Pathology of Tuberculosis: How the Pathology of Human Tuberculosis Informs and Directs Animal Models

Effect of IL-17A on the immune response to pulmonary tuberculosis induced by high- and low-virulence strains of Mycobacterium bovis

Tuberculosis (TB) is an infectious, chronic, and progressive disease occurring globally. Human TB is caused mainly by Mycobacterium tuberculosis (M. tuberculosis), while the main causative agent of bovine TB is Mycobacterium bovis (M. bovis). The latter is one of the most important cattle pathogens and is considered the main cause of zoonotic TB worldwide. The mechanisms responsible for tissue damage (necrosis) during post-primary TB remain elusive. Recently, IL-17A was reported to be important for protection against M. tuberculosis infection, but it is also related to the production of an intense inflammatory response associated with necrosis. We used two M. bovis isolates with different levels of virulence and high IL-17A production to study this important cytokine's contrasting functions in a BALB/c mouse model of pulmonary TB. In the first part of the study, the gene expression kinetics and cellular sources of IL-17A were determined by real time PCR and immunohistochemistry respectively. Non-infected lungs showed low production of IL-17A, particularly by the bronchial epithelium, while lungs infected with the low-virulence 534 strain showed high IL-17A expression on Day 3 post-infection, followed by a decrease in expression in the early stage of the infection and another increase during late infection, on Day 60, when very low bacillary burdens were found. In contrast, infection with the highly virulent strain 04-303 induced a peak of IL-17A expression on Day 14 of infection, 1 week before extensive pulmonary necrosis was seen, being lymphocytes and macrophages the most important sources. In the second part of the study, the contribution of IL-17A to immune protection and pulmonary necrosis was evaluated by suppressing IL-17A via the administration of specific blocking antibodies. Infection with M. bovis strain 534 and treatment with IL-17A neutralizing antibodies did not affect mouse survival but produced a significant increase in bacillary load and a non-significant decrease in inflammatory infiltrate and granuloma area. In contrast, mice infected with the highly virulent 04-303 strain and treated with IL-17A blocking antibodies showed a significant decrease in survival, an increase in bacillary loads on Day 24 post-infection, and significantly more and earlier necrosis. Our results suggest that high expression of IL-17A is more related to protection than necrosis in a mouse model of pulmonary TB induced by M. bovis strains.

B cells in perivascular and peribronchiolar granuloma-associated lymphoid tissue and B-cell signatures identify asymptomatic Mycobacterium tuberculosis lung infection in Diversity Outbred mice

Because most humans resist Mycobacterium tuberculosis infection, there is a paucity of lung samples to study. To address this gap, we infected Diversity Outbred mice with M. tuberculosis and studied the lungs of mice in different disease states. After a low-dose aerosol infection, progressors succumbed to acute, inflammatory lung disease within 60 days, while controllers maintained asymptomatic infection for at least 60 days, and then developed chronic pulmonary tuberculosis (TB) lasting months to more than 1 year. Here, we identified features of asymptomatic M. tuberculosis infection by applying computational and statistical approaches to multimodal data sets. Cytokines and anti-M. tuberculosis cell wall antibodies discriminated progressors vs controllers with chronic pulmonary TB but could not classify mice with asymptomatic infection. However, a novel deep-learning neural network trained on lung granuloma images was able to accurately classify asymptomatically infected lungs vs acute pulmonary TB in progressors vs chronic pulmonary TB in controllers, and discrimination was based on perivascular and peribronchiolar lymphocytes. Because the discriminatory lesion was rich in lymphocytes and CD4 T cell-mediated immunity is required for resistance, we expected CD4 T-cell genes would be elevated in asymptomatic infection. However, the significantly different, highly expressed genes were from B-cell pathways (e.g., Bank1, Cd19, Cd79, Fcmr, Ms4a1, Pax5, and H2-Ob), and CD20+ B cells were enriched in the perivascular and peribronchiolar regions of mice with asymptomatic M. tuberculosis infection. Together, these results indicate that genetically controlled B-cell responses are important for establishing asymptomatic M. tuberculosis lung infection.

MR1-restricted T cell clonotypes are associated with "resistance" to Mycobacterium tuberculosis infection

T cells are required for protective immunity against Mycobacterium tuberculosis. We recently described a cohort of Ugandan household contacts of tuberculosis cases who appear to "resist" M. tuberculosis infection (resisters; RSTRs) and showed that these individuals harbor IFN-γ-independent T cell responses to M. tuberculosis-specific peptide antigens. However, T cells also recognize nonprotein antigens via antigen-presenting systems that are independent of genetic background, known as donor-unrestricted T cells (DURTs). We used tetramer staining and flow cytometry to characterize the association between DURTs and "resistance" to M. tuberculosis infection. Peripheral blood frequencies of most DURT subsets were comparable between RSTRs and latently infected controls (LTBIs). However, we observed a 1.65-fold increase in frequency of MR1-restricted T (MR1T) cells among RSTRs in comparison with LTBIs. Single-cell RNA sequencing of 18,251 MR1T cells sorted from 8 donors revealed 5,150 clonotypes that expressed a common transcriptional program, the majority of which were private. Sequencing of the T cell receptor α/T cell receptor δ (TCRα/δ) repertoire revealed several DURT clonotypes were expanded among RSTRs, including 2 MR1T clonotypes that recognized mycobacteria-infected cells in a TCR-dependent manner. Overall, our data reveal unexpected donor-specific diversity in the TCR repertoire of human MR1T cells as well as associations between mycobacteria-reactive MR1T clonotypes and resistance to M. tuberculosis infection.

Comparative pathology of experimental pulmonary tuberculosis in animal models

Research in human tuberculosis (TB) is limited by the availability of human tissues from patients, which is often altered by therapy and treatment. Thus, the use of animal models is a key tool in increasing our understanding of the pathogenesis, disease progression and preclinical evaluation of new therapies and vaccines. The granuloma is the hallmark lesion of pulmonary tuberculosis, regardless of the species or animal model used. Although animal models may not fully replicate all the histopathological characteristics observed in natural, human TB disease, each one brings its own attributes which enable researchers to answer specific questions regarding TB immunopathogenesis. This review delves into the pulmonary pathology induced by Mycobacterium tuberculosis complex (MTBC) bacteria in different animal models (non-human primates, rodents, guinea pigs, rabbits, cattle, goats, and others) and compares how they relate to the pulmonary disease described in humans. Although the described models have demonstrated some histopathological features in common with human pulmonary TB, these data should be considered carefully in the context of this disease. Further research is necessary to establish the most appropriate model for the study of TB, and to carry out a standard characterisation and score of pulmonary lesions.

Spatial mapping reveals granuloma diversity and histopathological superstructure in human tuberculosis

The hallmark of tuberculosis (TB) is the formation of immune cell-enriched aggregates called granulomas. While granulomas are pathologically diverse, their tissue-wide heterogeneity has not been spatially resolved at the single-cell level in human tissues. By spatially mapping individual immune cells in every lesion across entire tissue sections, we report that in addition to necrotizing granulomas, the human TB lung contains abundant non-necrotizing leukocyte aggregates surrounding areas of necrotizing tissue. These cellular lesions were more diverse in composition than necrotizing lesions and could be stratified into four general classes based on cellular composition and spatial distribution of B cells and macrophages. The cellular composition of non-necrotizing structures also correlates with their proximity to necrotizing lesions, indicating these are foci of distinct immune reactions adjacent to necrotizing granulomas. Together, we show that during TB, diseased lung tissue develops a histopathological superstructure comprising at least four different types of non-necrotizing cellular aggregates organized as satellites of necrotizing granulomas.

The Role of Contrast-Enhanced Ultrasound in the Differential Diagnosis of Tuberous Vas Deferens Tuberculosis and Metastatic Inguinal Lymph Nodes

PURPOSE

To retrospective analysis and summary the features of tuberous vas deferens tuberculosis (VD TB) and inguinal metastatic lymph nodes (MLN) in routine ultrasound (US) and contrast-enhanced US (CEUS) as well as to assess the utility of CEUS in differentiating between the two diseases.

METHODS

The US and CEUS findings of patients with pathologically confirmed tuberous VD TB (n = 17) and inguinal MLN (n = 28), including the number of lesions, presence of bilateral disease, differences in internal echogenicity, a conglomeration of lesions, and blood flow within the lesions, were retrospectively analyzed.

RESULTS

Routine US showed no significant difference in the number of lesions, nodule size, internal echogenicity, sinus tract, or skin rupture; however, significant differences were observed between the two conditions in the conglomeration of lesions (χ² = 6.455; p = 0.023) and the degree, intensity, and echogenicity pattern on CEUS (χ² = 18.865, 17.455, and 15.074, respectively; p = 0.000 for all).

CONCLUSIONS

CEUS can show the blood supply of the lesion, and judge the physical condition of the lesion better than US. Homogeneous, centripetal, and diffuse enhancement should prompt a diagnosis of inguinal MLN, whereas lesions with heterogeneous and diffuse enhancement on CEUS should be considered as VD TB. CEUS has great diagnostic value in differentiating between tuberous VD TB and inguinal MLN.

Dual oxidase 1 is dispensable during Mycobacterium tuberculosis infection in mice

Introduction

Mycobacterium tuberculosis (Mtb) is the primary cause of human tuberculosis (TB) and is currently the second most common cause of death due to a singleinfectious agent. The first line of defense against airborne pathogens, including Mtb, is the respiratory epithelium. One of the innate defenses used by respiratory epithelial cells to prevent microbial infection is an oxidative antimicrobial system consisting of the proteins, lactoperoxidase (LPO) and Dual oxidase 1 (Duox1), the thiocyanate anion (SCN-) and hydrogen peroxide (H2O2), which together lead to the generation of antimicrobial hypothiocyanite (OSCN-) in the airway lumen. OSCN- kills bacteria and viruses in vitro, but the role of this Duox1-based system in bacterial infections in vivo remains largely unknown. The goal of this study was to assess whether Duox1 contributes to the immune response against the unique respiratory pathogen, Mtb.

Methods

Duox1-deficient (Duox1 KO) and wild-type (WT) mice were infected with Mtb aerosols and bacterial titers, lung pathology, cytokines and immune cell recruitment were assessed.

Results and discussion

Mtb titers in the lung, spleen and liver were not different 30 days after infection between WT and Duox1 KO mice. Duox1 did not affect lung histology assessed at days 0, 30, and 90 post-Mtb infection. Mtb-infected Duox1 KO animals exhibited enhanced production of certain cytokines and chemokines in the airway; however, this response was not associated with significantly higher numbers of macrophages or neutrophils in the lung. B cell numbers were lower, while apoptosis was higher in the pulmonary lesions of Mtb-infected Duox1 KO mice compared to infected WT animals. Taken together, these data demonstrate that while Duox1 might influence leukocyte recruitment to inflammatory cell aggregates, Duox1 is dispensable for the overall clinical course of Mtb lung infection in a mouse model.

Difference between the blood samples of patients with bone and joint tuberculosis and patients with tuberculosis studied using machine learning

Background

Tuberculosis (TB) is a chronic infectious disease. Bone and joint TB is a common type of extrapulmonary TB and often occurs secondary to TB infection. In this study, we aimed to find the difference in the blood examination results of patients with bone and joint TB and patients with TB by using machine learning (ML) and establish a diagnostic model to help clinicians better diagnose the disease and allow patients to receive timely treatment.

Methods

A total of 1,667 patients were finally enrolled in the study. Patients were randomly assigned to the training and validation cohorts. The training cohort included 1,268 patients: 158 patients with bone and joint TB and 1,110 patients with TB. The validation cohort included 399 patients: 48 patients with bone and joint TB and 351 patients with TB. We used three ML methods, namely logistic regression, LASSO regression, and random forest, to screen the differential variables, obtained the most representative variables by intersection to construct the prediction model, and verified the performance of the proposed prediction model in the validation group.

Results

The results revealed a great difference in the blood examination results of patients with bone and joint TB and those with TB. Infectious markers such as hs-CRP, ESR, WBC, and NEUT were increased in patients with bone and joint TB. Patients with bone and joint TB were found to have higher liver function burden and poorer nutritional status. The factors screened using ML were PDW, LYM, AST/ALT, BUN, and Na, and the nomogram diagnostic model was constructed using these five factors. In the training cohort, the area under the curve (AUC) value of the model was 0.71182, and the C value was 0.712. In the validation cohort, the AUC value of the model was 0.6435779, and the C value was 0.644.

Conclusion

We used ML methods to screen out the blood-specific factors-PDW, LYM, AST/ALT, BUN, and Na⁺-of bone and joint TB and constructed a diagnostic model to help clinicians better diagnose the disease in the future.

Essential oil of Gallesia integrifolia is active against mycobacteria

Background: There is critical need for new therapeutic options for treatment of diseases caused by mycobacteria. Materials & methods: Gallesia integrifolia essential oils (EOs) and crude extracts (CEs) were tested for their anti-Mycobacterium tuberculosis and anti-nontuberculous mycobacteria activity. Results: Minimum inhibitory concentration (MIC) of EOs ranged from 15.63 to 62.5 μg/ml against M. tuberculosis and 62.5 to >250 μg/ml against nontuberculous mycobacteria. CEs showed low activity. All EO tested demonstrated synergism with antituberculosis drugs. The cytotoxicity of EOs and CEs, in different cell lines, showed selectivity index from 2.2 to 9.8 and >0.056 to 2.0, respectively. Conclusion: G. integrifolia EOs are a candidate for the development of new therapeutic options in the treatment of tuberculosis and other mycobacterial diseases.

Coexpression Network Analysis-Based Identification of Critical Genes Differentiating between Latent and Active Tuberculosis

Methods

Three Gene Expression Omnibus (GEO) microarray datasets (GSE19491, GSE98461, and GSE152532) were downloaded, with GSE19491 and GSE98461 then being merged to form a training dataset. Hub genes capable of differentiating between ATB and LTBI were then identified through differential expression analyses and a WGCNA analysis of this training dataset. Receiver operating characteristic (ROC) curves were then used to gauge to the diagnostic accuracy of these hub genes in the test dataset (GSE152532). Gene expression-based immune cell infiltration and the relationship between such infiltration and hub gene expression were further assessed via a single-sample gene set enrichment analysis (ssGSEA).

Results

In total, 485 differentially expressed genes were analyzed, with the WGCNA approach yielding 8 coexpression models. Of these, the black module was the most closely correlated with ATB. In total, five hub genes (FBXO6, ATF3, GBP1, GBP4, and GBP5) were identified as potential biomarkers associated with LTBI progression to ATB based on a combination of differential expression and LASSO analyses. The area under the ROC curve values for these five genes ranged from 0.8 to 0.9 in the test dataset, and ssGSEA revealed the expression of these genes to be negatively correlated with lymphocyte activity but positively correlated with myeloid and inflammatory cell activity.

Conclusion

The five hub genes identified in this study may play a novel role in tuberculosis-related immunopathology and offer value as novel biomarkers differentiating LTBI from ATB.

Immunologic and imaging signatures in post tuberculosis lung disease

Post Tuberculosis Lung Disease (PTLD) affects millions of tuberculosis survivors and is a global health burden. The immune mechanisms that drive PTLD are complex and have historically been under investigated. Here, we discuss two immune-mediated paradigms that could drive human PTLD. We review the characteristics of a fibrotic granuloma that favors the development of PTLD via an abundance of T-helper-2 and T-regulatory cells and an upregulation of TGF-β mediated collagen deposition. Next, we discuss the post-primary tuberculosis paradigm and the complex mixture of caseous pneumonia, cavity formation and fibrosis that can also lead to PTLD. We review the delicate balance between cellular subsets and cytokines of the innate and adaptive immune system in conjunction with host-derived proteases that can perpetuate the parenchymal lung damage seen in PTLD. Next, we discuss the role of novel host directed therapies (HDT) to limit the development of PTLD and in particular, the recent repurposing of established medications such as statins, metformin and doxycycline. Finally, we review the emerging role of novel imaging techniques as a non-invasive modality for the early recognition of PTLD. While access to computed tomography imaging is unlikely to be available widely in countries with a high TB burden, its use in research settings can help phenotype PTLD. Due to a lack of disease-specific biomarkers and controlled clinical trials, there are currently no evidence-based recommendations for the management of PTLD. It is likely that an integrated antifibrotic strategy that could simultaneously target inflammatory and pro-fibrotic pathways will probably emerge as a successful way to treat this complex condition. In a disease spectrum as wide as PTLD, a single immunologic or radiographic marker may not be sufficient and a combination is more likely to be a successful surrogate that could aid in the development of successful HDTs.

Mycobacterium tuberculosis Rv0309 Dampens the Inflammatory Response and Enhances Mycobacterial Survival

To reveal functions of novel Mycobacterium tuberculosis (M. tb) proteins responsible for modulating host innate immunity is essential to elucidation of mycobacterial pathogenesis. In this study, we aimed to identify the role of a putative protein Rv0309 encoded within RD8 of M. tb genome in inhibiting the host inflammatory response and the underlying mechanism, using in-vitro and in-vivo experiments. A recombinant M. smegmatis strain Ms_rv0309 expressing Rv0309 and a mutant Bacillus Calmette-Guérin (BCG)ΔRS01790 strain with deletion of BCG_RS01790, 100% homologue of Rv0309 in BCG, were constructed. Rv0309 was found to localize in the cell wall and be able to decrease cell wall permeability. Purified recombinant rRv0309 protein inhibited lipopolysaccharide-induced IL-6 release in RAW264.7 cells. BCG_RS01790 in BCG or Rv0309 in Ms_rv0309 strain greatly inhibited production of IL-6, IL-1β, and TNF-α in RAW264.7 cells. Similarly, BCGΔRS01790 strongly induced expression of these cytokines compared with wild-type BCG and complement strain, cBCGΔRS01790::RS01790. Further BCG_RS01790 or Rv0309 suppressed cytokine production through NF-κB p65/IκBα and MAPK ERK/JNK signaling. Importantly, BCG_RS01790 in BCG and Rv0309 in Ms_rv0309 strain enhanced mycobacterial survival in macrophages. Mice infected with BCGΔRS01790 exhibited high levels of IFN-γ, TNF-α and IL-1β, and large numbers of neutrophils and lymphocytes in the early stage, and minimal lung bacterial load and inflammatory damage in late stage of the experiment. In conclusion, the cell wall protein Rv0309 or BCG_RS01790 enhanced mycobacterial intracellular survival after infection likely through inhibition of the pro-inflammatory response and decrease of bacterial cell wall permeability, thereby contributing to mycobacterial pathogenesis.

Tuberculosis vaccines in the era of Covid-19 - what is taking us so long?

The Mycobacterium bovis BCG vaccine was first used in 1921, but has not controlled the global spread of tuberculosis (TB). There are still no new licensed tuberculosis vaccines, although there much active research and a vaccine development pipeline, with vaccines designed to prevent infection, prevent disease, or accelerate TB treatment. These vaccines are of different types, and designed to replace BCG, or to boost immunity following BCG vaccination. This viewpoint discusses why, when it has been possible to develop new vaccines for SARS-CoV-2 so quickly, it is taking so long to develop new tuberculosis vaccines.

Do Anti-tuberculosis Drugs Reach Their Target?─High-Resolution Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging Provides Information on Drug Penetration into Necrotic Granulomas

Tuberculosis (TB) is characterized by mycobacteria-harboring centrally necrotizing granulomas. The efficacy of anti-TB drugs depends on their ability to reach the bacteria in the center of these lesions. Therefore, we developed a mass spectrometry (MS) imaging workflow to evaluate drug penetration in tissue. We employed a specific mouse model that─in contrast to regular inbred mice─strongly resembles human TB pathology. Mycobacterium tuberculosis was inactivated in lung sections of these mice by γ-irradiation using a protocol that was optimized to be compatible with high spatial resolution MS imaging. Different distributions in necrotic granulomas could be observed for the anti-TB drugs clofazimine, pyrazinamide, and rifampicin at a pixel size of 30 μm. Clofazimine, imaged here for the first time in necrotic granulomas of mice, showed higher intensities in the surrounding tissue than in necrotic granulomas, confirming data observed in TB patients. Using high spatial resolution drug and lipid imaging (5 μm pixel size) in combination with a newly developed data analysis tool, we found that clofazimine does penetrate to some extent into necrotic granulomas and accumulates in the macrophages inside the granulomas. These results demonstrate that our imaging platform improves the predictive power of preclinical animal models. Our workflow is currently being applied in preclinical studies for novel anti-TB drugs within the German Center for Infection Research (DZIF). It can also be extended to other applications in drug development and beyond. In particular, our data analysis approach can be used to investigate diffusion processes by MS imaging in general.

The Bovine Tuberculoid Granuloma

The bovine tuberculoid granuloma is the hallmark lesion of bovine tuberculosis (bTB) due to Mycobacterium bovis infection. The pathogenesis of bTB, and thereby the process of bovine tuberculoid granuloma development, involves the recruitment, activation, and maintenance of cells under the influence of antigen, cytokines and chemokines in affected lungs and regional lymph nodes. The granuloma is key to successful control of bTB by preventing pathogen dissemination through containment by cellular and fibrotic layers. Paradoxically, however, it may also provide a niche for bacterial replication. The morphologic and cellular characteristics of granulomas have been used to gauge disease severity in bTB pathogenesis and vaccine efficacy studies. As such, it is critical to understand the complex mechanisms behind granuloma initiation, development, and maintenance.

Early Lesion of Post-Primary Tuberculosis: Subclinical Driver of Disease and Target for Vaccines and Host-Directed Therapies

The characteristic lesion of primary tuberculosis is the granuloma as is widely studied in human tissues and animal models. Post-primary tuberculosis is different. It develops only in human lungs and begins as a prolonged subclinical obstructive lobular pneumonia that slowly accumulates mycobacterial antigens and host lipids in alveolar macrophages with nearby highly sensitized T cells. After several months, the lesions undergo necrosis to produce a mass of caseous pneumonia large enough to fragment and be coughed out to produce a cavity or be retained as the focus of a post-primary granuloma. Bacteria grow massively on the cavity wall where they can be coughed out to infect new people. Here we extend these findings with the demonstration of secreted mycobacterial antigens, but not acid fast bacilli (AFB) of M. tuberculosis in the cytoplasm of ciliated bronchiolar epithelium and alveolar pneumocytes in association with elements of the programmed death ligand 1 (PD-L1), cyclo-oxygenase (COX)-2, and fatty acid synthase (FAS) pathways in the early lesion. This suggests that M. tuberculosis uses its secreted antigens to coordinate prolonged subclinical development of the early lesions in preparation for a necrotizing reaction sufficient to produce a cavity, post-primary granulomas, and fibrocaseous disease.

Eosinophils are part of the granulocyte response in tuberculosis and promote host resistance in mice

Host resistance to Mycobacterium tuberculosis (Mtb) infection requires the activities of multiple leukocyte subsets, yet the roles of the different innate effector cells during tuberculosis are incompletely understood. Here we uncover an unexpected association between eosinophils and Mtb infection. In humans, eosinophils are decreased in the blood but enriched in resected human tuberculosis lung lesions and autopsy granulomas. An influx of eosinophils is also evident in infected zebrafish, mice, and nonhuman primate granulomas, where they are functionally activated and degranulate. Importantly, using complementary genetic models of eosinophil deficiency, we demonstrate that in mice, eosinophils are required for optimal pulmonary bacterial control and host survival after Mtb infection. Collectively, our findings uncover an unexpected recruitment of eosinophils to the infected lung tissue and a protective role for these cells in the control of Mtb infection in mice.

Radiological and functional evidence of the bronchial spread of tuberculosis: an observational analysis

BACKGROUND

Direct bronchial spread of tuberculosis was extensively described in pre-antibiotic human pathology literature but this description has been overlooked in the post-antibiotic era, in which most pathology data come from animal models that emphasise the granuloma. Modern techniques, such as [18F]2-fluoro-2-deoxy-D-glucose (FDG) PET-CT scans, might provide further insight. Our aim was to understand normal early tuberculosis resolution patterns on pulmonary PET-CT scans in treated patients with tuberculosis who were subsequently cured.

METHODS

In this observational analysis, we analysed data from PredictTB, an ongoing, prospective, randomised clinical trial that examined sequential baseline and week 4 FDG-PET-CT scans from participants successfully treated (sputum culture negative 18 months after enrolment) for drug-susceptible pulmonary tuberculosis in South Africa and China. Participants who were aged 18-75 years, GeneXpert MTB/RIF positive for tuberculosis and negative for rifampicin resistance, had not yet started tuberculosis treatment, had not been treated for active tuberculosis within the previous 3 years, and met basic safety laboratory criteria were included and participants with diabetes, HIV infection, or with extrapulmonary tuberculosis including pleural tuberculosis were excluded. Scans were assessed by two readers for the location of tuberculosis lesions (eg, cavities and consolidations), bronchial thickening patterns, and changes from baseline to week 4 of treatment.

FINDINGS

Among the first 124 participants (enrolled from June 22, 2017, to Sept 27, 2018) who were successfully treated, 161 primarily apical cavitary lesions were identified at baseline. Bronchial thickening and inflammation linking non-cavitary consolidative lesions to cavities were observed in 121 (98%) of 124 participants' baseline PET-CT scans. After 4 weeks of treatment, 21 (17%) of 124 participants had new or expanding lesions linked to cavities via bronchial inflammation that were not present at baseline, particularly participants with two or more cavities at baseline and participants from South Africa.

INTERPRETATION

In participants with pulmonary tuberculosis who were subsequently cured, the location of cavitary and non-cavitary lesions at baseline and new lesions at week 4 of treatment suggest a cavitary origin of disease and bronchial spread through the lungs. Bronchial spread from cavities might play a larger role in the spread of pulmonary tuberculosis than has been appreciated. Elucidating cavity lesion dynamics and Mycobacterium tuberculosis viability within cavities might better explain treatment outcomes and why some patients are cured and others relapse.

FUNDING

Bill & Melinda Gates Foundation, European and Developing Countries Clinical Trials Partnership, China Ministry of Science and Technology, National Natural Science Foundation of China, and National Institutes of Health.

TRANSLATIONS

For the Chinese, Afrikaans and Xhosa translations of the abstract see Supplementary Materials section.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb's development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound's effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound's development.

Local Pulmonary Immunological Biomarkers in Tuberculosis

Regardless of the eventual site of disease, the point of entry for Mycobacterium tuberculosis (M.tb) is via the respiratory tract and tuberculosis (TB) remains primarily a disease of the lungs. Immunological biomarkers detected from the respiratory compartment may be of particular interest in understanding the complex immune response to M.tb infection and may more accurately reflect disease activity than those seen in peripheral samples. Studies in humans and a variety of animal models have shown that biomarkers detected in response to mycobacterial challenge are highly localized, with signals seen in respiratory samples that are absent from the peripheral blood. Increased understanding of the role of pulmonary specific biomarkers may prove particularly valuable in the field of TB vaccines. Here, development of vaccine candidates is hampered by the lack of defined correlates of protection (COPs). Assessing vaccine immunogenicity in humans has primarily focussed on detecting these potential markers of protection in peripheral blood. However, further understanding of the importance of local pulmonary immune responses suggests alternative approaches may be necessary. For example, non-circulating tissue resident memory T cells (T_RM) play a key role in host mycobacterial defenses and detecting their associated biomarkers can only be achieved by interrogating respiratory samples such as bronchoalveolar lavage fluid or tissue biopsies. Here, we review what is known about pulmonary specific immunological biomarkers and discuss potential applications and further research needs.

An Overview of the Development of New Vaccines for Tuberculosis

Currently, there is only one licensed vaccine against tuberculosis (TB), the Bacillus Calmette–Guérin (BCG). Despite its protective efficacy against TB in children, BCG has failed to protect adults against pulmonary TB, lacks therapeutic value, and causes complications in immunocompromised individuals. Furthermore, it compromises the use of antigens present in the purified protein derivate of Mycobacterium tuberculosis in the diagnosis of TB. Many approaches, e.g., whole-cell organisms, subunit, and recombinant vaccines are currently being explored for safer and more efficacious TB vaccines than BCG. These approaches have been successful in developing a large number of vaccine candidates included in the TB vaccine pipeline and are at different stages of clinical trials in humans. This paper discusses current vaccination strategies, provides directions for the possible routes towards the development of new TB vaccines and highlights recent findings. The efforts for improved TB vaccines may lead to new licensed vaccines capable of replacing/supplementing BCG and conferring therapeutic value in patients with active/latent TB.

Teleost contributions to the understanding of mycobacterial diseases

Few pathogens have shaped human medicine as the mycobacteria. From understanding biological phenomena driving disease spread, to mechanisms of host-pathogen interactions and antibiotic resistance, the Mycobacterium genus continues to challenge and offer insights into the basis of health and disease. Teleost fish models of mycobacterial infections have progressed significantly over the past three decades, now supplying a range of unique tools and new opportunities to define the strategies employed by these Gram-positive bacteria to overcome host defenses, as well as those host antimicrobial pathways that can be used to limit its growth and spread. Herein, we take a comparative perspective and provide an update on the contributions of teleost models to our understanding of mycobacterial diseases.

Treatment-Shortening Effect of a Novel Regimen Combining Clofazimine and High-Dose Rifapentine in Pathologically Distinct Mouse Models of Tuberculosis

Clofazimine and high-dose rifapentine have each separately been associated with treatment-shortening activity when incorporated into tuberculosis (TB) treatment regimens. We hypothesized that both modifications, i.e., the addition of clofazimine and the replacement of rifampin with high-dose rifapentine, in the first-line regimen for drug-susceptible TB would significantly shorten the duration of treatment necessary for cure. We tested this hypothesis in a well-established BALB/c mouse model of TB chemotherapy and also in a C3HeB/FeJ mouse model in which mice can develop caseous necrotic lesions, an environment where rifapentine and clofazimine may individually be less effective. In both mouse models, replacing rifampin with high-dose rifapentine and adding clofazimine in the first-line regimen resulted in greater bactericidal and sterilizing activity than either modification alone, suggesting that a rifapentine- and clofazimine-containing regimen may have the potential to significantly shorten the treatment duration for drug-susceptible TB. These data provide preclinical evidence supporting the evaluation of regimens combining high-dose rifapentine and clofazimine in clinical trials.

The pathogenesis of post-primary tuberculosis. A game changer for vaccine development

A vaccine that prevents transmission of infection is urgently needed in the fight against tuberculosis (TB). Results of clinical trials have been disappointing. Major problems include lack of biomarkers and understanding of the mechanisms of disease and protection. A more fundamental problem is that the scientific community seldom recognizes that primary and post-primary TB are distinct disease entities. Nearly all vaccine candidates have been designed and tested in models of primary TB, while transmission of infection is mediated by post-primary TB. Post-primary TB is seldom studied because no animal develop complete symptoms of the disease as it exists in humans. Nevertheless, mice, guinea pigs and rabbits all develop infections that at certain points appear to be models of human post-primary TB. Slowly progressive pulmonary TB in immunocompetent mice is an example. It is characterized by an alveolitis with infected foamy macrophages that have multiple characteristics of the human disease. We demonstrated that inclusion of an immune modulating agent, lactoferrin, with a BCG vaccine in this model induced a sustained reduction in lung pathology, but not numbers of organisms in tissue. Since the animals die of expanding pathology, this demonstrates the feasibility of using selected animal models for studies of vaccines against post-primary TB.

Humanized Mouse Model Mimicking Pathology of Human Tuberculosis for in vivo Evaluation of Drug Regimens

Human immune system mice are highly valuable for in vivo dissection of human immune responses. Although they were employed for analyzing tuberculosis (TB) disease, there is little data on the spatial organization and cellular composition of human immune cells in TB granuloma pathology in this model. We demonstrate that human immune system mice, generated by transplanted human fetal liver derived hematopoietic stem cells develop a continuum of pulmonary lesions upon Mycobacterium tuberculosis aerosol infection. In particular, caseous necrotic granulomas, which contribute to prolonged TB treatment time, developed, and had cellular phenotypic spatial-organization similar to TB patients. By comparing two recommended drug regimens, we confirmed observations made in clinical settings: Adding Moxifloxacin to a classical chemotherapy regimen had no beneficial effects on bacterial eradication. We consider this model instrumental for deeper understanding of human specific features of TB pathogenesis and of particular value for the pre-clinical drug development pipeline.

Immunological responses of European badgers (Meles Meles) to infection with Mycobacterium bovis

Mycobacterium bovis is the main cause of bovine tuberculosis and its eradication is proving difficult in many countries because of wildlife reservoirs, including European badgers (Meles meles) in the UK Ireland. Following the development of badger specific immunological reagents, many studies have shown that some aspects of the cellular and serological immune responses of badgers to virulent M. bovis and the attenuated M. bovis BCG (Bacille of Calmette and Guérin) strain are similar to those seen in other animal hosts infected with M. bovis. However, badgers also appear to have developed specific immunological responses to M. bovis infection which may be associated with mild inflammatory responses. Badgers may therefore represent an interesting natural host for M. bovis that can provide a more thorough understanding of efficient immunological responses to tuberculosis.

The Pathogenesis of Tuberculosis: The Early Infiltrate of Post-primary (Adult Pulmonary) Tuberculosis: A Distinct Disease Entity

It has long been recognized that tuberculosis (TB) induces both protective and tissue damaging immune responses. This paper reviews nearly two centuries of evidence that protection and tissue damage are mediated by separate disease entities in humans. Primary TB mediates protective immunity to disseminated infection while post-primary TB causes tissue damage that results in formation of cavities. Both are necessary for continued survival of Mycobacterium tuberculosis (MTB). Primary TB has been extensively studied in humans and animals. Post-primary TB, in contrast, is seldom recognized or studied. It begins as an asymptomatic early infiltrate that may resolve or progress by bronchogenic spread to caseous pneumonia that either fragments to produce cavities or is retained to produce post-primary granulomas and fibrocaseous disease. Primary and post-primary TB differ in typical age of onset, histopathology, organ distribution, x-ray appearance, genetic predisposition, immune status of the host, clinical course and susceptibility to protection by BCG. MTB is a highly successful human parasite because it produces both primary and post-primary TB as distinct disease entities in humans. No animal reproduces this sequence of lesions. Recognition of these facts immediately suggests plausible solutions, animal models and testable hypotheses to otherwise inaccessible questions of the immunity and pathogenesis of TB.