ITI choice for the optimal management of inhibitor patients - from a clinical and pharmacoeconomic perspective

Preclinical studies of a factor X activator and a phase 1 trial for hemophilia patients with inhibitors

BACKGROUND

Bleeding episodes in hemophiliacs with inhibitors are difficult to control. Staidson protein-0601 (STSP-0601), a specific factor (F)X activator purified from the venom of Daboia russelii siamensis, has been developed.

OBJECTIVES

We aimed to investigate the efficacy and safety of STSP-0601 in preclinical and clinical studies.

METHODS

In vitro and in vivo preclinical studies were performed. A phase 1, first-in-human, multicenter, and open-label trial was conducted. The clinical study was divided into parts A and B. Hemophiliacs with inhibitors were eligible for this study. Patients received a single intravenous injection of STSP-0601 (0.01 U/kg, 0.04 U/kg, 0.08 U/kg, 0.16 U/kg, 0.32 U/kg, or 0.48 U/kg) in part A or a maximum of 6 4-hourly injections (0.16 U/kg) in part B. The primary endpoint for each part was the number of adverse events (AEs) from baseline to 168 hours after administration. This study was registered at clinicaltrials.gov (NCT-04747964 and NCT-05027230).

RESULTS

Preclinical studies showed that STSP-0601 could specifically activate FX in a dose-dependent manner. In the clinical study, 16 patients in part A and 7 patients in part B were enrolled. Eight (22.2%) AEs in part A and 18 (75.0%) AEs in part B were reported to be related to STSP-0601. Neither severe AEs nor dose-limiting toxicity events were reported. There were no thromboembolic event. The antidrug antibody of STSP-0601 was not detected.

CONCLUSION

Preclinical and clinical studies showed that STSP-0601 had a good ability to activate FX and had a good safety profile. STSP-0601 could be used as a hemostatic treatment in hemophiliacs with inhibitors.

Emicizumab for All Pediatric Patients with Severe Hemophilia A

Emicizumab is the first approved nonreplacement therapy for bleeding prophylaxis in hemophilia A (HA) patients. In 2018, it was licensed for HA patients with inhibitors, subsequently followed by an "European Medicines Agency (EMA)" approval for patients with severe HA in the absence of inhibitors in 2019. This is immediately raising the question whether emicizumab is suitable as a first-line treatment for all pediatric patients with severe HA. In this review, we want to discuss what we have, what we know, and what we would like to know. Severe HA is characterized by severe spontaneous and traumatic bleedings, particularly into muscles and joints leading to chronic joint damage. Standard of care is the regular, prophylactic replacement of factor VIII to prevent bleedings. Due to approval of emicizumab-the first nonreplacement therapy for bleeding prophylaxis-in HA patients with inhibitors, and severe HA patients without inhibitors, it is of pivotal interest whether emicizumab could be the first-line treatment in all pediatric patients with severe HA. Clinical trials and real-world observational studies could demonstrate a good efficacy and safety for bleeding prevention during emicizumab treatment in HA patients with and without inhibitors. This clearly indicates that emicizumab could improve HA treatment. However, some crucial and critical questions are remaining with regard to the use of emicizumab. Some of this missing information is already under investigation in the context of clinical trials. Until getting finalized data to shed insights into the points that are currently being discussed, there is a variety of expert and expert group recommendations, which are tackling questions concerning the treatment of HA patients. This review will address major information that is already available, but will also focus on important points that remain to be elucidated in the context of HA treatment.

Outcomes in children with hemophilia A with inhibitors: Results from a noninterventional study

BACKGROUND

Data regarding management of pediatric persons with hemophilia A (PwHA) with factor VIII (FVIII) inhibitors are limited. This prospective noninterventional study (NCT02476942) evaluated annualized bleeding rates (ABRs), safety, and health-related quality of life (HRQoL) in pediatric PwHA with FVIII inhibitors.

PROCEDURE

PwHA aged <12 years with current FVIII inhibitors and high-titer inhibitor history were enrolled. Participants remained on usual treatment; no interventions were applied. Outcomes included ABR, safety, and HRQoL.

RESULTS

Twenty-four PwHA aged 2-11 years (median 7.5) were enrolled and monitored for 8.7-44.1 weeks (median 23.4). In the episodic (n = 10) and prophylactic (n = 14) groups, respectively, 121 of 185 (65.4%) and 101 of 186 (54.3%) bleeds were treated using activated prothrombin complex concentrate (aPCC) and/or recombinant activated FVII (rFVIIa). ABRs (95% confidence interval) were 19.4 (13.2-28.4) and 18.5 (14.2-24.0) for treated bleeds, and 32.7 (20.5-52.2) and 33.1 (22.4-48.9) for all bleeds, respectively. Most prophylactic group participants (92.9%) were prescribed aPCC; 50% adhered to their prescribed treatment regimen. Adherence to prophylactic rFVIIa was not assessed. Serious adverse events included hemarthrosis (12.5%) and mouth hemorrhage (12.5%); the most common nonserious adverse event was viral upper respiratory tract infection (12.5%). HRQoL showed functional impairment at baseline; scores remained stable throughout, with little intergroup variation.

CONCLUSIONS

ABRs remained high in pediatric PwHA with inhibitors receiving standard treatment. This study demonstrates the need for more effective treatments, with reduced treatment burden, to prevent bleeds, increase prophylaxis adherence, and improve patient outcomes.

Low-dose Immune Tolerance Induction in Hemophilia: A Single-Center Experience

INTRODUCTION

The development of inhibitors against factors VIII/IX is the most serious complication in hemophilia. The best treatment strategy for inhibitor eradication is immune tolerance induction (ITI). The aim of this study was to evaluate patients treated with low-dose ITI at a single center with limited resources.

MATERIALS AND METHODS

In total, 29 (8.05%) of 360 hemophilia A patients exhibited inhibitors. The data from hemophilia patients with inhibitors undergoing ITI between 1999 and 2017 were collected and analyzed.

RESULTS

Seventeen ITIs administered to 15 hemophilia A patients with inhibitors were analyzed, and the data from 13 ITIs conducted in 12 patients were evaluated. The median age at ITI onset was 10 years (range: 1.25 to 52 y). The maximum inhibitor titer before ITI was 30 Bethesda Units (BU) (range: 4.48 to 135), and the median inhibitor titer was 1.25 BU (range: 0 to 5.6) at the onset of ITI. The median time interval between the inhibitor development and ITI onset was 60 months (range: 7 to 264 mo). The median inhibitor titer during ITI was 3.4 BU (range: 0 to 158.7). At the end of the treatment, 4 of the 12 patients (33.3%) exhibited a complete response, 4 (33.3%) had partial responses (with continuing ITI), and 4 (33.3%) exhibited ITI failure.

CONCLUSIONS

Treatment of hemophilia patients with inhibitors is challenging, and ITI is the best treatment method; however, a high-dose daily ITI regimen cannot be given to every patient in every country due to its high cost. Our results show that low-dose ITI may be a choice for selected patients with inhibitors.

Extended Half-Life Coagulation Factors: A New Era in the Management of Hemophilia Patients

Despite effective factor replacement and various treatment schedules, there remain several challenges and unmet needs in the prophylactic treatment of hemophilia limiting its adoption and thereby posing an increased risk of spontaneous bleeding. In this regard, extended half-life (EHL) recombinant factor VIII (rFVIII) and factor IX (rFIX) products promise optimal prophylaxis by decreasing the dose frequency, increasing the compliance, and improving the quality of life without compromising safety and efficacy. EHL products might lead to higher trough levels without increasing infusion frequency, or could facilitate the ability to maintain trough levels while reducing infusion frequency. This paper aims to provide a comprehensive review of the rationale for developing EHL coagulation factors and their utility in the management of hemophilia, with special emphasis on optimal techniques for half-life extension and criteria for defining EHL coagulation factors, as well as indications, efficacy, and safety issues of the currently available EHL-rFVIII and EHL-rFIX products. Potential impacts of these factors on quality of life, health economics, and immune tolerance treatment will also be discussed alongside the challenges in pharmacokinetic-driven prophylaxis and difficulties in monitoring the EHL products with laboratory assays.

Current and emerging biologics for the treatment of hemophilia

INTRODUCTION

The development of new biologic agents able to restore thrombin generation has become the focus of innovation in hemophilia management. There is growing interest in the proposal of novel, non-replacement therapy with alternative mechanisms of action and route of administration, hoping to solve still unmet needs in treatment of hemophilic patients with or without inhibitors.

AREAS COVERED

The review describes the new molecules, in particular the bi-specific antibody mimicking the coagulation function of FVIII and/or those which work by inhibiting the natural anticoagulants, their mechanism of action and the results of ongoing clinical trials.

EXPERT OPINION

Exciting results in enhancing the protection against bleeding and improving quality of life are emerging from clinical trials. However, these molecules with their mechanisms of action also open new problems. Treatment of bleeding and management of surgery in subjects with a rebalanced hemostasis may be difficult, especially for the lack of laboratory tests perfectly reflecting the in vivo coagulation status. A careful surveillance is required to evaluate the risk of thrombotic complication in patients with rebalanced hemostasis, in addition to understand whether these new products offer the same protection on joints as regular prophylaxis with the missing clotting factors.

Prevention of the anti-factor VIII memory B-cell response by inhibition of Bruton tyrosine kinase in experimental hemophilia A

Hemophilia A is a rare hemorrhagic disorder caused by the lack of functional pro-coagulant factor VIII. Factor VIII replacement therapy in patients with severe hemophilia A results in the development of inhibitory anti-factor VIII IgG in up to 30% of cases. To date, immune tolerance induction, with daily injection of large amounts of factor VIII, is the only strategy to eradicate factor VIII inhibitors. This strategy is, however, efficient in only 60-80% of patients. We investigated whether blocking B-cell receptor signaling upon inhibition of Bruton tyrosine kinase prevents anti-factor VIII immune responses in a mouse model of severe hemophilia A. Factor VIII-naïve and factor VIII-sensitized factor VIII-deficient mice were fed with the selective inhibitor of Bruton tyrosine kinase, (R)-5-amino-1-(1-cyanopiperidin-3-yl)-3-(4-[2,4-difluorophenoxyl] phenyl)-1H pyrazole-4-carboxamide (PF-06250112), to inhibit B-cell receptor signaling prior to challenge with exogenous factor VIII. The consequences on the anti-factor VIII immune response were studied. Inhibition of Bruton tyrosine kinase during the primary anti-factor VIII immune response in factor VIII-naïve mice did not prevent the development of inhibitory anti-factor VIII IgG. In contrast, the anti-factor VIII memory B-cell response was consistently reduced upon treatment of factor VIII-sensitized mice with the Bruton tyrosine kinase inhibitor. The Bruton tyrosine kinase inhibitor reduced the differentiation of memory B cells ex vivo and in vivo following adoptive transfer to factor VIII-naïve animals. Taken together, our data identify inhibition of Bruton tyrosine kinase using PF-06250112 as a strategy to limit the reactivation of factor VIII-specific memory B cells upon re-challenge with therapeutic factor VIII.

Inhibitors in haemophilia A and B: Management of bleeds, inhibitor eradication and strategies for difficult-to-treat patients

The standard therapy for patients with haemophilia is prophylactic treatment with replacement factor VIII (FVIII) or factor IX (FIX). Patients who develop inhibitors against FVIII/FIX face an increased risk of bleeding, and the likelihood of early development of progressive arthropathy, alongside higher treatment-related costs. Bypassing agents can be used to prevent and control bleeding, as well as the recently licensed prophylaxis, emicizumab, but their efficacy is less predictable than that of factor replacement therapy. Antibody eradication, by way of immune tolerance induction (ITI), is still the preferred management strategy for treating patients with inhibitors. This approach is successful in most patients, but some are difficult to tolerise and/or are unresponsive to ITI, and they represent the most complicated patients to treat. However, there are limited clinical data and guidelines available to help guide physicians in formulating the next treatment steps in these patients. This review summarises currently available treatment options for patients with inhibitors, focussing on ITI regimens and those ITI strategies that may be used in difficult-to-treat patients. Some alternative, non-ITI approaches for inhibitor management, are also proposed.

Tolerance induction in hemophilia: innovation and accomplishments

PURPOSE OF REVIEW

Hemophilia is an X-linked blood coagulation genetic disorder, which can cause significant disability. Replacement therapy for coagulation factor VIII (hemophilia A) or factor IX (hemophilia B) may result in the development of high-affinity alloantibodies ('inhibitors') to the replacement therapy, thus making it ineffective. Therefore, there is interest in directing immunological responses towards tolerance to infused factors.

RECENT FINDINGS

In this review, we will discuss latest advancements in the development of potentially less immunogenic replacement clotting factors, optimization of current tolerance induction protocols (ITI), preclinical and clinical data of pharmacological immune modulation, hepatic gene therapy, and the rapidly advancing field of cell therapies. We will also evaluate publications reporting data from preclinical studies on oral tolerance induction using chloroplast-transgenic (transplastomic) plants.

SUMMARY

Until now, no clinical prophylactic immune modulatory protocol exists to prevent inhibitor formation to infused clotting factors. Recent innovative technologies provide hope for improved eradication and perhaps even prevention of inhibitors.

Prophylactic versus on-demand treatments for hemophilia: advantages and drawbacks

INTRODUCTION

Early long-term prophylaxis is the standard of care to prevent joint bleeding and chronic arthropathy in patients with severe hemophilia. Areas covered: Despite the obvious prophylaxis advantages upon the clinical outcomes, there are still several drawbacks to be addressed for the optimal patients' compliance. Frequency of treatment due to short half-life of conventional FVIII and FIX concentrates, difficult venous access, adherence to the prescribed therapy and costs may represent significant critical issues. The development of inhibitors also makes replacement therapy ineffective, preventing patients from receiving long-term prophylaxis. This paper will review these drawbacks and the tools to overcome these limitations, mainly thanks to the use of extended half-life products and the development of novel non-conventional therapeutic approaches. Expert commentary: The use of extended half-life products may help in reducing the burden of the frequent intravenous administration and in better tailoring an individualized prophylaxis. The development of novel therapeutic approaches, like the bi-specific antibody mimicking the coagulation function of FVIII or inhibition of anticoagulant proteins may facilitate prophylaxis treatment not only in patients with inhibitors, but also in severe hemophilia patients without inhibitors. Exciting opportunities are emerging for improving prophylaxis in hemophilia.

Successful immune tolerance induction using turoctocog alfa in an adult haemophilia A patient

We present here the first known case of successful immune tolerance induction (ITI) using recombinant factor VIII (rFVIII), turoctocog alfa, in a patient with severe haemophilia A. The 38-year-old patient with a long-standing inhibitor required urgent surgery for severe arthropathy. rFVIII was administered throughout the surgical period. Surgery was considered successful, but on day 7 after surgery, an increased level of FVIII inhibitors were detected. ITI was attempted immediately thereafter according to the Bonn protocol. Inhibitors were no longer detected on day 17; 13 months later, successful ITI was achieved. This case suggests that a long-time interval between inhibitor appearance and the start of ITI therapy may not necessarily indicate poor prognosis.

New findings on inhibitor development: from registries to clinical studies

The high incidence of inhibitors against factor VIII (FVIII) concentrates in patients with haemophilia A has encouraged debate as to whether product-type plays a role. There is debate in the literature as to whether rFVIII concentrates are associated with a higher incidence of inhibitors compared to pdFVIII products. The management of haemophilia in patients with inhibitors includes on-demand/prophylaxis treatment with bypassing agents, and/or immune tolerance induction (ITI). However, these options create an economic and emotional burden on patients, their families and healthcare practitioners. Although ITI eliminates inhibitors successfully in 60-80% of cases, it is costly. Despite high costs, preliminary data from a decision analytical model have indicated that ITI is economically advantageous compared with on-demand/prophylactic treatment with bypassing agents. In patients with persistent inhibitors and those who are not candidates for ITI or have failed ITI, bleeding-related mortality and morbidity increase and quality of life decreases, compared with non-inhibitor patients. This article provides an update on the risk of inhibitor development and discusses best management approaches for patients with high-risk factors for inhibitor development.

What is the role of an extended half-life product in immune tolerance induction in a patient with severe hemophilia A and high-titer inhibitors?

A 10-year-old boy presents with a history of severe hemophilia A and high-titer inhibitor that had failed high-dose immune tolerance induction (ITI) with a recombinant factor VIII (rFVIII) product and a plasma-derived FVIII product. You are asked by his mother whether he should be tried on ITI with an extended half-life product, in particular, consideration of a rFVIIIFc concentrate.

Achievements, challenges and unmet needs for haemophilia patients with inhibitors: Report from a symposium in Paris, France on 20 November 2014

Over the past 20 years, there have been many advances in haemophilia treatment that have allowed patients to take greater control of their disease. However, the development of factor VIII (FVIII) inhibitors is the greatest complication of the disease and a challenge in the treatment of haemophilia making management of bleeding episodes difficult and surgical procedures very challenging. A meeting to discuss the unmet needs of haemophilia patients with inhibitors was held in Paris on 20 November 2014. Topics discussed were genetic and non-genetic risk factors for the development of inhibitors, immunological aspects of inhibitor development, FVIII products and inhibitor development, generation and functional properties of engineered antigen-specific T regulatory cells, suppression of immune responses to FVIII, prophylaxis in haemophilia patients with inhibitors, epitope mapping of FVIII inhibitors, current controversies in immune tolerance induction therapy, surgery in haemophilia patients with inhibitors and future perspectives for the treatment of haemophilia patients with inhibitors. A summary of the key points discussed is presented in this paper.

Human von Willebrand factor/factor VIII concentrates in the management of pediatric patients with von Willebrand disease/hemophilia A

Several plasma-derived intermediate and high-purity concentrates containing von Willebrand factor (VWF) and factor VIII (FVIII) are currently available. The main role of these products in the management of the pediatric population is represented by the replacement therapy in patients with severe or intermediate forms of von Willebrand disease, in whom other treatments are ineffective or contraindicated. Another important role of VWF/FVIII concentrates in children may be their use in immune tolerance induction (ITI) protocols. ITI is particularly recommended for hemophilia A children who have developed an inhibitor against FVIII, currently the most serious complication of substitutive treatment in hemophilia. Although recombinant concentrates may represent the preferred option in children with hemophilia A, VWF/FVIII concentrates may offer an advantage in rescuing patients who failed previous ITI.