A combination of TLR9 and STING agonists favors antigen cross-presentation and promotes Th1 immune response against influenza virus

Abstract

Abstract Adjuvants can boost the type, magnitude, breadth, and durability of vaccine responses. We have previously demonstrated that combining adjuvants through rational design can overcome age-specific impairments in inducing Th1 immunity, trigger antigen cross-presentation, and enable CD8-driven protective immunity of protein-based vaccine formulations. Here, we screened 78 adjuvant combinations to explore their molecular mechanism of action through human in vitro modeling and identified combinations that synergistically promote the expansion of antigen-specific CD4+ cells, induce cross-presentation on MHC class I resulting in activation of antigen-specific CD8+ cells, and redirect the type of immune response to favor the production of Th1-promoting cytokines. The combination of CpG (TLR9 agonist) and 2,3-cGAMP (STING agonist) promoted influenza-specific CD4+ and CD8+ T cell activation and selectively favored the secretion of Th1-polarizing cytokines TNF and IL-12p70. Activation of T-bet-expressing Th1 cells was also observed with this adjuvant combination. We also demonstrate the phenotypic reprogramming towards conventional type 1 dendritic cells by CpG + 2,3-cGAMP, and the ability of this adjuvant combination to induce similar immune responses in immune cells from newborns and older adults. Identification of the adjuvant combination CpG + 2,3-cGAMP may prove key to the future development of vaccines against intracellular pathogens such as respiratory viruses.