Antigen-presenting cell activation requires intrinsic and extrinsic STING signaling after the phagocytosis of DNA-damaged cells

Antigen-presenting cells (APCs) are readily activated after phagocytosing infected or DNA-damaged cells but not normal apoptotic cells for reasons that are not well understood. Here, we demonstrate that after DNA damage events, cytosolic dsDNA species trigger intrinsic STING signaling and the production of key immunogenic proteins, including CCL5, which renders such cells capable of APC activation upon phagocytosis. These events involve the generation of immunogenic STING-inducible endosomal vesicles (SIEVEs) additionally comprising critical autophagy-associated proteins associated with cytosolic DNA species. After phagocytosis, extrinsic cGAS-STING signaling is triggered via engulfed, immunogenic transactivating DNA vesicles resulting in APC stimulation. These results help explain how APCs are predominantly activated by DNA-damaged or infected cells in contrast with normal apoptotic cells and suggest that reconstitution of STING signaling or key inducible genes in cGAS-STING-defective malignancies could substantially augment cancer immunotherapies.