Synthetic STING agonists elicit powerful vaccine adjuvancy providing robust central memory and anti-tumour effects

Drugs that target the innate immune sensor STING are known to be effective in modulating the immune infiltrate of the tumour microenvironment. STING agonists have potential to enhance responses to checkpoint inhibitor therapy, however, their ability to influence and shape adaptive immune responses is poorly understood. Here, we investigated the impact of a range of synthetic STING agonists on antigen specific CD8+ T-cell responses to soluble antigen using the murine OT-1 adoptive transfer model with Ovalbumin as the antigen to monitor T cell responses. Our data demonstrate that synthetic STING agonists are able to stimulate antigen specific T-cell expansion in response to challenge in mice. This effect required expression of STING, an intact myeloid compartment and Type-I IFN and TNF signalling. Expanded T-cells post treatment differed from those induced by the established immune adjuvant, anti-CD40 antibody through lower induction of the immune checkpoint receptor PD-1. Furthermore, our data revealed a marked increase in the induction and persistence of CD8+ central memory cells after STING agonist and antigen challenge. Finally, we demonstrate that following rechallenge, STING agonism produced larger secondary responses that could be translated into enhanced tumour protection and survival. Therefore, synthetic STING agonists are capable of acting as potent immune adjuvants and can induce robust memory formation leading to better recall and tumour control. Critically, these benefits along with the lower expression of PD-1, have implications for their use as adjuvants for multiple immunotherapy and vaccine applications.