Leveraging Naturally Assembled Tumor Extracellular Vesicles as Self-Adjuvanting Nanovaccines to Potentiate Cancer Immunotherapy via cGAS/STING Activation

The activation of cyclic guanosine monophosphate-adenosine monophosphate (cGAS)/stimulator of interferon genes (STING) pathway has emerged as a promising cancer immunotherapy strategy. However, the clinical efficacy of STING agonists is hindered by poor pharmacological properties, asynchronous tumor antigen delivery, and unwanted side effects. Inspired by the observation that tumor cells excrete extracellular vesicles (EVs) enriched with tumor antigens and various proteins for intercellular communication, we leveraged a biological self-assembling pathway to construct a tumor vaccine for cancer immunotherapy through cGAS/STING activation, overcoming these limitations. The vaccine enriches double-stranded DNA (dsDNA), which serves as a natural adjuvant, enhancing antigen presentation in EVs and promoting T-cell activation via the cGAS/STING pathway. Specifically, we incubated metformin-loaded positively charged poly(d, l-lactide-<i>co</i>-glycolide) nanoparticles (Met-PC-NPs) with tumor cells to elevate intracellular reactive oxygen species (ROS) levels and subsequently harvested "waste" EVs containing both dsDNA entrapped by Met-PC-NPs and tumor antigens (Met-PC-EVs). Upon subcutaneous injection, Met-PC-EVs efficiently migrated to lymph nodes and activated antigen-presenting cells, enabling the cross-presentation of tumor antigens to CD8⁺ T-cells. This process led to robust tumor eradication in both prophylactic and therapeutic models, and it established long-term immune memory. Furthermore, Met-PC-EVs demonstrated a significant synergistic effect when coadministered with immune checkpoint inhibitors. Our approach successfully transformed "waste" Met-PC-EVs into valuable vaccines, leveraging cGAS/STING activation to bypass the current limitation of STING agonists, and offered a clinically translatable method for developing EV-based vaccines.