217. Thymic dependence of tolerance in vascularized composite tissue allografts under Cyclosporine A and ab-T Cell Receptor monoclonal antibody protocol

Abstract

Background In our previous studies, we have demonstrated that vascularized composite tissue allograft transplants treated with ab-TCR) monoclonal antibody (mAb) and Cyclosporine A (CsA) for 7 days developed robust tolerance across MHC barrier. In this paper we have investigated the role of host thymus in the induction ot tolerance in rat hind-limb allograft model. Material and Methods Five weeks old, euthymic (group A) and thymectomized (group B) Lewis recipients (LEW,RT1l) received vascularized hind-limb allografts from Lewis-Brown-Norway (LBNŕF1, RT1l+n) donors. Group lA (n=6) and 1B (n=6) and Group IIA (n=6) and IIB (n=6) served as the isograft and the allograft control groups, respectively. Groups IIIA (n=5) IIIB (n=5) and IVA (n=5) and IVB (n=5) received monotherapies of either ab-TCR mAb or CsA tor 7 days, respectively. In Groups VA(n=6) and VB (n=6) a treatment protocol of combined ab-TCR/CsA was applied for 7 days. Mixed lymphocyte reaction (MLR) and skin grafting were performed for the evaluation of the donor specific tolerance in vitro and in vivo, respectively. Flow cytometry analysis was applied for the determination of the efficacy ot immunosuppressive treatment and the presence of mixed donor specific, hematopoietic chimerism. Results Combined treatment with ab-TCR/CsA protocol resulted in indefinite survival of the euthymic rats from group VB (>100 days) and extended the survival of the animals from group VA up to 51 days, post-transplant. MLR showed donor specific tolerance in the group VA at day 100. Flow cytometry revealed stable, multillinege chimerism in the peripheral blood of euthymic rats (CD4+/RT1n–17.3% and CD8+/RT11n–13.9%) and transient chimerism in thymectiomized limb allograft recipients. Conclusions Thymus is necessary for the induction ot donor specific tolerance under ab-TCR/CsA protocol in vascularized composite tissue allograft model. Tolerogenic activity of the thymus resulted in the creation ot stable mixed hematopoietic macrochimeric state within recipient.