Identification and characterization of a WT1 (Wilms Tumor Gene) protein-derived HLA-DRB1*0405-restricted 16-mer helper peptide that promotes the induction and activation of WT1-specific cytotoxic T lymphocytes.

Effective tumor vaccine may be required to induce both cytotoxic T lymphocyte (CTL) and CD4+ helper T-cell responses against tumor-associated antigens. CD4 + helper T cells that recognize HLA class II-restricted epitopes play a central role in the initiation and maintenance of antitumor immune responses. The Wilms tumor gene WT1 is overexpressed in both leukemias and solid tumors, and the WT1 protein was demonstrated to be an attractive target antigen for cancer immunotherapy. In this study, we identified a WT1 protein-derived 16-mer peptide, WTl 332 (KRYFKLSHLQMHSRKH), which was restricted with HLA-DRB1*0405, one of the most common HLA class II types in Japanese, as a helper epitope that could elicit WT1-specific CD4 + T-cell responses. We established a WTl 332 -specific CD4 + helper T-cell clone (E04.1), which could respond to both HLA-DRB1*0405-positive, WT1-expressing transformed hematopoietic cells and autologous dendritic cells pulsed with apoptosis-induced WT1-expressing cells, indicating that the WTl 332 was a naturally processed helper epitope. Stimulation of peripheral blood mononuclear cells with both the CTL epitope (WTl 235 ) and the helper epitope (WTl 332 ) in the presence of WTl 332 -specific TH1-type CD4 + T cell clone strikingly enhanced the induction and the functional activity of WTl 235 -specific CTLs compared with that of peripheral blood mononuclear cells with the WTl 235 alone. These results indicated that a helper epitope, WTl 332 should be useful for improvement of the efficacy of CTL epitope-based cancer vaccine targeting WT1 in the clinical setting.