Efficient selection of MGMT P140K–expressing long-term hematopoiesis by BCNU/O6BG. The percentage of peripheral blood cells that expressed GFP was determined by FACS. Mice were treated monthly with BCNU/O6BG. Control mice underwent transplantation but did not receive the subsequent chemotherapy. (A) Efficient selection of MGMT P140K–expressing hematopoiesis in primary transplant recipient mice was observed only in those cohorts of mice that received 4 × 105 cells (squares) and monthly administrations of 20 μg/g O6BG and 5 μg/g BCNU (black symbols) (*P < .05). Triangles indicate 105 cells transplanted; squares, 4 × 105 cells transplanted; white, no O6BG/BCNU treatment; gray, 10 μg/g O6BG/2.5 μg/g BCNU; and black, 20 μg/g O6BG/5 μg/g BCNU; (n = 12 for each group). The higher dose of BCNU and O6BG allowed selection of marked hematopoiesis even after (B) secondary (n = 10, P < .05) and (C) tertiary (n = 11, P < .05) transplantation.
