Treatment of an autoimmune encephalomyelitis mouse model with nonmyeloablative conditioning and syngeneic bone marrow transplantation.

PURPOSE: Hematopoietic stem cell transplantation (HSCT) has been proposed as a novel therapy for multiple sclerosis (MS). CD4 + CD25 + regulatory T cells (Tregs) expressing Foxp3 play an important role in the maintenance of immune tolerance to self. Our study was conducted to confirm the efficiency of nonmyeloablative conditioning and syngeneic bone marrow transplantation (BMT) on experimental autoimmune encephalomyelitis (EAE) mice and to determine whether Tregs plays a role in the underlying mechanism.

METHODS: EAE were induced in C57BL/6 mice and were randomly divided into 4 groups: the Conditioning group received the conditioning regimen, the Normal-EAE BMT group received conditioning and bone marrow (BM) grafts from normal mice, the EAE-EAE BMT group received conditioning and BM grafts from EAE mice and the EAE control group received no further therapy. The cumulative clinical score was used to assess the efficacy of the different treatments, and the proportion of Tregs in the spleen was measured by flow cytometry on day 40, 80 and 120 after BMT. Foxp3 mRNA expression was assessed by real-time PCR, and the expression of Foxp3 protein was tested by western blot on day 120 after BMT.

RESULTS: Conditioning and conditioning with BMT led to a significant clinical improvement on day 80 after BMT compared with EAE without further treatment. On day 120 after BMT, the clinical score of the Conditioning group showed no significant difference from that of the EAE control group, whereas BMT led to a further amelioration of the disease score. On day 80 and day 120 after BMT, the proportions of Tregs of the two BMT groups were significantly higher than that in EAE control group, whereas no statistically significant difference was found between the Conditioning group and the EAE control group. On day 120 after BMT, the Foxp3 mRNA level and Foxp3 protein expression was higher in the two BMT groups than in EAE control group or Conditioning group.

CONCLUSIONS: Nonmyeloablative conditioning could temporarily reverse already established EAE, but it was not sufficient for the induction of long-term EAE remission. Transplantation by BM cells from healthy or diseased donors was necessary and responsible for complete and long-time remission of EAE, and these beneficial effects may be the result of the induction of Tregs and the Treg-related factor Foxp3.