Nonneutralizing FVIII-specific antibody signatures in patients with Hemophilia A and in healthy donors

Comprehensive domain-specific analysis and immunoglobulin G profiling of anti-factor VIII antibodies using a bead-based multiplex immunoassay

BACKGROUND

Antibodies against factor (F)VIII are a major complication in the treatment of patients with severe hemophilia A. The Nijmegen-Bethesda assay (NBA) is the gold standard for detection of neutralizing antibodies (inhibitors), whereas both inhibitors and nonneutralizing antibodies can be detected by immunoassays such as enzyme-linked immunosorbent assay (ELISA) and multiplex bead-based assays.

OBJECTIVES

Evaluation of an in-house Luminex bead-based assay (LumiTope) compared with a commercially available ELISA and NBA.

METHODS

The LumiTope method comprised full-length and B-domain-deleted FVIII as well as 9 purified FVIII single or multidomains. The respective proteins were coupled to magnetic beads to detect domain-specific immunoglobulin (IgG; IgG1-4) anti-FVIII antibodies in a large cohort of patients with hemophilia A with and without inhibitors.

RESULTS

Overall, LumiTope assay had a high sensitivity (94.9%) and specificity (91.2%), particularly in patients with low-titer inhibitors compared with ELISA (sensitivity of 72.2% vs 27.7%). IgG4 was the most abundant IgG subclass in NBA-positive patients. NBA-positive and -negative patients showed different domain profiles. Patients with genetic variants in the heavy chain predominantly exhibited antibodies specific to this chain, while those with a light-chain variant showed a more diverse distribution of antibody specificities. Patients with an intron 22 inversion resembled those with a light-chain defect, with a majority of antibodies targeting the light chain.

CONCLUSION

LumiTope assay provides a sensitive and specific method for not only detection but also domain specification of anti-FVIII-antibodies. Implementation of bead-based assays could improve antibody detection, profiling, and comparability of results and complement NBA.

The self-reactive FVIII T cell repertoire in healthy individuals relies on a short set of epitopes and public clonotypes

Non-mutated FVIII-specific CD4 T cell epitopes have been recently found to contribute to the development of inhibitors in patients with hemophilia A (HA), while auto-reactive CD4 T cells specific to FVIII circulate in the blood of healthy individuals at a frequency close to the foreign protein ovalbumin. Thus, although FVIII is a self-protein, the central tolerance raised against FVIII appears to be low. In this study, we conducted a comprehensive analysis of the FVIII CD4 T cell repertoire in 29 healthy donors. Sequencing of the CDR3β TCR region from isolated FVIII-specific CD4 T cells revealed a limited usage and pairing of TRBV and TRBJ genes as well as a mostly hydrophobic composition of the CDR3β region according to their auto-reactivity. The FVIII repertoire is dominated by a few clonotypes, with only 13 clonotypes accounting for half of the FVIII response. Through a large-scale epitope mapping of the full-length FVIII sequence, we identified 18 immunodominant epitopes located in the A1, A3, C1, and C2 domains and covering half of the T cell response. These epitopes exhibited a broad specificity for HLA-DR or DP molecules or both. T cell priming with this reduced set of peptides revealed that highly expanded clonotypes specific to these epitopes were responsible individually for up to 32% of the total FVIII repertoire. These FVIII T cell epitopes and clonotypes were shared among HLA-unrelated donors tested and previously reported HA patients. Our study highlights the role of the auto-reactive T cell response against FVIII in HA and its similarity to the response observed in healthy individuals. Thus, it provides valuable insights for the development of new tolerance induction and deimmunization strategies.

The spectrum of neutralizing and non-neutralizing anti-FVIII antibodies in a nationwide cohort of 788 persons with hemophilia A

Objectives

Anti-factor VIII (FVIII) antibodies have been reported to exhibit both neutralizing and non-neutralizing characteristics. This is the first study investigating the full spectrum of FVIII-specific antibodies, including non-neutralizing antibodies, very-low titer inhibitors, and inhibitors, in a large nationwide population of persons with hemophilia A of all severities.

Methods

All persons with hemophilia A (mild (FVIII > 5-40 IU/dL)/moderate [FVIII 1-5 IU/dL)/severe (FVIII < 1 IU/dL)] with an available plasma sample who participated in the sixth Hemophilia in the Netherlands study between 2018 and 2019 were included. The presence of anti-FVIII antibodies of the immunoglobulin A, M, and G isotypes and IgG subclasses, along with antibody titer levels, were assessed using direct-binding ELISAs. FVIII specificity was assessed using a competition-based ELISA approach. The inhibitor status was determined using the Nijmegen ultra-sensitive Bethesda assay (NusBA) and the Nijmegen Bethesda assay (NBA).

Results

In total, 788 persons with hemophilia A (336 (42.6%) mild, 123 (15.6%) moderate, 329 (41.8%) severe hemophilia) were included. The median age was 45 years (IQR 24-60), and the majority (50.9%) had over 150 exposure days to FVIII concentrates. Within our population, 144 (18.3%) individuals had non-neutralizing FVIII-specific antibodies, 10 (1.3%) had very low-titer inhibitors (NusBA positive; NBA negative), and 13 (1.6%) had inhibitors (both NusBA and NBA positive). IgG1 was the most abundant FVIII-specific antibody subclass, and the highest titer levels were found for IgG4. In individuals without a reported history of inhibitor development, no clear differences were observed in antibody patterns between those who were minimally or highly exposed to FVIII concentrates. IgG4 subclass antibodies were only observed in persons with a reported history of FVIII inhibitor or in those with a currently detected (very low-titer) inhibitor.

Conclusion

In this cross-sectional study, we identified non-neutralizing antibodies in a relatively large proportion of persons with hemophilia A. In contrast, in our population, consisting of persons highly exposed to FVIII concentrates, (very low-titer) inhibitors were detected only in a small proportion of persons, reflecting a well-tolerized population. Hence, our findings suggest that only a small subpopulation of non-neutralizing FVIII-specific antibodies is associated with clinically relevant inhibitors.

Two-center validation of assays for the detection of binding and neutralizing anti-factor VIII antibodies

INTRODUCTION

Patients with hemophilia A treated with coagulation Factor VIII (FVIII) products are at risk for developing anti-FVIII antibodies. The ABIRISK Consortium aimed to provide knowledge on the formation and detection of anti-drug antibodies against biopharmaceutical products, including FVIII. Accordingly, standardized and validated assays for the detection of binding (total) and neutralizing antibodies are needed.

AIM

Two-center validation of an ELISA for the detection of total FVIII-binding IgG-antibodies and Nijmegen-Bethesda assays for the quantification of FVIII-neutralizing antibodies according to consensus validation guidelines.

METHODS

Validation of assays at both sites was done according to published recommendations and included preanalytics, the determination of key assay parameters, including cut-points, assay sensitivity, precision, and FVIII interference.

RESULTS

The validated assays reproducibly detected FVIII-binding and -neutralizing antibodies with comparable performance in both laboratories. Floating screening cut-points were established for both assays. Determined mass-based sensitivity of both assays (all values ≤66 ng/mL) complied with the minimum sensitivity for the detection of anti-drug antibodies as recommended by the FDA (<100 ng/mL). Intra- and inter-assay coefficients of variation did not exceed 25%. Assay validation further revealed that pre-analytical heat treatment led to potentially false-positive ELISA results, while up to 0.15 IU/mL, residual FVIII showed no significant impact. Overall, good agreement of results was found for patient samples analyzed at both study sites.

CONCLUSION

Comprehensive validation of different anti-FVIII-antibody assays in two laboratories gave novel insights into the impact of pre-analytical sample treatment as well as the comparability of test results generated by the use of methodically different assays.

Anti-FVIII antibodies in Black and White hemophilia A subjects: do F8 haplotypes play a role?

The most common complication in hemophilia A (HA) treatment, affecting 25% to 30% of patients with severe HA, is the development of alloimmune inhibitors that foreclose the ability of infused factor VIII (FVIII) to participate in coagulation. Inhibitors confer significant pathology on affected individuals and present major complexities in their management. Inhibitors are more common in African American patients, and it has been hypothesized that this is a consequence of haplotype (H)-treatment product mismatch. F8 haplotypes H1 to H5 are defined by nonsynonymous single-nucleotide polymorphisms encoding sequence variations at FVIII residues 1241, 2238, and 484. Haplotypes H2 to H5 are more prevalent in individuals with Black African ancestry, whereas 80% to 90% of the White population has the H1 haplotype. This study used an established multiplex fluorescence immunoassay to determine anti-FVIII antibody titers in plasma from 394 individuals with HA (188 Black, 206 White), measuring their binding to recombinant full-length H1 and H2 and B-domain-deleted (BDD) H1/H2, H3/H5, and H4 FVIII proteins. Inhibitor titers were determined using a chromogenic assay and linear B-cell epitopes characterized using peptide microarrays. FVIII-reactive antibodies were readily detected in most individuals with HA, with higher titers in those with a current inhibitor, as expected. Neither total nor inhibitory antibody titers correlated with F8 haplotype mismatches, and peptides with D1241E and M2238V polymorphisms did not comprise linear B-cell epitopes. Interestingly, compared with the full-length FVIII products, the BDD-FVIII proteins were markedly more reactive with plasma antibodies. The stronger immunoreactivity of BDD-FVIII suggests that B-domain removal might expose novel B-cell epitopes, perhaps through conformational rearrangements of FVIII domains.

Methods for anti-factor VIII antibody levels in haemophilia A patients - validation of a multiplex immunoassay and comparability with assays measuring non-neutralising and neutralising antibodies (inhibitors)

INTRODUCTION

The development of neutralising (inhibitors) and non-neutralising antibodies (NNAs) is a complication to factor replacement therapy in haemophilia. The diagnostic methods available lack standardisation, have high inter-laboratory variation, and false-negative as well as false-positive results may affect treatment. Both functional inhibitors and NNAs may be detected with higher reproducibility, sensitivity and specificity using the immunological Luminex xMAP-based fluorescence-immunoassay (xFLI).

AIM

Validation of our xFLI and comparability with enzyme-linked immunosorbent assay (ELISA) and chromogenic Nijmegen-Bethesda assay (CBA) for anti-FVIII antibodies in haemophilia A (HA) patients.

METHODS

The xFLI method was developed with full-length and B-domain deleted factor coupled to magnetic beads, optimised and validated for performance characteristics. Comparability with ELISA and CBA was evaluated in HA patient samples (n = 112), serial samples in six inhibitor patients and reference interval and decision-limits in healthy donors (n = 44).

RESULTS

The intra- and inter-assay precision (CV%) for the xFLI method was below 6% and detection limit (LLOQ) .084 ng/mL (NovoEight). All ELISA-positive samples were positive with either Advate or NovoEight. Additionally, 10.7%-14.3% were xFLI-positive and ELISA-negative. All but one CBA-positive sample was above 3SD with xFLI; one was between 2 and 3SD. 29.1% were xFLI-positive and CBA negative. The overall concordance between xFLI and ELISA was 82.1% and xFLI and CBA 77.9%.

CONCLUSION

The anti-FVIII antibody xFLI method is adaptable to clinical practice and more sensitive and reproducible than ELISA and CBA. Actual NNA titers are determined to both full-length and B-domain deleted FVIII. The xFLI is thus valuable for confirmation of all anti-FVIII antibodies.

Immunogenicity of Current and New Therapies for Hemophilia A

Anti-drug antibody (ADA) development is a significant complication in the treatment of several conditions. For decades, the mainstay of hemophilia A treatment was the replacement of deficient coagulation factor VIII (FVIII) to restore hemostasis, control, and prevent bleeding events. Recently, new products have emerged for hemophilia A replacement therapy, including bioengineered FVIII molecules with enhanced pharmacokinetic profiles: the extended half-life (EHL) recombinant FVIII products. However, the main complication resulting from replacement treatment in hemophilia A is the development of anti-FVIII neutralizing alloantibodies, known as inhibitors, affecting approximately 25–30% of severe hemophilia A patients. Therefore, the immunogenicity of each FVIII product and the mechanisms that could help increase the tolerance to these products have become important research topics in hemophilia A. Furthermore, patients with inhibitors continue to require effective treatment for breakthrough bleedings and procedures, despite the availability of non-replacement therapy, such as emicizumab. Herein, we discuss the currently licensed treatments available for hemophilia A and the immunogenicity of new therapies, such as EHL-rFVIII products, compared to other products available.