Comparing thrombin generation in patients with hemophilia A and patients on vitamin K antagonists

Essentials It is unknown if hemophilia patients with atrial fibrillation need anticoagulation. Endogenous thrombin potentials (ETP) in hemophilia patients and patients on coumarins were compared. Severe hemophilia patients had comparable ETP to therapeutic international normalized ratio (INR). In non-severe hemophilia, 33% had higher ETP than therapeutic INR and may need anticoagulation. Click to hear Dr Negrier's perspective on global assays for assessing coagulation SUMMARY: Background It is unknown whether patients with hemophilia A with atrial fibrillation require treatment with vitamin K antagonists (VKAs) to the same extent as the normal population. Objective To compare hemostatic potential in hemophilia patients and patients on VKAs using thrombin generation (TG). Methods In this cross-sectional study, TG, initiated with 1pM tissue factor, was measured in 133 patients with severe (FVIII < 1%, n = 15) and non-severe (FVIII 1-50%, n = 118) hemophilia A, 97 patients on a VKA with an international normalized ratio (INR) ≥ 1.5 and healthy controls. Endogenous thrombin potential (ETP) (nm*min) was compared according to FVIII level (< 1%, 1-19% and 20-50%) with healthy controls and patients with sub-therapeutic INR (1.5-1.9) and therapeutic INR (≥ 2.0). Medians and interquartile ranges (IQRs) were calculated. Results Compared with healthy controls (898 [IQR 803-1004]), both hemophilia patients and patients on VKAs had lower median ETPs at 304 (196-449) and 176 (100-250), respectively. ETP was quite similar in severe hemophilia patients (185 [116-307]) and patients with a therapeutic INR (156 [90-225]). Compared with patients with therapeutic INR, ETP in patients with FVIII 1-19% and patients with FVIII 20-50% was higher at 296 (203-430) and 397 (219-632), respectively. All patients with therapeutic INR had an ETP < 400. Considering this threshold, 93% of severe hemophilia patients, 70% of patients with FVIII 1-19% and 52% of patients with FVIII 20-50% had an ETP < 400. Conclusion In severe hemophilia patients, TG was comparable to that in patients with a therapeutic INR. In one-third of non-severe hemophilia patients, TG was higher. These results suggest that anticoagulation therapy should be considered in a substantial proportion of non-severe hemophilia patients.

Bispecific antibody mimicking factor VIII

There are some issues in the current factor (F)VIII replacement therapy for severe hemophilia A. One is mental and physical burden for the multiple intravenous infusions, and the other is difficulty in the hemostatic treatment for the patients with FVIII inhibitor. The development of novel drug with fully hemostatic effect, simply procedure, and long-acting reaction has been expected. Recently, FVIIIa-mimicking humanized recombinant bispecific antibody (ACE910) against FIXa and FX was developed. In the non-human clinical study, primate model of acquired hemophilia A demonstrated that the ACE910 was effective on both on-going and spontaneous bleedings. A phase I clinical study was conducted in healthy adults by single subcutaneous infusion of ACE910, followed by the patients' part study, Japanese patients with severe hemophilia A without or with inhibitor were treated with once-weekly subcutaneous injection of ACE910 at three dose levels for 12 successive weeks. There was no significant adverse event related to ACE910 in the clinical and laboratorial findings, and t1/2 of ACE910 was ∼30 days. The median annual bleeding rates were reduced very markedly dose-dependently, independently of inhibitor. Furthermore, among the patients with dose escalation, bleeding rate was decreased as ACE910 dose was increased. In conclusion, ACE910 would have a number of promising features: its high subcutaneous bioavailability and long half-life make the patients possible to be injected subcutaneously with a once-a-week or less frequency. In addition, ACE910 would provide the bleeding prophylactic efficacy, independently of inhibitor.

The prevalence of factor VIII and IX inhibitors among Saudi patients with hemophilia: Results from the Saudi national hemophilia screening program

Hemophilia A and B are X-linked diseases that predominantly affect male patients. Patients can develop coagulation factor inhibitors, which exponentially increases the treatment cost. However, the prevalence of factor VIII and IX inhibitors in Saudi Arabia is unclear.This study aimed to determine the Saudi prevalence of factor VIII and IX inhibitors.This 4-year, 7-center, cross-sectional study evaluated the Saudi prevalences of hemophilia A and B. We collected the patients' clinical data, evaluated their disease, and tested for factor inhibitors.We included 202 patients with hemophilia (median age at diagnosis: 0.13 years, range: birth-34.8 years). The patients included 198 male patients (98%), 148 patients with hemophilia A (73.3%), and 54 patients with hemophilia B (26.7%). The patients exhibited severe factor VIII activity (<1%; 121 patients; 5.2%), moderate activity (1-5%; 7 patients; 4.9%), and mild activity (14 patients; 9.9%). Among the patients with care-related data, most patients were treated for episodic bleeding (76.8%) or received prophylaxis (22.6%); 1 patient received both treatments. Among the patients with source-related data, the factor replacements were derived from plasma (48.4%), recombinant concentrates (22.9%), both sources (14.6%), or fresh frozen plasma (14.1%). Factor VIII inhibitors were observed in 43 (29.3%) of the 147 patients, and only 1 of the 54 patients developed factor IX inhibitors. Most patients who developed inhibitors had severe hemophilia (40/44; 90.9%), and inhibitors were also common among patients who received recombinant products (14/43; 32.6%).The Saudi prevalence of factor inhibitors was similar to those among other ethnic populations.

Thrombin Generation Assays (TGAs)

In recent years, there has been a revival of interest in a time-honored tool of the clotting trade: the thrombin generation curve or thrombin generation (TG) assay (TGA) as we now call it. Thrombin generation is a key coagulation process that determines the extent of a hemostatic plug or a thrombotic process. The recent development of newer tests based on the continuous registration of TG under in vitro conditions that mimic more closely what occurs in vivo prompted us to reinvestigate the balance between procoagulants and anticoagulants in patients. Measurement of TG is accepted as a research tool, but the variety of sources and concentrations of reagents, as well as technical constraints, limit its potential for proper clinical use. The newer TGAs not only provide an overall assessment of hemostasis but also provide promising laboratory tools for investigating hemorrhagic coagulopathies and monitoring replacement therapy in several clinical conditions.

Chromogenic Factor VIII Assays for Improved Diagnosis of Hemophilia A

Hemophilia A is an inherited bleeding disorder caused by a reduced level of factor VIII coagulant activity (FVIII:C) in blood. Bleeding episodes may occur spontaneously in the severe form of hemophilia or after trauma in the milder forms. It is important that patients are diagnosed correctly, which includes placing them into the correct severity category of the disorder so that appropriate treatment can be given. Diagnosis is made by determination of the amount of FVIII:C in the blood, usually using a one-stage factor VIII:C assay. However, approximately one third of patients with mild or moderate hemophilia will have much lower results by the chromogenic assay, with some of them having normal results by the one-stage assay. The chromogenic factor VIII assay is used in some specialized hemophilia reference centers and is recommended for the diagnosis of mild hemophilia A, as this assay is considered to better reflect the severity status of hemophilia patients than the one-stage assay.

Detection and Measurement of Factor Inhibitors

Specific coagulation factor inhibitors, most notably to coagulation factor VIII, can develop in patients with hemophilia after exposure to replacement factor or as an acquired (autoimmune) event. Such inhibitors can be detected by a combination of prolonged coagulation screening tests, such as the activated partial thromboplastin time, plus a non-correcting mixing test. Non-correction may only be evident, or else may be extenuated, with incubation at 37 °C. The Bethesda assay for quantitation of inhibitor strength is based on a combination of mixing tests followed by specific factor assays.

One-Stage Factor VIII Assays

Coagulation factor assays using one-stage methodology are widely used to measure factor levels for the purpose of detecting a deficiency, or to monitor replacement therapy. In this chapter, we focus on a method to measure Factor VIII coagulant activity (FVIII:C) by the one-stage assay (FVIII:C-1), with extra information provided to also allow this method to apply to Factor IX (FIX), Factor XI (FXI), and Factor XII (FXII). From the perspective of laboratory testing, these factors are components of the "intrinsic" coagulation pathway and are all measured in test systems based on the correction of the Activated Partial Thromboplastin Time (APTT). Factor activity is assessed by measuring the ability of an unknown sample to correct the prolonged APTT of factor-deficient plasma (deficient in the factor of interest), relative to the effect of a known calibrator. These assays are used for the diagnosis of the many causes of reduced factor levels, including those causing a prolonged APTT. It is important for laboratory staff to understand the impact of method variations, limitations, and result interpretation and these aspects are also discussed.

What is the role of an extended half-life product in immune tolerance induction in a patient with severe hemophilia A and high-titer inhibitors?

A 10-year-old boy presents with a history of severe hemophilia A and high-titer inhibitor that had failed high-dose immune tolerance induction (ITI) with a recombinant factor VIII (rFVIII) product and a plasma-derived FVIII product. You are asked by his mother whether he should be tried on ITI with an extended half-life product, in particular, consideration of a rFVIIIFc concentrate.

New therapies for hemophilia

Individuals with severe hemophilia have benefitted from 5 decades of advances that have led to widespread availability of safe and efficacious factors VIII and IX, a multidisciplinary integrated care model through a network of specialized hemophilia treatment centers, and aggressive introduction of prophylactic replacement therapy to prevent bleeding and preserve joint health. Yet, there are remaining challenges and treatment gaps which have prevented complete abrogation of all joint bleeding, and progressive joint deterioration may continue in some affected individuals over the course of a lifetime. Some of these challenges can now be addressed with recombinant clotting factors with extended half-life that may improve adherence to prophylaxis regimens through more convenient infusion schedules, maintain higher plasma levels for longer when clinically necessary, and allow for better adaptation to individual phenotypic and pharmacokinetic variability. Real-world case studies will be presented that illustrate practical application of these newly approved therapies in clinical practice and the clinical trial data that have demonstrated the potential for improved clinical outcomes by implementing these strategies.

Hemophilia and inhibitors: current treatment options and potential new therapeutic approaches

The immune response to infused factor concentrates remains a major source of morbidity and mortality in the treatment of patients with hemophilia A and B. This review focuses on current treatment options and novel therapies currently in clinical trials. After a brief review of immune tolerance regimens, the focus of the discussion is on preventing bleeding in patients with hemophilia and inhibitors. Recombinant factor VIIa and activated prothrombin complex concentrates are the mainstays in treating bleeds in patients with inhibitors. Both agents have been shown to reduce bleeding episodes to a similar degree when infused prophylactically; however, individual patients may respond better to one agent over the other at any given time. The international immune tolerance trial revealed that a high-dose factor VIII regimen provided significantly better bleeding protection than the low-dose regimen. Given the high cost of treatment and the potential for a high-dose immune tolerance regimen to prevent bleeding in some patients, we discuss how we treat patients to maximize the prevention of bleeds while minimizing cost. Novel approaches to treatment of these patients are in development. These include agents that mimic factor VIII or augment thrombin generation by bypassing the inhibitor, as well as agents that inhibit the natural anticoagulants.

Baboon envelope pseudotyped lentiviral vectors efficiently transduce human B cells and allow active factor IX B cell secretion in vivo in NOD/SCIDγc-/- mice

Essentials B cells are attractive targets for gene therapy and particularly interesting for immunotherapy. A baboon envelope pseudotyped lentiviral vector (BaEV-LV) was tested for B-cell transduction. BaEV-LVs transduced mature and plasma human B cells with very high efficacy. BaEV-LVs allowed secretion of functional factor IX from B cells at therapeutic levels in vivo.

SUMMARY

Background B cells are attractive targets for gene therapy for diseases associated with B-cell dysfunction and particularly interesting for immunotherapy. Moreover, B cells are potent protein-secreting cells and can be tolerogenic antigen-presenting cells. Objective Evaluation of human B cells for secretion of clotting factors such as factor IX (FIX) as a possible treatment for hemophilia. Methods We tested here for the first time our newly developed baboon envelope (BaEV) pseudotyped lentiviral vectors (LVs) for human (h) B-cell transduction following their adaptive transfer into an NOD/SCIDγc-/- (NSG) mouse. Results Upon B-cell receptor stimulation, BaEV-LVs transduced up to 80% of hB cells, whereas vesicular stomatitis virus G protein VSV-G-LV only reached 5%. Remarkably, BaEVTR-LVs permitted efficient transduction of 20% of resting naive and 40% of resting memory B cells. Importantly, BaEV-LVs reached up to 100% transduction of human plasmocytes ex vivo. Adoptive transfer of BaEV-LV-transduced mature B cells into NOD/SCID/γc-/- (NSG) [non-obese diabetic (NOD), severe combined immuno-deficiency (SCID)] mice allowed differentiation into plasmablasts and plasma B cells, confirming a sustained high-level gene marking in vivo. As proof of principle, we assessed BaEV-LV for transfer of human factor IX (hFIX) into B cells. BaEV-LVs encoding FIX efficiently transduced hB cells and their transfer into NSG mice demonstrated for the first time secretion of functional hFIX from hB cells at therapeutic levels in vivo. Conclusions The BaEV-LVs might represent a valuable tool for therapeutic protein secretion from autologous B cells in vivo in the treatment of hemophilia and other acquired or inherited diseases.

Altered collagen turnover in factor VIII-deficient rats with hemophilic arthropathy identifies potential novel serological biomarkers in hemophilia

Essentials Joint bleeding in hemophilia may induce significant remodeling of the extracellular matrix. Biomarkers of collagen turnover were investigated in a F8-/- rat model of hemophilic arthropathy. Biomarkers of cartilage degradation increased significantly during development of arthropathy. Basement membrane and interstitial matrix turnover changed significantly following hemarthrosis.

SUMMARY

Background Hemophilic arthropathy is a severe complication of hemophilia. It is caused by recurrent bleeding into joint cavities, which leads to synovial inflammation, fibrosis, cartilage degradation and bone remodeling. Extracellular matrix remodeling of affected tissues is a hallmark of these pathological processes. Objectives The aim of this study was to use serological biomarkers of collagen turnover to evaluate extracellular matrix remodeling in a factor VIII-deficient rat model of hemophilic arthropathy. Methods F8-/- rats and wild-type littermate controls were subjected to repeated knee bleeds induced by needle puncture on days 0 and 14. Development of arthropathy was confirmed by histology after termination on day 28. Serum samples were collected at baseline and throughout the study and analyzed for biomarkers of collagen turnover, including collagens of the basement membrane (type IV collagen), the interstitial matrix (collagen types III, V and VI) and cartilage (type II collagen). Results In F8-/- rats, induced knee bleeding and subsequent development of arthropathy caused significant alterations in collagen turnover, measured as changes in serological biomarkers of basement membrane turnover, interstitial matrix turnover and cartilage degradation. Biomarkers of type II collagen degradation correlated significantly with cartilage degradation and degree of arthropathy. Hemophilic rats had a 50% higher turnover of the basement membrane than wild-type littermates at baseline. Conclusions Joint bleeding and hemophilic arthropathy cause changes in turnover of extracellular matrix collagens in hemophilic rats. Biomarkers of collagen turnover may be used to monitor joint bleeding and development of blood-induced joint disease in hemophilia.

Acquired FVIII and FIX Inhibitors after Pregnancy: A Case Report

Acquired hemophilia is a relatively rare clinical presentation, and most cases present with acquired FVIII inhibitor. The co-occurrence of inhibitors to multiple coagulation factors is uncommon. These autoantibodies may induce spontaneous life-threatening bleeding in patients who have had no previous bleeding disorder. Herein, we present a patient with postpartum acquired FVIII and FIX inhibitors who developed intramuscular hematoma and hemothorax during follow-up. She was then treated with activated prothrombin complex concentrate and methylprednisolone.

Soy Phosphatidylinositol-Containing Lipid Nanoparticle Prolongs the Plasma Survival and Hemostatic Efficacy of B-domain-Deleted Recombinant Canine Factor VIII in Hemophilia A Dogs

Soy phosphatidylinositol (PI)-containing lipid nanoparticles prolong plasma survival, improve hemostatic efficacy, and decrease immunogenicity of human B-domain-deleted factor VIII (BDD FVIII) in hemophilia A (HA) mice. We hypothesize that PI-associated BDD FVIII is more potent than the free protein and, using mathematical modeling, have projected that PI-associated BDD FVIII could be used for once-weekly prophylactic dosing in patients. To facilitate translation to the clinic, comparative plasma survival and ex vivo efficacy of PI-associated recombinant canine FVIII (PI-rcFVIII) were evaluated in HA dogs. Two HA dogs were administered a 50-U/kg intravenous dose of free or PI-rcFVIII. rcFVIII activity measurements and ex vivo efficacy analyses such as whole blood clotting time and thromboelastography were conducted on recovered plasma and whole blood samples. PI association decreased clearance (∼25%) and increased plasma exposure (∼1.4-fold) of rcFVIII. PI-rcFVIII-treated animals had prolonged improvements in whole blood clotting time and thromboelastography parameters compared to free rcFVIII-treated animals. Because rcFVIII is a BDD form of FVIII, these studies provide proof of principle that observations with human BDD FVIII in mice translate to higher animal species. In addition, PI-rcFVIII has potential applications in canine HA management and as a bypass therapy in inhibitor-positive HA patients.

Factor VIII chromogenic assays can be used for potency labeling and postadministration monitoring of N8-GP

Essentials Chromogenic assays may be less variable than one-stage clot assays for measuring modified factor VIII. Chromogenic assays were evaluated for N8-GP potency labeling and postadministration monitoring. There was no significant difference between chromogenic assay kits for measuring N8-GP potency. Postadministration monitoring of N8-GP was comparable to turoctocog alfa for all kits tested.

SUMMARY

Background Factor VIII activity (

FVIII

C) is commonly measured using one-stage activated partial thromboplastin time (aPTT)-based clot assays. Chromogenic assays are, however, an alternative, and potency assessment in Europe is performed using chromogenic assays. One-stage clot assays are in general associated with high variability, and modified FVIII products may add to this variability. FVIII chromogenic assays may be less affected. Objectives To evaluate available chromogenic assay kits for potency labeling of polyethylene glycol-glycoconjugated turoctocog alfa (turoctocog alfa pegol [N8-GP]) and to evaluate selected chromogenic kits for postadministration monitoring of N8-GP using turoctocog alfa (Novoeight(®) ) as comparator. Methods Six FVIII chromogenic assay kits were adapted to the European Pharmacopeia guidelines for potency labeling, including assessment of time to 50% FX activation. Four kits were adapted for postadministration monitoring using an ACL(®) TOP 500 analyzer. Severe hemophilia A plasma was spiked with N8-GP or turoctocog alfa to simulate postadministration samples. The World Health Organization (WHO) 8th International Standard (IS) FVIII concentrate was used as calibrator throughout. In addition, a plasma calibrator was used for postadministration samples. Results When measuring N8-GP potency, no significant difference using a 1% significance level was observed between kits. In simulated postadministration samples, all test kits were highly accurate and precise, except at low concentrations, with no significant difference between

FVIII

C (P > 0.05) measured using the different calibrators. However, values obtained using the WHO 8th IS were closer to labeled values. Conclusions Chromogenic assay kits tested measured consistent

FVIII

C for N8-GP potency and showed comparable results for N8-GP and turoctocog alfa in simulated postadministration samples.

Tailoring hemostatic therapies to lower inhibitor development in previously untreated patients with severe hemophilia A

After technological progress provided safer therapeutic products for patients with hemophilia A, the development of alloantibodies (inhibitors) neutralizing the coagulant activity of infused factor VIII (FVIII) remains the most serious complication of replacement therapy, predisposing patients to greater morbidity and causing higher treatment costs. The pathogenesis of inhibitors, which develop at a high rate in previously untreated children with severe hemophilia A, is multifactorial, resulting from complex interactions between genetic and environmental factors. Among non-genetic determinants, a key role is played by treatment-related factors, including the source of FVIII product (i.e., plasma derived or recombinant) and the mode of replacement therapy delivery (i.e., intensity, prophylaxis vs. on demand). We review the potential interventions on these modifiable factors that may help to lower the rate of inhibitor development. In addition, interest is currently directed toward the potential for lesser immunogenicity of novel hemostatic agents designed to decrease the dosing frequency or avoid/delay the need of FVIII replacement therapy.

Overestimation of N-glycoPEGylated factor IX activity in a one-stage factor IX clotting assay owing to silica-mediated premature conversion to activated factor IX

Essentials Nonacog beta pegol (N9-GP) activity is overestimated in clot method using silica-based reagents. Mimicking contact activation phase with silica reveals N9-GP activation before recalcification. Localization of N9-GP to silica facilitates activation by factor XIa and plasma kallikrein. Silica-based reagents to be used with caution when monitoring N9-GP therapy using clot method.

SUMMARY

Background Clinical laboratories routinely quantify factor IX (FIX) activity by measurement of the activated partial thromboplastin time (APTT) in a one-stage (OS) clotting assay. This assay can be performed with any of a plethora of differently composed APTT reagents, giving variable recovery when applied to nonacog beta pegol (N9-GP), an N-glycoPEGylated recombinant FIX. Objective To identify the cause of observed overestimations of N9-GP activity in an OS FIX clotting assay when most APTT reagents containing silica are used as the contact activator, and to elucidate the underlying mechanism. Methods Experiments mimicking the contact activation and clotting phases of the OS assay, combined with the use of plasmas with various deficiencies, were employed to shed light on the unique behavior of N9-GP. Confirmatory activations of N9-GP with purified enzymes and physical adsorption to silica particles were studied, and the influence of free polyethylene glycol (PEG) on these processes was investigated. Results N9-GP, but not native FIX, added to FIX-deficient plasma was prematurely converted to activated FIX (FIXa) during the contact activation phase of the clotting assay. Activated FXI (FXIa) and plasma kallikrein (PK) were responsible for the activation of N9-GP, an event that appeared to require the presence of a silica-containing APTT reagent. PEG-dependent adsorption of N9-GP to silica particles could be demonstrated. Conclusions The PEG moiety mediates colocalization of N9-GP with its activators FXIa and PK on silica surfaces, thereby facilitating premature conversion of N9-GP to FIXa during the contact activation phase, and leading to overestimation of the FIX activity in the OS clotting assay.

Thrombosis in Hemophiliacs with Prothrombotic Molecular Defect

Thrombosis in hemophiliacs is a very unusual event mostly reported in patients treated with concentrates containing large quantities of activated coagulation factors. A patient with hemophilia A is reported who had an acute myocardial infarction and in whom investigation for hereditary thrombophilia showed a prothrombotic molecular defect, the G20210A prothrombin mutation.

Severe Hemophilia and Physiologic Inhibitors of Coagulation

Patients with hemophilia demonstrate quite variable clinical phenotype even in cases with the same level of deficient factor or the same molecular abnormality. Different interacting factors including congenital and acquired alterations of coagulation inhibitors can modulate both clinical expression and severity of hemophilia. In this study, plasma levels of factor VIII (FVIII), factor IX (FIX) as well as protein C (PC), protein S (PS), and antithrombin (AT) plasma levels were measured in 80 patients with severe hemophilia A and B. Patients were divided into two groups according to the risk of bleeding: the first group (n = 32) with mild bleeding (< 2 bleeds/year), and the second group (n = 48) with severe bleeding (≥ 2 bleeds/year). Both hemophilia groups showed significantly decreased PC plasma levels compared to levels in healthy control subjects (the first group: p < 0.0001 and second group: p < 0.01). The difference in PC plasma levels between the first and second hemophilia group was significant (p < 0.05). Moreover, there was positive correlation between age and the functional PC in both hemophilia groups. Our results suggest that decreased PC plasma levels can testify to a slightly protective effect of the PC pathway on the severity and frequency of bleeding in patients with severe hemophilia A and B.

Fetal Gender Determination and BclI Polymorphism Using Nucleated Erythrocytes in Maternal Blood

This study demonstrated determination of fetal gender from nucleated red blood cells (NRBCs) in maternal blood and attempted to apply prenatal diagnosis of hemophilia A using BclI DNA polymorphism. Venous blood was drawn from 20 pregnant women, and NRBCs were recovered by magnetic activated cell sorting and anti-GPA (glycophorin A) immunostaining. After microdissector isolation of the NRBCs, primer extension preamplification (PEP) and nested PCR of the amelogenin gene were performed to determine fetal gender. We also performed PEP and nested PCR of BclI polymorphism to verify the validity of prenatal diagnosis of hemophilia A. DNA amplification was achieved in 107 cells (51.9%) and fetal gender determined with 65.0% accuracy. Unfortunately, we could not verify the validity within the scope of this study. However, in a larger number of cases that are informative in BclI polymorphism, we will be able to identify patients affected by hemophilia A using fetal NRBCs in maternal blood.