Administration of low doses of IL-2 combined to rapamycin promotes allogeneic skin graft survival in mice.

Human CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) prevent allogeneic graft rejection by inhibiting T cell activation, as has been shown in mouse models. Recently, low-dose IL-2 administration was shown to specifically activate Tregs but not pathogenic conventional T cells, leading to resolution of type 1 diabetes in nonobese diabetic mice. We therefore tested the ability of low-dose IL-2 to prevent allogeneic skin graft rejection. We found that while IL-2 alone was inefficient in preventing rejection, combined with rapamycin, IL-2 treatment promoted skin graft survival both in minor disparate and semi-allogeneic skin graft combinations. Tregs are activated by this combined treatment while conventional CD4(+) cell expansion and activation are markedly inhibited. Co-administration of anti-CD25 antibodies dramatically reduces the effect of the IL-2/rapamycin treatment, strongly supporting a central role for Treg activation. Thus, we provide the first preclinical data showing that low-dose IL-2 combined with rapamycin can significantly delay transplant rejection in mice. These findings may form the rational for clinical evaluation of this novel approach for the prevention of transplant rejection. © Copyright 2014 The American Society of Transplantation and the American Society of Transplant Surgeons.