Identifying immune correlates of control and protection to Mycobacterium tuberculosis (Mtb) infection is essential for designing vaccines for TB. The overall goals of our TBRU application are to identify antigen-specific T cell responses that are associated with distinct outcomes of Mtb infection: clearance, persistence, and progression to active disease. We currently lack the knowledge or tools to distinguish individuals who harbor persistent Mtb infection from those who may have resolved infection via immune-mediated clearance of bacteria. In Project 1 we will focus on "Identification of human Mtb-specific T cell signatures that are associated with resolved and persistent Mtb infection". We will test the hypothesis that distinct Mtb-specific memory T cell profiles are associated with bacterial clearance or persistence. This is supported by our data showing that distinct antigen-specific memory T cell phenotypes and functions are associated with LTBI, active TB disease and clinically resolved TB. We propose to use chemotherapy-mediated clearance to model immune-mediated clearance of Mtb, as the treatment regimen for LTBI should result in significant reduction or elimination of bacteria. We will enroll individuals with LTBI in a low-exposure setting (Atlanta, GA) and systematically compare their antigen-specific T cell responses before and after treatment. We will delineate the spectrum of antigens recognized by Mtb-specific memory CD4 and CD8 T cells, characterize their memory phenotypes, functional capacities and transcriptional profiles (Aim 1). Using statistical analyses, we will derive Mtb-specific T cell signatures that represent bacterial clearance and persistence and evaluate these (with Project 3), in non-human primates (NHP) and determine the prevalence of these signatures in treatment-naive individuals with LTBI in Kenya (Aim 2). We will longitudinally assess the dynamics of Mtb-specific memory T cell responses and their homeostatic turnover in LTBI (Aim3). We will also compare clearance/persistence signatures with those associated with progression to TB (with Project 2). Overall, these studies will provide insights into protective immunity to TB and new tools to evaluate Mtb persistence or clearance in LTBI.