 Human cancers express tumor antigens that can be targeted by cytolytic T lymphocytes CTL. These antigens consist of a small peptide, derived from endogenous proteins, that is presented at the cancer cells surface by an HLA class I molecule. Such antigenic peptides, including MAGE-3.A1 and NA17.A2, have been tested in experimental therapeutic vaccines to elicit CTL responses in cancer patients, mainly with metastatic melanoma. Up to now, only rare tumor responses have been observed. 