Tumor cell intrinsic RIG-I activation is sufficient to drive immune mediated tumor rejection

Targeting cytosolic nucleic acid sensors is a potent approach to drive type I interferon responses and anti-tumor immunity. Recent evidence suggests that activation of retinoic acid inducible gene-I (RIG-I) using synthetic hairpin RNA agonists decreases tumor progression in multiple preclinical models. However, the role of tumor cell intrinsic RIG-I in shaping tumor cell fates and the host immune microenvironment remains unclear. Here, we show that RIG-I expression is correlated with better overall survival and a distinct immune gene signature in specific human cancers including colorectal cancer. Activation of RIG-I in breast and colorectal cancer cells is sufficient to drive tumor cell death in vitro and significantly delay tumor growth in vivo in multiple preclinical models. Importantly, the efficacy of tumor cell RIG-I activation is lost in immune deficient mice suggesting the requirement of immune responses for this effect. We observe that tumor cell intrinsic RIG-I activation elicits a robust cellular and molecular immune response. We show that tumor cell RIG-I activation also leads to induction of specific immune checkpoints including PD-L1. Using a publicly available database, we found that RIG-I expression serves as an excellent prognostic marker for responders to checkpoint immunotherapy, particularly PD-L1/PD-1 across cancers. Finally, combination of tumor cell intrinsic RIG-I activation with anti-PD-L1 led to a synergistic decrease in tumor growth in a colorectal tumor model. Our findings suggest that tumor cell intrinsic RIG-I can be targeted to enhance anti-tumor immune responses and highlights a potential strategy for anti-cancer vaccines that can invigorate the immune system.