Regulatory T Cells Induced by 1 alpha ,25-Dihydroxyvitamin D sub(3) and Mycophenolate Mofetil Treatment Mediate Transplantation Tolerance

1 alpha ,25-Dihydroxyvitamin D sub(3), the active form of vitamin D sub(3), and mycophenolate mofetil, a selective inhibitor of T and B cell proliferation, modulate APC function and induce dendritic cells (DCs) with a tolerogenic phenotype. Here we show that a short treatment with these agents induces tolerance to fully mismatched mouse islet allografts that is stable to challenge with donor-type spleen cells and allows acceptance of donor-type vascularized heart grafts. Peritransplant macrophages and DCs from tolerant mice express down-regulated CD40, CD80, and CD86 costimulatory molecules. In addition, DCs from the graft area of tolerant mice secrete, upon stimulation with CD4 super(+) cells, 10-fold lower levels of IL-12 compared with DCs from acutely rejecting mice, and induce a CD4 super(+) T cell response characterized by selective abrogation of IFN- gamma production. CD4 super(+) but not CD8 super(+) or class II super(+) cells from tolerant mice, transferred into naive syngeneic recipients, prevent rejection of donor-type islet grafts. Graft acceptance is associated with impaired development of IFN- gamma -producing type 1 CD4 super(+) and CD8 super(+) cells and an increased percentage of CD4 super(+)CD25 super(+) regulatory cells expressing CD152 in the spleen and in the transplant-draining lymph node. Transfer of CD4 super(+)CD25 super(+) cells from tolerant but not naive mice protects 100% of the syngeneic recipients from islet allograft rejection. These results demonstrate that a short treatment with immunosuppressive agents, such as 1 alpha ,25-dihydroxyvitamin D sub(3)/mycophenolate mofetil, induces tolerance to islet allografts associated with an increased frequency of CD4 super(+)CD25 super(+) regulatory cells that can adoptively transfer transplantation tolerance.