Factor VIII inhibitors development following introduction of B-domain-deleted recombinant factor VIII in four hemophilia A previously treated patients

Natural history and clinical characteristics of inhibitors in previously treated haemophilia A patients: a case series

BACKGROUND

Development of inhibitors is the most serious complication in haemophilia A treatment. The assessment of risk for inhibitor formation in new or modified factor concentrates is traditionally performed in previously treated patients (PTPs). However, evidence on risk factors for and natural history of inhibitors has been generated mostly in previously untreated patients (PUPs). The purpose of this study was to examine cases of de novo inhibitors in PTPs reported in the scientific literature and to the EUropean HAemophilia Safety Surveillance (EUHASS) programme, and explore determinants and course of inhibitor development.

METHODS

We used a case series study design and developed a case report form to collect patient level data; including detection, inhibitor course, treatment, factor VIII products used and events that may trigger inhibitor development (surgery, vaccination, immune disorders, malignancy, product switch).

RESULTS

We identified 19 publications that reported 38 inhibitor cases and 45 cases from 31 EUHASS centres. Individual patient data were collected for 55/83 (66%) inhibitor cases out of 12 330 patients. The median (range) peak inhibitor titre was 4.4 (0.5-135.0), the proportion of transient inhibitors was 33% and only two cases of 12 undergoing immune tolerance induction failed this treatment. In the two months before inhibitor development, surgery was reported in nine (22%) cases, and high intensity treatment periods reported in seven (17%) cases.

CONCLUSIONS

By studying the largest cohort of inhibitor development in PTPs assembled to date, we showed that inhibitor development in PTPs, is on average, a milder event than in PUPs.

The prevalence of factor VIII and IX inhibitors among Saudi patients with hemophilia: Results from the Saudi national hemophilia screening program

Hemophilia A and B are X-linked diseases that predominantly affect male patients. Patients can develop coagulation factor inhibitors, which exponentially increases the treatment cost. However, the prevalence of factor VIII and IX inhibitors in Saudi Arabia is unclear.This study aimed to determine the Saudi prevalence of factor VIII and IX inhibitors.This 4-year, 7-center, cross-sectional study evaluated the Saudi prevalences of hemophilia A and B. We collected the patients' clinical data, evaluated their disease, and tested for factor inhibitors.We included 202 patients with hemophilia (median age at diagnosis: 0.13 years, range: birth-34.8 years). The patients included 198 male patients (98%), 148 patients with hemophilia A (73.3%), and 54 patients with hemophilia B (26.7%). The patients exhibited severe factor VIII activity (<1%; 121 patients; 5.2%), moderate activity (1-5%; 7 patients; 4.9%), and mild activity (14 patients; 9.9%). Among the patients with care-related data, most patients were treated for episodic bleeding (76.8%) or received prophylaxis (22.6%); 1 patient received both treatments. Among the patients with source-related data, the factor replacements were derived from plasma (48.4%), recombinant concentrates (22.9%), both sources (14.6%), or fresh frozen plasma (14.1%). Factor VIII inhibitors were observed in 43 (29.3%) of the 147 patients, and only 1 of the 54 patients developed factor IX inhibitors. Most patients who developed inhibitors had severe hemophilia (40/44; 90.9%), and inhibitors were also common among patients who received recombinant products (14/43; 32.6%).The Saudi prevalence of factor inhibitors was similar to those among other ethnic populations.

Switching treatments in haemophilia: is there a risk of inhibitor development?

Patients with haemophilia A (and their physicians) may be reluctant to switch factor VIII (FVIII) concentrates, often due to concerns about increasing the risk of inhibitors; this reluctance to switch may contribute to patients missing the clinical benefits provided by the arrival of new factor VIII products. This topic was explored at the Eleventh Zürich Haemophilia Forum. Clinical scenarios for which product switching may be cause for concern were discussed; when there is a clinical need, there are no absolute contraindications to switching, but some patients (e.g. previously untreated patients and those undergoing elective surgery) may require more careful consideration. Both patient and physician surveys indicate that the reluctance to switch, and the fear of inhibitor development, does not appear to be evidence based. The evaluation of more recent data did not support previous studies suggesting that particular products (e.g. recombinant vs. plasma-derived and full length vs. B-domain modified) may be associated with increased risk. In addition, data from three national product switches showed that switching was not associated with increased inhibitor risk, but highlighted the need for regular inhibitor testing and for a centralised, unbiased database of inhibitor incidence. To conclude, current evidence does not suggest that switching products significantly influences inhibitor development.

Long-term efficacy and safety of a pasteurized, plasma-derived factor VIII concentrate (Beriate® P) in patients with haemophilia A

Introduction

Beriate^® P was first introduced in Germany in 1990 as factor VIII (FVIII):C^® HS Behring and subsequent product improvements yielded an albumin-free formulation with a specific activity of approximately 170 IU/mg protein. In 1992, the concentration was raised to 100 IU FVIII/mL in the reconstituted product, with a mean specific activity of 270 IU/mg protein. Pathogen safety is achieved by careful donor selection and a combination of pasteurization and chromatographic purification steps.

Materials and methods

We analysed the efficacy and safety of Beriate^® P in the clinical setting from 1996 to 2005 with a focus on surgical patients. Of the 36 patients (mean age: 38 years; range 1–72 years), 29 had severe haemophilia A, two had moderate haemophilia, two had mild haemophilia, and three had sub-clinical haemophilia. Most patients (n = 28) had more than 100 exposure days, representing a total of 202 patient-years with a consumption of 27,811,500 IU of Beriate^® P.

Results

There was no evidence of seroconversion towards relevant viruses, no inhibitor development (35 previously treated patients, one previously untreated patient), no abnormal immunological findings or allergic reactions. In all 36 patients treated for acute bleeding and prophylaxis, and 24 surgeries (15 total joint replacements, eight orthopaedic procedures, one cholecystectomy) in 16 patients with severe haemophilia A, efficacy of Beriate^® P was always rated as “excellent” or “good”, and no thrombosis was reported.

Conclusion

Beriate^® P has an excellent efficacy and safety profile. Many patients who were initiated on Beriate^® P at our centre remain on the treatment today.

Can B-domain deletion alter the immunogenicity of recombinant factor VIII? A meta-analysis of prospective clinical studies

BACKGROUND

As a result of the infrequency of inhibitors in previously treated patients (PTPs) with hemophilia A and the small size of available clinical studies, the immunogenicity of factor (F)VIII products has been difficult to assess.

OBJECTIVES

A meta-analysis of prospective clinical studies was conducted to test the hypothesis that de novo inhibitor incidence differs between PTPs receiving full-length recombinant FVIII (FL-rFVIII) and B-domain deleted recombinant FVIII (BDD-rFVIII).

METHODS

Prospective studies with data on inhibitors in PTPs receiving FL-rFVIII or BDD-rFVIII were sought using systematic methods including bibliographic database searches. Data were secured from published study reports and inquiries to investigators. Between-group differences in inhibitor incidence rates were evaluated using mixed effects Cox regression.

RESULTS

Twenty-nine studies with 3012 total PTPs were included. Patients were at risk of de novo inhibitor development for a median of 79 exposure days. A total of 35 de novo inhibitors were observed. The cumulative hazard for all de novo inhibitors was 1.25% with a 95% confidence interval (CI) of 0.63-1.88%. The corresponding rate for high-titer de novo inhibitors [> 5 Bethesda units (BU)] was 0.29% (CI, 0.01-0.57%). Exposure to BDD-rFVIII was associated with an increased risk of all de novo inhibitors (hazard ratio, 7.26; CI, 2.12-24.9; P = 0.0016) and of high-titer de novo inhibitors (hazard ratio, 10.8; CI, 2.17-53.7; P = 0.0037), compared with FL-rFVIII.

CONCLUSIONS

This meta-analysis of prospective clinical studies suggests that recombinant FVIII products may differ in immunogenicity.

Inhibitors in previously treated patients: a review of the literature

Previously treated patients are the first patients to receive novel factor VIII products during clinical investigations under the rationale that a product with increased antigenicity is more likely to be detected in this population because of a low baseline risk of inhibitor formation compared with previously untreated patients. As clinical investigations of factor products are not typically randomized comparisons, the rate of new inhibitor formation in a clinical trial is compared with the expected rates based on prior reports. The published experience of inhibitors in previously treated patients (PTPs) informs the number of new inhibitors per cohort that are acceptable in a clinical trial. However, a single acceptable limit of new inhibitors fails to recognize the heterogeneity of inhibitors and their variable impact on clinical care. This review will discuss the published literature on epidemiology and clinical characteristics of inhibitors and possible risk factors for formation in PTPs.

Incidence of inhibitors in a cohort of 838 males with hemophilia A previously treated with factor VIII concentrates

BACKGROUND

Development of an inhibitory antibody to factor VIII is currently the most serious complication of hemophilia A treatment. The rate of inhibitor development in those that have been previously treated with factor concentrates is poorly defined. Understanding the baseline rate of inhibitor development in the population of previously treated patients (PTPs) is important when evaluating the effect of exposure to new factor replacement products on inhibitor formation.

OBJECTIVES

To determine the rate of inhibitor development in PTPs with hemophilia A.

METHODS

A cohort of males with hemophilia A who had data collected on four or more occasions prior to 30 March 2003, as part of the Center for Disease Control and Prevention's Universal Data Collection Project, were eligible for inclusion in the cohort. Patients were included in the cohort if they had at least two Bethesda assay measurements and did not have an inhibitor prior to or at the start of the study period. The overall incidence rate was estimated as the number of verified incident inhibitor cases divided by the total follow-up time in years multiplied by 1000 (cases per 1000 person-years).

RESULTS

A total of 838 patients were included in the study. The overall incidence rate was calculated to be 2.14 cases per 1000 person years. All incident cases had more than 50 exposure days prior to inhibitor development.

CONCLUSIONS

Given the low rate of inhibitor development in PTPs with hemophilia A, small, non-randomized studies are inadequate to determine the rate of inhibitor development after exposure to novel products. Ongoing, standardized, postmarketing surveillance is needed to determine if novel factor products pose an increased risk of inhibitor development.

Epidemiology of inhibitor formation with recombinant factor VIII replacement therapy

This article reviews the epidemiology of inhibitor formation in patients receiving recombinant factor VIII (rFVIII) replacement therapy for haemophilia A. Data from pivotal trial programmes, post-marketing surveillance studies, and pharmacovigilance studies for all available rFVIII products were reviewed. To date, no comparative studies have been performed, and in the non-comparative studies, there were differences in the patient population enrolled and study design (including the number of patient exposure days). In the absence of comparative clinical trials, it is not possible to make comparisons between inhibitor data for the various rFVIII products. This review of the epidemiological data shows that across the pivotal trial programmes for rFVIII products, the observed incidence of inhibitors was in the range of 15-32% in previously untreated patients (PUPs) and 0.9-2.9% in previously treated patients (PTPs). High-titre inhibitors (peak >5 BU) were detected in 10-16% of PUPs and 0-2.3% of PTPs. Several initiatives proposed to help standardize collection and interpretation of inhibitor data for patients receiving rFVIII treatment are described. Such standardization would help to clarify the epidemiology of inhibitor formation across FVIII treatments.

Impact of Choice of Treatment for Bleeding Episodes on Inhibitor Outcome in Patients With Mild/Moderate Hemophilia A and Inhibitors

Patients with mild/moderate hemophilia A (MHA) may develop inhibitors to factor VIII (FVIII). In this condition, FVIII clotting activity (FVIII:C) baseline levels may remain stable for some patients, but may be reduced to less than 0.01 U/mL for others. Several risk factors for the development of inhibitors in MHA have been proposed. Genetic factors, such as mutations in the FVIII gene, may play a central role; however, other influences, such as intensive treatment with FVIII products, may also be important. Optimal treatment regimens have yet to be determined, not only for the eradication of inhibitors, but also for the management or surgical prophylaxis of hemorrhages associated with this condition. Several treatment options for the control of bleeding in patients with MHA and inhibitors (MHAI) are currently available, and the choice of therapeutic strategy should be given careful consideration; some treatments may produce an anamnestic response, thus delaying the return to FVIII:C baseline levels and adversely affecting the duration of the severe bleeding phenotype. To increase our knowledge of MHAI, a retrospective collection of data is currently being performed among hemophilia centers in France and Belgium. Based on five examples of patients with MHAI collated from preliminary study data, we illustrate the impact on inhibitor outcome of the therapeutic choices used to treat bleeding episodes in these patients.

Inhibitors in congenital coagulation disorders

The development of inhibitory 'allo' antibodies to a deficient coagulation factor is arguably now the most severe and important complication of clotting factor concentrate exposure in haemophilia and other congenital coagulation disorders. Furthermore, development of an inhibitor to the factor VIII or factor IX transgene product remains a significant concern in gene therapy protocols for haemophilia. Although the development of an inhibitor does not usually change the rate, initial severity or pattern of bleeding, it does compromise the ability to manage haemorrhage in affected individuals, resulting in a greater rate of complications, cost and disability. The purpose of this review is to summarize current understanding of the epidemiology, immunobiology, laboratory evaluation and management of inhibitors arising in patients with congenital coagulation disorders. An attempt has been made to focus on recent advances in the immunology of inhibitors, and to speculate on their potential clinical application.

Efficacy and inhibitor development in previously treated patients with haemophilia A switched to a B domain-deleted recombinant factor VIII

There have been recent reports of unexpected poor efficacy of a B-domain-deleted recombinant factor VIII (BDD-rFVIII) in haemophiliacs, and inhibitor development in previously treated patients (PTPs) switched to BDD-rFVIII. The results of a 6-month prospective study of 25 PTPs and of a retrospective survey of 94 PTPs, all switched to BDD-rFVIII, were used to evaluate efficacy and inhibitor development. The prospective study showed that 89% of 362 bleeds were controlled by one to two infusions, reproducing the efficacy profiles of other recombinant products (rFVIIIs). One patient, previously treated with plasma-derived FVIII only, developed a high titre inhibitor (30 BU) after 5 days of exposure. The retrospective survey, carried out in the total Italian PTP population switched to BDD-rFVIII, involved 19 PTPs at higher inhibitor risk due to previous exposure of < or = 50 days and 75 PTPs at lower inhibitor risk due to previous exposure of > 50 days. One patient developed an inhibitor: he was a high-risk, severe PTP previously exposed to another rFVIII for 3 days only. Among the entire low-risk population of severe Italian PTPs switched to BDD-rFVIII (25 in the prospective study, 49 in the retrospective cohort) only one developed an inhibitor (1.3%). These data indirectly support the views that BDD-rFVIII is equivalent to other rFVIIIs in term of efficacy and inhibitor development.