Circadian tumor infiltration and function of CD8+ T cells dictate a temporal response to immunotherapy

The quantity and quality of tumor-infiltrating lymphocytes (TILs), particularly CD8+ T cells, are parameters linked to tumor control and response to immunotherapy. Yet, it is unknown whether these parameters are controlled in a circadian manner. Here, we show in murine and human cancers that the phenotype and number of TILs show time-of-day differences, which are driven by rhythmic leukocyte infiltration and depend on the circadian clock machinery. These rhythms can be harnessed therapeutically: chimeric antigen receptor (CAR) T cells or immune checkpoint blockers produce significant antitumor benefits when administered at the optimal time of the day, but have little effect when administered at other times. Furthermore, time-of-day-dependent T cell signatures in murine tumor models predict overall survival in melanoma patients and correlate with response to anti-PD-1 therapy. Our data provide unexpected evidence of circadian dynamics in the tumor microenvironment (TME), and suggest the importance of exploiting them in prospective clinical trials. Overall design: Tumors were harvested at different times of the day and tumor infiltrating leukocytes were isolated by fluorescence activated cell sorting: live CD45+ cells. Tumor infiltrating leukocytes were sequenced by scRNA-seq and analyzed.