Inflammatory macrophages exploit unconventional pro-phagocytic integrins for phagocytosis and anti-tumor immunity

Blockade of the inhibitory checkpoint SIRPα-CD47 promotes phagocytosis of cancer cells by macrophages and is a promising avenue in anti-cancer therapy. Productive phagocytosis is strictly predicated on co-engagement of pro-phagocytic receptors-namely, Fc receptors (FcRs), integrin CD11b, or SLAMF7-by their ligands on cancer cells. Here, we examine whether additional pro-phagocytic receptors could be harnessed to broaden the scope of phagocytosis. Inflammatory stimuli, including multiple cytokines and Toll-like receptor (TLR) ligands, augment phagocytosis efficiency and fully alleviate the requirement of FcRs, CD11b, and SLAMF7 for phagocytosis. These effects are mediated by the unconventional pro-phagocytic integrins CD11a and CD11c, which act with CD18 to initiate actin polarization, leading to phagocytosis. Some inflammatory stimuli enable phagocytosis even in the absence of SIRPα-CD47 blockade. Higher CD11c expression in macrophage-enriched tumors correlates with improved survival in clinical studies. Thus, inflammatory macrophages exploit unconventional pro-phagocytic integrins for improved phagocytosis and anti-tumor immunity.