Coagulation Factor VIII: Biological Basis of Emerging Hemophilia A Therapies.

Coagulation factor (F) VIII is essential for hemostasis. After activation, it combines with activated FIX (FIXa) on anionic membranes to form the intrinsic tenase enzyme complex, responsible for activating FX in the rate-limiting step of sustained coagulation. Hemophilia A and hemophilia B are due to inherited deficiencies in the activity of FVIII and FIX, respectively. Treatment of hemophilia A over the last decade has benefited from 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 FVIIIa 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 hemophilia A, including FVIII mimetic bispecific antibodies and recombinant adeno associated viral (rAAV) vector-based gene therapy. Biological insights into FVIII are also guiding the development and use of gain-of-function FVIII variants aimed at addressing limitations of first-generation rAAV vectors for hemophilia A. 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 hemophilia A will be necessary to achieve the ultimate goal of hemophilia therapy: normalizing hemostasis and optimizing well-being with minimal treatment burden for all patients worldwide.

Enhanced procoagulant activity of select hemophilia B causing factor IX variants with emicizumab.

ABSTRACT: Emicizumab improves the procoagulant activity of select loss-of-function factor IX (FIX) variants with likely dysfunctional assembly of the intrinsic Xase complex, resulting in hemophilia B (HB). FVIII mimetics may represent an alternative nonfactor therapy for select patients with HB.

Adeno-Associated Virus Gene Therapy for Hemophilia.

In vivo gene therapy is rapidly emerging as a new therapeutic paradigm for monogenic disorders. For almost three decades, hemophilia A (HA) and hemophilia B (HB) have served as model disorders for the development of gene therapy. This effort is soon to bear fruit with completed pivotal adeno-associated viral (AAV) vector gene addition trials reporting encouraging results and regulatory approval widely anticipated in the near future for the current generation of HA and HB AAV vectors. Here we review the clinical development of AAV gene therapy for HA and HB and examine outstanding questions that have recently emerged from AAV clinical trials for hemophilia and other monogenic disorders.

Multiyear Factor VIII Expression after AAV Gene Transfer for Hemophilia A.

BACKGROUND: The goal of gene therapy for patients with hemophilia A is to safely impart long-term stable factor VIII expression that predictably ameliorates bleeding with the use of the lowest possible vector dose. METHODS: In this phase 1-2 trial, we infused an investigational adeno-associated viral (AAV) vector (SPK-8011) for hepatocyte expression of factor VIII in 18 men with hemophilia A. Four dose cohorts were enrolled; the lowest-dose cohort received a dose of 5 × 1011 vector genomes (vg) per kilogram of body weight, and the highest-dose cohort received 2 × 1012 vg per kilogram. Some participants received glucocorticoids within 52 weeks after vector administration either to prevent or to treat a presumed AAV capsid immune response. Trial objectives included evaluation of the safety and preliminary efficacy of SPK-8011 and of the expression and durability of factor VIII. RESULTS: The median safety observation period was 36.6 months (range, 5.5 to 50.3). A total of 33 treatment-related adverse events occurred in 8 participants; 17 events were vector-related, including 1 serious adverse event, and 16 were glucocorticoid-related. Two participants lost all factor VIII expression because of an anti-AAV capsid cellular immune response that was not sensitive to immune suppression. In the remaining 16 participants, factor VIII expression was maintained; 12 of these participants were followed for more than 2 years, and a one-stage factor VIII assay showed no apparent decrease in factor VIII activity over time (mean [±SD] factor VIII activity, 12.9±6.9% of the normal value at 26 to 52 weeks when the participants were not receiving glucocorticoids vs. 12.0±7.1% of the normal value at >52 weeks after vector administration; 95% confidence interval [CI], -2.4 to 0.6 for the difference between matched pairs). The participants had a 91.5% reduction (95% CI, 88.8 to 94.1) in the annualized bleeding rate (median rate, 8.5 events per year [range, 0 to 43.0] before vector administration vs. 0.3 events per year [range, 0 to 6.5] after vector administration). CONCLUSIONS: Sustained factor VIII expression in 16 of 18 participants who received SPK-8011 permitted discontinuation of prophylaxis and a reduction in bleeding episodes. No major safety concerns were reported. (Funded by Spark Therapeutics and the National Heart, Lung, and Blood Institute; ClinicalTrials.gov numbers, NCT03003533 and NCT03432520.).

Combining Surface-Induced Dissociation and Charge Detection Mass Spectrometry to Reveal the Native Topology of Heterogeneous Protein Complexes.

Charge detection mass spectrometry (CDMS) enables the direct mass measurement of heterogeneous samples on the megadalton scale, as the charge state for a single ion is determined simultaneously with the mass-to-charge ratio (m/z). Surface-induced dissociation (SID) is an effective activation method to dissociate non-intertwined, non-covalent protein complexes without extensive gas-phase restructuring, producing various subcomplexes reflective of the native protein topology. Here, we demonstrate that using CDMS after SID on an Orbitrap platform offers subunit connectivity, topology, proteoform information, and relative interfacial strengths of the intact macromolecular assemblies. SID dissects the capsids (∼3.7 MDa) of adeno-associated viruses (AAVs) into trimer-containing fragments (3mer, 6mer, 9mer, 15mer, etc.) that can be detected by the individual ion mass spectrometry (I2MS) approach on Orbitrap instruments. SID coupled to CDMS provides unique structural insights into heterogeneous assemblies that are not readily obtained by traditional MS measurements.

Activated protein C has a regulatory role in factor VIII function.

Mechanisms thought to regulate activated factor VIII (FVIIIa) cofactor function include A2-domain dissociation and activated protein C (APC) cleavage. Unlike A2-domain dissociation, there is no known phenotype associated with altered APC cleavage of FVIII, and biochemical studies have suggested APC plays a marginal role in FVIIIa regulation. However, the in vivo contribution of FVIIIa inactivation by APC is unexplored. Here we compared wild-type B-domainless FVIII (FVIII-WT) recombinant protein with an APC-resistant FVIII variant (FVIII-R336Q/R562Q; FVIII-QQ). FVIII-QQ demonstrated expected APC resistance without other changes in procoagulant function or A2-domain dissociation. In plasma-based studies, FVIII-WT/FVIIIa-WT demonstrated dose-dependent sensitivity to APC with or without protein S, whereas FVIII-QQ/FVIIIa-QQ did not. Importantly, FVIII-QQ demonstrated approximately fivefold increased procoagulant function relative to FVIII-WT in the tail clip and ferric chloride injury models in hemophilia A (HA) mice. To minimize the contribution of FV inactivation by APC in vivo, a tail clip assay was performed in homozygous HA/FV Leiden (FVL) mice infused with FVIII-QQ or FVIII-WT in the presence or absence of monoclonal antibody 1609, an antibody that blocks murine PC/APC hemostatic function. FVIII-QQ again demonstrated enhanced hemostatic function in HA/FVL mice; however, FVIII-QQ and FVIII-WT performed analogously in the presence of the PC/APC inhibitory antibody, indicating the increased hemostatic effect of FVIII-QQ was APC specific. Our data demonstrate APC contributes to the in vivo regulation of FVIIIa, which has the potential to be exploited to develop novel HA therapeutics.

Digital haemophilia: Insights into the use of social media for haemophilia care, research and advocacy.

INTRODUCTION: The haemophilia community on Twitter is diverse, consisting of advocacy groups, patients, physicians, researchers and other users. However, the scope of this community is uncharacterized, and limited data is available regarding effective participation in this community. AIM: To assess the types of users active in the haemophilia community on Twitter, as well as major themes present in haemophilia-related tweets. METHODS: Forty-nine thousand five hundred and twelve tweets between September 2019 and September 2021 were classified using regular expressions. A subset of the classified tweets was manually analysed to identify prevalent discussion themes. RESULTS: Among the top 250 users by post count, the largest categories of users were support and advocacy groups, people with bleeding disorders and healthcare providers. The largest thematic categories of tweets were gene therapy, contaminated haemophilia blood products, haemophilia research, clinical management of haemophilia and COVID-19. While misinformation was rare, negative and incorrect perceptions of haemophilia were present among the general public. CONCLUSION: Our results demonstrate patterns of effective Twitter usage for patient care, research and advocacy purposes among the haemophilia community.

Appendix to the Society of Interventional Radiology Consensus Guidelines for the Periprocedural Management of Thrombotic and Bleeding Risk in Patients Undergoing Percutaneous Image-Guided Interventions: Pediatric Considerations.

PURPOSE: To provide guidance on the use of anticoagulant and antithrombotic agents in pediatric patients undergoing interventional radiology procedures. MATERIALS AND METHODS: A multidisciplinary writing group conducted a comprehensive literature search to identify studies on the topic of interest. Recommendations were developed for procedural risk and medication dosage and withholding. A modified Delphi technique was used to achieve consensus agreement on the recommendations. RESULTS: A total of 24 studies, including systematic reviews and meta-analyses, randomized controlled trials, and prospective and retrospective cohort studies, were identified as relevant. The expert writing group agreed on procedural risk categorization, laboratory testing thresholds, and medication dosage and withholding recommendations specific to pediatric practice. They additionally described the nuances of anticoagulation in clinical conditions specific to pediatrics. CONCLUSIONS: The Society of Interventional Radiology recommends following the guidance provided in the document when developing multidisciplinary management protocols for anticoagulation and antithrombotic treatment in pediatric patients undergoing interventional radiology procedures.

Mechanical ventilation variables associated with high pulmonary artery pressures in ARDS patients: a post hoc analysis.

BACKGROUND: The relationship between indices of mechanical ventilation and pulmonary artery pressures remains ill-defined in ARDS. As our understanding of mechanical ventilation has progressed, there is now a greater appreciation of the impact of high driving pressures and mechanical power in perpetuating lung injury. However, the relationship between the newer derived indices of mechanical ventilation and pulmonary artery pressure is unclear. We performed a post hoc analysis of the Fluid and Catheters Treatment Trial (FACTT) trial to investigate the associations between mechanical ventilation indices in ARDS patients and the prevalence of pulmonary hypertension. This may help elucidate future clinical targets for more, right ventricular protective, mechanical ventilation strategies. METHODS: We performed a post hoc analysis of the FACTT database to identify ARDS patients who had a pulmonary artery catheter (PAC) inserted and pulmonary artery pressure readings recorded. We excluded any patient with a PAC inserted who was spontaneously breathing, as driving pressure and mechanical power are not validated in this cohort. Three independent analyses were performed: a univariate analysis, to assess for associations between mPAP and mechanical ventilation parameters using Pearson correlation coefficients, a multivariate analysis, to assess for independent associations with mPAP using a multiple regression model according to Akaike's information criteria and finally an analysis for nonlinearity, using the best-fitting model according to the Bayesian information criterion (BIC) from linear, quadratic, fractional polynomial and restricted cubic spline models. RESULTS: All the ventilation parameters demonstrated a significant correlation with mPAP, except tidal volume (once adjusted for respiratory rate) in the univariate analysis. The multivariate analysis demonstrated that the blood pH level, P/F ratio, PaCO2 level, mean airway pressure and the mechanical power indexed to compliance were independently associated with mPAP. In the final nonlinear analysis, associations did not differ from linearity except for 4 variables for which the fractional polynomial was the best-fitting model. These were mechanical power (p = 0.01 compared to the linear model), respiratory rate (p = 0.04), peak pressure (p = 0.03) and mean airway pressure (p = 0.01). Two nonlinear variables associated with mPAP were assessed in more detail, respiratory rate and mechanical power. Inflexion points at a respiratory rate of 16.8 cycles per minute and a mechanical power of 8.8 J/min were demonstrated. CONCLUSIONS: The associations identified between mPAP and mechanical ventilation variables in this analysis would suggest that classical ARDS lung protective strategies, including low tidal volume ventilation and permissive hypercapnia, may negatively impact the management of the subset of ARDS patients with associated right ventricular dysfunction or ACP. Additionally, respiratory rates above 17 cycles per minute show an incremental increase in mPAP. Therefore, increases in tidal volume (within the limitation of driving pressure < 18 cmH20) may represent a more right ventricular protective way to control CO2 and pH.

Variable-Temperature Electrospray Ionization for Temperature-Dependent Folding/Refolding Reactions of Proteins and Ligand Binding.

Stabilities and structure(s) of proteins are directly coupled to their local environment or Gibbs free energy landscape as defined by solvent, temperature, pressure, and concentration. Solution pH, ionic strength, cofactors, chemical chaperones, and osmolytes perturb the chemical potential and induce further changes in structure, stability, and function. At present, no single analytical technique can monitor these effects in a single measurement. Mass spectrometry and ion mobility-mass spectrometry play increasingly essential roles in studies of proteins, protein complexes, and even membrane protein complexes; however, with few exceptions, the effects of the solution temperature on the stability and structure(s) of analytes have not been thoroughly investigated. Here, we describe a new variable-temperature electrospray ionization (vT-ESI) source that utilizes a thermoelectric chip to cool and heat the solution contained within the static ESI emitter. This design allows for solution temperatures to be varied from ∼5 to 98 °C with short equilibration times (<2 min) between precisely controlled temperature changes. The performance of the apparatus for vT-ESI-mass spectrometry and vT-ESI-ion mobility-mass spectrometry studies of cold- and heat-folding reactions is demonstrated using ubiquitin and frataxin. Instrument performance for studies on temperature-dependent ligand binding is shown using the chaperonin GroEL.

Gene Therapy for Inherited Bleeding Disorders.

Decades of preclinical and clinical studies developing gene therapy for hemophilia are poised to bear fruit with current promising pivotal studies likely to lead to regulatory approval. However, this recent success should not obscure the multiple challenges that were overcome to reach this destination. Gene therapy for hemophilia A and B benefited from advancements in the general gene therapy field, such as the development of adeno-associated viral vectors, as well as disease-specific breakthroughs, like the identification of B-domain deleted factor VIII and hyperactive factor IX Padua. The gene therapy field has also benefited from hemophilia B clinical studies, which revealed for the first time critical safety concerns related to immune responses to the vector capsid not anticipated in preclinical models. Preclinical studies have also investigated gene transfer approaches for other rare inherited bleeding disorders, including factor VII deficiency, von Willebrand disease, and Glanzmann thrombasthenia. Here we review the successful gene therapy journey for hemophilia and pose some unanswered questions. We then discuss the current state of gene therapy for these other rare inherited bleeding disorders and how the lessons of hemophilia gene therapy may guide clinical development.

Real-world cost estimates of initiating emicizumab in US patients with haemophilia A.

INTRODUCTION: Emicizumab is the first approved non-factor therapy for haemophilia A. It provides superior prophylactic bleeding control compared to other products in both patients with and patients without inhibitors. However, there is no real-world data about the monetary consequences of starting emicizumab. AIM: To examine the estimated costs of starting emicizumab in a cohort of real-world haemophilia A patients with and without inhibitors. METHODS: The cost of haemostatic therapy for 6 months before and after initiating emicizumab for participants in a multicentre observational study was calculated based on the type of product and dosing that was used for prophylaxis and treating breakthrough bleeds, the number of treated bleeds and the participant weight. RESULTS: Ninety-two patients were included, 18 with an active inhibitor. The median age was 8.7 years. The median total cost for all patients decreased from $176,720 to $128,099 (p = .04) after initiating emicizumab, largely because of decrease in the total cost of high-cost outliers. The cost of prophylaxis and the total cost of bleeds also significantly decreased after starting emicizumab, both for patient with and patients without inhibitors. CONCLUSIONS: Starting or switching to prophylaxis with emicizumab results in decreased costs for the treatment of patients with haemophilia A. This real-world data could inform on payer decisions as well as future cost-effective analysis.

Surface-induced dissociation of protein complexes on a cyclic ion mobility spectrometer.

We describe the implementation of a simple three-electrode surface-induced dissociation (SID) cell on a cyclic ion mobility spectrometer (cIMS) and demonstrate the utility of multipass mobility separations for resolving multiple conformations of protein complexes generated during collision-induced and surface-induced unfolding (CIU & SIU) experiments. In addition to CIU and SIU, SID of protein complexes is readily accomplished within the native instrument software and with no additional external power supplies by entering a single SID collision energy, a simplification in user experience compared to prior implementations. A set of cyclic homomeric protein complexes and a heterohexamer with known CID and SID behavior were analyzed to investigate mass and mobility resolution improvements, the latter of which improved by 20-50% (median: 33%) compared to a linear travelling wave device. Multiple passes of intact complexes, or their SID fragments, increased the mobility resolution by an average of 15% per pass, with the racetrack effect being observed after ∼3 or 4 passes, depending on the drift time spread of the analytes. Even with modest improvements to apparent mobility resolving power, multipass experiments were particularly useful for separating conformations produced from CIU and SIU experiments. We illustrate several examples where either (1) multipass experiments revealed multiple overlapping conformations previously unobserved or obscured due to limited mobility resolution, or (2) CIU or SIU conformations that appeared 'native' in a single pass experiment were actually slightly compacted or expanded, with the change only being measurable through multipass experiments. The work conducted here, the first utilization of multipass cyclic ion mobility for CIU, SIU, and SID of protein assemblies and a demonstration of a wholly integrated SIU/SID workflow, paves the way for widespread adoption of SID technology for native mass spectrometry and also improves our understanding of gas-phase protein complex CIU and SIU conformationomes.

Long-Term Follow-Up of the First in Human Intravascular Delivery of AAV for Gene Transfer: AAV2-hFIX16 for Severe Hemophilia B.

Adeno-associated virus (AAV) vectors are a leading platform for gene-based therapies for both monogenic and complex acquired disorders. The success of AAV gene transfer highlights the need to answer outstanding clinical questions of safety, durability, and the nature of the human immune response to AAV vectors. Here, we present longitudinal follow-up data of subjects who participated in the first trial of a systemically delivered AAV vector. Adult males (n = 7) with severe hemophilia B received an AAV2 vector at doses ranging from 8 × 1010 to 2 × 1012 vg/kg to target hepatocyte-specific expression of coagulation factor IX; a subset (n = 4) was followed for 12-15 years post-vector administration. No major safety concerns were observed. There was no evidence of sustained hepatic toxicity or development of hepatocellular carcinoma as assessed by liver transaminase values, serum α-fetoprotein, and liver ultrasound. Subjects demonstrated persistent, increased AAV neutralizing antibodies (NAbs) to the infused AAV serotype 2 (AAV2) as well as all other AAV serotypes tested (AAV5 and AAV8) for the duration of follow-up. These data represent the longest available longitudinal follow-up data of subjects who received intravascular AAV and support the preliminary safety of intravascular AAV administration at the doses tested in adults. Data demonstrate, for the first time, the persistence of high-titer, multi-serotype cross-reactive AAV NAbs for up to 15 years post- AAV vector administration. Our observations are broadly applicable to the development of AAV-mediated gene therapy.

Hemophilia B Gene Therapy with a High-Specific-Activity Factor IX Variant.

BACKGROUND: The prevention of bleeding with adequately sustained levels of clotting factor, after a single therapeutic intervention and without the need for further medical intervention, represents an important goal in the treatment of hemophilia. METHODS: We infused a single-stranded adeno-associated viral (AAV) vector consisting of a bioengineered capsid, liver-specific promoter and factor IX Padua (factor IX-R338L) transgene at a dose of 5×1011 vector genomes per kilogram of body weight in 10 men with hemophilia B who had factor IX coagulant activity of 2% or less of the normal value. Laboratory values, bleeding frequency, and consumption of factor IX concentrate were prospectively evaluated after vector infusion and were compared with baseline values. RESULTS: No serious adverse events occurred during or after vector infusion. Vector-derived factor IX coagulant activity was sustained in all the participants, with a mean (±SD) steady-state factor IX coagulant activity of 33.7±18.5% (range, 14 to 81). On cumulative follow-up of 492 weeks among all the participants (range of follow-up in individual participants, 28 to 78 weeks), the annualized bleeding rate was significantly reduced (mean rate, 11.1 events per year [range, 0 to 48] before vector administration vs. 0.4 events per year [range, 0 to 4] after administration; P=0.02), as was factor use (mean dose, 2908 IU per kilogram [range, 0 to 8090] before vector administration vs. 49.3 IU per kilogram [range, 0 to 376] after administration; P=0.004). A total of 8 of 10 participants did not use factor, and 9 of 10 did not have bleeds after vector administration. An asymptomatic increase in liver-enzyme levels developed in 2 participants and resolved with short-term prednisone treatment. One participant, who had substantial, advanced arthropathy at baseline, administered factor for bleeding but overall used 91% less factor than before vector infusion. CONCLUSIONS: We found sustained therapeutic expression of factor IX coagulant activity after gene transfer in 10 participants with hemophilia who received the same vector dose. Transgene-derived factor IX coagulant activity enabled the termination of baseline prophylaxis and the near elimination of bleeding and factor use. (Funded by Spark Therapeutics and Pfizer; ClinicalTrials.gov number, NCT02484092 .).

Collision Cross Sections of Charge-Reduced Proteins and Protein Complexes: A Database for Collision Cross Section Calibration.

The use of charge-reducing reagents to generate lower-charge ions has gained popularity in the field of native mass spectrometry (MS) and ion mobility mass spectrometry (IM-MS). This is because the lower number of charged sites decreases the propensity for Coulombic repulsions and unfolding/restructuring, helping to preserve the native-like structure. Furthermore, lowering the charge state consequently increases the mass-to-charge values (m/z), effectively increasing spacing between signals originating from small mass differences, such as different proteoforms or protein-drug complexes. IM-MS yields collision cross section (CCS, Ω) values that provide information about the three-dimensional structure of the ion. Traveling wave IM (TWIM) is an established and expanding technique within the native MS field. TWIM measurements require CCS calibration, which is achieved via the use of standard species of known CCS. Current databases for native-like proteins and protein complexes provide CCS values obtained using normal (i.e., non-charge-reducing) conditions. Herein, we explored the validity of using "normal" charge calibrants to calibrate for charge-reduced proteins and show cases where it is not appropriate. Using a custom linear field drift cell that enables the determination of ion mobilities from "first principles", we directly determined CCS values for 19 protein calibrant species under three solution conditions (yielding a broad range of charge states) and two drift gases. This has established a database of CCS and reduced-mobility (K0) values, along with their associated uncertainties, for proteins and protein complexes over a large m/z range. TWIM validation of this database shows improved accuracy over existing methods in calibrating CCS values for charge-reduced proteins.

Novel approaches to hemophilia therapy: successes and challenges.

New therapies for hemophilia A and hemophilia B will likely continue to change clinical practice. Ranging from extended half-life to nonfactor products and gene therapy, these innovative approaches have the potential to enhance the standard of care by decreasing infusion frequency to increase compliance, promoting prophylaxis, offering alternatives to inhibitor patients, and easing route of administration. Each category has intrinsic challenges that may limit the broader application of these promising therapies. To date, none specifically address the challenge of dispersing treatment to the developing world.

MYH9-macrothrombocytopenia caused by a novel variant (E1421K) initially presenting as apparent neonatal alloimmune thrombocytopenia.

MYH9-related disease is a rare cause of thrombocytopenia. We report an infant girl who presented with severe thrombocytopenia at birth and was initially diagnosed with and treated for neonatal alloimmune thrombocytopenia. However, persistent thrombocytopenia led to the suspicion of congenital thrombocytopenia and subsequent identification of a novel variant in MYH9 (E1421K). In silico analysis strongly predicts that this is a disruptive substitution. Immunofluorescent analysis of neutrophils demonstrates abnormal aggregates of MYH9 protein. This case also suggests that a very high immature platelet fraction (≥40%) may be useful for rapidly differentiating MYH9-related disease from other causes of neonatal thrombocytopenia.