Identification of novel immunogenic human leukocyte antigen‐A*2402‐binding epitopes of human papillomavirus type 16 E7 for immunotherapy against human cervical cancer

Abstract

BACKGROUND: A study was undertaken to identify new immunogenic human leukocyte antigen (HLA)-A 2402-restricted epitopes from human papillomavirus (HPV) type 16 E7 protein for immunotherapy against cervical cancer. METHODS: Synthetic overlapping peptides were screened by measuring the frequency of CD8(+) cytotoxic T lymphocytes (CTLs) producing intracellular interferon-γ (IFN-γ) using flow cytometry and were validated in SiHa cells with a Cr release cytotoxicity assay. In vivo antitumor effects of peptide-sensitized peripheral blood mononuclear cells (PBMCs) and isolated CD8(+) CTLs were evaluated using BALB/c nude mice with SiHa cell xenotransplants. RESULTS: Among 14 overlapping 15-amino acid peptides, E7(61-75) (CDSTLRLCVQSTHVD) and E7(67-81) (LCVQSTHVDIRTLED) induced significantly higher IFN-γ production (P < .05) and showed higher in vitro cytotoxicity against SiHa cells than did cells sensitized with the negative control. To determine the exact HLA-A 2402-restricted epitopes, a total of 25 overlapping 9- or 10-amino acid peptides spanning E7(61-75) and E7(67-81) were synthesized. E7(61-69) (CDSTLRLCV) and E7(67-76) (LCVQSTHVDI) induced significantly greater IFN-γ production as well as increased in vitro cytotoxicity against SiHa cells compared with those of other peptides and the negative control (P < .01), and the antitumor effects of these peptide-sensitized PBMCs were induced by CD8(+) CTLs. E7(61-69) -sensitized and E7(67-76) -sensitized PBMCs and isolated CD8(+) CTLs showed a much greater suppression of tumor growth in vivo compared with that of control groups treated with PBS (P < .01). The authors also confirmed the synergistic antitumor effect of cisplatin followed by E7(67-76) -sensitized PBMCs in vivo. CONCLUSIONS: E7(61-69) and E7(67-76) were identified as novel HPV type 16 E7 epitopes for HLA-A 2402, which could be used for immunotherapy against cervical cancer.