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

Enhancing therapeutic efficacy of in vivo platelet-targeted gene therapy in hemophilia A mice

Our previous studies demonstrated that intraosseous (IO) infusion of lentiviral vectors (LVs) carrying a modified B domain-deleted factor VIII (FVIII) transgene driven by a megakaryocyte-specific promoter (GP1Bα promoter; G-F8/N6-LV) successfully transduced hematopoietic stem cells (HSCs) to produce FVIII stored in the platelet α-granules. Platelet FVIII corrected the bleeding phenotype with limited efficacy in hemophilia A (HemA) mice with and without preexisting anti-FVIII inhibitors. The present study sought to further enhance the therapeutic efficacy of this treatment protocol by increasing both the efficiency of LV transduction and the functional activity of platelet FVIII. A combined drug regimen of dexamethasone and anti-CD8α monoclonal antibody enhanced the percentage of transduced bone marrow and HSCs over time. In G-F8/N6-LV-treated HemA mice, significant improvement in phenotypic correction was observed on day 84. To improve platelet FVIII functionality, genes encoding FVIII variant F8X10K12 with increased expression or F8N6K12RH with increased functional activity compared with F8/N6 were incorporated into LVs. Treatment with G-F8X10K12-LV in HemA mice produced a higher level of platelet FVIII but induced anti-FVIII inhibitors. After treatment with combined drugs and IO infusion of G-F8/N6K12RH-LV, HemA mice showed significant phenotypic correction without anti-FVIII inhibitor formation. These results indicate that new human FVIII variant F8/N6K12RH combined with immune suppression could significantly enhance the therapeutic efficacy of in vivo platelet-targeted gene therapy for murine HemA via IO delivery. This protocol provides a safe and effective treatment for hemophilia that may be translatable to and particularly beneficial for patients with preexisting inhibitory antibodies to FVIII.

Pharmacokinetics in routine haemophilia clinical practice: rationale and modalities-a practical review

Prophylactic therapy with exogenous clotting factor concentrates in haemophilia A and B aims to achieve levels of circulating FVIII or FIX that are adequate for the prevention or reduction of spontaneous joint bleeding. Historically, a minimum trough level of at least 1% of the normal levels of circulating clotting factor has been targeted using standardised protocols. However, clearance of clotting factor varies between products and patients, and other pharmacokinetic (PK) parameters such as the frequency and magnitude of peaks may be important for ensuring optimal coverage. Thus, it is increasingly recognised that an individualised, PK-based approach to prophylaxis is necessary to achieve optimal protection.

This review focuses on the clinical implications of using PK-guided, individualised prophylaxis in haemophilia to improve patient outcomes and considers practical methods of establishing patients’ PK parameters. The most useful PK parameters will depend on the aim of the specific treatment (e.g. preventing activity-related and traumatic bleeds or addressing subclinical bleeding). In clinical practice, lengthy and frequent post-infusion sampling for PK analysis is costly and a significant burden for patients. However, a Bayesian analysis allows for the estimation of different PK parameters (e.g. half-life, factor concentrations over time, etc.) with only a minimum number of samples (e.g. 4, 24 and 48 h for haemophilia A), by using the patient’s data to adjust a relevant population PK value towards the actual value. Numerous tools are available to aid in the practical use of Bayesian PK-guided dosing in the clinic, including the Web-based Application for the Population Pharmacokinetic Service hosted by McMaster University, Canada. The PK data can be used to determine the appropriate prophylaxis regimen for the individual patient, which can be monitored by assessment of the trough level at each clinic visit.

Collection of PK data and subsequent PK-guided dosing should become standard practice when determining treatment strategies for people with haemophilia.

Falsely decreased FVIII activity following pneumatic tube transport

INTRODUCTION

The pneumatic tube system (PTS) is widely used for sample delivery. We aimed to investigate the impacts of PTS on hemostasis assays.

METHODS

Triplicate samples from 30 healthy volunteers were delivered to the core laboratory manually by human courier or via the 500 m long-distance PTS or via the 1000 m long-distance PTS. Comparisons of 19 hemostasis tests were conducted.

RESULTS

Although PT, INR, APTT, FII, FV, FVII FIX, FX, FXII, DD, α2-PI, and PC had statistical significance (all P < .05), all had low average bias remaining within clinical acceptable limits. PTS transportation only resulted in a statistically significant and clinically relevant decrease in FVIII activity. In the 500 m-PTS group, 66.7% (20/30) of samples for FVIII testing had a bias greater than 8.3%. Moreover, in the 1000 m-PTS group, 96.7% (29/30) of samples had a bias of over 8.3%, and the maximal bias achieved 42.1%.

CONCLUSIONS

Pneumatic tube system in our institution could be used to deliver blood samples for hemostasis tests evaluated in this study except FVIII activity assay.

BIVV001 Fusion Protein as Factor VIII Replacement Therapy for Hemophilia A

BACKGROUND

Factor VIII replacement products have improved the care of patients with hemophilia A, but the short half-life of these products affects the patients' quality of life. The half-life of recombinant factor VIII ranges from 15 to 19 hours because of the von Willebrand factor chaperone effect. BIVV001 (rFVIIIFc-VWF-XTEN) is a novel fusion protein designed to overcome this half-life ceiling and maintain high sustained factor VIII activity levels. Data are lacking on the safety and pharmacokinetics of single-dose BIVV001.

METHODS

In this phase 1-2a open-label trial, we consecutively assigned 16 previously treated men (18 to 65 years of age) with severe hemophilia A (factor VIII activity, <1%) to receive a single intravenous injection of recombinant factor VIII at a dose of 25 IU per kilogram of body weight (lower-dose group) or 65 IU per kilogram (higher-dose group). This injection was followed by a washout period of at least 3 days. The patients then received a single intravenous injection of BIVV001 at the same corresponding dose of either 25 IU or 65 IU per kilogram. Adverse events and pharmacokinetic measurements were assessed.

RESULTS

No inhibitors to factor VIII were detected and no hypersensitivity or anaphylaxis events were reported up to 28 days after the injection of single-dose BIVV001. The geometric mean half-life of BIVV001 was three to four times as long as that of recombinant factor VIII (37.6 hours vs. 9.1 hours in the lower-dose group and 42.5 vs. 13.2 hours in the higher-dose group); the area under the curve (AUC) for product exposure was six to seven times as great in the two dose groups (4470 hours vs. 638 hours × IU per deciliter in the lower-dose group and 12,800 hours vs. 1960 hours × IU per deciliter in the higher-dose group). After the injection of BIVV001 in the higher-dose group, the mean factor VIII level was in the normal range (≥51%) for 4 days and 17% at day 7, which suggested the possibility of a weekly interval between treatments.

CONCLUSIONS

In a small, early-phase study involving men with severe hemophilia A, a single intravenous injection of BIVV001 resulted in high sustained factor VIII activity levels, with a half-life that was up to four times the half-life associated with recombinant factor VIII, an increase that could signal a new class of factor VIII replacement therapy with a weekly treatment interval. No safety concerns were reported during the 28-day period after administration. (Funded by Sanofi and Sobi; ClinicalTrials.gov number, NCT03205163.).

Gene Therapy for Hemophilia: Facts and Quandaries in the 21st Century

Therapy for hemophilia has evolved in the last 40 years from plasma-based concentrates to recombinant proteins and, more recently, to non-factor therapeutics. Along this same timeline, research in adeno-associated viral (AAV) based gene therapy vectors has provided the framework for early phase clinical trials initially for hemophilia B (HB) and now for hemophilia A. Successive lessons learned from early HB trials have paved the way for current advanced phase trials. Nevertheless, questions linger regarding 1) the optimal balance of vector dose to transgene expression, 2) amount and durability of transgene expression required, and 3) long-term safety. Some trials have demonstrated unique findings not seen previously regarding transient elevation of liver enzymes, immunogenicity of the vector capsid, and loss of transgene expression. This review will provide an update on the clinical AAV gene therapy trials in hemophilia and address the questions above. A thoughtful and rationally approached expansion of gene therapy to the clinics would certainly be a welcome addition to the arsenal of options for hemophilia therapy. Further, the global impact of gene therapy could be vastly improved by expanding eligibility to different patient populations and to developing nations. With the advances made to date, it is possible to envision a shift from the early goal of simply increasing life expectancy to a significant improvement in quality of life by reduction in spontaneous bleeding episodes and disease complications.

Mendelian Randomization Analysis of Hemostatic Factors and Their Contribution to Peripheral Artery Disease-Brief Report

BACKGROUND AND OBJECTIVE

Peripheral artery disease (PAD) is the third most common form of atherosclerotic vascular disease and is characterized by significant functional disability and increased cardiovascular mortality. Recent genetic data support a role for a procoagulation protein variant, the factor V Leiden mutation, in PAD. The role of other hemostatic factors in PAD remains unknown. We evaluated the role of hemostatic factors in PAD using Mendelian randomization. Approach and Results: Two-sample Mendelian randomization to evaluate the roles of FVII (factor VII), FVIII (factor VIII), FXI (factor XI), VWF (von Willebrand factor), and fibrinogen in PAD was performed using summary statistics from GWAS for hemostatic factors performed within the Cohorts for Heart and Aging Research in the Genome Epidemiology Consortium and from GWAS performed for PAD within the Million Veteran Program. Genetically determined FVIII and VWF, but not FVII, FXI, or fibrinogen, were associated with PAD in Mendelian randomization experiments (FVIII: odds ratio, 1.41 [95% CI, 1.23-1.62], P=6.0×10^-7, VWF: odds ratio, 1.28 [95% CI, 1.07-1.52], P=0.0073). In single variant sensitivity analysis, the ABO locus was the strongest genetic instrument for both FVIII and VWF.

CONCLUSIONS

Our results suggest a role for hemostasis, and by extension, thrombosis in PAD. Further study is warranted to determine whether VWF and FVIII independently affect the biology of PAD.

Comprehensive N- and O-glycosylation mapping of human coagulation factor V

BACKGROUND/OBJECTIVE

Coagulation factor V (FV), a multidomain glycoprotein, is an essential cofactor in the blood clotting cascade. FV deficiency is a rare bleeding disorder that results in poor clotting after an injury or surgery. The only treatment for the disease is infusions of fresh frozen plasma and blood platelets. Glycosylation affects the biological activity, pharmacokinetics, immunogenicity, and in vivo clearance rate of proteins in the plasma. The glycan profile of FV, as well as how it affects the activity, stability, and immunogenicity, remains unknown.

METHODS

In this study, we comprehensively mapped the glycosylation patterns of human plasma-derived FV by combining multienzyme digestion, hydrophilic interaction chromatography enrichment of glycopeptides, and alternated fragmentation mass spectrometry analysis.

RESULTS/CONCLUSION

A total of 57 unique N-glycopeptides and 51 O-glycopeptides were identified, which were categorized into 40 N-glycan and 17 O-glycan compositions. Such glycosylation details are fundamental for future functional studies and therapeutics development. In addition, the established methodology can be readily applied to analyze glycosylation patterns of proteins with more than 2000 amino acids.

Biological mechanisms underlying inter-individual variation in factor VIII clearance in haemophilia

Previous studies have highlighted marked inter‐individual variations in factor VIII (FVIII) clearance between patients with haemophilia (PWH). The half‐life of infused FVIII has been reported to vary from as little as 5.3 hours in some adult PWH, up to as long as 28.8 hours in other individuals. These differences in clearance kinetics have been consistently observed using a number of different plasma‐derived and recombinant FVIII products. Furthermore, recent studies have demonstrated that half‐life for extended half‐life (EHL‐) FVIII products also demonstrates significant inter‐patient variation. Since time spent with FVIII trough levels <1% has been shown to be associated with increased bleeding risk in PWH on prophylaxis therapy, this variability in FVIII clearance clearly has major clinical significance. Recent studies have provided significant novel insights into the cellular basis underlying FVIII clearance pathways. In addition, accumulating data have shown that endogenous plasma VWF levels, ABO blood group and age, all play important roles in regulating FVIII half‐life in PWH. Indeed, multiple regression analysis suggests that together these factors account for approximately 34% of the total inter‐individual variation in FVIII clearance observed between subjects with severe haemophilia A. In this review, we consider these and other putative modulators of FVIII half‐life, and discuss the biological mechanisms through which these factors impact upon FVIII clearance in vivo.

Hemophilia A Inhibitor Subjects Show Unique PBMC Gene Expression Profiles That Include Up-Regulated Innate Immune Modulators

Formation of pathological anti-FVIII antibodies, or "inhibitors," is the most serious complication of therapeutic FVIII infusions, affecting up to 1/3 of severe Hemophilia A (HA) patients. Inhibitor formation is a classical T-cell dependent adaptive immune response. As such, it requires help from the innate immune system. However, the roles of innate immune cells and mechanisms of inhibitor development vs. immune tolerance, achieved with or without Immune Tolerance Induction (ITI) therapy, are not well-understood. To address these questions, temporal transcriptomics profiling of FVIII-stimulated peripheral blood mononuclear cells (PBMCs) was carried out for HA subjects with and without a current or historic inhibitor using RNA-Seq. PBMCs were isolated from 40 subjects in the following groups: HA with an inhibitor that resolved either following ITI or spontaneously; HA with a current inhibitor; HA with no inhibitor history and non-HA controls. PBMCs were stimulated with 5 nM FVIII and RNA was isolated 4, 16, 24, and 48 h following stimulation. Time-series differential expression analysis was performed and distinct transcriptional signatures were identified for each group, providing clues as to cellular mechanisms leading to or accompanying their disparate anti-FVIII antibody responses. Subjects with a current inhibitor showed differential expression of 56 genes and a clustering analysis identified three major temporal profiles. Interestingly, gene ontology enrichments featured innate immune modulators, including NLRP3, TLR8, IL32, CLEC10A, and COLEC12. NLRP3 and TLR8 are associated with enhanced secretion of the pro-inflammatory cytokines IL-1β and TNFα, while IL32, which has several isoforms, has been associated with both inflammatory and regulatory immune processes. RNA-Seq results were validated by RT-qPCR, ELISAs, multiplex cytokine analysis, and flow cytometry. The inflammatory status of HA patients suffering from an ongoing inhibitor includes up-regulated innate immune modulators, which may act as ongoing danger signals that influence the responses to, and eventual outcomes of, ITI therapy.

Switching patients in the age of long-acting recombinant products?

Introduction: Prophylaxis with factor replacement therapy is the gold standard for the treatment of hemophilia, but this often requires frequent infusions. A number of long-acting factor products have been developed to reduce the burden on patients. Areas covered: This is an overview of information presented at two symposia held at the World Federation of Hemophilia and International Society on Thrombosis and Haemostasis - Scientific and Standardization Committee annual meetings. The pharmacokinetic, safety and efficacy data for long-acting recombinant products are reviewed, with a focus on recombinant factor IX albumin fusion protein (rIX-FP) and rVIII-SingleChain. This overview also provides a guide for managing a patient's switch to long-acting products. Expert opinion: Long-acting products may allow patients to maintain or decrease bleeding rates whilst increasing their dosing interval, which may in turn reduce the burden on patients and caregivers. When switching patients to long-acting products health-care professionals should provide balanced and thorough education to the patient, whilst supporting their emotional well-being. Regimens should address patients' needs and goals but should also be guided by clinical phenotype and pharmacokinetic assessment. Follow-up should assess safety concerns, bleeding rates, joint health and the impact of the regimen on patients' lifestyle.

Von Willebrand factor as a thrombotic and inflammatory mediator in critical illness

The endothelial exocytosis of high-molecular-weight multimeric von Willebrand factor (vWF) may occur in critical illness states, including trauma and sepsis, leading to the sustained elevation and altered composition of plasma vWF. These critical illnesses involve the common process of sympathoadrenal activation and loss of the endothelial glycocalyx. As a prothrombotic and proinflammatory molecule that interacts with the endothelium, the alterations exhibited by vWF in critical illness have been implicated in the development and damaging effects of downstream pathologies, such as disseminated intravascular coagulation and systemic inflammatory response syndrome. Given the role of vWF in these pathologies, there has been a recent push to further understand how the molecule may be involved in the pathophysiology of related diseases, such as trauma-induced coagulopathy and acute renal injury, which are also known to develop secondarily to critical illness states. Elucidation of the role of vWF across the broader spectrum of generalized pathologies may provide a basis for the development of novel preventative and restorative measures, while also bolstering the scaffold of more widely used treatments, such as the administration of plasma-containing blood products.

Comparing Physician and Patient Perspectives on Prophylactic Treatment with BAY 94-9027 for Severe Haemophilia A: A Post Hoc Analysis

Introduction

BAY 94-9027 is a newly developed extended half-life product to treat haemophilia, allowing for fewer injections than with standard products. This post hoc analysis aimed to compare physicians’ and patients’ opinions on BAY 94-9027 prophylaxis, and explore how qualitative interview data is aligned with the data from the Haemophilia-specific Quality of Life questionnaire for Adults (Haemo-QoL-A).

Methods

Exploratory qualitative interviews were conducted with physicians and patients by phone upon the exit of patients from the PROTECT VIII extension phase following a semi-directed guide. In this post hoc analysis, all transcripts were reviewed and reported concepts were compared to assess the level of concordance between physicians and patients. These qualitative data were compared with the Haemo-QoL-A mean global and subscale scores at baseline and end of main phase (36 weeks later).

Results

Ten physicians and 16 patients (mean age 47 years) from Israel, the Netherlands and the USA were interviewed. Significant improvements were reported by all physicians from baseline [e.g. lower frequency of bleeds (80%), improvement in emotional functioning (90%)], which is in concordance with patients’ reports. The improved confidence reported by physicians cascaded to greater participation in various activities, resulting in a better perceived emotional state and a significant improvement on the Haemo-QoL-A emotional impact subscale score (p = 0.04) between baseline and end of main phase. Most physicians (80%) reported improvement in bleed frequency, as patients did (88%). Improvement in physical functioning or mobility was not consistently reported in this 8-month study.

Conclusion

Interviewed physicians and patients generally agreed on the beneficial impact of BAY 94-9027, specifically regarding the increased level of self-confidence in patients and its subsequent positive impact on patients’ lives. These findings supported the observed improvement on the Haemo-QoL-A emotional impact subscale. Overall, this study highlights the concordance between physician and patient perspective on the positive experience with BAY 94-9027.

Peptides identified on monocyte-derived dendritic cells: a marker for clinical immunogenicity to FVIII products

The immunogenicity of protein therapeutics is an important safety and efficacy concern during drug development and regulation. Strategies to identify individuals and subpopulations at risk for an undesirable immune response represent an important unmet need. The major histocompatibility complex (MHC)-associated peptide proteomics (MAPPs) assay directly identifies the presence of peptides derived from a specific protein therapeutic on a donor's MHC class II (MHC-II) proteins. We applied this technique to address several questions related to the use of factor VIII (FVIII) replacement therapy in the treatment of hemophilia A (HA). Although >12 FVIII therapeutics are marketed, most fall into 3 categories: (i) human plasma-derived FVIII (pdFVIII), (ii) full-length (FL)-recombinant FVIII (rFVIII; FL-rFVIII), and (iii) B-domain-deleted rFVIII. Here, we investigated whether there are differences between the FVIII peptides found on the MHC-II proteins of the same individual when incubated with these 3 classes. Based on several observational studies and a prospective, randomized, clinical trial showing that the originally approved rFVIII products may be more immunogenic than the pdFVIII products containing von Willebrand factor (VWF) in molar excess, it has been hypothesized that the pdFVIII molecules yield/present fewer peptides (ie, potential T-cell epitopes). We have experimentally tested this hypothesis and found that dendritic cells from HA patients and healthy donors present fewer FVIII peptides when administered pdFVIII vs FL-rFVIII, despite both containing the same molar VWF excess. Our results support the hypothesis that synthesis of pdFVIII under physiological conditions could result in reduced heterogeneity and/or subtle differences in structure/conformation which, in turn, may result in reduced FVIII proteolytic processing relative to FL-rFVIII.

Hemophilia A and von Willebrand deficiency: therapeutic implications

: Hemophilia A is an X-linked bleeding disorder caused by a deficiency of factor VIII. Depending on the factor VIII activity in patient's plasma, we can have three different forms of hemophilia A: mild (5-40 IU/dl), moderate (1-5 IU/dl) and severe (<1 IU/dl). The most common symptoms include recurrent bleeding episodes of soft tissues and joints. The treatment is based on the prophylactic use of clotting factor concentrates to prevent bleeding episodes. We describe three cases of patients with initially diagnosis of hemophilia A that show different clinical severity, undergoing prophylactic therapies with low benefit. In these patients, the dosage of von Willebrand antigen revealed either low level or absence of this factor, which in one case was caused by the occurrence of a type III form of von Willebrand disease.

Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia

BACKGROUND

Acquired von Willebrand factor (VWF) deficiency was described in Philadelphia-negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored.

OBJECTIVES

To characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients.

PATIENTS/METHODS

We studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low-dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS-13, and factor VIII (FVIII) antigen.

RESULTS

In patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96-137] vs 93[79-107] IU/dL; activity: 114[95-128] vs 90[79-107] IU/dL, respectively, medians and interquartile, P < 0.01), with normal multimeric distribution. ADAMTS-13 levels were similar between patients with PV and healthy subjects. FVIII levels were higher in PV than in healthy subjects (141[119-169] versus 98[88-123] IU/dL, respectively, P < 0.01). By multivariable analysis, JAK2-p.V617F allelic burden, erythrocyte count, and male sex significantly predicted VWF antigen and activity levels. As compared to patients with ET, patients with PV showed similar VWF antigen levels but approximately 40% higher activity (79[49-104] vs 112[93-125] IU/dL, respectively, P < 0.01).

CONCLUSIONS

Patients with PV show increased VWF and FVIII levels, predicted by JAK2-p.V617F burden and erythrocyte count. At variance with ET, acquired VWF defect was not observed in PV. High VWF/FVIII levels may sustain the thrombotic diathesis of PV and may be investigated as biomarkers for risk stratification.

Sedimentation Velocity Analytical Ultracentrifugation of Oxidized Recombinant Full-Length Factor VIII

Anti-drug antibodies to coagulation factor VIII (fVIII), often termed inhibitors, present the greatest economical and treatment related obstacle in the management of hemophilia A. Although several genetic and environmental risk factors associated with inhibitor development have been identified, the precise mechanisms responsible for the immune response to exogenous fVIII therapies remain undefined. Clinical trials suggest there is an increased immunogenic potential of recombinant fVIII compared to plasma-derived products. Additional biochemical and immunological studies have demonstrated that changes in recombinant fVIII production and formulation can alter fVIII structure and immunogenicity. Recently, one study demonstrated increased immunogenicity of the recombinant fVIII product Helixate in hemophilia A mice following oxidation with hypochlorite (ClO⁻). It is widely reported that protein aggregates within drug products can induce adverse immune reactions in patients. Several studies have therefore investigated the prevalence of molecular aggregates in commercial recombinant products with and without use-relevant stress and agitation. To investigate the potential link between oxidation-induced immunogenicity and molecular aggregation, we analyzed the recombinant fVIII product, Helixate, via sedimentation velocity analytical ultracentrifugation following oxidation with ClO⁻. At 80 μM ClO⁻, a concentration that reduced the specific-activity by 67%, no detectable increase in large molecular aggregates (s > 12 S) was observed when compared to non-oxidized fVIII. This lack of aggregates was demonstrated both in commercial excipient as well as a HEPES buffered saline formulation. These data suggest that oxidation induced immunogenicity is independent of aggregate-mediated immune response. Therefore, our data support multiple, independent mechanisms underlying fVIII immunogenicity.

Unique surface-exposed hydrophobic residues in the C1 domain of factor VIII contribute to cofactor function and von Willebrand factor binding

BACKGROUND

The identity of the amino acid regions of factor VIII (FVIII) that contribute to factor IXa (FIXa) and von Willebrand factor (VWF) binding has not been fully resolved. Previously, we observed that replacing the FVIII C1 domain for the one of factor V (FV) markedly reduces VWF binding and cofactor function. Compared to the FV C1 domain, this implies that the FVIII C1 domain comprises unique surface-exposed elements involved in VWF and FIXa interaction.

OBJECTIVE

The aim of this study is to identify residues in the FVIII C1 domain that contribute to VWF and FIXa binding.

METHODS

Structures and primary sequences of FVIII and FV were compared to identify surface-exposed residues unique to the FVIII C1 domain. The identified residues were replaced with alanine residues to identify their role in FIXa and VWF interaction. This role was assessed employing surface plasmon resonance analysis studies and enzyme kinetic assays.

RESULTS

Five surface-exposed hydrophobic residues unique to the FVIII C1 domain, ie, F2035, F2068, F2127, V2130, I2139 were identified. Functional analysis indicated that residues F2068, V2130, and especially F2127 contribute to VWF and/or FIXa interaction. Substitution into alanine of the also surface-exposed V2125, which is spatially next to F2127, affected only VWF binding.

CONCLUSION

The surface-exposed hydrophobic residues in C1 domain contribute to cofactor function and VWF binding. These findings provide novel information on the fundamental role of the C1 domain in FVIII life cycle.

Hemophilia - Impact of Recent Advances on Management

There have been numerous advances in the field of hemophilia management in the past decade, including long acting factor products, non-factor products, and potentially curative interventions such as gene therapy. Each of these interventions introduces exciting treatment modalities to patients with both hemophilia A and B, however they also pose a daunting array of possible management options. Adverse reactions to novel agents are being reported as more patients are treated and long-term sustainability of interventions such as gene therapy is yet to be determined. The practicing hematologist should be aware of the intricacies involved in customizing care for their individual patients and be aware of the monitoring strategies for each interventional strategy to avoid adverse events. Upfront cost vs. long term benefit should be considered as choices of treatment strategies are made, especially in resource poor countries. The goal of the newer agents is to decrease annualized bleed rates and avoid debilitating arthropathy. This article looks at current treatment models for prophylaxis and management of inhibitors, reviews the recent advances in the field (with bioengineered factor products, non-factor products and gene therapy) and summarizes the incorporation of these new interventions in the treatment plan for patients with hemophilia.

Factor VIII: Perspectives on Immunogenicity and Tolerogenic Strategies

Therapeutic treatment of bleeds with FVIII can lead to an antibody response that effectively inhibits its function. Herein, we review the factors that contribute to this immunogenicity and possible ways to overcome it.

Bioengineering hemophilia A-specific microvascular grafts for delivery of full-length factor VIII into the bloodstream

Hemophilia A (HA) is a bleeding disorder caused by mutations in the F8 gene encoding coagulation factor VIII (FVIII). Current treatments are based on regular infusions of FVIII concentrates throughout a patient's life. Alternatively, viral gene therapies that directly deliver F8 in vivo have shown preliminary successes. However, hurdles remain, including lack of infection specificity and the inability to deliver the full-length version of F8 due to restricted viral cargo sizes. Here, we developed an alternative nonviral ex vivo gene-therapy approach that enables the overexpression of full-length F8 in patients' endothelial cells (ECs). We first generated HA patient-specific induced pluripotent stem cells (HA-iPSCs) from urine epithelial cells and genetically modified them using a piggyBac DNA transposon system to insert multiple copies of full-length F8. We subsequently differentiated the modified HA-iPSCs into competent ECs with high efficiency, and demonstrated that the cells (termed HA-FLF8-iECs) were capable of producing high levels of FVIII. Importantly, following subcutaneous implantation into immunodeficient hemophilic (SCID-f8ko) mice, we demonstrated that HA-FLF8-iECs were able to self-assemble into vascular networks, and that the newly formed microvessels had the capacity to deliver functional FVIII directly into the bloodstream of the mice, effectively correcting the clotting deficiency. Moreover, our implant maintains cellular confinement, which reduces potential safety concerns and allows effective monitoring and reversibility. We envision that this proof-of-concept study could become the basis for a novel autologous ex vivo gene-therapy approach to treat HA.

von Willebrand Factor and Platelet Glycoprotein Ib: A Thromboinflammatory Axis in Stroke

von Willebrand factor (VWF) and platelets are key mediators of normal hemostasis. At sites of vascular injury, VWF recruits platelets via binding to the platelet receptor glycoprotein Ibα (GPIbα). Over the past decades, it has become clear that many hemostatic factors, including VWF and platelets, are also involved in inflammatory processes, forming intriguing links between hemostasis, thrombosis, and inflammation. The so-called “thrombo-inflammatory” nature of the VWF-platelet axis becomes increasingly recognized in different cardiovascular pathologies, making it a potential therapeutic target to interfere with both thrombosis and inflammation. In this review, we discuss the current evidence for the thrombo-inflammatory activity of VWF with a focus on the VWF-GPIbα axis and discuss its implications in the setting of ischemic stroke.

SHP656, a polysialylated recombinant factor VIII (PSA-rFVIII): First-in-human study evaluating safety, tolerability and pharmacokinetics in patients with severe haemophilia A

Introduction

SHP656 is the first factor VIII (FVIII) product developed using polysialylation (PSA) technology, in which full‐length recombinant (r) FVIII (anti‐haemophilic factor [recombinant]) is conjugated with a 20 kDa PSA polymer.

Aim

To compare the safety, immunogenicity and pharmacokinetics of SHP656 vs the parent rFVIII (octocog alfa) after single infusions of 25‐75 IU/kg in patients with severe haemophilia A (FVIII activity <1%).

Methods

Multinational, phase 1, prospective, open‐label, two‐period, fixed‐sequence, dose‐escalation trial (clinicaltrials.gov NCT02716194). Patients received single doses of rFVIII and then SHP656 sequentially at the same dose: 25 ± 3 IU/kg (Cohort 1), 50 ± 5 IU/kg (Cohort 2) and 75 ± 5 IU/kg (Cohort 3).

Results

Forty patients received rFVIII: 11 in Cohort 1, 16 in Cohort 2 and 13 in Cohort 3. Two patients withdrew before receiving SHP656, leaving 38 patients who completed the study and received both treatments. No treatment‐related adverse events (AEs), serious AEs, deaths, study withdrawals, thrombotic events or allergic reactions were reported; and no significant treatment‐related changes in laboratory parameters or vital signs. No patients developed FVIII inhibitors or antibodies to PSA. FVIII activity was significantly prolonged following SHP656 administration vs rFVIII with an approximately 1.5‐fold extension in mean residence time (P < .05). Exposure increased proportional to the SHP656 dose over the 25‐75 IU/kg dose range.

Conclusion

Polysialylation of rFVIII confers a half‐life extension similar to that of approved extended half‐life products that use either PEGylation or Fc fusion technology and was not associated with any treatment‐related adverse events.

Rosuvastatin use improves measures of coagulation in patients with venous thrombosis

Aims

Observational studies indicate that statins reduce the risk of recurrent venous thrombosis (VT). However, trials have not been performed and the mechanism is unknown. We aimed to determine whether statin therapy improves the coagulation profile in patients with prior VT.

Methods and results

Randomized clinical trial (NCT01613794). Patients were randomized to rosuvastatin 20 mg/day for 4 weeks or no intervention. Blood was drawn at baseline and at end of study. The primary outcome was factor (F) VIII:C. In total, five coagulation factors were measured: FVIII:C, von Willebrand factor:Ag, FVII:C, FXI:C, and D-dimer. Among 247 randomized participants, mean age was 58 years, 62% were women and 49% had unprovoked VT. For all tested coagulation factors, mean levels were clearly decreased at end of study in rosuvastatin users, whereas they hardly differed in non-statin users. Results were most consistent for FVIII:C where mean FVIII:C levels were 7.2 IU/dL [95% CI (confidence interval) 2.9-11.5] lower in rosuvastatin users, while among non-users, no change in FVIII:C was observed (mean difference -0.1; 95% CI -3.0 to 2.9). The mean age and sex adjusted difference in FVIII:C change was -6.7 IU/dL (95% CI -12.0 to -1.4) in rosuvastatin users vs. non-users. Subgroup analyses revealed that the decrease in coagulation factors by rosuvastatin was more pronounced in participants with unprovoked VT and in those with cardiovascular risk factors.

Conclusion

Rosuvastatin 20 mg/day substantially improved the coagulation profile among patients with prior VT. These results suggest that statin therapy might be beneficial in patients at risk of recurrent VT.

Polysialic Acid-Mediated Activity Measurement of Polysialylated Recombinant Coagulation Factor VIII

Measurement of modified biologic including coagulation factors with extended half-life obtained, for example, by polysialylation pose an analytical challenge especially if both biological activity and presence of modification have to be determined. Analytical methods applied so far address only 1 of the 2 quality attributes of modified biologics. Here, we describe the development and bioanalytical validation of a polysialic acid-mediated factor VIII activity assay: Polysialic acid-specific capture of polysialylated recombinant factor VIII is combined with a chromogenic FVIII activity test using commercially available reagents. This assay principle enabled measurement of FVIII activity down to the pico mole-range without any interference by nonmodified factor VIII. To the best of our knowledge, this is the first method to selectively, accurately, and precisely measure simultaneously activity and modification integrity of a polysialylated biologic in complex matrices, as shown by the bioanalytical validation data. The convenience, robustness, and reliability of using this method has been demonstrated by its application for the nonclinical development of the polysialylated recombinant FVIII preparation. The method principle could be applied to protein modifications other than polysialylation and to activity tests other than the chromogenic FVIII assay.

Evaluation of Factor VIII Polysialylation: Identification of a Longer-Acting Experimental Therapy in Mice and Monkeys

Extended half-life (EHL) factor therapies are needed to reduce the burden of prophylaxis and improve treatment adherence in patients with hemophilia. BAX 826 is a novel polysialylated full-length recombinant factor VIII [polysialyic acid (PSA) rFVIII] with improved pharmacokinetics (PK), prolonged pharmacology, and maintained safety attributes to enable longer-acting rFVIII therapy. In factor VIII (FVIII)-deficient hemophilic mice, PSArFVIII showed a substantially higher mean residence time (>2-fold) and exposure (>3-fold), and prolonged efficacy in tail-bleeding experiments (48 vs. 30 hours) compared with unmodified recombinant FVIII (rFVIII), as well as a potentially favorable immunogenicity profile. Reduced binding to a scavenger receptor (low-density lipoprotein receptor-related protein 1) and von Willebrand factor (VWF) as well as a largely VWF-independent circulation time in mice provide a rationale for prolonged BAX 826 activity. The significantly improved PK profile versus rFVIII was confirmed in cynomolgus monkeys [mean residence time: 23.4 vs. 10.1 hours; exposure (area under the curve from time 0 to infinity): 206 vs. 48.2 IU/ml⋅h] and is in line with results from rodent studies. Finally, safety and toxicity evaluations did not indicate increased thrombogenic potential, and repeated administration of BAX 826 to monkeys and rats was well tolerated. The favorable profile and mechanism of this novel experimental therapeutic demonstrated all of the requirements for an EHL-rFVIII candidate, and thus BAX 826 was entered into clinical assessment for the treatment of hemophilia A. SIGNIFICANCE STATEMENT: Prolongation of FVIII half-life aims to reduce the burden of prophylaxis and improve treatment outcomes in patients with hemophilia. This study shows that polysialylation of PSArFVIII resulted in prolongations of rFVIII circulation time and procoagulant activity, together with a favorable nonclinical safety profile of the experimental therapeutic.

D' domain region Arg782-Cys799 of von Willebrand factor contributes to factor VIII binding

In the complex with von Willebrand factor (VWF) factor VIII (FVIII) is protected from rapid clearance from circulation. Although it has been established that the FVIII binding site resides in the N-terminal D'-D3 domains of VWF, detailed information about the amino acid regions that contribute to FVIII binding is still lacking. In the present study, hydrogen-deuterium exchange mass spectrometry was employed to gain insight into the FVIII binding region on VWF. To this end, time-dependent deuterium incorporation was assessed in D'-D3 and the FVIII-D'-D3 complex. Data showed reduced deuterium incorporation in the D' region Arg782-Cys799 in the FVIII-D'-D3 complex compared to D'-D3. This implies that this region interacts with FVIII. Site-directed mutagenesis of the six charged amino acids in Arg782-Cys799 into alanine residues followed by surface plasmon resonance analysis and solid phase binding studies revealed that replacement of Asp796 affected FVIII binding. A marked decrease in FVIII binding was observed for the D'-D3 Glu787Ala variant. The same was observed for D'-D3 variants in which Asp796 and Glu787 were replaced by Asn796 and Gln787. Site-directed mutagenesis of Leu786, which together with Glu787 and Cys789 forms a short helical region in the crystal structure of D'-D3, also had a marked impact on FVIII binding. The combined results show that the amino acid region Arg782-Cys799 is part of a FVIII binding surface. Our study provides new insight into FVIII-VWF complex formation and defects therein that may be associated with bleeding caused by markedly reduced levels of FVIII.

How I manage severe von Willebrand disease

Von Willebrand disease (VWD) is the most common inherited bleeding disorder. Most patients with mild and moderate VWD can be treated effectively with desmopressin. The management of severe VWD patients, mostly affected by type 2 and type 3 disease, can be challenging. In this article we review the current diagnosis and treatment of severe VWD patients. We will also discuss the management of severe VWD patients in specific situations, such as pregnancy, delivery, patients developing alloantibodies against von Willebrand factor and VWD patients with recurrent gastrointestinal bleeding. Moreover, we review emerging treatments that may be applied in future management of patients with severe VWD.

Fixed doses of N8-GP prophylaxis maintain moderate-to-mild factor VIII levels in the majority of patients with severe hemophilia A

BACKGROUND

N8-GP is an extended half-life recombinant factor VIII developed for prophylaxis and treatment of bleeds in patients with hemophilia A.

OBJECTIVE

To assess pharmacokinetic (PK) characteristics of N8-GP in previously treated patients with severe hemophilia A, model the time spent at hemophilia thresholds of ≥1 and ≤5 IU/dL (moderate) or >5 IU/dL (mild) FVIII levels during N8-GP prophylaxis, and investigate the relationship between N8-GP half-life and von Willebrand factor (vWF).

METHODS

PK assessments were obtained from patients with severe hemophilia A (FVIII < 1 IU/dL) participating in 4 clinical trials: pathfinder 1 (20-60 years); pathfinder 2 (12-17 and ≥18 years); pathfinder 5 (0-11 years), and pathfinder 7 (25-71 years). All PK profiles were assessed after washout and considered single-dose PK profiles. Pre- and postdose FVIII activity at steady state was measured at all visits.

RESULTS

From 69 patients, 108 PK profiles of N8-GP 50 IU/kg were assessed. Adults/adolescents received 50 IU/kg every 4 days, achieving mean trough levels of 3.0 IU/dL (95% confidence interval, 2.6-3.5, adults) and 2.7 IU/dL (1.8-4.0, adolescents). Children received 60 IU/kg twice weekly, leading to mean trough levels of 1.2 IU/dL (0.8-1.6, 0- to 5-year-olds) and 2.0 IU/dL (1.5-2.7, 6- to 11-year-olds). PK modeling predicted children dosed every 3 days and adults/adolescents dosed every 3 to 4 days would maintain FVIII levels >5 and >1 IU/dL for >80% and 100% of the time, respectively. N8-GP half-life correlated linearly with von Willebrand factor levels in adults/adolescents, less in children.

CONCLUSIONS

Prophylaxis with fixed intervals (Q4D/twice weekly) and fixed weight-based dosing (50/60 IU/kg) ensured >1 IU/dL FVIII trough levels in both adults and children.

Extended Half-Life Coagulation Factors: A New Era in the Management of Hemophilia Patients

Despite effective factor replacement and various treatment schedules, there remain several challenges and unmet needs in the prophylactic treatment of hemophilia limiting its adoption and thereby posing an increased risk of spontaneous bleeding. In this regard, extended half-life (EHL) recombinant factor VIII (rFVIII) and factor IX (rFIX) products promise optimal prophylaxis by decreasing the dose frequency, increasing the compliance, and improving the quality of life without compromising safety and efficacy. EHL products might lead to higher trough levels without increasing infusion frequency, or could facilitate the ability to maintain trough levels while reducing infusion frequency. This paper aims to provide a comprehensive review of the rationale for developing EHL coagulation factors and their utility in the management of hemophilia, with special emphasis on optimal techniques for half-life extension and criteria for defining EHL coagulation factors, as well as indications, efficacy, and safety issues of the currently available EHL-rFVIII and EHL-rFIX products. Potential impacts of these factors on quality of life, health economics, and immune tolerance treatment will also be discussed alongside the challenges in pharmacokinetic-driven prophylaxis and difficulties in monitoring the EHL products with laboratory assays.

The endothelial lectin clearance receptor CLEC4M binds and internalizes factor VIII in a VWF-dependent and independent manner

Essentials CLEC4M is an endocytic receptor for factor FVIII. CLEC4M interacts with FVIII in a VWF-dependent and independent manner. CLEC4M binds to mannose-containing glycans on FVIII. CLEC4M internalization of FVIII involves clathrin coated pits. SUMMARY: Background von Willebrand factor (VWF) and factor VIII (FVIII) circulate in the plasma as a non-covalent complex, and the majority of FVIII is likely to be cleared by VWF-dependent pathways. Clearance of VWF-free FVIII is rapid and underlies the pathological basis of some quantitative FVIII deficiencies. The receptor pathways that regulate the clearance of VWF-bound and VWF-free FVIII are incompletely uncharacterized. The human liver-expressed endothelial lectin CLEC4M has been previously characterized as a clearance receptor for VWF, although its influence on FVIII is unknown. Objective The interaction between FVIII and CLEC4M was characterized in the presence or absence of VWF. Methods FVIII interactions with CLEC4M were evaluated by in vitro cell-based and solid phase binding assays. Interactions between FVIII and CLEC4M or liver sinusoidal endothelial cells were evaluated in vivo by immunohistochemistry. Results CLEC4M-expressing HEK 293 cells bound and internalized recombinant and plasma-derived FVIII through VWF-dependent and independent mechanisms. CLEC4M binding to recombinant FVIII was dependent on mannose-exposed N-linked glycans. CLEC4M mediated FVIII internalization via a clathrin-coated pit-dependent mechanism, resulting in transport of FVIII from early and late endosomes for catabolism by lysosomes. In vivo hepatic expression of CLEC4M after hydrodynamic liver transfer was associated with a decrease in plasma levels of endogenous murine FVIII:C in normal mice, whereas infused recombinant human FVIII was associated with sinusoidal endothelial cells in the presence or absence of VWF. Conclusions These findings suggest that CLEC4M is a novel clearance receptor that interacts with mannose-exposed glycans on FVIII in the presence or absence of VWF.

New therapies for hemophilia

Hemophilia A (HA) and hemophilia B (HB) are the most common severe bleeding disorders. Replacement therapy, providing the missing coagulation factor, has been the mainstay of treatment both prophylactically and to treat bleeding. Despite widespread availability of safe and effective replacement therapy, patients with HA and HB continue to experience a tremendous burden of treatment, breakthrough bleeding, and progressive joint disease, as well as high rates of inhibitor development. These remaining challenges are now being addressed by incredible advances in bioengineering. Recombinant bioengineering has led to replacement therapies with easier modes of administration, decreased immunogenicity, increased efficacy, and extended half-lives. Emicizumab, a bispecific antibody that acts as a substitutive therapy for HA, has been approved for patients with and without inhibitors. Novel compounds are in development to exploit the natural balance of hemostasis by targeting the natural anticoagulants protein C, protein S, tissue factor pathway inhibitor, and antithrombin. The substitution and rebalancing therapies provide an opportunity for steady-state hemostatic control without exposure to immunogenic clotting factor proteins. As such, they may have broader applications outside those being investigated in the clinical trial programs.

Von Willebrand factor contribution to pathophysiology outside of von Willebrand disease

VWF is a procoagulant protein that plays a central role in the initiation of platelets aggregate formation and thrombosis. While von Willebrand disease has long been known to result from qualitative and quantitative deficiencies of VWF, it is recently that contribution of elevated levels of VWF to various pathological conditions including thrombosis, inflammation, angiogenesis, and cancer metastasis has been appreciated. Here, we discuss contribution of elevated levels of VWF to various thrombotic and nonthrombotic pathological conditions.

Bioengineered molecules for the management of haemophilia: Promise and remaining challenges

Recombinant DNA technology has led to accelerating introduction of novel therapeutics for the treatment of haemophilia. This technology has driven the development of recombinant clotting factors, extended half-life clotting factors, alternative biologics to promote haemostasis and enabled the launch of the gene therapy era for haemophilia. At the core of this technology is the ability to study the structure and function of the native molecules and to apply rational bioengineering to overcome limitations to the existing therapies. Through the study of haemophilia-causing mutations, site-directed mutagenesis, detailed structural models and a wide repertoire of animal models, new bioengineering strategies are helping overcome some of the remaining limitations and challenges of traditional clotting factor concentrates. Some of these bioengineering strategies are now being partnered with improvements in vectorology leading to the first wave of successful gene therapy approaches. This study will review past and present bioengineered molecules that are advancing care for haemophilia as well as novel approaches that promise to continue to improve care and outcomes for patients with haemophilia.

A factor VIII–nanobody fusion protein forming an ultrastable complex with VWF: effect on clearance and antibody formation

The fusion between FVIII and anti-VWF nanobodies increases affinity for VWF 25-fold without compromising FVIII activity. Stabilized VWF binding results in a twofold enhanced circulatory survival of FVIII and reduced anti-FVIII antibody formation.

The endothelial cell receptor stabilin-2 regulates VWF-FVIII complex half-life and immunogenicity

Quantitative abnormalities of the von Willebrand factor-factor VIII (VWF-FVIII) complex associate with inherited bleeding or thrombotic disorders. Receptor-mediated interactions between plasma VWF-FVIII and phagocytic or immune cells can influence their hemostatic and immunogenic activities. Genetic association studies have demonstrated that variants in the STAB2 gene, which encodes the scavenger receptor stabilin-2, associate with plasma levels of VWF-FVIII. However, the mechanistic basis and pathophysiological consequences of this association are unknown. We have demonstrated that stabilin-2-expressing cells bind and internalize human VWF and FVIII in a VWF-dependent manner, and stabilin-2-deficient mice displayed prolonged human VWF-FVIII half-life compared with controls. The stabilin-2 variant p.E2377K significantly decreased stabilin-2 expression and impaired VWF endocytosis in a heterologous expression system, and common STAB2 variants associated with plasma VWF levels in type 1 von Willebrand disease patients. STAB2-deficient mice displayed a decreased immunogenic response to human VWF-FVIII complex, while coinfusion of human VWF-FVIII with the stabilin-2 ligand hyaluronic acid attenuated the immune response to exogenous FVIII. Collectively, these data suggest that stabilin-2 functions as both a clearance and an immunoregulatory receptor for VWF-FVIII, making stabilin-2 a novel molecular target for modification of the half-life of VWF-FVIII and the immune response to VWF-FVIII concentrates.

Administration of DDAVP did not improve the pharmacokinetics of FVIII concentrate in a clinically significant manner

BACKGROUND

The half-life and mean residence time (MRT) of infused recombinant factor VIII (FVIII) concentrate are associated with pre-infusion levels of von Willebrand factor (VWF) in severely affected hemophilia A patients. It is currently unknown if individual FVIII concentrate half-life and MRT can be extended by increasing endogenous VWF levels. Aim: Our aim was to evaluate the effect of a 1-deamino-8-D-arginine vasopressin (DDAVP)-induced rise in VWF concentration on the pharmacokinetics of infused FVIII in hemophilia A patients.

METHODS

Four adult hemophilia A patients participated in this cross-over, placebo-controlled study. Each patient received either intravenous DDAVP or placebo, one hour prior to administration of 50 IU/kg plasma-derived immune-affinity purified FVIII concentrate.

RESULTS

The combined administration of DDAVP and FVIII concentrate was well tolerated. The levels of VWF Antigen (Ag) doubled after DDAVP, whereas they remained stable after placebo infusion. This rise in VWF Ag resulted in a slight modification of the pharmacokinetic parameters of FVIII concentrate. The MRT of FVIII concentrate increased in all patients (mean from 17.6 h to 19.9 h, p < 0.001, 95% CI for MRT change: +4.7 to -0.3 h). However, in vivo recoveries tended to decrease following DDAVP administration.

CONCLUSIONS

Collectively, these data show that administration of DDAVP did not improve the pharmacokinetics of FVIII concentrate in a clinically significant manner.

RELEVANCE FOR PATIENTS

Our results indicate that no clinical benefit is to be expected from the modification in FVIII pharmacokinetics resulting from DDAVP-administration prior to infusion of FVIII concentrate in hemophilia A patients.

In-depth comparison of N-glycosylation of human plasma-derived factor VIII and different recombinant products: from structure to clinical implications

Essentials Glycosylation heterogeneity of recombinant proteins affects pharmacokinetics and immunogenicity. N-glycomics/glycoproteomics of plasma-derived Factor VIII and 6 recombinant FVIIIs were compared. Depending on cell line, significant differences to plasma-derived FVIII were observed. Recombinant FVIIIs expressed distinct and immunologically relevant epitopes.

SUMMARY

Background/Objective Human factor VIII (FVIII) is a plasma glycoprotein, defects of which result in hemophilia A. Current substitution therapy uses FVIII products purified from human plasma or from various cell lines (recombinant FVIII) with different levels of B-domain deletion. Glycosylation is a post-translational protein modification in FVIII that has a substantial influence on its physical, functional and antigenic properties. Variation in glycosylation is likely to be the reason that FVIII products differ in their pharmacokinetics, pharmacodynamics and immunogenicity. However, the literature on FVIII glycosylation is inconsistent, preventing assembly into a coherent model. Seeking to better understand the glycosylation mechanisms underlying FVIII biology, we studied the N-glycosylation of human plasma-derived (pd)FVIII and six rFVIII products expressed in CHO, BHK or HEK cell lines. Methods FVIII samples were subjected to head-to-head detailed glycomic and glycoproteomic characterization using a combination of MALDI-MS and MS/MS, GC-MS and UPLC-UV-MSE technologies. Results/Conclusion The results of our study detail the N-glycan repertoire of pdFVIII to an unprecedented level, and for the first time, provide evidence of N-glycolylneuraminic acid (NeuGc) found on pdFVIII. Although site-specific glycosylation of rFVIII proved consistent with pdFVIII regardless of the expression system, the entire N-glycan content of each sample appeared significantly different. Although the proportion of biologically important epitopes common to all samples (i.e. sialylation and high-mannose) varied between samples, some recombinant products expressed distinct and immunologically relevant epitopes, such as LacdiNAc (LDN), fucosylated LacdiNAc (FucLDN), NeuGc, LewisX/Y and Galα1,3 Gal epitopes. rFVIII expressed in HEK cells showed the greatest glycomic differences to human pdFVIII.

Advances and innovations in haemophilia treatment

Haemophilia is a rare disease for which the approved therapeutic options have remained virtually unchanged for 50 years. In the past decade, however, there has been an explosion of innovation in the treatment options that are either in development or have been approved for haemophilia, including engineered clotting factors and an extensive pipeline of new approaches and modalities. Several of these new modalities, especially gene therapy, demonstrate proof of principle in haemophilia but could have broader applications. These advances, in combination with better diagnostics, are now enabling clinicians to improve the standard of care for people with haemophilia. The different mechanisms of action and modifications used in these therapies have implications for their safe and efficacious use, which must be balanced with their therapeutic utility. This Review focuses on the biological aspects of the most advanced and innovative approaches for haemophilia treatment and considers their future use.

Evolving Complexity in Hemophilia Management

Rapid expansion of therapeutic options have increased the complexity of hemophilia care. Previously, on-demand therapy aimed to reduce morbidity and early mortality; however, now aggressive prophylaxis, particularly in children, encourages an active lifestyle. Accurate diagnosis, recognition of early threats to musculoskeletal health, and optimization of therapy are critical for both males and females affected by hemophilia. The diversity of emerging hemophilia therapies, from modified factor protein concentrates, to gene therapy, to nonfactor hemostatic strategies, provide an exciting opportunity to target unmet needs in the bleeding disorder community.

Genotypes, phenotypes and whole genome sequence: Approaches from the My Life Our Future haemophilia project

INTRODUCTION

Information from the genes encoding factor VIII (F8) and IX (F9) is used in reproductive planning and to inform inhibitor formation, bleeding severity and response to therapies. Advances in technology and our understanding of the human genome now allows more comprehensive methods to study genomic variation and its impact on haemophilia.

AIMS

The My Life Our Future (MLOF) programme was begun in 2012 to provide genetic analysis and to expand research in haemophilia through a research repository.

METHODS

MLOF enrolled haemophilia A and B patients followed at haemophilia treatment centers in the U.S., including, since 2015, known and potential genetic carriers. Initial F8 and F9 DNA analysis was performed utilizing a next generation sequencing approach which allowed simultaneous detection of F8 inversions and other variants. Candidate variants were confirmed using a second method and multiplex ligation-dependent probe amplification was used to detect structural variants.

RESULTS

The initial phase of MLOF completed enrollment in December 2017 with 11,356 patients, genetic carriers, and potential carriers enrolled. In the 9453 subjects in whom analysis is complete, 687 unique previously unreported variants were found. Simultaneous sequencing of the F8 and F9 genes resulted in identification of non-deleterious variants previously reported as causative in haemophilia. DNA from 5141 MLOF subjects has undergone whole genome sequencing through the NHLBI TOPMed programme of the U.S. NIH.

CONCLUSION

MLOF has provided genetic information for patients and their families to help inform clinical care and has established a repository of data and biospecimens to further advance haemophilia research.

Emerging therapies for hemophilia: controversies and unanswered questions

Several new therapies for hemophilia have emerged in recent years. These strategies range from extended half-life factor replacement products and non-factor options with improved pharmacokinetic profiles to gene therapy aiming for phenotypic cure. While these products have the potential to change hemophilia care dramatically, several challenges and questions remain regarding broader applicability, long-term safety, and which option to pursue for each patient. Here, we review these emerging therapies with a focus on controversies and unanswered questions in each category.

Advances in Clinical and Basic Science of Coagulation: Illustrated abstracts of the 9th Chapel Hill Symposium on Hemostasis

This 9th Symposium on Hemostasis is an international scientific meeting held biannually in Chapel Hill, North Carolina. The meeting is in large measure the result of the close friendship between the late Dr. Harold R. Roberts of UNC Chapel Hill and Dr. Ulla Hedner of Novo Nordisk. When Novo Nordisk was developing the hemophilia therapy that would become NovoSeven, they sponsored a series of meetings to understand the basic biology and clinical applications of factor VIIa. The first meeting in Chapel Hill was held April 4-6, 2002 with Dr. Roberts as the organizer. Over the years, the conference emphasis has expanded from discussions of factor VIIa and tissue factor to additional topics in hemostasis and thrombosis. This year's meeting includes presentations by internationally renowned speakers that discuss the state-of-the-art on an array of important topics, including von Willebrand factor, engineering advances, coagulation and disease, tissue factor biology, therapeutic advances, and basic clotting factor biology. Included in this review article are illustrated abstracts provided by our speakers, which highlight the main conclusions of each invited talk. This will be the first meeting without Dr. Roberts in attendance, yet his commitment to excellent science and his focus on turning science to patient care are pervasively reflected in the presentations by our speakers.

Extended Half-Life Factor VIII and Factor IX Preparations

In the last couple of years, several extended half-life factor VIII and factor IX preparations were intensively studied and gained approval. In order to extend half-lives, techniques like fusion to protein conjugates (Fc part of IgG₁ or albumin), chemical modification (PEGylation), and protein sequence modification are implemented. With these techniques, it is possible to extend half-lives of factor IX products 4- to 6- fold, while half-life extension of factor VIII products is limited to 1.5- to 2-fold due to their interaction with von Willebrand factor. Nevertheless, both extended half-life factor VIII and IX products have improved and facilitated prophylactic factor replacement therapy in hemophilia A and B, respectively. Extended half-life factor concentrates pose challenges to coagulation laboratories because accurate therapy monitoring is not possible with all factor activity assays currently used.