Small molecule screening identifies CPX as a candidate modifier of human HSPCs ex vivo. (A-B) Results from primary screening of 584 small molecules at 2 different concentrations on CB-CD34⁺ cells. Y-axis represents the fold increase in CD34⁺CD90⁺ cell number after 6 days for each compound tested, relative to DMSO control, and red dots represent selected candidates from each library (L1-L8). (C) Dose titration of 48 top candidates from the primary screen. (D) Chemical structure of CPX. (E) Representative FACS plots and (F) numbers of CD34⁺CD90⁺ cells after 6 days culture of bulk CB CD34⁺ cells (n = 4). (G) Representative FACS plot and (H) number of CD34⁺CD90⁺EPCR⁺ cells after culture of bulk CD34⁺ cells in presence and absence of CPX. (I) Numbers of CD34⁺CD90⁺ cells after 6 days culture of human BM-CD34⁺ cells from 2 healthy donors. (J) Representative FACS plots from 1000 CB-derived CD34⁺CD38^–CD45RA^–CD90⁺ cells cultured for 6 days. (K) Cell division history measured by CFSE labeling on CD90⁺ cells and (L) quantification of cell frequency in each division. Number of divisions are quantified as relative number of divisions between the 2 conditions by referring to the highest CFSE peak as n number of divisions and the subsequent peaks as n + 1, n + 2, etc.