Objective To deplore the immunoregulatory function changes of mesenchymal stem cells(MSCs)from multiple myeloma(MM)patients and its effects on the pathogenesis of myeloma bone disease.Methods MSCs from MM patients and normal controls were isolated and the immunophenotype was detected.Real-time PCR was performed to detect the expressions of TGF-β1,TGF-β2,TGF-β3,IL-6,IL3,TNF-α,FasL and RANKL of MSCs.Transwell coculture systems were performed between MSCs and T cells.Lymphocyte proliferative assay was employed to detect the effect of MSCs on T cell proliferation.The effect of MSCs on T cell cycle and T cell activation markers CD25 and CD69 expression were analyzed by flow cytometry.Cleaved caspase 3 protein by western blot and hoechst 33258 staining were employed to detect the apotosis of T cells.Influence of T cells on the osteogenesis potential of MSCs were detected by Von kossa stain,real-time PCR and Western blot.Results MSCs from both MM patients and normal controls possessed similar morphology and immunophenotypes.MM derived MSCs exhibited increased expressions of TGF-β1,IL-6,IL-3,TNF-α and RANKL and decreased expression of TGF-β2,TGF-β3 and FasL.The inhibitory effect of MM derived MSCs on T cell proliferative ability was attenuated compared to control MSCs.MSCs from normal controls silence more T cells in Go/G1 phase than those from MM patients.The daupening effect of MM derived MSCs on activation-induced T apoptosis seemed to be enhanced.Expression of T cell activation markers were significantly inhibited by MSCs from normal controls.Both T cells cocultured with MM deprived MSCs and T cells directly from MM patients inhibited osteogenesis potential of MSCs from normal controls.Conclusion MSCs from MM patients showed impaired immunoregulatory capability on T cells.The activated T cells,in turn,inhibited the osteogenesis potential of MSCs.This may participate in the pathogenesis of myeloma bone disease.