Stimulation or adoptive-transfer of tumor-specific T cells are, at present promising new lines in cancer immunotherapy. For melanomas, tumor-selective peptides presented by HLA-molecules to cytotoxic T cells (CTL) have been identified, first clinical trials being underway. For many other tumors including colorectalcarcinomas, relevant information is not yet available, although candidate antigens for tumor-specific immunity are known, including mutated-RAS. The objective of this proposal is to definitely identify HLA-class-one presented peptides of mutated-RAS and other tumor-associated proteins (ex: p53 CEA) by a purely biochemical approach. Large number of colorectal-carcinoma cells will be produced, either by in vitro culture or by expansion in nude mice of cell lines already established at INSERM U395. HLA-molecules will be precipitated and associated peptides will be extracted using procedures well established in Dr. Rammensee's group. Resulting peptide mixtures will be screened by mass-spectrometry for peptides conform with those predicted based on the protein sequence of the candidate antigens and allele-specific HLA motifs that have been determined in Dr. Rammensee's laboratory. Results are expected to give the basis for experimental immunotherapy of colorectal-carcinomas, using peptide specific CTL.