After six months, patients in the tacrolimus arm who do not experience rejection will be randomized to continue on tacrolimus or to be converted to the combination of sirolimus and MMF. Individuals in this arm of the study who do not experience acute rejection, and demonstrate evidence of donor specific hyporesponsiveness at 9 months post-transplant (those staying on Tac + MMF) or 3 months post-conversion (those converted from Tac + MMF to sirolimus + MMF) will be weaned to MMF monotherapy.