INACTIVATION OF HEMATOPOIETIC STEM-CELLS BY SLOW ALPHA-PARTICLES

Inactivation of murine haemopoietic stem cells, assayed as spleen colony-forming units (CFU-S), has been determined after in vitro irradiation under well defined conditions with small numbers (0.15-3) of alpha-particles of incident energy 3.3 MeV (LET 121 keV mum-1). Exponential survival curves were obtained with inactivation dose coefficients of 1.83+/-0.11 and 1.63+/-0.06 Gy-1 for 8 and 12-day CFU-S, respectively, corresponding to inactivation cross sections of 35.6+/-2.1 and 31.7+/-1.2 mum2. The results indicate that these radiosensitive stem cells have a significant probability of surviving the passage of a single alpha-particle track, estimated at 8 and 18% per particle passage, respectively, if the cells have a diameter of 7 mum. However, this estimation is strongly dependent on the assumed diameter. Conversely, it is demonstrated that the cells cannot have mean geometric diameters of less than 6.7+/-0.2 and 6.4+/-0.1 mum, respectively. Associated experiments have shown that some cells from the irradiated population do survive to form colonies that express delayed non-clonal chromosome aberrations.