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.
