Engineering multivalent Fc display for FcγR blockade

Autoimmune diseases, driven by Fcγ receptor (FcγR) activation through autoantibody immune complexes (IC), present a complex therapeutic challenge of achieving pharmacological blockade of FcγR without triggering receptor activation. The assembly of ICs into polydisperse, higher-order structures is required for FcγR activation. However, engineered multimeric, monodisperse Fc assemblies have been reported to prevent FcγR activation, suggesting that Fc spatial organization determines FcγR activation. In this study, we engineered a functional single-chain Fc domain protein (scFc) for unidirectional, multivalent presentation by virus-like particles (VLPs), used as a display platform. We found that the multivalent display of scFc on the VLPs elicited distinct cellular responses compared with monovalent scFc, highlighting the importance of the structural context of scFc on its function. scFc-VLPs had minimal impact on the nanoscale spatial organization of FcγR at the cell membrane and caused limited receptor activation and internalization. In contrast, the monovalent scFc acted as an FcγR agonist, inducing receptor clustering, activation, and internalization. Increasing scFc valency in scFc-VLPs was associated with increased binding to monocytes, reaching a plateau at high valencies. Notably, the ability of scFc-VLPs to block IC-mediated phagocytosis in vitro increased with scFc valency. In a murine model of passive immune thrombocytopenia (ITP), a high valency scFc-VLP variant with a desirable immunogenicity profile induced attenuation of thrombocytopenia. Here we show that multivalent presentation of an engineered scFc on a display platform can be tailored to promote suppression of IC-mediated phagocytosis while preventing FcγR activation. This work introduces a new paradigm that can contribute to the development of therapies for autoimmune diseases. ### Competing Interest Statement The authors have declared no competing interest.