Emicizumab Use in Treatment of Acquired Hemophilia A: A Case Report

Inhibitor eradication and treatment for acquired hemophilia A

INTRODUCTION

Acquired hemophilia A (AHA) is a rare hemorrhagic autoimmune disorder characterized by autoantibodies against coagulation factor VIII (FVIII). In approximately half of the cases AHA does not recognize any cause (idiopathic form), while in the other cases it may be triggered by autoimmune disorders, cancers, drugs, infections, or pregnancy. Besides treating the underlying disorder, specific AHA treatment includes management of bleeding, if necessary, and inhibitor eradication.

AREAS COVERED

This narrative review summarizes the main epidemiological, clinical, laboratory, and therapeutic characteristics of AHA. In particular, it is focused on the current therapeutic options for the inhibitor eradication, also showing the latest findings on the innovative therapies. A literature search strategy was performed, without temporal limits, through Medline and PubMed electronic databases.

EXPERT OPINION

Various first-line and second-line immunosuppressive agents are currently available for the management of AHA. Among the latter, the anti-CD20 monoclonal antibody rituximab has been the object of intense research during the last years from investigators as innovative promising eradicating therapy for AHA. Preliminary data from the studies support the use of this drug as a first-line option for newly diagnosed AHA cases.

Emicizumab for acquired hemophilia A: Report of two cases and dosing strategies

Acquired hemophilia A (AHA) is a rare autoimmune bleeding disorder caused by autoantibodies against FVIII. Severe AHA is life-threatening. Currently, licensed hemostatic agents for the treatment of severe AHA have short half-lives and require intravenous administration, leading to a need for hospitalization, higher costs, and negative effects on quality of life. We present two cases of severe AHA with high inhibitor titers where emicizumab was safely and effectively used with intensive immunosuppression. These reports suggest in vivo efficacy even in high inhibitor environments. The optimal dosing regimen (accelerated vs. standard loading, maintenance frequency) is unknown and we discuss the current approaches.

Emicizumab in acquired hemophilia A: pros and cons of a new approach to the prevention and treatment of bleeding

Emicizumab, a monoclonal bispecific antibody that mimics the function of activated factor VIII (FVIII), is currently licensed for prophylactic use in patients with congenital hemophilia A with and without inhibitors. Acquired hemophilia A (AHA) is a very rare bleeding disorder caused by the development of autoantibodies that inhibit FVIII activity in plasma; males and females are equally affected. Therapeutic options for patients with AHA currently include eradication of the inhibitor with immunosuppressive treatments and management of acute bleeding with bypassing agents or recombinant porcine FVIII. More recently, several reports described the off-label use of emicizumab in patients with AHA and a phase III study is ongoing in Japan. The aims of this review are to describe the 73 reported cases, and to highlight the advantages and disadvantages of this novel approach to the prevention and treatment of bleeding in AHA.

Acquired Hemophilia A: Bleeding Pattern and Hemostatic Therapeutic Strategies

Acquired Hemophilia A (AHA) is a rare autoimmune disorder characterized by the onset of a sudden and unexpected bleeding episode in a patient with no personal or family history of bleeding diathesis, and with a typical laboratory feature, i.e., a prolonged activated partial thromboplastin time that is not otherwise explained. This bleeding disorder is caused by autoantibodies directed against the coagulation factor VIII (FVIII). AHA is idiopathic in 50% of cases and is secondary to well-defined diseases in the remaining 50%. AHA affects elderly patients although it has also been observed in the post-partum period. Bleeding manifestations are heterogeneous, ranging from mild to life-threatening bleeds involving limbs and organs. Severe bleeding with a significant decrease in hemoglobin levels must be promptly and adequately treated in order to avoid a worsening of the hemorrhages and their complications. According to international recommendations, the bypass agents (i.e., activated prothrombin complex concentrate and activated recombinant factor VII) and the replacement therapy with recombinant porcine FVIII are considered as the first-line therapy for bleeding control, due to their proven clinical efficacy. Plasma-derived or recombinant FVIII concentrates could be used as second-line treatments. Emicizumab may represent a valid and interesting therapeutic option for prophylaxis of bleeding recurrences.

Hemophilia B: A Pain in the Back

This case report describes an unusual manifestation of hemophilia B, in the form of a lateral chest wall hematoma. A 27-year-old hemophiliac male was found to have a lateral chest wall hematoma after presenting with back pain associated with localized chest wall swelling. Even more unusual than the location of his hematoma was the absence of any preceding triggers such as a fall or trauma to the area. To our knowledge, this is the first reported case of its kind in a patient with inherited hemophilia B. We believe the reporting of such rare presentations increases awareness of these possibilities and thus aids in the prompt diagnosis and treatment of other similar cases when they are encountered.

Acquired Hemophilia A: An Update on the Etiopathogenesis, Diagnosis, and Treatment

Acquired haemophilia A (AHA) is a rare bleeding disorder caused by inhibitory autoantibodies against coagulation factor VIII (FVIII). AHA is a disease that most commonly affects the elderly but has also been observed in children and in the postpartum period. AHA is idiopathic in 50% of cases and is associated with autoimmune diseases, malignancies, and infections in the remaining 50%. Recently, cases of association between AHA, COVID-19 vaccination, and infection have been reported in the literature. For diagnoses, determining FVIII levels is crucial to distinguish the different causes of aPTT prolongation. Treatment of AHA is based on bypassing agents (recombinant factor VIIa, activated prothrombin complex concentrate) and porcine FVIII to control the bleeding and immunosuppressive therapy (corticosteroids, rituximab, cyclophosphamide) to suppress autoantibody production. It is important to start a prophylactic regimen to prevent further bleeding episodes until the inhibitor is negative. Recently, the series of cases reported in the literature suggest that emicizumab may provide effective and safe haemorrhage prophylaxis in the outpatient setting.

Review of Potential Barriers to Effective Hemostatic Management of Acquired Hemophilia A by Non-Hemophilia Experts in the United States

Acquired hemophilia A (AHA) is an ultra-rare autoimmune disorder caused by autoantibodies against factor VIII. It often presents with life-threatening bleeding to non-hemophilia experts, who have limited awareness of this condition. This review evaluated hemostatic management and identified barriers to optimal management of AHA by non-hemophilia experts in the United States through a literature review. AHA case reports published by non-hemophilia experts from January 2016 through November 2021 in non-hematology journals were critically reviewed for a chronology of clinical course and management, consultation with a hemophilia expert, referencing of available AHA recommendations, discussion of all hemostatic options, and bleed control outcomes; 24 case reports representing 24 patients were identified. Twelve patients had an apparent delay in diagnosis, 17 cases did not seek expert consultation, and 15 did not reference the 2009 International AHA Recommendations, including six in whom hemostatic treatment was not consistent with the recommendations. Of the 17 articles published after the 2017 AHA Guidance, eight did not reference them. Of the five articles published after the 2020 International Recommendations for AHA, three did not reference them. Overall, 14 articles did not discuss all available hemostatic treatment options. Four patients died. Our findings reveal variability in hemostatic management of AHA by non-hemophilia experts in the United States. Lack of AHA awareness remains a primary barrier for optimal management of AHA among non-hemophilia experts. Increasing education about existing AHA guidelines, including available therapies and access to expert care at hemophilia treatment centers, may help improve the outcomes of patients with AHA.

Emicizumab: a novel drug in hemophilia A prophylaxis - a narrative review

INTRODUCTION

Hemophilia A is a genetically conditioned disease leading to hemostatic disorders due to factor VIII (FVIII) deficiency. The treatment of hemophilia has evolved throughout the past years and has significantly changed. One of the newest drugs for prophylactic treatment is the humanized bispecific IgG antibody - emicizumab, which binds with factor IXa and factor X, bridging those factors and thus mimicking the activity of factor VIII.

AREAS COVERED

The literature search was made via PubMed database, with the emphasis on clinical trials and case reports, describing the off-label emicizumab use. This review presents an extensive summary and considers advantages and disadvantages (side-effects) of emicizumab, describing additional clinical situations, where emicizumab has been successfully used. In our review we cover information about the mechanisms of action, indications, efficacy and discuss some chosen case reports about off-label emicizumab use.

EXPERT OPINION

Its convenient administration method (subcutaneous) and frequency of injections (from once a week to once a month) makes it a more comfortable treatment, limiting injection-site reactions, hospital stays, costs of prophylaxis, and significantly increasing patients' quality of life. Adverse effects are scarce and rarely serious - the most common ones are reactions at the injection-site and upper respiratory tract infections.

Recombinant porcine factor VIII in acquired hemophilia A: Experience from two patients and literature review

Background

Acquired hemophilia A (AHA) is a disease caused by antibody formation inhibiting the function of factor VIII, causing bleeding. Recombinant porcine factor VIII (rpFVIII) escapes human FVIII antibody recognition and can provide life-saving hemostasis. However, the development of antibodies against pFVIII can limit its use. We report two cases in which loss of response to rpFVIII occurred, likely because of inhibiting antibodies. In case 1, the patient achieved hemostasis but lost response to rpFVIII within a few days. In the second case, rpFVIII controlled bleeding but the patient experienced diminishing half-life of rpFVIII infusions over time, necessitating a switch to emicizumab which provided lasting hemostasis.

Key Clinical Question

Based on our experience with these cases, we reviewed the available literature regarding the use of rpFVIII in AHA. The Key Clinical Question was to determine how often inhibitors were associated with rpFVIII treatment failure.

Clinical approach and conclusions

We identified 43 AHA patients across five studies who were treated with rpFVIII. Twenty-two patients (51%) developed pFVIII inhibitors and seven cases (16%) reported loss of efficacy associated with an inhibitor. In conclusion, rpFVIII can be a life-saving therapy in AHA. However, clinicians should be aware that pFVIII antibody development can reduce the efficacy and duration of response. Recombinant pFVIII's limitations support the utility of further investigation of alternative therapies such as emicizumab in early AHA management.

Refractory acquired haemophilia A in a patient with HIV treated with Emicizumab

Acquired haemophilia is a rare coagulopathy characterized by acquired inhibitors directed against clotting factors resulting in bleeding episodes. A middle-aged woman with HIV developed refractory haemophilia with bleeding episodes resulting in recurrent hospitalizations despite several rounds of bypassing agents and several lines of immunosuppressive agents. She was eventually successfully treated with Emicizumab and has not had any major bleeding episodes for 3 years since initiation of this treatment. Emicizumab, which is a bispecific, FVIII-mimetic therapeutic antibody, has considerably reduced the annualized bleeding rates in congenital haemophiliacs with and without inhibitors and should be considered as an agent for acquired haemophilia to reduce recurrent bleeding episodes and even decrease inhibitor titer.

Anticoagulation for Stroke Prevention after Restoration of Haemostasis with Emicizumab in Acquired Haemophilia A

Acquired haemophilia A (AHA) is a rare haemorrhagic disorder caused by the development of autoantibodies inhibiting factor VIII function. It predominantly affects the elderly, who are often burdened with a considerable number of comorbidities, and can result in life-threatening bleeding. The management of AHA consists of two aspects: inhibitor eradication with an immunomodulator and bleed control with a bypassing agent. Here we present a case of AHA with a high titre inhibitor in a patient with extensive comorbidities and atrial fibrillation in whom inhibitor eradication could not be achieved within a few weeks using corticosteroids alone. Due to coronavirus disease (COVID)-19 restrictions and complications of care, emicizumab offered an effective and convenient therapy, not only sparing the need for continued and intensified inhibitor eradication, but also allowing anticoagulation for stroke prophylaxis.

LEARNING POINTS

Emicizumab may offer a suitable option for bleeding prophylaxis when inhibitor eradication is not achievable with immunotolerance treatment, especially in the age of the COVID-19 pandemic when the consequences of immunosuppression can be detrimental.Bleeding prophylaxis with emicizumab may enable long-term anticoagulation in patients with acquired haemophilia A during inhibitor eradication.The prothrombotic risks of emicizumab are not yet sufficiently characterized.

Off-label use of emicizumab in persons with acquired haemophilia A and von Willebrand disease: A scoping review of the literature

INTRODUCTION

Since the approval of emicizumab, a bispecific, factor VIII-mimetic antibody, for use in persons with congenital haemophilia A in 2018, there have been increasing case reports and case series of off-label use of emicizumab in other bleeding disorders, including acquired haemophilia A (AHA) and von Willebrand disease (VWD).

AIM

We conducted a scoping review on the use of emicizumab in AHA and VWD, focusing on the clinical presentation and outcomes.

METHODS

We conducted a comprehensive search in PubMed, EMBASE and Scopus up to July 15, 2021. The following criteria were applied to the studies identified in the initial search: patients had a diagnosis of AHA or VWD; and the study reported on the clinical outcome of emicizumab use.

RESULTS

Seventeen studies were included in the final review for a total of 41 patients (33 AHA, eight type 3 VWD). The majority of AHA patients and all type 3 VWD patients were started on emicizumab for active/recurrent bleeds. The dosing regimen of emicizumab used varied significantly in AHA patients. All patients had a clinical response to emicizumab use. One AHA patient developed a stroke on emicizumab use in association with concomitant recombinant FVIIa use for surgery. Data on adverse events from emicizumab use were not specifically reported in 24.4% of patients (four AHA, six type 3 VWD).

CONCLUSION

Based on published case reports and case series, emicizumab appears to be an effective haemostatic therapy for AHA and VWD. Larger confirmatory clinical trials are needed to confirm these findings.

Acquired Hemophilia A

Acquired hemophilia A is a potentially severe bleeding disorder caused by antibodies against the patient's own factor VIII. Acquired hemophilia A is rare. It is most commonly diagnosed in older individuals; about one-half of cases of acquired hemophilia are associated with underlying conditions, including autoimmune disease, cancer, and pregnancy. The diagnosis of acquired hemophilia A can be suspect with an isolated activated partial thromboplastin time elevation, and confirmed with demonstration of reduced factor VIII activity and the presence of a specific factor VIII inhibitor. Treatment of acquired hemophilia A involves control of bleeding, and eradication of the inhibitor.

A low-dose rituximab regimen for first-line treatment of acquired haemophilia A

A low-dose rituximab regimen for first-line treatment of acquired haemophilia A.

INTRODUCTION

Acquired haemophilia A (AHA) is a rare disease caused by the development of autoantibodies against FVIII. Diagnosis involves confirmation of FVIII deficiency and the presence of an inhibitor via the Bethesda assay. Severe bleeding is often managed with bypassing agents such as recombinant factor VII. This is then followed by eradication of the inhibitor with immunosuppression which typically includes a corticosteroid backbone.

AIM

Review the current management and outcomes of AHA in Queensland, Australia. Determine the incidence, demographics and clinical characteristics of AHA patients.

METHODS

Retrospective case series of AHA diagnosed between May 2014 and August 2018. Data were derived from the Australian Bleeding Disorders Registry and state-wide pathology database. Data collection proforma was completed by the treating haematologist and reviewed/compiled centrally.

RESULTS

24 patients were identified (incidence 1 in 1.27 million). The median age was 76.5 years. Median follow-up was 20 months. Index bleed was atraumatic and skin/soft tissue in the majority of patients. Recombinant FVIIa was the most commonly used haemostatic therapy and effective in 85% of patients. Immunosuppression and steroid usage were uniform. Upfront second agent was used in 75% of patients and was most commonly rituximab. 87.5% of patients achieved a complete remission in a median time of 48 days. Low-dose rituximab was frequently used and equally as efficacious as standard dose.

CONCLUSION

Immunosuppression with combination therapy, notably rituximab, appears to be non-inferior and has a favourable side effect profile.

Emicizumab in acquired haemophilia A: about two clinical cases and literature review

Acquired haemophilia A (AHA) is a rare and severe haemorrhagic autoimmune disease caused by autoantibodies directed against factor VIII (FVIII). Treatment is based on two principles, including haemostatic control to compensate FVIII inhibition and eradication of inhibiting antibodies using immunosuppressive therapy. Rapid recognition and proper management are essential to avoid excess morbidity and mortality. Effective and safe treatments can be challenging, given that AHA patients are often elderly, with multiple comorbidities. Emicizumab, a bispecific antibody that mimics the action of FVIII, has proven effective in managing patients with congenital haemophilia, with or without inhibitors. Likewise, its mode of action suggests theoretical efficacy in AHA patients. We herein describe two AHA cases with comorbidities that were treated effectively using emicizumab combined with immunosuppressive therapy. We have also reviewed the current literature regarding the promising use of emicizumab in this indication.

Emicizumab for the treatment of acquired hemophilia A

Acquired hemophilia A (AHA) is a severe bleeding disorder caused by inhibiting autoantibodies to coagulation factor VIII (FVIII). For hemostatic treatment, bypassing agents and human or porcine FVIII are currently standard of care. Emicizumab is a bispecific, FVIII-mimetic therapeutic antibody that reduced the annualized bleeding rates in congenital hemophiliacs. Here, we report on 6 male and 6 female patients with AHA treated with emicizumab (all data medians and interquartile range), age 74 (64-80) years, initial FVIII <1%; inhibitor titer 22.3 Bethesda units (BU)/mL (range, 3-2000). Eight patients had severe bleeding. Emicizumab was started, 3 mg/kg subcutaneously, weekly for 2 to 3 doses, followed by 1.5 mg/kg every 3 weeks to keep the lowest effective FVIII levels. For FVIII monitoring, chromogenic assays with human and bovine reagents were used. All patients received immunosuppression with steroids and/or rituximab. After the first dose of emicizumab, activated partial thromboplastin time normalized in 1 to 3 days, FVIII (human reagents) exceeded 10% after 11 (7.5-12) days. Hemostatic efficacy was obtained and bypassing therapy stopped after 1.5 (1-4) days. FVIII (bovine reagents) exceeded 50%, indicating complete remission after 115 (67-185) days, and emicizumab was stopped after 31 (15-79) days. A median of 5 injections (range, 3-9) were given. No patient died of bleeding or thromboembolism, and no breakthrough bleeding was observed after the first dose of emicizumab. In conclusion, emicizumab seems to be an effective hemostatic therapy for AHA, with the advantages of subcutaneous therapy, good hemostatic efficacy, early discharge, and reduction of immunosuppression and adverse events.

Principles of care for acquired hemophilia

Objective

To establish clear priorities for the care of patients with acquired hemophilia A (AHA) by proposing 10 key principles of practical, holistic AHA management.

Method

These principles were developed by the Zürich Haemophilia Forum, an expert panel of European hemophilia specialists comprising physicians and nursing and laboratory specialists.

Results

The 10 proposed principles for AHA care are as follows: (a) Improving initial diagnosis of AHA; (b) Differential diagnosis of AHA: laboratory assessment of patients with unusual bleeding; (c) Effective communication between laboratories, physicians, and specialists; (d) Improving clinical care: networking between healthcare professionals in the treating hospital and specialist hemophilia centers; (e) Comprehensive assessment of bleeding; (f) Appropriate use of bypassing agents; (g) Long‐term follow‐up and monitoring for efficacy and safety of immunosuppressive treatment; (h) Inpatient/outpatient settings; (i) Access to innovative and disruptive treatments; (j) Promotion of international collaborative research.

Conclusion

The proposed principles for holistic AHA care aim to ensure swift diagnosis and optimal patient management. Key to achieving this goal is training for healthcare personnel in non‐specialist hospitals and collaboration between different specialists. We hope these principles will increase awareness of AHA in the wider medical community and catalyze efforts toward improving its practical, multidisciplinary management.

Hemostatic therapy as a management strategy for acquired hemophilia: what does the future hold?

Introduction: Acquired hemophilia A (AHA) is a rare autoimmune disease caused by autoantibodies that bind and inactivate factor VIII (FVIII), predisposing to a potentially life-threatening bleeding.Areas covered: The main epidemiological, clinical, laboratory and therapeutic features of AHA are critically discussed. In particular, we focus on the hemostatic management of AHA patients analyzing the currently available treatment options and showing the latest data on the innovative hemostatic agents still under investigation. Authors searched the Medline and PubMed electronic databases for publication on AHA in the last twenty years.Expert opinion: While a rapid recognition of suspected cases of AHA is essential to make a correct diagnosis and appropriately and timely treat the hemorrhagic manifestations, the multidisciplinary approach to this challenging, rare and life-threatening bleeding disorder is of equal importance to improve patients' outcome. Although promising, the safety and efficacy of the clinical use of emicizumab in AHA needs to be validated by trials including an adequate number of patients, before registering the drug also for this indication.

Should emicizumab be used in patients with acquired hemophilia A?

Emicizumab is currently approved to prevent bleeding in patients with congenital hemophilia A with or without neutralizing antibodies (inhibitors) against factor VIII (FVIII). Here, we present a case-based discussion of its potential use in acquired hemophilia A (AHA), a severe bleeding disorder caused by autoantibodies against FVIII. State-of-the-art management is based on bypassing agents (recombinant factor VIIa, activated prothrombin complex concentrate) and recombinant porcine FVIII; immunosuppressive therapy (corticosteroids, rituximab, cyclophosphamide) is used to suppress autoantibody formation. Case reports and one series suggest that emicizumab can reduce the risk of bleeding and the requirement for hemostatic therapy until remission of AHA is achieved. Further, it may allow to postpone the start of immunosuppressive therapy or to use less intense regimens. However, the risk-benefit assessment of emicizumab in AHA is difficult because demographic and clinical characteristics are different compared with congenital hemophilia. Prospective clinical trials are needed before the use of emicizumab can be recommended in AHA.

Ex Vivo Prediction of Comprehensive Coagulation Potential Using Simulated Blood Concentrations of Emicizumab in Patients with Acquired Hemophilia A

INTRODUCTION

 Emicizumab prophylaxis improves coagulation function in congenital hemophilia A, regardless of inhibitor presence. We recently reported that emicizumab enhanced the coagulant potentials, ex vivo, in plasmas from patients with acquired hemophilia A (PwAHAs) at diagnosis. However, coagulant effects of emicizumab in PwAHAs during the clinical course remain unclear.

AIM

 To assess ex vivo coagulant effects of emicizumab in PwAHAs during the clinical course.

METHODS/RESULTS

 Blood samples were obtained from 14 PwAHAs on (median) days 0 and 6 during a severe-bleeding phase, and days 27 and 59 during a reduced-bleeding phase with elevated endogenous factor VIII (FVIII) and decreased inhibitor titers. If administered a single dose of 3 or 6 mg/kg, or two doses at 6 mg/kg followed by 3 mg/kg, estimated plasma emicizumab concentrations (10/5/2.5, 20/10/5, and 30/15/7.5 µg/mL on days 0-7/30/60, respectively) could be used to represent potential changes, based on the half-life (T _1/2: ∼30 days). Emicizumab concentrations that covered maximum plasma concentrations of each dosage were used for spiking on day 0. Ex vivo addition of estimated emicizumab to PwAHA's plasma containing endogenous FVIII and/or inhibitor, without and with recombinant (r)FVIIa administration during immunosuppressive therapy, increased the calculated Ad|min1| values, assessed by clot waveform analysis, and their coagulant potentials were below normal levels. Rotational thromboelastometry revealed that ex vivo emicizumab addition resulted in the further improvement of coagulant potentials in whole bloods when combined with rFVIIa administration.

CONCLUSION

 Based on ex vivo and in vitro data, emicizumab has the potential to be effective in clinical situations for PwAHAs.

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.

Reduced-intensity, risk factor-stratified immunosuppression for acquired hemophilia A: single-center observational study

Immunosuppressive therapy (IST) is administered to patients with acquired hemophilia A (AHA) to eradicate autoantibodies against coagulation factor VIII (FVIII). Data from registries previously demonstrated that IST is often complicated by adverse events, in particular infections. This pilot study was set out to assess the feasibility of reduced-intensity, risk factor–stratified IST. We followed a single-center consecutive cohort of twenty-five patients with AHA receiving IST according to a new institutional treatment standard. Based on results from a previous study, GTH-AH 01/2020, patients were stratified into “poor risk” (FVIII < 1 IU/dl or inhibitor ≥ 20 Bethesda units (BU)/ml) or “good risk” (FVIII ≥ 1 IU/dl and inhibitor < 20 BU/ml). Outcomes were compared between the current cohort and the GTH registry as a historic control (n = 102). Baseline characteristics of the cohort were not different from the historic control. Partial remission, defined as FVIII recovered to > 50 IU/dl, was achieved by 68% of patients after a median time of 112 days, which was lower and significantly later than in the historic control (hazard ratio: 1.8, 95% confidence interval 1.2–2.8). Complete remission, overall survival, and frequency of fatal infections were not different. Grade 3 and 4 infections were more frequent. The impact of risk factors that was observed in the historic cohort was no longer apparent, as partial and complete remission and overall survival were similar in “good risk” and “poor risk” patients. In conclusion, reduced-intensity, risk factor–stratified IST is feasible in AHA but did not decrease the risk of infections and mortality in this cohort.

Acquired Haemophilia A: An Intriguing Disease

Abstract. Acquired Haemophilia A is a rare acquired bleeding disorder caused by Factor VIII autoantibodies, which neutralise FVIII activity. These inhibitors differ from alloantibodies against FVIII, which can occur in congenital Haemophilia A after repeated exposures to plasma-derived or recombinant FVIII products. In most cases, the disease occurs suddenly in subjects without a personal or familiar history of bleedings, with symptoms that may be mild, moderate, or severe. However, only laboratory alterations are present in ~ 30% of patients. The incidence varies from 1 to 4 cases per million/year; more than 80% of patients are elderly, males and females are similarly affected. There is a small peak of incidence related to pregnancy in young women aged 20–40 years. The disease may be underdiagnosed in the elderly. The diagnostic algorithm is based on an isolated prolonged activated partial thromboplastin time, normal thrombin time, absence of Lupus Anticoagulant, and a mixing test that reveals the presence of an inhibitor: the finding of reduced FVIII activity and the detection of neutralising autoantibodies against FVIII lead to the diagnosis. The disease is idiopathic in 44%–63% of cases, while in the others etiological factors are present. Bleeding prevention and treatment are based on therapeutic tools as by-passing agents, recombinant porcine FVIII concentrate or, in a limited number of cases, FVIII concentrates and desmopressin. As soon as the diagnosis has been made, immunosuppressive therapy must be started to eradicate the inhibitor. Better knowledge of the disease, optimal management of bleeding and eradication of the inhibitor have significantly reduced morbidity and mortality in most patients.

Utilization of Emicizumab in Acquired Factor VIII Deficiency

BACKGROUND Acquired hemophilia A (AHA) is a rare autoimmune disease caused by immunoglobulins that bind and inactive factor VIII, thereby predisposing to life-threatening bleeding. Bleeding is typically stabilized by utilizing bypassing agents, such as recombinant factor VIIa (rVIIa). Select case reports have demonstrated the success of alternative prophylaxis for clearance of factor VIII inhibitors through the use of emicizumab, a current FDA approved medication for treatment of congenital hemophilia A. In this case report we present the efficacy of utilizing emicizumab as a prophylactic agent in a patient that was unable to tolerate first-line therapy for prophylaxis. CASE REPORT A 91-year-old male presented for ongoing hematuria for 5 weeks with prior workup unrevealing. He was given a day's course of recombinant factor VIIa to stabilize his bleeding and was started on cyclophosphamide and prednisone after a revealing hematological workup including activated partial thromboplastin time (aPTT) >100 seconds and factor VIII inhibitor level of 44 BU/mL. He continued to require VIIa infusions to control his bleeding and was started on emicizumab once stabilized. His bleeding remained controlled and his inhibitor decreased after 6 months of therapy with repeat factor VIII inhibitor level of 1.9 BU/mL. CONCLUSIONS The success of utilizing emicizumab for bleeding prophylaxis in AHA is demonstrated by this patient's resolution of bleeding. The high frequency of dosing and higher risk for thrombosis with factor VIIa, in conjunction with our patient's medical history and ease of administration, make emicizumab an ideal agent for bleeding prophylaxis while awaiting clearance of factor VIII inhibitors.

Novel Insights and New Developments Regarding Coagulation Revealed by Studies of the Anti-Factor IXa (Activated Factor IX)/Factor X Bispecific Antibody, Emicizumab

Emicizumab is a humanized anti-FIXa/FX (factor IXa/X) bispecific monoclonal antibody that mimics FVIIIa (activated factor VIII) cofactor function. The hemostatic efficacy of emicizumab has been confirmed in clinical studies of patients with hemophilia A, irrespective of the presence of FVIII inhibitors. Emicizumab differs in some properties from FVIIIa molecule. Emicizumab requires no activation by thrombin and is not inactivated by activated protein C, but emicizumab-mediated coagulation is regulatable and maintains hemostasis. A small amount of FIXa (activated factor IX) is required to initiate emicizumab-mediated hemostasis, whereas tissue factor/FVIIa (activated factor VII)-mediated FXa (activated factor X) and thrombin activation initiates FVIIIa-mediated hemostasis. Fibrin formation, followed by fibrinolysis, appears to be similar between emicizumab- and FVIIIa-mediated hemostasis. These results suggest possible future uses of emicizumab for treating hemorrhagic diseases other than hemophilia A and reveal previously unobservable behaviors of procoagulation and anticoagulation factors in conventional hemostasis. Here, we have reviewed novel insights and new developments regarding coagulation highlighted by emicizumab.

An anti-factor IXa/factor X bispecific antibody, emicizumab, improves ex vivo coagulant potentials in plasma from patients with acquired hemophilia A

INTRODUCTION

Acquired hemophilia A (AHA) is caused by autoantibodies against factor (F)VIII, and is characterized by severe, spontaneous bleeding, which can be life-threatening. Emicizumab, an anti-FIXa/FX bispecific antibody, significantly reduces bleeding events in congenital hemophilia A (HA) with and without inhibitors. The known pathophysiological mechanisms and current preclinical data in HA suggest that emicizumab could provide effective treatment for AHA, but the coagulation activities of emicizumab in these patients remain unknown.

AIM

To evaluate the coagulant effects of emicizumab in plasma from AHA patients.

METHODS AND RESULTS

Tissue factor-triggered thrombin generation assays using normal plasma preincubated with anti-FVIII monoclonal antibodies recognizing different epitopes demonstrated that 20 µg/mL emicizumab recovered the depressed peak levels of thrombin generation to 46% to 72%. Further studies were devised, therefore, to simulate the clinical course in AHA patients, including during the acute phase for severe bleeding requiring FVIII-bypassing therapy, and during the subacute/chronic phase with less bleeding. Various concentrations of emicizumab were used to represent the potential changes in plasma levels based on the half-life of the antibody (~30 days). The ex vivo addition of emicizumab to plasma samples from AHA patients (n = 16) increased peak thrombin in all cases, irrespective of the inhibitor epitope specificity. Thrombin generation at 20 and 100 µg/mL emicizumab was restored to (median) 43.9% and 92.2%, respectively. Differences were evident in some cases, however, and recovery rates appeared likely to be greater in patients with type 2 inhibitor than those with type 1.

CONCLUSION

Emicizumab improved ex vivo coagulation potential in plasma from AHA patients.