OVERLAPPING EPITOPES ENCOMPASSING A POINT MUTATION (12 GLY-]ARG) IN P21 RAS CAN BE RECOGNIZED BY HLA-DR, HLA-DP AND HLA-DQ RESTRICTED T-CELLS

Mutations in ras genes which result in transforming gene products carr ying amino acid substitutions in position 12, 13 or 61 are common in h uman cancer. Peptides encompassing these mutations in ras are shown to be immunogenic in both mice and humans. The potential usefulness of s uch peptides in cancer therapy, depends on their ability to bind to HL A molecules. We therefore stimulated T cells from healthy donors with mutated ras-derived peptides. By repeated in vitro stimulation of peri pheral blood mononuclear cells, several T cells clones could be genera ted which recognized a p21 ras derived peptide carrying a position 12 Gly --> Arg substitution. This peptide (1-25,12 Arg) could be specific ally recognized by T cells restricted by either HLA-DQ7 or -DP3. Previ ously, we showed that this peptide is also recognized by a T cell clon e restricted by HLA-DR2. The core region of the peptide was determined to span positions 9-16 for all three HLA restriction elements, and ac cordingly contains the mutational hot spots in position 12 and 13. The observation that the mutant 1-25,12 Arg ras-derived peptide may conta in a promiscuous epitope encompassing the Gly --> Arg mutation in posi tion 12 indicates that lack of peptide presentation by given HLA molec ules may not be a major constraint in responsiveness against ras mutat ions.