Analysis of hematopoietic stem and progenitor cells in MDS-RS. (A) Representative FACS analysis of SF3B1-mutated MDS-RS BM (patient 4). Shown are FACS analyses of viable, lineage-negative, CD34-enriched cells further gated as CMPs (7AAD⁻Lin⁻CD34⁺CD38⁺CD90⁻CD123⁺CD45RA⁻), MEPs (7AAD⁻Lin⁻CD34⁺CD38⁺CD90⁻CD123⁻CD45RA⁻), GMPs (7AAD⁻Lin⁻CD34⁺CD38⁺CD90⁻CD123⁺CD45RA⁺), and HSCs (7AAD⁻Lin⁻CD34⁺CD38⁻CD90⁺CD45RA⁻). (B) Mean (standard error of the mean [SEM]) frequencies of HSCs and progenitors in SF3B1-mutated MDS-RS patients (n = 9) and healthy NBM (n = 4). (C) Mean (SEM) erythroid and myeloid colony formation from purified CMPs, GMPs, and MEPs from 8 MDS-RS patients and 4 NBMs. (D) Representative images of an erythroid colony (BFU-E) from an MDS-RS patient and a healthy NBM control. Original magnification for light microscopy ×10. (E) LTC-CFC activity in HSCs, CMPs, GMPs, and MEPs from MDS-RS patients (n = 8) and healthy NBM controls (n = 5). Results are mean (SEM) values for all patients and healthy controls, in each case derived from the mean of 3 technical replicates for each cell population and patient. **P < .005.