Identification of Naturally Processed Mumps Virus Epitopes by Mass Spectrometry: Confirmation of Multiple CD8+ T-Cell Responses in Mumps Patients

Background. The re-emergence of mumps among vaccinated young adults has become a global issue. Besides waning of antibody responses, suboptimal induction of T-cell responses may reduce protection. In a recent study, we observed a dominant polyfunctional CD8(+) T-cell response after natural mumps virus (MuV) infection that was not present after vaccination. Unraveling the MuV epitope repertoire can provide insight in the specificity, functionality, and breadth of the T-cell response against MuV. Methods. Peptides were eluted from human leukocyte antigen (HLA) class I molecules of MuV-infected cells and characterized by advanced mass spectrometry. Selected identified MuV peptides were tested for in vitro and ex vivo immunogenicity. Results. In this study, we identified a broad landscape of 83 CD8(+)T-cell epitopes of MuV, 41 of which were confirmed based on synthetic peptide standards. For 6 epitopes, we showed induction of an HLA-A*02-restriced CD8(+)T-cell response. Moreover, robust T-cell responses against 5 selected MuV epitopes could be detected in all tested mumps patients using peptide/HLA-A*02:01 dextramers. Conclusions. The identified CD8(+)T-cell epitopes will help to further characterize MuV-specific T-cell immunity after natural MuV infection or vaccination. These MuV epitopes may provide clues for a better understanding of, and possibly for preventing, mumps vaccine failure.