The present invention provides compositions and methods for the prevention and treatment of aggressive immune processes to life-saving grafts, such as xenograft rejection, and for attenuating host responses in transplantation of tissues, cells and organs. More specifically, the compositions and methods of the present invention relate to combined therapies comprising treatment of alpha-1-antitrypsin (AAT) and temporary T-cell depletion including but not limited to anti-CD4 and anti-CD8 antibodies.