Cyclic di-GMP (c-di-GMP) serves as an intracellular signaling molecule synthesized by bacteria. Recent studies have shown that administering c-di-GMP can elicit robust immune responses both in laboratory settings and within living organisms. This cyclic dinucleotide (CDN) has been found to stimulate the production of cytokines, including type I interferons, via activation of the STING/TBK1/IRF3 pathway. As an adjuvant, it facilitates the recruitment of monocytes and granulocytes and promotes the maturation of dendritic cells. In bacterial systems, c-di-GMP functions prominently as an intracellular messenger, influencing various cellular processes.