SEQUENCE MOTIFS OF HUMAN HER-2 PROTOONCOGENE IMPORTANT FOR PEPTIDE BINDING TO HLA-A2

Tumor progression and metastasis are often associated with overexpress ion of specific cellular proteins. In 1991, we introduced a hypothesis that epitopes of nonmutated overexpressed proteins can be targets of a specific cellular immune response against tumor mediated by T cells (Mol Carcinogen 6: 77-81, 1992) and that, when T cell epitopes are pre sent, distinction between tumor immunity/autoimmunity and unresponsive ness can be predicated on the protein concentration as a limiting fact or of epitope supply. In support of this hypothesis, we demonstrated t hat CTL from patients with ovarian tumors which overexpress HER-2 prot o-oncogene can recognize both autologous tumor and synthetic analogs o f a specific epitope from HER-2, which was identified based on the con vergence of all criteria for selection of HLA-A2 associated epitopes r ecognized by T cells. In this study, we identified all epitopes in HER -2 containing nonapeptides with HLA-A2 anchors. Of these, analysis of potential amphiphilic sites identified both sequences and specific mut ations that positively affected the reactivity of conformationally dep endent HLA-A2 specific mAb which served as an indication of HER-2 pept ide binding. We also report the in vitro induction of cellular respons es to these peptides by PBMC from healthy HLA-A2+ volunteers as an ind ication of their ability to stimulate/ restimulate pre-existing T cell responses to HER-2. The peptides induced proliferative responses in o ne of four donors tested and CTL responses (one of three peptides test ed in two of three donors). This strategy may allow selection of immun ogenic HER-2 peptides and elucidation of mechanisms operating in induc tion of tolerance to defined epitopes on self-proteins.