Asymptomatic Human CD4 + Cytotoxic T-Cell Epitopes Identified from Herpes Simplex Virus Glycoprotein B

Abstract

The identification of “asymptomatic” (i.e., protective) epitopes recognized by T cells from herpes simplex virus (HSV)-seropositive healthy individuals is a prerequisite for an effective vaccine. Using the PepScan epitope mapping strategy, a library of 179 potential peptide epitopes (15-mers overlapping by 10 amino acids) was identified from HSV type 1 (HSV-1) glycoprotein B (gB), an antigen that induces protective immunity in both animal models and humans. Eighteen groups (G1 to G18) of 10 adjacent peptides each were first screened for T-cell antigenicity in 38 HSV-1-seropositive but HSV-2-seronegative individuals. Individual peptides within the two immunodominant groups (i.e., G4 and G14) were further screened with T cells from HLA-DR-genotyped and clinically defined symptomatic ( n = 10) and asymptomatic ( n = 10) HSV-1-seropositive healthy individuals. Peptides gB 161-175 and gB 166-180 within G4 and gB 661-675 within G14 recalled the strongest HLA-DR-dependent CD4 + T-cell proliferation and gamma interferon production. gB 166-180 , gB 661-675 , and gB 666-680 elicited ex vivo CD4 + cytotoxic T cells (CTLs) that lysed autologous HSV-1- and vaccinia virus (expressing gB)-infected lymphoblastoid cell lines. Interestingly, gB 166-180 and gB 666-680 peptide epitopes were strongly recognized by CD4 + T cells from 10 of 10 asymptomatic patients but not by CD4 + T cells from 10 of 10 symptomatic patients ( P < 0.0001; analysis of variance posttest). Inversely, CD4 + T cells from symptomatic patients preferentially recognized gB 661-675 ( P < 0.0001). Thus, we identified three previously unrecognized CD4 + CTL peptide epitopes in HSV-1 gB. Among these, gB 166-180 and gB 666-680 appear to be “asymptomatic” peptide epitopes and therefore should be considered in the design of future herpes vaccines.