Establishment Of A New Model Of Vascularized Bone Marrow Transplantation: Partial Femur Transplant

The induction of donor specific tolerance to transplanted organs and tissues hasalways been the final goal of transplantation. At present, bone marrow transplantation(BMT), as a traditional way to induce tolerance, has been applied in clinical kidneytransplantation. Some composite tissue allografts (CTA) themselves include a vascularizedbone marrow component such as hands, so we also term it vascularized bone marrowtransplantation (VBMT). The vascularized bone marrow components within CTA havethe advantages in promoting induction and maintenance of chimerism over the traditionalBMT. However, the previous VBMT models contain multiple components and existtechnical complexity and high mortality. So tolerance has been difficult to studyextensively in VBMT.Objective To establish a purer and simpler model of vascularized bone marrowtransplantation, the partial femur graft was developed. The comparison between partialfemur and whole femur was also performed. Establishment of this model will provide anew tool for the study of immune induction of CTA.Methods Fully MHC mismatched Brown Norway (BN, RT1n) and Lewis (RT11) ratswere used as donors and recipients respectively, the2/3femur from donor wastransplanted into the recipients inguinal region, and their femoral vessels wereanastomosed with recipients vessels.4experimental groups were carried out: The syngeneic group, syngeneic partial femur transplant between Lewis rats; The rejectiongroup, allogeneic partial femur transplants without immunosuppression served asrejection controls. The experimental groups, allogeneic partial femur transplant withcyclosporine A (CSA) monotherapy; The positive group, allogeneic whole femurtransplants under the same dosage of CSA with experimental groups served as positivecontrol. All of the allografts were performed across major MHC barrier between BNdonors and Lewis recipients. Operative time and ischemia time was recorded during theoperation. Gross examination and bone specimens were evaluated for the viability ofpartial femur components, and the multilineage chimerism was assessed by flowcytometry among the experimental and positive groups at different times postallotransplantation. Besides, donor cell engraftment into recipients’thymus, spleen, lymphnodes, and bone marrow was also evaluated at day60posttransplant.Results The partial femur model shortened the operative time and ischemia time withhigher success rate when compared with the whole femur model. Gross and histologicappearance confirmed the viability of bone grafts in both experimental group andsyngeneic group, and HE staining showed numerous basophil bone marrow cells withinbone marrow and viable osteocytes in lacunae. But the grafts in rejection group wereclearly rejected, and the number of bone marrow cells decreased sharply with almost nochimerism. On the contrary, in the experimental group, donor-specific multilineagechimerism including lymphoid and myeloid lineage was continuously confirmed inperipheral blood at1,2,3,4,8weeks post-transplant, and the chimerism level induced bypartial femur showed no significant differences compared to whole femur transplantation(P<0.05). Furthermore, long-term engraftment of donor-origin cell was also detected inrecipients’bone marrow, lymph node, and spleen but not thymus.Conclusion Vascularized partial femur grafting is a simple and reliable method forvascularized bone marrow transplantation. The transplanted partial femur can acts as aconstant and reliable source for bone marrow delivery and may facilitate inducingchimerism for studying the role of bone marrow in composite allografts.