Donor-specific tolerance induction in composite tissue allografts

BACKGROUND: Although prolonged composite tissue allograft (CTA) survival is achievable in animals using immunosuppressive drugs, long-term immunosuppr ession of CTAs in the clinical setting would be unacceptable for most patie nts. The purpose of this study was to develop a model for reliable CTA tole rance induction in the adult rat across a strongly antigenic MHC mismatch w ithout the need for long-term immunosuppression. METHODS: Chimeras were prepared using rat strains with strong MHC incompati bility [WF (RT1A(u)) + ACI (RT1A(a)) --> WF, n = 13]. Syngeneic (WF) and al logeneic (ACI) bone marrow (BM) was harvested and T-cell depleted. Followin g confirmation of T-cell depletion by flow cytometry, a mixture of T-cell d epleted syngeneic and allogeneic BM was injected into the recipient animals (all recipients pretreated with low-dose irradiation, 500 to 700 cGy). In addition, the recipient animals received a single dose of ALS (10 mg) 5 day s prior to bone marrow transplantation (BMT) and tacrolimus (1 mg/kg/day) f rom the day prior to BMT to 10 days postoperatively. Rat chimeras were char acterized by flow cytometry at 3 and 12 months after BM reconstitution and following hindlimb transplantation. RESULTS: Peripheral blood lymphocyte chimerism (WF/ACI) remained stable >12 months after BM reconstitution in 10 of 13 animals. Multilineage chimerism of both lymphoid and myeloid lineages was present, suggesting that engraft ment of the pluripotent rat stem cell had occurred. In animals with donor c himerism >60%, there was no sign of limb rejection for the duration of the study. All animals with chimerism <20% developed moderate signs of rejectio n clinically and histologically, Gross motor and sensory reinnervation (wei ght bearing, Poe spread) occurred at >60 days in 6 of 9 rats. Postoperative flow cytometry studies demonstrated stable chimerism in all animals studie d (n = 7). CONCLUSIONS: Stable mixed allogeneic chimerism can be achieved in a rat hin dlimb model of composite tissue allotransplantation. Hindlimb allografts to mixed allogeneic chimeras exhibit prolonged, rejection-free survival. This represents the first reliable model demonstrating rejection-free CTA survi val in an adult animal without the long-term use of immunosuppressive agent s across a strongly antigenic MHC mismatch. Am J Surg. 1998;176:418-421. (C ) 1998 by Excerpta Medica, Inc.