In patients with mild hemophilia A, the addition of polyethylene glycol (PEG) to recombinant therapeutic factor VIII (rFVIII) has been shown to improve pharmacokinetic parameters, according to findings from a study published in the Journal of Thrombosis and Haemostasis.

In patients with hemophilia, standard treatment involves replacement with FVIII therapeutics. In an effort to extend the short circulating half-life of wild-type FVIII protein, PEG can be combined with therapeutic FVIII as an effective treatment. Immunologically, any alteration in FVIII might have the ability to modify the risk for development of antidrug antibodies.

PEGylation involves “covalent conjugation of PEG polymers to a carrier.” The use of PEG-conjugation impacts the physiochemical properties of the target protein without changing its structure, thus enhancing solubility of the proteins in the bloodstream.

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The researchers sought to determine a reproducible procedure to detect anti-PEG antibodies. They report on the initial real-world experiences with neutralizing antidrug antibodies against a 40 kDa PEG (40 polyethylene glycol-conjugated B-domain-deleted factor FVIII [40PEG-BDDFVIII]) in 2 individuals with mild hemophilia A. The anti-PEG antibodies exhibited differing immunoglobulin (Ig) isotype profiles.

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Patient 1 was a 21-year-old male who had a family history of mild hemophilia A that harbored a genetic variant in exon 7 of the F8 gene. Patient 2 was a 20-year-old male with mild hemophilia A that harbored a genetic variant in exon 7 of the F8 gene as well. An additional 44 individuals with hemophilia A (the controls) who received 40PEG-BDDFVIII treatment were also screened for anti-PEG antibodies.

The researchers developed an in-house bead-based immunoassay to describe and verify the specificity of all antibodies that were detected. A modified Nijmegan-Bethesda assay was performed to establish the neutralizing nature of the antibodies toward PEGylated therapeutics.

Results of the study showed that 2 of the 46 participants who received treatment with 40PEG-BDDFVIII exhibited inhibitor antibodies toward the agent. In both of these individuals, changing to a non-PEGylated FVIII successfully increased their levels of FVIII activity.

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In the first patient, antibodies were elevated against FVIII and PEG. In this individual, the anti-FVIII antibodies were of the IgG isotype; in contrast, the anti-PEG antibodies were of the IgA, IgG, and IgM isotypes. In the second patient, antibodies of the IgA and IgG isotypes were directed against the PEG moiety only.

Use of competitive binding immunoassays verified the specificity of the antibodies against PEG. Application of the Nijmegan-Bethesda assay demonstrated that anti-PEG antibodies, as well as AGP3—an antibody against the backbone of PEG—can inhibit all currently available PEGylated therapeutics, albeit to varying degrees. There were no inhibitory FVIII antibodies detected.

The authors concluded, “This is the first report on real-world experiences with the development of neutralizing anti-PEG antibodies after treatment with PEGylated FVIII therapeutic in [patients] with mild hemophilia A.”


Pezeshkpoor B, Sereda N, Berkemeier A-C, et al. Anti-drug antibodies against the PEG moiety inhibit the procoagulant activity of therapeutic PEGylated FVIII. J Thromb Haemost. Published online March 17, 2023. doi:10.1016/j.jtha.2023.03.011