Beginning on Day -2, tacrolimus will be given by vein over 24 hours to help lower the risk of graft-versus-host disease (GVHD). This will be changed to pills once you can tolerate swallowing pills. If no active cancer is detected and there is no GVHD, you will then swallow 1 or more tacrolimus pills a day for only about 3-4 months, instead of the usual period of 6 months. This is done to boost the donor immune system against the cancer.