Neutralizing antidrug antibody to emicizumab in patients with severe hemophilia A: Case report of a first noninhibitor patient and review of the literature
Hande Kızılocak, Michael F. Guerrera, Guy Young
Abstract
Background: Hemophilia A (HA) is a genetic bleeding disorder characterized by the deficiency of the coagulation protein factor (F) VIII (FVIII). The development of neutralizing antidrug antibodies (ADAs) to factor concentrates (inhibitors) created an unmet need for novel therapies. The first agent to address this need is emicizumab. Key Clinical Question: Can emicizumab ADA occur in patients with HA without FVIII inhibitors? Clinical Approach: A new case (the first in a noninhibitor patient) presented with unexpected and excessive bleeding and a prolonged activated partial thromboplastin time. The patient was evaluated by assessing FVIII levels, and the previously published modified version of the Bethesda assay was used to determine the level of ADA to emicizumab. Conclusion: Although emicizumab is very effective and has minimal immunogenicity, ADAs, albeit rare, can still occur. There have been 4 previously published anti-emicizumab ADA cases with severe HA with inhibitors, and herein, we describe 1 new case with severe HA without inhibitors.