Macrophage-Targeted Therapy Unlocks Antitumoral Cross-talk between IFN gamma-Secreting Lymphocytes and IL12-Producing Dendritic Cells

Macrophages often abound within tumors, express colony-stimulating factor 1 receptor (CSF1R), and are linked to adverse patient survival. Drugs blocking CSF1R signaling have been used to suppress tumor-promoting macrophage responses; however, their mechanisms of action remain incompletely understood. Here, we assessed the lung tumor immune microenvironment in mice treated with BLZ945, a prototypical small-molecule CSF1R inhibitor, using single-cell RNA sequencing and mechanistic validation approaches. We showed that tumor control was not caused by CSF1R thorn cell depletion; instead, CSF1R targeting reshaped the CSF1R thorn cell landscape, which unlocked cross-talk between antitumoral CSF1R- cells. These cells included IFNg- producing natural killer and T cells, and an IL12-producing dendritic cell subset, denoted as DC3, which were all necessary for CSF1R inhibitor-mediated lung tumor control. These data indicate that CSF1R targeting can activate a cardinal cross-talk between cells that are not macrophages and that are essential to mediate the effects of T cell-targeted immunotherapies and promote antitumor immunity.