Prolonged Survival Following Pig-to-Primate Liver Xenotransplantation Utilizing Exogenous Coagulation Factors and Costimulation Blockade

Abstract

Since the first attempt of pig-to-primate liver xenotransplantation (LXT) in 1968, survival has been limited. We evaluated a model utilizing α-1,3-galactosyltransferase knockout donors, continuous posttransplant infusion of human prothrombin concentrate complex, and immunosuppression including anti-thymocyte globulin, FK-506, methylprednisone, and costimulation blockade (belatacept, n = 3 or anti-CD40 mAb, n = 1) to extend survival. Baboon 1 remained well until postoperative day (POD) 25, when euthanasia was required because of cholestasis and plantar ulcers. Baboon 2 was euthanized following a seizure on POD 5, despite normal liver function tests (LFTs) and no apparent pathology. Baboon 3 demonstrated initial stable liver function but was euthanized on POD 8 because of worsening LFTs. Pathology revealed C4d positivity, extensive hemorrhagic necrosis, and a focal cytomegalovirus inclusion. Baboon 4 was clinically well with stable LFTs until POD29, when euthanasia was again necessitated by plantar ulcerations and rising LFTs. Final pathology was C4d negative and without evidence of rejection, inflammation, or thrombotic microangiopathy. Thus, nearly 1-mo rejection-free survival has been achieved following LXT in two of four consecutive recipients, demonstrating that the porcine liver can support life in primates for several weeks and has encouraging potential for clinical application as a bridge to allotransplantation for patients with acute-on-chronic or fulminant hepatic failure.

Keywords: basic (laboratory) research/science; coagulation and hemostasis; fusion proteins and monoclonal antibodies: costimulation molecule specific; graft survival; immunosuppressant; immunosuppressive regimens; xenotransplantation.

Figure 1

Circulating platelet counts following pig-to-baboon liver xenotransplantation for Baboons #1–4.

Figure 2

Baboon #1: Post-transplant antibody FACS analysis demonstrating evidence of circulating baboon anti-pig cytotoxic IgM (but not IgG) between POD 7-14, correlating with clinical evidence of mild rejection and successfully treated with pulse dose steroids. A similar pattern of IgM (but not IgG) expression was seen for B-3 on POD 8.

Figure 3

Baboon #3: (A) POD 8 H&E 40× demonstrating marked hemorrhage, necrosis and inflammation within the xenograft. (B) POD 8 immunohistochemistry staining positive for peripheral C4d positivity consistent with antibody mediated rejection.

Figure 4

Baboon #4: (A) Post-transplant LFT’s. (B) Post-transplant blood counts, transfusion requirements and platelet counts. (C) POD 29 necropsy image demonstrating evidence of acute portal vein thrombosis. (D) POD 29 H&E 100× demonstrating portal vein thrombosis, minimal inflammation and absence of necrosis and TMA.

Figure 5

Baboon #4: (A) Post-transplant Vitamin K dependent coagulation factor activity. (B) Post-transplant non-Vitamin K dependent coagulation factor activity. (C) Post-transplant fibrinogen production.