Transplantation is an exciting field of clinical medicine with great potential for alleviating human disease. Because of its intimate association with immunology, this field provides an opportunity for fertile interactions between basic scientists and clinicians. The availability of outstanding teams of M.D. and Ph.D. scientists devoted to all aspects of transplantation, from studies at the level of basic molecular mechanisms clinical transplantation of tissues and organs, provides the Harvard Medical School environment with an outstanding opportunity to foster productive interactions among these investigators. The purpose of this Program is to train young scientists and physician scientists in basic and translational research, on a wide variety of topics related to transplantation biology, in a multi-disciplinary environment, with emphases on immunological mechanisms and on translational application. Participating faculty members with diverse but complementary research interests, a successful record of collaboration, and a commitment to training young investigators, have been assembled to provide trainees with exposure to topics related to transplantation immunology including immunogenetics, tolerance induction, antigen processing and presentation, bone marrow transplantation, regulation of lymphocyte development, pathology of graft rejection, complement biology, autoimmune disease, dendritic cell biology, chemokines and lymphoctye trafficking, B and T cell biology, regulatory T cells, mucosal immunology, and xenotransplantation. This program is directed toward development of outstanding independent investigators capable of addressing fundamental questions in the field of transplantation and of applying the answers to achieve clinical goals. Pre- doctoral trainees will be selected from students currently enrolled in the Immunology Program at Harvard University's Division of Medical Sciences who express an interest in pursuing their thesis research in the field of transplantation immunology. Training for pre-doctoral students will take approximately 4-5 years. Support is requested for 2 pre-doctoral trainees per year, distributed between students in their 3rd, 4th or 5th year of thesis research. Post-doctoral trainees currently holding a degree of M.D., Ph.D., or M.D./Ph.D. will be selected based on having outstanding potential to pursue a career in research and teaching and a commitment to independent investigation. Training will require 2-3 years. Support is requested for 5 post- doctoral trainees in each year of the grant.