Antidrug antibodies against the polyethylene glycol moiety inhibit the procoagulant activity of therapeutic polyethylene glycolated factor VIII

Background: The standard therapy for patients with hemophilia A (HA) is the replacement with factor VIII (FVIII) therapeutics. To overcome the limitation of short half-life of wild-type FVIII protein, polyethylene glycol (PEG) can be coupled to therapeutic FVIII to improve pharmacokinetics.Objectives: We aimed to characterize antibodies developed against a FVIII therapeutic PEGylated with a 40-kDa PEG (40PEG-BDDFVIII) in 2 patients with mild HA.Methods: An inhouse bead-based immunoassay was developed to characterize and confirm the specificity of the detected antibodies. The neutralizing nature of the antibodies toward PEGylated therapeutics was determined by a modified NijmegenResults: Two out of 46 patients treated with 40PEG-BDDFVIII developed inhibitory antibodies toward the drug. Switching to a non-PEGylated FVIII successfully increased the FVIII activity in both patients. In patient 1, antibodies were raised against FVIII and PEG. Anti-FVIII antibodies were of the immunoglobulin (Ig)G isotype, whereas anti-PEG antibodies were of IgG, IgM, and IgA isotypes. In patient 2, antibodies of IgG and IgA isotypes were directed only against the PEG moiety. Competitive assays confirmed the specificity of the antibodies against PEG. The applied Nijmegen-Bethesda assay revealed that patients' anti-PEG antibodies and AGP3, an antibody against the backbone of PEG, can inhibit all currently available PEGylated therapeutics but to different degrees. No inhibitory FVIII antibodies were detected.Conclusion: Antibodies against the PEG moiety of 40PEG-BDDFVIII abolished the efficacy of the drug. This is the first report on real-world experiences with the