Background Systemic infusion of allogenic mesenchymal stem cells (MSC) have shown therapeutic effects on a variety of autoimmune diseases, but the underlying mechanisms of MSC-based immunoregulation are not fully understood.
Objectives To investigate the effect of allogenic MSC transplantation (MSCT) in patients with systemic sclerosis (SS) and the difference in inducing T cells apoptosis by bone marrow (BM) derived MSC between SS patients and healthy individuals.
Methods Allogenic BM MSC from healthy individuals were isolated, expanded and infused into 5 refractory SS patients (4 females and 1 male, in the age range of 44 to 61 years old, average 51 years old, one million cells per kilogram of bodyweight each transplantation). Clinical evaluations by assessment of modified rodnan skin score (MRSS) and Health Assessment Questionnaire (HAQ-DI) were evaluated pre and 1, 3, 6 and 12 months post-transplantation. Peripheral blood were collected pre- and 2, 6, 24 and 72 hours post-MSCT, to determine the changes of T cells apoptosis and the percentage of T regulatory cells (Treg) by flow cytometry. Serum levels of TGF-β were detected by ELISA. BM MSC from SS patients and healthy individuals were isolated and used to examine Fas and MCP-1 expressions by flow cytometry, ELISA, real-time PCR or western blot. In vitro, SS peripheral blood T cells were cocultured with SS or normal BM MSC, to determine the difference in the induction of T cells apoptosis and the upregulation of Treg cells by flow cytometry.
Results MRSS score significantly decreased 1, 3, 6 and 12 months after allogenic MSCT in all patients, in paralleled with amelioration of HAQ-DI scores at different visit times. Allogenic MSC infusion induced a decreased number of CD3+ T cells and increased number of apoptotic CD3+ T cells in peripheral blood of SS patients, starting 2 hours, reaching the peak 6 hours, and lasting until 72 hours post-transplantation. Meanwhile, peripheral blood CD4+CD25highFoxp3+ T cell percentage and serum TGF-β increased 72 hours after MSCT. In vitro coculture of allogenic normal bone marrow MSC and activated T cells from SS patients resulted in increased apoptosis of CD3+T cells and percentage of Tregs, while that was not case in the coculture with SS bone marrow derived MSC. Further analysis between normal and SS BMMSC demonstrated significant lower expressions of Fas (by RT-PCR and western blot) and MCP-1 (by RT-PCR and ELISA) on SS BMMSC, compared to normal BMMSC. Intervention of Fas expression by siRNA on normal BMMSC resulted in significant reduced MCP-1 expression both at gene and protein levels. In addition, Fas siRNA MSC failed to induce T cells apoptosis and upregulate Treg cells in SS T cells in vitro coculture.
Conclusions Our data demonstrated that allogenic BMMSC could induce Fas/FasL mediated T cells apoptosis by MCP-1, subsequently triggered high levels of TGF-β that in turn led to upregulation of Treg cells in SS patients. However, SS patients BMMSC were defective in MCP-1 and Fas expressions, and failed to upregulate Treg. Our results provide a new mechanism for the clinical application of MSCT.
Disclosure of Interest None Declared