Recombinant human antithrombin prevents xenogenic activation of hemostasis in a model of pig-to-human kidney transplantation

Background Xenogenic activation of hemostasis (XAH) represents a major hurdle for the transplantation of discordant animal organs into humans as it results in thrombotic microangiopathy (TMA). We have previously shown that recombinant human-activated protein C (rhAPC) mitigates XAH and TMA in an ex vivo model of pig-to-human kidney transplantation. However, the use of rhAPC may not be feasible in a perioperative setting due to possible bleeding complications. Methods Here, we explored the effects of another natural inhibitor of coagulation, human recombinant antithrombin (rhAT), in comparison with rhAPC. Unmodified porcine kidneys (n=25) were perfused ex vivo with porcine blood, human blood, or human blood supplemented with rhAPC or rhAT. Surrogate parameters of organ survival, markers of XAH (D- Dimer, thrombin-antithrombin complex [TAT], fibrinogen, antithrombin activity, plasminogen), endothelial cell and platelet activation (E-selectin, P-selectin), platelet function tests and histological signs of TMA were evaluated. Results Perfusion was feasible for >240min in all experiments with autologous porcine blood, but limited to 126 +/- 78 min with human blood due to increased vascular resistance. Addition of rhAT protected from TMA and allowed for perfusion times >240min. In addition, there were less signs of XAH with reduced release of P-selectin and overexpression of E-selectin, whereas the progressive loss of platelet function, observed during discordant perfusion, was prevented. The effect of rhAT was dose-dependent with maximum protection obtained at 3IU/ml. Conclusion In conclusion, in this ex vivo model of discordant xenotransplantation, rhAT reduced XAH and prevented TMA in doses that appear feasible for use in clinical or preclinical transplantation settings.