Rebecca S. Hasse

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.

Operational tolerance to class I disparate lungs can be induced despite pretransplant immunization with class I allopeptides

Background. Using a class I-disparate swine lung transplant model, we examined whether an intensive course of tacrolimus could induce operational tolerance and whether preoperative allopeptide immunization would prevent the development of tolerance. Methods. Left lung grafts were performed using class I-disparate (class II-matched) donors. Recipients were treated with 12 days of postoperative tacrolimus. Three recipients were immunized prior to transplantation with class I allopeptides. Three other recipients were not immunized. Results. The nonimmunized recipients maintained their grafts long term (>497, >451, and >432 days), without developing chronic rejection. The immunized swine also maintained their grafts long term (>417, >402, >401 days), despite developing a variety of in vitro and in vivo responses to the immunizing peptides, as well as having strong mixed lymphocyte reactions to donor cells prior to transplantation. Conclusions. Using only a brief course of tacrolimus, we have been able to induce a state of operational tolerance in a class I-disparate preclinical lung transplant model. Moreover, preoperative alloimmunization did not block tolerance induction or induce chronic rejection. These data show that it is possible to create a state of operational tolerance to lung allografts even in the presence of donor-sensitized cells.