Characterization of the neutralizing anti-emicizumab antibody in a patient with hemophilia A and inhibitor

J Thromb Haemost. 2021 Mar;19(3):711-718. doi: 10.1111/jth.15226. Epub 2021 Feb 1.


Background: The genetically engineered, humanized, bispecific monoclonal antibody emicizumab (Hemlibra) that mimics the cofactor activity of activated factor VIII (FVIII) has been approved for treatment of hemophilia A patients with and without inhibitor. In the pivotal premarketing clinical trials, emicizumab prophylaxis significantly reduced bleeding rates compared with previous treatments and was well tolerated. However, a consequence of this novel therapy may be the host immune response to a foreign protein.

Objective: Characterization of the neutralizing anti-emicizumab antibody associated with the loss of treatment efficacy.

Patient: A pediatric hemophilia A patient with inhibitor enrolled in the HAVEN2 (Study of Emicizumab Administered Subcutaneously (SC) in Pediatric Participants With Hemophilia A and Factor VIII (FVIII) Inhibitors) clinical trial.

Methods: The anti-emicizumab antibody has been characterized with Western blot and enzyme-linked immunosorbent assay (ELISA). The antibody was affinity purified and sequenced. Binding affinity to full-length and papain-digested emicizumab was analyzed using surface plasmon resonance and byo-layer interferometry.

Results: The neutralizing anti-emicizumab antibody was highly polyclonal with high-affinity binding mainly to the Fab portion of emicizumab with a small amount of binding to the Fc portion. Molecular interaction experiments between emicizumab and the purified antibody indicated the presence of at least two components with similar affinities.

Conclusions: Although the incidence of neutralizing anti-emicizumab antibody is rare, this study highlights the importance of a close monitoring and the need of a simple laboratory assay to promptly detect these antibodies in patients with a history of poor drug efficacy.

Keywords: anti-drug antibody; emicizumab; hemophilia; immunoassay; surveillance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Bispecific*
  • Antibodies, Monoclonal, Humanized
  • Antibodies, Neutralizing
  • Child
  • Factor VIII
  • Hemophilia A* / diagnosis
  • Hemophilia A* / drug therapy
  • Humans


  • Antibodies, Bispecific
  • Antibodies, Monoclonal, Humanized
  • Antibodies, Neutralizing
  • emicizumab
  • Factor VIII