Monitoring somatic mutation over time in vivo in the HPRT gene of lymphocytes of people accidentally exposed to high doses of ionizing radiation

On September 1987 a highly radioactive Cesium-137 source was removed from its protective housing in an abandoned radiotherapy clinic in Goiania, Brazil. Subsequently the source was ruptured and for several days many people were exposed, both externally and internally, to significant levels of ionizing radiation of Cesium-137. More than 50 people received doses up to 7 Gy. Because of its mutagenic and carcinogenic effects, the genetic health of the accident victims has been the subject of continuous studies. The detection and characterization of somatic cell mutation occurring in vivo in humans have been made possible by the development of the selection assay of 6-thioguanine-resistant T lymphocytes from the peripheral blood. The mutants are selected by their ability to survive, proliferate, and form colonies in the presence of the purine analogue 6-thioguanine. Studies were performed on individuals with doses ranging from 1 to 7 Gy in the three years following the accident. Those expected had high mutation frequencies. The averages of mutant frequencies during those three years are 28 x 10-6 (1990), 19 x 10-6 (1991) and 11 x 10-6 (1992). We thus also demonstrate that the hprt T-cell assay has a por long term memory. The data also show a positive correlation with age, and a negative correlation with plating efficiency as expected