Expression of CD56 by human papillomavirus E7-specific CD8+ cytotoxic T lymphocytes correlates with increased intracellular perforin expression and enhanced cytotoxicity against HLA-A2-matched cervical tumor cells.

Human papillomavirus (HPV) infection represents the most important risk factor for developing cervical cancer. In this study, we examine the potential of full-length E7-pulsed autologous dendritic cells (DCs) to induce antigen-specific CTL responses from the peripheral blood of healthy individuals against HLA-A2-matched HPV-16 and HPV-18-positive tumor target cells in vitro. We show that DCs pulsed with E7 oncoprotein can consistently stimulate antigen-specific CTL responses that recognize and lyse HPV-16 or HPV-18-positive naturally infected cervical cancer cell lines. HPV-negative, EBV-transformed lymphoblastoid cell lines (LCLs) sharing the HLA haplotype of the target tumor cells, as well as autologous donor LCLs, were not significantly killed by E7-specific CTLs. Cytotoxicity against HLA-A2-matched HPV-16 and HPV-18 tumor target cells could be significantly inhibited by anti-HLA class I and by anti-HLA-A2 monoclonal antibodies. CD8+ CTLs expressed variable levels of CD56 and showed a strongly polarized Type 1 cytokine profile. Sorting of the CD8+ T cells on the basis of CD56 expression demonstrated that the most highly cytotoxic CTLs were CD56+ and expressed higher levels of perforin and IFN-gamma, compared with the CD8+/CD56- population. Taken together, these data demonstrate that full-length, E7-pulsed DCs can consistently induce E7-specific CD8+ CTL responses in healthy individuals that are able to kill naturally HPV-16 and HPV-18-infected cancer cells, and that CD56 expression defines a subset of CD8+ CTLs with high cytolytic activity against tumor cells.