• Robert D Foster, Si Pham, Sen Li, and Abdelouahab Aitouche.
• Division of Plastic Surgery, University of California, San Francisco, San Francisco, CA 94143, USA. fosterr@surgery.ucsf.edu
• Transplantation. 2003 Sep 27; 76 (6): 988-94.

BackgroundClinical composite-tissue (hand) transplantation between genetically disparate individuals currently requires potent, nonspecific immunosuppressive agents that are neither completely successful in preventing acute episodes of rejection nor free from complications. The reliance on long-term immunosuppression has prompted this study to achieve donor-specific transplantation tolerance in adult recipients using a nontoxic, nonmyeloablative protocol.MethodsFully mismatched, 4- to 6-week-old ACI (RT1Aa) and Wistar Furth (WF) rats were used as donors and recipients, respectively. Recipients were administered CTLA4-Ig at 2 mg/kg per day (alternate days) in combination with tacrolimus at 1 mg/kg per day (daily) from day 0 through day +10, antilymphocyte serum at 10 mg at day +10 (single dose), and total-body irradiation t 300 cGy (day 0) before bone-marrow transplantation (BMT) (day 0) with 100 x 10(6) T-cell-depleted bone marrow cells. Hindlimb transplants were performed 4 weeks postBMT. Multilineage donor hematopoiesis was determined pre- and posttransplant using flow cytometry. In vitro T-cell responses were evaluated by mixed lymphocyte reactivity assays.ResultsCD28 blockade in a transplant model of mixed chimerism effectively aborts T-cell clonal expansion in vitro and in vivo, inhibits the development of acute and chronic rejection of vascularized hindlimb allografts in rats (ACI limbs to ACI-->WF chimeras, n=5; WF limbs to ACI-->WF chimeras, n=4), and subsequently leads to long-term survival of allogeneic skin grafts (n=9). Third-party (F344, n=4) transplants were uniformly rejected within 14 days posttransplant. Multilineage donor hematopoiesis was demonstrated pre- and posttransplant. Donor chimerism, present postBMT, increased throughout the study (pretransplant range 2-28%, mean 17%; posttransplant range 5-49%, mean 34%). Transplant recipients maintained full reactivity to respond to third-party antigens without harmful manifestations of graft-versus-host disease.ConclusionsAlthough efforts have been made to induce tolerance to composite tissue allografts in adult recipients, thus far, none have succeeded without toxic, myeloablative host preconditioning. Our demonstration that tolerance can be achieved with minimal preconditioning provides a rationale for application to large animals and humans and suggests that although composite tissue allografts may have a significant skin component (and are therefore felt to be highly antigenic), protocols used to induce tolerance to organ transplants may be equally applicable to composite-tissue allotransplantation.

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