N-Glycosylation of monoclonal antibody therapeutics: A comprehensive review on significance and characterization.

N-glycosylation of therapeutic antibodies starts as a co-translational step followed by a set of post-translational modifications and is considered as one of the critical quality attributes because of its impact on biological functions as well as therapy outcome. In addition to detailed product characterization of these glycans by the manufacturers, their comprehensive analysis is also a regulatory requirement. However, the structural complexity and heterogeneity of these N-linked carbohydrates make their characterization quite challenging. In this review, we give a comprehensive overview of N-glycosylation diversity and its functional importance for monoclonal antibody therapeutic products. A descriptive coverage is also provided for the various strategies and techniques employed for oligosaccharide characterization, that include analysis of intact-glycoproteins, their sub-units, glycopeptides as well as released glycans through chromatographic, electrophoretic and spectroscopic techniques. To assist the readers, relevant examples from the literature are cited and critically discussed for each of the strategies and techniques. To conclude, a discussion on unique challenges associated with the analysis of this important post-translational modification is presented.