Studies on Radioresistance with HeLa Cells. Establishment of a Radioresistant Line

HeLa cells were successively irradiated with 1 kR of x-rays. After receiving 3, 5, and 8 kR the HeLa cells showed progressively increasing radioresistance. To investigate the mechanism of acquiring radioresistance, subcultures from a single HeLa clone were irradiated with 1 kR of x-rays. The results suggest that in a homogeneous cell strain it is difficult to acquire radioresistance; mutation and selection must act together. The generation time of HeLa cells increased slightly with increasing radioresistance. It was found, however, that the decreased x-ray damage in the resistant strain was due to some factor other than merely the prolongation of the generation time.