Immune tolerance induction in paediatric patients with haemophilia A and inhibitors receiving emicizumab prophylaxis.

Introduction The formation of neutralizing antifactor VIII (fVIII) antibodies, called inhibitors, is the most common complication in modern haemophilia A care. Novel non-factor replacement therapies, such as emicizumab, have sought to address the limitations of bypassing agents for bleeding management in patients with inhibitors. However, immune tolerance induction (ITI) remains the primary method for eradicating inhibitors and restoring the hemostatic response to fVIII. Aim The aim of this study was to review a case series of paediatric patients with haemophilia A and inhibitors who have received ITI for inhibitor eradication concomitantly with emicizumab prophylaxis for bleeding prevention. Methods Single institution retrospective chart review of paediatric patients with severe haemophilia A receiving ITI and emicizumab. Results Seven patients were included in this cohort. Six patients used three different recombinant fVIII products at 100 IU/kg three times per week, and one patient used a plasma-derived fVIII product at an initial dose of 50 IU/kg three times per week. Three patients achieved a negative inhibitor titre <0.6 Chromogenic Bethesda Units per mL (CBU/mL), and two patients achieved a normal fVIII recovery >= 66%. There were nine bleeding events in four patients, but no thrombotic events. All patients remained on ITI and emicizumab. Conclusion Immune tolerance induction while on emicizumab prophylaxis is a feasible approach in paediatric haemophilia A patients with inhibitors. This is the first report of the concomitant use of ITI in patients receiving emicizumab prophylaxis described as the 'Atlanta Protocol'.