Identification of human telomerase reverse transcriptase-derived peptides that induce HLA-A24-restricted antileukemia cytotoxic T lymphocytes.

Human telomerase reverse transcriptase (hTERT) is considered a potential target for cancer immunotherapy because it is preferentially expressed in malignant cells. hTERT-derived peptides carrying motifs for HLA-A24 (HLA-A*2402), the most common allele among Japanese and also frequently present in persons of European descent, were examined for their capacity to elicit antileukemia cytotoxic T lymphocytes (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. This cytotoxicity was inhibited by the addition of hTERT peptide-loaded autologous cells, suggesting that hTERT is naturally processed in leukemia cells and that hTERT-derived peptides are expressed on these cells and are recognized by CTLs in the context of HLA-A24. Taken together with the currently identified HLA-A2-restricted CTL epitopes derived from hTERT, identification of new CTL epitopes presented by HLA-A24 increases the feasibility of immunotherapy for leukemia using hTERT-derived peptides.