Protective Asymptomatic Human Leukocyte Antigen (HLA)-A*0201-Restricted CD8+ Cytotoxic T-Lymphocyte Epitopes Identified from Herpes Simplex Virus Glycoprotein B

Abstract

Purpose: : Evidence obtained from B6 mice suggests that CD8⁺ T-cells specific for herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) contributes to protective immunity against ocular herpes. However, gB-specific human CD8⁺ T-cell epitopes remain largely undefined. In this study, we sought to identify protective human CD8⁺ T cell epitopes on HSV-1 gB that are restricted to HLA-A*0201, a haplotype that covers over 50% of the human population.

Methods: : The 904-amino acid HSV-1 (strain 17) sequences were screened for potential CD8⁺ T cell epitopes, presented by HLA-A*0201 using a variety of prediction algorithms and immunological parameters.

Results: : Ten potential epitope peptides, each nine amino acids in length, were identified, synthesized and tested for affinity to HLA-A*0201 molecule. Two of these peptide epitopes, gB_441-449 and gB_561-569, exhibited high affinity for soluble HLA-A*0201 molecules. Peptide-specific CD8⁺ T cell proliferation (CFSE dilution) and CD107a/b cytotoxic degranulation were demonstrated against the same two epitopes in 30 sequentially studied asymptomatic HLA-A*0201-positive, HSV-1 seropositive individuals. CD8+ T cells from 4 symptomatic individuals did not recognize these two epitopes. Luminex cytokine staining for IFN-γ, IL-2, and TNF-α revealed dual- and triple-positive T cells. These CD8⁺ T cells were primed during natural infection, because they were absent from seronegative non-infected individuals. Moreover, a heterologous lipopeptide/rAdv5 prime/boost vaccine expressing these two asymptomatic gB CD8⁺ epitopes induced a strong and long lasting CD8⁺ T-cell protective immunity against ocular herpes in a susceptible HLA-A*0201 transgenic mice.

Conclusions: : The HSV-gB-epitope repertoire for human CD8⁺ T cells appeared to be more restricted than hitherto suspected. The newly identified asymptomatic gB epitopes: (i) are recognized by (poly)functional CD8⁺ T cells in seropositive asymptomatic individuals (i.e. during control of ocular herpetic disease) and (ii) are able to induce protective CD8⁺ T cell dependent immunity in HLA transgenic mice. Mapping of human protective asymptomatic CD8⁺ T-cell epitopes on HSV-1 proteins should continue to provide new insight into immune correlates of protection and aid in the development of a safe and efficient immunotherapeutic vaccine for ocular herpes.

Keywords: herpes simplex virus • inflammation • immunomodulation/immunoregulation