One-stage Clotting Research Articles

Modulation of Extravascular Binding of Recombinant Factor IX Impacts duration of Efficacy in Mouse Models.

There is an emerging concept that in addition to circulating coagulation factor IX (FIX), extravascular FIX contributes to hemostasis. Evaluate efficacy of extravascular FIX using animal models of tail clip bleeding and ferric chloride induced thrombosis. Mutant rFIX proteins with described enhanced (rFIXK5R) or reduced (rFIXK5A) binding to extracellular matrix were generated and characterized using in vitro aPTT, one stage clotting and modified FX assays. Using hemophilia B mice, pharmacokinetic parameters and in vivo efficacy of these proteins was compared against rFIX wild type protein (rFIXWT) in a tail clip bleeding and FeCl3-induced thrombosis model. Respective tissue disposition of FIX was evaluated using immunofluorescence. In vitro characterization demonstrated comparable clotting activity of rFIX proteins. Pharmacokinetic profile showed that rFIXK5A displayed highest plasma exposure compared to rFIXWT and rFIXK5R. Immunofluorescence evaluation of liver tissue showed that rFIXK5R was detectable up to 24h, where as rFIXWT and rFIXK5A were detectable only at 15 minutes. In the tail clip bleeding model, rFIXK5R displayed significant hemostatic protection against bleeding incidence for up to 72h post intravenous administration of 50 IU/kg, whereas the efficacy of rFIXK5A was already reduced at 24h. Similarly, in the mesenteric artery thrombus model, rFIXK5R and rFIXWT demonstrated prolonged efficacy compared to rFIXK5A. Using two different in vivo models of hemostasis and thrombosis, we demonstrate that mutated rFIX protein with enhanced binding (rFIXK5R) to extravascular space confers prolonged hemostatic efficacy in vivo despite lower plasma exposure, while rFIXK5A rapidly lost its efficacy despite higher plasma exposure.

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

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

Analysis of an Inherited FXII Deficiency Pedigree Associated with Double Heterozygous Mutations in the F12 Gene.

This article is intended to identify the potential mutations of the FXII gene (F12) in an inherited FXII deficiency pedigree and illuminate the pathogenesis of the disease. The coagulation FXII activity (FXII:C) and FXII antigen (FXII:Ag) were inspected by one-stage clotting assay and enzyme-linked immunosorbent assay(ELISA), respectively. Polymerase chain reaction amplification (PCR) was performed and the F12 gene was sequenced directly. A molecular model of FXIIprotein was established for further analysis. ClustalX-2.1-win and online bioinformatic software were used to estimate the conservatism and possible impact of the protein change. The proband presented prolonged APTT(180s) and extreme low FXII:C and FXII:Ag (both < 1%, reference range:72-113%). A compound heterozygous were found by the direct sequencing of the F12 gene. One was a deletion mutation c.1792_1796delGTCTA, which is a novel mutation; the other was an insertion mutation, c.1092_1093insC. Bioinformatic and modeling analyses indicated that the the two frameshift mutations may be deleterious and possibly alter the structure and the function of the protein. The mutations c.1792_1796delGTCTA and c.1092_1093insC could be the main causes of reducing FXII in this pedigree, and c.1792_1796delGTCTA mutation was the first report in the world.

Analysis of F12 gene variants and molecular mechanisms in patients with coagulation factor Ⅻ deficiency

To analyze the sequence of the F12 gene and molecular mechanism for 20 patients with coagulation factor Ⅻ (FⅫ) deficiency. The patients were selected from the outpatient department of the Second Hospital of Shanxi Medical University from July 2020 to January 2022. The activity of coagulation factor Ⅷ (FⅧ:C), factor Ⅸ (FⅨ:C), factor Ⅺ (FⅪ:C) and factor Ⅻ (FⅫ:C) were determined by using a one-stage clotting assay. All exons and 5' and 3' UTR of the F12 gene were analyzed by Sanger sequencing to detect the potential variants. Bioinformatic software was used to predict the pathogenicity of the variants, conservation of amino acids, and protein models. The FⅫ:C of the 20 patients has ranged from 0.07% to 20.10%, which was far below the reference values, whilst the other coagulation indexes were all normal. Sanger sequencing has identified genetic variants in 10 patients, including 4 with missense variants [c.820C>T (p.Arg274Cys), c.1561G>A (p.Glu521Lys), c.181T>C (p.Cys61Arg) and c.566.G>C (p.Cys189Ser)], 4 deletional variants c.303_304delCA(p.His101GlnfsX36), 1 insertional variant c.1093_1094insC (p.Lys365GlnfsX69) and 1 nonsense variant c.1763C>A (p.Ser588*). The remaining 10 patients only harbored the 46C/T variant. The heterozygous c.820C>T(p.Arg274Cys) missense variant in patient 1 and the homozygous c.1763C>A (p.Ser588*) nonsense variant in patient 2 were not included in the ClinVar and the Human Gene Mutation Database. Bioinformatic analysis predicted that both variants were pathogenic, and the corresponding amino acids are highly conserved. The protein prediction models suggested that the c.820C>T (p.Arg274Cys) variant may affect the stability of the secondary structure of FⅫ protein by disrupting the original hydrogen bonding force and truncating the side chain, leading to changes in the vital domain. c.1763C>A (p.Ser588*) may produce a truncated C-terminus which may alter the spatial conformation of the protein domain and affect the serine protease cleavage site, resulting in extremely reduced FⅫ:C. Among individuals with low low FⅫ:C detected by one-stage clotting assay, 50% have harbored variants of the F12 gene, among which the c.820C>T and c.1763C>A were novel variants underlying the reduced coagulating factor FⅫ.

POSTER ABSTRACTS

POSTER ABSTRACTS

Measurement of extended half-life recombinant FVIII molecules: In vitro and ex vivo evidence of relevant assay discrepancies

BackgroundExtended half-life recombinant FVIII products (EHL-rFVIIIs) have been engineered to improve the pharmacokinetic profile of FVIII, enabling better hemostatic protection with a reduced number of injections in persons with hemophilia. Previous studies showed several discrepancies in FVIII activity (FVIII:C) measurements for EHL-rFVIIIs comparing one-stage clotting assay (OSA) and chromogenic assay (CSA), although a systematic investigation of this phenomenon is still lacking. ObjectiveEvaluation of the accuracy and precision of measurement of all available EHL-rFVIIIs with 5 different assays both in vitro and ex vivo. MethodsDamoctocog alfa pegol, rurioctocog alfa pegol, turoctocog alfa pegol, and efmoroctocog alfa were tested with 3 OSA types: (1) aPTT-based commercial reagents with colloidal silica (Synthasil, Werfen-IL); (2) ellagic acid, Synthafax (Werfen-IL); and (3) OSA calibrated with each EHL-rFVIII product and colloidal silica. Measurements were also carried out with 2 different commercially available CSA reagents (Coamatic Factor VIII, Chromogenix-Werfen) and Trinichrom FVIII (Tcoag-Stago). A Bland–Altman analysis was performed to compare all assays. ResultsThe simple OSA showed significant discrepancies between the expected and measured EHL-rFVIII concentrations as CSA methods, whereas the calibrated OSA assay was accurate and precise in determining the activity of all EHL-rFVIIIs in the in vitro setting. Comparable results were found using ex vivo plasma samples. ConclusionIn this study, only OSA with a calibration curve constructed with each EHL-rFVIII product showed acceptable accuracy and precision in EHL-rFVIIIs measurements.

Measuring Emicizumab Levels in the Hemostasis Laboratory.

Emicizumab is a bi-specific antibody that in recent years has been introduced in many countries as a prophylactic agent for bleed prevention in cases of severe hemophilia A, and in some cases of moderate HA. It can be used in individuals with HA with and without FVIII inhibitors, because the drug is not a target for these inhibitors. Emicizumab was developed as a fixed weight-based dose and does not normally need laboratory monitoring, but in some circumstances such as a treated HA patient with unexpected bleeding episodes, a laboratory assay is justified. This chapter describes to performance of a one-stage clotting assay to measure emicizumab.

Personalization of Clotting Factor VIII Replacement Therapy Based on Population Pharmacokinetics in Adult Patients with Severe Hemophilia a Who Frequently Switch Factor VIII Concentrates

Interindividual pharmacokinetic differences in clotting factor VIII (FVIII) metabolism impede the dosing regimen optimization in patients with hemophilia A. The population pharmacokinetic (PK) analysis enables the estimation of FVIII pharmacokinetics in individual patients which is used to personalize dosing regimens. Therefore, we conducted a prospective study on adult patients with severe hemophilia A who received different FVIII concentrates for tertiary prophylaxis and whose dosage of FVIII was adjusted based on individual PK results. We aimed to compare the number of bleeding episodes and FVIII consumption before and after dosing adjustment. The study, conducted for 18 months for each participant, was divided into 3 phases: (1) pre-PK: assessments before FVIII dosing adjustment, (2) dosing adjustment based on the PK analysis of FVIII, and (3) assessments after FVIII dosing adjustment. All patients gave informed consent before enrolment, and all procedures were carried out according to the Declaration of Helsinki. During the study patients frequently changed FVIII concentrates (each patient used 3-5 different products) which reflects the standard of care in adult patients with hemophilia in Poland. During phase 1 of the study, over 5-13 months [median: 11.0 months, mean(standard deviation - SD): 10.8(1.9) months], patients recorded FVIII consumption and bleedings using electronic diaries (myPKFiT® licensed for octocog alfa). In phase 2 of the study, a PK analysis (clearance, half-time, time to reach the 1 IU/dl concentration) was performed: following the 72-hour washout period, blood samples were collected, and patients received the infusion of octocog alfa with the mean dose (SD) of 51.1(1.7) IU/kg. Two more blood samples were collected 3-4 h and 24-36 h after the infusion. Plasma FVIII activity was measured with a one-stage clotting assay, and the FVIII inhibitor with the Nijmegen modification of the standard Bethesda method. The myPKFiT® was used to obtain individualized FVIII dosing regimens based on PK analysis results. The dosing adjustment was offered to patients who experienced breakthrough bleeds during phase 1 or in whom the pre-PK treatment did not secure FVIII trough level of >1 IU/dl. In case of favorable PK results and no breakthrough bleeds during phase 1, a less intensive regimen was implemented. In phase 3 of the study (which lasted for 5-13 months, median: 7.7 months, mean(SD): 7.6(1.6) months), patients continued treatment with locally available FVIII concentrates and used electronic diaries to record FVIII consumption and bleedings. All bleeding rates were annualized (annualized bleeding rates - ABR). The final analysis set included 22 male patients, aged 23-68 years. The clearance of octocog alpha ranged from 0.014 to 0.051 dL/h/kg [mean(SD), 0.030±0.010 dL/h/kg; coefficient of variation (CV)=33%], half-life - from 9.1 to 27.9 h (14.6(4.3) h, CV=29%), and time to reach 1 IU/dl - from 51 to 179 h [91(29) h, CV=32%]. Three individuals were categorized as slow metabolizers (clearance of 0.014, 0.018, and 0.019 dL/h/kg), and 2 as fast metabolizers (clearance of 0.048 and 0.051 dL/kg/h). FVIII inhibitor was undetectable (<0.5 BU/ml) in all patients. After the PK analysis, 21 of 22 patients met the criteria of FVIII dosing adjustment. Four patients did not agree to change the regimen. Seventeen patients modified it according to the PK results (10 of them had FVIII trough levels of >1 IU/dl and 7 of them of <1 IU/dl in phase 1 of the study). Changing the dosing regimen in the 17 patients resulted in ABR reduction compared to the pre-PK phase: a decrease of 3.1-fold in total ABR (p=0.045 for dependent samples t-test); 3.2-fold in spontaneous ABR (p=0.046); and 3.1-fold in injury-related ABR (p=0.072). The consumption of FVIII due to bleeds had decreased by 77% (p=0.034). In conclusion, personalizing the FVIII replacement therapy based on population PK models helps to lower bleeding risk and drug consumption in patients with severe hemophilia A. Presented results suggest that prophylaxis regimen based on PK analysis carried out with octocog alfa and myPKFiT® application is clinically effective also with the use of other FVIII concentrates.

Discrepancy between the Results of One-Stage and Chromogenic Factor VIII Assays: Switch in Diagnosis from Mild to Moderate Hemophilia a in Three Cases

Introduction Factor VIII (FVIII) activity can be measured with different methods including one-stage clotting assay (OSA) or chromogenic substrate assay (CSA). Some persons with mild hemophilia A (HA) have a significant discrepancy between the assays which has been previously reported. Discrepancy between these two methods, albeit less frequent, can also lead to a switch in diagnosis from mild to moderate HA. Herein, we report 3 persons with HA (PwHA) whose diagnosis changed from mild to moderate HA after obtaining FVIII levels assessed by CSA. Materials and Methods Data were extracted from the medical records of the PwHA including demographics, bleeding rates, and factor levels. FVIII activity was measured using the OSA on an ACL Top 500 with SynthaSil aPTT reagent (Instrumentation Laboratories Bedford, MA, USA). Factor VIII activity was also determined photometrically via the Chromogenix Coatest® SP4 FVIII chromogenic assay kit (bovine chromogenic FVIII activity, Diapharma Group, West Chester, OH). Results Data were collected from 3 PwHA who were previously diagnosed with mild HA yet were noted to have a bleeding phenotype worse than expected for mild HA (Table-1). Case 1 is 26 years old and had been experiencing multiple joint bleeds. His OSA FVIII level was 6.8%. He was on clotting factor concentrate (CFC) on demand. After having severe hemophilic arthropathy affecting his social life, prophylaxis with CFC was commenced. Significant improvement was observed after the initiation of prophylaxis. His CSA FVIII level was 2.7%, consistent with his bleeding phenotype, and he has been on emicizumab prophylaxis for a year without any bleeding events. Case 2 is 22 years old and had been experiencing frequent muscle bleeds. His OSA FVIII level was 6.1% and CSA FVIII level was 2.7%. He remains on CFC on demand based on his preference despite the frequent bleeding. Case 3 is 15 years old and was diagnosed with mild HA at the age of 8 after recurrent joint bleeds. His OSA FVIII level was 13.8% and CSA FVIII level was 1.5%. He has been on emicizumab prophylaxis for 10 months without any bleeding event. Conclusion While discrepancies between assays in mild hemophilia have been widely reported, there are fewer reports on an assay discrepancy changing a diagnosis from mild to moderate HA. As such, we strongly suggest performing both OSA and CSA for the diagnosis and classification of HA especially if the PwHA has more bleeding episodes than expected. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

BAX 335 Hemophilia B Gene Therapy Phase 1/2 Clinical Trial: Long-Term Safety and Efficacy Follow-up

Background: BAX 335 is an adeno-associated virus serotype 8 (AAV8)-based clotting factor IX (FIX) Padua (R338L) gene therapy for the treatment of hemophilia B. A phase 1/2 safety and efficacy study dosed 8 participants with BAX 335 between 2013 and 2015 (NCT01687608). Infusions with BAX 335 were generally well tolerated; however, 7 of 8 participants did not achieve significant levels of durable transgene expression despite the use of glucocorticoids and resumed FIX replacement by 52 weeks (Konkle et al, Blood 2021;137:763-74). A root-cause analysis identified CpG content in the vector as a potential immunogenic trigger for the innate immune response, resulting in loss of expression. One participant demonstrated high levels of durable FIX expression, with detectable FIX activity levels between 0.1 and 0.4 IU/mL after 4 years and was found to have a missense variant in the IL6R gene. This study is the longest ongoing clinical gene therapy trial using a FIX R338L transgene. Aims: (1) To report long-term safety and participant disposition; (2) to describe persistence of endogenous FIX R338L transgene expression; and (3) to report long term persistence of neutralizing anti-capsid antibodies. Methods: Eight adult male participants with hemophilia B (FIX activity ≤2%) received BAX 335 in 1 of 3 intravenous dose cohorts (2.0 x 1011, 1.0 x 1012, or 3.0 x 1012 vector genomes/kg). The primary study objective was to assess the safety of BAX 335. Secondary assessments included the kinetics of plasma FIX activity, the need for exogenous FIX replacement, and systemic immune responses to BAX 335 and vector transgene protein. FIX clotting activity was measured using the one-stage clotting assay at the central laboratory. Serum neutralizing antibodies against the AAV8 and AAV2 capsids were measured to Year 5 following BAX 335 infusion using an in vitro transduction inhibition assay. Laboratory and in-person assessments were conducted for the first 5 years after BAX 335 infusion (one unscheduled visit was made at 7.2 Years). This was followed by annual liver ultrasound scans and telephone questionnaires assessing health status with the aim of completing 15 years of follow-up per participant. The study was approved by the institutional review boards of all participating sites, and all participants provided written informed consent. Results: Of 8 participants enrolled (aged 20-69 years), 2 discontinued from the study approximately 1 and 3 years after receiving BAX 335 infusion, and another participant withdrew consent 2 weeks prior to the data cutoff of May 6, 2022. Data from the 6 participants who had >5 years of long-term safety follow-up were included in this analysis. At data cutoff, 176 adverse events (AEs) were reported in all 8 dosed participants, most (72%) occurred in Years 1 and 2. In total, 6 serious adverse events (SAEs) were reported in 3 participants, of these 2 SAEs (post-procedural hemorrhage, arthritis) were reported after the interim analysis reported by Konkle et al. 2021. None were considered to be related to BAX 335 and all resolved. Although long-term hemostatic protection from bleeds was not observed in most of the participants in this analysis, 1 participant had continued FIX activity (Figure 1), with a most recent value of 0.078 IU/mL at 7.2 years after BAX 335 infusion. This participant has neither experienced any bleeds nor needed FIX replacement therapy after the second week of vector infusion. No FIX inhibitors have been observed. At Year 5, AAV neutralizing antibodies persisted at high titers in most participants (reciprocal of serum dilution: AAV2, <5 to 10,240; AAV8, 80 to 40,960). Conclusions: No additional BAX 335-related AEs, malignancy or thrombosis were reported in this long-term follow-up analysis of a phase 1/2 study. One participant achieved persistent FIX transgene activity in the circulation for 7.2 years and remains free from bleeding and the need for FIX replacement therapy. This is the longest duration of FIX R338L expression reported. Consistent with other studies, AAV neutralizing antibodies remained persistent at titers that would limit re-dosing with current AAV platforms. Future studies should explore patient-specific factors that may predict persistent transgene expression. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Escaping Ability of Human-Porcine Hybrid Factor VIII from Anti-Factor VIII Inhibitors with an A2 or C2 Epitope

Porcine (p) factor (F)VIII has limited cross-reactivity to inhibitors against human (h) FVIII (Lollar P, JBC 1991). Plasma-derived or recombinant pFVIII agents, therefore, have been used as therapeutics for uncontrollable bleedings in congenital or acquired hemophilia A (HA). Alternatively, most of FVIII inhibitors bind to the epitopes located in the A2, C2 and/or A3-C1 domains of FVIII (Scandella D, Blood 1989, Fulcher C, PNAS 1985), and monospecific inhibitors for domains other than A2 and C2 are infrequent (Prescott R, Blood 1997). In the present study, based on a hypothesis that human-porcine hybrid (hp)FVIII could escape the FVIII-inhibitory effects by inhibitors, we converted A2 domain and/or C2 domain of hFVIII into corresponding sequence of pFVIII, respectively, and investigated the escaping ability of these mutants from inhibitors. Three mutants were created using stable BHK cell line by converting hFVIII A2 domain and/or C2 domain into corresponding sequence of pFVIII, termed by hp(A2), hp(C2), and hp(A2/C2), respectively. Specific activity assessed by a one-stage clotting assay of hp(A2), hp(C2) and hp(A2/C2) was 0.75, 0.94 and 0.60 relative to hFVIII respectively. First, the escaping ability of these mutants from commercial anti-FVIII A2 or C2 monoclonal antibody (mAb) was investigated. Each of two different anti-hFVIII A2 mAbs and two different anti-C2 mAbs was spiked into FVIII-deficient plasma (FVIIId), respectively at the Bethesda titer of 2.7-4.4 BU/mL, followed by spiking hFVIII or hpFVIII at the concentration of 1 nM each. Incubation of each sample at 37 °C was initiated and FVIII activity was determined (FVIII:C) sequentially, calculating the FVIII:C at the fold of initial (no addition of inhibitor). In anti-A2 mAbs, FVIII:C of hFVIII and hp(C2) were immediately attenuated, resulting in suppression under 20% of initial level after 30 min, however, hp(A2) and hp(A2/C2) were not suppressed at all. In contrast, with anti-C2 mAbs, FVIII:C in hFVIII and hp(A2) was attenuated, whilst hp(C2) and hp(A2/C2) maintained their FVIII:C. Next, similar experiment was conducted with the purified IgG from the HA patients with inhibitor whose inhibitor was confirmed to recognize A2 only or both A2/C2 domains by Western blotting. Four patients with anti-A2 and anti-A2/C2 inhibitors (2 patients each) were investigated. Mutants converted certain domain(s) could escape inhibitory effect of purified IgG recognizing the corresponding domain(s), although partial attenuation exhibited even in the corresponding mutants. To further investigation, thrombin generation assay (TGA) and rotation thromboelastometry (ROTEM) were used. In TGA, purified IgG from patient with anti-A2 or anti-A2/C2 inhibitor was added to FVIIId, followed by spiking hFVIII or hpFVIII at the concentration of 1 nM. In the absence of IgG, peak thrombin of FVIIId was 128.0 nM, and then by adding hFVIII, hp(A2), hp(C2) and hp(A2/C2), the parameter enhanced to 228.8, 208.6, 207.3, and 219.9 nM, respectively. In the presence of anti-A2 inhibitor (5.0 BU/mL), peak thrombin of hp(A2) and hp(A2/C2) was not attenuated (203.1 and 257.1 nM), whilst those of hFVIII and hp(C2) was suppressed equally to FVIIId (137.3 and 134.5 nM respectively). As for anti-A2/C2 inhibitor (2.8 BU/mL), only hp(A2/C2) was not attenuated, whereas the others were suppressed comparable to FVIIId . Whole bloods collected from severe HA with anti-A2 inhibitor (3.1 BU/mL) were mixed with hFVIII or hpFVIII at the concentration of 2 nM, respectively, and were measured by ROTEM. Without any FVIII spiking, clot time (CT) was 7,151 sec and clot formation time (CFT) was undetectable. The addition of hp(A2) and hp(A2/C2) shortened CT/CFT to 1,525/536 sec and 1,987/690 sec, respectively, whilst hFVIII or hp(C2) was not effective (4,257/2,270 and 3,200/1,022 sec, respectively). On the other hand, purified IgG from patients with anti-A2/C2 inhibitor was added to whole blood from another severe HA without inhibitor. Under this condition (4.7 BU/mL), only hp(A2/C2) addition shortened CT/CFT from 6,482/2,163 to 1,724/503 sec, whereas the addition of the other FVIII resulted in limited effect to CT/CFT (2,703-4,796/551-2,024). We concluded that hybrid FVIII converted into porcine A2 and/or C2 domain sequences were able to escape corresponding inhibitors and that hpFVIII could be effective therapeutically for HA patients with inhibitors. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

A Population Pharmacokinetic (PopPK) Model to Characterize Efanesoctocog Alfa (BIVV001) Factor VIII (FVIII) Activity Levels in Patients with Severe Hemophilia A

Introduction Efanesoctocog alfa (formerly BIVV001) is a new class of FVIII replacement therapy uniquely engineered to decouple recombinant FVIII from endogenous von Willebrand factor (VWF) and overcome the VWF-imposed half-life ceiling. Once-weekly efanesoctocog alfa provides high sustained FVIII activity in the normal to near-normal range for most of the week and demonstrated superior bleed protection compared with prior FVIII prophylaxis. FVIII activity data have been collected from 5 clinical studies (Phase 1/2a single- and repeat-dose studies [NCT03205163 and EudraCT 2018-001535-51, respectively] in adults, and Phase 3 studies in adults and adolescents ≥12 years of age [XTEND-1, NCT04161495] and children ≥1 year to <12 years [XTEND-Kids, NCT04759131] and Phase 3 long-term extension study [XTEND-ed, NCT04644575]). We aimed to develop a popPK model to characterize FVIII activity after efanesoctocog alfa dosing, identify intrinsic and extrinsic factors affecting pharmacokinetics (PK), and assess PK variability. Methods FVIII activity levels used to develop the popPK model were measured by the one-stage clotting assay from 3054 blood samples from 199 adults and adolescents and 61 children who received efanesoctocog alfa in the aforementioned studies. Body weight and VWF antigen level ranged from 12.5 kg-133 kg and 40 IU/dL-339 IU/dL, respectively. A one-compartment model with linear elimination was used to characterize FVIII activity with an estimated allometric body weight effect on clearance (CL) and volume of central compartment (V) to account for the dependence of CL and V on body size. Baseline VWF, baseline hematocrit, race (White and Asian), hepatitis C virus and human immunodeficiency virus status, and blood types (A, B, O) were tested for statistical significance in the covariate analysis. The final popPK model was used to simulate various dose regimens in a virtual population of adult and adolescent patients generated using baseline body weight distribution from the Phase 1/2a studies and XTEND-1. Results The final popPK model described the FVIII activity over time profile, captured inter-individual variability in FVIII activity, and precisely estimated moderate inter-individual variability in CL and V (Table). Body weight effect allometric exponents showed that absolute CL and V increase with body weight, with overall faster elimination with lower body weight. Asian race was identified as a statistically significant covariate on CL (P<0.001); CL in Asians was 10.4% lower than in non-Asians. Baseline VWF level was not identified as a statistically significant covariate in the final popPK model, consistent with prior studies that demonstrate that the PK of efanesoctocog alfa is VWF-independent. Simulated steady-state FVIII activity over time for efanesoctocog alfa is presented in the Figure. The final popPK model showed that a once-weekly efanesoctocog alfa (50 IU/kg) prophylaxis regimen achieves a steady state Ctrough of >10 IU/dL and the time to 40 IU/dL FVIII activity was 3 to 4 days in the majority of adult and adolescent patients, irrespective of body weight and race. Simulations for perioperative management during major surgery and treatment of major bleeds showed that a loading dose of 50 IU/kg, followed by 30 IU/kg every 3 days in the postoperative period, met the World Federation of Hemophilia guidelines for peak FVIII activity for most adults and adolescents. Similarly, for minor surgeries and treatment of moderate to minor bleeds, a single dose of 50 IU/kg efanesoctocog alfa resulted in peak FVIII activity that met these guidelines. Conclusions A linear one-compartment popPK model was able to adequately characterize FVIII activity in patients with severe hemophilia A. Although CL and V depended on body weight and Asian race was identified as a covariate on CL, body weight and Asian race's limited influence on FVIII exposure was not considered clinically meaningful. PopPK simulations demonstrated that 50 IU/kg once weekly efanesoctocog alfa achieved sustained FVIII activity in the normal to near-normal range (>40 IU/dL) for 3-4 days and >10 IU/dL at Day 7 in most adults and adolescents. PopPK simulations also supported the Phase 3 dose regimens selected for regular prophylaxis, treatment of bleeds, and perioperative management. Study was funded by Sanofi and Sobi. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

The Implication of New Developments in Hemophilia Treatment on Its Laboratory Evaluation.

Laboratories monitor hemophilia replacement therapy by specific coagulation factor measurement before and after the infusion of human-derived or recombinant factors. Bypassing agents are now used for patients with inhibitors. Recently, modified long-acting coagulation factors have been introduced, for which discrepant results may be expected when the measurement is performed with one-stage clotting or chromogenic assays. Currently, novel drugs not based on coagulation factors are being developed andfurther tested in clinical studies. These drugs do require new methods, and therefore, laboratory evaluation of hemophilia will undergo dramatic changes in the near future. Accordingly, present laboratory methods for monitoring, which include one-stage clotting or chromogenic assays, used to measure either factor VIII (FVIII) or factor IX (FIX), will not be sufficient. A thrombin generation test (TGT) or thromboelastometry may be used to monitor bypassing agents. For measuring modified long-acting coagulation factors, chromogenic assays will be probably more suitable than one-stage clotting assays. Novel drugs that are not based on coagulation factors, such as emicizumab, fitusiran, or concizumab,will require alternative methods.

Prolonged α-thrombin-related activation and delayed active protein C-associated degradation confer mild phenotype in a patient with severe hemophilia A with F8 p.H118R.

In hemophilia A, bleeding mostly correlates with factor VIII activity (FVIII:C), although some patients show discrepancy in bleeding severity and FVIII:C. We report a novel procoagulant mechanism associated with F8 p.H118R (c.353A > G) in a young Japanese man with few bleeding episodes despite low levels of FVIII:C (< 1IU/dL). Plasma FVIII:C was < 1IU/dL measured by one-stage clotting assay (OSA) and chromogenic substrate assay (CSA), whereas FVIII antigen (FVIII:Ag) was 9.7%. The global coagulation assay showed higher max speed in clot waveform analysis (CWA), shorter clotting time in rotation thromboelastometry (ROTEM) (1605 vs. > 5000s), shorter lag time (4.87 vs. 12.47min) and larger ETP (207.9 vs. 53.3nM*min) in thrombin generation assay, compared with FVIII-deficient control. Expressed recombinant H118R mutant in culture media showed low FVIII:C (1-5IU/dL) by OSA, with non-hemophilia level of FVIII:Ag. Western blot analysis using recombinant H118R showed longer persistence of heavy-chain of H118R after incubation with α-thrombin, compared with wild-type. Incubation of H118R with activated protein C (APC) also showed longer persistence of A1-A2 domain. In conclusion, H118R showed prolonged activation by α-thrombin and delayed APC-related FVIII degradation. These properties may confer the procoagulant activity and few bleeding episodes despite low FVIII:C.

Emicizumab assay evaluations and results from an Australian field study of emicizumab measurement

Emicizumab is a recombinant, humanised bispecific antibody which acts as a FVIII mimetic and is a therapeutic option for haemophilia A. Plasma emicizumab levels may sometimes be required. Multiple one-stage clotting assays (OSA) and one human component chromogenic assay (CSA) were used to measure emicizumab both centrally and by a field study. The study samples drug concentrations range included within therapy range of 35-70μg/mL. All assays were modified from traditional FVIII assays to enable replacement of plasma calibrators with emicizumab calibrators. Central laboratory OSA mean recovery levels (target) for six spike levels of emicizumab were close to target at 120.5 (120), 81.6 (80), 40.9 (40), 21.4 (20), 10.7 (10) and 5.5 (5)μg/mL. Field study OSA mean recoveries were similarly close to target. Between method coefficients of variation were <9% in both the central laboratory and field study assays, except for the 5μg/mL sample which was 12.3%. CSA mean recoveries were within 10% of target at 80, 50 and 20μg/mL levels. This study affirms that emicizumab can be measured by OSA using many types of activated partial thromboplastin time (APTT) reagents and is also measurable by the human CSA. The assays showed good precision, accuracy and linearity both locally and in a field study setting.

A novel prothrombotic role of proprotein convertase subtilisin kexin 9: the generation of procoagulant extracellular vesicles by human mononuclear cells.

BackgroundProprotein convertase subtilisin kexin 9 (PCSK9) is a serin protease synthesized mainly in the liver that binds the receptor of low-density lipoprotein and promotes its degradation in lysosomes. PCSK9 is considered a promising target for the development of new therapies for the treatment of hypercholesterolemia and related cardiovascular diseases. Extracellular vesicles represent a heterogeneous population of vesicles, ranging in size between 0.05 and 1 μm involved in numerous pathophysiological processes, including blood coagulation. We investigated whether PCSK9 stimulation induces the release of procoagulant extracellular vesicles from human mononuclear cells (PBMCs) and THP-1 cells.Methods and resultsPBMCs and THP-1 cells were stimulated whit PCSK9, the generation of EV was assessed by the prothrombinase assay and by cytofluorimetric analysis. EV-associated tissue factor activity was assessed by a one-stage clotting assay. PCSK9 induced an increase in extracellular generation by PBMCs and THP-1 cells as well as an increase in extracellular vesicle-associated tissue factor. Pre-treatment with inhibitors of the toll like receptor, TLR4 (C34), and of NF-κB signaling (BAY 11-7082), downregulated PCSK9-induced extracellular vesicle generation and of extracellular- bound tissue factor. Similar effect was obtained by an anti-PCSK9 human-monoclonal antibody.ConclusionsPCSK9-mediated generation of procoagulant EV could contribute to increase the prothrombotic status in patients with cardiovascular diseases.

An Update on Laboratory Diagnostics in Haemophilia A and B.

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

Reference values of coagulation assays performed for thrombophilia screening after a first venous thrombosis and their intra-patient associations

IntroductionNo reference values are currently available for coagulation assays performed for thrombophilia screening prescribed according to guidelines, after a first venous thromboembolic (VTE) event, and we have no idea of the intra-patient associations between results. MethodsWe performed a retrospective study of consecutive prescriptions fulfilling guidelines in a French university hospital from 2010 to 2019 (n = 3842) from the Glims® laboratory information system. We collected results of 12 parameters: aPTT, PT, fibrinogen (Fg), one-stage clotting methods for factors VIII, IX, XI and II (FVIII, FIX, FXI, FII), antithrombin (using an amidolytic assay: AT), protein C and S (using clotting assays: PC and PS) and mixing tests of a lupus-anticoagulant sensitive aPTT and of DRVVT. ResultsWe show the results of the 12 parameters from 3603 individual files with less than 6 missing values, then describe these distributions and correlations between results from 2930 files with no missing value. We give the frequency of results described as indicating a risk of first VTE or of VTE recurrence. We propose 2 quantitative scores linking the 12 parameters at the individual level and reflecting their degree of dispersion with respect to their mean, describe the values of these scores and their associations with thrombophilic results. ConclusionsThese normal values should help laboratory workers to validate process results and to assess their degree of originality. Our 2 scores should help to determine the intra-patient plausibility of associations of results. The usefulness of these laboratory scores for predicting clinically-relevant outcomes deserves to be investigated.

300 PCSK9 induces a prothrombotic response by activation of NFKB signalling pathway in mononuclear cells

Abstract Aims Strong evidence both experimental and clinical studies point out to an involvement of proprotein convertase subtilisin/kexin 9 (PCSK9), as an important player in hypercholesterolemia and atherosclerosis pathophysiology, identifying it, as a key molecule in the development of new cholesterol-lowering drugs and therapeutic target for atherosclerosis and related diseases. Emerging evidence shown that PCSK9 is straight implicated in inflammatory process where it may directly influence the activity of various cell types through NFkB activation, a key transcription factor involved in the induction of both pro-inflammatory cytokines and Tissue Factor (TF) expression, a major regulator of haemostasis and thrombosis in monocytes. Deductive reasoning makes therefore plausible to investigate a mechanistic link between circulation PCSK9 levels and TF expression, both in monocytes as well as on the surface of microparticles (MPs) generated from the same cells, with NFkB acting as the chain in the link. To investigate the involvement of NFkB signalling pathway in PCSK9-induced TF expression. Methods THP-1 cell line were stimulated with human (h) PCSK9 (5 μg/mL) or pre-incubated with BAY-117082 (BAY, 10−5M) an NFκB inhibitor, CLI-095 (3 × 10−6M), a highly TLR-4 signalling specific inhibitor and LPS-RS(5 μg/mL) a TLR-4 antagonist. TF procoagulant activity (PCA) was assessed by one-stage clotting assay using a STart Max semi-automated coagulation analyser. Concentration of TF-bearing MPs was determined using the Zymuphen MP-activity kit. Results hPCSK9 stimulated TF activity in THP-1 (PCA: from 50 ± 20 to 120 ± 20 ρg/mL, n = 10, P &amp;lt; 0.01). BAY, an NFkB inhibitor (PCA: −71 ± 23%, n = 5, P &amp;lt; 0.01) and CLI-095, a TLR-4 signalling inhibitor, (PCA: −86 ± 26%, n = 3, P &amp;lt; 0.05) and LPS-RS (PCA: −71 ± 23%, n = 5, P &amp;lt; 0.01) down-regulated PCSK9-induced TF activity completely. Furthermore THP-1stimulation with hPCSK9 causes the release of prothrombotic MPs-TF+ (MPs release from: 0.13 ± 0.07 to 0.42 ± 0.1 nM PS, n = 7, P &amp;lt; 0.05; PCA-MP+ from: 14 ± 3 to 44 ± 28 ρg/mL, n = 5, P &amp;lt; 0.05). Conclusions These data confirm the pivotal role of monocytes in the response PCSK9-induced TF-expression as well as the involvement of PCSK9 in inflammatory-thrombotic diseases through a direct stimulation of TF procoagulant activity and by the release of TF-bearing MPs. The possible mechanism of action involves recognition of PCSK9 by TLRs 2 and/or 4, on monocytes membrane surface, leading to activation of the transcription factor NFκB via an intracellular signalling cascade. Further studies will be needed to better understand the regulatory mechanisms underlying this complex set of biological responses that bind PCSK9, and coagulation events.

Biomarkers of thromboinflammation correlate to COVID-19 infection and admission status in emergency department patients

BackgroundCOVID-19-associated coagulopathy is incompletely understood. ObjectivesTo characterize thrombin generation, Von Willebrand Factor (VWF), neutrophil extracellular traps (NETs), and their role in COVID-19 risk stratification in the emergency department (ED). Patients/methodsPlasma samples from 67 ED COVID-19 patients were compared to 38 healthy volunteers (HVs). Thrombin generation (calibrated automated thrombogram, CAT) was expressed as lag time (LT, min), peak height (PH, min), and time to peak (ttPeak, min). Citrullinated nucleosomes and histones were quantified with ELISA, VWF antigen and activity (IU/dL) through latex immunoassay, Factor VIII (IU/dL) through one-stage optical clot detection, and VWF multimers with Western blot densitometry. Wilcoxon testing and multivariable logistic regression were performed. Results presented as median [Q1, Q3]; p < 0.05 significant. ResultsCOVID-19 patients had longer LT (4.00 [3.26, 4.67]; 2.95 [2.67, 3.10], p < 0.001) and ttPeak (7.33 [6.33, 8.04]; 6.45 [6.00, 7.50], p = 0.004), greater VWF antigen (212 [158, 275]; 110 [91, 128], p < 0.001) and Factor VIII levels (148 [106, 190]; 106 [86, 129], p < 0.001), with decreased high molecular weight multimers (Normalized multimer ratio 0.807 [0.759, 0.869]; 0.891 [0.858, 0.966], p < 0.001), than HVs. COVID-19 patients requiring admission from the ED had longer LT and ttPeak with greater VWF antigen and Factor VIII levels than those not admitted. Two and three variable models of CAT parameters and VWF correlated with COVID-19 and admission status (C-statistics 0.677 to 0.922). ConclusionsThrombin generation kinetics and VWF levels, independent of NETs, may have a role in predicting admission need for COVID-19 patients.