In type 1 diabetes, allogeneic pancreatic islet transplant restores insulin production, but life-threatening immunosuppression is required to avoid graft rejection. Induction of antigen (Ag)–specific tolerance by cell therapy with regulatory T-cells (Tregs) represents an attractive alternative approach but its therapeutic efficacy in islet transplant remains to be determined. Among the different subsets of CD4⁺ Tregs, the T inducible regulatory type 1 (Tr1) cells can be generated from naive T-cells in the presence of interleukin-10 (IL-10) and represent one promising therapeutic choice. This study was designed to define the efficacy of Tr1-cell therapy in preclinical models of islet transplant.

Non–Ag-specific polyclonal Tr1 cells and donor Ag-specific Tr1 cells were transferred, in the absence of any pharmacological treatment, in two distinct mouse models of islet transplant. The two models differed in their therapeutic stringency, based on the mean rejection time of untreated mice that underwent a transplant.

Transfer of polyclonal Tr1 cells engendered graft tolerance only in the nonstringent mouse model. Conversely, cell therapy with Ag-specific Tr1 cells induced an IL-10–dependent tolerance in the stringent mouse model of islet transplant. The therapeutic advantage of Ag-specific Tr1 cells over polyclonal Tr1 cells was due to their donor Ag specificity.

These results demonstrate that Tr1-cell therapy leads to tolerance in settings of islet transplant and that its therapeutic efficacy is highly dependent on the antigen specificity of these cells.