Mechanisms that mediate graft versus host disease after composite tissue allotransplantation

Mixed allogeneic chimerism induced tolerance to composite tissue allografts like hand transplants, could obviate the need for long term immunosuppression, and revolutionize reconstructive surgery. Our overall goal is to induce tolerance through mixed chimerism in a rat hind limb composite tissue allograft model using a protocol that eliminates graft versus host disease and is achieved in a clinically feasible time frame.; Naive host WF rats transplanted with donor ACI limbs were controls. (ACI+WF) chimeras were prepared by irradiating host WF rats with 950 cGy of TBI and reconstitution with ACI bone marrow (depleted of alphabeta and gammadelta TCR T cells). 28 days later, these chimeras received irradiated (1050 cGy) ACI donor limbs, syngeneic WF limbs or third party Fisher rat limbs. Naive WF rats underwent irradiation with 950 cGy of TBI, donor ACI rat hind limb transplantation and reconstitution with ACI bone marrow (depleted of alphabeta and gammadelta TCR T cells), on the same day. These animals were divided into those that received no additional treatment and those treated with FK 506 and mycophenolate mofetil for 30 days after BM reconstitution.; Unmanipulated non-chimeric controls rejected their limbs in 5.7 +/- 1.5 days. WF hosts that were immunosuppressed with FK 506 and mycophenolate mofetil demonstrated prolonged survival of limbs for 142 +/- 11 days. 100% of (ACI+WF) chimeras developed severe graft versus host disease, 22.4 +/- 2.8 days after transplantation of unmanipulated donor limbs. (ACI+WF) chimeras prepared by performing limb transplantation and bone marrow reconstitution simultaneously, demonstrated prolonged survival for 160.5 +/- 3.6 days. Chimeras prepared by a similar protocol but receiving immunosuppression survived for 50.7 +/- 24.6 days. (ACI+WF) chimeras transplanted with irradiated ACI limbs or unmanipulated syngeneic WF limbs showed no signs of rejection or graft versus host disease at five months.; Conditioning of the host (WF) rats with 950 cGy of irradiation led to high levels of mixed allogeneic chimerism without graft versus host disease prior to limb transplant. The mature T-cell content of unmanipulated (non-irradiated) donor limbs caused graft versus host disease in 100% of tolerant mixed chimeric hosts and inactivating these cells with irradiation prevents graft versus host disease and permits rejection free graft acceptance.