Sometimes the infused donor cells cause inflammation of the skin, liver, and gut, and a reaction called graft-versus-host disease (GVHD) occurs. To prevent GVHD, tacrolimus will be given by vein non-stop starting 2 days before the transplant. It will be changed to oral tablets before you leave the hospital. You will take tacrolimus for about 6-8 months after the transplant. Methotrexate will be given for the same purpose on Days 1, 3, and 6 after the transplant by vein over a few minutes. Patients receiving a matched unrelated or mismatched donor will also be given methotrexate on day 11 after the transplant.