Site-selective chemoenzymatic glycoengineering of Fab and Fc glycans of a therapeutic antibody.

The N-glycans attached to the Fab and Fc domains play distinct roles in modulating the functions of antibodies. However, posttranslational site-selective modifications of glycans in antibodies and other multiply glycosylated proteins remain a challenging task. Here, we report a chemoenzymatic method that permits independent manipulation of the Fab and Fc N-glycans, using cetuximab as a model therapeutic monoclonal antibody. Taking advantage of the substrate specificity of three endoglycosidases (Endo-S, Endo-S2, and Endo-F3) and their glycosynthase mutants, together with an unexpected substrate site-selectivity of a bacterial α1,6-fucosidase from Lactobacillus casei (AlfC), we were able to synthesize an optimal homogeneous glycoform of cetuximab in which the heterogeneous and immunogenic Fab N-glycans were replaced with a single sialylated N-glycan, and the core-fucosylated Fc N-glycans were remodeled with a nonfucosylated and fully galactosylated N-glycan. The glycoengineered cetuximab demonstrated increased affinity for the FcγIIIa receptor and significantly enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) activity.