Composite vascularized skin/bone transplantation models for bone marrow-based tolerance studies.

There is an ongoing need to understand the mechanisms of bone marrow-based allograft tolerance. This is important in clarifying the diverse variables influencing the ultimate outcome of the solid organ and composite tissue transplants. To establish bone marrow transplantation as a routine clinical application, further experimental studies should be conducted to overcome the obstacles related to the bone marrow transplantation. These obstacles include graft versus host disease, immunocompetence, and toxicity of the conditioning regimens. For these purposes, novel experimental models are needed. In an attempt to provide a reliable research tool for bone marrow-based tolerance induction studies, we introduced different experimental models of modified vascularized skin/bone marrow (VSBM) transplantation technique for tolerance induction, monitoring, and maintenance studies. In this skin/bone transplantation model, the technical feasibility of concurrent or consecutive transplantation of the combination of bilateral vascularized skin, vascularized bone marrow, or vascularized skin/bone marrow transplants was investigated. Isograft transplantations were performed between genetically identical Lewis (LEW, RT1) rats. Five different experimental designs in 5 groups of 5 animals each were studied. Group I: Bilateral vascularized skin (VS) transplantation; group II: bilateral vascularized skin/bone transplantation; group III: vascularized skin transplantation on one side and vascularized skin/bone transplantation on the contralateral side; group IV: vascularized bone transplantation on one side and vascularized skin/bone transplantation on the contralateral side; group V: vascularized bone transplantation on one side and vascularized skin transplantation on the contralateral side. Successful transplantations were performed in all groups. The survival of the isograft transplants was evaluated clinically and histologically. All skin flaps remained pink and pliable and grew new hair. The viability of the compact bone, bone marrow and skin at 100 days posttransplant was confirmed by histologic evaluation, and bone marrow revealed active hematopoiesis. Bilateral skin/bone transplantation model may serve as an experimental tool to study new strategies in tolerance induction by altering the amount of the immunogenic load in the form of skin transplant and bone marrow delivery in the vascularized form, allowing for expedited engraftment of stem and progenitor cells.