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A once-weekly oral dose of isoniazid and rifapentine for 3 months (3HP) is recommended by the CDC for treatment of latent tuberculosis infection (LTBI). The aim of this study is to assess 3HP-mediated clearance of M. tuberculosis bacteria in macaques with asymptomatic LTBI. Twelve Indian-origin rhesus macaques were infected with a low dose (~10 CFU) of M. tuberculosis CDC1551 via aerosol. Six animals were treated with 3HP and 6 were left untreated. The animals were imaged via PET/CT at frequent intervals. Upon treatment completion, all animals except 1 were coinfected with SIV to assess reactivation of LTBI to active tuberculosis (ATB). Four of 6 treated macaques showed no evidence of persistent bacilli or extrapulmonary spread until the study end point. PET/CT demonstrated the presence of significantly more granulomas in untreated animals relative to the treated group. The untreated animals harbored persistent bacilli and demonstrated tuberculosis (TB) reactivation following SIV coinfection, while none of the treated animals reactivated to ATB. 3HP treatment effectively reduced persistent infection with M. tuberculosis and prevented reactivation of TB in latently infected macaques., Introduction Most people infected with Mycobacterium tuberculosis do not progress to active tuberculosis (ATB) but instead contain the bacteria and develop asymptomatic, latent tuberculosis (TB) infection (LTBI) (1). However, these [...]

While the advent of combination antiretroviral therapy (ART) has significantly improved survival, tuberculosis (TB) remains the leading cause of death in the HIV-infected population. We used Mycobacterium tuberculosis/simian immunodeficiency virus-coinfected (M. tuberculosis/SIV-coinfected) macaques to model M. tuberculosis/HIV coinfection and study the impact of ART on TB reactivation due to HIV infection. Although ART significantly reduced viral loads and increased [CD4.sup.+] T cell counts in blood and bronchoalveolar lavage (BAL) samples, it did not reduce the relative risk of SIV-induced TB reactivation in ART-treated macaques in the early phase of treatment. [CD4.sup.+] T cells were poorly restored specifically in the lung interstitium, despite their significant restoration in the alveolar compartment of the lung as well as in the periphery. IDO1 induction in myeloid cells in the inducible bronchus-associated lymphoid tissue (iBALT) likely contributed to dysregulated T cell homing and impaired lung immunity. Thus, although ART was indispensable for controlling viral replication, restoring [CD4.sup.+] T cells, and preventing opportunistic infection, it appeared inadequate in reversing the clinical signs of TB reactivation during the relatively short duration of ART administered in this study. This finding warrants the modeling of concurrent treatment of TB and HIV to potentially reduce the risk of reactivation of TB due to HIV to inform treatment strategies in patients with M. tuberculosis/HIV coinfection., Introduction The modern combination antiretroviral therapy (cART) regimen, which is known for its high efficacy and reduced toxicity, has significantly improved life expectancy in people living with HIV (PLHIV). Yet [...]

HIV is a major driver of tuberculosis (TB) reactivation. Depletion of [CD4.sup.+] T cells is assumed to be the basis behind TB reactivation in individuals with latent tuberculosis infection (LTBI) coinfected with HIV. Nonhuman primates (NHPs) coinfected with a mutant simian immunodeficiency virus (SIV[DELTA]GY) that does not cause depletion of tissue [CD4.sup.+] T cells during infection failed to reactivate TB. To investigate the contribution of [CD4.sup.+] T cell depletion relative to other mechanisms of SIV-induced reactivation of LTBI, we used CD4R1 antibody to deplete [CD4.sup.+] T cells in animals with LTBI without lentiviral infection. The mere depletion of [CD4.sup.+] T cells during LTBI was insufficient in generating reactivation of LTBI. Instead, direct cytopathic effects of SIV resulting in chronic immune activation, along with the altered effector T cell phenotypes and dysregulated T cell homeostasis, were likely mediators of reactivation of LTBI. These results revealed important implications for TB control in HIV-coinfected individuals., Introduction Tuberculosis (TB) and HIV coinfection are a global syndemic (1). Approximately 90% of HIV-negative Mycobacterium tuberculosis-infected (Mtb-infected) individuals lack clinical signs of TB and are considered to have latent [...]

Studies using the nonhuman primate model of Mycobacterium tuberculosis/simian immunodeficiency virus coinfection have revealed protective [CD4.sup.+] T cell-independent immune responses that suppress latent tuberculosis infection (LTBI) reactivation. In particular, chronic immune activation rather than the mere depletion of [CD4.sup.+] T cells correlates with reactivation due to SIV coinfection. Here, we administered combinatorial antiretroviral therapy (cART) 2 weeks after SIV coinfection to study whether restoration of [CD4.sup.+] T cell immunity occurred more broadly, and whether this prevented reactivation of LTBI compared to cART initiated 4 weeks after SIV. Earlier initiation of cART enhanced survival, led to better control of viral replication, and reduced immune activation in the periphery and lung vasculature, thereby reducing the rate of SIV-induced reactivation. We observed robust [CD8.sup.+] T effector memory responses and significantly reduced macrophage turnover in the lung tissue. However, skewed [CD4.sup.+] T effector memory responses persisted and new TB lesions formed after SIV coinfection. Thus, reactivation of LTBI is governed by very early events of SIV infection. Timing of cART is critical in mitigating chronic immune activation. The potential novelty of these findings mainly relates to the development of a robust animal model of human M. tuberculosis/HIV coinfection that allows the testing of underlying mechanisms., Introduction The tuberculosis and HIV copandemic continues to pose a major healthcare burden in resource-limited countries (1). HIV coinfection predisposes the host to reactivation of latent tuberculosis infection (LTBI), resulting [...]

BACKGROUND. The identification and treatment of individuals with tuberculosis (TB) is a global public health priority. Accurate diagnosis of pulmonary active TB (ATB) disease remains challenging and relies on extensive medical evaluation and detection of Mycobacterium tuberculosis (Mtb) in the patient's sputum. Further, the response to treatment is monitored by sputum culture conversion, which takes several weeks for results. Here, we sought to identify blood-based host biomarkers associated with ATB and hypothesized that immune activation markers on Mtb-specific [CD4.sup.+] T cells would be associated with Mtb load in vivo and could thus provide a gauge of Mtb infection. METHODS. Using polychromatic flow cytometry, we evaluated the expression of immune activation markers on Mtb-specific [CD4.sup.+] T cells from individuals with asymptomatic latent Mtb infection (LTBI) and ATB as well as from ATB patients undergoing anti-TB treatment. RESULTS. Frequencies of Mtb-specific IFN-[[gamma].sup.+][CD4.sup.+] T cells that expressed immune activation markers CD38 and HLA-DR as well as intracellular proliferation marker Ki-67 were substantially higher in subjects with ATB compared with those with LTBI. These markers accurately classified ATB and LTBI status, with cutoff values of 18%, 60%, and 5% for [CD38.sup.+]IFN-[[gamma].sup.+], [HLA-DR.sup.+]IFN-[[gamma].sup.+], and [Ki-67.sup.+]IFN-[[gamma].sup.+], respectively, with 100% specificity and greater than 96% sensitivity. These markers also distinguished individuals with untreated ATB from those who had successfully completed anti-TB treatment and correlated with decreasing mycobacterial loads during treatment. CONCLUSION. We have identified host blood-based biomarkers on Mtb-specific [CD4.sup.+] T cells that discriminate between ATB and LTBI and provide a set of tools for monitoring treatment response and cure. TRIAL REGISTRATION. Registration is not required for observational studies. FUNDING. This study was funded by Emory University, the NIH, and the Yerkes National Primate Center., Introduction Diagnosis of pulmonary active tuberculosis (ATB) currently relies on evaluation of clinical symptoms, radiological assessments, and detection of Mycobacterium tuberculosis (Mtb) in patient respiratory samples, such as sputum. Microscopic [...]