Mesenchymal Stem Cells Improve Platelet Counts in Mice with ITP

INTRODUCTION: Patients with chronic refractory immune thrombocytopenia (ITP) have the high risk of death and complications, which urge us to seek for new treatment alternatives. Currently, bone marrow-derived mesenchymal stem cells (BMSCs) have been extensively utilized for autoimmune diseases. However, it is still lack of evidence in vivo about the therapeutic benefits and the possible underlying mechanisms of BMSCs in ITP, which is also known as an acquired autoimmune disease. In this study, we transplanted BMSCs into a passive ITP mouse model to explore the therapeutic effects and immunosuppressive mechanisms of BMSCs in ITP disease.

METHODS: The passive ITP mouse model was induced by dose-escalation injection of monoclonal antibody MWReg30. Mice were randomly divided into two groups: experimental group (2-4×10⁶ BMSCs were injected into each ITP mouse through the tail vein on Day 3) and control group (ITP mice). PLT counts were enumerated by an automatic blood cell counter. The serum levels of cytokines (IL-10 and TGF-β1) were examined by ELISAs and the frequency of Treg cells by flow cytometry. The statistical analysis was processed by SPSS software version 19.0.

RESULTS: We successfully induced a passive ITP mouse model with very low levels of PLT counts for 8 days (PLT counts were reduced to half of the initial values by 24 hours and were relatively constant throughout the study). The PLT counts in experimental group on Day 4 to Day 8 were (263±17)×10⁹/L, (482±35)×10⁹/L, (367±38)×10⁹/L, (385±107)×10⁹/L, and (317±48)×10⁹/L, which were significantly higher than those in control group [ (159±19)×10⁹/L, (238±20)×10⁹/L, (175±32))×10⁹/L, (129±7)×10⁹/L, and (170±16)×10⁹/L, respectively ]. The levels of serum TGF-β1 and IL-10 were significantly higher in experimental group compared with the control group [ (116.61±12.59)pg/ml and (348.89±44.49)pg/ml vs. (72.78±15.70) pg/ml and (134.61±27.59)pg/ml; p <0.05]. The ratios of Treg cells both in splenocytes and peripheral blood were significantly higher after transplantation of BMSCs [ (15.79±0.55)% and (6.37±0.45)% vs. (10.25±0.55)% and (4.80±0.26)%; p<0.05].

CONCLUSIONS: BMSCs transplantation is an effective treatment for ITP in mice. The key mechanisms underlying the positive therapeutic impact may due to the BMSCs secreting suppressive cytokines TGF-β1 and IL-10 and increasing the proportion of Treg cells, which play key roles in both the maintenance of immune tolerance and the inactivation of macrophage.