Project Summary/Abstract Chronic viral infections are associated with functional impairment of innate and adaptive immunity, including the development of T cell exhaustion. We and others recently showed that these functional defects persist even after cure of chronic viremia and are associated with irreversible molecular and epigenetic “scars”. With the rise of treatment options, ranging from antivirals to immunomodulatory therapies or even therapeutic vaccines, attention in biomedical research has shifted to understanding the long-term immune sequelae of chronic infection: how does the irreversible regulatory wiring within virus-specific exhausted T cells mediate dysfunction? How does chronic infection exposure impact bystander innate as well as adaptive responses and how durable are these effects? This is an important knowledge gap preventing the identification of regulatory pathways as well as relevant cell types that can be targeted to reverse long-lasting immune dysregulation in chronic infection. In Project 2, we focus on a fundamental, yet understudied aspect of persistent viral infection: the impact on existing as well as de novo antiviral responses, and we explore new strategies for modulating immune dysfunction. This problem is ideally studied in human cohorts since animal models cannot mimic the breadth and timescale of immune exposures in humans. Chronic HCV infection is a unique model system in humans to study fundamental principles of antiviral immunity – it can cause self-limited acute infection or progress to chronic disease in healthy adults and remains the only persistent virus that can be fully cured. Therefore, we propose to use HCV as a pathognomonic disease context to test our overarching hypothesis that chronic infection leads to broadly dysregulated innate and adaptive responses and that targeted modulation of key molecular pathways can rescue immune dysfunction. Specifically, we will 1) test whether reversal of known immune sequelae/”scars” in chronic infection through epigenetic reprogramming can rescue T cell exhaustion, 2) assess the impact of chronic infection and its cure on bystander T cell differentiation and function, and 3) test how altered innate myeloid responses following chronic viral infection (HCV) affects inflammatory setpoint and heterologous vaccine responses. Upon completion of this Project, we will have identified specific mechanistic interventions that can restore exhausted T cell function by reversing previously defined regulatory “scars”. We will also have delineated more broadly the immune sequelae of chronic infection on bystander innate and adaptive cells. These studies are intended to establish new paradigms for antiviral immunity in humans and will ultimately act as proof- of-concept for new intervention strategies that can enhance or modulate anti-viral immunity with high specificity. Importantly, this Project will closely interact with Projects 1 and 3, to compare and contrast the immune pert...