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The genome organization of the novel human papillomavirus type 108 (HPV108), isolated from a low-grade cervical lesion, deviates from those of other HPVs in lacking an E6 gene. The three related HPV types HPV103, HPV108, and HPV101 were isolated from cervicovaginal cells taken from normal genital mucosa (HPV103) and low-grade (HPV108) and high-grade cervical (HPV101) intraepithelial neoplasia (Z. Chen, M. Schiffman, R. Herrero, R. DeSalle, and R. D. Burk, Virology 360:447-453, 2007, and this report). Their unusual genome organization, against the background of considerable phylogenetic distance from the other HPV types usually associated with lesions of the genital tract, prompted us to investigate whether HPV108 E7 per se is sufficient to induce the above-mentioned clinical lesions. Expression of HPV108 E7 in organotypic keratinocyte cultures increases proliferation and apoptosis, focal nuclear polymorphism, and polychromasia. This is associated with irregular intra- and extracellular lipid accumulation and loss of the epithelial barrier. These alterations are linked to HPV108 E7 binding to pRb and inducing its decrease, an increase in PCNA expression, and BrdU incorporation, as well as increased p53 and p21(CIP1) protein levels. A delay in keratin K10 expression, increased expression of keratins K14 and K16, and loss of the corneal proteins involucrin and loricrin have also been noted. These modifications are suggestive of infection by a high-risk papillomavirus.

Induction of effective immune responses may help prevent cancer progression. Tumor-specific antigens, such as those of human papillomaviruses involved in cervical cancer, are targets with limited intrinsic immunogenicity. Here we show that immunization with low doses (10(6) infectious units/dose) of a recombinant human adenovirus type 5 encoding a fusion of the E7 oncoprotein of human papillomavirus type 16 to the carboxyl terminus of the surface antigen of hepatitis B virus (HBsAg) induces remarkable E7-specific humoral and cellular immune responses. The HBsAg/E7 fusion protein assembled efficiently into virus-like particles, which stimulated antibody responses against both carrier and foreign antigens, and evoked antigen-specific kill of an indicator cell population in vivo. Antibody and T-cell responses were significantly higher than those induced by a control adenovirus vector expressing wild-type E7. Such responses were not affected by preexisting immunity against either HBsAg or adenovirus. These data demonstrate that the presence of E7 on HBsAg particles does not interfere with particle secretion, as it occurs with bigger proteins fused to the C terminus of HBsAg, and results in enhancement of CD8(+)-mediated T-cell responses to E7. Thus, fusion to HBsAg is a convenient strategy for developing cervical cancer therapeutic vaccines, since it enhances the immunogenicity of E7 while turning it into an innocuous secreted fusion protein.