In Vitro–expanded Antigen-specific Regulatory T Cells Suppress Autoimmune Diabetes

The low number of CD4⁺ CD25⁺ regulatory T cells (T_regs), their anergic phenotype, and diverse antigen specificity present major challenges to harnessing this potent tolerogenic population to treat autoimmunity and transplant rejection. In this study, we describe a robust method to expand antigen-specific T_regs from autoimmune-prone nonobese diabetic mice. Purified CD4⁺ CD25⁺ T_regs were expanded up to 200-fold in less than 2 wk in vitro using a combination of anti-CD3, anti-CD28, and interleukin 2. The expanded T_regs express a classical cell surface phenotype and function both in vitro and in vivo to suppress effector T cell functions. Most significantly, small numbers of antigen-specific T_regs can reverse diabetes after disease onset, suggesting a novel approach to cellular immunotherapy for autoimmunity.