 If you are found to be eligible to participate in this study, you will be randomly assigned as in the toss of a coin to 1 of 2 groups. Participants in Group 1 will receive a higher dose of ATG by vein. Participants in Group 2 will receive a lower dose of ATG by vein. You will have an equal chance of being in 1 of the 2 groups. Participants in both groups will receive doses of ATG over 4-6 hours, 1 time a day every other day for a total of 3 doses. 