The influence of dead space in blood sampling needle on FVIII level and pharmacokinetic profiles in children with hemophilia

OBJECTIVE

To investigate the influence of the dead space in disposable blood sampling needle on activated partial thromboplastin time (APTT), FVIII level and pharmacokinetic (PK) profiles in children with hemophilia.

METHODS

Children (<18 years) with severe hemophilia A were enrolled. After three days' washout-period, blood samples were collected at pre-dose, 1 h, 3 h, 9 h, 24 h and 48 h post-infusion. At each timepoint, two 2 mL vacuum tubes with 3.2% trisodium citrate were used. The first tube was signed as 'non-standard' (NS) and the second tube was signed as 'standard' (S). FVIII activities were evaluated by one-stage assay. WAPPS-Hemo was used to generate PK profiles like half-life time (t1/2), clearance (CL), trough level and time to 1, 2 and 5IU/dL after a dose of 50 ± 10IU/dL. The FVIII activities at 9 h and 24 h post-infusion were put into WAPPS and thus brought four combinations by true or biased FVIII level that used.

RESULT

Compared with standard-collected blood samples, prolonged APTT results (P-values < 0.01) and decreased FVIII activity (P-values < 0.05) were revealed in those non-standard blood samples. The corresponding bias was in positive relation to both APTT-S (r = 0.44, P < 0.0001) and FVIII-S level(r = 0.68, P < 0.001). The FVIII bias percentage got larger as FVIII-S level reduced (r = -0.24, P < 0.01). During the four combinations of FVIII activity at 9 h and 24 h, statistically longer t1/2, lower CL and longer time to 1, 2 or 5IU/dL were observed in 9H-S&24H-S group and 9H-NS&24H-S group.

CONCLUSION

While using vacuum tubes for clotting indicators and PK profiles, the dead space of blood sampling needle should be eliminated in advance.

Exploring the effects of Factor Xa inhibitors on thrombin generation in people with haemophilia

Optimal management of cardiovascular disease (CVD) in people with haemophilia (PWH) is a growing issue, given the continuing improvement in life expectancy among PWH. The evolving treatment paradigms targeting higher trough levels and the advent of non-factor replacement therapies (NFRT) means much of the 'protection' PWH were thought to have against CVD may be lost. There is a paucity of evidence regarding the safety of using anticoagulants in PWH. We designed a study assessing the thrombin generation (TG) of PWH of different severities and treatments, compared to non-haemophilia patients receiving a Factor Xa (FXa) inhibitor (apixaban or rivaroxaban), healthy controls, and assessing TG parameters of adding FXa inhibitor to the plasma of PWH receiving emicizumab prophylaxis. In total, 40 patients were included. TG was initiated with 5pM tissue factor (TF) using the calibrated automated thrombinoscope. Compared to those with mild haemophilia, patients receiving a FXa inhibitor had higher endogenous thrombin potential (ETP) (1278.42 vs 1831.36) and velocity index (40.71 vs 112.56), but both had a similar peak height (154.0 vs 262.63) and time to peak (both 5.83). People with severe haemophilia receiving emicizumab had significantly improved TG parameters compared to those not receiving emicizumab - ETP 1678.11 vs 809.96 and peak height 233.8 vs 92.05; however, when FXa inhibitor was added their TG parameters deteriorated to the severe haemophilia range (ETP 1179.60 and peak height 103.05). TG may provide additional useful information regarding the use of anticoagulants in PWH.

Recommendations for a minimum data set for monitoring gene therapy in hemophilia: communication from the ISTH SSC Working Group on Gene Therapy

Independent data collection is crucial in addressing the challenges associated with gene therapy for hemophilia, which is a promising treatment option but requires careful monitoring and management of short-term and potential long-term safety concerns. The International Society on Thrombosis and Haemostasis has identified a minimum efficacy and safety data set included in the World Federation of Hemophilia Gene Therapy Registry that should be collected on a national basis at specific time points for each patient who has been treated with the gene therapy products. This Gene Therapy Minimum Data Set (GT-MDS) was developed to facilitate data collection and to ensure capturing the most relevant data and most known and unknown safety and efficacy parameters recently cited by the European Medicine Agencies. The concept of assembling a minimum data set is not about creating a new data set but rather about identifying a subset of critical and essential topics that should always be included. The GT-MDS is structured into 3 sections and comprises an abridged list of 6 topics during routine gene therapy follow-up, keeping the number of data points low but allowing for rapid and independent data evaluation. The World Federation of Hemophilia Gene Therapy Registry data set, developed by the World Federation of Hemophilia, the International Society on Thrombosis and Haemostasis, and other organizations, including industry partners in 2020, is comprehensive. The GT-MDS reports the minimum relevant information that should not be lost and is mandatory to be collected for all patients who undergo gene therapy. Therefore, the implementation of the gene therapy registry and the minimum data set empowers and enhances data collection at a global level.

Reduced plasma factor X is associated with a lack of response to recombinant activated factor VII in patients with hemophilia A and inhibitor, but does not impair emicizumab-driven hemostasis in vitro

BACKGROUND

The hemostatic effect of recombinant (r) factor (F)VIIa after repetitive intermittent administration may be attenuated in patients with hemophilia A (PwHA) with inhibitors (PwHAwI) creating a clinically unresponsive status, although mechanism(s) remain to be clarified. In patients receiving prophylaxis treatment with emicizumab, concomitant rFVIIa is sometimes utilized in multiple doses for surgical procedures or breakthrough bleeding.

AIM AND METHODS

We identified 'unresponsiveness' to rFVIIa, based on global coagulation function monitored using rotational thromboelastometry (ROTEM) in 11 PwHAwI and 5 patients with acquired HA, and investigated possible mechanisms focusing on the association between plasma FX levels and rFVIIa-mediated interactions.

RESULTS

Our data demonstrated that FX antigen levels were lower in the rFVIIa-unresponsive group than in the rFVIIa-responsive group (0.46 ± 0.14 IU/mL vs. 0.87 ± 0.15 IU/mL, p < 0.01). This relationship was further examined by thrombin generation assays using a FX-deficient PwHAwI plasma model. The addition of FX with rFVIIa was associated with increased peak thrombin (PeakTh) generation. At low levels of FX (<0.5 IU/mL), rFVIIa failed to increase PeakTh to the normal range, consistent with clinical rFVIIa-unresponsiveness. In the presence of emicizumab (50 μg/mL), PeakTh was increased maximally to 80 % of normal, even at low levels of FX (0.28 IU/mL).

CONCLUSIONS

Unresponsiveness to rFVIIa was associated with reduced levels of FX in PwHAwI. Emicizumab exhibited in vitro coagulation potential in the presence of FX at concentrations that appeared to limit the clinical response to rFVIIa therapy.

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.).

Predictors of the outcome of immune tolerance induction in patients with haemophilia A and inhibitors: The Brazilian Immune Tolerance (BrazIT) Study protocol

The development of inhibitors is the main complication of haemophilia A (HA) treatment. Immune tolerance induction (ITI) is the treatment of choice for inhibitor eradication. We describe the methodology of the Brazilian Immune Tolerance Induction (BrazIT) Study, aimed to identify clinical, genetic, and immune biomarkers associated with response to ITI and inhibitor recurrence. This cohort study includes people with HA (PwHA) and inhibitors (a) who require bypassing agents to treat and/or prevent bleeding, and (b) who are at any stage of ITI treatment. Patients are included in each haemophilia treatment centre (HTC). Factor VIII (FVIII) and inhibitor assessments are performed at local laboratories of each HTC. The ITI regimen followed the national protocol of the Brazilian Ministry of Health. All PwHA starts with low-dose ITI (50 IU/kg three times weekly); high-dose regimen (100 IU/kg daily) is used if there is lack of response to the low-dose ITI. Outcomes are classified as total or partial success, and failure. Standardized case report forms with clinical, laboratory, and treatment data are collected from medical files and interviews. Blood samples are collected for genetic and immune biomarkers at the time of inclusion in the study and at the end of ITI. The study is ongoing and, currently, 202/250 (80.8%) PwHA from 15 HTCs have been included. BrazIT Study is the largest cohort of PwHA and inhibitor under treatment with the same ITI regimen reported to date. This study is likely to contribute with novel predictors of ITI response.

Recombinant factor VIII Fc for the treatment of haemophilia A

Prophylaxis with factor VIII (FVIII) is the current therapeutic approach for people with haemophilia A. However, standard half-life (SHL) FVIII products must be injected frequently, imposing a substantial burden on the individual and making it difficult to tailor therapy according to patient need and lifestyle, which could impact adherence. Recombinant FVIII Fc fusion protein (rFVIIIFc; Elocta® , Sobi; Eloctate® , Sanofi) is a recombinant fusion protein that undergoes slower clearance from the body than SHL FVIII products. This pharmacokinetic property of rFVIIIFc allows prophylactic administration every 3-5 days, or once weekly in selected patients, with doses adjusted to patient needs and clinical outcomes. Higher FVIII levels can be achieved maintaining dosing frequency similar to that usually applied with SHL FVIII. This review provides a summary of recent data from the A-LONG, Kids A-LONG, ASPIRE and PUPs A-LONG studies and recently published real-world experience relevant to rFVIIIFc use in individualised regimens. The review also introduces ongoing studies of rFVIIIFc, including its use for induction of immune tolerance, and discusses some aspects to consider when switching patients to rFVIIIFc and managing ongoing treatment. In summary, rFVIIIFc is suitable for individualised prophylaxis regimens that can be tailored according to patient clinical needs and lifestyle.

Acquired hemophilia A associated with Epstein-Barr-virus-associated T/natural killer-cell lymphoproliferative disease: A case report

INTRODUCTION

Acquired hemophilia A (AHA) is a rare bleeding disorder caused by autoantibodies against factor VIII (FVIII). Hematological malignancies, especially lymphoid malignancies, are known to be underlying causes of AHA; however, thus far, there is no report of AHA associated with Epstein-Barr-virus-associated T/natural killer-cell lymphoproliferative disease (EBV-T/NK-LPD). Here, we present a case of AHA that developed during treatment for EBV-T/NK-LPD.

HISTORY

A 69-year-old man visited our hospital because of general fatigue. Blood examination showed pancytopenia, and computed tomography revealed whole-body lymphadenopathy, but there were no findings indicating hematological malignancy from bone marrow aspiration and cervical lymph node biopsy. The level of EBV DNA in peripheral blood was extremely high, and he was diagnosed with EBV-T/NK-LPD. EBV-T/NK-LPD improved with prednisolone (PSL) administration. Seventeen months after starting treatment, the patient complained of back and right leg pain. At that time, he had been treated with low-dose PSL, and EBV-T/NK-LPD was well controlled. Imaging revealed hematoma of the right iliopsoas muscle. Prolonged activated partial thromboplastin time (APTT) was the only abnormal finding in a screening coagulation test. FVIII coagulant activity was below detection limit, and FVIII inhibitor level was increased. From these results, he was diagnosed with AHA.A higher dose of PSL was administered, and, after 1 month of treatment, FVIII activity gradually increased, and FVIII inhibitor level became undetectable. APTT also normalized, and complete remission was achieved and maintained for 13 months with low-dose PSL. During treatment, EBV-T/NK-LPD was well controlled.

CONCLUSION

It is speculated that proliferating lymphocytes interfere with normal immune functions and that abnormal autoantibodies are produced from those lymphocytes in patients with LPD. Therefore, we speculate that EBV-infected and proliferating monoclonal NK cells might have modulated the immune system and produced autoantibodies against FVIII, thus causing AHA in this patient with EBV-T/NK-LPD.

A Preconditioning Strategy to Augment Retention and Engraftment Rate of Donor Cells During Hepatocyte Transplantation

BACKGROUND

Hepatocyte transplantation has been extensively investigated as an alternative to orthotopic liver transplantation. However, its application in routine clinical practice has been restricted because of low initial engraftment and subsequent repopulation.

METHODS

Using mice as a model, we have developed a minimally invasive and nontoxic preconditioning strategy based on preadministration of antibodies against hepsin to increase donor hepatocyte retention and engraftment rate.

RESULTS

Liver sinusoid diameters decreased significantly with antihepsin pretreatment, and graft cell numbers increased nearly 2-fold in the recipients' liver parenchyma for 20 days after hepatocyte transplantation. Postoperative complications such as hepatic ischemia injury or apparent immune cell accumulation were not observed in recipients. In a hemophilia B mouse model, antihepsin preconditioning enhanced the expression and clotting activity of coagulation factor IX (FIX) to nearly 2-fold that of immunoglobulin G-treated controls and maintained higher plasma FIX clotting activity relative to the prophylactic range for 50 days after hepatocyte transplantation. Antihepsin pretreatment combined with adeno-associated virus-transduced donor hepatocytes expressing human FIX-Triple, a hyperfunctional FIX variant, resulted in plasma FIX levels similar to those associated with mild hemophilia, which protected hemophilia B mice from major bleeding episodes for 50 days after transplantation. Furthermore, antihepsin pretreatment and repeated transplantation resulted in extending the therapeutic period by 30 days relative to the immunoglobulin G control.

CONCLUSIONS

Thus, this antihepsin strategy improved the therapeutic effect of hepatocyte transplantation in mice with tremendous safety and minimal invasion. Taken together, we suggest that preconditioning with antihepsin may have clinical applications for liver cell therapy.

Clot waveform analysis for perioperative hemostatic monitoring of arthroscopic synovectomy in a pediatric patient with hemophilia A and inhibitor receiving emicizumab prophylaxis

Emicizumab reduces bleeding in patients with hemophilia A and inhibitors (PwHA-I). Coagulation potential during the perioperative period in emicizumab-treated PwHA-I undergoing surgery remains to be evaluated. We describe a 14-year-old boy with HA-I receiving emicizumab prophylaxis who experienced arthroscopic synovectomy. He was treated with a bolus infusion of recombinant factor VIIa (rFVIIa; 80 μg/kg) immediately before surgery, and treatment continued at the same dose every 3 h on day 1, every 4 h on day 2, and every 6 h on day 3. Treatment with rFVIIa was discontinued on day 4. No perioperative bleeding or thrombotic events were observed. Coagulation potential throughout the perioperative period was retrospectively assessed with an easy-to-use clot waveform analysis (CWA). Measurements from CWA returned to within or near the normal range, suggesting successful hemostatic management. Coagulation potentials assessed by CWA showed a significant correspondence with those from a thrombin generation assay (TGA) that is already in use. CWA and TGA could both provide useful data for assessing coagulation potential in the perioperative hemostatic management of emicizumab-treated PwHA-I.

The Progression of Hemophilic Arthropathy: The Role of Biomarkers

BACKGROUND

Hemophilia A and B are X-linked congenital bleeding disorders characterized by recurrent hemarthroses leading to specific changes in the synovium and cartilage, which finally result in the destruction of the joint: this process is called hemophilic arthropathy (HA). This review highlights the most prominent molecular biomarkers found in the literature to discuss their potential use in the clinical practice to monitor bleeding, to assess the progression of the HA and the effectiveness of treatments.

METHODS

A review of the literature was performed on PubMed and Embase, from 3 to 7 August 2020. Study selection and data extraction were achieved independently by two authors and the following inclusion criteria were determined a priori: English language, available full text and articles published in peer-reviewed journal. In addition, further articles were identified by checking the bibliography of relevant articles and searching for the studies cited in all the articles examined.

RESULTS

Eligible studies obtained at the end of the search and screen process were seventy-three (73).

CONCLUSIONS

Despite the surge of interest in the clinical use of biomarkers, current literature underlines the lack of their standardization and their potential use in the clinical practice preserving the role of physical examination and imaging in early diagnosis.

Rituximab for treating inhibitors in people with inherited severe hemophilia

BACKGROUND

Hemophilia A and B are inherited coagulation disorders characterized by a reduced or absent level of factor VIII or factor IX respectively. The severe form is characterized by a factor level less than 0.01 international units (IU) per milliliter. The development of inhibitors in hemophilia is the main complication of treatment, because the presence of these antibodies, reduces or even nullifies the efficacy of replacement therapy, making it very difficult to control the bleeding. People with inhibitors continue to have significantly higher risks of morbidity and mortality, with considerable treatment costs. Given the wide 'off-label' use of rituximab for treating people with hemophilia and inhibitors, its efficacy and safety need to be evaluated. This is an update of a previously published Cochrane Review.

OBJECTIVES

To assess the efficacy and safety of rituximab for treating inhibitors in people with inherited severe hemophilia A or B.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, complied from electronic database searches and handsearching of journals and conference abstract books. We searched the reference lists of relevant articles and reviews and also searched for ongoing or unpublished studies. We also undertook further searches of other bibliographic databases and trial registries. Date of last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register: 19 March 2020.

SELECTION CRITERIA

Randomized controlled trials and controlled clinical trials investigating the efficacy and safety of rituximab for treating inhibitors in people with hemophilia.

DATA COLLECTION AND ANALYSIS

No randomized controlled trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No randomized controlled trials on rituximab for treating inhibitors in people with hemophilia were identified.

AUTHORS' CONCLUSIONS

We were unable to identify any relevant trials on the efficacy and safety of rituximab for treating inhibitors in people with hemophilia. The research evidence available is from case reports and case series. Randomized controlled trials are needed to evaluate the efficacy and safety of rituximab for this condition. However, prior to the publication of any possible future randomized controlled trials, meta-analysis of case reports and case series may provide some evidence.

Tissue-inhibitors of metalloproteinase-1 and vascular-endothelial growth-factor in severe haemophilia A children on low dose prophylactic recombinant factor VIII: Relation to subclinical arthropathy

BACKGROUND

Subclinical synovitis occur long before clinical haemophilic arthropathy (HA). New biomarkers are needed for early detection of HA.

AIM

To compare the levels of tissue inhibitors of metalloproteinase-1 (TIMP-1) and vascular endothelial growth factor (VEGF)in severe haemophilia A boys on prophylaxis and on-demand therapy to healthy boys and correlate them with the haemophilia joint health score (HJHS) & the Denver magnetic resonance imaging (MRI) scale; hence, determine their values in early detection of HA.

METHODS

Haemophilia joint health score, serum TIMP-1, VEGF and Denver MRI score were assessed in 50 boys with severe haemophilia A (31 on prophylactic factor VIII therapy (62%) with a dose of 15 IU/kg/twice weekly) and 50 age-matched healthy boys.

RESULTS

Boys with severe haemophilia A had significantly higher TIMP-1 240 ng/mL, SD200-350 (P < .001) and VEGF 600 pg/mL, SD400-1100 (P < .001). Their mean HJHS was 4.5 ± 3.0 (0-11) and their mean Denver MRI score was 5.55 ± 1.6 (2.00-8.00). A significant positive correlation was found between TIMP-1 and VEGF (P < .001), BMI Z-score (P = .029), HJHS (P = .041)and total MRI score (<.001). Significant correlations were found between VEGF and age (P < .001), HJHS (P = .003) and total MRI score (P < .001). Boys with severe haemophilia A on prophylaxis therapy had significantly lower HJHS (P = .021), VEGF (P < .001), TIMP-1 (P = .002) and total MRI score (P = .021) than those on on-demand therapy. Receiver operating characteristic curve, defined a cut-off value of 160 ng/mL for TIMP-1 with a sensitivity of 90% and specificity of 60% and that of 350 pg/mL for VEGF with a sensitivity of 78% and specificity of 88% for discrimination between severe haemophilia A and healthy boys.

CONCLUSION

Vascular endothelial growth factor and TIMP-1 can be used for early detection of HA. Further prospective studies should include larger study populations. In addition, studies should address the role of various anti-VEGFs as potential therapy for HA and their impact on prevention and treatment of HA.

Recombinant FIX Fc fusion protein activity assessment with the one-stage clotting assay: A multicenter, assessor-blinded, prospective study in Japan (J-Field Study)

INTRODUCTION

The one-stage clotting assay is used to measure factor IX (FIX) activity in patients' plasma samples and in FIX products for hemophilia treatment. However, the diversity of reagents and instruments has resulted in significant FIX assay variability.

METHODS

The accuracy of the one-stage clotting assay to measure recombinant FIX Fc fusion protein (rFIXFc) activity was evaluated by major Japanese hemophilia treatment centers and commercial laboratories that measure factor IX activity for a majority of hemophilia B patients in Japan. Plasma-derived FIX (pdFIX) and recombinant FIX (rFIX) products were used as comparators. FIX-deficient plasma was spiked with four levels of FIX products based on label potency and measured under blinded conditions by routine one-stage clotting assay procedures in 19 participating laboratories. Interlaboratory coefficient of variation and spike recovery were calculated.

RESULTS

Interlaboratory coefficient of variation of rFIXFc was not significantly different from that of rFIX, but appeared larger than that of pdFIX. Mean spike recovery for rFIXFc was generally comparable to rFIX and pdFIX. However, larger discrepancies between pdFIX and rFIX were observed in three of nine laboratories using ellagic acid-based activated partial thromboplastin time reagents.

CONCLUSION

Recombinant FIX Fc fusion protein activity was found to be similar to that of rFIX or pdFIX by the one-stage clotting assay. However, minimizing interlaboratory variability is vital for optimizing future patient care.

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.

A single-domain antibody that blocks factor VIIa activity in the absence but not presence of tissue factor

BACKGROUND

Activated factor VII (FVIIa) is pertinent to the initiation of blood coagulation. Proteolytic and amidolytic activity of FVIIa are greatly enhanced by its cofactor, tissue factor (TF).

OBJECTIVE

We aimed to generate a single-domain antibody (sdAb) that recognizes free FVIIa rather than TF-bound FVIIa.

METHODS

A llama-derived phage library was used to screen for anti-FVIIa sdAbs.

RESULTS

One sdAb, KB-FVIIa-004, bound to FVIIa, but not to its precursor FVII or to homologous proteins (prothrombin, factor X, or their activated derivatives). FVIIa amidolytic activity was inhibited by KB-FVIIa-004 (Ki  = 28-45 nM) in a competitive manner. KB-FVIIa-004 also inhibited FVIIa-mediated FX activation (Ki  = 26 nM). In contrast, KB-FVIIa-004 was inefficient in prolonging the clotting time of the prothrombin time-test, which was prolonged by a maximum of 10 s at high sdAb concentrations (10 μM). Furthermore, FVIIa/TF amidolytic activity or FVIIa/TF-mediated FX activation remained unaffected up to a 50-fold to 1000-fold molar excess of KB-FVIIa-004. These data suggest that KB-FVIIa-004 loses its inhibitory activity in the presence of TF. A KB-FVIIa-004/albumin fusion-protein (004-HSA) was generated for in vivo testing. By using 004-HSA, we observed that this sdAb blocked the therapeutic capacity of FVIIa to correct bleeding in FVIII-deficient mice.

DISCUSSION

This observation is compatible with the view that FVIIa functions independently of TF under these conditions. In conclusion, we have generated a sdAb that specifically blocks TF-independent activity of FVIIa. This antibody can be used to gain insight into the roles of TF-bound and TF-free FVIIa.

Factor VIII replacement is still the standard of care in haemophilia A

Prophylactic factor VIII (FVIII) has dramatically improved haemophilia A treatment, preventing joint bleeding and halting the deterioration of joint status. FVIII products with an extended plasma half-life further improve patients' quality of life and increase therapeutic adherence. New licensed classes of non-replacement products include prophylactic emicizumab, which is administered subcutaneously up to every 4 weeks. However, this drug is not suitable for acute bleeding episodes or management of major surgery, and long-term data on the impact of emicizumab on joint health, FVIII inhibitor development and thrombotic risk are awaited. Prophylaxis with FVIII replacement remains the standard of care in haemophilia A, with the aim of achieving a level of haemostasis control that allows patients to meet their lifestyle goals.

Evaluation of N8-GP Activity Using a One-Stage Clotting Assay: A Single-Center Experience

N8-GP (ESPEROCT®; turoctocog alfa pegol; Novo Nordisk A/S, Bagsvaerd, Denmark) is an extended half-life recombinant factor VIII (FVIII) molecule. FVIII-deficient plasma spiked with N8-GP can be accurately measured using many activated partial thromboplastin time (aPTT)-based one-stage clotting assay reagents with normal human plasma calibrators. To date, there are few data on the measurement accuracy of samples from patients treated with N8-GP. Here, we measure patient samples during routine treatment monitoring. Three previously treated patients with severe hemophilia A (HA) without inhibitors (baseline FVIII activity <0.01 IU/mL) received 50 IU/kg N8-GP every fourth day or twice weekly over 5 years as part of the pathfinder2 trial. Patient samples were monitored using the Pathromtin® SL aPTT reagent (Siemens Healthcare GmbH, Erlangen, Germany), a BCS® XP System analyzer (Siemens), and Standard Human Plasma (Siemens) or product-specific calibrators. Patient age ranged from 36 to 62 years. Overall, measurements performed using product-specific or Standard Human Plasma calibrators were in good agreement, with ratios randomly distributed around 1.0. Peak ratios tended to be closer to 1.0 than trough samples. Pathromtin® SL with Standard Human Plasma calibrator consistently and accurately measured FVIII activity in samples from severe HA patients receiving N8-GP prophylaxis.

Engineering a protein Z-dependent protease inhibitor (ZPI) mutant as a novel antagonist of ZPI anticoagulant function for hemophilia treatment

BACKGROUND

Protein Z-dependent protease inhibitor (ZPI), is an important anticoagulant protein in plasma that functions in complex with its cofactor, protein Z (PZ) to rapidly inhibit activated factor X (FXa) on a procoagulant membrane surface. Recent studies suggest that the ZPI-PZ anticoagulant complex is a promising target for restoring hemostasis in hemophilia (Girard, et al, J Thromb Haemost, 2019, 17, 149-156).

OBJECTIVE

Engineering a ZPI mutant as a novel antagonist of ZPI anticoagulant function.

METHODS

We engineered two alanine mutations in human ZPI, one in the reactive loop P1 Y387 residue to inactivate the FXa/FXIa inhibitory function, and the second in the K239 binding interface residue to enhance the affinity of the inactive ZPI for PZ. The mutant was expressed, purified, and characterized by in vitro and plasma assays.

RESULTS

The mutant, Y387A/K239A (ZPI-2A), bound PZ >20-fold tighter than WT ZPI or a PZ antibody (PZAb). FXa inhibition assays showed that ZPI-2A effectively neutralized ZPI/PZ anti-FXa activity with a ~three-fold molar excess over wild type ZPI (WT ZPI) whether FXa was bound to FVa in prothrombinase or unbound. Thrombin generation assays in a purified system or in normal/hemophilia plasmas showed that ZPI/PZ activity was reversed by ZPI-2A in a dose-dependent manner, with a three-fold molar excess sufficient to fully reverse ZPI/PZ inhibition of thrombin generation.

CONCLUSIONS

ZPI-2A is a potent antagonist of ZPI/PZ anticoagulant function, capable of fully blocking the anti-FXa activity of plasma levels of ZPI/PZ at significantly lower doses than a PZAb and thus a promising prophylactic agent for treating hemophilia.

Thrombin-generating potential, plasma clot formation, and clot lysis are impaired in patients with bleeding of unknown cause

BACKGROUND

In a large proportion of patients with a mild to moderate bleeding tendency no diagnosis can be established (bleeding of unknown cause, BUC).

OBJECTIVES

To investigate possible dysfunctions in thrombin generation and plasma clot formation and lysis in patients with BUC from the Vienna Bleeding Biobank (VIBB).

PATIENTS AND METHODS

Thrombin generation and plasma clot properties of 382 BUC patients were compared to those of 100 healthy controls and 16 patients with factor VIII (FVIII) activity ≤50%.

RESULTS

Thrombin generation was significantly impaired in BUC patients compared to healthy controls, exhibiting a prolonged lag time and time to peak and decreased maximum thrombin generation, velocity index, and area under the curve (AUC). The assessment of clot formation and lysis in BUC patients revealed a lower clot formation rate (Vmax), resulting in a longer TTP, increased absorbance (ΔAbs), and a shorter clot lysis time (CLT) than in healthy controls. Comparing patients with FVIII activity ≤ 50% to those with BUC, parameters of thrombin generation and clot formation and lysis were either stronger or comparably impaired. Bleeding severity did not correlate with parameters of thrombin generation, clot formation, or clot lysis.

CONCLUSION

Patients with BUC have an impaired hemostatic capacity reflected by a lower thrombin-generation potential, a lower clot formation rate, increased clot turbidity, and shorter clot lysis time, which might contribute to their increased bleeding tendency. Assays monitoring these parameters can alert physicians of hemostatic impairment and should be considered in situations where traditional hemostatic lab tests fail to reveal the clinical bleeding tendency.

Direct comparison of two extended-half-life recombinant FVIII products: a randomized, crossover pharmacokinetic study in patients with severe hemophilia A

BAY 94-9027 is an extended-half-life, recombinant factor VIII (rFVIII) product conjugated with a 60-kDa branched polyethylene glycol (PEG) molecule indicated for use in previously treated patients (aged ≥ 12 years) with hemophilia A. This randomized, open-label, two-way crossover study compared the pharmacokinetics (PK) of BAY 94-9027 and rFVIII Fc fusion protein (rFVIIIFc) in patients with hemophilia A. Patients aged 18-65 years with FVIII < 1% and ≥ 150 exposure days to FVIII were randomized to receive intravenous single-dose BAY 94-9027 60 IU/kg followed by rFVIIIFc 60 IU/kg or vice versa, with ≥ 7-day wash-out between doses. FVIII activity was measured by one-stage assay. PK parameters, including area under the curve from time 0 to the last data point (AUClast, primary parameter), half-life, and clearance were calculated. Eighteen patients were randomized and treated. No adverse events were observed. In the analysis set excluding one outlier, geometric mean (coefficient of variation [%CV, 95% confidence interval {CI}]) AUClast was significantly higher for BAY 94-9027 versus rFVIIIFc (2940 [37.8, 2440-3550] IU h/dL versus 2360 [31.8, 2010-2770] IU h/dL, p = 0.0001). A population PK model was developed to simulate time to reach FVIII threshold levels; median time to 1 IU/dL was approximately 13 h longer for BAY 94-9027 versus rFVIIIFc after a single infusion of 60 IU/kg. In conclusion, BAY 94-9027 had a superior PK profile versus rFVIIIFc. ClinicalTrials.gov : NCT03364998.

Functional polymorphisms in the LDLR and pharmacokinetics of Factor VIII concentrates

BACKGROUND

Optimization of factor VIII (FVIII) infusion in hemophilia A would benefit from identification of FVIII pharmacokinetics (PK) determinants. The low-density lipoprotein receptor (LDLR) contains an FVIII-binding site and might influence FVIII clearance. Consistently, LDLR polymorphisms have been associated with FVIII levels.

OBJECTIVE

To investigate the relationships between individual FVIII PK and functional LDLR polymorphisms.

PATIENTS/METHODS

Thirty-three hemophilia A patients (FVIII coagulant activity [FVIII:C] ≤2 IU/dL) without inhibitors underwent 85 FVIII single-dose (21.4-51.8 IU/kg) PKs with different FVIII concentrates. Twenty patients underwent repeated PKs (2-6).

FVIII

C measured up to 72 hours was analyzed by two-compartment model. Parameters were evaluated in relation to F8 mutations, ABO blood-group and LDLR genotypes.

RESULTS

F8 mutation types were not associated with PK parameters. ABO and LDLR c.1773C/T polymorphism were associated with Alpha, Alpha HL, CLD2, K1-2, and K2-1 parameters, suggesting an influence on the FVIII initial distribution phase. Regression analysis showed an independent association of both ABO and LDLR c.1773C/T with PK parameters (Alpha, β-coefficient -0.311 vs 0.348; CLD2, β-coefficient -0.335 vs 0.318), giving rise to an additive effect in subjects stratified by combined phenotypes. Differently, the LDLR c.81C/T was associated with FVIII clearance and volume of distribution at steady state, which could be related to distinct effects of polymorphisms, potentially linked to LDLR intracellular distribution and FVIII binding behavior.

CONCLUSIONS

With the limitation of different FVIII concentrates and low number of patients, our data show plausible associations of LDLR polymorphisms with FVIII PK parameters, thus supporting their investigation as candidate functional determinants of FVIII PK.

Comparative pharmacokinetics of two extended half-life FVIII concentrates (Eloctate and Adynovate) in adolescents with hemophilia A: Is there a difference?

Essentials The PK parameters of Eloctate vs Adynovate were compared using one-stage and chromogenic assays in 25 boys (12-18 years). The FVIII levels were taken at 3, 24, 48, and 72 hours following a dose of either FVIII; levels analyzed by WAPPS PK program. The PK profiles (half-life, clearance, and time to 5%, 3%, and 1%) were not statistically different for the two EHL FVIIIs. The significant interpatient variability in PK is mainly related to VWF levels (and blood group).

BACKGROUND

A head-to-head comparison of the pharmokinetcs (PK) of extended half-life (EHL) factor VIII (FVIII) concentrates in the same subjects has not been reported. Recently, boys (ages 12-18 years) with hemophilia A in Canada were required to switch from Eloctate to Adynovate.

OBJECTIVES

Compare the PK profiles of Eloctate vs Adynovate in the same boys.

METHODS

Boys switching from Eloctate to Adynovate prophylaxis had FVIII levels sampled at 3, 24, 48, and 72 hours following a regular prophylactic infusion of Eloctate and then 1-3 months later, of Adynovate. Testing was done by one-stage assay (OSA) and chromogenic assay (CA). The PK parameters were determined with the Web Accessible Population Pharmacokinetic Service (WAPPS)-Hemo PK tool.

RESULTS

Twenty-five boys (mean age 15.3 years; range: 12.1-18.4; 9 O blood group) underwent switching. Mean (range) terminal half-lives with the OSA were 16.1 hours (10.4 to 23.4; Eloctate) and 16.7 hours (11.0 to 23.6; Adynovate) (NS). With the CA, these were 18.0 hours (12.0 to 25.5; Eloctate) and 16.0 hours (10.3 to 22.9; Adynovate) (P = 0.001). There were no significant differences between the two EHL-FVIIIs in clearance, area under the concentration vs time curve (AUC), Vss, or time for FVIII levels to drop to 5%, 3%, and 1%. At the 72-h time point, mean observed FVIII levels following a mean dose of 39.3 IU/kg of Eloctate were 4.4% (OSA) and 4.4% (CA). For Adynovate, these were 5.1% (OSA) and 5.3% (CA) following similar doses. There was considerable interpatient variation in PK, mainly explained by differences in blood group/von Willebrand factor (VWF) levels.

CONCLUSIONS

Eloctate and Adynovate have almost identical PK parameters. When switching from one to another no prophylaxis regimen change is needed.

Severe hemophilia A caused by an unbalanced chromosomal rearrangement identified using nanopore sequencing

Essentials No F8 genetic abnormality is detected in about 2% of severe hemophilia A patients. Detection of F8 structural variants remains a challenge. We identified a new F8 rearrangement in a severe hemophilia A patient using nanopore sequencing. We highlight the value of single-molecule long-read sequencing technologies in a genomics laboratory.

BACKGROUND

No F8 genetic abnormality is detected in about 2% of severe hemophilia A patients using conventional genetic approaches. In these patients, deep intronic variation or F8 disrupting genomic rearrangement could be causal.

OBJECTIVE

To characterize, in a genetically unresolved severe hemophilia A patient, a new Xq28 rearrangement disrupting F8 using comprehensive molecular techniques including nanopore sequencing.

RESULTS

Long-range polymerase chain reaction (PCR) performed throughout F8 identified a nonamplifiable region in intron 25 indicating the presence of a genomic rearrangement. F8 messanger ribonucleic acid (mRNA) analysis including 3'rapid amplification of complementary deoxyribonucleic acid (cDNA) ends and nanopore sequencing found the presence of a F8 fusion transcript in which F8 exon 26 was replaced by a 742-bp pseudoexon corresponding to a noncoding region located at the beginning of the long arm of chromosome X (Xq12; chrX: 66 310 352-66 311 093, GRCh37/hg19). Cytogenetic microarray analysis found the presence of a Xq11.1q12 gain of 3.8 Mb. The PCR amplification of junction fragments and fluorescent in situ hybridization (FISH) analysis found that the Xq11q12 duplicated region was inserted in the F8 intron 25 genomic region.

CONCLUSION

We characterized a novel genomic rearrangement in which a 3.8-Mb Xq11.1q12 gain inserted in the F8 intron 25 led to an aberrant fusion transcript in a patient with severe hemophilia A (HA), using comprehensive molecular techniques. This study highlights the value of single-molecule long-read sequencing technologies for molecular diagnosis of HA especially when conventional genetic approaches have failed.

Intrinsic differences between FVIIIa mimetic bispecific antibodies and FVIII prevent assignment of FVIII-equivalence

Essentials Non-factor VIII (FVIII) therapies for hemophilia A, such as bispecific antibodies (bsAbs), are in development. Bispecific antibodies are intrinsically different from FVIII and lack many of the same regulatory mechanisms. These differences complicate assignment and interpretation of FVIII-equivalent activity. Inability to assign FVIII equivalence compromises our capacity to assess hemostatic potential of bsAb therapies.

BACKGROUND

Activated factor VIII (FVIIIa) mimetic bsAbs aim to enable prophylactic treatment of hemophilia A patients with and without inhibitors. With different mechanisms of action, benchmarking their activity against FVIII to determine efficacious yet safe dosage is difficult.

OBJECTIVE

To compare the activities of sequence identical emicizumab (SI-Emi) and another bsAb, BS-027125, to recombinant FVIII (rFVIII) using clinical and nonclinical assays and to evaluate our ability to assign a FVIII-equivalent value to bsAbs and implications thereof.

METHODS

Activities of SI-Emi, BS-027125, and rFVIII were measured by one-stage clotting assay, chromogenic factor Xa generation assay, and thrombin generation assay. We also assessed the activity of anti-FIXa and anti-FX bivalent homodimers of each bsAb and probed the effect of different reagents in thrombin generation assay (TGA).

RESULTS

The FVIII-like activity of SI-Emi and BS-027125 ranged greatly across each assay, varying both by parameter measured within an assay and by reagents used. Notably, SI-Emi anti-FIXa bivalent homodimer had meaningful activity in several assays, whereas BS-027125 anti-FIXa bivalent homodimer only had activity in the chromogenic assay. Surprisingly, SI-Emi displayed activity in the absence of phospholipids, while BS-027125 had minimal phospholipid-independent activity.

CONCLUSIONS

Bispecific antibodies demonstrate little consistency between assays tested here owing to intrinsic differences between FVIII and bsAbs. While some trends are shared, the bsAbs also differ in mechanism. These inconsistencies complicate assignment of FVIII-equivalent values to bsAbs. Ultimately, a deeper mechanistic understanding of bsAbs as well as bsAb-tailored assays are needed to monitor and predict their hemostatic potential and long-term efficacy and safety confidently.

Diagnosis and treatment of hemophilia

Hemophilia A and B are inherited bleeding disorders characterized by deficiency or dysfunction of coagulation protein factors VIII and IX, respectively. Recurrent joint and muscle bleeds are the major clinical manifestations. Replacement therapy with clotting factors, either at the time of bleeding or as part of a prophylactic regimen, is adapted to individual patient needs. The major complication of therapy is the development of neutralizing antibodies. In response, researchers have developed novel agents to both reduce the treatment burden and prevent bleeding regardless of the presence of inhibitors. Another new development, gene therapy, has the potential for a definitive cure. This review summarizes the pathophysiology, clinical presentation, diagnosis, and treatment of hemophilia, as well as information regarding neutralizing antibodies, immune tolerance induction, novel agents, and gene therapy.

Impact of capacity-limited binding on recombinant factor VIII and von Willebrand factor pharmacokinetics in hemophilia A rats

Essentials Knowledge of the interplay between FVIII and VWF pharmacokinetics (PK) is lacking. We characterized the capacity-limited PK of FVIII and VWF. The PK model described the PK of FVIII and VWF over a broad range of rFVIII doses. High-dose rFVIII treatment can reduce the endogenous VWF levels.

BACKGROUND

Understanding of the pharmacokinetics (PK) interplay between factor VIII (FVIII) and von Willebrand factor (VWF) following high-dose FVIII treatment is lacking.

OBJECTIVES

To characterize the PK of recombinant FVIII (rFVIII), VWF, and the rFVIII:VWF complex in hemophilia A rats following intravenous administration of rFVIII using PK modeling. A second aim was to investigate the effect of high daily dosing and constant expression of rFVIII on VWF exposure using PK simulations.

METHODS

We developed a population PK model based on the principles of target-mediated drug disposition modeling, using data on total rFVIII and VWF plasma concentrations, and the rFVIII:VWF complex luminescent oxygen channeling immunoassay signal in hemophilia A rats following intravenous administration of rFVIII (17.5, 100, 1000, and 5000 IU kg-1 ). Additionally, we evaluated the influence of high-dose rFVIII treatment on the exposure of VWF using PK simulations.

RESULTS

The plasma concentration-time profiles of total rFVIII and VWF, and the luminescent oxygen channeling immunoassay signal-time profiles of the rFVIII:VWF complex were adequately described using a two-compartment quasi-steady-state target-mediated drug disposition model (Kss  = 0.14 nmol L-1 ). The elimination half-life of the rFVIII:VWF complex was dependent on the unbound plasma concentration of rFVIII. Additionally, we showed that high-dose rFVIII treatment may significantly reduce the endogenous VWF levels.

CONCLUSIONS

We developed a population-based PK model describing the time-course of total rFVIII, total VWF, and the rFVIII:VWF complex over a broad range of rFVIII doses in hemophilia A rats.

Design of a prospective observational study on the effectiveness and real-world usage of recombinant factor VIII Fc (rFVIIIFc) compared with conventional products in haemophilia A: the A-SURE study

INTRODUCTION

Haemophilia A is a rare bleeding disorder caused by coagulation factor VIII (FVIII) deficiency. This is treated with factor VIII, conventionally using products with a half-life of 8-12 hours typically administered every 2-3 days. Recombinant FVIII Fc (rFVIIIFc) represents a new generation of products with an extended half-life allowing higher FVIII levels and longer dosing interval. The efficacy and safety of rFVIIIFc have been established in clinical studies and several years of postmarketing use. However, there remains a need to compare treatment outcome with conventional products in routine clinical use.

METHODS AND ANALYSIS

A-SURE is an ongoing, non-interventional European study with the primary objective to compare the clinical effectiveness of rFVIIIFc with conventional factor products used for haemophilia A prophylaxis. Data covering a 24-month prospective period and a 12-month retrospective period will be collected. Three primary endpoints: bleeding rate, injection frequency and factor consumption will be used to evaluate treatment outcomes. Enrolment of 175 patients on rFVIIIFc and 175 on conventional products is planned. All eligible patients from participating centres will be invited to participate. Visits and treatments follow routine clinical practice. Bias will be reduced by patient matching for age at baseline and the last weekly prophylaxis dose of a conventional product prior to baseline. Propensity scores will be calculated based on prognostic factors and potential confounders assessed at baseline and adjusted for in the estimation of the treatment effect.

ETHICS AND DISSEMINATION

Study approval was obtained by local independent ethics committees and/or authorities, and informed consent from patients or their legal representative is a requirement for participation. Names of ethical committees and approval numbers are provided as supplementary information. The study results will be submitted for publication in a peer-reviewed scientific journal and presented at scientific conferences.

TRIAL REGISTRATION NUMBER

NCT02976753, Pre-results.

Routine clinical care data for population pharmacokinetic modeling: the case for Fanhdi/Alphanate in hemophilia A patients

Fanhdi/Alphanate is a plasma derived factor VIII concentrate used for treating hemophilia A, for which there has not been any dedicated model describing its pharmacokinetics (PK). A population PK model was developed using data extracted from the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) project. WAPPS-Hemo provided individual PK profiles for hemophilia patients using sparse observations as provided in routine clinical care by hemophilia centers. Plasma factor activity measurements and covariate data from hemophilia A patients on Fanhdi/Alphanate were extracted from the WAPPS-Hemo database. A population PK model was developed using NONMEM and evaluated for suitability for Bayesian forecasting using prediction-corrected visual predictive check (pcVPC), cross validation, limited sampling analysis and external evaluation against a population PK model developed on rich sampling data. Plasma factor activity measurements from 92 patients from 12 centers were used to derive the model. The PK was best described by a 2-compartment model including between subject variability on clearance and central volume, fat free mass as a covariate on clearance, central and peripheral volumes, and age as covariate on clearance. Evaluations showed that the developed population PK model could predict the PK parameters of new individuals based on limited sampling analysis and cross and external evaluations with acceptable precision and bias. This study shows the feasibility of using real-world data for the development of a population PK model. Evaluation and comparison of the model for Bayesian forecasting resulted in similar results as a model developed using rich sampling data.

Desmopressin treatment combined with clotting factor VIII concentrates in patients with non-severe haemophilia A: protocol for a multicentre single-armed trial, the DAVID study

INTRODUCTION

Haemophilia A is an inherited bleeding disorder characterised by factor VIII (FVIII) deficiency. In patients with non-severe haemophilia A, surgery and bleeding are the main indications for treatment with FVIII concentrate. A recent study reported that standard dosing frequently results in FVIII levels (FVIII:C) below or above FVIII target ranges, leading to respectively a bleeding risk or excessive costs. In addition, FVIII concentrate treatment carries a risk of development of neutralising antibodies. An alternative is desmopressin, which releases endogenous FVIII and von Willebrand factor. In most patients with non-severe haemophilia A, desmopressin alone is not enough to achieve FVIII target levels during surgery or bleeding. We hypothesise that combined pharmacokinetic (PK)-guided administration of desmopressin and FVIII concentrate may improve dosing accuracy and reduces FVIII concentrate consumption.

METHODS AND ANALYSIS

In the DAVID study, 50 patients with non-severe haemophilia A (FVIII:C ≥0.01 IU/mL) with a bleeding episode or undergoing surgery will receive desmopressin and FVIII concentrate combination treatment. The necessary dose of FVIII concentrate to reach FVIII target levels after desmopressin administration will be calculated with a population PK model. The primary endpoint is the proportion of patients reaching FVIII target levels during the first 72 hours after start of the combination treatment. This approach was successfully tested in one pilot patient who received perioperative combination treatment.

ETHICS AND DISSEMINATION

The DAVID study was approved by the medical ethics committee of the Erasmus MC. Results of the study will be communicated trough publication in international scientific journals and presentation at (inter)national conferences.

TRIAL REGISTRATION NUMBER

NTR5383; Pre-results.

The impact of GPIbα on platelet-targeted FVIII gene therapy in hemophilia A mice with pre-existing anti-FVIII immunity

Essentials Platelet-specific FVIII gene therapy is effective in hemophilia A mice even with inhibitors. The impact of platelet adherence via VWF/GPIbα binding on platelet gene therapy was investigated. GPIbα does not significantly affect platelet gene therapy of hemophilia A with inhibitors. Platelet gene therapy induces immune tolerance in hemophilia A mice with pre-existing immunity. SUMMARY: Background We have previously demonstrated that von Willebrand factor (VWF) is essential in platelet-specific FVIII (2bF8) gene therapy of hemophilia A (HA) with inhibitory antibodies (inhibitors). At the site of injury, platelet adherence is initiated by VWF binding to the platelet GPIb complex. Objective To investigate the impact of GPIbα on platelet gene therapy of HA with inhibitors. Methods Platelet-FVIII expression was introduced by 2bF8 lentivirus (2bF8LV) transduction of hematopoietic stem cells (HSCs) from GPIbαnull (Ibnull ) mice or rhF8-primed FVIIInull (F8null ) mice followed by transplantation into lethally irradiated rhF8-primed F8null recipients. Animals were analyzed by flow cytometry, FVIII assays and the tail bleeding test. Results After transplantation, 99% of platelets were derived from donors. The macrothrombocytopenia phenotype was maintained in F8null mice that received 2bF8LV-transduced Ibnull HSCs (2bF8-Ibnull /F8null ). The platelet-FVIII expression level in 2bF8-Ibnull /F8null recipients was similar to that obtained from F8null mice that received 2bF8LV-transduced F8null HSCs (2bF8-F8null /F8null ). The tail bleeding test showed that the remaining hemoglobin level in the 2bF8-Ibnull /F8null group was significantly higher than in the F8null control group, but there was no significant difference between the 2bF8-Ibnull /F8null and 2bF8-F8null /F8null groups. The half-life of inhibitor disappearance time was comparable between the 2bF8-Ibnull /F8null and 2bF8-F8null /F8null groups. The rhF8 re-challenge did not elicit a memory immune response once inhibitor titers dropped to undetectable levels after 2bF8 gene therapy. Conclusion GPIbα does not significantly impact platelet gene therapy of HA with inhibitors. 2bF8 gene therapy restores hemostasis and promotes immune tolerance in HA mice with pre-existing immunity.

Administration of recombinant FVIIa (rFVIIa) to concizumab-dosed monkeys is safe, and concizumab does not affect the potency of rFVIIa in hemophilic rabbits

Essentials Hemophilia patients on concizumab prophylaxis may need rFVIIa to treat breakthrough bleeds. Effect and safety of concizumab + rFVIIa were tested in vitro and in vivo. Concizumab + rFVIIa had no additive effects on bleeding in hemophilic rabbits. High steady-state levels of concizumab did not affect the safety of rFVIIa in cynomolgus monkeys. SUMMARY: Background Concizumab is a monoclonal antibody (mAb) against tissue factor pathway inhibitor (TFPI), currently in clinical development as a subcutaneous prophylactic therapy for hemophilia A/B with and without inhibitors. In patients with inhibitors, the treatment choice for breakthrough bleeding will comprise bypassing agents, e.g. activated recombinant FVIIa (rFVIIa) or activated prothrombin complex concentrates. Objectives To explore the effect and safety of concizumab and rFVIIa when they are simultaneously present. Methods Human blood made hemophilic with a FVIII antibody was spiked with increasing concentrations of concizumab, rFVIIa, or concizumab and rFVIIa in combination, and this was followed by thrombin generation test or thromboelastography. Blood loss in hemophilic rabbits was measured when concizumab, rFVIIa or concizumab + rFVIIa was administered either before or during cuticle bleeding. In a safety study, cynomolgus monkeys were exposed to high steady-state concizumab concentrations and given three doses of rFVIIa, and then subjected to full necropsy and histopathological examination. Results In human blood, concizumab + rFVIIa had more pronounced procoagulant effects under hemophilic conditions than the sum of individual responses. In contrast, concizumab + rFVIIa had no additional effects on blood loss in hemophilic rabbits as compared with rFVIIa or concizumab alone. In cynomolgus monkeys, the macroscopic and microscopic pathological examinations revealed no thrombi or other signs of excessive coagulation activation. Both rFVIIa and concizumab caused increases in thrombin-antithrombin and D-dimer concentrations; this effect tended to be additive with concomitant administration. Conclusions Concizumab did not affect the potency or safety of rFVIIa in vivo. These results support a clinical evaluation of rFVIIa at standard dose (90 μg kg-1 ) to treat breakthrough bleeds in concizumab clinical trials.

Case Report: Development of Factor VIII Inhibitor in a Patient with an Uncommon de novo Mutation in the Factor VIII Gene

The development of factor VIII inhibitors remains a significant clinical challenge in the management of hemophilia A. We present a patient of mixed ethnicity with severe hemophilia A who was found to have a F8 gene hemizygous c.5815G>T mutation resulting in an Ala1939Ser substitution (Ala1920Ser in legacy nomenclature) and possible splice site change that has been reported in only 1 patient previously. He developed an inhibitor shortly after starting replacement recombinant factor VIII (Advate®; Baxalta, Bannockburn, IL, USA) and was successfully treated with immune tolerance therapy. Our report describes the second patient reported to have severe hemophilia due to this mutation and the only case of a factor VIII inhibitor associated with this mutation.

Inhibitors: A Need for Eradication?

The development of inhibitors against factor VIII (FVIII) concentrates represents a significant treatment complication for hemophilia. Immune tolerance induction (ITI) therapy eradicates inhibitors in 60-80% of patients, resulting in a normal FVIII response. This article, based on presentations at the 6th International Coagulation Meeting, held in Barcelona, Spain, in September 2017, provides an overview of management approaches for patients with inhibitors and briefly tabulates four cases of ITI therapy (first-line or rescue ITI therapy in pediatric and adult patients) with successful outcomes. Switching FVIII product from recombinant FVIII to plasma-derived FVIII/VWF concentrate may be helpful in eradicating inhibitors. The rate of decline of inhibitor titer in the initial stages of ITI therapy is a good indicator of the success or failure of therapy, although prognostic biomarkers are needed. The development of the bispecific monoclonal antibody emicizumab, which was recently shown to reduce bleeding in inhibitor patients, offers a potential alternative therapeutic option. However, the benefits of inhibitor eradication, including a wider choice of cheaper therapeutic products for preventing and treating bleeds, suggest that at least one attempt of ITI therapy should be offered to patients who develop inhibitors.

Factor VIII with a 237 amino acid B-domain has an extended half-life in F8-knockout mice

Essentials Factor (F)VIII with an intermediate-length B-domain showed higher levels in murine gene therapy. FVIII with different B-domain lengths were analysed. FVIII variants with B-domains between 186 and 240 amino acids (aa) have extended half-life in mice. Reduced cell binding of FVIII with a 237aa B-domain may explain the extended half-life. SUMMARY: Background Factor VIII consists of the A1-domain, A2-domain, B-domain, A3-domain, C1-domain, and C2-domain. FVIII with an intermediate-length B-domain of 226 amino acids (aa) has previously been evaluated in murine gene therapy studies. Objective To characterize FVIII with intermediate-length B-domains in vitro and in vivo in F8-knockout (KO) mice. Methods and results FVIII molecules with B-domains of 186-240aa had longer half-lives in F8-KO mice than FVIII molecules with shorter or longer B-domains. FVIII with a B-domain containing the 225 N-terminal aa fused to the 12 C-terminal aa of the wild-type B-domain (FVIII-237) had a 1.6-fold extended half-life in F8-KO mice as compared with FVIII with a 21aa B-domain (FVIII-21). The in vitro and in vivo activity of FVIII-237 were comparable to those of FVIII-21, as was binding to von Willebrand factor. Cell binding to LDL receptor-related protein 1 (LRP-1)-expressing cells was markedly reduced for FVIII-237 as compared with FVIII-21, whereas the affinity for LRP-1 was not reduced in surface plasmon resonance (SPR) studies. FVIII-21 cell binding and internalization could be inhibited by a fragment consisting of the 226 N-terminal aa of the FVIII B-domain, and SPR analysis suggested that this B-domain fragment might bind with weak affinity to FVIII-21. Conclusion Reduced cell binding of FVIII-237 might explain the observed extended half-life in F8-KO mice. This may contribute to the increased FVIII levels measured in murine gene therapy studies using FVIII constructs with similar B-domain lengths.

Suppressing protein Z-dependent inhibition of factor Xa improves coagulation in hemophilia A

Essentials Protein Z (PZ) catalyzes PZ-dependent proteinase inhibitor (ZPI) inactivation of factor (F)Xa. Gene-deletion of PZ or ZPI improves coagulation in hemophilia (FVIII knockout) mice. A PZ blocking antibody enhances thrombin generation in human hemophilia plasma. Suppression of the PZ/ZPI pathway may ameliorate the phenotype of severe hemophilia. SUMMARY: Background Hemostasis requires a balance between procoagulant and anticoagulant factors. Hemophiliacs bleed because of a procoagulant deficiency. Targeted reduction in the activity of endogenous anticoagulant pathways is currently being investigated as a means of improving hemostasis in hemophilia. Protein Z (PZ) is a cofactor that serves as a catalyst for PZ-dependent protease inhibitor (ZPI) inactivation of activated factor X at phospholipid surfaces. Objectives To evaluate the effects of PZ or ZPI gene deletion in hemophilic mice, and of blocking PZ in human hemophilic plasma. Methods A tail vein rebleeding assay (TVRB) was developed on the basis of the serial disruption of clots forming over a period of 15 min following tail vein laceration in an anesthetized mouse. Wild-type (WT)/FVIII knockout FVIIIKO, PZ knockout PZKO/FVIIIKO and ZPI knockout ZPIKO/FVIIIKO mice were evaluated in this model, and their plasmas were tested in thrombin generation assays. A mAb against PZ was evaluated in human hemophilic plasma thrombin generation assays. Results The numbers of clot disruptions (mean ± standard error of the mean) in the TVRB were: 4.0 ± 0.9 for WT/FVIIIKO mice; 23.8 ± 1.1 for WT/FVIIIKO mice supplemented with 100% FVIII; 15.2 ± 1.1 for PZKO/FVIIIKO mice; and 14.7 ± 1.2 for ZPIKO/FVIIIKO mice. Thrombin generation in PZKO/FVIIIKO and ZPIKO/FVIIIKO mouse plasmas was similar to that in FVIIIKO plasma supplemented with ~ 15% recombinant FVIII. A mAb against PZ added to human hemophilic plasma enhanced thrombin generation to an extent similar to the addition of ~ 15% FVIII. Conclusions Blockade of the PZ/ZPI system may be sufficient to ameliorate the phenotype of severe hemophilia.

The future of bypassing agents for hemophilia with inhibitors in the era of novel agents

Bypassing agents are presently the standard of care for the treatment of bleeding episodes in patients with hemophilia and high-titer inhibitors and are also used for bleed prevention. Only two bypassing agents are available to patients, and these products trace their lineage to the 1970s (activated prothrombin complex concentrates) and the 1980s (recombinant factor VIIa). Given the limited repertoire of available products, clinicians have relied on experience, empirical observation, registry data and individualized care to improve clinical outcomes on a case-by-case basis. Research over the past two decades has culminated in a greatly improved understanding of human coagulation; resulting from this, new products have been developed that offer treatment options and mechanisms of actions that differ from current bypassing agents. The most advanced in clinical development is emicizumab, a bispecific antibody that mimics the function of FVIIIa in the intrinsic Xase complex and is indicated for once-weekly or every-other-week prophylactic dosing in inhibitor patients. Other non-traditional products in clinical development include fitusiran and antibodies directed against tissue factor pathway inhibitor. As non-factor-based therapies become more widely utilized over time, the use of bypassing agents may be expected to decrease; however, bypassing agents will remain essential for the foreseeable future. As such, clinical development of bypassing agents continues, with some products (e.g. eptacog beta) under regulatory review. In this review we examine the optimal use of bypassing agents and their mechanism of action. We also discuss newer products and how these might theoretically be administered in conjunction with traditional bypassing agents.

Phase 1, single-dose escalating study of marzeptacog alfa (activated), a recombinant factor VIIa variant, in patients with severe hemophilia

Essentials Marzeptacog alfa (activated) [MarzAA] is a novel variant of activated human factor VII. A phase 1 dose escalation trial of MarzAA was conducted in subjects with severe hemophilia. MarzAA was safe and tolerated at intravenous doses up to 30 μg kg-1 Data observed support further trials for hemophilia patients with inhibitors to factors VIII/IX.

SUMMARY

Background Marzeptacog alfa (activated) (MarzAA), a new recombinant activated human factor VII (rFVIIa) variant with four amino acid substitutions, was developed to provide increased procoagulant activity and a longer duration of action in people with hemophilia. Objectives To investigate the safety, tolerability, immunogenicity, pharmacokinetics (PK) and pharmacodynamics (PD) of single ascending intravenous bolus doses of MarzAA in non-bleeding patients with congenital hemophilia A or B with or without inhibitors. Methods This international, phase 1, open-label study (NCT01439971) enrolled males aged 18-64 years with severe hemophilia A or B, with or without FVIII or FIX inhibitors. Subjects were assigned to single-dose MarzAA cohorts (0.5, 4.5, 9, 18 or 30 μg kg-1 ). Blood sampling was performed predose and postdose, and subjects were monitored for 60 days postdose. Safety endpoints included adverse events, vital sign changes, electrocardiograms, laboratory abnormalities, and immunogenicity; secondary endpoints included evaluation of PK and PD. Results Overall, in 25 patients, MarzAA was well tolerated at all dose levels tested, and was not associated with dose-limiting toxicity. No treatment-emergent severe or serious adverse events occurred. MarzAA showed linear dose-response PK across the 4.5-30 μg kg-1 dose range, with a terminal half-life of ⁓ 3.5 h. Dose-dependent shortening of the activated partial thromboplastin time and prothrombin time, and evidence of an increase in peak thrombin as determined with a thrombin generation assay, were observed at all doses. Conclusions MarzAA was tolerated at doses up to 30 μg kg-1 . The safety profile and pharmacological effects observed support further clinical trials for the treatment of hemophilic patients with inhibitors.

[Efficacy of short-term full-dose prophylaxis in adult Chinese patients with severe hemophilia A]

OBJECTIVE

To investigate the efficacy of short-term full-dose prophylaxis in adult Chinese patients with severe hemophilia A.

METHODS

Thirteen adult Chinese patients with severe hemophilia A receiving on-demand or low-dose prophylaxis underwent ultrasound examination of the target joints and evaluation of Hemophilia Joint Health Score (HJHS). The data of annual bleeding episodes in the period of on-demand or low-dose prophylaxis were collected retrospectively from the patients, and the changes in bleeding and joint condition (ultrasound findings of the target joints and HJHS) were observed during short-term full-dose prophylaxis. The activity intensity of the patients was assessed using the IPAQ questionnaire, and the 72 h FⅧ trough activity was measured during full-dose prophylaxis.

RESULTS

The median age of the 13 patients was 26.0 (20.5-29.0) years. For full-dose prophylaxis, the patients received a median therapeutic dose of 31.0 (29.1-33.0) IU/kg, administered for 3 times per week; the median 72 h FⅧ trough activity of patients was 1.7% (1.3-3.4%). During the follow-up period for 3 months, the annual bleeding rates (ABR) and annual joint bleeding rates (AJBR) decreased significantly in all the patients (P=0.001 and 0.001, respectively), but zero bleeding was achieved in only 4 patients (30.8%) and zero joint bleeding in 7 patients (53.8%); 9 patients (69.2%) still experienced breakthrough bleeding. The damage severity of target joints assessed by ultrasound and HJHS in 6 patients (46.2%)was worse than before and no obvious progression of target joints damage was found in 7 patients (53.8%). Compared with the patients without progression, the patients with worsened joint damage had poorer baseline joint condition, higher bleeding frequencies before and during the follow-up, a higher intensity of physical activity, and a lower baseline FⅧ activity.

CONCLUSIONS

At present, although short-term full-dose prophylaxis can significantly reduce the bleeding and partially prevent the progression of joint damage, it is not yet possible to achieve the goal of zero bleeding for all adult patients with severe hemophilia A in China, nor can it completely prevent further joint damage. For adult patients with different clinical bleeding phenotypes, joint conditions and physical activity intensity, individualized therapy involving additional evaluation methods should be implemented, and physiotherapy and surgical intervention can be considered when necessary.

Serum proteins C and S levels as early biomarkers for kidney dysfunction in hemophilic patients

BACKGROUND

Hemophilia is an inherited genetic disease characterized by the inability to coagulate blood after injury. The rationale of the current study was to evaluate serum proteins S and C and correlate to kidney function test in hemophilic patients for early diagnosis of abnormality in renal function.

SUBJECTS AND METHODS

This study was conducted on 80 males subjects divided into four groups. Group I: Control: Healthy subjects. Group II: Renal dysfunction (serum Creatinine >2mg/dl): Group III: Hemophilic patients. Group IV: Hemophilic patients with renal disorder. Serum urea, creatinine, sodium, potassium, protein C and protein S level were determined.

RESUTS

Protein C and S levels showed a significant decrease in hemophilic/and with renal dysfunction (P < 0.001, p<0.001). The level of plasma protein C and S levels were positively correlated with increased urinary albumin (P < 0.01). Urinary albumin was increased about 15 folds in hemophilic patients with renal dysfunction and nephrotic patients as compared with the control group. The cut-off value in 90% patients at the hemophilic patients with renal dysfunction 70%. Positive correlations were observed between urinary albumin (r=0.66), and creatinine (r=0.73).

CONCLUSION

These biomarkers showed good predictive values with regard to ROC-AUC (0.41 and 0.75 for Proteins C and S, respectively).

Tolerance induction in hemophilia: innovation and accomplishments

PURPOSE OF REVIEW

Hemophilia is an X-linked blood coagulation genetic disorder, which can cause significant disability. Replacement therapy for coagulation factor VIII (hemophilia A) or factor IX (hemophilia B) may result in the development of high-affinity alloantibodies ('inhibitors') to the replacement therapy, thus making it ineffective. Therefore, there is interest in directing immunological responses towards tolerance to infused factors.

RECENT FINDINGS

In this review, we will discuss latest advancements in the development of potentially less immunogenic replacement clotting factors, optimization of current tolerance induction protocols (ITI), preclinical and clinical data of pharmacological immune modulation, hepatic gene therapy, and the rapidly advancing field of cell therapies. We will also evaluate publications reporting data from preclinical studies on oral tolerance induction using chloroplast-transgenic (transplastomic) plants.

SUMMARY

Until now, no clinical prophylactic immune modulatory protocol exists to prevent inhibitor formation to infused clotting factors. Recent innovative technologies provide hope for improved eradication and perhaps even prevention of inhibitors.

Improved Pharmacokinetics with BAY 81-8973 Versus Antihemophilic Factor (Recombinant) Plasma/Albumin-Free Method: A Randomized Pharmacokinetic Study in Patients with Severe Hemophilia A

Background

BAY 81-8973 is a full-length, unmodified, recombinant human factor VIII (FVIII) for the treatment of hemophilia A.

Objective

The aim of this study was to compare the pharmacokinetic (PK) profile of BAY 81-8973 with antihemophilic factor (recombinant) plasma/albumin-free method (rAHF-PFM)

Patients/Methods

In this phase I, open-label, crossover study, men aged 18–65 years with severe hemophilia A and ≥150 exposure days to FVIII were randomized to receive a single intravenous infusion of 50 IU/kg BAY 81-8973 or rAHF-PFM, followed by crossover to a single infusion of the other treatment. FVIII levels were measured in plasma over 48 h using one-stage and chromogenic assays. PK parameters, including area under the curve from time zero to the last data point (AUC_last; primary outcome) and half-life (t_½) were calculated. A population PK model was developed to simulate various treatment scenarios.

Results

Eighteen patients were randomized and analyzed. Using both assays, geometric mean (coefficient of variation [%CV]) AUC_last was significantly higher, and t_½ was significantly longer, for BAY 81-8973 versus rAHF-PFM (one-stage, AUC_last: 1660 IU·h/dL [29.4] vs. 1310 IU·h/dL [29.0], p < 0.0001; one-stage, t_½: 14.5 [25.7] vs. 11.7 h [27.3], p < 0.0001). Simulations showed that median time to 1 IU/dL was approximately 27% longer for BAY 81-8973 versus rAHF-PFM over doses of 25–50 IU/kg; plasma levels >1 IU/dL could be maintained with 14.4 IU/kg BAY 81-8973 or 39.1 IU/kg rAHF-PFM 3×/week.

Conclusions

BAY 81-8973 showed a superior PK profile versus rAHF-PFM. The same FVIII trough threshold level could be achieved with lower doses of BAY 81-8973 versus rAHF-PFM.

ClinicalTrials.gov: NCT02483208.

Abrogating fibrinolysis does not improve bleeding or rFVIIa/rFVIII treatment in a non-mucosal venous injury model in haemophilic rodents

Essentials The efficacy of systemic antifibrinolytics for hemophilic non-mucosal bleeding is undetermined. The effect of systemically inhibiting fibrinolysis in hemophilic mice and rats was explored. Neither bleeding nor the response to factor treatment was improved after inhibiting fibrinolysis. The non-mucosal bleeding phenotype in hemophilia A appears largely unaffected by fibrinolysis.

SUMMARY

Background Fibrinolysis may exacerbate bleeding in patients with hemophilia A (HA). Accordingly, antifibrinolytics have been used to help maintain hemostatic control. Although antifibrinolytic drugs have been proven to be effective in the treatment of mucosal bleeds in the oral cavity, their efficacy in non-mucosal tissues remain an open question of significant clinical interest. Objective To determine whether inhibiting fibrinolysis improves the outcome in non-mucosal hemophilic tail vein transection (TVT) bleeding models, and to determine whether a standard ex vivo clotting/fibrinolysis assay can be used as a predictive surrogate for in vivo efficacy. Methods A highly sensitive TVT model was employed in hemophilic rodents with a suppressed fibrinolytic system to examine the effect of inhibiting fibrinolysis on bleeding in non-mucosal tissue. In mice, induced and congenital hemophilia models were combined with fibrinolytic attenuation achieved either genetically or pharmacologically (tranexamic acid [TXA]). In hemophilic rats, tail bleeding was followed by whole blood rotational thromboelastometry evaluation of the same animals to gauge the predictive value of such assays. Results The beneficial effect of systemic TXA therapy observed ex vivo could not be confirmed in vivo in hemophilic rats. Furthermore, neither intravenously administered TXA nor congenital knockout of the fibrinolytic genes encoding plasminogen or tissue-type plasminogen activator markedly improved the TVT bleeding phenotype or response to factor therapy in hemophilic mice. Conclusions The findings here suggest that inhibition of fibrinolysis is not effective in limiting the TVT bleeding phenotype of HA rodents in non-mucosal tissues.

Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti-idiotype monoclonal antibodies

Essentials Emicizumab (Emi) affects the APTT-based assays of factor (F)VIII activity and inhibitor titer. A mixture of two anti-Emi monoclonal antibodies (mAb) effectively neutralized the Emi activity. Anti-Emi mAbs completely eliminated the influence of Emi on FVIII activity and inhibitor titer. The inclusion of anti-Emi mAbs in routine FVIII assays would be useful for Emi-treated patients.

SUMMARY

Background Emicizumab is an anti-factor (F)IXa/X bispecific monoclonal antibody (mAb), mimicking the factor (F)VIIIa cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time (APTT) is more pronounced than that of factor (F)VIII. APTT-based FVIII activity (FVIII:C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab. Aim To establish a reliable APTT-based assay to measure FVIII in the presence of emicizumab. Methods Plasmas from hemophilia A (HA) patients without or with inhibitors were studied using one-stage FVIII:C and Bethesda inhibitor assays. Two recombinant anti-idiotype mAbs to emicizumab (anti-emicizumab mAbs) were prepared, rcAQ8 to anti-FIXa-Fab and rcAJ540 to anti-FX-Fab. Results The combined anti-idiotype mAbs (2000 nm each) eliminated the effects of emicizumab on APTTs of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX(a)/FX(a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 μm = ~150 μg mL-1 ) at all reference levels of FVIII. The addition of anti-emicizumab mAbs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII:C. Anti-FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti-FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti-idiotype mAbs, allowing accurate assessment of inhibitor titers. Conclusion The in vitro inclusion of anti-emicizumab mAbs in the standard one-stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII:C and inhibitor titers.