In vivo differentiation potential of CD45RA subsets. Sublethally irradiated immune-deficient neonates were injected with in vitro–derived or ex vivo–derived indicated cells at concentrations ranging from 0.1 to 1 × 10⁵ cells per mouse. After 4 to 7 weeks, mice were sacrificed and thymi and/or BM cells were analyzed by flow cytometry for shown markers. (A,D) The percentage of donor CD45⁺ cells in BM and/or thymus from mice injected with CD45RA^int derived from OP9-DL4^low or OP9-Ctrl cultures (15 and 7 mice, respectively). (B,D) The percentage of CD45⁺ marker positive cells found in BM and/or thymus of mice injected with CD45RA^hi derived from OP9-DL4^low or OP9-Ctrl cultures (5 and 4 mice, respectively) or (C-D) ex vivo CD45RA^int (7-8 mice).