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Graft vs. Host REAction Generated By Porcine Livers Perfused With Human Blood.

We have successfully perfused porcine livers with human blood for up to 72 hours using an extracorporeal perfusion apparatus. Previous work demonstrated that these perfused livers exhibit metabolic and synthetic function approaching normal parameters. We now present evidence that porcine livers perfused with human blood generate both humoral and phagocytic cell mediated graft vs. host reactions.
Over the course of a 3 day perfusion, the hematocrit of the perfusing human blood decreased to 15 % of starting value (non-transgenic livers, n=5) and < 1% (transgenic livers, n=5). In contrast, the hematocrit of porcine blood perfusing porcine livers (n=5) decreased to 85% of starting value. Immunohistochemistry, light microscopy and electron microscopy (transmission and scanning) have implicated porcine Kupffer cells as the main source of red cell loss. Direct and indirect assays for porcine anti-human red blood cell (RBC) antibodies have failed to demonstrate a role of antibodies in this erythrocyte loss.
Evidence of complement production has been demonstrated. After 68 hours perfusion, mean complement activity (CH50) was 110% of starting value (anhepatic control 0%). While this complement is capable of causing lysis of sheep RBC, lysis of human RBC has not been demonstrated. ELISA analysis demonstrated porcine IgG (transgenic 203 µg/ml, non-transgenic 94 µg/ml, normal pig serum control 6836 µg/ml) and porcine IgM (transgenic 33 µg/ml, non-transgenic 28 µg/ml, normal pig serum control 2101 µg/ml) in the human blood following porcine liver perfusion. FACS analysis showed that a proportion of these antibodies were specific for antigens on fresh human WBC. In 3 of 5 transgenic and 2 of 5 non-transgenic liver perfusions, human-specific porcine IgG levels increased with time suggesting a response by previously primed lymphocytes.
Thus, while humoral mechanisms have not been implicated as a cause of the erythrocyte loss during porcine liver perfusion with human blood, a rapid (within 3 days) anti-human porcine immunoglobulin and phagocytic cell response has been demonstrated.

Michael A. Rees, Andrew J. Butler, Hugh Davis, Eleanor Bolton, Derek G.J. Wight, David J.G. White, Peter J. Friend. Departments of Surgery and Pathology, University of Cambridge, England. Supported by The Wellcome Trust and in collaboration with Imutran (Novartis).