Prepared By Piotr Miłek, Paulina Toboła, and Adam Tuszyner
Glycosylation stands as a pivotal post-translational modification of antibodies, profoundly influencing their physicochemical attributes and functionality, particularly in therapeutic immunoglobulins produced by mammalian cell lines like CHO. Predominantly occurring in the Fc fragment, glycosylation constitutes a significant portion, around 2-3%, of an antibody's total molecular mass. Two primary types of protein glycosylation exist: N-linked and O-linked. N-linked glycosylation involves the addition of a 14-monosaccharide chain to the asparagine (Asn) residue, while O-linked glycosylation entails the sequential addition of monosaccharides to the hydroxyl groups of serine and threonine. The influence of glycosylation is contingent upon both the composition and positioning of the glycans within the protein structure.
Essential effector functions of monoclonal antibodies, such as antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), are profoundly impacted by glycosylation, alongside pharmacokinetic properties. Monitoring glycan content during monoclonal antibody manufacturing is imperative, with glycosylation recognized as a critical quality attribute, particularly in biosimilar development. Although minor discrepancies in glycosylation between biosimilars and reference products may be permissible, pharmaceutical companies must demonstrate that these differences do not have clinically meaningful impacts on pharmacology.
To illustrate these points, we examine rituximab, a chimeric monoclonal antibody commonly utilized in rheumatic and oncologic conditions treatment, and its biosimilars. Rituximab, belonging to the IgG1 subclass, targets the CD20 antigen on B cells, facilitating their lysis and depletion from the bloodstream.