Abstract 721: Development of a therapeutic HPV vaccine based on mass spectrometry-verified target epitopes

Abstract

For rational therapeutic vaccine design, detailed knowledge about target epitopes that are truly presented on cancer cells is essential. Many potential tumor-specific epitopes, such as viral epitopes or mutation-derived neoepitopes, are presented at low abundance. Thus, detection of these epitopes remains a challenge. We have developed a high-sensitivity targeted mass spectrometry (MS) approach for direct detection of low-abundant epitopes. We used human papillomavirus (HPV) as a model system, as high-risk HPVs cause over 600,000 cervical, anogenital and oropharyngeal cancer cases per year. Moreover, the HPV oncoproteins E6 and E7 are essential for the induction and maintenance of the malignant phenotype, and thus are ideal targets for immunotherapy. Potential HPV16 E6 and E7 target epitopes were predicted in silico and their HLA-binding verified in cellular binding assays. HLA-peptide complexes were immunoprecipitated from HPV16-positive cancer cells and the purified peptides were analyzed by MS. Identified HPV epitopes were assessed for immunogenicity in vitro with PBMC from healthy donors and in vivo in the MHC-humanized mouse model A2.DR1. The binding assays resulted in the identification of known and novel HPV16-derived HLA-binding peptides. Furthermore, we used this data to formulate rules on how to optimally use epitope prediction tools to increase the chances of predicting true HLA ligands. 14 HLA-A2-restricted HPV16 epitopes were detected on the surface of CaSki and 866 cervical cancer cells, 9 of which were novel. 13 out of the 14 MS-detected peptides were immunogenic in ELISpot assays. Vaccination of A2.DR1 mice with one selected epitope induced high numbers of specific cytotoxic T-cells, and caused anti-tumor effects in a newly developed HPV16 E6/E7-expressing A2.DR1-compatible tumor model. We conclude that our epitope detection and validation approach is suitable for validating even low-abundant candidate epitopes to be true immunotherapy targets. MS-detection of epitopes appears to be a good predictor of immunogenicity, which makes this approach an attractive platform for determining target epitopes for therapeutic cancer vaccines. Citation Format: Sebastian Kruse, Maria Bonsack, Sara Becker, Nitya Mohan, Alina Steinbach, Stephanie Hoppe, Renata Blatnik, Angelika B. Riemer. Development of a therapeutic HPV vaccine based on mass spectrometry-verified target epitopes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 721.