ABSTRACT Thymically-derived regulatory T-cells (Tregs) are critical for controlling immune responses and preventing autoimmunity. In the setting of viral infection, Tregs are important modulators of anti-viral immune responses and help to prevent excessive tissue damage. The subset of Tregs responsible for responding to viral infections and what types of antigens they are recognizing is not well understood. This proposal aims to address this gap in knowledge. In single-cell RNA sequencing experiments of thymic Tregs and Treg progenitors, I have observed a unique cell subset that express a strong interferon stimulated gene (ISG) signature. I hypothesize that thymic Tregs receiving IFN stimulation are enriched for expression of TCRs that recognize ISG-derived antigens presented by thymic APCs. Furthermore, I propose that these Tregs are important responders to IFN-induced inflammation in the periphery including viral infection and help to limit immune responses in these settings. I will test this hypothesis in two specific aims: In aim 1 I will use a novel mouse model in which Tregs expressing the ISG-signature will be deleted following administration of diphtheria toxin. Treg responses to influenza virus infection will be evaluated in this context to determine the importance of these ISG-signature Tregs in responding to IFN-induced inflammation. In aim 2 I will use mice with conditional knockout of Stat1 in thymic epithelial cells and dendritic cells to determine how Treg responses to IFN-induced inflammation are altered when they develop in the absence of interaction with ISG antigens in the thymus. Additionally, I will use spatial transcriptomic technology to visualize the thymic niche expressing IFNs and ISGs, as well as the progenitor and mature ISG-signature Treg subsets.