Abstract 1346: Phagocytosis of solid tumors favors macrophage clusters and cooperativity in tumor elimination

Abstract

Abstract Macrophages are abundant in many solid tumors and are potential effector cells for monoclonal antibody-based immunotherapies because they can in principle phagocytose IgG-opsonized cancer cells. However, it remains unknown whether phagocytic macrophages can overcome the cohesive forces between cancer cells in solid tumors. We show that maximum phagocytosis of B16 melanoma tumors and ‘tumoroids’ requires IgG-opsonization and very deep suppression of the macrophage checkpoint ligand CD47. Under these conditions, phagocytic macrophages cluster or ‘phase separate’, and the elimination exhibits clear cooperativity with respect to macrophage number and phagocytic activity. In vitro disruption of phagocytic clusters specifically implicates Mg2+ and macrophage integrins. Cytokine treatments and other inhibitors further implicate roles for integrins and phagocytic surface receptors. Although tumor-associated macrophages correlate with negative prognoses in many cancers, our findings are among the first to reveal advantages of high macrophage numbers, macrophage clusters, and resulting cooperative effects when combined with opsonizing antibodies and CD47 disruption. Lastly, the challenging B16 tumors are durably eliminated by the approach and induce de novo IgG's that also drive anti-cancer phagocytosis. Citation Format: Dennis E. Discher. Phagocytosis of solid tumors favors macrophage clusters and cooperativity in tumor elimination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1346.