Overexpression of Bcl2 did not restore DNA repair capacity in Ku70^−/−HSCs. (A) Three-month-old WT, Ku70^−/−, TgBcl2, and TgBcl2/Ku70^−/− mice were irradiated with 2 Gy. BM cells were isolated and plated in methylcellulose in the presence of interleukin-3, interleukin-6, and stem cell factor. Colony-forming units were counted 14 days later. Shown is the representative result of 2 independent experiments. Error bars indicate SD, and significance was determined by a 2-tailed Student t test. *P < .001. (B) BM cells from 3-month-old WT, Ku70^−/−, TgBcl2 and TgBcl2/Ku70^−/− mice were transplanted into lethally irradiated BoyJ recipients. Then 12 weeks posttransplantation, the recipients were irradiated with 2 Gy radiation and survival of the recipients was monitored (n = 5 per group). (C) Three-month-old WT, Ku70^−/−, TgBcl2, and TgBcl2/Ku70^−/− mice were irradiated with 2 Gy and at each time point BM cells were isolated and analyzed by FACS to assess the levels of γH2AX in the SLAM-LSK fraction. Shown is the representative result of 2 independent experiments. CFU, colony-forming units; IR, irradiation.