Cytotoxic Human Leukocyte Antigen (HLA)-DR-Restricted CD4+ T-Cell Epitopes Identified From Herpes Simplex Virus Type 1 Glycoprotein B Following Ocular Infection

Abstract

Purpose: : HSV-1 gB has great potential as a vaccine candidate against ocular herpes. As part of the development of a lipopeptide T cell epitope-based vaccine against ocular herpes, we undertook the identification of immunodominant human CD4+ T cell epitopes from HSV-1 gB and then determined if these epitopes are recognized following ocular infection.

Methods: : Using the PepScan epitope-mapping strategy, a library of 15-mer gB peptides, overlapping by 10 aa, was identified, constructed, and divided into 18 groups (G1 to G18). CD4+ T cell responses to each group were studied in HSV seropositive asymptomatic patients (n = 30), using: (i) IFN-gamma ELISpot; (ii) in vitro proliferation; (iii) expression of CD69, an early T-cell marker of activation; and (iv) cytotoxic CD107a/b degranulation assays. Immunodominant human epitopes were confirmed by assessing the T cell responses induced in HLA-DRB1*0101 and HLA-DRB1*0401 transgenic (Tg) mice ocularly infected with HSV-1.

Results: : Based on responder prevalence and magnitude of induced T-cell responses, two immuno-dominant groups of gB peptides (G4 and G14) were found. The human response to these two groups was gender-dependent. Peptides gB161-175 and gB166-180, in G4, and peptides gB661-675 and gB666-680 in G14 showed the strongest CD4+ T cell proliferation. gB161-175, gB166-180 and gB661-675 elicited ex-vivo CD107a/b degranulation of CD4+ T cells, suggesting that the epitopes contained at least one cytotoxic epitope. These responses were abrogated by anti-HLA-DR mAb showing HLA-DR-dependence of the T cell response. After ocular HSV-1 infection of all DRB1*0101 and DRB1*0401 Tg mice developed HLA-DR-restricted T cell responses directed at the same 3 epitopes identified in naturally infected asymptomatic patients. Higher magnitude of T cell responses were induced in female DRB1*0101 and DRB1*0401 Tg mice compared to males.

Conclusions: : We identified (i) three previously unrecognized promiscuous HLA-DR-restricted cytotoxic CD4+ T cell epitopes from HSV-1 gB (ii) gB166-180 was an immunodominant CD4+ T-cell epitope. These 3 gB epitopes are candidates for incorporation in an effective epitope based HSV vaccine.

Keywords: herpes simplex virus • immunomodulation/immunoregulation • keratitis