With this approach, an extracorporeal circuit perfuses blood from the femoral vein, incorporates a centrifugal pump and a tissue oxygenator which lead to the porcine liver (which is kept in a sterile temperature controlled environment at the bedside), and then returns the blood to the patient through the jugular or axillary vein.(Fig. 9.1) This approach has been successful in the past in providing both biochemical and neurological improvement in patients. More recently, successful 'bridging' to successful liver transplantation has been achieved.13 The limiting factor with porcine livers has been a vascular rejection that occurs within 2 to 4 hours of perfusion due to preformed human antibodies to porcine endothelium.

Because of severe organ shortages, recent interest in xenotransplantation has led to strategies which have overcome the early rejection associated with pig to primate transplantation.14 The most exciting of these approaches has been the development of pigs which are transgenic for human complement regulatory proteins (CD55 and CD59). In this setting, complement activation does not occur in pig endothelium and early rejection can be potentially avoided. Transplantation of organs from transgenic pigs to non-human primates extends kidney graft survivals from hours to weeks when compared to organs from non-transgenic pigs. Therefore, it is anticipated that prolongation of survival will provide a period of hepatic support, which will clearly exceed that experienced with non-transgenic pig livers.

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