Aglycosylated Immunoglobulin G1 Fc Stabilized Through Disulfide Bond Addition Exhibits Compositional Homogeneity and Retains Fc γ Receptor IIIa/CD16a Binding

Background: The interaction between human immunoglobulin G (IgG)1 Fc and the Fc gamma receptor (FcγR) IIIa/CD16a elicits protective immune responses. Antibody N-glycosylation stabilizes the FcγR-binding interface and is thus essential for interaction with wildtype IgG1 Fc. Furthermore, the N-glycan introduces substantial compositional and functional heterogeneity, with distinct glycoforms providing different affinities and discrete responses in vivo. Accordingly, various engineering endeavors to improve antibody binding strive to boost the therapeutic efficacy of monoclonal antibodies but do not directly address compositional heterogeneity. Objective: Here, we describe a previously unexplored approach to engineer IgG1 Fc. We eliminated carbohydrate heterogeneity by removing the N-glycan but stabilizing the FcγR-binding interface with disulfide bonds. Conclusions: These newly generated Fc domains served as a starting point for protein engineering through yeast surface display to enhance receptor-binding affinity. We recovered Fc variants from this approach that demonstrated FcγRIIIa binding affinities comparable to the starting sequence and thus serve as a proof-of-principle for this strategy.