Background
A profound thrombocytopenia limits hepatic xenotransplantation in the pig-to-primate model. Porcine livers also have shown the ability to phagocytose human platelets in the absence of immune-mediate injury. Recently, inactivation of the porcine ASGR1 gene has been shown to decrease this phenomenon. Inactivating GGTA1 and CMAH genes has reduced the antibody-mediated barrier to xenotransplantation; herein we describe the effect that these modifications have on xenogeneic consumption of human platelets in the absence of immune-mediated graft injury.
Methods
WT, ASGR1−/−, GGTA1−/−, and GGTA1−/−CMAH−/− knockout pigs were compared for their xenogeneic hepatic consumption of human platelets. An in vitro assay was established to measure the association of human platelets with liver sinusoidal endothelial cells (LSECs) by immunohistochemistry. Perfusion models were used to measure human platelet uptake in livers from WT, ASGR1−/−, GGTA1−/−, and GGTA1−/− CMAH−/− pigs.
Results
GGTA1−/−, CMAH−/− LSECs exhibited reduced levels of human platelet binding in vitro, when compared to GGTA1−/− and WT LSECs. In a continuous perfusion model, GGTA1−/− CMAH−/− livers consumed fewer human platelets than GGTA1−/− and WT livers. GGTA1−/− CMAH−/− livers also consumed fewer human platelets than ASGR1−/− livers in a single pass model.
Conclusions
Silencing the porcine carbohydrate genes necessary to avoid antibody-mediated rejection in a pig-to-human model also reduces the xenogeneic consumption of human platelets by the porcine liver. The combination of these genetic modifications may be an effective strategy to limit the thrombocytopenia associated with pig-to-human hepatic xenotransplantation.