Authors show systemic UVR exposure increases circulating regulatory T cells and induces an immunosuppressive signature within colorectal and melanoma mouse tumors, thereby impairing the efficacy of immunotherapy.

Through in-depth cellular and molecular profiling of mice and human tumours, the authors identify the mechanisms by which anti-inflammatory drugs targeting the COX-2/PGE2/EP2-4 axis rapidly alter the tumour immune landscape to enhance the response to immune checkpoint inhibition.