune response in a patient, comprising administering to a patient a vaccine according to any one of claims 15, 19, 21, 24 or 30-32, and thereby enhancing or inducing an immune response specific for WTl or a cell expressing WTl in the patient. 39. A method for inhibiting the development of a malignant disease associated with WTl expression in a human patient, comprising administering to a human patient a pharmaceutical composition comprising: (a) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a physiologically acceptable carrier or excipient; and thereby inhibiting the development of a malignant disease associated with WTl expression in the human patient. 40. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising administering to a patient a pharmaceutical composition according to any one of claims 11. 14, 23 or 26-29, and thereby inhibiting the development of a malignant disease in the patient. 41. A method for inhibiting the development of a malignant disease associated with WTl expression in a human patient, comprising administering to a patient a vaccine comprising: (a) a WTl polypeptide that comprises an immunogenic portion of a native WTl or a variant thereof that differs in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antibodies and/or T cell lines or clones is not substantially diminished; and (b) a non-specific immune response enhancer: and thereby inhibiting the development of a malignant disease in the patient. 42. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising administering to a patient a vaccine according to any one of claims 15, 19, 21. 24 or 30-32, and thereby inhibiting the development of a malignant disease in the patient. 43. A method according to claim 39 or claim 41, wherein the malignant disease is a leukemia. 44. A method according to claim 43, wherein the leukemia is acute myeloid leukemia, acute lymphocytic leukemia or chronic myeloid leukemia. 45. A method according to claim 39 or claim 41, wherein the malignant disease is a cancer. 46. A method according to claim 45, wherein the cancer is breast, lung, thyroid or gastrointestinal cancer or a melanoma. 47. A method according to claim 40, wherein the malignant disease is a leukemia. 48. A method according to claim 47, wherein the leukemia is acute myeloid leukemia, acute lymphocytic leukemia or chronic myeloid leukemia. 49. A method according to claim 40, wherein the malignant disease s a cancer. 50. A method according to claim 49, wherein the cancer is breast, lung, thyroid or gastrointestinal cancer or a melanoma. 51. A method according to claim 42, wherein the malignant disease is a leukemia. 52. A method according to claim 51, wherein the leukemia is acute myeloid leukemia, acute lymphocytic leukemia or chronic myeloid leukemia. 53. A method according to claim 42, wherein the malignant disease is a cancer. 54. A method according to claim 53, wherein the cancer is breast, lung, thyroid or gastrointestinal cancer or a melanoma. 55. A method according to claim 39, wherein the pharmaceutical composition comprises a WTl polypeptide that comprises a sequence selected from the group consisting of sequences recited in one or more of Tables II - XL VI and variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T- cell lines or clones is not diminished. 56. A method according to claim 39, wherein the pharmaceutical composition comprises a WTl polypeptide that comprises a sequence selected from the group consisting of ALLPAVPSL (SEQ ID NO:34), GATLKGVAA (SEQ ID NO:88), CMTWNQMNL (SEQ ID NOs: 49 and 258), SCLESQPTI (SEQ ID NOs: 199 and 296), SCLESQPAI (SEQ ID NO: 198), NLYQMTSQL (SEQ ID NOs: 147 and 284), ALLPAVSSL (SEQ ID NOs: 35 and 255); RMFPNAPYL (SEQ ID NOs: 185 and 293) and variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T- cell lines or clones is not diminished. 57. A method according to claim 41, wherein the vaccine comprises a WTl polypeptide that comprises a sequence selected from the group consisting of sequences recited in one or more of Tables II - XL VI and variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not diminished. 58. A method according to claim 41, wherein the vaccine comprises a WTl polypeptide that comprises a sequence selected from the group consisting of ALLPAVPSL (SEQ ID NO:34), GATLKGVAA (SEQ ID NO:88), CMTWNQMNL (SEQ ID NOs: 49 and 258), SCLESQPTI (SEQ ID NOs: 199 and 296), SCLESQPAI (SEQ ID NO: 198), NLYQMTSQL (SEQ ID NOs: 147 and 284), ALLPAVSSL (SEQ ID NOs: 35 and 255), RMFPNAPYL (SEQ ID NOs: 185 and 293) and variants of the foregoing sequences that differ in one or more substitutions, deletions, additions and/or insertions such that the ability of the variant to react with antigen-specific antisera and/or T-cell lines or clones is not diminished. 59. A method for removing cells expressing WTl from bone marrow, peripheral blood, or a fraction of bone marrow or peripheral blood, comprising contacting bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood with T cells that specifically react with a WTl polypeptide, wherein the step of contacting is performed under conditions and for a time sufficient to permit the removal of WTl positive cells to less than 10%) of the number of myeloid or lymphatic cells in the bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood. 60. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising administering to a patient bone marrow, peripheral blood or a fraction or bone marrow or peripheral blood prepared according to the method of claim 59. 61. A method according to claim 60, wherein the bone marrow, peripheral blood or fraction is autologous. 62. A method according to claim 60, wherein the bone marrow, peripheral blood or fraction is syngeneic or allogeneic. 63. A method for stimulating and/or expanding T cells, comprising contacting T cells with a WTl polypeptide, a polynucleotide encoding a WTl polypeptide and/or an antigen presenting cell that expresses a WTl polypeptide under conditions and for a time sufficient to permit the stimulation and/or expansion off cells. 64. A method according to claim 63, wherein the T cells are present within bone marrow, peripheral blood or a fraction of bone marrow or peripheral blood. 65. A method according to claim 63, wherein the bone marrow, peripheral blood or fraction is obtained from a patient afflicted with a malignant disease associated with WTl expression. 66. A method according to claim 63, wherein the bone marrow, peripheral blood or fraction is obtained from a mammal that is not afflicted with a malignant disease associated with WTl expression. 67. A method according to claim 63, wherein the T cells are cloned prior to expansion. 68. A method for stimulating and/or expanding T cells in a mammal, comprising administering to a mammal a pharmaceutical composition comprising: (a) one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen-presenting cell that expresses a WTl polypeptide; and (b) a physiologically acceptable carrier or excipient; and thereby stimulating and/or expanding T cells in a mammal. 69. A method for stimulating and/or expanding T cells in a mammal, comprising administering to a mammal a vaccine comprising: (a) one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen-presenting cell that expresses a WTl polypeptide; and (b) a non-specific immune response enhancer; and thereby stimulating and/or expanding T cells in a mammal. 70. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising administering to a patient T cells prepared according to the method of claim 63. 71. A method according to claim 70. wherein the bone marrow, peripheral blood or fraction is obtained from a patient afflicted with a malignant disease associated with WTl expression. 72. A method according to claim 70, wherein the bone marrow, peripheral blood or fraction is obtained from a mammal that is not afflicted with a malignant disease associated with WTl expression. 73. A method for monitoring the effectiveness of an immunization or therapy for a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating a first biological sample with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen-presenting cell that expresses a WTl polypeptide wherein the first biological sample is obtained from a patient prior to a therapy or immunization, and wherein the incubation is performed under conditions and for a time sufficient to allow immunocomplexes to form; (b) detecting immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide; (c) repeating steps (a) and (b) using a second biological sample obtained from the patient following therapy or immunization; and (d) comparing the number of immunocomplexes detected in the first and second biological samples, and therefrom monitoring the effectiveness of the therapy or immunization in the patient. 74. A method according to claim 73, wherein the step of detecting comprises (a) incubating the immunocomplexes with a detection reagent that is capable of binding to the immunocomplexes, wherein the detection reagent comprises a reporter group, (b) removing unbound detection reagent, and (c) detecting the presence or absence of the reporter group. 75. A method according to claim 74, wherein the detection reagent comprises a second antibody, or antigen-binding fragment thereof, capable of binding to the antibodies that specifically bind to the WTl polypeptide. 76. A method according to claim 74, wherein the detection reagent comprises Protein A. 77. A method according to claim 74, wherein the reporter group is selected from the group consisting of radioisotopes, fluorescent groups, luminescent groups, enzymes, biotin and dye particles. 78. A method according to claim 73 wherein a reporter group is bound to the WTl polypeptide, and wherein the step of detecting comprises removing unbound WTl polypeptide and subsequently detecting the presence or absence of the reporter group. 79. A method for monitoring the effectiveness of an immunization or therapy for a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating a first biological sample with one or more of: (i) a WTl polypeptide; (ii) a WTl polynucleotide encoding a WTl polypeptide; or (iii) an antigen-presenting cell that expresses a WTl polypeptide; wherein the biological sample comprises CD4+ and/or CD8+ T cells and is obtained from a patient prior to a therapy or immunization, and wherein the incubation is performed under conditions and for a time sufficient to allow specific activation, proliferation and/or lysis of T cells; (b) detecting an amount of activation, proliferation and or lysis of the T cells; (c) repeating steps (a) and (b) using a second biological sample comprising CD4+ and/or CD8+ T cells, wherein the second biological sample is obtained from the same patient following therapy or immunization; and (d) comparing the amount of activation, proliferation and/or lysis " of T cells in the first and second biological samples, and therefrom monitoring the effectiveness of the therapy or immunization in the patient. 80. A method according to claim 73 or claim 79, wherein the malignant disease is a cancer or a leukemia. 81. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + T cells isolated from a patient with one or more of: (i) a WTl polypeptide: (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; such that the T cells proliferate; and (b) administering to the patient an effective amount of the proliferated T cells, and therefrom inhibiting the development of a malignant disease in the patient. 82. A method according to claim 81, wherein the malignant disease is a cancer or a leukemia. 83. A method according to claim 81, wherein the step of incubating the T cells is repeated one or more times. 84. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; such that the T cells proliferate; (b) cloning one or more cells that proliferated in the presence of WTl polypeptide; and (c) administering to the patient an effective amount of the cloned T cells. 85. A method according to claim 84, wherein the malignant disease is a cancer or a leukemia. 86. A method for inhibiting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD8 + T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell expressing a WTl polypeptide; such that the T cells proliferate; and (b) administering to the patient an effective amount of the proliferated T cells, and therefrom inhibiting the development of a malignant disease in the patient. 87. A method according to claim 86, wherein the malignant disease is a cancer or a leukemia. 88. A method according to claim 86, wherein the step of incubating the T cells is repeated one or more times. 89. A method for inhi biting the development of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD8 + T cells isolated from a patient with one or more of: (i) a WTl polypeptide (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; such that the T cells proliferate; (b) cloning one or more cells that proliferated in the presence of WTl polypeptide; and (c) administering to the patient an effective amount of the cloned T cells. 90. A method according to claim 89, wherein the malignant disease is a cancer or a leukemia. 91. A method for determining the presence or absence of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD4 + T cells isolated from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; and (b) detecting the presence or absence of specific activation of the T cells, therefrom determining the presence or absence of a malignant disease associated with WTl expression. 92. A method according to claim 91, wherein the malignant disease is a cancer or a leukemia. 93. A method according to clairn 91, wherein the step of detecting comprises detecting the presence or absence of proliferation of the T cells. 94. A method for determining the presence or absence of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating CD8 + T cells isolated from a patient with a one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; and (b) detecting the presence or absence of specific activation of the T cells, thereby determining the presence or absence of a malignant disease associated with WTl expression. 95. A method according to claim 94, wherein the malignant disease is a cancer or a leukemia. 96. A method according to claim 94 wherein the step of detecting comprises detecting the presence or absence of generation of cytolytic activity. 97. A method for determining the presence or absence of a malignant disease associated with WTl expression in a patient, comprising the steps of: (a) incubating a biological sample obtained from a patient with one or more of: (i) a WTl polypeptide; (ii) a polynucleotide encoding a WTl polypeptide; or (iii) an antigen presenting cell that expresses a WTl polypeptide; wherein the incubation is performed under conditions and for a time sufficient to allow immunocomplexes to form; and (b) detecting immunocomplexes formed between the WTl polypeptide and antibodies in the biological sample that specifically bind to the WTl polypeptide; and therefrom determining the presence or absence of a malignant disease associated with WTl expression. 98. A method according to claim 97, wherein the malignant disease is a cancer or a leukemia. 99. A method according to claim 97, wherein the step of detecting comprises (a) incubating the immunocomplexes with a detection reagent that is capable of binding to the immunocomplexes, wherein the detection reagent comprises a reporter group, (b) removing unbound detection reagent, and (c) detecting the presence or absence of the reporter group. 100. A method according to claim 99, wherein the detection reagent comprises a second antibody, or antigen-binding fragment thereof, capable of binding to the antibodies that specifically bind to the WTl polypeptide. 101. A method according to claim 99, wherein the detection reagent comprises Protein A. 102. A method according to claim 99, wherein the reporter group is selected from the group consisting of radioisotopes, fluorescent groups, luminescent groups, enzymes, biotin and dye particles. 103. A method according to claim 97 wherein a reporter group is bound to the WTl polypeptide, and wherein the step of detecting comprises removing unbound WTl polypeptide and subsequently detecting the presence or absence of the reporter group. 104. A polypeptide according to any of claims 1-9, for use as an active therapeutic substance. 105. A polypeptide according to any of claims 1-9, for use in the manufacture of a medicament for enhancing or inducing an immune response in a patient.

Inventors: CHEEVER MARTIN, GAIGER ALEXANDER, CHEEVER, MARTIN, GAIGER, ALEXANDER
Applicants: CHEEVER MARTIN, CORIXA CORP, GAIGER ALEXANDER, CHEEVER, MARTIN, CORIXA CORPORATION, GAIGER, ALEXANDER
Application year: 1999
Main classification: C07K14
IPC codes: A61K38, A61K39, A61K48, A61P15, A61P35, A61P37, C07K7, C07K14, C07K16, C12N15, C12Q1, G01N33