Occurrence of inhibitors in previously untreated or minimally treated patients with haemophilia A after exposure to a plasma-derived solvent-detergent factor VIII concentrate

Efficacy, Safety and Pharmacokinetic Results of a Phase III, Open-Label, Multicenter Study with a Plasma-Derived Von Willebrand Factor (VWF)/Factor VIII (FVIII) Concentrate in Pediatric Patients <12 Years of Age with Hemophilia A (SWIFTLY-HA Study)

Background

Plasma-derived von Willebrand factor/factor VIII (pdVWF/FVIII; VONCENTO^®, CSL Behring) is a high-concentration, low-volume, high-purity concentrate, with a high level of VWF high-molecular-weight multimers and a VWF/FVIII ratio of ~2.4:1.

Methods

This study (NCT01229007) investigated the pharmacokinetics (PK), efficacy and safety of pdVWF/FVIII in 35 previously treated (minimum 20 exposure days [EDs]) pediatric patients (<12 years) with severe hemophilia A. PK was evaluated with a single 50 IU FVIII/kg dose of pdVWF/FVIII. Efficacy and safety analyses were performed during on-demand treatment (n=17) or prophylaxis (n=18) for up to 100 EDs with a maximum study duration of 12 months.

Results

PK profiles were similar for patients aged <6 years and those aged 6–12 years, and, as expected, the youngest patients had an increased clearance. On-demand patients reported 320 non-surgical bleeding (NSB) events and received a median number of 29.0 infusions (median dose 34.2 IU FVIII/kg). Hemostatic efficacy was assessed by the investigator as excellent/good in all cases (24%/76%). The 18 patients in the prophylaxis arm experienced 173 NSB events (97 NSBs [56%] in three patients). Five patients (28%) had no NSB events. Overall, patients received a median number of 92 infusions (median dose 30.6 IU FVIII/kg). The majority of bleeds (92%) were successfully controlled with only one infusion. Hemostatic efficacy was assessed by the investigator as excellent (86%) or good (14%). Inhibitors occurred in three patients of which two were transient (low titer) and one persisted (high titer). These three patients had known risk factors for inhibitor development.

Conclusion

This study demonstrated comparable PK profiles for pediatric patients aged <6 years and aged 6–12 years, and an excellent efficacy and safety profile in this population. The adverse events reported were mostly mild to moderate with inhibitor rates within the expected incidence range.

Immune Responses to Plasma-Derived Versus Recombinant FVIII Products

The most severe side effect of hemophilia treatment is the inhibitor development occurring in 30% of patients, during the earliest stages of treatment with factor (F)VIII concentrates. These catastrophic immune responses rapidly inactivate the infused FVIII, rendering the treatment ineffective. This complication is associated with a substantial morbidity and mortality. The risk factors involved in the onset of the inhibitors are both genetic and environmental. The source of FVIII products, i.e. plasma-derived or recombinant FVIII products, is considered one of the most relevant factors for inhibitor development. Numerous studies in the literature report conflicting data on the different immunogenicity of the products. The SIPPET randomized trial showed an increased in the inhibitor rate in patients using recombinant FVIII products than those receiving plasma-derived products in the first exposure days. The SIPPET randomized trial showed an increase in the inhibitor rate in patients using recombinant FVIII products compared to those treated with plasma-derived products in the first days of exposure. The potential increase in the immunogenicity of recombinant products can be attributed to several factors such as: the different post-translational modification in different cell lines, the presence of protein aggregates, and the role played by the chaperon protein of FVIII, the von Willebrand factor, which modulates the uptake of FVIII by antigen presenting cells (APCs). Furthermore, the presence of non-neutralizing antibodies against FVIII has shown to be in increased inhibitor development as demonstrated in a sub-analysis of the SIPPET study. In addition, the presence of the specific subclasses of the immunoglobulins may also be an important biomarker to indicate whether the inhibitor will evolve into a persistent neutralizing antibody or a transient one that would disappear without any specific treatment. Recently, the availability of novel non-replacement therapies as well as emicizumab, administered by weekly subcutaneous infusion, have significantly changed the quality of life of patients with inhibitors showing a considerable reduction of the annual bleeding rate and in most patients the absence of bleeding. Although, these novel drugs improve patients' quality of life, they do not abolish the need to infuse FVIII during acute bleeding or surgery. Therefore, the issue of immunogenicity against FVIII still remains an important side effect of hemophilia treatment.

Epidemiological Challenges in Rare Bleeding Disorders: FVIII Inhibitor Incidence in Haemophilia A Patients-A Known Issue of Unknown Origin

There is a broad range of factor products approved in Germany for haemophilia A treatment. Since the introduction of recombinant coagulation factor VIII (FVIII) products in the 1990s, there has been substantial debate whether there is a difference in inhibitor incidence between single FVIII products or product classes. Neither haemophilia registries nor clinical studies, including a randomised controlled clinical trial, provided a consistent and definite answer. The reasons were mainly related to methodological challenges in conducting controlled studies in a rare disease. In this analysis, the most relevant epidemiological challenges and main problems were examined, including study bias, potential overlap of individual studies and advanced development of therapy and methods in the course of time. Meta-analyses on two levels showed that therapies using recombinant products resulted in different event rates when compared to plasma-derived products. These results are accompanied by substantial study heterogeneity evidenced by Cochran's Q tests. Only three studies have been identified that meet the standards of current clinical guidance. To finally resolve this ongoing and disputable safety issue of replacement therapy, collaboration among registry owners, academia and regulators must be fostered.

Safety and efficacy of turoctocog alfa in the prevention and treatment of bleeds in previously untreated paediatric patients with severe haemophilia A: Results from the guardian 4 multinational clinical trial

Introduction

Turoctocog alfa is a recombinant, B domain‐truncated factor VIII (FVIII) approved for patients with haemophilia A.

Aim

To evaluate the safety and efficacy of turoctocog alfa in previously untreated patients (PUPs) with severe haemophilia A.

Methods

Guardian 4 was a multicentre, multinational, non‐randomized, open‐label phase 3 trial comprising a main and extension phase. The former concluded once ≥ 50 patients had received treatment for ≥ 50 exposure days (EDs) or developed inhibitors. Patients received turoctocog alfa intravenously for prevention and treatment of bleeds. The primary endpoint was the incidence rate of FVIII inhibitors (≥0.6 Bethesda Units) reported during the first 50 EDs.

Results

Of the 58 patients who completed the main phase, 25 (43.1%) patients developed inhibitors (detected within 6‐24 [mean: 14.2] EDs from treatment start). High‐risk mutations were identified in 60% of patients who developed inhibitors in the main phase and were a significant predictor of inhibitor development (P = .003). Of the 21 patients who started immune tolerance induction therapy, 85.7% completed treatment with a negative inhibitor test (note that data on the last 3 patients completing ITI are based on information collated from sites prior to the final database lock). Haemostatic response (including missing values as failure) was rated as ‘excellent’ or ‘good’ for 86.1% of bleeds occurring during prophylaxis. The estimated mean annualized bleeding rate for patients on prophylaxis was 4.26 bleeds/patient/year (95% CI: 3.34 − 5.44).

Conclusions

Turoctocog alfa was effective at preventing and stopping bleeds and was well tolerated. Inhibitor development was within the expected range for this PUP population.

Product type and other environmental risk factors for inhibitor development in severe hemophilia A

The development of FVIII inhibitory antibodies is currently the most challenging complication of treatment, affecting ~30% of severe hemophilia A patients. These inhibitors inactivate FVIII, rendering the treatment ineffective, causing disability and increasing morbidity and mortality. Inhibitor development results from a complex multicausal immune response involving both genetic and environmental risk factors. One of the most important modifiable risk factors is the source of FVIII products, eg, plasma-derived or recombinant FVIII. Other environmental risk factors, such as age at first treatment, regimen, and intensity of treatment, could contribute to inhibitor development. Severe bleeds, surgery, concomitant infections, or vaccinations may all be events initiating danger signaling resulting in an immune reaction towards administered FVIII. All in all, the etiology of inhibitor development still remains unclear. The risk factors have been stratified into genetic and environmental, but there are no definitive data to determine the impact of each of them.

Bayesian approach to the assessment of the population-specific risk of inhibitors in hemophilia A patients: a case study

Background

Developing inhibitors is a rare event during the treatment of hemophilia A. The multifacets and uncertainty surrounding the development of inhibitors further complicate the process of estimating inhibitor rate from the limited data. Bayesian statistical modeling provides a useful tool in generating, enhancing, and exploring the evidence through incorporating all the available information.

Methods

We built our Bayesian analysis using three study cases to estimate the inhibitor rates of patients with hemophilia A in three different scenarios: Case 1, a single cohort of previously treated patients (PTPs) or previously untreated patients; Case 2, a meta-analysis of PTP cohorts; and Case 3, a previously unexplored patient population – patients with baseline low-titer inhibitor or history of inhibitor development. The data used in this study were extracted from three published ADVATE (antihemophilic factor [recombinant] is a product of Baxter for treating hemophilia A) post-authorization surveillance studies. Noninformative and informative priors were applied to Bayesian standard (Case 1) or random-effects (Case 2 and Case 3) logistic models. Bayesian probabilities of satisfying three meaningful thresholds of the risk of developing a clinical significant inhibitor (10/100, 5/100 [high rates], and 1/86 [the Food and Drug Administration mandated cutoff rate in PTPs]) were calculated. The effect of discounting prior information or scaling up the study data was evaluated.

Results

Results based on noninformative priors were similar to the classical approach. Using priors from PTPs lowered the point estimate and narrowed the 95% credible intervals (Case 1: from 1.3 [0.5, 2.7] to 0.8 [0.5, 1.1]; Case 2: from 1.9 [0.6, 6.0] to 0.8 [0.5, 1.1]; Case 3: 2.3 [0.5, 6.8] to 0.7 [0.5, 1.1]). All probabilities of satisfying a threshold of 1/86 were above 0.65. Increasing the number of patients by two and ten times substantially narrowed the credible intervals for the single cohort study (1.4 [0.7, 2.3] and 1.4 [1.1, 1.8], respectively). Increasing the number of studies by two and ten times for the multiple study scenarios (Case 2: 1.9 [0.6, 4.0] and 1.9 [1.5, 2.6]; Case 3: 2.4 [0.9, 5.0] and 2.6 [1.9, 3.5], respectively) had a similar effect.

Conclusion

Bayesian approach as a robust, transparent, and reproducible analytic method can be efficiently used to estimate the inhibitor rate of hemophilia A in complex clinical settings.

Efficacy, safety and pharmacokinetic profiles of a plasma-derived VWF/FVIII concentrate (VONCENTO®) in subjects with haemophilia A (SWIFT-HA study)

INTRODUCTION

VONCENTO® (CSL Behring) is a plasma-derived, high-concentration, low-volume, high-purity concentrate,which contains a high level of von Willebrand factor (VWF) high-molecular-weight multimers and aVWF/factor VIII (FVIII) ratio of ~2.4:1, similar to Haemate® P (CSL Behring).

METHODS

The pharmacokinetic, efficacy and safety profiles of VONCENTO® were investigated in this multicentre,double-blind, randomised study. Subjects aged ≥ 12 years with haemophilia A who required treatment of nonsurgical bleeds, treatment during surgical events or who were receiving prophylaxis were included. Pharmacokinetics were investigated with a single dose of 50 IU FVIII/kg body weight of either VONCENTO® or BIOSTATE® reference product (Biostate-RP) (Day 1; Day 8 [n= 16], repeated on Day 180 [VONCENTO® only; n=15]). Efficacy and safety analyses were performed either during on-demand treatment (n=52) or prophylaxis (n=29)for ≥ 6 months and ≥ 50 exposure days, respectively.

RESULTS

Besides the confirmation of bioequivalence between VONCENTO® and Biostate-RP, which displayed comparable PK profiles, haemostatic efficacy was rated by the investigators as either 'excellent' or 'good' in 96.4% of all bleeding events (96.5% spontaneous, 96.6% traumatic, 96.9% joint bleeds) as well as in 80% of major and 100% of minor surgical procedures at discharge. The median number of annualised bleeding events per subject [range] was significantly lower in the prophylaxis group (2.0 [0.0-34.6]) than in the on-demand group (14.0 [0.0-87.8], p = 0.0013).VONCENTO® was well tolerated and no inhibitory antibodies were identified during the study period.

CONCLUSIONS

This study demonstrated the bioequivalence of VONCENTO® to Biostate-RP, and its excellent efficacy and safety profile in haemophilia A subjects.

The role of previously untreated patient studies in understanding the development of FVIII inhibitors

Development of inhibitors against factor VIII (FVIII), the major complication of haemophilia A treatment today, is influenced by multiple factors. Genetic (F8 mutation, family history, ethnicity, polymorphisms in immune modulating genes) and non-genetic (intensive exposure to FVIII, presence of pro-inflammatory signals as might occur with large bleeds, infections, surgery, or other immune stimulants [e.g. vaccines]) risk factors as well as their complex inter-relationships contribute to the inhibitor risk profile of haemophilia patients, particularly in the previously untreated patient (PUP) population. Studies in PUPs have been fundamental to furthering the understanding of FVIII inhibitor development, as well as discovering previously unappreciated risk factors. The multi-factorial nature of inhibitor development makes it difficult to ascertain the contribution of FVIII products in inhibitor development through individual PUP studies. Sufficiently powered studies of large cohorts may overcome these limitations but interpretations should be conducted cautiously. Proper design and implementation of PUP safety studies will become even more important with the introduction of new molecules, such as extended half-life or human cell-line derived FVIII that propose reduced immunogenicity. Despite these difficulties, carefully performed clinical studies in PUPs may provide important insights into the natural history of the immune response to FVIII and may suggest targets for intervention to reduce immunogenicity.

Surgery and inhibitor development in hemophilia A: a systematic review

BACKGROUND

Although the association between intensive treatment and the formation of inhibiting antibodies towards factor VIII (FVIII) in hemophilia A has been demonstrated, the contributing effect of surgery is presently unclear. The release of immunological danger signals resulting from tissue damage during surgery in the presence of a high FVIII antigen load may elicit the formation of FVIII antibodies. The aim of this systematic review was to investigate the role of surgery in the inhibitor risk associated with intensive treatment as compared with treatment for bleeding and prophylactic administration of FVIII.

METHODS

A comprehensive literature search was performed that identified four cohort studies and three case control studies, comprising 342 inhibitor patients among a total of 957 hemophilia A patients.

RESULTS

Intensive treatment increased the inhibitor risk, most pronounced with intensive treatment of ≥ 5 exposure days (EDs) compared with < 3 EDs (OR, 4.1; 95% confidence interval, 2.6-6.5). Pooled odds ratio for inhibitor development in severe hemophilia patients that received intensive treatment for surgery at first exposure was 4.1 (95% confidence interval, 2.0-8.4) compared with treatment for bleeding or prophylaxis. Information on continuous infusion, previously treated patients and non-severe hemophilia A was insufficient for valid meta-analyses.

CONCLUSIONS

Intensive FVIII treatment for surgery at first exposure leads to a higher inhibitor risk in hemophilia A patients compared with intensive treatment for bleeding.

Pharmacotherapy of haemophilia A

INTRODUCTION

Haemophilia A is due to factor VIII (FVIII) deficiency. The main treatment is replacement therapy with FVIII concentrates. However, these concentrates carried a high risk of blood-borne viral infections and still have a high risk of inducing anti-FVIII inhibitors.

AREAS COVERED

An overview of products available and therapeutic options for haemophilia A management in order to help in decision making. A literature search using Medline with the keywords: 'haemophilia', 'factor VIII', 'therapy', 'inhibitor', 'concentrate', 'bleeding', 'prophylaxis', 'on demand', 'plasma-derived', 'recombinant', 'coagulation factors', 'immunotolerance' was performed. The years 1960 - 2010 are included.

EXPERT OPINION

Progress in management of patients with haemophilia A has allowed increased life expectancy and quality of life. There is evidence that prophylaxis prevents or, at least, slows down arthropathy development when started early in childhood. FVIII concentrates have achieved high levels of blood-borne pathogen safety. However, treatment is frequently complicated by development of FVIII-neutralizing inhibitors, which prevent control of bleeding and predispose to a high morbidity and mortality risk. Bypassing agents are effective in bleeding treatment in a high percentage of cases. Prophylaxis with bypassing agents and their use in combination are offering opportunities in management of inhibitor patients. More evidence is necessary to understand how to prevent and manage this complication.

Advances in hemophilia: experimental aspects and therapy

This article describes recent clinical and research advances in hemophilia therapy. Different prophylactic regimens for the management of severe hemophilia are described along with the use of adjuvant treatment options to achieve hemostasis. The safety and efficacy of radionuclide synovectomy with phosphorus 32-sulfur colloid to treat existing joint arthropathy also are described. The development of inhibitors to factor VIII or IX remains a challenge for hemophilia care and recent approaches to achieve immune tolerance induction are discussed. Finally, recent advances in hemophilia are mentioned, including the role of iron, inflammation, and angiogenesis in the pathogenesis of hemophilic arthropathy.

Non-genetic risk factors and the development of inhibitors in haemophilia: a comprehensive review and consensus report

SUMMARY

The development of inhibitors to the infused factor in patients with haemophilia is a serious clinical problem. Recent evidence suggests that alongside the strong genetic contribution to inhibitor formation, there are a number of non-genetic factors--perceived by the immune system as danger signals--which promote formation of inhibitors. This study provides a comprehensive review of clinical studies relating to these factors and also presents a survey of opinion concerning their importance and clinical influence, conducted among the members of the European Haemophilia Treatment Standardisation Board (EHTSB). Taken together, this information highlights the lack of robust data concerning the influence of several non-genetic risk factors on inhibitor development, and an urgent need for prospective, well-conducted studies that adhere to recommendations made by the European Medicines Agency (EMEA) for studying inhibitors. Based on current literature, the EHTSB formulated consensus recommendations. It is desirable to minimize intensive treatment wherever possible, given the clinical situation. Prophylaxis should be offered to all children, although we still need to determine optimal dosing with respect to inhibitor development, and age for starting treatment. Vaccinations should be given subcutaneously and concomitant factor concentrate infusions avoided. According to the board, there is no evidence in the literature supporting suggestions that the type of concentrate influences inhibitor risk; but all patients should be monitored during their first exposures. Furthermore, there is no evidence to support an association between pregnancy-related issues, breast feeding and treatment-related factors (e.g. route of administration, or use of blood components) and inhibitor development.

Advances in hemophilia: experimental aspects and therapy

This article describes recent clinical and research advances in hemophilia therapy. Different prophylactic regimens for the management of severe hemophilia are described along with the use of adjuvant treatment options to achieve hemostasis. The safety and efficacy of radionuclide synovectomy with phosphorus 32-sulfur colloid to treat existing joint arthropathy also are described. The development of inhibitors to factor VIII or IX remains a challenge for hemophilia care and recent approaches to achieve immune tolerance induction are discussed. Finally, recent advances in hemophilia are mentioned, including the role of iron, inflammation, and angiogenesis in the pathogenesis of hemophilic arthopathy.

Basic aspects of inhibitors to factors VIII and IX and the influence of non-genetic risk factors

The appearance of polyclonal antibodies inhibiting the function of exogenous factors VIII (FVIII) and IX (FIX) continues to be a major challenge in the treatment of patients with congenital haemophilia. Why these inhibitors develop in 10-20% of patients with haemophilia A, and in 1-5% of patients with haemophilia B, remains largely unexplained. The antibodies, however, are characterized by several features that may have implications for the immune process by which they occur. The FVIII antibodies are mainly directed towards the A2, A3 and C2 domains, thereby interfering with the function of the factor Xase complex, the binding of FVIII to von Willebrand factor, and the binding of FVIII to phospholipid membranes. The FIX epitopes are localized to the NH(2)-terminal gamma-carboxyglutamic acid region and the serine protease domain. Genetic risk factors are known to be of importance in the development of inhibitors, whereas the impact of non-genetic factors is less clear. However, based on studies of related subjects, it is obvious that non-genetic factors are of importance as well. Putative factors currently debated include age at the start of treatment, treatment in association with immune challenges, the type of product, and the mode of administration. Most of the findings reported to date, however, derive from small cohorts that have not been sufficiently well characterized with respect to genetic risk profile. Therefore, additional studies are required to quantify the impact of non-genetic factors on the pathophysiologic process of inhibitor development.

Recombinant vs. plasma-derived products, especially those with intact VWF, regarding inhibitor development

The development of inhibitors in previously untreated patients (PUPs) with haemophilia A is correlated with a variety of endogenous and exogenous risk factors. It is still controversial whether recombinant factor VIII (rFVIII) products pose a higher risk for inhibitor development than plasma-derived (pd) FVIII concentrates, particularly with intact von Willebrand factor (VWF). A systematic review on the epidemiology of inhibitors in haemophilia A investigated the influence of different FVIII products on inhibitor formation. Patients treated with a single pd product had a lower cumulative incidence (0-12.4%) than those treated with a single recombinant concentrate (36.0-38.7%) independent of disease severity, study size, or inhibitor testing frequency. However, this analysis does not take into account the heterogeneity of the study populations. A study investigating the effects of different variables on inhibitor development in PUPs was started 13 years ago by the Paediatric Committee of the German, Austrian and Swiss Society on Thrombosis and Haemostasis Research. This prospectively conducted study revealed a slight difference (P = 0.08) in terms of type of concentrate. In the group of severe haemophiliacs treated with pdFVIII concentrate (n = 57), 12 patients developed an inhibitor (21%), whereas 17 of 47 patients receiving rFVIII (36%) were affected by this complication. This observation was substantiated by retrospective Italian and French analyses. These results, as well as hypothetical considerations, indicate that there is a body of evidence that FVIII products with VWF may be less immunogenic in PUPs. However, in order to provide more evidence a well-designed randomized study is needed.

Should hemophilia treaters switch to albumin-free recombinant factor VIII concentrates

PURPOSE OF REVIEW

To discuss the advantages and disadvantages of the albumin-free recombinant factor VIII concentrates in the treatment of hemophilia A.

RECENT FINDINGS

The third-generation recombinant factor VIII product Advate has been found to be safe and effective in treating bleeding associated with hemophilia A.

SUMMARY

Multiple issues must be considered when selecting a factor VIII concentrate for patients with hemophilia A including efficacy, availability, risk of transmission of infectious agents, risk of inhibitor development and cost. Third-generation recombinant factor VIII concentrates have been shown to be safe and effective. A theoretical improvement in risk of infectious agent transmission has been achieved by production of the products without human or animal plasma proteins. Controversy exists, however, with regard to a higher risk of inhibitor development with recombinant products. The higher cost of Advate can also potentially play a role in product choice. Overall every patient and their family must be presented with the advantages and disadvantages of all factor VIII concentrates, and be allowed to make an informed decision about which product to use for treatment.

The Role of Immunomodulation in the Management of Factor VIII Inhibitors

Approximately 25% of persons with hemophilia A will have their treatment complicated by the development of anti-FVIII inhibitory antibodies. This adverse event requires the use of alternative hemostatic agents to treat bleeding and the consideration of a protocol to generate immunological tolerance to FVIII. The pathogenetic factors contributing to FVIII inhibitor generation include both patient- and concentrate-related characteristics. The FVIII genotype contributes to this risk as do other, less well defined, immunogenetic factors. The role of the type of FVIII concentrate as a precipitant for inhibitor generation appears to be less influential. Immunomodulatory management of FVIII inhibitors requires sustained and repeated exposure to FVIII through a variety of intravenous immune tolerance induction (ITI) protocols. Certain pre-ITI characteristics predict for the likelihood of success, most especially the pre-ITI anti-FVIII inhibitor titer. Currently, two major areas of debate remain unresolved with relation to the optimal form of ITI schedule. The best FVIII dose to generate FVIII tolerance is under investigation in an international prospective trial, while the issue of whether von Willebrand factor–containing concentrates may provide more powerful tolerizing effects remains open for further discussion. With a variety of ITI protocols, success rates of approximately 80% have been achieved with good-risk patients. In those that fail initial attempts at ITI, additional treatments using agents such rituximab are now being explored with further evidence of success in 60–80% of these salvage patients. Finally, several pre-clinical studies of innovative approaches to achieving FVIII tolerance suggest that combinations of immunomodulatory therapy may be of benefit in the future.