Plants offer a cost-effective means for producing recombinant human proteins. However, the therapeutic value of the plant-derived product is often limited by the difference between plant and mammalian post-translational modifications—in particular, glycosylation. This barrier has in part been lowered by the creation of a hybrid/transgenic plant expressing the human version of α1,4-galactosyltransferase (GalT) (Proc. Natl. Acad. Sci. 98, 2899–2904, 2001). Hans Bakker and colleagues at Plant Research International (Wageningen, The Netherlands) genetically modified a tobacco plant to express human GalT. The team then crossed the modified tobacco plant with a plant engineered to manufacture a mouse antibody. The resulting plant-derived antibody (“plantibody”) had a glycosylation pattern that more closely resembled a mammalian antibody than any plantibody produced to date. Further modifications are needed to eradicate the remaining plant-specific modifications of the antibodies, namely the attachment of xylose and fucose sugars. Bakker says that the next challenge will be get plants to manufacture sialic acid: “This sugar is required for many [mammalian] serum proteins.” This will require adding another five genes.
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Fletcher, L. Humanizing plantibodies. Nat Biotechnol 19, 319 (2001). https://doi.org/10.1038/86699