Recombinant anti‐hCG antibodies retained in the endoplasmic reticulum of transformed plants lack core‐xylose and core‐α(1,3)‐fucose residues

Summary Plant‐based expression systems are attractive for the large‐scale production of pharmaceutical proteins. However, glycoproteins require particular attention as inherent differences in the N‐glycosylation pathways of plants and mammals result in the production of glycoproteins bearing core‐xylose and core‐α(1,3)‐fucose glyco‐epitopes. For treatments requiring large quantities of repeatedly administered glycoproteins, the immunological properties of these non‐mammalian glycans are a concern. Recombinant glycoproteins could be retained within the endoplasmic reticulum (ER) to prevent such glycan modifications occurring in the late Golgi compartment. Therefore, we analysed cPIPP, a mouse/human chimeric IgG1 antibody binding to the β‐subunit of human chorionic gonadotropin (hCG), fused to a C‐terminal KDEL sequence, to investigate the efficiency of ER retrieval and the consequences in terms of N‐glycosylation. The KDEL‐tagged cPIPP antibody was expressed in transgenic tobacco plants or Agrobacterium ‐infiltrated tobacco and winter cherry leaves. N‐Glycan analysis showed that the resulting plantibodies contained only high‐mannose (Man)‐type Man‐6 to Man‐9 oligosaccharides. In contrast, the cPIPP antibody lacking the KDEL sequence was found to carry complex N‐glycans containing core‐xylose and core‐α(1,3)‐fucose, thereby demonstrating the secretion competence of the antibody. Furthermore, fusion of KDEL to the diabody derivative of PIPP, which contains an N‐glycosylation site within the heavy chain variable domain, also resulted in a molecule lacking complex glycans. The complete absence of xylose and fucose residues clearly shows that the KDEL‐mediated ER retrieval of cPIPP or its diabody derivative is efficient in preventing the formation of non‐mammalian complex oligosaccharides.