Abstract Number: PB1159
Meeting: ISTH 2020 Congress
Background: A genetically engineered, humanized, bispecific monoclonal antibody, Emicizumab, mimicking the cofactor activity of activated Factor VIII, has been developed for treatment of Hemophilia A patients, with and without inhibitor. Among 398 patients enrolled in the Clinical Trials, 14 (3.5%) developed anti-drug antibodies (ADAs), 3 of which were classified with potential neutralizing activity. One of those patients, after 5 Exposure Days, developed a stable, high titre, neutralizing ADA, associated with loss of treatment efficacy. In this study we report the biochemical characterization of this antibody.
Aims: Biochemical characterization of the neutralizing anti-Emicizumab antibody developed in a Hemophilia A patient treated with Emicizumab.
- Total and specific ADA purification and sequencing;
- Confirmation of ADA by Western blot;
- Binding between ADA and Emicizumab, the whole molecule and the papain digested fragments, by using Surface Plasmon Resonance (SPR) and Biolayer Interferometry (BI);
Results: The development of ADA was confirmed by Western blot on the total IgG fraction. The sequencing of specific ADA (recovery 1.3% of total IgGs content) showed an extreme polyclonality (in excess of 12 different CDR-H3 variant peptides). This was confirmed by SPR, which identified at least two populations of antibodies binding Emicizumab with different affinities (35nM and 5nM). Moreover, BI analysis carried out after papain digestion of Emicizumab, showed binding of ADA towards both Fab and Fc fragments.
Conclusions: The present study reports the biochemical characterization of the first neutralizing anti-Emicizumab antibody developed in a Hemophilia A patient with inhibitor.
Until now, about 6500 patients have been treated with Emicizumab with few data on the drug immunogenicity in clinical practice. Therefore, the incidence of the anti-Emicizumab antibodies is not clear, yet. A prospective cohort study of patients, treated with Emicizumab, will help to determine the frequency of the anti-Emicizumab antibodies, with and without neutralizing activity.
To cite this abstract in AMA style:Valsecchi C, Gobbi M, Schiavone L, Beeg M, Adams TE, Mancuso ME, Huntington JA, Peyvandi F. Characterization of Neutralizing Anti-emicizumab Antibody Developed in a Hemophilia A Patient [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/characterization-of-neutralizing-anti-emicizumab-antibody-developed-in-a-hemophilia-a-patient/. Accessed January 28, 2022.
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