| In recent years, induction of allograft immune tolerance has been the focus subject in the field of organ transplantation. Allograft tolerance is to induce specific immune tolerance to organ allografts derived from the marrow donors, which means host immune system appears no or low responsiveness to donor antigens, but normal responsiveness to the third party antigens. It is sharply distinguished from induced by immunosuppressive agents and immune defects. A wide variety of host-conditioning regimens have demonstrated the feasibility of the induction of hematopoietic chimerism and donor-specific immune tolerance across the histocompatibility barrier in adult laboratory animals including mice, rats, dogs and monkeys. However, most of these regimens failed to result in stable chimerism and long-term specific tolerance in human beings. As a pre-clinical experimental research,our major targets of this subject studies would be (l)with comparing variety of host-conditioning regimens, we selected a superior perioperative conditioning regimen which should be low-toxic,sutable for clinical practice tolerance. We also demonstrated the powerful theoretical and experimental proofs to the further clinical application of this protocol. (2) We evaluated the roles of anti-donor antigen host mature T cells in acute rejection, engraftment of donor hematopoietic cells and induction of tolerance at the early stage of allograft, which would be highly instructice in clinical application.This project included the following two parts. 1. Comparision of variety of conditioning regimens in induction oflong-term specific tolerance to allogeneic heart grafts-a preclinicalexperimental researchThe recipients, BALB/C mice(H-2Kd), were conditioned with variety of combination of TBI, ATS and infusion of bone marrow cells (50X106) from donor C57BL/6 mice (H-2Kb) and divided into 11 groups and then neonatal donor heartallografts were transplanted into the pinna of the ear of recipients without any other immunosuppressive therapies. Heart grafts were monitored daily for visible contractions under microscope (magnification, 10), and survival was based on the time interval until contractions stopped. Stopped beating heart grafts were proved tobe rejection by histopathologic examination. Chimera in peripheral blood of hosts were routinely analyzed by Flow Cytometry on day 28 after BMT.Results: (1) comparison of heart graft survival time (days) among groups: 9 of 10 heart grafts in hosts conditionated with combination of ATS+sublethal TBI (450cGy) + BMT survived for more than 100 days, and 1 of 10 heart grafts in the group survived for 69 days. Heart graft survival time was non-significantly different between ATS + TBI (450 cGy) + BMT grou[ and lethal TBI (800 cGy) + BMT group (>0.05). Heart graft survival time in hosts treated by TBI (450 cGy) + BMT was 22.1+9.4 days averagely, which was significantly different from that in the previous two groups (P<0.001). Hosts administered by ATS, ATS + TBI (450cGy) , TBI(450cGy) or ATS+BMT rejected their allogeneic heart grafts within 45 days after heart transplantation. (2) Analyses of chimensm in peripheral blood of hosts: All of Hosts conditioned with TBI (450 or 800 cGy) + BMT and ATS + TBI(450 cGy) + BMT got complete donor-cell chimera in blood on day 28 after BMT, which chimeric indexes were more than 99% and non-significantly different in three groups (P>0.05). But the percentage of donor T cells in groups of TBI (800cGy) + BMT and ATS + TBI(450cGy) + BMT was significantly higher than that of group TBI(450cGy) + BMT(P<0.01), which demonstrated that condition with TBI(800cGy) or ATS+TBI(450cGy) facilitated engraftment of donor T cells. No chimera was detected 28 days after BMT in hosts treated by ATS + BMT (No TMI), which implied that hosts conditioned with ATS only resulted in loss of chimera at early stage after BMT. In control groups (No BMT), on day28 after heart transplantation, percentage of host T cells in blood of hosts treated by TBI(450cGy) was significantly lower than that of g...
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