Pharmacologic targeting of coagulation factors XII and XI by monoclonal antibodies reduces thrombosis in nitinol stents under flow.

BACKGROUND: Cardiovascular implantable devices, such as vascular stents, are critical for the treatment of cardiovascular diseases. However, their success is dependent on robust and often long-term antithrombotic therapies. Yet, the current standard-of-care therapies often pose significant bleeding risks to patients. Coagulation factor (F)XI and FXII have emerged as potentially safe and efficacious targets to safely reduce pathologic thrombin generation in medical devices. OBJECTIVES: To study the efficacy of monoclonal antibody-targeting FXII and FXI of the contact pathway in preventing vascular device-related thrombosis. METHODS: The effects of inhibition of FXII and FXI using function-blocking monoclonal antibodies were examined in a nonhuman primate model of nitinol stent-related thrombosis under arterial and venous flow conditions. RESULTS: We found that function-blocking antibodies of FXII and FXI reduced markers of stent-induced thrombosis in vitro and ex vivo. However, FXI inhibition resulted in more effective mitigation of thrombosis markers under varied flow conditions. CONCLUSION: This work provides further support for the translation of contact pathway of coagulation inhibitors for their adjunctive clinical use with cardiovascular devices.

Contact Activation Inhibitor and Factor XI Antibody, AB023, Produces Safe, Dose-Dependent Anticoagulation in a Phase 1 First-In-Human Trial.

Objective- Factor XI (FXI) contributes to thrombotic disease while playing a limited role in normal hemostasis. We generated a unique, humanized anti-FXI antibody, AB023, which blocks factor XIIa-mediated FXI activation without inhibiting FXI activation by thrombin or the procoagulant function of FXIa. We sought to confirm the antithrombotic activity of AB023 in a baboon thrombosis model and to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics in healthy adult subjects. Approach and Results- In a primate model of acute vascular graft thrombosis, AB023 reduced platelet and fibrin accumulation within the grafts by >75%. To evaluate the safety of AB023, we performed a first-in-human study in healthy adult volunteers without any serious adverse events. Overall, 10 of 21 (48%) subjects experienced 20 treatment-emergent adverse events, with 7 of 16 (44%) subjects following active treatment and 3 of 5 (60%) subjects following placebo. AB023 did not increase bleeding or prothrombin times. Anticoagulation was verified by a saturable ≈2-fold prolongation of the partial thromboplastin time for over 1 month after the highest dose. Conclusions- AB023, which inhibits contact activation-initiated blood coagulation in vitro and experimental thrombus formation in primates, produced a dose-dependent duration of limited anticoagulation without drug-related adverse effects in a phase 1 trial. When put in context with earlier observations suggesting that FXI contributes to venous thromboembolism and cardiovascular disease, although contributing minimally to hemostasis, our data further justify clinical evaluation of AB023 in conditions where contact-initiated FXI activation is suspected to have a pathogenic role. Clinical Trial Registration- URL: http://www.clinicaltrials.gov . Unique identifier: NCT03097341.

Inhibition of contact-mediated activation of factor XI protects baboons against S aureus-induced organ damage and death.

Staphylococcus aureus infections can produce systemic bacteremia and inflammation in humans, which may progress to severe sepsis or septic shock, even with appropriate antibiotic treatment. Sepsis may be associated with disseminated intravascular coagulation and consumptive coagulopathy. In some types of mouse infection models, the plasma coagulation protein factor XI (FXI) contributes to the pathogenesis of sepsis. We hypothesize that FXI also contributes to the pathogenesis of sepsis in primates, and that pharmacological interference with FXI will alter the outcome of Staphylococcus aureus-induced lethality in a baboon model. Pretreatment of baboons with the anti-FXI antibody 3G3, a humanized variant of the murine monoclonal 14E11 that blocks FXI activation by FXIIa, substantially reduced the activation of coagulation, as reflected by clotting times and plasma complexes of coagulation proteases (FXIIa, FXIa, FIXa, FXa, FVIIa, and thrombin) with serpins (antithrombin or C1 inhibitor) following infusion of heat-inactivated S aureus 3G3 treatment reduced fibrinogen and platelet consumption, fibrin deposition in tissues, neutrophil activation and accumulation in tissues, cytokine production, kininogen cleavage, cell death, and complement activation. Overall, 3G3 infusion protected the structure and function of multiple vital organs, including lung, heart, liver, and kidney. All treated animals reached the end point survival (7 days), whereas all nontreated animals developed terminal organ failure within 28 hours. We conclude that FXI plays a role in the pathogenesis of S aureus-induced disseminated intravascular coagulation and lethality in baboons. The results provide proof of concept for future therapeutic interventions that may prevent sepsis-induced organ failure and save lives in certain forms of sepsis.

Interaction of the Human Contact System with Pathogens-An Update.

The name human contact system is related to its mode of action, as "contact" with artificial negatively charged surfaces triggers its activation. Today, it is generally believed that the contact system is an inflammatory response mechanism not only against artificial material but also against misfolded proteins and foreign organisms. Upon activation, the contact system is involved in at least two distinct (patho)physiologic processes:i. the trigger of the intrinsic coagulation via factor XI and ii. the cleavage of high molecular weight kininogen with release of bradykinin and antimicrobial peptides (AMPs). Bradykinin is involved in the regulation of inflammatory processes, vascular permeability, and blood pressure. Due to the release of AMPs, the contact system is regarded as a branch of the innate immune defense against microorganisms. There is an increasing list of pathogens that interact with contact factors, in addition to bacteria also fungi and viruses bind and activate the system. In spite of that, pathogens have developed their own mechanisms to activate the contact system, resulting in manipulation of this host immune response. In this up-to-date review, we summarize present research on the interaction of pathogens with the human contact system, focusing particularly on bacterial and viral mechanisms that trigger inflammation via contact system activation.

Essential roles for platelets during neutrophil-dependent or lymphocyte-mediated defense against bacterial pathogens.

Emerging evidence from animal models suggests that platelets may participate in a wide variety of processes including the immune response against infection. More than 200 whole blood samples from patients and healthy controls were run in the System XE-5000 analyzer, and plasma fractions were separated for the following tests by ELISA, Luminex and light scattering. We describe two mechanisms by which platelets may contribute to immune function against various bacterial pathogens based on increased mean platelet volume in gram-positive bacterial infections and increased platelet counts in gram-negative bacterial infections. Gram-negative bacteria activate platelets to recruit neutrophils, which participate in the immune response against infection. During this process, fractalkine, macrophage inflammatory protein-1ß, interleukin-17A, tumor necrosis factor-α and platelet-activating factor were higher in patients infected with Escherichia coli; additionally, giant platelets were observed under the microscope. Meanwhile, we found that platelets played a different role in gram-positive bacterial infections. Specifically, they could actively adhere to gram-positive bacteria in circulation and transfer them to immune sites to promote antibacterial lymphocyte expansion. During this process, complement C3 and factor XI were more highly expressed in patients infected with Staphylococcus aureus; additionally, we detected more small platelets under the microscope. Platelets participate in the immune response against both gram-negative and gram-positive bacteria, although the mechanisms differ. These results will help us understand the complex roles of platelets during infections, and direct our use of antibiotics based on clinical platelet data.

Current challenges in the management of hemophilia.

Hemophilia is characterized by genetic mutations resulting in the deficiency of factors critical to the normal process of coagulation, sometimes resulting in spontaneous bleeding into soft tissue, joints, and internal organs. The 2 most common subtypes are hemophilia A, or factor VIII deficiency, and hemophilia B, or factor IX deficiency. Hemophilia affects an estimated 20,000 individuals in the United States. The diagnosis and management of patients with severe hemophilia is complex, and requires preventive treatment (prophylaxis) to avoid bleeding episodes and related complications and the use of replacement therapy with coagulation factors during acute bleeding episodes. To achieve optimal long-term results, the treatment of patients with hemophilia requires a comprehensive approach coordinated by a multidisciplinary team of specialists. Hemophilia imposes a substantial burden from economic, societal, and patient perspectives.

Factor XI replacement for inherited factor XI deficiency in routine clinical practice: results of the HEMOLEVEN prospective 3-year postmarketing study.

Factor XI (FXI)-deficient patients may develop excessive bleeding after trauma or surgery. Replacement therapy should be considered in high-risk situations, especially when FXI levels are below 20 IU dL(-1) . HEMOLEVEN is a human plasma-derived factor XI concentrate available in France since 1992, but there are few data regarding its use by physicians. This prospective study assessed the use, efficacy and safety of HEMOLEVEN in common clinical practice. HEMOLEVEN was evaluated in FXI-deficient patients in 13 French centres in a 3-year postmarketing study. Forty-four patients (30 females, 14 males) received 67 treatments. The median age was 37 years (8 months-91 years). Basal FXI levels were <1 to 51 IU dL(-1) (median: 5.5); 29 patients were severely FXI-deficient (<20 IU dL(-1) ). FXI was administered prophylactically before 43 surgical procedures, 10 invasive procedures, 8 vaginal deliveries, or as curative treatment for six bleeds. The efficacy was assessed as excellent/good in 63, moderate in two and undetermined in two treatments. Seven patients experienced seven adverse effects, including two rated as serious: one sudden massive pulmonary embolism with fatal outcome and one case of inhibitor to FXI. HEMOLEVEN is effective for bleeding prevention in FXI deficiency. However, considering the benefit/risk ratio observed in relation to dosage in this study; firstly, it should be used sparingly due to its potential prothrombotic effect; secondly, new prescription procedures should be defined to adapt the dosage, especially in patients with intrinsic and/or acquired risk factors for thrombosis.

Antigen levels of coagulation factor XII, coagulation factor XI and prekallikrein, and the risk of myocardial infarction and ischemic stroke in young women.

BACKGROUND: High levels of activated protein­inhibitor complexes of the intrinsic coagulation proteins are associated with ischemic stroke (IS) but not with myocardial infarction (MI). This study was aimed at determining whether the antigen levels of coagulation factors(factor XII, FXII, and FXI and prekallikrein (PK)are associated with MI and IS, and whether this association is independent of levels of activated protein­inhibitor complexes. PATIENTS AND METHODS: The RATIO study included young women (< 50 years) with MI (N = 205)and IS (N = 175), and 638 healthy controls. Antigen levels of FXII, FXI and PK were measured and expressed as percentages of of those in pooled normal plasmas. Odds ratios (ORs) and corresponding 99% confidence intervals (CIs) were calculated for high levels (i.e. ≥ 90th percentile of controls) as measures of rate ratios. RESULTS: After adjustment for potential confounders, high levels of FXII antigen were not associated with MI risk or IS risk(OR(MI) 1.18, 99% CI 0.51­2.74; ORIS 1.03, 9% CI 0.41­2.55). High levels of FXI antigen were slightly associated with an increase in MI risk (OR(MI) 1.55, 9% CI 0.74­3.21), whereas there was a substantial association with IS risk (ORIS 2.65, 9% CI 1.27­5.56). PK antigen was slightly associated with MI risk but not with IS risk(ORMI 1.54, 9% CI 0.67­3.52; ORIS 0.90, 9% CI 0.35­2.33). All associations remained similar after adjustment for levels of protein­inhibitor complexes. CONCLUSION: Increased levels of FXI antigen were associated with an increase in IS risk, whereas they showed only a marginal association with MI risk. FXII antigen and PK antigen levels were not substantially associated with MI risk and IS risk.

Two novel inhibitory anti-human factor XI antibodies prevent cessation of blood flow in a murine venous thrombosis model.

Coagulation factor XI (FXI) is a promising target for anticoagulation, because of its major role in thrombosis and relatively minor role in haemostasis. This implies that inhibition of FXI can prevent thrombosis without causing bleeding. It was our aim to investigate the antithrombotic properties of two novel inhibitory anti-human FXI antibodies (αFXI-175 and αFXI-203). The in vitro properties of both antibodies were analysed using standard clotting assays and calibrated automated thrombography. For the in vivo model we used FXI knockout mice, in which FXI plasma levels were restored with purified human FXI. Thrombosis was induced by applying ferric chloride to the vena cava inferior, after which time to occlusion was analysed. A tail bleeding assay was used to investigate the safety of both antibodies. Using calibrated automated thrombography, both antibodies inhibited thrombin generation initiated via the intrinsic pathway. In contrast, upon tissue factor (TF)-initiated thrombin generation, αFXI-203 did not inhibit thrombin generation, while αFXI-175 inhibited thrombin generation only at low concentrations of TF. In the murine thrombosis model, the vena cava inferior remained patent for 25 minutes (min) in mice treated with αFXI-175 and for 12.5 min in αFXI-203 treated animals, which was significantly longer than in placebo-treated animals (5 min, p<0.05). Neither antibody caused severe blood loss in a tail bleeding assay. In conclusion, the two inhibitory antibodies against FXI prevented cessation of blood flow in a murine thrombosis model without inducing a bleeding tendency.

[Long-term response to rituximab in a patient with acquired hemophilia]. / Respuesta a largo plazo con rituximab en una paciente con hemofilia adquirida.

A 28 year-old female without history of previous disease. In the seventh month of her first pregnancy she developed hemorrhagic tendency that worsened in the early postpartum period. Activated partial thromboplastin time was 110 sec (control=35.8 sec) with negative tests for lupus anticoagulant. Factor VIII was <1% and a factor VIII inhibitor titer was 84 Bethesda Units/mL (BU). Initial therapy included methylprednisolone, prednisone, and cyclophosphamide. After two weeks of treatment, clinical conditions of the patient improved slightly and she was discharged. Outpatient therapy included azathioprine, and prednisone for a period of 22 months but in-hospital management was several times required. We initiated rituximab 375 mg/m2/week/4 weeks. A clinical improvement and increased levels of factors VIII and XI were observed 10 weeks later and factor VIII inhibitor decreased to undetectable levels. After a 82-month follow-up period (since the first rituximab infusion), she is asymptomatic and factor VIII and factor XI plasma levels are 70% and 94%, respectively FVIII inhibitor level is still undetectable. Rituximab seems an alternative for the treatment of acquired hemophilia refractory to standard treatment.

Factor XI deficiency--resolving the enigma?

The management of factor XI deficiency is not straightforward for three reasons: firstly, the role of this factor in the coagulation pathway is not clearly understood; secondly, the bleeding tendency, although mild, is unpredictable and does not clearly relate to the factor XI level; and thirdly, all treatment products, although available, have some potentially serious side effects. These factors (or enigmas) contribute to the variable management of patients with this coagulation factor deficiency, but recent research is helping to clarify some of these areas.

Cataract extraction without prophylactic treatment in patients with severe factor XI deficiency.

PURPOSE: To assess the risks of intraoperative and postoperative bleeding associated with cataract extraction without prophylactic treatment in patients with severe factor XI (FXI) deficiency. DESIGN: Prospective interventional case series. SETTING: Single institute. STUDY POPULATION: Consecutive unrelated patients with severe FXI deficiency who underwent cataract extraction under topical anesthesia, with a clear corneal incision, phacoemulsification, and implantation of a foldable posterior chamber intraocular lens (PCIOL) were enrolled. Patients with associated intraocular conditions that could complicate the surgery were excluded. INTERVENTION: Cataract extraction without prophylactic treatment for the FXI deficiency. MAIN OUTCOME MEASURES: Assessment of intraoperative and postoperative ocular bleeding and other related complications. RESULTS: Seven patients ranging in age from 61 to 95 years (median, 79) underwent phacoemulsification and PCIOL implantation in 11 eyes. Five patients (71%) were homozygotes for type II mutation of the FXI gene (activity level of <1 U/dl), 1 patient was a homozygote for type III mutation (activity level of 11 U/dl), and 1 patient was a compound heterozygote for types II and III (activity level of 3 U/dl). Three of the patients (43%), all type II homozygotes, also had an inhibitor antibody to FXI. All 7 patients were followed for at least 1 week after the operation. The surgery was uneventful in all eyes, and neither major nor minor bleeding events were observed in any of the operated eyes during surgery and follow-up. CONCLUSIONS: Cataract extraction by phacoemulsification in uncomplicated eyes can be performed safely without prophylactic treatment in patients with severe FXI deficiency with or without inhibitor antibodies against FXI.

Prevention of vascular graft occlusion and thrombus-associated thrombin generation by inhibition of factor XI.

The protease thrombin is required for normal hemostasis and pathologic thrombogenesis. Since the mechanism of coagulation factor XI (FXI)-dependent thrombus growth remains unclear, we investigated the contribution of FXI to thrombus formation in a primate thrombosis model. Pretreatment of baboons with a novel anti-human FXI monoclonal antibody (aXIMab; 2 mg/kg) inhibited plasma FXI by at least 99% for 10 days, and suppressed thrombin-antithrombin (TAT) complex and beta-thromboglobulin (betaTG) formation measured immediately downstream from thrombi forming within collagen-coated vascular grafts. FXI inhibition with aXIMab limited platelet and fibrin deposition in 4-mm diameter grafts without an apparent increase in D-dimer release from thrombi, and prevented the occlusion of 2-mm diameter grafts without affecting template bleeding times. In comparison, pretreatment with aspirin (32 mg/kg) prolonged bleeding times but failed to prevent graft occlusion, supporting the concept that FXI blockade may offer therapeutic advantages over other antithrombotic agents in terms of bleeding complications. In whole blood, aXIMab prevented fibrin formation in a collagen-coated flow chamber, independent of factor XII and factor VII. These data suggest that endogenous FXI contributes to arterial thrombus propagation through a striking amplification of thrombin generation at the thrombus luminal surface.

Acquired factor XI inhibitor in systemic lupus erythematosus--case report and literature review.

OBJECTIVES: Rare patients with systemic lupus erythematosus (SLE) patients exhibit anticoagulants that interfere in the earlier stages of the intrinsic coagulation pathway, such as those involving factor XI (FXI). The objectives of our study were to describe the presence of an acquired inhibitor to FXI causing a life-threatening bleeding disorder in an SLE patient and to review the association of this coagulopathy with SLE. METHODS: We describe the clinical presentation of an SLE patient with an acquired FXI inhibitor. We reviewed the scientific literature using the MEDLINE database searching the following combinations of terms: "SLE and Factor XI," "SLE and Factor XI inhibitor," and "Factor XI inhibitor," from 1964 to 2007. RESULTS: A 20-year-old woman with a 6-year history of SLE was admitted to the hospital because of severe life-threatening abdominal bleeding due to a ruptured ovarian cyst. This hemorrhagic event was related to the presence of an FXI inhibitor. We reviewed another 13 SLE patients with this condition, 8 of whom had bleeding events. Most patients had manifestations of active SLE, and prednisone was used as the primary treatment. CONCLUSIONS: SLE activity seems to be associated with the production of antibodies directed against FXI, which may cause important coagulopathies, especially bleeding events. The inhibitor disappeared after immunosuppressive therapy for SLE in most cases, suggesting that the appearance of this inhibitor is immune mediated. Although the majority of cases with the FXI inhibitor are not fatal, it should be suspected and investigated in SLE patients, especially those with abnormal clotting tests.

[Acquired factor XI inhibitor and chronic lymphocytic leukemia]. / Allongement du TCA chez un patient atteint de leucémie lymphoïde chronique : à propos de la très rare découverte d'un autoanticorps antifacteur XI.

Autoimmune phenomena, most frequently autoimmune hemolytic anemia, is a well-known complication of lymphoproliferative diseases. We report a very rare association of a chronic lymphocytic leukemia with an acquired factor XI inhibitor. A 87-year-old man presented with auto-immune hemolytic anemia. He had untreated chronic lymphocytic leukemia for the past three years and renal insufficiency. Before surgical procedure for arteriovenous fistula, we discovered a very prolonged activated partial thromboplastin time (APTT), and an acquired factor XI inhibitor was detected. The patient was successfully treated with immunosuppressive therapy. Among patients with lymphoproliferative disorders the discovery of a prolonged APTT implies to search for rare autoimmune phenomena like acquired coagulation factor inhibitors.

Induction of an inhibitor antibody to factor XI in a patient with severe inherited factor XI deficiency by Rh immune globulin.

In this paper, we report an inhibitor antibody to factor XI (FXI) in a woman with severe inherited FXI deficiency, induced by FXI present in an Rh immune globulin preparation. The patient is homozygous for the Glu117Stop mutation, associated with a FXI level of less than 1 U/dL. Unlike all previously described patients with severe FXI deficiency and an inhibitor, the patient had never been exposed to blood products. Following 3 injections of Rh immune globulin during pregnancy, she developed an inhibitor to FXI (8 Bethesda units) that was shown to bind specifically to FXI and inhibit factor IX cleavage by purified FXIa. The administered Rh immune globulin and 2 other similar products were shown to contain FXI. Clinicians should be aware of the potential for immunization of severely FXI-deficient patients by FXI present in Rh immune globulin preparations.

ADAMTS13 related markers and von Willebrand factor in plasma from patients with thrombotic microangiopathy (TMA).

The ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type I domain 13) related markers were measured in the plasma of healthy volunteers and thrombotic microangiopathy (TMA) patients including thrombotic thrombocytopenic purpura (TTP) to examine their efficacy in the diagnosis of TTP. The plasma levels of the ADAMTS13 antigen and ADAMTS13-factor XI complex were significantly lower in TMA patients with a significant decreased ADAMTS13 activity (and these patients were considered to have TTP) than in the healthy volunteers. The plasma levels of ADAMTS13 antigens closely correlated with those of ADAMTS13-factor XI complex. Autoantibody for ADAMTS 13 was also positive in almost all TTP patients. In addition, the ratio of von Willebrand factor (VWF)/ADAMTS13 activity was significantly high in TTP suggesting that this ratio might be more useful for the differential diagnosis of TTP than the ADAMTS13 assay alone. These findings suggest that ADAMTS13 related markers are useful for the diagnosis and analysis of TTP.