Mutated p53 gene encodes a nonmutated epitope recognized by HLA-B*4601-restricted and tumor cell-reactive CTLs at tumor site.

Mutations of p53 gene occur in approximately 50% of human cancers, and accumulated p53 protein may be an appropriate target molecule to use for cancer immunotherapy. Indeed, mutated or nonmutated p53-derived peptides can induce HLA class I-restricted and tumor cell-reactive CTLs in vitro. However, to our knowledge, evidence that p53-derived peptides are truly recognized by CTLs at tumor sites has not yet been obtained. This study revealed that a mutated p53 gene encoded a nonmutated nonapeptide recognized by a HLA-B46-restricted and tumor cell-reactive CTL line that was established from T cells infiltrating a colon cancer lesion with the p53 mutation. This p53 peptide, at amino acid positions 99-107, had the ability to induce HLA-B46-restricted and peptide-specific CTLs reactive to tumor cells with the p53 mutation from the peripheral blood mononuclear cells of cancer patients, but not from those of healthy donors. These peptide-induced CTLs did not react to either HLA-B46(+) tumor cells without the p53 mutation or to HLA-B46(+) phytohemagglutinin-blastoid cells. These results provide a scientific basis for the development of p53-directed specific immunotherapy for HLA-B46(+) cancer patients.