Expression of human thrombomodulin on porcine endothelial cells can reduce platelet aggregation but did not reduce activation of complement or endothelium – an experimental study

Abstract

Summary Clinical xenotransplantation will only be feasible when present limitations can be controlled sufficiently. Activation of endothelium and complement as well as coagulopathy and thrombotic microangiopathy (TMA) is important barriers. Transgenic expression of hTBM on porcine endothelial cells is a reasonable approach to reduce activation of haemostasis. Endothelial cells from wild‐type pigs as well from pigs expressing hTBM alone or in combination with hCD46 and knockout of the alpha‐1,3,‐galactosyltransferase (GTKO) were perfused with platelet‐rich plasma in a microfluidic flow chamber. Platelet aggregation and activation, coagulation, complement and endothelial cell activation were assessed. Perfusion of wild‐type porcine aortic endothelial cells (PAEC) resulted in distinct platelet aggregation. Expression of hTBM in either mono‐transgenic or triple‐transgenic (GTKO/hCD46/hTBM) PAEC showed significantly reduced or absent platelet aggregation. Flow cytometric analysis of platelets showed an increased CD62P expression in wild‐type PAEC and significantly reduced expression in mono‐ or triple‐transgenic PAEC. Activation of coagulation measured by TAT occured in WT PAEC and was clearly reduced in hTBM and GTKO/hCD46/hTBM PAEC. Activation of complement and endothelial cells was only reduced in GTKO/hCD46/hTBM but not in PAEC expressing hTBM alone. Expression of hTBM was able to prevent activation of coagulation and platelet aggregation in mono‐ and triple‐transgenic PAEC, while activation of complement and endothelial cells was not reduced in mono‐transgenic PAEC.

Differences in platelet aggregometers to study platelet function and coagulation dysregulation in xenotransplantation

“…In flow cytometry‐based methods, antibodies such as anti‐human CD41 (GPIIb/IIIa, α subunit), anti‐human CD62P (P‐selectin), anti‐human CD42a (GP IX), and anti‐human PAC‐1 (GPIIb/IIIa, α IIb β 3 ) were used to detect platelet activation and aggregation 14,15,53,56,57 . While storability of samples is a great advantage of ELISA and flow cytometry methods, the time spent, dependence of quality of the kit, and manual procedures (operator‐dependence) are disadvantages.…”

hEPCR.hTBM.hCD47.hHO‐1 with donor clodronate and DDAVP treatment improves perfusion and function of GalTKO.hCD46 porcine livers perfused with human blood

“…8 Finally, porcine thrombomodulin, while capable of binding human thrombin, does not efficiently mediate activation of human protein C, resulting in a procoagulant phenotype. 9 Recent advances in heart and kidney xenotransplant models were associated with genetic modifications additional to GalTKO.hCD46, including expression of humanized thrombomodulin (hTBM) and endothelial protein C receptor (hEPCR), [10][11][12] and with several different pharmacologic interventions, including ε-aminocaproic acid, 13 DDAVP, 14,15 and platelet GPIb blockade. 16 hEPCR amplifies the production of activated protein C (APC) by hTBM 17 and provides protection against thrombodysregulation and inflammatory injury 18 that are associated with xenotransplantation.…”