Frequent display of human papillomavirus type 16 E6-specific memory t-Helper cells in the healthy population as witness of previous viral encounter

Genital human papillomavirus (HPV) infection is common and the majority of infected individuals successfully deal with this virus. Clearance of HPV is presumably mediated by T cells but HPV-16-specific T-cell memory was usually detected in patients with progressive disease and not in healthy subjects, suggesting that HPV-immunity comes too late. We now show the presence of HPV-16 E6-specific memory T-helper (Th) responses in a major fraction (12 of 20) of healthy individuals by application of the IFN-gamma-ELISPOT assay. Although nearly all E6-peptides were recognized, the majority of the responders targeted peptide sequences of the COOH-terminal half (E6(81-158)) of HPV-16 E6. In a direct comparison, the presence of HPV-16 E6-specific T cells coincided with HPV-16 E2-specific T-cell reactivity in healthy individuals, whereas hardly any HPV-16 E7-specific Th immunity was found. This indicates that the induction of T-cell reactivity against HPV-16 E7 is suboptimal during infection when compared with that against HPV-16 E2 and HPV-16 E6. In conclusion, the presence of HPV-16 E6-specific Th memory in the healthy population demonstrates that HPV infection leads to T-cell immunity against immediate early proteins expressed during infection. Because this HPV-16 E6-specific T-cell immunity was frequently detected in healthy subjects, our data suggest that the observed IFN-gamma-producing proliferating T cells circulating in the peripheral blood play a role in protection against persistent HPV infection and associated development of malignancies.