N-Glycosylation of Recombinant Pharmaceutical Glycoproteins Produced in Transgenic Plants Towards an Humanisation of Plant N-Glycans

The number of therapeutic proteins successfully produced in plants is steadily increasing and is expected to grow even more rapidly in the future. Most therapeutic proteins are glycoproteins and N-glycosylation is often essential for their stability, folding and biological activity. Recombinant glycoproteins of mammalian origin expressed in transgenic plants largely retain their biological activity. However, plants are not ideal for production of pharmaceutical proteins because they produce molecules with glycans that are not compatible with therapeutic applications in humans. As a consequence, strategies to humanise plant N-glycans are now developed. Some of these strategies involve the retention of the recombinant glycoprotein in the endoplasmic reticulum while others are related to the inhibition of endogenous Golgi glycosyltransferases or addition of new glycosyltransferases. Data on both the N-glycosylation of therapeutic glycoproteins produced in transgenic plants and current strategies to humanise their N-glycosylation will be discussed in this review.