Abstract
Optimal immune-based therapies for type 1 diabetes (T1D) should restore self-tolerance without inducing chronic immunosuppression. CD4+Foxp3+ regulatory T cells (Tregs) are a key cell population capable of facilitating durable immune tolerance. However, clinical trials with expanded Tregs in T1D and solid-organ transplant recipients are limited by poor Treg engraftment without host manipulation. We showed that Treg engraftment and therapeutic benefit in nonautoimmune models required ablative host conditioning. Here, we evaluated Treg engraftment and therapeutic efficacy in the nonobese diabetic (NOD) mouse model of autoimmune diabetes using nonablative, combinatorial regimens involving the anti-CD3 (αCD3), cyclophosphamide (CyP), and IAC (IL-2/JES6-1) antibody complex. We demonstrate that αCD3 alone induced substantial T-cell depletion, impacting both conventional T cells (Tconv) and Tregs, subsequently followed by more rapid rebound of Tregs Despite robust depletion of host Tconv and host Tregs, donor Tregs failed to engraft even with interleukin-2 (IL-2) support. A single dose of CyP after αCD3 depleted rebounding host Tregs and resulted in a 43-fold increase in donor Treg engraftment, yet polyclonal donor Tregs failed to reverse diabetes. However, infusion of autoantigen-specific Tregs after αCD3 alone resulted in robust Treg engraftment within the islets and induced remission in all mice. This novel combinatorial therapy promotes engraftment of autoantigen-specific donor Tregs and controls islet autoimmunity without long-term immunosuppression.