Role of N-Glycosylation in FcγRIIIa interaction with IgG.

Immunoglobulins G (IgG) and their Fc gamma receptors (FcγRs) play important roles in our immune system. The conserved N-glycan in the Fc region of IgG1 impacts interaction of IgG with FcγRs and the resulting effector functions, which has led to the design of antibody therapeutics with greatly improved antibody-dependent cell cytotoxicity (ADCC) activities. Studies have suggested that also N-glycosylation of the FcγRIII affects receptor interactions with IgG, but detailed studies of the interaction of IgG1 and FcγRIIIa with distinct N-glycans have been hindered by the natural heterogeneity in N-glycosylation. In this study, we employed comprehensive genetic engineering of the N-glycosylation capacities in mammalian cell lines to express IgG1 and FcγRIIIa with different N-glycan structures to more generally explore the role of N-glycosylation in IgG1:FcγRIIIa binding interactions. We included FcγRIIIa variants of both the 158F and 158V allotypes and investigated the key N-glycan features that affected binding affinity. Our study confirms that afucosylated IgG1 has the highest binding affinity to oligomannose FcγRIIIa, a glycan structure commonly found on Asn162 on FcγRIIIa expressed by NK cells but not monocytes or recombinantly expressed FcγRIIIa.

Glycoengineering design options for IgG1 in CHO cells using precise gene editing.

Precise gene editing technologies are providing new opportunities to stably engineer host cells for recombinant production of therapeutic glycoproteins with different glycan structures. The glycosylation of recombinant therapeutics has long been a focus for both quality and consistency of products and for optimizing and improving pharmacokinetic properties as well as bioactivity. Structures of glycans on therapeutic glycoproteins are important for circulation, biodistribution and bioactivity. In particular, the latter has been demonstrated for therapeutic IgG1 antibodies where the core α1,6Fucose on the conserved N-glycan at Asn297 have remarkable dampening effects on antibody effector functions. We previously explored precise gene engineering and design options for N-glycosylation in CHO cells, and here we focus on engineering options possible for N-glycans on human IgG1. We demonstrate stable precise gene engineering of rather homogenous biantennary N-glycans with and without galactose (G0F, G2F) as well as the α2,6-linked monosialylated (G2FS1) glycoform. We were unable to introduce substantial disialylated glycoforms. Instead we engineered a novel monoantennary homogeneous N-glycan design with complete α2,6-linked sialic acid capping. All N-glycoforms may be engineered with and without core α1,6Fucose. The stably engineered design options enable production of human IgG antibodies with an array of distinct glycoforms for testing and selection of optimal design for different therapeutic applications.