EX-VIVO CHARACTERIZATION OF HUMAN ANTIPORCINE HYPERACUTE CARDIAC REJECTION

Hyperacute rejection (HAR) currently precludes the use of discordant o rgans for human transplantation. In order to comprehensively evaluate HAR in a clinically applicable species combination, we have developed an ex vivo perfusion model utilizing a neonatal extracorporeal membran e oxygenator circuit; this model allows for functional and sequential biopsy studies of working piglet hearts sustained by human, single don or AB+ type blood. A detailed description of the methods employed is i ncluded. Hearts perfused by allogeneic pig blood sustained normal func tion throughout the study period, while those perfused with human bloo d lost organized ventricular contraction in 25-34 min with markedly at tenuated function. Compared with biopsies from piglet hearts perfused with allogeneic blood and biopsies taken prior to human blood perfusio n (t=0), biopsies of hearts perfused with human blood at t=15 and 30 m in demonstrated significant inflammatory changes involving vessels (en dothelial and myointimal swelling and reaction) as well as myocardium (injury and necrosis). By immunohistology, significant vascular deposi tion of IgM, IgG, fibrinogen, C3, and C1q was seen, along with infiltr ates of human leukocytes consisting predominantly of neutrophils, macr ophages, and T cells, with occasional B cells and NK cells. Sequential studies of circulating blood demonstrated the progressive consumption of human leukocytes and human anti-porcine antibodies, but no decreas e in complement activity as measured by CH50. These findings indicate that the rapid loss of function seen in human anti-porcine cardiac HAR is associated with deposition of IgM and IgG xenoreactive antibody an d early complement components and that extensive infiltration by infla mmatory cells occurs within 15-30 min. This model provides a useful sy stem for the study of human anti-porcine HAR.