GDF15 enhances the clonogenic growth of MM. (A) Primary and secondary colony formation (CFC) of NCI-H929 cells cultured with GDF15 for 7 days. *P < .05 compared with 0 ng/mL GDF15. (B) Survival of NSG mice after injection of NCI-H929 cells treated ex vivo with or without GDF15 (100 ng/mL) for 14 days (n = 5 for each condition). (C) Survival of mice after secondary transplantation of GDF15 cells. (D) MM colony formation by primary clinical bone marrow specimens after treatment with GDF15 ± anti-GDF15 antibody (Ab) for 3 days. *P < .05 compared with 0 ng/mL GDF15.