Abstract: Objective　To investigate the effects and mechanism of bone marrow mesenchymal stem cells (BMSCs) transplantation on Type 1 diabetes mellitus (T1DM) mice.　Methods　Isolation, culture and identification of BMSCs were performed. BMSCs supernatant was used to be the conditioned medium after third passage (P3), co-cultured with 2 weeks NOD splenocytes, and the proliferation and activation of CD4+ and CD8+T cells were detected by FACS. Two weeks female NOD mice were randomly divided into three groups: a BMSCs group, a PBS group and a control group (6 mice in each group). Mice in the control group were killed at 2 weeks. 100 μl (2×107 cells) BMSCs or equal volume PBS was injected intraperitoneally at 12 weeks in the BMSCs group and the PBS group respectively, then the mice were monitored for blood glucose and body weight till 26 weeks. Inflammatory cells infiltration of pancreases was detected by H&E, immunohistochemical and immunofluorescent staining. The splenocytes were extracted to observe the proliferation and activation of CD4+ and CD8+T cells by FACS.　Results　BMSCs were successfully isolated and cultured. BMSCs conditioned medium inhibited the proliferation and activation of CD4+ and CD8+T cells (P<0.05). Mice body weight of BMSCs group was higher than that of PBS group (P<0.05), the incidence rate of diabetes and inflammatory infiltration decreased (P<0.05) as well as the proliferation and activation of CD4+ and CD8+ T cells in the spleen (P<0.05).　Conclusions　BMSCs transplantation may attenuate T1DM by immune suppressing T cells.

Key words: BMSCs, 　NOD/ShiLtJ mice, 　T1DM Immunosuppression, 　T cells