BACKGROUND: Factor (F)VIII inhibitors are measured using labor- and resource-expensive Nijmegen or Bethesda assays, which lack sensitivity for low-titer inhibitors and show high variations in quality surveys, mainly because of manual assay procedures.
OBJECTIVE: The goal of this study was the development of a fast and fully automated FVIII inhibitor assay by using recombinant (r)FVIII as substrate and dedicated equipment for execution of the test.
METHODS: A new rapid, fully automated, FVIII inhibitor assay is presented, the core of which is use of full-length recombinant FVIII (rFVIII; Kovaltry, Bayer) as inhibitor substrate instead of plasma FVIII, resulting in rapid binding of inhibitors to rFVIII due to absence of von Willebrand factor. Dramatic shortening of incubation time facilitated full automation on an analyzer capable of 3 subsequent sample dilution steps and 3 reagent additions. Equal volume mixtures of sample and rFVIII (1.0 U/mL) were incubated for 10 minutes at 37 °C, whereafter remaining FVIII activity was analyzed with a kinetic chromogenic assay, allowing inhibitor activity calculation without preceding FVIII activity calibration, using a Ceveron s100 analyzer (Technoclone).
RESULTS: Mean titer in 60 nonhemophiliacs was 0.0 BU/mL (SD, 0.1), yielding a limit of blank of 0.1 BU/mL and lower limit of quantification of 0.2 BU/mL. Analyses were performed with the new method and a Nijmegen assay in 28 inhibitor-positive clinical samples, 14 containing emicizumab and 14 without. Correlation coefficient in emicizumab-free type I inhibitor samples was 1.0. Emicizumab dependency of the method was excluded in spiking experiments with inhibitor-positive samples. Reproducibility was tested by analyzing 7 samples in 3 laboratories for 5 days, twice daily; coefficients of variation of all samples were <15%.
CONCLUSIONS: We present development data of a sensitive and specific rapid, automated FVIII inhibitor assay generating results within 20 minutes that is less resource-intensive than standard assays with potential to improve assay variability.

Hemophilia is a genetic disorder linked to the sex chromosomes, resulting in impaired blood clotting due to insufficient intrinsic coagulation factors. There are approximately one million individuals worldwide with hemophilia, with hemophilia A being the most prevalent form. The current treatment for hemophilia A involves the administration of clotting factor VIII (FVIII) through regular and costly injections, which only provide temporary relief and pose inconveniences to patients. In utero transplantation (IUT) is an innovative method for addressing genetic disorders, taking advantage of the underdeveloped immune system of the fetus. This allows mesenchymal stromal cells to play a role in fetal development and potentially correct genetic abnormalities. The objective of this study was to assess the potential recovery of coagulation disorders in FVIII knockout hemophilia A mice through the administration of human amniotic fluid mesenchymal stromal cells (hAFMSCs) via IUT at the D14.5 fetal stage. The findings revealed that the transplanted human cells exhibited fusion with the recipient liver, with a ratio of approximately one human cell per 10,000 mouse cells and produced human FVIII protein in the livers of IUT-treated mice. Hemophilia A pups born to IUT recipients demonstrated substantial improvement in their coagulation issues from birth throughout the growth period of up to 12 weeks of age. Moreover, FVIII activity reached its peak at 6 weeks of age, while the levels of FVIII inhibitors remained relatively low during the 12-week testing period in mice with hemophilia. In conclusion, the results indicated that prenatal intrahepatic therapy using hAFMSCs has the potential to improve clotting issues in FVIII knockout mice, suggesting it as a potential clinical treatment for individuals with hemophilia A.

BACKGROUND: Simoctocog alfa (Nuwiq®) is a 4th generation recombinant FVIII with proven efficacy for the prevention and treatment of bleeding episodes (BEs) in previously treated patients with severe haemophilia A. The NuProtect study assessed the immunogenicity, efficacy and safety of simoctocog alfa in 108 previously untreated patients (PUPs). The incidence of high-titre inhibitors was 16.2% and no patients with non-null F8 mutations developed inhibitors.
OBJECTIVE: To report the efficacy and safety results from the NuProtect study.
METHODS: PUPs received simoctocog alfa for prophylaxis, treatment of BEs, or as surgical prophylaxis. The efficacy of prophylaxis (during inhibitor-free periods) was assessed using annualised bleeding rates (ABRs). The efficacy in treating BEs and in surgical prophylaxis was assessed using a 4-point scale. Adverse events were recorded throughout the study.
RESULTS: Of 108 PUPs treated with simoctocog alfa, 103 received at least one prophylactic dose and 50 received continuous prophylaxis for at least 24 weeks. In patients on continuous prophylaxis, the median ABR was 0 (mean 0.5) for spontaneous BEs and 2.5 (mean 3.6) for all BEs. In 85 patients who had BEs, efficacy of BE treatment was excellent or good for 92.9% (747/804) of rated BEs; 92.3% of BEs were treated with 1 or 2 infusions. The efficacy of surgical prophylaxis was excellent or good for 94.7% (18/19) of rated procedures. There were no safety concerns and no thromboembolic events.
CONCLUSIONS: Simoctocog alfa was efficacious and well tolerated as prophylaxis, surgical prophylaxis and for the treatment of BEs in PUPs with severe haemophilia A.

The Medical Directors of nine Italian Hemophilia Centers reviewed and discussed the key issues concerning the replacement therapy of hemophilia patients during a one-day consensus conference held in Rome one year ago. Particular attention was paid to the replacement therapy needed for surgery using continuous infusion (CI) versus bolus injection (BI) of standard and extended half-life Factor VIII (FVIII) concentrates in severe hemophilia A patients. Among the side effects, the risk of development of neutralizing antibodies (inhibitors) and thromboembolic complications was addressed. The specific needs of mild hemophilia A patients were described, as well as the usage of bypassing agents to treat patients with high-responding inhibitors. Young hemophilia A patients may take significant advantages from primary prophylaxis three times or twice weekly, even with standard half-life (SHL) rFVIII concentrates. Patients affected by severe hemophilia B probably have a less severe clinical phenotype than severe hemophilia A patients, and in about 30% of cases may undergo weekly prophylaxis with an rFIX SHL concentrate. The prevalence of missense mutations in 55% of severe hemophilia B patients allows the synthesis of a partially changed FIX molecule that can play some hemostatic role at the level of endothelial cells or the subendothelial matrix. The flow back of infused rFIX from the extravascular to the plasma compartment allows a very long half-life of about 30 h in some hemophilia B patients. Once weekly, prophylaxis can assure a superior quality of life in a large severe or moderate hemophilia B population. According to the Italian registry of surgery, hemophilia B patients undergo joint replacement by arthroplasty less frequently than hemophilia A patients. Finally, the relationships between FVIII/IX genotypes and the pharmacokinetics of clotting factor concentrates have been investigated.

The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.

Emicizumab is a humanized recombinant bispecific antibody, bridging together activated factor IX (FIXa) and factor X (FX), thus mimicking the activity of FVIII in vivo. Emicizumab is designed for long-term prophylaxis in patients with severe hemophilia A with and without inhibitors. This approach provides constant protection, with significant reduction in bleeding rate and improved quality of life. However, protection provided by emicizumab is not absolute, and clotting factor concentrates (FVIII, rFVIIa, aPCC) may be necessary for post-traumatic bleeding or surgery, with a potential thrombotic risk or difficulty in preventing bleeding. Real world evidence is still scanty, especially for managing major surgery. In this study, 75 surgeries were managed in 28 patients (27 major procedures in 15 patients and 48 minor procedures in 20 patients. In 17 patients without inhibitors, 30 minor surgeries were carried out by using FVIII in 5, with only a bleeding event, which was successfully treated with FVIII concentrate. Six major surgeries were uneventfully performed with FVIII concentrate. Eleven PWHA and high-titer inhibitors underwent 39 surgical procedures (18 minor and 21 major surgeries). Minor surgeries were mostly performed without prophylaxis with rFVIIa, with only a single bleeding complication. All 21 major surgeries were covered with a homogeneous protocol using rFVIIa. In four instances, bleeding complications occurred, treated with rFVIIa. Of them, a single patient only failed to respond and died because of an uncontrollable bleeding from a large ruptured retroperitoneal pseudotumor. Surgery in patients with emicizumab can be safely carried out with the use of appropriate replacement therapy protocols.

Hemophilia A is a severe bleeding disorder caused by the deficiency of functionally active coagulation factor VIII (FVIII). The induction of neutralizing anti-drug antibodies is a major complication in the treatment of hemophilia A patients with FVIII replacement therapies. Why some patients develop neutralizing antibodies (FVIII inhibitors) while others do not is not well understood. Previous studies indicated that the induction of FVIII inhibitors requires cognate interactions between FVIII-specific B cells and FVIII-specific CD4+ T cells in germinal center reactions. In this study, we investigated the FVIII peptide repertoire presented by antigen-presenting cells (APCs) under different microenvironment conditions that are expected to alter the uptake of FVIII by APCs. The aim of this study was to better understand the association between different microenvironment conditions during FVIII uptake and the FVIII peptide patterns presented by APCs.
We used a FVIII-specific CD4+ T cell hybridoma library derived from humanized HLA-DRB1*1501 (human MHC class II) hemophilic mice that were treated with human FVIII. APCs obtained from the same mouse strain were preincubated with FVIII under different conditions which are expected to alter the uptake of FVIII by APCs. Subsequently, these preincubated APCs were used to stimulate the FVIII-specific CD4+ T cell hybridoma library. Stimulation of peptide-specific CD4+ T-cell hybridoma clones was assessed by analyzing the IL-2 release into cell culture supernatants.
The results of this study indicate that the specific microenvironment conditions during FVIII uptake by APCs determine the peptide specificities of subsequently activated FVIII-specific CD4+ T cell hybridoma clones. Incubation of APCs with FVIII complexed with von Willebrand Factor, FVIII activated by thrombin or FVIII combined with a blockade of receptors on APCs previously associated with FVIII uptake and clearance, resulted in distinct peptide repertoires of subsequently activated hybridoma clones.
Based on our data we conclude that the specific microenvironment during FVIII uptake by APCs determines the FVIII peptide repertoire presented on MHC class II expressed by APCs and the peptide specificity of subsequently activated FVIII-specific CD4+ T cell hybridoma clones.

Background  Immune tolerance induction (ITI) with repeated factor VIII (FVIII) administration is the only strategy proven to eradicate inhibitors. The observational ITI study is evaluating ITI with a range of FVIII products. Methods  This subgroup analysis reports prospective interim data for patients treated with a plasma-derived, von Willebrand factor-stabilized FVIII concentrate (pdFVIII/VWF, octanate). Complete success (CS) of ITI required achievement of three criteria: inhibitor titer < 0.6 BU/mL; FVIII recovery ≥ 66%; FVIII half-life ≥6 hours. Partial success (PS) required achievement of two criteria and partial response (PR) one. ITI success was defined as CS or PS. Data were analyzed for patients who achieved CS, had 36 months\' observation, or failed ITI. Results  One-hundred prospectively enrolled patients were included in the analysis; 91 had poor prognosis factors for ITI success. The mean (standard deviation) daily ITI dose was 116.4 (61.1) IU FVIII/kg in 14 low responders (< 5 BU/mL) and 173.7 (112.0) IU FVIII/kg in 86 high responders (≥ 5 BU/mL). Inhibitor titers < 0.6 BU/mL were achieved in 71% of patients in a median of 4.01 months, accompanied by a 93% reduction in bleeding rate. ITI success was achieved by 70% of patients and 56 of 72 (78%) primary (first-line) ITI patients. PR was achieved by 5 patients; ITI failed in 25 patients. PS and CS were achieved in a median of 5.55 and 11.25 months, respectively. Conclusions  ITI with pdFVIII/VWF led to rapid eradication of FVIII inhibitors, normalization of FVIII pharmacokinetics in the majority of patients, and a significant reduction in bleeding rates.

BACKGROUND: Presence of von Willebrand factor (VWF) in FVIII concentrates offers protection against neutralizing inhibitors in haemophilia A (HA). Whether this protection is more evident in plasma-derived (pd) FVIII/VWF or recombinant (r) FVIII concentrates remains controversial.
OBJECTIVE: We investigated the protection exerted by VWF against FVIII inhibitors in an in vivo mouse model of HA exposed to pdFVIII/VWF or to various rFVIII concentrates.
METHODS: Haemophilia A mice received the different FVIII concentrates after administration of vehicle or an inhibitory IgG purified from a commercial pool of HA plasma with inhibitors and FVIII:C recoveries were measured. Furthermore, using a novel clinically oriented ex vivo approach, Bethesda inhibitory activities (BU) of a commercial pool of HA plasma with inhibitors were assessed using normal plasma, or plasma from severe HA patients, without inhibitors, after treatment with the same concentrates.
RESULTS: in vivo studies showed that pdFVIII/VWF offers markedly higher protection against inhibitors when compared with any of the FVIII products without VWF. More importantly, in the ex vivo studies, plasma from patients treated with pdFVIII/VWF showed higher protection against inhibitors (P values ranging .05-.001) in comparison with that observed in plasma from patients who received FVIII products without VWF, regardless of the type of product evaluated.
CONCLUSIONS: Data indicate that FVIII+VWF complexes assembled in the circulation after rFVIII infusion are not equivalent to the naturally formed complex in pdFVIII/VWF. Therefore, rFVIII infused into HA patients with inhibitors would be less protected by VWF than the FVIII in pdFVIII/VWF concentrates.

BACKGROUND: Haemophilia A (HA) is an x-linked recessive disease due to deficiency of coagulation factor VIII (FVIII). The development of neutralizing antibodies (inhibitors) against infused FVIII is a major concern. B cell activating factor (BAFF) has been implicated in several autoimmune diseases.
OBJECTIVE: We aimed to evaluate the possible association of BAFF rs9514828 gene polymorphism and the risk of the development of FVIII inhibitor in children with severe HA.
METHODS: This cohort study was carried out on 100 newly diagnosed boys with severe HA who were never treated before with FVIII concentrate. Assessment of serum levels of BAFF and BAFF rs9514828 genotyping at first diagnosis was performed and the patients were followed up for the completion of a total of 50 exposure days or the development of inhibitors whichever occurred first. The patients were divided as positive or negative according to the presence or absence of inhibitors.
RESULTS: The risk allele for BAFF rs9514828 (T) was significantly more frequent in the inhibitor positive patients than the inhibitor negative patients (P = .003). In addition, CT+TT genotypes were associated with increased risk of FVIII inhibitor development. Receiver operating characteristics (ROC) analysis showed that BAFF levels could predict the development of FVIII inhibitors at a cut-off value of ≥ .92 with a sensitivity of 85.9% and a specificity of 80.2%.
CONCLUSIONS: BAFF rs9514828 gene polymorphism could be independent risk factor and elevated BAFF levels might be useful prognostic marker for the development of FVIII inhibitor in newly diagnosed children with severe HA.