Antibody:CD47 ratio regulates macrophage phagocytosis through competitive receptor phosphorylation

Abstract

Cancer immunotherapies often modulate macrophage effector function by introducing either targeting antibodies that activate Fc gamma receptors or blocking antibodies that disrupt inhibitory SIRPα-CD47 engagement. Yet how these competing signals are integrated is poorly understood mechanistically, raising questions about how to effectively titrate immune responses. Here we find that macrophage phagocytic decisions are regulated by the ratio of activating ligand to inhibitory ligand on targets over a broad range of absolute molecular densities. Using endogenous as well as chimeric receptors, we show that activating:inhibitory ligand ratios of at least 10:1 are required to promote phagocytosis of model antibody-opsonized CD47-inhibited targets and that lowering this ratio reduces FcγR phosphorylation due to inhibitory phosphatases recruited to CD47-bound SIRPα. We demonstrate that ratiometric signaling is critical for phagocytosis of tumor cells and can be modified by blocking SIRPα in vitro, indicating that balancing targeting and blocking antibodies may be important for controlling macrophage phagocytosis in cancer immunotherapy.

Quantitative contributions of TNF receptor superfamily members to CD8 + T‐cell responses

“…However, a shortcoming of this system is that the presented ligands are immobile. In the case of IgSF co‐signalling receptors, it has been demonstrated that co‐clustering between receptors is important because cytoplasmic enzymes bound to one receptor modify another (Dushek et al , 2012; Hui et al , 2017; Suter et al , 2021). Although mobility is important for this receptor‐proximal signal integration (Dushek et al , 2012), it is less clear whether it is important for co‐signalling by TNFRSF members that integrate their signals more distally (Watts, 2005; Zapata et al , 2018).…”

Antibody binding reports spatial heterogeneities in cell membrane organization

“…Indeed, Chung et al found that trastuzumab and pertuzumab attenuate tubule structures enriched in HER2, suggesting that biophysical interactions like crowding may influence the potency of mAb therapies (84). Our crowding measurements may also help inform the biophysical mechanisms governing antibody-dependent phagocytosis, which have been recently shown to have a strong dependence on the relative heights of the macrophage Fc γ receptor and the target cell surface proteins (13, 85). In conclusion, our sensors may be used to inform important physiological processes, like antibody binding to buried surface receptors, membrane organization of lipid raft-like domains, and cellular phagocytosis.…”

SHP2 deneddylation mediates tumor immunosuppression in colon cancer via the CD47/SIRPα axis

“…Macrophages mediate ADCP by recognizing and destroying antibody-opsonized cells in cancer therapy (44). As CD47/SIRPα engagement disrupts ADCP (45) and SHP2 serves as a signal molecular downstream of SIRPα, we wanted to investigate how SHP2 regulated the CD47 checkpoint. Therefore, reconstituted targets imitating antibody opsonized tumor cells were used (Figure 5A), and macrophage-specific Shp2 mφ-/mice were generated (Supplemental Figure 5A).…”