Evaluation of factor VIII pharmacokinetics and anti-factor VIII antibodies in four boys with haemophilia A and a poor clinical response to factor VIII

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.

Nonneutralizing antibodies against factor VIII and risk of inhibitor development in severe hemophilia A

Nonneutralizing antibodies against FVIII are detected in untreated or minimally treated patients with hemophilia A. The presence of nonneutralizing antibodies is associated with a substantially increased risk of inhibitor development.

FVIII-binding IgG modulates FVIII half-life in patients with severe and moderate hemophilia A without inhibitors

FVIII-specific IgG antibodies modulate FVIII half-life in patients with hemophilia A, independent of VWF antigen levels and age. Screening for FVIII-specific IgG may be beneficial in tailoring FVIII prophylactic regimens for hemophilia A patients.

High-affinity, noninhibitory pathogenic C1 domain antibodies are present in patients with hemophilia A and inhibitors

Inhibitor formation in hemophilia A is the most feared treatment-related complication of factor VIII (fVIII) therapy. Most inhibitor patients with hemophilia A develop antibodies against the fVIII A2 and C2 domains. Recent evidence demonstrates that the C1 domain contributes to the inhibitor response. Inhibitory anti-C1 monoclonal antibodies (mAbs) have been identified that bind to putative phospholipid and von Willebrand factor (VWF) binding epitopes and block endocytosis of fVIII by antigen presenting cells. We now demonstrate by competitive enzyme-linked immunosorbent assay and hydrogen-deuterium exchange mass spectrometry that 7 of 9 anti-human C1 mAbs tested recognize an epitope distinct from the C1 phospholipid binding site. These mAbs, designated group A, display high binding affinities for fVIII, weakly inhibit fVIII procoagulant activity, poorly inhibit fVIII binding to phospholipid, and exhibit heterogeneity with respect to blocking fVIII binding to VWF. Another mAb, designated group B, inhibits fVIII procoagulant activity, fVIII binding to VWF and phospholipid, fVIIIa incorporation into the intrinsic Xase complex, thrombin generation in plasma, and fVIII uptake by dendritic cells. Group A and B epitopes are distinct from the epitope recognized by the canonical, human-derived inhibitory anti-C1 mAb, KM33, whose epitope overlaps both groups A and B. Antibodies recognizing group A and B epitopes are present in inhibitor plasmas from patients with hemophilia A. Additionally, group A and B mAbs increase fVIII clearance and are pathogenic in a hemophilia A mouse tail snip bleeding model. Group A anti-C1 mAbs represent the first identification of pathogenic, weakly inhibitory antibodies that increase fVIII clearance.

Long-term anti-FVIII antibody response in Bethesda-negative haemophilia A patients receiving continuous replacement therapy

It has previously been shown that patients with haemophilia A may develop non-neutralizing anti-factor VIII (FVIII) antibodies (NNA) that escape detection by the Bethesda assay, but are detected using immune-based assays. We and others found NNAs to be directed not only towards non-functional parts of the protein, but towards all regions of the FVIII protein. We also showed a heterogeneous antibody response towards different FVIII products. However, the clinical relevance and the natural history of NNA remain unclear. Therefore, we followed a cohort of unrelated subjects with haemophilia A for 4 years with the goal of exploring the long-term development of NNA using an enzyme-linked immunosorbent assay (ELISA). Ten of 78 subjects (12·8%) exhibited an immune response that was transient and heterogeneous, and none of the subjects developed an FVIII inhibitor. The result of the ELISA was examined in relation to clinical variables and no significant associations between a positive ELISA and age, F8 mutation, port-à-cath implantation and HCV infection were shown. Interestingly, patients with NNA had significantly fewer bleeding episodes (P = 0·048) compared with NNA-negative subjects. The results indicate that the immune response to FVIII products within an individual may vary over time. However, the clinical impact of NNA remains unclear.

Comparison of clot-based, chromogenic and fluorescence assays for measurement of factor VIII inhibitors in the US Hemophilia Inhibitor Research Study

BACKGROUND

Detection and validation of inhibitors (antibodies) to hemophilia treatment products are important for clinical care, evaluation of product safety and assessment of population trends.

METHODS

Centralized monitoring for factor VIII (FVIII) inhibitors was conducted for patients in the Hemophilia Inhibitor Research Study using a previously reported modified Nijmegen-Bethesda clotting assay (NBA), a chromogenic Bethesda assay (CBA) and a novel fluorescence immunoassay (FLI).

RESULTS

NBA and CBA were performed on 1005 specimens and FLI on 272 specimens. CBA was negative on 880/883 specimens (99.7%) with Nijmegen-Bethesda units (NBU) < 0.5 and positive on 42/42 specimens (100%) with NBU ≥ 2.0 and 43/80 specimens (53.8%) with NBU 0.5-1.9. Among specimens with positive NBA and negative CBA, 58.1% were FLI negative, 12.9% had evidence of lupus anticoagulant, and 35.5% had non-time-dependent inhibition. CBA and FLI were positive on 72.4% and 100% of 1.0-1.9 NBU specimens and 43.1% and 50.0% of 0.5-0.9 NBU specimens. FLI detected antibodies in 98.0% of CBA-positive and 81.6% of NBA-positive specimens (P = 0.004). Among 21 new inhibitors detected by NBA, five (23.8%) with 0.7-1.3 NBU did not react in CBA or FLI. Among previously positive patients with 0.5-1.9 NBU, 7/25 (28%) were not CBA or FLI positive. FLI was positive on 36/169 NBU-negative specimens (21.3%).

CONCLUSIONS

FVIII specificity could not be demonstrated by CBA or FLI for 26% of inhibitors of 0.5-1.9 NBU; such results must be interpreted with caution. Low titer inhibitors detected in clot-based assays should always be repeated, with consideration given to evaluating their reactivity with FVIII using more specific assays.

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.