Picrasidine S Induces cGAS‐Mediated Cellular Immune Response as a Novel Vaccine Adjuvant

New adjuvants that trigger cellular immune responses are urgently needed for the effective development of cancer and virus vaccines. Motivated by recent discoveries that show activation of type I interferon (IFN‐I) signaling boosts T cell immunity, this study proposes that targeting this pathway can be a strategic approach to identify novel vaccine adjuvants. Consequently, a comprehensive chemical screening of 6,800 small molecules is performed, which results in the discovery of the natural compound picrasidine S (PS) as an IFN‐I inducer. Further analysis reveals that PS acts as a powerful adjuvant, significantly enhancing both humoral and cellular immune responses. At the molecular level, PS initiates the activation of the cGAS‐IFN‐I pathway, leading to an enhanced T cell response. PS vaccination notably increases the population of CD8+ central memory (TCM)‐like cells and boosts the CD8+ T cell‐mediated anti‐tumor immune response. Thus, this study identifies PS as a promising candidate for developing vaccine adjuvants in cancer prevention. This study performs a comprehensive chemical screening of 6800 small molecules and identifies picrasidine S (PS) as a potent IFN‐I inducer. PS acts as a powerful adjuvant, significantly enhancing both humoral and cellular immune responses. It activates the cGAS‐IFN‐I pathway, leading to an increase in CD8+ central memory (TCM)‐like cells and improves CD8+ T cell‐mediated anti‐tumor immunity.