The deglycosylated form of 1E12 inhibits platelet activation and prothrombotic effects induced by VITT antibodies.

In order to improve the safety of COVID-19 vaccines, there is an urgent need to unravel the pathogenesis of vaccineinduced immune thrombotic thrombocytopenia (VITT), a severe complication of recombinant adenoviral vector vaccines used to prevent COVID-19, and likely due to anti-platelet factor 4 (PF4) IgG antibodies. In this study, we demonstrated that 1E12, a chimeric anti-PF4 antibody with a human Fc fragment, fully mimics the effects of human VITT antibodies, as it activates platelets to a similar level in the presence of platelet factor 4 (PF4). Incubated with neutrophils, platelets and PF4, 1E12 also strongly induces NETosis, and in a microfluidic model of whole blood thrombosis, it triggers the formation of large platelet/leukocyte thrombi containing fibrin(ogen). In addition, a deglycosylated form of 1E12 (DG-1E12), which still binds PF4 but no longer interacts with Fcγ receptors, inhibits platelet, granulocyte and clotting activation induced by human anti-PF4 VITT antibodies. This strongly supports that 1E12 and VITT antibodies recognize overlapping epitopes on PF4. In conclusion, 1E12 is a potentially important tool to study the pathophysiology of VITT, and for establishing mouse models. On the other hand, DG-1E12 may help the development of a new drug that specifically neutralizes the pathogenic effect of autoimmune anti-PF4 antibodies, such as those associated with VITT.

Prévention du risque thromboembolique veineux et surveillance de l’hémostase chez les patients hospitalisés pour COVID-19 : propositions réactualisées (avril 2021). Groupe d’intérêt en hémostase périopératoire (GIHP) et groupe d’étude sur l’hémostase et la thrombose (GFHT) Prevention of venous thromboembolism and haemostasis monitoring in patients with COVID-19: Updated proposals (April 2021): From the French working group on perioperative haemostasis (GIHP) and the French study group on thrombosis and haemostasis (GFHT), in collaboration with the French society of anaesthesia and intensive care (SFAR)

<h4>Contexte</h4> La COVID-19 est associée à un risque thromboembolique veineux élevé, en particulier chez les patients sévères. Depuis les premières propositions GIHP/GFHT publiées en avril 2020, de nouvelles connaissances sont apparues. L’objet du présent travail était de réactualiser ces propositions. <h4>Méthodes</h4> Un groupe de travail a défini sept questions et effectué une revue critique de la littérature. Les propositions ont été formulées après consensus entre les membres du groupe de travail et les autres membres du GIHP/GFHT. <h4>Résultats</h4> Chez les patients hospitalisés non sévères et certains patients ambulatoires à risque, nous suggérons l’administration d’une thromboprophylaxie à dose standard. Chez les patients sévères, nous suggérons une thromboprophylaxie à dose intermédiaire ou thérapeutique selon le taux de D-dimères et son évolution. Sept à dix jours après l’admission, nous suggérons de revenir à une dose standard pour réduire le risque hémorragique. Chez les patients présentant un très haut risque thrombotique, ayant reçu une thromboprophylaxie à dose thérapeutique, nous suggérons un dépistage systématique de la thrombose avant la désescalade. Nous suggérons d’ajuster l’anticoagulation au poids des patients. Nous suggérons un monitorage régulier des paramètres d’hémostase, incluant les D-dimères, chez les patients sévères. Nous suggérons un monitorage de l’anticoagulation à dose intermédiaire et thérapeutique par l’activité anti-Xa. <h4>Conclusion</h4> Les propositions réactualisées suivent une approche standard de la thromboprophylaxie, visant à diminuer l’incidence des évènements thromboemboliques veineux symptomatiques. Chez les patients sévères, nous proposons une stratégie séquentielle tenant compte de la relation temporelle entre le risque thrombotique et le risque hémorragique.

Prévention du risque thromboembolique veineux et surveillance de l’hémostase chez les patients hospitalisés pour COVID-19 : propositions réactualisées (avril 2021). Groupe d’intérêt en hémostase périopératoire (GIHP) et groupe d’étude sur l’hémostase et la thrombose (GFHT)

Résumé Contexte La COVID-19 est associée à un risque thromboembolique veineux élevé, en particulier chez les patients sévères. Depuis les premières propositions GIHP/GFHT publiées en avril 2020, de nouvelles connaissances sont apparues. L’objet du présent travail était de réactualiser ces propositions. Méthodes Un groupe de travail a défini sept questions et effectué une revue critique de la littérature. Les propositions ont été formulées après consensus entre les membres du groupe de travail et les autres membres du GIHP/GFHT. Résultats Chez les patients hospitalisés non sévères et certains patients ambulatoires à risque, nous suggérons l’administration d’une thromboprophylaxie à dose standard. Chez les patients sévères, nous suggérons une thromboprophylaxie à dose intermédiaire ou thérapeutique selon le taux de D-dimères et son évolution. Sept à dix jours après l’admission, nous suggérons de revenir à une dose standard pour réduire le risque hémorragique. Chez les patients présentant un très haut risque thrombotique, ayant reçu une thromboprophylaxie à dose thérapeutique, nous suggérons un dépistage systématique de la thrombose avant la désescalade. Nous suggérons d’ajuster l’anticoagulation au poids des patients. Nous suggérons un monitorage régulier des paramètres d’hémostase, incluant les D-dimères, chez les patients sévères. Nous suggérons un monitorage de l’anticoagulation à dose intermédiaire et thérapeutique par l’activité anti-Xa. Conclusion Les propositions réactualisées suivent une approche standard de la thromboprophylaxie, visant à diminuer l’incidence des évènements thromboemboliques veineux symptomatiques. Chez les patients sévères, nous proposons une stratégie séquentielle tenant compte de la relation temporelle entre le risque thrombotique et le risque hémorragique.

Hypotheses behind the very rare cases of thrombosis with thrombocytopenia syndrome after SARS-CoV-2 vaccination.

As of 4 April 2021, a total of 169 cases of cerebral venous sinus thrombosis (CVST) and 53 cases of splanchnic vein thrombosis were reported to EudraVigilance among around 34 million people vaccinated in the European Economic Area and United Kingdom with COVID-19 Vaccine AstraZeneca, a chimpanzee adenoviral vector (ChAdOx1) encoding the spike protein antigen of the SARS-CoV-2 virus. The first report of the European Medicines Agency gathering data on 20 million people vaccinated with Vaxzevria® in the UK and the EEA concluded that the number of post-vaccination cases with thromboembolic events as a whole reported to EudraVigilance in relation to the number of people vaccinated was lower than the estimated rate of such events in the general population. However, the EMA's Pharmacovigilance Risk Assessment Committee concluded that unusual thromboses with low blood platelets should be listed as very rare side effects of Vaxzevria®, pointing to a possible link. The same issue was identified with the COVID-19 Vaccine Janssen (Ad26.COV2.S). Currently, there is still a sharp contrast between the clinical or experimental data reported in the literature on COVID-19 and the scarcity of data on the unusual thrombotic events observed after the vaccination with these vaccines. Different hypotheses might support these observations and should trigger further in vitro and ex vivo investigations. Specialized studies were needed to fully understand the potential relationship between vaccination and possible risk factors in order to implement risk minimization strategies.

Impact of High-Dose Prophylactic Anticoagulation in Critically Ill Patients With COVID-19 Pneumonia.

BACKGROUND: Because of the high risk of thrombotic complications (TCs) during SARS-CoV-2 infection, several scientific societies have proposed to increase the dose of preventive anticoagulation, although arguments in favor of this strategy are inconsistent. RESEARCH QUESTION: What is the incidence of TC in critically ill patients with COVID-19 and what is the relationship between the dose of anticoagulant therapy and the incidence of TC? STUDY DESIGN AND METHODS: All consecutive patients referred to eight French ICUs for COVID-19 were included in this observational study. Clinical and laboratory data were collected from ICU admission to day 14, including anticoagulation status and thrombotic and hemorrhagic events. The effect of high-dose prophylactic anticoagulation (either at intermediate or equivalent to therapeutic dose), defined using a standardized protocol of classification, was assessed using a time-varying exposure model using inverse probability of treatment weight. RESULTS: Of 538 patients included, 104 patients experienced a total of 122 TCs with an incidence of 22.7% (95% CI, 19.2%-26.3%). Pulmonary embolism accounted for 52% of the recorded TCs. High-dose prophylactic anticoagulation was associated with a significant reduced risk of TC (hazard ratio, 0.81; 95% CI, 0.66-0.99) without increasing the risk of bleeding (HR, 1.11; 95% CI, 0.70-1.75). INTERPRETATION: High-dose prophylactic anticoagulation is associated with a reduction in thrombotic complications in critically ill patients with COVID-19 without an increased risk of hemorrhage. Randomized controlled trials comparing prophylaxis with higher doses of anticoagulants are needed to confirm these results. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT04405869; URL: www.clinicaltrials.gov.

COVID-19 patients often show high-titer non-platelet-activating anti-PF4/heparin IgG antibodies.

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is a severe adverse reaction to heparin caused by heparin-dependent, platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Heparin is a cornerstone of treatment in critically ill COVID-19 patients. HIT antibodies can be detected by antigen tests and functional tests. Often strong reactivity in the antigen test is used as a surrogate marker for the presence of clinically relevant, platelet-activating antibodies. We observed an unexpectedly high percentage of COVID-19 patients, clinically suspected to have HIT, with high titer anti-PF4/heparin antibodies, but a negative functional test. OBJECTIVE: We investigated whether in COVID-19 patients a serum-derived factor inhibits the heparin-induced platelet activation test (HIPA). METHODS AND RESULTS: Twelve COVID-19 patients with suspected HIT were tested. Three samples tested negative in all assays; nine samples tested positive by antigen tests, among which only three tested also positive by HIPA. When we spiked COVID-19 serum or control serum with the human HIT antibody like monoclonal antibody 5B9, reactivity of 5B9 remained the same. Also, the purified IgG fractions of COVID-19 sera testing strongly positive in the PF4/heparin antigen test but negative in the functional test did not show increased reactivity in the functional test in comparison to the original serum. Both results make a functionally inhibitory factor in the serum/plasma of COVID-19 patients highly unlikely. CONCLUSION: COVID-19 patients often present with strong reactivity in PF4/heparin antigen tests without the presence of platelet-activating antibodies. Diagnosis of HIT requires confirmation of heparin-dependent, platelets activating antibodies to avoid overdiagnosis and overtreatment with non-heparin anticoagulants.

[Management of the thrombotic risk associated with COVID-19: what is the role of the hemostasis laboratory?] / Apport du laboratoire d'hémostase dans la gestion du risque thrombotique associé au Covid-19.

COVID-19 is associated with disturbances of hemostasis in the laboratory and an increased thrombotic risk. Routine laboratory tests - activated partial thromboplastin time (aPTT), prothrombin time, Clauss fibrinogen and D-dimers levels measurement - are used for the evaluation of the thrombotic risk and the monitoring of hemostasis, but are subject to several drawbacks that may affect the reliability and clinical relevance of the delivered results. Another challenge for the hemostasis laboratory is the monitoring of heparin treatment. For instance, the issue of the monitoring of unfractionated heparin remains debated, the more so when there is a tremendous inflammatory response. This brief review considers the role of laboratory tests of hemostasis in the management of COVID-19 and discusses their main limitations to be kept in mind.

Prevention of thrombotic risk in hospitalized patients with COVID-19 and hemostasis monitoring.

COVID-19 is an infection induced by the SARS-CoV-2 coronavirus, and severe forms can lead to acute respiratory distress syndrome (ARDS) requiring intensive care unit (ICU) management. Severe forms are associated with coagulation changes, mainly characterized by an increase in D-dimer and fibrinogen levels, with a higher risk of thrombosis, particularly pulmonary embolism. The impact of obesity in severe COVID-19 has also been highlighted.In this context, standard doses of low molecular weight heparin (LMWH) may be inadequate in ICU patients, with obesity, major inflammation, and hypercoagulability. We therefore urgently developed proposals on the prevention of thromboembolism and monitoring of hemostasis in hospitalized patients with COVID-19.Four levels of thromboembolic risk were defined according to the severity of COVID-19 reflected by oxygen requirement and treatment, the body mass index, and other risk factors. Monitoring of hemostasis (including fibrinogen and D-dimer levels) every 48 h is proposed. Standard doses of LMWH (e.g., enoxaparin 4000 IU/24 h SC) are proposed in case of intermediate thrombotic risk (BMI < 30 kg/m2, no other risk factors and no ARDS). In all obese patients (high thrombotic risk), adjusted prophylaxis with intermediate doses of LMWH (e.g., enoxaparin 4000 IU/12 h SC or 6000 IU/12 h SC if weight > 120 kg), or unfractionated heparin (UFH) if renal insufficiency (200 IU/kg/24 h, IV), is proposed. The thrombotic risk was defined as very high in obese patients with ARDS and added risk factors for thromboembolism, and also in case of extracorporeal membrane oxygenation (ECMO), unexplained catheter thrombosis, dialysis filter thrombosis, or marked inflammatory syndrome and/or hypercoagulability (e.g., fibrinogen > 8 g/l and/or D-dimers > 3 µg/ml). In ICU patients, it is sometimes difficult to confirm a diagnosis of thrombosis, and curative anticoagulant treatment may also be discussed on a probabilistic basis. In all these situations, therapeutic doses of LMWH, or UFH in case of renal insufficiency with monitoring of anti-Xa activity, are proposed.In conclusion, intensification of heparin treatment should be considered in the context of COVID-19 on the basis of clinical and biological criteria of severity, especially in severely ill ventilated patients, for whom the diagnosis of pulmonary embolism cannot be easily confirmed.