BCG overexpressing an endogenous STING agonist provides enhanced protection against pulmonary tuberculosis

Stimulator of interferon genes (STING) has emerged as a key signaling receptor that induces proinflammatory cytokines, and small molecule STING agonists are being developed as anticancer and antiviral agents. Here we report a strategy of delivering a STING agonist from within live BCG. We generated a recombinant BCG (BCG-disA-OE) that overexpresses the endogenous mycobacterial diadenylate cyclase gene and releases high levels of the STING agonist c-di-AMP. In macrophages BCG-disA-OE elicited statistically significantly stronger TNF-, IL-6, IL-1{beta}, IRF3, and IFN-{beta} levels than BCG-WT. In a 24-week guinea pig vaccination-Mtb challenge model, BCG-disA-OE reduced lung weights, pathology scores, and Mtb CFU counts in lungs by 28% (p<0.05), 34%, and 2.0 log10 CFU units (p < 0.5) compared with BCG-WT, respectively. Overproduction of the STING agonist c-di-AMP significantly enhanced the protective efficacy of BCG against pulmonary and extrapulmonary tuberculosis. Our findings support the development of BCG-vectored STING agonists as a TB vaccine strategy.