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

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.