NOD HSCs are more radioresistant. The ability of HSCs to survive after exposure to ionizing radiation was determined by exposing whole BMCs (A) or purified KSL cells (B) to the indicated doses of irradiation. (A) The percent KSL cells surviving after a 20-hour culture was determined by flow cytometry. ○ indicates NOD; ▪, B10.BR. Results are the average survival plus and minus the standard deviation of cells from 3 individual animals in one of 2 different experiments (^*P < .05). (B) The ability of irradiated KSL cells to produce colonies in methylcellulose plus growth factors was determined. Data expressed as plus and minus the standard deviation (^*P < .05). Results are the average of quadruplicate wells from one of 2 (NOR [□] and B10 [⬡]) or 3 (NOD [⋄] and B10.BR [▴]) experiments, expressed as percent of unirradiated KSL cells.