Cytotoxic NK cells impede response to checkpoint immunotherapy in melanoma with an immune-excluded phenotype

The inability of lymphocytes to infiltrate the tumor nest drastically limits immune checkpoint blockade (ICB) responsiveness. Analyzing the immune landscape of matched pre- and early on-treatment biopsies of melanoma patients undergoing ICB therapy, we observed a significant increase in cytotoxic NK cells in early on-treatment biopsies from non-responders. Spatial OMICs revealed that while NK cells colocalized with CD8 T cells within the tumor bed in responding lesions, they were excluded from the tumor parenchyma in non-responding lesions. Strikingly, depletion of NK cells using a NK1.1 antibody or the FDA-approved drug Daratumumab in a unique melanoma mouse model exhibiting an immune-excluded phenotype unleashed immune infiltration of the tumor core and tumor clearance upon ICB exposure. Mechanistically, we show that NK cells are actively recruited to immune-excluded areas upon ICB exposure via the chemokine receptor CX3CR1 to suppress tumor infiltration and antitumor function of CD8 T cells, possibly by promoting ferroptosis.