Eligible participants will be randomized to the experimental or control groups. The experimental group will receive intravenous infusions of CTLA-4 Ig. The first infusion will occur at the time of randomization, followed by another infusion 2 and 4 weeks later. Subsequent infusions will be given monthly for two years during the treatment phase of the study. There is a total of 27 infusions during the treatment phase of the study.