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

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.