The viral vectored vaccine targeting Thymosin β10 controls tumour growth in a murine model of prostate cancer

Direct analysis of MHC-presented antigens by mass spectrometry has been successfully applied for the evaluation of the antigenic landscape of different human tissues and malignancies in the past. In the current study, for the first time this approach has been applied to investigate a murine prostate cancer peptidome for the development of next generation prostate cancer vaccines using the TRansgenic Adenocarcinoma of Mouse Prostate, TRAMP, model. We have performed immunopeptidomic analysis of the normal mouse prostate and mouse prostate adenocarcinoma samples and identified a number of peptides overexpressed on tumour tissue compared to the normal prostate. We selected two of these proteins previously reported to play a role in carcinogenesis, thymosin beta 4 (Thyβ4) and thymosin beta 10 (Thyβ10), expressed them in the chimpanzee adenovirus (ChAdOx1) and Modified Vaccinia Ankara (MVA) recombinant viral vectors and evaluated these constructs as a candidate prostate cancer vaccine in a murine prostate cancer model. We have found that the vaccine encoding the Thyβ10 polypeptide tethered to the MHC class II associated invariant chain, CD74, significantly delayed outgrowth of established tumours in an ectopic TRAMP-C1 mouse model of prostate cancer. The observed tumour-protective efficacy was not associated with Thyβ10-specific cellular or antibody responses, suggesting an existence of other mechanisms underlying anti-tumour effect in this model that are yet to be elucidated.