Porcine liver xenotransplant survival has been historically compromised by a profound consumptive thrombocytopenia that begins immediately upon xenograft reperfusion. Nonhuman primate recipients who survive porcine liver xenotransplantation recover their platelet count 7-10 days post transplantation. Given the transient nature of the thrombocytopenia, pharmacotherapy, as opposed to genetic modifications, may be a more suitable approach to address this issue. Here, we used an ex vivo machine perfusion model to examine the effect of dual agent inhibition of platelet activation and adhesion by GPIb and GPIIb/IIIa mechanisms.

Livers were procured from beating heart porcine donors from Pig 2.F, a multiplex genome engineered pig that contains knockout for GGTA1, β4GALNT2, CMAH plus modifications targeting complement, inflammation, and coagulation regulation. Livers underwent normothermic machine perfusion with heparinized human whole blood and plasma. In the treated group, the perfusate was treated with 6B4 (anti-GPIb fragmented murine antibody (ab)), and eptifibatide (GPIIb/IIIa inhibitor) prior to initiation of perfusion (n=3). Perfusions without pharmacotherapy (n=3) were performed as untreated controls. Perfusion was terminated when the vascular resistance prevented portal venous flow. Platelet count was measured throughout the perfusion by hematocytometer and remotely analyzed by flow cytometry using 1% paraformaldehyde fixed samples.

The mean perfusion time was 12 hours for the treated group, and 10 hours for the untreated group. There was no difference between groups in combined artery and portal venous flow or lactate clearance (Figure 1). Treatment with ab/eptifibatide reduced thrombocytopenia (Figure 2) in the first 4 hours of perfusion when compared to untreated group, confirmed by platelet flow cytometry (Figure 2b).

Co-inhibition of platelet GPIb and GPIIb/IIIa appears to delay, but not prevent, thrombocytopenia during liver xenogeneic perfusion. This delay is not accompanied by improved hemodynamics, increased duration of perfusion, or increased lactate clearance. Future work will include trial of additional agents in different platelet activation pathways, histological and cytokine analysis, and ultimately use of co-inhibition in a nonhuman primate xenotransplantation model.