Immunogene therapy of cancer and virus infections using immortalized T-cell clones

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1. The WT1 gene encodes a zinc finger transcription factor, which is preferentially expressed in acute leukemia cells and chronic myelogenous leukemia cells in blast crisis, but not in most normal cells. These findings strongly suggest that WT1 is a potential target of immunotherapy for human leukemia. We have established a CD8+ cytotoxic Tlymphocyte (CTL) clone, designated TAK-1, which is specific for a WT1-derived 9-mer peptide consisting of HLA-A24-binding anchor motifs. TAK-1 lysed both HLA-A24-positive allogeneic cells and autologous cells that were loaded with a WT1-derived peptide. TAK-1 was cytotoxic to HLA-A24-positive leukemia cells, but not to HLA-A24-positive lymphoma cells that did not express WT1, to HLA-A24-negative leukemia cells, or to HLA-A24-positive normal cells. Treating leukemia cells with an antisense oligonucleotide complementary to WT1 reduced TAK-1-mediated cytotoxicity. TAK-1 did not inhibit colony formation of HLA-A24-positive normal bone marrow cells.2. Because hTERT is preferentially expressed in malignant cells but not in normal cells, it is considered to be a potential target for cancer immunotherapy. We examined hTERT-derived peptides carrying motifs for HLA-A24 (HLA-A^*2402) for their capacity to elicit anti-leukemia cytotoxic Tlymphocytes (CTLs). Two of the 5 peptides tested, VYAETKHFL and VYGFVRACL, appeared capable of generating hTERT peptide-specific and HLA-A24-restricted CTLs. The CD8+ CTL clones specific for these hTERT peptides exerted cytotoxicity against leukemia cells in an HLA-A24-restricted manner. The cytotoxicity was inhibited by adding hTERT peptide-loaded autologous-LCLs, suggesting that hTERT peptide is naturally processed and expressed on leukamia cells, and can be lysed by these CTLs. Taken together with the currently identified HLA-A2-restricted CTL epitopes derived from hTERT, identification of CTL epitopes presented by HLA-A24 extends the feasibility of immunotherapy for leukemia using hTERT-derived peptides.