Dissimilar Immunogenicities of Human Papillomavirus E7 and Adenovirus E1A Proteins Influence Primary Tumor Development

Although human papillomaviruses (HPV) and adenoviruses (Ad) both transform cells by expressing functionally related oncogenes (Ad-E1A/E1B; HPV-E7/E6), only HPV are oncogenic in humans. Prior studies have shown that HPV-transformed cells are resistant to NK cell lysis and E7- and E6-specific CTL are inefficiently generated in women with HPV-induced cervical cancer. Therefore, we postulated that the dissimilar oncogenicities of Ad and HPV may be caused by a protective NK and T cell response that is triggered by transformed cells expressing E1A, but not by E7. To test this hypothesis, mice that were either immunologically intact, lacked T cells, or lacked both NK and T cells were challenged with Ad serotype 5 (Ad5)-E1A- or HPV16-E7-transfected tumor cells. E7-expressing tumor cells were resistant to NK cell lysis in vitro and failed to elicit a measurable anti-tumor NK or T cell response in vivo. The concomitant expression of E6 did not change this phenotype. In contrast, E1A-expressing tumor cells were sensitive to NK lysis in vitro and triggered a protective NK and T cell immune response in vivo. These data suggest differences in the capacities of E1A or E7 oncoproteins to trigger protective anti-tumor immune responses may contribute to the dissimilar oncogenicities of Ad and HPV in humans.