Galactose-extended glycans of antibodies produced by transgenic plants

Plant-specific N-glycosylation can represent an important limitation for th e use of recombinant glycoproteins of mammalian origin produced by transgen ic plants. Comparison of plant and mammalian N-glycan biosynthesis indicate s that beta1,4-galactosyltransferase is the most important enzyme that is m issing for conversion of typical plant N-glycans into mammalian-like N-glyc ans. Here, the stable expression of human beta1,4-galactosyltransferase in tobacco plants is described. Proteins isolated from transgenic tobacco plan ts expressing the mammalian enzyme bear N-glycans, of which about 15% exhib it terminal beta1,4-galactose residues in addition to the specific plant N- glycan epitopes. The results indicate that the human enzyme is fully functi onal and localizes correctly in the Golgi apparatus. Despite the fact that through the modified glycosylation machinery numerous proteins have acquire d unusual N-glycans with terminal beta1,4-galactose residues, no obvious ch anges in the physiology of the transgenic plants are observed, and the feat ure is inheritable. The crossing of a tobacco plant expressing human beta1, 4-galactosyltransferase with a plant expressing the heavy and light chains of a mouse antibody results in the expression of a plantibody that exhibits partially galactosylated N-glycans (30%), which is approximately as abunda nt as when the same antibody is produced by hybridoma cells. These results are a major step in the in planta engineering of the N-glycosylation of rec ombinant antibodies.