Engineering multivalent Fc display for FcγR blockade

Autoimmune diseases, driven by Fc{gamma} receptor (Fc{gamma}R) activation through autoantibody immune complexes (IC), present a complex therapeutic challenge of achieving pharmacological blockade of Fc{gamma}R without triggering receptor activation. The assembly of ICs into polydisperse, higher-order structures is required for Fc{gamma}R activation. However, engineered multimeric, monodisperse Fc assemblies have been reported to prevent Fc{gamma}R activation, suggesting that Fc spatial organization determines Fc{gamma}R 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 Fc{gamma}R at the cell membrane and caused limited receptor activation and internalization. In contrast, the monovalent scFc acted as an Fc{gamma}R 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 Fc{gamma}R activation. This work introduces a new paradigm that can contribute to the development of therapies for autoimmune diseases.