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.

Budget impact and cost-utility analysis of prophylactic emicizumab versus on-demand bypassing agents for adolescent severe haemophilia A patients with inhibitors in India

Introduction

Severe Haemophilia A patients with inhibitors are currently being treated with bypassing agents like activated prothrombin complex concentrates (aPCC) and recombinant factor VIIa. Emicizumab is a recombinant humanized monoclonal antibody, introduced to reduce the bleeding events, improve treatment adherence, and quality of life. However, cost-effectiveness and long-term sustainability of the intervention is not studied in a low middle income setting like India.

Aim

The primary objective of this study was to evaluate the cost-utility of Emicizumab compared to traditional bypassing agents in the treatment of severe haemophilia A patients with inhibitors in India. Secondary objective was to analyze the budgetary impact of introducing Emicizumab for this patient population from the perspective of public health system in India.

Methods

Markov model was created to compare the prophylactic emicizumab therapy against bypassing agents for a hypothetical cohort of 10-year-old adolescents in India. The time horizon was 10 years and model built based on health system perspective. Cost utility was expressed as costs per quality-adjusted life-years (QALYs) gained. All costs were expressed as 2021 US dollars. Probabilistic sensitivity analysis was performed to check the robustness of the estimates.

Results

Prophylactic emicizumab was a cost saving intervention with negative Incremental Cost Utility Ratio (ICUR) against recombinant factor VIIa of -853,573 USD (INR -63,109,773), and negative ICUR of -211,675 USD (INR -15,650,403) against APCC. The estimated total budget for treating all the severe Haemophilia A patients with inhibitors in India was USD 59,042,000 (INR 4,365,329,312) for 10 years' time horizon (per patient cost of USD 295,210 [INR 21,826,646.56]).

Conclusion

Prophylactic emicizumab therapy is a cost saving intervention when compared to both the bypassing agents as it is less costly and more effective for severe Haemophilia A patients with inhibitors in India.

Nothing short of a revolution: Novel extended half-life factor VIII replacement products and non-replacement agents reshape the treatment landscape in hemophilia A

Hemophilia A, an X-linked genetic disorder, is characterized by a deficiency or dysfunction of clotting Factor VIII. The treatment landscape has substantially changed by introducing novel extended half-life factor VIII (EHL-FVIII) replacement therapies such as efanesoctocog Alfa and non-factor replacement therapy such as emicizumab. These agents signal a shift from treatments requiring multiple weekly infusions to advanced therapies with long half-lives, offering superior protection against bleeding and improving patient adherence and quality of life. While EHL-FVIII treatment might lead to inhibitor development in some patients, non-factor replacement therapy carries thrombotic risks. Therefore, ongoing research and the generation of robust clinical evidence remain vital to guide the selection of optimal and cost-effective first-line therapies for hemophilia A patients.

[Efficacy and safety of prophylaxis with emicizumab in hemophilia A: A study of 13 patients]

INTRODUCTION

Emicizumab is the first non-replacement therapy for prophylaxis in severe hemophilia A.

AIMS

The principal aim of this study is to describe the results of our patients in prophylaxis with emicizumab, according to the usual clinical practice.

MATERIAL AND METHODS

Follow-up of 13 patients from the start of prophylaxis, recording of bleeding, surgeries, adverse reactions and the need or not for factor therapy. Plasma levels were measured at follow-up visits, the technique was coagulative in one stage, modified by 1:20 dilution.

RESULTS

Median plasma levels were 52.2mg [30.7-71.9]. Prophylaxis was safe and effective; only one spontaneous haemorrhage was recorded over time and no treatment was required. There were no thromboembolic events or serious hypersensitivity, anaphylaxis or anaphylactoid reactions. The incidence of injection site reactions was 8%. Perioperative management in minor interventions was carried out without adjuvant factorial therapy, in 2 major surgeries a dose of plasmatic FVIII concentrate was required in the patient with hemophilia A without inhibitor and FVII in the patient with inhibitor, and it was sufficient to stop the bleeding.

CONCLUSION

This study demonstrated emicizumab pharmacokinetics and its half life ensure optimal levels with prophylaxis treatment at doses established in the technical data sheet.

Association of physical activity with bleeding events and safety in patients with haemophilia A starting emicizumab prophylaxis: an interim analysis of the TSUBASA study

INTRODUCTION

Little information exists on the relationship between bleeding outcomes and physical activity in patients with haemophilia A (PwHA).

AIM

This interim analysis of the TSUBASA study (UMIN-CTR ID: UMIN000037448) evaluated the association of physical activity with bleeding and safety in PwHA starting emicizumab.

METHODS

PwHA without factor VIII inhibitors were recruited. Physical activity and bleed data were obtained using an electronic patient-reported outcome application and wearable activity tracker. Adverse events (AEs) were documented.

RESULTS

At data cut-off (31-May-2021), 107 PwHA were enrolled, with a median (range) age of 35 (0-73) years. Physical activity data were obtained for 74 participants. Of these, 47 (63.5%) recorded a total of 396 exercise events. The most common exercise events were walking (32.4%), cycling (14.9%), and football (5.4%). Two (0.5%) exercise events in the same individual were associated with bleeding (running, weight training). The safety analysis population consisted of 106 participants treated with emicizumab (median observation period: 241.5 days). Twenty-one (19.8%) participants experienced a total of 39 AEs. Five (4.7%) experienced a serious AE, none of which was emicizumab-related, and three (2.8%) experienced an adverse drug reaction.

CONCLUSIONS

PwHA receiving emicizumab in the TSUBASA study experienced minimal bleeding associated with physical activity.

TRIAL REGISTRATION

Trial registration: UMIN-CTR ID: UMIN000037448.

Longitudinal dynamic changes in factor VIII inhibitor titers in patients with hemophilia A and inhibitors receiving emicizumab prophylaxis

Emicizumab prophylaxis dramatically reduces bleeding events in patients with hemophilia A (PwHA) with or without factor VIII (FVIII) inhibitors. However, long-term dynamic changes in FVIII inhibitor titers during emicizumab prophylaxis remain to be investigated. We conducted a retrospective follow-up study of FVIII inhibitor titers after initiation of emicizumab prophylaxis in 25 PwHA carrying current or historical FVIII inhibitors. Nineteen PwHA had FVIII inhibitors at initiation of emicizumab prophylaxis (age: median 22 [range 4-60] years and inhibitor titer: 30 [1.0-1450] BU/mL). In 17 of the 19 patients, the inhibitor titers markedly decreased to a median of 1.2 (< 0.6-58) BU/mL at a median follow-up of 71 (38-111) months. In two patients, titers were slightly elevated after initiation of emicizumab but decreased in the long term. The remaining six patients had negative inhibitor status (< 0.6 BU/mL) when switched to emicizumab from FVIII prophylaxis. Five patients maintained negative titers. One patient had inhibitor recurrence, with a peak titer of 1.6 BU/mL that decreased to 0.9 BU/mL. In most cases, FVIII inhibitor titers can be expected to decrease spontaneously during emicizumab prophylaxis, but regular follow-up is necessary to manage breakthrough bleeds.

Awareness of individual goals, preferences, and priorities of persons with severe congenital haemophilia A for a tailored shared decision-making approach to liver-directed gene therapy. A practical guideline

In clinical medicine, shared decision making (SDM) is a well-recognized strategy to enhance engagement of both patients and clinicians in medical decisions. The success of liver-directed gene therapy (GT) to transform severe congenital haemophilia A (HA) from an incurable to a curable disease has launched a shift beyond current standards of treatment. However, GT acceptance remains low in the community of HA persons. We argue for both persons with haemophilia (PWH) and specialists in HA care including clinicians, as needing SDM-oriented educational programs devoted to GT. Here, we provide an ad hoc outline to implement education to SDM and tailor clinician information on GT to individual PWHs. Based on routine key components of SDM: patient priorities; recommendations based on individual risk reduction; adverse effects; drug-drug interactions; alternatives to GT; and ongoing re-assessment of the objectives as risk factors (and individual priorities) change, this approach is finalized to exploit efficacious communication.

Successful transfemoral prosthesis in a patient with haemophilia A and factor VIII inhibitors: A case report

Haemophilia A patients who develop factor VIII inhibitors pose a challenge with respect to bleeding and orthopaedic management. This is particularly relevant in cases requiring amputation. We present here a case of a patient with severe haemophilia A and inhibitors who had a history of multiple surgeries due to periprosthetic joint infection and a non-healing wound which led to above-knee amputation. Following the implementation of appropriate and suitable transfemoral prosthesis and emicizumab therapy, the patient experienced a significant improvement in mobility and quality of life without any adverse events or bleeding episodes. Additional studies are required to more fully understand treatment options for lower limb amputations in the haemophilia population.

Clot waveform analysis for perioperative hemostatic monitoring in a hemophilia A patient on emicizumab undergoing liver transplantation

How to optimize perioperative factor VIII (FVIII) replacement through hemostatic monitoring is critically important to manage hemophilia A patients. The bispecific antibody emicizumab binds activated FIX (FIXa) and FX to functionally mimic FVIIIa. While being used for hemostatic control in hemophilia A, this therapeutic antibody inconveniently interferes with coagulation tests using human FIXa and FX, such as activated partial thromboplastin time (APTT) and FVIII activity measurement based on one-stage clotting assays. Clot waveform analysis (CWA) extends the interpretation of measurement curves for coagulation time to provide global information. We performed APTT-CWA to monitor perioperative hemostasis in a hemophilia A patient on emicizumab undergoing liver transplantation. Plasma samples were treated with anti-idiotype monoclonal antibodies against emicizumab to enable accurate coagulation assays. Kinetics of maximum coagulation velocity and acceleration mimicked that of FVIII activity. These CWA parameters better correlated with FVIII activity than APTT. The plateaus of them were observed at FVIII activity of 100% or more, supporting the protocol for perioperative FVIII replacement. Thus, CWA may measure coagulation potential in hemophilia A patients undergoing liver transplantation, aiding in optimizing perioperative hemostasis.

Hemophilia A: Emicizumab monitoring and impact on coagulation testing

Hemophilia A is an X-linked recessive bleeding disorder characterized by absent or ineffective coagulation factor VIII, a condition that could result in a severe and potentially life-threatening bleed. Although the current standard of care involves prophylactic replacement therapy of factor VIII, the development of neutralizing anti-factor VIII alloantibody inhibitors often complicates such therapeutic treatment. Emicizumab (Hemlibra®), a novel recombinant therapeutic agent for patients with hemophilia A, is a humanized asymmetric bispecific IgG4 monoclonal antibody designed to mimic activated factor VIII by bridging factor IXa and factor X thus effecting hemostasis. Importantly, this drug eliminates the need for factor VIII and complications associated with inhibitor generation. Emicizumab has been approved for use in several countries including the United States and Japan for prophylaxis of bleeding episodes in hemophilia A with and without FVIII inhibitors. Therapy is also approved in the European Union for routine prophylaxis of bleeds in hemophilia A with inhibitors or severe hemophilia A without inhibitors. Unfortunately, emicizumab therapy presents unique challenges for routine and specialty coagulation tests currently used to monitor hemophilia A. In this review, hemophilia A is presented, the biochemistry of factor VIII is discussed, and the impact of the therapeutic agent emicizumab is highlighted.

A factor IX variant that functions independently of factor VIII mitigates the hemophilia A phenotype in patient plasma

BACKGROUND

Recombinant factor (F)IX-FIAV has previously been shown to function independently of activated FVIII (FVIIIa) and ameliorate the hemophilia A (HA) phenotype in vitro and in vivo.

OBJECTIVES

To assess the efficacy of FIX-FIAV in HA patient plasma using thrombin generation (TG) and intrinsic clotting activity (APTT) analyses.

PATIENTS/METHODS

Plasma obtained from 21 HA patients (>18yrs; 7 mild, 7 moderate, and 7 severe) was spiked with FIX-FIAV. The FXIa-triggered TG lag time and APTT were quantified in terms of FVIII-equivalent activity using FVIII calibration for each patient plasma.

RESULTS

The linear, dose-dependent improvement of the TG lag time and APTT reached its maximum with ∼400-600% FIX-FIAV in severe HA plasma and with ∼200-250% FIX-FIAV in non-severe HA plasma. The cofactor-independent contribution of FIX-FIAV was therefore suggested and confirmed by addition of inhibitory anti-FVIII antibodies to non-severe HA plasma, resulting in a FIX-FIAV response similar to severe HA plasma. Addition of 100% (5 μg/mL) FIX-FIAV mitigated the HA phenotype from severe to moderate (from <0.01% to 2.9% [IQR 2.3-3.9%] FVIII-equivalent activity), from moderate to mild (3.9% [IQR 3.3-4.9] to 16.1% [IQR 13.7-18.1%] FVIII-equivalent activity), and from mild to normal (19.8% [IQR 9.2-24.0%] to 48.0% [IQR 34.0-67.5%] FVIII-equivalent activity). No substantial effects were observed when combining FIX-FIAV with current HA therapies.

CONCLUSION

FIX-FIAV is capable of increasing the FVIII-equivalent activity and coagulation activity in HA patient plasma, thereby mitigating the HA phenotype. Hence, FIX-FIAV could serve as a potential treatment for HA with or without inhibitors.

Data mining and analysis for emicizumab adverse event signals based on the Food and Drug Administration Adverse Event Reporting System database

BACKGROUND

Emicizumab is the latest treatment for patients with hemophilia A. Its safety in real-world data is limited, and regulatory agencies and clinical researchers have raised concerns about the risk of adverse events.

AIM

This study aimed to detect potential adverse event signals of emicizumab using the FDA Adverse Event Reporting System (FAERS) database.

METHOD

Data in FAERS from the fourth quarter of 2017 to the second quarter of 2021 were searched. Cases of adverse events were extracted using the Preferred Term in the Medical Dictionary for Regulatory Activities (version 24.0). Disproportionality analysis was performed using the reporting odds ratio (ROR) and information component (IC) methods based on statistical shrinkage transformation.

RESULTS

A total of 5,598,717 patients were included, of which 1,244 took emicizumab. A total of 703 emicizumab-related adverse event signals were mined, and 101 positive signals were detected. Haemarthrosis (ROR/ROR₉₇₅/ROR₀₂₅ = 155.62/184.34/131.38, IC/IC₉₇₅/IC₀₂₅ = 7.28/7.48/7.01), haemorrhage (ROR/ROR₉₇₅/ROR₀₂₅ = 71.01/81.18/62.12, IC/IC₉₇₅/IC₀₂₅ = 6.15/6.31/5.94), muscle haemorrhage (ROR/ROR₉₇₅/ROR₀₂₅ = 53.38/75.83/37.58, IC/IC₉₇₅/IC₀₂₅ = 5.74/6.16/5.15), traumatic haemorrhage (ROR/ROR₉₇₅/ROR₀₂₅ = 27.78/46.29/16.67, IC/IC₉₇₅/IC₀₂₅ = 4.80/5.40/3.92), haematoma (ROR/ROR₉₇₅/ROR₀₂₅ = 18.15/26.35/12.51, IC/IC₉₇₅/IC₀₂₅ = 4.18/4.63/3.55), device-related thrombosis (ROR/ROR₉₇₅/ROR₀₂₅ = 21.27/37.57/12.04, IC/IC₉₇₅/IC₀₂₅ = 4.41/5.08/3.43), and activated partial thromboplastin time prolonged (ROR/ROR₉₇₅/ROR₀₂₅ = 20.68/36.51/11.71, IC/IC₉₇₅/IC₀₂₅ = 4.37/5.04/3.39) had the strongest signal intensities. Haemorrhage, haemarthrosis, arthralgia, fall, and injection site pain were reported more frequently.

CONCLUSION

This study found that mild arthralgia and injection site reaction were associated with emicizumab. Attention should also be paid to other serious adverse events related to emicizumab, such as acute myocardial infarction and sepsis, to ensure patient safety.

Cerebellar hematoma in severe hemophilia with inhibitor on emicizumab prophylaxis: a case report

BACKGROUND

Emicizumab is a novel prophylactic medication used to treat patients with hemophilia A. It is indicated to minimize the frequency of bleeding episodes and the severity of serious bleeding in patients with hemophilia A utilizing inhibitors. However, some cases of bleeding episodes have been reported, and more data are needed regarding their management and expected outcomes.

CASE PRESENTATION

We report a case of a 4-year-old Saudi Arabian boy with severe hemophilia A who presented with a post-traumatic cerebral hemorrhage. The patient, with high titer inhibitors, was on emicizumab prophylaxis therapy. On hospital admission, he received tranexamic acid (10 mg intravenously, every 6 hours), and recombinant activated factor VII 120 µg/kg every 2 hours for 2 days then every 4 hours for 4 days. On follow-up, the patient showed no signs of neurological deficit. There was no need for emergency neurosurgical intervention since the bleeding had been controlled throughout the first 2 days. There were no recorded thrombotic sequelae or neurological complications, with complete resolution within 10 days.

CONCLUSIONS

This case implies that low-dose recombinant activated factor VII might be used safely and effectively with patients with hemophilia A on emicizumab prophylaxis, to reduce the risk of cerebral hemorrhage or another episode of serious bleeding along with its long-term complications.

In vitro validation of chromogenic substrate assay for evaluation of surrogate FVIII-activity of emicizumab

[Introduction] Emicizumab, a bispecific antibody mimicking activated factor VIII (FVIII), is increasingly used in prophylaxis against bleeding in hemophilia A. Human factor-based chromogenic substrate assay (hCSA) shows concentration-dependency between emicizumab and reported FVIII activity. However, the assay measurement settings have not been optimized for emicizumab, and the reported FVIII activity cannot be directly referred as surrogate FVIII activity. [Materials and Methods] For in vitro validation of hCSA-reported surrogate FVIII activity, we compared the equation curves for emicizumab concentration with surrogate FVIII activity using spiked plasma in the thrombin generation assay (TGA), hCSA, and clot waveform analysis (CWA). Then, we generated conversion equations for hCSA-reported surrogate FVIII value to that of TGA. We also assessed the additive effect of rFVIII onto 340 nM (i.e., 50 μg/mL) emicizumab using the same assays. [Results] With 1:20 diluted plasma, halving hCSA-reported surrogate FVIII activity can be approximated to that in TGA triggered by the extrinsic pathway reagent (27.3 IU/dL vs. 13.9 IU/dL) under therapeutic emicizumab concentration. Both in TGA and hCSA, the additive effect of added FVIII on therapeutic emicizumab concentration (340 nM) was maintained at low levels of FVIII but gradually decreased at higher levels. [Conclusions] Surrogate FVIII activity can be estimated simply by halving hCSA-reported FVIII value, and the additive effect of FVIII on emicizumab diminishes at high concentrations. Based on our in vitro study, a clinical study is currently being conducted to compare individual variation of surrogate FVIII activity in hCSA and TGA.

Chromogenic Factor VIII Assay for Patients with Hemophilia A and on Emicizumab Therapy

This chapter will describe a method for measuring endogenous and infused Factor VIII (FVIII) in patients on emicizumab therapy (Hemlibra, Genetec, Inc). Emicizumab is a bispecific monoclonal antibody used in patients with hemophilia A, with or without inhibitors. The mechanism of action for emicizumab is novel and mimics the role that FVIII plays in vivo by binding and bridging FIXa and FX. It is vital that the laboratory understands the effect this drug has on coagulation tests and uses a suitable chromogenic assay which is not affected by emicizumab, for determination of FVIII coagulant activity and inhibitors.

Measuring Emicizumab Levels in the Hemostasis Laboratory

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

[Successful treatment of traumatic intramuscular hemorrhage with coagulation factor VIII replacement in a patient with congenital hemophilia A with decreased inhibitor activity by emicizumab therapy]

The patient is a 45-year-old man who was diagnosed with severe hemophilia A during childhood and received FVIII replacement therapy, which became ineffective due to inhibitor production (5-225 BU/ml). After initiating emicizumab therapy, bleeding symptoms markedly improved, but he developed an intramuscular hematoma at the right thigh due to a fall. He was hospitalized and maintained on bed rest; however, the size of the hematoma increased, and anemia developed. Since the inhibitor level was markedly decreased at 0.6 BU/ml, a recombinant FVIII preparation was administered, and the size of the hematoma decreased along with an increase in FVIII activity. Levels of the inhibitor increased to 54.2 BU/ml, but tended to decrease during continued emicizumab treatment. Emicizumab therapy seems useful in hemophilia A patients with inhibitor production.

Real-world study of rurioctocog alfa pegol and emicizumab in US clinical practice among patients with hemophilia A

BACKGROUND

FVIII replacement is standard treatment for hemophilia A without inhibitors, but non-factor therapies, such as emicizumab, are changing the treatment landscape. We explore the ramifications of switching treatment.

METHODS

Pharmacy database data (July 2017-May 2020) from patients with hemophilia A without inhibitors who switched to rurioctocog alfa pegol or emicizumab prophylaxis after ≥6 months' prophylaxis with another FVIII product were analyzed for total mean weekly consumption, dosing frequency, product wastage, and ABR.

RESULTS

Post-switch mean weekly consumption of prophylactic rurioctocog alfa pegol and emicizumab were 6224 IU/kg and 109 mg, respectively. Dosing schedules for emicizumab were primarily weekly (48.2%) and every 2 weeks (40.0%). Most patients in the rurioctocog alfa pegol cohort received treatment twice-weekly (83.3%). Mean product wastage of emicizumab (8.4%) was significantly higher versus rurioctocog alfa pegol (-0.3%; P < 0.001). Mean annualized emicizumab and rurioctocog alfa pegol wastage during prophylaxis was 330.82 mg and -974.80 IU, respectively. ABR change was not significantly different (P = 0.527) for patients switching to emicizumab (-1.05) or rurioctocog alfa pegol (-1.53).

CONCLUSIONS

Bleed rates were similar for patients receiving prophylaxis with emicizumab or rurioctocog alfa pegol after switching from prophylaxis with another FVIII. However, wastage associated with dispensing inaccuracies was greater with emicizumab.

Emicizumab in children: bleeding episodes and outcome before and after transition to Emicizumab

PURPOSE

Real-world data and study data regarding therapy with Emicizumab in pediatric cohorts with haemophilia A is scarce. Especially, data on previously untreated pediatric patients (PUPs) and minimally treated patients (MTPs) are missing.

METHODS

Thirteen pediatric patients with haemophilia A and treatment with Emicizumab were retrospectively evaluated for Annual Bleeding Rates (ABR) pre-and post-Emicizumab treatment. Safety data and data on management of minor surgery as well as laboratory results were collected. Additionally, we describe the clinical features of two PUPs and one MTP that are included in our cohort.

RESULTS

Median age at initiation of Emicizumab was 5.3 (range: 0.26-17.5) years, three patients were younger than one year at initiation of treatment with Emicizumab. Median follow-up time on Emicizumab was 23.8 (range: 0.7-40) months. Total ABR (p = 0.009) as well as spontaneous (p = 0.018), traumatic (p = 0.018), and joint (p = 0.027) ABR reduced significantly post-Emicizumab transition. Safety profile was favourable as only one local site reaction occurred; no cessation of treatment was necessary. Surgery was successfully performed in three patients receiving rFVlla pre- and post-surgery. Emicizumab trough levels showed a median of 43.2 μg/ml (range: 23.9-56.8) after three doses of 3 mg/kg and 51.9 μg/ml (range: 30.4-75) at first follow-up with 1.5 mg/kg.

CONCLUSION

Emicizumab is safe and efficient in pediatric patients with and without inhibitors. More data on larger multicenter cohorts and especially on PUPs/MTPs are still needed.

Advances in Hemophilia A Management

Hemophilia A is an inherited insufficiency of Factor VIII (FVIII), one of the critical clotting factors. The gold standard for the management of moderate-to-severe hemophilia A is prophylaxis using regular replacement therapy with clotting factor concentrates. Compared with conventional treatment, extended half-life products reduce the burden of frequent factor replacement injections. Of note, up to 30% of patients with hemophilia A receiving prophylactic factor infusions develop "inhibitors," neutralizing anti-FVIII autoantibodies. Therapeutic options for patients with hemophilia A and inhibitors include the immune tolerance induction (ie, eradication of inhibitors) and the management of acute bleeds with bypassing agents and/or emicizumab. Emicizumab is a biphasic monoclonal antibody mimicking activated FVIII, approved for patients with hemophilia A with/without inhibitors. Gene therapy is an emerging therapy for hemophilia A, essentially curing patients with hemophilia A or transforming them to a milder phenotype by establishing continuous endogenous expression of FVIII after one-time treatment.

An Update on the Dental Management of Children with Haemophilia

Children with haemophilia present a bleeding risk and a challenge for dentists. Guidelines on the dental management of haemophilia patients are largely based on expert consensus. Many existing guidelines also provide generic guidance mainly for adult patients, which have been adapted for children. However, children have unique needs that require additional considerations. With limited evidence available, it is important that dentists have an understanding of the principles of both medical and dental management and have a close collaboration with the haematologist at all times. Therefore, this paper provides some key principles related to various aspects of dental management of children with haemophilia. Furthermore, there has been a recent update to the World Federation of Haemophilia (WFH) Guidelines for the Management of Haemophilia,¹ with references to novel medical therapies for haemophilia. Hence, this paper also aims to inform dentists with the standard and newer medical therapies for haemophilia, including a specific focus on the novel agent Emicizumab and the associated dental considerations.

[Hemostatic management of hemophilia]

Replacement therapy is the basic treatment for hemophilia by infusing deficient clotting factors, including replacement therapy for prophylaxis (i.e., prevention of breakthrough bleeding for physical activity), episodic replacement therapy, replacement therapy during and after procedures and surgery, and replacement therapy for physical activity, each administered at doses and intervals appropriate for the purpose and the product used. Although emicizumab is increasingly used for prophylaxis in severe hemophilia A, the combination of replacement therapy is necessary, especially during severe bleeding, highly invasive procedures, and major surgery. Furthermore, the usual APTT measurements cannot be used for monitoring the replacement therapy and detecting the presence of inhibitors while patients are receiving emicizumab. Hemostatic management of patients with inhibitors should be implemented based on the purpose of the therapy, the latest inhibitor titer, and the clinical response to the product, with the choice of inhibitor neutralization or bypass agent therapy. When bypassing agents are used in patients with hemophilia A with emicizumab inhibitor during and after bleeding, procedures, and surgery, the choice of agent and dose adjustment should be made with attention to thrombotic complications.

Bispecific antibody characterization by a combination of intact and site-specific/chain-specific LC/MS techniques

Bispecific antibodies (bsAbs) are considered as an important class of biopharmaceutical drugs, with about 160 products in clinical trials. From an analytical point of view, the correct chain-association is one of the most critical challenge to monitor during bsAbs development and production. In the present study, a full analytical workflow has been developed based on the use of various chromatographic modes: size exclusion chromatography (SEC), ion exchange chromatography (IEX), reversed phase liquid chromatography (RPLC), and hydrophilic interaction chromatography (HILIC), all combined with high resolution mass spectrometry (MS). This analytical strategy was applied to Hemlibra® (emicizumab), which is certainly the most successful commercial bsAb to date. Using this strategy, it was possible to monitor the presence of mispaired bsAb species and detect and identify additional post-translational modifications (PTMs).

[Spontaneous disappearance of the inhibitor during emicizumab therapy in a patient with mild hemophilia A]

From a young age, a 63-year-old Japanese man had experienced difficulties with hemostasis during tooth extraction and epistaxis and swelling of bruised areas. He had previously been diagnosed with mild hemophilia (FVIII:C 8.5%) at age of 60 due to swelling of a right hip bruise and was administered FVIII concentrate for the first time. He had frequent bleeding around his shoulder joints and was given FVIII concentrates every time, but his hemostasis was poor. He was referred to our hospital because his FVIII activity decreased to<1% and a low-titer inhibitor (2.0 BU/ml) was detected. Because of a shoulder hematoma and new subcutaneous bleeding on both forearms, recombinant FVIIa was used to perform the hemostatic treatment. Following hemostasis, emicizumab was administered subcutaneously every 2 weeks at a dose of 3.0 mg/kg. Approximately 2 months after starting emicizumab, inhibitors were no longer detected, and FVIII activity increased to 8% after 9 months. We encountered a case of mild hemophilia A with an inhibitor that was first diagnosed in old age. The incidence of inhibitors in non-severe hemophilia A is about 10%, and about 70% of those resolves spontaneously. In this case, suppression of bleeding by emicizumab may have contributed to the spontaneous disappearance of the inhibitor.

[Treatment of haemophilia: From replacement to gene therapy]

Haemophilia A and B are congenital bleeding disorders characterized by missing or defective factor VIII or factor IX, respectively. Factor replacement therapy has been the gold standard for prophylaxis and treatment of bleeding complications. However, the inconvenience of regular intravenous administration, along with progression of arthropathy and development of inhibitors has driven the need for alternative treatment options, such as extended half-life products, non-factor coagulation products, such as subcutaneous emicizumab, blocking natural anticoagulants (rebalancing haemostatic agents) and gene therapy, which have been useful to control bleeding or are currently under late-phase clinical investigation.

Emicizumab Associated Rhabdomyolysis in Hemophilia A

Emicizumab is increasingly the front-line treatment for patients with Hemophilia A with or without inhibitors. Rhabdomyolysis is a syndrome of muscle necrosis and release of intracellular muscle constituents into the circulation. Creatine kinase (CK) levels are typically markedly elevated, and muscle pain and myoglobinuria may be present. The severity of illness ranges from asymptomatic elevations in serum muscle enzymes to life-threatening disease associated with extreme enzyme elevations, electrolyte imbalances, acute kidney injury and disseminated intravascular coagulation. We present a case of an African American male with severe hemophilia A and history of factor VIII inhibitor, maintained on emicizumab prophylaxis, who developed rhabdomyolysis with a symptomatic hyperCKemia. To date, there is no known link between rhabdomyolysis to emicizumab. This report brings to light the possibility of symptomatic rhabdomyolysis as a potential side effect of emicizumab after moderate exertional activity.

Advances in the management of haemophilia: emerging treatments and their mechanisms

Mainstay haemophilia treatment, namely intravenous factor replacement, poses several clinical challenges including frequent injections due to the short half-life of recombinant factors, intravenous administration (which is particularly challenging in those with difficult venous access), and the risk of inhibitor development. These impact negatively upon quality of life and treatment compliance, highlighting the need for improved therapies. Several novel pharmacological therapies developed for haemophilia aim to rebalance the clotting cascade and potentially circumvent the aforementioned challenges. These therapies utilise a range of different mechanisms, namely: the extension of the circulating half-life of standard recombinant factors; the mimicking of factor VIII cofactor activity; rebalancing of coagulation through targeting of natural anticoagulants such as antithrombin and tissue factor pathway inhibitor; and inducing the production of endogenous factors with gene therapy. These therapies carry the potential of revolutionising haemophilia treatment by alleviating the current challenges presented by mainstay factor replacement. This review will provide an overview of the key trial findings related to novel therapies based on the mechanisms described above.

[Update on factor (F) VIII structure and function-related hemostatic coagulation and its regulatory mechanism (s)]

Blood coagulation factor VIII (FVIII) functions as a cofactor for activated factor IX on the phospholipid membrane in the coagulation reaction. FVIII deficiency causes hemophilia A, and conversely, the thrombotic patients show high FVIII levels. Therefore, FVIII is a key coagulant factor involved in the contradictory pathology of hemorrhage and thrombosis. From the crystal structure of the FVIII molecule and bispecific antibody that substitutes for FVIII cofactor function, FVIIIa function and role on the FXase complex are drawing attention. It has been also supported that a concept that the extrinsic coagulation system involved in the initial phase of the coagulation process, the intrinsic coagulation system involved in the thrombin burst, the anti-coagulation system by activated protein C pathway, and the fibrinolytic system involved the dissolving fibrin clot intertwine each other and progress during the coagulation reaction process. FVIII-related FVIIa coagulation system and FVIII-related plasmin regulation system have been also elucidated. We greatly expect that the developmental elucidation of thrombus formation mechanism (s) centered on FVIII/FVIIIa could lead to the development of more effective new FVIII product and antithrombotic drugs.

Bispecific antibodies for the treatment of hemophilia A

INTRODUCTION

Emicizumab is a bispecific antibody exerting cofactor function of FVIIIa irrespective of the presence of FVIII inhibitors. Long-term data of phase 1/2 and phase 3 studies have been accumulated. Various questions such as indicated patients, ITI, application to PUPs, hemostatic treatment including surgeries, and emicizumab-related morbidity remain to be solved.

AREAS COVERED

The review describes the mode of action, data from pre-/post-marketing and ongoing clinical studies according to PubMed search and our own works.

EXPERT OPINION

For patients with a persistent inhibitor, emicizumab is a definite therapeutic option, although the possibility of BPAs-associated thromboembolic/TMA events raises concerns. The use of ITI together with emicizumab prophylaxis is being examined in clinical trials. For non-inhibitor, especially pediatric patients, emicizumab prophylaxis can be an option. Outcome assessment 'beyond ABR' such as joint health, physical/mental activity, QOL is required. Furthermore, continuous data collection for emicizumab-related adverse events and morbidity would be recommended.

Perspective - The case for zero bleeds and drug bioequivalence in the treatment of congenital hemophilia A in 2021

Not all patients with severe hemophilia A (HA) respond optimally to a given dose of a given product. Within-individual variance in cross-over studies makes each patient unique in the response to each standard half-life (SHL) factor VIII (FVIII) product in pharmacokinetic (PK) terms. This hampers the prediction of efficacy when a SHL FVIII product is employed. PK data showing that half-lives of SHL rFVIII are unsatisfactory to achieve zero bleeding in individual HA patients provide the rationale for switching from SHL to extended half-life (EHL) products. However, not all subjects receiving prophylaxis with EHL products achieve zero bleeding, the most cogent objective of personalized prophylaxis. Known determinants of FVIII half-life (age, von Willebrand factor [VWF] levels, blood group) cumulatively account for one third of the total inter-individual variation in FVIII clearance in subjects with severe HA. Investigations into precision, and accuracy of laboratory measurement to be employed; newer pathways for the clearance of both free-FVIII and VWF-bound FVIII, and adequately powered studies on omics and phenotypic heterogeneity, are likely to provide additional information on the remaining two thirds of inter-individual variation in FVIII clearance in HA. Variability in the clinical response has also been documented in patients when FVIII activity is mimicked by fixed subcutaneous doses of the bispecific antibody emicizumab. National registries that collect PK data of available FVIII products and ad hoc information on the individual response to emicizumab should be encouraged, to establish newer standards of care and ease personalized clinical decisions to achieve zero bleeding.

Costs of the management of hemophilia A with inhibitors in Spain

Introduction

Emicizumab is a first-in-class monoclonal antibody, recently authorized for the treatment of hemophilia A with inhibitors. This study aims to estimate the direct and indirect costs of the management of hemophilia A with inhibitors, in adult and pediatric patients, including the prophylaxis with emicizumab.

Methods

We calculated the costs of the on-demand and prophylactic treatments with bypassing agents (activated prothrombin complex concentrate and recombinant activated factor VII) and the emicizumab prophylaxis, from the societal perspective, over 1 year. The study considered direct healthcare costs (drugs, visits, tests, and hospitalizations), direct non-healthcare costs (informal caregivers), and indirect costs (productivity loss). Data were obtained from a literature review and were validated by an expert group. Costs were expressed in 2019 euros.

Results

Our results showed that the annual costs of the prophylactic treatment per patient varied between €543,062.99 and €821,415.77 for adults, and €182,764.43 and €319,826.59 for children, while on-demand treatment was €532,706.84 and €789,341.91 in adults, and €167,523.05 and €238,304.71 in pediatric patients. In relation to other prophylactic therapies, emicizumab showed the lowest costs, with up to a 34% and 43% reduction in the management cost of adult and pediatric patients, respectively. It reduced the bleeding events and administration costs, as this drug is less frequently administered by subcutaneous route. Emicizumab prophylaxis also decreased the cost of other healthcare resources such as visits, tests, and hospitalizations, as well as indirect costs.

Conclusion

In comparison to prophylaxis with bypassing agents, emicizumab reduced direct and indirect costs, resulting in cost savings for the National Health System and society.

Post-authorization pharmacovigilance for hemophilia in Europe and the USA: Independence and transparency are keys

The regulatory process is currently designed to ensure drug safety during the pre-marketing process. Due to limitations of the pivotal studies owing to their short duration and small number of highly selected cases, some adverse drug reactions (ADRs) are not detected, particularly the rarest and those which appear a long time after exposure. Thus it is essential to foster pharmacovigilance run totally independently from marketing authorization holders in order to attain transparent surveillance. This challenge is relevant for hemophilia drugs, after recent advances offered innovative replacement and non-replacement medicines that warrant monitoring due to the occurrence of predicted but also unexpected and rare ADRs. This article contains an overview of pharmacovigilance systems in the European Union and USA, describing the main ADRs related to traditional and recently available hemophilia medications and suggests how to involve stakeholders other than marketing authorization holders for an independent and transparent pharmacovigilance targeted to detect not only early ADRs but also those emerging post-marketing.

Safety evaluation of emicizumab prophylaxis in individuals with haemophilia A

INTRODUCTION

Emicizumab is a bispecific-humanized monoclonal antibody that improves hemostasis by bridging activated factor IX and factor X to substitute for the function of missing activated FVIII. It is an alternative to prophylaxis with factor VIII replacement and is associated with improved outcomes in individuals with hemophilia A with and without inhibitors.

AREAS COVERED

Emicizumab is efficacious in reducing bleeding events when compared to on-demand treatment and factor-based prophylaxis. Except for the few thrombotic microangiopathy and thrombotic event cases mainly seen in the HAVEN 1 trial, emicizumab has an overall excellent safety profile with minimal side effects.

EXPERT OPINION

Knowledge gaps include the efficacy and safety of emicizumab in younger age groups and those with mild or moderate hemophilia A. Future directions for research include exploring the risk of inhibitor recurrence in patients with a history of high titer inhibitor who have been successfully tolerized, who switch from factor prophylaxis to emicizumab, as well as conducting 'real world studies' to evaluate the patient's perception of emicizumab in regard to ease and tolerability in order to optimize individualized treatment plans.

Predicted coagulation potential using an in vitro simulated model of emicizumab prophylaxis and immune tolerance induction therapy in hemophilia A patients with inhibitor

Emicizumab reduces bleeding in hemophilia A patients with inhibitor (HA-inh). A combination of immune tolerance induction therapy (ITI) and emicizumab prophylaxis may provide additional benefits, but coagulation potential during this treatment remains unknown. We assessed coagulation potentials in simulated ITI models in vitro using modified-clot waveform analysis. Factor (F)VIII-deficient plasma preincubated with anti-A2 and anti-C2 monoclonal antibodies was reacted with emicizumab (50 µg/mL) (emicizumab-HA-plasma), then spiking bypassing agents (BPAs): activated prothrombin complex concentrates (aPCC 1.3 IU/mL; 50 IU/kg), recombinant factor (rF)VIIa (2.2 µg/mL; 90 µg/kg), and FVIIa/FX (1.5 µg/mL; 60 µg/kg), and/or FVIII (100, 200 IU/dL). Coagulation potentials in emicizumab-HA-plasma (10 BU/mL) remained within the normal range when BPA and FVIII were both present. In emicizumab-HA-plasma (1 BU/mL) with BPA and FVIII (200 IU/dL), they were near or beyond the normal range, but those with a half concentration of rFVIIa based on the half-life in blood were within the normal range. In samples without inhibitor, coagulation potentials with combined BPA and FVIII were far beyond the normal range but with FVIII (100 IU/dL) and rFVIIa at half concentration they remained within the normal range. These results may provide information on the feasibility of concurrent ITI under emicizumab prophylaxis.

[Current developments in hemostatic treatment for patients with hemophilia]

The supplementation of factor (F-) VIII or F-IX products for hemophilia treatment has helped in preventing arthropathy and considerably improving the quality of life (QOL) of patients. However, serious issues related to hemostatic treatment of hemophilia include the need for repeated intravenous infusion of products, inhibitor development, and hemostatic treatment for patients with inhibitors. To overcome these issues, some extended half-life products and nonclotting factor products were developed. An anti-F-IX/F-X bispecific antibody, emicizumab, which has a longer half life and can be administered subcutaneously, has achieved significant reduction in bleeding in patients with severe hemophilia, irrespective of the inhibitor. Furthermore, clinical trials of si-RNA anti-antithrombin therapy and antitissue factor pathway inhibitor antibody therapy, based on the concept of rebalancing coagulation, have been ongoing. Moreover, gene therapy has been currently developed by the improvement of vector. These newly developed therapies for hemophilia, as a paradigm shift in hemophilia treatment, could provide further improvement in the QOL of patients.

The potential role of emicizumab prophylaxis in severe von Willebrand disease

BACKGROUND

Severe von Willebrand disease (VWD) may be associated with chronic joint damage and may require prophylactic therapy. Emicizumab is a humanized bispecific antibody, which mimics the function of coagulation factor VIII (FVIII), and it has been approved for prophylaxis in hemophilia A.

METHODS

This is the first study assessing the potential future role of emicizumab as an alternative prophylactic treatment in patients with severe VWD, based upon a thrombin generation (TG) ex vivo analysis. We report 51 weeks of successful off label emicizumab prophylaxis in a child with severe VWD and recurrent hemarthroses and progressive arthropathy despite adherence to previous prophylaxis with replacement therapy.

RESULTS AND CONCLUSIONS

Our work demonstrated that ex vivo spiking with emicizumab increased TG in plasma from patients with type 3 VWD. Similar TG results were observed in our treated patient, whose therapy was well tolerated without any adverse events. Both in vitro and ex vivo TG data support sufficient hemostasis without exceeding the range seen in healthy volunteers. Further collaborative studies on the efficacy and safety of emicizumab prophylaxis in severe VWD is warranted.

The evolving landscape of gene therapy for congenital haemophilia: An unprecedented, problematic but promising opportunity for worldwide clinical studies

With liver-directed gene therapy, congenital haemophilia has the potential to progress from an incurable to a phenotypically curable condition. However, the proportion of haemophilia population likely to benefit from gene therapy remains to be established. Achieving a phenotypic curative goal is presently hampered by: 1) availability of effective treatments (e.g. extended half-life products, non-factor therapies) that address major unmet needs in haemophilia; 2) key differences between hope and reality that patients undergoing gene therapy face (e.g. unknown risks and long-term follow-up, durability of the therapeutic effect, possibility of re-administering the vector), 3) lack of expertise of health care professionals (HCP) in managing/monitoring unexpected side effects in patients, and 4) lack of expertise of HCP in advising payers on key issues for cost-effectiveness analyses of gene therapy (e.g., eligibility criteria, predictability of response, unknown risks, long-term complications). There is also uncertainty about the possibility to absorb the cost of the "one-time, one-dose cure" by payers that are used to different payment models. An active partnership between regulators, payers, patients and health care professionals is key to identify patient sub-populations that might benefit the most from gene therapy, and to align the interests of patients (needing effective disease correction and improved quality of life) and pharma companies (reluctant to lose the profitability of lifelong repeated treatments). Educational programs will provide the healthcare chain with information on the strategy that is expected to transform morbidity and mortality patterns and how it should be regarded as part of the future therapeutic options in haemophilia.

[Successful treatment by switching from activated prothrombin complex concentrate to emicizumab therapy in a hemophilia A patient with inhibitors]

A 7-month-old male infant with severe hemophilia A who received on-demand therapy with recombinant factor VIII (rFVIII) vomited because of acute intracranial bleeding. With rFVIII treatment for suppressing bleeding, there was development of high-titer (≤673 BU/ml) inhibitors. The patient was administered bypassing agents followed by immune tolerance induction therapy (ITI) with 50 U/kg of FVIII thrice weekly. In addition, he was treated with weekly and thrice weekly prophylaxis with 50 U/kg of activated prothrombin complex concentrate (aPCC). Despite ITI and aPCC prophylaxis treatments, it was difficult to control the hemorrhage, and the annualized bleeding ratio (ABR) remained high (5-13 bleeding episodes per year). We started emicizumab 2 weeks after completing the administration of aPCC. Weekly subdermal injections of 1.5 mg/kg emicizumab after loading dramatically decreased ABR (one bleeding episode per year), although biweekly injections of 3 mg/kg emicizumab for several months were associated with one joint hemorrhage. Compared to regular aPCC administration, our observations suggest that weekly emicizumab treatments can improve the ABR in a hemophilia patient with inhibitors and improve the quality of life of patient without limitations in terms of school events.

[Emicizumab: a paradigm shift in hemophilia treatment]

Regular prophylaxis using clotting factor (F) VIII products to prevent hemorrhage in patients with hemophilia A results in considerable suppression in chronic arthropathy development and greatly improves their quality of life. However, there have been some concerns regarding hemostatic treatment for these patients, such as frequent intravenous infusion of FVIII and the development of FVIII inhibitors. A humanized recombinant anti-FIXa/FX bispecific antibody and FVIIIa cofactor function-mimetic (emicizumab) was developed. Several clinical trials have demonstrated that emicizumab remarkably decreases bleeding events by simple subcutaneous infusion and it is currently available as a regular infusion to prevent hemorrhage in congenital hemophilia A patients with or without FVIII inhibitors. There is now a paradigm shift in hemophilia treatment with emicizumab, which is a non-factor product. However, there are some concerns with emicizumab that require clinical attention, such as thromboembolism in cases of concomitant treatment with a bypassing agent, hemostasis monitoring, perioperative hemostatic management, and preventative effects in patients with a proactive lifestyle.

Efficacy of emicizumab prophylaxis versus factor VIII prophylaxis for treatment of hemophilia A without inhibitors: network meta-analysis and sub-group analyses of the intra-patient comparison of the HAVEN 3 trial

Objectives: To compare the efficacy of emicizumab prophylaxis with that of factor VIII (FVIII) prophylaxis in patients with hemophilia A without inhibitors using two approaches: network meta-analyses (NMA) and additional sub-group analyses from the HAVEN 3 trial.Methods: The NMA used data from trials identified using a systematic literature review and compared bleed rates in patients receiving emicizumab prophylaxis and patients receiving FVIII prophylaxis using a Bayesian, random effects generalized linear model with log link Poisson likelihood. Additional sub-groups of the HAVEN 3 trial included here were defined as patients whose dose-taking behavior met either European label or World Federation of Hemophilia guidelines. A negative binomial regression model was used to conduct an intra-patient comparison of bleed rates within the sub-groups, during treatment with FVIII prophylaxis before entering HAVEN 3 and treatment with emicizumab prophylaxis during HAVEN 3.Results: Four studies were included in the base-case NMA. Evidence showed that the total treated bleed rate was lower with emicizumab prophylaxis compared with FVIII prophylaxis (rate ratio [RR] = 0.36 [95% credible interval (CrI) = 0.13-0.95]). Similar associations were observed in sensitivity analyses. The additional HAVEN 3 analyses also showed lower rates of treated bleeds with emicizumab prophylaxis than with FVIII prophylaxis (RRs [95% confidence interval (CI)] = 0.380 [0.186-0.790] and 0.472 [0.258-0.866] in two sub-groups). These results confirm the original HAVEN 3 intra-patient comparison findings.Conclusions: Combined findings from NMA and additional sub-group analyses of HAVEN 3 support the superiority of emicizumab prophylaxis over FVIII prophylaxis in patients with hemophilia A without inhibitors.

The evolution of recombinant factor replacement for hemophilia

Hemophilia A and Hemophilia B are the most common of the severe bleeding disorders and are caused by a deficiency in blood clotting factor VIII or factor IX respectively. Factor replacement therapy has been the cornerstone of treatment to treat life threatening bleeds and prevent joint disease. The treatment of hemophilia has evolved tremendously over the past five decades from fresh frozen plasma as the only available therapy to more specific plasma-derived and recombinant-derived factor replacement. Now due to innovations in bioengineering, there are even more efficacious factor replacement options available to patients. Here we review these recent advancements and their impact on the treatment and management of hemophilia.

[Emicizumab, a bispecific antibody mimicking factor VIII: a novel alternative therapy for hemophilia A with inhibitors]

Regular prophylaxis using factor (F) VIII products to prevent bleeding in patients with hemophilia A (PWHAs) results in markedly suppressed onset of arthropathy and greatly contributes to improved quality of life. However, some issues remain with the use of clotting factor replacement therapy. The need for multiple intravenous infusions is associated with substantial mental and physical burden, and the inhibitor development results in difficulty of hemostatic management. To overcome these unmet needs, a recombinant humanized anti-FIXa/FX bispecific antibody mimicking FVIIIa function (emicizumab) was created. In phase 1/2 clinical studies, Japanese patients with PWHAs were treated with once-weekly subcutaneous administration of emicizumab. The annual bleeding rates were markedly reduced, irrespective of inhibitor use. A phase 3 global study for PWHA with inhibitor demonstrated a statistically significant efficacy, whereas thrombotic microangiopathy and thromboembolism were reported in 5 patients treated with emicizumab concomitantly with multiple infusions of activated prothrombin complex concentrates. In Japan, emicizumab (HEMLIBRA^®) was approved for treatment of PWHAs with inhibitor on March 2018. In conclusion, emicizumab has promising features. Its subcutaneous bioavailability and long half-life (T1/2; approximately 30 days) enable effective bleeding prophylactic treatment at inhibitor status. Additional studies are warranted to establish clinical data on its safety and to define suitable assays for hemostatic monitoring.

Hemophilia in a Changing Treatment Landscape

The mainstay of hemophilia management has been the regular, prophylactic infusion of missing coagulation factors VIII/IX. This approach is limited by the need for frequent intravenous infusions, high cost, limited availability, and the development of inhibitory antibodies to factors VIII/IX. Numerous recent breakthroughs are addressing many of these limitations. These include the development of extended half-life factors that require less frequent infusions and the development of various novel agents that can be given subcutaneously and infrequently, including FVIII-mimetic antibody and downregulators of natural anticoagulants. Finally, gene therapy is set to offer patients a possibility for a cure.

[Congenital hemophilia: a new treatment paradigm]

Hemophilia is the most common congenital coagulation disorder, characterized by a tendency to bleed severely. Treatment is based on the replacement of defective FVIII or FIX. Following the introduction of recombinant FVIII and FIX, the treatment paradigm of the disease is shifting from episodic to prophylactic treatment with regular the infusion of factor concentrates. Since 2000, several new recombinant FVIII and FIX products with longer half-life have been developed by pegylation protein modification and other technologies, resulting in improved quality of life for patients with hemophilia. Recently, therapeutics with novel hemostatic mechanisms have been developed to overcome several unmet needs. FVIII (a), mimicking bispecific antibody recognizing FIX (a) /FX, has been approved in Japan. The product has several advantages, including a much longer half-life spanning 30 days, subcutaneous injectability, and effectiveness irrespective of the presence of FVIII inhibitor. The paradigm of hemophilia treatment is now shifting towards intact joint function and higher activity.

Emicizumab (ACE910): Clinical background and laboratory assessment of hemophilia A

Congenital hemophilia A, a relatively common and sometimes life-threatening bleeding disorder, is caused by inherited deficiency of clotting factor (F) VIII. The adoption of an appropriate medical and environmental prophylaxis is critical for long-term management of hemophilia because it will considerably reduce the number of both mild and severe bleeding episodes. Among the many therapeutic options that have become available over the past decades, ACE910 (also known as emicizumab) is a bispecific immunoglobulin G antibody characterized by its unique ability to bind FIX or FIXa on one arm and FX on the other, thus abrogating FVIII activity in vivo. Several phase I to III clinical trials have now been published, confirming the clinical efficacy and relative safety of this new agent for long-term prophylaxis of hemophilia A, especially those patients having FVIII inhibitors. The recent regulatory clearance of ACE910 in many countries will hence impose additional challenges to clinical laboratories because the panel of available tests will need to address the emerging issue of monitoring patients treated with this novel anti-hemophilic agent by using conventional as well as innovative approaches. Therefore, this article is aimed to provide an update on clinical background and challenges of laboratory assessment in hemophilia A patients undergoing ACE910 administration.

Emicizumab for routine prophylaxis to prevent bleeding episodes in patients with hemophilia A

Hemophilia A is an X-linked bleeding disorder caused by defects in the gene encoding factor VIII (FVIII). Routine prophylaxis with exogenous FVIII requires frequent intravenous injections. One of the most challenging issues in the treatment of hemophilia A is the development of alloantibodies against infused FVIII. Presence of inhibitors results in an ineffective factor replacement therapy and increases the risk of morbidity and mortality in these patients. Therefore, there is growing interest in the development of new strategies for the prophylaxis and prevention of bleeding in patients with hemophilia to circumvent these drawbacks. Emicizumab (ACE-910; Roche, Genentech and Chugai Pharmaceutical) is a recombinant humanized bispecific antibody that restores the function of missing FVIII by bridging activated FIX and FX, simulating the cofactor function of FVIII.

The Potential Close Future of Hemophilia Treatment - Gene Therapy, TFPI Inhibition, Antithrombin Silencing, and Mimicking Factor VIII with an Engineered Antibody

Summary Hemophilia is one of the best researched monogenic diseases. Hemophilia A will affect approximately 1:5,000 male live births. In recent decades, great progress has been made with the introduction of recombinant proteins in the 1990s for therapy and prophylaxis, securing adequate availability and, with the introduction of the prophylaxis concept, reducing the negative impact of hemophilia on morbidity (especially arthropathy). Despite this progress, there are still challenges to overcome to secure adequate prophylaxis and treatment: for the time being, causal pharmacological hemophilia prophylaxis and therapy requires repeated i.v. application on a regular basis. Although this approach leads to a reduced comorbidity, it does not yet represent an optimized approach with continuous reversal of the hemophilic defect, which would be the ideal solution. This review summarizes the very new treatment strategies for the treatment of hemophilia A and B.