Anti-factor VIII antibodies in brothers with haemophilia A share similar characteristics

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.

Longitudinal profiling of anti-factor VIII antibodies in Japanese patients with congenital hemophilia A during factor VIII replacement and immune-tolerance induction therapy

When patients with hemophilia A develop factor VIII (FVIII) inhibitors, FVIII replacement therapy becomes ineffective. Although immune-tolerance induction (ITI) therapy has been used to eradicate inhibitors, treatment is unsuccessful in approximately 30% of cases. However, the mechanism behind treatment failure remains unclarified. We retrospectively examined the longitudinal profiles of immunoglobulin G (IgG) subclasses and/or the inhibitory activities of FVIII in plasma samples from 14 Japanese patients with congenital hemophilia A during hemostatic, FVIII replacement, and/or ITI therapies. In five patients, an increase in IgG4 was observed simultaneously with a decrease in IgG1 when the patient had a history of relatively high FVIII inhibitor titers, reflecting an apparent change in humoral immunity. In addition, we examined the reactivity and specificity of the patients' anti-FVIII IgG1 and IgG4 to FVIII domains by immunoblotting. Under our experimental conditions, plasma from three patients with historically higher inhibitor titers appeared to have high titers of antibodies against the A2-a2 domain, which did not necessarily correlate with ITI failure. These observations may improve scientific understanding of the immune response to infused FVIII in patients with hemophilia A.

First observation of inhibitor development against efmoroctocog alfa in France

In patients with severe haemophilia receiving clotting factor concentrates, the risk of immunisation against their usual treatment is still patent and feared. New haemophilia drug treatments with an extended half-life have become available over the past few years. The risk of inhibitor development to these new treatments is unclear. We report the case of a 51-year-old man with severe haemophilia A, who was previously treated with no history of inhibitor development. Soon after a switch in his treatment to efmoroctocog alfa he developed an inhibitor against this recombinant Fc fusion extended half-life FVIII (rFc-FVIII) product. The patient was on an on-demand treatment regimen and was treated for mucosal bleeding. The inhibitor was characterised as type I, with classical epitope mapping. The spontaneous evolution of this inhibitor was favourable, but an anamnestic response led to a switch in his treatment to emicizumab.