SR1-expanded HSPCs can develop into T-lineage progenitors in vitro. (A) Flow cytometric analysis of CD34, CD7, CD5, and CD1a as markers for early T-progenitor expansion on thawed naive HSPCs or SR1-expanded HSPCs (day-0 coculture with OP9-DL1 cells). (B) Flow cytometric analysis of day-14 coculture for CD34, CD7, CD5, and CD1a expression. The results shown are representative of 4 independent experiments. (C) Percentage of CD34⁺CD7⁺, CD34⁻CD7⁺, and CD7⁺CD5⁺ subsets in naive UCB cocultures compared with SR1 UCB cocultures, shown as a proportion of total live cells in culture. (D) Fold cell expansion of naive vs SR1-expanded HSPC–derived proT cells in OP9-DL1 coculture. (E) Fold cell expansion of naive vs SR1-expanded HSPC–derived proT cells in OP9-DL1 coculture normalized to initial CD34⁺ input cell number during HSPC expansion (n = 4). Error bars correspond to standard error of the mean. **P < .005, representing statistical significance as determined by unpaired Student t tests.