HPV immortalization of human oral epithelial cells: a model for carcinogenesis

Human papillomavirus (HPV) has been implicated in the etiology of oral and cervical cancers. Normal oral epithelial cells at passage two were infected with recombinant retrovirus containing the E6/E7 open reading frames of HPV type 16. The G418-selected cells that were immortalized and express HPV 16 E6/E7 have been in culture for over 4 years and 350 passages. In contrast, the normal oral epithelial cells did not survive the culture environment beyond 7 to 9 passages. Fifteen clones were selected from the pooled population. By Northern blot analysis all clones demonstrated the presence of E6solidusE7 genes. Keratin expression of both normal and immortalized oral epithelial cells was studied in organotypic culture. Both cell types were positive with antibodies AE1, AE3, and 34BE12. Both were focally positive with AE8, which stains for keratin 13 (specific for oral and esophageal epithelial cells). The normal control cells were focally positive for filaggrin, while the HPV 16-immortalized cells (IHGK cells-immortalized human gingival keratinocytes) were negative. The IHGK cells were strongly positive with KS19.1, which stains the embryonal keratin K19, an indicator of premalignant or malignant changes, while the normal control cells were only lightly and focally positive. In conclusion, we present an oral epithelial cell line successfully immortalized with HPV E6/E7 which will facilitate further research on the involvement of HPV in oral carcinogenesis.