Senescent human diploid cells in culture: survival, DNA synthesis and morphology.

Senescent human diploid cell cultures (WI-38 and WI-26) were studied during Phase III for survival time, ability to synthesize DNA, and nuclear morphology. Periodic transfers made during a 6-month period of Phase III showed that cultures were maintained with only slight variations in cell number. No sign of spontaneous acquisition of infinite proliferative potential was observed. The increase in the number of multinucleated cells found during the period of observation showed that progressive changes occur in Phase III. A certain proportion of cells maintained the ability to incorporate tritiated thymidine throughout the period of observation.