Divergent immune impacts elicited by chemically dissimilar agonists of the STING protein

Abstract Vaccines comprised of inert antigen are very safe, yet they are typically only weakly immunogenic and thus require co-administration of factors such as adjuvants that enhance immunostimulation. Unfortunately, very few adjuvants are approved for clinical use and the mechanistic bases of their function are poorly understood. Stimulator of Interferon Genes (STING) is the PRR that senses intracellular cyclic dinucleotides (CDN) synthesized by the enzyme cGAS following its sensing of cytosolic DNA. Numerous molecules have been identified and developed that directly induce STING-mediated activity and can enhance establishment of the adaptive immune response. However, a significant barrier to clinical utilization of STING-based adjuvants exist including an understanding of their mechanisms of action and the unexpected diversity in molecular and cellular responses that correlate with chemical nature of the agonists. We utilized a mouse model of vaccination with the model antigen ovalbumin, in combination with chemically distinct STING agonists. While all CDNs and small molecules directly bind to and activate STING, we determined that downstream immune reactivity to antigens varied significantly. We have identified key dissimilarities including agonist-specific gene transcription patterns, cytokine induction, APC maturation, TFH enhancement, and T helper polarization biases. Furthermore, we observed these differences using two clinically relevant VLP-based vaccine antigens against Chikungunya and Zika viruses. Our findings provide new insights into STING-initiated immune responses, which can direct future research toward an optimization of adjuvants directed toward this and other innate immune pathways.