An Ex Vivo Perfusion Model To Study the Treatment of Thrombotic Microangiopathy during Pig-to-Human Xenogenic Kidney Transplantation.

Early rejection of xenogenic organs is associated with thrombotic microangiopathy and changes of coagulation resembling disseminated intravascular coagulation (DIC). Here, we used an ex vivo perfusion circuit as a model of pig-to-human kidney transplantation to study the nature and treatment of this pathology. Porcine kidneys were obtained following in situ cold perfusion with HTK organ preservation solution and immediately connected to a perfusion circuit containing porcine (“autologous”) or human (“xenogenic”) AB blood supplemented with complement component C1 inhibitor (1 U/ml) and heparin (1 U/ml). Perfusion of porcine kidneys with autologous blood was feasible for >240 min in all experiments. In contrast, perfusion of porcine kidneys with xenogenic human blood was limited by a dramatic increase of flow resistance after 30 to 240 min. Increased concentrations of C3a as a marker for complement activation were associated with early perfusion failure. In addition, a dramatic increase of thrombin-antithrombin complex (TAT) and D Dimer (DD) was observed together with consumption of platelets, fibrinogen and antithrombin (AT). Histological examination demonstrated extensive thrombotic microangiopathy. Supplementation recombinant human activated protein C (rhAPC, 300 ug/l*h, n=3) or recombinant human antithrombin (rhAT, 3 U/ml, n=3) abolished the increase of flow resistance and allowed for a xenogenic kidney survival of >240 min in all experiments. Increase of DD was abolished and the consumption of fibrinogen was abrogated by both treatments as compared to control, whereas the increase of TAT was abolished only by rhAPC. Histological examination revealed no evidence of thrombotic microangiopathy for both treatments as compared to control. In conclusion, the perfusion model introduced here is a suitable tool for studying coagulopathy during early rejection in xenotransplantation. Thrombotic microangiopathy and DIC-like activation of coagulation is associated with an increased flow resistance and failure of perfusion in this model. Pharmacological intervention such as the supplementation of rhAPC or rhAT can be studied using this model and has been shown to prevent coagulopathy and thrombotic microangiopathy.