ABSENCE OF HYPERACUTE REJECTION IN PIG-TO-PRIMATE ORTHOTOPIC PULMONARY XENOGRAFTS

The shortage of organ donors for transplantation is more pronounced fo r the lung than for any other solid organ. To address this problem, we evaluated the feasibility of pulmonary xenotransplantation. Prelimina ry investigations demonstrated that orthotopically placed pig lungs in cynomologous monkey recipients could be engrafted up to 9 hr after re perfusion without evidence of hyperacute rejection. In this study, the rejection reaction of pig lungs transplanted orthotopically into babo ons (n=6) was further investigated by ELISA and immunohistochemistry. Four baboon recipients were killed at 24 hr and 2 recipients were kill ed at 72 hr after transplantation. Pulmonary arterial flow measurement s demonstrated flow to the grafts, and systemic arterial and xenograft pulmonary venous blood gas analysis suggested function of the donor l ungs during the course of engraftment. Serum levels of baboon anti-pig endothelial cell xenoantibody were normal and decreased minimally ove r time. Immunohistochemical staining of biopsies demonstrated trace Ig G; and IgM along graft endothelium 2 hr after reperfusion. At 8 hr, bi opsy samples showed no immunoglobulin bound to endothelial cells. Stai ning for complement was negative. Fibrin and platelets were detected a long xenograft endothelium. Despite these findings, the lung xenograft s appeared injured and clinically rejected. During the first 8 hr afte r reperfusion, the grafts were hyperemic and subsequently became focal ly ecchymotic. showed progressive pulmonary congestion. These findings suggest that the lung may be relatively resistant to antibody-mediate d hyperacute rejection and efforts are being directed toward identifyi ng the mechanism of the observed xenograft lung injury.