cGAS mRNA-Based Immune Agonist Promotes Vaccine Responses and Antitumor Immunity.

mRNA vaccines are a potent tool for immunization against viral diseases and cancer. However, the lack of a vaccine adjuvant limits the efficacy of these treatments. In this study, we used cGAS mRNA, which encodes the DNA innate immune sensor, complexed with lipid nanoparticles (LNP), to boost the immune response. By introducing specific mutations in human cGAS mRNA (hcGASK187N/L195R), we significantly enhanced cGAS activity, resulting in a more potent and sustained stimulator of interferon gene (STING)-mediated IFN response. cGAS mRNA-LNPs exhibited stimulatory effects on maturation, antigen engulfment, and antigen presentation by antigen-presenting cells, both in vitro and in vivo. Moreover, the hcGASK187N/L195R mRNA-LNP combination demonstrated a robust adjuvant effect and amplified the potency of mRNA and protein vaccines, which was a result of strong humoral and cell-mediated responses. Remarkably, the hcGASK187N/L195R mRNA-LNP complex, either alone or in combination with antigens, demonstrated exceptional efficacy in eliciting antitumor immunity. In addition to its immune-boosting properties, hcGASK187N/L195R mRNA-LNP exerted antitumor effects with IFNγ directly on tumor cells, further promoting tumor restriction. In conclusion, we developed a cGAS mRNA-based immunostimulatory adjuvant compatible with various vaccine forms to boost the adaptive immune response and cancer immunotherapies.