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Review
, 16 (2), 214-21

Controlling Coagulation Dysregulation in Xenotransplantation

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Review

Controlling Coagulation Dysregulation in Xenotransplantation

Peter J Cowan et al. Curr Opin Organ Transplant.

Abstract

Purpose of review: Deletion of the α1,3-galactosyltransferase (GalT) gene in pigs has removed a major xenoantigen but has not eliminated the problem of dysregulated coagulation and vascular injury. Rejecting GalT knockout organ xenografts almost invariably show evidence of thrombosis and platelet sequestration, and primate recipients frequently develop consumptive coagulopathy. This review examines recent findings that illuminate potential mechanisms of this current barrier to successful xenotransplantation.

Recent findings: The coagulation response to xenotransplantation differs depending on the type of organ and quite likely the distinct vasculatures. Renal xenografts appear more likely to initiate consumptive coagulopathy than cardiac xenografts, possibly reflecting differential transcriptional responses. Liver xenografts induce rapid and profound thrombocytopenia resulting in recipient death within days due to bleeding; ex-vivo data suggest that liver endothelial cells and hepatocytes are responsible for platelet consumption by a coagulation-independent process.It has been proposed that expression of recipient tissue factor on platelets and monocytes is an important trigger of consumptive coagulopathy. Finally, pigs transgenic for human anticoagulants and antithrombotics are slowly but surely coming on line, but have not yet been rigorously tested to date.

Summary: Successful control of coagulation dysregulation in xenotransplantation may require different combinatorial pharmacological and genetic strategies for different organs.

Figures

Figure 1
Figure 1. Initiation and propagation of coagulation
Interaction of tissue factor (TF) with traces of circulating FVIIa triggers the initiation phase (top), resulting in the generation of a ‘trickle’ of thrombin. Thrombin activates components of the intrinsic pathway and signals via protease-activated receptors (PARs) on platelets, leukocytes and endothelial cells, resulting in propagation of coagulation and formation of a stable fibrin clot (bottom). Dashed arrows signify thrombin-mediated reactions. PolyP; inorganic polyphosphate released by activated platelets.

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