Cancer-associated fibroblasts serve as decoys to suppress NK cell anti-cancer cytotoxicity

Cancer associated fibroblasts (CAFs) are among the most abundant components of the breast tumor microenvironment (TME) and major contributors to immune modulation. CAFs are well-known to regulate the activity of diverse types of immune cells including T cells, macrophages and dendritic cells, however little is known about their interaction with Natural killer (NK) cells, which constitute an important arm of anti-tumor immunity. Here we find, using mouse models of cancer and ex-vivo co-cultures, that CAFs inhibit NK cell cytotoxicity towards cancer cells. We unravel the mechanism by which this suppression occurs, through ligand-receptor engagement between NK cells and CAFs leading to CAF cytolysis, which in turn diminishes the expression of activating receptors on NK cells, promoting cancer escape from NK cell surveillance. Analysis of breast cancer patient samples reveals enrichment of NK cells in CAF-rich regions, and upregulation of NK binding ligands on CAFs which is correlated with poor disease outcome. These results reveal a CAF-mediated immunosuppressive decoy mechanism with implications for treatment of solid tumors.