Identification of a First Human Norovirus CD8+ T Cell Epitope Restricted to HLA-A*0201 Allele.

Maria Malm,Timo Vesikari,Vesna Blazevic

doi:10.3389/fimmu.2018.02782

Abstract

Norovirus (NoV) causes a substantial global burden of acute gastroenteritis in all age groups and the development of NoV vaccine is a high priority. There are still gaps in understanding of protective NoV-specific immunity. Antibody mediated immune responses have been widely studied, but in contrast, the research on NoV-specific human T cell-mediated immunity is very limited. We have recently reported NoV capsid VP1-specific 18-mer peptide (134SPSQVTMFPHIIVDVRQL151) to induce strong CD8+ T cell immune responses in healthy adult donors. This work extends to identify the precise NoV T cell epitope and the restricting human leucocyte antigen (HLA). Pentamer technology was used to detect HLA-A*0201-restricted T cell-mediated responses to 10-mer peptide 139TMFPHIIVDV148 of four healthy adult blood donors. Immunogenicity of the 10-mer epitope was confirmed by ELISPOT IFN-γ and intracellular cytokine staining (ICS) on flow cytometry. A population of CD3+CD8+ T lymphocytes binding to HLA-A*0201/TMFPHIIVDV pentamers was identified in two HLA-A*0201-positive donors. Recognition of the 10-mer epitope by T cells resulted in a strong IFN-γ secretion as shown by ELISPOT assay. In addition, ICS confirmed that high proportion (31 and 59%) of the TMFPHIIVDV epitope-responsive CD3+CD8+ T cells in the two donors had multifunctional phenotype, simultaneously producing IFN-γ, IL-2 and TNF-α cytokines. In the present study novel human NoV HLA-A*0201-restricted minimal 10-mer epitope 139TMFPHIIVDV148 in the capsid VP1 was identified. The HLA-peptide pentamer staining of T cells from healthy donor PBMCs and cytokine responses in ex-vivo ELISPOT and ICS assays suggest that this epitope is recognized during NoV infection and activates memory phenotype of the epitope-specific multifunctional CD8+ T cells. The importance of this epitope in protection from NoV infection remains to be determined.

Highlights

Noroviruses (NoV) are group of very contagious viruses that cause >90% of non-bacterial and approximately half of all-cause epidemic gastroenteritis worldwide
Using matrix peptide approach we have recently identified a NoV-specific 18-mer peptide (134SPSQVTMFPHIIVDVRQL151) containing CD8+ T cell epitope likely restricted to human leukocyte antigen (HLA)-A∗0201 allele [17]
When comparing the aa sequence of different NoV genotypes (Table 1) the 10-mer epitope was found to be highly conserved among different GII.4 variants and more distant NoV genotypes belonging to GII and GI

Summary

Introduction

Noroviruses (NoV) are group of very contagious viruses that cause >90% of non-bacterial and approximately half of all-cause epidemic gastroenteritis worldwide. NoV gastroenteritis is a significant public health problem with high clinical and economic costs, that is estimated to cause over 200,000 deaths annually, mainly in resource-limited countries [1]. Human Norovirus T Cell Epitopes mainly to GI and GII, that include over 30 genotypes and numerous intra-genotype variants [4]. The antigenic diversity of NoVs is likely to have major impact on evading host immune responses and complicates designing of NoV vaccines. NoV research is further limited due to the lack of small animal model and efficient NoV propagation in cell culture [7, 8], but spontaneously formed NoV VP1 virus-like particles (VLPs) are successfully utilized as viral surrogates for assaying immune responses and as vaccine candidates [9, 10]

Objectives

Methods

Results

Conclusion