If your stem cell donor is not someone who is related to you, you will receive antithymocyte globulin (ATG) through the CVC once a day from Day -3 through Day -1. On Day -3, it will be given over at least 6 hours. On Days -2 and -1, it will be given over at least 4 hours. This drug is given in order to weaken your immune system in order to lower the risk of your immune system rejecting the transplanted cells.