Similar simian virus 40-induced immortalization frequency of fibroblasts and epithelial cells from human large airways.

Several previous studies have shown that when Simian virus 40 (SV40) genes were introduced into normal human fibroblasts, a very small proportion (< 2%) of the resulting transformed clones were immortalization-competent. In separate studies with normal human epithelial cells, SV40 genes were shown to induce a much higher proportion (30-100%) of immortalization-competent clones. In this study, a direct comparison was made of the immortalization frequencies of clones of normal epithelial cells and fibroblasts derived from the same individual. The results demonstrate that fibroblasts and epithelial cells can be immortalized at similarly high frequencies when transfected with an SV40 early region origin-minus expression plasmid, without the need for a selectable marker. We conclude that there is no intrinsic difference between the SV40 early region-induced immortalization potentials of human fibroblasts and epithelial cells. Comparison of this study with other studies of the immortalization of human fibroblasts suggests that removal of SV40 late region genes from the transfected plasmid is important for obtaining a high proportion of immortalization-competent clones.