AML1+/– cells produce a higher engraftment level in a competitive long-term repopulating assay. (A) Schematic diagram of the in vivo competitive repopulating assay. 2 × 10⁵ test BM cells from 2 to 3 AML1+/– or +/+ mice (Ly5.2⁺) were mixed together with a 10-fold higher number (2 × 10⁶) of competitor cells (Ly5.1⁺) and then transplanted into lethally irradiated Ly5.1⁺ mice (n = 10-12 mice/group). The percentage of Ly5.2⁺ cells in the peripheral blood was determined by FACS every 4 week after transplantation. (B) Percentage of Ly5.2⁺ cells in the blood at week 24 after transplantation.