Immunological basis of early clearance of Mycobacterium tuberculosis infection: the role of natural killer cells

Mycobacterium tuberculosis: immune response, biomarkers, and therapeutic intervention

Although tuberculosis (TB) is an infectious disease, the progression of the disease following Mycobacterium tuberculosis (MTB) infection is closely associated with the host's immune response. In this review, a comprehensive analysis of TB prevention, diagnosis, and treatment was conducted from an immunological perspective. First, we delved into the host's immune response mechanisms against MTB infection as well as the immune evasion mechanisms of the bacteria. Addressing the challenges currently faced in TB diagnosis and treatment, we also emphasized the importance of protein, genetic, and immunological biomarkers, aiming to provide new insights for early and personalized diagnosis and treatment of TB. Building upon this foundation, we further discussed intervention strategies involving chemical and immunological treatments for the increasingly critical issue of drug-resistant TB and other forms of TB. Finally, we summarized TB prevention, diagnosis, and treatment challenges and put forward future perspectives. Overall, these findings provide valuable insights into the immunological aspects of TB and offer new directions toward achieving the WHO's goal of eradicating TB by 2035.

Vaccine development against tuberculosis before and after Covid-19

Coronavirus disease (Covid-19) has not only shaped awareness of the impact of infectious diseases on global health. It has also provided instructive lessons for better prevention strategies against new and current infectious diseases of major importance. Tuberculosis (TB) is a major current health threat caused by Mycobacterium tuberculosis (Mtb) which has claimed more lives than any other pathogen over the last few centuries. Hence, better intervention measures, notably novel vaccines, are urgently needed to accomplish the goal of the World Health Organization to end TB by 2030. This article describes how the research and development of TB vaccines can benefit from recent developments in the Covid-19 vaccine pipeline from research to clinical development and outlines how the field of TB research can pursue its own approaches. It begins with a brief discussion of major vaccine platforms in general terms followed by a short description of the most widely applied Covid-19 vaccines. Next, different vaccination regimes and particular hurdles for TB vaccine research and development are described. This specifically considers the complex immune mechanisms underlying protection and pathology in TB which involve innate as well as acquired immune mechanisms and strongly depend on fine tuning the response. A brief description of the TB vaccine candidates that have entered clinical trials follows. Finally, it discusses how experiences from Covid-19 vaccine research, development, and rollout can and have been applied to the TB vaccine pipeline, emphasizing similarities and dissimilarities.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

Natural Killer Repertoire Restoration in TB/HIV Co-Infected Individuals Experienced an Immune Reconstitution Syndrome (CAMELIA Trial, ANRS 12153)

IRIS is a common complication in HIV-infected patients treated for tuberculosis (TB) and cART. Our aim was to evaluate NK cell reconstitution in HIV-infected patients with TB-IRIS compared to those without IRIS. 147 HIV-infected patients with TB from the CAMELIA trial were enrolled. HIV+TB+ patients were followed for 32 weeks. The NK cell repertoire was assessed in whole blood at different time points. As CAMELIA has two arms (early and late cART initiation), we analysed them separately. At enrolment, individuals had low CD4 cell counts (27 cells/mm3) and high plasma viral loads (5.76 and 5.50 log/mL for IRIS and non-IRIS individuals, respectively). Thirty-seven people developed IRIS (in the early and late arms). In the early and late arms, we observed similar proportions of total NK and NK cell subsets in TB-IRIS and non-IRIS individuals during follow-up, except for the CD56dimCD16pos (both arms) and CD56dimCD16neg (late arm only) subsets, which were higher in TB-IRIS and non-IRIS individuals, respectively, after cART. Regarding the repertoire and markers of NK cells, significant differences (lower expression of NKp30, NKG2A (CD159a), NKG2D (CD314) were observed in TB-IRIS compared to non-IRIS individuals after the start of cART. In the late arm, some changes (increased expression of CD69, NKG2C, CD158i) were observed in TB-IRIS compared to non-IRIS individuals, but only before cART initiation (during TB treatment). KIR expression by NK cells (CD158a and CD158i) was similar in both groups. CD69 expression by NK cells decreased in all groups. Expression of the NCR repertoire (NKp30, NKp44, NKp46) has similar kinetics in TB-IRIS subjects compared to non-IRIS subjects regardless of the arm analysed. NK cell reconstitution appeared to be better in TB-IRIS subjects. Although NK cell reconstitution is impaired in HIV infection after cART, as previously reported, it does not appear to be affected by the development of IRIS in HIV and TB-infected individuals.

Initial immune response after exposure to Mycobacterium tuberculosis or to SARS-COV-2: similarities and differences

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) and Coronavirus disease-2019 (COVID-19), whose etiologic agent is severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), are currently the two deadliest infectious diseases in humans, which together have caused about more than 11 million deaths worldwide in the past 3 years. TB and COVID-19 share several aspects including the droplet- and aerosol-borne transmissibility, the lungs as primary target, some symptoms, and diagnostic tools. However, these two infectious diseases differ in other aspects as their incubation period, immune cells involved, persistence and the immunopathological response. In this review, we highlight the similarities and differences between TB and COVID-19 focusing on the innate and adaptive immune response induced after the exposure to Mtb and SARS-CoV-2 and the pathological pathways linking the two infections. Moreover, we provide a brief overview of the immune response in case of TB-COVID-19 co-infection highlighting the similarities and differences of each individual infection. A comprehensive understanding of the immune response involved in TB and COVID-19 is of utmost importance for the design of effective therapeutic strategies and vaccines for both diseases.

Decreased Expression of CD314 by NK Cells Correlates with Their Ability to Respond by Producing IFN-γ after BCG Moscow Vaccination and Is Associated with Distinct Early Immune Responses

The immune response to vaccines is complex and results in various outcomes. BCG vaccination induces innate and specific responses that can lead to protection against tuberculosis, and cross-protection against other infections. NK cells have been associated with BCG-induced protection. Therefore, we hypothesize that differences in NK cell status before BCG vaccination may have a role in the ability of BCG to activate the immune response. Participants of a clinical trial were evaluated after BCG vaccination. The participants were assigned to different groups according to variation in IFN-γ expression by NK cells between days 1 and 15 after BCG vaccination. Individuals that presented a higher increase in IFN-γ expression by NK cells presented reduced CD314 expression at day 1, and after vaccination an increase in inflammatory NK cells and CD4 T-cell expression of IL-17. A negative correlation between expression of CD314 at day 1 and that of IFN-γ by NK cells after BCG vaccination was observed. Participants with lower of IFN-γ expression by NK cells after BCG vaccination presented an increase in the cytotoxic NK subpopulation and CD4 T-cell expression of IL-17 and IFN-γ. In conclusion, the expression of CD314 by NK cells before BCG vaccination influences their IFN-γ responses, generation of NK subpopulations, and the specific T immune response at 15 days after vaccination.

NK cell phenotypic profile during active TB in people living with HIV-evolution during TB treatment and implications for bacterial clearance and disease severity

Natural killer (NK) cells, key effector cells of the innate immune system, play an important role in the clearance and control of Mycobacterium tuberculosis and HIV infections. Here, we utilized peripheral blood specimens from the Improving Retreatment Success CAPRISA 011 study to characterize NK cell phenotypes during active TB in individuals with or without HIV co-infection. We further assessed the effects of TB treatment on NK cell phenotype, and characterized the effects of NK cell phenotypes during active TB on mycobacterial clearance and TB disease severity measured by the presence of lung cavitation. TB/HIV co-infection led to the expansion of functionally impaired CD56neg NK cell subset. TB treatment completion resulted in restoration of total NK cells, NK cell subset redistribution and downregulation of several NK cell activating and inhibitory receptors. Higher percentage of peripheral CD56bright cells was associated with longer time to culture conversion, while higher expression of NKp46 on CD56dim NK cells was associated with lower odds of lung cavitation in the overall cohort and the TB/HIV co-infected participants. Together these results provide a detailed description of peripheral NK cells in TB and TB/HIV co-infection and yield insights into their role in TB disease pathology.

Immune checkpoint modulating T cells and NK cells response to Mycobacterium tuberculosis infection

Many subversive mechanisms promote the occurrence and development of chronic infectious diseases and cancer, among which the down-regulated expression of immune-activating receptors and the enhanced expression of immune-inhibitory receptors accelerate the occurrence and progression of the disease. Recently, the use of immune checkpoint inhibitors has shown remarkable efficacy in the treatment of tumors in multiple organs. However, the expression of immune checkpoint molecules on natural killer (NK) cells by Mycobacterium tuberculosis (Mtb) infection and its impact on NK cell effector functions have been poorly studied. In this review, we focus on what is currently known about the expression of various immune checkpoints in NK cells following Mtb infection and how it alters NK cell-mediated host cytotoxicity and cytokine secretion. Unraveling the function of NK cells after the infection of host cells by Mtb is crucial for a comprehensive understanding of the innate immune mechanism of NK cells involved in tuberculosis and the evaluation of the efficacy of immunotherapies using immune checkpoint inhibitors to treat tuberculosis. In view of some similarities in the immune characteristics of T cells and NK cells, we reviewed the molecular mechanism of the interaction between T cells and Mtb, which can help us to further understand and explore the specific interaction mechanism between NK cells and Mtb.

Identification of autoimmune markers in pulmonary tuberculosis

Introduction

Pathogenesis of many autoimmune diseases is mainly promoted by poorly regulated and/or wrong targeted immune response to pathogens including M. tuberculosis. Autoimmunity is one of the processes with are characteristics of tuberculosis (Tbc). The aim was to determine the autoimmune clinical and immunological features in patients with pulmonary Tbc.

Materials and methods

A prospective comparative study was performed in 2017 - 2019 with the inclusion of 46 patients with Tbc. The trigger factors and clinical manifestations, autoantibodies, peripheral blood B cell subsets were stained with fluorochrome-conjugated monoclonal antibodies. 40 healthy volunteers in the control group, were matched for age with no chronic diseases, contacts with TB patients and changes in their laboratory parameters. A statistical analysis was done with GraphPad Prism 6, Statistica 10 (Statsoft) and MedCalc - version 18.2.1 values.

Results

There were no significant ASIA triggers in Tbc patients and control group. 21.1% of Tbc patients had a high level of a rheumatoid factor and in 47.4% complement system factor C3 was high; anti-MCV was detected in 60.7% of Tbc patients. Relative and absolute frequencies of "naïve" Bm1 cells and eBm5 were significantly decreased and activated pre-germinal-center Bm2' cells were significantly increased in Tbc patients. The CD24++CD38++ B cells were increased in Tbc vs control group (10.25% vs 5.42%), p < 0.001, and 19 cell/1μL (10; 290 vs 11 cell/1μL (6; 20), p = 0.029, respectively). The frequency of CXCR3+CCR4- Tfh1 cells was significantly lower in Tbc vs control one (26.52% vs. 31.00%, p = 0.004), while CXCR3-CCR4+ Tfh2 cells were increased in Tbc (20.31% vs. controls (16.56%, p = 0.030). The absolute numbers of Tfh1 cells were decreased in the Tbc vs. control (24 cell/1μL vs. 37 cell/1μL p = 0.005).

Conclusion

The results of our study showed that the detection of a rheumatoid factor, the components of complement system and anti-MCV in complex with alterations in B cells and follicular Th cell subsets may indicate a presence of autoimmunity in the pathogenesis of tuberculosis, but they are not specific. The indicators of autoimmune-related provide new opportunities in the Tbc treatment.

Attenuated Cytokine-Induced Memory-Like Natural Killer Cell Responses to Mycobacterium tuberculosis in Tuberculosis Patients

Purpose

This study aimed to investigate the phenotype, proliferation and functional alterations of cytokine-induced memory-like natural killer (CIML NK) cells from healthy subjects and TB patients, and assessed the efficacy of CIML NK cells in response to H37Rv-infected U937 cells in vitro.

Methods

Fresh peripheral blood mononuclear cells (PBMCs) were isolated from healthy people and tuberculosis patients and activated for 16h using low-dose IL-15, or IL-12, IL-15, IL-18 combination or IL-12, IL-15, IL-18 and MTB H37Rv lysates, respectively, followed by low-dose IL-15 maintenance for another 7 days. Then, the PBMCs were co-cultured with K562 and H37Rv-infected U937, and the purified NK cells were co-cultured with H37Rv infected U937. The phenotype, proliferation and response function of CIML NK cells were assessed using flow cytometry. Finally, colony forming units were enumerated to confirm the survival of intracellular MTB.

Results

CIML NK phenotypes from TB patients were similar to healthy controls. CIML NK cells undergo higher rates of proliferation after IL-12/15/18 pre-activation. Moreover, the poor expansion potential of CIML NK cells co-stimulated with MTB lysates. CIML NK cells from healthy individuals showed enhanced IFN-γ functional to H37Rv infected U937 cells, along with significantly enhanced killing of H37Rv. However, the CIML NK cells from TB patients show attenuated IFN-γ production and now enhanced the ability of killing intracellular MTB compared to those from healthy donors after co-cultured with H37Rv infected U937.

Conclusion

CIML NK cells from healthy individuals exist the increased ability of IFN-γ secretion and boosted anti-MTB activity in vitro, which from TB patients show impaired IFN-γ production and no enhanced anti-MTB activity compared to those from healthy donors. Additionally, we observe the poor expansion potential of CIML NK cells co-stimulated with antigens from MTB. These results open up new possibilities for NK cell-based anti-tuberculosis immunotherapeutic strategies.

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.

Impact of an Immune Modulator Mycobacterium-w on Adaptive Natural Killer Cells and Protection Against COVID-19

The kinetics of NKG2C+ adaptive natural killer (ANK) cells and NKG2A+inhibitory NK (iNK) cells with respect to the incidence of SARS-CoV-2 infection were studied for 6 months in a cohort of healthcare workers following the administration of the heat-killed Mycobacterium w (Mw group) in comparison to a control group. In both groups, corona virus disease 2019 (COVID-19) correlated with lower NKG2C+ANK cells at baseline. There was a significant upregulation of NKG2C expression and IFN-γ release in the Mw group (p=0.0009), particularly in those with a lower baseline NKG2C expression, along with the downregulation of iNK cells (p<0.0001). This translated to a significant reduction in the incidence and severity of COVID-19 in the Mw group (incidence risk ratio-0.15, p=0.0004). RNA-seq analysis at 6 months showed an upregulation of the ANK pathway genes and an enhanced ANK-mediated antibody-dependent cellular cytotoxicity (ADCC) signature. Thus, Mw was observed to have a salutary impact on the ANK cell profile and a long-term upregulation of ANK-ADCC pathways, which could have provided protection against COVID-19 in a non-immune high-risk population.