Induction in transgenic mice of HLA-A2.1-restricted cytotoxic T cells specific for a peptide sequence from a mutated p21ras protein

Cytotoxic T cells (CTL) recognize short peptides that are derived from the proteolysis of endogenous cellular proteins and presented on the cell surfa ce as a complex with MHC class I molecules. CTL can recognize single amino acid substitutions in proteins, including those involved in malignant trans formation. The mutated sequence of an oncogene may be presented on the cell surface as a peptide, and thus represents a potential target antigen for t umour therapy. The p21(ras) gene is mutated in a wide variety of tumours an d since the transforming mutations result in amino acid substitutions at po sitions 12, 13 and 61 of the protein, a limited number of ras peptides coul d potentially be used in the treatment of a wide variety of malignancies. A common substitution is Val for Gly at position 12 of p21(ras). In this stu dy, we show that the peptide sequence from position 5 to position 14 with V al at position 12-ras p5-14 (Val-12)-has a motif which allows it to bind to HLA-A2.1. HLA-A2.1-restricted ras p5-14 (Val-12)-specific CTL were induced in mice transgenic for both HLA-A2.1 and human beta(2)-micro-globulin afte r in vivo priming with the peptide. The murine CTL could recognize the ras p5-14 (Val-12) peptide when they were presented on both murine and human ta rget cells bearing HLA-A2.1. No crossreactivity was observed with the nativ e peptide ras p5-14 (Gly-12), and this peptide was not immunogenic in HLA-A 2.1 transgenic mice. This represents an interesting model for the study of an HLA-restricted CD8 cytotoxic T cell response to a defined tumour antigen in vivo.