Mechanisms of genomic instability dictate cytosolic DNA composition and dendritic cell mediated anti-tumor immunity

Patients with microsatellite instable (MSI) colorectal cancers (CRC) face better prognosis than those with the more common chromosomal instable (CIN) subtype due to improved anti-tumor immune responses characterized by high cytotoxic T cell infiltration. Previous investigation identified the cytosolic DNA (cyDNA) sensor STING as necessary for chemokine-mediated T cell recruitment in MSI CRCs. Here, we find cyDNA from MSI CRC cells is inherently more capable of inducing STING activation and induces improved cytotoxic T cell activation by dendritic cells (DCs). Sequencing indicates MSI cyDNA is enriched for microsatellites, which upon DC uptake induce anti-tumor immunity in a manner consistent with clinical MSI CRCs. Radiation also modulates cyDNA stimulation capacity through larger cyDNA size and increased mitochondrial DNA content. Identifying highly stimulatory cyDNA arising from genomic instability such as in MSI CRCs allows for optimized development of DNA-based STING agonist therapies to improve responses of CIN CRC patients to immunotherapies.