Fine-tuning of T cell responses during infection

A comprehensive review of immune checkpoint inhibitors for cancer treatment

Immunology-based therapies are emerging as an effective cancer treatment, using the body's immune system to target tumors. Immune checkpoints, which regulate immune responses to prevent tissue damage and autoimmunity, are often exploited by cancer cells to avoid destruction. The discovery of checkpoint proteins like PD-1/PD-L1 and CTLA-4 was pivotal in developing cancer immunotherapy. Immune checkpoint inhibitors (ICIs) have shown great success, with FDA-approved drugs like PD-1 inhibitors (Nivolumab, Pembrolizumab, Cemiplimab), PD-L1 inhibitors (Atezolizumab, Durvalumab, Avelumab), and CTLA-4 inhibitors (Ipilimumab, Tremelimumab), alongside LAG-3 inhibitor Relatlimab. Research continues on new checkpoints like TIM-3, VISTA, B7-H3, BTLA, and TIGIT. Biomarkers like PDL-1 expression, tumor mutation burden, interferon-γ presence, microbiome composition, and extracellular matrix characteristics play a crucial role in predicting responses to immunotherapy with checkpoint inhibitors. Despite their effectiveness, not all patients experience the same level of benefit, and organ-specific immune-related adverse events (irAEs) such as rash or itching, colitis, diarrhea, hyperthyroidism, and hypothyroidism may occur. Given the rapid advancements in this field and the variability in patient outcomes, there is an urgent need for a comprehensive review that consolidates the latest findings on immune checkpoint inhibitors, covering their clinical status, biomarkers, resistance mechanisms, strategies to overcome resistance, and associated adverse effects. This review aims to fill this gap by providing an analysis of the current clinical status of ICIs, emerging biomarkers, mechanisms of resistance, strategies to enhance therapeutic efficacy, and assessment of adverse effects. This review is crucial to furthering our understanding of ICIs and optimizing their application in cancer therapy.

Tuberculosis and T cells: Impact of T cell diversity in tuberculosis infection

Tuberculosis is a global threat and is still a leading cause of death due to an infectious agent. The infection is spread through inhalation of M. tb containing aerosol droplets. Bacteria after reaching the lung alveoli are engulfed by alveolar macrophages, leading to an immune response. Then, pro-inflammatory cytokines are released by these macrophages, recruiting other antigen-presenting cells like dendritic cells. These cells phagocytose the bacteria and present mycobacterial antigens to naïve T cells. After activation by DCs, T cells differentiate into various T cells subsets, viz. CD4+, CD8+, Th17, Treg, Tfh cells and others display enormous diversification in their characteristics and functions. This review comprises a comprehensive literature on conventional and unconventional T cells, highlighting the polyfunctional T cells as well, their role in controlling TB infection, and their implications in the spectrum of TB infection. While some subsets such as CD4+ T cells are extensively studied, some T cell subsets such as gamma delta T cells and Tfh cells remain poorly understood in the pathophysiology of tuberculosis, despite having significant potential implications. The goal of TB eradication can be assisted by development of better vaccines against TB, which can effectively induce a robust and long-term T cells memory. The same has been discussed in the latter part of this review. BCG being the standalone commercialised TB vaccine so far has its limitations. Strategies for the enhancement of BCG along with novel studies in vaccine development, has also been discussed in great detail. Lastly, T cells display a complex interplay of an adaptive immune response against TB, with activation and enhancement of the innate immune responses. Therefore, it is critical to fully understand the role of various T cells subsets in pathophysiology of tuberculosis to provide better therapeutic inventions and improve patient care.

Circular RNAs in tuberculosis: From mechanism of action to potential diagnostic biomarker

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis), continues to be a major global health concern. Understanding the molecular intricacies of TB pathogenesis is crucial for developing effective diagnostic and therapeutic approaches. Circular RNAs (circRNAs), a class of single-stranded RNA molecules characterized by covalently closed loops, have recently emerged as potential diagnostic biomarkers in various diseases. CircRNAs have been demonstrated to modulate the host's immunological responses against TB, specifically by reducing monocyte apoptosis, augmenting autophagy, and facilitating macrophage polarization. This review comprehensively explores the roles and mechanisms of circRNAs in TB pathogenesis. We also discuss the growing body of evidence supporting their utility as promising diagnostic biomarkers for TB. By bridging the gap between fundamental circRNA biology and TB diagnostics, this review offers insights into the exciting potential of circRNAs in combatting this infectious disease.

Contribution of IL-38 in Lung Immunity during Pseudomonas Aeruginosa-induced Pneumonia

OBJECTIVE

Interleukin-38 (IL-38), a new type of cytokine, is involved in processes such as tissue repair, inflammatory response, and immune response. However, its function in pneumonia caused by Pseudomonas aeruginosa (P. aeruginosa) is still unclear.

METHODS

In this study, we detected circulating IL-38 and cytokines such as IL-1β, IL-6, IL-17A, TNF-α, IL-8, and IL-10 in adults affected by early stage pneumonia caused by P. aeruginosa. Collected clinical data of these patients, such as the APACHE II score, levels of PCT, and oxygenation index when they entering the ICU. Using P. aeruginosa-induced pneumonia WT murine model to evaluate the effect of IL-38 on Treg differentiation, cell apoptosis, survival, tissue damage, inflammation, and bacterial removal.

RESULTS

In clinical research, although IL-38 is significantly increased during the early stages of clinical P. aeruginosa pneumonia, the concentration of IL-38 in the serum of patients who died with P. aeruginosa pneumonia was relatively lower than that of surviving patients. It reveals IL-38 may insufficiently secreted in patients who died with P. aeruginosa pneumonia. Besides, the serum IL-38 level of patients with P. aeruginosa pneumonia on the day of admission to the ICU showed significantly positive correlations with IL-10 and the PaO2/FiO2 ratio but negative correlations with IL-1β, IL-6, IL-8, IL-17, TNF-α, APACHE II score, and PCT In summary, IL-38 might be a molecule for adjuvant therapy in P. aeruginosa pneumonia. In experimental animal models, first recombinant IL-38 improved survival, whereas anti-IL-38 antibody reduced survival in the experimental pneumonia murine model. Secondly, IL-38 exposure reduced the inflammatory response, as suggested by the lung injury, and reduced cytokine levels (IL-1β, IL-6, IL- 17A, TNF-α, and IL-8, but not IL-10). It also increased bacterial clearance and reduced cell apoptosis in the lungs. Furthermore, IL-38 was shown to reduce TBK1 expression in vitro when naive CD4+ T lymphocytes were differentiated to Tregs and played a protective role in P. aeruginosa pneumonia.

CONCLUSIONS

To summarize, the above findings provide additional insights into the mechanism of IL-38 in the treatment of P. aeruginosa pneumonia.

Consensus guidelines for the definition, detection and interpretation of immunogenic cell death

Cells succumbing to stress via regulated cell death (RCD) can initiate an adaptive immune response associated with immunological memory, provided they display sufficient antigenicity and adjuvanticity. Moreover, multiple intracellular and microenvironmental features determine the propensity of RCD to drive adaptive immunity. Here, we provide an updated operational definition of immunogenic cell death (ICD), discuss the key factors that dictate the ability of dying cells to drive an adaptive immune response, summarize experimental assays that are currently available for the assessment of ICD in vitro and in vivo, and formulate guidelines for their interpretation.

Peripheral CD4+ T-cell changes in connective tissue diseases

Connective tissue diseases (CTDs) are all characterized by changes in the adaptive immune system. In the last few decades several CD4 + T lymphocytes and their products have been associated with the development, progression, organ involvement, or therapeutic response of different CTDs. The T helper (Th) T-cell subsets are easy to measure in the peripheral blood, however changes are difficult to interpret. This review summarizes data about Th1/Th2/Th17 and regulatory T-cell (Treg) changes in the most common CTDs. Concordance and divergence of data might help in the better understanding of the common processes of these different systemic autoimmune disorders and might give future clues for differences in disease behavior and treatment response.

Opportunities for the development of novel therapies based on host-microbial interactions

Immune responses are fundamental for protecting against most infectious agents. However, there is now much evidence to suggest that the pathogenesis and tissue damage after infection are not usually related to the direct action of the replication of microorganisms, but instead to altered immune responses triggered after the contact with the pathogen. This review article discusses several mechanisms necessary for the host to protect against microbial infection and focuses in aspects that cause altered inflammation and drive immunopathology. These basic findings can ultimately reveal pathways amenable to host-directed therapy in adjunct to antimicrobial therapy for future improved control measures for many infectious diseases. Therefore, modulating the effects of inflammatory pathways may represent a new therapy during infection outcome and disease.

Fascinating interaction between host and pathogen

Clinical manifestations of disease depend upon host's immune response that is induced by pathogen and modified by the host's innate and adaptive immunity. Immunocompetent children of similar age and nutrition evoke different responses to the same pathogen varying from benign to potentially fatal condition. This results in diverse clinical presentations of a disease, that is different from the standard expected pattern and thus, poses a diagnostic challenge. Even, subsequent progression of a disease is also variable. It is the balance between immune stimulation, immune suppression and immune tolerance that decides the outcome. In case of balanced response, child recovers completely without any damage. However at times, cure is at the expense of permanent sequalae while in case of unfavourable immune response, survival may not be certain inspite of successful therapy. Symptoms and physical signs of primary disease often overlap with those caused by host's immune response. In such a situation, it is difficult to decide whether therapy of primary disease has failed due to drug resistance or whether persistence or deterioration is the result of immune response. Occasionally pathogen can transform into "superantigen" that may lead to "cytokine storm". Resulting immune-mediated complications may endanger life and at best, treated symptomatically. Immune suppressive drugs such as steroids, chemotherapeutic agents, IVIG or specific antibodies may not be able to suppress undesirable immune response. It is not just the immune suppression that is required but ideally immune modulation. Immune modulation refers to enhancing protective responses while avoiding destructive ones. At present, science falls short of anticipating harmful immune responses and lacks specific immune intervention.Laboratory test results are also dependent on host response and hence need cautious interpretation based on clinical profile in consideration with multiple variables. In final analysis, fight between host and pathogen is a complex one and often unpredictable. It is hoped that most children evoke favourable response but pediatrician has to be watchful even in the most benign disease.

Tuberculosis vaccine development: strength lies in tenacity

The past decade has witnessed a tremendous increase in the development of novel vaccines against tuberculosis (TB). In mice, each of these vaccine candidates stimulates an immune response that reduces the bacillary load, reflecting control but not sterilization of infection. Yet, the immune mechanisms underlying vaccine efficacy are only partially understood. In parallel to clinical assessment of current candidates, the next generation of vaccine candidates still needs to be developed. This requires basic research on how to induce the most efficacious immune response. Equally important is the dissection of immune responses in patients, latently infected healthy individuals, and participants of clinical vaccine trials. Amalgamation of this information will foster the way towards more efficacious vaccination strategies that not only prevent disease, but prevent or abolish infection.

For better or for worse: the immune response against Mycobacterium tuberculosis balances pathology and protection

Tuberculosis (TB) is a complex disease, and the success of the bacterium as an intracellular pathogen is the outcome of its close and longstanding coevolution with the mammalian host. The dialogue between Mycobacterium tuberculosis and the host is becoming understandable at the molecular, cellular, and tissue level. This has led to the elucidation of the (i) interaction between pattern recognition receptors and pathogen-associated molecular patterns, (ii) cross-talk between immune cells, and (iii) mechanisms underlying granuloma development. Disease as an eventual but not a necessary consequence of infection results from a sensitive balance between protective immunity and destructive pathology. Early events, governed largely by conserved mechanisms of host recognition, impact not only on type and course of adaptive immunity but also on lung parenchymal function. New interpretations of how these responses shape the lung environment and direct granuloma development emphasize that the disease results from pathologic consequences of non-resolving inflammation. We review recent advances in TB research within the context of this ambitious view of TB.

New approaches in the diagnosis and treatment of latent tuberculosis infection

With nearly 9 million new active disease cases and 2 million deaths occurring worldwide every year, tuberculosis continues to remain a major public health problem. Exposure to Mycobacterium tuberculosis leads to active disease in only ~10% people. An effective immune response in remaining individuals stops M. tuberculosis multiplication. However, the pathogen is completely eradicated in ~10% people while others only succeed in containment of infection as some bacilli escape killing and remain in non-replicating (dormant) state (latent tuberculosis infection) in old lesions. The dormant bacilli can resuscitate and cause active disease if a disruption of immune response occurs. Nearly one-third of world population is latently infected with M. tuberculosis and 5%-10% of infected individuals will develop active disease during their life time. However, the risk of developing active disease is greatly increased (5%-15% every year and ~50% over lifetime) by human immunodeficiency virus-coinfection. While active transmission is a significant contributor of active disease cases in high tuberculosis burden countries, most active disease cases in low tuberculosis incidence countries arise from this pool of latently infected individuals. A positive tuberculin skin test or a more recent and specific interferon-gamma release assay in a person without overt signs of active disease indicates latent tuberculosis infection. Two commercial interferon-gamma release assays, QFT-G-IT and T-SPOT.TB have been developed. The standard treatment for latent tuberculosis infection is daily therapy with isoniazid for nine months. Other options include therapy with rifampicin for 4 months or isoniazid + rifampicin for 3 months or rifampicin + pyrazinamide for 2 months or isoniazid + rifapentine for 3 months. Identification of latently infected individuals and their treatment has lowered tuberculosis incidence in rich, advanced countries. Similar approaches also hold great promise for other countries with low-intermediate rates of tuberculosis incidence.

Future vaccination strategies against tuberculosis: thinking outside the box

With almost a dozen vaccine candidates in clinical trials, tuberculosis (TB) research and development is finally reaping the first fruits of its labors. Vaccine candidates in clinical trials may prevent TB disease reactivation by efficiently containing the pathogen Mycobacterium tuberculosis (Mtb). Future research should target vaccines that achieve sterile eradication of Mtb or even prevent stable infection. These are ambitious goals that can be reached only by highly cooperative engagement of basic immunologists, vaccinologists, and clinical researchers--or in other words, by translation from basic immunology to vaccine research and development, as well as reverse translation of insights from clinical trials back to hypothesis-driven research in the basic laboratory. Here, we review current and future strategies toward the rational design of novel vaccines against TB, as well as the progress made thus far, and the hurdles that need to be overcome in the near and distant future.

Human gene expression profiles of susceptibility and resistance in tuberculosis

Tuberculosis (TB) still poses a profound burden on global health, owing to significant morbidity and mortality worldwide. Although a fully functional immune system is essential for the control of Mycobacterium tuberculosis infection, the underlying mechanisms and reasons for failure in part of the infected population remain enigmatic. Here, whole-blood microarray gene expression analyses were performed in TB patients and in latently as well as uninfected healthy controls to define biomarkers predictive of susceptibility and resistance. Fc gamma receptor 1B (FCGRIB)was identified as the most differentially expressed gene, and, in combination with four other markers, produced a high degree of accuracy in discriminating TB patients and latently infected donors. We determined differentially expressed genes unique for active disease and identified profiles that correlated with susceptibility and resistance to TB. Elevated expression of innate immune-related genes in active TB and higher expression of particular gene clusters involved in apoptosis and natural killer cell activity in latently infected donors are likely to be the major distinctive factors determining failure or success in controlling M. tuberculosis infection. The gene expression profiles defined in this study provide valuable clues for better understanding of progression from latent infection to active disease and pave the way for defining predictive correlates of protection in TB.

New vaccines for tuberculosis

New vaccines are urgently needed if we want to reach the goal of substantially reducing the incidence of tuberculosis by 2050. Despite a steady increase in funding over the past decade, there is still a striking financial shortfall for vaccine research and development for tuberculosis. Yet, around ten vaccine candidates have left the laboratory stage and entered clinical trials. These vaccines are either aimed at replacing the present vaccine, BCG, or at enhancing immunity induced by BCG. However, these pre-exposure candidates are designed for prevention of disease and will therefore neither eradicate the pathogen, nor prevent stable infection. Long-term vaccination strategies need to target these more ambitious goals. Even though vaccine development will have a price, the return of investment will greatly exceed original costs.

Novel tuberculosis vaccination strategies based on understanding the immune response

The current tuberculosis (TB) vaccine bacillus Calmette-Guérin (BCG) fails to protect against adult pulmonary TB. Yet, its capacity to control miliary TB in newborn infants forms the basis for development of novel vaccine candidates. These either exploit genetic modification of BCG to create a viable replacement vaccine or use BCG to prime the immune response followed by boost with a novel subunit vaccine. This could ultimately result in a combination vaccination schedule comprising a prime with a live BCG replacement followed by a subunit vaccine boost. Ultimately, vaccination strategies that achieve sterile eradication of, or prevent infection with, tubercle bacilli would be an ambitious highly promising goal.

The immunology of tuberculosis: from bench to bedside

Tuberculosis (TB) is an international public health priority and kills almost two million people annually. TB is out of control in Africa due to increasing poverty and HIV coinfection, and drug-resistant TB threatens to destabilize TB control efforts in several regions of the world. Existing diagnostic tools and therapeutic interventions for TB are suboptimal. Thus, new vaccines, immunotherapeutic interventions and diagnostic tools are urgently required to facilitate TB control efforts. An improved understanding of the immunopathogenesis of TB can facilitate the identification of correlates of immune protection, the design of effective vaccines, the rational selection of immunotherapeutic agents, the evaluation of new drug candidates, and drive the development of new immunodiagnostic tools. Here we review the immunology of TB with a focus on aspects that are clinically and therapeutically relevant. An immunologically orientated approach to tackling TB can only succeed with concurrent efforts to alleviate poverty and reduce the global burden of HIV.

The adaptor molecule CARD9 is essential for tuberculosis control

The cross talk between host and pathogen starts with recognition of bacterial signatures through pattern recognition receptors (PRRs), which mobilize downstream signaling cascades. We investigated the role of the cytosolic adaptor caspase recruitment domain family, member 9 (CARD9) in tuberculosis. This adaptor was critical for full activation of innate immunity by converging signals downstream of multiple PRRs. Card9(-/-) mice succumbed early after aerosol infection, with higher mycobacterial burden, pyogranulomatous pneumonia, accelerated granulocyte recruitment, and higher abundance of proinflammatory cytokines and granulocyte colony-stimulating factor (G-CSF) in serum and lung. Neutralization of G-CSF and neutrophil depletion significantly prolonged survival, indicating that an exacerbated systemic inflammatory disease triggered lethality of Card9(-/-) mice. CARD9 deficiency had no apparent effect on T cell responses, but a marked impact on the hematopoietic compartment. Card9(-/-) granulocytes failed to produce IL-10 after Mycobacterium tuberculosis infection, suggesting that an absent antiinflammatory feedback loop accounted for granulocyte-dominated pathology, uncontrolled bacterial replication, and, ultimately, death of infected Card9(-/-) mice. Our data provide evidence that deregulated innate responses trigger excessive lung inflammation and demonstrate a pivotal role of CARD9 signaling in autonomous innate host defense against tuberculosis.

Epigenomics of T cell activation, differentiation, and memory

Activation of T cells is an essential step in the immunological response to infection. Although activation of naïve T cells results in proliferation and slow differentiation into cytokine-producing effector cells, antigen engagement with memory cells leads to cytokine production immediately. Even though the cell surface signaling events are similar in both the cases, the outcome is different, suggesting that distinct regulatory mechanisms may exist downstream of the activation signals. Recent advances in the understanding of global epigenetic patterns in T cells have resulted in the appreciation of the role of epigenetic mechanisms in processes such as activation and differentiation. In this review we discuss recent data suggesting that naïve T cell activation, differentiation, and lineage commitment result in epigenetic changes and a fine balance between different histone modifications is required. On the other hand, memory T cells are poised and do not require epigenetic changes for short-term activation.

Waging war against uropathogenic Escherichia coli: winning back the urinary tract

Urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) is a substantial economic and societal burden-a formidable public health issue. Symptomatic UTI causes significant discomfort in infected patients, results in lost productivity, predisposes individuals to more serious infections, and usually necessitates antibiotic therapy. There is no licensed vaccine available for prevention of UTI in humans in the United States, likely due to the challenge of targeting a relatively heterogeneous group of pathogenic strains in a unique physiological niche. Despite significant advances in the understanding of UPEC biology, mechanistic details regarding the host response to UTI and full comprehension of genetic loci that influence susceptibility require additional work. Currently, there is an appreciation for the role of classic innate immune responses-from pattern receptor recognition to recruitment of phagocytic cells-that occur during UPEC-mediated UTI. There is, however, a clear disconnect regarding how factors involved in the innate immune response to UPEC stimulate acquired immunity that facilitates enhanced clearance upon reinfection. Unraveling the molecular details of this process is vital in the development of a successful vaccine for prevention of human UTI. Here, we survey the current understanding of host responses to UPEC-mediated UTI with an eye on molecular and cellular factors whose activity may be harnessed by a vaccine that stimulates lasting and sterilizing immunity.