Development and application of adjuvant immunotherapy for cancer

Recent progress in immunology have revealed that the immune system is capable of fight- ing against cancer by not only activation of innate and adaptive immune responses, but also by inhibition of various types of the cancer-associated immune suppression. In addition to immune check-point inhibitors and cancer vaccines, many conventional and new generations of vaccine adjuvants are in the limelight, many of which are known as potent immuno- stimulators through specific innate immune receptors and signaling pathways. For example, TLR agonist targeting the tumor microenvironment, or combination of certain TLR agonist with STING ligand can act not only as a potent adjuvant for various modality of cancer vac- cines, but also as a mono-therapeutic agent for various cancer animal models. Their precise mechanisms of action have not been fully elucidated, but evidence suggest that adjuvants mentioned above reverse an immune suppressive tumor microenvironment into an optimal vaccination spot by providing protective tumor (neo) antigens and immunogenic cell death.