[Isolation and characterization of immortalized human fibroblasts]

A clone of immortalized human fibroblasts with an extended life span in culture was obtained after infection with a temperature-sensitive mutant (tsA 239) of SV40. In comparison with the parental cells, the clone exhibited an increase in the efficiency of plating, decreased doubling time, and serum dependence. No anchorage independence was observed. This means that the immortalized cells were not fully malignant, since growth in soft agar is one of the most typical features of malignancy. The PCR analysis has revealed the presence of viral DNA at early (25th) passages after infection and its absence after prolonged culturing (46th passage). These results support the data obtained after studies of T antigen expression by the indirect immunofluorescence method. No reversion to the normal phenotype was observed after transfer of the immortalized cells from the permissive temperature to the temperature restrictive for the virus (33 degrees and 39 degrees C, respectively). We deem it probable that the mutagenic effect of SV40 is realized after the hit-and-run mechanism, hence, its presence is not indispensable for the maintenance of the transformed phenotype.