Biological activity of human interleukin-22 expressed in Nicotiana benthamiana is independent of its N-glycosylation

In the last decade plants have emerged as a suitable expression platform for several therapeutic proteins, but the expression of cytokines in plants has been challenging so far. Interleukin-22 (IL-22) is a member of the IL-10 cytokine family and has only recently been shown to have therapeutic potential. IL-22 is an unusual cytokine, as it does not act directly on immune cells, but mainly on epithelial cells. IL-22 controls the differentiation, proliferation and expression of anti-microbial proteins of epithelial cells, thereby maintaining epithelial barrier function. IL-22 activity is mediated via IL-22R1 and IL-10R2, the latter being shared by other members of the IL-10 cytokine family. Furthermore, IL-22 activity is reported to be dependent on the glycosylation of asparagine 54 (Asn54) as core a1,6-fucose on this N-glycan enables binding to IL-10R2. Surprisingly, bacterial expressed IL-22 is active, while lacking N-glycans. In this study we investigated the possibility to express human IL-22 transiently in Nicotiana benthamiana and in more detail the role of N-glycosylation on IL-22 activity. Yield obtained for IL-22 was up to 90 µg IL-22/gram fresh weight and IL-22 could be efficiently purified from the leaf apoplast fluid. Plant-produced IL-22 was shown to be biologically active, but most strikingly as active as bacterial and human cell expressed IL-22. Further examination of the role of N-glycosylation of IL-22 by mutagenesis of Asn54, in vivo deglycosylation with PNGase F or glyco-engineering by co-expression of human a1,6-fucosyltransferase (Fut8) revealed that N-glycosylation of IL-22 is not required for biological activity. All in all our data demonstrate that plants are a promising platform for the expression of IL-22, but also offer a great toolbox for studying the role of N-glycans on glycoprotein function.