Condensate nanovaccine adjuvants augment CD8+ T-Cell-dependent antitumor immunity through mtDNA leakage-triggered cGAS-STING axis activation.

The variety and functionality of current clinical vaccine adjuvants remain limited. Conventional aluminum-based adjuvants predominantly induce Th2-biased humoral immunity but exhibit a limited capacity to elicit Th1-mediated cellular immune responses, particularly tumor antigen-specific cytotoxic CD8+ T lymphocytes (CTLs), which are essential for effective cancer vaccine performance. Inspired by natural biomolecular condensates, we developed a versatile noncovalent protein self-assembly strategy distinct from traditional approaches requiring structural domain modifications or bifunctional crosslinkers. Our methodology employs amphiphilic molecules (sodium myristate/SMA and sodium dodecyl thiolate/SDT) as molecular bridges to mediate protein‒protein interactions through hydrophobic forces and disulfide bond formation. This process generates nanoscale protein condensate (PCD) vaccines with exceptional stability. As a novel adjuvant system, these synthetic condensates significantly enhance antigen cross-presentation by optimizing key parameters: antigen loading capacity, lymph node targeting, cytosolic delivery, and lysosomal escape. Consequently, they induce robust antigen-specific CTL responses and humoral immunity, demonstrating potent antitumor efficacy. Importantly, we found that the synthetic protein condensate (PCD) alone can act as a nanoadjuvant. By increasing mitochondrial membrane permeability, PCD induces mitochondrial DNA leakage into the cytosol, activating the cGAS‒STING pathway and promoting DC maturation. This safe and scalable platform eliminates the need for complex covalent modifications or genetic engineering, and it facilitates the design of diverse modular antigens, including neoantigens and viral antigens. Given its straightforward manufacturing process and superior immunogenicity, this synthetic PCD vaccine adjuvant has significant potential for clinical application and translation.