MSCs of MM patients are functionally altered and have an impaired long-term ability to support HSPCs. (A) Bar charts show cumulative population doublings (CPD; left) and number of passages (right) of healthy donors and MM MSCs. (B) At the end of the primary incubation period, colonies > 50 cells (CFU-F) were counted by light microscopy. Bar chart displays the number of CFU-F per 1 × 10⁷ MNCs for healthy donors and MM patients. (C) Micrographs depict morphology of healthy donors and MM patients' MSCs. For assessment of the differentiation capacity, MSCs were differentiated into osteogenic, adipogenic, and chondrogenic lineages. (D) Representative micrographs of the osteogenic, adipogenic, and chondrogenic differentiation of healthy donors' and patients MSCs (each one of 5 experiments performed). To determine the long-term ability of MSCs to support HSPCs, 34⁺ HSPCs from the BM of healthy donors were plated (22 replicates per concentration: 180, 60, 20, 7.5 cells/well) onto MSCs from healthy donors and MM patients (with or without SD-208) subcultured in 96-well plates and maintained for 5 weeks. (E) After 5 weeks, the liquid medium was replaced by methylcellulose medium and secondary CFCs were scored after 2 weeks. The absolute frequency of LTC-ICs was calculated using Lda STAT software. LTC-IC frequency of healthy donor BM HSPCs maintained on MSCs of 5 healthy donors or 8 MM patients with or without SD-208 is shown. Error bars represent SEM. The Student t test was used to detect statistically significant differences. *P < .05; **P < .01; ***P < .001.