A method of providing a pancreatic, lymphoid/hematopietic or pulmonary organ and/or tissue function to a mammalian subject is provided. The method comprises transplanting into the subject a developing mammalian pancreatic, lymphoid/hematopietic or pulmonary organ/tissue graft, respectively, thereby generating a functional pancreatic, lymphoid/hematopietic or pulmonary organ and/or tissue, respectively, for providing the pancreatic, lymphoid/hematopietic or pulmonary organ and/or tissue function, respectively, to the subject.