Wild-type sBCMA decoy receptor treatment inhibits proliferation and promotes tumor cell death in MM . (A) Terminal tumor weight of mice inoculated with INA-6 MM tumors and treated with vehicle control or 10 mg/kg of sBCMA-Fc (n = 10); P = 0.0082. (B) Representative images of Ki67-positive cells in the vehicle control and sBCMA-Fc–treated INA-6 (top panels) and MM1.R (bottom panels) MM tumors analyzed by IHC staining. Scale bar, 50 μm. Quantification of Ki67 staining on right. INA-6, P < 0.0001; MM1.R, P < 0.0001. (C) Representative images of TUNEL-positive cells in the vehicle control and sBCMA-Fc–treated INA-6 (top panels) and MM1.R (bottom panels) MM tumors analyzed by IHC staining. Quantification of TUNEL staining on right. INA-6, P = 0.0001; MM1.R, P < 0.0001. Scale bar, 50 μm. (D) Tumor growth kinetics of MM1.R tumors treated with vehicle control, sBCMA-Fc V3 (10 mg/kg; P < 0.0001), IgG-Fc control (10 mg/kg), and nonbinding Fc control (10 mg/kg; n = 5). Statistical analysis was conducted using t test and one-way ANOVA for comparing between treatment groups. Repeated ANOVA used for changes in tumor growth over time. *, P < 0.05; **, P < 0.01; ***, P < 0.001.