Hepatic Function After Genetically Engineered Pig Liver Transplantation in Baboons

Abstract

Background If ‘bridging’ to allotransplantation is to be achieved by a pig liver xenograft, adequate hepatic function needs to be assured. Methods We have studied hepatic function in baboons after transplantation of livers from α1,3-galactosyltransferase gene-knockout (GTKO,n=1) or GTKO pigs transgenic for CD46 (GTKO/CD46,n=5). Monitoring was by liver function tests and coagulation parameters. Pig-specific proteins in the baboon serum/plasma were identified by Western blot. In 4 baboons, coagulation factors were measured. The results were compared with values from healthy humans, baboons, and pigs. Results Recipient baboons died or were euthanized after 4-7 days following internal bleeding associated with profound thrombocytopenia. However, parameters of liver function, including coagulation, remained in the near-normal range, except for some cholestasis. Western blot demonstrated that pig proteins (albumin, fibrinogen, haptoglobin, plasminogen) were produced by the liver from day 1. Production of several pig coagulation factors was confirmed. Conclusions After the transplantation of genetically-engineered pig livers into baboons (1) many parameters of hepatic function, including coagulation, were normal or near-normal; (2) there was evidence for production of pig proteins, including coagulation factors, and (3) these appeared to function adequately in baboons, though inter-species compatibility of such proteins remains to be confirmed.

A Bridge to Somewhere

“…Early work demonstrated reasonable xenogeneic production of essential proteins, but with survival limited to a week or less due to profound thrombocytopenia, bleeding, and notable cholestasis, thought to be due to interspecies incompatibilities. 1 Although previous work in our laboratory did extend survival up to 9 days after liver xenotransplantation (LXT), recipient baboons required intensive platelet transfusions, antifibrinolytic agents, and on average 70 to 80 mLs of packed red blood cell (PRBC) transfusions daily. 2 Based upon our observation of marginal coagulation factor production in baboon recipients of porcine livers, we recently developed a novel approach utilizing the continuous administration of exogenous human coagulation factors after LXT.…”

Liver xenotransplantation

“…(19, 20) Ekser et al reported the first results of LXT with GTKO pigs as well as those polytransgenic for GTKO and CD46. (15, 21) Clinically, this study suggested that survival from 4–7 days could be achieved and during this time, the liver xenograft was capable of adequate protein synthesis (including albumin, fibrinogen, haptoglobin, plasminogen, and coagulation factors). (15, 21) Unfortunately, however, recipients developed profound thrombocytopenia which began to develop within an hour after reperfusion and eventually resulted in spontaneous hemorrhage which did not allow for survival beyond one week.…”

“…(15, 21) Clinically, this study suggested that survival from 4–7 days could be achieved and during this time, the liver xenograft was capable of adequate protein synthesis (including albumin, fibrinogen, haptoglobin, plasminogen, and coagulation factors). (15, 21) Unfortunately, however, recipients developed profound thrombocytopenia which began to develop within an hour after reperfusion and eventually resulted in spontaneous hemorrhage which did not allow for survival beyond one week. (21) In a subsequent study of GTKO liver xenografts preformed by Kim et al, utilizing a different immunosuppression regimen (FIGURE 1), survival of 6, 8, and 9 days was accomplished.…”

“…(15, 16) Applying developments in genetic engineering, the introduction of genes in donor pigs for complement-regulatory proteins or the deletion of specific genes responsible for producing antigens for which primates have natural antibodies has been performed. In 2000, Ramirez et al performed the first pig-to-NHP LXT using a genetically engineered pig expressing human complement regulatory decay accelerating factor (h-DAF or CD55).…”

Recent advances in understanding xenotransplantation: implications for the clinic

“…For example, even though some of the products of the pig liver seem to function adequately in NHPs [96], it is unlikely that the multiple products of the pig liver will fulfill all of the metabolic needs of the human recipient. Here again, in selected instances where it is essential to correct a deficiency, genetic manipulation of the source-pig may enable any discrepancies to be overcome.…”