Antigen-specific CD8(+) T cells and protective immunity to tuberculosis

One Health Approach to the Computational Design of a Lipoprotein-Based Multi-Epitope Vaccine Against Human and Livestock Tuberculosis

Tuberculosis (TB) remains a major cause of ill health and one of the leading causes of death worldwide, with about 1.25 million deaths estimated in 2023. Control measures have focused principally on early diagnosis, the treatment of active TB, and vaccination. However, the widespread emergence of anti-tuberculosis drug resistance remains the major public health threat to progress made in global TB care and control. Moreover, the Bacillus Calmette-Guérin (BCG) vaccine, the only licensed vaccine against TB in children, has been in use for over a century, and there have been considerable debates concerning its effectiveness in TB control. A multi-epitope vaccine against TB would be an invaluable tool to attain the Global Plan to End TB 2023-2030 target. A rational approach that combines several B-cell and T-cell epitopes from key lipoproteins was adopted to design a novel multi-epitope vaccine candidate. In addition, interactions with TLR4 were implemented to assess its ability to elicit an innate immune response. The conservation of the selected proteins suggests the possibility of cross-protection in line with the One Health approach to disease control. The vaccine candidate was predicted to be both antigenic and immunogenic, and immune simulation analyses demonstrated its ability to elicit both humoral and cellular immune responses. Protein-protein docking and normal-mode analyses of the vaccine candidate with TLR4 predicted efficient binding and stable interaction. This study provides a promising One Health approach for the design of multi-epitope vaccines against human and livestock tuberculosis. Overall, the designed vaccine candidate demonstrated immunogenicity and safety features that warrant further experimental validation in vitro and in vivo.

Tuberculosis vaccine - A timely analysis of the drawbacks for the development of novel vaccines

The BCG vaccine, Bacille Calmette Guerin, holds the distinction of being the most widely administered vaccine. Remarkably, a century has passed since its discovery; however, puzzlingly, questions persist regarding the effectiveness of the immune response it triggers. After years of diligent observation, it has been deduced that BCG imparts immunity primarily to a specific age group, namely children. This prompts a significant query: the rationale behind BCG's limited efficacy against TB in particular age groups and populations remains elusive. Beyond vaccinations, drug therapy has emerged as an alternative route for TB prevention. Nonetheless, this approach faces challenges in the contemporary landscape, marked by the emergence of new instances of MDR-TB and XDR-TB, compounded by the financial burden of treatment. It's noteworthy that BCG remains the sole WHO-approved vaccine for TB. This comprehensive review delves into several aspects, encompassing the immune response during infection, the shortcomings of BCG in conferring immunity, and the various factors contributing to its limitations. Within this discourse, we explore potential explanations for the observed deficiencies of the BCG vaccine and consider how these insights could catalyze the development of future vaccines. The current landscape of novel vaccine development for TB is illuminated, including a spotlight on the latest vaccine candidates.

A novel method for characterizing cell-cell interactions at single-cell resolution reveals unique signatures in blood T cell-monocyte complexes during infection

Communication between immune cells through direct contact is a critical feature of immune responses. Here, we developed a novel high-throughput method to study the transcriptome and adaptive immune receptor repertoire of single cells forming complexes without needing bioinformatic deconvolution. We found that T cells and monocytes forming complexes in blood during active tuberculosis (TB) and dengue hold unique transcriptomic signatures indicative of TCR/MCH-II immune synapses. Additionally, T cells in complexes showed enrichment for effector phenotypes, imaging and transcriptomic features of active TCR signaling, and increased immune activity at diagnosis compared to after anti-TB therapy. We also found evidence for bidirectional RNA exchange between T cells and monocytes, since complexes were markedly enriched for "dual-expressing" cells (i.e., co-expressing T cell and monocyte genes). Thus, studying immune cell complexes at a single-cell resolution offers novel perspectives on immune synaptic interactions occurring in blood during infection.

Mycobacterium tuberculosis-Human Immunodeficiency Virus Infection and the Role of T Cells in Protection

Tuberculosis (TB), primarily caused by Mycobacterium tuberculosis (M. tb), remains a widespread fatal health issue that becomes significantly detrimental when coupled with HIV. This study explores the host's innate and adaptive immune system response to TB in HIV immunocompromised patients, highlighting the significant role of CD8+ T cells. While the crucial role of macrophages and cytokines, like TNF-α and IFN-γ, in managing the host's immune response to M. tb is examined, the emphasis is on the changes that occur as a result of HIV coinfection. With the progression of HIV infection, the primary source of IFN-γ changes from CD4+ to CD8+ T cells, especially when latent TB advances to an active state. This study sheds light on the necessity of developing new preventative measures such as vaccines and new treatment approaches to TB, especially for immunocompromised patients, who are at a higher risk of life-threatening complications due to TB-HIV coinfection.

TB/FLU-06E Influenza Vector-Based Vaccine in the Complex Therapy of Drug-Susceptible and Drug-Resistant Experimental Tuberculosis

The steady rise of drug-resistant tuberculosis (TB), which renders standard therapy regimens ineffective, necessitates the development of innovative treatment approaches. Immunotherapeutic vaccines have the potential to effectively regulate the anti-TB immune response and enhance the efficacy of anti-TB treatment. In the present study, we aimed to evaluate the potency of the mucosal vector vaccine TB/FLU-06E as part of a complex treatment regimen for drug-susceptible (DS) or drug-resistant (DR) tuberculosis in C57BL/6 mice. Incorporating TB/FLU-06E into the treatment protocol significantly increased the effectiveness of therapy for both forms of tuberculosis. It was evidenced by higher survival rates and reduced pulmonary bacterial load (1.83 lg CFU for DS tuberculosis and 0.93 lg CFU for DR tuberculosis). Furthermore, the treatment reduced pathomorphological lesions in the lungs and stimulated the local and systemic T-helper 1 (Th1) and cytotoxic T-lymphocyte (CTL) anti-TB immune responses. Thus, therapeutic immunization with the TB/FLU-06E vaccine significantly enhances the efficacy of tuberculosis treatment, which is particularly important in DR tuberculosis.

Advances in Antiretroviral Therapy for Patients with Human Immunodeficiency Virus-Associated Tuberculosis

Tuberculosis is one of the most common opportunistic infections and a prominent cause of death in patients with human immunodeficiency virus (HIV) infection, in spite of near-universal access to antiretroviral therapy (ART) and tuberculosis preventive therapy. For patients with active tuberculosis but not yet receiving ART, starting ART after anti-tuberculosis treatment can complicate clinical management due to drug toxicities, drug-drug interactions and immune reconstitution inflammatory syndrome (IRIS) events. The timing of ART initiation has a crucial impact on treatment outcomes, especially for patients with tuberculous meningitis. The principles of ART in patients with HIV-associated tuberculosis are specific and relatively complex in comparison to patients with other opportunistic infections or cancers. In this review, we summarize the current progress in the timing of ART initiation, ART regimens, drug-drug interactions between anti-tuberculosis and antiretroviral agents, and IRIS.

Exploration and improvement of QuantiFERON-TB assay in patients with indeterminate results in clinical practice: A head-to-head study

BACKGROUND

We implemented the QuantiFERON-TB Gold In-Tube (QFT-GIT) based on peripheral blood mononuclear cells (QFT-PBMCs) and QFT Gold Plus (QFT-Plus) in patients with indeterminate results, and use Mit-Nil value to identify false negatives and impaired cellular immunity.

METHODS

One hundred seventy-one out of 2480 patients who had a QFT-GIT test were prospectively recruited and classified as high Nil (n = 35), low Mit (n = 75) and control (n = 61) cohorts. Head-to-head comparisons, i.e., QFT-PBMCs vs. QFT-GIT in high Nil cohort, QFT-Plus vs. QFT-GIT in low Mit cohort, and QFT-PBMCs vs. QFT-GIT in controls, were performed. Lymphocyte subsets counts were conducted in low Mit and control cohorts.

RESULTS

A significant reduction of positive rate only occurred in Mit-Nil < 6 IU/ml (p < 0.001). QFT-PBMCs yielded 100 % valid results and had a significant Nil decline in high Nil cohort (0.98 ± 1.06 vs. 9.55 ± 0.64 IU/ml, p < 0.0001), while correlated well with QFT-GIT for qualitative (Cohen's k = 0.93) and quantitative (TB-Ag [R2 = 0.91] and Mit [R2 = 0.94]) analyses. QFT-Plus produced 61.3 % valid results and had a significant Mit increase in low Mit cohort (0.82 ± 0.95 vs. 0.17 ± 0.11 IU/ml, p < 0.0001). Mit-Nil value significantly correlated with lymphocyte subsets counts (R:0.49-0.56, p < 0.0001), separately corresponding to thresholds of 4.26, 5.33, 5.55 and 5.81 IU/ml for predicting decreased total lymphocyte, T lymphocyte, CD4+ and CD8+ cells.

CONCLUSIONS

QFT that replacing whole blood with PBMCs should be recommended to handle high Nil samples, and QFT-Plus can declined the frequency of low Mit results. In addition, Mit-Nil < 6 and 5.81 IU/ml are potential thresholds to identify the risk of false negatives and impaired cellular immunity, respectively.

Acute inflammation alters lung lymphocytes and potentiates innate-like behavior in young mouse lung CD8 T cells, resembling lung CD8 T cells from old mice

Inflammation plays a significant role in lung infection including that caused by Mycobacterium tuberculosis, in which both adaptive and innate lymphocytes can affect infection control. How inflammation affects infection is understood in a broad sense, including inflammaging (chronic inflammation) seen in the elderly, but the explicit role that inflammation can play in regulation of lymphocyte function is not known. To fill this knowledge gap, we used an acute lipopolysaccharide (LPS) treatment in young mice and studied lymphocyte responses, focusing on CD8 T cell subsets. LPS treatment decreased the total numbers of T cells in the lungs of LPS mice while also increasing the number of activated T cells. We demonstrate that lung CD8 T cells from LPS mice became capable of an antigen independent innate-like IFN-γ secretion, dependent on IL-12p70 stimulation, paralleling innate-like IFN-γ secretion of lung CD8 T cells from old mice. Overall, this study provides information on how acute inflammation can affect lymphocytes, particularly CD8 T cells, which could potentially affect immune control of various disease states.

Clinical characteristics of patients with non-tuberculous mycobacterial pulmonary disease: a seven-year follow-up study conducted in a certain tertiary hospital in Beijing

Background

The incidence of non-tuberculous mycobacterial pulmonary disease (NTM-PD) has increased in recent years. However, the clinical and immunologic characteristics of NTM-PD patients have received little attention.

Methods

NTM strains, clinical symptoms, underlying diseases, lung CT findings, lymphocyte subsets, and drug susceptibility tests (DSTs) of NTM-PD patients were investigated. Then, the counts of immune cells of NTM-PD patients and their correlation were evaluated using principal component analysis (PCA) and correlation analysis.

Results

135 NTM-PD patients and 30 healthy controls (HCs) were enrolled from 2015 to 2021 in a certain tertiary hospital in Beijing. The number of NTM-PD patients increased every year, and Mycobacterium intracellulare (M. intracellulare), M. abscessus, M. avium, and M. kansasii were the major pathogens of NTM-PD. The main clinical symptoms of NTM-PD patients were cough and sputum production, and the primary lung CT findings were thin-walled cavity, bronchiectasis, and nodules. In addition, we identified 23 clinical isolates from 87 NTM-PD patients with strain records. The DST showed that almost all of M. abscessus and M. avium and more than half of the M. intracellulare and M. avium complex groups were resistant to anti-tuberculosis drugs tested in this study. M. xenopi was resistant to all aminoglycosides. M. kansasii was 100% resistant to kanamycin, capreomycin, amikacin, and para-aminosalicylic acid, and sensitive to streptomycin, ethambutol, levofloxacin, azithromycin, and rifamycin. Compared to other drugs, low resistance to rifabutin and azithromycin was observed among NTM-PD isolates. Furthermore, the absolute counts of innate and adaptive immune cells in NTM-PD patients were significantly lower than those in HCs. PCA and correlation analysis revealed that total T, CD4⁺, and CD8⁺ T lymphocytes played an essential role in the protective immunity of NTM-PD patients, and there was a robust positive correlation between them.

Conclusion

The incidence of NTM-PD increased annually in Beijing. Individuals with bronchiectasis and COPD have been shown to be highly susceptible to NTM-PD. NTM-PD patients is characterized by compromised immune function, non-specific clinical symptoms, high drug resistance, thin-walled cavity damage on imaging, as well as significantly reduced numbers of both innate and adaptive immune cells.

Comparative transcriptomes reveal pro-survival and cytotoxic programs of mucosal-associated invariant T cells upon Bacillus Calmette-Guérin stimulation

Mucosal-associated invariant T (MAIT) cells are protective against tuberculous and non-tuberculous mycobacterial infections with poorly understood mechanisms. Despite an innate-like nature, MAIT cell responses remain heterogeneous in bacterial infections. To comprehensively characterize MAIT activation programs responding to different bacteria, we stimulated MAIT cells with E. coli to compare with Bacillus Calmette-Guérin (BCG), which remains the only licensed vaccine and a feasible tool for investigating anti-mycobacterial immunity in humans. Upon sequencing mRNA from the activated and inactivated CD8+ MAIT cells, results demonstrated the altered MAIT cell gene profiles by each bacterium with upregulated expression of activation markers, transcription factors, cytokines, and cytolytic mediators crucial in anti-mycobacterial responses. Compared with E. coli, BCG altered more MAIT cell genes to enhance cell survival and cytolysis. Flow cytometry analyses similarly displayed a more upregulated protein expression of B-cell lymphoma 2 and T-box transcription factor Eomesodermin in BCG compared to E.coli stimulations. Thus, the transcriptomic program and protein expression of MAIT cells together displayed enhanced pro-survival and cytotoxic programs in response to BCG stimulation, supporting BCG induces cell-mediated effector responses of MAIT cells to fight mycobacterial infections.

Long-Term Immunogenicity and In Vitro Prophylactic Protective Efficacy of M. tuberculosis Fusion Protein DR2 Combined with Liposomal Adjuvant DIMQ as a Boosting Vaccine for BCG

The resuscitation of dormant Mycobacterium tuberculosis is an important cause of adult tuberculosis (TB) transmission. According to the interaction mechanism between M. tuberculosis and the host, the latency antigen Rv0572c and region of difference 9 (RD9) antigen Rv3621c were selected in this study to prepare the fusion protein DR2. Stimulating clinically diagnosed active tuberculosis infections (i.e., TB patients), latent tuberculosis infections, and healthy controls confirmed that T lymphocytes could recognize DR2 protein in the peripheral blood of TB-infected individuals more than subcomponent protein. The DR2 protein was then emulsified in the liposome adjuvant dimethyl dioctadecyl ammonium bromide, and imiquimod (DIMQ) was administered to C57BL/6 mice immunized with Bacillus Calmette-Guérin (BCG) vaccine to evaluate their immunogenicity. Studies have shown that DR2/DIMQ, a booster vaccine for BCG primary immunization, can elicit robust CD4⁺ Th1 cell immune response and predominant IFN-γ⁺ CD4⁺ effector memory T cells (T_EM) subsets. Furthermore, the serum antibody level and the expression of related cytokines increased significantly with the extension of immunization time, with IL2⁺, CD4⁺, or CD8⁺ central memory T cells (T_CM) subsets predominant in the long term. This immunization strategy showed matched prophylactic protective efficacy by performing in vitro challenge experiment. This result provides robust evidence that the novel subunit vaccine prepared by fusion protein DR2 combined with liposomal adjuvant DIMQ is a promising TB vaccine candidate for further preclinical trials as a booster vaccine for BCG.

An RNA-Based Vaccine Platform for Use against Mycobacterium tuberculosis

Mycobacterium tuberculosis (M.tb), a bacterial pathogen that causes tuberculosis disease (TB), exerts an extensive burden on global health. The complex nature of M.tb, coupled with different TB disease stages, has made identifying immune correlates of protection challenging and subsequently slowing vaccine candidate progress. In this work, we leveraged two delivery platforms as prophylactic vaccines to assess immunity and subsequent efficacy against low-dose and ultra-low-dose aerosol challenges with M.tb H37Rv in C57BL/6 mice. Our second-generation TB vaccine candidate ID91 was produced as a fusion protein formulated with a synthetic TLR4 agonist (glucopyranosyl lipid adjuvant in a stable emulsion) or as a novel replicating-RNA (repRNA) formulated in a nanostructured lipid carrier. Protein subunit- and RNA-based vaccines preferentially elicit cellular immune responses to different ID91 epitopes. In a single prophylactic immunization screen, both platforms reduced pulmonary bacterial burden compared to the controls. Excitingly, in prime-boost strategies, the groups that received heterologous RNA-prime, protein-boost or combination immunizations demonstrated the greatest reduction in bacterial burden and a unique humoral and cellular immune response profile. These data are the first to report that repRNA platforms are a viable system for TB vaccines and should be pursued with high-priority M.tb antigens containing CD4+ and CD8+ T-cell epitopes.

mRNA vaccines: a new opportunity for malaria, tuberculosis and HIV

The success of the first licensed mRNA-based vaccines against COVID-19 has created a widespread interest on mRNA technology for vaccinology. As expected, the number of mRNA vaccines in preclinical and clinical development increased exponentially since 2020, including numerous improvements in mRNA formulation design, delivery methods and manufacturing processes. However, the technology faces challenges such as the cost of raw materials, the lack of standardization, and delivery optimization. MRNA technology may provide a solution to some of the emerging infectious diseases as well as the deadliest hard-to-treat infectious diseases malaria, tuberculosis, and human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), for which an effective vaccine, easily deployable to endemic areas is urgently needed. In this review, we discuss the functional structure, design, manufacturing processes and delivery methods of mRNA vaccines. We provide an up-to-date overview of the preclinical and clinical development of mRNA vaccines against infectious diseases, and discuss the immunogenicity, efficacy and correlates of protection of mRNA vaccines, with particular focus on research and development of mRNA vaccines against malaria, tuberculosis and HIV.

Transporter Associated with Antigen Processing 1 Gene Polymorphisms Increase the Susceptibility to Tuberculosis

Purpose

Tuberculosis (TB) is known to result from a complex interaction between the host immune response and Mycobacterium infection. The transporter associated with antigen processing (TAP) plays an important role in the processing and presentation pathways for the Mycobacterium tuberculosis (M. tb) antigen. To investigate the possible association of the TAP1 and TAP2 genes with TB.

Patients and Methods

A total of 449 TB patients and 435 control subjects were included in this study, and single nucleotide polymorphisms (SNPs) in the TAP gene, as well as TAP1 and TAP2 alleles, were genotyped.

Results

TAP gene association analysis of TB diseases showed that rs41551515-T in the TAP1 gene was significantly associated with susceptibility to TB (P=7.96E-04, OR=4.124, 95% CI: 1.683-10.102), especially pulmonary TB (PTB, P=6.84E-04, OR=4.350, 95% CI: 1.727-10.945), and the combination of rs1057141-T-rs1135216-C in the TAP1 gene significantly increased the risk of TB susceptibility (P=5.51E-05, OR=10.899, 95% CI: 2.555-46.493). Five novel TAP1 alleles were detected in Yunnan Han people, and the allele frequency of TAP1*unknown_3 (rs41555220-rs41549617-rs1057141-rs1135216-rs1057149-rs41551515: C-A-T-C-C-T) was notably increased in all TB patients, including in the PTB and EPTB subgroups, and was significantly associated with the risk of susceptibility to TB. However, no association between the TAP2 gene and TB was found in this study.

Conclusion

Host genetic variants of rs41551515-T and the combination rs1057141-T-rs1135216-C, as well as TAP1*unknown_3 may play a critical role in susceptibility to TB disease.

Immunogenicity and protection against Mycobacterium avium with a heterologous RNA prime and protein boost vaccine regimen

Prophylactic efficacy of two different delivery platforms for vaccination against Mycobacterium avium (M. avium) were tested in this study; a subunit and an RNA-based vaccine. The vaccine antigen, ID91, includes four mycobacterial antigens: Rv3619, Rv2389, Rv3478, and Rv1886. We have shown that ID91+GLA-SE is effective against a clinical NTM isolate, M. avium 2-151 smt. Here, we extend these results and show that a heterologous prime/boost strategy with a repRNA-ID91 (replicon RNA) followed by protein ID91+GLA-SE boost is superior to the subunit protein vaccine given as a homologous prime/boost regimen. The repRNA-ID91/ID91+GLA-SE heterologous regimen elicited a higher polyfunctional CD4+ TH1 immune response when compared to the homologous protein prime/boost regimen. More significantly, among all the vaccine regimens tested only repRNA-ID91/ID91+GLA-SE induced IFN-γ and TNF-secreting CD8+ T cells. Furthermore, the repRNA-ID91/ID91+GLA-SE vaccine strategy elicited high systemic proinflammatory cytokine responses and induced strong ID91 and an Ag85B-specific humoral antibody response a pre- and post-challenge with M. avium 2-151 smt. Finally, while all prophylactic prime/boost vaccine regimens elicited a degree of protection in beige mice, the heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen provided greater pulmonary protection than the homologous protein prime/boost regimen. These data indicate that a prophylactic heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen augments immunogenicity and confers protection against M. avium.

Latent tuberculosis reactivation in the setting of SARS-Cov-2 infection: The analysis of the radiologic features that help the diagnosis

In Italy tuberculosis is a relatively rare disease and people coming from developing nations are usually affected. The radiological findings are variable and depend on the tuberculosis activity, if primary or post-primary. In literature, few data are reported about the co-existence of COVID-19 and lung tuberculosis. In this case report, authors describe the imaging features of latent lung tuberculosis in a patient with SARS-CoV-2 disease. The important role of CT imaging in identifying and diagnosing other infectious lung diseases presenting in the setting of the polymorphism and severity of SARS-CoV-2 disease is also discussed.

It Takes a Village: The Multifaceted Immune Response to Mycobacterium tuberculosis Infection and Vaccine-Induced Immunity

Despite co-evolving with humans for centuries and being intensely studied for decades, the immune correlates of protection against Mycobacterium tuberculosis (Mtb) have yet to be fully defined. This lapse in understanding is a major lag in the pipeline for evaluating and advancing efficacious vaccine candidates. While CD4+ T helper 1 (TH1) pro-inflammatory responses have a significant role in controlling Mtb infection, the historically narrow focus on this cell population may have eclipsed the characterization of other requisite arms of the immune system. Over the last decade, the tuberculosis (TB) research community has intentionally and intensely increased the breadth of investigation of other immune players. Here, we review mechanistic preclinical studies as well as clinical anecdotes that suggest the degree to which different cell types, such as NK cells, CD8+ T cells, γ δ T cells, and B cells, influence infection or disease prevention. Additionally, we categorically outline the observed role each major cell type plays in vaccine-induced immunity, including Mycobacterium bovis bacillus Calmette-Guérin (BCG). Novel vaccine candidates advancing through either the preclinical or clinical pipeline leverage different platforms (e.g., protein + adjuvant, vector-based, nucleic acid-based) to purposefully elicit complex immune responses, and we review those design rationales and results to date. The better we as a community understand the essential composition, magnitude, timing, and trafficking of immune responses against Mtb, the closer we are to reducing the severe disease burden and toll on human health inflicted by TB globally.

High Dimensionality Reduction and Immune Phenotyping of Natural Killer and Invariant Natural Killer Cells in Latent Tuberculosis-Diabetes Comorbidity

Natural killer (NK) and invariant NKT (iNKT) cells are unique innate lymphocytes that coordinate diverse immune responses and display antimycobacterial potential. However, the role of NK and iNKT cells expressing cytokines, cytotoxic, and immune markers in latent tuberculosis (LTB), diabetes mellitus (DM), or preDM (PDM) and nonDM (NDM) comorbidities is not known. Thus, we have studied the unstimulated (UNS), Mycobacterium tuberculosis (Mtb [PPD, WCL]), and mitogen (P/I)-stimulated NK and iNKT cells expressing Type 1 (IFNγ, TNFα, and IL-2), Type 17 (IL-17A, IL-17F, and IL-22) cytokines, cytotoxic (perforin, granzyme B, and granulysin) and immune (GMCSF, PD-1, and CD69) markers in LTB comorbidities by dimensionality reduction and flow cytometry. Our results suggest that LTB DM and PDM individuals express diverse NK and iNKT cell immune clusters compared to LTB NDM individuals. In UNS condition, frequencies of NK and iNKT cells expressing markers are not significantly different. After Mtb antigen stimulation, NK cell expressing [Type 1 (IFNγ, TNFα, and IL-2), GMCSF in PPD and IFNγ in WCL), Type 17 [(IL-17A), PD-1 in PPD), (IL-17A, IL-17F, and IL-22), PD-1 in WCL], and cytotoxic (perforin, granzyme B in PPD, and WCL)] marker frequencies were significantly reduced in LTB DM and/or PDM individuals compared to LTB NDM individuals. Similarly, iNKT cells expressing [Type 1 (IFNγ, IL-2), GMCSF in PPD), TNFα, GMCSF in WCL), Type 17 (IL-17A), PD-1 in PPD, IL-17F in WCL) cytokines were increased and cytotoxic or immune (perforin, granzyme B, granulysin), CD69 in PPD, perforin and CD69 in WCL] marker frequencies were significantly diminished in LTB DM and/or PDM compared to LTB NDM individuals. Finally, NK and iNKT cell frequencies did not exhibit significant differences upon positive control antigen stimulation between the study population. Therefore, altered NK cell and iNKT cells expressing cytokines, cytotoxic, and immune markers are characteristic features in LTB PDM/DM comorbidities.

Protease-Based Subunit Vaccine in Mice Boosts BCG Protection against Mycobacterium tuberculosis

The significant number of people with latent and active tuberculosis infection requires further efforts to develop new vaccines or improve the Bacillus Calmette-Guérin (BCG), which is the only approved vaccine against this disease. In this study, we developed a recombinant fusion protein (PEPf) containing high-density immunodominant epitope sequences from Rv0125, Rv2467, and Rv2672 Mycobacterium tuberculosis (Mtb) proteases that proved immunogenic and used it to develop a recombinant BCG vaccine expressing the fusion protein. After challenging using Mtb, a specific immune response was recalled, resulting in a reduced lung bacterial load with similar protective capabilities to BCG. Thus BCG PEPf failed to increase the protection conferred by BCG. The PEPf was combined with Advax4 adjuvant and tested as a subunit vaccine using a prime-boost strategy. PEPf + Advax4 significantly improved protection after Mtb challenge, with a reduction in bacterial load in the lungs. Our results confirm that Mtb proteases can be used to develop vaccines against tuberculosis and that the use of the recombinant PEPf subunit protein following a prime-boost regimen is a promising strategy to improve BCG immunity.

Photochemically-Mediated Inflammation and Cross-Presentation of Mycobacterium bovis BCG Proteins Stimulates Strong CD4 and CD8 T-Cell Responses in Mice

Conventional vaccines are very efficient in the prevention of bacterial infections caused by extracellular pathogens due to effective stimulation of pathogen-specific antibodies. In contrast, considering that intracellular surveillance by antibodies is not possible, they are typically less effective in preventing or treating infections caused by intracellular pathogens such as Mycobacterium tuberculosis. The objective of the current study was to use so-called photochemical internalization (PCI) to deliver a live bacterial vaccine to the cytosol of antigen-presenting cells (APCs) for the purpose of stimulating major histocompatibility complex (MHC) I-restricted CD8 T-cell responses. For this purpose, Mycobacterium bovis BCG (BCG) was combined with the photosensitiser tetraphenyl chlorine disulfonate (TPCS2a) and injected intradermally into mice. TPCS2a was then activated by illumination of the injection site with light of defined energy. Antigen-specific CD4 and CD8 T-cell responses were monitored in blood, spleen, and lymph nodes at different time points thereafter using flow cytometry, ELISA and ELISPOT. Finally, APCs were infected and PCI-treated in vitro for analysis of their activation of T cells in vitro or in vivo after autologous vaccination of mice. Combination of BCG with PCI induced stronger BCG-specific CD4 and CD8 T-cell responses than treatment with BCG only or with BCG and TPCS2a without light. The overall T-cell responses were multifunctional as characterized by the production of IFN-γ, TNF-α, IL-2 and IL-17. Importantly, PCI induced cross-presentation of BCG proteins for stimulation of antigen-specific CD8 T-cells that were particularly producing IFN-γ and TNF-α. PCI further facilitated antigen presentation by causing up-regulation of MHC and co-stimulatory proteins on the surface of APCs as well as their production of TNF-α and IL-1β in vivo. Furthermore, PCI-based vaccination also caused local inflammation at the site of vaccination, showing strong infiltration of immune cells, which could contribute to the stimulation of antigen-specific immune responses. This study is the first to demonstrate that a live microbial vaccine can be combined with a photochemical compound and light for cross presentation of antigens to CD8 T cells. Moreover, the results revealed that PCI treatment strongly improved the immunogenicity of M. bovis BCG.

Analysis of CD4 and CD8 expression in multidrug-resistant tuberculosis infection with diabetes mellitus: An experimental study in mice

BACKGROUND

Tuberculosis (TB) remains a major global health problem, in the top 10 causes of death. As a regulator of the immune response, T-helper (Th) cells activate other lymphocytes from the immune system, such as B cells, to destroy the TB pathogen by releasing CD4 and CD8 Th cells. Diabetes mellitus (DM) is a known cause of developing active pulmonary TB. Few studies have examined the biomolecular expression affecting Mycobacterium tuberculosis (MTB) and multidrug-resistant (MDR) MTB, which are associated with low immunity represented by TB in diabetes and CD4 and CD8 levels.

MATERIALS AND METHODS

This animal study used a post-test control group design. We performed an experimental study using 30 BALB/c mice, each weighing 25 g. It included six experimental animal groups, of which three had a diabetes condition induced using intraperitoneal streptozotocin, and all were infected with MTB or MDR TB. We evaluated the CD4 and CD8 levels in each group and analyzed the differences.

RESULTS

We found a significant difference in CD4 and CD8 levels in MTB and MDR TB conditions.

CONCLUSION

This study shows that acute infection in experimental mice with MTB and MDR TB with or without diabetes had the highest levels of both CD4 and CD8 cells, which can be a sign of increased cellular immunity in a mice model.

Reactivation of Mycobacterium simiae after the recovery of COVID-19 infection

There are limited studies on the coinfection of coronavirus disease 2019 (COVID-19) with nontuberculous mycobacteria. Here, we briefly describe the reactivation of Mycobacterium simiae infection in a patient who had recovered from COVID-19 in October 2020, Iran. During the pandemic of COVID-19, other infectious agents should not be ignored.

Co-Administration of Anticancer Candidate MK-2206 Enhances the Efficacy of BCG Vaccine Against Mycobacterium tuberculosis in Mice and Guinea Pigs

The failure of M. bovis BCG to induce long-term protection has been endowed to its inability to escape the phagolysosome, leading to mild activation of CD8⁺ mediated T cell response. Induction of apoptosis in host cells plays an important role in potentiating dendritic cells-mediated priming of CD8⁺ T cells, a process defined as “cross-priming.” Moreover, IL-10 secretion by infected cells has been reported to hamper BCG-induced immunity against Tuberculosis (TB). Previously, we have reported that apoptosis of BCG-infected macrophages and inhibition of IL-10 secretion is FOXO3 dependent, a transcription factor negatively regulated by the pro-survival activated threonine kinase, Akt. We speculate that FOXO3-mediated induction of apoptosis and abrogation of IL-10 secretion along with M. bovis BCG immunization might enhance the protection imparted by BCG. Here, we have assessed whether co-administration of a known anti-cancer Akt inhibitor, MK-2206, enhances the protective efficacy of M. bovis BCG in mice model of infection. We observed that in vitro MK-2206 treatment resulted in FOXO3 activation, enhanced BCG-induced apoptosis of macrophages and inhibition of IL-10 secretion. Co-administration of M. bovis BCG along with MK-2206 also increased apoptosis of antigen-presenting cells in draining lymph nodes of immunized mice. Further, MK-2206 administration improved BCG-induced CD4⁺ and CD8⁺ effector T cells responses and its ability to induce both effector and central memory T cells. Finally, we show that co-administration of MK-2206 enhanced the protection imparted by M. bovis BCG against Mtb in aerosol infected mice and guinea pigs. Taken together, we provide evidence that MK-2206-mediated activation of FOXO3 potentiates BCG-induced immunity and imparts protection against Mtb through enhanced innate immune response.

COVID-19 promoting the development of active tuberculosis in a patient with latent tuberculosis infection: A case report

We report the case of a 40-year-old female diagnosed with COVID-19 after presenting to our institution with fever, cough and myalgia for three days. Her nasopharyngeal swab tested positive for SARS COV-2 by real time PCR and her plain chest radiograph was reported as normal. She did not require hospitalization and at telephone follow up she confirmed her illness lasted 11 days. Seven weeks later she presented with chest pain, dyspnea and fever for two days. Her repeat chest imaging showed right upper zone consolidation and this culminated in a microbiological diagnosis of pulmonary tuberculosis. The patient's daughter had been treated for tuberculosis two years earlier and unfortunately family screening for latent TB was not undertaken.

This case appears to confirm the concerns that the CD4⁺ T-cell depletion associated with COVID-19 may promote the development of active tuberculosis from latent infection much like HIV does. If this effect is widespread it may have a significant impact on the worldwide TB burden. We suggest vigilance to ensure patients are diagnosed early and meticulous contact tracing is undertaken to treat those with latent tuberculosis.

Relationship between expression mRNA gene Treg, Treg, CD4+, and CD8+ protein levels with TST in tuberculosis children: A nested case-control

BACKGROUND

The ability of Mycobacterium tuberculosis to survive intracellularly, provides a cellular adaptive immune response played by specific T cells to defend against tuberculosis. The adaptive immune response to Bacillus of Calmette and Guerin (BCG) immunization is responded to by B cells, T Follicular B helper, T regulatory, restriction CD1, CD8+, CD4+, Th1, Th2, and Th17. BCG immunization can cause a tuberculin test reaction to being positive. The tuberculin test is a method for diagnosing TB infection and for screening individuals for latent infection and assessing the rate of TB infection in a given population.

METHODS

a nested case-control survey was conducted on patients with a diagnosis of TB and parents 0-18 years of age from 3 hospitals in Indonesia during September-November 2019 with a total sample of 69 people undergoing clinical examinations, supporting and diagnosing subjects, blood sampling 1-2 cc for examination mRNA gene Treg, Treg, CD 4+, and CD 8+, then centrifuged at 3000 rpm for 10 min to support blood cells and serum.

RESULTS

There was a significant relationship between expression of mRNA gene Treg with TST (p = 0,000), Treg with TST (p = 0,000), and CD4+ with TST (p = 0,000). Meanwhile, CD8 + was not significantly associated with TST (p = 0.118).

CONCLUSIONS

It is necessary to check the expression of mRNA gene Treg, Treg, CD4+, and CD8+ with more samples to find the mean value that shows the protective value of further TB.

Integrating fish models in tuberculosis vaccine development

Tuberculosis is a chronic infection by Mycobacterium tuberculosis that results in over 1.5 million deaths worldwide each year. Currently, there is only one vaccine against tuberculosis, the Bacillus Calmette–Guérin (BCG) vaccine. Despite widespread vaccination programmes, over 10 million new M. tuberculosis infections are diagnosed yearly, with almost half a million cases caused by antibiotic-resistant strains. Novel vaccination strategies concentrate mainly on replacing BCG or boosting its efficacy and depend on animal models that accurately recapitulate the human disease. However, efforts to produce new vaccines against an M. tuberculosis infection have encountered several challenges, including the complexity of M. tuberculosis pathogenesis and limited knowledge of the protective immune responses. The preclinical evaluation of novel tuberculosis vaccine candidates is also hampered by the lack of an appropriate animal model that could accurately predict the protective effect of vaccines in humans. Here, we review the role of zebrafish (Danio rerio) and other fish models in the development of novel vaccines against tuberculosis and discuss how these models complement the more traditional mammalian models of tuberculosis.

Summary: In this Review, we discuss how zebrafish (Danio rerio) and other fish models can complement the more traditional mammalian models in the development of novel vaccines against tuberculosis.

Inhibiting Histone Deacetylases in Human Macrophages Promotes Glycolysis, IL-1β, and T Helper Cell Responses to Mycobacterium tuberculosis

Tuberculosis (TB) is the leading infectious killer in the world. Mycobacterium tuberculosis (Mtb), the bacteria that causes the disease, is phagocytosed by alveolar macrophages (AM) and infiltrating monocyte-derived macrophages (MDM) in the lung. Infected macrophages then upregulate effector functions through epigenetic modifications to make DNA accessible for transcription. The metabolic switch to glycolysis and the production of proinflammatory cytokines are key effector functions, governed by epigenetic changes, that are integral to the ability of the macrophage to mount an effective immune response against Mtb. We hypothesised that suberanilohydroxamic acid (SAHA), an FDA-approved histone deacetylase inhibitor (HDACi), can modulate epigenetic changes upstream of the metabolic switch and support immune responses during Mtb infection. The rate of glycolysis in human MDM, infected with Mtb and treated with SAHA, was tracked in real time on the Seahorse XFe24 Analyzer. SAHA promoted glycolysis early in the response to Mtb. This was associated with significantly increased production of IL-1β and significantly reduced IL-10 in human MDM and AM. Since innate immune function directs downstream adaptive immune responses, we used SAHA-treated Mtb-infected AM or MDM in a co-culture system to stimulate T cells. Mtb-infected macrophages that had previously been treated with SAHA promoted IFN-γ, GM-CSF, and TNF co-production in responding T helper cells but did not affect cytotoxic T cells. These results indicate that SAHA promoted the early switch to glycolysis, increased IL-1β, and reduced IL-10 production in human macrophages infected with Mtb. Moreover, the elevated proinflammatory function of SAHA-treated macrophages resulted in enhanced T helper cell cytokine polyfunctionality. These data provide an in vitro proof-of-concept for the use of HDACi to modulate human immunometabolic processes in macrophages to promote innate and subsequent adaptive proinflammatory responses.

Mucosal-Associated Invariant T Cells Develop an Innate-Like Transcriptomic Program in Anti-mycobacterial Responses

Conventional T cells exhibit a delayed response to the initial priming of peptide antigens presented by major histocompatibility complex (MHC) proteins. Unlike conventional T cells, mucosal-associated invariant T (MAIT) cells quickly respond to non-peptidic metabolite antigens presented by MHC-related protein 1 (MR1). To elucidate the MR1-dependent activation program of MAIT cells in response to mycobacterial infections, we determined the surface markers, transcriptomic profiles, and effector responses of activated human MAIT cells. Results revealed that mycobacterial-incubated antigen-presenting cells stimulated abundant human CD8⁺ MAIT cells to upregulate the co-expression of CD69 and CD26, as a combinatorial activation marker. Further transcriptomic analyses demonstrated that CD69⁺CD26⁺⁺ CD8⁺MAIT cells highly expressed numerous genes for mediating anti-mycobacterial immune responses, including pro-inflammatory cytokines, cytolytic molecules, NK cell receptors, and transcription factors, in contrast to inactivated counterparts CD69^+/−CD26^+/− CD8⁺MAIT cells. Gene co-expression, enrichment, and pathway analyses yielded high statistical significance to strongly support that activated CD8⁺ MAIT cells shared gene expression and numerous pathways with NK and CD8⁺ T cells in activation, cytokine production, cytokine signaling, and effector functions. Flow cytometry detected that activated CD8⁺MAIT cells produced TNFα, IFNγ, and granulysin to inhibit mycobacterial growth and fight mycobacterial infection. Together, results strongly support that the combinatorial activation marker CD69⁺CD26⁺⁺ labels the activated CD8⁺MAIT cells that develop an innate-like activation program in anti-mycobacterial immune responses. We speculate that the rapid production of anti-mycobacterial effector molecules facilitates MAIT cells to fight early mycobacterial infection in humans.

Quantitative and Qualitative Perturbations of CD8+ MAITs in Healthy Mycobacterium tuberculosis-Infected Individuals

CD8 T cells are considered important contributors to the immune response against Mycobacterium tuberculosis, yet limited information is currently known regarding their specific immune signature and phenotype. In this study, we applied a cell population transcriptomics strategy to define immune signatures of human latent tuberculosis infection (LTBI) in memory CD8 T cells. We found a 41-gene signature that discriminates between memory CD8 T cells from healthy LTBI subjects and uninfected controls. The gene signature was dominated by genes associated with mucosal-associated invariant T cells (MAITs) and reflected the lower frequency of MAITs observed in individuals with LTBI. There was no evidence for a conventional CD8 T cell–specific signature between the two cohorts. We, therefore, investigated MAITs in more detail based on Vα7.2 and CD161 expression and staining with an MHC-related protein 1 (MR1) tetramer. This revealed two distinct populations of CD8⁺Vα7.2⁺CD161⁺ MAITs: MR1 tetramer⁺ and MR1 tetramer⁻, which both had distinct gene expression compared with memory CD8 T cells. Transcriptomic analysis of LTBI versus noninfected individuals did not reveal significant differences for MR1 tetramer⁺ MAITs. However, gene expression of MR1 tetramer⁻ MAITs showed large interindividual diversity and a tuberculosis-specific signature. This was further strengthened by a more diverse TCR-α and -β repertoire of MR1 tetramer⁻ cells as compared with MR1 tetramer⁺. Thus, circulating memory CD8 T cells in subjects with latent tuberculosis have a reduced number of conventional MR1 tetramer⁺ MAITs as well as a difference in phenotype in the rare population of MR1 tetramer⁻ MAITs compared with uninfected controls.

LIOFeron®TB/LTBI: A novel and reliable test for LTBI and tuberculosis

OBJECTIVES

High accuracy diagnostic screening tests for tuberculosis (TB) are required to improve the diagnosis of both active TB and latent Mycobacterium tuberculosis (MTB) infection (LTBI). The novel IGRA LIOFeron®TB/LTBI assay was tested and its accuracy was compared to the QuantiFERON®-TB Gold Plus assay.

METHODS

A total of 389 subjects were enrolled in two cohorts and classified as healthy, active TB or LTBI persons. The blood of all the patients was tested with LIOFeron®TB/LTBI assay, containing MTB alanine dehydrogenase, able to differentiate active TB from LTBI diagnosis. The results obtained with both IGRAs, performed on the same 250 samples, were finally compared.

RESULTS

The two assays demonstrated an excellent concordance of their results with patients' diagnosis of MTB infection. ROC analysis for QuantiFERON®-TB Gold Plus showed sensitivity and specificity respectively of 98% and 97% in diagnosing active TB patients and 85% and 94% in diagnosing LTBI subjects. LIOFeron®TB/LTBI assay showed sensitivity and specificity respectively of 90% and 98% in diagnosing active TB patients and 94% and 97% in diagnosing LTBI subjects.

CONCLUSIONS

The two IGRAs displayed the same high accuracy in diagnosing MTB infection/TB disease, and LIOFeron®TB/LTBI assay demonstrated higher sensitivity than QuantiFERON®-TB Gold Plus test in LTBI detection.

PD-1/PD-L1 Pathway Modulates Macrophage Susceptibility to Mycobacterium tuberculosis Specific CD8+ T cell Induced Death

CD8⁺T cells contribute to tuberculosis (TB) infection control by inducing death of infected macrophages. Mycobacterium tuberculosis (Mtb) infection is associated with increased PD-1/PD-L1 expression and alternative activation of macrophages. We aimed to study the role of PD-1 pathway and macrophage polarization on Mtb-specific CD8⁺T cell-induced macrophage death. We observed that both PD-L1 on CD14⁺ cells and PD-1 on CD8⁺T cells were highly expressed at the site of infection in pleurisy TB patients’ effusion samples (PEMC). Moreover, a significant increase in CD8⁺T cells’ Mtb-specific degranulation from TB-PEMC vs. TB-PBMC was observed, which correlated with PD-1 and PDL-1 expression. In an in vitro model, M1 macrophages were more susceptible to Mtb-specific CD8⁺T cells’ cytotoxicity compared to M2a macrophages and involved the transfer of cytolytic effector molecules from CD8⁺T lymphocytes to target cells. Additionally, PD-L1 blocking significantly increased the in vitro Ag-specific CD8⁺T cell cytotoxicity against IFN-γ-activated macrophages but had no effect over cytotoxicity on IL-4 or IL-10-activated macrophages. Interestingly, PD-L1 blocking enhanced Mtb-specific CD8⁺ T cell killing of CD14⁺ cells from human tuberculous pleural effusion samples. Our data indicate that PD-1/PD-L1 pathway modulates antigen-specific cytotoxicity against M1 targets in-vitro and encourage the exploration of checkpoint blockade as new adjuvant for TB therapies.

Mycobacterial Lipoprotein Z Triggers Efficient Innate and Adaptive Immunity for Protection Against Mycobacterium tuberculosis Infection

Mycobacterial lipoproteins are considered to be involved in both virulence and immunoregulatory processes during Mycobacterium tuberculosis (M.tb) infection. In our previous investigations on the immunoreactivity of more than 30 M.tb proteins in active TB patients, we identified mycobacterial lipoprotein Z (LppZ) as one of the most immune dominant antigens. How LppZ triggers immune responses is still unclear. In this study, we analyzed LppZ-mediated innate and adaptive immunity using a murine air pouch model and an M.tb infection model, respectively. We found that LppZ could not only recruit inflammatory cells but also induce the production of proinflammatory cytokines inside the pouches. LppZ could also induce strong Th1 responses following immunization and confer protection against challenge with M.tb virulent strain H37Rv at a similar level to BCG vaccination but with less pathological damage in the lungs. Furthermore, we revealed the presence of LppZ-specific functional CD4⁺ T cells in the lungs of the challenged mice that were capable of secreting double or triple cytokines, including IFN-γ, IL-2, and TNF-α. Our study thus demonstrates that LppZ is of strong immunogenicity during M.tb infection in both humans and mice and has the ability to trigger effective innate and cellular immunity. Considering the limitations of candidate antigens in the pipeline of TB vaccine development, LppZ-mediated immune protection against M.tb challenge in the mouse model implies its potential application in vaccine development.

Study of CD27 and CCR4 Markers on Specific CD4+ T-Cells as Immune Tools for Active and Latent Tuberculosis Management

The immunological characterization of different cell markers has opened the possibility of considering them as immune tools for tuberculosis (TB) management, as they could correlate with TB latency/disease status and outcome. CD4⁺ T-cells producing IFN-γ⁺ with a low expression of CD27 have been described as an active TB marker. In addition, there are unknown homing receptors related to TB, such as CCR4, which might be useful for understanding TB pathogenesis. The aim of our study is focused on the assessment of several T-cell subsets to understand immune-mechanisms in TB. This phenotypic immune characterization is based on the study of the specific immune responses of T-cells expressing CD27 and/or CCR4 homing markers. Subjects enrolled in the study were: (i) 22 adult patients with active TB, and (ii) 26 individuals with latent TB infection (LTBI). Blood samples were drawn from each patient. The expression of CD27 and/or CCR4 markers were analyzed within CD4⁺ T-cells producing: (i) IFN-γ⁺, (ii) TNF-α⁺, (iii) TNF-α⁺IFN-γ⁺, and (iv) IFN-γ⁺ and/or TNF-α⁺. The percentage of CD27⁻ within all CD4⁺ T-cell populations analyzed was significantly higher on active TB compared to LTBI after PPD or ESAT-6/CFP-10 stimulation. As previously reported, a ratio based on the CD27 median fluorescence intensity (MFI) was also explored (MFI of CD27 in CD4⁺ T-cells over MFI of CD27 in IFN-γ⁺CD4⁺ T-cells), being significantly increased during disease (p < 0.0001 after PPD or ESAT-6/CFP-10 stimulation). This ratio was also assessed on the other CD4⁺ T-cells functional profiles after specific stimulation, being significantly associated with active TB. Highest diagnostic accuracies for active TB (AUC ≥ 0.91) were achieved for: (i) CD27 within IFN-γ⁺TNF-α⁺CD4⁺ T-cells in response to ESAT-6/CFP-10, (ii) CD27 and CCR4 markers together within IFN-γ⁺CD4⁺ T-cells in response to PPD, and (iii) CD27 MFI ratio performed on IFN-γ⁺TNF-α⁺CD4⁺ T-cells after ESAT-6/CFP-10 stimulation. The lowest diagnostic accuracy was observed when CCR4 marker was evaluated alone (AUC ≤ 0.77). CD27 and CCR4 expression detection could serve as a good method for immunodiagnosis. Moreover, the immunological characterization of markers/subset populations could be a promising tool for understanding the biological basis of the disease.

The Regulation of Inflammation by Innate and Adaptive Lymphocytes

Inflammation plays an essential role in the control of pathogens and in shaping the ensuing adaptive immune responses. Traditionally, innate immunity has been described as a rapid response triggered through generic and nonspecific means that by definition lacks the ability to remember. Recently, it has become clear that some innate immune cells are epigenetically reprogrammed or “imprinted” by past experiences. These “trained” innate immune cells display altered inflammatory responses upon subsequent pathogen encounter. Remembrance of past pathogen encounters has classically been attributed to cohorts of antigen-specific memory T and B cells following the resolution of infection. During recall responses, memory T and B cells quickly respond by proliferating, producing effector cytokines, and performing various effector functions. An often-overlooked effector function of memory CD4 and CD8 T cells is the promotion of an inflammatory milieu at the initial site of infection that mirrors the primary encounter. This memory-conditioned inflammatory response, in conjunction with other secondary effector T cell functions, results in better control and more rapid resolution of both infection and the associated tissue pathology. Recent advancements in our understanding of inflammatory triggers, imprinting of the innate immune responses, and the role of T cell memory in regulating inflammation are discussed.

Elevated Pre-Antiretroviral Therapy CD39+CD8+ T Cell Frequency Is Associated With Early Mortality in Advanced Human Immunodeficiency Virus/Tuberculosis Co-infection

Correlates of death soon after antiretroviral therapy (ART) initiation remain unclear. We investigated the association between expression of CD39, a novel immune exhaustion marker, and early mortality in patients with human immunodeficiency virus/tuberculosis co-infection. Elevated pre-ART CD39+CD8+ T cell frequency was independently associated with mortality within 6 months of ART initiation.

Recombinant BCG Expressing ESX-1 of Mycobacterium marinum Combines Low Virulence with Cytosolic Immune Signaling and Improved TB Protection

Recent insights into the mechanisms by which Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, is recognized by cytosolic nucleotide sensors have opened new avenues for rational vaccine design. The only licensed anti-tuberculosis vaccine, Mycobacterium bovis BCG, provides limited protection. A feature of BCG is the partial deletion of the ESX-1 type VII secretion system, which governs phagosomal rupture and cytosolic pattern recognition, key intracellular phenotypes linked to increased immune signaling. Here, by heterologously expressing the esx-1 region of Mycobacterium marinum in BCG, we engineered a low-virulence, ESX-1-proficient, recombinant BCG (BCG::ESX-1^Mmar) that induces the cGas/STING/TBK1/IRF-3/type I interferon axis and enhances AIM2 and NLRP3 inflammasome activity, resulting in both higher proportions of CD8⁺ T cell effectors against mycobacterial antigens shared with BCG and polyfunctional CD4⁺ Th1 cells specific to ESX-1 antigens. Importantly, independent mouse vaccination models show that BCG::ESX-1^Mmar confers superior protection relative to parental BCG against challenges with highly virulent M. tuberculosis.

Listeria-Vectored Vaccine Expressing the Mycobacterium tuberculosis 30-Kilodalton Major Secretory Protein via the Constitutively Active prfA* Regulon Boosts Mycobacterium bovis BCG Efficacy against Tuberculosis

A potent vaccine against tuberculosis, one of the world's deadliest diseases, is needed to enhance the immunity of people worldwide, most of whom have been vaccinated with the partially effective Mycobacterium bovis BCG vaccine. Here we investigate novel live attenuated recombinant Listeria monocytogenes (rLm) vaccines expressing the Mycobacterium tuberculosis 30-kDa major secretory protein (r30/antigen 85B [Ag85B]) (rLm30) as heterologous booster vaccines in animals primed with BCG. Using three attenuated L. monocytogenes vectors, L. monocytogenes ΔactA (LmI), L. monocytogenes ΔactA ΔinlB (LmII), and L. monocytogenes ΔactA ΔinlB prfA* (LmIII), we constructed five rLm30 vaccine candidates expressing r30 linked in frame to the L. monocytogenes listeriolysin O signal sequence and driven by the hly promoter (h30) or linked in frame to the ActA N-terminal 100 amino acids and driven by the actA promoter (a30). All five rLm30 vaccines secreted r30 in broth and macrophages; while rLm30 expressing r30 via a constitutively active prfA* regulon (rLmIII/a30) expressed the largest amount of r30 in broth culture, all five rLm30 vaccines expressed equivalent amounts of r30 in infected macrophages. In comparative studies, boosting of BCG-immunized mice with rLmIII/a30 induced the strongest antigen-specific T-cell responses, including splenic and lung polyfunctional CD4⁺ T cells expressing the three cytokines interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and interleukin-2 (IL-2) (P < 0.001) and splenic and lung CD8⁺ T cells expressing IFN-γ (P < 0.0001). In mice and guinea pigs, the rLmIII/a30 and rLmI/h30 vaccines were generally more potent booster vaccines than r30 with an adjuvant and a recombinant adenovirus vaccine expressing r30. In a setting in which BCG alone was highly immunoprotective, boosting of mice with rLmIII/a30, the most potent of the vaccines, significantly enhanced protection against aerosolized M. tuberculosis (P < 0.01).

Comprehensive definition of human immunodominant CD8 antigens in tuberculosis

Despite widespread use of the Bacillus Calmette-Guerin vaccine, tuberculosis, caused by infection with Mycobacterium tuberculosis, remains a leading cause of morbidity and mortality worldwide. As CD8⁺ T cells are critical to tuberculosis host defense and a phase 2b vaccine trial of modified vaccinia Ankara expressing Ag85a that failed to demonstrate efficacy, also failed to induce a CD8⁺ T cell response, an effective tuberculosis vaccine may need to induce CD8⁺ T cells. However, little is known about CD8, as compared to CD4, antigens in tuberculosis. Herein, we report the results of the first ever HLA allele independent genome-wide CD8 antigen discovery program. Using CD8⁺ T cells derived from humans with latent tuberculosis infection or tuberculosis and an interferon-γ ELISPOT assay, we screened a synthetic peptide library representing 10% of the Mycobacterium tuberculosis proteome, selected to be enriched for Mycobacterium tuberculosis antigens. We defined a set of immunodominant CD8 antigens including part or all of 74 Mycobacterium tuberculosis proteins, only 16 of which are previously known CD8 antigens. Immunogenicity was associated with the degree of expression of mRNA and protein. Immunodominant antigens were enriched in cell wall proteins with preferential recognition of Esx protein family members, and within proteins comprising the Mycobacterium tuberculosis secretome. A validation study of immunodominant antigens demonstrated that these antigens were strongly recognized in Mycobacterium tuberculosis-infected individuals from a tuberculosis endemic region in Africa. The tuberculosis vaccine field will likely benefit from this greatly increased known repertoire of CD8 immunodominant antigens and definition of properties of Mycobacterium tuberculosis proteins important for CD8 antigenicity.

Specific bacterial proteins have been found that drive effective immune responses to tuberculosis, with use in making more effective vaccines. Immunity to tuberculosis (TB) is facilitated by two types of white blood cell; however, most research has focused on one: the CD4⁺ T cell. Deborah A. Lewinsohn and David Lewinsohn, of the Oregon Health & Science University, USA, and collaborators lay out the essential functions of the oft-neglected CD8⁺ T cell, and undertook a broad approach to catalogue and define the bacterial proteins that activate the CD8⁺ T cell response. The team found that TB-infected humans reacted strongly to their protein library, and described several characteristics of CD8⁺ T cell ‘antigens’ (activators of immune cells) that will likely prove highly useful in the design of more protective TB vaccines.

Expression of Cathepsin S in BCG converts it into a pro-apoptotic and highly immunogenic strain

BACKGROUND

BCG vaccine, introduced almost 100years ago, is the only option to prevent TB disease. It effectively protects newborns from meningeal TB but fails to prevent adult pulmonary TB. TB kills 1.3million people annually in areas where BCG vaccination is widely practiced. Thus, more effective TB vaccines are urgently needed. Others and we have shown that BCG mimics features of virulent M. tuberculosis, in particular attenuation of essential macrophage functions such as phagosome maturation and antigen presentation. One of these studies revealed that defect in antigen presentation is largely due to down-regulation of the cysteine protease Cathepsin S (CatS), which prevents MHC II molecule maturation and proper antigen peptide loading. Recent studies also suggested a potential role for cysteine proteases in the regulation of apoptosis, a key cellular process used by the macrophage to (i) contain and process ingested bacteria and (ii) facilitate cross-talk antigen presentation between the macrophage and dendritic cells.

METHOD

To reverse the phenotype of vaccine-mediated macrophage attenuation, we engineered a novel BCG strain that expresses and secretes active CatS (rBCG-CatS) to examine its pro-apoptotic properties in vitro, and subsequently, immunogenicity in mice.

RESULTS

Transcriptomic profiling of macrophages infected with rBCG-CatS, but not BCG, revealed upregulation of key pro-apoptotic genes and downregulation of anti-apoptotic genes, which were further confirmed by RT-qPCR analyses of expression of selected genes. Macrophages infected with rBCG-CatS undergo apoptosis as indicated by increased levels of annexin V staining and intracellular caspase-3 cleavage. Consistent with these findings, mice vaccinated with rBCG-CatS showed increased antigen-specific CD4⁺ T-cell responses, as well as enhanced cytokine production and proliferation in CD4⁺ upon ex vivo re-stimulation.

CONCLUSION

Collectively, this study shows that a pro-apoptotic BCG strain alleviates adverse traits of the wild-type strain, resulting in a highly immunogenic TB vaccine.

Targeting Innate-Like T Cells in Tuberculosis

Peptide-specific conventional T cells have been major targets for designing most antimycobacterial vaccines. Immune responses mediated by conventional T cells exhibit a delayed onset upon primary infection and are highly variable in different human populations. In contrast, innate-like T cells quickly respond to pathogens and display effector functions without undergoing extensive clonal expansion. Specifically, the activation of innate-like T cells depends on the promiscuous interaction of highly conserved antigen-presenting molecules, non-peptidic antigens, and likely semi-invariant T cell receptors. In antimicrobial immune responses, mucosal-associated invariant T cells are activated by riboflavin precursor metabolites presented by major histocompatibility complex-related protein I, while lipid-specific T cells including natural killer T cells are activated by lipid metabolites presented by CD1 proteins. Multiple innate-like T cell subsets have been shown to be protective or responsive in mycobacterial infections. Through rapid cytokine secretion, innate-like T cells function in early defense and memory response, offering novel advantages over conventional T cells in the design of anti-tuberculosis strategies.

Role and contribution of pulmonary CD103+ dendritic cells in the adaptive immune response to Mycobacterium tuberculosis

Despite international control programmes, the global burden of tuberculosis remains enormous. Efforts to discover novel drugs have largely focused on targeting the bacterium directly. Alternatively, manipulating the host immune response may represent a valuable approach to enhance immunological clearance of the bacilli, but necessitates a deeper understanding of the immune mechanisms associated with protection against Mycobacterium tuberculosis infection. Here, we examined the various dendritic cells (DC) subsets present in the lung and draining lymph nodes (LN) from mice intra-tracheally infected with M. tuberculosis. We showed that although limited in number, pulmonary CD103⁺ DCs appeared to be involved in the initial transport of mycobacteria to the draining mediastinal LN and subsequent activation of T cells. Using CLEC9A-DTR transgenic mice enabling the inducible depletion of CD103⁺ DCs, we established that this DC subset contributes to the control of mycobacterial burden and plays a role in the early activation of T cells, in particular CD8⁺ T cells. Our findings thus support a previously unidentified role for pulmonary CD103⁺ DCs in the rapid mobilization of mycobacteria from the lungs to the draining LN soon after exposure to M. tuberculosis, which is a critical step for the development of the host adaptive immune response.

Metformin: Candidate host-directed therapy for tuberculosis in diabetes and non-diabetes patients

Despite major advances in tuberculosis (TB) control, TB continues to be a leading cause of death worldwide. The discovery of new anti-TB treatment drugs and regimens that target drug-sensitive and drug-resistant TB are being complemented with a search for adjunct host-directed therapies that synergize for Mycobacterium tuberculosis (Mtb) elimination. The goal of host-directed therapies is to boost immune mechanisms that diminish excess inflammation to reduce lung tissue damage and limit Mtb growth. Metformin is the most commonly-used medication for type 2 diabetes, and a candidate for host-directed therapy for TB. Preliminary data suggests metformin may be beneficial for TB control by reducing the deleterious inflammation associated with immune pathology and enhancing the anti-mycobacterial activity of immune cells. In this review I summarize current findings, knowledge gaps and the potential benefits as well as points of caution for using metformin as adjunct therapy for TB in patients with and without type 2 diabetes.

Adenylate kinase: a novel antigen for immunodiagnosis and subunit vaccine against tuberculosis

Mycobacterium tuberculosis (M.tb)-derived antigens capable of inducing strong cellular and/or humoral responses are potential targets for both immunodiagnosis and vaccine development against tuberculosis (TB). In the present study, we identified adenylate kinase (ADK, Rv0733) as an antigen that induces high cellular and antibody responses in active TB patients. We consequently tested the use of ADK-specific T cells and antibodies as biomarkers for TB diagnosis. The ADK-specific IFN-γ-producing cells detected by ELISPOT assay showed a sensitivity of 85.0 % and specificity of 94.15 % for TB diagnosis while ADK-specific IgG antibody showed a sensitivity of 40.35 % and specificity of 96.43 %. Combining ADK-specific cellular and antibody responses increased the sensitivity to 91.59 % and the specificity to 96.15 %. Immunogenicity and protection against M.tb infection were further tested in a murine model. Immunization with ADK protein elicited strong specific T- and B-cell responses, and provided protection against the virulent H37Rv stain of M.tb resulting in lower bacilli load in the spleens and lungs. More ADK-specific polyfunctional Th1 cells were observed in the lungs when compared to adjuvant-immunized mice. ADK thus may serve as a novel M.tb antigen for TB immunodiagnosis and development of subunit vaccines.

KEY MESSAGES

ADK induces strong immune responses both in humans and mice. ADK-specific IFN-γ production and B-cell responses have high potential for TB diagnosis. ADK immunization provides protection against M.tb infection.