Two Human Leukocyte Antigen (HLA)-A*0201-Restricted Epitopes Identified from Herpes Simplex Virus Glycoprotein B are Recognized Exclusively by CD8+ T cells from Asymptomatic Individuals and Protect Against Ocular Herpes

Abstract

Purpose: Mouse CD8+ T cells specific for HSV-1 glycoprotein B (gB) appear to play a critical role in preventing virus reactivation and subsequent ocular disease. However, the repertoire, in vivo frequency, and functionality of human CD8+ T cells in symptomatic individuals (who get clinical HSV) vs. asymptomatic individuals (who do not) remains largely undefined. Here we identify gB “symptomatic” vs. “asymptomatic” human HLA-A*0201-restricted CD8+ T cell epitopes.. This haplotype covers >50% of the human population.

Methods: The gB sequence was screened for potential HLA-A*0201 CD8+T cell epitopes using a variety of algorithms. The ability of these epitopes to induce multi-functional CD8+ T cell responses was compared in 10 “symptomatic” vs. 10 “asymptomatic” individuals.

Results: Ten potential epitope peptides, each nine amino acids in length, were identified, synthesized and tested for affinity to HLA-A*0201. gB441-449 and gB561-569 exhibited high affinity for HLA-A*0201 molecules and significantly stabilized MHC class I molecules on the surface of T2 cells. Peptide-specific CD8+ T cell proliferation (CFSE dilution) and CD107a/b cytotoxic degranulation against these two epitopes were found in all 10 HSV-1 seropositive asymptomatic individuals. Recognition by asymptomatic CD8+ T cells was validated for the two epitopes using HLA/peptide tetramers. Luminex cytokine staining for IFN-γ, IL-2, and TNF-α revealed dual- and triple-positive CD8+ T cells, indicating that these gB peptide-specific CD8+ T cells were (poly)functional. The CD8+ T cell responses to these two epitopes were absent in “symptomatic” individuals. A lipopeptide/rAdv5 prime/boost mucosal vaccine using these asymptomatic CD8+ epitopes induced strong, long lasting CD8+ T-cell protective immunity against ocular herpes in susceptible HLA-A*0201 “humanized” transgenic mice.

Conclusions: The HSV-gB-epitope repertoire for human CD8+ T cells is more restricted than previously suspected. Identification of human “asymptomatic” HSV-1 epitopes that induce (poly)functional CD8+ T cells would help in designing a protective immunotherapeutic vaccine against ocular herpes.

Keywords: 545 herpes simplex virus • 555 immunomodulation/immunoregulation • 573 keratitis