The spectrum of neutralizing and non-neutralizing anti-FVIII antibodies in a nationwide cohort of 788 persons with hemophilia A.

Anti-factor VIII (FVIII) antibodies have been reported to exhibit both neutralizing and non-neutralizing characteristics. This is the first study investigating the full spectrum of FVIII-specific antibodies, including non-neutralizing antibodies, very-low titer inhibitors, and inhibitors, in a large nationwide population of persons with hemophilia A of all severities. All persons with hemophilia A (mild (FVIII > 5-40 IU/dL)/moderate [FVIII 1-5 IU/dL)/severe (FVIII < 1 IU/dL)] with an available plasma sample who participated in the In total, 788 persons with hemophilia A (336 (42.6%) mild, 123 (15.6%) moderate, 329 (41.8%) severe hemophilia) were included. The median age was 45 years (IQR 24-60), and the majority (50.9%) had over 150 exposure days to FVIII concentrates. Within our population, 144 (18.3%) individuals had non-neutralizing FVIII-specific antibodies, 10 (1.3%) had very low-titer inhibitors (NusBA positive; NBA negative), and 13 (1.6%) had inhibitors (both NusBA and NBA positive). IgG1 was the most abundant FVIII-specific antibody subclass, and the highest titer levels were found for IgG4. In individuals without a reported history of inhibitor development, no clear differences were observed in antibody patterns between those who were minimally or highly exposed to FVIII concentrates. IgG4 subclass antibodies were only observed in persons with a reported history of FVIII inhibitor or in those with a currently detected (very low-titer) inhibitor. In this cross-sectional study, we identified non-neutralizing antibodies in a relatively large proportion of persons with hemophilia A. In contrast, in our population, consisting of persons highly exposed to FVIII concentrates, (very low-titer) inhibitors were detected only in a small proportion of persons, reflecting a well-tolerized population. Hence, our findings suggest that only a small subpopulation of non-neutralizing FVIII-specific antibodies is associated with clinically relevant inhibitors.

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Copyright © 2024 Oomen, Verhagen, Miranda, Allacher, Beckers, Blijlevens, Bom, Coppens, Driessens, Eikenboom, Fijnvandraat, Hassan, van Heerde, Hooimeijer, Jansen, Kaijen, Leebeek, Meijer, Paul, Rijpma, Rosendaal, Smit, van Vulpen, Voorberg, Schols and Gouw.

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IO was supported by an unrestricted research grant from SOBI, the EAHAD research grant, the Heimburger Award, and the Martin Villar research grant. MM received funding from the European Community H2020-MSCA-ITN-2019 project 859974 EDUC8. SG received unrestricted research funding from SOBI, EAHAD, CSL Behring Heimburger Award, Grifols Martin Villar Award, and the Netherlands Organization for Scientific Research NWO. KF has received unrestricted research grants from CSL Behring, SOBI, and Novo Nordisk and consultancy fees from SOBI, Novo Nordisk, and Roche all fees to the institution. FL has received grants/research funding from CSL Behring, UniQure, SOBI, and Takeda and consultancy fees from Biomarin, CSL Behring, Takeda, and Uniqure all fees to the institution. FL also served as a DSMB member for a study sponsored by Roche. JE received research funding from CSL Behring funds to the institution. MC has received financial support for research from Anthos, Bayer, CSL Behring, Novo Nordisk, and Roche, as well as an honoraria for lecturing or consultancy from Alexion, Bayer, CSL Behring, Daiichi Sankyo, Octapharma, Pfizer, SOBI, and Viatris. Nonfinancial conflict of interest: member of the gene therapy working group of the European Association for Haemophilia and Allied Disorders EAHAD, member of the European Reference Network ERN EuroBloodNet, chair of the working group thrombosis and hemostasis of the Dutch Society of Vascular Medicine NVIVG, part of the Dutch Internist’s Society NIV. JV is listed as an inventor on a patent application on ADAMTS13 variants. SS has received a research grant from Bayer. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.