To provide a scientific basis for specific immunotherapy of colon cancer, this study focused on the identification of tumor-associated antigens recognized by HLA-A2-restricted and cancer-reactive cytotoxic T lymphocytes (CTLs) from tumor-infiltrating lymphocytes (TIL) of a colon cancer patient. We identified a gene coding a member of the ATP-binding cassette transporter (ABCE1), which is known as an inhibitor to the 2-5A/RNase L system, a central pathway of interferon action, and its gene expression is amplified in drug-resistant cells. The ABCE1 mRNA was ubiquitously expressed in tumor cell lines, as well as normal cells or tissues. Among 21 peptides with the HLA-A2 binding motifs, 2 ABCE1-derived peptides were recognized by the colon cancer-reactive CTLs in a dose-dependent manner. CTL precursors reactive to these 2 ABCE1 peptides were detected in the peripheral blood mononuclear cells (PBMCs) of the colon cancer patient, from whom the TILs had been obtained. In addition, these ABCE1 peptides had the potential to generate HLA-A2-restricted and colon cancer-reactive CTLs from the PBMCs of colon cancer patients, but not from those of healthy donors. Their cytotoxicity against colon cancer was mainly ascribed to peptide-specific and CD8+ CTLs. No definite cytotoxicity was observed against normal T cell blasts, irrespective of the expression of the ABCE1 mRNA. These results indicate that the ABCE1 and its peptides could be target molecules in specific immunotherapy for HLA-A2+ colon cancer patients.

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