FVIII Inhibitors Research Articles

Immunogenicity of a Plasma-Derived Von Willebrand Factor/Factor VIII Concentrate during the Wil-31 Prophylaxis Study in Patients with Von Willebrand Disease

Background: Long-term prophylaxis with a von Willebrand factor (VWF) concentrate is recommended in people with von Willebrand disease (VWD) with a history of frequent and severe bleeds. The WIL-31 study demonstrated the efficacy of prophylaxis with a plasma-derived VWF/factor VIII (pdVWF/FVIII) concentrate containing VWF and FVIII in a 1:1 activity ratio (wilate ®) in adults and children with VWD of all types. The primary endpoint was met, showing a decrease in mean total annualized bleeding rate (ABR) of 84% compared with prior on-demand treatment. Aim: To assess the immunogenicity of pdVWF/FVIII when used during the WIL-31 study in children and adults with VWD of all types. Methods: WIL-31 (NCT04052698) was a prospective, non-controlled, international, multicenter phase 3 trial that enrolled male/female patients aged ≥6 years with VWD type 1 (VWF: RCo <30 IU/dL), type 2 (except 2N) or type 3. Prior to entering the WIL-31 study, all patients had received on-demand treatment with a VWF-containing product during a 6-month, prospective, observational, run-in study (WIL-29); patients who experienced at least 6 bleeding episodes (BEs), excluding menstrual bleeds, of which ≥2 were treated with a VWF-containing product, were eligible to enter WIL-31. During WIL-31, patients received regular pdVWF/FVIII (containing VWF and FVIII in a 1:1 activity ratio) prophylaxis 2-3 times per week at a dose of 20-40 IU/kg for 12 months. FVIII (chromogenic and one-stage assays) and VWF (VWF:RCo assay) activities were assessed at baseline and throughout the study. Retention samples were collected at screening and baseline visits for possible later inhibitor testing (to be performed at a central laboratory using the Nijmegen-Bethesda assay for FVIII inhibitors and the mixing study based on VWF:RCo for VWF inhibitors). Inhibitor testing was also performed if inhibitor development was suspected. Results: Inhibitor testing was performed in 2 of 33 patients because of unusual pharmacokinetic results at the 6-month visits, even though neither patient had any clinical signs of an inhibitor. The VWF inhibitors were detected in samples from two brothers taken at their 6-month visits. However, when retained blood samples from the screening visits of both boys were tested, both samples tested inhibitor-positive, demonstrating that both boys had developed the inhibitors prior to starting prophylaxis during WIL-31. During and before the WIL-29 run-in study, both boys had been treated on demand with another pdVWF/FVIII concentrate. The boys had both been diagnosed with VWD shortly after birth, and it was suspected that they had type 2A based on family history and were 15 (patient A) and 11 years old (patient B) at the start of WIL-31. They had a family history of VWD (both parents were diagnosed with VWD), but no family history of inhibitors. After the completion of WIL-31, both patients were reclassified to type 3 VWD following further investigation including next-generation sequencing. Baseline VWF activity indicated low VWF:RCo levels (Patient A: 0.092 IU/mL and Patient B: 0.65 IU/mL; Figure 1). The boys received 38 (patient A) and 34 IU/kg (patient B) pdVWF/FVIII respectively, twice weekly during WIL-31, and their mean total ABRs decreased by 85% and 91%, respectively, during WIL-31 compared with WIL-29. All bleeding episodes during WIL-31 were spontaneous nose bleeds. Both boys continued the same prophylactic regimen until the end of WIL-31. In one patient the inhibitor titer was negative by the end of the study. Conclusion: VWF inhibitors were detected in 2 of the 33 patients on prophylaxis with pdVWF/FVIII in the WIL-31 study and subsequent investigation revealed that both patients were already positive for VWF inhibitors prior to the study start. In one of the patients, the inhibitor resolved during continued prophylaxis. Despite the inhibitors, prophylaxis was effective in both patients with an ≥85% reduction in ABR compared to on demand treatment.

Incorporation of O-Glycopeptides into FVIII Decreases Its Immunogenicity

Introduction For patients with hemophilia A, the generation of inhibitors (neutralizing antibodies against FVIII) during treatment remains a significant complication. Clinical studies have demonstrated that patients treated with plasma-derived FVIII (pdFVIII) have a lower incidence of inhibitor development compared to those treated with recombinant FVIII (rFVIII) products. Different post-translational modifications on rFVIII proteins expressed in various cell lines may contribute to the differences in FVIII immunogenicity. Our recent study showed that N-glycosylation affects the development of inhibitors. On the other hand, the presence, and effects of O-glycans on FVIII inhibitor development are less studied, though they are found on >80% of the mammalian surface and secreted proteins. We recently identified highly and differentially expressed O-glycans on various FVIII products. This work aims to investigate how additional O-linked glycosylation might impact the immunogenicity of recombinant FVIII. Method FVIII-α2HS and FVIII-FibA plasmids were constructed by incorporating sequences encoding 6 repeats of short peptide of α-2-HS and Fibrinogen A (FibA), respectively into B-domain deleted FVIII (BDD-FVIII) plasmid. These short peptides are known to be highly O-glycosylated. The FVIII expression and immunogenicity were evaluated by introducing the plasmids into hemophilia A mice through hydrodynamic injection. Subsequently, the FVIII-FibA and BDD-FVIII proteins were expressed in BHK cells and purified for LC-MS/MS-based glycomics analysis. We assessed the activity and half-life of FVIII proteins using an aPTT assay with mouse plasma samples collected at various time points within 96 hours after a single intravenous injection. The immunogenicity of FVIII proteins was evaluated using the Bethesda assay from plasma samples collected from hemophilia A mice after weekly intravenous injection for four weeks. Results Mice treated with plasmid containing α-2-HS and FibA sequences had lower inhibitor titers, especially mice with FVIII-FibA plasmid showing significantly lower inhibitor titers than FVIII-BDD group at week 4 and week 8 after the injection, despite no difference in FVIII activity. Glycosylation analysis revealed that the FVIII-FibA protein displayed a relatively higher abundance of O-glycans throughout all domains compared to the BDD-FVIII protein. The inserted FibA sequence itself is O-glycosylated. Similar to plasmid treatment, mice injected with FVIII-FibA protein had significantly lower inhibitor titers (1.3±1.0 BU) than mice injected with BDD-FVIII protein (37.5±37.2 BU) and commercial rFVIII products (19.8±20.2 BU) with no observed difference in in vivo activity and protein half-life. Conclusion The introduction of extra O-linked glycosylated peptides between A2 and A3 domains of FVIII altered O-glycosylation pattern and substantially reduced the immunogenicity without affecting FVIII activity. Our findings underscore the significant impact of post-translational modification on protein immunogenicity, particularly in the case of FVIII. Additionally, FVIII-FibA shows promising potential for clinical applications, not only in the development of new recombinant FVIII products but also in gene therapy approaches.

Effect of emicizumab-neutralizing antibodies on activated partial thromboplastin time–based clotting time test results in patients treated with emicizumab

BackgroundEmicizumab is a bispecific humanized monoclonal antibody that shortens the activated partial thromboplastin time (aPTT), making aPTT-based tests unreliable. ObjectivesTo evaluate the efficacy of a mixture of 2 anti-idiotype monoclonal antibodies (anti-emi) in neutralizing emicizumab in samples from persons with hemophilia A treated with emicizumab. MethodsFifty samples from persons with hemophilia A treated with emicizumab were analyzed for aPTT and factor VIII procoagulant activity; FVIII inhibitor titer was measured using Nijmegen-Bethesda assay in 50 plasma samples of additional patients (positive for FVIII inhibitor) treated with emicizumab. FVIII procoagulant activity and inhibitor titer were measured using 1-stage (Actin FS, Siemens) and chromogenic assays with bovine regents (Factor VIII Chromogenic Assay, Siemens). Emicizumab concentration was measured by modified a 1-stage assay calibrated with a drug-specific calibrator (r2 Diagnostics Inc). All the tests were performed on Sysmex CS-2400 (Sysmex) before and after the addition of anti-emi (Chugai Pharmaceutical). ResultsEmicizumab concentrations measured after neutralization were <1.6 μg/mL in all samples. FVIII levels were >480 IU/dL with an aPTT of <30.8 seconds in all samples before neutralization and were <1 IU/dL with an aPTT of >70 seconds after adding anti-emi. FVIII inhibitor resulted in a false negative result in 44 of 50 samples measured with the 1-stage assay before neutralization. A good correlation (r = 0.98) was found between inhibitor titer measured using the chromogenic (insensitive to emicizumab) and 1-stage assays after neutralization. ConclusionThe anti-emi antibodies were shown to completely neutralize emicizumab, making samples pretreated with anti-emi analyzable with the 1-stage assay.

Management and Outcomes of Invasive Procedures in Individuals with Hemophilia A on Emicizumab Prophylaxis: A Single Center Experience.

Prophylactic treatment with emicizumab has become an important and effective bleeding prevention for people with hemophilia A (PwHA). Perioperative management of PwHA using emicizumab prophylaxis is still challenging due to a lack of experience. Medical records of perioperative management and outcomes were reviewed, and data were collected for adult PwHA receiving emicizumab and undergoing surgical procedures between August 2019 and July 2022 at the University Medical Center Ljubljana. Twelve surgical procedures were performed in eight PwHA (one with FVIII inhibitors) while on emicizumab prophylaxis. Three minor procedures included cataract surgery, cystoscopic lithotripsy, and percutaneous coronary intervention. Nine major surgeries included four osteosyntheses, necrectomy of chronic osteomyelitis with new ankle arthrodesis, two below-knee amputations, total knee replacement, and placement of ventriculostomy after a spontaneous intraventricular hemorrhage. No major bleeds, thrombotic events or deaths, or new inhibitors appeared. Our real-world experience demonstrates that minor and major surgeries can be performed safely in PwHA on emicizumab prophylaxis. Additional data are needed to optimize dosing/duration of additional hemostatic agents in diverse invasive procedures and complex clinical situations.

The Nijmegen ultra-sensitive Bethesda Assay detects very low-titer factor VIII inhibitors in patients with congenital and acquired hemophilia A

BackgroundAn inhibitor can develop in congenital hemophilia A (HA) patients against exogenous infused factor (F)VIII, whereas in acquired HA (AHA) inhibitors initially develop against endogenous FVIII. Inhibitors can be detected with the Nijmegen Bethesda Assay (NBA), which has an international cut-off level of 0.60 Nijmegen Bethesda Units/mL (NBU/mL). Thereby, very low-titer inhibitors may remain undetected. AimTo describe the design and validation of the Nijmegen ultra-sensitive Bethesda Assay (NusBA) for the detection of very low-titer inhibitors. MethodsThe NusBA is a modification of the NBA in which the ratio of patient plasma to normal pooled plasma is changed from 1:1 to 9:1. Analytical validation was performed according to the CLSI EP10 guideline in order to determine trueness and reproducibility. Clinical validation was performed in two cohorts of congenital HA patients (82 adults) with pharmacokinetic data and four AHA patients. The limit of quantitation (LOQ) was determined by measuring plasma samples spiked with inhibitor levels in the low range (0.05–0.80 NBU/mL). ResultsThe LOQ for the NusBA was 0.10 NusBU/mL, with a coefficient of variation of 24.2 %. Seven (8.5 %) congenital HA patients had a positive NusBA result, of which only one was detected with the NBA. There was no correlation between NusBA and FVIII half-life. In three of the AHA patients the NusBA remained positive, when the NBA became negative. DiscussionThe NusBA is able to detect very low-titer FVIII inhibitors of ≥0.10 NBU/mL. Thereby, it may have added value in early inhibitor detection and therapy adjustments in patients with congenital HA and AHA.

OC 43.4 Effectiveness of Emicizumab Under Real-World Conditions in Patients of All Ages with Hemophilia a with and Without FVIII Inhibitors: Interim Analysis of the Non-Interventional Study EMIIL

OC 43.4 Effectiveness of Emicizumab Under Real-World Conditions in Patients of All Ages with Hemophilia a with and Without FVIII Inhibitors: Interim Analysis of the Non-Interventional Study EMIIL

PB0164 Full Characterization of Three F8 Deletions Causing Severe Hemophilia A with High Responding FVIII Inhibitors may be Associated with the Mechanism of Microhomology-Mediated Break-Induced Replication

PB0164 Full Characterization of Three F8 Deletions Causing Severe Hemophilia A with High Responding FVIII Inhibitors may be Associated with the Mechanism of Microhomology-Mediated Break-Induced Replication

OC 77.5 Development of a Rapid and Fully Automated FVIII Inhibitor Assay Insensitive to the Presence of Emicizumab

OC 77.5 Development of a Rapid and Fully Automated FVIII Inhibitor Assay Insensitive to the Presence of Emicizumab

OC 44.5 A Gut Metabolite-Based Dietary Therapy Influences FVIII Inhibitor Production with Novel Relationships between the Gut Microbiota, Blood Metabolome, and Immune Cell Frequencies

OC 44.5 A Gut Metabolite-Based Dietary Therapy Influences FVIII Inhibitor Production with Novel Relationships between the Gut Microbiota, Blood Metabolome, and Immune Cell Frequencies

Risk factors for coagulation inhibitor development in children with severe hemophilia A

Aim of the study: to examine the role of potential risk factors in inhibitor development in previously untreated patients (PUPs) (or minimally treated patients) with severe hemophilia A. The study was approved by the Independent Ethics Committee and the Scientific Council of the Belarusian Research Center for Pediatric Oncology, Hematology and Immunology (the Republic of Belarus). The study included 89 boys who underwent regular follow-up for severe hemophilia A at the Belarusian Research Center for Pediatric Oncology, Hematology and Immunology (the Republic of Belarus) from 1998 to 2022. The median age (10th–90th percentile) at diagnosis of hemophilia was 8.0 (1.0–21.0) months, the baseline factor VIII activity was 0.7% (0.4–0.95%). Age at first exposure to factor VIII concentrate was 11.0 (1.0–31.0) months. Out of 89 patients, 23 children had severe hemophilia A with inhibitors. The cumulative incidence of inhibitors in the whole group of PUPs was 31.0 ± 5.6%. The cumulative incidence of hemophilia A with inhibitors was higher in the patients with null mutations (37.0 ± 6.9%) than in the patients with non-null mutations (6.5 ± 6.0%) (the log-rank test, p = 0.041). The use of plasma-derived FVIII concentrate (approved for use in neonates and for prophylaxis) from one manufacturer was associated (c2 = 8.53; p = 0.004) with a lower incidence of factor VIII inhibitors (up to 21.3 ± 8.5%) compared with the incidence in the group of patients treated with FVIII concentrates from different manufacturers (45.2 ± 7.8%). Age (&gt; 1 year old or &lt; 1 year old) at first exposure to FVIII had no effect on the formation of inhibitors (the log-rank test, p = 0.746). Such factors as age at diagnosis of hemophilia (odds ratio (OR) 0.99; 95% confidence interval (CI) 0.93–1.024; p = 0.991) and baseline factor VIII activity (OR 0.99; 95% CI 0.8–1.06; p = 0.09) were not associated with inhibitor development. The first measurements of activated partial thromboplastin time (APTT) ratio (patient APTT value over the APTT reference value) (OR 1.89; 95% CI 0.72–5.09; p = 0.21) and FVIII recovery in vivo (OR 0.74; 95% CI 0.27–2.01; p = 0.55) were not associated with inhibitor development either. We have confirmed that one of the main risk factors for FVIII inhibitor development is F8 gene mutations. The incidence of inhibitors among the patients who received plasma-derived FVIII concentrates (recommended for use in PUPs in the neonatal period) from one manufacturer was lower than among those who received FVIII from different manufacturers.

Functional determination of emicizumab in presence of factor VIII activity

BackgroundAccurate measurement of emicizumab in the presence of factor (F) VIII is required in patients with severe hemophilia A treated with emicizumab, as well as additional need for FVIII substitution or emicizumab prophylaxis in patients with acquired or moderate to mild hemophilia A. However, the presence of FVIII potentially biases the results. ObjectivesTo assess the impact of plasma FVIII activity on determined emicizumab levels and evaluate different strategies for correction for or preanalytical inhibition of FVIII. MethodsEvaluated strategies comprised of the following: (1) calculation of actual emicizumab plasma levels based on measured FVIII activities and FVIII-affected emicizumab values, (2) preanalytical heat treatment (56 °C for 40 minutes), and (3) neutralization of FVIII activity using FVIII inhibitors. Emicizumab levels and FVIII activities were measured using a modified FVIII one-stage clotting assay and a chromogenic FVIII assay based on bovine factors, respectively. ResultsSpiking experiments revealed a consistent linear association between FVIII activities and determined (FVIII-affected) emicizumab results at different emicizumab input levels (∼0.12 μg/mL per IU/dL of FVIII). This principally allowed for mathematical correction of measured emicizumab levels in the presence of FVIII. While a 40% to 50% activity loss of intrinsic plasma emicizumab through heat treatment was observed in patient samples, emicizumab spiked into FVIII-deficient plasma was not or only marginally affected. Application of inhibitor-based FVIII neutralization led to good agreement of results when compared with direct quantification of emicizumab by liquid chromatography-tandem mass spectrometry. ConclusionInhibitor-based FVIII neutralization appears to be a feasible strategy for accurate measurement of plasma emicizumab levels in the presence of FVIII activity.

Acquired Postpartum Hemophilia A Presentation of Severe Hematuria: A Case Report

BACKGROUND: Acquired hemophilia A (AHA) is a rare, severe bleeding disorder caused by the development of autoantibodies against FVIII that may be idiopathic or secondary to medical conditions. Postpartum AHA can occur as early as 1–4 months after delivery or as late as 1-year postpartum. CASE REPORT: A 20-year-old female presented with vaginal bleeding 20 days after delivery, then ecchymotic patches developed 2 months later, followed by hematuria 2 months after that. Laboratory investigation revealed isolated, prolonged partial thromboplastin time that was not corrected by mixing 50:50 with fresh normal plasma. FVIII activity was markedly deficient, with a high titer of immediate-acting FVIII inhibitor antibodies. CONCLUSION: The case was diagnosed as postpartum AHA with a good response to the combined steroids and cyclophosphamide treatment.

Report on 4 cases with decreased recovery due to neutralizing antibodies specific for PEGylated recombinant factor VIII

BackgroundThe immunogenicity, safety, and efficacy of recombinant factor VIII (rFVIII) have gained increasing interest after the introduction of extended half-life products with various modifications of the rFVIII molecule, such as covalent attachment of polyethylene glycol (PEG). Anti-PEG antibodies may be associated with a temporary reduction of FVIII recovery, but according to previous studies, they usually disappear after continuous dosing. Anti-PEG antibodies with an inhibitory capacity have never been demonstrated in patients treated with PEGylated rFVIII products. ObjectivesTo routinely switch from standard half-life to PEGylated extended half-life rFVIII products in patients with hemophilia A. MethodsFrom December 2022 until May 2023, 83 adults with hemophilia A attending Oslo Haemophilia Comprehensive Care Centre received a test dose with a PEGylated rFVIII product to switch treatment. Four patients presented with decreased recovery without the presence of an FVIII inhibitor. Accordingly, we performed a variant inhibitor test utilizing different rFVIII concentrates as a source of FVIII and enzyme-linked immunosorbent assay to search for anti-PEG antibodies. ResultsWe found inhibitory anti-PEG/anti-PEGylated rFVIII antibodies in 4 patients (5%), both persistent and transient, explaining the impaired recovery. The patients had neutralizing anti-PEG antibodies prior to the first dosing of PEGylated rFVIII. We demonstrated neutralizing antibodies (mainly immunoglobuline G) specific for PEG and all 3 commercially available PEGylated rFVIII products. ConclusionThe number of patients with inhibitory anti-PEG antibodies was significant, and the presence of inhibitors against PEGylated rFVIII emphasizes the importance of individual monitoring when switching FVIII concentrates to ensure safety and efficacy of the treatment.

Difficulties in laboratory diagnosis of coexistent lupus anticoagulant and factor VIII inhibitors: case report and review of literature.

Whereas lupus anticoagulant (LA) and anti-factor VIII (anti-VIII) antibody are both acquired autoimmune coagulation inhibitors, they exhibit different pathophysiologic mechanisms and opposite clinical manifestations. Distinguishing between these two inhibitors is therefore essential for optimizing appropriate management. Harboring both antibodies, which is a rare condition, is of a challenging and confounding laboratory work-up. We illustrate a case report of a 39-year-old man admitted for the management of recurrent deep-vein thrombosis. Curiously, the initial physical examination revealed several hematoma and bruises of varying sizes. Biologically, a prolonged activated partial thromboplastin time (APTT) was objectified and was not corrected by the mixing study. The following detection of synchronous LA and anti-VIII was made using specific assays. Through this case, we illustrate the complexity of diagnosing coexistent LA and FVIII inhibitors. In fact, the biological hallmark of both inhibitors is an isolated prolonged APTT that does not correct by the mixing study. Despite the progress in LA and anti-VIII assays and the ongoing updating of standardized recommendations, the lack of specific tests for LA and the limited availability of VIII quantification tests other than the clot-based assays make it difficult to distinguish adequately between the two inhibitors. Therefore, it is crucial to correlate test results with clinical features and patient evaluation.

Imlifidase, a new option to optimize the management of patients with hemophilia A on emicizumab

BackgroundEmicizumab is a bispecific, chimeric, humanized immunoglobulin G (IgG)4 that mimics the procoagulant activity of factor (F) VIII (FVIII). Its long half-life and subcutaneous route of administration have been life-changing in treating patients with hemophilia A (HA) with or without FVIII inhibitors. However, emicizumab only partially mimics FVIII activity; it prevents but does not treat acute bleeds. Emergency management is particularly complicated in patients with FVIII inhibitors receiving emicizumab prophylaxis in whom exogenous FVIII is inefficient. We have shown recently that Imlifidase (IdeS), a bacterial IgG-degrading enzyme, efficiently eliminates human anti-FVIII IgG in a mouse model of severe HA with inhibitors and opens a therapeutic window for the administration of exogenous FVIII. ObjectivesTo investigate the impact of IdeS treatment in inhibitor-positive HA mice injected with emicizumab. MethodsIdeS was injected to HA mice reconstituted with human neutralizing anti-FVIII IgG and treated with emicizumab. ResultsIdeS hydrolyzed emicizumab in vitro and in vivo, albeit, at slower rates than another recombinant human monoclonal IgG4. While F(ab’)2 fragments were rapidly cleared from the circulation, thus leading to a rapid loss of emicizumab procoagulant activity, low amounts of single-cleaved intermediate IgG persisted for several days. Moreover, the IdeS-mediated elimination of the neutralizing anti-FVIII IgG and restoration of the hemostatic efficacy of exogenous FVIII were not impaired by the presence of emicizumab and polyclonal human IgG in inhibitor-positive HA mice. ConclusionOur results suggest that IdeS could be administered to inhibitor-positive patients with HA receiving emicizumab prophylaxis to improve and ease the management of breakthrough bleeds or programmed major surgeries.

Long-term immunogenicity, efficacy and tolerability of simoctocog alfa in patients with severe haemophilia A who had completed the NuProtect study in previously untreated patients.

The NuProtect study reported data on the immunogenicity, efficacy and tolerability of simoctocog alfa (Nuwiq® ) in 108 previously untreated patients with severe haemophilia A planned to be treated for ≥100 exposure days or up to 5years. The NuProtect-Extension study collected long-term prophylaxis data in children with severe haemophilia A. Patients who completed the NuProtect study according to the protocol were eligible for the NuProtect-Extension study, a prospective, multinational, non-controlled, Phase 3b study. Of 48 patients who entered the extension study, 47 (median age 2.8years) received prophylaxis with simoctocog alfa for a median of 24months, with 82%-88% on a twice-weekly or less regimen. No patient developed FVIII inhibitors during the extension study. The median (IQR) annualized bleeding rate (ABR) during prophylaxis was 0 (0-0.5) for spontaneous bleeding episodes (BEs) and 1.00 (0-1.95) for all BEs. ABRs estimated using a negative binomial model were .28 (95% CI: .15, .53) for spontaneous and 1.62 (95% CI: 1.09, 2.42) for all BEs. During the median follow-up of 24months, 34 (72%) patients had zero spontaneous BEs and 46 (98%) had zero spontaneous joint BEs. Efficacy in treating BEs was excellent or good for 78.2% of rated BEs, and efficacy of surgical prophylaxis was excellent for two rated surgeries. No treatment-related adverse events were reported. No FVIII inhibitors developed during long-term prophylaxis in the NuProtect-Extension study. Prophylaxis with simoctocog alfa was efficacious and well-tolerated, and is therefore an attractive long-term option for children with severe haemophilia A.

Emicizumab for acquired haemophilia A: A case series.

Emicizumab is approved to prevent bleeding in patients with congenital haemophilia A with or without inhibitors. However, no randomized trials addressed the efficacy of emicizumab in acquired haemophilia A (AHA). To report the clinical and biochemical response of emicizumab in AHA. This single-centre retrospective study included seven adults with AHA between November 2020 and May 2022. We collected patient characteristics, laboratory coagulation parameters, the use of haemostatic agents, bleeds and thrombotic events. Treatment was monitored using chromogenic FVIII assays. The assay with human reagents assesses both the emicizumab FVIII-like-activity and native patient FVIII-activity. The assay with bovine reagents only measures the patients' native FVIII-activity as emicizumab does not bind to bovine reagents. Patients presented with spontaneous hematoma (n=7), intramuscular bleeding (n=2), haematuria (n=2) and/or gastro-intestinal bleeding (n=2). Six patients had major bleedings. At diagnosis, APTT was prolonged (91 seconds, IQR 73-103), FVIII activity was 0% (IQR 0-1) and FVIII inhibitor 182 BU/mL (IQR 104-228). Emicizumab was administered weekly (3mg/kg) for 4 weeks, and thereafter every 2 weeks until regression of the inhibitor. Three patients received activated FVIIa (cumulative dose of 1.7mg/kg, IQR 1.2-2.2). All bleedings were controlled after treatment initiation, without further bleeds. After starting emicizumab, FVIII-like activity reached ≥5% at 12 days (IQR 7-14), whereas recovery of the intrinsic FVIII-activity ≥5% occurred at 128 days (IQR 88-173), coinciding with the disappearance of the FVIII inhibitor. There were no safety issues. In this AHA case series, no new clinically relevant bleeds were observed after initiation of emicizumab in conjunction with standard immunosuppressive therapy.

No immunological changes after factor VIII product switch: An in depth analysis in haemophilia A patients.

A challenging complication in the treatment of haemophilia A is the formation of neutralizing anti-FVIII antibodies (inhibitors). There is ongoing debate on the effect of FVIII product and inhibitor risk, rendering patients and physicians reluctant to switch FVIII-products. This study aimed to evaluate changes in the immune profile of haemophilia A patients after switching FVIII products and their possible relation to inhibitor development. Secondary, FVIII efficacy after switching were assessed. Patients, who switched FVIII-products between 2017-2019, were included in this single centre cohort study. Prospective comparison of immunoregulatory cells and markers by flow-cytometry before and after the switch was performed in a subgroup. For the total cohort clinical data regarding inhibitor development and FVIII efficacy 1 year before and after switching were retrospectively collected. One-hundred patients (including 39 with prospective immunological assessment) were analyzed, of which 31% switched from plasma-derived (pdFVIII) to recombinant standard half-life FVIII (SHL-rFVIII), 47% between different SHL-rFVIII, and 22% from pdFVIII/SHL-rFVIII to rFVIII-Fc. No remarkable changes in immunoregulatory cell functions were observed after switching, regardless the type of switch. None of the patients developed an inhibitor. FVIII efficacy, that is, FVIII usage, half-life and annual bleeding rate (ABR), was similar before and after switch for the SHL products, whereas rFVIII-Fc associated with a longer half-life (13.1 vs. 15.0h) and lower ABR (3.0 vs. 1.0). Switching to a different FVIII product was not associated with inhibitor development, nor with differences in the immune profile. Switching to rFVIII-Fc lead to lower ABR.

Switching from Sucrose-Formulated rFVIII to Octocog Alfa (BAY 81-8973) Prophylaxis Improves Bleed Outcomes in the LEOPOLD Clinical Trials.

Previous clinical trials established the efficacy and safety of sucrose-formulated recombinant factor (F) VIII (rFVIII-FS/Kogenate FS®/Helixate FS®) and octocog alfa (BAY 81-8973/Kovaltry®; LEOPOLD trials). To report the results of a post hoc subgroup analysis assessing efficacy and safety outcomes in patients with hemophilia A who were receiving rFVIII-FS prior to enrolling into the LEOPOLD I Part B and LEOPOLD Kids Part A clinical trials and switching to octocog alfa. LEOPOLD I Part B (NCT01029340) and LEOPOLD Kids Part A (NCT01311648) were octocog alfa Phase 3, multinational, open-label studies in patients with severe hemophilia A aged 12-65 years and ≤12 years, respectively. Annualized bleeding rate (ABR) was the efficacy endpoint for both studies. Safety endpoints included adverse events (AEs) and development of FVIII inhibitors. Of the 113 patients in both LEOPOLD trials, 40 (35.4%) patients received rFVIII-FS prophylaxis pre-study and had data available for pre-study total ABR. In LEOPOLD I Part B (n = 22, 35.5%), median (Q1; Q3) total ABR decreased from 2.5 (0.0; 9.0) pre-study to 1.0 (0.0; 6.8), and from 1.0 (0.0; 6.0) pre-study to 0.0 (0.0; 6.02) in LEOPOLD Kids Part A (n = 18, 35.3%). Octocog alfa was well tolerated, and no patients had drug-related serious AEs or inhibitors. Treatment with octocog alfa prophylaxis appeared to have a favorable risk-benefit profile compared with rFVIII-FS and thus could be an effective and improved alternative strategy for individualized treatment for children, adolescent and adult patients with severe hemophilia A currently on rFVIII-FS treatment.

Factor VIII inhibitors in hemophilia A treated with emicizumab: longitudinal follow-up of outcomes

BackgroundUsing emicizumab in lieu of immune tolerance induction (ITI) for patients with hemophilia A (HA) and factor (F)VIII inhibitors has been well described. However, decisions regarding ITI initiation, regimen, and preservation of tolerance remain to be elucidated. ObjectivesTo study the course of FVIII inhibitors in patients with HA and a history of FVIII inhibitors receiving emicizumab prophylaxis. MethodsPatients with HA, with and without FVIII inhibitors, initiating emicizumab prophylaxis were prospectively followed up in our center. All patients with current or previous inhibitors were included in this analysis. Plasma samples for FVIII inhibitor assays were obtained every 3 to 6 months or following FVIII exposure. Patients documented annual bleeding rate and any FVIII exposure days (EDs). ResultsOf 162 emicizumab-treated participants, 51 met the inclusion criteria. A decrease in annual bleeding rate was observed in all 51 participants followed up for a median of 3.3 years, with 31 breakthrough bleeding episodes reported in 22 of 51 participants. FVIII inhibitor level transiently increased following FVIII exposures in 5 of 15 failed ITI participants. Eight of 21 participants who did not undergo ITI were exposed to FVIII (1-2 EDs)), and 1 of these 8 participants demonstrated increased FVIII inhibitor levels after head trauma (following 1 ED). Among participants who underwent successful ITI, 8 of 15 patients were exposed to FVIII over a total of 13 EDs (1-2 ED(s) each) for traumatic breakthrough bleeds. In all these participants, inhibitor levels remained zero, indicating successful tolerance maintenance. ConclusionOur longitudinal follow-up of emicizumab-treated patients with HA and FVIII inhibitors shows that occasional exposure to FVIII may induce a transient anamnestic response. Nonetheless, no FVIII inhibitor recurrence was noted following FVIII exposures in patients who underwent successful ITI.