N-glycosylation of a mouse IgG expressed in transgenic tobacco plants

Since plants are emerging as an important system for the expression of reco mbinant glycoproteins, especially those intended for therapeutic purposes, it is important to scrutinize to what extent glycans harbored by mammalian glycoproteins produced in transgenic plants differ from their natural count erpart. We report here the first detailed analysis of the glycosylation of a functional mammalian glycoprotein expressed in a transgenic plant. The st ructures of the N-linked glycans attached to the heavy chains of the monocl onal antibody Guy's 13 produced in transgenic tobacco plants (plantibody Gu y's 13) were identified and compared to those found in the corresponding Ig G1 of murine origin. Both N-glycosylation sites located on the heavy chain of the plantibody Guy's 13 are N-glycosylated as in mouse. However, the num ber of Guy's 13 glycoforms is higher in the plant than in the mammalian exp ression system. Despite the high structural diversity of the plantibody N-g lycans, glycosylation appears to be sufficient for the production of a solu ble and biologically active IgG in the plant system. In addition to high-ma nnose-type N-glycans, 60% of the oligosaccharides N-linked to the plantibod y have beta(1, 2)-xylose and alpha(1, 3)-fucose residues linked to the core Man(3)GlcNAc(2). These plant-specific oligosaccharide structures are not a limitation to the use of plantibody Guy's 13 for topical immunotherapy, Ho wever, their immunogenicity may raise concerns for systemic applications of plantibodies in human.