Human papillomavirus 16 and 18 DNA can solely induce oncogenic transformation of mammalian cells in primary culture

To compare the tumorigenic activity of HPV 6, 11, 16, and 18 DNA in mammalian cells in primary culture, HPV DNAs were transfected to Syrian hamster embryo (SHE) cells. Morphologically transformed foci were observed in all the HPV DNA-transfected cultures and cells propagated from these foci were immortalized. All these cell lines at early passages were not tumorigenic in nude mice. However, a cell line derived from HPV 16 transfection became tumorigenic after 25 passages and a cell line derived from HPV 18 transfection also revealed tumorigenicity after 48 passages. Overexpression of the Ha-ras proto-oncogene occurred in these transformed cell lines. No tumorigenic activity was observed in HPV 6 and HPV 11-transfected cell lines. All these observations suggest that HPVs 16 and 18 have a higher transforming potential than do HPVs 6 and 11 and can solely induce tumorigenic transformation of cells in primary cultures, with continuous passage.