The immunoglobulin G1 N-glycan composition affects binding to each low affinity Fc γ receptor

Immunoglobulin G1 (IgG1) is the most abundant circulating human antibody and also the scaffold for many therapeutic monoclonal antibodies (mAbs). The destruction of IgG-coated targets by cell-mediated pathways begins with an interaction between the IgG Fc region and multiple varieties of membrane-bound Fc γ receptors (FcγRs) on the surface of leukocytes. This interaction requires the presence of an asparagine-linked (N-)glycan on the Fc, and variations in the N-glycan composition can affect the affinity of CD16A binding (an FcγR). Contemporary efforts to glycoengineer mAbs focus on increasing CD16A affinity, and thus treatment efficacy, but it is unclear how these changes affect affinity for the other FcγRs. Here, we measure binding of the extracellular Fc-binding domains for human CD16A and B, CD32A, B and C, and CD64 to 6 well-defined IgG1 Fc glycoforms that cover ∼85% of the pool of human IgG1 Fc glycoforms. Core α1-6 fucosylation showed the greatest changes with CD16B (8.5-fold decrease), CD16A (3.9-fold decrease) and CD32B/C (1.8-fold decrease), but did not affect binding to CD32A. Adding galactose to the non-reducing termini of the complex-type, biantennary glycan increased affinity for all CD16s and 32s tested by 1.7-fold. Sialylation did not change the affinity of core-fucosylated Fc, but increased the affinity of afucosylated Fc slightly by an average of 1.16-fold for all CD16s and CD32s tested. The effects of fucose and galactose modification are additive, suggesting the contributions of these residues to Fc γ receptor affinity are independent.