Characteristics of hemophilia patients with factor VIII inhibitors detected by prospective screening

Adeno-associated virus-mediated expression of activated factor V (FVa) for hemophilia phenotypic correction

Adeno-associated virus (AAV) gene therapy has been successfully applied in hemophilia patients excluding patients with inhibitors. During the coagulation pathway, activated factor V (FVa) functions downstream as a cofactor of activated factor X (FXa) to amplify thrombin generation. We hypothesize that the expression of FVa via gene therapy can improve hemostasis of both factor IX and FVIII deficiencies, regardless of clotting factor inhibitor. A human FVa (hFVa) expression cassette was constructed, and AAV8 vectors encoding hFVa (AAV8/TTR-hFVa) were intravenously administrated into mice with hemophilia A and B with or without FVIII inhibitors. Hemostasis, including hFVa level, activated partial thromboplastin time (aPTT), tail clip, and the saphenous vein bleeding assay (SVBA), was evaluated. In hemophilia B mice, a dose of 4 × 1013 vg/kg AAV8/TTR-hFVa vectors achieved a complete phenotypic correction over 28 weeks. In hemophilia A mice, hemostasis improvement was also achieved, regardless of FVIII inhibitor development. In vivo hemostasis efficacy was confirmed by tail clip and SVBA. Interestingly, while minimal shortening of aPTT was observed at a lower dose of AAV8 vectors, hemostasis improvement was still achieved via in vivo bleeding assays. Collectively, FVa-based AAV gene therapy shows promise for hemostasis correction in hemophilia, regardless of inhibitor development and no potential risk for thrombosis.

An Update on Laboratory Diagnostics in Haemophilia A and B

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

Long-term safety and efficacy of emicizumab for up to 5.8 years and patients' perceptions of symptoms and daily life: A phase 1/2 study in patients with severe haemophilia A

Introduction

Safety and efficacy results of the phase 1 study and phase 1/2 extension study of the bispecific antibody emicizumab in patients with severe haemophilia A with or without factor VIII inhibitors for up to 2.8 years were reported previously.

Aim

To evaluate further longer‐term data including patients’ perceptions at study completion.

Methods

Emicizumab was administered subcutaneously once weekly at maintenance doses of 0.3, 1 or 3 mg/kg with potential up‐titration. All patients were later switched to the approved maintenance dose of 1.5 mg/kg.

Results

Eighteen patients received emicizumab for up to 5.8 years. Most adverse events were mild and unrelated to emicizumab. Annualized bleeding rates (ABRs) for bleeds treated with coagulation factors decreased from pre‐emicizumab rates or remained zero in all patients. The median ABRs were low at 1.25, 0.83 and 0.22 during the 0.3, 1 and 3 mg/kg dosing periods, respectively. Of 8 patients who decreased their doses from 3 to 1.5 mg/kg, ABRs decreased in 4, remained at zero in 2, and increased in 2. Total time spent with symptoms associated with treated bleeds decreased in all patients except 2. All patients answered ‘improved’ for bleeding severity and time until bleeding stops, except 1 answering ‘slightly improved’. Most patients answered ‘improved’ or ‘slightly improved’’ for daily life and feelings; in particular, all patients except 1 answered ‘improved’ or ‘slightly improved’ for anxiety.

Conclusions

Long‐term emicizumab prophylaxis for up to 5.8 years was safe and efficacious, and may improve patients’ daily lives and feelings, regardless of inhibitor status.

Exploring the Potential Feasibility of Intra-Articular Adeno-Associated Virus-Mediated Gene Therapy for Hemophilia Arthropathy

Hemophilia arthropathy (HA) represents the majority of morbidity in severe hemophilia patients, especially in resource-limited countries. Adeno-associated virus (AAV)-mediated gene therapy is showing promise for managing hemophilia. However, patients with neutralizing antibodies (NAbs) against AAV, and inhibitors to clotting factors, are excluded from such therapy. This study explored the feasibility of AAV-mediated local gene therapy for HA. Factor VIII knockout (FVIII^-/-) mice, with or without a FVIII inhibitor, were subjected to hemarthrosis induction and treated with either intravenous (IV) or intraarticular (IA) recombinant human factor VIII (rhFVIII). To investigate whether rhFVIII carried the risk to develop a FVIII inhibitor, FVIII^-/- mice were treated with three doses of IV or IA rhFVIII and inhibitor development was measured. In patients with established HA requiring synovial fluid aspiration, plasma, and synovial fluid were collected and measured for anti-AAV capsid IgG (serotypes 1-9 and 843) and NAbs for AAV843. IA rhFVIII provided better protection from synovitis compared with IV rhFVIII, with or without the FVIII inhibitor. While IV rhFVIII led to all FVIII^-/- mice developing an FVIII inhibitor (n = 31, median 4.9 Bethesda units [BU]/mL), only 50% of the mice developed a FVIII inhibitor by IA administration, and at a lower titer (median 0.55 BU/mL). In hemophilia patients, total anti-AAV IgG was lowest for AAV4 and AAV5, both in plasma and synovial fluid. Anti-AAV IgGs in synovial fluid for most samples were lower or similar to the plasma levels. These results show that direct IA rhFVIII administration yields better protection against bleeding-induced joint damage, even in the presence of an inhibitor antibody. IA rhFVIII delivery carried a lower risk of FVIII inhibitor formation compared with IV FVIII. The anti-AAV antibody level in synovial fluid was similar or lower than the plasma level, supporting the feasibility of local gene therapy for managing HA.

Prevalence of inhibitors and clinical characteristics in patients with haemophilia in a middle-income Latin American country

INTRODUCTION

Development of inhibitors is the most serious complication in patients with haemophilia (PWH). The prevalence of inhibitors in patients with severe haemophilia A (HA) is approximately 25%-30%. Inhibitor prevalence differs among populations. Some studies report a prevalence of almost twice in Hispanic as compared to Caucasian patients. Most data available, on the prevalence of inhibitors and their predisposing factors, originate from centres in developed countries.

AIM

Establish the prevalence of inhibitors of FVIII and FIX in Mexico.

METHODS

This was an observational, cross-sectional and descriptive study. The records of all patients diagnosed with haemophilia A (HA) or B (HB), with and without inhibitors, were included. Clinical and demographical characteristics of patients with inhibitors were assessed. Statistical analysis was performed using IBM SPSS version 22. The Ethics Committees of the various participating institutions approved this study.

RESULTS

A total of 1455 patients from the 20 participating centres were recruited, from which 1208 (83.02%) had HA and 247 (16.97%) were diagnosed with HB. The presence of inhibitors in severe HA was reported in 93/777(11.96%), and 10/162 (6.17%) in severe HB. Of them, 91.7% exhibited high titres in HA and 100% in HB.

CONCLUSION

In Mexico, the general prevalence of inhibitors varies considerably among centres. This study established a basis of comparison for future development and advances in the treatment and follow-up of patients. These findings also augment our understanding of risk factors related to inhibitor development.

Distinguishing lupus anticoagulants from factor VIII inhibitors in haemophilic and non-haemophilic patients

INTRODUCTION

Accurate diagnosis of an inhibitor, a neutralizing antibody to infused factor VIII (FVIII), is essential for appropriate management of haemophilia A (HA). Low-titre inhibitors may be difficult to diagnose due to high rates of false-positive inhibitor results in that range. Transient low-titre inhibitors and false-positive inhibitors may be due to the presence of a lupus anticoagulant (LA) or other non-specific antibodies. Fluorescence immunoassay (FLI) to detect antibodies to FVIII is a sensitive method to identify inhibitors in HA. Evaluations of antibody profiles by various groups have demonstrated that haemophilic inhibitors detected by Nijmegen-Bethesda (NBA) and chromogenic Bethesda (CBA) assays correlate with positivity for anti-FVIII immunoglobulin (Ig) G1 and G4.

AIM

This study sought to determine whether FLI could distinguish false-positive FVIII inhibitor results related to LAs from clinically relevant FVIII inhibitors in HA patients.

METHODS

Samples from haemophilic and non-haemophilic subjects were tested for LA, specific FVIII inhibitors by NBA and CBA, and anti-FVIII immunoglobulin profiles by FLI.

RESULTS

No samples from LA-positive non-haemophilic subjects were positive by FLI for anti-FVIII IgG4. Conversely, 91% of NBA-positive samples from haemophilia subjects were positive for anti-FVIII IgG4. Two of 11 haemophilia subjects had samples negative for anti-FVIII IgG4 and CBA, which likely represented LA rather than FVIII inhibitor presence.

CONCLUSIONS

Assessment of anti-FVIII profiles along with the CBA may be useful to distinguish a clinically relevant low-titre FVIII inhibitor from a transient LA in HA patients.

An Observational Study from Long-Term AAV Re-administration in Two Hemophilia Dogs

Adeno-associated virus (AAV) vectors have been successfully applied in hemophilia clinical trials. However, this approach is limited to patients without AAV-neutralizing antibodies (NAbs). In this study, we explored the feasibility of AAV re-administration in hemophilia A dogs treated initially 8 years ago with AAV8.canine FVIII. After the re-administration in two NAb-negative dogs with AAV8 vectors carrying human factor VIII (hFVIII), along with the proteasome inhibitor bortezomib, we observed a phenotypic improvement in both dogs that persisted in one dog. Phenotypic improvement disappeared at 59 days after re-administration in the other dog, and specific cytotoxic T lymphocytes (CTLs) to the capsid were detected at day 17, but not to hFVIII. hFVIII inhibitors were observed at day 59 and gradually increased. Mechanistic studies demonstrated an increase in pro-inflammatory cytokines, a decrease in immunomodulatory cytokines, as well as lower Tregs after re-administration. These results suggest that hFVIII inhibitor development may contribute to the therapeutic failure via immune response activation. Interestingly, it takes about 30–50 days for AAV NAb titers to decrease by half. Collectively, this study suggests that re-administration of the same AAV serotype after long-term follow-up is feasible and that the study of AAV NAb kinetics will provide important information for predicating the efficacy of re-administration.

Anti-Drug Antibodies: Emerging Approaches to Predict, Reduce or Reverse Biotherapeutic Immunogenicity

The development of anti-drug antibodies (ADAs) following administration of biotherapeutics to patients is a vexing problem that is attracting increasing attention from pharmaceutical and biotechnology companies. This serious clinical problem is also spawning creative research into novel approaches to predict, avoid, and in some cases even reverse such deleterious immune responses. CD4⁺ T cells are essential players in the development of most ADAs, while memory B-cell and long-lived plasma cells amplify and maintain these responses. This review summarizes methods to predict and experimentally identify T-cell and B-cell epitopes in therapeutic proteins, with a particular focus on blood coagulation factor VIII (FVIII), whose immunogenicity is clinically significant and is the subject of intensive current research. Methods to phenotype ADA responses in humans are described, including T-cell stimulation assays, and both established and novel approaches to determine the titers, epitopes and isotypes of the ADAs themselves. Although rational protein engineering can reduce the immunogenicity of many biotherapeutics, complementary, novel approaches to induce specific tolerance, especially during initial exposures, are expected to play significant roles in future efforts to reduce or reverse these unwanted immune responses.

Limit of detection and threshold for positivity of the Centers for Disease Control and Prevention assay for factor VIII inhibitors

Essentials Immunologic methods detect factor VIII (FVIII) antibodies in some inhibitor-negative specimens. Specimens were tested by modified Nijmegen-Bethesda assay (NBA) and fluorescence immunoassay. The NBA with preanalytical heat inactivation detects FVIII inhibitors down to 0.2 NBU. IgG4 frequency validates the established threshold for positivity of ≥ 0.5 NBU for this NBA.

SUMMARY

Background The Bethesda assay for measurement of factor VIII inhibitors called for quantification of positive inhibitors by using dilutions producing 25-75% residual activity (RA), corresponding to 0.4-2.0 Bethesda units, with the use of 'more sensitive methods' for samples with RA closer to 100% being recommended. The Nijmegen modification (Nijmegen-Bethesda assay [NBA]) changed the reagents used but not these calculations. Some specimens negative by the NBA have been shown to have FVIII antibodies detectable with sensitive immunologic methods. Objective To examine the performance at very low inhibitor titers of the Centers for Disease Control and Prevention (CDC)-modified NBA (CDC-NBA), which includes preanalytic heat inactivation to liberate bound anti-FVIII antibodies. Methods Specimens with known inhibitors were tested with the CDC-NBA. IgG4 anti-FVIII antibodies were measured by fluorescence immunoassay (FLI). Results Diluted inhibitors showed linearity below 0.4 Nijmegen-Bethesda units (NBU). With four statistical methods, the limit of detection of the CDC-NBA was determined to be 0.2 NBU. IgG4 anti-FVIII antibodies, which correlate most strongly with functional inhibitors, were present at rates above the background rate of healthy controls in specimens with titers ≥ 0.2 NBU and showed an increase in frequency from 14.3% at 0.4 NBU to 67% at the established threshold for positivity of 0.5 NBU. Conclusions The CDC-NBA can detect inhibitors down to 0.2 NBU. The FLI, which is more sensitive, demonstrates anti-FVIII IgG4 in some patients with negative (< 0.5) NBU. The sharp increase in IgG4 frequency between 0.4 and 0.5 NBU validates the established threshold for positivity of ≥ 0.5 NBU for the CDC-NBA, supporting the need for method-specific thresholds.