Immunomodulation Followed by Antigen-Specific Treg Infusion Controls Islet Autoimmunity

Optimal immune-based therapies for type 1 diabetes (T1D) should restore self-tolerance without inducing chronic immunosuppression. CD4(+)Foxp3(+) regulatory T cells (T-regs) are a key cell population capable of facilitating durable immune tolerance. However, clinical trials with expanded T-regs in T1D and solid-organ transplant recipients are limited by poor T-reg engraftment without host manipulation. We showed that T-reg engraftment and therapeutic benefit in nonautoimmune models required ablative host conditioning. Here, we evaluated T-reg engraftment and therapeutic efficacy in the nonobese diabetic (NOD) mouse model of autoimmune diabetes using nonablative, combinatorial regimens involving the anti-CD3 (alpha CD3), cyclophosphamide (CyP), and IAC (IL-2/JES6-1) antibody complex. We demonstrate that alpha CD3 alone induced substantial T-cell depletion, impacting both conventional T cells (T-conv) and T-regs, subsequently followed by more rapid rebound of T-regs. Despite robust depletion of host T-conv and host T-regs, donor T-regs failed to engraft even with interleukin-2 (IL-2) support. A single dose of CyP after alpha CD3 depleted rebounding host T-regs and resulted in a 43-fold increase in donor T-reg engraftment, yet polyclonal donor T-regs failed to reverse diabetes. However, infusion of autoantigen-specific T-regs after alpha CD3 alone resulted in robust T-reg engraftment within the islets and induced remission in all mice. This novel combinatorial therapy promotes engraftment of autoantigen-specific donor T-regs and controls islet autoimmunity without long-term immunosuppression.