Grant: Project Grant

Mycobacterium tuberculosis (Mtb), the cause of tuberculosis (TB), is transmitted by aerosol from incident TB cases to uninfected contacts. The inhaled Mtb bacilli make their way into the alveoli of the lower respiratory tract. In the alveoli, Mtb is rapidly phagocytosed by alveolar macrophages (AM). For infection to establish itself, infected AM leave the alveoli and migrate into lung parenchyma where they trigger the formation of infectious granuloma. A hallmark of granuloma formation is the development of anti-Mtb T cell dependent immunity. Since Mtb cannot be detected in the human host at this stage of TB pathogenesis, it is the emergence of Mtb-specific CD4+ and CD8+ T cell immunity that is used as surrogate to establish infection with Mtb. Hence, if Mtb has not emigrated from alveoli, a person is considered uninfected despite possible presence of Mtb in their alveoli. Persons who despite documented exposure to Mtb do not develop CD4/CD8 cell immunity are called "resisters" to Mtb infection. Employing single cell RNA sequencing (scRNAseq) to characterize alveolar cells from people with HIV (PWH) who resist infection with Mtb we discovered that resister AM are in an activated state. Following ex vivo infection with Mtb these activated AM overexpress the MICA gene. MICA is the ligand for the activating NKG2D NK cell receptor. In resisters, the NKG2D receptor is overexpressed by poly-cytotoxic CD8+ T cells (poly-CTL) that occur at increased numbers in resister alveoli. The present application is focused on obtaining a more detailed mechanistic understanding of the above resister phenotype. We will perform multi-omics and T cell receptor (TCR) sequencing to characterize the chromatin structure of resister and control cells using specialized techniques. We will also employ a novel assay to study killing of Mtb in infected AM by poly-CTL. Our results will provide key pre-clinical data for the development of Mtb transmission blocking vaccines.