CAR Tregs protect alloimmune islets against autoimmune destruction

Abstract Regulatory T cell (Treg) therapy is a promising approach to induce tolerance of transplanted tissues and/or self antigens that drive autoimmunity. Early clinical trials with polyclonal Tregs have proven feasible, safe and tolerable. The next wave of Treg therapies is genetically enhanced with antigen specificity. We have previously shown that Tregs engineered to express a chimeric antigen receptor specific for HLA-A2 (A2-CAR) delay rejection of HLA-A2+ grafts; however, it was unknown whether they would limit T cell responses targeting antigens other than HLA-A2 via bystander suppression. To investigate this possibility, we used a model of HLA-A2-mismatched islet transplantation and asked if A2-CAR Tregs could inhibit rejection mediated by diabetogenic T cells. HLA-A2+ islets (150–200) isolated from NOD-HLA-A2+ mice were transplanted into immunodeficient NSG mice. After 3.5 weeks, diabetogenic BDC2.5 CD4+ T cells were adoptively transferred with or without polyclonal or A2-CAR Tregs (1 CD4+:5 Tregs). Mice that received BDC2.5 CD4+ T cells without Tregs or polyclonal Tregs rapidly developed hyperglycemia. In contrast, mice that received A2-CAR Tregs were completely protected from hyperglycemia. Longitudinal monitoring of injected Tregs showed that A2-CAR Tregs were more numerous and activated relative to polyclonal Tregs. Removal of the HLA-A2+ islet graft from a protected A2-CAR Treg-treated mouse did not induce hyperglycemia, suggesting that the ability of BDC2.5 CD4+ T cells to mediate autoimmune attack of the endogenous (HLA-A2-) pancreas was suppressed. These data suggest that A2-CAR Tregs mediate bystander suppression in vivo and may have the ability to induce long-term tolerance to both allo- and autoantigens. Supported by a CIHR Canada Graduate Scholarship doctoral research award and a CIHR foundation grant (FDN-154304).