The Wilms' tumor gene WT1 is overexpressed in leukemias and various types of solid tumors, and the WT1 protein was demonstrated to be an attractive target antigen for immunotherapy against these malignancies. Here, we report the outcome of a phase I clinical study of WT1 peptide-based immunotherapy for patients with breast or lung cancer, myelodysplastic syndrome, or acute myeloid leukemia. The WT1 gene was isolated as a gene responsible for Wilms' tumor, a pediatric renal cancer, and encodes a zinc finger transcription factor, which is involved in cell proliferation and differentiation, apoptosis, and organ development (3-6). Although the WT1 gene was first categorized as a tumor suppressor gene, we have proposed that the wild-type WT1 gene functions as an oncogene rather than a tumor-suppressor gene on the basis of the following findings. The first is high expression of the wild-type WT1 gene in both leukemias and solid tumors (7-18), the second is growth inhibition of leukemic and solid tumor cells by treatment with WT1 antisense oligomers (14,19), and the third is block of differentiation, but induction of proliferation, of wild-type WT1 gene-transfected myeloid progenitor cells in response to granulocyte colony-stimulating factor (20, 21). The last two are block of thymocyte differentiation but induction of thymocyte proliferation in the transgenic mice with the lck promoter-driven WT1 gene (22), and WT1 gene expression in the majority of dimethylbenzanthracene-induced erythroblastic leukemia and a stronger tendency of the cells with high levels of WT1 to develop into leukemias (23).Expression of the wild-type WT1 gene has been found in most cases of acute myelocytic leukemia (AML), acute lymphocytic leukemia, chronic myelocytic leukemia, and myelodysplastic syndrome (MDS) at higher levels than those in normal bone marrow (BM) or peripheral blood (7-13). Furthermore, various types of solid tumors, including lung, breast, thyroid, and colorectal cancers, expressed the wild-type WT1 gene at higher levels compared to those in corresponding normal tissues (15-18). These results indicated that the wild-type WT1 gene product may be a promising target for cancer immunotherapy (24,25).We tested the potential of the WT1 gene product to serve as a target antigen for tumor-specific immunotherapy. Human WT1-specific CTLs have been found to induce lysis of endogenously WT1-expressing tumor cells in vitro, but not to cause damage to physiologically WT1-expressing normal cells (24,(26)(27)(28). We used a mouse in vivo system to demonstrate that immunization of mice with either MHC class I-restricted WT1 peptide or WT1 cDNA induced WT1-specific CTLs. We also showed that the immunized mice rejected challenges of WT1-expressing tumor cells, whereas the induced CTLs did not affect normal healthy tissues that physiologically expressed WT1 nor damaged the normal tissues (25, 29). These results indicated that the WT1 protein could be a novel tumor rejection antigen for cancer immunotherapy (24)(25)(26)(27)(28)(29)(30)(31)(32).In...

The product of the Wilms' tumor gene WT1 is a transcription factor overexpressed not only in leukemic blast cells of almost all patients with acute myeloid leukemia, acute lymphoid leukemia, and chronic myeloid leukemia, but also in various types of solid tumor cells. Thus, it is suggested that the WT1 gene plays an important role in both leukemogenesis and tumorigenesis. Here we tested the potential of WT1 to serve as a target for immunotherapy against leukemia and solid tumors. Four 9-mer WT1 peptides that contain HLA-A2.1-binding anchor motifs were synthesized. Two of them, Db126 and WH187, were determined to bind to HLA-A2.1 molecules in a binding assay using transporter associated with antigen processing-deficient T2 cells. Peripheral blood mononuclear cells from an HLA-A2.1-positive healthy donor were repeatedly sensitized in vitro with T2 cells pulsed with each of these two WT1 peptides, and CD8(+) cytotoxic T lymphocytes (CTLs) that specifically lyse WT1 peptide-pulsed T2 cells in an HLA-A2.1-restricted fashion were induced. The CTLs also exerted specific lysis against WT1-expressing, HLA-A2.1-positive leukemia cells, but not against WT1-expressing, HLA-A2.1-negative leukemia cells, or WT1-nonexpressing, HLA-A2. 1-positive B-lymphoblastoid cells. These data provide the first evidence of human CTL responses specific for the WT1 peptides, and provide a rationale for developing WT1 peptide-based adoptive T-cell therapy and vaccination against leukemia and solid tumors.

Expression of theThe Wilms' tumor gene WT1 was originally isolated as a tumorsuppressor gene responsible for Wilms' tumor, a kidney neoplasm of childhood. 1 However, we proposed that WT1 played an oncogenic role in leukemogenesis based on the following findings: 2 (i) the wild-type WT1 gene was expressed at high levels in leukemic blast cells, 3,4 (ii) there was a clear and inverse correlation between WT1 expression levels and prognosis in acute leukemia, 3 (iii) WT1 expression increased at relapse of acute leukemia, 5 (iv) growth of leukemic blast cells was inhibited by the treatment of WT1 antisense oligomers 6 and (v) constitutive expression of WT1 blocked differentiation and instead induced proliferation in response to granulocyte colony-stimulating factor in 32D cl3 myeloid progenitor cells 7 and normal myeloid progenitor cells. 8 Furthermore, we demonstrated that the wild-type WT1 as expressed in various types of cell line derived from lung cancer, gastric cancer, colon cancer and breast cancer and that growth of these WT1-expressing tumor cells was inhibited by the treatment of WT1 antisense oligomers. 9 These data suggested an oncogenic role of the WT1 gene in tumorigenesis. However, the involvement of the WT1 gene in de novo solid tumors remained unclear. In the present study, we examined WT1 expression in de novo lung cancer using quantitative real-time RT-PCR and immunohistochemistry and demonstrated that the wild-type WT1 was overexpressed in 54/56 (96%) de novo non-small cell lung cancers (NSCLCs) and 5/6 (83%) de novo small cell lung cancers (SCLCs) examined.

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In acute-type leukemia, no method for the prediction of relapse following allogeneic stem cell transplantation based on minimal residual disease (MRD) levels is established yet. In the present study, MRD in 72 cases of allogeneic transplantation for acute myeloid leukemia, acute lymphoid leukemia, and chronic myeloid leukemia (accelerated phase or blast crisis) was monitored frequently by quantitating the transcript of WT1 gene, a "panleukemic MRD marker," using reverse transcriptase-polymerase chain reaction. Based on the negativity of expression of chimeric genes, the background level of WT1 transcripts in bone marrow following allogeneic transplantation was significantly decreased compared with the level in healthy volunteers. The probability of relapse occurring within 40 days significantly increased step-by-step according to the increase in WT1 expression level (100% for 1.0 ؋ 10 ؊2 -5.0 ؋ 10 ؊2 , 44.4% for 4.0 ؋ 10 ؊3 -1.0 ؋ 10 ؊2 , 10.2% for 4.0 ؋ 10 ؊4 -4.0 ؋ 10 ؊3 , and 0.8% for < 4.0 ؋ 10 ؊4 ) when WT1 level in K562 was defined as 1.0). WT1 levels in patients having relapse increased exponentially with a constant doubling time. The doubling time of the WT1 level in patients for whom the discontinuation of immunosuppressive agents or donor leukocyte infusion was effective was significantly longer than that for patients in whom it was not (P < .05). No patients with a short doubling time of WT1 transcripts (< 13 days) responded to these immunomodulation therapies. These findings strongly suggest that the WT1 assay is very useful for the prediction and management of relapse following allogeneic stem cell transplantation regardless of the presence of chimeric gene

The Wilms’ tumor gene WT1 is expressed at high levels not only in acute myelocytic and lymphocytic leukemia and in chronic myelocytic leukemia but also in various types of solid tumors including lung cancers. To determine whether the WT1 protein can serve as a target Ag for tumor-specific immunity, three 9-mer WT1 peptides (Db126, Db221, and Db235), which contain H-2Db-binding anchor motifs and have a comparatively higher binding affinity for H-2Db molecules, were tested in mice (C57BL/6, H-2Db) for in vivo induction of CTLs directed against these WT1 peptides. Only one peptide, Db126, with the highest binding affinity for H-2Db molecules induced vigorous CTL responses. The CTLs specifically lysed not only Db126-pulsed target cells dependently upon Db126 concentrations but also WT1-expressing tumor cells in an H-2Db-restricted manner. The sensitizing activity to the Db126-specific CTLs was recovered from the cell extract of WT1-expressing tumor cells targeted by the CTLs in the same retention time as that needed for the synthetic Db126 peptide in RP-HPLC, indicating that the Db126-specific CTLs recognize the Db126 peptide to kill WT1-expressing target cells. Furthermore, mice immunized with the Db126 peptide rejected challenges by WT1-expressing tumor cells and survived for a long time with no signs of autoaggression by the CTLs. Thus, the WT1 protein was identified as a novel tumor Ag. Immunotherapy targeting the WT1 protein should find clinical application for various types of human cancers.

Although a small uncontrolled nonrandomized trial, this study showed that WT1 vaccine therapy for patients with WT1/HLA-A*2402-positive recurrent GBM was safe and produced a clinical response. Based on these results, further clinical studies of WT1 vaccine therapy in patients with malignant glioma are warranted.

The Wilms tumor gene, WT1, is overexpressed not only in leukemias and myelodysplastic syndrome (MDS) but also in various types of solid tumors, including lung and breast cancer, and the WT1 protein is a tumor antigen for these malignancies. In clinical trials of WT1 peptide-based cancer immunotherapy, patients with overt leukemia from MDS or MDS with myelofibrosis were injected intradermally with 0.3 mg of an HLA-A*2402-restricted, 9-mer WT1 peptide emulsified with Montanide ISA51 adjuvant. Only a single dose of WT1 vaccination resulted in an increase in WT1-specific cytotoxic T-lymphocytes, which was followed by a rapid reduction in leukemic blast cells. Severe leukopenia and local erythema at the injection sites of WT1 peptide were observed as adverse effects. These results have provided us with the first clinical evidence suggesting that WT1 peptide-based immunotherapy is an attractive treatment for patients with leukemias or MDS.