Dissecting the molecular regulation of T cell localization and function within the Mycobacterium tuberculosis granuloma - PROJECT SUMMARY/ABSTRACT Mycobacterium tuberculosis (Mtb) infection is a major global health problem. Despite widespread immunization with Bacillus Calmette–Guérin and availability of antibiotic therapy, there are 10 million new cases and 1.4 million deaths annually, underscoring the need for improved treatment strategies. CD4 T cell-mediated immunity is critical for protection against Mtb infection, and is governed by 1) appropriate trafficking of CD4 T cells to distinct compartments within the Mtb-infected lung, including sites of infection, and 2) robust effector function at these sites. We have uncovered a spatially-resolved immunosuppressive mechanism by which localized TGFβ signal plays a dominant role in limiting the presence and function of T effector cells within the granuloma, with the greatest effect directly adjacent to infected cells. We have shown that ablation of T cell TGFβR-signaling reverses this suppression and results in reduced bacterial burdens. Here we propose to dissect the mechanistic underpinnings of these observations and address the central hypothesis that: Inappropriate localization of CD4 T cells, in combination with pleiotropic inhibition by localized TGFβ activation within the granuloma core limits effective immunity to Mtb pulmonary infection. To address this hypothesis, we will use a tractable yet physiologic murine ultra-low dose model of Mtb infection and advanced analytical microscopy, then confirm concepts learned in mice in human pulmonary granulomas as follows: 1) We will comprehensively characterize how individual chemokine receptors contribute to CD4 T cell localization, activation, function and ultimately, infection outcome. These findings will be corroborated in human granulomas. 2) We will also characterize how TGFβ activation by individual cell types limits localized CD4 T cell activation, function and infection outcome. This will be validated in granulomas from patients who die from active TB and those with asymptomatic Mtb infection who die from other causes, an unparalleled resource in the antibiotic era. These studies will also yield information about additional inhibitory pathways that are present within pulmonary granuloma and provide a framework for their characterization which can be pursued in future R01 applications. Thus, this proposal will leverage the strengths of our ULD Mtb mouse model and innovative imaging tools to understand how T cells traffic to infected sites and characterize a dominant immunosuppressive factor within this space, which has important implications for vaccine design and host-directed therapy. Dr. Gern’s career development plan builds on a background of using advanced imaging to study pulmonary pathogens with coursework and hands-on training in advanced immunology, Mtb pathogenesis, advanced microscopy, and laboratory management. A K08 award will allow Dr. Gern to make maximal use of SCRI and UW’s extensive scientific resources to achieve scientific independence, advancing his career goal to understand the factors dictating immune cell trafficking and function within different tissue microenvironments during Mtb infection, with the ultimate goal of improving tuberculosis treatment.
