BMSC-derived exosomes increase MM cell viability and proliferation. 5T33MMvt (A,B) or 5T33MMvv (D,E) cells in serum-free medium were incubated with indicated amounts of naive (A,D) or 5T33 (B,E) BMSC-derived exosomes for 24 or 48 hours, and cell viability was measured using a luminescent cell viability assay. 5T33MMvt (C) or 5T33MMvv (F) cells in serum-free medium were treated with 40 μg/mL naive or 5T33 BMSC-derived or 5T33MMvt cell-derived exosomes for 24 or 48 hours, and cell viability was determined. 5T33MMvt (G) or 5T33MMvv (H) cells in serum-free medium were treated with 40 μg/mL naive or 5T33 BMSC-derived or 5T33MMvt cell-derived exosomes for 24 or 48 hours, and cell proliferation was measured using a BrdU cell proliferation assay. Ten percent serum was used as a positive control. Mean values ± standard deviation for 3 independent experiments are shown. *P < .05; **P < .01; ***P < .001.