The Human CD4⁺T Cell Response against Mumps Virus Targets a Broadly Recognized Nucleoprotein Epitope

Abstract

Mumps outbreaks among vaccinated young adults stress the need for a better understanding of mumps virus (MuV)-induced immunity. Antibody responses to MuV are well characterized, but studies on T cell responses are limited. We recently isolated a MuV-specific CD4+ T cell clone by stimulating peripheral blood mononuclear cells (PBMCs) from a mumps case with the viral nucleoprotein (MuV-N). In this study, we further explored the identity and relevance of the epitope recognized by the CD4+ T cell clone and ex vivo by T cells in a cohort of mumps cases. Using a two-dimensional matrix peptide pool of 15-mer peptides covering the complete MuV-N, we identified the epitope recognized by the T cell clone as MuV-N110–124 GTYRLIPNARANLTA, present in a well-conserved region of the viral protein. Upon peptide-specific stimulation, the T cell clone expressed the activation marker CD137 and produced gamma interferon, tumor necrosis factor, and interleukin-10 in a HLA-DR4-restricted manner. Moreover, the CD4+ T cells exerted a cytotoxic phenotype and specifically killed cells presenting MuV-N110–124. Furthermore, the identified peptide is widely applicable to the general population since it is predicted to bind various common HLA-DR molecules, and epitope-specific CD4+ T cells displaying cytotoxic/Th1-type properties were found in all tested mumps cases expressing different HLA-DR alleles. This first broadly recognized human MuV-specific CD4+ T cell epitope could provide a useful tool to detect and evaluate virus-specific T cell responses upon MuV infection or following vaccination. IMPORTANCE Recent outbreaks of mumps among vaccinated young adults have been reported worldwide. Humoral responses against mumps virus (MuV) are well characterized, although no correlate of protection has been elucidated, stressing the need to better understand cellular MuV-specific immunity. In this study, we identified the first MuV T cell epitope, which is derived from the viral nucleoprotein (MuV-N) and was recognized by a cytotoxic/Th1 CD4+ T cell clone that was isolated from a mumps case. Moreover, the epitope was predicted to bind a broad variety of common HLA-DRB1 alleles, which was confirmed by the epitope-specific cytotoxic/Th1 CD4+ T cell responses observed in multiple mumps cases with various HLA-DRB1 genotypes. The identified epitope is completely conserved among various mumps strains. These findings qualify this promiscuous MuV T cell epitope as a useful tool for further in-depth exploration of MuV-specific T cell immunity after natural mumps virus infection or induced by vaccination.

Mumps Outbreaks in Vaccinated Populations—Is It Time to Re-assess the Clinical Efficacy of Vaccines?

“…Although, it has also been shown that natural mumps infection or vaccination do not always induce both cellular and humoral immunity. de Wit et al (199,236,237) has shown the presence of Th1-type CD4 + T-cells recognizing a MuV epitope in a HLR-DR restricted manner. In addition, the response of IFN-γ and TNF producing CD8 + T-cells specific to MuV epitopes are lower in vaccinated individuals when compared to individuals who were naturally infected (199,213,(236)(237)(238).…”

“…de Wit et al (199,236,237) has shown the presence of Th1-type CD4 + T-cells recognizing a MuV epitope in a HLR-DR restricted manner. In addition, the response of IFN-γ and TNF producing CD8 + T-cells specific to MuV epitopes are lower in vaccinated individuals when compared to individuals who were naturally infected (199,213,(236)(237)(238). Utilizing current knowledge and new technologies may help define a better surrogate correlate of protection and potentially determine a cut-off between the immunity of a vaccinated individual and a secondary mumps infection.…”

Novel mumps virus epitopes reveal robust cytotoxic T cell responses after natural infection but not after vaccination

“…APIQGTNLL (V/P/I 27-35 ), KPRTSTPVTEF (V/P/I 142-152 ), IPNARANL (NP 115-122 )), each inducing a strong T cell response in expanded effector T cells obtained from three different HLA-B*07:02-positive mumps patients. Interestingly, the first described MuV-specific CD4 + T-helper cell epitope, GTYRLIPNARANLTA (NP 110-124 ), which we recently discovered 18 , contains the newly identified HLA-B*07:02-restricted CD8 + T cell epitope IPNARANL (NP 115-122 ). This opens the possibility of using synthetic peptides, containing both epitope sequences, to stimulate CD4 + and CD8 + T cell responses simultaneously.…”

“…A flow cytometry-based killing assay was used to determine the cytotoxic capacity of the various epitope-specific T cell lines 18 . For this purpose, BLCL as antigen-presenting cells were labeled with 0.1 µM CellTrace violet (C34557, Thermo Fisher Scientific) and pulsed with one of the five selected peptides (5 µM) or medium or non-immunogenic MuV peptide as negative control.…”

Genetic Analysis Reveals Differences in CD8+ T Cell Epitope Regions That May Impact Cross-Reactivity of Vaccine-Induced T Cells against Wild-Type Mumps Viruses

“…Analysis of T cell epitopes can be a useful tool to characterize the CD8 + T cell response after vaccination, and explore the cross-reactive potency of the T cells induced by vaccination towards circulating strains. Recently, we described the first set of T cell epitopes of MuV [ 16 , 17 ]. CD8 + T cell epitopes of MuV were identified by eluting peptides from HLA Class I (HLA-I) molecules from antigen-presenting cells that were infected with MuV, using a genotype G outbreak strain.…”