Differential binding to frequent HLA-A alleles of p21 RAS derived peptides bearing oncogenic substitutions at position 12 or 13.

Abstract RAS oncogenic proteins are frequently found mutated in human cancers, where they are known to be implicated in the tumoral process. Mutations occur preferentially at positions 12, 13 or 61. Identification of potential T cell epitopes is the first step to determine if RAS mutated proteins can generate tumor specific antigens which could be further used as targets for cancer immunotherapy protocols. We have investigated the capacity of synthetic wild-type and mutant RAS derived peptides encompassing positions 12 and 13 to bind to three frequent HLA-A alleles: HLA-A∗0201, HLA-A∗0301 and HLA-A∗1101. Binding was evaluated by two methods using TAP-defective cell lines: a cytometric assay based on HLA molecules stabilization at the cell surface, and an assembly assay detecting interactions between solubilized HLA molecules and peptides. Positive HLA binding was observed for two sets of synthetic peptides, one specific for HLA-A∗0201 allele (RAS 5–14), and the other one specific for HLA-A∗0301 and HLA-A∗1101 alleles (RAS 8–16). Interestingly, the different substitutions at positions 12 and 13 were not equivalent for HLA binding. These observations will be useful for the in vitro generation of restricted CD8 + T lymphocytes specific for mutated RAS proteins and recognizing tumoral cells expressing such RAS mutations.