The function of transgenic human DAF-expressing porcine livers during hemoperfusion with human blood

Xenotransplantation for liver therapy or: Can porcine hepatocytes generate physiological functions sufficient for a human patient in ALF?

Detailed knowledge about physiology, biochemistry and function is required before artificial liver devices using porcine hepatocytes may be used successfully. Improvement of cell culture conditions and tissue engineering may permit the generation of human hepatocytes as substitutes for grafts in a transplantation setting. The physiological functions of xenografts have to be compatible with those of the recipient. However, first observations indicate that most physiological interaction in widely divergent species combinations such as pig and man are considerably different. This may be crucial for the selection of a suitable organ, tissue or cell for a clinical set-up. These differences vary from organ to organ and cell to cell. Only very conservative molecules, like for example insulin or calcitonin function properly in both species, while others such as complement, albumin and erythropoietin do not fulfill their task properly or not at all.

HDAF transgenic pig livers are protected from hyperacute rejection during ex vivo perfusion with human blood

The aim of this study was to determine if human decay-accelerating factor (hDAF) protects against hyperacute rejection in an ex vivo liver perfusion system using human blood. Pig livers were perfused ex vivo via the portal vein for an average of 5-6 h using a membrane oxygenator. Three groups were studied. Group I: Wild-type pig livers were alloperfused with fresh pig blood (n = 5). Group II: Wild-type pig livers were xenoperfused with fresh human blood (n = 5). Group III: hDAF transgenic pig livers were xenoperfused with fresh human blood (n = 5). The graft ischemic time, ratio of perfusate volume to liver weight, flow rate, and perfusate hematocrit were similar in each group. The hDAF livers perfused with human blood (Group III) had a lower ALT level, less protein and albumin losses, lower bilirubin levels in the perfusate, less weight gain, and greater bile production than the wild-type livers perfused with human blood. Histology showed classic features of hyperacute rejection in Group II, including massive hemorrhage, severe vasculitits, fibrin and C5b-9 deposition, and endothelial damage within 1 h of perfusion, whereas liver histology studies in Groups I and III were near normal. IgG and IgM deposits were seen in the xenoperfused livers. Electron microscopy (EM) and immuno-EM showed loss of endothelial cells, trapping of white blood cells and platelets, and diffuse fibrin deposits in Group II only. hDAF pig livers perfused with human blood showed superior function and histology when compared with wild-type pig livers. These data suggest that (1) hyperacute rejection may contribute to the inconsistent results using wild-type pig livers for extracorporeal liver support and (2) genetically modified pigs that express hDAF may provide a better donor source than wild-type pigs for extracorporeal liver support.

Impact of immunoadsorption on xenogeneic extracorporeal pig liver perfusion: assessment of organ function during autologous reperfusion

The shortage of liver grafts has resulted in an intensive search for alternative strategies of liver support in acute liver failure. Extracorporeal perfusion of pig livers (ECLP) is not a new concept, but recent improvements in cardiopulmonary bypass technology and new knowledge about xenogeneic immunologic mechanisms have made it a potential therapeutic modality. In previous suboptimal experimental and clinical models, no statements about the beneficial effect of long-lasting periods of ECLP were made. The aim of this study was to evaluate the capacity of pig liver for metabolic regeneration after xenogeneic ECLP under largely physiologic conditions. To delay hyperacute rejection (HAR), we utilized immunoadsorption (IA) of naturally preformed xenogeneic antibodies (XNAbs). This led to a stable xenogeneic ECLP for 45 min. However, IA was not able to prevent completely organ damage or loss of function resulting from insufficient autologous reperfusion. The inability to regenerate during autologous reperfusion provides a new measure of the function of a xenogeneic perfused pig liver. In addition, our results implicate that patients with fulminant liver failure will benefit from short perfusions with several fresh organs rather than from long perfusion with a single pig liver.