cGAS/STING and NLRP3 cooperatively activate CD8+ T cell-mediated anti-tumor immunity in colorectal cancer

Colorectal cancer (CRC) is a highly prevalent and deadly disease that is largely refractory to immunotherapy. The only CRC subset that responds to these therapies is characterized by prevalent microsatellite instability (MSI), extensive CD8+ T cell infiltration and high expression of innate immune signaling pathways. Endogenous activation of the cGAS/STING pathway is essential for the CD8+ T cell antitumor response in MSI CRCs, suggesting that activating it in other CRCs could boost immunotherapy response rates. We show that cGAS/STING signaling can be enhanced by costimulation of the NLRP3 inflammasome and that dual stimulation increases CD8+ T cell-mediated antitumor immunity in both MSI and non-MSI CRCs. The ability of NLRP3 to boost cGAS/STING signaling was specific and did not occur with activation of other innate immune pathways such as AIM2 or TLRs. Cooperativity between cGAS/STING and NLRP3 proceeded via a positive feedback loop that was inflammasome-independent and required early crosstalk between the signaling mediators and regulation of their gene expression. Notably, increased cGAS/STING signaling enhanced CD8+ T cell activation when in conjunction with anti-PD1 immunotherapy, suggesting that signaling via NLRP3 could further boost this response and render otherwise resistant CRC susceptible to immunotherapy. SignificanceInnate immune signaling pathways cooperatively regulate CD8+ T cell-mediated antitumor immunity in both hot and cold tumors. In addition to serving as predictive biomarkers, these pathways can be therapeutically targeted to increase response rates to immunotherapy while minimizing undesirable adverse events.