To rationally design therapeutic human papillomavirus (HPV) vaccines, it is important to know which T cell epitopes are present on HPV-transformed cells. HPV affects the cellular antigen processing machinery, thus not every epitope derived from viral proteins is necessarily presented by Human Leukocyte Antigen (HLA)-molecules on the cancer cell surface.
HPV16 has been identified as the causative agent in 50% of all cervical cancer cases and in approximately 95% of all extra-cervical mucosal HPV-induced tumors. The transforming potential of high-risk HPVs is mediated by two consistently expressed viral oncoproteins, E6 and E7. As the induction and maintenance of the malignant phenotype depend on these two proteins, they are ideal targets for immunotherapy. A therapeutic vaccine that is applicable to everyone without prior HLA typing needs to contain epitopes for all HLA-types. Definition of epitopes for the five major HLA supertypes allows >95% population coverage.
To date, HPV T cell epitopes have mostly been determined for the most prevalent HLA type, HLA-A2. We now aim to identify HPV16 E6 and E7 T cell epitopes for the HLA-A3, HLA-A11 and HLA-A24 supertypes.
Different in silico prediction algorithms were used to predict prospective epitopes from the HPV16 E6 and E7 proteins for the mentioned HLA supertypes. In total, 64 epitopes, comprised of 8- to 11-mer peptides, were predicted for HLA-A3, 90 epitopes for HLA-A11 and 115 epitopes for HLA-A24. In competition-based binding assays, 15 previously known binding peptides were confirmed and 93 novel binding peptides were identified. For the generation of peptide-specific short term T cell lines, peripheral blood mononuclear cells (PBMCs) from buffy coats with known HLA types were stimulated with previously identified HLA-matching peptides and cultured for twelve days. Several peptides induced interferon gamma (IFNγ)-responses. Immunogenicity of the four most promising candidate peptides for HLA-A24 is currently assessed by generation of peptide-specific long term T cell lines from healthy donors. Functional assays, such as IFNγ-ELISpot assays and cytotoxicity assays, are conducted to determine the best vaccine candidates. The presence of binding peptides on HPV16-transformed cells is additionally analyzed by mass spectrometry analysis of immunoprecipitated HLA-peptide complexes.
In conclusion, we identified several new HPV16 E6 and E7 T cell epitopes. Verified epitopes are the basis of rational therapeutic vaccine design and also important for immunomonitoring purposes.
Citation Format: Stephanie Hoppe, Jan Winter, Renata Blatnik, Julia Schessner, Lisa Dressler, Alina Steinbach, Hadeel Khallouf, Martin Wuehl, Alexandra Klevenz, Angelika B. Riemer. Identification of target T cell epitopes for a therapeutic HPV16 vaccine. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B31.
- ©2015 American Association for Cancer Research.