All animals possess a robust innate immune response that depends on their ability to recognize viral double- stranded RNA (dsRNA) as foreign. Yet, animal cells also encode and express dsRNA, and this cellular dsRNA must be distinguished as ?self? to prevent an aberrant immune response. Adenosine deaminases that act on RNA, or ADARs, deaminate dsRNA to mark it as self and prevent an aberrant immune response. In this capacity ADARs serve as an ?Innate Immune Checkpoint? (IIC), and recent studies reveal that a decrease in ADAR activity in tumors releases this IIC, eliciting an immune response that leads to cell death. ADARs are the only IIC known to date, and proposed studies are designed to fill this gap in knowledge towards the goal of new immunotherapies. Comparative phylogenetic analyses will be complemented with molecular biology and biochemistry experiments to identify mitigators, such as ADARs, that prevent inappropriate deployment of antiviral defense, and ancient incompatibilities, such as invertebrate proteins that may activate an antiviral response when introduced into vertebrates. Experiments in mammalian cells and mice, and the invertebrate model organism, C. elegans, will provide a wide phylogenetic sampling to identify, test, and compare new IICs. Engineered mice and cell lines are in hand, and established assays are in place, to monitor effects on the immune pathway of both animals. Known dsRNA binding proteins, as well as those identified by immunoprecipitation strategies, will be prioritized by phylogenetic assays for testing as IICs. In vitro biochemistry experiments, and structural analyses, will guide subsequent rounds of phylogenetic comparisons. Mammalian ADAR1 p150 prevents an interferon response by modulating the MDA5 arm of the vertebrate innate immune pathway, and IICs for the RIG-I arm have not been reported. Strategies to identify IICs for the RIG-I arm will focus on enzymes known to modify the 5' terminus of RNA, a known epitope for RIG-I recognition. The culmination of proposed studies will be the evaluation of candidate IICs in experimental models of tumorigenesis.
Harnessing immune pathways to attack a diseased state, or immunotherapy, is a proven and powerful way to treat disease such as cancer. Yet, there are many natural checkpoints in place to prevent an aberrant immune response. Proposed studies are designed to identify and modulate innate immune checkpoints to reveal previously unsuspected ways to exploit innate immune pathways to treat disease.
