Treatment with myeloid suppressor cells in late stage autoimmune insulitis in order to prevent type 1 diabetes onset in the NOD mouse model

Objectives: Myeloid suppressor cells (MSC) are precursers of dendritic cells, which were well charactherized by our group in vitro and show strong immunosuppressive activity (1). We have shown earlier, that onset of type 1 diabetes can be prevented by i.v. injection of MSC in 8 week old female NOD mice. Here we investigate the effect of MSC in the prevention of diabetes onset in late stage autoimmune insulitis (12 week old female NOD mice). Methods: MSC were harvested from the bone marrow of NOD mice (tested non-diabetic) and incubated in vitro with GM-CSF. MSC cells were injected into the tail vein of prediabetic female NOD-mice: Group 1: 4 female NOD mice 1×4 million MSC at the age of 8 weeks Group 2: 4 female NOD mice 4×4 million MSC at the age of 8 weeks Group 3: 9 female NOD mice 1×4 million MSC at the age of 12 weeks Control group: 10 female NOD mice (treated with PBS at 8 weeks of age). All mice were examined for glucosuria until the age of 30 weeks. Splenocytes were investigated by ELISPOT assay (expression of IL-10, IL-4, IFN-gamma. Results: 5 of the 9 mice in group 3 remained diabetes-free during the observation period, whereas in the control group 9 of 10 mice became diabetic (p<0.001). Group 1 and 2 showed no glucosuria until the age of thirty weeks. Interestingly, the mean count of mononuclear splenocytes of MSC-treated mice was two times higher as in the control group. ELISPOT revealed a tendency towards more IL-4 expressing cells in the MSC-treated animals vs. the control group. IL-10 expression was similar in all groups. Conclusion: Treatment with MSC in 12-week-old female NOD mice can reduce but not completely prevent diabetes onset. In vivo MSC apparently induce an increase in mononuclear cells in the spleen and seem to amplify the number of IL-4 expressing lymphocytes. 1) Rössner et al., Eur J Immunol. 2005;35: 3533–3544