IDENTIFICATION OF WILD-TYPE AND MUTANT P53 PEPTIDES BINDING TO HLA-A2ASSESSED BY A PEPTIDE LOADING-DEFICIENT CELL-LINE ASSAY AND A NOVEL MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I PEPTIDE BINDING ASSAY

Mutations of the p53 gene are the most frequently observed genetic cha nges in human cancers; often leading to an overexpression of the wild- type (wt) p53 protein. Demonstrable T cell reactivity against tumor ce lls overexpressing wt or mutant p53-derived peptides could support the application of such epitopes in cancer immunotherapies. As the bindin g of peptide to MHC class I molecules is a prerequisite for antigen-sp ecific T cell recognition, we evaluated the ability of wt and mutant p 53 peptides to bind to HLA-A2.1 using two independent flow cytometry-b ased assay systems, the T2 major histocompatibility complex (MHC) clas s I peptide stabilization assay (stabilization assay) and the peptide- induced MHC class I reconstitution assay (reconstitution assay). The t wenty selected wt sequences each conformed to the previously reported HLA-A2.1 peptide binding motif. Seven of the wt p53 and 2/13 mutant p5 3 peptides derived from the previously chosen wt peptides bound to HLA -A2.1 in both the stabilization and the reconstitution assays. An addi tional six wt and six mutant p53 peptides, presumably exhibiting lower affinity for HLA-A2.1, were identified only in the reconstitution ass ay. Those p53 peptides binding HLA-A2.1 may provide useful immunogens for the generation of HLA-A2.1-restricted cytolytic T lymphocytes in v itro and in vivo.