Donor-specific tolerance in fully major histocompatibility major histocompatibility complexmismatched limb allograft transplants under an anti- alpha beta T-cell receptor monoclonal antibody and cyclosporine A protocol

Background. Recent studies have demonstrated that treatment with alpha beta -T-cell receptor (TCR) monoclonal antibody and cyclosporine A (CsA) can extend survival in composite tissue allografts (CTA). The purpose of this study was to induce tolerance in fully major histocompatibility complex (MHC)-mismatched rat limb allografts under 7 days of a combined alpha beta -TCR-CsA protocol. Methods. The authors performed 30 hind-limb allotransplantations across the MHC barrier between Brown Norway donors (BN; RT1 super(n)) and Lewis recipients (LEW; RT1 super(l)). Isograft and allograft controls received no treatment. The experimental groups received monotherapy of alpha beta -TCR and CsA or a combination of alpha beta -TCR and CsA for 7 days only. Donor-specific tolerance and immunocompetence were determined by standard skin grafting in vivo and mixed lymphocyte reaction (MLR) in vitro. The efficacy of immunosuppressive therapy and the level of donor-specific chimerism were determined by flow cytometry. Results. Long-term survival (>350 days) was achieved in allograft recipients (n=6) under the 7-day protocol of combined alpha beta -TCR-CsA. Donor-specific tolerance and immunocompetence of long-term chimeras were confirmed by acceptance of skin grafts from the donors and rejection of the third-party alloantigens (AxC Irish). At day 120, MLR demonstrated unresponsiveness to the host and donor antigens but strong reactivity against third-party alloantigens. Flow cytometry confirmed the high efficacy of immunosuppressive treatment and the development of donor-specific chimerism (7.6% of CD4 super(+)-RT1 super(n+) cells, 1.3% of CD8 super(+)-RT1 super(n+) cells, and 16.5% of CD45RA super(+)-RT1 super(n+) cells) in the periphery of tolerated recipients. Conclusions. Combined therapy of alpha beta -TCR-CsA for 7 days resulted in tolerance induction in fully MHC-mismatched rat hind-limb allografts. Tolerance was directly associated with stable, donor-specific chimerism.