PRE-TRANSPLANT DONOR-SPECIFC TRANSFUSIONS COMBINED WITH CYCLOSPORINE BUT NOT WITH RAPAMYCIN INDUCE TOLERANCE TO MHC CLASS I-MISMATCHED CARDIAC ALLOGRAFTS IN MINIATURE SWINE

Abstract

P1125 Aims: To evaluate the effect of pretransplant donor-specific transfusion combined with cyclosporine A and rapamycin on tolerance induction to cardiac allografts in a clinically relevant large-animal model. Methods: Heterotopic cardiac transplants were performed across a major histocompatibility complex (MHC) class I barrier in MHC-inbred miniature swine. Experimental animals were treated with two donor-specific transfusions (DSTs), each containing 1.4x108 viable peripheral blood mononuclear cells, 14 and 7 days prior to heart transplantation. All animals received a 12-day course of cyclosporine (CyA) (trough level 300-800 ng/ml) or rapamycin (RPM) (trough level 10-20 ng/ml) starting on post-operative day (POD) 0. Control groups received CyA or RPM alone, DST alone or no treatment. Cell mediated lympholysis (CML) assays were performed at regular intervals. T cell priming and activation induced cell death (AICD) were assessed by carboxyfluoroscein succinimidyl ester (CFSE) proliferation assays and Annexin V staining. Results: Untreated (n=2) and DST-only (n=2) treated control animals rejected between POD 6 and 8. Animals treated with CyA (n=3) or RPM (n=3) alone exhibited graft survival to 53, 52 and 59 days or 41, 50 and 53 days, respectively. In contrast, DST-pretreatment combined with CyA (n=3) led to stable graft function for >200 days in all animals. Grafts in recipients treated with pretransplant DST and RPM (n=4) survived 52, 45, 100 and >200 days. Like the controls, long-term acceptors in the DST+CyA group and DST+RPM group mostly maintained peripheral CML response against donor and third party antigen. Following DSTs, the donor-specific proliferative response of CD8+ recipient T cells was significantly increased on CFSE assay (p=0.011), and a significant number of recipient CD8+ T cells underwent apoptosis (10.1% on POD 0 versus 5.2% on POD –14; p=0.04). Conclusions: The combination of pre-transplant DST and a short course of CyA consistently prolongs the survival of MHC class I disparate cardiac allografts in miniature swine. The sustained peripheral anti-donor CML response and the fact that alloreactive T cells were primed by the DST prior to transplantation suggest an active regulatory mechanism rather than peripheral deletion. In contrast, rapamycin did not demonstrate with the tolerogenic effect of pretransplant DST potentially because it failed to achieve appropriate regulatory cells.