Life in the shadow of a dominant partner: the FVIII-VWF association and its clinical implications for hemophilia A

Heterogeneity in the half-life of factor VIII concentrate in patients with hemophilia A is due to variability in the clearance of endogenous von Willebrand factor

BACKGROUND

Previous studies have reported marked interindividual variation in factor VIII (FVIII) clearance in patients with hemophilia (PWH) and proposed a number of factors that influence this heterogeneity.

OBJECTIVES

To investigate the importance of the clearance rates of endogenous von Willebrand factor (VWF) compared with those of other FVIII half-life modifiers in adult PWH.

METHODS

The half-life of recombinant FVIII was determined in a cohort of 61 adult PWH. A range of reported modifiers of FVIII clearance was assessed (including plasma VWF:antigen and VWF propeptide levels; VWF-FVIII binding capacity; ABO blood group; and nonneutralizing anti-FVIII antibodies). The FVIII-binding region of the VWF gene was sequenced. Finally, the effects of variation in FVIII half-life on clinical phenotype were investigated.

RESULTS

We demonstrated that heterogeneity in the clearance of endogenous plasma VWF is a key determinant of variable FVIII half-life in PWH. Both ABO blood group and age significantly impact FVIII clearance. The effect of ABO blood group on FVIII half-life in PWH is modulated entirely through its effect on the clearance rates of endogenous VWF. In contrast, the age-related effect on FVIII clearance is, at least in part, VWF independent. In contrast to previous studies, no major effects of variation in VWF-FVIII binding affinity on FVIII clearance were observed. Although high-titer immunoglobulin G antibodies (≥1:80) were observed in 26% of PWH, these did not impact FVIII half-life. Importantly, the annual FVIII usage (IU/kg/y) was significantly (p = .0035) increased in patients with an FVIII half-life of <12 hours.

CONCLUSION

Our data demonstrate that heterogeneity in the half-life of FVIII concentrates in patients with hemophilia A is primarily attributable to variability in the clearance of endogenous VWF.

Genetic determinants of enhanced von Willebrand factor clearance from plasma

BACKGROUND

Enhanced von Willebrand factor (VWF) clearance from plasma is associated with von Willebrand disease (VWD). However, the genetic background of this disease mechanism is not well defined.

OBJECTIVE

To determine VWF variants that are associated with reduced VWF survival.

METHODS

Two hundred fifty-four patients with VWD (type 1 = 50 and type 2 = 204) were investigated, and the results were compared with 120 healthy controls. The patients were comprehensively characterized for phenotypic and genetic features. The ratio of VWF propeptide (VWFpp)/VWF antigen (VWFpp ratio) was used to establish in each patient the VWF clearance state.

RESULTS

Out of 92 variants associated with type 1 (7 were novel) and type 2 VWD, 19 had a VWFpp ratio ranging from 1.7 to 2.2, 24 had a VWFpp ratio between 2.3 and 2.9, and 24 variants had a ratio of ≥3. The VWFpp median ratio in healthy controls was 0.98 (0.55-1.6) so that a cut-off value of >1.6 was considered an indicator of accelerated VWF clearance from plasma. An enhanced VWF clearance was observed in 34% of type 1 cases, 100% of type 1 Vicenza cases, 81% of 2A cases, 77% of 2B cases, 88% of 2M cases, and 36% of 2N cases.

CONCLUSIONS

An accelerated VWF clearance was found in most patients with type 2A, 2B, and 2M VWD, with a lower proportion of type 1 and 2N. Sixty-seven different variants alone or in combination with other variants were associated with an increased VWFpp ratio. The variants with the highest VWFpp ratio were mostly located in the D3-A1 VWF domains.

Biological activity of a new recombinant human coagulation factor VIII and its efficacy in a small animal model

Deficiency in human coagulation factor VIII (FVIII) causes hemophilia A (HA). Patients with HA may suffer from spontaneous bleeding, which can be life-threatening. Recombinant FVIII (rFVIII) is an established treatment and prevention agent for bleeding in patients with HA. Human plasma-derived FVIII (pdFVIII), commonly used in clinical practice, is relatively difficult to prepare. In this study, we developed a novel B-domain-deleted rFVIII, produced and formulated without the use of animal or human serum-derived components. rFVIII promoted the generation of activated factor X and downstream thrombin, and, similar to that of other available FVIII preparations, its activity was inhibited by FVIII inhibitors. In addition, rFVIII has ideal binding affinity to human von Willebrand factor. Activated FVIII (FVIIIa) could be degraded by activated protein C and lose its procoagulant activity. In vitro, commercially available recombinant FVIII (Xyntha) and pdFVIII were used as controls, and there were no statistical differences between rFVIII and commercial FVIII preparations, which demonstrates the satisfactory efficacy and potency of rFVIII. In vivo, HA mice showed that infusion of rFVIII rapidly corrected activated partial thromboplastin time, similar to Xyntha. Moreover, different batches of rFVIII were comparable. Overall, our results demonstrate the potential of rFVIII as an effective strategy for the treatment of FVIII deficiency.

Polyphosphate Activates von Willebrand Factor Interaction with Glycoprotein Ib in the Absence of Factor VIII In Vitro

Polyphosphate (polyP), a phosphate polymer released by activated platelets, may modulate various stages of hemostasis by binding to blood proteins. In this context, we previously reported that polyP binds to the von Willebrand factor (VWF). One of the most significant functions of VWF is to bind to and protect the blood circulating Factor VIII (FVIII). Therefore, here, we study the role of polyP in the VWF-FVIII complex in vitro and suggest its biological significance. Surface plasmon resonance and electrophoretic mobility assays indicated that polyP binds dynamically to VWF only in the absence of FVIII. Using the VWF Ristocetin Cofactor assay, the most accepted method for studying VWF in platelet adhesion, we found that polyP activates this role of VWF only at low levels of FVIII, such as in plasmas with chemically depleted FVIII and plasmas from severe hemophilia A patients. Moreover, we demonstrated that FVIII competes with polyP in the activation of VWF. Finally, polyP also increases the binding of VWF to platelets in samples from patients with type 2 and type 3 von Willebrand disease. We propose that polyP may be used in designing new therapies to activate VWF when FVIII cannot be used.

Early stage clinical trials for the treatment of hemophilia A

INTRODUCTION

Hemophilia A is a severe bleeding disorder affecting about 1 in 5,000 males. The gold standard for prophylaxis and treatment of acute bleeding has been factor (F) VIII concentrate. A multitude of treatment modalities are now available and under clinical investigation.

AREAS COVERED

This review discusses ongoing/recently completed early-phase clinical trials registered on ClinicalTrials.gov in patients with hemophilia A through April 2022. These new pipeline therapies are focused on addressing the safety and efficacy of new factor-related products, non-factor related products, and gene therapy options for hemophilia.

EXPERT OPINION

Current standard of care effectively prevents and treats acute bleeding and has significantly improved the quality of life in hemophilia. The biggest challenges in the improvement of care are treatment-related burden and the burden of cost in developing countries. New drugs under development are likely to enter practice by the end of this decade and address many of the unmet needs particularly of those with severe disease. Data is limited in unique populations (e.g. congenital/inherited FVIII inhibitors, non-severe hemophilia A, women/girls with hemophilia and children) which are important areas for future research; additional clinical trials and long-term outcome data are necessary prior to incorporating these new therapies in our treatment arsenal.

The VWF binding aptamer rondoraptivon pegol increases platelet counts and VWF/FVIII in type 2B von Willebrand disease

Type 2B von Willebrand disease (VWD) is characterized by an increased binding affinity of von Willebrand factor (VWF) to platelet glycoprotein Ib. This can lead to clearance of high-molecular-weight (HMW) multimers and thrombocytopenia with a resulting moderate-severe bleeding phenotype. Rondoraptivon pegol (BT200) is a pegylated aptamer binding to the A1 domain of VWF with a novel mechanism of action: it enhances VWF/factor VIII (FVIII) levels by decreasing their clearance. To study the potential benefit of rondoraptivon pegol in patients with type 2B VWD, we conducted a prospective phase 2 trial. Patients with type 2B VWD received 3 mg rondoraptivon pegol subcutaneously on study days 1, 4, and 7, followed by 6 to 9 mg every week until day 28. Five patients (male:female ratio = 3:2) were included. Rondoraptivon pegol rapidly tripled platelet counts from a median of 60 to 179 × 10E9/L (P < .001). Circulating VWF antigen increased from a median of 64% to 143%, which doubled FVIII activity levels from 67% to 134%. In all thrombocytopenic patients, plasma levels of VWF:GPIbM normalized, VWF ristocetin cofactor and VWF collagen-binding activity increased, and HMW multimers appeared. These pronounced improvements reversed during washout of the drug, thus demonstrating causality. The A1 domain binding aptamer directly corrects the underlying defect of type 2B VWD, thus providing a novel potential option for prophylaxis and treatment of patients with this VWD type. These data provide the basis for a phase 2b/3 trial in such patients. This trial was registered at www.clinicaltrials.gov as #NCT04677803.

The More Recent History of Hemophilia Treatment

The availability first in the 1970s of plasma-derived and then in the 1990s of recombinant clotting factor concentrates represented a milestone in hemophilia care, enabling not only treatment of episodic bleeding events but also implementation of prophylactic regimens. The treatment of hemophilia has recently reached new landmarks. The traditional clotting factor replacement therapy for hemophilia has been substituted over the last 10 years by novel treatments such as bioengineered factor VIII and IX molecules with extended half-life and non-factor treatments including the bispecific antibody emicizumab. This narrative review is dedicated to these newer therapies, which are contributing significantly to improving the long-term management of prophylaxis in hemophilia patients. Another section is focused on the current state of gene therapy, which is a promising definitive cure for severe hemophilia A and B.

In-Silico Characterization of von Willebrand Factor Bound to FVIII

Factor VIII belongs to the coagulation cascade and is expressed as a long pre-protein (mature form, 2351 amino acids long). FVIII is deficient or defective in hemophilic A patients, who need to be treated with hemoderivatives or recombinant FVIII substitutes, i.e., biologic drugs. The interaction between FVIII and von Willebrand factor (VWF) influences the pharmacokinetics of FVIII medications. In vivo, full-length FVIII (FL-FVIII) is secreted in a plasma-inactive form, which includes the B domain, which is then proteolyzed by thrombin protease activity, leading to an inactive plasma intermediate. In this work, we analyzed through a computational approach the binding of VWF with two structure models of FVIII (secreted full-length with B domain, and B domain-deleted FVIII). We included in our analysis the atomic model of efanesoctocog alfa, a novel and investigational recombinant FVIII medication, in which the VWF is covalently linked to FVIII. We carried out a structural analysis of VWF/FVIII interfaces by means of protein–protein docking, PISA (Proteins, Interfaces, Structures and Assemblies), and protein contact networks (PCN) analyses. Accordingly, our computational approaches to previously published experimental data demonstrated that the domains A3-C1 of B domain-deleted FVIII (BDD-FVIII) is the preferential binding site for VWF. Overall, our computational approach applied to topological analysis of protein–protein interface can be aimed at the rational design of biologic drugs other than FVIII medications.

Efanesoctocog alfa elicits functional clot formation that is indistinguishable to that of recombinant factor VIII

BACKGROUND

Factor VIII (FVIII) binding to endogenous von Willebrand factor (VWF) has constrained half-life extension of recombinant FVIII (rFVIII) products for hemophilia A. Efanesoctocog alfa (rFVIIIFc-VWF-XTEN; BIVV001) is a novel fusion protein designed to decouple FVIII from VWF in circulation and maximize half-life prolongation by XTEN® polypeptides and Fc fusion. FVIII, VWF, and platelets interact to achieve normal hemostasis. Thus, bioengineered FVIII replacement products, such as efanesoctocog alfa, require comprehensive assessment of their hemostatic potential.

OBJECTIVES

We compared functional clot formation and injury-induced platelet accumulation between efanesoctocog alfa and rFVIII.

PATIENTS/METHODS

The hemostatic potential of efanesoctocog alfa and rFVIII were assessed by measuring their dose-dependent effects on in vitro fibrin generation in hemophilic plasma and in vivo injury-induced platelet accumulation using intravital microscopy and repeat saphenous vein laser-induced injuries in hemophilia A mice.

RESULTS

Equal concentrations of efanesoctocog alfa or rFVIII (up to 1 IU/ml) added to plasma from patients with hemophilia A elicited similar kinetics for dose-dependent fibrin polymerization between factor products. In the presence of tissue plasminogen activator (tPA), clots formed had similar stability between products. Single intravenous doses (50, 100, or 150 IU/kg) of efanesoctocog alfa or rFVIII shortly before repeat saphenous vein laser-induced injuries increased platelet accumulation over time in a dose-dependent manner in hemophilia A mice. Platelet deposition kinetics were similar between products.

CONCLUSIONS

Equivalent doses of efanesoctocog alfa and rFVIII had similar efficacy in promoting fibrin clot formation and injury-induced platelet accumulation. The hemostatic potential of efanesoctocog alfa was indistinguishable from that of rFVIII.

[Coagulation diagnostics in the clinical routine-Part 1 : Evaluation of the risk of bleeding before surgery, interventions and diagnostics in bleeding diathesis]

This article on coagulation diagnostics is published in two parts covering five common clinical scenarios for coagulation diagnostics. Part 1 deals with the diagnostics prior to invasive interventions and coagulation diagnostics to clarify a tendency to bleeding. The global parameters Quick and activated partial thromboplastin time are established for monitoring certain anticoagulants; however, they are not predictive with respect to the risk of bleeding prior to elective invasive interventions. In this context, disorders of primary hemostasis are frequent, which are insufficiently detected by the global parameters. Most clinical bleeding tendencies are due to acquired causes. These include anticoagulants and diseases which can be accompanied by tendency to bleeding. For coagulation tests preanalytical issues are essential in order to avoid false results. The interpretation should always be made in the context of the current physiological state.

Does difference between label and actual potency of factor VIII concentrate affect pharmacokinetic‐guided dosing of replacement therapy in haemophilia A?

Background

Aim

Methods

Results

Conclusion

Towards novel treatment options in von Willebrand disease

Deficiency or dysfunction of von Willebrand factor (VWF) is associated with a bleeding disorder known as von Willebrand disease (VWD). The clinical manifestations of VWD are heterogeneous, and are in part dictated by the structural or functional defects of VWF. The tools to control bleeding in VWD are dominated by VWF concentrates, desmopressin and antifibrinolytic therapy. In view of these treatments being considered as effective, it is surprising that quality-of-life studies consistently demonstrate a significant mental and physical burden in VWD patients, particularly in women. Apparently, the current weaponry to support the management of VWD is insufficient to fully address the needs of the patients. It is important therefore to continue to search for innovative treatment options which could better serve the VWD patients. In this short review, two of such options are discussed in more detail: emicizumab to correct for the deficiency of factor VIII (FVIII), and the pegylated aptamer BT200 to increase endogenous levels of the VWF/FVIII complex.

Hemophilia A: Strategies for Improving Long-Term Holistic Management, Adherence, and Quality of Life

Hemophilia A is a rare inherited bleeding disorder characterized by a deficiency in factor VIII. The evolution of currently approved prophylaxis therapy in hemophilia A will be reviewed, including the clinical value of prophylaxis, real-world experience with prophylaxis, and patient quality-of-life factors that must be considered when choosing treatment options for these patients.

Impact of novel hemophilia therapies around the world

Hemophilia A and B are hereditary bleeding disorders, characterized by factor VIII or IX deficiencies, respectively. For many decades, prophylaxis with coagulation factor concentrates (replacement therapy) was the standard‐of‐care approach in hemophilia. Since the 1950s, when prophylaxis started, factor concentrates have been improved with virus inactivation and molecule modification to extend its half‐life. The past years have brought an intense revolution in hemophilia care, with the development of nonfactor therapy and gene therapy. Emicizumab is the first and only nonreplacement agent to be licensed for prophylaxis in people with hemophilia A, and real‐world data show similar efficacy and safety from the pivotal studies. Other nonreplacement agents and gene therapy have ongoing studies with promising results. Innovative approaches, like subcutaneous factor VIII and lipid nanoparticles, are in the preclinical phase. These novel agents, such as extended half‐life concentrates and emicizumab, have been available in resource‐constrained countries through the constant efforts of the World Federation of Haemophilia Humanitarian Aid Program. Despite the wide range of new approaches and therapies, the main challenge remains the same: to guarantee treatment for all. In this article, we discuss the evolution of hemophilia care, global access to hemophilia treatment, and the current and future strategies that are now under development. Finally, we summarize relevant new data on this topic presented at the ISTH 2021 virtual congress.

Efanesoctocog alfa for hemophilia A: results from a phase 1 repeat-dose study

Efanesoctocog alfa (rFVIIIFc-VWF-XTEN; BIVV001) is a new class of factor VIII (FVIII) replacement that breaks the von Willebrand factor-imposed FVIII half-life ceiling. In a phase 1/2a study, single-dose efanesoctocog alfa was well tolerated, and no safety concerns were identified. We evaluated the safety, tolerability, and pharmacokinetics of repeat-dose efanesoctocog alfa in a phase 1 study in previously treated adults (≥150 exposure days) with severe hemophilia A. Participants received 4 once weekly doses of efanesoctocog alfa (cohort 1, 50 IU/kg; cohort 2, 65 IU/kg). All enrolled participants (cohort 1, n = 10; cohort 2, n = 14) completed the study. Inhibitor development to FVIII was not detected. After the last dose of efanesoctocog alfa, geometric mean (range) FVIII activity half-life, area under the activity-time curve, and steady-state maximum concentration for cohort 1 and cohort 2 were 41.3 (34.2-50.1) and 37.3 (28.9-43.8) hours, 8290 (5810-10 300) and 11 200 (7040-15 800) hours × IU/dL, and 131 (96-191) and 171 (118-211) IU/dL, respectively. There was minimal accumulation after 4 doses. Mean FVIII activity for cohort 1 and cohort 2, respectively, was 46% and 69% on day 3 postdose and 10% and 12% on day 7 postdose. Overall, 4 once-weekly doses of efanesoctocog alfa were well tolerated, no safety concerns were identified, and no bleeds were reported during the treatment period. Once-weekly efanesoctocog alfa provided high sustained FVIII activity within the normal to near-normal range for 3 to 4 days postdose and may improve protection against bleeds in patients with hemophilia A. The trial is study 2018-001535-51 in the EU Clinical Trials Register.

The lesson learned from the new c.2547-1G>T mutation combined with p.R854Q:when a type 2N mutation reveals a quantitative von Willebrand factor defect

Type 2N is a rare von Willebrand disease (VWD) variant involving an impairment in the FVIII carrier function of von Willebrand factor (VWF). It has a phenotype that mimics hemophilia A, and FVIII binding to VWF (VWF:FVIIIB) is tested to differentiate between the two disorders. Type 2N VWF defects may also be associated with quantitative VWF mutations (type 2N/type 1), further complicating the identification of cases. We report on a new quantitative VWF mutation (c.2547-1G>T) revealed by a p.R854Q type 2N mutation acting as homozygous despite being carried as a heterozygous defect. The proband had near-normal VWF levels (initially ruling out a defective VWF synthesis) and slightly reduced FVIII levels, while a VWF:FVIIIB test showed significantly reduced binding. Routine tests on type 2N homozygotes or heterozygotes combined with quantitative VWF defects in our cohort showed reduced FVIII levels in both groups, but it was only in the former that the FVIII/VWF:Ag ratio was always significantly reduced. The two tests are therefore not enough to identify all forms of type 2N VWD. While relatives of type 2N homozygotes usually have normal FVIII levels and FVIII/VWF:Ag ratios, relatives of type 2N/type 1 may have high FVIII/VWF:Ag ratios, but their VWF:FVIIIB and/or VWF:FVIIIB/VWF:Ag ratios are always low. Measuring FVIII and VWF levels may therefore suggest type 2N VWD in patients carrying type 2N mutations alone, but not in type 2N combined with quantitative VWF defects. The VWF:FVIIIB test should consequently always be included when exploring VWF function, whatever VWD patient’s phenotype.

FVIII regulates the molecular profile of endothelial cells: functional impact on the blood barrier and macrophage behavior

Hemophilia A is an inherited X-linked recessive bleeding disorder caused by deficient activity of blood coagulation factor VIII (FVIII). In addition, hemophilia patients show associated diseases including osteopenia, altered inflammation and vascular fragility which may represent the consequence of recurrent bleeding or may be related to the direct FVIII deficiency. Nowadays, recombinant FVIII is proposed to treat hemophilia patients with no circulating FVIII inhibitor. Initially described as a coenzyme to factor IXa for initiating thrombin generation, there is emerging evidence that FVIII is involved in multiple biological systems, including bone, vascular and immune systems. The present study investigated: (i) the functional activities of recombinant human FVIII (rFVIII) on endothelial cells, and (ii) the impact of rFVIII activities on the functional interactions of human monocytes and endothelial cells. We then investigated whether rFVIII had a direct effect on the adhesion of monocytes to the endothelium under physiological flow conditions. We observed that direct biological activities for rFVIII in endothelial cells were characterized by: (i) a decrease in endothelial cell adhesion to the underlying extracellular matrix; (ii) regulation of the transcriptomic and protein profiles of endothelial cells; (iii) an increase in the vascular tubes formed and vascular permeability in vitro; and (iv) an increase in monocyte adhesion activated endothelium and transendothelial migration. By regulating vascular permeability plus leukocyte adhesion and transendothelial migration, the present work highlights new biological functions for FVIII.

Acquired Von Willebrand Syndrome and Desmopressin Resistance During Venovenous Extracorporeal Membrane Oxygenation in Patients With COVID-19

OBJECTIVES

Although COVID-19 is associated with high von Willebrand factor (vWF) parameters promoting thrombosis, venovenous extracorporeal membrane oxygenation (vvECMO) is associated with the development of acquired von Willebrand syndrome (AVWS) promoting bleeding. This study was designed to assess both the incidence and severity of AVWS in COVID-19 patients undergoing vvECMO, and the benefit of comprehensive vWF analyses.

DESIGN

Prospective observational study.

SETTING

ICU at a tertiary-care center.

PATIENTS

Twenty-seven consecutive COVID-19 patients with acute respiratory distress syndrome (ARDS) requiring vvECMO.

MEASUREMENTS AND MAIN RESULTS

Comprehensive vWF analyses (including sodium dodecyl-sulfate polyacrylamide gel electrophoresis) were performed before, during, and after vvECMO. In a subgroup of 12 patients with AVWS, effectiveness of treatment with desmopressin was assessed. The patients' mean age was 53 years (range, 23-73), 70% were male, and all had various comorbidities. Following markedly elevated vwf antigen (vWF: Ag; mean, 546% ( sd , 282]), vWF collagen binding capacity (mean, 469% [ sd , 271]), vWF activity (vWF:A; mean, 383% [ sd , 132]), and factor VIII activity (mean, 302% [ sd , 106]), and only borderline decreases in high-molecular-weight (HMW) vWF multimers before vvECMO, all of these variables decreased and HMW vWF multimers became undetectable within hours following initiation of vvECMO. All variables fully recovered within 3-38 hours after discontinuation of vvECMO. During vvECMO, decreases in the vWF:A/vWF:Ag ratio correlated with absent HMW vWF multimers. Desmopressin did not affect vWF parameters.

CONCLUSIONS

In patients with COVID-19-associated ARDS, AVWS developed soon after initiation of vvECMO. The vWF:A/vWF:Ag ratio was a suitable screening test for AVWS. As desmopressin was ineffective, bleeding during vvECMO-associated AVWS should preferably be treated with concentrates containing vWF.

Managing Severe Hemophilia A in Children: Pharmacotherapeutic Options

Hemophilia A is the most common severe inherited bleeding disorder in males. Initial treatment strategies focused on the use of factor concentrates to prevent joint bleeding and the development of long-term crippling arthropathy. The current standard of care has evolved from regular replacement of factor VIII concentrates which has significantly improved the quality of life for those with severe disease to include and consider novel therapies that augment or bypass the hemostatic pathway (ie, emicizumab, Mim8). Other pipeline therapies that suppress specific natural anticoagulant pathways (ie, antithrombin, TFPI) to reestablish hemostatic balance are under Phase 3 trial investigation. These novel therapeutics have allowed providers more variety in dosing regimens and ease of administration while also maintaining effective bleeding prevention. The possibility of "curative" gene therapy is under exploration, with ongoing clinical trials in adult males.

A proximity-based in silico approach to identify redox-labile disulfide bonds: The example of FVIII

Allosteric disulfide bonds permit highly responsive, transient 'switch-like' properties that are ideal for processes like coagulation and inflammation that require rapid and localised responses to damage or injury. Haemophilia A (HA) is a rare bleeding disorder managed with exogenous coagulation factor(F) VIII products. FVIII has eight disulfide bonds and is known to be redox labile, but it is not known how reduction/oxidation affects the structure-function relationship, or its immunogenicity-a serious complication for 30% severe HA patients. Understanding how redox-mediated changes influence FVIII can inform molecular engineering strategies aimed at improving activity and stability, and reducing immunogenicity. FVIII is a challenging molecule to work with owing to its poor expression and instability so, in a proof-of-concept study, we used molecular dynamics (MD) to identify which disulfide bonds were most likely to be reduced and how this would affect structure/function; results were then experimentally verified. MD identified Cys1899-Cys1903 disulfide as the most likely to undergo reduction based on energy and proximity criteria. Further MD suggested this reduction led to a more open conformation. Here we present our findings and highlight the value of MD approaches.

A novel mouse model of type 2N VWD was developed by CRISPR/Cas9 gene editing and recapitulates human type 2N VWD

A novel type 2N VWD mouse model was established in which VWF is incapable of binding FVIII but is otherwise fully functional.

VWF^2N/2N mice exhibited a severe bleeding phenotype after tail tip amputation but not in lateral tail vein or ventral artery injury models.

Type 2N von Willebrand disease is caused by mutations in the factor VIII (FVIII) binding site of von Willebrand factor (VWF), resulting in dysfunctional VWF with defective binding capacity for FVIII. We developed a novel type 2N mouse model using CRISPR/Cas9 technology. In homozygous VWF^2N/2N mice, plasma VWF levels were normal (1167 ± 257 mU/mL), but the VWF was completely incapable of binding FVIII, resulting in 53 ± 23 mU/mL of plasma FVIII levels that were similar to those in VWF-deficient (VWF^−/−) mice. When wild-type human or mouse VWF was infused into VWF^2N/2N mice, endogenous plasma FVIII was restored, peaking at 4 to 6 hours post-infusion, demonstrating that FVIII expressed in VWF^2N mice is viable but short-lived unprotected in plasma due to dysfunctional 2N VWF. The whole blood clotting time and thrombin generation were impaired in VWF^2N/2N but not in VWF^−/− mice. Bleeding time and blood loss in VWF^2N/2N mice were similar to wild-type mice in the lateral tail vein or ventral artery injury model. However, VWF^2N/2N mice, but not VWF^−/− mice, lost a significant amount of blood during the primary bleeding phase after a tail tip amputation injury model, indicating that alternative pathways can at least partially restore hemostasis when VWF is absent. In summary, we have developed a novel mouse model by gene editing with both the pathophysiology and clinical phenotype found in severe type 2N patients. This unique model can be used to investigate the biological properties of VWF/FVIII association in hemostasis and beyond.

Osteonecrosis of the Jaws in Patients with Hereditary Thrombophilia/Hypofibrinolysis-From Pathophysiology to Therapeutic Implications

Osteonecrosis of the jaws (ONJ) usually has a clear etiology. Local infection or trauma, radiotherapy and drugs that disrupt the vascular supply or bone turnover in the jaws are its major contributors. The thrombotic occlusion of the bone's venous outflow that occurs in individuals with hereditary thrombophilia and/or hypofibrinolysis has a less known impact on jaw health and healing capability. Our research provides the most comprehensive, up-to-date and systematized information on the prevalence and significance of hereditary thrombophilia and/or hypofibrinolysis states in ONJ. We found that hereditary prothrombotic abnormalities are common in patients with ONJ refractory to conventional medical and dental treatments. Thrombophilia traits usually coexist with hypofibrinolysis traits. We also found that frequently acquired prothrombotic abnormalities coexist with hereditary ones and enhance their negative effect on the bone. Therefore, we recommend a personalized therapeutic approach that addresses, in particular, the modifiable risk factors of ONJ. Patients will have clear benefits, as they will be relieved of persistent pain and repeated dental procedures.

Tissue dynamics of von Willebrand factor characterized by a novel fluorescent protein-von Willebrand factor chimera

BACKGROUND

Tissue dynamics of von Willebrand factor (VWF) that are vital to its biological function have not been fully characterized.

OBJECTIVE

To develop a new fluorescent protein--VWF chimera (FP-VWF) that has similar hematologic function to wild-type VWF and use it to monitor the tissue dynamics of VWF distribution.

METHODS

Genotyping, platelet counting, tail bleeding time assay, agarose gels, western blot, platelet aggregation, proteolytic analysis, and ELISA were applied in characterizing the function of FP-VWF; fluorescence spectrometer and confocal fluorescence microscope were used to monitor the plasma and tissue distribution of FP-VWF.

RESULTS

The transgenic mice that carry the FP-VWF retain hematologic activity of VWF with plasma levels of FP-VWF reduced by 50% and there are reduced high molecular weight FP-VWF multimers compared to the wild-type mice. The GPIb-binding and ADAMTS-13 (A Disintegrin and Metalloprotease with ThrombSpondin type 1 motif, member 13) proteolytic efficiency of FP-VWF are similar to wild-type VWF. The tissue distribution of FP-VWF was probed directly through its intrinsic fluorescence at normal or stimulated status, which indicated that the medicine-stimulated endogenous FP-VWF seems primarily released from the aorta and cleared in the spleen. Similar results were observed in non-fluorescent mice through a standard immunofluorescence approach. The fluorescence signals of FP-VWF were also similar to the standard dye-based approach in detecting the FeCl3 -induced blood clotting in vivo.

CONCLUSIONS

Together, these results suggest that this novel FP-VWF chimera is valuable in probing the tissue dynamics of VWF in quite a few biological and pharmaceutical applications.

Stepwise PEG synthesis featuring deprotection and coupling in one pot

The stepwise synthesis of monodisperse polyethylene glycols (PEGs) and their derivatives usually involves using an acid-labile protecting group such as DMTr and coupling the two PEG moieties together under basic Williamson ether formation conditions. Using this approach, each elongation of PEG is achieved in three steps - deprotection, deprotonation and coupling - in two pots. Here, we report a more convenient approach for PEG synthesis featuring the use of a base-labile protecting group such as the phenethyl group. Using this approach, each elongation of PEG can be achieved in two steps - deprotection and coupling - in only one pot. The deprotonation step, and the isolation and purification of the intermediate product after deprotection using existing approaches are no longer needed when the one-pot approach is used. Because the stepwise PEG synthesis usually requires multiple PEG elongation cycles, the new PEG synthesis method is expected to significantly lower PEG synthesis cost.

Clinical Utility of Subcutaneous Factor VIII Replacement Therapies in Hemophilia A: A Review of the Evidence

Hemophilia therapies have tremendously improved over the last decades with the development of prolonged half-life factor VIII (FVIII) and FIX concentrates, non-factor therapies, such as emicizumab, anti-TFPI antibodies or siRNA antithrombin and gene therapy. All of these new molecules significantly reduced the burden of the disease and improved the quality of life of patients with severe hemophilia. Emicizumab, a non-factor therapy, is currently the only subcutaneous molecule available for prophylactic treatment of severe hemophilia A. Because of the subcutaneous route of delivery and similar efficacy to FVIII replacement therapy, emicizumab has been rapidly adopted by patients and their families. This clinical observation emphasizes the relevance and need for the development of subcutaneous FVIII concentrates. Here, we report evidence-based advantages and interest in the subcutaneous route of administration for the treatment of hemophilia A and review the stages of development of the different subcutaneous FVIII molecules.

Increased potency of recombinant VWF D'D3 albumin fusion proteins engineered for enhanced affinity for coagulation factor VIII

BACKGROUND

We have recently reported on a recombinant von Willebrand factor (VWF) D'D3 albumin fusion protein (rD'D3-FP) developed to extend the half-life of coagulation factor VIII (FVIII) for the treatment of hemophilia A. Based on predictive modelling presented in this study, we hypothesized that modifying rD'D3-FP to improve FVIII interaction would reduce exchange with endogenous VWF and provide additional FVIII half-life benefit.

OBJECTIVES

The aim of this study was to identify novel rD'D3-FP variants with enhanced therapeutic efficacy in extending FVIII half-life.

METHODS

Through both directed mutagenesis and random mutagenesis using a novel mammalian display platform, we identified novel rD'D3-FP variants with increased affinity for FVIII (rVIII-SingleChain) under both neutral and acidic conditions and assessed their ability to extend FVIII half-life in vitro and in vivo.

RESULTS

In rat preclinical studies, rD'D3-FP variants with increased affinity for FVIII displayed enhanced potency, with reduced dose levels required to achieve equivalent rVIII-SingleChain half-life extension. In cell-based imaging studies in vitro, we also demonstrated reduced dissociation of rVIII-SingleChain from the rD'D3-FP variants within acidic endosomes and more efficient co-recycling of the rD'D3-FP/rVIII-SingleChain complex via the FcRn recycling system.

CONCLUSIONS

In summary, at potential clinical doses, the rD'D3-FP variants provide marked benefits with respect to dose levels and half-life extension of co-administered FVIII, supporting their development for use in the treatment of hemophilia A.

Stabilin-2 deficiency increases thrombotic burden and alters the composition of venous thrombi in a mouse model

BACKGROUND

Stabilin-2 is an endocytic scavenger receptor that mediates the clearance of glycosaminoglycans, phosphatidylserine-expressing cells, and the von Willebrand factor-factor VIII (FVIII) complex. In a genome-wide screening study, pathogenic loss-of-function variants in the human STAB2 gene associated with an increased incidence of unprovoked venous thromboembolism (VTE). However, the specific mechanism(s) by which stabilin-2 deficiency influences the pathogenesis of VTE is unknown.

OBJECTIVES

The aim of this study was to assess the influence of stabilin-2 on deep vein thrombosis (DVT) and to characterize the underlying prothrombotic phenotype of stabilin-2 deficiency in a mouse model.

METHODS

DVT was induced using the inferior vena cava (IVC) stenosis model in two independent cohorts (littermates and non-littermates) of wild-type (Stab2+/+ ) and stabilin-2 (Stab2-/- )-deficient mice. Thrombus structure and contents were quantified by immunohistochemistry. Plasma procoagulant activity was assessed and complete blood counts were performed.

RESULTS

Incidence of thrombus formation was not altered between Stab2+/+ and Stab2-/- mice. When thrombi were formed, Stab2-/- mice developed significantly larger thrombi than Stab2+/+ controls. Thrombi from Stab2-/- mice contained significantly more leukocytes and citrullinated histone H3 than Stab2+/+ thrombi. Stab2-/- mice had increased FVIII activity. Circulating levels of monocytes and granulocytes were significantly elevated in Stab2-/- mice, and Stab2-/- mice had elevated plasma cell-free DNA 24 hours post-IVC stenosis compared to their Stab2+/+ counterparts.

CONCLUSIONS

These data suggest that stabilin-2 deficiency associates with a prothrombotic phenotype involving elevated levels of neutrophil extracellular trap-releasing leukocytes coupled with endogenous procoagulant activity, resulting in larger and qualitatively distinct venous thrombi.

Advances in the management of haemophilia: emerging treatments and their mechanisms

Mainstay haemophilia treatment, namely intravenous factor replacement, poses several clinical challenges including frequent injections due to the short half-life of recombinant factors, intravenous administration (which is particularly challenging in those with difficult venous access), and the risk of inhibitor development. These impact negatively upon quality of life and treatment compliance, highlighting the need for improved therapies. Several novel pharmacological therapies developed for haemophilia aim to rebalance the clotting cascade and potentially circumvent the aforementioned challenges. These therapies utilise a range of different mechanisms, namely: the extension of the circulating half-life of standard recombinant factors; the mimicking of factor VIII cofactor activity; rebalancing of coagulation through targeting of natural anticoagulants such as antithrombin and tissue factor pathway inhibitor; and inducing the production of endogenous factors with gene therapy. These therapies carry the potential of revolutionising haemophilia treatment by alleviating the current challenges presented by mainstay factor replacement. This review will provide an overview of the key trial findings related to novel therapies based on the mechanisms described above.

Matching-Adjusted Indirect Comparison of Efficacy and Consumption of rVIII-SingleChain Versus Two Recombinant FVIII Products Used for Prophylactic Treatment of Adults/Adolescents with Severe Haemophilia A

Introduction

Given the relatively small number of patients with haemophilia A, head-to-head comparisons between recombinant FVIII (rFVIII) products are difficult to conduct. This study compared the efficacy and consumption of rVIII-SingleChain (lonoctocog alfa, AFSTYLA^®) with rAHF-PFM (octocog alfa, Advate^®) and rFVIIIFc (efmoroctocog alfa, Elocta^®), for the prophylaxis and treatment of bleeding episodes in previously treated adolescents/adults with severe haemophilia A, through a matching-adjusted indirect comparison (MAIC).

Methods

A systematic literature review identified published clinical trials for rAHF-PFM and rFVIIIFc. Individual patient data for rVIII-SingleChain were used to match baseline patient characteristics to those from published trials, using an approach similar to propensity score weighting. After matching, annualized bleeding rates (ABR), percentage of patients with zero bleeds, and rFVIII consumption were compared across trial populations.

Results

Published data were identified from two rAHF-PFM trials and one rFVIIIFc trial. rVIII-SingleChain had similar ABR (risk ratio [RR]: 0.74 [0.16; 3.48]; RR: 1.18 [0.85; 1.65]) and percentage of patients with zero bleeds (odds ratio [OR]: 1.34 [0.56; 3.22]; OR: 0.78 [0.47; 1.31]) versus rAHF-PFM and rFVIIIFc, respectively. Annual rVIII-SingleChain consumption was significantly lower than rAHF-PFM (mean difference: − 1507.66 IU/kg/year [− 2011.71; − 1003.61]) and equivalent to rFVIIIFc (RR: 0.96 [0.62; 1.49]).

Conclusion

Although limited to published information for comparator trials, these results suggest that with an annualized rFVIII consumption comparable to rFVIIIFc, but significantly lower than rAHF-PFM, routine prophylaxis with rVIII-SingleChain is able to maintain a similar ABR and percentage of patients with zero bleeds, attesting to the long-acting nature of rVIII-SingleChain.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-021-01853-0.

It is difficult to directly compare different recombinant FVIII products in head-to-head studies because there are few patients with haemophilia A. This study aimed to indirectly compare the efficacy and consumption of different recombinant FVIII products in the prophylactic treatment of haemophilia A using published clinical data. A proven method for performing indirect comparisons of products is referred to as a matching-adjusted indirect comparison. Using this approach, we were able to compare rVIII-SingleChain with two other recombinant FVIII products (rAHF-PFM and rFVIIIFc). Our results suggest that annual FVIII consumption with rVIII-SingleChain is comparable to rFVIIIFc, but is significantly lower than rAHF-PFM, while maintaining a similar bleeding rate. These results highlight the long-acting nature of the product.

Current therapeutic approaches in the management of hemophilia-a consensus view by the Romanian Society of Hematology

Hemophilia A (HA) and hemophilia B (HB) are rare disorders, being caused by the total lack or under-expression of two factors from the coagulation cascade coded by genes of the X chromosome. Thus, in hemophilic patients, the blood does not clot properly. This results in spontaneous bleeding episodes after an injury or surgical intervention. A patient-centered regimen is considered optimal. Age, pharmacokinetics, bleeding phenotype, joint status, adherence, physical activity, personal goals are all factors that should be considered when individualizing therapy. In the past 10 years, many innovations in the diagnostic and treatment options were presented as being either approved or in development, thus helping clinicians to improve the standard-of-care for patients with hemophilia. Recombinant factors still remain the standard of care in hemophilia, however they pose a challenge to treatment adherence because they have short half-life, which where the extended half-life (EHL) factors come with the solution, increasing the half-life to 96 hours. Gene therapies have a promising future with proven beneficial effects in clinical trials. We present and critically analyze in the current manuscript the pros and cons of all the major discoveries in the diagnosis and treatment of HA and HB, as well as identify key areas of hemophilia research where improvements are needed.

The Asialoglycoprotein Receptor Minor Subunit Gene Contributes to Pharmacokinetics of Factor VIII Concentrates in Hemophilia A

BACKGROUND

 The asialoglycoprotein receptor (ASGPR) binds with high affinity factor VIII (FVIII) through its N-linked oligosaccharides. However, its contribution to the wide inter-individual variation of infused FVIII pharmacokinetics (PK) in hemophilia A (HA) is unknown.

OBJECTIVE

 To investigate the variability in FVIII PK outcomes in relation to genetic variation in the ASGR2, encoding the ASGPR2 subunit.

METHODS

 Thirty-two HA patients with FVIII:C ≤2 IU/dL underwent 66 single-dose FVIII PK studies. PK parameters were evaluated in relation to ASGR2 5' untranslated region (5'UTR) polymorphisms, which were investigated by recombinant and white blood cell reverse transcription-polymerase chain reaction approaches.

RESULTS

 The 5'UTR polymorphisms determine a frequent and conserved haplotype (HT1) in a regulatory region. The HT1 homozygotes may differ in the amounts of alternatively spliced mRNA transcripts and thus ASGPR2 isoforms. Compared with the other ASGR2 genotypes, the c.-95TT homozygotes (n = 9), showed threefold longer Alpha HL (3.60 hours, 95% confidence interval: 1.44-5.76, p = 0.006), and the c.-95TC heterozygotes (n = 17) showed 25% shorter mean residence time (MRT; 18.5 hours, 15.0-22.0, p = 0.038) and 32% shorter Beta HL (13.5 hours, 10.9-16.0, p = 0.016). These differences were confirmed in patients (n = 27) undergoing PK studies (n = 54) with full-length FVIII only. In different linear regression models, the contribution of the ASGR2 genotypes remained significant after adjustment by ABO genotypes and von Willebrand factor (VWF) antigen levels, and explained 14% (MRT), 15 to 18% (Beta HL), and 22% (Alpha HL) of parameter variability.

CONCLUSIONS

 Infused FVIII distribution was modulated by frequent ASGR2 genotypes, independently from and together with ABO and VWF antigen levels, which has potential implications for genetically tailored substitutive treatment in HA.

FVIII at the crossroad of coagulation, bone and immune biology: Emerging evidence of biological activities beyond hemostasis

Hemophilia A is an X-linked hereditary disorder that results from deficient coagulation factor VIII (FVIII) activity, leading to spontaneous bleeding episodes, particularly in joints and muscles. FVIII deficiency has been associated with altered bone remodeling, dysregulated macrophage polarization, and inflammatory processes that are associated with the neoformation of abnormal blood vessels. Treatment based on FVIII replacement can lead to the development of inhibitors that render FVIII concentrate infusion ineffective. In this context, hemophilia has entered a new therapeutic era with the development of new drugs, such as emicizumab, that seek to restore the hemostatic balance by bypassing pathologically acquired antibodies. We discuss the potential extrahemostatic functions of FVIII that may be crucial for defining future therapies in hemophilia.

Factor VIII-Fc Activates Natural Killer Cells via Fc-Mediated Interactions With CD16

The most challenging complication associated with Factor VIII (FVIII) replacement therapy is the development of neutralizing anti-drug antibodies, or inhibitors, which occur in 23-35% of severe (FVIII level <1%) hemophilia A (HA) patients and are a serious hindrance to effective management of HA. Consequently, strategies that can either prevent anti-FVIII inhibitors from developing or "tolerize" individuals who develop such antibodies represent a clinically important unmet need. One intervention for patients with high-titer inhibitors is immune tolerance induction (ITI) therapy. Although ITI therapy is the only clinically proven strategy to eradicate anti-FVIII inhibitors, mechanisms of inhibitor reduction remain unknown. Factor VIII Fc-fusion (rFVIIIFc) is an enhanced half-life antihemophilic factor used in replacement therapy for HA. Fc-fusion is a successful protein bio-engineering platform technology. In addition to enhancement of plasma half-life via neonatal Fc receptor (FcRn) binding, other Fc-mediated interactions, including engagement with Fc gamma receptors (FcγR), may have immunological consequences. Several case reports and retrospective analyses suggest that rFVIIIFc offers superior outcomes with respect to ITI compared to other FVIII products. Previously we and others demonstrated rFVIIIFc interactions with activating FcγRIIIA/CD16. Here, we investigated if rFVIIIFc activates natural killer (NK) cells via CD16. We demonstrated rFVIIIFc signaling via CD16 independent of Von Willebrand Factor (VWF):FVIII complex formation. We established that rFVIIIFc potently activated NK cells in a CD16-dependent fashion resulting in IFNγ secretion and cytolytic perforin and granzyme B release. We also demonstrated an association between rFVIIIFc-mediated NK cell IFNγ secretion levels and the high-affinity (158V) CD16 genotype. Furthermore, we show that rFVIIIFc-activated CD16⁺ NK cells were able to lyse a B-cell clone (BO2C11) bearing an anti-FVIII B-cell receptor in an antibody-dependent cellular cytotoxicity (ADCC) assay. These in vitro findings provide an underlying molecular mechanism that may help explain clinical case reports and retrospective studies suggesting rFVIIIFc may be more effective in tolerizing HA patients with anti-FVIII inhibitors compared to FVIII not linked to Fc. Our in vitro findings suggest a potential use of Fc-fusion proteins acting via NK cells to target antigen-specific B-cells, in the management of unwanted immune responses directed against immunogenic self-antigens or therapeutic protein products.

Population pharmacokinetics of the von Willebrand factor-factor VIII interaction in patients with von Willebrand disease

Recent studies have reported that patients with von Willebrand disease treated perioperatively with a von Willebrand factor (VWF)/factor VIII (FVIII) concentrate with a ratio of 2.4:1 (Humate P/Haemate P) often present with VWF and/or FVIII levels outside of prespecified target levels necessary to prevent bleeding. Pharmacokinetic (PK)-guided dosing may resolve this problem. As clinical guidelines increasingly recommend aiming for certain target levels of both VWF and FVIII, application of an integrated population PK model describing both VWF activity (VWF:Act) and FVIII levels may improve dosing and quality of care. In total, 695 VWF:Act and 894 FVIII level measurements from 118 patients (174 surgeries) who were treated perioperatively with the VWF/FVIII concentrate were used to develop this population PK model using nonlinear mixed-effects modeling. VWF:Act and FVIII levels were analyzed simultaneously using a turnover model. The protective effect of VWF:Act on FVIII clearance was described with an inhibitory maximum effect function. An average perioperative VWF:Act level of 1.23 IU/mL decreased FVIII clearance from 460 mL/h to 264 mL/h, and increased FVIII half-life from 6.6 to 11.4 hours. Clearly, in the presence of VWF, FVIII clearance decreased with a concomitant increase of FVIII half-life, clarifying the higher FVIII levels observed after repetitive dosing with this concentrate. VWF:Act and FVIII levels during perioperative treatment were described adequately by this newly developed integrated population PK model. Clinical application of this model may facilitate more accurate targeting of VWF:Act and FVIII levels during perioperative treatment with this specific VWF/FVIII concentrate (Humate P/Haemate P).

FVIII half-life extension by coadministration of a D'D3 albumin fusion protein in mice, rabbits, rats, and monkeys

A novel mechanism for extending the circulatory half-life of coagulation factor VIII (FVIII) has been established and evaluated preclinically. The FVIII binding domain of von Willebrand factor (D'D3) fused to human albumin (rD'D3-FP) dose dependently improved pharmacokinetics parameters of coadministered FVIII in all animal species tested, from mouse to cynomolgus monkey, after IV injection. At higher doses, the half-life of recombinant FVIII (rVIII-SingleChain) was calculated to be increased 2.6-fold to fivefold compared with rVIII-SingleChain administered alone in rats, rabbits, and cynomolgus monkeys, and it was increased 3.1-fold to 9.1-fold in mice. Sustained pharmacodynamics effects were observed (ie, activated partial thromboplastin time and thrombin generation measured ex vivo). No increased risk of thrombosis was observed with coadministration of rVIII-SingleChain and rD'D3-FP compared with rVIII-SingleChain alone. At concentrations beyond the anticipated therapeutic range, rD'D3-FP reduced the hemostatic efficacy of coadministered rVIII-SingleChain. This finding might be due to scavenging of activated FVIII by the excessive amount of rD'D3-FP which, in turn, might result in a reduced probability of the formation of the tenase complex. This observation underlines the importance of a fine-tuned balance between FVIII and its binding partner, von Willebrand factor, for hemostasis in general.

Characterisation and application of recombinant FVIII-neutralising antibodies from haemophilia A inhibitor patients

The development of anti-drug antibodies (ADAs) is a serious outcome of treatment strategies involving biological medicines. Coagulation factor VIII (FVIII) is used to treat haemophilia A patients, but its immunogenicity precludes a third of severe haemophiliac patients from receiving this treatment. The availability of patient-derived anti-drug antibodies can help us better understand drug immunogenicity and identify ways to overcome it. Thus, there were two aims to this work: (i) to develop and characterise a panel of recombinant, patient-derived, monoclonal antibodies covering a range of FVIII epitopes with varying potencies, kinetics and mechanism of action, and (ii) to demonstrate their applicability to assay development, evaluation of FVIII molecules and basic research. For the first objective we used recombinant antibodies to develop a rapid, sensitive, flexible and reproducible ex vivo assay that recapitulates inhibitor patient blood using blood from healthy volunteers. We also demonstrate how the panel can provide important information about the efficacy of FVIII products and reagents without the need for patient or animal material. These materials can be used as experimental exemplars or controls, as well as tools for rational, hypothesis-driven research and assay development in relation to FVIII immunogenicity and FVIII-related products.

Perspective - The case for zero bleeds and drug bioequivalence in the treatment of congenital hemophilia A in 2021

Not all patients with severe hemophilia A (HA) respond optimally to a given dose of a given product. Within-individual variance in cross-over studies makes each patient unique in the response to each standard half-life (SHL) factor VIII (FVIII) product in pharmacokinetic (PK) terms. This hampers the prediction of efficacy when a SHL FVIII product is employed. PK data showing that half-lives of SHL rFVIII are unsatisfactory to achieve zero bleeding in individual HA patients provide the rationale for switching from SHL to extended half-life (EHL) products. However, not all subjects receiving prophylaxis with EHL products achieve zero bleeding, the most cogent objective of personalized prophylaxis. Known determinants of FVIII half-life (age, von Willebrand factor [VWF] levels, blood group) cumulatively account for one third of the total inter-individual variation in FVIII clearance in subjects with severe HA. Investigations into precision, and accuracy of laboratory measurement to be employed; newer pathways for the clearance of both free-FVIII and VWF-bound FVIII, and adequately powered studies on omics and phenotypic heterogeneity, are likely to provide additional information on the remaining two thirds of inter-individual variation in FVIII clearance in HA. Variability in the clinical response has also been documented in patients when FVIII activity is mimicked by fixed subcutaneous doses of the bispecific antibody emicizumab. National registries that collect PK data of available FVIII products and ad hoc information on the individual response to emicizumab should be encouraged, to establish newer standards of care and ease personalized clinical decisions to achieve zero bleeding.

Von Willebrand Factor, Factor VIII, and Other Acute Phase Reactants as Biomarkers of Inflammation and Endothelial Dysfunction in Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGvHD) is an immune mediated late complication of allogeneic hematopoietic stem cell transplantation (alloHSCT). Discovery of adequate biomarkers could identify high-risk patients and provide an effective pre-emptive intervention or early modification of therapeutic strategy, thus reducing prevalence and severity of the disease among long-term survivors of alloHSCT. Inflammation, endothelial injury, and endothelial dysfunction are involved in cGvHD development. Altered levels of acute phase reactants have shown a strong correlation with the activity of several immune mediated disorders and are routinely used in clinical practice. Since elevated von Willebrand factor (VWF) and factor VIII (FVIII) levels have been described as acute phase reactants that may indicate endothelial dysfunction and inflammation in different settings, including chronic autoimmune diseases, they could serve as potential candidate biomarkers of cGvHD. In this review we focused on reported data regarding VWF and FVIII as well as other markers of inflammation and endothelial dysfunction, evaluating their potential role in cGvHD.

Von Willebrand disease type 2N: An update

Quantitative or qualitative defects of von Willebrand factor (VWF) are responsible for the most common inherited bleeding disorder, von Willebrand disease (VWD). Type 2N VWD is an uncommon recessive disorder that results from gene mutations located in the region coding for the binding site of VWF for factor VIII (FVIII). This narrative review describes the pathophysiology, diagnostic procedures and treatment as well as the molecular biology of type 2N VWD. Although other VWF-dependent functions like binding to platelets and collagen are preserved, FVIII plasma levels are low due to the rapid clearance of this moiety in the absence or reduction of its binding to VWF. The diagnosis of type 2N should be considered in patients with low FVIII coagulant activity (FVIII:C) and disproportionally higher VWF antigen, especially when they present with an autosomal recessive pattern of inheritance. Because an accurate diagnosis is essential for genetic counseling and optimal treatment, type 2N must be distinguished from mild/moderate hemophilia A and its carrier state. This differential diagnosis can be obtained by using the laboratory assay of the FVIII binding capacity of VWF (VWF:FVIIIB) or analysis of the FVIII binding site on the VWF gene.

Characterization of protein unable to bind von Willebrand factor in recombinant factor VIII products

BACKGROUND

Therapeutic products with coagulation factor VIII (FVIII) have a wide range of specific activities, implying presence of protein with altered structure. Previous studies showed that recombinant FVIII products (rFVIII) contain a fraction (FVIIIFT ) unable to bind von Willebrand factor (VWF) and reported to lack activity. Because of loss of function(s), FVIIIFT can be defined as a product-related impurity, whose properties and levels in rFVIII products should be investigated.

OBJECTIVE

To isolate and characterize the FVIIIFT fraction in rFVIII products.

METHODS

Protein fractions unable (FVIIIFT ) and able (FVIIIEL ) to bind VWF were isolated from rFVIII products using immobilized VWF affinity chromatography (IVAC) and characterized by gel electrophoresis, immunoblotting, FVIII activity test, surface plasmon resonance, mass spectrometry, and for plasma clearance in mice.

RESULTS AND CONCLUSIONS

A robust IVAC methodology was developed and applied for analysis of 10 rFVIII products marketed in the United States. FVIIIFT was found at various contents (0.4%-21.5%) in all products. Compared with FVIIIEL , FVIIIFT had similar patterns of polypeptide bands by gel electrophoresis, but lower functional activity. In several representative products, FVIIIFT was found to have reduced sulfation at Tyr1680, important for VWF binding, decreased interaction with a low-density lipoprotein receptor-related protein 1 fragment, and faster plasma clearance in mice. These findings provide basic characterization of FVIIIFT and demonstrate a potential for IVAC to control this impurity in rFVIII products to improve their efficacy in therapy of hemophilia A.

Effects of Shear Stress on Production of FVIII and vWF in a Cell-Based Therapeutic for Hemophilia A

Microfluidic technology enables recapitulation of organ-level physiology to answer pertinent questions regarding biological systems that otherwise would remain unanswered. We have previously reported on the development of a novel product consisting of human placental cells (PLC) engineered to overexpress a therapeutic factor VIII (FVIII) transgene, mcoET3 (PLC-mcoET3), to treat Hemophilia A (HA). Here, microfluidic devices were manufactured to model the physiological shear stress in liver sinusoids, where infused PLC-mcoET3 are thought to lodge after administration, to help us predict the therapeutic outcome of this novel biological strategy. In addition to the therapeutic transgene, PLC-mcoET3 also constitutively produce endogenous FVIII and von Willebrand factor (vWF), which plays a critical role in FVIII function, immunogenicity, stability, and clearance. While vWF is known to respond to flow by changing conformation, whether and how shear stress affects the production and secretion of vWF and FVIII has not been explored. We demonstrated that exposure of PLC-mcoET3 to physiological levels of shear stress present within the liver sinusoids significantly reduced mRNA levels and secreted FVIII and vWF when compared to static conditions. In contrast, mRNA for the vector-encoded mcoET3 was unaltered by flow. To determine the mechanism responsible for the observed decrease in FVIII and vWF mRNA, PCR arrays were performed to evaluate expression of genes involved in shear mechanosensing pathways. We found that flow conditions led to a significant increase in KLF2, which induces miRNAs that negatively regulate expression of FVIII and vWF, providing a mechanistic explanation for the reduced expression of these proteins in PLC under conditions of flow. In conclusion, microfluidic technology allowed us to unmask novel pathways by which endogenous FVIII and vWF are affected by shear stress, while demonstrating that expression of the therapeutic mcoET3 gene will be maintained in the gene-modified PLCs upon transplantation, irrespective of whether they engraft within sites that expose them to conditions of shear stress.

Von Willebrand Factor Multimer Densitometric Analysis: Validation of the Clinical Accuracy and Clinical Implications in Von Willebrand Disease

Von Willebrand factor (VWF) multimer analysis is important in the classification of von Willebrand disease (VWD). Current visual VWF multimer analysis is time consuming and inaccurate in detecting subtle changes in multimer patterns. Although VWF multimer densitometric analysis may be useful, the accuracy needs further investigation before it can be widely applied. In this study we aimed to validate VWF multimer densitometric analysis in a large cohort of VWD patients and to identify patient characteristics associated with densitometric outcomes. Patients were included from the Willebrand in the Netherlands (WiN) study, in which a bleeding score (BS) was obtained, and blood was drawn. For multimer analysis, citrated blood was separated on an agarose gel and visualized by Western blotting. IMAGEJ was used to generate densitometric images and medium-large VWF multimer index was calculated. We included 560 VWD patients: 328 type 1, 211 type 2, and 21 type 3 patients. Medium-large VWF multimer index performed excellent in distinguishing visually classified normal VWF multimers from reduced high-molecular-weight (HMW) multimers (area under the curve [AUC]: 0.96 [0.94-0.98], P < 0.001), normal multimers from absence of HMW multimers (AUC 1.00 [1.00-1.00], P < 0.001), and type 2A and 2B from type 2M and 2N (AUC: 0.96 [0.94-0.99], P < 0.001). Additionally, higher medium-large VWF multimer index was associated with lower BS in type 1 VWD: β = -7.6 (-13.0 to -2.1), P = 0.007, adjusted for confounders. Densitometric analysis of VWF multimers had an excellent accuracy compared with visual multimer analysis and may contribute to a better understanding of the clinical features such as the bleeding phenotype of VWD patients.

Characterization of ADAMTS13 and von Willebrand factor levels in septic and non-septic ICU patients

Sepsis is a life-threatening disease characterized by excessive host response to infection that can lead to activation of the coagulation system. Von Willebrand Factor (VWF) and ADAMTS13 are important regulators of hemostasis and their dysregulation during sepsis progression is not well understood. Herein we characterize ADAMTS13 and VWF in septic and non-septic patients. ADAMTS13 activity, ADAMTS13 antigen, VWF antigen, myeloperoxidase, and protein C, were measured in plasma collected from 40 septic patients (20 non-survivors and 20 survivors) and 40 non-septic patients on the first and last day of their ICU stay. ADAMTS13 activity and ADAMTS13 antigen were reduced, whereas VWF antigen was elevated among septic patients compared to non-septic patients and healthy controls. Non-septic patients also exhibited elevated VWF antigen and reduced ADAMTS13 activity, but to a lesser extent than septic patients. Non-survivor septic patients exhibited the lowest levels of ADAMTS13 activity. ADAMTS13 activity:antigen ratio was similar across all patient cohorts suggesting that the specific activity of ADAMTS13 remains unchanged. Therefore, reduced ADAMTS13 function in circulation is likely due to a reduction in circulating levels. We suggest that massive release of VWF in response to inflammation consumes limited circulating ADAMTS13, resulting in the imbalance observed between VWF and ADAMTS13 among septic and to a lesser extent in non-septic ICU patients. Changes to ADAMTS13 did not correlate with myeloperoxidase or protein C levels. Reduced ADAMTS13 activity and antigen, and elevated VWF antigen observed among all patient cohorts on admission remained unchanged in survivors at ICU discharge. Prolonged reduction in ADAMTS13 activity and antigen in septic patients coincides with elevated levels of VWF. The persistent abnormalities in ADAMTS13 and VWF in sepsis patients discharged from the ICU may contribute to a sustained prothrombotic state.

The changing treatment landscape in haemophilia: from standard half-life clotting factor concentrates to gene editing

Congenital haemophilia A (factor VIII deficiency) and B (factor IX deficiency) are X-linked bleeding disorders. Replacement therapy has been the cornerstone of the management of haemophilia, aiming to reduce the mortality and morbidity of chronic crippling arthropathy. Frequent intravenous injections are burdensome and costly for patients, consequently with poor adherence and restricted access to therapy for many patients worldwide. Bioengineered clotting factors with enhanced pharmacokinetic profiles can reduce the burden of treatment. However, replacement therapy is associated with a risk for inhibitor development that adversely affects bleeding prevention and outcomes. Novel molecules that are subcutaneously delivered provide effective prophylaxis in the presence or absence of inhibitors, either substituting for the procoagulant function of clotting factors (eg, emicizumab) or targeting the natural inhibitors of coagulation (ie, antithrombin, tissue factor pathway inhibitor, or activated protein C). The ultimate goal of haemophilia treatment would be a phenotypical cure achievable with gene therapy, currently under late phase clinical investigation.

Molecular determinants of the factor VIII/von Willebrand factor complex revealed by BIVV001 cryo-electron microscopy

Interaction of factor VIII (FVIII) with von Willebrand factor (VWF) is mediated by the VWF D'D3 domains and thrombin-mediated release is essential for hemostasis after vascular injury. VWF-D'D3 mutations resulting in loss of FVIII binding are the underlying cause of von Willebrand disease (VWD) type 2N. Furthermore, the FVIII-VWF interaction has significant implications for the development of therapeutics for bleeding disorders, particularly hemophilia A, in which endogenous VWF clearance imposes a half-life ceiling on replacement FVIII therapy. To understand the structural basis of FVIII engagement by VWF, we solved the structure of BIVV001 by cryo-electron microscopy to 2.9 Å resolution. BIVV001 is a bioengineered clinical-stage FVIII molecule for the treatment of hemophilia A. In BIVV001, VWF-D'D3 is covalently linked to an Fc domain of a B domain-deleted recombinant FVIII (rFVIII) Fc fusion protein, resulting in a stabilized rFVIII/VWF-D'D3 complex. Our rFVIII/VWF structure resolves BIVV001 architecture and provides a detailed spatial understanding of previous biochemical and clinical observations related to FVIII-VWF engagement. Notably, the FVIII acidic a3 peptide region (FVIII-a3), established as a critical determinant of FVIII/VWF complex formation, inserts into a basic groove formed at the VWF-D'/rFVIII interface. Our structure shows direct interaction of sulfated Y1680 in FVIII-a3 and VWF-R816 that, when mutated, leads to severe hemophilia A or VWD type 2N, respectively. These results provide insight on this key coagulation complex, explain the structural basis of many hemophilia A and VWD type 2N mutations, and inform studies to further elucidate how VWF dissociates rapidly from FVIII upon activation.

Glyco-engineered HEK 293-F cell lines for the production of therapeutic glycoproteins with human N-glycosylation and improved pharmacokinetics

N-glycosylated proteins produced in human embryonic kidney 293 (HEK 293) cells often carry terminal N-acetylgalactosamine (GalNAc) and only low levels of sialylation. On therapeutic proteins, such N-glycans often trigger rapid clearance from the patient bloodstream via efficient binding to asialoglycoprotein receptor (ASGP-R) and mannose receptor (MR). This currently limits the use of HEK 293 cells for therapeutic protein production. To eliminate terminal GalNAc, we knocked-out GalNAc transferases B4GALNT3 and B4GALNT4 by CRISPR/Cas9 in FreeStyle 293-F cells. The resulting cell line produced a coagulation factor VII-albumin fusion protein without GalNAc but with increased sialylation. This glyco-engineered protein bound less efficiently to both the ASGP-R and MR in vitro and it showed improved recovery, terminal half-life and area under the curve in pharmacokinetic rat experiments. By overexpressing sialyltransferases ST6GAL1 and ST3GAL6 in B4GALNT3 and B4GALNT4 knock-out cells, we further increased factor VII-albumin sialylation; for ST6GAL1 even to the level of human plasma-derived factor VII. Simultaneous knock-out of B4GALNT3 and B4GALNT4, and overexpression of ST6GAL1 further lowered factor VII-albumin binding to ASGP-R and MR. This novel glyco-engineered cell line is well-suited for the production of factor VII-albumin and presumably other therapeutic proteins with fully human N-glycosylation and superior pharmacokinetic properties.

2021 clinical trials update: Innovations in hemophilia therapy

Therapies engineered to prolong clotting factor protein circulation time, manipulate the balance of pro-coagulant and anti-coagulant proteins, or introduce new genetic material to enable endogenous factor protein production dominate the clinical trial landscape of hemophilia. The availability of clotting factor concentrates and the establishment of primary prophylaxis have dramatically improved health outcomes for hemophilia patients. But, the burden of hemostatic therapy remains significant, and many barriers to consistent longitudinal use of prophylaxis exist. Several types of emerging therapeutics including engineered factor concentrates, substitutive therapies, rebalancing therapies, and gene transfer/editing all aim to reduce the challenges of current hemophilia treatment. Emerging treatment options may reduce treatment frequency or need for intravenous administration. They may also introduce new challenges in laboratory assessment of hemostasis. These novel therapies must not introduce significant new health risks and continue to support similar or improved outcomes. The potential ramifications of rebalancing the coagulation cascade, particularly in a stress or inflammatory state, or introduction of new genetic material are not trivial. The focus of this review is to provide an overview of active and recently completed clinical trials as well as emerging preclinical data investigating new therapeutic possibilities for hemophilia patients and potentially other rare bleeding disorders.

BIVV001, a new class of factor VIII replacement for hemophilia A that is independent of von Willebrand factor in primates and mice

Factor VIII (FVIII) replacement products enable comprehensive care in hemophilia A. Treatment goals in severe hemophilia A are expanding beyond low annualized bleed rates to include long-term outcomes associated with high sustained FVIII levels. Endogenous von Willebrand factor (VWF) stabilizes and protects FVIII from degradation and clearance, but it also subjects FVIII to a half-life ceiling of ∼15 to 19 hours. Increasing recombinant FVIII (rFVIII) half-life further is ultimately dependent upon uncoupling rFVIII from endogenous VWF. We have developed a new class of FVIII replacement, rFVIIIFc-VWF-XTEN (BIVV001), that is physically decoupled from endogenous VWF and has enhanced pharmacokinetic properties compared with all previous FVIII products. BIVV001 was bioengineered as a unique fusion protein consisting of a VWF-D'D3 domain fused to rFVIII via immunoglobulin-G1 Fc domains and 2 XTEN polypeptides (Amunix Pharmaceuticals, Inc, Mountain View, CA). Plasma FVIII half-life after BIVV001 administration in mice and monkeys was 25 to 31 hours and 33 to 34 hours, respectively, representing a three- to fourfold increase in FVIII half-life. Our results showed that multifaceted protein engineering, far beyond a few amino acid substitutions, could significantly improve rFVIII pharmacokinetic properties while maintaining hemostatic function. BIVV001 is the first rFVIII with the potential to significantly change the treatment paradigm for severe hemophilia A by providing optimal protection against all bleed types, with less frequent doses. The protein engineering methods described herein can also be applied to other complex proteins.