Radiation quality affects the efficiency of induction and the molecular spectrum of HPRT mutations in human T cells.

Human T lymphocytes can be used to determine the frequency and molecular spectrum of somatic cell gene mutations induced by ionizing radiations both in vivo and in vitro. In vitro exposure of these G0 cells to low-LET 137Cs gamma rays results in the induction of HPRT mutations and a predominant molecular spectrum of DNA deletions and rearrangements, particularly total gene deletions (11-12%). Similar results are found in samples from humans exposed to low-LET radiation from 131I. The doubling dose for mutation induction is calculated to be 0.8 and 1.0 Gy from these exposures performed in vitro and in vivo, respectively. In vitro studies of the effects of high-LET radiation from exposure to 222Rn also showed an induction of HPRT mutations, with a doubling dose of approximately 0.2 Gy. With this radiation, the predominant mutations were small partial deletions, with less than 2% total gene deletions. Studies of humans exposed to high-LET radiation from 239Pu showed an increased HPRT mutant frequency for the group, although no significant dosimetry could be defined. In contrast to the humans exposed to 131I, no increase in the frequency of total gene deletions was found. This is consistent with the results for 222Rn in vitro. The available data show that radiation quality affects both the efficiency of induction and the molecular spectrum of HPRT mutations in human T lymphocytes both in vitro and in vivo. The mutational spectrum may be relatively specific for radiations of different quality and thus allow a more precise measurement of the induction of somatic gene mutations resulting from individual exposures to radiation, and thereby provide more sensitive assessments of health risks.