Purpose: Vascularized bone marrow allotransplantation is known to be the most effective way of multilineage chimerism induction in the experimental and clinical models. In this study, we introduce combined vascularized skin/vascularized bone transplantation model (VS/BM) to evaluate the effect of the vascularized bone transplantation on tolerance induction across strong MHC barrier, under 7 days αβ-T-cell receptor antibody (a b TCR) and cyclosporine-A (CsA) treatment protocol

Methods: Thirty-six transplantations between Brown Norway (RT1ⁿ) donors to Lewis (RT1^l) recipients were performed in three experimental groups (Table 1) of six animals each. In isograft control group and allograft rejection control group no treatment was applied. The experimental group III of vascularized skin /vascularized bone allograft (VS/BM) was treated with a b -TCR/CsA for 7 days only. The efficacy of immunosuppressive treatment and the level of chimerism in the peripheral blood of recipients were determined by flow cytometry (FC). Standard H+E technique was applied for the evaluation of the grade of graft rejection.

Results: The Isograft Control Group I transplants survived indefinitely. In allograft rejection control transplants were rejected between 5 and 9 days post-transplant. The survival time was significantly (p<0.05) extended in the VS/BM group up to 90-125 days after treatment cessation (Table 1). FC showed >95% efficacy of the combined a b TCR/CsA immunosuppressive treatment. MLR assay performed in VS/BM recipients revealed no response to the host and donor antigens but strong reactivity to the third party (ACI) alloantigens. Two-color FC analysis of the RT1ⁿ antigen expression in the peripheral blood of the VSBM recipients confirmed the presence of the donor specific chimerism which ranged form 12% to 25% at day 63 after transplantation. In VS recipients the transient donor specific chimerism ranged from 2% to 7% at day 7 post-transplant was observed . At day 63 post-transplant the skin biopsies from VS/BM recipients revealed no signs of rejection.

Conclusion: Transplantation of the vascularized skin with vascularized bone resulted in significant prolongation of the allograft survival. Allotransplantation of the vascularized bone with marrow natural micro-anatomic environment increases of the potential of the donor-derived stem and progenitor cells engraftment and leads to the establishment of the stable, donor specific chimerism within recipient.