Topology‐Driven X‐Shaped DNA as a cGAS Stimulator to Promote Dendritic Cell Activation and Antitumor Vaccine Efficacy

ABSTRACT Vaccine adjuvants are essential for enhancing immune responses, yet the development of safe and potent adjuvants remains challenging. Here, we report a topology‐guided nucleic acid adjuvant based on a four‐way Holliday junction framework (X‐DNA) designed to potentiate cGAS‐STING signaling. In contrast to linear dsDNA, X‐DNA presents a flexible, multibranched architecture that increases local DNA density and multivalent interaction potential, thereby favoring productive cGAS assembly. Molecular dynamics simulations demonstrate that X‐DNA forms a more stable complex with cGAS and facilitates the establishment of the active 2:2 cGAS‐DNA core assembly. Consistent with this mechanism, X‐DNA markedly enhances cGAMP production and IFN‐β secretion, promotes dendritic cell maturation and antigen presentation, and, when conjugated with antigenic peptides, strengthens antigen‐specific CD8 + T‐cell responses in vivo. In murine tumor models, X‐DNA significantly improves the therapeutic efficacy of peptide vaccination and suppresses tumor progression. These findings identify DNA topology as a programmable determinant of cGAS activation and establish X‐DNA as a structurally defined nucleic acid adjuvant for enhancing antitumor subunit vaccine efficacy.