Emicizumab prophylaxis among infants and toddlers with severe hemophilia A and inhibitors-a single-center cohort

The changing treatment landscape in haemophilia: from standard half-life clotting factor concentrates to gene editing

Congenital haemophilia A (factor VIII deficiency) and B (factor IX deficiency) are X-linked bleeding disorders. Replacement therapy has been the cornerstone of the management of haemophilia, aiming to reduce the mortality and morbidity of chronic crippling arthropathy. Frequent intravenous injections are burdensome and costly for patients, consequently with poor adherence and restricted access to therapy for many patients worldwide. Bioengineered clotting factors with enhanced pharmacokinetic profiles can reduce the burden of treatment. However, replacement therapy is associated with a risk for inhibitor development that adversely affects bleeding prevention and outcomes. Novel molecules that are subcutaneously delivered provide effective prophylaxis in the presence or absence of inhibitors, either substituting for the procoagulant function of clotting factors (eg, emicizumab) or targeting the natural inhibitors of coagulation (ie, antithrombin, tissue factor pathway inhibitor, or activated protein C). The ultimate goal of haemophilia treatment would be a phenotypical cure achievable with gene therapy, currently under late phase clinical investigation.

Establishment of a framework for assessing mortality in persons with congenital hemophilia A and its application to an adverse event reporting database

BACKGROUND

Despite recent therapeutic advances, life expectancy in persons with congenital hemophilia A (PwcHA) remains below that of the non-HA population. As new therapies are introduced, a uniform approach to the assessment of mortality is required for comprehensive evaluation of risk-benefit profiles, timely identification of emerging safety signals, and comparisons between treatments.

OBJECTIVES

Develop and test a framework for consistent reporting and analysis of mortality across past, current, and future therapies.

PATIENTS/METHODS

We identified known causes of mortality in PwcHA through literature review, analysis of the US Food and Drug Administration Adverse Event Reporting System (FAERS) database, and expert insights. Leading causes of death in general populations are those recognized by the Centers for Disease Control and Prevention and the World Health Organization. We developed an algorithm for assessing fatalities in PwcHA and used this to categorize FAERS data as a proof of concept.

RESULTS

PwcHA share mortality causes with the non-HA population including cardiovascular disease, malignancy, infections, pulmonary disease, dementias, and trauma/suicide. Causes associated with HA include hemorrhage, thrombosis, human immunodeficiency virus, hepatitis C virus, and liver dysfunction. We propose an algorithm employing these classes to categorize fatalities and use it to classify FAERS fatality data between 01/01/2000 and 03/31/2020; the most common causes were hemorrhage (22.2%) and thrombosis (10.4%).

CONCLUSIONS

A conceptual framework for examining mortality in PwcHA receiving any hemophilia therapy is proposed to analyze and interpret fatalities, enabling consistent and objective assessment. Application of the framework using FAERS data suggests a generally consistent pattern of reported mortality across HA treatments, supporting the utility of this unified approach.

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.

Comparison of bypassing agents in patients on emicizumab using global hemostasis assays

INTRODUCTION

Emicizumab is a humanized bispecific monoclonal antibody licensed for patients with severe haemophilia A with and without inhibitors. Management of breakthrough bleeding in patients with inhibitors on emicizumab involves episodic treatment with bypassing agents (BPA), activated prothrombin complex concentrate (aPCC) or recombinant activated factor VII (rFVIIa). Thrombotic events and thrombotic microangiopathy were reported when patients on emicizumab received concomitant aPCC at relatively high doses yet such events were not reported with rFVIIa. We studied the effect of spiking various concentrations of BPA on plasma taken from patients on emicizumab.

MATERIAL AND METHODS

Eleven patients with severe haemophilia A with inhibitors who are on emicizumab were recruited to participate. Blood samples drawn from patients were spiked in vitro with varying concentrations of aPCC and rFVIIa. All samples were tested utilizing global haemostasis assays, thromboelastography and thrombin generation assay.

RESULTS

Thrombin generation increased with higher concentrations of spiked BPA with a normalized endogenous thrombin potential at a concentration of 0.05 IU/ml and 4 mcg/ml for aPCC and rFVIIa, respectively. Concentrations of aPCC in the range of licensed dosing led to excessive thrombin generation. Thromboelastography was not sufficiently sensitive.

CONCLUSION

Due to the known thrombotic complications when emicizumab is used in conjunction with aPCC, there has been a large-scale abandonment of the use of aPCC in patients on emicizumab. However, it is possible that aPCC can be used safely with emicizumab albeit with lower doses than are typically prescribed. It would be important to test this hypothesis in a clinical study.

Bridging the Missing Link with Emicizumab: A Bispecific Antibody for Treatment of Hemophilia A

Hemophilia A, characterized by absent or ineffective coagulation factor VIII (FVIII), is a serious bleeding disorder that entails severe and potentially life-threatening bleeding events. Current standard therapy still involves replacement of FVIII, but is often complicated by the occurrence of neutralizing alloantibodies (inhibitors). Management of patients with inhibitors is challenging and necessitates immune tolerance induction for inhibitor eradication and the use of bypassing agents (activated prothrombin complex concentrates or recombinant activated factor VII), which are expensive and not always effective. Emicizumab is the first humanized bispecific monoclonal therapeutic antibody designed to replace the hemostatic function of activated FVIII by bridging activated factor IX and factor X (FX) to activate FX and allow the coagulation cascade to continue. In the majority of hemophilic patients with and without inhibitors, emicizumab reduced the annualized bleeding rate to almost zero in several clinical trials and demonstrated a good safety profile. However, the concurrent use of emicizumab and activated prothrombin complex concentrate imposes a high risk of thrombotic microangiopathy and thromboembolic events on patients and should be avoided. Yet, the management of breakthrough bleeds and surgery remains challenging with only limited evidence-based recommendations being available. This review summarizes published clinical trials and preliminary reports of emicizumab and discusses the clinical implications of emicizumab in treatment of hemophilia A.

Clinical Evidence and Safety Profile of Emicizumab for the Management of Children with Hemophilia A

Emicizumab is a bispecific, humanized, monoclonal antibody mimicking the factor (F) VIII cofactor activity in mediating the generation of FXa by FIXa in patients with hemophilia A (HA). This subcutaneous non-factor agent has been recently extensively approved for the prophylaxis of patients of HA patients with and without FVIII-inhibitors of all ages, although few data are currently available in children. In Phase 3 clinical trials and case series, emicizumab prophylaxis significantly reduced bleeding rates compared to previous treatment in HA adolescents and children with or without FVIII-inhibitors and was generally well tolerated. In addition, subcutaneous administration of emicizumab provided beneficial effects on health-related quality of life, and lessened the burden of the disease in HA patients as well as in their caregivers. However, additional prospective studies are required to evaluate the long-term safety of emicizumab prophylaxis in very young patients, including previously untreated patients. The aim of this paper was to review the limited data available on the use of emicizumab prophylaxis in children and to highlight the need for further studies to address remaining concerns.

Economic impact model of delayed inhibitor development in patients with hemophilia a receiving emicizumab for the prevention of bleeding events

Aims: Cumulative exogenous factor VIII (FVIII) exposure is an important predictor of developing neutralizing antibodies (inhibitors) to FVIII in patients with persons with hemophilia A (PwHA). The aim of this study was to model the costs of emicizumab versus FVIII prophylaxis and total treatment costs for patients with severe HA.Materials and Methods: An Excel-based decision model was developed to calculate cumulative costs in PwHA over a 20-year time horizon from the US payer perspective. The model considered persons with severe HA beginning at age 12 months with no prior FVIII exposure and initiating prophylaxis with emicizumab or FVIII. PwHA could develop inhibitors on accumulation of 20 FVIII exposure days. PwHA with inhibitors replaced FVIII with bypassing agents until inhibitors resolved spontaneously, following immune tolerance induction (ITI), or at the end of the time horizon. The primary model outcome was the difference in emicizumab versus FVIII treatment costs in 2019 USD. Sensitivity analyses were performed to test the robustness of results.Results: Total incremental cost over 20 years was -$1,945,480 (emicizumab arm, $4,919,058; FVIII arm, $6,864,538). Prophylaxis costs (emicizumab arm, $4,096,105; FVIII arm, $6,290,919) comprised the majority of costs in both groups, followed by breakthrough bleed treatment for the FVIII arm ($342,652) and ITI costs for the emicizumab arm ($733,671). Higher costs in the FVIII group reflected earlier inhibitor development (FVIII, 4 months; emicizumab, 162 months) and switch to bypassing agents.Limitations: The model design reflects a simplified treatment pathway for patients with severe HA who initiate FVIII or emicizumab prophylaxis. In the absence of clinical data, a key conservative assumption of the model is that patients receiving emicizumab and FVIII prophylaxis have the same risk of developing inhibitors.Conclusions: This study suggests that prophylaxis with emicizumab results in cost savings compared to FVIII prophylaxis in HA.

Allergy and inhibitors in hemophilia - a rare complication with potential novel solutions

INTRODUCTION

Hemophilia is a rare bleeding disorder caused by a deficiency of the plasma coagulation factors VIII and IX (hemophilia A [HA] and hemophilia B [HB], respectively). Replacement therapy with clotting factor concentrates is the mainstay of treatment. Unlike in patients with HB, anaphylaxis in patients with HA is extremely rare.

METHODS

A retrospective study of prospectively collected data on patients with hemophilia who experienced anaphylaxis was conducted in our center. Demographic and clinical data were collected, and laboratory workups that included thrombin generation were conducted.

RESULTS

Our first patient underwent successful immune tolerance induction (ITI) following the administration of rituximab. The second patient was transitioned to emicizumab. The third patient receives recombinant activated VIIa (rFVIIa) on demand. Thrombin generation was performed following current medical management protocols for supporting hemostasis.

DISCUSSION

Our case series illustrates the difficulty in managing patients with anaphylaxis to replacement therapy. In the era of novel therapies, such as emicizumab, the management of HA patients who experience anaphylaxis to replacement therapy is becoming easier and may obviate the need for ITI. Current treatment strategies for HB patients with such anaphylaxis, however, are limited to rFVIIa, and it continues to pose a challenge.

Emergency management in patients with haemophilia A and inhibitors on prophylaxis with emicizumab: AICE practical guidance in collaboration with SIBioC, SIMEU, SIMEUP, SIPMeL and SISET

Emicizumab has been approved in several countries for regular prophylaxis in patients with congenital haemophilia A and FVIII inhibitors because it substantially reduces their bleeding risk and improves quality of life. However, although significantly less frequent, some breakthrough bleeds may still occur while on emicizumab, requiring treatment with bypassing or other haemostatic agents. Thrombotic complications have been reported with the associated use of activated prothrombin complex concentrates. In addition, when surgery/invasive procedures are needed while on emicizumab, their management requires multidisciplinary competences and direct supervision by experts in the use of this agent. Given this, and in order to expand the current knowledge on the use of emicizumab and concomitant haemostatic agents, and reduce the risk of complications in this setting, the Italian Association of Haemophilia Centres (AICE) here provides guidance on the management of breakthrough bleeds and surgery in emergency situations in patients with haemophilia A and inhibitors on emicizumab prophylaxis. This paper has been shared with other National Scientific Societies involved in the field.