The effects of x-irradiation on hematopoietic stem cell compartments in the mouse.

The sensitivity for x-irradiation of a series of hematopoietic stem cell populations has been determined. The most primitive cells identified, cells with marrow-repopulating ability (MRA), showed the highest degree of radioresistance. These MRA cells which generate many secondary day-twelve spleen colony-forming units (MRA[CFU-S-12]) or colony-forming units in culture (MRA[CFU-C]) in the marrow of primary recipients had Do values equal to 1.18 and 1.13 Gy, respectively. The more mature CFU-S-12 had intermediate radiosensitivity (Do = 0.94 Gy), whereas the less primitive CFU-S-7 were the most radiosensitive (Do = 0.71 Gy). The in vitro colony-forming precursor cells (CFU-C) showed low radiosensitivity. These data clearly show that the most primitive hematopoietic stem cell measured is less sensitive to ionizing radiation than generally has been assumed on the basis of measurements on CFU-S-7 or CFU-S-12.