Increased competitive repopulating LT-HSCs in Mll^PTD/WT BM cells. (A) Experimental setup. Lethally irradiated groups of CD45.1⁺/CD45.2⁺ WT recipient mice are intravenously injected with 1.5 × 10⁶ BM-MNCs from WT or Mll^PTD/WT (CD45.2⁺) mice together with an equal number of CD45.1⁺ competitor cells. PB is collected from recipients monthly and analyzed by FACS for the presence of CD45.2⁺ donor-derived cells. Secondary competitive BMT is performed 16 weeks after transplantation, with purified CD45.2⁺ BM cells from primary recipients together with CD45.1⁺ competitor cells at a 1:1 ratio. Chimerisms in primary BMT (B) and secondary competitive BMT (C) were assessed monthly. Data shown are the mean percentage ± SD of donor-derived cells (CD45.2⁺) in PB (n = 8). *P < .05. **P < .01. (D) The competitive repopulation unit (CRU) was calculated 16 weeks after BMT according to the formula: donor RU = % donor × competitor cell number/(100 − % donor), and compared between Mll^PTD/WT with WT. (E) WT or Mll^PTD/WT (CD45.2⁺) donor cells in a serial diluted dose were transplanted into lethally irradiated CD45.1⁺/CD45.2⁺ WT recipient mice along with 1 × 10⁵ WT (CD45.1⁺) helper cells, and the donor engraftment in recipient blood was determined monthly (n = 4).