BM-CAFs promote MM proliferation and impair BCMA-CART-cell function. (A) Luciferase⁺ BCMA⁺ SLAMF7⁺ MM1.S were cocultured with indicated ratios of BM-CAFs in vitro. The growth of MM1.S was assessed by BLI at 48 hours. (Mean and standard error of the mean [SEM]; **P < .005, ^⋆⋆⋆P = .001, one-way analysis of variance; n = 3, two replicates). (B) Then, 2.5 × 10⁵ luciferase⁺ BCMA⁺ SLAMF7⁺ OPM-2 were subcutaneously injected with or without 2.5 × 10⁵ BM-CAFs into the right flank of NSG mice. Tumor growth was assessed by BLI three weeks after the injection (mean and SEM; ***P < .005, unpaired, two-sided t test; n = 6). (C and D) Then, 1 × 10⁶ luciferase⁺ OPM-2 were intravenously injected with (MM-TME model) or without (OPM-2 xenograft) 1 × 10⁶ BM-CAFs. Tumor growth was monitored by serial BLI (mean and SEM; **P < .005, ****P < .0001, unpaired, two-sided t test; n = 6). (E) Kaplan-Meier survival curve for MM-TME model and OPM-2 xenograft. MM-TME model vs OPM-2 xenograft hazard ratio, 35.68; 95% confidence interval, 2.687-473.6; **P = .0067 (log-rank test). (F) Immunohistochemical analysis of BM from MM-TME model. Magnification ×10. (G) Percentage of cells showing positive FSP-1 staining in BM from MM-TME model (***P < .005, unpaired, two-sided t test; n = 3). (H) Multiplex assay with the supernatant samples from the coculture of BCMA-CART cells and irradiated MM1.S, in the absence or presence of BM-CAFs (*P < .05, **P < .01, ***P < .005, unpaired, two-sided t test; n = 2, two replicates). FGF-2, fibroblast growth factor-2; GM-CSF, granulocyte macrophage colony-stimulating factor; GRO, growth-regulated oncogene; H&E, hematoxylin and eosin; IFN-γ, interferon-γ; sCD40L, soluble CD40 ligand; TNF, tumor necrosis factor.