PROJECT SUMMARY Group 1 CD1-restricted T cells are a subset of the unconventional T cells that recognize lipid and glycolipid antigens presented by CD1a, CD1b, and CD1c molecules. The role of group 1 CD1-restricted T cells has been best established in Mycobacterium tuberculosis (Mtb) infection in which a wide variety of lipid antigens have been identified. Analysis of the T cell response during human Mtb infection indicated that infected individuals have increased CD1-restricted T cell responses to lipid antigens compared to Mtb na"ive controls. CD1 brestricted T cells present in bronchioalveolar fluid were shown to limit Mtb growth ex vivo and the frequency of these polycycotoxic Mtb lipid-reactive T cells correlated with protection from active tuberculosis disease. Furthermore, we have previously shown that Mtb lipid-specific group 1 CD1-restricted T cells were able to expand during Mtb infection in humanized CD1 transgenic (hCD1Tg) mice. Adoptive transfer of transgenic T cells specific to mycolic acid presented by CD1 b led to decreased bacterial burden in Mtb-infected Ragdeficient mice in a group 1 CD1-dependent manner. Taken together, these studies show that Mtb lipid-specific group 1 CD1-restricted T cells are an important component of the cellular immune response to Mtb. While most of group 1 CD1-restricted T cells express diverse αβ TCRs, most humans harbor a population of CD1b-restricted T cells known as "germline encoded mycolyl-reactive" (GEM) T cells that express an invariant TRAV1-2-TRAJ9 TCR-α chain. GEM T cells show high affinity binding to CD1b/glucose monomycolate (GMM) and secrete IFN-γ and TNF-α in response to GMM stimulation. To investigate the in vivo function of this conserved CD1b/GMM-specific T cell subset during Mtb infection, we generated a hCD1Tg background TCR transgenic mice encoding GEM TCR specific for CD1b/GMM. In Aim 1, we propose to determine if the expression of CD4 or CD8 co-receptor affects the antigen response of GEM T cells. In addition, we will assess the ability of GEM T cells to traffic to the lung and confer protection against Mtb infection. The effector functions important for GEM T cell-mediated anti-mycobacterial immunity will also be evaluated. In Aim 2, we propose to address whether GEM T cells have the capacity to generate memory T cell responses. We will use a novel vaccination and re-challenge model that allows for complete clearance of an attenuated Mtb strain prior to challenge with fully virulent Mtb to study memory GEM T cell responses. Using this approach, we will compare the activation kinetics, tissue localization, and effector functions of GEM T cells during primary and secondary response to Mtb infection. We will also analyze gene expression profiles of memory GEM T cells and compare to that of conventional memory T cells. Collectively, these studies will yield a better understanding of how group 1 CD1-restricted T cells contribute to the overall immune response against Mtb and whether t...