Mesenchymal Stem Cells Ameliorate Thymic Functions in aGVHD Patients after Allogenetic Haematopoietic Stem Cell Transplantation

Background Mesenchymal stem cells (MSCs) have been considered as a promising strategy for the prevention and treatment of graft-versus-host disease (aGVHD), but the mechanism of MSCs ameliorating GVHD is still not fully understood. In mice aGVHD model, some studies proposed that MSCs ameliorated GVHD via enhancements in proliferation and function of thymic epithelial cells, but it is not performed in patients.

Methods Twenty-five refractory aGVHD patients were enrolled in this study, including 13 patients receiving MSCs treatment and 12 without MSCs treatment as the control group. MSCs derived from bone marrow (BM) of a third-party donor and given at a median dose of 1×10⁶ cells/kg once weekly until aGVHD got complete response (CR) or MSCs were infused for a total of 8 doses. CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) in peripheral blood were analyzed by flow cytometry and signal joint T-cell receptor excision circle (sjTREC) was monitored by real-time polymerase chain reaction (PCR) before and 4, 8, 12, 16, 24 and 36 weeks after treatments.

Results In MSCs group,the overall response (OR) rate for aGVHD was 76.9%, including complete response (CR) in 53.8% and partial response (PR) in 23.1%, while the OR rate in non-MSCs group was 33.3%, including CR in 25% and PR in 8.3%. The OR rate in MSC group is significantly higher than those in the control group (P=0.028). No evident difference of CD4⁺CD25⁺Foxp3⁺Tregs and sjTREC were shown between the patients in MSCs and the control groups before the study treatment (P=0.762, P=0.870). In the evaluated patients, the level of sjTREC in MSCs group is significantly higher at 8, 16, 24 weeks than the control group after treatments (P=0.043, P=0.0301 and P=0.039, respectively.). The level of sjTREC significantly increased at 8 weeks after MSCs treatment, compared with pre-MSCs treatment (P=0.034), and sustained to 36 weeks after MSCs treatment. In the control group, sjTREC increased, but did not change significantly before and after treatments (P>0.05). The level of sjTREC in CR patients is significantly higher than non-response patients at 8, 12, 16, and 24 weeks after MSCs treatment, and sjTREC levels correlated with the response of MSCs treatment (r=0.782). With respect to CD4⁺CD25⁺Foxp3⁺Tregs, they were significantly higher in MSC group at 8, 12 weeks after treatment than the control group (P=0.026 and P=0.029). In MSCs group, the proportion of CD4⁺CD25⁺Foxp3⁺Tregs showed a significant increase at 8 weeks compared with pre-MSCs treatment (P=0.012), and sustained to 36 weeks after MSCs treatment. In the control group, CD4⁺CD25⁺Foxp3⁺Tregs did not significantly change before and after treatment.

Conclusions MSCs derived from BM of a third-party donor are effective to refractory aGVHD. MSCs ameliorated aGVHD via repairing thymus, including the enhancements of thymic output function and inducing the generation of Tregs.