INDUCTION AND CHARACTERIZATION OF CYTOTOXIC T-LYMPHOCYTES RECOGNIZINGA MUTATED P21RAS PEPTIDE PRESENTED BY HLA-A-ASTERISK-0201

The ras oncogene is frequently found to be activated in human cancer t hrough point mutations at codons 12, 13 or 61. We explored whether the se altered p21ras protein sequences contain peptide sequences that can activate naive CD8(+) cytotoxic T lymphocytes (CTL). Several wild-typ e and mutated p21ras peptides were identified that carry a binding mot if for human leukocyte antigen (HLA)-A0201. Two peptides were found t o bind strongly to this allele. CD8(+) CTL bulk cultures specifically reacting with one of these peptides could be induced, using processing defective T2 cells loaded with peptide CLLDILDTAGL as stimulators. Th e peptide is derived from p21ras, position 51-61, and carries a 61 Gin --> Leu mutation. In contrast, a 9-mer peptide CLLDILDTA correspondin g to amino acid sequence 51-59 of wild-type p21ras did not yield react ive CTL cultures. T-cell clones with low affinity for the 11-mer pepti de were isolated from CLLDILDTAGL-reactive bulk cultures. These T cell s did not lyse melanoma cells transfected with 61-Leu N-ras, although lysis was found when these transfectants were pulsed with the 11-mer p eptide. Possibly, T cells of higher affinity may be required to demons trate processed peptide on the cell surface. The combined experiments suggest that a peptide derived from mutated p21ras can be recognized b y HLA class I-restricted CTL, whereas an analogous wild-type p21 ras p eptide may not be immunogenic. (C) 1995 Wiley-Liss, Inc.