Prophylactic bypassing agent use before and during immune tolerance induction in patients with haemophilia A and inhibitors toFVIII

Assessing the value of bypassing agent therapy used prophylactic versus on-demand, during immune tolerance induction for treatment of inhibitors: a retrospective chart review

BACKGROUND

Haemophilia A is a bleeding disorder caused by deficiency of coagulation factor VIII (FVIII) which leads to severe and repeated bleedings. There is a need to understand the optimal treatment pathway for FVIII inhibitors with the use of immune tolerance induction (ITI) and the role of haemostatic 'bypassing' agents (BPA) on-demand (OD) or prophylactically (Px). The aim of this study was to gain a better understanding of the real-world use of BPA therapy administered prophylactically or on-demand concomitant with ITI, for the treatment of an inhibitor to FVIII replacement therapy in patients with severe haemophilia A.

METHODS

Retrospective observational data were used to capture disease management information for patients who were aged 16 or under and had received ITI and BPA treatment for their most recent inhibitor from Jan-2015 to Jan-2019, for 47 patients in the UK and Germany. Descriptive comparisons of the clinical effectiveness and resource utilisation of Px and OD BPA therapy during ITI were conducted.

RESULTS

During ITI and BPA treatment, for an inhibitor, bleeding events averaged 1.5 and 1.2 for Px and OD treatment respectively. Compared to only BPA therapy we see 3.4 and 1.4 bleeding events for Px and OD respectively during an inhibitor.

CONCLUSION

Baseline disease characteristics differed between BPA therapy cohorts and this resulted in higher clinical effectiveness of ITI treatment alongside BPA Px than BPA OD during an inhibitor.

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.

Predicted coagulation potential using an in vitro simulated model of emicizumab prophylaxis and immune tolerance induction therapy in hemophilia A patients with inhibitor

Emicizumab reduces bleeding in hemophilia A patients with inhibitor (HA-inh). A combination of immune tolerance induction therapy (ITI) and emicizumab prophylaxis may provide additional benefits, but coagulation potential during this treatment remains unknown. We assessed coagulation potentials in simulated ITI models in vitro using modified-clot waveform analysis. Factor (F)VIII-deficient plasma preincubated with anti-A2 and anti-C2 monoclonal antibodies was reacted with emicizumab (50 µg/mL) (emicizumab-HA-plasma), then spiking bypassing agents (BPAs): activated prothrombin complex concentrates (aPCC 1.3 IU/mL; 50 IU/kg), recombinant factor (rF)VIIa (2.2 µg/mL; 90 µg/kg), and FVIIa/FX (1.5 µg/mL; 60 µg/kg), and/or FVIII (100, 200 IU/dL). Coagulation potentials in emicizumab-HA-plasma (10 BU/mL) remained within the normal range when BPA and FVIII were both present. In emicizumab-HA-plasma (1 BU/mL) with BPA and FVIII (200 IU/dL), they were near or beyond the normal range, but those with a half concentration of rFVIIa based on the half-life in blood were within the normal range. In samples without inhibitor, coagulation potentials with combined BPA and FVIII were far beyond the normal range but with FVIII (100 IU/dL) and rFVIIa at half concentration they remained within the normal range. These results may provide information on the feasibility of concurrent ITI under emicizumab prophylaxis.

Hemophilia A with inhibitor: Immune tolerance induction (ITI) in the mirror of time

Inhibitor (neutralizing antibodies) development remains the most significant complication in patients with severe congenital hemophilia A receiving exogenous factor VIII (FVIII). Although our understanding of the pathophysiology of inhibitor development has advanced, the knowledge gained has not yet translated into a robust decline in incidence, with the overall risk remaining at ∼30%. Immune Tolerance Induction (ITI) is the only current method to successfully eradicate an inhibitor and achieve long-term tolerance. Although current practice utilizes a wide variety of ITI regimens, identification of an optimal regimen has not emerged. Over the last decade, the number of replacement products available in hemophilia has greatly expanded. The cumulative evidence with each product for use in ITI is often lacking. Most recently emicizumab, a humanized monoclonal bi-specific antibody that substitutes for the scaffolding effect of FVIIIa was approved; this agent prevents bleeding in both inhibitor and non-inhibitor patients. The use of emicizumab will bring about a new era in care that will require clinicians to challenge current practice paradigms including use and administration of ITI. This review will summarize the main clinical ITI data and practices for patients with severe congenital hemophilia A with inhibitors (CHAwI) over the last four decades and will highlight current studies in the field, with attention to open questions.