Background: To identify the novel epitopes from the human papillomavirus type 18 E7 which can sensitize PBMCs of four different major HLA class I A allele.
Methods: Twenty-four synthetic overlapping 15-amino acid peptides were screened by measuring the frequency of CD8+ cytotoxic T lymphocytes (CTLs)-producing interferon-γ (IFN-γ) by using flow cytometry and ELISpot assays and selected peptides were validated for cytolytic activity by using the 51Cr release assay. Truncated peptides in the selected epitopes were tested to determine the important residues using ELISpot and 51Cr release assay.
Results: Among 24 peptides, E781-95DDLRAFQQLFLNTLS (#21) and E789-103LFLNTLSFVCPWCAS (#23) induced significantly higher Th 1 response including IFN-γ production and in vitro cytotoxicity of PBMCs of four different HLA-A alleles against cervical cancer cells than that of other peptides and the negative control (no peptide sensitization). In E781-95 (#21), amino acid position 81, 82 (N-terminus) and 92, 94, 95 (C-terminus) for HLA-A*02:02 and 24:02, and 81, 82 (N-terminus) and 92, 95 (C-terminus) for HLA-A*11:01 and 33:03 were important to elicit Th1 response of PBMCS. In E789-103 (#23), residue 100 and103 (C-terminus) were important to elicit the CD8+ CTL response in HLA-A*02:01, 11:01 and 33:03 and 100, 101, and 103 (C-terminus) were important to elicit the CD8+ CTL response in HLA-A*24:02.
Conclusions: E781-95 (#21) and E789-103 (#23) were identified as novel epitopes from HPV18 E7 which could sensitized PBMCs of four different HLA class I (HLA-A*02:01, 24:02, 11:01 and 33:03). These epitopes could be useful for immune monitoring and immunotherapy for HPV 18+ cervical cancer.