Peripheral tolerance to human papillomavirus E7 oncoprotein occurs by cross-tolerization, is largely Th-2-independent, and is broken by dendritic cell immunization

The E7 oncoprotein of human papillomavirus 16 functions as a tumor-specific antigen in transformed epithelial cells of the uterine cervix to which immunotherapeutic strategies aimed at CTL induction may be directed. We previously have shown in mice transgenic for the E7 gene driven off an epithelial specific (keratin-14) promoter, that expression of E7 protein in peripheral epithelium is sufficient to tolerize E7-directed CTL precursors (pCTL; Doan et al, J. Virol., 73: 6166-1670, 1999). Here we show that E7 is presented to T cells for tolerization by cells of bone marrow origin ("cross-tolerization"). We demonstrate that tolerization of E7-directed pCTLs occurs within 2 weeks of exposure to E7 in epithelium. It is maintained in the near absence of CD4+ cells and in the absence of the thymus, and is independent of a coexisting E7-directed Th2-type antibody response. Tolerance was broken by immunization with E7 CTL epitope-pulsed dendritic cells. These findings have implications for immunotherapy of patients with human papillomavirus 16-associated cervical carcinoma, whose immune systems may have experienced long-term exposure to E7-expressing epithelial cells.