Pre-existing SIV Infection Increases Susceptibility to Tuberculosis in Mauritian Cynomolgus Macaques

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), is the leading cause of death among HIV positive patients. The precise mechanisms by which HIV impairs host resistance to a subsequent M.tb infection are unknown. We modeled this co-infection in Mauritian cynomolgus macaques (MCM) using SIV as an HIV surrogate. We infected seven MCM with SIVmac239 intrarectally and six months later co-infected them via bronchoscope with ~10 CFU M.tb. Another eight MCM were infected with M.tb alone. TB progression was monitored by clinical parameters, by culturing bacilli in gastric and bronchoalveolar lavages, and by serial 18F-FDG PET/CT imaging. The eight MCM infected with M.tb alone displayed dichotomous susceptibility to TB, with four animals reaching humane endpoint within 13 weeks and four animals surviving >19 weeks post M.tb infection. In stark contrast, all seven SIV+ animals exhibited rapidly progressive TB following co-infection and all reached humane endpoint by 13 weeks. Serial PET/CT imaging confirmed dichotomous outcomes in MCM infected with M.tb alone and marked susceptibility to TB in all SIV+ MCM. Notably, imaging revealed a significant increase in TB granulomas between four and eight weeks post M.tb infection in SIV+, but not in SIV-naive MCM and implies that SIV impairs the ability of animals to contain M.tb dissemination. At necropsy, animals with pre-existing SIV infection had more extrapulmonary TB disease, more overall pathology, and increased bacterial loads than animals infected with M.tb alone. We thus developed a tractable MCM model in which to study SIV-M.tb co-infection and demonstrate that pre-existing SIV dramatically diminishes the ability to control M.tb co-infection.Author summaryMycobacterium tuberculosis (M.tb) is the etiologic agent of tuberculosis (TB) and infects a tremendous number of individuals. TB causes millions of deaths each year and is the leading cause of death in human immunodeficiency virus (HIV)-positive individuals. Currently, the mechanisms by which pre-existing HIV infection increases susceptibility to subsequent M.tb infection and predisposes an individual to TB disease are poorly understood. We developed a simian immunodeficiency virus (SIV) - M.tb co-infection model in Mauritian cynomolgus macaques (MCM) to investigate how SIV impairs the immune response to a subsequent M.tb infection. We show that naive MCM display variable resistance to TB while all SIV-infected MCM failed to control M.tb infection. Using quantitative measures of disease and serial PET/CT imaging, we show that SIV+ co-infected animals uniformly exhibit rapid TB progression, more tuberculosis disease dissemination, and increased mortality. This coinfection model will facilitate studies, provide unique insights into the defects underlying TB susceptibility in HIV+ individuals and will help us develop approaches to overcome these defects.