The combination of tacrolimus and methotrexate is standard therapy for prevention of GVHD, however, our recent experience has demonstrated that the substitution of sirolimus for methotrexate provides superior GVHD control with reduced transplant-related toxicity. One limitation to the use of calcineurin inhibitors in GVHD prevention is the disruption in Treg function and proliferation. Based on our evolving understanding of the role of Treg in the development of chronic GVHD, we propose a GVHD prophylactic regimen that is effective in prevention of acute GVHD, but by virtue of the maintenance of Treg activity may be able to prevent chronic GVHD. We hypothesize that the substitution of mycophenolate mofetil for tacrolimus as well as the addition of bortezomib may provide similar protection against acute GVHD and prevent chronic GVHD while minimizing renal toxicity after transplantation.