Mechanisms of anergy in tuberculosis

Whole blood RNA signatures in tuberculosis patients receiving H56:IC31 vaccine as adjunctive therapy

Introduction

Therapeutic vaccination in tuberculosis (TB) represents a Host Directed Therapy strategy which enhances immune responses in order to improve clinical outcomes and shorten TB treatment. Previously, we have shown that the subunit H56:IC31 vaccine induced both humoral and cellular immune responses when administered to TB patients adjunctive to standard TB treatment (TBCOX2 study, NCT02503839). Here we present the longitudinal whole blood gene expression patterns in H56:IC31 vaccinated TB patients compared to controls receiving standard TB treatment only.

Methods

The H56:IC31 group (N=11) and Control group (N=7) underwent first-line TB treatment for 182 days. The H56:IC31 group received 5 micrograms of the H56:IC31 vaccine (Statens Serum Institut; SSI, Valneva Austria GmbH) intramuscularly at day 84 and day 140. Total RNA was extracted from whole blood samples collected in PAXgene tubes on days 0, 84, 98, 140, 154, 182 and 238. The expression level of 183 immune-related genes was measured by high-throughput microfluidic qPCR (Biomark HD system, Standard BioTools).

Results

The targeted gene expression profiling unveiled the upregulation of modules such as interferon (IFN) signalling genes, pattern recognition receptors and small nucleotide guanosine triphosphate (GTP)-ases in the vaccinated group compared to controls two weeks after administration of the first H56:IC31 vaccine. Additionally, the longitudinal analysis of the Adolescent Cohort Study-Correlation of Risk (ACS-COR) signature showed a progressive downregulation in both study arms towards the end of TB treatment, in congruence with reported treatment responses and clinical improvements. Still, two months after the end of TB treatment, vaccinated patients, and especially those developing both cellular and humoral vaccine responses, showed a lower expression of the ACS-COR genes compared to controls.

Discussion

Our data report gene expression patterns following H56:IC31 vaccination which might be interpreted as a lower risk of relapse in therapeutically vaccinated patients. Further studies are needed to conclude if these gene expression patterns could be used as prognostic biosignatures for therapeutic TB vaccine responses.

Adaptive immunity in different CT patterns of active tuberculosis and possible variability according to patients' geographic provenience

Background

It is still unclear if low lymphocyte levels are directly related to immunological modifications induced by the TB infection or if they depend on the general pre-existing health impairment of affected patients. Our aim was to detect eventual differences in the immunological status of patients with pulmonary TB compared to an age and sex-matched group of hospitalized patients with other bacterial community-acquired pneumonia (CAP). In addition, we tried to assess an association between alterations in the peripheral lymphocyte subsets and the development of different CT patterns of active TB and to discover differences in the immunological status and in the radiological patterns of TB presentation between patients of different geographic proveniences.

Methods

This observational study included 48 patients with TB and 48 sex- and age-matched patients affected by other bacterial CAP. The presence of HIV/AIDS, other immunocompromising conditions, and confounding chronic pulmonary comorbidities was excluded. Flow cytometry was performed on all the enrolled subjects at admission, before starting the appropriate antibiotic therapy. Patients with TB also underwent a computed tomography (CT) scan.

Results

Patients with TB showed a decrease in the absolute count of all the lymphocyte subsets compared to the CAP group. Only the reduction in the percentage of CD4+ T-lymphocytes was significant, while the percentage of CD8+ T-lymphocytes was significantly increased. Patients presenting exudative forms with atypical locations of TB showed a significant reduction in the absolute count and percentage of CD19+ B-lymphocytes compared to those affected by productive TB forms with the typical location. Despite being younger, our black Sub-Saharan Africans showed a significant reduction in the CD4+ T-lymphocytes compartment and a higher prevalence of atypical and exudative forms of TB compared with white Europeans.

Conclusion

Tuberculosis itself may alter peripheral blood lymphocyte subsets compared to other CAP. An impaired CD19+ B-lymphocyte compartment may result in an abnormal exudative response in atypical locations and a suboptimal bacterial control. Other constitutive or environmental causes may influence immunological differences found in patients with TB, particularly in case of different geographic origins. Anyhow, flow cytometry may be of great value in evaluating the immune function of these patients.

Adult pulmonary tuberculosis as a pathological manifestation of hyperactive antimycobacterial immune response

The intricate relationship between tuberculosis (TB) and immune system remains poorly understood. It is generally believed that weakening of the immune response against Mycobacterium tuberculosis leads to reactivation of latent infection into the active pulmonary disease. However, heterogeneous nature of TB and failure of rationally designed vaccines in clinical trials raises serious questions against the simplistic view of TB as an outcome of weakened immunity. In the wake of accumulating human TB data, it is argued here that a hyperactive antimycobacterial immune response is to blame for the pathogenesis of pulmonary TB in immunocompetent adults. Direct and indirect evidence supporting this notion is presented in this article. Revisiting the role of immune system in TB pathogenesis will pave the way for effective anti-TB vaccines.

Mycobacterium tuberculosis evades host immunity by recruiting mesenchymal stem cells

Tuberculosis (TB) is the cause of 2 million deaths each year, which is the second highest cause of mortality from a single infectious disease worldwide. Resistance of these organisms to drugs has emerged as an important health concern. Alternative approaches to the prevention and treatment of tuberculosis are therefore urgently needed. Despite the generation of robust host immune responses, Mycobacterium tuberculosis (M. tb) successfully evades host immunity and establishes a persistent infection. The mechanism(s) by which M. tuberculosis manages to persist in the face of potent host immune responses remain(s) incompletely understood. Here, we demonstrate that M. tb suppresses T-lymphocyte responses by recruiting mesenchymal stem cells (MSCs) to the site of infection. We found that MSCs infiltrated tissues in mice containing M. tb organisms and T lymphocytes. We further demonstrate that MSCs suppressed T-cell responses by producing nitric oxide. Our findings reveal a key role of MSCs in the capacity of M. tb to evade host immune responses and identify these cells as unique targets for therapeutic intervention in tuberculosis.

Transmission of Mycobacterium tuberculosis undetected by tuberculin skin testing

RATIONALE

The development of tuberculin skin test (TST) positivity following infection by Mycobacterium tuberculosis is not invariable and may depend on bacillary as well as host factors.

OBJECTIVES

First, to compare the diagnostic performance of the TST and a form of in vitro IFN-gamma release assay (IFNGRA) in the circumstances of a contact investigation prompted by an unusually severe index case of infectious pulmonary tuberculosis. Second, to investigate the ability of the strain of M. tuberculosis responsible to induce cytokine secretion from monocytes in vitro.

METHODS

A routine TST-based tuberculosis-contact screening procedure supplemented by the use of an "in house" IFNGRA that assays the T-cell response to the M. tuberculosis-specific antigens ESAT-6, CFP-10 (presented as a fusion protein within the inactivated adenylate cyclase of Bordetella pertussis), and purified protein derivative of M. tuberculosis. Isolation and genetic typing of the strain of M. tuberculosis responsible, and investigation of its ability to induce cytokine secretion from monocytes in vitro.

MEASUREMENTS AND MAIN RESULTS

TST screening suggested a low rate of transmission with just 2/75 unequivocally positive responses. By contrast, the IFNGRA suggested an infection rate of 16/75 (22%). When compared with two reference strains of M. tuberculosis (H37Rv and CDC1551), the outbreak strain induced lower levels of tumor necrosis factor-alpha and interleukin-12p40 (p < 0.04), cytokines associated with the development of delayed-type hypersensitivity.

CONCLUSIONS

These data suggest that infection by M. tuberculosis can be undetected by TST, and that this may partially relate to strain differences in immunogenicity.

Immune regulation of gammadelta T cell responses in mycobacterial infections

Antigen-specific gammadelta T cells may play a role in anti-mycobacterial immunity. Studies done in humans and animal models have demonstrated complex patterns of gammadelta T cell immune responses during early mycobacterial infections and chronic tuberculosis. Recent studies have also shown a clinical correlation between major recall expansion of antigen-specific gammadelta T cells and immunity against fatal early mycobacterial diseases. Multiple host and microbial factors can regulate diverse immune responses of phosphoantigen-specific gammadelta T cells during mycobacterial infections.

Interleukin-2 and loss of immunity in experimental Mycobacterium avium infection

Experimental infection of mice with a virulent strain of Mycobacterium avium leads to a slowly progressive disease, which we have previously shown culminates in loss of gamma interferon (IFN-gamma) production by T lymphocytes and death of the animals approximately 40 weeks after infection. Here we investigated the changes in T-cell activation, the production of interleukin-2 (IL-2), and the response to IL-2 throughout M. avium infection as a possible explanation for this loss. We found that there is a steady increase in the percentage of T cells expressing activation markers right to the end of infection. However, in vivo T-cell proliferation, measured as a percentage of CD4(+) and CD8(+) cells incorporating 5-bromo-2'-deoxyuridine, initially increased but then remained constant. In the final stages of infection there was a decline in proliferation of activated (CD62L(-)) T cells. Since IL-2 is a major driver of T-cell proliferation, we asked whether this was due to loss of IL-2 responsiveness or production. However, CD25 (IL-2Ralpha) continued to be highly expressed in the terminal stages of infection, and although IL-2 production declined, addition of recombinant IL-2 to cultures could not rescue the final loss of IFN-gamma production.

Il-4 influences apoptosis of mycobacterium-reactive lymphocytes in the presence of TNF-alpha

T cell apoptosis is associated with defective cell-mediated effector functions in several infectious diseases. In tuberculosis, there is evidence that T cell apoptosis may be cytokine mediated, but the mechanisms are not clearly understood. Type 2 cytokines have recently been associated with disease extent in human tuberculosis, but they have not previously been linked to apoptosis in mycobacterium-reactive T cells. This study presents evidence that PBLs from healthy donors respond to sonicated Mycobacterium tuberculosis Ags with increased IL-4 gene activation, CD30 expression, and apoptosis. The changes were significantly greater than those observed when cells were stimulated with Ags from nonpathogenic Mycobacterium vaccae. A hypothesis linking these observations was tested. CD30 expression and TNF-alpha-mediated lymphocyte apoptosis were both down-regulated by inhibiting IL-4 in this model. TNFR-associated factor 2 (TRAF2) expression was down-regulated in CD30(+) cells, and addition of anti-TNF-alpha Ab significantly reduced apoptosis in the CD30(+) but not the CD30(-) population. These observations support the hypothesis that increased IL-4 expression in M. tuberculosis-activated lymphocytes promotes CD30 expression, which sensitizes the lymphocytes to TNF-alpha-mediated apoptosis via TRAF2 depletion. This may be one mechanism by which IL-4 is associated with immunopathological consequences in human tuberculosis.

Combinatorial use of antibodies to secreted mycobacterial proteins in a host immune system-independent test for tuberculosis

Laboratory diagnosis of tuberculosis is often difficult. Immunodetection of circulating Mycobacterium tuberculosis proteins shed during active infection would not depend on an intact host immune response and could take advantage of the speed and low costs afforded by antibody-based assays. We previously showed that patients with active tuberculosis had increased levels of circulating antigen 85 (Ag85) proteins independent of their tuberculin skin test status (S. I. Bentley-Hibbert, X. Quan, T. Newman, K. Huygen, and H. P. Godfrey, Infect. Immun. 67:581-588, 1999). To extend these observations to a Mycobacterium bovis BCG-vaccinated population and to another secreted mycobacterial protein, Ag85 and PstS-1 (protein antigen B, p38 antigen) were quantified in sera from 97 Chilean tuberculosis patients and healthy controls (many of whom had received BCG as children) using dot immunobinding, mouse monoclonal anti-BCG Ag85 complex antibody, and chicken antipeptide antibodies reactive with M. tuberculosis Ag85B and PstS-1. The latter antibodies had been raised to peptide-derived immunogens expressed on a novel proprietary protein carrier in Escherichia coli. Median serum Ag85 levels measured by using either anti-Ag85 antibody were significantly higher in patients with active tuberculosis than in healthy controls (P, <0.001 to 0.01); the median serum PstS-1 levels were similar in patients and controls. The sensitivity of significantly elevated circulating Ag85 levels in patients with pulmonary tuberculosis measured by anti-Ag85 complex or anti-Ag85B antibodies was 60 and 55%, respectively, but increased to 77% when results obtained with both anti-Ag85 antibodies were considered jointly (P < 0.02). The corresponding specificities for individual and joint consideration were 95, 85, and 80%, respectively. These results indicate that elevated Ag85 levels can be detected in patients with active tuberculosis even after BCG vaccination and suggest that combinatorial use of antibodies directed at different epitopes of this protein could provide a viable strategy for developing new host immune response-independent diagnostic tests for tuberculosis.

Increased numbers of ESAT-6- and purified protein derivative-specific gamma interferon-producing cells in subclinical and active tuberculosis infection

Numbers of gamma interferon (IFN-gamma)-producing cells reactive to ESAT-6 antigen were increased in recent converters to purified protein derivative positivity and in tuberculosis patients but not in unvaccinated or Mycobacterium bovis BCG-vaccinated healthy donors. ESAT-6-reactive IFN-gamma-producing cells in recent converters and tuberculosis patients recognized similar synthetic peptides. Thus, ESAT-6 is a potential candidate for use in detection of early, as well as active, tuberculosis and for control of the disease.

Th1/Th2 balance in infection

Cytokines produced by T helper (Th) cells are of critical importance for the outcome of many infectious diseases. Producing the "right" set of cytokines in response to an infectious agent can be a matter of life or death. The Th1/Th2 dichotomy, although an oversimplification has proven useful in the analysis of immune responses to infections. In some infectious diseases, most notably leishmaniasis or infections with gastrointestinal helminths, one Th subset is indispensable for clearing the infection, whereas the opposite Th subset is detrimental. More frequently, both Th1 and Th2 responses are required at different time points to effectively eradicate an infectious agent. The granuloma responses to either Mycobacterium tuberculosis or Schistosoma mansoni provide illustrative examples and are discussed in this review. There is accumulating evidence for frequent coexpression of Th1 and Th2 cytokines during the in vivo immune response to infections. The mechanisms by which infectious agents modulate Th1/Th2 phenotype development are summarized here. Finally, we review here the current evidence for cytokine imbalances induced by infections as pathogenic or protective factors in autoimmunity and allergy.

T-Cell hyporesponsiveness induced by activated macrophages through nitric oxide production in mice infected with Mycobacterium tuberculosis

In active tuberculosis, T-cell response to Mycobacterium tuberculosis is known to be reduced. In the course of Mycobacterium tuberculosis infection in mice, we observed that T-cell proliferation in response to M. tuberculosis purified protein derivative (PPD) reached the maximum level on day 7, then declined to the minimal level on day 14, and persisted at a low level through day 28 postinfection. The frequency of PPD-specific CD4 T cells in the spleen on day 28 decreased to one-sixth on day 7. To further investigate the mechanism of this T-cell hyporesponsiveness, we next analyzed the suppressive activity of spleen macrophages on T-cell function. The nonspecific proliferative response of naive T cells and the PPD-specific proliferative response of T cells were suppressed by day 28 macrophages, but not by day 7 macrophages or naive macrophages. This reduction of proliferative response was restored by addition of nitric oxide synthesis inhibitor, NG-monoethyl-L-arginine monoacetate, but not by monoclonal antibody against interleukin 10 or transforming growth factor beta. These data indicate that the macrophages from mice chronically infected with M. tuberculosis suppress T-cell response through production of nitric oxide, suggesting that nitric oxide-induced elimination mediated by activated macrophages may reduce the T-cell response and the number of mycobacterium-specific CD4 T cells in vivo.

Mycobacterium bovis Bacille Calmette-Guérin Enhances Pathogenicity of Simian Immunodeficiency Virus Infection and Accelerates Progression to AIDS in Macaques: A Role of Persistent T cell Activation in AIDS Pathogenesis

It has recently been proposed that Mycobacterium tuberculosis may enhance the pathogenicity of HIV infections and accelerate the course of HIV disease. This hypothesis has been tested in the present study using a simian immunodeficiency virus of macaques (SIVmac)/Mycobacterium bovis bacille Calmette-Guérin (BCG)-coinfected macaque model. Naive and chronically SIVmac-infected monkeys were evaluated. Following BCG inoculation, the SIVmac-infected monkeys exhibited the dominant responses of TCR-β complementarity-determining region 3-restricted T cell subpopulations. This BCG-driven T cell activation correlated with a marked increase in viral loads in SIVmac-infected monkeys. Moreover, the prolonged T cell activation coincided with the enhanced decline of CD4+ PBL counts and the accelerated progression to clinical AIDS in the coinfected monkeys, suggesting that Mycobacterium-driven T cell activation may be the mechanism underlying the enhanced pathogenicity of AIDS virus infection in the coinfected individuals. Within 2 to 7 mo after BCG coinfection, all chronically SIVmac-infected monkeys died from SIV-induced AIDS including tuberculosis-like disease. Surprisingly, the naive monkeys manifested a T cell activation-related toxic shock syndrome and a profound depletion of CD4+ lymphocytes 2 wk after simultaneous SIVmac/BCG inoculation. These naive animals died 2 mo after SIVmac/BCG inoculation, with the evidence of the persistent SIV p27 antigenemia and SIVmac-induced disease. In contrast, the normal monkeys not infected with SIVmac survived BCG infection; the control SIVmac-infected animals showed a natural course of chronic SIV infection. Thus, results from this SIV/BCG coinfection model strongly support the hypothesis that active coinfection with HIV and Mycobacterium can impact remarkably on the AIDS virus-induced disease.