Abstract: An ex vivo method for generating a population of Treg capable of suppressing rejection of an organ or tissue transplant from a donor animal, comprises culturing CD4+ T cells from a recipient animal in the presence of IFN-? plus either donor specific or third-party antigen presenting cells, and harvesting a population of Treg capable of suppressing rejection in the recipient animal. The Treg can be administered, for example intravenously to the recipient, preferably immediately prior to the transplant to suppress transplant rejection. A similar strategy applicable to generating a population of Treg capable of suppressing an autoimmune condition in an animal wherein the animal mounts an immune reaction against an autoantigen, comprises culturing CD4+ T cells from the animal in the presence of cells presenting the autoantigen and IFN-? and harvesting a population of autoantigen reactive Treg.