Normal human fibroblasts immortalized by introduction of human papillomavirus type 16 (HPV-16) E6-E7 genes

This report demonstrates that normal human fibroblasts can be immortalized by the introduction of HPV-16 E6-E7 genes. We designed zinc- inducible expression plasmids with HPV-16 E6, E7 or both. Each plasmid was introduced into normal human fibroblasts (TIG-3 cells) using lipofection methods. Only transfectants with the HPV-16 E6-E7 zinc-inducible expression plasmid, which were cultured in medium supplemented with 100 μM ZnSO₄, overcame crisis and could be cultured over 200 population doubling levels (PDLs). These cell lines showed the reactivation of telomerase after crisis, and morphological alterations were also observed.