Background and Aims

Type 1 diabetes is due to the autoimmune destruction of pancreatic islet beta-cells. This study was aimed to assess whether the G3c monoclonal antibody (mAb), which triggers the glucocorticoid-induced TNFR-related (GITR) costimulatory receptor, promotes the expansion of regulatory T cells (Tregs) in diabetic-prone NOD mice and prevents diabetes onset.

Methods

G3c mAb was delivered via G3C hybridoma cells enveloped in alginate-based microcapsules that were grafted intraperitoneally into mice under general anesthesia. For each mouse, 1.5x10⁶ G3C hybridoma cells in 1 mL of microcapsules (G3C/cps) or 1 mL of empty microcapsules (e/cps) as a control, were grafted.

Results

Three weeks after G3C/cps graft, we observed expansion of conventional CD4⁺CD25⁺GITR^highFoxp3⁺ Tregs and non-conventional CD4⁺CD25^-/lowFoxp3^lowGITR^int/high (GITRsp) Tregs in the spleen. Expansion of both Treg subsets, including antigen-specific Tregs, was observed also in the pancreas of G3C/cps-treated as compared to e/cps-treated NOD mice. Moreover, the number of intact islets was higher in G3C/cps-treated than in e/cps-treated and untreated animals.

Consequently, all but two G3C/cps-treated mice (95%) did not develop diabetes and all but one survived till the end of the 24-week study. In comparison, only 50% of untreated NOD mice survived at the end of the study. Interestingly, the level of FoxP3 mRNA in the pancreas of G3C/cps-treated mice was 4000 fold higher than in the pancreas of e/cps and untreated diabetic mice.

Conclusions

In conclusion, long-term GITR triggering induces Treg expansion, thereby delaying/preventing diabetes development in NOD mice. This therapeutic approach may have promising clinical potential for the treatment of inflammatory and autoimmune diseases.