Reference values for thromboelastometry (ROTEM®) in cynomolgus monkeys (Macaca fascicularis)

USE OF VISCOELASTIC COAGULATION TESTING IN MEGACHIROPTERA (PTEROPUS HYPOMELANUS AND PTEROPUS VAMPYRUS) REVEALS HIGH VARIABILITY IN CLOT KINETICS

Megachiroptera is a mammalian suborder that includes old world fruit bats. Common clinical problems among captive Megachiroptera, such as liver disease (e.g., iron storage disease), kidney disease (e.g., protein-losing nephropathy), and heart disease (e.g., dilated cardiomyopathy), carry elevated risk for hemostatic derangements. The assessment of viscoelastic coagulation assays, however, has not yet been reported in bats. The main objective of the study was to describe viscoelastography data using the Viscoelastic Coagulation Monitor (VCM) Vet in captive large flying foxes (Pteropus vampyrus) (n = 20) and variable flying foxes (Pteropus hypomelanus) (n = 10). Additional objectives were to compare viscoelastic and clotting parameters (1) between healthy P. vampyrus and P. hypomelanus bats and (2) between untreated bats and those treated with meloxicam or aspirin, and (3) to examine relationships between activated partial thromboplastin time (aPTT) and potentially homologous viscoelastic parameters clotting time (CT) and clot formation time (CFT). The results showed marked variability among clinically normal bats. The intrinsic pathway, as measured by aPTT, had prolonged times compared with most terrestrial mammals, but similar times to birds, marine mammals, and sea turtles. A search of P. vampyrus genome found stop codons present in two exons of the factor XI gene; alterations in factor XI expression would be expected to alter intrinsic coagulation. Because of the high variability, no statistically significant findings were noted in the secondary objectives. Correlation between aPTT and CT or CFT was not strong (rs = 0.406 or 0.192, respectively). The results from this study suggest that clot kinetics vary widely among Megachiroptera when using the VCM Vet with untreated blood. A prolonged intrinsic coagulation pathway, as has been found in other megachiropteran species, and activation of the extrinsic coagulation pathway during venipuncture may be responsible for the inconsistent results.

Cryptogenic ischemic stroke in cardiac transthyretin amyloidosis and sinus rhythm: a case report

Cardiac amyloidosis is a group of diseases characterized by the deposition of amyloid fibers in cardiac tissue. Two forms are mainly reported: light chain (AL) and transthyretin (ATTR) amyloidosis. Among the complications of transthyretin amyloidosis there are thrombotic events and, to a lesser extent, hemorrhagic events. The latter are likely caused by perivascular amyloid deposition resulting in capillary fragility, in addition to INR lability during anticoagulant therapy. The onset of thrombotic events may be caused by the high prevalence of atrial fibrillation (AF), mechanical cardiac dysfunction and atrial myopathy observed in patients with transthyretin amyloidosis. It remains unclear why thromboembolic events occur even in patients with sinus rhythm or adequate anticoagulation, though a hypercoagulable state or underlying inflammation may be involved. We report a case of cryptogenic ischemic stroke in an 86-year-old woman with transthyretin amyloidosis and sinus rhythm. Traditional coagulation tests, whole blood rotational thromboelastometry and impedance aggregometry did not show a hypercoagulable state. The thrombin generation assay did not reveal a prothrombotic state. However, the study of extracellular vesicles highlighted underlying immune-mediated endothelial damage likely responsible for the thrombotic diathesis. It could be hypothesized that inflammation plays a role in the hypercoagulability of patients with transthyretin amyloidosis. Larger prospective studies are needed to validate our hypothesis.

A combination of clot formation abnormalities in thromboelastometry has a high prognostic value in patients with acute-on-chronic liver failure

BACKGROUND

Global coagulation tests offer a better tool to assess procoagulant and anticoagulant pathways, fibrinolysis and clot firmness and evaluate more accurately coagulation defects compared to conventional coagulation tests. Their prognostic role in acute-on-chronic liver disease (ACLF) or acute decompensation (AD) has not been well established.

AIMS

To assess the properties and prognostic value of the coagulation profile measured by rotational thromboelastometry (ROTEM) in ACLF and AD.

METHODS

84 consecutive patients (35 ACLF and 49 AD) were prospectively studied. Twenty healthy persons matched for age and gender were used as controls. 'Hypocoagulable' or 'hypercoagulable' profiles on admission were assessed based on nine ROTEM parameters and mortality was recorded at 30 and 90 days.

RESULTS

Individual ROTEM parameters denoted significantly more hypocoagulability in patients compared to controls. 'Hypocoagulable' profile (defined as a composite of 4 or more ROTEM parameters outside the range) was associated with more severe liver disease assessed either as MELD or Child-Pugh scores ( P  < 0.001 for both) and higher 30-day mortality (Log-rank P  = 0.012). 'Hypocoagulable' profile (HR 3.160, 95% CI 1.003-9.957, P  = 0.049) and ACLF status (HR 23.786, 95% CI 3.115-181.614, P  = 0.002) were independent predictors of 30-day mortality, in multivariate model. A higher early mortality rate was shown in ACLF patients with 'hypocoagulable' phenotype compared to those without (Log-rank P  = 0.017). 'Hypocoagulable' profile was not associated with mortality in AD.

CONCLUSION

'Hypocoagulable' profile was associated with more advanced liver disease and higher short-term mortality in patients with ACLF.

The Non-Activated Thromboelastometry (NATEM) Assay's Application among Adults and Neonatal/Pediatric Population: A Systematic Review

The non-activated thromboelastometry (NATEM) assay is a point-of-care assay that can provide a comprehensive insight into the actual hemostatic mechanism. However, there are very limited data about its use in clinical practice. The aim of this study was to systematically review the literature for any data regarding the use of NATEM in several clinical settings. A systematic review of PubMed and Scopus databases was conducted through 20 January 2022 for studies evaluating the use of the NATEM assay in different clinical settings. The literature search yielded a total of 47 publications, 30 of which met the eligibility criteria for this review. Evaluation of NATEM’s detecting ability for hemostasis disorders is limited in the literature. The results of the included studies indicate that NATEM seems to be a sensitive method for the detection of hyperfibrinolysis and may have an advantage in the diagnosis of hemostatic disorders. It could be more informative than the other ROTEM assays for detecting changes in coagulation parameters in patients who receive anticoagulants. However, the reported outcomes are highly varying among the included studies. NATEM has a high sensitivity to detect hypo- or hypercoagulability and provides a detailed insight into the whole hemostatic process from clot formation to clot breakdown. It could be a useful technique in variable fields of medicine, not only in adults, but also in pediatric and neonatal populations, to guide different hemostatic treatments and predict coagulation disorders or mortality/morbidity; this issue remains to be further investigated.

Coagulopathy is not predictive of bleeding in patients with acute decompensation of cirrhosis and acute-on-chronic liver failure

BACKGROUND & AIMS

Understanding factors responsible for the increased bleeding tendency in acute-on-chronic liver failure (ACLF) would improve the management of these complications. We investigated coagulation alterations in ACLF and assessed whether they were predictive of bleeding.

METHODS

Cirrhosis patients with ACLF (cases) and acute decompensation (AD, controls) were prospectively recruited and underwent an extensive haemostatic assessment including standard tests, pro and anticoagulant factors, thrombomodulin-modified thrombin generation (TG) and thromboelastometry (ROTEM^® ). In study part 1 (case-control), we compared coagulation in ACLF vs AD. In study part 2 (prospective), all patients were followed for bleeding, and predictors of outcome were assessed.

RESULTS

Ninety-one patients were included (51 with ACLF, 40 with AD). Infections and ascites/renal dysfunction were the most common precipitating and decompensating events. Platelet count was lower while INR and activated partial thrombin time were longer in ACLF cohort vs AD. Regarding clotting factors, fibrinogen and factor VIII were comparable between groups while protein C and antithrombin were significantly reduced in ACLF. Endogenous thrombin potential by TG was comparable between groups. Clotting formation time and clot stability by ROTEM^® were significantly lower in ACLF, indicative of a more hypocoagulable state. No haemostasis alteration could discriminate between patients who had bleeding complications during hospitalization and those who did not.

CONCLUSION

We found coagulation changes in ACLF to largely overlap with that of AD and evidence of preserved coagulation capacity in both groups. ROTEM alterations were indicative of a more pronounced hypocoagulable state in ACLF; however, no correlation was found between such alterations and bleeding.

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

Xenotransplantation (ie, cross-species transplantation) using genetically engineered pig organs could be a limitless source to solve the shortage of organs and tissues worldwide. However, despite prolonged survival in preclinical pig-to-nonhuman primate xenotransplantation trials, interspecies coagulation dysregulation remains to be overcome in order to achieve continuous long-term success. Different platelet aggregometry methods have been previously used to study the coagulation dysregulation with wild-type and genetically engineered pig cells, including the impact of possible treatment options. Among these methods, while thromboelastography and rotational thromboelastometry measure the change in viscoelasticity, optical aggregometry measures the change in opacity. Recently, impedance aggregometry has been used to measure changes in platelet aggregation in electrical conductance, providing more information to our understanding of coagulation dysregulation in xenotransplantation compared to previous methods. The present study reviews the merits and differences of the above-mentioned platelet aggregometers in xenotransplantation research.

A canine model of mechanical thrombectomy in stroke

Purpose

To develop a preclinical model of stroke with a large vessel occlusion treated with mechanical thrombectomy.

Materials and methods

An ischemic stroke model was created in dogs by the introduction of an autologous clot into the middle cerebral artery (MCA). A microcatheter was navigated to the clot and a stent retriever thrombectomy was performed with the goal to achieve Thrombolysis in Cerebral Ischemia (TICI) 2b/3 reperfusion. Perfusion and diffusion MRI was acquired after clot placement and following thrombectomy to monitor the progression of restricted diffusion as well as changes in ischemia as a result of mechanical thrombectomy. Post-mortem histology was done to confirm MCA territory infarct volume.

Results

Initial MCA occlusion with TICI 0 flow was documented in all six hound-cross dogs entered into the study. TICI 2b/3 revascularization was achieved with one thrombectomy pass in four of six animals (67%). Intra-procedural events including clot autolysis leading to spontaneous revascularization (n=1) and unresolved vasospasm (n=1) accounted for thrombectomy failure. In one case, iatrogenic trauma during microcatheter navigation resulted in a direct arteriovenous fistula at the level of the cavernous carotid. Analysis of MRI indicated that a volume of tissue from the initial perfusion deficit was spared with reperfusion following thrombectomy, and there was also a volume of tissue that infarcted between MRI and ultimate recanalization.

Conclusion

We describe a large animal stroke model in which mechanical thrombectomy can be performed. This model may facilitate, in a preclinical setting, optimization of complex multimodal stroke treatment paradigms for clinical translation.

A review of pig liver xenotransplantation: Current problems and recent progress

Pig liver xenotransplantation appears to be more perplexing when compared to heart or kidney xenotransplantation, even though great progress has been achieved. The relevant molecular mechanisms involved in xenogeneic rejection, including coagulopathy, and particularly thrombocytopenia, are complex, and need to be systematically investigated. The deletion of expression of Gal antigens in the liver graft highlights the injurious impact of nonGal antigens, which continue to induce humoral rejection. Innate immunity, particularly mediated by macrophages and natural killer cells, interplays with inflammation and coagulation disorders. Kupffer cells and liver sinusoidal endothelial cells (LSECs) together mediate leukocyte, erythrocyte, and platelet sequestration and phagocytosis, which can be exacerbated by increased cytokine production, cell desialylation, and interspecies incompatibilities. The coagulation cascade is activated by release of tissue factor which can be dependent or independent of the xenoreactive immune response. Depletion of endothelial anticoagulants and anti-platelet capacity amplify coagulation activation, and interspecies incompatibilities of coagulation-regulatory proteins facilitate dysregulation. LSECs involved in platelet phagocytosis and transcytosis, coupled with hepatocyte-mediated degradation, are responsible for thrombocytopenia. Adaptive immunity could also be problematic in long-term liver graft survival. Currently, relevant evidence and study results of various genetic modifications to the pig donor need to be fully determined, with the aim of identifying the ideal transgene combination for pig liver xenotransplantation. We believe that clinical trials of pig liver xenotransplantation should initially be considered as a bridge to allotransplantation.

Viscoelasticity and structure of blood clots generated in-vitro by rheometry: A comparison between human, horse, rat, and camel

BACKGROUND

Although the coagulation system is evolutionary well preserved, profound species differences exist in viscoelastic as well as in common laboratory tests of coagulation.

OBJECTIVE

Evaluating differences in clot formation and material characterisation of clots of four mammalian species on macro-, micro- and nanoscales by the means of rheometry, scanning electron microscopy (SEM) and small angle x-ray scattering (SAXS).

METHODS

Blood samples were collected from healthy human volunteers, laboratory rats (HL/LE inbred strain), warmblood horses and dromedary camels. Clot formation was observed by oscillating shear rheometry until plateau formation of the shear storage modulus G', at which point selected clots were prepared for scanning electron microscopy. SEM images were analysed for fibre diameter and fractal dimension. Additionally, scattering profiles for plasma and whole blood samples were obtained with SAXS.

RESULTS

Viscoelasticity of clots showed great interspecies variation: clots of rats and horses exhibited shorter clotting times and higher G' plateau values, when compared to human clots. Camel clots showed unique clotting characteristics with no G' plateau formation in the timeframe observed. Less differentiating features were found with SEM and SAXS, although the rat fibre network appears to be more convoluted and dense, which resulted in a higher fractal dimension.

CONCLUSION

Clotting kinetic differs between the species, which is not only of clinical interest, but could also be an important finding for animal models of blood coagulation.

Tranexamic acid is associated with selective increase in inflammatory markers following total knee arthroplasty (TKA): a pilot study

BACKGROUND

Tranexamic acid (TXA) is commonly used in orthopedic surgery to reduce excessive bleeding and transfusion requirements. Our aim was to examine if TXA was required in all osteoarthritis patients undergoing TKA surgery, and its possible effects on systemic inflammation and coagulation properties.

METHODS

Twenty-three patients (Oxford Score 22-29) were recruited consecutively; 12 patients received TXA before (IV, 1.2 g/90 kg) and immediately after surgery (intra-articular, 1.4 g/90 kg). Inflammatory mediators and ROTEM parameters were measured in blood at baseline, after the first bone-cut, immediately after surgery, and postoperative days 1 and 2.

RESULTS

After the bone cut and surgery, TXA significantly increased MCP-1, TNF-α, IL-1β and IL-6 levels compared to non-TXA patients, which was further amplified postoperatively. During surgery, TXA significantly prolonged EXTEM clot times, indicating a thrombin-slowing effect, despite little or no change in clot amplitude or fibrinogen. TXA was associated with three- to fivefold increases in FIBTEM maximum lysis (ML), a finding counter to TXA's antifibrinolytic effect. Maximum lysis for extrinsic and intrinsic pathways was < 8%, indicating little or no hyperfibrinolysis. No significant differences were found in postoperative hemoglobin between the two groups.

CONCLUSIONS

TXA was associated with increased systemic inflammation during surgery compared to non-TXA patients, with further amplification on postoperative days 1 and 2. On the basis of little or no change in viscoelastic clot strength, fibrinogen or clot lysis, there appeared to be no clinical justification for TXA in our group of patients. Larger prospective, randomized trials are required to investigate a possible proinflammatory effect in TKA patients.

The role of platelets in coagulation dysfunction in xenotransplantation, and therapeutic options

Xenotransplantation could resolve the increasing discrepancy between the availability of deceased human donor organs and the demand for transplantation. Most advances in this field have resulted from the introduction of genetically engineered pigs, e.g., α1,3-galactosyltransferase gene-knockout (GTKO) pigs transgenic for one or more human complement-regulatory proteins (e.g., CD55, CD46, CD59). Failure of these grafts has not been associated with the classical features of acute humoral xenograft rejection, but with the development of thrombotic microangiopathy in the graft and/or consumptive coagulopathy in the recipient. Although the precise mechanisms of coagulation dysregulation remain unclear, molecular incompatibilities between primate coagulation factors and pig natural anticoagulants exacerbate the thrombotic state within the xenograft vasculature. Platelets play a crucial role in thrombosis and contribute to the coagulation disorder in xenotransplantation. They are therefore important targets if this barrier is to be overcome. Further genetic manipulation of the organ-source pigs, such as pigs that express one or more coagulation-regulatory genes (e.g., thrombomodulin, endothelial protein C receptor, tissue factor pathway inhibitor, CD39), is anticipated to inhibit platelet activation and the generation of thrombus. In addition, adjunctive pharmacologic anti-platelet therapy may be required. The genetic manipulations that are currently being tested are reviewed, as are the potential pharmacologic agents that may prove beneficial.

Kidney xenotransplantation

Xenotransplantation using pigs as donors offers the possibility of eliminating the chronic shortage of donor kidneys, but there are several obstacles to be overcome before this goal can be achieved. Preclinical studies have shown that, while porcine renal xenografts are broadly compatible physiologically, they provoke a complex rejection process involving preformed and elicited antibodies, heightened innate immune cell reactivity, dysregulated coagulation, and a strong T cell-mediated adaptive response. Furthermore, the susceptibility of the xenograft to proinflammatory and procoagulant stimuli is probably increased by cross-species molecular defects in regulatory pathways. To balance these disadvantages, xenotransplantation has at its disposal a unique tool to address particular rejection mechanisms and incompatibilities: genetic modification of the donor. This review focuses on the pathophysiology of porcine renal xenograft rejection, and on the significant genetic, pharmacological, and technical progress that has been made to prolong xenograft survival.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Platelet aggregation in humans and nonhuman primates: relevance to xenotransplantation

INTRODUCTION

Platelet activation/aggregation plays a key role in the dysregulation of coagulation and the development of thrombotic microangiopathy in nonhuman primate recipients of pig xenografts. As a preliminary to the study of anti-platelet therapy in vitro and in vivo, the present study aimed to compare platelet aggregation in whole blood from humans, baboons, and cynomolgus monkeys.

METHODS

Using "Chrono-log" technology (two-sample four-channel Chrono-log Whole Blood Aggregometer), we studied aggregation of platelets in healthy humans (n = 8), baboons (n = 5), and monkeys (n = 8). Whole blood (WB) samples were collected, and platelet aggregation was assessed using three different volumes of blood (1, 0.5, and 0.25 ml). Platelet activation was induced using collagen (at 3 and 5 μg/ml), ristocetin (at 0.5 and 1.0 mg/ml), adenosine diphosphate (ADP; at 10, 20, and 40 μm), or thrombin (at 1 and 5 IU/ml). Inhibition of agonist-induced platelet aggregation by heparin and low molecular weight heparin (LMWH) (at 1, 10, and 100 IU/ml) was evaluated.

RESULTS

Mean platelet counts were 222.1, 263.2, and 276.1 (×10(3) /μl) in humans, baboons, and monkeys, respectively. In all three species, platelet aggregation was induced by collagen, ristocetin, ADP, or thrombin in a dose-dependent manner. A blood volume of 0.5 ml provided the most consistent results with all agonists in all three species. Dilution studies indicated that there was a significant positive correlation between platelet count and percent aggregation of platelets (P < 0.05). Collagen (3 and 5 μg/ml), ADP (10, 20, and 40 μm), and thrombin (1 and 5 IU/ml) induced significantly greater platelet aggregation in humans than in baboons. ADP (20 and 40 μm) and thrombin (1 and 5 IU/ml) induced significantly greater platelet aggregation in monkeys than in baboons. There was no species difference with ristocetin (0.5 or 1.0 mg/ml). In all species, thrombin (1 or 5 IU) induced greater platelet aggregation than any of the other reagents. Heparin at 1 IU/ml and LMWH at 10 IU/ml in all species almost completely abrogated thrombin-induced platelet aggregation. Heparin at 100 IU/ml effectively inhibited platelet aggregation induced by collagen, but only partially inhibited aggregation induced by ADP or ristocetin. LMWH only partially inhibited aggregation induced by collagen, ristocetin, and ADP.

CONCLUSIONS

The "Chrono-log" technology proved to be a reliable method of evaluating platelet activation and aggregation in vitro in primates. Species differences may play a role in platelet aggregation, with the monkey being more comparable to the human than the baboon, although overall trends were similar. In all species, thrombin induced greater platelet aggregation than other agonists. Even a concentration of heparin of 1 IU/ml, which is probably the maximal concentration that is clinically-applicable, prevented platelet aggregation induced by thrombin, but was less effective in preventing aggregation induced by collagen, ADP, or, particularly, ristocetin.

Similarities in thromboelastometric (ROTEM®) findings between humans and baboons

INTRODUCTION

Interest in visco-elastic testing in different clinical scenarios has increased but few data are available on thromboelastometric findings in primates.

MATERIALS AND METHODS

Blood cell count (hemoglobin, hematocrit, platelet count), coagulation parameters (prothrombin time, International Normalized Ratio, fibrinogen), and ROTEM® (Tem International GmbH, Munich, Germany) variables were analyzed using blood from 25 anesthetized male baboons and 21 non-anesthetized healthy volunteers. The platelet component of the clot was calculated as the difference in maximum clot elasticity (MCE) between the whole blood clot (EXTEM test) and the fibrin-based clot (FIBTEM test). In subgroups of each species, 10 μg abciximab was added to the regular FIBTEM reagent (cytochalasin D) for additional platelet inhibition.

RESULTS

Blood cell count was comparable between humans and primates. Both fibrinogen concentration (p<0.0001) and maximum clot firmness (MCF) in FIBTEM assays were significantly lower in baboons (p>0.0001, and p=0.006, respectively). PT, INR, and clotting time in NATEM assays were significantly prolonged in humans compared with baboons. MCF in NATEM, EXTEM and INTEM assays was not different between baboons and humans. Clot lysis in NATEM, EXTEM and INTEM assays was significantly higher in humans (p<0.0001). In contrast FIBTEM clot lysis was significantly higher in baboons (p=0.01). Addition of abciximab into the FIBTEM assay resulted in a significant reduction in MCF and MCE (p<0.001) and, consequently, the platelet component increased similar in both humans and baboons (p<0.001).

CONCLUSION

Activated ROTEM® tests revealed broad similarities between humans and baboons. ROTEM® assays developed for use in humans can also be used in baboons.

Controlling coagulation dysregulation in xenotransplantation

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.