Effects of sialic acid linkage on antibody-fragment crystallizable receptor binding and antibody dependent cytotoxicity depend on levels of fucosylation/bisecting.

 Fragment crystallizable (Fc) glycosylation of immunoglobulin G-type monoclonal antibodies applied to therapeutic applications is regarded a critical quality attribute and can influence bioactivity, pharmacokinetics and/or immunogenicity/safety. Investigating the impact of certain Fc N-glycans is therefore of importance to assess its criticality for a therapeutic product. This has been done for N-glycan types like fucosylation, galactosylation or sialylation. There were contradictory results reported for functionality especially with regard to sialylation. We elucidated the effect of terminal sialic acid residues on Fcγ receptor binding and antibody dependent cytotoxicity activity of two immunoglobulin G1 antibodies with different levels of fucosylation/bi-secting. We found the impact to be specific to the sialylation linkage type, in other words, α2,3- versus α2,6-linked sialic acid attached to the terminal galactose residues.