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 (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 non-autoimmune models required ablative host conditioning. Here, we evaluated Treg engraftment and therapeutic efficacy in the non-obese diabetic (NOD) mouse model of autoimmune diabetes using non-ablative, combinatorial regimens involving 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 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 IL-2 (interleukin-2) support. A single-dose of CyP after αCD3 depleted rebounding host-Tregs, resulted in a 43-fold increase in donor-Treg engraftment, yet polyclonal donor-Tregs failed to reverse diabetes. However, infusion of autoantigen-specific Tregs following 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.