Enhancing IFN-β production through synergy between the STING pathway and TLR pathways

Abstract

Abstract Previous work from our lab has shown that tumors activate the STING pathway in antigen presenting cells. STING signaling leads to IFN-β production which is required for T cell priming and recruitment. IFN-β transcription is induced by multiple transcription factors including NF-κB and IRF3. Enhancing STING activation and downstream IFN-β production has therapeutic potential, and STING agonists are currently being evaluated in clinical trials. However, innate immune activation in response to a pathogen rarely occurs by activating only one signaling pathway, and activating multiple innate immune pathways similar to a natural infection could improve the efficacy of STING agonists. To test this, we performed experiments with the STING agonist DMXAA alone or in combination with several TLR agonists. We found that LPS + DMXAA induced significantly greater IFN-β transcription than the sum of either agonist alone. To explain this synergy, we assayed each step of STING pathway signaling. LPS did not increase STING aggregation beyond that induced by DMXAA. Additionally, LPS did not increase IRF3 phosphorylation nor IRF3 nuclear translocation in combination with DMXAA. LPS did increase the phosphorylation and nuclear translocation of the NF-κB subunit p65. These results suggest that the synergy in IFN-β production is achieved through IRF3 activation downstream of STING signaling and NF-κB activation downstream of TLR4 signaling. Intratumoral injection of LPS + DMXAA resulted in significantly improved tumor control of B16 melanoma in vivo than either agonist alone, suggesting that combining activation of these pathways improves the anti-tumor innate immune response in a way that is therapeutically beneficial.