Identification of a naturally processed HLA-A*0201 HPV18 E7 T cell epitope by tumor cell mediated in vitro vaccination

Abstract

Immunotherapy of HPV-associated disease such as cervical cancer is moving from preclinical investigation to clinical trials. The viral oncoproteins E6 and E7 are ideal target antigens because their expression is mandatory in HPV-transformed tumor cells. T cells are the most important effector cells for therapeutic vaccination strategies. Therefore, the identification and characterization of HPV E6 and E7 T cell epitopes is necessary. Methods to date rely on screening for immunogenicity of peptides predicted by algorithms. Presentation of the identified peptides on tumor cells, however, needs to be confirmed. In our study, we have improved the method to identify peptide epitopes of HPV18 E7 that are actually presented by tumor cells. We induced allogeneic T-cell lines by stimulation with HPV18-positive, CD80 and HLA-A*0201 transfected cervical cancer cells. Sensitized T cells were probed against an array of a HPV18 E7 20mer peptide-library. We found specific reactivity to one of the 20mer peptides. This sequence was then screened via algorithms for putative epitopes. One putative HLA-A2 restricted epitope was confirmed to bind to HLA-A2, to be immunogenic and to induce IFN gamma-release in ELISpot assays. Epitope-specific T cells were cytolytic toward autologous peptide pulsed targets and HPV18 transformed tumor cells. The identification of epitope-specific T cells in tumor infiltrating lymphocytes of a HPV18-positive HLA-matched cervical cancer patient suggests an in vivo relevance of the identified epitope. We suggest that our approach is advantageous over conventional methods, because it yields candidate peptides that are relevant CTL epitopes that are expressed, processed and presented by tumor cells.