The Rate of CD4 T Cell Entry into the Lungs during Mycobacterium tuberculosis Infection Is Determined by Partial and Opposing Effects of Multiple Chemokine Receptors

Heterogeneity in lung macrophage control of Mycobacterium tuberculosis is modulated by T cells

Following Mycobacterium tuberculosis infection, alveolar macrophages are initially infected but ineffectively restrict bacterial replication. The distribution of M. tuberculosis among different cell types in the lung changes with the onset of T cell immunity when the dominant infected cellular niche shifts from alveolar to monocyte-derived macrophages (MDM). We hypothesize that changes in bacterial distribution among different cell types is driven by differences in T cell recognition of infected cells and their subsequent activation of antimicrobial effector mechanisms. We show that CD4 and CD8 T cells efficiently eliminate M. tuberculosis infection in alveolar macrophages, but they have less impact on suppressing infection in MDM, which may be a bacterial niche. Importantly, CD4 T cell responses enhance MDM recruitment to the lung. Thus, the outcome of infection depends on the interaction between the T cell subset and the infected cell; both contribute to the resolution and persistence of the infection.

Oxysterols in Infectious Diseases

Oxysterols have emerged as important bioactive lipids in the immune response to infectious diseases. This chapter discusses our current knowledge of oxysterols and their receptors in bacterial and viral infections of the respiratory and gastrointestinal tracts. Oxysterols are produced in response to infections and have multiple roles including chemotaxis of immune cells to the site of infection and regulation of inflammation. Some oxysterols have been shown to possess antiviral or antibacterial activity.Lastly, we delve into the emerging mechanisms of action of oxysterols. Oxysterols can enhance host cell resistance via reduction of membrane accessible cholesterol, modulate membrane immune signalling, and impact inflammasome activation and efferocytosis.

CD30 co-stimulation drives differentiation of protective T cells during Mycobacterium tuberculosis infection

Control of Mycobacterium tuberculosis (Mtb) infection requires generation of T cells that migrate to granulomas, complex immune structures surrounding sites of bacterial replication. Here we compared the gene expression profiles of T cells in pulmonary granulomas, bronchoalveolar lavage, and blood of Mtb-infected rhesus macaques to identify granuloma-enriched T cell genes. TNFRSF8/CD30 was among the top genes upregulated in both CD4 and CD8 T cells from granulomas. In mice, CD30 expression on CD4 T cells is required for survival of Mtb infection, and there is no major role for CD30 in protection by other cell types. Transcriptomic comparison of WT and CD30-/- CD4 T cells from the lungs of Mtb-infected mixed bone marrow chimeric mice showed that CD30 directly promotes CD4 T cell differentiation and the expression of multiple effector molecules. These results demonstrate that the CD30 co-stimulatory axis is highly upregulated on granuloma T cells and is critical for protective T cell responses against Mtb infection.

HIF-1 stabilization in T cells hampers the control of Mycobacterium tuberculosis infection

The hypoxia-inducible factors (HIFs) regulate the main transcriptional pathway of response to hypoxia in T cells and are negatively regulated by von Hippel-Lindau factor (VHL). But the role of HIFs in the regulation of CD4 T cell responses during infection with M. tuberculosis isn’t well understood. Here we show that mice lacking VHL in T cells (Vhl cKO) are highly susceptible to infection with M. tuberculosis, which is associated with a low accumulation of mycobacteria-specific T cells in the lungs that display reduced proliferation, altered differentiation and enhanced expression of inhibitory receptors. In contrast, HIF-1 deficiency in T cells is redundant for M. tuberculosis control. Vhl cKO mice also show reduced responses to vaccination. Further, VHL promotes proper MYC-activation, cell-growth responses, DNA synthesis, proliferation and survival of CD4 T cells after TCR activation. The VHL-deficient T cell responses are rescued by the loss of HIF-1α, indicating that the increased susceptibility to M. tuberculosis infection and the impaired responses of Vhl-deficient T cells are HIF-1-dependent.

The role of hypoxia inducible factors in infection and immune response is unclear. Here, the authors study their impact on the regulation of T cells responses during Mycobacteria tuberculosis infection using transcriptomics, flow cytometry and in vivo infection.

Mathematical Modeling to Guide Experimental Design: T Cell Clustering as a Case Study

Mathematical modeling provides a rigorous way to quantify immunological processes and discriminate between alternative mechanisms driving specific biological phenomena. It is typical that mathematical models of immunological phenomena are developed by modelers to explain specific sets of experimental data after the data have been collected by experimental collaborators. Whether the available data are sufficient to accurately estimate model parameters or to discriminate between alternative models is not typically investigated. While previously collected data may be sufficient to guide development of alternative models and help estimating model parameters, such data often do not allow to discriminate between alternative models. As a case study, we develop a series of power analyses to determine optimal sample sizes that allow for accurate estimation of model parameters and for discrimination between alternative models describing clustering of CD8 T cells around Plasmodium liver stages. In our typical experiments, mice are infected intravenously with Plasmodium sporozoites that invade hepatocytes (liver cells), and then activated CD8 T cells are transferred into the infected mice. The number of T cells found in the vicinity of individual infected hepatocytes at different times after T cell transfer is counted using intravital microscopy. We previously developed a series of mathematical models aimed to explain highly variable number of T cells per parasite; one of such models, the density-dependent recruitment (DDR) model, fitted the data from preliminary experiments better than the alternative models, such as the density-independent exit (DIE) model. Here, we show that the ability to discriminate between these alternative models depends on the number of parasites imaged in the analysis; analysis of about [Formula: see text] parasites at 2, 4, and 8 h after T cell transfer will allow for over 95% probability to select the correct model. The type of data collected also has an impact; following T cell clustering around individual parasites over time (called as longitudinal (LT) data) allows for a more precise and less biased estimates of the parameters of the DDR model than that generated from a more traditional way of imaging individual parasites in different liver areas/mice (cross-sectional (CS) data). However, LT imaging comes at a cost of a need to keep the mice alive under the microscope for hours which may be ethically unacceptable. We finally show that the number of time points at which the measurements are taken also impacts the precision of estimation of DDR model parameters; in particular, measuring T cell clustering at one time point does not allow accurately estimating all parameters of the DDR model. Using our case study, we propose a general framework on how mathematical modeling can be used to guide experimental designs and power analyses of complex biological processes.

Two sides of the same coin: Protective versus pathogenic CD4+ resident memory T cells

The ability of the adaptive immune system to form memory is key to providing protection against secondary infections. Resident memory T cells (T_RM) are specialized T cell populations that reside within tissue sites where they await reencounter with their cognate antigen. T_RM are distinct from circulating memory cells, including central and effector memory T cells, both functionally and transcriptionally. Since the discovery of T_RM, most research has focused on CD8⁺ T_RM, despite that CD4⁺ T_RM are also abundant in most tissues. In the past few years, more evidence has emerged that CD4⁺ T_RM can contribute both protective and pathogenic roles in disease. A complexity inherent to the CD4⁺ T_RM field is the ability of CD4⁺ T cells to polarize into a multitude of distinct subsets and recognize not only viruses and intracellular bacteria but also extracellular bacteria, fungi, and parasites. In this review, we outline the key features of CD4⁺ T_RM in health and disease, including their contributions to protection against SARS-CoV-2 and potential contributions to immunopathology associated with COVID-19.

Designing of a Chimeric Vaccine Using EIS (Rv2416c) Protein Against Mycobacterium tuberculosis H37Rv: an Immunoinformatics Approach

Mycobacterium tuberculosis (Mtb) is a respiratory pathogen that causes tuberculosis (TB). There are a large number of proteins that are involved in the pathogenesis of TB. Stimulating the immune response against TB is very important to clear the pathogens from host. In the present study, an immunoinformatics conduit is used for designing an epitope based chimeric vaccine against TB. Enhanced intracellular survival (EIS) protein from Mtb is used for designing the chimeric vaccine. One B cell epitope, 8 cytotoxic T lymphocyte (CTL), and 6 helper T lymphocyte (HTL) epitopes were predicted based on the MHC allele binding, immunogenicity, antigenicity, allergenicity, toxicity and IFN epitopes. The selected epitopes were used for chimeric vaccine designing. Furthermore, 3D structure elucidation, structural refinement and validation of the designed chimeric vaccine were carried out. The 3D structure was used for protein-protein docking studies with Toll-like receptor 4 (TLR-4), followed by molecular dynamic simulation (MDS) and the interaction between the chimeric vaccine and TLR-4 complex was verified.

Early IL-10 promotes vasculature-associated CD4+ T cells unable to control Mycobacterium tuberculosis infection

Cytokine-producing CD4⁺ T cells play a crucial role in the control of Mycobacterium tuberculosis infection; however, there is a delayed appearance of effector T cells in the lungs following aerosol infection. The immunomodulatory cytokine IL-10 antagonizes control of M. tuberculosis infection through mechanisms associated with reduced CD4⁺ T cell responses. Here, we show that IL-10 overexpression only before the onset of the T cell response impaired control of M. tuberculosis growth; during chronic infection, IL-10 overexpression reduced the CD4⁺ T cell response without affecting the outcome of infection. IL-10 overexpression early during infection did not, we found, significantly impair the kinetics of CD4⁺ T cell priming and effector differentiation. However, CD4⁺ T cells primed and differentiated in an IL-10–enriched environment displayed reduced expression of CXCR3 and, because they did not migrate into the lung parenchyma, their ability to control infection was limited. Importantly, these CD4⁺ T cells maintained their vasculature phenotype and were unable to control infection, even after adoptive transfer into low IL-10 settings. Together our data support a model wherein, during M. tuberculosis infection, IL-10 acts intrinsically on T cells, impairing their parenchymal migratory capacity and ability to engage with infected phagocytic cells, thereby impeding control of infection.

A recombinant bovine adenoviral mucosal vaccine expressing mycobacterial antigen-85B generates robust protection against tuberculosis in mice

Although the BCG vaccine offers partial protection, tuberculosis remains a leading cause of infectious disease death, killing ∼1.5 million people annually. We developed mucosal vaccines expressing the autophagy-inducing peptide C5 and mycobacterial Ag85B-p25 epitope using replication-defective human adenovirus (HAdv85C5) and bovine adenovirus (BAdv85C5) vectors. BAdv85C5-infected dendritic cells (DCs) expressed a robust transcriptome of genes regulating antigen processing compared to HAdv85C5-infected DCs. BAdv85C5-infected DCs showed enhanced galectin-3/8 and autophagy-dependent in vitro Ag85B-p25 epitope presentation to CD4 T cells. BCG-vaccinated mice were intranasally boosted using HAdv85C5 or BAdv85C5 followed by infection using aerosolized Mycobacterium tuberculosis (Mtb). BAdv85C5 protected mice against tuberculosis both as a booster after BCG vaccine (>1.4-log10 reduction in Mtb lung burden) and as a single intranasal dose (>0.5-log10 reduction). Protection was associated with robust CD4 and CD8 effector (TEM), central memory (TCM), and CD103+/CD69+ lung-resident memory (TRM) T cell expansion, revealing BAdv85C5 as a promising mucosal vaccine for tuberculosis.

Leukocytes from Patients with Drug-Sensitive and Multidrug-Resistant Tuberculosis Exhibit Distinctive Profiles of Chemokine Receptor Expression and Migration Capacity

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains as a leading infectious cause of death worldwide. The increasing number of multidrug-resistant TB (MDR-TB) cases contributes to the poor control of the TB epidemic. Currently, little is known about the immunological requirements of protective responses against MDR-TB. This is of major relevance to identify immune markers for treatment monitoring and targets for adjuvant immunotherapies. Here, we hypothesized that MDR-TB patients display unique immunophenotypical features and immune cell migration dynamics compared to drug-sensitive TB (DS-TB). Hence, we prospectively conducted an extensive characterization of the immune profile of MDR-TB patients at different time points before and after pharmacological therapy. For this purpose, we focused on the leukocyte expression of chemokine receptors, distribution of different monocyte and lymphocyte subsets, plasma levels of chemotactic factors, and in vitro migration capacity of immune cells. Our comparative cohort consisted of DS-TB patients and healthy volunteer donors (HD). Our results demonstrate some unique features of leukocyte migration dynamics during MDR-TB. These include increased and prolonged circulation of CD3+ monocytes, CCR4+ monocytes, EM CD4+ T cells, EM/CM CD8+ T cells, and CXCR1+CXCR3+ T cells that is sustained even after the administration of anti-TB drugs. We also observed shared characteristics of both MDR-TB and DS-TB that include CCR2+ monocyte depletion in the blood; high plasma levels of MPC-1, CCL-7, and IP-10; and increased responsiveness of leukocytes to chemotactic signals in vitro. Our study contributes to a better understanding of the MDR-TB pathobiology and uncovers immunological readouts of treatment efficacy.

In Vivo Antigen Expression Regulates CD4 T Cell Differentiation and Vaccine Efficacy against Mycobacterium tuberculosis Infection

Tuberculosis, caused by Mtb, constitutes a global health crisis of massive proportions, and the impact of the current coronavirus disease 2019 (COVID-19) pandemic is expected to cause a rise in tuberculosis-related deaths. Improved vaccines are therefore needed more than ever, but a lack of knowledge on protective immunity hampers their development.

New vaccines are urgently needed against Mycobacterium tuberculosis (Mtb), which kills more than 1.4 million people each year. CD4 T cell differentiation is a key determinant of protective immunity against Mtb, but it is not fully understood how host-pathogen interactions shape individual antigen-specific T cell populations and their protective capacity. Here, we investigated the immunodominant Mtb antigen, MPT70, which is upregulated in response to gamma interferon (IFN-γ) or nutrient/oxygen deprivation of in vitro-infected macrophages. Using a murine aerosol infection model, we compared the in vivo expression kinetics of MPT70 to a constitutively expressed antigen, ESAT-6, and analyzed their corresponding CD4 T cell phenotype and vaccine protection. For wild-type Mtb, we found that in vivo expression of MPT70 was delayed compared to ESAT-6. This delayed expression was associated with induction of less differentiated MPT70-specific CD4 T cells but, compared to ESAT-6, also reduced protection after vaccination. In contrast, infection with an MPT70-overexpressing Mtb strain promoted highly differentiated KLRG1⁺CX3CR1⁺ CD4 T cells with limited lung-homing capacity. Importantly, this differentiated phenotype could be prevented by vaccination, and against the overexpressing strain, vaccination with MPT70 conferred protection similar to vaccination with ESAT-6. Together, our data indicate that high in vivo antigen expression drives T cells toward terminal differentiation and that targeted vaccination with adjuvanted protein can counteract this phenomenon by maintaining T cells in a protective less differentiated state. These observations shed new light on host-pathogen interactions and provide guidance on how future Mtb vaccines can be designed to tip the immune balance in favor of the host.

Classical CD4 T cells as the cornerstone of antimycobacterial immunity

Tuberculosis is a significant health problem without an effective vaccine to combat it. A thorough understanding of the immune response and correlates of protection is needed to develop a more efficient vaccine. The immune response against Mycobacterium tuberculosis (Mtb) is complex and involves all aspects of the immune system, however, the optimal protective, non‐pathogenic T cell response against Mtb is still elusive. This review will focus on discussing CD4 T cell immunity against mycobacteria and its importance in Mtb infection with a primary focus on human studies. We will in particular discuss the large heterogeneity of immune cell subsets that have been revealed by recent immunological investigations at an unprecedented level of detail. These studies have identified specific classical CD4 T cell subsets important for immune responses against Mtb in various states of infection. We further discuss the functional attributes that have been linked to the various subsets such as upregulation of activation markers and cytokine production. Another important topic to be considered is the antigenic targets of Mtb‐specific immune responses, and how antigen reactivity is influenced by both disease state and environmental exposure(s). These are key points for both vaccines and immune diagnostics development. Ultimately, these factors are holistically considered in the definition and investigations of what are the correlates on protection and resolution of disease.

In vivo antigen expression regulates CD4 T cell differentiation and vaccine efficacy against Mycobacterium tuberculosis infection

New vaccines are urgently needed against Mycobacterium tuberculosis (Mtb), which kills more than 1.4 million people each year. CD4 T cell differentiation is a key determinant of protective immunity against Mtb, but it is not fully understood how host-pathogen interactions shape individual antigen-specific T cell populations and their protective capacity. Here, we investigated the immunodominant Mtb antigen, MPT70, which is upregulated in response to IFN-γ or nutrient/oxygen deprivation of in vitro infected macrophages. Using a murine aerosol infection model, we compared the in vivo expression kinetics of MPT70 to a constitutively expressed antigen, ESAT-6, and analysed their corresponding CD4 T cell phenotype and vaccine-protection. For wild-type Mtb, we found that in vivo expression of MPT70 was delayed compared to ESAT-6. This delayed expression was associated with induction of less differentiated MPT70-specific CD4 T cells but, compared to ESAT-6, also reduced protection after vaccination. In contrast, infection with an MPT70-overexpressing Mtb strain promoted highly differentiated KLRG1+CX3CR1+ CD4 T cells with limited lung-homing capacity. Importantly, this differentiated phenotype could be prevented by vaccination and, against the overexpressing strain, vaccination with MPT70 conferred similar protection as ESAT-6. Together our data indicate that high in vivo antigen expression drives T cells towards terminal differentiation and that targeted vaccination with adjuvanted protein can counteract this phenomenon by maintaining T cells in a protective less-differentiated state. These observations shed new light on host-pathogen interactions and provide guidance on how future Mtb vaccines can be designed to tip the immune-balance in favor of the host.

Legend of the Sentinels: Development of Lung Resident Memory T Cells and Their Roles in Diseases

SARS-CoV-2 is wreaking havoc around the world. To get the world back on track, hundreds of vaccines are under development. A deeper understanding of how the immune system responds to SARS-CoV-2 re-infection will certainly help. Studies have highlighted various aspects of T cell response in resolving acute infection and preventing re-infections. Lung resident memory T (TRM) cells are sentinels in the secondary immune response. They are mostly differentiated from effector T cells, construct specific niches and stay permanently in lung tissues. If the infection recurs, locally activated lung TRM cells can elicit rapid immune response against invading pathogens. In addition, they can significantly limit tumor growth or lead to pathologic immune responses. Vaccines targeting TRM cells are under development, with the hope to induce stable and highly reactive lung TRM cells through mucosal administration or "prime-and-pull" strategy. In this review, we will summarize recent advances in lung TRM cell generation and maintenance, explore their roles in different diseases and discuss how these cells may guide the development of future vaccines targeting infectious disease, cancer, and pathologic immune response.

Rescuing ESAT-6 Specific CD4 T Cells From Terminal Differentiation Is Critical for Long-Term Control of Murine Mtb Infection

In most cases, Mycobacterium tuberculosis (Mtb) causes life-long chronic infections, which poses unique challenges for the immune system. Most of the current tuberculosis (TB) subunit vaccines incorporate immunodominant antigens and at this point, it is poorly understood how the CD4 T cell subsets recognizing these antigens are affected during long-term infection. Very little is known about the requirements for sustainable vaccine protection against TB. To explore this, we screened 62 human-recognized Mtb antigens during chronic murine Mtb infection and identified the four most immunodominant antigens in this setting (MPT70, Rv3020c, and Rv3019c and ESAT-6). Combined into a subunit vaccine, this fusion protein induced robust protection both in a standard short-term model and in a long-term infection model where immunity from BCG waned. Importantly, replacement of ESAT-6 with another ESAT-6-family antigen, Rv1198, led to similar short-term protection but a complete loss of bacterial control during chronic infection. This observation was further underscored, as the ESAT-6 containing vaccine mediated sustainable protection in a model of post-exposure vaccination, where the ESAT-6-replacement vaccine did not. An individual comparison of the CD4 T cell responses during Mtb infection revealed that ESAT-6-specific T cells were more terminally differentiated than the other immunodominant antigens and immunization with the ESAT-6 containing vaccine led to substantially greater reduction in the overall T cell differentiation status. Our data therefore associates long-term bacterial control with the ability of a vaccine to rescue infection-driven CD4T cell differentiation and future TB antigen discovery programs should focus on identifying antigens with the highest accompanying T cell differentiation, like ESAT-6. This also highlights the importance of long-term readouts in both preclinical and clinical studies with TB vaccines.