T lymphocyte surface expression of exhaustion markers as biomarkers of the efficacy of chemotherapy for tuberculosis

Association of tuberculosis risk with genetic polymorphisms of the immune checkpoint genes PDCD1, CTLA-4, and TIM3

The immune checkpoint proteins were reported to involve to host resistance to Mycobacteria tuberculosis (Mtb). Here, we evaluated 11 single nucleotide polymorphisms (SNPs) in PDCD1, CTLA4, and HAVCR2 genes between participants with and without TB infection. Genomic DNA isolated from 285 patients with TB and 270 controls without TB infection were used to perform the genotyping assay. Odds ratios were used to characterize the association of 11 SNPs with TB risk. In this study, the various genotypes of the 11 SNPs did not differ significantly in frequency between the non-TB and TB groups. When patients were stratified by sex, however, men differed significantly from women in genotype frequencies at HAVCR2 rs13170556. Odds ratios indicated that rs2227982, rs13170556, rs231775, and rs231779 were sex-specifically associated with TB risk. In addition, the combinations of rs2227982/rs13170556 GA/TC in men and the A-C-C haplotype of rs231775-rs231777-rs231779 in women were significantly associated with TB risk. Our results indicate that rs2227982 in PDCD1 and rs13170556 in HAVCR2 are associated with increased TB susceptibility in men and that the CTLA4 haplotype appears protective against TB in women.

Therapeutic efficacy against Mycobacterium tuberculosis using ID93 and liposomal adjuvant formulations

Mycobacterium tuberculosis (M.tb) has led to approximately 1.3 million deaths globally in 2020 according to the World Health Organization (WHO). More effective treatments are therefore required to prevent the transmission of M.tb. Although Bacille Calmette-Guérin (BCG), a prophylactic vaccine against M.tb, already exists, other vaccines are being developed that could help boost BCG's noted incomplete protection. This includes ID93 + GLA-SE, an adjuvanted protein vaccine which is being tested in Phase 2 clinical trials. The aim of this study was to test new lipid-based adjuvant formulations with ID93 in the context of a therapeutic vaccine, which we hypothesize would act as an adjunct to drug treatment and provide better outcomes, such as survival, than drug treatment alone. The recent success of another adjuvanted recombinant protein vaccine, M72 + AS01_E (GlaxoSmithKline Biologicals), which after 3 years provided approximately 50% efficacy against TB pulmonary disease, is paving the way for new and potentially more effective vaccines. We show that based on selected criteria, including survival, T helper 1 cytokine responses, and resident memory T cells in the lung, that a liposomal formulation of GLA with QS-21 (GLA-LSQ) combined with ID93 provided enhanced protection over drug treatment alone.

The Yin and Yang of Targeting KLRG1+ Tregs and Effector Cells

The literature surrounding KLRG1 has primarily focused on NK and CD8⁺ T cells. However, there is evidence that the most suppressive Tregs express KLRG1. Until now, the role of KLRG1 on Tregs has been mostly overlooked and remains to be elucidated. Here we review the current literature on KLRG1 with an emphasis on the KLRG1⁺ Treg subset role during cancer development and autoimmunity. KLRG1 has been recently proposed as a new checkpoint inhibitor target, but these studies focused on the effects of KLRG1 blockade on effector cells. We propose that when designing anti-tumor therapies targeting KLRG1, the effects on both effector cells and Tregs will have to be considered.

An immunosuppressive scoring system to predict recurrence and assist in decision regarding postoperative adjuvant treatment in gastric cancer

Inhibition of the immune microenvironment is the main cause of tumor recurrence after surgery in patients with gastric cancer (GC). In this study, immunohistochemistry and multiple immunofluorescence staining were used to evaluate immunosuppressive indicators and immune biomarkers in 825 patients with gastric cancer from three centers. We constructed an immunosuppressive recurrence score (IRS) using LASSO Cox regression based on the expression of six immunosuppressive indicators and found that the IRS and IRS-based nomogram were significantly accurate and reliable in predicting recurrence. Moreover, an elevated IRS was associated with locoregional recurrence and postoperative adjuvant chemotherapy failure. Furthermore, an increase in IRS indicated inhibition of the antitumor effect of CD8⁺ tumor-infiltrating lymphocytes in the invasive margin. Thus, we propose that the IRS can predict the recurrence outcome of patients with GC by distinguishing the immunosuppressive status, which is helpful in the selection of individualized adjuvant treatment plans.

Type 1 Cytotoxic T Cells Increase in Placenta after Intrauterine Inflammation

CD8+ T cells recognize non-self antigen by MHC class I molecules and kill the target cells by the release of proinflammatory cytokines such as interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α). Our group previously reported an increase of CD8+ T‐cell trafficking in the placenta with exposure to Lipopolysaccharides (LPS). CD8+ cytotoxic T cells have been classified into distinct subsets based upon cytokine production: Tc1 cells produce IFN-γ, Tc2 cells produce interleukin 4 (IL-4). Accordingly, the purpose of this research is to analyze the subsets of placenta CD8+ T cells. We hypothesized that LPS injection would induce a change of properties of CD8+ T cell and Tc1/Tc2 ratio. We investigated the subsets of CD8+ T cell infiltration to placenta and their specific function in response to LPS-induced inflammation in a mouse model. At embryonic (E) day 17, pregnant CD-1 dams received an intrauterine injection of 25 µg LPS in100 μl PBS or 100 μl of PBS only. Flow cytometry was used to quantify CD8+ T cells, evaluate the phenotype and subtypes, and detect markers of Tc1 and Tc2 cells in placenta, at 6 hours and 24 hours post injection (hpi). Intracellular staining and flow cytometry were performed to characterize cytokines produced by CD8+ T cells. Standard statistical analysis were employed. After 6 and 24 hours of LPS injection, total CD8 T cells increased (P<0.05). Tc1 cells expanded (P<0.05) in LPS-treated dams compared with the PBS group. The Tc1/Tc2 ratio was significantly higher in the LPS group than the PBS group (P<0.05). The expression of TNF-α and IFN-γ were increased in LPS group both at 6hpi and 24 hpi (P<0.05). We identified functional placental CD8+ T cell subtypes and found a significant increase ratio of Tc1/Tc2. Following IUI, CD8+ T cells induced inflammatory response in the placenta primarily via the production of Type 1 cytokines such as IFN-γ and TNF-α. We have provided evidence of a Tc1-bias response and cytokines in the mouse model of IUI.

Regulation of Th1 T Cell Differentiation by Iron via Upregulation of T Cell Immunoglobulin and Mucin Containing Protein-3 (TIM-3)

Iron plays an important role in host–pathogen interactions, in being an essential element for both pathogen and host metabolism, but also by impacting immune cell differentiation and anti-microbial effector pathways. Iron has been implicated to affect the differentiation of T lymphocytes during inflammation, however, so far the underlying mechanism remained elusive. In order to study the role of iron in T cell differentiation we here investigated how dietary iron supplementation affects T cell function and outcome in a model of chronic infection with the intracellular bacterium Salmonella enterica serovar typhimurium (S. Typhimurium). Iron loading prior to infection fostered bacterial burden and, unexpectedly, reduced differentiation of CD4⁺ T helper cells type 1 (Th1) and expression of interferon-gamma (IFNγ), a key cytokine to control infections with intracellular pathogens. This effect could be traced back to iron-mediated induction of the negative immune checkpoint regulator T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), expressed on the surface of this T cell subset. In vitro experiments demonstrated that iron supplementation specifically upregulated mRNA and protein expression of TIM-3 in naïve Th cells in a dose-depdendent manner and hindered priming of those T cells towards Th1 differentiation. Importantly, administration of TIM-3 blocking antibodies to iron-loaded mice infected with S. Typhimurium virtually restored Th1 cell differentiation and significantly improved bacterial control. Our data uncover a novel mechanism by which iron modulates CD4⁺ cell differentiation and functionality and hence impacts infection control with intracellular pathogens. Specifically, iron inhibits the differentiation of naive CD4⁺ T cells to protective IFNγ producing Th1 lymphocytes via stimulation of TIM-3 expression. Finally, TIM-3 may serve as a novel drug target for the treatment of chronic infections with intracellular pathogens, specifically in iron loading diseases.

The double-edged sword of Tregs in M tuberculosis, M avium, and M absessus infection

Immunity against different Mycobacteria species targeting the lung requires distinctly different pulmonary immune responses for bacterial clearance. Many parameters of acquired and regulatory immune responses differ quantitatively and qualitatively from immunity during infection with Mycobacteria species. Nontuberculosis Mycobacteria species (NTM) Mycobacterium avium- (M avium), Mycobacterium abscessus-(M abscessus), and the Mycobacteria species Mycobacterium tuberculosis-(Mtb). Herein, we discuss the potential implications of acquired and regulatory immune responses in the context of animal and human studies, as well as future directions for efforts to treat Mycobacteria diseases.

The Role of β-Catenin in Th1 Immune Response against Tuberculosis and Profiles of Expression in Patients with Pulmonary Tuberculosis

β-Catenin is a key molecule of canonical Wnt/β-catenin pathway. Its roles and expression profiles in T cells of tuberculosis (TB) remain unclear. The aim of this study was to explore the role of β-catenin in CD4⁺ T cells and its expression characteristics in patients with pulmonary tuberculosis (PTB). In this study, CD4⁺ T cell-specific β-catenin conditional knockout mice (β-CAT-cKO mice) were aerosol infected with Mycobacteria tuberculosis (Mtb) H37R_V with wild-type mice as controls. Four weeks after infection, the mRNA expression of IFN-γ, TNF-α, and TCF-7 in the lungs of mice was measured. CD4, CD8, β-catenin, IFN-γ, and TNF-α in mononuclear cells from the lungs and spleens were measured by flow cytometry, and the pathological changes of lungs were also observed. Patients with PTB were enrolled, with blood samples collected and PBMCs isolated. The expressions of β-catenin, IFN-γ, TNF-α, and PD-1 in CD4⁺ and CD8⁺ T cells were measured by flow cytometry. Results showed a decreased frequency of and reduced IFN-γ/TNF-α mRNA expression and secretion by CD4⁺ T cells in the lungs of infected β-CAT-cKO mice compared with infected wild-type controls, and only slightly more inflammatory changes were observed in the lungs. β-catenin expressions in CD4⁺ and CD8⁺ T cells were significantly decreased in blood cells of patients with severe PTB compared with those in mild PTB. The stimulation of peripheral blood mononuclear cells (PBMCs) with lithium chloride (LiCl), a stimulant of β-catenin, resulted in the increase in CD4⁺ T cell frequency, as well as their secretion of IFN-γ and TNF-α. β-Catenin demonstrated a moderately positive correlation with PD-1 in CD4⁺ T cells. β-Catenin along with PD-1 and IFN-γ in CD4⁺ T cells had a high correlation with those in CD8⁺ T cells. In conclusion, β-catenin may be involved in the regulation of Th1 response and CD4⁺ T cell frequency in TB.

Programmed cell death protein 1 (PD-1) in infection

Exhausted and dysfunctional T cells triggered by infection and cancer render the immune system unable to eliminate these pathogens. Pharmacologic blockade of the surface receptors that inhibit T-cell function has shown remarkable success in patients with various malignancies. In this Review, we discuss the emerging evidence of inhibiting checkpoint pathways as a potential role in controlling or clearing infectious diseases. Though interesting tendencies, much work is still needed in order to develop safe strategies that can be translated into clinically relevant outcomes in patients with infections.

Genetic and Immune Changes Associated with Disease Progression under the Pressure of Oncolytic Therapy in A Neuroblastoma Outlier Patient

Little is known about the effect of oncolytic adenovirotherapy on pediatric tumors. Here we present the clinical case of a refractory neuroblastoma that responded positively to Celyvir (ICOVIR-5 oncolytic adenovirus delivered by autologous mesenchymal stem cells) for several months. We analyzed samples during tumor evolution in order to identify molecular and mutational features that could explain the interactions between treatment and tumor and how the balance between both of them evolved. We identified a higher adaptive immune infiltration during stabilized disease compared to progression, and also a higher mutational rate and T-cell receptor (TCR) diversity during disease progression. Our results indicate an initial active role of the immune system controlling tumor growth during Celyvir therapy. The tumor eventually escaped from the control exerted by virotherapy through acquisition of resistance by the tumor microenvironment that exhausted the initial T cell response.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

The Role of KLRG1 in Human CD4+ T-Cell Immunity Against Tuberculosis

Background

KLRG1 is a marker of terminally differentiated CD8+ T cells in viral infection, but its role in human Mycobacterium tuberculosis infection remains elusive.

Methods

A set of cohorts of patients with tuberculosis was designed, and the expression profiles and functions of KLRG1+CD4+ T cells were determined with and without antibody blocking.

Results

KLRG1 expression on CD4+ T cells was significantly increased in patients with active tuberculosis, compared with healthy controls and patients without tuberculosis. Upon M. tuberculosis-specific stimulation, the ability to secrete interferon γ, interleukin 2, and tumor necrosis factor α was significantly greater in KLRG1-expressing CD4+ T cells than in their KLRG-negative counterparts and was accompanied by a decreased proportion of regulatory T cells and increased Akt signaling. However, KLRG1-expressing CD4+ T cells had a shorter life-span, which was associated with a higher apoptosis rate but a similar proliferative response. Blockade of KLRG1 signaling significantly enhanced interferon γ and interleukin 2 secretion without affecting either cell apoptosis or multiplication. Addition of a specific Akt inhibitor prevented this increased cytokine response, implicating the Akt signaling pathway.

Conclusions

Our study delineated the profile of KLRG1+CD4+ T cells in patients with tuberculosis and suggests that M. tuberculosis infection drives CD4+ T cells to acquire increased effector function in a terminally differentiated state, which is restrained by KLRG1 via KLRG1/Akt signaling pathway.

Multivariate Computational Analysis of Gamma Delta T Cell Inhibitory Receptor Signatures Reveals the Divergence of Healthy and ART-Suppressed HIV+ Aging

Even with effective viral control, HIV-infected individuals are at a higher risk for morbidities associated with older age than the general population, and these serious non-AIDS events (SNAEs) track with plasma inflammatory and coagulation markers. The cell subsets driving inflammation in aviremic HIV infection are not yet elucidated. Also, whether ART-suppressed HIV infection causes premature induction of the inflammatory events found in uninfected elderly or if a novel inflammatory network ensues when HIV and older age co-exist is unclear. In this study we measured combinational expression of five inhibitory receptors (IRs) on seven immune cell subsets and 16 plasma markers from peripheral blood mononuclear cells (PBMC) and plasma samples, respectively, from a HIV and Aging cohort comprised of ART-suppressed HIV-infected and uninfected controls stratified by age (≤35 or ≥50 years old). For data analysis, multiple multivariate computational algorithms [cluster identification, characterization, and regression (CITRUS), partial least squares regression (PLSR), and partial least squares-discriminant analysis (PLS-DA)] were used to determine if immune parameter disparities can distinguish the subject groups and to investigate if there is a cross-impact of aviremic HIV and age on immune signatures. IR expression on gamma delta (γδ) T cells exclusively separated HIV+ subjects from controls in CITRUS analyses and secretion of inflammatory cytokines and cytotoxic mediators from γδ T cells tracked with TIGIT expression among HIV+ subjects. Also, plasma markers predicted the percentages of TIGIT+ γδ T cells in subjects with and without HIV in PSLR models, and a PLS-DA model of γδ T cell IR signatures and plasma markers significantly stratified all four of the subject groups (uninfected younger, uninfected older, HIV+ younger, and HIV+ older). These data implicate γδ T cells as an inflammatory driver in ART-suppressed HIV infection and provide evidence of distinct “inflamm-aging” processes with and without ART-suppressed HIV infection.

Screening and identification of potential protein biomarkers for evaluating the efficacy of intensive therapy in pulmonary tuberculosis

This research aimed to discover potential biomarkers for evaluating the therapeutic efficacy of intensive therapy in pulmonary tuberculosis (TB). Protein profiles in 2-months intensively treated TB patients, untreated TB patients, and healthy controls were investigated with iTRAQ-2DLC-MS/MS technique. 71 differential proteins were identified in 2-months intensively treated TB patients. Significant differences in complement component C7 (CO7), apolipoprotein A-IV (APOA4), apolipoprotein C-II (APOC2), and angiotensinogen (ANGT) were found by ELISA validation. CO7 and ANGT were also found significantly different in sputum negative patients, compared with sputum positive patients after intensive treatment. Clinical analysis showed that after 2-months intensive treatment several indicators were significantly changed, and the one-year cure rate of sputum negative patients were significantly higher than sputum positive patients. Diagnostic models consisting of APOC2, CO7 and APOA4 were established to distinguish intensively treated TB patients from untreated TB patients and healthy controls with the AUC value of 0.910 and 0.935. Meanwhile, ANGT and CO7 were combined to identify sputum negative and sputum positive TB patients after intensive treatment with 89.36% sensitivity, 71.43% specificity, and the AUC value of 0.853. The results showed that APOC2, CO7, APOA4, and ANGT may be potential biomarkers for evaluating the efficacy of intensive anti-TB therapy.

Trying to See the Forest through the Trees: Deciphering the Nature of Memory Immunity to Mycobacterium tuberculosis

The purpose of vaccination against tuberculosis and other diseases is to establish a heightened state of acquired specific resistance in which the memory immune response is capable of mediating an accelerated and magnified expression of protection to the pathogen when this is encountered at a later time. In the earliest studies in mice infected with Mycobacterium tuberculosis, memory immunity and the cells that express this were definable both in terms of kinetics of emergence, and soon thereafter by the levels of expression of markers including CD44, CD62L, and the chemokine receptor CCR7, allowing the identification of effector memory and central memory T cell subsets. Despite these initial advances in knowledge, more recent information has not revealed more clarity, but instead, has created a morass of complications—complications that, if not resolved, could harm correct vaccine design. Here, we discuss two central issues. The first is that we have always assumed that memory is induced in the same way, and consists of the same T cells, regardless of whether that immunity is generated by BCG vaccination, or by exposure to M. tuberculosis followed by effective chemotherapy. This assumption is almost certainly incorrect. Second, a myriad of additional memory subsets have now been described, such as resident, stem cell-like, tissue specific, among others, but as yet we know nothing about the relative importance of each, or whether if a new vaccine needs to induce all of these, or just some, to be fully effective.

Aberrant plasma IL-7 and soluble IL-7 receptor levels indicate impaired T-cell response to IL-7 in human tuberculosis

T-cell proliferation and generation of protective memory during chronic infections depend on Interleukin-7 (IL-7) availability and receptivity. Regulation of IL-7 receptor (IL-7R) expression and signalling are key for IL-7-modulated T-cell functions. Aberrant expression of soluble (s) and membrane-associated (m) IL-7R molecules is associated with development of autoimmunity and immune failure in acquired immune deficiency syndrome (AIDS) patients. Here we investigated the role of IL-7/IL-7R on T-cell immunity in human tuberculosis. We performed two independent case-control studies comparing tuberculosis patients and healthy contacts. This was combined with follow-up examinations for a subgroup of tuberculosis patients under therapy and recovery. Blood plasma and T cells were characterised for IL-7/sIL-7R and mIL-7R expression, respectively. IL-7-dependent T-cell functions were determined by analysing STAT5 phosphorylation, antigen-specific cytokine release and by analysing markers of T-cell exhaustion and inflammation. Tuberculosis patients had lower soluble IL-7R (p < 0.001) and higher IL-7 (p < 0.001) plasma concentrations as compared to healthy contacts. Both markers were largely independent and aberrant expression normalised during therapy and recovery. Furthermore, tuberculosis patients had lower levels of mIL-7R in T cells caused by post-transcriptional mechanisms. Functional in vitro tests indicated diminished IL-7-induced STAT5 phosphorylation and impaired IL-7-promoted cytokine release of Mycobacterium tuberculosis-specific CD4⁺ T cells from tuberculosis patients. Finally, we determined T-cell exhaustion markers PD-1 and SOCS3 and detected increased SOCS3 expression during therapy. Only moderate correlation of PD-1 and SOCS3 with IL-7 expression was observed. We conclude that diminished soluble IL-7R and increased IL-7 plasma concentrations, as well as decreased membrane-associated IL-7R expression in T cells, reflect impaired T-cell sensitivity to IL-7 in tuberculosis patients. These findings show similarities to pathognomonic features of impaired T-cell functions and immune failure described in AIDS patients.

IL-7 is important for the development and homeostasis of T cells and promotes antigen-specific T-cell responses. Aberrant expression of plasma IL-7 and soluble IL-7R are found in autoimmune diseases and chronic viral infections. In AIDS patients—especially those who fail to reconstitute T-cell numbers during therapy—impaired IL-7-promoted T-cell functions indicated T-cell exhaustion/senescence. In order to evaluate the potential impact of IL-7 on tuberculosis, we characterised various parameters involved in the IL-7-response of tuberculosis patients and healthy contacts. Despite IL-7 being available at higher plasma levels among tuberculosis patients, the T-cell response to IL-7 was impaired when compared to healthy contacts. Soluble IL-7R levels were aberrantly low in plasma during acute tuberculosis but did not account for impaired IL-7 usage. Chronic inflammation in tuberculosis patients—reflected by increased IL-6 plasma levels—did not account for dysfunctional T-cell responses and analysed T-cell exhaustion markers were only moderately correlated. Our findings demonstrate that availability of IL-7 alone is not sufficient to promote protective T-cell immunity against tuberculosis. We describe aberrant IL-7/soluble IL-7R expression and impaired IL-7-mediated T-cell functions in tuberculosis patients with similarities and differences to described IL-7 dysregulation seen in patients with AIDS.

Tuberculosis as a three-act play: A new paradigm for the pathogenesis of pulmonary tuberculosis

Lack of access to human tissues with untreated tuberculosis (TB) has forced generations of researchers to use animal models and to adopt a paradigm that granulomas are the characteristic lesion of both primary and post primary TB. An extended search of studies of human lung tissues failed to find any reports that support this paradigm. We found scores of publications from gross pathology in 1804 through high resolution CT scans in 2015 that identify obstructive lobular pneumonia, not granulomas, as the characteristic lesion of developing post-primary TB. This paper reviews this literature together with other relevant observations to formulate a new paradigm of TB with three distinct stages: a three-act play. First, primary TB, a war of attrition, begins with infection that spreads via lymphatics and blood stream before inducing systemic immunity that contains and controls the organisms within granulomas. Second, post-primary TB, a sneak attack, develops during latent TB as an asymptomatic obstructive lobular pneumonia in persons with effective systemic immunity. It is a paucibacillary process with no granulomas that spreads via bronchi and accumulates mycobacterial antigens and host lipids for 1-2 years before suddenly undergoing caseous necrosis. Third, the fallout, is responsible for nearly all clinical post primary disease. It begins with caseous necrotic pneumonia that is either retained to become the focus of fibrocaseous disease or is coughed out to leave a cavity. This three-stage paradigm suggests testable hypotheses and plausible answers to long standing questions of immunity to TB.

KLRG1 and PD-1 expression are increased on T-cells following tuberculosis-treatment and identify cells with different proliferative capacities in BCG-vaccinated adults

In cancer and chronic infectious diseases, immune checkpoint-blockade of inhibitory receptors can enhance T-cell immunity. In tuberculosis (TB), a chronic infectious disease, prolonged antigen exposure can potentially drive terminal T-cell differentiation towards functional 'exhaustion': in human TB T-cells express PD-1 (programmed cell death protein-1) and CTLA-4 (cytotoxic T-lymphocyte-associated protein-4). However, in murine TB not PD-1 but rather killer cell lectin-like receptor subfamily-G1 (KLRG1) was a superior indicator of terminal T-cell differentiation. We therefore compared expression of KLRG1, PD-1 and CTLA-4 on T-cells in different stages of human TB, and also analysed their induction following BCG-vaccination. KLRG1, PD-1 and CTLA-4-expression were highest on in vitro BCG-stimulated CD4(+) T-cells following recent TB-treatment; KLRG1 and PD-1-expression on CD4(+) T-cells in active--but not latent--TB were only slightly increased compared to healthy donors. BCG-vaccination induced KLRG1-expression on BCG-stimulated CD8(+) but not CD4(+) T-cells, while neither PD-1 nor CTLA-4-expression increased. KLRG1-expressing CD8(+) T-cells exhibited markedly decreased proliferation, whereas PD-1(+) T-cells proliferated after in vitro BCG-stimulation. Thus, we demonstrate the presence of increased KLRG1-expressing T-cells in TB-treated individuals, and present KLRG1 as a marker of decreased human T-cell proliferation following BCG-vaccination. These results expand our understanding of cell-mediated immune control of mycobacterial infections.

PD-1, PD-L1 and PD-L2 Gene Expression on T-Cells and Natural Killer Cells Declines in Conjunction with a Reduction in PD-1 Protein during the Intensive Phase of Tuberculosis Treatment

Background

The PD-1 axis is a cell intrinsic immunoregulatory pathway that mediates T cell exhaustion in chronic infection particularly in some viral infections. We hypothesized that PD-1, PD-L1 and PD-L2 would be highly expressed in untreated tuberculosis patients compared to controls due to their chronic infection and would decrease with successful TB treatment.

Materials and Methods

Untreated tuberculosis patients (n = 26) were recruited at diagnosis and followed up during treatment. Household contacts (n = 24) were recruited to establish baseline differences. Blood gene expression ex vivo was investigated using qRT-PCR. Flow cytometry was performed to establish protein expression patterns.

Results

PD-L1 gene expression was found to be elevated in active TB disease; however, this was not observed for PD-1 or PD-L2. The intensive phase of TB treatment was associated with a significant decline in PD-1, PD-L1 and PD-L2 gene expression. PD-1 protein expression on the surface of NK cells, CD8⁺ and CD4⁺ T cells was similar in patients with active TB disease compared to controls but declined with successful TB treatment, with the greatest decline occurring on the NK cells followed by CD8⁺ T cells and then CD4⁺ T cells. Granzyme B/PD-1 co-expression declined with successful intensive phase treatment.

Conclusion

Modulation of PD-1/PD-L1 pathway through TB treatment indicates changes in the peripheral T cell response caused by live Mycobacterium tuberculosis (Mtb) followed by the response to dead bacilli, antigen-release and immuno-pathology resolution. The PD-1 axis could be a host drug target for immunomodulatory treatments in the future.

Inhibitory Receptors Beyond T Cell Exhaustion

Inhibitory receptors (iRs) are frequently associated with "T cell exhaustion". However, the expression of iRs is also dependent on T cell differentiation and activation. Therapeutic blockade of various iRs, also referred to as "checkpoint blockade", is showing -unprecedented results in the treatment of cancer patients. Consequently, the clinical potential in this field is broad, calling for increased research efforts and rapid refinements in the understanding of iR function. In this review, we provide an overview on the significance of iR expression for the interpretation of T cell functionality. We summarize how iRs have been strongly associated with "T cell exhaustion" and illustrate the parallel evidence on the importance of T cell differentiation and activation for the expression of iRs. The differentiation subsets of CD8 T cells (naïve, effector, and memory cells) show broad and inherent differences in iR expression, while activation leads to strong upregulation of iRs. Therefore, changes in iR expression during an immune response are often concomitant with T cell differentiation and activation. Sustained expression of iRs in chronic infection and in the tumor microenvironment likely reflects a specialized T cell differentiation. In these situations of prolonged antigen exposure and chronic inflammation, T cells are "downtuned" in order to limit tissue damage. Furthermore, we review the novel "checkpoint blockade" treatments and the potential of iRs as biomarkers. Finally, we provide recommendations for the immune monitoring of patients to interpret iR expression data combined with parameters of activation and differentiation of T cells.

Differential expression of CD57 in antigen-reactive CD4+ T cells between active and latent tuberculosis infection

The development of diagnostic tests that predict the progression of latent tuberculosis infection to active disease is pivotal for the eradication of tuberculosis. As an initial step to achieve this goal, our study's aim was to identify biomarkers that differentiate active from latent tuberculosis infection. We compared active and latent tuberculosis infection groups in terms of the precursor frequency, functional subset differentiation, and senescence/exhaustion surface marker expression of antigen-specific CD4(+) T cells, which were defined as dividing cells upon their encountering with Mycobacterium (M.) tuberculosis antigens. Among several parameters shown to have statistically significant differences between the two groups, the frequency of CD57-expressing cells could differentiate effectively between active disease and latent infection. Our results suggest that the expression of CD57 in M. tuberculosis-reactive CD4(+) T cells could be a promising candidate biomarker with which to identify individuals with latent tuberculosis infection prone to progression to active disease.

Blockade of the programmed death-1 pathway restores sarcoidosis CD4(+) T-cell proliferative capacity

RATIONALE

Effective therapeutic interventions for chronic, idiopathic lung diseases remain elusive. Normalized T-cell function is an important contributor to spontaneous resolution of pulmonary sarcoidosis. Up-regulation of inhibitor receptors, such as programmed death-1 (PD-1) and its ligand, PD-L1, are important inhibitors of T-cell function.

OBJECTIVES

To determine the effects of PD-1 pathway blockade on sarcoidosis CD4(+) T-cell proliferative capacity.

METHODS

Gene expression profiles of sarcoidosis and healthy control peripheral blood mononuclear cells were analyzed at baseline and follow-up. Flow cytometry was used to measure ex vivo expression of PD-1 and PD-L1 on systemic and bronchoalveolar lavage-derived cells of subjects with sarcoidosis and control subjects, as well as the effects of PD-1 pathway blockade on cellular proliferation after T-cell receptor stimulation. Immunohistochemistry analysis for PD-1/PD-L1 expression was conducted on sarcoidosis, malignant, and healthy control lung specimens.

MEASUREMENTS AND MAIN RESULTS

Microarray analysis demonstrates longitudinal increase in PDCD1 gene expression in sarcoidosis peripheral blood mononuclear cells. Immunohistochemistry analysis revealed increased PD-L1 expression within sarcoidosis granulomas and lung malignancy, but this was absent in healthy lungs. Increased numbers of sarcoidosis PD-1(+) CD4(+) T cells are present systemically, compared with healthy control subjects (P < 0.0001). Lymphocytes with reduced proliferative capacity exhibited increased proliferation with PD-1 pathway blockade. Longitudinal analysis of subjects with sarcoidosis revealed reduced PD-1(+) CD4(+) T cells with spontaneous clinical resolution but not with disease progression.

CONCLUSIONS

Analogous to the effects in other chronic lung diseases, these findings demonstrate that the PD-1 pathway is an important contributor to sarcoidosis CD4(+) T-cell proliferative capacity and clinical outcome. Blockade of the PD-1 pathway may be a viable therapeutic target to optimize clinical outcomes.

Orchestration of pulmonary T cell immunity during Mycobacterium tuberculosis infection: immunity interruptus

Despite the introduction almost a century ago of Mycobacterium bovis BCG (BCG), an attenuated form of M. bovis that is used as a vaccine against Mycobacterium tuberculosis, tuberculosis remains a global health threat and kills more than 1.5 million people each year. This is mostly because BCG fails to prevent pulmonary disease--the contagious form of tuberculosis. Although there have been significant advances in understanding how the immune system responds to infection, the qualities that define protective immunity against M. tuberculosis remain poorly characterized. The ability to predict who will maintain control over the infection and who will succumb to clinical disease would revolutionize our approach to surveillance, control, and treatment. Here we review the current understanding of pulmonary T cell responses following M. tuberculosis infection. While infection elicits a strong immune response that contains infection, M. tuberculosis evades eradication. Traditionally, its intracellular lifestyle and alteration of macrophage function are viewed as the dominant mechanisms of evasion. Now we appreciate that chronic inflammation leads to T cell dysfunction. While this may arise as the host balances the goals of bacterial sterilization and avoidance of tissue damage, it is becoming clear that T cell dysfunction impairs host resistance. Defining the mechanisms that lead to T cell dysfunction is crucial as memory T cell responses are likely to be subject to the same subject to the same pressures. Thus, success of T cell based vaccines is predicated on memory T cells avoiding exhaustion while at the same time not promoting overt tissue damage.

Memory T cell subsets in tuberculosis: what should we be targeting?

The purpose of vaccination is to establish a stable population of long lived memory T cells. In the context of tuberculosis, the BCG vaccine has been widely used for well over 60 years, but during that time its weaknesses, particularly its ineffectiveness in adults, has been increasingly recognized. In this commentary we review what is known about memory T cells, both in general and in the context of their role in expressing specific acquired resistance to tuberculosis. Current knowledge indicates that both effector memory and central memory can be generated, depending on the experimental conditions, but both in animal models and in clinical studies it is clear that effector memory T cells are the predominant subset. These issues are of importance, given the concerted effort to make new TB vaccines, not all of which may work in precisely the same manner. At the present time whether a TB vaccine would work better if it targeted one specific T cell subset rather than another is as yet completely unknown, and this is now further complicated by new evidence that suggests other subsets such as IL-17 secreting CD4 T cells and cells with stem cell-like qualities may also play important roles.

Inhibitory Receptor Expression Depends More Dominantly on Differentiation and Activation than "Exhaustion" of Human CD8 T Cells

Under conditions of chronic antigen stimulation, such as persistent viral infection and cancer, CD8 T cells may diminish effector function, which has been termed "exhaustion." Expression of inhibitory Receptors (iRs) is often regarded as a hallmark of "exhaustion." Here we studied the expression of eight different iRs by CD8 T cells of healthy humans, including CTLA-4, PD1, TIM3, LAG3, 2B4, BTLA, CD160, and KLRG1. We show that many iRs are expressed upon activation, and with progressive differentiation to effector cells, even in absence of long-term ("chronic") antigenic stimulation. In particular, we evaluated the direct relationship between iR expression and functionality in CD8 T cells by using anti-CD3 and anti-CD28 stimulation to stimulate all cells and differentiation subsets. We observed a striking up-regulation of certain iRs following the cytokine production wave, in agreement with the notion that iRs function as a negative feedback mechanism. Intriguingly, we found no major impairment of cytokine production in cells positive for a broad array of iRs, as previously shown for PD1 in healthy donors. Rather, the expression of the various iRs strongly correlated with T cell differentiation or activation states, or both. Furthermore, we analyzed CD8 T cells from lymph nodes (LNs) of melanoma patients. Interestingly, we found altered iR expression and lower cytokine production by T cells from metastatic LNs, but also from non-metastatic LNs, likely due to mechanisms which are not related to exhaustion. Together, our data shows that expression of iRs per se does not mark dysfunctional cells, but is rather tightly linked to activation and differentiation. This study highlights the importance of considering the status of activation and differentiation for the study and the clinical monitoring of CD8 T cells.

PD-1/PD-Ls pathways between CD4(+) T cells and pleural mesothelial cells in human tuberculous pleurisy

Programmed death 1 (PD-1), PD-ligand 1 (PD-L1), and PD-L2 have been demonstrated to be involved in tuberculosis immunity, however, the expression and regulation of PD-1/PD-Ls pathways in pleural mesothelial cells (PMCs) and CD4(+) T cells in tuberculous pleural effusion (TPE) have not been investigated. Expression of PD-1 on CD4(+) T cells and expressions of PD-L1 and PD-L2 on PMCs in TPE were determined. The impacts of PD-1/PD-Ls pathways on proliferation, apoptosis, adhesion, and migration of CD4(+) T cells were explored. Concentrations of soluble PD-l, but not of soluble PD-Ls, were much higher in TPE than in serum. Expressions of PD-1 on CD4(+) T cells in TPE were significantly higher than those in blood. Expressions of PD-Ls were much higher on PMCs from TPE when compared with those from transudative effusion. Interferon-γ not only upregulated the expression of PD-1 on CD4(+) T cells, but also upregulated the expressions of PD-Ls on PMCs. Blockage PD-1/PD-Ls pathways abolished the inhibitory effects on proliferation and adhesion activity of CD4(+) T cells induced by PMCs. PD-1/PD-Ls pathways on PMCs inhibited proliferation and adhesion activity of CD4(+) T cells, suggesting that Mycobacterium tuberculosis might exploit PD-1/PD-Ls pathways to evade host cell immune response in human.

Inhibiting the programmed death 1 pathway rescues Mycobacterium tuberculosis-specific interferon γ-producing T cells from apoptosis in patients with pulmonary tuberculosis

BACKGROUND

Overexpression of programmed death 1 (PD-1) receptor is thought to inhibit the effector T-cell response in human tuberculosis. However, the precise mechanism of such inhibition remains unclear. The present study addresses the role of PD-1 in dampening host T-cell function among patients with pulmonary tuberculosis.

METHODS

Expression of PD-1 and its ligands (PD-L1/L2) on T cells, B cells, and monocytes was evaluated by flow cytometry (FACS). In vitro stimulation of peripheral blood mononuclear cells in the presence of Mycobacterium tuberculosis antigens was performed with and without blocking PD-1, and intracellular cytokine production was measured by FACS.

RESULTS

We showed higher frequencies of T cells, monocytes, and B cells expressing PD-1 and its ligand(s) among patients with pulmonary tuberculosis. Infections with live M. tuberculosis upregulated PD-L1 expression on monocytes. In vitro PD-1 blocking rescued M. tuberculosis-specific interferon γ (IFN-γ)-producing T cells from undergoing apoptosis. The number of PD-1-expressing T cells decreased significantly during therapy and inversely correlated with IFN-γ-dominant T-cell response against M. tuberculosis.

CONCLUSIONS

Manipulation of PD-1 signaling may restore the host T-cell response and thus may have therapeutic potential. PD-1 also may serve as a biomarker to monitor host immunity among patients with tuberculosis during therapy and vaccine studies.

Killer cell lectin-like receptor G1 deficiency significantly enhances survival after Mycobacterium tuberculosis infection

The expression of T cell differentiation markers is known to increase during Mycobacterium tuberculosis infection, and yet the biological role of such markers remains unclear. We examined the requirement of the T cell differentiation marker killer cell lectin-like receptor G1 (KLRG1) during M. tuberculosis infection using mice deficient in KLRG1. KLRG1(-/-) mice had a significant survival extension after M. tuberculosis infection compared to wild-type controls, and maintained a significantly lower level of pulmonary M. tuberculosis throughout chronic infection. Improved control of M. tuberculosis infection was associated with an increased number of activated pulmonary CD4(+) T cells capable of secreting gamma interferon (IFN-γ). Our report is the first to show an in vivo impact of KLRG1 on disease control.

Enhanced upper genital tract pathologies by blocking Tim-3 and PD-L1 signaling pathways in mice intravaginally infected with Chlamydia muridarum

Background

Although Tim-3 & PD-L1 signaling pathways play important roles in negatively regulating immune responses, their roles in chlamydial infection have not been evaluated.

Methods

Neutralization antibodies targeting Tim-3 and PD-L1 were used to treat mice. Following an intravaginal infection with C. muridarum organisms, mice with or without the dual antibody treatment were compared for live chlamydial organism shedding from the lower genital tract and inflammatory pathology in the upper genital tract.

Results

Mice treated with anti-Tim-3 and anti-PD-L1 antibodies displayed a time course of live organism shedding similar to that of mice treated with equivalent amounts of isotype-matched IgG molecules. The combined antibody blocking failed to alter either the lower genital tract cytokine or systemic humoral and cellular adaptive responses to C. muridarum infection. However, the antibody blocking significantly enhanced C. muridarum-induced pathologies in the upper genital tract, including more significant hydrosalpinx and inflammatory infiltration in uterine horn and oviduct tissues.

Conclusions

The Tim-3 and PD-L1-mediated signaling can significantly reduce pathologies in the upper genital tract without suppressing immunity against chlamydial infection, suggesting that Tim-3 and PD-L1-mediated negative regulation may be manipulated to attenuate tubal pathologies in women persistently infected with C. trachomatis organisms.

Importance of confirming data on the in vivo efficacy of novel antibacterial drug regimens against various strains of Mycobacterium tuberculosis

In preclinical testing of antituberculosis drugs, laboratory-adapted strains of Mycobacterium tuberculosis are usually used both for in vitro and in vivo studies. However, it is unknown whether the heterogeneity of M. tuberculosis stocks used by various laboratories can result in different outcomes in tests of antituberculosis drug regimens in animal infection models. In head-to-head studies, we investigated whether bactericidal efficacy results in BALB/c mice infected by inhalation with the laboratory-adapted strains H37Rv and Erdman differ from each other and from those obtained with clinical tuberculosis strains. Treatment of mice consisted of dual and triple drug combinations of isoniazid (H), rifampin (R), and pyrazinamide (Z). The results showed that not all strains gave the same in vivo efficacy results for the drug combinations tested. Moreover, the ranking of HRZ and RZ efficacy results was not the same for the two H37Rv strains evaluated. The magnitude of this strain difference also varied between experiments, emphasizing the risk of drawing firm conclusions for human trials based on single animal studies. The results also confirmed that the antagonism seen within the standard HRZ regimen by some investigators appears to be an M. tuberculosis strain-specific phenomenon. In conclusion, the specific identity of M. tuberculosis strain used was found to be an important variable that can change the apparent outcome of in vivo efficacy studies in mice. We highly recommend confirmation of efficacy results in late preclinical testing against a different M. tuberculosis strain than the one used in the initial mouse efficacy study, thereby increasing confidence to advance potent drug regimens to clinical trials.