On Day 0, you will receive the donor's stem cells by vein. The infusion will last anywhere from about 30 minutes to several hours. After the stem cell infusion, you will begin receiving mycophenolate mofetil (MMF) by vein over about 2 hours, 3 times a day. When your doctor thinks you can tolerate taking it by mouth, you will switch to taking MMF by mouth 3 times a day with food. If you do not have GVHD by Day 60, MMF will be stopped. If you miss a dose of MMF you should tell your study doctor. You should not try to make up the dose later. If you develop GVHD, you may have to take MMF for a longer period of time.