You will receive tacrolimus by vein as a nonstop infusion until you are able to take it by mouth to help lower the risk of GVHD. You will then take tacrolimus by mouth 2 times a day for about 3 months. After that, your tacrolimus dose may be lowered if you do not have GVHD. Your doctor will discuss this with you. On Days 1, 3, and 6, if your stem cells are from a related or matched unrelated donor, you will receive methotrexate over 30 minutes each day by vein to help lower the risk of GVHD. Participants receiving a matched unrelated donor will also receive methotrexate on Day 11 after the transplant.