Expansion of functional endogenous antigen-specific CD4+CD25+ regulatory T cells from nonobese diabetic mice

CD(4+)CD25(+)Foxp(3+) regulatory T cells (T-reg) are critical for controlling autoinummity. Evidence suggests that T-reg development, peripheral maintenance, and suppressive function are dependent on Ag specificity. However, there is little direct evidence that the T-reg responsible for controlling autoimmunity in NOD mice or other natural settings are Ag specific. In fact, some investigators have argued that polyclonal Ag-nonspecific T-reg are efficient regulators of immunity. Thus, the goal of this study was to identify, expand, and characterize islet Ag-specific T-reg in NOD mice. Ag-specific Treg from NOD mice were efficiently expanded in vitro using IL-2 and beads coated with recombinant islet peptide mimic-MHC class II and anti-CD28 mAb. The expanded Ag-specific T-reg expressed prototypic surface markers and cytokines. Although activated in an Ag-specific fashion, the expanded T-reg were capable of bystander suppression both in vitro and in vivo. Importantly, the islet peptide mimic-specific T-reg were more efficient than polyclonal Treg in suppressing autoimmune diabetes. These results provide a direct demonstration of the presence of autoantigen-specific T-reg in the natural setting that can be applied as therapeutics for organ-specific autoimmunity.