Review of recombinant anti-haemophilic porcine sequence factor VIII in adults with acquired haemophilia A

Strategies for Performing Factor Assays in the Presence of Emicizumab or Other Novel/Emerging Hemostatic Agents

For several decades, therapeutic options for inherited deficiencies of factor VIII or IX (hemophilia A or B, respectively) have largely been the replacement of the missing clotting factor with plasma-derived or recombinant products. Hemostasis laboratories use standard activated partial thromboplastin time (aPTT)-based clotting or chromogenic assays to monitor plasma factor levels to guide therapy. The emergence in the past 10 years of extended half-life replacement products and other novel therapies for hemophilia has led to a reappraisal of assay suitability, with studies of product measurement showing some existing assay types or reagents to be unsuitable for some products. The hemostasis laboratory must adapt to the changing landscape by adding new assays or modifying existing assays to ensure accurate results for product measurement. These strategies include switching from a chromogenic assay to a clotting assay, or vice versa, changing an aPTT reagent brand, or introducing product specific calibrators. This article evaluates the effects of some of the newer treatment options on the laboratory testing of factor levels and related assays.

Clot formation and fibrinolysis assays reveal functional differences among hemostatic agents in hemophilia A plasma

Background

Measuring the activity of hemostatic agents used to treat hemophilia A often requires drug-specific assays. In vitro assays show hemophilic clots have abnormal characteristics, including prolonged clotting time and decreased resistance to fibrinolysis. The ability of certain agents to correct these parameters in vitro is associated with hemostatic efficacy in vivo.

Objectives

To compare effects of established and emerging hemostatic agents on clot formation and fibrinolysis in hemophilia A plasma.

Methods

Pooled and individual hemophilia A platelet-poor plasmas were spiked with replacement (recombinant factor VIII [rFVIII], PEGylated rFVIII, polysialylated rFVIII, and porcine rFVIII) or bypassing (emicizumab, rFVIIa, and activated prothrombin complex concentrate) products. Effects on tissue factor-initiated clot formation and fibrinolysis were measured by turbidity.

Results

Compared to normal pooled plasma, hemophilia-pooled plasma showed reduced clot formation and increased fibrinolysis, and all replacement agents improved these characteristics. rFVIII and PEGylated rFVIII produced similar effects at similar concentrations, whereas polysialylated rFVIII produced slightly higher and porcine rFVIII slightly lower effects at these concentrations. Bypassing agents enhanced clot formation and stability, but patterns differed from replacement agents. The clotting rate showed a concentration-response relationship for all agents. High concentrations of all products produced effects that exceeded the normal range in at least some parameters. Responses of individual donors varied, but all agents improved clot formation and stability in all donors tested.

Conclusion

Clotting and fibrinolysis assays reveal hemostatic effects of replacement and bypassing therapies at clinically relevant concentrations. These assays may help characterize hemostatic agents and optimize dosing.

Hybrid human-porcine factor VIII proteins partially escape the inhibitory effects of anti-factor VIII inhibitor alloantibodies having A2 or C2 domain specificity

INTRODUCTION

Porcine factor (pF)VIII has low cross-reactivity with anti-human (h)FVIII inhibitor alloantibodies. Clinical trials of pFVIII in congenital haemophilia A patients with inhibitor (PwHA-I) are in progress. Most polyclonal anti-hFVIII inhibitors recognize its A2 and/or C2 domain(s), and recombinant human-porcine hybrid (hp)FVIII proteins may escape neutralization by these inhibitors.

AIM

To evaluate the ability of hpFVIII to limit the anti-FVIII activity of inhibitor alloantibodies.

METHODS

Three hybrid proteins were created by substituting the hFVIII A2, C2 domain or both with the corresponding domains of pFVIII [termed hp(A2), hp(C2) and hp(A2/C2), respectively]. The reactivity of these hybrids was assessed by one-stage clotting assays (OSA), thrombin generation assays (TGA) and rotational thromboelastometry (ROTEM) by adding them to FVIII-deficient samples.

RESULTS

OSA demonstrated that the hybrid proteins avoided neutralization by anti-FVIII A2 or C2 monoclonal antibodies (mAb) and polyclonal inhibitor-antibodies (polyAb) from PwHA-I. In TGA, thrombin generation with hp(A2) and hp(A2/C2) was not attenuated in the presence of patient IgG recognizing anti-A2 domain. In contrast, that with hFVIII and hp(C2) was suppressed by this IgG to levels equivalent to those of FVIII-deficient plasma. With anti-A2/C2 polyAb, the activity of hp(A2/C2) was unaffected. ROTEM demonstrated that the addition of hp(A2) or hp(A2/C2) to anti-A2 polyAb shortened clot times/clot formation times, whilst hFVIII or hp(C2) were ineffective. Similarly with anti-A2/C2 polyAb, hp(A2/C2) restored coagulation potential to a greater extent than hp(A2) and hp(C2).

CONCLUSION

Hybrid FVIII proteins containing porcine FVIII A2 and/or C2 domain(s) could support effective therapy in PwHA-I by avoiding neutralization.

Real-world safety and effectiveness of recombinant porcine sequence factor VIII in acquired haemophilia A: A non-interventional, post-authorization safety study

INTRODUCTION

Recombinant porcine factor VIII (rpFVIII, susoctocog alfa) is indicated for the treatment of bleeding episodes in adults with acquired haemophilia A (AHA).

AIM

To provide long-term real-world safety and effectiveness data for rpFVIII in the management of AHA bleeding episodes.

METHODS

US PASS (NCT02610127) was a multicentre, uncontrolled, open-label, post-marketing safety surveillance study conducted in adults with AHA. Data were collected retrospectively or prospectively for 180 days after rpFVIII treatment. The primary outcome was the incidence of treatment-related serious adverse events (SAEs). Secondary outcomes included haemostatic effectiveness of rpFVIII and rpFVIII utilization.

RESULTS

Fifty-three patients were enrolled from December 2015 to June 2019 (prospective, n = 30; retrospective, n = 23). Six patients experienced seven treatment-related SAEs (incidence 12.0%). The most common treatment-related SAE was FVIII inhibition (inhibiting antibodies to rpFVIII; incidence 8.0%, 95% CI: 2.2-19.2). Five patients reported seven thromboembolic events; one was an SAE and possibly related to rpFVIII. Of bleeding events treated with rpFVIII, 80.3% (57/71) of bleeds resolved with rpFVIII. The median (range) dose of rpFVIII per infusion was 50 (10-300) units/kg, with a median (range) of 6.0 (1-140) infusions and a median (range) time from bleed onset to bleed resolution of 14.0 (2.0-132.7) days.

CONCLUSION

In this real-world study of rpFVIII for AHA, no new safety signals were identified compared with previous clinical trial findings. Eighty percent of bleeds resolved with rpFVIII treatment.

Acquired Haemophilia A: A Review of What We Know

Autoantibodies against plasma coagulation factors could be developed by some individuals inducing severe and sometimes fatal bleedings. This clinical entity is called acquired haemophilia. It should be suspected in subjects with acute abnormal bleedings, without personal or familiar history of congenital bleeding disorders with an unexplained prolonged aPTT. It is rare disease, although its incidence may be underestimated due to the low knowledge about it by many specialists, the frequent use of anticoagulant or antiplatelet therapies in the affected population that can mask the diagnosis and, sometimes, a so withering effect that avoid its confirmation. Mortality ranges between 9% and 33% depending on the series in the first 2 months after diagnosis. This mortality is attributed in up to 40% of the cases to infections in the context of immunosuppressive treatments used to eliminate the inhibitor. Factor VIII levels below 1% and high inhibitor titers are conditions of worse response rates. Advanced age, patient's ECOG, and underlying conditions are key prognostic factors for response to treatment and patient survival. To reduce morbidity and mortality in these patients, it is important to have clinical knowledge and access to guidelines to achieve an early diagnosis and to optimize the haemostatic and immunosuppressive treatment. This review aims to contribute to the dissemination of basic concepts on the epidemiology etiopathogenesis, diagnosis, treatment and management of these patients, as well as risk factors to get remission and the longest overall survival to allow individualized care. Especial awareness will be proposed in patients with some underlying conditions like cancer, autoimmune diseases, children, pregnancy or drugs.

Acquired bleeding disorders

Acquired bleeding disorders can accompany hematological, neoplastic, autoimmune, cardiovascular or liver diseases, but can sometimes also arise spontaneously. They can manifest as single factor deficiencies or as complex hemostatic abnormalities. This review addresses (a) acquired hemophilia A, an autoimmune disorder characterized by inhibitory autoantibodies against coagulation factor VIII; (b) acquired von Willebrand syndrome in patients with cardiovascular disorders, where shear stress abnormalities result in destruction of von Willebrand factor; and (c) liver function disorders that comprise complex changes in pro- and anti-hemostatic factors, whose clinical implications are often difficult to predict. The article provides an overview on the pathophysiology, diagnostic tests and state-of-the-art treatment strategies.

Recombinant porcine factor VIII corrects thrombin generation in vitro in plasma from patients with congenital hemophilia A and inhibitors

Background

Neutralizing factor VIII (FVIII) antibodies are a major complication in hemophilia A. Antihemophilic factor VIII (recombinant), porcine sequence (rpFVIII; susoctocog alfa; Baxalta US Inc., a Takeda company) has low cross-reactivity to anti-human FVIII antibodies and can provide functional FVIII activity in the presence of FVIII inhibitors.

Objectives

Evaluate in vitro thrombin generation and clot formation responses to rpFVIII in blood from patients with congenital hemophilia A.

Methods

In this multicenter study, blood was obtained for in vitro analyses that included human and porcine FVIII inhibitors, low <5 Bethesda units (BU)/ml or high ≥5 BU/ml titer (Nijmegen-modified Bethesda assay); thrombin generation assay (TGA), clot viscoelasticity (thromboelastography), fibrin clot structure analysis (scanning electron microscopy), and epitope mapping.

Results

Blood samples were from 20 patients with congenital hemophilia A (FVIII activity <1%, mean [range] inhibitor titers: anti-human FVIII, 14 [1-427] BU/ml [n = 13 high, n = 6 low, n = 1 data unavailable]); anti-porcine FVIII, 12 (0-886) BU/ml (n = 11 high, n = 8 low, n = 1 data unavailable). Porcine inhibitor titer and TGA response measured by endogenous thrombin potential showed an inverse correlation (2.7-10.8 U/ml rpFVIII Spearman correlation coefficient: -0.594 to -0.773; p < 0.01). Clot structures in low anti-porcine inhibitor titer plasmas were similar to those in noninhibitor plasma.

Conclusions

Recombinant porcine factor VIII demonstrated a dose-dependent correction of thrombin generation and clot formation in vitro, dependent on the anti-porcine FVIII inhibitor titer. Procoagulant responses to rpFVIII occurred in plasma containing FVIII inhibitors.

Management of Acquired Factor VIII Inhibitors With NovoSeven and Obizur

Acquired hemophilia A (AHA) is a rare hemorrhagic disorder caused by the production of autoantibodies against coagulation factor VIII (FVIII). AHA is associated with significant morbidity and mortality primarily as a result of bleeding. Although many disorders are associated with the development of these inhibitors, up to 50% of cases remain idiopathic. The approach to therapy involves an initial strategy often to control acute bleeding episodes followed by definitive treatment to eradicate the inhibitor with immunosuppressive agents. We present the case of a 63-year-old Caucasian male hospitalized for severe Covid-19 who developed bleeding due to an acquired FVIII inhibitor that had never been treated definitively. Our case presentation focuses on in-hospital management of this patient's acute bleeding episodes with by-passing agents and recombinant porcine factor VIII.

Unexplained hemorrhagic syndrome? Consider acquired hemophilia A or B

There is a dire need to develop an algorithm to improve the recognition of acquired hemophilia A and B (AHA and AHB) in clinical practice. Initial and intensive care unit (ICU) management of the disorder is particular and represents a challenge for the internist/hematologist and the ICU physician. A delay in the proper treatment of bleeding episodes can lead to a life-threatening event. Expert advice should be sought as soon as possible. Succesful resolution involves accurate diagnosis, bleeding control with hemostatic and immunotherapy, and eradication of the autoantibodies to improve overall survival. Current treatment guidelines are based on the literature in the form of cases and observational studies due to a lack of randomized controlled trials. AH can be triggered by many pathologies, presenting as a paraneoplastic syndrome in case of malignancies or as surgical associated acquired hemophilia (SAHA). We have reviewed the literature from 2015 to 2021 regarding the new case reports to further assess if there is an improvement in the clinical approach.

Treatment of high-risk bleeding with susoctocog alfa in a patient with acquired haemophilia A and a nosocomial severe acute respiratory syndrome coronavirus 2 infection

We report the case of a man in his early 70s with idiopathic acquired haemophilia A and persistent high-titre type II inhibitors on immunosuppressive treatment to eradicate the inhibitor. As complications, he had a nosocomial severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which caused severe pneumonia and an explosive inflammatory reaction that required tocilizumab and remdesivir treatment, and a high-risk retroperitoneal haematoma. Recombinant porcine factor VIII, susoctocog alfa, was requested from the Pharmacy Service in view of the extreme risk of thromboembolism resulting from the concomitant inflammatory storm caused by SARS-CoV-2. Improvement in the SARS-CoV-2 infection made it possible to complete the immunosuppressive treatment with rituximab. The patient was discharged with mycophenolate mofetil as immunosuppressive treatment after 89 days in hospital and 22 days of treatment with susoctocog alfa. His SARS-CoV-2 infection resolved and the haematoma evolved favourably.

Recombinant porcine FVIII for bleed treatment in acquired hemophilia A: findings from a single-center, 18-patient cohort

Acquired hemophilia A (AHA) is a rare bleeding disorder in which acquired autoantibodies to endogenous factor VIII (FVIII) decrease FVIII activity and lead to a bleeding phenotype. A substantial majority of individuals who develop AHA present with severe bleeding. Effective treatment requires both immunosuppressive therapy and prompt hemostatic treatment. Bleeding is commonly treated with bypassing agents (BPAs) such as recombinant activated FVII (rFVIIa) or activated prothrombin complex concentrates Disadvantages to BPAs include the inability to monitor response with standard laboratory assays, inconsistent hemostatic efficacy, and thrombosis. Recombinant porcine FVIII (rpFVIII: Obizur, Baxter, Deerfield, IL) was approved by the US Food and Drug Administration (FDA) for bleed treatment in AHA in 2014, and has the advantage of laboratory monitoring of FVIII activity levels and known hemostatic efficacy in the presence of anti-human FVIII inhibitors and after failure of BPAs. Using an algorithm-based approach, rpFVIII has been used to successfully treat 18 patients with AHA at our center with substantially lower doses than the current FDA-recommended dosing. Additionally, data from our cohort show that the preexposure anti-porcine Bethesda titer does not reliably predict the clinical response to rpFVIII treatment and is not correlated with the anti-human Bethesda titer. We also present data showing lower total rpFVIII use for initial bleed resolution when rpVIII is used upfront, as compared with use as rescue therapy. We validated our dosing algorithm, which uses much lower than FDA-recommended doses with 14 more patients than in our previously reported patient series.

Minimal Essential Human Factor VIII Alterations Enhance Secretion and Gene Therapy Efficiency

One important limitation for achieving therapeutic expression of human factor VIII (FVIII) in hemophilia A gene therapy is inefficient secretion of the FVIII protein. Substitution of five amino acids in the A1 domain of human FVIII with the corresponding porcine FVIII residues generated a secretion-enhanced human FVIII variant termed B-domain-deleted (BDD)-FVIII-X5 that resulted in 8-fold higher FVIII activity levels in the supernatant of an in vitro cell-based assay system than seen with unmodified human BDD-FVIII. Analysis of purified recombinant BDD-FVIII-X5 and BDD-FVIII revealed similar specific activities for both proteins, indicating that the effect of the X5 alteration is confined to increased FVIII secretion. Intravenous delivery in FVIII-deficient mice of liver-targeted adeno-associated virus (AAV) vectors designed to express BDD-FVIII-X5 or BDD-FVIII achieved substantially higher plasma FVIII activity levels for BDD-FVIII-X5, even when highly efficient codon-optimized F8 nucleotide sequences were employed. A comprehensive immunogenicity assessment using in vitro stimulation assays and various in vivo preclinical models of hemophilia A demonstrated that the BDD-FVIII-X5 variant does not exhibit an increased immunogenicity risk compared to BDD-FVIII. In conclusion, BDD-FVIII-X5 is an effective FVIII variant molecule that can be further developed for use in gene- and protein-based therapeutics for patients with hemophilia A.

Acquired bleeding disorders

Acquired bleeding disorders can accompany hematological, neoplastic, autoimmune, cardiovascular or liver diseases, but can sometimes also arise spontaneously. They can manifest as single factor deficiencies or as complex hemostatic abnormalities. This review addresses (a) acquired hemophilia A, an autoimmune disorder characterized by inhibitory autoantibodies against coagulation factor VIII; (b) acquired von Willebrand syndrome in patients with cardiovascular disorders, where shear stress abnormalities result in destruction of von Willebrand factor; and (c) liver function disorders that comprise complex changes in pro- and anti-hemostatic factors, whose clinical implications are often difficult to predict. The article provides an overview on the pathophysiology, diagnostic tests and state-of-the-art treatment strategies.

Advances in managing rare acquired bleeding disorders

INTRODUCTION

Rare acquired bleeding disorders include a wide spectrum of coagulopathies characterized by spontaneous or post-trauma and post-surgery hemorrhages in patients without a previous personal or family history of bleeding.

AREAS COVERED

This review, based on a Medline/PubMed search during the last 20 years, will focus mainly on rare acquired bleeding disorders caused by autoantibodies against coagulation factors, including autoantibodies against factor VIII (acquired hemophilia A), von Willebrand factor (acquired von Willebrand syndrome) and other coagulation factors (factors V, X, XI, and XIII). The pathogenic, laboratory, and clinical features of these rare hemorrhagic conditions will be discussed, with particular attention to their management.

EXPERT OPINION

The treatment of rare acquired bleeding disorders includes the control of bleeding and the elimination of the autoantibody and of the underlying disease, when present. As the bleeding clinical phenotype is often severe, the management of affected patients is particularly challenging. Thus, while an early diagnosis of the acquired coagulopathy is essential to start the most appropriate treatment and to improve patients' outcomes, the support of specialized centers is equally important to provide a correct management of such complicated cases.

Cross-reacting inhibitors against recombinant porcine factor VIII in acquired hemophilia A: Data from the GTH-AH 01/2010 Study

BACKGROUND

Recombinant porcine factor VIII (rpFVIII, OBI-1, susoctocog alfa) is used for the treatment of acute bleeds in patients with acquired hemophilia A (AHA). Inhibitors in AHA can sometimes cross-react with rpFVIII.

OBJECTIVES

To assess the frequency, strength, and determinants of cross-reactivity.

PATIENTS/METHODS

Baseline samples from 70 patients of the prospective, observational cohort study GTH-AH 01/2010 were assessed for anti-human FVIII and anti-rpFVIII inhibitors using modified Nijmegen-Bethesda assays, as well as anti-human FVIII domain reactivity using enzyme-linked immunoassay (ELISA).

RESULTS

Anti-human FVIII inhibitors were present in all samples ranging between 0.7 and 3891 Bethesda Units (BU)/mL. Inhibitors from 31 of 70 patients (44%) partially inhibited rpFVIII with anti-rpFVIII titers ranging between 0.5 and 471 BU/mL. Anti-rpFVIII titers were ≤5 BU in most patients. Patients with cross-reacting inhibitors, as compared to patients without, had significantly higher anti-human FVIII titers (27.8 versus 5.4 BU/mL) and lower baseline FVIII activity (<1 versus 2.6 IU/dL). The ratio between anti-rpFVIII to anti-human titers was highest for inhibitors involving the C1 domain. Cross-reactivity was very rare, if inhibitors reacted only with the C2 domain of FVIII (6%). An anti-human FVIII titer of >100 BU/mL predicted cross-reactivity with 97% likelihood, whereas an anti-human FVIII titer of <3.8 BU/mL predicted absent cross-reactivity with 90% likelihood.

CONCLUSION

Cross-reacting inhibitors should be considered when choosing a treatment for bleeding patients with AHA. Cross-reactivity is frequent in patients with anti-human FVIII titers of >100 BU/mL.

An economic analysis of different treatments for bleeding in patients with acquired haemophilia

BACKGROUND

Acquired haemophilia A (AHA), with potentially high risk of morbidity and mortality, occurs as a result of inhibitors against factor VIII. Bleeding due to AHA can be treated with activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa) or recently, recombinant porcine-sequence factor VIII (rpFVIII). We extended our previous cost-effectiveness analysis (CEA) comparing rpFVIII against the available traditional options.

METHODS

For high-titred, haemorrhaging AHA patients treated with either aPCC, rFVIIa or rpFVIII, over the course of 6-days, a Markov simulation was conducted to evaluate the outcomes when these patients transitioned into any of the four following health states: (1) continuous bleeding, (2) thrombosis, (3) stop bleeding and (4) death, with states (2), (3) and (4) modelled as absorbing states. All model parameters were obtained from the medical literature, except the costs of aPCC, rFVIIa and the factor VIII assay, which came from our institutional data.

RESULTS

Excluding the cost of the initial treatment on day 0, the total subsequent treatment cost of rFVIIa was substantially more than the costs of aPCC and rpFVIII ($13 925 vs. $1778 vs. $6957, respectively). The average quality-adjusted life days (QALDs) gained from rpFVIII was lowest (4·89 vs. 4·9 for rFVIIa and 4·91 for aPCC). Overall, aPCC dominated the other two treatments. The model was determined to be robust across the tested ranges for all input variables.

CONCLUSION

Based on this economic model, for AHA patients with high titres who were bleeding, aPCC was the most cost-effective treatment option and may be considered for use if there is no clinical contraindication.

Acquired Hemophilia A: A Case Report

Hemophilia A, also known as factor VIII deficiency, is a rare disorder caused by an insufficient level of factor VIII, an essential clotting protein. Hemophilia A can be inherited or acquired. Inherited hemophilia A is caused by a mutation to the factor VIII gene on the X chromosome, which is commonly passed down from parents to children. However, in about one-third of cases, the cause is a spontaneous mutation in that gene. Acquired hemophilia A is due to an autoantibody to factor VIII, which is termed an inhibitor. This rare disorder can cause life-threatening bleeding complications. Management relies on a rapid and accurate diagnosis, control of bleeding episodes, and eradication of the inhibitor by immunosuppression therapy. Most treatment strategies are centered around anecdotal reports or small case series. This case report summarizes the successful treatment of a patient with acquired hemophilia A and major bleeding following a surgical procedure, with the use of desmopressin, recombinant factor VIIa, repeated doses of recombinant factor VIII, rituximab, and prednisone.

Management of Acquired Hemophilia A in Elderly Patients

This report describes six elderly patients with acquired hemophilia A (AHA), including four individuals aged ≥90 years. Bleeding symptoms were subcutaneous or intramuscular hemorrhage (n=4), hematuria (n=1), and hemorrhagic shock after tooth extraction (n=1). Factor VIII (FVIII) activity ranged from <1.0% to 3.0%, and anti-FVIII inhibitor titers ranged from 8.8 to 240 BU/mL. Treatment was administered at the discretion of the responsible physician. Hemostatic agents applied in the six patients comprised rFVIIa (NovoSeven®) (n=4), APCC (Feiba®) (n=2), and fresh frozen plasma/plasma exchange (n=1). Agents employed for inhibitor eradication comprised prednisolone only (n=3), prednisolone with cyclophosphamide (n=1), prednisolone with cyclosporine (n=1), and prednisolone with rituximab (n=1). In five patients, management was successful, with complete response. Treatment failed in the patient with the highest inhibitor level (240 BU/mL) in whom treatment with APCC (Feiba®; 100 U/kg/dose, three doses) and prednisolone (0.5 mg/kg/day) was followed by several episodes of relapse. The present data demonstrate that AHA severity shows wide variation in elderly subjects, indicating the necessity of individualized management.