Cytomegalovirus-Induced Immune Remodeling and Susceptibility to Mycobacterium tuberculosis

About This Grant

ABSTRACT: Tuberculosis (TB) is the leading cause of death from an infectious disease caused by a single pathogen: Mycobacterium tuberculosis (Mtb). Most individuals exposed to Mtb do not progress to TB disease. An important emerging hypothesis is that viral infections may contribute to the heterogeneity of outcomes following Mtb exposure by impairing immune responses critical for controlling Mtb. Among common viruses, Cytomegalovirus (CMV) infection has been shown to increase risk of TB disease in several human cohorts, despite vaccination with Bacille Calmette-Guérin (BCG), the only licensed vaccine against TB. The prevalence of CMV infections is particularly high in low- and middle-income countries where TB is also endemic. Importantly it is well known that CMV remodels both the innate and adaptive arms of the immune system, but it is unclear how the sequalae of CMV infection modulates immunity against Mtb. CMV also directly infects non-hematopoietic cells, primarily fibroblasts and epithelial cells, and thus, likely remodels the lung environment where Mtb-infected macrophages reside. Our central hypothesis is that CMV pre-infection hinders immunity against Mtb through direct and indirect mechanisms. To define the immunological mechanisms underlying the impact of CMV on Mtb control, we will use a murine co-infection model where we infect C57BL/6 mice with mouse-adapted CMV (MCMV) a month before Mtb infection and compare them to MCMV-naïve control mice. We will leverage fluorescent reporter Mtb and CMV strains to allow for sorting of infected and bystander cells, as well as imaging the infected cells in situ. In the first aim, we will follow the mice to determine the impact of MCMV pre-infection on survival, lung pathology, and immune characteristics following Mtb infection. We will complement the in vivo model with a series of in vitro co-infection experiments in primary mouse bone marrow-derived macrophages, and primary human monocyte- derived macrophages and macrophage-like cells. In these experiments, we will pre-infect the macrophages overnight with MCMV or human-adapted CMV (HCMV), based on the macrophage source, followed by Mtb, and monitor the bacterial load, cell death, and extent of co-infection with both CMV and Mtb. Since MCMV is known to transcriptionally reprogram both infected and bystander macrophage subsets, we hypothesize that CMV pre- infection will increase susceptibility to Mtb in both CMV-infected and bystander macrophages. In the second aim, we propose to profile the co-infected mouse lungs with confocal microscopy, spectral cytometry, and Cellular Indexing of Transcriptomes and Epitopes by sequencing (CITE-seq). We will perform two sets of profiling experiments, where we specifically enrich for macrophages, or comprehensively analyze hematopoietic and non- hematopoietic subsets in the lung. The outcomes from the mouse model will provide important insights on how lung immunity is rewired in the course of co-infection with these two prevalent pathogens to mediate co- pathogenesis. The findings from our study will guide translational approaches to interrupt CMV-induced TB pathogenesis, which is clinically observed in many human cohorts.