Expression of Recombinant Antibodies

Frenzel, André; Hust, Michael; Schirrmann, Thomas

Differences in the glycosylation pattern between mammalia and plants are one of the main obstacles researchers have to overcome when developing therapeutic antibodies expressed in plants. Although plants are able to perform complex glycosylation, differences in glycosylation patterns, in particular β1,2-xylose and α1,3fucose, can lead to immunogenicity of the therapeutic proteins (192) (193) (194) . Therefore, different strategies have been developed to express recombinant proteins with a more mammalian-like glycosylation pattern. The first one is the retention of the protein in the endoplasmic reticulum (eR) as eR-associated N-glycosylation leads to the generation of oligomannose-type N -glycans which are identical in plants and mammalians (192, 195) . One side effect of this localization is the accumulation to higher levels in the eR (196, 197) . A second approach for the expression of proteins with mammalian-like glycosylation patterns is the usage of glycoengineered plants. In most cases, RNA interference (RNAi) is used for the down-regulation of endogenous beta1,2-xylosyltransferase and alpha1,3-fucosyltransferase leading to a reduction of the xylosylated and core-fucosylated N -glycans (198) (199) (200) . A second type of glyco-engineering in plants is the coexpression of genes which facilitates the expression of human-like N -glycans (201) or even Frontiers in Immunology | B Cell Biology the in planta protein sialylation by the coexpression of six mammalian genes (202) . An increasing effort has been put into the adaptation of N-glycosylation, but there are also some efforts in the engineering of sialylated mucin-type O-glycans to achieve the most human-like glycosylation patterns (203, 204) . Alternatively, non-glycosylated antibodies which mediate protection against an inhalation anthrax spore challenge in non-human primates showed an improvement of the half-life in serum (205) . Rodriguez and colleagues showed that the aglycosylated form of Nimotuzumab (currently in a phase II clinical study in the USA and Canada) produced in tobacco shares the in vitro and in vivo properties as well as the antitumor effect in nude mice with the glycosylated form (206) .