(A) Growth inhibitory effects of bortezomib on U266 and LP-1 cells detected by cell counting kit-8 (CCK-8) assay. The 50% growth inhibitory concentrations (IC50) of U266 and LP-1 cells after 48 h of treatment with bortezomib was approximately 20 nmol/L; (B) inhibitory effects of anti-CXCL13 at different concentrations on bortezomib resistance of U266 and LP-1 cells co-cultured with mesenchymal stem cells (MSCs). With a rising anti-CXCL13 concentration, the growth inhibition rates of U266 and LP-1 cells also increased; (C) MSCs enhanced bortezomib resistance of U266 and LP-1 cells via the CXCL13-mediated signaling pathway, which was blocked by anti-CXCL13. After co-culture of U266 and LP-1 cells with MSCs for 48 h, three different experimental groups were set up for each cell line: individual multiple myeloma (MM) group, MM + MSCs group, and MM + MSCs + anti-CXCL13 group. Each experimental group was added bortezomib at a final concentration of 20 nmol/L. After 48 h, the growth inhibition rate was calculated. MSCs enhanced the resistance of U266 and LP-1 cells to bortezomib, which was blocked by anti-CXCL13. *p < 0.05.