L.G Ledgerwood

Indirect recognition of MHC class I allopeptides accelerates lung allograft rejection in miniature swine.

The role of indirect allorecognition in graft rejection is examined in two experiments using a swine lung transplantation model. First, two swine received class I mismatched grafts without immunosuppression; another two recipients were treated postoperatively with cyclosporine (CsA). These swine exhibited acute and chronic rejection, respectively. All four recipients developed T‐cell reactivity to donor‐derived class I major histocompatibility complex (MHC) peptides. Second, six swine were immunized with synthetic donor‐derived class I allopeptides prior to transplantation. Control groups consisted of nonimmunized recipients (n = 6) and recipients immunized with an irrelevant peptide (n = 3). These recipients all received a 12‐day course of post‐operative CsA. Swine immunized with allopeptides exhibited accelerated graft rejection, as compared to both control groups (p < 0.01 and p = 0.03, respectively). Within the experimental group, the dominant histologic finding was acute rejection (AR). Obliterative bronchiolitis (OB) was seen in the graft with the longest survival. Both control groups showed a lesser degree of AR, with four out of six nonimmunized swine ultimately developing OB. These studies suggest that indirect allorecognition is operative during lung allograft rejection, and that pre‐transplant sensitization to donor‐derived MHC allopeptides can accelerate graft rejection.

The effects of tolerance on allograft damage caused by the innate immune system.

Background. It is not known whether tolerance can be induced in a strong proinflammatory milieu or whether the induction of tolerance can prevent interferon (IFN)-&ggr;-associated graft injury. To address these questions, we studied the effects of rIFN-&ggr; infusion on porcine cardiac allograft survival. Methods. Recombinant interferon (rIFN)-&ggr; was continuously infused into the left anterior descending artery of hearts transplanted into major histocompatibility complex-inbred miniature swine treated with a 12-day course of cyclosporine A. Group 1 recipients received a nearly syngeneic heart, group 2 recipients received a class I disparate heart, and group 3 recipients were cotransplanted with a class I-disparate heart and kidney, a procedure demonstrated to induce tolerance to both grafts. A fourth group of animals were not transplanted but received intracoronary rIFN-&ggr; infusion into the native heart. Results. rIFN-&ggr; perfusion not only accelerated the acute rejection of class I-disparate hearts (mean survival time, 19±7.21 vs. 38±8.19; P=0.025) but caused near-syngeneic heart transplants, which otherwise survived indefinitely, to reject within 35 days. In contrast, rIFN-&ggr; perfusion had no demonstrable effects on hearts grafts in tolerant recipients or on autologous hearts. Conclusions. These results suggest that tolerance induction can occur in the presence of IFN-&ggr;-mediated inflammation, and that tolerance induction can prevent the tissue injury caused by the overproduction of IFN-&ggr;. This suggests that the beneficial effects of tolerance may include protection from nonspecific inflammatory responses, such as those produced by ischemia-reperfusion injury and brain death.

Combination treatment with donor-specific transfusions and cyclosporine a induces long-term survival of cardiac allografts in miniature swine

Background. To evaluate whether pretransplant donor-specific transfusions (DST) can induce tolerance to cardiac allografts in large animals, heterotopic cardiac transplants were performed across a class I MHC barrier in inbred miniature swine. Methods. Experimental animals received two DSTs, each containing 1.4x108 viable peripheral blood mononuclear cells, 14 and 7 days prior to transplantation together with a 12-day course of cyclosporine (CyA) (13 mg/kg IV) starting on postoperative day (POD) 0. Results. Untreated (n=2) and DST-only (n=2) treated control animals rejected between POD 6 and 8. Animals treated with CyA alone (n=3) exhibited graft survival to 53, 52 and 59 days. In contrast, the combination of DST and CyA (n=3) led to stable graft function for >200 days. Long-term survivors maintained peripheral CML response against donor antigen. Following DSTs, the donor-specific proliferative response of CD8+ recipient T cells was significantly increased (P=0.011), and a significant number of CD8+ T cells underwent apoptosis (10.1% on POD 0; 5.2% on POD –14; P=0.04). None of the DST-treated animals developed donor-specific antibodies. Conclusions. These results are the first to demonstrate the ability of DST to induce operational tolerance to cardiac allografts in large animals, and they suggest that peripheral mechanisms of tolerance mediate this effect.

Recipients of MHC class I disparate lung grafts develop T cell reactivity to donor MHC class I allopeptides in an orthotopic swine model

logical reactivity to donor antigens, followed by vascularized heterotopic heart transplantation to determine if CAV still develops in the tolerant recipient. Procedures: In mice, specific immunological nonreactivity was achieved in recipients by (1) neonatal administration of allogeneic spleen cells from F1 donors between class I mismatched donor and recipient strains, (2) acheivement of mixed chimerism by bone marrow infusion of irradiated adult recipients, (3) use of genetically immunodeficient recipients (RAG1-/or SCID). In swine, reduced reactivity was achieved through the induction of mixed chimerism. After nonreactivity was induced and verified through extended persistence of skin grafts, hearts from donors were heterotopically transplanted into the recipients. Results: Most hearts transplanted into tolerant or immunodeficeint mice developed striking vasculopathy in their coronary arteries (neonatal tolerance: 12 of 15, mixed chimeras: 15 of 23, immunodeficient recipients: 16 of 31). In contrast, isotransplants were virtually free of CAV. Three of the four transplanted swine hearts showed neointimal proliferation characteristic of CAV in 1%-6% of donor coronary arteries. Control hearts transplanted into untreated recipients across similar minor antigen barriers were acutely rejected within 44 days whereas control isografts survived indefinitely without evidence of CAV. Conclusions: Elimination of T and B cell immune responses was not sufficient to prevent the development of CAV. Other immune effectors, perhaps NK cells, could play a role in the development of CAV in this immunodeficient state. Additional results on these alternate effectors will be presented.

Intracoronary interferon-γ accellerates cardiac allograft rejection in miniature swine

Purpose: The effect of interferon(IFN) on allograft rejection remains controversial. Some have proposed that IFNhas a protective effect on the microcirculation of allografts, while others have shown IFNto be deleterious. We investigated the effects of intracoronary IFNon cardiac rejection in a preclinical large animal model. Methods: MHC class I disparate hearts were heterotopically transplanted into swine treated with a 12-day course of cyclosporine (10-14mg/kg/day) (n 3). An Alzet osmotic mini-pump delivered IFNinto the coronary vasculature at a rate of 100ng/day. Control recipients were treated with a similar course of cyclosporine but without IFN(n 3). Results: Swine treated with IFNdeveloped an earlier onset of high grade acute rejection as compared to controls, and rejected their allografts in 19 days vs. 46 days for controls (p 0.02). Elastin staining of the cytokine treated allografts showed severe endothelialitis and intimal thickening as early as POD 13. Conclusion: The delivery of IFNinto the coronary circulation of cardiac allografts appears to accelerate both acute and chronic rejection. Targeting IFNin antirejection regimens may ameliorate both of these processes.