Mechanisms underlying T cell ageing

Emerging cellular senescence-centric understanding of immunological aging and its potential modulation through dietary bioactive components

Immunological aging is strongly associated with the observable deleterious effects of human aging. Our understanding of the causes, effects, and therapeutics of aging immune cells has long been considered within the sole purview of immunosenescence. However, it is being progressively realized that immunosenescence may not be the only determinant of immunological aging. The cellular senescence-centric theory of aging proposes a more fundamental and specific role of immune cells in regulating senescent cell (SC) burden in aging tissues that has augmented the notion of senescence immunotherapy. Now, in addition, several emerging studies are suggesting that cellular senescence itself may be prevalent in aging immune cells, and that senescent immune cells exhibiting characteristic markers of cellular senescence, similar to non-leucocyte cells, could be among the key drivers of various facets of physiological aging. The present review integrates the current knowledge related to immunosenescence and cellular senescence in immune cells per se, and aims at providing a cohesive overview of these two phenomena and their significance in immunity and aging. We present evidence and rationalize that understanding the extent and impact of cellular senescence in immune cells vis-à-vis immunosenescence is necessary for truly comprehending the notion of an 'aged immune cell'. In addition, we also discuss the emerging significance of dietary factors such as phytochemicals, probiotic bacteria, fatty acids, and micronutrients as possible modulators of immunosenescence and cellular senescence. Evidence and opportunities related to nutritional bioactive components and immunological aging have been deliberated to augment potential nutrition-oriented immunotherapy during aging.

Reference range of naïve T and T memory lymphocyte subsets in peripheral blood of healthy adult

Naïve T and T memory cell subsets are closely related to immune response and can provide important information for the diagnosis and treatment of immunological and hematological disorders. Lymphocyte compartment undergoes dramatic changes during adulthood; age-related reference values derived from healthy individuals are crucial. However, extensively detailed reference values of peripheral blood lymphocytes in the whole spectrum of adulthood detected by multi-color flow cytometry on a single platform are rare. Three hundred and nine healthy adult volunteers were recruited from Tianjin in China. The absolute counts and percentages of CD3+CD4+ T cells, CD3+CD8+ T cells, naïve T cells (Tn), T memory stem cells (Tscm), central memory T cells (Tcm), effector memory T cells (Tem), and terminal effector T cells (Tte) were detected by flow cytometry with single platform technologies. Reference range of absolute counts and percentage of T lymphocyte subsets were formulated by different age and gender. The results showed that Tn and Tscm cells, which had stem cell properties, decreased with aging; while, Tcm and Tem increased with aging, which increased from 18 to 64 years old but presented no significant change over the 65 years old. Gender had an influence on the fluctuation of lymphocyte subsets, the absolute count of CD3+CD8+, CD8+Tcm, CD8+Tem in males were higher than those in females. The reference values of percentages and absolute numbers of naïve T and T memory cell subsets can help doctors to understand the immune state of patients and evaluate conditions of prognosis then adjust the treatment for patients. (Chinese Clinic Trial Registry number: ChiCTR-IOR-17014139.).

Immunosenescence and Autoimmunity: Exploiting the T-Cell Receptor Repertoire to Investigate the Impact of Aging on Multiple Sclerosis

T-cell receptor (TCR) repertoire diversity is a determining factor for the immune system capability in fighting infections and preventing autoimmunity. During life, the TCR repertoire diversity progressively declines as a physiological aging progress. The investigation of TCR repertoire dynamics over life represents a powerful tool unraveling the impact of immunosenescence in health and disease. Multiple Sclerosis (MS) is a demyelinating, inflammatory, T-cell mediated autoimmune disease of the Central Nervous System in which age is crucial: it is the most widespread neurological disease among young adults and, furthermore, patients age may impact on MS progression and treatments outcome. Crossing knowledge on the TCR repertoire dynamics over MS patients' life is fundamental to investigate disease mechanisms, and the advent of high- throughput sequencing (HTS) has significantly increased our knowledge on the topic. Here we report an overview of current literature about the impact of immunosenescence and age-related TCR dynamics variation in autoimmunity, including MS.

Early Thymectomy Is Associated With Long-Term Impairment of the Immune System: A Systematic Review

Background and Aims

Congenital heart diseases (CHDs) are diagnosed in approximately 9 in 1,000 newborns, and early cardiac corrective surgery often requires partial or complete thymectomy. As the long-term effect of early thymectomy on the subsequent development of the immune system in humans has not been completely elucidated, the present study aimed to evaluate the effects of thymus removal on the functional capacity of the immune system after different periods.

Methods

A systematic review of the literature was performed using MEDLINE, EMBASE, LILACS and Scopus. The inclusion criteria were original studies that analyzed any component of the immune system in patients with CHD who had undergone thymectomy during cardiac surgery in the first years of life. The results were evaluated for the quality of evidence.

Results

Twenty-three studies were selected and showed that patients who underwent a thymectomy in the first years of life tended to exhibit important alterations in the T cell compartment, such as fewer total T cells, CD4+, CD8+, naïve and CD31+ T cells, lower TRECs, decreased diversity of the TCR repertoire and higher peripheral proliferation (increased Ki-67 expression) than controls. However, the numbers of memory T cells and Treg cells differed across the selected studies.

Conclusions

Early thymectomy, either partial or complete, may be associated with a reduction in many T cell subpopulations and TCR diversity, and these alterations may persist during long-term follow-up. Alternative solutions should be studied, either in the operative technique with partial preservation of the thymus or through the autograft of fragments of the gland.

Systematic Review Registration

Prospero [157188].

Putative Association between Low Baseline Gene Expression in the Peripheral Blood and Clinical Remission in Rheumatoid Arthritis Patients Treated with Tofacitinib

We investigated the importance of the baseline expression of genes involved in energy generation, as prognostic biomarkers of the treatment response to tofacitinib in patients with rheumatoid arthritis (RA). Peripheral blood samples were obtained from 28 patients with RA who received 3 months of tofacitinib therapy from 26 healthy controls. Clinical response was evaluated based on the disease activity score, the erythrocyte sedimentation rate (DAS28-ESR), and the serum levels of ACPA, RF, CRP, and ESR. Clinical remission was assessed based on DAS28 score <2.6. Protein concentrations were measured using ELISA. Total RNA isolated from whole blood was used for gene expression analysis using quantitative RT-PCR. All patients were diagnosed with Steinbrocker’s radiographic stage II-III at baseline, and most showed erosive arthritis with ACPA and RF positivity. Tofacitinib treatment significantly decreased the disease activity. Upon study completion, seven patients showed remission. Before and after TOFA therapy, a significantly higher expression of succinate dehydrogenase and pyruvate kinase genes was observed in all the examined patients compared to healthy subjects. However, the pre-therapy expression of these genes and corresponding proteins was significantly (p ≤ 0.05) lower in patients who showed remission than in other patients with RA. Moreover, we observed that, during follow-up, patients who developed remission showed an increasing trend in the expression of the examined genes, whereas the others showed some decreases in gene expression, although this was not statistically significant. We concluded that, compared with RA patients maintaining persistent moderate or high disease activity, those with clinical remission following tofacitinib treatment showed a significantly lower baseline expression of genes involved in energy generation.

Hallmarks of the aging T-cell system

The adaptive immune system has the enormous challenge to protect the host through the generation and differentiation of pathogen-specific short-lived effector T cells while in parallel developing long-lived memory cells to control future encounters with the same pathogen. A complex regulatory network is needed to preserve a population of naïve cells over lifetime that exhibit sufficient diversity of antigen receptors to respond to new antigens, while also sustaining immune memory. In parallel, cells need to maintain their proliferative potential and the plasticity to differentiate into different functional lineages. Initial signs of waning immune competence emerge after 50 years of age, with increasing clinical relevance in the 7th-10th decade of life. Morbidity and mortality from infections increase, as drastically exemplified by the current COVID-19 pandemic. Many vaccines, such as for the influenza virus, are poorly effective to generate protective immunity in older individuals. Age-associated changes occur at the level of the T-cell population as well as the functionality of its cellular constituents. The system highly relies on the self-renewal of naïve and memory T cells, which is robust but eventually fails. Genetic and epigenetic modifications contribute to functional differences in responsiveness and differentiation potential. To some extent, these changes arise from defective maintenance; to some, they represent successful, but not universally beneficial adaptations to the aging host. Interventions that can compensate for the age-related defects and improve immune responses in older adults are increasingly within reach.

CD153-CD30 signaling promotes age-dependent tertiary lymphoid tissue expansion and kidney injury

Tertiary lymphoid tissues (TLTs) facilitate local T and B cell interactions in chronically inflamed organs. However, the cells and molecular pathways that govern TLT formation are poorly defined. Here, we identified TNF superfamily CD153/CD30 signaling between 2 unique age-dependent lymphocyte subpopulations, CD153⁺PD-1⁺CD4⁺ senescence-associated T (SAT) cells and CD30⁺T-bet⁺ age-associated B cells (ABCs), as a driver for TLT expansion. SAT cells, which produced ABC-inducing factors IL-21 and IFN-γ, and ABCs progressively accumulated within TLTs in aged kidneys after injury. Notably, in kidney injury models, CD153 or CD30 deficiency impaired functional SAT cell induction, which resulted in reduced ABC numbers and attenuated TLT formation with improved inflammation, fibrosis, and renal function. Attenuated TLT formation after transplantation of CD153-deficient bone marrow further supported the importance of CD153 in immune cells. Clonal analysis revealed that SAT cells and ABCs in the kidneys arose from both local differentiation and recruitment from the spleen. In the synovium of aged rheumatoid arthritis patients, T peripheral helper/T follicular helper cells and ABCs also expressed CD153 and CD30, respectively. Together, our data reveal a previously unappreciated function of CD153/CD30 signaling in TLT formation and propose targeting the CD153/CD30 signaling pathway as a therapeutic target for slowing kidney disease progression.

Aging, Bone Marrow and Next-Generation Sequencing (NGS): Recent Advances and Future Perspectives

The aging of bone marrow (BM) remains a very imperative and alluring subject, with an ever-increasing interest among fellow scientists. A considerable amount of progress has been made in this field with the established ‘hallmarks of aging’ and continued efforts to investigate the age-related changes observed within the BM. Inflammaging is considered as a low-grade state of inflammation associated with aging, and whilst the possible mechanisms by which aging occurs are now largely understood, the processes leading to the underlying changes within aged BM remain elusive. The ability to identify these changes and detect such alterations at the genetic level are key to broadening the knowledgebase of aging BM. Next-generation sequencing (NGS) is an important molecular-level application presenting the ability to not only determine genomic base changes but provide transcriptional profiling (RNA-seq), as well as a high-throughput analysis of DNA–protein interactions (ChIP-seq). Utilising NGS to explore the genetic alterations occurring over the aging process within alterative cell types facilitates the comprehension of the molecular and cellular changes influencing the dynamics of aging BM. Thus, this review prospects the current landscape of BM aging and explores how NGS technology is currently being applied within this ever-expanding field of research.

SARS-CoV-2, COVID-19 and the Ageing Immune System

The coronavirus disease 2019 (COVID-19) pandemic is a global health threat with particular risk for severe disease and death in older adults and in adults with age-related metabolic and cardiovascular disease. Recent advances in the science of ageing have highlighted how ageing pathways control not only lifespan but also healthspan, the healthy years of life. Here, we discuss the ageing immune system and its ability to respond to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We specifically focus on the intersect of severe COVID-19 and immunosenescence to highlight pathways that may be determinant for the risk of complications and death following infection with SARS-CoV-2. New or adapted therapeutics that target ageing-associated pathways may be important tools to reduce the burden of death and long-term disability caused by this pandemic. Proposed interventions aimed at immunosenescence could enhance immune function not only in the elderly but in susceptible younger individuals as well, ultimately improving complications of severe COVID-19 for all ages.

Aging weakens Th17 cell pathogenicity and ameliorates experimental autoimmune uveitis in mice

Aging-induced changes in the immune system are associated with a higher incidence of infection and vaccination failure. Lymph nodes, which filter the lymph to identify and fight infections, play a central role in this process. However, careful characterization of the impact of aging on lymph nodes and associated autoimmune diseases is lacking. We combined single-cell RNA sequencing (scRNA-seq) with flow cytometry to delineate the immune cell atlas of cervical draining lymph nodes (CDLNs) of both young and old mice with or without experimental autoimmune uveitis (EAU). We found extensive and complicated changes in the cellular constituents of CDLNs during aging. When confronted with autoimmune challenges, old mice developed milder EAU compared to young mice. Within this EAU process, we highlighted that the pathogenicity of T helper 17 cells (Th17) was dampened, as shown by reduced GM-CSF secretion in old mice. The mitigated secretion of GM-CSF contributed to alleviation of IL-23 secretion by antigen-presenting cells (APCs) and may, in turn, weaken APCs’ effects on facilitating the pathogenicity of Th17 cells. Meanwhile, our study further unveiled that aging downregulated GM-CSF secretion through reducing both the transcript and protein levels of IL-23R in Th17 cells from CDLNs. Overall, aging altered immune cell responses, especially through toning down Th17 cells, counteracting EAU challenge in old mice.

IL-33 causes thermogenic failure in aging by expanding dysfunctional adipose ILC2

Aging impairs the integrated immunometabolic responses, which have evolved to maintain core body temperature in homeotherms to survive cold stress, infections, and dietary restriction. Adipose tissue inflammation regulates the thermogenic stress response, but how adipose tissue-resident cells instigate thermogenic failure in the aged are unknown. Here, we define alterations in the adipose-resident immune system and identify that type 2 innate lymphoid cells (ILC2s) are lost in aging. Restoration of ILC2 numbers in aged mice to levels seen in adults through IL-33 supplementation failed to rescue old mice from metabolic impairment and increased cold-induced lethality. Transcriptomic analyses revealed intrinsic defects in aged ILC2, and adoptive transfer of adult ILC2s are sufficient to protect old mice against cold. Thus, the functional defects in adipose ILC2s during aging drive thermogenic failure.

Leukocyte Counts and T-Cell Frequencies Differ Between Novel Subgroups of Diabetes and Are Associated With Metabolic Parameters and Biomarkers of Inflammation

Frequencies of circulating immune cells are altered in those with type 1 and type 2 diabetes compared with healthy individuals and are associated with insulin sensitivity, glycemic control, and lipid levels. This study aimed to determine whether specific immune cell types are associated with novel diabetes subgroups. We analyzed automated white blood cell counts (n = 669) and flow cytometric data (n = 201) of participants in the German Diabetes Study with recent-onset (<1 year) diabetes, who were allocated to five subgroups based on data-driven analysis of clinical variables. Leukocyte numbers were highest in severe insulin-resistant diabetes (SIRD) and mild obesity-related diabetes (MOD) and lowest in severe autoimmune diabetes (SAID). CD4⁺ T-cell frequencies were higher in SIRD versus SAID, MOD, and mild age-related diabetes (MARD), and frequencies of CCR4⁺ regulatory T cells were higher in SIRD versus SAID and MOD and in MARD versus SAID. Pairwise differences between subgroups were partially explained by differences in clustering variables. Frequencies of CD4⁺ T cells were positively associated with age, BMI, HOMA2 estimate of β-cell function (HOMA2-B), and HOMA2 estimate of insulin resistance (HOMA2-IR), and frequencies of CCR4⁺ regulatory T cells with age, HOMA2-B, and HOMA2-IR. In conclusion, different leukocyte profiles exist between novel diabetes subgroups and suggest distinct inflammatory processes in these diabetes subgroups.

Understanding T cell aging to improve anti-viral immunity

T cells are a critical component of the immune system and required for protection against viral and bacterial infections. However, the capacity of these cells to provide sufficient protection declines with age, leading to an increased susceptibility to and mortality from infection in older individuals. In many cases, it also contributes to poor vaccine-induced immunity. Understanding the basic biology behind T cell aging is key to unraveling these defects and, in turn, designing more effective vaccines and therapeutics for the older population. Here, we will discuss recent studies that have provided significant insight into the features of T cell aging, how these features may contribute to poor immune responses with advancing age and newer avenues of research that may further enhance anti-viral immunity in older individuals.

Single-cell sequencing reveals antitumor characteristics of intratumoral immune cells in old mice

Background

Aging has long been thought to be a major risk factor for various types of cancers. However, accumulating evidence indicates increased resistance of old animals to tumor growth. An in-depth understanding of how old individuals defend against tumor invasion requires further investigations.

Methods

We revealed age-associated alterations in tumor-infiltrating immune cells between young and old mice using single-cell RNA and coupled T cell receptor (TCR) sequencing analysis. Multiple bioinformatics methods were adopted to analyze the characteristics of the transcriptome between two groups. To explore the impacts of young and old CD8⁺ T cells on tumor growth, mice were treated with anti-CD8 antibody every 3 days starting 7 days after tumor inoculation. Flow cytometry was used to validate the differences indicated by sequencing analysis between young and old mice.

Results

We found a higher proportion of cytotoxic CD8⁺ T cells, naturally occurring Tregs, conventional dendritic cell (DC), and M1-like macrophages in tumors of old mice compared with a higher percentage of exhausted CD8⁺ T cells, induced Tregs, plasmacytoid DC, and M2-like macrophages in young mice. Importantly, TCR diversity analysis showed that top 10 TCR clones consisted primarily of exhausted CD8⁺ T cells in young mice whereas top clones were predominantly cytotoxic CD8⁺ T cells in old mice. Old mice had more CD8⁺ T cells with a ‘progenitor’ and less ‘terminally’ exhausted phenotypes than young mice. Consistently, trajectory inference demonstrated that CD8⁺ T cells preferentially differentiated into cytotoxic cells in old mice in contrast to exhausted cells in young mice. Importantly, elimination of CD8⁺ T cells in old mice during tumor growth significantly accelerated tumor development. Moreover, senescent features were demonstrated in exhausted but not cytotoxic CD8⁺ T cells regardless of young and old mice.

Conclusions

Our data revealed that a significantly higher proportion of effector immune cells in old mice defends against tumor progression, providing insights into understanding the altered kinetics of cancer development and the differential response to immunotherapeutic modulation in elderly patients.

Influenza Vaccines: Successes and Continuing Challenges

Influenza vaccines have been available for over 80 years. They have contributed to significant reductions in influenza morbidity and mortality. However, there have been limitations in their effectiveness, in part due to the continuous antigenic evolution of seasonal influenza viruses, but also due to the predominant use of embryonated chicken eggs for their production. The latter furthermore limits their worldwide production timelines and scale. Therefore today, alternative approaches for their design and production are increasingly pursued, with already licensed quadrivalent seasonal influenza vaccines produced in cell cultures, including based on a baculovirus expression system. Next-generation influenza vaccines aim at inducing broader and longer-lasting immune responses to overcome seasonal influenza virus antigenic drift and to timely address the emergence of a new pandemic influenza virus. Tailored approaches target mechanisms to improve vaccine-induced immune responses in individuals with a weakened immune system, in particular older adults.

T Cell Immunosenescence in Aging, Obesity, and Cardiovascular Disease

Although advances in preventive medicine have greatly improved prognosis, cardiovascular disease (CVD) remains the leading cause of death worldwide. This clearly indicates that there remain residual cardiovascular risks that have not been targeted by conventional therapies. The results of multiple animal studies and clinical trials clearly indicate that inflammation is the most important residual risk and a potential target for CVD prevention. The immune cell network is intricately regulated to maintain homeostasis. Ageing associated changes to the immune system occurs in both innate and adaptive immune cells, however T cells are most susceptible to this process. T-cell changes due to thymic degeneration and homeostatic proliferation, metabolic abnormalities, telomere length shortening, and epigenetic changes associated with aging and obesity may not only reduce normal immune function, but also induce inflammatory tendencies, a process referred to as immunosenescence. Since the disruption of biological homeostasis by T cell immunosenescence is closely related to the development and progression of CVD via inflammation, senescent T cells are attracting attention as a new therapeutic target. In this review, we discuss the relationship between CVD and T cell immunosenescence associated with aging and obesity.

Targeting immune dysfunction in aging

Human aging is a multifactorial phenomenon that affects numerous organ systems and cellular processes, with the immune system being one of the most dysregulated. Immunosenescence, the gradual deterioration of the immune system, and inflammaging, a chronic inflammatory state that persists in the elderly, are among the plethora of immune changes that occur during aging. Almost all populations of immune cells change with age in terms of numbers and/or activity. These alterations are in general highly detrimental, resulting in an increased susceptibility to infections, reduced healing abilities, and altered homeostasis that promote the emergence of age-associated diseases such as cancer, diabetes, and other diseases associated with inflammation. Thanks to recent developments, several strategies have been proposed to target central immunological processes or specific immune subpopulations affected by aging. These therapeutic approaches could soon be applied in the clinic to slow down or even reverse specific age-induced immune changes in order to rejuvenate the immune system and prevent or reduce the impact of various diseases. Due to its systemic nature and interconnection with all the other systems in the body, the immune system is an attractive target for aging intervention because relatively targeted modifications to a small set of cells have the potential to improve the health of multiple organ systems. Therefore, anti-aging immune targeting therapies could represent a potent approach for improving healthspan. Here, we review aging changes in the major components of the immune system, we summarize the current immune-targeting therapeutic approaches in the context of aging and discuss the future directions in the field of immune rejuvenation.

T cells mediate cell non-autonomous arterial ageing in mice

KEY POINTS

Increased large artery stiffness and impaired endothelium-dependent dilatation occur with advanced age. We sought to determine whether T cells mechanistically contribute to age-related arterial dysfunction. We found that old mice exhibited greater proinflammatory T cell accumulation around both the aorta and mesenteric arteries. Pharmacologic depletion or genetic deletion of T cells in old mice resulted in ameliorated large artery stiffness and greater endothelium-dependent dilatation compared with mice with T cells intact.

ABSTRACT

Ageing of the arteries is characterized by increased large artery stiffness and impaired endothelium-dependent dilatation. T cells contribute to hypertension in acute rodent models but whether they contribute to chronic age-related arterial dysfunction is unknown. To determine whether T cells directly mediate age-related arterial dysfunction, we examined large elastic artery and resistance artery function in young (4-6 months) and old (22-24 months) wild-type mice treated with anti-CD3 F(ab'2) fragments to deplete T cells (150 μg, i.p. every 7 days for 28 days) or isotype control fragments. Old mice exhibited greater numbers of T cells in both aorta and mesenteric vasculature when compared with young mice. Old mice treated with anti-CD3 fragments exhibited depletion of T cells in blood, spleen, aorta and mesenteric vasculature. Old mice also exhibited greater numbers of aortic and mesenteric IFN-γ and TNF-α-producing T cells when compared with young mice. Old control mice exhibited greater large artery stiffness and impaired resistance artery endothelium-dependent dilatation in comparison with young mice. In old mice, large artery stiffness was ameliorated with anti-CD3 treatment. Anti-CD3-treated old mice also exhibited greater endothelium-dependent dilatation than age-matched controls. We also examined arterial function in young and old Rag-1^-/- mice, which lack lymphocytes. Rag-1^-/- mice exhibited blunted increases in large artery stiffness with age compared with wild-type mice. Old Rag-1^-/- mice also exhibited greater endothelium-dependent dilatation compared with old wild-type mice. Collectively, these results demonstrate that T cells play an important role in age-related arterial dysfunction.

Elementary Laboratory Assays as Biomarkers of Ageing: Support for Treatment of COVID-19?

Youth, working age and the elderly: On a timeline, chronological age (CA) and biological age (BA) may dissociate; nosological entities manifest themselves at different BAs. In determining which disease corresponds to a given age decade, statistical registries of causes of death are unreliable and this does not change with SARS CoV-2 infection. Beyond adolescence, ageing metrics involve estimations of changes in fitness, including prediction models to estimate the number of remaining years left to live. A substantial disparity in biomarker levels and health status of ageing can be observed: the difference in CA and BA in the large cohorts under consideration is glaring. Here, we focus more closely on ageing and senescence metrics in order to make information available for risk analysis non the least with COVID-19, including the most recent risk factors of ABO blood type and 3p21.31 chromosome cluster impacting on C5a and SC5b-9 plasma levels. From the multitude of routine medical laboratory assays, a potentially meaningful set of assays aimed to best reflect the stage of individual senescence; hence risk factors the observational prospective SENIORLABOR study of 1,467 healthy elderly performed since 2009 and similar approaches since 1958 can be instantiated as a network to combine a set of elementary laboratory assays quantifying senescence.

Evolution of Human Memory B Cells From Childhood to Old Age

High quality medical assistance and preventive strategies, including pursuing a healthy lifestyle, result in a progressively growing percentage of older people. The population and workforce is aging in all countries of the world. It is widely recognized that older individuals show an increased susceptibility to infections and a reduced response to vaccination suggesting that the aged immune system is less able to react and consequently protect the organism. The SARS-CoV-2 pandemic is dramatically showing us that the organism reacts to novel pathogens in an age-dependent manner. The decline of the immune system observed in aging remains unclear. We aimed to understand the role of B cells. We analyzed peripheral blood from children (4-18 years); young people (23-60 years) and elderly people (65-91 years) by flow cytometry. We also measured antibody secretion by ELISA following a T-independent stimulation. Here we show that the elderly have a significant reduction of CD27dull memory B cells, a population that bridges innate and adaptive immune functions. In older people, memory B cells are mostly high specialized antigen-selected CD27bright. Moreover, after in vitro stimulation with CpG, B cells from older individuals produced significantly fewer IgM and IgA antibodies compared to younger individuals. Aging is a complex process characterized by a functional decline in multiple physiological systems. The immune system of older people is well equipped to react to often encountered antigens but has a low ability to respond to new pathogens.

Allotransplantation Is Associated With Exacerbation of CD8 T-Cell Senescence: The Particular Place of the Innate CD8 T-Cell Component

Immunosenescence is a physiological process that is associated with changes in the immune system, particularly among CD8 T-cells. Recent studies have hypothesized that senescent CD8 T-cells are produced with chronologic age by chronic stimulation, leading to the acquisition of hallmarks of innate-like T-cells. While conventional CD8 T-cells are quite well characterized, CD8 T-cells sharing features of NK cells and memory CD8 T-cells, are a newly described immune cell population. They can be distinguished from conventional CD8 T-cells by their combined expression of panKIR/NKG2A and Eomesodermin (E), a unique phenotype closely associated with IFN-γ production in response to innate stimulation. Here, we first provided new evidence in favor of the innate character of panKIR/NKG2A(+) E(+) CD8 T-cells in normal subjects, documenting their position at an intermediate level in the innateness gradient in terms of both innate IFN-γ production and diminished mitochondrial mass. We also revealed that CD8 E(+) panKIR/NKG2A(+) T-cells, hereafter referred to as Innate E(+) CD8 T-cells, exhibit increased senescent (CD27(-) CD28(-)) phenotype, compared to their conventional memory counterparts. Surprisingly, this phenomenon was not dependent on age. Given that inflammation related to chronic viral infection is known to induce NK-like marker expression and a senescence phenotype among CD8 T-cells, we hypothesized that innate E(+) CD8 T-cells will be preferentially associated with exacerbated cellular senescence in response to chronic alloantigen exposure or CMV infection. Accordingly, in a pilot cohort of stable kidney allotransplant recipients, we observed an increased frequency of the Innate E(+) CD8 T-cell subset, together with an exacerbated senescent phenotype. Importantly, this phenotype cannot be explained by age alone, in clear contrast to their conventional memory counterparts. The senescent phenotype in CD8 T-cells was further increased in cytomegalovirus (CMV) positive serology transplant recipients, suggesting that transplantation and CMV, rather than aging by itself, may promote an exacerbated senescent phenotype of innate CD8 T-cells. In conclusion, we proposed that kidney transplantation, via the setting of inflammatory stimuli of alloantigen exposure and CMV infection, may exogenously age the CD8 T-cell compartment, especially its innate component. The physiopathological consequences of this change in the immune system remain to be elucidated.

The Role of T Cell Senescence in Neurological Diseases and Its Regulation by Cellular Metabolism

Immunosenescence is a state of dysregulated leukocyte function characterised by arrested cell cycle, telomere shortening, expression of markers of cellular stress, and secretion of pro-inflammatory mediators. Immunosenescence principally develops during aging, but it may also be induced in other pathological settings, such as chronic viral infections and autoimmune diseases. Appearance of senescent immune cells has been shown to potentially cause chronic inflammation and tissue damage, suggesting an important role for this process in organismal homeostasis. In particular, the presence of senescent T lymphocytes has been reported in neurological diseases, with some works pointing towards a direct connection between T cell senescence, inflammation and neuronal damage. In this minireview, we provide an overview on the role of T cell senescence in neurological disorders, in particular in multiple sclerosis and Alzheimer disease. We also discuss recent literature investigating how metabolic remodelling controls the development of a senescence phenotype in T cells. Targeting metabolic pathways involved in the induction of senescent T cells may indeed represent a novel approach to limit their inflammatory activity and prevent neuroinflammation and neurodegeneration.

Short Telomeres and a T-Cell Shortfall in COVID-19: The Aging Effect

The slow pace of global vaccination and the rapid emergence of SARS-CoV-2 variants suggest recurrent waves of COVID-19 in coming years. Therefore, understanding why deaths from COVID-19 are highly concentrated among older adults is essential for global health. Severe COVID-19 T-cell lymphopenia is more common among older adults, and it entails poor prognosis. Much about the primary etiology of this form of lymphopenia remains unknown, but regardless of its causes, offsetting the decline in T-cell count during SARS-CoV-2 infection demands fast and massive T-cell clonal expansion, which is telomere length (TL)-dependent. We have built a model that captures the effect of age-dependent TL shortening in hematopoietic cells and its effect on T-cell clonal expansion capacity. The model shows that an individual with average hematopoietic cell TL (HCTL) at age twenty years maintains maximal T-cell clonal expansion capacity until the 6th decade of life when this capacity plummets by more than 90% over the next ten years. The collapse coincides with the steep increase in COVID-19 mortality with age. HCTL metrics may thus explain the vulnerability of older adults to COVID-19. That said, the wide inter-individual variation in HCTL across the general population means that some younger adults with inherently short HCTL might be at risk of severe COVID-19 lymphopenia and mortality from the disease.

The epidemiologic and biologic basis for classifying older age as a high-risk, immunocompromising condition for pneumococcal vaccine policy

INTRODUCTION

Immunosenescence is a normal biologic process involving deterioration of protective immune responses. Consequently, older adults experience increased risk of infectious diseases, particularly pneumonia, and its leading bacterial cause, Streptococcus pneumoniae. Pneumococcal vaccine recommendations are often limited to adults with specific medical conditions despite similar disease risks among older adults due to immunosenescence.

AREAS COVERED

This article reviews epidemiologic, biologic, and clinical evidence supporting the consideration of older age due to immunosenescence as an immunocompromising condition for the purpose of pneumococcal vaccine policy and the role vaccination can play in healthy aging.

EXPERT OPINION

Epidemiologic and biologic evidence suggest that pneumococcal disease risk increases with age and is comparable for healthy older adults and younger adults with immunocompromising conditions. Because immunocompromising conditions are already indicated for pneumococcal conjugate vaccines (PCVs), a comprehensive public health strategy would also recognize immunosenescence. Moreover, older persons should be vaccinated before reaching the highest risk ages, consistent with the approach for other immunocompromising conditions. To facilitate PCV use among older adults, vaccine technical committees (VTCs) could classify older age as an immunocompromising condition based on the process of immunosenescence. With global aging, VTCs will need to consider immunosenescence and vaccine use during 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.

Naïve T Cell Quiescence in Immune Aging

Naïve T cells are critical for protection against emerging viral and bacterial infections. However, the ability of these cells to elicit effective long-term immune responses declines with age and contributes to increased disease susceptibility in older individuals. This decline has been linked with the breakdown of cellular quiescence that causes partial differentiation of naïve T cells with age, but the underlying mediators of this breakdown are unclear. Comparisons to stem cell quiescence in mice and man offer insight into naïve T cells and aging. However, the utilization of single cell technologies in combination with advances in the biology of human tissue aging is needed to provide further understanding of naïve T cell complexity and quiescence breakdown with age.

Senescence and Aging: Does It Impact Cancer Immunotherapies?

Cancer incidence increases drastically with age. Of the many possible reasons for this, there is the accumulation of senescent cells in tissues and the loss of function and proliferation potential of immune cells, often referred to as immuno-senescence. Immune checkpoint inhibitors (ICI), by invigorating immune cells, have the potential to be a game-changers in the treatment of cancer. Yet, the variability in the efficacy of ICI across patients and cancer types suggests that several factors influence the success of such inhibitors. There is currently a lack of clinical studies measuring the impact of aging and senescence on ICI-based therapies. Here, we review how cellular senescence and aging, either by directly altering the immune system fitness or indirectly through the modification of the tumor environment, may influence the cancer-immune response.

Ketogenic diet restrains aging-induced exacerbation of coronavirus infection in mice

Increasing age is the strongest predictor of risk of COVID-19 severity and mortality. Immunometabolic switch from glycolysis to ketolysis protects against inflammatory damage and influenza infection in adults. To investigate how age compromises defense against coronavirus infection, and whether a pro-longevity ketogenic diet (KD) impacts immune surveillance, we developed an aging model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain-A59 (MHV-A59). When inoculated intranasally, mCoV is pneumotropic and recapitulates several clinical hallmarks of COVID-19 infection. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue, and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Activation of ketogenesis in aged mice expands tissue protective γδ T cells, deactivates the NLRP3 inflammasome, and decreases pathogenic monocytes in lungs of infected aged mice. These data establish harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against coronavirus infection in the aged.

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.

The role of T cells in age-related diseases

Age-related T cell dysfunction can lead to failure of immune tolerance mechanisms, resulting in aberrant T cell-driven cytokine and cytotoxic responses that ultimately cause tissue damage. In this Review, we discuss the role of T cells in the onset and progression of age-associated conditions, focusing on cardiovascular disorders, metabolic dysfunction, neuroinflammation and defective tissue repair and regeneration. We present different mechanisms by which T cells contribute to inflammageing and might act as modulators of age-associated diseases, including through enhanced pro-inflammatory and cytotoxic activity, defective clearance of senescent cells or regulation of the gut microbiota. Finally, we propose that 'resetting' immune system tolerance or targeting pathogenic T cells could open up new therapeutic opportunities to boost resilience to age-related diseases.

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.

Association of Premature Immune Aging and Cytomegalovirus After Solid Organ Transplant

Immune function is altered with increasing age. Infection with cytomegalovirus (CMV) accelerates age-related immunological changes resulting in expanded oligoclonal memory CD8 T cell populations with impaired proliferation, signaling, and cytokine production. As a consequence, elderly CMV seropositive (CMV⁺) individuals have increased mortality and impaired responses to other infections in comparison to seronegative (CMV^–) individuals of the same age. CMV is also a significant complication after organ transplantation, and recent studies have shown that CMV-associated expansion of memory T cells is accelerated after transplantation. Thus, we investigated whether immune aging is accelerated post-transplant, using a combination of telomere length, flow cytometry phenotyping, and single cell RNA sequencing. Telomere length decreased slightly in the first year after transplantation in a subset of both CMV⁺ and CMV^– recipients with a strong concordance between CD57⁺ cells and short telomeres. Phenotypically aged cells increased post-transplant specifically in CMV⁺ recipients, and clonally expanded T cells were enriched for terminally differentiated cells post-transplant. Overall, these findings demonstrate a pattern of accelerated aging of the CD8 T cell compartment in CMV⁺ transplant recipients.

Hallmarks of T cell aging

The aged adaptive immune system is characterized by progressive dysfunction as well as increased autoimmunity. This decline is responsible for elevated susceptibility to infection and cancer, as well as decreased vaccination efficacy. Recent evidence indicates that CD4⁺ T cell-intrinsic alteratins contribute to chronic inflammation and are sufficient to accelerate an organism-wide aging phenotype, supporting the idea that T cell aging plays a major role in body-wide deterioration. In this Review, we propose ten molecular hallmarks to represent common denominators of T cell aging. These hallmarks are grouped into four primary hallmarks (thymic involution, mitochondrial dysfunction, genetic and epigenetic alterations, and loss of proteostasis) and four secondary hallmarks (reduction of the TCR repertoire, naive-memory imbalance, T cell senescence, and lack of effector plasticity), and together they explain the manifestation of the two integrative hallmarks (immunodeficiency and inflammaging). A major challenge now is weighing the relative impact of these hallmarks on T cell aging and understanding their interconnections, with the final goal of defining molecular targets for interventions in the aging process.

Aging and Options to Halt Declining Immunity to Virus Infections

Immunosenescence is a process associated with aging that leads to dysregulation of cells of innate and adaptive immunity, which may become dysfunctional. Consequently, older adults show increased severity of viral and bacterial infections and impaired responses to vaccinations. A better understanding of the process of immunosenescence will aid the development of novel strategies to boost the immune system in older adults. In this review, we focus on major alterations of the immune system triggered by aging, and address the effect of chronic viral infections, effectiveness of vaccination of older adults and strategies to improve immune function in this vulnerable age group.

Biomaterial-based immunoengineering to fight COVID-19 and infectious diseases

Infection by SARS-CoV-2 virus often induces the dysregulation of immune responses, tissue damage, and blood clotting. Engineered biomaterials from the nano- to the macroscale can provide targeted drug delivery, controlled drug release, local immunomodulation, enhanced immunity, and other desirable functions to coordinate appropriate immune responses and to repair tissues. Based on the understanding of COVID-19 disease progression and immune responses to SARS-CoV-2, we discuss possible immunotherapeutic strategies and highlight biomaterial approaches from the perspectives of preventive immunization, therapeutic immunomodulation, and tissue healing and regeneration. Successful development of biomaterial platforms for immunization and immunomodulation will not only benefit COVID-19 patients, but also have broad applications for a variety of infectious diseases.

Aging-associated deficit in CCR7 is linked to worsened glymphatic function, cognition, neuroinflammation, and β-amyloid pathology

Aging leads to a progressive deterioration of meningeal lymphatics and peripheral immunity, which may accelerate cognitive decline. We hypothesized that an age-related reduction in C-C chemokine receptor type 7 (CCR7)-dependent egress of immune cells through the lymphatic vasculature mediates some aspects of brain aging and potentially exacerbates cognitive decline and Alzheimer's disease-like brain β-amyloid (Aβ) pathology. We report a reduction in CCR7 expression by meningeal T cells in old mice that is linked to increased effector and regulatory T cells. Hematopoietic CCR7 deficiency mimicked the aging-associated changes in meningeal T cells and led to reduced glymphatic influx and cognitive impairment. Deletion of CCR7 in 5xFAD transgenic mice resulted in deleterious neurovascular and microglial activation, along with increased Aβ deposition in the brain. Treating old mice with anti-CD25 antibodies alleviated the exacerbated meningeal regulatory T cell response and improved cognitive function, highlighting the therapeutic potential of modulating meningeal immunity to fine-tune brain function in aging and in neurodegenerative diseases.

The influence of 17β-oestradiol on lymphopoiesis and immune system ontogenesis in juvenile sea bass, Dicentrarchus labrax

The female sex steroid 17β-oestradiol (E2) is involved in the regulation of numerous physiological functions, including the immune system development and performance. The role of oestrogens during ontogenesis is, however, not well studied. In rodents and fish, thymus maturation appears to be oestrogen-dependent. Nevertheless, little is known about the function of oestrogen in immune system development. To further the understanding of the role of oestrogens in fish immune system ontogenesis, fingerlings of European sea bass (Dicentrarchus labrax) were exposed for 30 days to 20 ng E2·L^-1, at two ages tightly related to thymic maturation, i.e., 60 or 90 days post hatch (dph). The expression of nuclear and membrane oestrogen receptors was measured in the thymus and spleen, and the expression of several T cell-related gene markers was studied in both immune organs, as well as in the liver. Waterborne E2-exposure at 20.2 ± 2.1 (S.E.) ng·L^-1 was confirmed by radioimmunoassay, leading to significantly higher E2-contents in the liver of exposed fish. The majority of gene markers presented age-dependent dynamics in at least one of the organs, confirming thymus maturation, but also suggesting a critical ontogenetic window for the implementation of liver resident γδ and αβ T cells. The oestrogen receptors, however, remained unchanged over the age and treatment comparisons with the exception of esr2b, which was modulated by E2 in the younger cohort and increased its expression with age in the thymus of the older cohort, as did the membrane oestrogen receptor gpera. These results confirm that oestrogen-signalling is involved in thymus maturation in European sea bass, as it is in mammals. This suggests that esr2b and gpera play key roles during thymus ontogenesis, particularly during medulla maturation. In contrast, the spleen expressed low or non-detectable levels of oestrogen receptors. The E2-exposure decreased the expression of tcrγ in the liver in the cohort exposed from 93 to 122 dph, but not the expression of any other immune-related gene analysed. These results indicate that the proliferation/migration of these innate-like T cell populations is oestrogen-sensitive. In regard to the apparent prominent role of oestrogen-signalling in the late thymus maturation stage, the thymic differentiation of the corresponding subpopulations of T cells might be regulated by oestrogen. To the best of our knowledge, this is the first study investigating the dynamics of both nuclear and membrane oestrogen receptors in specific immune organs in a teleost fish at very early stages of immune system development as well as to examine thymic function in sea bass after an exposure to E2 during ontogenesis.

Senescence-associated β-galactosidase reveals the abundance of senescent CD8+ T cells in aging humans

Aging leads to a progressive functional decline of the immune system, rendering the elderly increasingly susceptible to disease and infection. The degree to which immune cell senescence contributes to this decline remains unclear, however, since markers that label immune cells with classical features of cellular senescence accurately and comprehensively have not been identified. Using a second-generation fluorogenic substrate for β-galactosidase and multi-parameter flow cytometry, we demonstrate here that peripheral blood mononuclear cells (PBMCs) isolated from healthy humans increasingly display cells with high senescence-associated β-galactosidase (SA-βGal) activity with advancing donor age. The greatest age-associated increases were observed in CD8+ T-cell populations, in which the fraction of cells with high SA-βGal activity reached average levels of 64% in donors in their 60s. CD8+ T cells with high SA-βGal activity, but not those with low SA-βGal activity, were found to exhibit features of telomere dysfunction-induced senescence and p16-mediated senescence, were impaired in their ability to proliferate, developed in various T-cell differentiation states, and had a gene expression signature consistent with the senescence state previously observed in human fibroblasts. Based on these results, we propose that senescent CD8+ T cells with classical features of cellular senescence accumulate to levels that are significantly higher than previously reported and additionally provide a simple yet robust method for the isolation and characterization of senescent CD8+ T cells with predictive potential for biological age.

Immune Reconstitution in the Aging Host: Opportunities for Mechanism-Based Therapy in Allogeneic Hematopoietic Cell Transplantation

Older patients with hematologic malignancies are increasingly considered for allogeneic hematopoietic cell transplantation with encouraging outcomes. While aging-related thymic dysfunction remains a major obstacle to optimal and timely immune reconstitution post- transplantation, recent accumulating evidence has suggested that various aging hallmarks such as cellular senescence, inflamm-aging, and hematopoietic stem cell exhaustion, could also impact immune reconstitution post-transplantation in both thymic-dependent and independent manner. Here we review molecular and cellular aspects of immune senescence and immune rejuvenation related to allogeneic hematopoietic cell transplantation among older patients and discuss potential strategies for mechanism-based therapeutic intervention.

Pattern of inflammatory immune response determines the clinical course and outcome of COVID-19: unbiased clustering analysis

The objective of the study was to identify distinct patterns in inflammatory immune responses of COVID-19 patients and to investigate their association with clinical course and outcome. Data from hospitalized COVID-19 patients were retrieved from electronic medical record. Supervised k-means clustering of serial C-reactive protein levels (CRP), absolute neutrophil counts (ANC), and absolute lymphocyte counts (ALC) was used to assign immune responses to one of three groups. Then, relationships between patterns of inflammatory responses and clinical course and outcome of COVID-19 were assessed in a discovery and validation cohort. Unbiased clustering analysis grouped 105 patients of a discovery cohort into three distinct clusters. Cluster 1 (hyper-inflammatory immune response) was characterized by high CRP levels, high ANC, and low ALC, whereas Cluster 3 (hypo-inflammatory immune response) was associated with low CRP levels and normal ANC and ALC. Cluster 2 showed an intermediate pattern. All patients in Cluster 1 required oxygen support whilst 61% patients in Cluster 2 and no patient in Cluster 3 required supplementary oxygen. Two (13.3%) patients in Cluster 1 died, whereas no patient in Clusters 2 and 3 died. The results were confirmed in an independent validation cohort of 116 patients. We identified three different patterns of inflammatory immune response to COVID-19. Hyper-inflammatory immune responses with elevated CRP, neutrophilia, and lymphopenia are associated with a severe disease and a worse outcome. Therefore, targeting the hyper-inflammatory response might improve the clinical outcome of COVID-19.

Promising Therapy for Heart Failure in Patients with Severe COVID-19: Calming the Cytokine Storm

The coronavirus disease 19 (COVID-19) pandemic poses a serious global threat to human health and the economy. Based on accumulating evidence, its continuous progression involves not only pulmonary injury but also damage to the cardiovascular system due to intertwined pathophysiological risks. As a point of convergence in the pathophysiologic process between COVID-19 and heart failure (HF), cytokine storm induces the progression of COVID-19 in patients presenting pre-existing or new onset myocardial damage and even HF. Cytokine storm, as a trigger of the progression of HF in patients with COVID-19, has become a novel focus to explore therapies for target populations. In this review, we briefly introduce the basis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and illuminate the mechanism and links among COVID-19, cytokine storm, and HF. Furthermore, we discuss drugs and therapeutic targets for patients with COVID-19 and HF.

Missing Insight Into T and B Cell Responses in Dermatitis Herpetiformis

Dermatitis herpetiformis is a cutaneous form of celiac disease manifesting as an itching rash typically on the elbows, knees and buttocks. It is driven by the ingestion of gluten-containing cereals and characterized by granular deposits of immunoglobulin A in the papillary dermis. These antibodies target transglutaminase (TG) 3 and in the majority of patients they are also found in circulation. The circulating antibodies disappear and skin symptoms resolve as a result of gluten-free diet but the cutaneous anti-TG3 IgA deposits may persist for several years. In dermatitis herpetiformis, plasma cells secreting antibodies against TG3 are located in the intestinal mucosa similarly to those producing TG2 antibodies characteristic for celiac disease. In fact, both TG2- and TG3-specific plasma cells and gluten responsive T cells are found in dermatitis herpetiformis patients but the interplay between these cell populations is unknown. The small bowel mucosal damage in celiac disease is believed to be mediated by co-operation of cytotoxic intraepithelial T cells and the inflammatory milieu contributed by gluten-reactive CD4+ T cells, whereas the skin lesions in dermatitis herpetiformis appear to be devoid of gluten reactive T cells. Thus, how celiac disease-type intestinal T and B cell responses develop into an autoimmune condition affecting the skin is still incompletely understood. Finally, the skin and small bowel lesions may reappear upon reintroduction of gluten in patients treated with gluten-free diet but virtually nothing is known about the long-lived B cell and memory T cell populations activating in response to dietary gluten in dermatitis herpetiformis.

A booster dose enhances immunogenicity of the COVID-19 vaccine candidate ChAdOx1 nCoV-19 in aged mice

BACKGROUND

The spread of SARS-CoV-2 has caused a worldwide pandemic that has affected almost every aspect of human life. The development of an effective COVID-19 vaccine could limit the morbidity and mortality caused by infection and may enable the relaxation of social-distancing measures. Age is one of the most significant risk factors for poor health outcomes after SARS-CoV-2 infection; therefore, it is desirable that any new vaccine candidates elicit a robust immune response in older adults.

METHODS

Here, we use in-depth immunophenotyping to characterize the innate and adaptive immune response induced upon intramuscular administration of the adenoviral vectored ChAdOx1 nCoV-19 (AZD-1222) COVID-19 vaccine candidate in mice.

FINDINGS

A single vaccination generates spike-specific Th1 cells, Th1-like Foxp3⁺ regulatory T cells, polyfunctional spike-specific CD8⁺ T cells. and granzyme-B-producing CD8 effectors. Spike-specific IgG and IgM are generated from both the early extrafollicular antibody response and the T follicular helper cell-supported germinal center reaction, which is associated with the production of virus-neutralizing antibodies. A single dose of this vaccine generated a similar type of immune response in aged mice but of a reduced magnitude than in younger mice. We report that a second dose enhances the immune response to this vaccine in aged mice.

CONCLUSIONS

This study shows that ChAdOx1 nCoV-19 induces both cellular and humoral immunity in adult and aged mice and suggests a prime-boost strategy is a rational approach to enhance immunogenicity in older persons.

FUNDING

This study was supported by BBSRC, Lister institute of Preventative Medicine, EPSRC VaxHub, and Innovate UK.

Thymic Aging May Be Associated with COVID-19 Pathophysiology in the Elderly

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the global pandemic of coronavirus disease 2019 (COVID-19) and particularly exhibits severe symptoms and mortality in elderly individuals. Mounting evidence shows that the characteristics of the age-related clinical severity of COVID-19 are attributed to insufficient antiviral immune function and excessive self-damaging immune reaction, involving T cell immunity and associated with pre-existing basal inflammation in the elderly. Age-related changes to T cell immunosenescence is characterized by not only restricted T cell receptor (TCR) repertoire diversity, accumulation of exhausted and/or senescent memory T cells, but also by increased self-reactive T cell- and innate immune cell-induced chronic inflammation, and accumulated and functionally enhanced polyclonal regulatory T (Treg) cells. Many of these changes can be traced back to age-related thymic involution/degeneration. How these changes contribute to differences in COVID-19 disease severity between young and aged patients is an urgent area of investigation. Therefore, we attempt to connect various clues in this field by reviewing and discussing recent research on the role of the thymus and T cells in COVID-19 immunity during aging (a synergistic effect of diminished responses to pathogens and enhanced responses to self) impacting age-related clinical severity of COVID-19. We also address potential combinational strategies to rejuvenate multiple aging-impacted immune system checkpoints by revival of aged thymic function, boosting peripheral T cell responses, and alleviating chronic, basal inflammation to improve the efficiency of anti-SARS-CoV-2 immunity and vaccination in the elderly.

Severe covid-19 pneumonia: pathogenesis and clinical management

Severe covid-19 pneumonia has posed critical challenges for the research and medical communities. Older age, male sex, and comorbidities increase the risk for severe disease. For people hospitalized with covid-19, 15-30% will go on to develop covid-19 associated acute respiratory distress syndrome (CARDS). Autopsy studies of patients who died of severe SARS CoV-2 infection reveal presence of diffuse alveolar damage consistent with ARDS but with a higher thrombus burden in pulmonary capillaries. When used appropriately, high flow nasal cannula (HFNC) may allow CARDS patients to avoid intubation, and does not increase risk for disease transmission. During invasive mechanical ventilation, low tidal volume ventilation and positive end expiratory pressure (PEEP) titration to optimize oxygenation are recommended. Dexamethasone treatment improves mortality for the treatment of severe and critical covid-19, while remdesivir may have modest benefit in time to recovery in patients with severe disease but shows no statistically significant benefit in mortality or other clinical outcomes. Covid-19 survivors, especially patients with ARDS, are at high risk for long term physical and mental impairments, and an interdisciplinary approach is essential for critical illness recovery.

Innate and Adaptive Immunity in Giant Cell Arteritis

Autoimmune diseases can afflict every organ system, including blood vessels that are critically important for host survival. The most frequent autoimmune vasculitis is giant cell arteritis (GCA), which causes aggressive wall inflammation in medium and large arteries and results in vaso-occlusive wall remodeling. GCA shares with other autoimmune diseases that it occurs in genetically predisposed individuals, that females are at higher risk, and that environmental triggers are suspected to beget the loss of immunological tolerance. GCA has features that distinguish it from other autoimmune diseases and predict the need for tailored diagnostic and therapeutic approaches. At the core of GCA pathology are CD4⁺ T cells that gain access to the protected tissue niche of the vessel wall, differentiate into cytokine producers, attain tissue residency, and enforce macrophages differentiation into tissue-destructive effector cells. Several signaling pathways have been implicated in initiating and sustaining pathogenic CD4⁺ T cell function, including the NOTCH1-Jagged1 pathway, the CD28 co-stimulatory pathway, the PD-1/PD-L1 co-inhibitory pathway, and the JAK/STAT signaling pathway. Inadequacy of mechanisms that normally dampen immune responses, such as defective expression of the PD-L1 ligand and malfunction of immunosuppressive CD8⁺ T regulatory cells are a common theme in GCA immunopathology. Recent studies are providing a string of novel mechanisms that will permit more precise pathogenic modeling and therapeutic targeting in GCA and will fundamentally inform how abnormal immune responses in blood vessels lead to disease.

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 (T_FH) 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 T_FH 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.

The GSK3β-β-catenin-TCF1 pathway improves naive T cell activation in old adults by upregulating miR-181a

MicroRNAs play an important role in the regulation of T cell development, activation, and differentiation. One of the most abundant microRNAs in lymphocytes is miR-181a, which controls T cell receptor (TCR) activation thresholds in thymic selection as well as in peripheral T cell responses. We previously found that miR-181a levels decline in T cells in the elderly. In this study, we identified TCF1 as a transcriptional regulator of pri-miR-181a. A decline in TCF1 levels in old individuals accounted for the reduced miR-181a expression impairing TCR signaling. Inhibition of GSK3ß restored expression of miR-181a by inducing TCF1 in T cells from old adults. GSK3ß inhibition enhanced TCR signaling to increase downstream expression of activation markers and production of IL-2. The effect involved the upregulation of miR-181a and the inhibition of DUSP6 expression. Thus, inhibition of GSK3ß can restore responses of old T cells by inducing miR-181a expression through TCF1.

Immunosenescence Study of T Cells: A Systematic Review

Background

Aging is accompanied by alterations in immune response which leads to increased susceptibility to infectious diseases, cancer, autoimmunity, and inflammatory disorders. This decline in immune function is termed as immunosenescence; however, the mechanisms are not fully elucidated. Experimental approaches of adaptive immunity, particularly for T cells, have been the main focus of immunosenescence research. This systematic review evaluates and discusses T cell markers implicated in immunosenescence.

Objective

To determine the best flow cytometry markers of circulating T cells associated with immunosenescence.

Methods

We systematically queried PubMed, MEDLINE, EBSCO, and BVS databases for original articles focused on two age groups of healthy humans: 18–44 (young adults) and >60 (older adults) years. In accordance with the Cochrane methodology, we synthesized data through qualitative descriptions and quantitative random effects meta-analysis due to extensive heterogeneity.

Results

A total of 36 studies conducted in the last 20 years were included for the qualitative analysis and four out of these studies were used to perform the meta-analysis. A significant decrease in naïve T cell subset was observed in older adults compared to young adults. Primary markers used to identify senescent cells were loss of CD28 and increased expression of CD57 and KLRG1 in terminally-differentiated memory T cell subset in older adults. Moreover, we observed an increase in proinflammatory cytokines and decrease in telomere length in old adult T cells. It was not possible to perform quantitative synthesis on cell markers, cytokines, and telomere length because of the significant variations between the groups, which is attributed to differences in protocols and unreported measurements, thus generating a high risk of bias.

Conclusions

Heterogeneity among studies in terms of data report, measurement techniques and high risk of bias were major impediments for performing a robust statistical analysis that could aid the identification of eligible flow cytometry markers of immunosenescence phenotype in T cells.