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

Predicting the effects of single pathological mutations in hemophilia A and type 2N von Willebrand diseases using AlphaFold2-multimer and AlphaFold3

Most factor VIII (FVIII) in circulation exists in a complex with von Willebrand factor (vWF). The interaction between FVIII and vWF is vital for normal hemostatic function, and disruptions in this interaction can lead to bleeding disorders such as von Willebrand disease or hemophilia. However, the impact of pathological mutations on the binding between FVIII and vWF remains largely uncharacterized. In the current study, we used AlphaFold2-multimer and AlphaFold3 to predict the complex involving FVIII and vWF. Additionally, we explored how known mutations in FVIII or vWF, which can result in mild to severe forms of hemophilia and type 2N von Willebrand disease, affect this complex. Our predictions confirm that AlphaFold2 and AlphaFold3 can accurately model the FVIII/vWF complex in a manner consistent with existing cryogenic electron microscopy structures. However, the single pathological mutations can generally disrupt the complex interface predicted by AlphaFold2-multimer but not AlphaFold3. Molecular dynamic simulations showed that the flexibility of several common regions was affected by single pathological mutations. We further designed a new FVIII construct using AlphaFold2, which holds promise as a more effective therapeutic agent with reduced autoimmune responses. In summary, our findings suggest that in combination with molecular dynamics, AlphaFold2 is a valuable tool for swiftly assessing the impact of both known and novel mutations on hemophilia, with potential applications in precision medicine and the development of novel therapeutic interventions. SIGNIFICANCE STATEMENT: This study provides novel insights into the protein structure of the factor VIII and von Willebrand factor complex. This research demonstrates that AlphaFold2-multimer rather than AlphaFold3 can better predict the variations in the complex corresponding to clinical observations of disease severity. These findings not only deepen our comprehension of hemostatic mechanisms but also establish AlphaFold2 in combination with molecular dynamics as a useful tool for hemophilia research, with potential applications in precision medicine and the development of novel therapeutic interventions.

Binding Promiscuity of Therapeutic Factor VIII

The binding promiscuity of proteins defines their ability to indiscriminately bind multiple unrelated molecules. Binding promiscuity is implicated, at least in part, in the off-target reactivity, nonspecific biodistribution, immunogenicity, and/or short half-life of potentially efficacious protein drugs, thus affecting their clinical use. In this review, we discuss the current evidence for the binding promiscuity of factor VIII (FVIII), a protein used for the treatment of hemophilia A, which displays poor pharmacokinetics, and elevated immunogenicity. We summarize the different canonical and noncanonical interactions that FVIII may establish in the circulation and that could be responsible for its therapeutic liabilities. We also provide information suggesting that the FVIII light chain, and especially its C1 and C2 domains, could play an important role in the binding promiscuity. We believe that the knowledge accumulated over years of FVIII usage could be exploited for the development of strategies to predict protein binding promiscuity and therefore anticipate drug efficacy and toxicity. This would open a mutational space to reduce the binding promiscuity of emerging protein drugs while conserving their therapeutic potency.

Plasma proteomics in patients with von Willebrand disease and hemophilia A highlights von Willebrand factor as main determinant of response to desmopressin treatment

Background

Desmopressin, 1-deamino-8-D-arginin vasopressin (DDAVP), is a treatment option for people with von Willebrand disease (VWD) and hemophilia A (HA) with a large interindividual variation in response. DDAVP elicits the release of von Willebrand Factor (VWF) from endothelial cells, thereby increasing the levels of circulating VWF and coagulation factor (F)VIII. However, we currently lack detailed insight on additional systemic effects of DDAVP administration on plasma protein levels.

Objectives

This study aimed to investigate plasma proteomic profiles associated with DDAVP administration.

Methods

Longitudinal plasma samples of 13 patients with VWD and 9 people with mild HA up to 24 hours after DDAVP infusion were analyzed using mass spectrometry-based proteomics.

Results

Among 408 proteins quantified in plasma, only VWF and VWF propeptide (pp) increased significantly at 1 and 2 hours after DDAVP infusion in people with HA and VWD, respectively. VWF antigen levels were in agreement with mass spectrometry-based VWF intensity levels (ρ = 0.89). A slower clearance was observed for VWF compared with that for VWFpp, accompanied with higher interindividual variation. In 4 people with HA, C-reactive protein levels increased 24 hours after DDAVP infusion, which correlated with serum amyloid A1/A2 levels.

Conclusion

This study showed the selective increase of VWF and VWFpp 1 to 2 hours after DDAVP infusion and highlighted the interindividual variance in VWF clearance. Additionally, a delayed acute-phase response in a subgroup of patients suggested the potential role of inflammatory mechanisms contributing to heterogeneity of response.

The severe von Willebrand disease variant p.M771V leads to impaired anterograde trafficking of von Willebrand factor in patient-derived and base-edited endothelial colony-forming cells

BACKGROUND

von Willebrand disease (VWD) is the most common inherited bleeding disorder caused by quantitative or qualitative defects in von Willebrand factor (VWF). The p.M771V VWF variant leads to a severe bleeding phenotype in homozygous patients. However, the exact molecular mechanism remains unclear, which prevents personalized treatment of those VWD patients.

OBJECTIVES

This study aimed to characterize the underlying molecular mechanisms of the p.M771V variant in multiple representative ex vivo cell models.

METHODS

Endothelial colony-forming cells (ECFCs) were isolated from venous blood of VWD patients from the Willebrand in the Netherlands cohort carrying homozygous and heterozygous p.M771V VWF variants. The p.M771V variant was also introduced in cord blood-derived ECFCs (CB-ECFCs) through adenine base editing and was overexpressed in HEK293 cells. Biosynthesis, storage, and secretion of VWF was studied using biochemical methods and confocal microscopy.

RESULTS

Two unrelated homozygous p.M771V patients presented with very low VWF activity and antigen levels in plasma. Patient ECFCs showed impaired uncleaved VWF processing into mature VWF, with secreted VWF being severely reduced when compared to ECFCs of healthy donors. Multimer analysis of p.M771V ECFCs showed a deficiency of high molecular weight VWF multimers. Immunofluorescent staining revealed VWF retention in the endoplasmic reticulum; this was confirmed in various populations of base-edited CB-ECFCs harboring the p.M771V variant.

CONCLUSION

The severe endothelial phenotype observed in patient-derived p.M771V ECFCs, HEK293 cells, and an original base-edited CB-ECFC modeling system show that endoplasmic reticulum retention of VWF and failure to undergo subsequent proteolytic processing underpins the severe bleeding phenotype of patients with homozygous variants at M771.

Factor Replacement Treatment for Hemophilia A: Achievements and Perspectives

The mainstay of treatment for persons with hemophilia A (PwHA) with severe bleeding phenotype is prophylaxis. The pharmacokinetic (PK) profile of native factor VIII (FVIII) imposes the need for rather frequent intravenous injections to ensure effective prophylaxis, but this represents a relevant treatment burden and is associated with suboptimal adherence to treatment. In this light, the advent of extended half-life (EHL) FVIII molecules has improved prophylaxis feasibility and outcomes by favoring treatment individualization and tailoring protection according to specific clinical and nonclinical needs. Different technologies have been used to enhance FVIII PK properties including Fc-fusion and conjugation with polyethylene glycol. Data from clinical development programs for such molecules, together with growing real-world experience, have shown numerous benefits related to the use of EHL FVIII in PwHA. Recently a new class of ultra-long-acting EHL FVIII has been developed to further improve protection against bleeding episodes and achieve the ambitious goal of providing PwHA with hemostatic protection in the nonhemophilia range over longer time periods, hence ensuring very low bleeding rates and improving joint health and quality of life. In this review, the achievements and perspectives of replacement therapies for PwHA are summarized and discussed.

Pharmacokinetic evaluation of efanesoctocog alfa: breakthrough factor VIII therapy for hemophilia A

INTRODUCTION

Blood coagulation factor (F)VIII functions as a cofactor in the tenase complex responsible for phospholipid-dependent FIXa-mediated activation of FX in plasma. Congenital defect of FVIII causes severe bleeding disorder, hemophilia (H) A. Intravenous FVIII replacement therapy is the gold standard therapy in patients with HA (PwHA) but requirement for frequent dosing of FVIII owing to pharmacokinetics burdens PwHA a lot. Efanesoctocog alfa is a new class of recombinant FVIII and has the ability to overcome conceivable unmet needs in treatment for PwHA.

AREAS COVERED

Efanesoctocog alfa is a B domain-deleted single-chain fusion FVIII connected to the Fc-region of human immunoglobulin G1, D'D3-fragment of von Willebrand factor (VWF), and unstructured hydrophilic recombinant polypeptides (XTEN). Owing to its novel design, it can function independently of endogenous VWF and elicits 2 to 4 times longer half-life compared to other existing FVIII products. The prolonged half-life contributes to maintain high level of FVIII activity for most of the week and has led to excellent hemostatic effect by once-weekly administration in phase 3 clinical trials.

EXPERT OPINION

Efanesoctocog alfa with outstanding pharmacological properties, well tolerated in the clinical trials, is a promising FVIII therapy for PwHA. Future studies should include long-term safety, especially in previously untreated patients.

Patient Experience With Efanesoctocog Alfa for Severe Hemophilia A: Results From the XTEND-1 Phase 3 Clinical Study Exit Interviews

PURPOSE

Hemophilia A is a rare bleeding disorder that leads to recurrent hemarthrosis, which can ultimately result in reduced mobility and poor quality of life. Qualitative exit interviews provide insights into patient perspectives and support the interpretation of quantitative trial data, such as patient-reported outcome measures. In the Phase 3 XTEND-1 study (NCT04161495) of efanesoctocog alfa in participants with severe hemophilia A, exit interviews were conducted to understand pre- and post-study experiences with pain and physical functioning and to evaluate participants' treatment experiences.

METHODS

In XTEND-1, participants (≥12 years old) received once-weekly efanesoctocog alfa prophylaxis 50 IU/kg for 52 weeks (Arm A) or on-demand efanesoctocog alfa 50 IU/kg for 26 weeks followed by 26 weeks once-weekly prophylaxis (50 IU/kg; Arm B). Optional qualitative exit interviews were conducted using a semi-structured guide in a subset of participants following study completion. Interviews included open-ended questions about participants' pre- and post-study experiences with hemophilia A and targeted questions relating to improvements in patient-reported outcomes assessed during XTEND-1, including the Haemophilia Quality of Life Questionnaire for Adults Physical Health subscale (Haem-A-QoL PH). Content validity of the Patient-Reported Outcomes Measurement Information System (PROMIS) Pain Intensity 3a measure was also assessed, particularly the worst pain item.

FINDINGS

Exit interviews were conducted with 29 of 159 patients enrolled in XTEND-1 (mean [range] age 40 [16-73] years). Of 17 participants enrolled in Arm A, 13 (76.5%) reported a "wearing off" feeling with pre-study treatment, including more aches/pain, breakthrough bleeds, and limited physical activities. Joint pain was the most reported pre-study symptom (96.6%; n = 28/29), followed by a reduced ability to move without pain (89.7%, n = 26/29). Improvements following efanesoctocog alfa prophylaxis in ≥1 Haem-A-QoL PH domain were reported by 89.7% (n = 26/29) of participants, with improvements in joint pain, the ability to move without pain, and painful swellings reported by at least 21 (84%) participants. Participants reported that the PROMIS Pain Intensity 3a items were relevant, clear, and easy to answer. Most participants (96.6%) were "quite satisfied" or "very satisfied" with efanesoctocog alfa prophylaxis. All participants preferred efanesoctocog alfa over pre-study treatment.

IMPLICATIONS

The exit interviews demonstrated that once-weekly efanesoctocog alfa prophylaxis resulted in patient-relevant and meaningful improvements in pain and physical functioning, consistent with the quantitative findings from XTEND-1. These results support the validity of the Haem-A-QoL PH and PROMIS Pain Intensity 3a assessed during XTEND-1, demonstrating the potential for change with efficacious treatment.

TRIAL REGISTRY

ClinicalTrials.gov TRIAL REGISTRATION NUMBER: NCT04161495 REGISTRY URL: https://clinicaltrials.gov/study/NCT04161495.

Endothelial colony-forming cells in the spotlight: insights into the pathophysiology of von Willebrand disease and rare bleeding disorders

Endothelial cells deliver a vital contribution to the maintenance of hemostasis by constituting an anatomical as well as functional barrier between the blood and the rest of the body. Apart from the physical barrier function, endothelial cells maintain the hemostatic equilibrium by their pro- and anticoagulant functions. An important part of their procoagulant contribution is the production of von Willebrand factor (VWF), which is a carrier protein for coagulation factor VIII and facilitates the formation of a platelet plug. Thus, VWF is indispensable for both primary and secondary hemostasis, which is exemplified by the bleeding disorder von Willebrand disease that results from qualitative or quantitative deficiencies in VWF. A cellular model that was found to accurately reflect the endothelium and its secretory organelles are endothelial colony-forming cells, which can be readily isolated from peripheral blood and constitute a robust ex vivo model to investigate the donor's endothelial cell function. This review summarizes some of the valuable insights on biology of VWF and pathogenic mechanisms of von Willebrand disease that have been made possible using studies with endothelial colony-forming cells derived from patients with bleeding disorders.

Coagulation factor VIII: biological basis of emerging hemophilia A therapies

ABSTRACT

Coagulation factor VIII (FVIII) is essential for hemostasis. After activation, it combines with activated FIX (FIXa) on anionic membranes to form the intrinsic Xase enzyme complex, responsible for activating FX in the rate-limiting step of sustained coagulation. Hemophilia A (HA) and hemophilia B are due to inherited deficiencies in the activity of FVIII and FIX, respectively. Treatment of HA over the last decade has benefited from an improved understanding of FVIII biology, including its secretion pathway, its interaction with von Willebrand factor in circulation, the biochemical nature of its FIXa cofactor activity, the regulation of activated FVIII by inactivation pathways, and its surprising immunogenicity. This has facilitated biotechnology innovations with first-in-class examples of several new therapeutic modalities recently receiving regulatory approval for HA, including FVIII-mimetic bispecific antibodies and recombinant adeno-associated viral (rAAV) vector-based gene therapy. Biological insights into FVIII also guide the development and use of gain-of-function FVIII variants aimed at addressing the limitations of first-generation rAAV vectors for HA. Several gain-of-function FVIII variants designed to have improved secretion are currently incorporated in second-generation rAAV vectors and have recently entered clinical trials. Continued mutually reinforcing advancements in the understanding of FVIII biology and treatments for HA are necessary to achieve the ultimate goal of hemophilia therapy: normalizing hemostasis and optimizing well-being with minimal treatment burden for all patients worldwide.

How unique structural adaptations support and coordinate the complex function of von Willebrand factor

ABSTRACT

von Willebrand factor (VWF) is a multimeric protein consisting of covalently linked monomers, which share an identical domain architecture. Although involved in processes such as inflammation, angiogenesis, and cancer metastasis, VWF is mostly known for its role in hemostasis, by acting as a chaperone protein for coagulation factor VIII (FVIII) and by contributing to the recruitment of platelets during thrombus formation. To serve its role in hemostasis, VWF needs to bind a variety of ligands, including FVIII, platelet-receptor glycoprotein Ib-α, VWF-cleaving protease ADAMTS13, subendothelial collagen, and integrin α-IIb/β-3. Importantly, interactions are differently regulated for each of these ligands. How are these binding events accomplished and coordinated? The basic structures of the domains that constitute the VWF protein are found in hundreds of other proteins of prokaryotic and eukaryotic organisms. However, the determination of the 3-dimensional structures of these domains within the VWF context and especially in complex with its ligands reveals that exclusive, VWF-specific structural adaptations have been incorporated in its domains. They provide an explanation of how VWF binds its ligands in a synchronized and timely fashion. In this review, we have focused on the domains that interact with the main ligands of VWF and discuss how elucidating the 3-dimensional structures of these domains has contributed to our understanding of how VWF function is controlled. We further detail how mutations in these domains that are associated with von Willebrand disease modulate the interaction between VWF and its ligands.

The aptamer BT200 blocks interaction of K1405-K1408 in the VWF-A1 domain with macrophage LRP1

ABSTRACT

Rondaptivon pegol (previously BT200) is a pegylated RNA aptamer that binds to the A1 domain of von Willebrand factor (VWF). Recent clinical trials demonstrated that BT200 significantly increased plasma VWF-factor VIII levels by attenuating VWF clearance. The biological mechanism(s) through which BT200 attenuates in vivo clearance of VWF has not been defined. We hypothesized that BT200 interaction with the VWF-A1 domain may increase plasma VWF levels by attenuating macrophage-mediated clearance. We observed that full-length and VWF-A1A2A3 binding to macrophages and VWF-A1 domain binding to lipoprotein receptor-related protein 1 (LRP1) cluster II and cluster IV were concentration-dependently inhibited by BT200. Additionally, full-length VWF binding to LRP1 expressed on HEK293T (HEK-LRP1) cells was also inhibited by BT200. Importantly, BT200 interacts with the VWF-A1 domain in proximity to a conserved cluster of 4 lysine residues (K1405, K1406, K1407, and K1408). Alanine mutagenesis of this K1405-K1408 cluster (VWF-4A) significantly (P < .001) attenuated binding of VWF to both LRP1 clusters II and IV. Furthermore, in vivo clearance of VWF-4A was significantly (P < .001) reduced than that of wild-type VWF. BT200 did not significantly inhibit binding of VWF-4A to LRP1 cluster IV or HEK-LRP1 cells. Finally, BT200 interaction with the VWF-A1 domain also inhibited binding to macrophage galactose lectin and the SR-AI scavenger receptor. Collectively, our findings demonstrate that BT200 prolongs VWF half-life by attenuating macrophage-mediated clearance and specifically the interaction of K1405-K1408 in the VWF-A1 domain with macrophage LRP1. These data support the concept that targeted inhibition of VWF clearance pathways represents a novel therapeutic approach for von Willebrand disease and hemophilia A.

Novel functions for von Willebrand factor

ABSTRACT

For many years, it has been known that von Willebrand factor (VWF) interacts with factor VIII, collagen, and platelets. In addition, the key roles played by VWF in regulating normal hemostasis have been well defined. However, accumulating recent evidence has shown that VWF can interact with a diverse array of other novel ligands. To date, over 60 different binding partners have been described, with interactions mapped to specific VWF domains in some cases. Although the biological significance of these VWF-binding interactions has not been fully elucidated, recent studies have identified some of these novel ligands as regulators of various aspects of VWF biology, including biosynthesis, proteolysis, and clearance. Conversely, VWF binding has been shown to directly affect the functional properties for some of its ligands. In keeping with those observations, exciting new roles for VWF in regulating a series of nonhemostatic biological functions have also emerged. These include inflammation, wound healing, angiogenesis, and bone metabolism. Finally, recent evidence supports the hypothesis that the nonhemostatic functions of VWF directly contribute to pathogenic mechanisms in a variety of diverse diseases including sepsis, malaria, sickle cell disease, and liver disease. In this manuscript, we review the accumulating data regarding novel ligand interactions for VWF and critically assess how these interactions may affect cellular biology. In addition, we consider the evidence that nonhemostatic VWF functions may contribute to the pathogenesis of human diseases beyond thrombosis and bleeding.

Blood coagulation in Prediabetes clusters-impact on all-cause mortality in individuals undergoing coronary angiography

BACKGROUND

Metabolic clusters can stratify subgroups of individuals at risk for type 2 diabetes mellitus and related complications. Since obesity and insulin resistance are closely linked to alterations in hemostasis, we investigated the association between plasmatic coagulation and metabolic clusters including the impact on survival.

METHODS

Utilizing data from the Ludwigshafen Risk and Cardiovascular Health (LURIC) study, we assigned 917 participants without diabetes to prediabetes clusters, using oGTT-derived glucose and insulin, high-density lipoprotein cholesterol, triglycerides, and anthropometric data. We performed a comprehensive analysis of plasmatic coagulation parameters and analyzed their associations with mortality using proportional hazards models. Mediation analysis was performed to assess the effect of coagulation factors on all-cause mortality in prediabetes clusters.

RESULTS

Prediabetes clusters were assigned using published tools, and grouped into low-risk (clusters 1,2,4; n = 643) and high-risk (clusters 3,5,6; n = 274) clusters. Individuals in the high-risk clusters had a significantly increased risk of death (HR = 1.30; CI: 1.01 to 1.67) and showed significantly elevated levels of procoagulant factors (fibrinogen, FVII/VIII/IX), D-dimers, von-Willebrand factor, and PAI-1, compared to individuals in the low-risk clusters. In proportional hazards models adjusted for relevant confounders, elevated levels of fibrinogen, D-dimers, FVIII, and vWF were found to be associated with an increased risk of death. Multiple mediation analysis indicated that vWF significantly mediates the cluster-specific risk of death.

CONCLUSIONS

High-risk prediabetes clusters are associated with prothrombotic changes in the coagulation system that likely contribute to the increased mortality in those individuals at cardiometabolic risk. The hypercoagulable state observed in the high-risk clusters indicates an increased risk for cardiovascular and thrombotic diseases that should be considered in future risk stratification and therapeutic strategies.

Joint health and pain in the changing hemophilia treatment landscape

INTRODUCTION

Hemophilia is an inherited bleeding disorder. Bleeding, and in particular joint hemorrhage results in chronic arthropathy and disability. Acute and chronic pain are frequent and limit activity and participation and result in decreased health-related quality of life. Remarkable progress has been made in the diagnosis and treatment of hemophilia but bleeding continues to prove recalcitrant to currently available treatments and joint disease remains problematic. Physiotherapy and pain management are mainstays of current multidisciplinary integrated care of people with hemophilia (PWH). The focus of this review is on preservation of joint health in the era of new and innovative therapies.

AREAS COVERED

A search of the PubMed Central was conducted on 1 February 2024 using the MeSH Major Topic terms identified as keywords for the manuscript. This review will highlight what is known and unknown about joint bleeding and arthropathy, including insights on pain as a related complication.

EXPERT OPINION

Recent advances in therapeutic interventions aimed at promoting healthy joints in PWH will be discussed, including both the pharmacological treatment landscape and related strategies to promote joint health.

Efanesoctocog alfa: the renaissance of Factor VIII replacement therapy

Efanesoctocog alfa (Altuviiio,TM Sanofi-SOBI) is a B domain-deleted single-chain Factor VIII (FVIII) connected to D'D3 domain of von Willebrand Factor (vWF). Its ingenious design allows efanesoctocog alfa to operate independently of endogenous vWF and results in an outstanding 3-4 times longer half-life compared to standard and extended half-life (EHL) FVIII products. The prolonged half-life ensures sustained high levels of factor activity, maintaining normal to near-normal ranges for the majority of the week, facilitating the convenience of once-weekly administration. Efanesoctocog alfa received regulatory approval in 2023 for application in both adults and children with inherited hemophilia A in the United States and Japan. Its sanctioned use encompasses both prophylaxis and 'on demand' treatment for bleeding episodes. The European Medicines Agency (EMA) is currently undertaking a comprehensive review of Altuviiio. TM This comprehensive review focuses on the immunological profile of efanesoctocog alfa, a highly sophisticated new class of EHL FVIII molecule. The integration of the vWF D'D3 domain, XTEN polypeptides, and potential regulatory T-cell epitopes within various segments of efanesoctocog alfa collectively serves as a mitigating factor against the development of a neutralizing T-cell-mediated immune response. We hypothesize that such distinctive attribute may significantly reduce the risk of neutralizing antibodies, particularly in previously untreated patients. The discussion extends beyond regulatory approval to encompass the preclinical and clinical development of efanesoctocog alfa, including considerations for laboratory monitoring. The review also highlights areas that warrant further investigation to deepen our understanding of this groundbreaking therapeutic agent.

von Willebrand disease

von Willebrand disease (VWD) is the most common inherited bleeding disorder. The disorder is characterized by excessive mucocutaneous bleeding. The most common bleeding manifestations of this condition include nosebleeds, bruising, bleeding from minor wounds, menorrhagia or postpartum bleeding in women as well as bleeding after surgery. Other less frequent symptoms include gastrointestinal bleeding, haematomas or haemarthroses. VWD pathophysiology is complex and results from defects in von Willebrand factor (VWF) glycoprotein. Quantitative deficiencies are responsible for type 1 VWD with a partial decrease of VWF and type 3 with the complete absence of VWF. Qualitative abnormalities cause type 2 VWD, being further divided into types 2A, 2B, 2M and 2N. Although common, VWD is at risk of misdiagnosis, overdiagnosis and underdiagnosis owing to several factors, including complex diagnosis, variability of bleeding symptoms, presence of external variables (blood groups and other physiological modifiers such as exercise, thyroid hormones, oestrogens, and ageing), and lack of disease awareness among non-specialist health-care providers. Establishing the correct VWD diagnosis requires an array of specialized phenotypic assays and/or molecular genetic testing of the VWF gene. The management of bleeding includes increasing endogenous VWF levels with desmopressin or infusion of exogenous VWF concentrates (plasma-derived or recombinant). Fibrinolytic inhibitors, topical haemostatic agents and hormonal therapies are used as effective adjunctive measures.

Efanesoctocog Alfa Prophylaxis for Children with Severe Hemophilia A

BACKGROUND

Once-weekly efanesoctocog alfa provides high sustained factor VIII activity with superior bleeding prevention as compared with prestudy factor VIII prophylaxis in previously treated patients 12 years of age or older with severe hemophilia A. Data on outcomes of efanesoctocog alfa treatment in children younger than 12 years of age with severe hemophilia A are limited.

METHODS

We conducted a phase 3, open-label study involving previously treated patients younger than 12 years of age with severe hemophilia A. Patients received prophylaxis with once-weekly efanesoctocog alfa (50 IU per kilogram of body weight) for 52 weeks. The primary end point was the occurrence of factor VIII inhibitors (neutralizing antibodies against factor VIII). Secondary end points included annualized rates of treated bleeding episodes, bleeding treatment, safety, and pharmacokinetics.

RESULTS

A total of 74 male patients were enrolled (38 with an age of <6 years and 36 with an age of 6 to <12 years). No factor VIII inhibitors developed. Most adverse events were nonserious. No serious adverse events that were assessed by the investigator as being related to efanesoctocog alfa were reported. In the 73 patients treated according to the protocol, the median and model-based mean annualized bleeding rates were 0.00 (interquartile range, 0.00 to 1.02) and 0.61 (95% confidence interval, 0.42 to 0.90), respectively. A total of 47 patients (64%) had no treated bleeding episodes, 65 (88%) had no spontaneous bleeding episodes, and 61 (82%) had no episodes of bleeding into joints. A total of 41 of 43 bleeding episodes (95%) resolved with one injection of efanesoctocog alfa. Mean factor VIII activity at steady state was more than 40 IU per deciliter for 3 days and more than 10 IU per deciliter for almost 7 days after dose administration. The geometric mean terminal half-life was 40.0 hours.

CONCLUSIONS

In children with severe hemophilia A, once-weekly prophylaxis with efanesoctocog alfa provided high sustained factor VIII activity in the normal to near-normal range (>40 IU per deciliter) for 3 days and more than 10 IU per deciliter for almost 7 days after administration, leading to effective bleeding prevention. Efanesoctocog alfa was associated with mainly nonserious adverse events. (Funded by Sanofi and Sobi; XTEND-Kids ClinicalTrials.gov number, NCT04759131.).

Ultra-Long factor VIII: a major step forward toward a hemophilia-free mind

A remarkable step forward in the treatment of hemophilia A has recently been achieved with the development of an Ultra-Long modified factor (F)VIII. Leveraging expertise gained with fusion to immunoglobulin Fc fragments, disconnecting FVIII from endogenous von Willebrand factor (via a D'-D3 fragment), and benefiting from the pharmacokinetic prolongation provided by the addition of hydrophilic polypeptides, efanesoctocog alfa opens a new era in the treatment of hemophilia A. The term Ultra-Long FVIII has been proposed to designate it and differentiate it from extended half-life FVIII. The level of FVIII correction within the normal range for several days provided by this molecule should allow an increasing number of patients to free themselves from the physical and psychological constraints of hemophilia A. Certainly, the burden of weekly intravenous infusions persists but is compensated by a correction of hemostasis whose amplitude and duration remain unmatched by other therapeutic options currently available.

Therapeutic Applications of Aptamers

Affinity reagents, or target-binding molecules, are quite versatile and are major workhorses in molecular biology and medicine. Antibodies are the most famous and frequently used type and they have been used for a wide range of applications, including laboratory techniques, diagnostics, and therapeutics. However, antibodies are not the only available affinity reagents and they do have significant drawbacks, including laborious and costly production. Aptamers are one potential alternative that have a variety of unique advantages. They are single stranded DNA or RNA molecules that can be selected for binding to many targets including proteins, carbohydrates, and small molecules-for which antibodies typically have low affinity. There are also a variety of cost-effective methods for producing and modifying nucleic acids in vitro without cells, whereas antibodies typically require cells or even whole animals. While there are also significant drawbacks to using aptamers in therapeutic applications, including low in vivo stability, aptamers have had success in clinical trials for treating a variety of diseases and two aptamer-based drugs have gained FDA approval. Aptamer development is still ongoing, which could lead to additional applications of aptamer therapeutics, including antitoxins, and combinatorial approaches with nanoparticles and other nucleic acid therapeutics that could improve efficacy.

Classification of recombinant factor VIII products and implications for clinical practice: A systematic literature review

INTRODUCTION

Consensus over the definition of recombinant factor VIII (rFVIII) product classification in haemophilia A is lacking. rFVIII products are often classified as standard half-life (SHL) or extended half-life (EHL); despite this, no universally accepted definition currently exists. One proposed definition includes half-life, area under the curve, and technology designed to extend half-life; however, the International Society on Thrombosis and Haemostasis defines activity over time as the most intuitive information for building treatment regimens and the World Federation of Hemophilia describes rFVIII product classification in terms of infusion frequency.

AIM

To summarise published data on the clinical and pharmacokinetic criteria used to define rFVIII product classification.

METHODS

PubMed and EMBASE database searches of English-language articles (2002-2022) were conducted using search strings to identify the relevant population, intervention, and outcomes (e.g., clinical and pharmacokinetic parameters). Articles then underwent title/abstract and full-text screens.

RESULTS

Among 1147 identified articles, 62 were included. Half-life was the most widely reported outcome with no clear trends or product groupings observed. No clear groupings emerged among other outcomes, including infusion frequency, consumption, and efficacy. As activity over time was reported in few articles, further investigation of its relevance to rFVIII product classification is warranted.

CONCLUSION

The findings of this systematic literature review suggest that parameters other than half-life might be important for the development of a comprehensive and clinically relevant rFVIII product classification definition. There seems to be an opportunity to consider parameters that are clinically meaningful and useful for shared decision-making in haemophilia A treatment.

Deciphering the triad of endothelial glycocalyx, von Willebrand Factor, and P-selectin in inflammation-induced coagulation

This review examines the endothelial glycocalyx's role in inflammation and explores its involvement in coagulation. The glycocalyx, composed of proteins and glycosaminoglycans, interacts with von Willebrand Factor and could play a crucial role in anchoring it to the endothelium. In inflammatory conditions, glycocalyx degradation may leave P-selectin as the only attachment point for von Willebrand Factor, potentially leading to uncontrolled release of ultralong von Willebrand Factor in the bulk flow in a shear stress-dependent manner. Identifying specific glycocalyx glycosaminoglycan interactions with von Willebrand Factor and P-selectin can offer insights into unexplored coagulation mechanisms.

Factor VIII moiety of recombinant Factor VIII Fc fusion protein impacts Fc effector function and CD16+ NK cell activation

Recombinant Factor VIII-Fc fusion protein (rFVIIIFc) is an enhanced half-life therapeutic protein product used for the management of hemophilia A. Recent studies have demonstrated that rFVIIIFc interacts with Fc gamma receptors (FcγR) resulting in the activation or inhibition of various FcγR-expressing immune cells. We previously demonstrated that rFVIIIFc, unlike recombinant Factor IX-Fc (rFIXFc), activates natural killer (NK) cells via Fc-mediated interactions with FcγRIIIA (CD16). Additionally, we showed that rFVIIIFc activated CD16+ NK cells to lyse a FVIII-specific B cell clone. Here, we used human NK cell lines and primary NK cells enriched from peripheral blood leukocytes to study the role of the FVIII moiety in rFVIIIFc-mediated NK cell activation. Following overnight incubation of NK cells with rFVIIIFc, cellular activation was assessed by measuring secretion of the inflammatory cytokine IFNγ by ELISA or by cellular degranulation. We show that anti-FVIII, anti-Fc, and anti-CD16 all inhibited indicating that these molecules were involved in rFVIIIFc-mediated NK cell activation. To define which domains of FVIII were involved, we used antibodies that are FVIII domain-specific and demonstrated that blocking FVIII C1 or C2 domain-mediated membrane binding potently inhibited rFVIIIFc-mediated CD16+ NK cell activation, while targeting the FVIII heavy chain domains did not. We also show that rFVIIIFc binds CD16 with about five-fold higher affinity than rFIXFc. Based on our results we propose that FVIII light chain-mediated membrane binding results in tethering of the fusion protein to the cell surface, and this, together with increased binding affinity for CD16, allows for Fc-CD16 interactions to proceed, resulting in NK cellular activation. Our working model may explain our previous results where we observed that rFVIIIFc activated NK cells via CD16, whereas rFIXFc did not despite having identical IgG1 Fc domains.

Impact of allele-selective silencing of von Willebrand factor in mice based on a single nucleotide allelic difference in von Willebrand factor

INTRODUCTION

Von Willebrand factor (VWF) plays a pathophysiological role in hemostatic disorders. Partial inhibition of the VWF gene through small interfering RNA (siRNA)-mediated allele-selective silencing could be a promising therapeutic strategy. For von Willebrand disease, allele-selectively inhibiting dominant-negative VWF-alleles might ameliorate the phenotype. For thrombotic disorders, partial VWF reduction can lower thrombotic risk, while avoiding bleeding. Previously, we demonstrated the feasibility of Vwf-silencing in homozygous C57BL/6J (B6) or 129S1/SvImJ (129S) mice. The present study investigated allele-selective Vwf-silencing in a complex heterozygous setting of crossed B6 and 129S mice and its subsequent hemostatic impact.

MATERIALS AND METHODS

Heterozygous B6.129S mice were treated with siRNAs targeting Vwf expressed from either B6- (siVwf.B6) or 129S-alleles (siVwf.129S). Plasma VWF and lung Vwf mRNA were determined. siVwf.B6-treated B6.129S mice were subjected to ferric chloride-induced mesenteric vessel thrombosis and tail-bleeding.

RESULTS

In B6.129S mice, siVwf.B6 reduced Vwf mRNA of the targeted B6-allele by 72% vs. only 12% of the non-targeted 129S-allele (41% total mRNA reduction), lowering plasma VWF by 46%. Oppositely, siVwf.129S reduced Vwf mRNA by 45%, now selectively inhibiting the 129S-allele over the B6-allele (58% vs. 9%), decreasing plasma VWF by 43%. The allele-selective VWF reduction by siVwf.B6 coincided with decreased thrombus formation in mesenteric arterioles, without prolonging tail-bleeding times.

CONCLUSIONS

This study demonstrates the feasibility of allele-selective Vwf-silencing in a heterozygous setting, achieving a controlled close to 50% reduction of plasma VWF. The observed thromboprotection and absence of prolonged bleeding times underline the potential of allele-selective Vwf-silencing as a therapeutic strategy in hemostatic disorders.

Identification of the Efficient Enhancer Elements in FVIII-Padua for Gene Therapy Study of Hemophilia A

Hemophilia A (HA) is a common X-linked recessive hereditary bleeding disorder. Coagulation factor VIII (FVIII) is insufficient in patients with HA due to the mutations in the F8 gene. The restoration of plasma levels of FVIII via both recombinant B-domain-deleted FVIII (BDD-FVIII) and B-domain-deleted F8 (BDDF8) transgenes was proven to be helpful. FVIII-Padua is a 23.4 kb tandem repeat mutation in the F8 associated with a high F8 gene expression and thrombogenesis. Here we screened a core enhancer element in FVIII-Padua for improving the F8 expression. In detail, we identified a 400 bp efficient enhancer element, C400, in FVIII-Padua for the first time. The core enhancer C400 extensively improved the transcription of BDDF8 driven by human elongation factor-1 alpha in HepG2, HeLa, HEK-293T and induced pluripotent stem cells (iPSCs) with different genetic backgrounds, as well as iPSCs-derived endothelial progenitor cells (iEPCs) and iPSCs-derived mesenchymal stem cells (iMSCs). The expression of FVIII protein was increased by C400, especially in iEPCs. Our research provides a novel molecular target to enhance expression of FVIII protein, which has scientific value and application prospects in both viral and nonviral HA gene therapy strategies.

Loss of factor VIII in zebrafish rebalances antithrombin deficiency but has a limited bleeding diathesis

Deficiencies in coagulation factor VIII (FVIII, F8) result in the bleeding disorder hemophilia A. An emerging novel therapeutic strategy for bleeding disorders is to enhance hemostasis by limiting natural anticoagulants, such as antithrombin (AT3). To study pro/anticoagulant hemostatic balance in an in vivo model, we used genome editing to create null alleles for f8 and von Willebrand factor (vwf) in zebrafish, a model organism with a high degree of homology to the mammalian hemostatic system and unique attributes, including external development and optical transparency. f8 homozygous mutant larvae surprisingly formed normal thrombi when subjected to laser-mediated endothelial injury, had no overt signs of hemorrhage, but had a modest increase in mortality. We have previously shown that at3 -/- larvae develop disseminated intravascular coagulation (DIC), with spontaneous thrombosis and fibrinogen consumption, resulting in bleeding phenotype marked by secondary lack of induced thrombus formation upon endothelial injury. We found that with loss of FVIII (f8 -/-;at3 -/-), larvae no longer developed spontaneous fibrin thrombi and did produce clots in response to endothelial injury. However, homozygous loss of zebrafish Vwf failed to rescue the at3 DIC phenotype. These studies demonstrate an altered balance of natural anticoagulants that mitigates FVIII deficiency in zebrafish, similar to human clinical pipeline products. The data also suggest that zebrafish FVIII might circulate independently of Vwf. Further study of this unique balance could provide new insights for management of hemophilia A and von Willebrand disease.

Nothing short of a revolution: Novel extended half-life factor VIII replacement products and non-replacement agents reshape the treatment landscape in hemophilia A

Hemophilia A, an X-linked genetic disorder, is characterized by a deficiency or dysfunction of clotting Factor VIII. The treatment landscape has substantially changed by introducing novel extended half-life factor VIII (EHL-FVIII) replacement therapies such as efanesoctocog Alfa and non-factor replacement therapy such as emicizumab. These agents signal a shift from treatments requiring multiple weekly infusions to advanced therapies with long half-lives, offering superior protection against bleeding and improving patient adherence and quality of life. While EHL-FVIII treatment might lead to inhibitor development in some patients, non-factor replacement therapy carries thrombotic risks. Therefore, ongoing research and the generation of robust clinical evidence remain vital to guide the selection of optimal and cost-effective first-line therapies for hemophilia A patients.

REVIEWING THE DYSREGULATION OF ADAMTS13 AND VWF IN SEPSIS

ABSTRACT

Sepsis is defined as a life-threatening organ dysfunction caused by excessive host response to infection, and represents the most common cause of in-hospital deaths. Sepsis accounts for 30% of all critically ill patients in the intensive care unit (ICU), and has a global mortality rate of 20%. Activation of blood coagulation during sepsis and septic shock can lead to disseminated intravascular coagulation, which is characterized by microvascular thrombosis. Von Willebrand factor (VWF) and ADAMTS13 are two important regulators of blood coagulation that may be important links between sepsis and mortality in the ICU. Herein we review our current understanding of VWF and ADAMTS13 in sepsis and other critical illnesses and discuss their contribution to disease pathophysiology, their use as markers of severe illness, and potential targets for new therapeutic development.

Efficacy of Wilate Prophylaxis in Reducing Nosebleeds in Patients with Severe VWD - A Post-hoc Analysis of the WIL-31 Study

BACKGROUND

Prophylaxis with a von Willebrand factor (VWF) concentrate is recommended in von Willebrand disease (VWD) patients with a history of frequent and severe bleeds. Despite nosebleeds being a frequent manifestation of VWD, few studies have investigated the efficacy of factor prophylaxis in preventing nosebleeds in patients with severe VWD.

METHODS

This post-hoc analysis of a prospective, 12-month, phase 3 study assessed the efficacy of wilate in the prevention of nosebleeds in 33 patients aged ≥6 years with severe type 1, type 2 or type 3 VWD. All patients previously participated in a 6-month prospective study of on-demand treatment with any VWF concentrate. Prophylactic efficacy was assessed by comparing total and spontaneous annualized bleeding rates for nosebleeds (TABR and SABR, respectively) during prophylaxis with rates during on-demand treatment.

RESULTS

The mean TABR and SABR for nosebleeds were reduced by 76% and 81% respectively during prophylaxis versus on-demand treatment (2.7 vs 11.0 and 2.1 vs 10.9). During the second 6 months of prophylaxis, mean TABR was 49% lower and mean SABR 57% lower versus the first 6 months. The percentage of patients with zero nosebleeds was 19% during 6 months of on-demand treatment, 55% during the first 6 months of prophylaxis, and 68% during the second 6 months of prophylaxis. The efficacy of wilate in the treatment of breakthrough nosebleeds was rated excellent in 99% of cases.

CONCLUSION

This post-hoc analysis demonstrated the efficacy of wilate prophylaxis in the prevention and treatment of nosebleeds in children and adults with severe VWD.

Safety, pharmacokinetics and efficacy of a subcutaneous recombinant FVIII (OCTA101) in adult patients with severe haemophilia A

INTRODUCTION

Regular, prophylactic intravenous (i.v.) FVIII can be challenging for some patients with haemophilia A. Subcutaneous (s.c.) FVIII administration could provide an alternative treatment option with greater convenience and without the complications associated with venous access.

AIM

To assess the safety, pharmacokinetics (PK), bioavailability and efficacy of s.c. OCTA101, a recombinant FVIII with a recombinant von Willebrand factor fragment dimer.

METHODS

This was a single-centre, prospective, open-label, phase I/II study (NCT04046848). Previously treated male patients (≥18 years) with severe haemophilia A were eligible for the study. The primary objective of the study was to assess the safety (including immunogenicity) of OCTA101. Secondary objectives included assessments of PK, bioavailability, and the efficacy of prophylaxis.

RESULTS

Thirty patients were treated with OCTA101. FVIII inhibitors developed in five (16.7%) patients during daily prophylaxis with 40-60 IU/kg (three cases) and 12.5 IU/kg (two cases) OCTA101. The trial was therefore terminated. OCTA101 had a 2.5-fold longer terminal half-life compared with i.v. rFVIII, and bioavailability was 16.6%. Efficacy data at study termination indicated that daily prophylaxis with 40-60 IU/kg OCTA101 was efficacious in the absence of FVIII inhibitors.

CONCLUSIONS

Despite promising PK and efficacy results, the trial was terminated due to the incidence of FVIII inhibitors. The occurrence of inhibitors at two dose levels suggests that their development may be related to the subcutaneous route of administration.

von Willebrand factor Ristocetin co-factor activity to von Willebrand factor antigen level ratio for diagnosis of acquired von Willebrand syndrome caused by aortic stenosis

Background

Severe aortic stenosis (AS) causes acquired von Willebrand syndrome by the excessive shear stress-dependent cleavage of high molecular weight multimers of von Willebrand factor (VWF). While the current standard diagnostic method is so-called VWF multimer analysis that is western blotting under nonreducing conditions, it remains unclear whether a ratio of VWF Ristocetin co-factor activity (VWF:RCo) to VWF antigen levels (VWF:Ag) of <0.7, which can be measured with an automated coagulation analyzer in clinical laboratories and is used for the diagnosis of hereditary von Willebrand disease.

Objectives

To evaluated whether the VWF:RCo/VWF:Ag is useful for the diagnosis of AS-induced acquired von Willebrand syndrome.

Methods

VWF:RCo and VWF:Ag were evaluated with the VWF large multimer index as a reference, which represents the percentage of a patient's VWF high molecular weight multimer ratio to that of standard plasma in the VWF multimer analysis.

Results

We analyzed 382 patients with AS having transaortic valve maximal pressure gradients of >30 mmHg, 27 patients with peripheral artery disease, and 46 control patients free of cardiovascular disease with osteoarthritis, diabetes, and so on. We assumed a large multimer index of <80% as loss of VWF large multimers since 59.0% of patients with severe AS had the indices of <80%, while no control patients or patients with peripheral artery disease, except for 2 patients, exhibited the indices of <80%. The VWF:RCo/VWF:Ag ratios, measured using an automated blood coagulation analyzer, were correlated with the indices (rs = 0.470, P < .001). When the ratio of <0.7 was used as a cut-off point, the sensitivity and specificity to VWF large multimer indices of <80% were 0.437 and 0.826, respectively.

Conclusion

VWF:RCo/VWF:Ag ratios of <0.7 may indicate loss of VWF large multimers with high specificity, but low sensitivity. VWF:RCo/VWF:Ag ratios in patients with AS having a ratio of <0.7 may be useful for monitoring the loss of VWF large multimers during their clinical courses.

von Willebrand factor modulates immune complexes and the recall response against factor VIII in a murine hemophilia A model

Achieving tolerance toward factor VIII (FVIII) remains an important goal of hemophilia treatment. Up to 40% of patients with severe hemophilia A (HA) develop neutralizing antibodies against FVIII, and the only proven treatment to achieve tolerance is infusion of FVIII over prolonged periods in the context of immune tolerance induction. Here, we addressed the role of von Willebrand factor (VWF) as a modulator of anti-FVIII antibody effector functions and the FVIII-specific recall response in an HA mouse model. Analytical ultracentrifugation was used to demonstrate formation of FVIII-containing immune complexes (FVIII-ICs). VWF did not fully prevent FVIII-IC formation but was rather incorporated into larger macromolecular complexes. VWF prevented binding of FVIII-ICs to complement C1q, most efficiently when it was preincubated with FVIII before the addition of antibodies. It also prevented binding to immobilized Fc-γ receptor and to bone marrow-derived dendritic cells. An in vitro model of the anti-FVIII recall response demonstrated that addition of VWF to FVIII abolished the proliferation of FVIII-specific antibody-secreting cells. After adoptive transfer of sensitized splenocytes into immunocompetent HA mice, the FVIII recall response was diminished by VWF. In summary, these data indicate that VWF modulates the formation and effector functions of FVIII-ICs and attenuates the secondary immune response to FVIII in HA mice.

Targeting higher factor VIII levels for prophylaxis in haemophilia A: a narrative review

INTRODUCTION

The standard of care in severe haemophilia A is prophylaxis, which has historically aimed for a factor VIII (FVIII) trough level of ≥1%. However, despite prophylactic treatment, people with haemophilia remain at risk of bleeds that have physical and quality of life implications, and that impact everyday life.

AIM

The aim of this review was to evaluate evidence supporting the relationship between targeting higher FVIII activity levels with prophylaxis and improved outcomes in people with haemophilia A.

METHODS

We conducted a narrative review that defined the unmet needs and treatment goals in people with haemophilia A, evaluated evidence to support targeting higher FVIII activity levels, and highlighted therapies that may support higher and sustained FVIII activity levels and improved outcomes for people with haemophilia A.

RESULTS

Despite recent advances in treatment, unmet needs remain, and people with haemophilia continue to experience joint and functional impairment, acute and chronic pain, and poor mental health. All these negatively impact their health-related quality of life. Evidence suggests that FVIII activity levels of up to 50% may be needed to achieve a near-zero joint bleed rate. However, achieving high FVIII activity levels with current standard and extended half-life (EHL) FVIII replacement therapies is associated with a high treatment burden. Innovative treatment options may provide high sustained FVIII activity levels and improved patient outcomes.

CONCLUSION

Evidence suggests that FVIII activity levels in people with haemophilia A should be sustained at higher levels to improve joint and patient outcomes and enable progression towards health equity.

The contribution of the sinusoidal endothelial cell receptors CLEC4M, stabilin-2, and SCARA5 to VWF-FVIII clearance in thrombosis and hemostasis

Quantitative abnormalities in factor VIII (FVIII) and its binding partner, von Willebrand factor (VWF), are associated with an increased risk of bleeding or thrombosis, and pathways that regulate the clearance of VWF-FVIII can strongly influence their plasma levels. In 2010, the Cohorts for Heart and Aging Research in Genome Epidemiology (CHARGE) on genome-wide association study meta-analysis identified variants in the genes for the sinusoidal endothelial receptors C-type lectin domain family 4 member M (CLEC4M), stabilin-2, and scavenger receptor class A member 5 (SCARA5) as being associated with plasma levels of VWF and/or FVIII in normal individuals. The ability of these receptors to bind, internalize, and clear the VWF-FVIII complex from the circulation has now been reported in a series of studies using in vitro and in vivo models. The receptor stabilin-2 has also been shown to modulate the immune response to infused VWF-FVIII concentrates in a murine model. In addition, the influence of genetic variants in CLEC4M, STAB2, and SCARA5 on type 1 von Willebrand disease/low VWF phenotype, FVIII pharmacokinetics, and the risk of venous thromboembolism has been described in a number of patient-based studies. Understanding the role of these receptors in the regulation of VWF-FVIII clearance has led to significant insights into the genomic architecture that modulates plasma VWF and FVIII levels, improving the understanding of pathways that regulate VWF-FVIII clearance and the mechanistic basis of quantitative VWF-FVIII pathologies.

von Willebrand factor binds to angiopoietin-2 within endothelial cells and after release from Weibel-Palade bodies

BACKGROUND

The von Willebrand factor (VWF) is a multimeric plasma glycoprotein essential for hemostasis, inflammation, and angiogenesis. The majority of VWF is synthesized by endothelial cells (ECs) and stored in Weibel-Palade bodies (WPB). Among the range of proteins shown to co-localize to WPB is angiopoietin-2 (Angpt-2), a ligand of the receptor tyrosine kinase Tie-2. We have previously shown that VWF itself regulates angiogenesis, raising the hypothesis that some of the angiogenic activity of VWF may be mediated by its interaction with Angpt-2.

METHODS

Static-binding assays were used to probe the interaction between Angpt-2 and VWF. Binding in media from cultured human umbilical vein ECs s and in plasma was determined by immunoprecipitation experiments. Immunofluorescence was used to detect the presence of Angpt-2 on VWF strings, and flow assays were used to investigate the effect on VWF function.

RESULTS

Static-binding assays revealed that Angpt-2 bound to VWF with high affinity (KD,app ∼3 nM) in a pH and calcium-dependent manner. The interaction was localized to the VWF A1 domain. Co-immunoprecipitation experiments demonstrated that the complex persisted following stimulated secretion from ECs and was present in plasma. Angpt-2 was also visible on VWF strings on stimulated ECs. The VWF-Angpt-2 complex did not inhibit the binding of Angpt-2 to Tie-2 and did not significantly interfere with VWF-platelet capture.

CONCLUSIONS

Together, these data demonstrate a direct binding interaction between Angpt-2 and VWF that persists after secretion. VWF may act to localize Angpt-2; further work is required to establish the functional consequences of this interaction.

Acquired von Willebrand Syndrome in a Patient Undergoing Extracorporeal Membrane Oxygenation: A Case Report

Acquired von Willebrand syndrome (AvWS) is a rare bleeding disorder caused by dysfunction of the von Willebrand factor (vWF), leading to bleeding manifestations. It usually occurs due to an underlying disorder in patients with no family or personal history of bleeding diathesis. The exact mechanism causing this syndrome is not fully understood, but it involves a complex interplay of factors. Specifically, vWF deficiency or reduced activity can occur due to antibodies, adsorption of vWF onto tumor cells, shear stress, or increased proteolysis. We describe a patient with severe, right-sided heart failure secondary to idiopathic pulmonary hypertension. The patient was admitted to the intensive care unit to be placed on a venoarterial extracorporeal membrane oxygenation (VA ECMO) machine while awaiting bilateral lung transplantation. A few hours after initiation of VA ECMO, the patient experienced epistaxis and continuous bleeding from the cannula tips. The laboratory investigations were based on the measurements of vWF antigen (vWF:Ag), vWF ristocetin cofactor activity (vWF:RCo), and multimer analysis. The obtained results revealed a decreased VWF:RCo/VWF:Ag ratio (<0.7) and the loss of high-molecular-weight multimers of vWF, thus confirming the diagnosis of AvWS. This report reviews how to make the clinical diagnosis of AvWS, including a discussion of necessary laboratory results and their pitfalls, and highlights the importance of having a high index of suspicion of AvWS in the ECMO population so that laboratory values are obtained on time to allow for treatment and successful recovery.

Desmopressin in nonsevere hemophilia A: patient perspectives on use and efficacy

Background

Desmopressin increases plasma factor VIII and von Willebrand factor levels in persons with nonsevere hemophilia A. Patients' perspectives on desmopressin are relevant to increase and optimize its suboptimal use. However, patients' views on desmopressin are not reported.

Objectives

To evaluate the perspectives of persons with nonsevere hemophilia A on desmopressin use, barriers for its use, side effects, and their knowledge about desmopressin's efficacy and side effects.

Methods

Persons with nonsevere hemophilia A were included in a cross-sectional, national, multicenter study. Questionnaires were filled out by adult patients and children aged ≥12 years themselves. Caretakers filled out questionnaires for children aged <12 years.

Results

In total, 706 persons with nonsevere hemophilia A were included (544 mild, 162 moderate, [age range, 0-88 years]). Of 508 patients, 234 (50%) patients reported previous desmopressin use. Desmopressin was considered as at least moderately effective in 171 of 187 (90%) patients. Intranasal administration was the modality of choice for 138 of 182 (76%) patients. Flushing was the most reported side effect in 54 of 206 (26%) adults and 7 of 22 (32%) children. The most frequently reported advantage and disadvantage were the convenience of intranasal, out-of-hospital administration by 56% (126/227) and side effects in 18% (41/227), respectively. Patients' self-perceived knowledge was unsatisfactory or unknown in 28% (63/225).

Conclusion

Overall, desmopressin was most often used intranasally and considered effective, with flushing as the most common side effect. The most mentioned advantage was the convenience of intranasal administration and disadvantage was side effects. More information and education on desmopressin could answer unmet needs in patients with current or future desmopressin treatment.

Efanesoctocog alfa for the prevention and treatment of bleeding in patients with hemophilia A

INTRODUCTION

Hemophilia A is an inherited bleeding disorder due to a deficiency of coagulation factor VIII (FVIII). Prevention and treatment of bleeding is traditionally through intravenous infusion of a FVIII concentrate. Modifications of recombinant FVIII (rFVIII) with an aim to prolong the half-life have been modest, thought because FVIII is dependent on plasma von Willebrand factor (VWF) for its half-life. Efanesoctocog alfa (ALTUVIIIO), approved by the Federal Drug Administration (FDA) in February 2023, was made independent of endogenous VWF by linking of the FVIII-binding D'D3 domain of VWF to B-domain deleted single chain FVIII.

AREAS COVERED

This review will outline the development of efanesoctocog alfa and the pharmacokinetic and safety data from clinical trials, as well as efficacy data from the phase 3 trials. These data formed the basis for the FDA approval.

EXPERT OPINION

Efanesoctocog alfa is a new type of FVIII replacement with an extended half-life allowing once weekly dosing to achieve hemostasis and FVIII trough levels of 13-15 IU/dL. This provides a highly effective option for treatment and prevention of bleeding in hemophilia A, where FVIII levels are easily measured. It also provides an option for treatment of bleeding and coverage for surgery with few infusions.

Plasma Clearance of Coagulation Factor VIII and Extension of Its Half-Life for the Therapy of Hemophilia A: A Critical Review of the Current State of Research and Practice

Factor VIII (FVIII) is an important component of blood coagulation as its congenital deficiency results in life-threatening bleeding. Current prophylactic therapy of the disease (hemophilia A) is based on 3-4 intravenous infusions of therapeutic FVIII per week. This poses a burden on patients, demanding reduction of infusion frequency by using FVIII with extended plasma half-life (EHL). Development of these products requires understanding FVIII plasma clearance mechanisms. This paper overviews (i) an up-to-date state of the research in this field and (ii) current EHL FVIII products, including recently approved efanesoctocog alfa, for which the plasma half-life exceeds a biochemical barrier posed by von Willebrand factor, complexed with FVIII in plasma, which results in ~1 per week infusion frequency. We focus on the EHL FVIII products' structure and function, in particular related to the known discrepancy in results of one-stage clotting (OC) and chromogenic substrate (CS) assays used to assign the products' potency, dosing, and for clinical monitoring in plasma. We suggest a possible root cause of these assays' discrepancy that is also pertinent to EHL factor IX variants used to treat hemophilia B. Finally, we discuss approaches in designing future EHL FVIII variants, including those to be used for hemophilia A gene therapy.

Pharmacokinetics of recombinant factor VIII in adults with severe hemophilia A: fixed-sequence single-dose study of octocog alfa, rurioctocog alfa pegol, and efanesoctocog alfa

Background

Efanesoctocog alfa is a new class of factor (F) VIII replacement therapy designed to provide high sustained factor levels for longer by overcoming the von Willebrand factor half-life ceiling.

Objectives

To assess the pharmacokinetics and safety of standard half-life (octocog alfa) and extended half-life (rurioctocog alfa pegol) FVIIIs and efanesoctocog alfa.

Methods

This phase 1 study (NCT05042440; EudraCT 2021-000228-37) enrolled previously treated adult men with severe hemophilia A. Patients received sequential single 50-IU/kg doses of octocog alfa, rurioctocog alfa pegol, and efanesoctocog alfa after appropriate washout periods between each dose.

Results

Thirteen participants were enrolled. Geometric mean elimination half-life of octocog alfa, rurioctocog alfa pegol, and efanesoctocog alfa was 11.0, 15.4, and 43.3 hours, respectively, and area under the FVIII activity-time curve was 1670, 2820, and 10,100 IU × h/dL, respectively. Efanesoctocog alfa maintained mean FVIII activity levels of >40 IU/dL for up to 4 days and at ∼10 IU/dL on day 7. Corresponding times for >40 IU/dL and >10 IU/dL were <1 and <2 days, respectively, for octocog alfa and 1 day and <3 days, respectively, for rurioctocog alfa pegol. No serious treatment-emergent adverse events were reported for efanesoctocog alfa, and no inhibitor development to FVIII was detected.

Conclusion

Efanesoctocog alfa had 3- to 4-fold longer elimination half-life and 3- to 6-fold greater exposure (area under the FVIII activity-time curve, 6.03 and 3.57 folds) than octocog alfa and rurioctocog alfa pegol. Efanesoctocog alfa provided high sustained FVIII activity in the normal-to-near-normal range (>40 IU/dL) for up to 4 days after the dose and at ∼10 IU/dL on day 7.

Efanesoctocog Alfa: First Approval

Efanesoctocog alfa (ALTUVIIIO^TM; [antihemophilic factor (recombinant), Fc-VWF-XTEN fusion protein-ehtl]), a von Willebrand factor (VWF) independent, recombinant DNA-derived Factor VIII (FVIII) concentrate, has been developed by Bioverativ Therapeutics, Inc (a Sanofi company) and Swedish Orphan Biovitrum AB (Sobi). Efanesoctocog alfa was approved in February 2023 in the USA for use in adults and children with hemophilia A (congenital FVIII deficiency) for: routine prophylaxis to reduce the frequency of bleeding episodes; on-demand treatment and control of bleeding episodes; perioperative management of bleeding. This article summarizes the milestones in the development of efanesoctocog alfa leading to this first approval for hemophilia A.

Macrophage Galactose Lectin Contributes to the Regulation of FVIII (Factor VIII) Clearance in Mice-Brief Report

BACKGROUND

Although most plasma FVIII (Factor VIII) circulates in complex with VWF (von Willebrand factor), a minority (3%-5%) circulates as free-FVIII, which is rapidly cleared. Consequently, 20% of total FVIII may be cleared as free-FVIII. Critically, the mechanisms of free-FVIII clearance remain poorly understood. However, recent studies have implicated the MGL (macrophage galactose lectin) in modulating VWF clearance.

METHODS

Since VWF and FVIII share similar glycosylation, we investigated the role of MGL in FVIII clearance. FVIII binding to MGL was assessed in immunosorbent and cell-based assays. In vivo, FVIII clearance was assessed in MGL1-/- and VWF-/-/FVIII-/- mice.

RESULTS

In vitro-binding studies identified MGL as a novel macrophage receptor that binds free-FVIII in a glycan-dependent manner. MGL1-/- and MGL1-/- mice who received an anti-MGL1/2 blocking antibody both showed significantly increased endogenous FVIII activity compared with wild-type mice (P=0.036 and P<0.0001, respectively). MGL inhibition also prolonged the half-life of infused FVIII in FVIII-/- mice. To assess whether MGL plays a role in the clearance of free FVIII in a VWF-independent manner, in vivo clearance experiments were repeated in dual VWF-/-/FVIII-/- mice. Importantly, the rapid clearance of free FVIII in VWF-/-/FVIII-/- mice was significantly (P=0.012) prolonged in the presence of anti-MGL1/2 antibodies. Finally, endogenous plasma FVIII levels in VWF-/- mice were significantly increased following MGL inhibition (P=0.016).

CONCLUSIONS

Cumulatively, these findings demonstrate that MGL plays an important role in regulating macrophage-mediated clearance of both VWF-bound FVIII and free-FVIII in vivo. We propose that this novel FVIII clearance pathway may be of particular clinical importance in patients with type 2N or type 3 Von Willebrand disease.

Current Understanding of Inherited Modifiers of FVIII Pharmacokinetic Variation

The inherited bleeding disorder hemophilia A involves the quantitative deficiency of the coagulation cofactor factor VIII (FVIII). Prophylactic treatment of severe hemophilia A patients with FVIII concentrates aims to reduce the frequency of spontaneous joint bleeding and requires personalized tailoring of dosing regimens to account for the substantial inter-individual variability of FVIII pharmacokinetics. The strong reproducibility of FVIII pharmacokinetic (PK) metrics between repeat analyses in the same individual suggests this trait is genetically regulated. While the influence of plasma von Willebrand factor antigen (VWF:Ag) levels, ABO blood group, and patient age on FVIII PK is well established, estimates suggest these factors account for less than 35% of the overall variability in FVIII PK. More recent studies have identified genetic determinants that modify FVIII clearance or half-life including VWF gene variants that impair VWF-FVIII binding resulting in the accelerated clearance of VWF-free FVIII. Additionally, variants in receptors that regulate the clearance of FVIII or the VWF-FVIII complex have been associated with FVIII PK. The characterization of genetic modifiers of FVIII PK will provide mechanistic insight into a subject of clinical significance and support the development of personalized treatment plans for patients with hemophilia A.

The von Willebrand factor-binding aptamer rondaptivon pegol as a treatment for severe and nonsevere hemophilia A

Factor VIII (FVIII) circulates in a noncovalent complex with von Willebrand Factor (VWF), the latter determining FVIII half-life. The VWF-binding aptamer rondaptivon pegol (BT200) increases plasma levels of VWF/FVIII in healthy volunteers. This trial assessed its safety, pharmacokinetics, and pharmacodynamics in hemophilia A. Nineteen adult patients (ages 20-62 years, 4 women) with hemophilia A (8 mild, 2 moderate, and 9 severe) received subcutaneous injections of rondaptivon pegol. After an initial fixed dose of 3 mg on days 0 and 4, patients received weekly doses of 2 to 9 mg until day 28. Severe hemophilia A patients underwent sparse-sampling population pharmacokinetics individual profiling after the final dose of rondaptivon pegol. Adverse events, pharmacokinetics, and pharmacodynamics were assessed. FVIII activity and VWF levels were measured. All patients tolerated rondaptivon pegol well. The geometric mean half-life of rondaptivon pegol was 5.4 days and rondaptivon pegol significantly increased VWF levels. In severe hemophilia A, 6 doses of rondaptivon pegol increased the half-lives of 5 different FVIII products from a median of 10.4 hours to 31.1 hours (range, 20.8-56.0 hours). Median FVIII increased from 22% to 48% in mild hemophilia A and from 3% to 7.5% in moderate hemophilia A. Rondaptivon pegol is a first-in-class prohemostatic molecule that extended the half-life of substituted FVIII approximately 3-fold and increased endogenous FVIII levels approximately 2-fold in hemophilia patients. This trial was registered at www.clinicaltrials.gov as #NCT04677803.

New directions to develop therapies for people with hemophilia

INTRODUCTION

The past few decades have seen a tremendous advancement in the management of hemophilia. Whether it is improved methods to attenuate critical viruses, recombinant bioengineering with decreased immunogenicity, extended half-life replacement therapies to mitigate the burden of repeated infusion treatments, novel nonreplacement products to avoid the drawback of inhibitor development with its attractive subcutaneous administration and then the introduction of gene therapy, the management has trodden a long way.

AREAS COVERED

This expert review describes the progress in the treatment of hemophilia over the years. We discuss, in detail, the past and current therapies, their benefits, drawbacks, along with relevant studies leading to approval, efficacy and safety profile, ongoing trials, and future prospects.

EXPERT OPINION

The technological advances in the treatment of hemophilia with convenient modes of administration and innovative modalities offer a chance for a normal existence of the patients living with this disease. However, it is imperative for clinicians to be aware of the potential adverse effects and the need for further studies to establish causality or chance association of these events with novel agents. Thus, it is crucial for clinicians to engage patients and their families in informed decision-making and tailor individual concerns and necessities.

Efanesoctocog Alfa Prophylaxis for Patients with Severe Hemophilia A

BACKGROUND

Efanesoctocog alfa provides high sustained factor VIII activity by overcoming the von Willebrand factor-imposed half-life ceiling. The efficacy, safety, and pharmacokinetics of efanesoctocog alfa for prophylaxis and treatment of bleeding episodes in previously treated patients with severe hemophilia A are unclear.

METHODS

We conducted a phase 3 study involving patients 12 years of age or older with severe hemophilia A. In group A, patients received once-weekly prophylaxis with efanesoctocog alfa (50 IU per kilogram of body weight) for 52 weeks. In group B, patients received on-demand treatment with efanesoctocog alfa for 26 weeks, followed by once-weekly prophylaxis with efanesoctocog alfa for 26 weeks. The primary end point was the mean annualized bleeding rate in group A; the key secondary end point was an intrapatient comparison of the annualized bleeding rate during prophylaxis in group A with the rate during prestudy factor VIII prophylaxis. Additional end points included treatment of bleeding episodes, safety, pharmacokinetics, and changes in physical health, pain, and joint health.

RESULTS

In group A (133 patients), the median annualized bleeding rate was 0 (interquartile range, 0 to 1.04), and the estimated mean annualized bleeding rate was 0.71 (95% confidence interval [CI], 0.52 to 0.97). The mean annualized bleeding rate decreased from 2.96 (95% CI, 2.00 to 4.37) to 0.69 (95% CI, 0.43 to 1.11), a finding that showed superiority over prestudy factor VIII prophylaxis (P<0.001). A total of 26 patients were enrolled in group B. In the overall population, nearly all bleeding episodes (97%) resolved with one injection of efanesoctocog alfa. Weekly prophylaxis with efanesoctocog alfa provided mean factor VIII activity of more than 40 IU per deciliter for the majority of the week and of 15 IU per deciliter at day 7. Prophylaxis with efanesoctocog alfa for 52 weeks (group A) improved physical health (P<0.001), pain intensity (P = 0.03), and joint health (P = 0.01). In the overall study population, efanesoctocog alfa had an acceptable side-effect profile, and the development of inhibitors to factor VIII was not detected.

CONCLUSIONS

In patients with severe hemophilia A, once-weekly efanesoctocog alfa provided superior bleeding prevention to prestudy prophylaxis, normal to near-normal factor VIII activity, and improvements in physical health, pain, and joint health. (Funded by Sanofi and Sobi; XTEND-1 ClinicalTrials.gov number, NCT04161495.).

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

Enzymes catalyze biochemical reactions and play critical roles in human health and disease. Enzyme variants and deficiencies can lead to variable expression of glycans, which can affect physiology, influence predilection for disease, and/or directly contribute to disease pathogenesis. Although certain well-characterized enzyme deficiencies result in overt disease, some of the most common enzyme deficiencies in humans form the basis of blood groups. These carbohydrate blood groups impact fundamental areas of clinical medicine, including the risk of infection and severity of infectious disease, bleeding risk, transfusion medicine, and tissue/organ transplantation. In this review, we examine the enzymes responsible for carbohydrate-based blood group antigen biosynthesis and their expression within the human population. We also consider the evolutionary selective pressures, e.g. malaria, that may account for the variation in carbohydrate structures and the implications of this biology for human disease.