Implications of the presence of N-glycolylneuraminic acid in recombinant therapeutic glycoproteins

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Recombinant glycoprotein therapeutics produced in nonhuman mammalian cell lines and/or with animal serum are often modified with the nonhuman sialic acid N-glycolylneuraminic acid (Neu5Gc; refs. 1,2). This documented contamination has generally been ignored in drug development because healthy individuals were not thought to react to Neu5Gc (ref. 2). However, recent findings indicate that all humans have Neu5Gc-specific antibodies, sometimes at high levels3,4. Working with two monoclonal antibodies in clinical use, we demonstrate the presence of covalently bound Neu5Gc in cetuximab (Erbitux) but not panitumumab (Vectibix). Anti-Neu5Gc antibodies from healthy humans interact with cetuximab in a Neu5Gc-specific manner and generate immune complexes in vitro. Mice with a human-like defect in Neu5Gc synthesis generate antibodies to Neu5Gc after injection with cetuximab, and circulating anti-Neu5Gc antibodies can promote drug clearance. Finally, we show that the Neu5Gc content of cultured human and nonhuman cell lines and their secreted glycoproteins can be reduced by adding a human sialic acid to the culture medium. Our findings may be relevant to improving the half-life, efficacy and immunogenicity of glycoprotein therapeutics.

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Figure 1: ELISA and western blot detection of Neu5Gc on biotherapeutic antibodies by Neu5Gc IgY antibodies from chickens or IgG antibodies from normal human serum.
Figure 2: Effects of Neu5Gc-specific antibodies on the kinetics of therapeutic antibodies in mice with a human-like Neu5Gc deficiency, levels of anti-Neu5Gc IgG in mice after injections of the therapeutic antibodies, and binding of IgG Neu5Gc-specific antibodies from whole human serum to Neu5Gc on the Fab fragment of cetuximab.
Figure 3: An approach to reducing Neu5Gc contamination in biotherapeutic products.


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This work was supported by US National Institutes of Health grants R01-GM32373 and R01-CA38701 to A.V. and The International Sephardic Education Foundation for V.P.-K. Haemophilus influenzae strain 2019 was a generous gift from M. Apicella, Department of Microbiology, University of Iowa.

Author information

All authors helped design the studies; D.G. and S.D. performed the research; R.E.T. and V.P.-K. generated crucial reagents; D.G. and A.V. wrote the paper; and all authors read the paper.

Correspondence to Ajit Varki.

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Competing interests

None of the authors has a personal financial interest in any of the companies whose products are mentioned. A.V. is a co-founder of, and shareholder in Sialix, Inc. (formerly Gc-Free, Inc.), a startup biotech company focused on solving problems arising from Neu5Gc contamination of foods and drugs. D.G. is currently an employee of Sialix, Inc.

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