Biophysical Evaluation of Rhesus Macaque Fc Gamma Receptors Reveals Similar IgG Fc Glycoform Preferences to Human Receptors

Abstract

Rhesus macaques are a common non-human primate model used in the evaluation of human monoclonal antibodies, molecules whose effector functions depend on a conserved N-linked glycan in the Fc region. This carbohydrate is a target of glycoengineering efforts aimed at altering antibody effector function by modulating the affinity of Fcγ receptors. For example, a reduction in the overall core fucose content is one such strategy that can increase antibody-mediated cellular cytotoxicity by increasing Fc-FcγRIIIa affinity. While the position of the Fc glycan is conserved in macaques, differences in the frequency of glycoforms and the use of an alternate monosaccharide in sialylated glycan species add a degree of uncertainty to the testing of glycoengineered human antibodies in rhesus macaques. Using a panel of 16 human IgG1 glycovariants, we measured the affinities of macaque FcγRs for differing glycoforms via surface plasmon resonance. Our results suggest that macaques are a tractable species in which to test the effects of antibody glycoengineering.

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

“…Stabilizing the Fc glycan might be a factor that contributes to the higher affinity for the Man5 produced receptor to the macaque IgG2, IgG3, and IgG4 as compared to IgG1 and to the Val 158 variant. In summary, as has been the case for afucosylated glycans on the Fc for macaque IgGs ( 64 ), changes to the glycan composition on the macaque FcγRIII receptor can lead to changes in affinity to IgG. It remains to be seen if this change in affinity will translate to a change in function, particularly with regard to NK cells and their potentially altered FcγRIII glycan composition as has been the case for humans ( 65 ).…”

“…Despite the close evolutionary proximity between humans and Rhesus macaques, Macacca mulata (Mm), there are many important differences in immune system genes and function between the two species that can confound the interpretation of results when macaques are used as an animal model. Some have been well documented, such as the gene duplication event that gave rise to FcγRIIIa and FcγRIIIb in humans ( 12 ) or the extended hinge region only present in human IgG3 ( 9 , 63 ), but others such as the effect of IgG glycoform on FcγRIII affinity in macaques have only more recently been examined ( 64 ).…”

Alteration of rhesus macaque serum N-glycome during infection with the human parasitic filarial nematode Brugia malayi

“…Interestingly, the importance of sialic acid on N-glycans of the IgG Fc region is unclear. Some studies have suggested that sialylation of Fc N-glycan is necessary for the IgG anti-inflammatory properties 65 , 66 while more recent work showed that sialic acid does not affect recognition by Fc γ receptors (FcγRs) III 36 , 67 , 68 . Thus, despite major differences in IgG N-glycans, including the type of sialic acid, rhesus macaques might have Antibody-Dependent Cellular Toxicity mechanisms that are highly similar to humans.…”

“…However, extrapolation of preclinical findings from macaques to humans can be compromised when subtle differences in biology exist. For example, interspecies differences between immunoglobulins and their Fc receptors raise questions about the suitability of macaques for development of human antibody therapies and vaccines, and the extent to which data from animal trials can be translated clinically 33 , 35 , 36 . Nonetheless, as of today, studies of rhesus macaque glycoconjugates have been limited to IgG N-glycans 28 , 37 .…”

Role of Fc Core Fucosylation in the Effector Function of IgG1 Antibodies

“…Nonetheless one should bear in mind that mice do not have the equivalent of FcɣRIIIB, which therefore makes this species not completely adequate to test the role of PMN in antibody efficacy in vivo , unless fully humanized models are used ( 119 ). Despite these caveats, it is worth noting that afucosylated or low fucose anti-cancer mAbs have consistently been shown to control tumor growth more efficiently than their fully fucosylated parent molecules in mice ( 69 , 84 , 92 , 122 ), as well as macaque, the latter having a more similar pattern of FcɣRs to humans ( 123 ). These results have led to an increased attention to the N-glycan profile of therapeutic mAbs ( 124 ), as well as the development of new afucosylated therapeutic antibodies in a variety of clinical contexts.…”