Haemophilia Inhibitor Genetics Study - evaluation of a model for studies of complex diseases using linkage and association methods

Prevalence and Incidence of Non-neutralizing Antibodies in Congenital Hemophilia A- A Systematic Review and Meta-Analysis

Objectives: In hemophilia A the presence of non-neutralizing antibodies (NNAs) against Factor VIII (FVIII) may predict the development of neutralizing antibodies (inhibitors) and accelerate the clearance of administrated FVIII concentrates. This systematic review aimed to assess: (1) the prevalence and incidence of NNAs in patients with congenital hemophilia without inhibitors and (2) the association between NNAs and patient and treatment characteristics.

Methods: We conducted a search in MEDLINE, Embase, Web of Science and the Cochrane database. We included cross-sectional and longitudinal studies reporting on NNAs in patients with hemophilia A and B, who were inhibitor-negative at the start of the observation period. Data were extracted on: hemophilia type and severity, patient and treatment characteristics, NNA prevalence and incidence, NNA assays and inhibitor development. Two independent reviewers performed study selection, data extraction and risk of bias assessment, using adapted criteria of the Joanna Briggs Institute. Studies were classified as high-quality when ≥5/9 criteria were met. NNA assays were classified as high-quality when both quality criteria were met: (1) use of positive controls and (2) competition with FVIII to establish FVIII-specificity. We reported NNA prevalence and incidence for each study. The pooled NNA prevalence was assessed for well-designed studies in previously treated patients, employing high-quality NNA assays.

Results: We included data from 2,723 inhibitor-negative patients with hemophilia A, derived from 28 studies. Most studies were cross-sectional (19/28) and none reported on NNAs in hemophilia B. Study design was of high quality in 16/28 studies and the NNA assay quality was high in 9/28 studies. Various NNA assays were used, predominantly ELISA (18/28) with different cut-off values. We found a large variety in NNA prevalence (Range, 0–100%). The pooled NNA prevalence in high-quality studies was 25% (95% CI, 16–38%). The incidence of new NNA development was reported in one study (0.01 NNA per person-exposure day).

Conclusion: This systematic review identified studies that were heterogeneous in study design, patient population and NNA assay type, with NNA prevalence ranging from 0 to 100% in inhibitor-negative patients with hemophilia A. The pooled NNA prevalence was 25% in high-quality studies including only previously treated patients and performing high-quality NNA assays.

Changes in bleeding patterns in von Willebrand disease after institution of long-term replacement therapy: results from the von Willebrand Disease Prophylaxis Network

Clinically, the leading symptom in von Willebrand disease (VWD) is bleeding, chiefly of mucosal type, for example, epistaxis, gingival, or gastrointestinal bleeding, and menorrhagia. In severe forms of VWD with secondary deficiency of factor VIII, spontaneous joint bleeding, resembling that observed in severe haemophilia A, may also be observed. The bleeding patterns of VWD can affect quality of life, and may be life-threatening. The von Willebrand Disease Prophylaxis Network is an international study group formed with the goal of investigating the role of prophylaxis in clinically severe VWD. The objective of the present study is to investigate the response to prophylaxis focusing primarily on epistaxis, joint bleeding, gastrointestinal bleeding, and heavy bleeding associated with menses. Data from 105 subjects, 10 enrolled in a prospective study and 95 in a retrospective study between 2008 and 2013, were available for analysis. The median annualized rate reductions in bleeding were significant for epistaxis (P < 0.0001), gastrointestinal bleeding (P = 0.0003), joint bleeding (P < 0.0001), and menorrhagia (P = 0.008). Doses on a group level were approximately the same prior to and during prophylaxis, but more patients with gastrointestinal bleeding had prophylaxis three or more times per week as well as higher dosages. Our study, which primarily used retrospective data, indicates that prospective studies are needed to better delineate the doses and dose intervals that should be used for prophylactic treatment of VWD.

Antibody formation and specificity in Bethesda-negative brother pairs with haemophilia A

Antibodies directed towards non-neutralizing epitopes on the factor VIII protein (FVIII) may be detected in patients with haemophilia A. We evaluated the prevalence of non-neutralizing antibodies, in 201 inhibitor-negative brother pairs with severe haemophilia A, enrolled in the Malmö International Brother Study and the Haemophilia Inhibitor Genetics Study. To evaluate binding specificity of the antibodies, ELISA plates were coated with two recombinant full-length (FL) FVIII-products and one recombinant B-domain-deleted (BDD) product. Seventy-nine patients (39.3%) had a history of positive inhibitor titre measured by Bethesda assay, and FVIII antibodies were detected in 20 of them (25.3%). Additional 23 samples from subjects without a history of FVIII inhibitors were ELISA-positive corresponding to a frequency of non-neutralizing antibodies of 18.9%. The antibody response towards the different FVIII products was heterogenous, and was raised not only towards the non-functional B-domain but also towards both FL-rFVIII and BDD-rFVIII. In patients considered successfully treated with immune tolerance induction, 25.4% had remaining FVIII antibodies. The number of families with an antibody response in all siblings was increased when the total antibody response was taken into account, further supporting the concept of a genetic predisposition of the immune response. Further studies and careful monitoring over time are required to appreciate the immune response on the risk of inhibitor development or recurrence in the future.

Inhibitor development

The immune response to factor VIII and the development of inhibitory antibodies is a complex multi-factorial process involving a variety of immune regulatory genes and cells, several of which have the potential to determine risk. A better understanding of the mechanisms involved will increase the likelihood of development of new therapeutic options for patients with hemophilia. This review summarizes genetic and non-genetic risk factors currently under evaluation, and the potential modulative effect of the von Willebrand factor on factor VIII immuno- and antigenicity. In addition, the role of T-regulatory cells in the pathogenicity of inhibitors will be discussed.

Recombinant tissue plasminogen activator may reduce frequency of central venous access device infection in hemophilia patients undergoing immune tolerance therapy

Many patients with hemophilia, particularly those with inhibitory antibodies, utilize central venous access devices (CVADs) to facilitate frequent infusions. Infection of these devices is a common complication of factor replacement therapy. This communication reports our center's experience with CVAD infection in three patients with severe hemophilia A undergoing immune tolerance therapy (ITT) in whom intermittent infusions of recombinant tissue plasminogen activator (rTPA, Cathflo Activase) were utilized. In this small experience, patients experienced a decreased frequency of gram-positive infections when receiving routine rTPA treatments. Larger randomized trial should be performed in this patient population at high risk of CVAD infection.

The epidemiology of factor VIII inhibitors

Risk factors for inhibitor development include specific factor VIII (FVIII) genotypes, a family history of inhibitor development amongst first-degree relatives, certain HLA haplotypes and non-caucasian ethnicity. Patients with major FVIII deletions or rearrangements have a higher risk of inhibitor development than those with small deletions or missense mutations. Studies of HLA-DR amongst northern European patients with the intron 22 inversion indicate that certain HLA haplotypes may also confer either increased or decreased inhibitor risk. However, although brothers of patients with inhibitor have a high risk of inhibitor development, concordance is not 100%, and other constitutional factors must also operate. Disputed risk factors for inhibitor development include early age at first FVIII exposure, the use of recombinant rather than plasma-derived FVIII and product switching. Two studies suggest that inhibitor risk is increased by very early FVIII exposure (P = 0.03), but this is disputed by a third study; larger studies addressing the question are ongoing. Studies investigating the relative inhibitor risk of plasma-derived vs. recombinant FVIII have been similarly inconclusive and will be reviewed. Other environmental or treatment variables such as concomitant infection or vaccination are suspected to influence inhibitor risk but have not yet been fully investigated.

The need for previously untreated patient population studies in understanding the development of factor VIII inhibitors

The presence of inhibitory antibodies to factor VIII (FVIII) remains one of the most serious complications of haemophilia therapy. Accordingly, understanding risk factors that may contribute to inhibitor developments in young patients with haemophilia A continues to be an area of great interest. Previously untreated patient (PUP) population studies have been instrumental in understanding the aetiology of inhibitor development. These studies have revealed the importance of risk factors such as clotting factor exposure history, ethnicity, and FVIII genotype in the development of inhibitors, while also providing insights into potential risk factors that may be related to therapeutic practice. However, due to differences in study designs and patient populations among previous PUP studies, there are limitations to the value of these studies in deciphering the role of potential risk factors. Therefore, future PUP studies should be prospective, consistent in their study designs and consider all established parameters and also those that possibly may influence inhibitor formation, thereby facilitating a better understanding of the aetiology of inhibitor formation in haemophilia A patients.