Effect of radiation in different dose rates and fractions on human leukemic cells, HL-60

The radiation factors, such as fractions and dose rates, may play an important role in the treatment of malignant and non-malignant hemopoietic disorders by total body irradiation followed by bone marrow transplantation. The capacity of human hemopoietic cells to repair sublethal radiation damage has been a controversial subject. The authors studied the effect of single and fractionated radiation in different dose rates on human leukemic cells. HL-60 cells, exponentially growing in culture, were irradiated with 220 kVp X-rays in a single dose and 2-doses or with /sup 137/Cs in a single exposure at different dose rates. The irradiated cells were seeded in 0.3% agar bed and incubated for clone formation. The Do and Dq were 85 and 100 rads, respectively, when the cells were irradiated with X-rays at 80 rad/min. Fractionation of 800 rads into two-equal doses of 400 rads by intervals of longer than 3 hr. resulted in an increase in cell survivals by a factor of about 5. A significant dose-rate effect was also observed within the range from 7 to 80 rad/min. It was apparent that HL-60 human leukemic cells have considerable capacity to repair sublethal radiation damage