Abstract 880: Accumulation of cytosolic single-stranded DNA triggers innate immune responses via a novel sting-independent mechanism

Abstract Immune checkpoint blockade (ICB) has shown durable responses in a subset of patients with hypermutated cancers. Although some non-hypermutated cancer patients have also demonstrated clinical responses to ICB, the majority do not respond, prompting research into novel combination immunotherapies. Ongoing clinical trials have explored such combinations, but challenges like hematological toxicities and resistance have limited their effectiveness. Therefore, there is an urgent need for more effective therapies. Recent studies suggest that mislocalized cytoplasmic DNA may serve as a potent mediator of innate immune responses, potentially enhancing ICB efficacy. However, the mechanisms by which intracellular single-stranded DNA (ssDNA) activates the innate immune system remain poorly understood. In this study, we report that accumulation of cytosolic ssDNA in cancer cells by silencing TREX1 improves ICB response and promotes the infiltration of immune cells via DDX3X. Additionally, we further developed mRNA-based therapeutic agents HIM-mRNA-001 to enhance tumor sensitivity to ICB with minimal toxicities. These findings suggest that targeting cytosolic ssDNA accumulation could provide a new therapeutic strategy for non-hypermutated cancers, offering a promising alternative to current immunotherapies. Citation Format: Jing Zhang. Accumulation of cytosolic single-stranded DNA triggers innate immune responses via a novel sting-independent mechanism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 880.