Thromboelastographic evaluation of coagulative profiles in pig-to-monkey kidney xenotransplantation

Activation of the clotting cascade is central in acute xenograft rejection (AHXR) that occurs when pig organs are transplanted into primates. The coagulopathy reported in this model is a very complex process that involves simultaneously coagulation factors, platelets and phospholipid-bearing cells (i.e., leukocytes, red blood cells, and endothelial cells). Choosing whole blood for coagulation analysis theoretically appears more favorable compared with plasma. Whole blood rotation thromboelastometry (ROTEM(®) ) is a point-of-care global coagulation analyzer able to evaluate the characteristics of clot formation and lysis by dynamic monitoring. The aim of this study was to record thromboelastographic profiles, performed by ROTEM(®) , in a series of immunosuppressed nephrectomized primates that received a life-supporting kidney.

Of the eight primates, n = 4 received a pig kidney transgenic for human decay-accelerating factor (hDAF/Gal+); n = 2, an α 1,3-galactosyltransferase gene-knockout (GT-KO) pig kidney transgenic for human CD39, CD55, CD59 and fucosyltransferase (HTF); and n = 2, a GT-KO pig kidney transgenic for hDAF. Blood samples were collected before and at least once per week after transplantation till euthanasia. Intrinsic (INTEM) and extrinsic (EXTEM) coagulation pathways and the function of fibrinogen (FIBTEM) were evaluated. Thromboelastographic parameters considered were clotting time (CT, seconds) and clot formation time (CFT, seconds) in INTEM and EXTEM and maximum clot firmness (MCF, mm) in FIBTEM. The correlations between CT in INTEM and activated partial thromboplastin time (aPTT), CT in EXTEM and PT, CFT in INTEM and EXTEM, and platelet counts and MCF in FIBTEM and fibrinogen plasma levels were also considered.

In all animals, thromboelastographic profiles showed progressive prolongation of CT (activation of coagulative cascade) in INTEM. A close correspondence was observed between (i) the prolongation of the CFT values (propagation of clot formation), both in INTEM and EXTEM, and the decrease in platelet counts; (ii) the reduction in MCF values (clot firmness) ​​in FIBTEM and the decrease in fibrinogen plasma levels. No concordance between CT in INTEM and aPTT and between CT in EXTEM and PT was observed.

Our study demonstrated that ROTEM(®) analyzer could be a useful and complementary tool to study the consumptive coagulopathy, either "compensated" or "non-compensated," that takes place when transgenic pig kidneys are transplanted into primates. Larger and prospective studies are needed to confirm our results and to evaluate the role of ROTEM(®) to guide the management of consumptive coagulopathy in order to prolong the survival of the transplanted organ.