Targeting CD37 promotes macrophage-dependent phagocytosis of multiple cancer cell types and facilitates tumor clearance in mice

Macrophages play vital roles in innate and adaptive immunity, and their functions are mediated via phagocytosis and antigen presentation. Despite the effort to identify phagocytic checkpoints and explore their mechanism of action, current checkpoint-scanning strategies cannot provide a complete and systematic list of such immune checkpoints. Here, we perform in vitro phagocytosis assays using primary healthy donor macrophages co-cultured with breast cancer cells followed by ribosome profiling of sorted macrophages, to identify immune system-specific checkpoints. We observe a downregulation of CD37 in phagocytic macrophages and demonstrate that targeting CD37 with a specific antibody promotes the phagocytosis of multiple cancer cells in vitro. Mechanistically, tumorous macrophage migration inhibitory factor (MIF) directly binds to CD37, promoting the phosphorylation of CD37Y13 and activating a transduction cascade that involves the recruitment of SHP1 and inhibition of AKT signaling, ultimately impairing phagocytosis. In vivo, targeting CD37 promotes tumor clearance in multiple preclinical mouse models and synergizes with anti-CD47 therapy. Thus, our study identifies a previously unidentified phagocytic checkpoint and provides new potential for precise therapy. Cancer cells evade the immune system by disrupting phagocytic clearance. Here, the authors identify CD37 as a potential checkpoint molecule expressed on non-phagocytes and propose that binding to tumor-derived MIF reduces the phagocytic ability via inhibiting the AKT pathway. In preclinical mouse models, anti-CD37-based therapy enhances phagocytosis by macrophages, facilitating tumor clearance.