Mapping of cytotoxic T lymphocytes epitopes in E7 antigen of human papillomavirus type 11

One of the critical steps in the progression to condyloma acuminatum (CA) is the establishment of a persistent human papillomavirus (HPV) infection, majority of HPV type 6 and 11. Cytotoxic T lymphocytes (CTL), which can be induced by the epitope-based peptides in vitro, are thought to be able to recognize and destroy virus-infected cells. In order to screen and identify HLA-A*0201 restricted HPV-11E7 CTL epitopes, five epitope peptides and tetramers were selected including HPV-11E7 7–15 (TLKDIVLDL), 15–23 (LQPPDPVGL), 47–55 (PLTQHYQIL), 81–89 (DLLLGTLNI) and 82–90 (LLLGTLNIV). Human monocyte-derived dendritic cells (DCs) from HLA-A*0201 healthy individuals were pulsed with these peptides to assess the expression of CD83, CD86, HLA-DR and the secretion of IL-12. The ability of peptide-loaded mature DCs to activate autologous T cells was evaluated by analyzing the frequency of specific tetramer⁺ CD8⁺ T cells using flow cytometry, and the level of IFN-γ secretion by ELISA. The ability of the epitope-specific CTLs to kill the target cells was also analysed. It was found that the immature DCs could be fully activated by all the five HPV-11E7 peptides and peptide-loaded mature DCs were able to stimulate the epitope-specific T cells in vitro. There was an increased frequency of CD8⁺ T cells specific for the E7 7–15 epitope when compared to other four predicted epitopes of HPV-11E7 (P < 0.05). The epitope-specific CTLs for E7 7–15 induced the strongest cytotoxicity to HPV-11E7 expressing cell line at an E:T ratio of 50:1 (P < 0.05). Taken together, these findings demonstrate that E7 7–15 (TLKDIVLDL) is an HLA-A*0201-restricted CTL epitope of HPV type 11. We propose that this epitope could be more helpful in the characterization of HPV control mechanism and be useful for the development of immunotherapeutic approaches for low-risk HPV infectious diseases such as CA.