Introduction: New protocols are needed for tolerance induction in composite tissue allograft (CTA). It is well documented that bone marrow transplantation induces donor–specific immune-tolerance through mixed macrochimerism, which is the existence of two genetically disparate cell populations in the same organism.Donor sensitization with the recipient bone marrow before transplantation is a new approach to induce immunotolerance. We demonstrated the effect of donor sensitization on the immune response to vascularized skin allografts.

Methods: Twenty transplantations were performed in 4 experimental groups of 5 animals each. Allograft transplants were performed between Presensitized ACI donors and Lewis recipients. The ACI (RT1^a) donor rats were presentisized with Lewis (RT1^l) bone marrow (80x 10⁶ cells) injected intraosseously and these donors received αβ-TCR and cyclosporine (CSA) treatment therapy before the cells transplantation. Bone marrow cells were isolated from tibia and femoral bones by flushing technique, cell viability was determined by tryptan blue staining, and the cells where then stained with PKH to allow their late tracing.
At either 24 hours or 72 hours after sensitization, the vascularized skin allografts (VSA) were transplanted to Lewis (RT1 ^I) recipients. In Group I and II no immunosuppressive treatment was given after transplantation, whereas group III and IV received αβ TCR and CSA protocol for 7 days. Assessment included flap viability, flow cytometry for donor specific chimerism, skin biopsies for histological evaluation, hematoxylin eosin staining for the grading of rejection (0 to 3) and immunohistochemistry.

Result: In the control groups (group I, II) VSA were acutely rejected within 2 to 6 days post transplant. The mean survival of VSA was 82 days in Group III and 73 days in group IV, with longest survival of 115 days. Donor specific chimerism in peripheral blood was estimated by presence of T and B cells. Total chimerism levels for Group III at day 7, 21, 35 and 63 were 4.93%, 1.75%, 2.46%, 1.45% respectively and Group IV 3.6%, 2.37%, 1.87%, and 0.48% respectively.

Conclusions: Donor presensitization with bone morrow cells of recipient origin modifies the recipient’s responsiveness and extends survival of vascularized skin allografts under short-term protocol of αβ-TCR and cyclosporine (CSA) therapy. This new approach to induce immunotolerance, could be promising for composite tissue allotransplantations in reconstructive surgery as well as for solid organ transplantations.