Decoding human-macaque interspecies differences in Fc-effector functions: The structural basis for CD16-dependent effector function in Rhesus macaques

Abstract

Fc mediated effector functions of antibodies play important roles in immunotherapies and vaccine efficacy but assessing those functions in animal models can be challenging due to species differences. Rhesus macaques, Macaca mulatta (Mm) share approximately 93% sequence identity with humans but display important differences in their adaptive immune system that complicates their use in validating therapeutics and vaccines that rely on Fc effector functions. In contrast to humans, macaques only have one low affinity FcγRIII receptor, CD16, which shares a polymorphism at position 158 with human FcγRIIIa with Ile158 and Val158 variants. Here we describe structure-function relationships of the Ile/Val158 polymorphism in Mm FcγRIII. Our data indicate that the affinity of the allelic variants of Mm FcγRIII for the macaque IgG subclasses vary greatly with changes in glycan composition both on the Fc and the receptor. However, unlike the human Phe/Val158 polymorphism in FcγRIIIa, the higher affinity variant corresponds to the larger, more hydrophobic side chain, Ile, even though it is not directly involved in the binding interface. Instead, this side chain appears to modulate glycan-glycan interactions at the Fc/FcγRIII interface. Furthermore, changes in glycan composition on the receptor have a greater effect for the Val158 variant such that with oligomannose type glycans and with glycans only on Asn45 and Asn162, Val158 becomes the variant with higher affinity to Fc. These results have implications not only for the better interpretation of nonhuman primate studies but also for studies performed with human effector cells carrying different FcγRIIIa alleles.

Defining genetic diversity of rhesus macaque Fcγ receptors with long-read RNA sequencing

“…Prior work by Chan and collaborators also found that the I158 allotype (FcγR3A-1) had slightly higher binding capabilities than the V158 allotype (FcγR3A-3) when measured using BLI although the differences were not significant ( 27 ). The greater IgG binding capabilities of I158 compared to V158 was confirmed by Tolbert et al., except for rhesus FcγRIII V158 binding more tightly to rhesus IgG4 than I158 ( 38 ). Further, both Chan et al.…”

“…We also identified three synonymous SNPs. AlphaFold2 predictions indicate that SNPs V215I and V211M occur in the cytoplasmic tail, and I158V and A8S occur in the extracellular domain ( Figure 5B ) ( 29 , 38 ). The I158V SNP occurs at the same Fc-FcR contact region ( Figure S2D ) as the human FcγRIIIa V158F.…”

“…and Tolbert et al. observed that FcγRIII IgG binding affinity can be altered based on FcγR glycosylation status ( 27 , 38 ). Tolbert et al.…”

Relationship of maternal cytomegalovirus-specific antibody responses and viral load to vertical transmission risk following primary maternal infection in a rhesus macaque model

“…Antibody-dependent cellular cytotoxicity was measured by NK cell degranulation using NK92.rh.158I.Bb11, an engineered NK cell line expressing the Ile 158 variant of rhesus macaque CD16 (33). Confluent TeloRF cells were infected with 1 MOI UCD52 RhCMV in low serum (5%) medium in T75 flasks (ThermoFisher).…”

Identification of the Linear Fc-Binding Site on the Bovine IgG1 Fc Receptor (boFcγRIII) Using Synthetic Peptides

“…In contrast, FcγRIIIB has no transmembrane region and intracellular region, but is anchored to the cell membrane by glycosylphosphatidylinositol (GPI), which is effective for human IgG1 and IgG3 binding [ 7 , 8 ]. To date, several structures of the extracellular domain of huFcγRIII in complex with IgG1-Fc showed that the EC2 domain of the low-affinity FcγRIII is docked into the horseshoe opening of a homodimeric Fc region on IgG1, providing a novel strategy to design small peptides for regulating the interaction of IgG1 to FcγRIII [ 9 , 10 , 11 , 12 , 13 , 14 ]. It has actually been reported that the peptides of human IgG are able to bind with FcγR molecules [ 15 , 16 , 17 ].…”