Epigenetics of T cell aging

T cell aging and exhaustion: Mechanisms and clinical implications

T cell senescence and exhaustion represent critical aspects of adaptive immune system dysfunction, with profound implications for health and the development of disease prevention and therapeutic strategies. These processes, though distinct, are interconnected at the molecular level, leading to impaired effector functions and reduced proliferative capacity of T cells. Such impairments increase susceptibility to diseases and diminish the efficacy of vaccines and treatments. Importantly, T cell senescence and exhaustion can dynamically influence each other, particularly in the context of chronic diseases. A deeper understanding of the molecular mechanisms underlying T cell senescence and exhaustion, as well as their interplay, is essential for elucidating the pathogenesis of related diseases and restoring dysfunctional immune responses. This knowledge will pave the way for the development of targeted therapeutic interventions and strategies to enhance immune competence. This review aims to summarize the characteristics, mechanisms, and disease associations of T cell senescence and exhaustion, while also delineating the distinctions and intersections between these two states to enhance our comprehension.

Metabolic Signaling as a Driver of T Cell Aging

Aging significantly diminishes T cell immunity, increasing susceptibility to infections and reducing vaccine efficacy in older individuals. Metabolism plays a key role in T cell function, shaping their energy requirements, activation, and differentiation. Recent studies highlight altered metabolic signaling as a pivotal factor in T cell aging, influencing the ability of T cells to maintain quiescence, respond to activation, and differentiate into functional subsets. Aberrant metabolic pathways disrupt the quiescence of aged T cells and skew their differentiation toward short-lived, pro-inflammatory effector T cells while hindering the generation of long-lived memory and T follicular helper cells. These changes contribute to a hyper-inflammatory state, exacerbate chronic low-grade inflammation, and compromise immune homeostasis. In this review, we explore how metabolic signaling is altered during T cell aging and the resulting functional impacts. We also discuss therapeutic approaches aimed at restoring proper T cell differentiation, improving vaccine responses, and rejuvenating immune function in older populations.

An in-depth understanding of the role and mechanisms of T cells in immune organ aging and age-related diseases

T cells play a critical and irreplaceable role in maintaining overall health. However, their functions undergo alterations as individuals age. It is of utmost importance to comprehend the specific characteristics of T-cell aging, as this knowledge is crucial for gaining deeper insights into the pathogenesis of aging-related diseases and developing effective therapeutic strategies. In this review, we have thoroughly examined the existing studies on the characteristics of immune organ aging. Furthermore, we elucidated the changes and potential mechanisms that occur in T cells during the aging process. Additionally, we have discussed the latest research advancements pertaining to T-cell aging-related diseases. These findings provide a fresh perspective for the study of T cells in the context of aging.

Decoding T cell senescence in cancer: Is revisiting required?

Senescence is an inherent cellular mechanism triggered as a response to stressful insults. It associates with several aspects of cancer progression and therapy. Senescent cells constitute a highly heterogeneous cellular population and their identification can be very challenging. In fact, the term "senescence" has been often misused. This is also true in the case of immune cells. While several studies indicate the presence of senescent-like features (mainly in T cells), senescent immune cells are poorly described. Under this prism, we herein review the current literature on what has been characterized as T cell senescence and provide insights on how to accurately discriminate senescent cells against exhausted or anergic ones. We also summarize the major metabolic and epigenetic modifications associated with T cell senescence and underline the role of senescent T cells in the tumor microenvironment (TME). Moreover, we discuss how these cells associate with standard clinical therapeutic interventions and how they impact their efficacy. Finally, we underline the importance of precise identification and thorough characterization of "truly" senescent T cells in order to design successful therapeutic manipulations that would delay cancer incidence and maximize efficacy of immunotherapy.

Conserved epigenetic hallmarks of T cell aging during immunity and malignancy

Chronological aging correlates with epigenetic modifications at specific loci, calibrated to species lifespan. Such 'epigenetic clocks' appear conserved among mammals, but whether they are cell autonomous and restricted by maximal organismal lifespan remains unknown. We used a multilifetime murine model of repeat vaccination and memory T cell transplantation to test whether epigenetic aging tracks with cellular replication and if such clocks continue 'counting' beyond species lifespan. Here we found that memory T cell epigenetic clocks tick independently of host age and continue through four lifetimes. Instead of recording chronological time, T cells recorded proliferative experience through modification of cell cycle regulatory genes. Applying this epigenetic profile across a range of human T cell contexts, we found that naive T cells appeared 'young' regardless of organism age, while in pediatric patients, T cell acute lymphoblastic leukemia appeared to have epigenetically aged for up to 200 years. Thus, T cell epigenetic clocks measure replicative history and can continue to accumulate well-beyond organismal lifespan.

Regulatory RNAs in immunosenescence

BACKGROUND

Immunosenescence is a multifactorial stress response to different intrinsic and extrinsic insults that cause immune deterioration and is accompanied by genomic or epigenomic perturbations. It is now widely recognized that genes and proteins contributing in the process of immunosenescence are regulated by various noncoding (nc) RNAs, including microRNAs (miRNAs), long ncRNAs, and circular RNAs.

AIMS

This review article aimed to evaluate the regulatore RNAs roles in the process of immunosenescence.

METHODS

We analyzed publications that were focusing on the different roles of regulatory RNAs on the several aspects of immunosenescence.

RESULTS

In the immunosenescence setting, ncRNAs have been found to play regulatory roles at both transcriptional and post-transcriptional levels. These factors cooperate to regulate the initiation of gene expression programs and sustaining the senescence phenotype and proinflammatory responses.

CONCLUSION

Immunosenescence is a complex process with pivotal alterations in immune function occurring with age. The extensive network that drive immunosenescence-related features are are mainly directed by a variety of regulatory RNAs such as miRNAs, lncRNAs, and circRNAs. Latest findings about regulation of senescence by ncRNAs in the innate and adaptive immune cells as well as their role in the immunosenescence pathways, provide a better understanding of regulatory RNAs function in the process of immunosenescence.

Genetic and environmental factors in interstitial lung diseases: current and future perspectives on early diagnosis of high-risk cohorts

Within the wide scope of interstitial lung diseases (ILDs), familial pulmonary fibrosis (FPF) is being increasingly recognized as a specific entity, with earlier onset, faster progression, and suboptimal responses to immunosuppression. FPF is linked to heritable pathogenic variants in telomere-related genes (TRGs), surfactant-related genes (SRGs), telomere shortening (TS), and early cellular senescence. Telomere abnormalities have also been identified in some sporadic cases of fibrotic ILD. Air pollution and other environmental exposures carry additive risk to genetic predisposition in pulmonary fibrosis. We provide a perspective on how these features impact on screening strategies for relatives of FPF patients, interstitial lung abnormalities, ILD multi-disciplinary team (MDT) discussion, and disparities and barriers to genomic testing. We also describe our experience with establishing a familial interstitial pneumonia (FIP) clinic and provide guidance on how to identify patients with telomere dysfunction who would benefit most from genomic testing.

Transcriptome-based measurement of CD8+ T cell age and its applications

The ability of T cells to undergo robust cell division in response to antigenic stimulation is essential for competent T cell function. However, this ability is reduced with aging and contributes to increased susceptibility to infectious diseases, cancers, and other diseases among older adults. To better understand T cell aging, improved measurements of age-related cellular changes in T cells are necessary. The recent development of machine learning (ML)-assisted transcriptome-based quantification of individual CD8+ T cell age represents a significant step forward in this regard. It reveals both prominent and subtle changes in gene expression and points to potential functional alterations of CD8+ T cells with aging. I argue that single-cell transcriptome-based age prediction in the immune system may have promising future applications.

Epigenomic variability is associated with age-specific naïve CD4 T cell response to activation in infants and adolescents

Childhood is a critical period of immune development. During this time, naïve CD4 (nCD4) T cells undergo programmed cell differentiation, mediated by epigenetic changes, in response to external stimuli leading to a baseline homeostatic state that may determine lifelong disease risk. However, the ontogeny of epigenetic signatures associated with CD4 T cell activation during key developmental periods are yet to be described. We investigated genome-wide DNA methylation (DNAm) changes associated with nCD4 T activation following 72 h culture in media+anti-CD3/CD28 beads in healthy infants (aged 12 months, n = 18) and adolescents (aged 10-15 years, n = 15). We integrated these data with transcriptomic and cytokine profiling from the same samples. nCD4 T cells from both age groups show similar extensive epigenetic reprogramming following activation, with the majority of genes involved in the T cell receptor signaling pathway associated with differential methylation. Additionally, we identified differentially methylated probes showing age-specific responses, that is, responses in only infants or adolescents, including within a cluster of T cell receptor (TCR) genes. These encoded several TCR alpha joining (TRAJ), and TCR alpha variable (TRAV) genes. Cytokine data analysis following stimulation revealed enhanced release of IFN-γ, IL-2 and IL-10, in nCD4 T cells from adolescents compared with infants. Overlapping differential methylation and cytokine responses identified four probes potentially underpinning these age-specific responses. We show that DNAm in nCD4T cells in response to activation is dynamic in infancy and adolescence, with additional evidence for age-specific effects potentially driving variation in cytokine responses between these ages.

T cell aging as a risk factor for autoimmunity

Immune aging is a complex process rendering the host susceptible to cancer, infection, and insufficient tissue repair. Many autoimmune diseases preferentially occur during the second half of life, counterintuitive to the concept of excess adaptive immunity driving immune-mediated tissue damage. T cells are particularly susceptible to aging-imposed changes, as they are under extreme proliferative pressure to fulfill the demands of clonal expansion and of homeostatic T cell repopulation. T cells in older adults have a footprint of genetic and epigenetic changes, lack mitochondrial fitness, and fail to maintain proteostasis, diverging them from host protection to host injury. Here, we review recent progress in understanding how the human T-cell system ages and the evidence detailing how T cell aging contributes to autoimmune conditions. T cell aging is now recognized as a risk determinant in two prototypic autoimmune syndromes; rheumatoid arthritis and giant cell arteritis. The emerging concept adds susceptibility to autoimmune and autoinflammatory disease to the spectrum of aging-imposed adaptations and opens new opportunities for immunomodulatory therapy by restoring the functional intactness of aging T cells.

T cell aging and Alzheimer's disease

The brain has long been considered an immune-privileged organ due to the presence of the blood-brain barrier (BBB). However, recent discoveries have revealed the underestimated role of T cells in the brain through the meningeal lymphatic system. Age is the primary risk factor for Alzheimer's disease (AD), resulting in marked age-dependent changes in T cells. Manipulating peripheral T cell immune response has been shown to impact AD, but the relationship between T cell aging and AD remains poorly understood. Given the limited success of targeting amyloid beta (Aβ) and the growing evidence of T cells' involvement in non-lymphoid organ aging, a deeper understanding of the relationship between T cells and AD in the context of aging is crucial for advancing therapeutic progress. In this review, we comprehensively examine existing studies on T cells and AD and offer an integrated perspective on their interconnections in the context of aging. This understanding can inform the development of new interventions to prevent or treat AD.

Transcriptional activation of Jun and Fos members of the AP-1 complex is a conserved signature of immune aging that contributes to inflammaging

Diverse mouse strains have different health and life spans, mimicking the diversity among humans. To capture conserved aging signatures, we studied long-lived C57BL/6J and short-lived NZO/HILtJ mouse strains by profiling transcriptomes and epigenomes of immune cells from peripheral blood and the spleen from young and old mice. Transcriptional activation of the AP-1 transcription factor complex, particularly Fos, Junb, and Jun genes, was the most significant and conserved aging signature across tissues and strains. ATAC-seq data analyses showed that the chromatin around these genes was more accessible with age and there were significantly more binding sites for these TFs with age across all studied tissues, targeting pro-inflammatory molecules including Il6. Age-related increases in binding sites of JUN and FOS factors were also conserved in human peripheral blood ATAC-seq data. Single-cell RNA-seq data from the mouse aging cell atlas Tabula Muris Senis showed that the expression of these genes increased with age in B, T, NK cells, and macrophages, with macrophages from old mice expressing these molecules more abundantly than other cells. Functional data showed that upon myeloid cell activation via poly(I:C), the levels of JUN protein and its binding activity increased more significantly in spleen cells from old compared to young mice. In addition, upon activation, old cells produced more IL6 compared to young cells. In sum, we showed that the aging-related transcriptional activation of Jun and Fos family members in AP-1 complex is conserved across immune tissues and long- and short-living mouse strains, possibly contributing to increased inflammation with age.

Role of T Cells in the Pathogenesis of Rheumatoid Arthritis: Focus on Immunometabolism Dysfunctions

Evidence demonstrated that metabolic-associated T cell abnormalities could be detected in the early stage of RA development. In this context, molecular evaluations have revealed changes in metabolic pathways, leading to the aggressive phenotype of RA T cells. A growing list of genes is downregulated or upregulated in RA T cells, and most of these genes with abnormal expression fall into the category of metabolic pathways. It has been shown that RA T cells shunt glucose towards the pentose phosphate pathway (PPP), which is associated with a high level of nicotinamide adenine dinucleotide phosphate (NADPH) and intermediate molecules. An increased level of NADPH inhibits ATM activation and thereby increases the proliferation capabilities of the RA T cells. Defects in the DNA repair nuclease MRE11A cause failures in repairing mitochondrial DNA, resulting in inhibiting the fatty acid oxidation pathway and further elevated cytoplasmic lipid droplets. Accumulated lipid droplets employ to generate lipid membranes for the cell building program and are also used to form the front-end membrane ruffles that are accomplices with invasive phenotypes of RA T cells. Metabolic pathway involvement in RA pathogenesis expands the pathogenic concept of the disease beyond the common view of autoimmunity triggered by autoantigen recognition. Increased knowledge about metabolic pathways' implications in RA pathogenesis paves the way to understand better the environment/gene interactions and host/microbiota interactions and introduce potential therapeutic approaches. This review summarized emerging data about the roles of T cells in RA pathogenesis with a focus on immunometabolism dysfunctions and how these metabolic alterations can affect the disease process.

Maintaining a 'fit' immune system: the role of vaccines

INTRODUCTION

Conventionally, vaccines are thought to induce a specific immune response directed against a target pathogen. Long recognized but poorly understood nonspecific benefits of vaccination, such as reduced susceptibility to unrelated diseases or cancer, are now being investigated and may be due in part to "trained immunity'.

AREAS COVERED

We discuss 'trained immunity' and whether vaccine-induced 'trained immunity' could be leveraged to prevent morbidity due to a broader range of causes.

EXPERT OPINION

The prevention of infection i.e. maintaining homeostasis by preventing the primary infection and resulting secondary illnesses, is the pivotal strategy used to direct vaccine design and may have long-term, positive impacts on health at all ages. In the future, we anticipate that vaccine design will change to not only prevent the target infection (or related infections) but to generate positive modifications to the immune response that could prevent a wider range of infections and potentially reduce the impact of immunological changes associated with aging. Despite changing demographics, adult vaccination has not always been prioritized. However, the SARS-CoV-2 pandemic has demonstrated that adult vaccination can flourish given the right circumstances, demonstrating that harnessing the potential benefits of life-course vaccination is achievable for all.

Measuring biological age using omics data

Age is the key risk factor for diseases and disabilities of the elderly. Efforts to tackle age-related diseases and increase healthspan have suggested targeting the ageing process itself to 'rejuvenate' physiological functioning. However, achieving this aim requires measures of biological age and rates of ageing at the molecular level. Spurred by recent advances in high-throughput omics technologies, a new generation of tools to measure biological ageing now enables the quantitative characterization of ageing at molecular resolution. Epigenomic, transcriptomic, proteomic and metabolomic data can be harnessed with machine learning to build 'ageing clocks' with demonstrated capacity to identify new biomarkers of biological ageing.

Possibilities of using T-cell biophysical biomarkers of ageing

Ageing is interrelated with the development of immunosenescence. This article focuses on one of the cell sets of the adaptive immune system, T cells, and provides a review of the known changes in T cells associated with ageing. Such fundamental changes affect both cell molecular content and internal ordering. However, acquiring a complete description of the changes at these levels would require extensive measurements of parameters and, furthermore, important fine details of the internal ordering that may be difficult to detect. Therefore, an alternative approach for the characterisation of cells consists of the performance of physical measurements of the whole cell, such as deformability measurements or migration measurements: the physical parameters, complementing the commonly used chemical biomarkers, may contribute to a better understanding of the evolution of T-cell states during ageing. Mechanical measurements, among other biophysical measurements, have the advantage of their relative simplicity: one single parameter agglutinates the complex effects of the variety of changes that gradually appear in cells during ageing.

Transcriptome Analysis of Tumor-Infiltrating Lymphocytes Identifies NK Cell Gene Signatures Associated With Lymphocyte Infiltration and Survival in Soft Tissue Sarcomas

Purpose

Clinical successes using current T-cell based immunotherapies have been limited in soft tissue sarcomas (STS), while pre-clinical studies have shown evidence of natural killer (NK) cell activity. Since tumor immune infiltration, especially tumor-infiltrating lymphocytes, is associated with improved survival in most solid tumors, we sought to evaluate the gene expression profile of tumor and blood NK and T cells, as well as tumor cells, with the goal of identifying potential novel immune targets in STS.

Experimental Design

Using fluorescence-activated cell sorting, we isolated blood and tumor-infiltrating CD3^-CD56⁺ NK and CD3⁺ T cells and CD45^- viable tumor cells from STS patients undergoing surgery. We then evaluated differential gene expression (DGE) of these purified populations with RNA sequencing analysis. To evaluate survival differences and validate primary DGE results, we also queried The Cancer Genome Atlas (TCGA) database to compare outcomes stratified by bulk gene expression.

Results

Sorted intra-tumoral CD3⁺ T cells showed significant upregulation of established activating (CD137) and inhibitory genes (TIM-3) compared to circulating T cells. In contrast, intra-tumoral NK cells did not exhibit upregulation of canonical cytotoxic genes (IFNG, GZMB), but rather significant DGE in mitogen signaling (DUSP4) and metabolic function (SMPD3, SLC7A5). Tumors with higher NK and T cell infiltration exhibited significantly increased expression of the pro-inflammatory receptor TLR4 in sorted CD45^- tumor cells. TCGA analysis revealed that tumors with high TLR4 expression (P = 0.03) and low expression of STMN1 involved in microtubule polymerization (P < 0.001) were associated with significantly improved survival.

Conclusions

Unlike T cells, which demonstrate significant DGE consistent with upregulation of both activating and inhibiting receptors in tumor-infiltrating subsets, NK cells appear to have more stable gene expression between blood and tumor subsets, with alterations restricted primarily to metabolic pathways. Increased immune cell infiltration and improved survival were positively correlated with TLR4 expression and inversely correlated with STMN1 expression within tumors, suggesting possible novel therapeutic targets for immunotherapy in STS.

Understanding the role of host metabolites in the induction of immune senescence: Future strategies for keeping the ageing population healthy

Advancing age is accompanied by significant remodelling of the immune system, termed immune senescence, and increased systemic inflammation, termed inflammageing, both of which contribute towards an increased risk of developing chronic diseases in old age. Age-associated alterations in metabolic homeostasis have been linked with changes in a range of physiological functions, but their effects on immune senescence remains poorly understood. In this article, we review the recent literature to formulate hypotheses as to how an age-associated dysfunctional metabolism, driven by an accumulation of key host metabolites (saturated fatty acids, cholesterol, ceramides and lactate) and loss of other metabolites (glutamine, tryptophan and short-chain fatty acids), might play a role in driving immune senescence and inflammageing, ultimately leading to diseases of old age. We also highlight the potential use of metabolic immunotherapeutic strategies targeting these processes in counteracting immune senescence and restoring immune homeostasis in older adults. LINKED ARTICLES: This article is part of a themed issue on Inflammation, Repair and Ageing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.9/issuetoc.

Clinical perspectives on the age-related increase of immunosuppressive activity

The aging process is associated with a remodeling of the immune system involving chronic low-grade inflammation and a gradual decline in the function of the immune system. These processes are also called inflammaging and immunosenescence. The age-related immune remodeling is associated with many clinical changes, e.g., risk for cancers and chronic infections increases, whereas the efficiency of vaccination and immunotherapy declines with aging. On the other hand, there is convincing evidence that chronic inflammatory states promote the premature aging process. The inflammation associated with aging or chronic inflammatory conditions stimulates a counteracting immunosuppression which protects tissues from excessive inflammatory injuries but promotes immunosenescence. Immunosuppression is a driving force in tumors and chronic infections and it also induces the tolerance to vaccination and immunotherapies. Immunosuppressive cells, e.g., myeloid-derived suppressor cells (MDSC), regulatory T cells (Treg), and type M2 macrophages, have a crucial role in tumorigenesis and chronic infections as well as in the tolerance to vaccination and immunotherapies. Interestingly, there is substantial evidence that inflammaging is also associated with an increased immunosuppressive activity, e.g., upregulation of immunosuppressive cells and anti-inflammatory cytokines. Given that both the aging and chronic inflammatory states involve the activation of immunosuppression and immunosenescence, this might explain why aging is a risk factor for tumorigenesis and chronic inflammatory states and conversely, chronic inflammatory insults promote the premature aging process in humans.

Metabolic programs tailor T cell immunity in viral infection, cancer, and aging

Productive T cell responses to infection and cancer rely on coordinated metabolic reprogramming and epigenetic remodeling among the immune cells. In particular, T cell effector and memory differentiation, exhaustion, and senescence/aging are tightly regulated by the metabolism-epigenetics axis. In this review, we summarize recent advances of how metabolic circuits combined with epigenetic changes dictate T cell fate decisions and shape their functional states. We also discuss how the metabolic-epigenetic axis orchestrates T cell exhaustion and explore how physiological factors, such as diet, gut microbiota, and the circadian clock, are integrated in shaping T cell epigenetic modifications and functionality. Furthermore, we summarize key features of the senescent/aged T cells and discuss how to ameliorate vaccination- and COVID-induced T cell dysfunctions by metabolic modulations. An in-depth understanding of the unexplored links between cellular metabolism and epigenetic modifications in various physiological or pathological contexts has the potential to uncover novel therapeutic strategies for fine-tuning T cell immunity.

Age as a risk factor in vasculitis

Two vasculitides, giant cell arteritis (GCA) and Takayasu arteritis (TAK), are recognized as autoimmune and autoinflammatory diseases that manifest exclusively within the aorta and its large branches. In both entities, the age of the affected host is a critical risk factor. TAK manifests during the 2nd-4th decade of life, occurring while the immune system is at its height of performance. GCA is a disease of older individuals, with infrequent cases during the 6th decade and peak incidence during the 8th decade of life. In both vasculitides, macrophages and T cells infiltrate into the adventitia and media of affected vessels, induce granulomatous inflammation, cause vessel wall destruction, and reprogram vascular cells to drive adventitial and neointimal expansion. In GCA, abnormal immunity originates in an aged immune system and evolves within the aged vascular microenvironment. One hallmark of the aging immune system is the preferential loss of CD8⁺ T cell function. Accordingly, in GCA but not in TAK, CD8⁺ effector T cells play a negligible role and anti-inflammatory CD8⁺ T regulatory cells are selectively impaired. Here, we review current evidence of how the process of immunosenescence impacts the risk for GCA and how fundamental differences in the age of the immune system translate into differences in the granulomatous immunopathology of TAK versus GCA.

Immunosuppressive network promotes immunosenescence associated with aging and chronic inflammatory conditions

The functional competence of the immune system gradually declines with aging, a process called immunosenescence. The age-related remodelling of the immune system affects both adaptive and innate immunity. In particular, a chronic low-grade inflammation, termed inflammaging, is associated with the aging process. Immunosenescence not only is present in inflammaging state, but it also occurs in several pathological conditions in conjunction with chronic inflammation. It is known that persistent inflammation stimulates a counteracting compensatory immunosuppression intended to protect host tissues. Inflammatory mediators enhance myelopoiesis and induce the generation of immature myeloid-derived suppressor cells (MDSC) which in mutual cooperation stimulates the immunosuppressive network. Immunosuppressive cells, especially MDSCs, regulatory T cells (Treg), and M2 macrophages produce immunosuppressive factors, e.g., TGF-β, IL-10, ROS, arginase-1 (ARG1), and indoleamine 2,3-dioxygenase (IDO), which suppress the functions of CD4/CD8T and B cells as well as macrophages, natural killer (NK) cells, and dendritic cells. The immunosuppressive armament (i) inhibits the development and proliferation of immune cells, (ii) decreases the cytotoxic activity of CD8T and NK cells, (iii) prevents antigen presentation and antibody production, and (iv) suppresses responsiveness to inflammatory mediators. These phenotypes are the hallmarks of immunosenescence. Immunosuppressive factors are able to control the chromatin landscape, and thus, it seems that the immunosenescence state is epigenetically regulated.

Vaccination as a preventative measure contributing to immune fitness

The primary goal of vaccination is the prevention of pathogen-specific infection. The indirect consequences may include maintenance of homeostasis through prevention of infection-induced complications; trained immunity that re-programs innate cells to respond more efficiently to later, unrelated threats; slowing or reversing immune senescence by altering the epigenetic clock, and leveraging the pool of memory B and T cells to improve responses to new infections. Vaccines may exploit the plasticity of the immune system to drive longer-term immune responses that promote health at a broader level than just the prevention of single, specific infections. In this perspective, we discuss the concept of “immune fitness” and how to potentially build a resilient immune system that could contribute to better health. We argue that vaccines may contribute positively to immune fitness in ways that are only beginning to be understood, and that life-course vaccination is a fundamental tool for achieving healthy aging.

Immune Aging and Immunotherapy in Cancer

Immune functions decline as we age, while the incidence of cancer rises. The advent of immune checkpoint blockade (ICB) has not only revolutionized cancer therapy, but also spawned great interest in identifying predictive biomarkers, since only one third of patients show treatment response. The aging process extensively affects the adaptive immune system and thus T cells, which are the main target of ICB. In this review, we address age-related changes regarding the adaptive immune system with a focus on T cells and their implication on carcinogenesis and ICB. Differences between senescence, exhaustion, and anergy are defined and current knowledge, treatment strategies, and studies exploring T cell aging as a biomarker for ICB are discussed. Finally, novel approaches to improve immunotherapies and to identify biomarkers of response to ICB are presented and their potential is assessed in a comparative analysis.

miR-181a-regulated pathways in T-cell differentiation and aging

MicroRNAs (miRNAs) are regulatory noncoding RNAs important for many aspects of cellular processes including cell differentiation and proliferation. Functions of numerous miRNAs have been identified in T cells, with miR-181a regulating T cell activation thresholds during thymic T cell development and during activation of peripheral T cells. Intriguingly, miR-181a is implicated in defective antiviral and vaccine responses in older individuals, as its expression declines in naïve T cells with increasing age. Here, we review the pathways that are regulated by miR-181a and that explain the unique role of miR-181a in T cell development, T cell activation and antiviral T cell responses. These studies provide a framework for understanding how a decline in miR-181a expression in T cells could contribute to age-related defects in adaptive immunity. We furthermore review the mechanisms that cause the age-related decline in miR-181a expression and discuss the potential of restoring miR-181a expression or targeting miR-181a-regulated pathways to improve impaired T cell responses in older individuals.

Histone deficiency and accelerated replication stress in T cell aging

With increasing age, individuals are more vulnerable to viral infections such as with influenza or the SARS-CoV-2 virus. One age-associated defect in human T cells is the reduced expression of miR-181a. miR-181ab1 deficiency in peripheral murine T cells causes delayed viral clearance after infection, resembling human immune aging. Here we show that naive T cells from older individuals as well as miR-181ab1-deficient murine T cells develop excessive replication stress after activation, due to reduced histone expression and delayed S-phase cell cycle progression. Reduced histone expression was caused by the miR-181a target SIRT1 that directly repressed transcription of histone genes by binding to their promoters and reducing histone acetylation. Inhibition of SIRT1 activity or SIRT1 silencing increased histone expression, restored cell cycle progression, diminished the replication-stress response, and reduced the production of inflammatory mediators in replicating T cells from old individuals. Correspondingly, treatment with SIRT1 inhibitors improved viral clearance in mice with miR-181a-deficient T cells after LCMV infection. In conclusion, SIRT1 inhibition may be beneficial to treat systemic viral infection in older individuals by targeting antigen-specific T cells that develop replication stress due to miR-181a deficiency.

The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies

Infectious diseases and infections remain a leading cause of death in low-income countries and a major risk to vulnerable groups, such as infants and the elderly. The immune system plays a crucial role in the susceptibility, persistence, and clearance of these infections. With 70–80% of immune cells being present in the gut, there is an intricate interplay between the intestinal microbiota, the intestinal epithelial layer, and the local mucosal immune system. In addition to the local mucosal immune responses in the gut, it is increasingly recognized that the gut microbiome also affects systemic immunity. Clinicians are more and more using the increased knowledge about these complex interactions between the immune system, the gut microbiome, and human pathogens. The now well-recognized impact of nutrition on the composition of the gut microbiota and the immune system elucidates the role nutrition can play in improving health. This review describes the mechanisms involved in maintaining the intricate balance between the microbiota, gut health, the local immune response, and systemic immunity, linking this to infectious diseases throughout life, and highlights the impact of nutrition in infectious disease prevention and treatment.

Deep immune profiling of MIS-C demonstrates marked but transient immune activation compared to adult and pediatric COVID-19

Pediatric COVID-19 following SARS-CoV-2 infection is associated with fewer hospitalizations and often milder disease than in adults. A subset of children, however, present with Multisystem Inflammatory Syndrome in Children (MIS-C) that can lead to vascular complications and shock, but rarely death. The immune features of MIS-C compared to pediatric COVID-19 or adult disease remain poorly understood. We analyzed peripheral blood immune responses in hospitalized SARS-CoV-2 infected pediatric patients (pediatric COVID-19) and patients with MIS-C. MIS-C patients had patterns of T cell-biased lymphopenia and T cell activation similar to severely ill adults, and all patients with MIS-C had SARS-CoV-2 spike-specific antibodies at admission. A distinct feature of MIS-C patients was robust activation of vascular patrolling CX3CR1+ CD8+ T cells that correlated with the use of vasoactive medication. Finally, whereas pediatric COVID-19 patients with acute respiratory distress syndrome (ARDS) had sustained immune activation, MIS-C patients displayed clinical improvement over time, concomitant with decreasing immune activation. Thus, non-MIS-C versus MIS-C SARS-CoV-2 associated illnesses are characterized by divergent immune signatures that are temporally distinct from one another and implicate CD8+ T cells in the clinical presentation and trajectory of MIS-C.

Senescence in Pulmonary Fibrosis: Between Aging and Exposure

To date, chronic pulmonary pathologies represent the third leading cause of death in the elderly population. Evidence-based projections suggest that >65 (years old) individuals will account for approximately a quarter of the world population before the turn of the century. Genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication, are described as the nine “hallmarks” that govern cellular fitness. Any deviation from the normal pattern initiates a complex cascade of events culminating to a disease state. This blueprint, originally employed to describe aberrant changes in cancer cells, can be also used to describe aging and fibrosis. Pulmonary fibrosis (PF) is the result of a progressive decline in injury resolution processes stemming from endogenous (physiological decline or somatic mutations) or exogenous stress. Environmental, dietary or occupational exposure accelerates the pathogenesis of a senescent phenotype based on (1) window of exposure; (2) dose, duration, recurrence; and (3) cells type being targeted. As the lung ages, the threshold to generate an irreversibly senescent phenotype is lowered. However, we do not have sufficient knowledge to make accurate predictions. In this review, we provide an assessment of the literature that interrogates lung epithelial, mesenchymal, and immune senescence at the intersection of aging, environmental exposure and pulmonary fibrosis.

Understanding host immune responses to pneumococcal proteins in the upper respiratory tract to develop serotype-independent pneumococcal vaccines

Introduction: Nasopharyngeal colonization is a precondition for mucosal and invasive pneumococcal disease. Prevention of colonization may reduce pneumococcal transmission and disease incidence. Therefore, several protein-based pneumococcal vaccines are currently under investigation. Areas covered: We aimed to better understand the host immune responses to pneumococcal proteins in the upper respiratory tract (URT) that could facilitate the development of serotype-independent pneumococcal vaccines. English peer-reviewed papers reporting immunological mechanisms involved in host immune response to pneumococcal proteins in the URT were retrieved through a PubMed search using the terms 'pneumococcal proteins,' 'nasopharyngeal colonization' and/or 'cellular/humoral host immune response.' Expert opinion: Although pneumococcal protein antigens induce humoral immune responses, as well as IL-17A-mediated immunity, none of them, when used as single antigen, is sufficient to control and broadly protect against pneumococcal colonization. Novel vaccines should contain multiple conserved protein antigens to activate both arms of the immune system and evoke protection against the whole spectrum of pneumococcal variants by reducing, rather than eradicating, pneumococcal carriage. The highest efficacy would likely be achieved when the vaccine is intranasally applied, inducing mucosal immunity and enhancing the first line of defense by restricting pneumococcal density in the URT, which in turn will lead to reduced transmission and protection against disease.

Deep Immune Profiling of MIS-C demonstrates marked but transient immune activation compared to adult and pediatric COVID-19

Pediatric COVID-19 following SARS-CoV-2 infection is associated with fewer hospitalizations and often milder disease than in adults. A subset of children, however, present with Multisystem Inflammatory Syndrome in Children (MIS-C) that can lead to vascular complications and shock, but rarely death. The immune features of MIS-C compared to pediatric COVID-19 or adult disease remain poorly understood. We analyzed peripheral blood immune responses in hospitalized SARS-CoV-2 infected pediatric patients (pediatric COVID-19) and patients with MIS-C. MIS-C patients had patterns of T cell-biased lymphopenia and T cell activation similar to severely ill adults, and all patients with MIS-C had SARS-CoV-2 spike-specific antibodies at admission. A distinct feature of MIS-C patients was robust activation of vascular patrolling CX3CR1+ CD8 T cells that correlated with use of vasoactive medication. Finally, whereas pediatric COVID-19 patients with acute respiratory distress syndrome (ARDS) had sustained immune activation, MIS-C patients displayed clinical improvement over time, concomitant with decreasing immune activation. Thus, non-MIS-C versus MIS-C SARS-CoV-2 associated illnesses are characterized by divergent immune signatures that are temporally distinct and implicate CD8 T cells in clinical presentation and trajectory of MIS-C.

The metabolic signature of T cells in rheumatoid arthritis

PURPOSE OF REVIEW

Rheumatoid arthritis (RA) is a prototypic autoimmune disease manifesting as chronic inflammation of the synovium and leading to acceleration of cardiovascular disease and shortening of life expectancy. The basic defect causing autoimmunity has remained elusive, but recent insights have challenged the notion that autoantigen is the core driver.

RECENT FINDINGS

Emerging data have added metabolic cues involved in the proper maintenance and activation of immune cells as pathogenic regulators. Specifically, studies have unveiled metabolic pathways that enforce T cell fate decisions promoting tissue inflammation; including T cell tissue invasiveness, T cell cytokine release, T cell-dependent macrophage activation and inflammatory T cell death. At the center of the metabolic abnormalities lies the mitochondria, which is consistently underperforming in RA T cells. The mitochondrial defect results at least partially from insufficient DNA repair and leads to lipid droplet accumulation, formation of invasive membrane ruffles, inflammasome activation and pyroptotic T cell death.

SUMMARY

T cells in patients with RA, even naïve T cells never having been involved in inflammatory lesions, have a unique metabolic signature and the changes in intracellular metabolites drive pathogenic T cell behavior. Recognizing the role of metabolic signals in cell fate decisions opens the possibility for immunomodulation long before the end stage synovial inflammation encountered in clinical practice.

The Transcription Factor TCF1 in T Cell Differentiation and Aging

The transcription factor T cell factor 1 (TCF1), a pioneer transcription factor as well as a downstream effector of WNT/β-catenin signaling, is indispensable for T cell development in the thymus. Recent studies have highlighted the additional critical role of TCF1 in peripheral T cell responses to acute and chronic infections as well as cancer. Here, we review the regulatory functions of TCF1 in the differentiation of T follicular helper cells, memory T cells and recently described stem-like exhausted T cells, where TCF1 promotes less differentiated stem-like cell states by controlling common gene-regulatory networks. These studies also provide insights into the mechanisms of defective T cell responses in older individuals. We discuss alterations in TCF1 expression and related regulatory networks with age and their consequences for T cell responses to infections and vaccination. The increasing understanding of the pathways regulating TCF1 expression and function in aged T cells holds the promise of enabling the design of therapeutic interventions aiming at improving T cell responses in older individuals.

Pathogenesis of Giant Cell Arteritis and Takayasu Arteritis-Similarities and Differences

PURPOSE OF REVIEW

Giant cell arteritis (GCA) and Takayasu arteritis (TAK) are auto-inflammatory and autoimmune diseases with a highly selective tissue tropism for medium and large arteries. In both diseases, CD4⁺ T cells and macrophages form granulomatous lesions within the arterial wall, a tissue site normally protected by immune privilege. Vascular lesions can be accompanied by an extravascular component, typically an intense hepatic acute phase response that produces well-known laboratory abnormalities, e.g., elevated ESR and CRP. It is unclear whether GCA and TAK lie on a spectrum of disease or whether they represent fundamentally different disease processes.

RECENT FINDINGS

GCA and TAK share many clinical features, but there are substantial differences in genetics, epidemiology, disease mechanisms, response to treatment, and treatment complications that give rise to different disease trajectories. A significant difference lies in the composition of the wall-infiltrating immune cell compartment, which in TAK includes a significant population of CD8⁺ T cells as well as natural killer cells, specifying disparate disease effector pathways mediating tissue damage and vessel wall remodeling. Despite the similarities in tissue tropism and histomorphology, GCA and TAK are two distinct vasculitides that rely on separate disease mechanisms and require disease-specific approaches in diagnosis and management.

The lethal sex gap: COVID-19

While Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is disrupting lives across the globe for everyone, it has a more devastating impact on the health of older adults, especially that of older men. This pandemic has highlighted the crucial importance of considering an individual’s age and biological sex in the clinic in addition to other confounding diseases (Kuchel, G.A, J Am Geriatr Soc, 67, 203, 2019, Tannenbaum, C., Nature, 575 451-458, 2009) As an interdisciplinary team of scientists in immunology, hematology, genomics, bioinformatics, and geriatrics, we have been studying how age and sex shape the human immune system. Herein we reflect on how our recent findings on the alterations of the immune system in aging might contribute to our current understanding of COVID-19 infection rate and disease risk.

Influence of immune aging on vaccine responses

Impaired vaccine responses in older individuals are associated with alterations in both the quantity and quality of the T-cell compartment with age. As reviewed herein, the T-cell response to vaccination requires a fine balance between the generation of inflammatory effector T cells versus follicular helper T (TFH) cells that mediate high-affinity antibody production in tandem with the induction of long-lived memory cells for effective recall immunity. During aging, we find that this balance is tipped where T cells favor short-lived effector but not memory or TFH responses. Consistently, vaccine-induced antibodies commonly display a lower protective capacity. Mechanistically, multiple, potentially targetable, changes in T cells have been identified that contribute to these age-related defects, including posttranscription regulation, T-cell receptor signaling, and metabolic function. Although research into the induction of tissue-specific immunity by vaccines and with age is still limited, current mechanistic insights provide a framework for improved design of age-specific vaccination strategies that require further evaluation in a clinical setting.

FOXO1 deficiency impairs proteostasis in aged T cells

T cell differentiation involves the dynamic regulation of FOXO1 expression, which rapidly declines after activation and is subsequently restored. Reexpression is impaired in naïve CD4+ T cell responses from older individuals. Here, we show that FOXO1 promotes lysosome function through the induction of the key transcription factor for lysosomal proteins, TFEB. Subdued FOXO1 reexpression in activated CD4+ T cells impairs lysosomal activity, causing an expansion of multivesicular bodies (MVBs). Expansion of the MVB compartment induces the sequestration of glycogen synthase kinase 3β (GSK3β), thereby suppressing protein turnover and enhancing glycolytic activity. As a consequence, older activated CD4+ T cells develop features reminiscent of senescent cells. They acquire an increased cell mass, preferentially differentiate into short-lived effector T cells, and secrete exosomes that harm cells in the local environment through the release of granzyme B.

Monocytes present age-related changes in phospholipid concentration and decreased energy metabolism

Age‐related changes at the cellular level include the dysregulation of metabolic and signaling pathways. Analyses of blood leukocytes have revealed a set of alterations that collectively lower their ability to fight infections and resolve inflammation later in life. We studied the transcriptomic, epigenetic, and metabolomic profiles of monocytes extracted from younger adults and individuals over the age of 65 years to map major age‐dependent changes in their cellular physiology. We found that the monocytes from older persons displayed a decrease in the expression of ribosomal and mitochondrial protein genes and exhibited hypomethylation at the HLA class I locus. Additionally, we found elevated gene expression associated with cell motility, including the CX3CR1 and ARID5B genes, which have been associated with the development of atherosclerosis. Furthermore, the downregulation of two genes, PLA2G4B and ALOX15B, which belong to the arachidonic acid metabolism pathway involved in phosphatidylcholine conversion to anti‐inflammatory lipoxins, correlated with increased phosphatidylcholine content in monocytes from older individuals. We found age‐related changes in monocyte metabolic fitness, including reduced mitochondrial function and increased glycose consumption without the capacity to upregulate it during increased metabolic needs, and signs of increased oxidative stress and DNA damage. In conclusion, our results complement existing findings and elucidate the metabolic alterations that occur in monocytes during aging.

Aging and the Immune System: the Impact of Immunosenescence on Viral Infection, Immunity and Vaccine Immunogenicity

Immunosenescence is characterized by a progressive deterioration of the immune system associated with aging. Multiple components of both innate and adaptive immune systems experience aging-related changes, such as alterations in the number of circulating monocytic and dendritic cells, reduced phagocytic activities of neutrophils, limited diversity in B/T cell repertoire, T cell exhaustion or inflation, and chronic production of inflammatory cytokines known as inflammaging. The elderly are less likely to benefit from vaccinations as preventative measures against infectious diseases due to the inability of the immune system to mount a successful defense. Therefore, aging is thought to decrease the efficacy and effectiveness of vaccines, suggesting aging-associated decline in the immunogenicity induced by vaccination. In this review, we discuss aging-associated changes in the innate and adaptive immunity and the impact of immunosenescence on viral infection and immunity. We further explore recent advances in strategies to enhance the immunogenicity of vaccines in the elderly. Better understanding of the molecular mechanisms underlying immunosenescence-related immune dysfunction will provide a crucial insight into the development of effective elderly-targeted vaccines and immunotherapies.

Metabolic reprogramming in memory CD4 T cell responses of old adults

To determine whether aging affects the ability of T cells to undergo metabolic reprogramming upon activation, we compared CD4 T cell responses after polyclonal in vitro stimulation. Compared to younger adults, CD4 memory T cells from healthy older individuals exhibited a higher upregulation of oxidative phosphorylation with increased production of reactive oxygen species and intracellular and secreted ATP. Increased ATP secretion led to increased purinergic signaling and P2X7-dependent increases in cytoplasmic calcium. The increased mitochondrial activity was not due to a difference in activation-induced mitochondrial biogenesis. Expression of carnitine palmitoyl transferase 1 was higher, conversely that of fatty acid synthase was reduced in older T cells, resulting in increased fatty acid oxidation, while depleting intracellular lipid stores. The aged CD4 memory T cells therefore maintain a more catabolic state in lipid metabolism, while their ability to upregulate glycolysis upon activation is preserved.

Mechanisms underlying T cell ageing

T cell ageing has a pivotal role in rendering older individuals vulnerable to infections and cancer and in impairing the response to vaccination. Easy accessibility to peripheral human T cells as well as an expanding array of tools to examine T cell biology have provided opportunities to examine major ageing pathways and their consequences for T cell function. Here, we review emerging concepts of how the body attempts to maintain a functional T cell compartment with advancing age, focusing on three fundamental domains of the ageing process, namely self-renewal, control of cellular quiescence and cellular senescence. Understanding these critical elements in successful T cell ageing will allow the design of interventions to prevent or reverse ageing-related T cell failure.

Transcription factor networks in aged naïve CD4 T cells bias lineage differentiation

With reduced thymic activity, the population of naïve T cells in humans is maintained by homeostatic proliferation throughout adult life. In young adults, naïve CD4 T cells have enormous proliferative potential and plasticity to differentiate into different lineages. Here, we explored whether naïve CD4 T-cell aging is associated with a partial loss of this unbiased multipotency. We find that naïve CD4 T cells from older individuals have developed a propensity to develop into TH9 cells. Two major mechanisms contribute to this predisposition. First, responsiveness to transforming growth factor β (TGFβ) stimulation is enhanced with age due to an upregulation of the TGFβR3 receptor that results in increased expression of the transcription factor PU.1. Secondly, aged naïve CD4 T cells display altered transcription factor profiles in response to T-cell receptor stimulation, including enhanced expression of BATF and IRF4 and reduced expression of ID3 and BCL6. These transcription factors are involved in TH9 differentiation as well as IL9 transcription suggesting that the aging-associated changes in the transcription factor profile favor TH9 commitment.

Patterns of DNA methylation as an indicator of biological aging: State of the science and future directions in precision health promotion

BACKGROUND

A rapidly expanding literature suggests that individuals of the same chronological age show significant variation in biological age.

PURPOSE

The purpose of this article is to review the literature surrounding epigenetic age as estimated by DNA methylation, involving the addition or removal of methyl groups to DNA that can alter gene expression without changing the DNA sequence.

METHODS

This state of the science literature review summarizes current approaches in epigenetic age determination and applications of aging algorithms.

FINDINGS

A number of algorithms estimate epigenetic age using DNA methylation markers, primarily among adults. Algorithm application has focused on determining predictive value for risk of disease and death and identifying antecedents to age acceleration. Several studies have incorporated epigenetic age to evaluate intervention effectiveness.

DISCUSSION

As the research community continues to refine aging algorithms, there may be opportunity to promote health from a precision health perspective.

Immune Cells and Immunosenescence

Aging is associated with progressive loss of physiological integrity, leading to impaired physical and mental functions as well as increased morbidity and mortality. With advancing age, the immune system is no longer able to adequately control autoimmunity, infections, or cancer. The abilities of the elderly to slow down undesirable effects of aging may depend on the genetic background, lifestyle, geographic region, and other presently unknown factors. Although most aspects of the immunity are constantly declining in relation to age, some features are retained, while e.g. the ability to produce high levels of cytokines, response to pathogens by increased inflammation, and imbalanced proteolytic activity are found in the elderly, and might eventually cause harm. In this context, it is important to differentiate between the effect of immunosenescence that is contributing to this decline and adaptations of the immune system that can be quickly reversed if necessary.