Reduced CD71 surface expression coincides with ex vivo expansion of HSC subsets. (A) FACS profiles showing kinetics of CD71 surface expression (as proxy for MYC transcriptional activity) on CD34⁺ CB cells cultured for 7 days in presence of DMSO or UM171 (35 nM). (B) Percentage of CD71^lo cells in CD34^hi primitive subsets generated in DMSO or UM171 culture conditions over a 7-day culture period. (C) Percentage of CD34^hi CD45RA^lo primitive cells. (D) Bar graph showing total cell and (E) CD34^hiCD45RA^loCD90⁺CD71^lo cells fold expansion over day 0 in the indicated group. Representative of 3 independent experiments (2-sided Mann-Whitney U test; ∗P < .05, ∗∗P < .01, and ∗∗∗P < .001).