Immunological ignorance of an E7-encoded cytolytic T-lymphocyte epitope in transgenic mice expressing the E7 and E6 oncogenes of human papillomavirus type 16.

Certain human papillomaviruses (HPV) have been implicated in the etiology of cervical malignancies, and the E7 and E6 gene products of HPV type 16 are frequently expressed in these lesions. However, cytolytic T-lymphocyte (CTL)-mediated responses to HPV are rarely detectable in patients with cervical cancer. To examine whether the T-cell response is deficient during the HPV-induced transformation, we produced lines of transgenic (Tg) mice that expressed the E6 and E7 oncogenes in keratinized epithelia. The mice developed severe hypertrophy of all keratinized epithelia, but no malignancies were observed. Although epithelial cells from Tg mice could present at least an E7-encoded CTL epitope (E7 49-57), CTLs from these mice were neither primed to nor made tolerant of this epitope. No quantitative or qualitative differences were seen in the CTL responses of the Tg mice compared to those of their littermates following immunization with the peptide E7 49-57. Immunization of Tg mice with the E7 49-57 peptide protected them against a subcutaneous challenge with tumor cells expressing a transfected E7 gene, yet the skin was unaffected, although the cultured skin epithelial cells from Tg mice expressed E7. Our results suggest that the Tg mice were immunologically ignorant of HPV oncoproteins with respect to a CTL response and that a similar type of ignorance may explain why HPV-associated cervical cancer cells can escape immunological destruction.