Reappearance of inhibitor in a tolerized patient with severe haemophilia A during FVIII‐free emicizumab therapy.

Neutralizing anti-FVIII IgG5 and FVIII-specific CD4+ T cells6 have been detected in some patients after successful ITI; this suggests that active FVIII-specific tolerance is mediated by anti-idiotypic antibodies5 and probably regulatory T cells, rather than resulting from the mere elimination of FVIII-specific immune effectors. Keywords: emicizumab; FVIII inhibitor; haemophilia A; immune tolerance induction EN emicizumab FVIII inhibitor haemophilia A immune tolerance induction e581 e584 4 07/21/21 20210701 NES 210701 ACKNOWLEDGEMENTS We acknowledge Sadyo Darame for her technical assistance. However, around 30% of patients develop neutralizing antibodies against FVIII (also known as "inhibitors"), and those with high inhibitor titres become resistant to FVIII replacement therapy. In high-titre inhibitor-positive patients, however, the cautious use of FVIII bypassing agents in conjunction with emicizumab therapy is the only option.2 The availability of emicizumab raises several questions, particularly concerning FVIII prophylaxis after successful ITI. [Extracted from the article]