The Human CD4(+) T Cell Response against Mumps Virus Targets a Broadly Recognized Nucleoprotein Epitope
JOURNAL OF VIROLOGY
Authors: de Wit, Jelle; Emmelot, Maarten E.; Poelen, Martien C. M.; Lanfermeijer, Josien; Han, Wanda G. H.; van Els, Odle A. C. M.; Kaaijk, Patricia
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 MuVN110- 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 HLADRB1 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.
Functional consequences of attenuating mutations in the haemagglutinin-neuraminidase, fusion and polymerase proteins of a wild-type mumps virus strain
JOURNAL OF GENERAL VIROLOGY
Authors: Malik, Tahir; Wolbert, Candie; Mauldin, Jeremy; Sauder, Christian; Carbone, Kathryn M.; Rubin, Steven A.
Wild-type mumps viruses (MuVs) are highly neurotropic and, prior to widespread vaccination programmes, were a major cause of viral meningitis and encephalitis in most developed countries. At present, there are no markers for virus attenuation, apart from the failure of a passaged isolate to produce clinical symptoms in vaccinees. Indeed, some MuV vaccines have retained residual neurovirulence properties and have caused aseptic meningitis in vaccinees. Three amino acid changes associated with the neuroattenuation of a wild-type MuV strain were identified previously. This study evaluated the impact of these changes on the function of the respective proteins. The data demonstrated that the Ser -> Asp amino acid substitution at position 466 in the haemagglutinin-neuraminidase protein resulted in decreased receptor binding and neuraminiclase activity, the Ala/Thr -> Thr selection in the fusion protein resulted in decreased fusion activity, and the Ile -> Val substitution in the polymerase resulted in increased replicative/transcriptional activity. These data suggest a polygenic component (i.e. specific and inter-related roles of these amino acid changes) to MuV neuroattenuation.