Human BMSC-derived exosomes increase the MM cell viability and induce drug resistance to bortezomib. (A) Transmission electron microscopy images of exosomes derived from ND and MM patients’ BMSCs. The scale bars indicate 100 nm, and the arrows indicate the typical exosomes. (B) Exosomal positive markers CD63 and flotillin-1 were detected in ND and MM BMSC-derived exosomes using western blot. (C) RPMI 8226 cells in serum-free medium were treated with different amounts of ND or MM BMSC-derived exosomes for 48 hours, and cell viability was measured and presented as the fold of control. (D) RPMI 8226 cells in serum-free medium were cultured with 40 μg/mL exosomes derived from 3 ND BMSCs or MM BMSCs for 48 hours, and cell viability was measured. (E) RPMI 8226 cells were cultured in serum-free medium with 80 μg/mL ND or MM BMSC-derived exosomes in the absence or presence of Btz (2 nM) for 48 hours, and cell viability was measured. (F) RPMI 8226 cells in serum-free medium were treated with ND or MM BMSC-derived exosomes (80 μg/mL) in the absence or presence of Btz (2 nM), and the live cells were measured using fluorescence-activated cell sorter staining. Mean values ± standard deviation for 3 independent experiments are shown. *P < .05; **P < .01; ***P < .001.