TBI causes sustained reduction of HSC clonogenic activity and long-term repopulating ability. (A) Two months after 6 Gy TBI, total BM cells (BMCs) were harvested from control (CTL) and irradiated (TBI) mice and were analyzed by CAFC assays. The numbers of 1-, 2-, 4-, and 6-week CAFCs were counted and expressed as mean ± SD (n = 3-4 mice per group) of CAFCs per 100 000 BMCs. *P < .05 and **P < .01, TBI vs CTL. (B) Diagram illustrating the competitive repopulating assay. (C) Representative gating strategy for flow cytometric analysis of CD45.2 donor cell engraftment with anti-CD45.2-FITC antibody. B cells were labeled with anti-B220-APC and B220-PE, T cells with anti-Thy1.2-APC, and myeloid (M) cells with anti-CD11b-PE and Gr-1-PE. (D) Percentages of total donor-derived (CD45.2) hematopoietic cells in peripheral blood of the recipients are presented as mean ± SD (CTL: n = 6; TBI: n = 8). ***P < .001, TBI vs CTL. (E) Percentages of T, B, and M cells in donor-derived hematopoietic cells in peripheral blood of the recipients are presented as mean ± SD (CTL: n = 6; TBI: n = 8). *P < .05, **P < .01, and ***P < .001, TBI vs CTL.