Aging is associated with increased regulatory T-cell function

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.

Clinical benefit of immune checkpoint inhibitors in elderly cancer patients: Current evidence from immunosenescence pathophysiology to clinical trial results

The age-related decline in immunity appears to be associated not only with cancer development but also with differential responses to immune checkpoint inhibitors (ICIs). Despite their increasing utility across various malignancies and therapeutic settings, limited data -derived primarily from subgroup analyses of randomized controlled trials (RCTs), pooled meta-analyses, and retrospective studies- are available on the effects of aging on their efficacy and toxicity. Immunosenescence, characterized by the progressive decline of the function of the immune system, and inflammaging, a state of persistent low-grade sterile inflammation, may influence ICI outcomes. Additionally, the incidence, severity, and subtypes of immune-related adverse events (irAEs) may differ between older and younger individuals due to loss of immunotolerance. In the current review, starting from a a comprehensive discussion of the pathophysiology of immunosenescence, we proceed to critically review age-related retrospective and randomized evidence supporting FDA-approved ICIs. We highlight similarities or differences across age groups and the clinical benefit of ICIs in elderly versus younger cancer patients. The optimal integration of ICIs in geriatric oncology necessitates greater inclusion of this patient demographic in RCTs along with real-world data in order to acquire robust data which will guide evidence-based treatment decisions for this population.

Optimising vaccine immunogenicity in ageing populations: key strategies

Vaccination has been shown to be the most effective means of preventing infectious diseases, although older people commonly have a suboptimal immune response to vaccines and thus impaired protection against subsequent adverse outcomes. This Review provides an overview of the existing mechanistic insights into compromised vaccine response for respiratory infectious diseases in older people, defined as aged 65 years and older, including immunosenescence, epigenetic regulation, trained immunity, and gut microbiota. We further summarise the latest proven or potential strategies to strengthen weakened immunogenicity. Insights from these analyses will be conducive to the development of the next generation of vaccines.

Immunosenescence and age-related immune cells: causes of age-related diseases

Immunosenescence is a weakening of the immune system due to aging, characterized by changes in immune cells and dysregulated immune function. Age-related immune cells are increasing with aging. They are associated with chronic prolonged inflammation, causing tissue dysfunction and age-related diseases. Here, we discuss increased pro-inflammatory activity of aged macrophages, accumulation of lymphocytes with an age-associated phenotype, and specific alterations in both functions and characteristics of these immune cells. These cellular changes are associated with development of age-related diseases. Additionally, we reviewed various therapeutic strategies targeting age-related immunosenescence, providing pathways to mitigate effects of age-related diseases.

Age-Dependent Bi-Phasic Dynamics of Ly49+CD8+ Regulatory T Cell Population

Aging is tightly associated with reduced immune protection but increased risk of autoimmunity and inflammatory conditions. Regulatory T cells are one of the key cells to maintaining immune homeostasis. The age-dependent changes in CD4+Foxp3+ regulatory T cells (Tregs) have been well documented. However, the nonredundant Foxp3-CD8+ Tregs were never examined in the context of aging. This study first established clear distinctions between phenotypically overlapping CD8+ Tregs and virtual memory T cells. Then, we elucidated the dynamics of CD8+ Tregs across the lifespan in mice and further extended our investigation to human peripheral blood mononuclear cells (PBMCs). In mice, we discovered a bi-phasic dynamic shift in the frequency of CD8+CD44hiCD122hiLy49+ Tregs, with a steady increase in young adults and a notable peak in middle age followed by a decline in older mice. Transcriptomic analysis revealed that mouse CD8+ Tregs upregulated a selected set of natural killer (NK) cell-associated genes, including NKG2D, with age. Importantly, NKG2D might negatively regulate CD8+ Tregs. Additionally, by analyzing a scRNA-seq dataset of human PBMC, we found a distinct CD8+ Treg-like subset (Cluster 10) with comparable age-dependent frequency changes and gene expression, suggesting a conserved aging pattern in CD8+ Treg across mice and humans. In summary, our findings highlight the importance of CD8+ Tregs in immune regulation and aging.

GDF15/MIC-1: a stress-induced immunosuppressive factor which promotes the aging process

The GDF15 protein, a member of the TGF-β superfamily, is a stress-induced multifunctional protein with many of its functions associated with the regulation of the immune system. GDF15 signaling provides a defence against the excessive inflammation induced by diverse stresses and tissue injuries. Given that the aging process is associated with a low-grade inflammatory state, called inflammaging, it is not surprising that the expression of GDF15 gradually increases with aging. In fact, the GDF15 protein is a core factor secreted by senescent cells, a state called senescence-associated secretory phenotype (SASP). Many age-related stresses, e.g., mitochondrial and endoplasmic reticulum stresses as well as inflammatory, metabolic, and oxidative stresses, induce the expression of GDF15. Although GDF15 signaling is an effective anti-inflammatory modulator, there is robust evidence that it is a pro-aging factor promoting the aging process. GDF15 signaling is not only an anti-inflammatory modulator but it is also a potent immunosuppressive enhancer in chronic inflammatory states. The GDF15 protein can stimulate immune responses either non-specifically via receptors of the TGF-β superfamily or specifically through the GFRAL/HPA/glucocorticoid pathway. GDF15 signaling stimulates the immunosuppressive network activating the functions of MDSCs, Tregs, and M2 macrophages and triggering inhibitory immune checkpoint signaling in senescent cells. Immunosuppressive responses not only suppress chronic inflammatory processes but they evoke many detrimental effects in aged tissues, such as cellular senescence, fibrosis, and tissue atrophy/sarcopenia. It seems that the survival functions of GDF15 go awry in persistent inflammation thus promoting the aging process and age-related diseases.

Regulatory T-cells: The Face-off of the Immune Balance

Regulatory T-cells (Tregs) play a crucial role in maintaining immune homeostasis, ensuring a balanced immune response. Tregs primarily operate in an antigen-specific fashion, facilitated by their distinct distribution within discrete niches. Tregs have been studied extensively, from their point of origin in the thymus origin to their fate in the periphery or organs. Signals received from antigen-presenting cells (APCs) stimulate Tregs to dampen inflammation. Almost all tumors are characterized by a pathological abundance of immune suppression in their microenvironment. Conversely, the lack thereof proves detrimental to immunological disorders. Achieving a balanced expression of Tregs in relation to other immune compartments is important in establishing an effective and adaptable immune tolerance towards cancer cells and autoantigens. In the context of cancer, it is essential to decrease the frequency of Tregs to overcome tumor suppression. A lower survival rate is associated with the presence of excessive exhausted effector immune cells and an increased frequency of regulatory cells. However, when it comes to treating graft rejection and autoimmune diseases, the focus lies on immune tolerance and the transfer of Tregs. Here, we explore the complex mechanisms that Tregs use in human disease to balance effector immune cells.

Inhibitory immune checkpoints suppress the surveillance of senescent cells promoting their accumulation with aging and in age-related diseases

The accumulation of pro-inflammatory senescent cells within tissues is a common hallmark of the aging process and many age-related diseases. This modification has been called the senescence-associated secretory phenotype (SASP) and observed in cultured cells and in cells isolated from aged tissues. Currently, there is a debate whether the accumulation of senescent cells within tissues should be attributed to increased generation of senescent cells or to a defect in their elimination from aging tissues. Emerging studies have revealed that senescent cells display an increased expression of several inhibitory immune checkpoint ligands, especially those of the programmed cell death protein-1 (PD-1) ligand-1 (PD-L1) proteins. It is known that the PD-L1 ligands, especially those of cancer cells, target the PD-1 receptor of cytotoxic CD8+ T and natural killer (NK) cells disturbing their functions, e.g., evoking a decline in their cytotoxic activity and promoting their exhaustion and even apoptosis. An increase in the level of the PD-L1 protein in senescent cells was able to suppress their immune surveillance and inhibit their elimination by cytotoxic CD8+ T and NK cells. Senescent cells are known to express ligands for several inhibitory immune checkpoint receptors, i.e., PD-1, LILRB4, NKG2A, TIM-3, and SIRPα receptors. Here, I will briefly describe those pathways and examine whether these inhibitory checkpoints could be involved in the immune evasion of senescent cells with aging and age-related diseases. It seems plausible that an enhanced inhibitory checkpoint signaling can prevent the elimination of senescent cells from tissues and thus promote the aging process.

Immunosenescence, immunotolerance and rejection: clinical aspects in solid organ transplantation

As a consequence of increased lifespan and rising number of elderly individuals developing end-stage organ disease, the higher demand for organs along with a growing availability for organs from older donors pose new challenges for transplantation. During aging, dynamic adaptations in the functionality and structure of the biological systems occur. Consistently, immunosenescence (IS) accounts for polydysfunctions within the lymphocyte subsets, and the onset of a basal but persistent systemic inflammation characterized by elevated levels of pro-inflammatory mediators. There is an emerging consensus about a causative link between such hallmarks and increased susceptibility to morbidities and mortality, however the role of IS in solid organ transplantation (SOT) remains loosely addressed. Dissecting the immune-architecture of immunologically-privileged sites may prompt novel insights to extend allograft survival. A deeper comprehension of IS in SOT might unveil key standpoints for the clinical management of transplanted patients.

Mechanisms of age-related Treg dysfunction in an arthritic environment

Rheumatoid arthritis (RA) is an autoimmune disease characterized by a polyarticular synovitis. In recent years, elderly onset rheumatoid arthritis (EORA) has been increasing. Treg cells in RA have been reported to be dysfunctional, but the relationship between aging and their functional changes is unclear. Here, we found that Treg cells from EORA patients had increased percentages, but decreased activity compared to those from younger onset RA (YORA) patients. In experiments using arthritis model mice, decreased suppressive function and oxygen consumption rate (OCR) were observed in Treg cells only from old arthritic mice. Furthermore, type I interferon (IFN) signaling was upregulated in Treg cells from old GIA mice, and IFN-β decreased the suppressive function of Treg cells. Our findings demonstrate that increased type I IFN signaling in old Treg cells is induced only in the arthritic environment and relates to decreased suppressive function of Treg cells, gets involved in EORA.

Epigenetic biomarkers in aging and longevity: Current and future application

The aging process has been one of the most necessary research fields in the current century, and knowing different theories of aging and the role of different genetic, epigenetic, molecular, and environmental modulating factors in increasing the knowledge of aging mechanisms and developing appropriate diagnostic, therapeutic, and preventive ways would be helpful. One of the most conserved signs of aging is epigenetic changes, including DNA methylation, histone modifications, chromatin remodeling, noncoding RNAs, and extracellular RNAs. Numerous biological processes and hallmarks are vital in aging development, but epigenomic alterations are especially notable because of their importance in gene regulation and cellular identity. The mounting evidence points to a possible interaction between age-related epigenomic alterations and other aging hallmarks, like genome instability. To extend a healthy lifespan and possibly reverse some facets of aging and aging-related diseases, it will be crucial to comprehend global and locus-specific epigenomic modifications and recognize corresponding regulators of health and longevity. In the current study, we will aim to discuss the role of epigenomic mechanisms in aging and the most recent developments in epigenetic diagnostic biomarkers, which have the potential to focus efforts on reversing the destructive signs of aging and extending the lifespan.

The role of the immunosuppressive PD-1/PD-L1 checkpoint pathway in the aging process and age-related diseases

The accumulation of senescent cells within tissues is a hallmark of the aging process. Senescent cells are also commonly present in many age-related diseases and in the cancer microenvironment. The escape of abnormal cells from immune surveillance indicates that there is some defect in the function of cytotoxic immune cells, e.g., CD8+ T cells and natural killer (NK) cells. Recent studies have revealed that the expression of programmed death-ligand 1 (PD-L1) protein is abundantly increased in senescent cells. An increase in the amount of PD-L1 protein protects senescent cells from clearance by the PD-1 checkpoint receptor in cytotoxic immune cells. In fact, the activation of the PD-1 receptor suppresses the cytotoxic properties of CD8+ T and NK cells, promoting a state of immunosenescence. The inhibitory PD-1/PD-L1 checkpoint pathway acts in cooperation with immunosuppressive cells; for example, activation of PD-1 receptor can enhance the differentiation of regulatory T cells (Treg), myeloid-derived suppressor cells (MDSC), and M2 macrophages, whereas the cytokines secreted by immunosuppressive cells stimulate the expression of the immunosuppressive PD-L1 protein. Interestingly, many signaling pathways known to promote cellular senescence and the aging process are crucial stimulators of the expression of PD-L1 protein, e.g., epigenetic regulation, inflammatory mediators, mTOR-related signaling, cGAS-STING pathway, and AhR signaling. It seems that the inhibitory PD-1/PD-L1 immune checkpoint axis has a crucial role in the accumulation of senescent cells and thus it promotes the aging process in tissues. Thus, the blockade of the PD-1/PD-L1 checkpoint signaling might be a potential anti-aging senolytic therapy. KEY MESSAGES: Senescent cells accumulate within tissues during aging and age-related diseases. Senescent cells are able to escape immune surveillance by cytotoxic immune cells. Expression of programmed death-ligand 1 (PD-L1) markedly increases in senescent cells. Age-related signaling stimulates the expression of PD-L1 protein in senescent cells. Inhibitory PD-1/PD-L1 checkpoint pathway suppresses clearance of senescent cells.

Regulatory T cells limit age-associated retinal inflammation and neurodegeneration

BACKGROUND

Ageing is the principal risk factor for retinal degenerative diseases, which are the commonest cause of blindness in the developed countries. These conditions include age-related macular degeneration or diabetic retinopathy. Regulatory T cells play a vital role in immunoregulation of the nervous system by limiting inflammation and tissue damage in health and disease. Because the retina was long-considered an immunoprivileged site, the precise contribution of regulatory T cells in retinal homeostasis and in age-related retinal diseases remains unknown.

METHODS

Regulatory T cells were selectively depleted in both young (2-4 months) and aged (18-23 months) FoxP3-DTR mice. We evaluated neuroretinal degeneration, gliosis, subretinal space phagocyte infiltration, and retinal pigmented epithelium morphology through immunofluorescence analysis. Subsequently, aged Treg depleted animals underwent adoptive transfer of both young and aged regulatory T cells from wild-type mice, and the resulting impact on neurodegeneration was assessed. Statistical analyses employed included the U-Mann Whitney test, and for comparisons involving more than two groups, 1-way ANOVA analysis followed by Bonferroni's post hoc test.

RESULTS

Our study shows that regulatory T cell elimination leads to retinal pigment epithelium cell dysmorphology and accumulation of phagocytes in the subretinal space of young and aged mice. However, only aged mice experience retinal neurodegeneration and gliosis. Surprisingly, adoptive transfer of young but not aged regulatory T cells reverse these changes.

CONCLUSION

Our findings demonstrate an essential role for regulatory T cells in maintaining age retinal homeostasis and preventing age-related neurodegeneration. This previously undescribed role of regulatory T cells in limiting retinal inflammation, RPE/choroid epithelium damage and subsequently photoreceptor loss with age, opens novel avenues to explore regulatory T cell neuroprotective and anti-inflammatory properties as potential therapeutic approaches for age-related retinal diseases.

Ageing impairs the regenerative capacity of regulatory T cells in mouse central nervous system remyelination

Myelin regeneration (remyelination) is essential to prevent neurodegeneration in demyelinating diseases such as Multiple Sclerosis, however, its efficiency declines with age. Regulatory T cells (Treg) recently emerged as critical players in tissue regeneration, including remyelination. However, the effect of ageing on Treg-mediated regenerative processes is poorly understood. Here, we show that expansion of aged Treg does not rescue age-associated remyelination impairment due to an intrinsically diminished capacity of aged Treg to promote oligodendrocyte differentiation and myelination in male and female mice. This decline in regenerative Treg functions can be rescued by a young environment. We identified Melanoma Cell Adhesion Molecule 1 (MCAM1) and Integrin alpha 2 (ITGA2) as candidates of Treg-mediated oligodendrocyte differentiation that decrease with age. Our findings demonstrate that ageing limits the neuroregenerative capacity of Treg, likely limiting their remyelinating therapeutic potential in aged patients, and describe two mechanisms implicated in Treg-driven remyelination that may be targetable to overcome this limitation.

Inflammation promotes aging-associated oncogenesis in the lung

Background

Lung cancer is the leading cause of cancer death in the world. While cigarette smoking is the major preventable factor for cancers in general and lung cancer in particular, old age is also a major risk factor. Aging-related chronic, low-level inflammation, termed inflammaging, has been widely documented; however, it remains unclear how inflammaging contributes to increased lung cancer incidence. Aim: To establish connections between aging-associated changes in the lungs and cancer risk.

Methods

We analyzed public databases of gene expression for normal and cancerous human lungs and used mouse models to understand which changes were dependent on inflammation, as well as to assess the impact on oncogenesis.

Results

Analyses of GTEx and TCGA databases comparing gene expression profiles from normal lungs, lung adenocarcinoma, lung squamous cell carcinoma of subjects across age groups revealed upregulated pathways such as inflammatory response, TNFA signaling via NFκB, and interferon-gamma response. Similar pathways were identified comparing the gene expression profiles of young and old mouse lungs. Transgenic expression of alpha 1 antitrypsin (AAT) partially reverses increases in markers of aging-associated inflammation and immune deregulation. Using an orthotopic model of lung cancer using cells derived from EML4-ALK fusion-induced adenomas, we demonstrated an increased tumor outgrowth in lungs of old mice while NLRP3 knockout in old mice decreased tumor volumes, suggesting that inflammation contributes to increased lung cancer development in aging organisms.

Conclusions

These studies reveal how expression of an anti-inflammatory mediator (AAT) can reduce some but not all aging-associated changes in mRNA and protein expression in the lungs. We further show that aging is associated with increased tumor outgrowth in the lungs, which may relate to an increased inflammatory microenvironment.

Accelarated immune ageing is associated with COVID-19 disease severity

BACKGROUND

The striking increase in COVID-19 severity in older adults provides a clear example of immunesenescence, the age-related remodelling of the immune system. To better characterise the association between convalescent immunesenescence and acute disease severity, we determined the immune phenotype of COVID-19 survivors and non-infected controls.

RESULTS

We performed detailed immune phenotyping of peripheral blood mononuclear cells isolated from 103 COVID-19 survivors 3-5 months post recovery who were classified as having had severe (n = 56; age 53.12 ± 11.30 years), moderate (n = 32; age 52.28 ± 11.43 years) or mild (n = 15; age 49.67 ± 7.30 years) disease and compared with age and sex-matched healthy adults (n = 59; age 50.49 ± 10.68 years). We assessed a broad range of immune cell phenotypes to generate a composite score, IMM-AGE, to determine the degree of immune senescence. We found increased immunesenescence features in severe COVID-19 survivors compared to controls including: a reduced frequency and number of naïve CD4 and CD8 T cells (p < 0.0001); increased frequency of EMRA CD4 (p < 0.003) and CD8 T cells (p < 0.001); a higher frequency (p < 0.0001) and absolute numbers (p < 0.001) of CD28-ve CD57+ve senescent CD4 and CD8 T cells; higher frequency (p < 0.003) and absolute numbers (p < 0.02) of PD-1 expressing exhausted CD8 T cells; a two-fold increase in Th17 polarisation (p < 0.0001); higher frequency of memory B cells (p < 0.001) and increased frequency (p < 0.0001) and numbers (p < 0.001) of CD57+ve senescent NK cells. As a result, the IMM-AGE score was significantly higher in severe COVID-19 survivors than in controls (p < 0.001). Few differences were seen for those with moderate disease and none for mild disease. Regression analysis revealed the only pre-existing variable influencing the IMM-AGE score was South Asian ethnicity ([Formula: see text] = 0.174, p = 0.043), with a major influence being disease severity ([Formula: see text] = 0.188, p = 0.01).

CONCLUSIONS

Our analyses reveal a state of enhanced immune ageing in survivors of severe COVID-19 and suggest this could be related to SARS-Cov-2 infection. Our data support the rationale for trials of anti-immune ageing interventions for improving clinical outcomes in these patients with severe disease.

Single-cell transcriptomics of Treg reveals hallmarks and trajectories of immunological aging

Age-related immunosenescence is characterized by progressive dysfunction of adaptive immune response and increased autoimmunity. Nevertheless, the impact of aging on CD4+ regulatory T cells that are master regulators of the immune system remains largely unclear. Here, we report cellular and molecular hallmarks of regulatory T cells derived from murine lymphoid and adipose tissues at 3, 18, and 24 mo of age, respectively, by analyzing their heterogeneity that displays dynamic changes in transcriptomic effector signatures at a single-cell resolution. Although the proportion of regulatory T cells among total Cd4+ T cells, as well as their expression levels of Foxp3, did not show any global change with time, we have identified 6 transcriptomically distinct clusters of regulatory T cells with cross-tissue conserved hallmarks of aging, including increased numbers of proinflammatory regulatory T cells, reduced precursor cells, increased immature and mature T follicular regulatory cells potentially supported by a metabolic switch from oxidative phosphorylation to glycolysis, a gradual loss of CD150hi regulatory T cells that support hematopoiesis, and increased adipose tissue-specific regulatory T cells that are associated with metabolic disease. To dissect the impact of immunosenescence on humoral immunity, we propose some potential mechanisms underlying T follicular regulatory cell-mediated dysfunction by interactome analysis on T follicular regulatory cells, T follicular helper cells, and B cells during aging. Lastly, spatiotemporal analysis further revealed trajectories of regulatory T-cell aging that demonstrate the most significant changes in marrow and adipose tissues that might contribute to the development of age-related immunosenescence and type 2 diabetes. Taken together, our findings could provide a better understanding of age-associated regulatory T-cell heterogeneity in lymphoid and adipose tissues, as well as regulatory T-cell hallmarks during progressive adaptation to aging that could be therapeutically targeted for rejuvenating the aging immune system in the future.

Single-cell profiling reveals age-associated immunity in atherosclerosis

AIMS

Aging is a dominant driver of atherosclerosis and induces a series of immunological alterations, called immunosenescence. Given the demographic shift towards elderly, elucidating the unknown impact of aging on the immunological landscape in atherosclerosis is highly relevant. While the young Western diet-fed Ldlr-deficient (Ldlr-/-) mouse is a widely used model to study atherosclerosis, it does not reflect the gradual plaque progression in the context of an aging immune system as occurs in humans.

METHODS AND RESULTS

Here, we show that aging promotes advanced atherosclerosis in chow diet-fed Ldlr-/- mice, with increased incidence of calcification and cholesterol crystals. We observed systemic immunosenescence, including myeloid skewing and T-cells with more extreme effector phenotypes. Using a combination of single-cell RNA-sequencing and flow cytometry on aortic leucocytes of young vs. aged Ldlr-/- mice, we show age-related shifts in expression of genes involved in atherogenic processes, such as cellular activation and cytokine production. We identified age-associated cells with pro-inflammatory features, including GzmK+CD8+ T-cells and previously in atherosclerosis undefined CD11b+CD11c+T-bet+ age-associated B-cells (ABCs). ABCs of Ldlr-/- mice showed high expression of genes involved in plasma cell differentiation, co-stimulation, and antigen presentation. In vitro studies supported that ABCs are highly potent antigen-presenting cells. In cardiovascular disease patients, we confirmed the presence of these age-associated T- and B-cells in atherosclerotic plaques and blood.

CONCLUSIONS

Collectively, we are the first to provide comprehensive profiling of aged immunity in atherosclerotic mice and reveal the emergence of age-associated T- and B-cells in the atherosclerotic aorta. Further research into age-associated immunity may contribute to novel diagnostic and therapeutic tools to combat cardiovascular disease.

Immunosenescence and cancer: Opportunities and challenges

As individuals age, cancer becomes increasingly common. This continually rising risk can be attributed to various interconnected factors that influence the body's susceptibility to cancer. Among these factors, the accumulation of senescent cells in tissues and the subsequent decline in immune cell function and proliferative potential are collectively referred to as immunosenescence. Reduced T-cell production, changes in secretory phenotypes, increased glycolysis, and the generation of reactive oxygen species are characteristics of immunosenescence that contribute to cancer susceptibility. In the tumor microenvironment, senescent immune cells may promote the growth and spread of tumors through multiple pathways, thereby affecting the effectiveness of immunotherapy. In recent years, immunosenescence has gained increasing attention due to its critical role in tumor development. However, our understanding of how immunosenescence specifically impacts cancer immunotherapy remains limited, primarily due to the underrepresentation of elderly patients in clinical trials. Furthermore, there are several age-related intervention methods, including metformin and rapamycin, which involve genetic and pharmaceutical approaches. This article aims to elucidate the defining characteristics of immunosenescence and its impact on malignant tumors and immunotherapy. We particularly focus on the future directions of cancer treatment, exploring the complex interplay between immunosenescence, cancer, and potential interventions.

Accumulation of immune-suppressive CD4 + T cells in aging - tempering inflammaging at the expense of immunity

The 'immune risk profile' has been shown to predict mortality in the elderly, highlighting the need to better understand age-related immune dysfunction. While aging leads to many defects affecting all arms of the immune system, this review is focused on the accrual of immuno-suppressive CD4 + T cell populations, including FoxP3 + regulatory T cells, and subsets of IL-10-producing T follicular helper cells. New data suggest that such accumulations constitute feedback mechanisms to temper the ongoing progressive low-grade inflammation that develops with age, the so-called "inflammaging", and by doing so, how they have the potential to promote healthier aging. However, they also impair effector immune responses, notably to infections, or vaccines. These studies also reinforce the idea that the aged immune system should not be considered as a poorly functional version of the young one, but more as a dynamic system in which CD4 + T cells, and other immune/non-immune subsets, differentiate, interact with their milieu and function differently than in young hosts. A better understanding of these unique interactions is thus needed to improve effector immune responses in the elderly, while keeping inflammaging under control.

T cell control of inflammaging

T cells are a critical component of the immune system, found in abundance in blood, secondary lymphoid organs, and peripheral tissues. As individuals age, T cells are particularly susceptible to changes, making them one of the most affected immune subsets. These changes can have significant implications for age-related dysregulations, including the development of low-grade inflammation - a hallmark of aging known as inflammaging. In this review, we first present age-related changes in the functionality of the T cell compartment, including dysregulation of cytokine and chemokine production and cytotoxicity. Next, we discuss how these changes can contribute to the development and maintenance of inflammaging. Furthermore, we will summarize the mechanisms through which age-related changes in T cells may drive abnormal physiological outcomes.

Considerations and Approaches for Cancer Immunotherapy in the Aging Host

Advances in cancer immunotherapy are improving treatment successes in many distinct cancer types. Nonetheless, most tumors fail to respond. Age is the biggest risk for most cancers, and the median population age is rising worldwide. Advancing age is associated with manifold alterations in immune cell types, abundance, and functions, rather than simple declines in these metrics, the consequences of which remain incompletely defined. Our understanding of the effects of host age on immunotherapy mechanisms, efficacy, and adverse events remains incomplete. A deeper understanding of age effects in all these areas is required. Most cancer immunotherapy preclinical studies examine young subjects and fail to assess age contributions, a remarkable deficit given the known importance of age effects on immune cells and factors mediating cancer immune surveillance and immunotherapy efficacy. Notably, some cancer immunotherapies are more effective in aged versus young hosts, while others fail despite efficacy in the young. Here, we review our current understanding of age effects on immunity and associated nonimmune cells, the tumor microenvironment, cancer immunotherapy, and related adverse effects. We highlight important knowledge gaps and suggest areas for deeper enquiries, including in cancer immune surveillance, treatment response, adverse event outcomes, and their mitigation.

The paradox of aging: Aging-related shifts in T cell function and metabolism

T cell survival, differentiation after stimulation, and function are intrinsically linked to distinct cellular metabolic states. The ability of T cells to readily transition between metabolic states enables flexibility to meet the changing energy demands defined by distinct effector states or T cell lineages. Immune aging is characterized, in part, by the loss of naïve T cells, accumulation of senescent T cells, severe dysfunction in memory phenotype T cells in particular, and elevated levels of inflammatory cytokines, or 'inflammaging'. Here, we review our current understanding of the phenotypic and functional changes that occur with aging in T cells, and how they relate to metabolic changes in the steady state and after T cell activation. We discuss the apparent contradictions in the aging T cell phenotype - where enhanced differentiation states and metabolic profiles in the steady state can correspond to a diminished capacity to adapt metabolically and functionally after T cell activation. Finally, we discuss key recent studies that indicate the enormous potential for aged T cell metabolism to induce systemic inflammaging and organism-wide multimorbidity, resulting in premature death.

Immune senescence in aged APP/PS1 mice

Objectives

To evaluate the linkage between age and deficits in innate and adaptive immunity which heralds both Alzheimer's disease (AD) onset and progression. The pathobiological events which underlie and tie these outcomes remain not fully understood.

Methods

To investigate age-dependent immunity in AD, we evaluated innate and adaptive immunity in coordinate studies of regulatory T cell (Treg) function, T cell frequencies, and microglial integrity. These were assessed in blood, peripheral lymphoid tissues, and the hippocampus of transgenic (Tg) amyloid precursor protein/presenilin 1 (APP/PS1) against non-Tg mice. Additionally, immune arrays of hippocampal tissue were performed at 4, 6, 12, and 20 months of age.

Results

APP/PS1 mice showed progressive impairment of Treg immunosuppressive function with age. There was partial restoration of Treg function in 20-month-old mice. Ingenuity pathway analyses of hippocampal tissues were enriched in inflammatory, oxidative, and cellular activation pathways that paralleled advancing age and AD-pathobiology. Operative genes in those pathways included, but were not limited to triggering receptor on myeloid cells 1 (TREM1), T helper type 1 (Th1), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathways. Interleukin-17 (IL-17), nitric oxide, acute phase, and T cell receptor signaling pathways were also perturbed. Significant inflammation was observed at 6- and 12-months. However, at 20-months, age associated partial restoration of Treg function reduced inflammatory phenotype.

Conclusions

Impaired Treg function, inflammation and oxidative stress were associated with AD pathology. Age associated partial restoration of Treg function in old mice reduced the hippocampal inflammatory phenotype. Restoring Treg suppressive function can be a therapeutic modality for AD.

Methylation across the central dogma in health and diseases: new therapeutic strategies

The proper transfer of genetic information from DNA to RNA to protein is essential for cell-fate control, development, and health. Methylation of DNA, RNAs, histones, and non-histone proteins is a reversible post-synthesis modification that finetunes gene expression and function in diverse physiological processes. Aberrant methylation caused by genetic mutations or environmental stimuli promotes various diseases and accelerates aging, necessitating the development of therapies to correct the disease-driver methylation imbalance. In this Review, we summarize the operating system of methylation across the central dogma, which includes writers, erasers, readers, and reader-independent outputs. We then discuss how dysregulation of the system contributes to neurological disorders, cancer, and aging. Current small-molecule compounds that target the modifiers show modest success in certain cancers. The methylome-wide action and lack of specificity lead to undesirable biological effects and cytotoxicity, limiting their therapeutic application, especially for diseases with a monogenic cause or different directions of methylation changes. Emerging tools capable of site-specific methylation manipulation hold great promise to solve this dilemma. With the refinement of delivery vehicles, these new tools are well positioned to advance the basic research and clinical translation of the methylation field.

Counteracting Immunosenescence-Which Therapeutic Strategies Are Promising?

Aging attenuates the overall responsiveness of the immune system to eradicate pathogens. The increased production of pro-inflammatory cytokines by innate immune cells under basal conditions, termed inflammaging, contributes to impaired innate immune responsiveness towards pathogen-mediated stimulation and limits antigen-presenting activity. Adaptive immune responses are attenuated as well due to lowered numbers of naïve lymphocytes and their impaired responsiveness towards antigen-specific stimulation. Additionally, the numbers of immunoregulatory cell types, comprising regulatory T cells and myeloid-derived suppressor cells, that inhibit the activity of innate and adaptive immune cells are elevated. This review aims to summarize our knowledge on the cellular and molecular causes of immunosenescence while also taking into account senescence effects that constitute immune evasion mechanisms in the case of chronic viral infections and cancer. For tumor therapy numerous nanoformulated drugs have been developed to overcome poor solubility of compounds and to enable cell-directed delivery in order to restore immune functions, e.g., by addressing dysregulated signaling pathways. Further, nanovaccines which efficiently address antigen-presenting cells to mount sustained anti-tumor immune responses have been clinically evaluated. Further, senolytics that selectively deplete senescent cells are being tested in a number of clinical trials. Here we discuss the potential use of such drugs to improve anti-aging therapy.

Attenuation of OX40 signaling suppression by age disrupts peripheral deletion of CD4+ T cells specific for the epidermal autoantigen desmoglein 3

Various autoimmune responses increase with age, but the underlying mechanism is not clear. In this study, we used CD4⁺ T cells expressing a transgenic T cell receptor specific for desmoglein 3 (Dsg3), which is the target antigen of the autoimmune bullous disease pemphigus vulgaris, to examine how peripheral immunological tolerance against pathogenic autoreactive CD4⁺ T cells changes with age. Dsg3-specific T cells were deleted within 14 days after adoptive transfer into young mice (8 weeks old), while they escaped deletion when transferred into older mice over 42 weeks old. Dsg3-specific T cells produced higher levels of the proinflammatory cytokine IFN-γ in aged mice than in young mice. In addition, the expression levels of both OX40 and Birc5, which are important for cell survival in T cell clonal proliferation, were higher in aged than in young mice. The dysfunction in suppressing proinflammatory cytokine secretion and Birc5 upregulation in Dsg3-specific autoreactive T cells may reflect an aspect of the preliminary steps in autoimmune disease development in the aged population. Understanding this mechanism may lead to better risk evaluation of autoimmune disease development and to onset prevention.

Amplified Natural Killer Cell Activity and Attenuated Regulatory T-cell Function Are Determinants for Corneal Alloimmunity in Very Young Mice

BACKGROUND

Corneal transplantation outcomes are generally less favorable in young children compared with adults. The purpose of this study was to determine the immunological mechanisms underlying this difference.

METHODS

A murine model of allogeneic corneal transplantation was used in the study, and graft survival was determined by evaluating opacity scores for 8 wk. Syngeneic transplantation in the very young host served as a surgical control. The frequencies of total and activated natural killer (NK) cells in cornea posttransplantation were kinetically evaluated using flow cytometry. The regulatory T cell (Treg) frequency and function in naive animals were assessed by flow cytometry and in vitro suppression assays, respectively. Finally, graft survival and immune responses were determined in NK cell-depleted, or adult naive Treg-transferred, young hosts.

RESULTS

Corneal allograft survival in the very young recipients was significantly lower than in adult hosts. The frequencies of total NK cells and their interferon gamma-expressing subset in the cornea were significantly higher in the very young mice posttransplantation. In ungrafted mice, frequencies of Treg in draining lymph nodes as well as their capabilities to suppress NK-cell secretion of interferon gamma were lower in the very young compared with adults. In NK cell-depleted or adult Treg--transferred very young recipients, the allograft survival was significantly improved along with the suppressed NK-cell response.

CONCLUSIONS

Our data demonstrate that amplified activity of NK cells, together with lower suppressive function of Treg, contributes to early rejection of corneal allografts in very young graft recipients.

Regulatory T lymphocytes as a therapy for ischemic stroke

Unrestrained excessive inflammatory responses exacerbate ischemic brain injury and impede post-stroke brain recovery. CD4+CD25+Foxp3+ regulatory T (Treg) cells play important immunosuppressive roles to curtail inflammatory responses and regain immune homeostasis after stroke. Accumulating evidence confirms that Treg cells are neuroprotective at the acute stage after stroke and promote brain repair at the chronic phases. The beneficial effects of Treg cells are mediated by diverse mechanisms involving cell-cell interactions and soluble factor release. Multiple types of cells, including both immune cells and non-immune CNS cells, have been identified to be cellular targets of Treg cells. In this review, we summarize recent findings regarding the function of Treg cells in ischemic stroke and the underlying cellular and molecular mechanisms. The protective and reparative properties of Treg cells endorse them as good candidates for immune therapy. Strategies that boost the numbers and functions of Treg cells have been actively developing in the fields of transplantation and autoimmune diseases. We discuss the approaches for Treg cell expansion that have been tested in stroke models. The application of these approaches to stroke patients may bring new hope for stroke treatments.

Extremely Differentiated T Cell Subsets Contribute to Tissue Deterioration During Aging

There is a dramatic remodeling of the T cell compartment during aging. The most notorious changes are the reduction of the naive T cell pool and the accumulation of memory-like T cells. Memory-like T cells in older people acquire a phenotype of terminally differentiated cells, lose the expression of costimulatory molecules, and acquire properties of senescent cells. In this review, we focus on the different subsets of age-associated T cells that accumulate during aging. These subsets include extremely cytotoxic T cells with natural killer properties, exhausted T cells with altered cytokine production, and regulatory T cells that gain proinflammatory features. Importantly, all of these subsets lose their lymph node homing capacity and migrate preferentially to nonlymphoid tissues, where they contribute to tissue deterioration and inflammaging.

Regulatory T cell expansion promotes white matter repair after stroke

Recent research highlights the function of regulatory T cells (Tregs) in white matter integrity in CNS diseases. Approaches that expand the number of Tregs have been utilized to improve stroke recovery. However, it remains unclear if Treg augmentation preserves white matter integrity early after stroke or promotes white matter repair. This study evaluates the effect of Treg augmentation on white matter injury and repair after stroke. Adult male C57/BL6 mice randomly received Treg or splenocyte (2 million, iv) transfer 2 h after transient (60 min) middle cerebral artery occlusion (tMCAO). Immunostaining showed improved white matter recovery after tMCAO in Treg-treated mice compared to mice received splenocytes. In another group of mice, IL-2/IL-2 antibody complexes (IL-2/IL-2Ab) or isotype IgG were administered (i.p) for 3 consecutive days starting 6 h after tMCAO, and repeated on day 10, 20 and 30. The IL-2/IL-2Ab treatment boosted the number of Tregs in blood and spleen and increased Treg infiltration into the ischemic brain. Longitudinal in vivo and ex vivo diffusion tensor imaging analysis revealed an increase in fractional anisotropy 28d and 35d, but not 14d, after stroke in IL-2/IL-2Ab-treated mice compared to isotype-treated mice, suggesting a delayed improvement in white matter integrity. IL-2/IL-2Ab also improved sensorimotor functions (rotarod test and adhesive removal test) 35d after stroke. There were correlations between white matter integrity and behavior performance. Immunostaining confirmed the beneficial effects of IL-2/IL-2Ab on white matter structures 35d after tMCAO. IL-2/IL-2Ab treatment starting as late as 5d after stroke still improved white matter integrity 21d after tMCAO, suggesting long-term salutary effects of Tregs on the late-stage tissue repair. We also found that IL-2/IL-2Ab treatment reduced the number of dead/dying OPCs and oligodendrocytes in the brain 3d after tMCAO. To confirm the direct effect of Tregs on remyelination, Tregs were cocultured with lysophosphatidyl choline (LPC)-treated organotypic cerebella. LPC exposure for 17 h induced demyelination in organotypic cultures, followed by gradual spontaneous remyelination upon removal of LPC. Co-culture with Tregs accelerated remyelination in organotypic cultures 7d after LPC. In conclusion, Boosting the number of Tregs protects oligodendrocyte lineage cells early after stroke and promotes long-term white matter repair and functional recovery. IL-2/IL-2Ab represents a feasible approach of Treg expansion for stroke treatment.

Tregs dysfunction aggravates postoperative cognitive impairment in aged mice

OBJECTIVES

Enhanced neuroinflammation is an important mechanism underlying perioperative neurocognitive disorders. Regulatory T cells (Tregs) play a crucial role in regulating systemic immune responses. The present study was aimed to investigate the participation of Tregs in the development of postoperative cognitive dysfunction (POCD).

METHODS

Surgery-associated neurocognitive disorder was induced in 18-month-old mice subjected to internal fixation of tibial fracture. Morris water maze was used to examine mice cognitive function. Splenic Tregs were collected for RNA sequencing and flow cytometry. Levels of inflammatory factors in the circulation and hippocampus were measured by enzyme-linked immunosorbent assay. Protein presences of tight junction proteins were detected by immunofluorescence.

RESULTS

Surgery of internal fixation of tibial fracture induced cognitive impairment in aged mice, accompanied by elevated plasma levels of inflammatory factors and increased circulating Tregs. Transfusion of Tregs from young mice partially restored the structure of the blood-brain barrier and alleviated POCD in aged mice. Compared with young Tregs, differentially expressed genes in aged Tregs were enriched in tumor necrosis factor (TNF) signaling pathway and cytokine-cytokine receptor interaction. Flow cytometry revealed that aged Tregs had blunted functions under basal and stimulated conditions. Blockade of the CD25 epitope protected the blood-brain barrier structure, reduced TNF-α levels in the hippocampus, and improved surgery-associated cognition in aged mice.

CONCLUSIONS

Blocking peripheral regulatory T cells improves surgery-induced cognitive function in aged mice. Therefore, aged Tregs play an essential role in the occurrence of POCD.

The Increased Risk of Hypertension Caused by Irrational Dietary Pattern May Be Associated with Th17 Cell in the Middle-Aged and Elderly Rural Residents of Beijing City, Northern China: A 1:1 Matched Case-Control Study

An irrational diet has been widely considered as one of the vital risk factors of hypertension. Previous studies have indicated that immune dysfunction may be involved in the pathogenic process of hypertension, while fewer studies have mentioned whether CD4+ T cells are involved in the association between dietary pattern and hypertension. This present 1:1 matched case-control study was conducted to analyze the association among dietary pattern, CD4+ T cells and hypertension. A total of 56 patients with diagnosed hypertension and 56 subjects without diagnosed hypertension in the rural area of Beijing City, northern China, were matched by age and gender, and then classified into a case group and a control group, respectively. Compared with the control group, higher frequencies of pro-inflammatory CD4+ T cells, such as Th1, Th1(IFN-γ), Th17(IL-17A), and Th1/17 (IFN-γ/IL-17A), were found in the case group (p < 0.05). A significantly higher level of circulating IL-17A was also found in the case group (7.4 pg/mL vs. 8.2 pg/mL, p < 0.05). Five dietary patterns were identified using exploratory factor analysis. An irrational dietary pattern, characterized by high-factor loadings of refined wheat (0.65), meat (0.78), poultry (0.76), and alcoholic beverage (0.73), was positively associated with SBP (β = 5.38, 95%CI = 0.73~10.03, p < 0.05) in the multiple linear regression model with the adjustment of potential covariates. The other dietary patterns showed no significant association with blood pressure. Furthermore, meat, processed meat, and animal viscera were positively correlated with the peripheral Th17 or Th1/17. In conclusion, the irrational dietary pattern characterized by refined wheat, meat, poultry, and alcoholic beverage, was positively correlated with blood pressure, and may increase the risk of hypertension in the rural area of Beijing, northern China. Th17, a subset of the CD4+ T helper cells, may be involved in the association between irrational dietary pattern and hypertension.

Age-associated remodeling of T cell immunity and metabolism

Aging results in remodeling of T cell immunity and is associated with poor clinical outcomes in age-related diseases such as cancer. Among the hallmarks of aging, changes in host and cellular metabolism critically affect the development, maintenance, and function of T cells. Although metabolic perturbations impact anti-tumor T cell responses, the link between age-associated metabolic dysfunction and anti-tumor immunity remains unclear. In this review, we summarize recent advances in our understanding of aged T cell metabolism, with a focus on the bioenergetic and immunologic features of T cell subsets unique to the aging process. We also survey insights into mechanisms of metabolic T cell dysfunction in aging and discuss the impacts of aging on the efficacy of cancer immunotherapy. As the average life expectancy continues to increase, understanding the interplay between age-related metabolic reprogramming and maladaptive T cell immunity will be instrumental for the development of therapeutic strategies for older patients.

Transplantation of gut microbiota from old mice into young healthy mice reduces lean mass but not bone mass

Aging is associated with low bone and lean mass as well as alterations in the gut microbiota (GM). In this study, we determined whether the reduced bone mass and relative lean mass observed in old mice could be transferred to healthy young mice by GM transplantation (GMT). GM from old (21-month-old) and young adult (5-month-old) donors was used to colonize germ-free (GF) mice in three separate studies involving still growing 5- or 11-week-old recipients and 17-week-old recipients with minimal bone growth. The GM of the recipient mice was similar to that of the donors, demonstrating successful GMT. GM from old mice did not have statistically significant effects on bone mass or bone strength, but significantly reduced the lean mass percentage of still growing recipient mice when compared with recipients of GM from young adult mice. The levels of propionate in the cecum of mice receiving old donor GM were significantly lower than those in mice receiving young adult donor GM. Bacteroides ovatus was enriched in the microbiota of recipient mice harboring GM from young adult donors. The presence of B. ovatus was not only significantly associated with high lean mass percentage in mice, but also with lean mass adjusted for fat mass in the large human HUNT cohort. In conclusion, GM from old mice reduces lean mass percentage but not bone mass in young, healthy, still growing recipient mice. Future studies are warranted to determine whether GM from young mice improves the musculoskeletal phenotype of frail elderly recipient mice.

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.

A Novel Strategy to Model Age-Related Cancer for Elucidation of the Role of Th17 Inflammaging in Cancer Progression

Cancer is a disease of aging, but most studies on cancer are in young but not aged animal models, and cancer clinical trials are rarely performed in older adults. Recognition of the connections between aging and cancer and improvement of treatment for elderly cancer patients has become one of the most critical medical issues with the global increase in the elderly population. Mouse models are essential experimental tools for understanding the molecular mechanisms of complex processes and related gene pathways of biological aging. However, few mouse models can be used to understand the role of aging in cancer development and the underlying mechanisms. One of the hallmarks of aging is chronic inflammation, often called inflammaging. This is our rationale for examining the role of aging-related inflammation in prostate cancer, a major aging malignancy. We have now developed a novel method to generate age-related cancer models in mice to better understand how age impacts cancer initiation and progression in the natural aging process. We discuss its application to elucidate some of the contributing mechanisms.

The dark side of Tregs during aging

In the last century, we have seen a dramatic rise in the number of older persons globally, a trend known as the grey (or silver) tsunami. People live markedly longer than their predecessors worldwide, due to remarkable changes in their lifestyle and in progresses made by modern medicine. However, the older we become, the more susceptible we are to a series of age-related pathologies, including infections, cancers, autoimmune diseases, and multi-morbidities. Therefore, a key challenge for our modern societies is how to cope with this fragile portion of the population, so that everybody could have the opportunity to live a long and healthy life. From a holistic point of view, aging results from the progressive decline of various systems. Among them, the distinctive age-dependent changes in the immune system contribute to the enhanced frailty of the elderly. One of these affects a population of lymphocytes, known as regulatory T cells (Tregs), as accumulating evidence suggest that there is a significant increase in the frequency of these cells in secondary lymphoid organs (SLOs) of aged animals. Although there are still discrepancies in the literature about modifications to their functional properties during aging, mounting evidence suggests a detrimental role for Tregs in the elderly in the context of bacterial and viral infections by suppressing immune responses against non-self-antigens. Interestingly, Tregs seem to also contribute to the reduced effectiveness of immunizations against many pathogens by limiting the production of vaccine-induced protective antibodies. In this review, we will analyze the current state of understandings about the role of Tregs in acute and chronic infections as well as in vaccination response in both humans and mice. Lastly, we provide an overview of current strategies for Treg modulation with potential future applications to improve the effectiveness of vaccines in older individuals.

Immunosenescence, aging and successful aging

Aging induces a series of immune related changes, which is called immunosenescence, playing important roles in many age-related diseases, especially neurodegenerative diseases, tumors, cardiovascular diseases, autoimmune diseases and coronavirus disease 2019(COVID-19). However, the mechanism of immunosenescence, the association with aging and successful aging, and the effects on diseases are not revealed obviously. In order to provide theoretical basis for preventing or controlling diseases effectively and achieve successful aging, we conducted the review and found that changes of aging-related phenotypes, deterioration of immune organ function and alterations of immune cell subsets participated in the process of immunosenescence, which had great effects on the occurrence and development of age-related diseases.

A diminished immune response underlies age-related SARS-CoV-2 pathologies

Morbidity and mortality in response to SARS-CoV-2 infection are significantly elevated in people of advanced age. To understand the underlying biology of this phenotype, we utilize the golden hamster model to compare how the innate and adaptive immune responses to SARS-CoV-2 infection differed between younger and older animals. We find that while both hamster cohorts showed similar virus kinetics in the lungs, the host response in older animals was dampened, with diminished tissue repair in the respiratory tract post-infection. Characterization of the adaptive immune response also revealed age-related differences, including fewer germinal center B cells in older hamsters, resulting in reduced potency of neutralizing antibodies. Moreover, older animals demonstrate elevated suppressor T cells and neutrophils in the respiratory tract, correlating with an increase in TGF-β and IL-17 induction. Together, these data support that diminished immunity is one of the underlying causes of age-related morbidity.

Accumulation of pTreg cells is detrimental in late-onset (aged) mouse model of multiple sclerosis

Although typically associated with onset in young adults, multiple sclerosis (MS) also attacks the elderly, which is termed late-onset MS. The disease can be recapitulated and studied in a mouse model, experimental autoimmune encephalomyelitis (EAE). The onset of induced EAE is delayed in aged mice, but disease severity is increased relative to young EAE mice. Given that CD4⁺ FoxP3⁺ regulatory T (Treg) cells play an ameliorative role in MS/EAE severity, and the aged immune system accumulates peripheral Treg (pTreg) cells, failure of these cells to prevent or ameliorate EAE disease is enigmatic. When analyzing the distribution of Treg cells in EAE mice, the aged mice exhibited a higher proportion of polyclonal (pan-) pTreg cells and a lower proportion of antigen-specific pTreg cells in the periphery but lower proportions of both pan- and antigen-specific Treg cells in the central nervous system (CNS). Furthermore, in the aged inflamed CNS, CNS-Treg cells exhibited a higher plasticity, and T effector (CNS-Teff) cells exhibited greater clonal expansion, disrupting the Treg/Teff balance. Transiently inhibiting FoxP3 or depleting pTreg cells partially corrected Treg distribution and restored the Treg/Teff balance in the aged inflamed CNS, thereby ameliorating the disease in the aged EAE mice. These results provide evidence and mechanism that accumulated aged pTreg cells play a detrimental role in neuronal inflammation of aged MS.

Role of thymus in health and disease

The thymus is a primary lymphoid organ, essential for the development of T-cells that will protect from invading pathogens, immune disorders, and cancer. The thymus decreases in size and cellularity with age referred to as thymus involution or atrophy. This involution causes decreased T-cell development and decreased naive T-cell emigration to the periphery, increased proportion of memory T cells, and a restricted, altered T-cell receptor (TCR) repertoire. The changes in composition and function of the circulating T cell pool as a result of thymic involution led to increased susceptibility to infectious diseases including the recent COVID and a higher risk for autoimmune disorders and cancers. Thymic involution consisting of both structural and functional loss of the thymus has a deleterious effect on T cell development, T cell selection, and tolerance. The mechanisms which act on the structural (cortex and medulla) matrix of the thymus, the gradual accumulation of genetic mutations, and altered gene expressions may lead to immunosenescence as a result of thymus involution. Understanding the molecular mechanisms behind thymic involution is critical for identifying diagnostic biomarkers and targets for treatment help to develop strategies to mitigate thymic involution-associated complications. This review is focused on the consequences of thymic involution in infections, immune disorders, and diseases, identifying potential checkpoints and potential approaches to sustain or restore the function of the thymus particularly in elderly and immune-compromised individuals.

Male rat leukocyte population dynamics predict a window for intervention in aging

Many age-associated changes in the human hematopoietic system have been reproduced in murine models; however, such changes have not been as robustly explored in rats despite the fact these larger rodents are more physiologically similar to humans. We examined peripheral blood of male F344 rats ranging from 3 to 27 months of age and found significant age-associated changes with distinct leukocyte population shifts. We report CD25⁺ CD4⁺ population frequency is a strong predictor of healthy aging, generate a model using blood parameters, and find rats with blood profiles that diverge from chronologic age indicate debility; thus, assessments of blood composition may be useful for non-lethal disease profiling or as a surrogate measure for efficacy of aging interventions. Importantly, blood parameters and DNA methylation alterations, defined distinct juncture points during aging, supporting a non-linear aging process. Our results suggest these inflection points are important considerations for aging interventions. Overall, we present rat blood aging metrics that can serve as a resource to evaluate health and the effects of interventions in a model system physiologically more reflective of humans.

Our blood contains many types of white blood cells, which play important roles in defending the body against infections and other threats to our health. The number of these cells changes with age, and this in turn contributes to many other alterations that happen in the body as we get older. For example, the immune system generally gets weaker at fighting infections and preventing other cells from developing into cancer. On top of that, the white blood cells themselves can become cancerous, resulting in several types of blood cancer that are more likely to happen in older people.

Many previous studies have examined how the number of white blood cells changes with age in humans and mice. However, our understanding of this process in rats is still poor, despite the fact that the way the human body works has more in common with the rat body than the mouse body.

Here, Yanai, Dunn et al. have studied samples of blood from rats between three to 27 months old. The experiments found that it is possible to accurately predict the age of healthy rats by measuring the frequency of populations of white blood cells, especially a certain type known as CD25+ CD4+ cells. If the animals had any form of illness, their predicted age deviated from their actual age. Furthermore, while some changes in the blood were gradual and continuous, others displayed distinct shifts when the rats reached specific ages.

In the future, these findings may be used as a tool to help researchers diagnose illnesses in rats before the animals develop symptoms, or to more easily establish if a treatment is having a positive effect on the rats’ health. The work of Yanai, Dunn et al. also provides new insights into aging that could potentially aid the design of new screening methods to predict cancer and intervene using a model system that is more similar to humans.

Depletion of CD38-positive regulatory T cells by anti-CD38 monoclonal antibodies induces a durable response to SARS-CoV-2 vaccination in patients with plasma cell dyscrasia

This study reports the relationship between CD38+ regulatory T cells (Tregs) and messenger RNA coronavirus disease 2019 (mRNA-COVID-19) vaccination in 60 patients with plasma cell dyscrasia. Patients treated with anti-CD38 monoclonal antibodies (mAbs) had significantly lower CD38+ Tregs than those not treated (0.9 vs. 13.2/μl). Late-responders, whose antibody titres increased from weeks 4-12 after the second vaccination, had significantly lower CD38+ Treg counts than non-late-responders (2.5 vs. 10.3/μl). Antibody titres in patients with lower CD38+ Treg levels were maintained from weeks 4-12 but decreased in those with higher CD38+ Treg levels. Therefore, depletion of CD38+ Tregs by anti-CD38 mAbs may induce a durable response to mRNA-COVID-19 vaccination.

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.

The Influence of Heterochronic Non-Myeloablative Bone Marrow Transplantation on the Immune System, Frailty, General Health, and Longevity of Aged Murine Recipients

The stem cell theory of aging postulates that stem cells become inefficient at maintaining the original functions of the tissues. We, therefore, hypothesized that transplanting young bone marrow (BM) to old recipients would lead to rejuvenating effects on immunity, followed by improved general health, decreased frailty, and possibly life span extension. We developed a murine model of non-myeloablative heterochronic BM transplantation in which old female BALB/c mice at 14, 16, and 18(19) months of age received altogether 125.1 ± 15.6 million nucleated BM cells from young male donors aged 7–13 weeks. At 21 months, donor chimerism was determined, and the immune system’s innate and adaptive arms were analyzed. Mice were then observed for general health and frailty until spontaneous death, when their lifespan, post-mortem examinations, and histopathological changes were recorded. The results showed that the old mice developed on average 18.7 ± 9.6% donor chimerism in the BM and showed certain improvements in their innate and adaptive arms of the immune system, such as favorable counts of neutrophils in the spleen and BM, central memory Th cells, effector/effector memory Th and Tc cells in the spleen, and B1a and B1b cells in the peritoneal cavity. Borderline enhanced lymphocyte proliferation capacity was also seen. The frailty parameters, pathomorphological results, and life spans did not differ significantly in the transplanted vs. control group of mice. In conclusion, although several favorable effects are obtained in our heterochronic non-myeloablative transplantation model, additional optimization is needed for better rejuvenation effects.

Shared genetic and epigenetic changes link aging and cancer

Aging is a universal biological process that increases the risk of multiple diseases including cancer. Growing evidence shows that alterations in the genome and epigenome, driven by similar mechanisms, are found in both aged cells and cancer cells. In this review, we detail the genetic and epigenetic changes associated with normal aging and the mechanisms responsible for these changes. By highlighting genetic and epigenetic alterations in the context of tumorigenesis, cancer progression, and the aging tumor microenvironment, we examine the possible impacts of the normal aging process on malignant transformation. Finally, we examine the implications of age-related genetic and epigenetic alterations in both tumors and patients for the treatment of cancer.

Immune phenotype of the CD4+ T cells in the aged lymphoid organs and lacrimal glands

Aging is associated with a massive infiltration of T lymphocytes in the lacrimal gland. Here, we aimed to characterize the immune phenotype of aged CD4⁺ T cells in this tissue as compared with lymphoid organs. To perform this, we sorted regulatory T cells (Tregs, CD4⁺CD25⁺GITR⁺) and non-Tregs (CD4⁺CD25^negGITR^neg) in lymphoid organs from female C57BL/6J mice and subjected these cells to an immunology NanoString® panel. These results were confirmed by flow cytometry, live imaging, and tissue immunostaining in the lacrimal gland. Importantly, effector T helper 1 (Th1) genes were highly upregulated on aged Tregs, including the master regulator Tbx21. Among the non-Tregs, we also found a significant increase in the levels of EOMES^med/high, Tbet^negIFN-γ⁺, and CD62L⁺CD44^negCD4⁺ T cells with aging, which are associated with cell exhaustion, immunopathology, and the generation of tertiary lymphoid tissue. At the functional level, aged Tregs from lymphoid organs are less able to decrease proliferation and IFN-γ production of T responders at any age. More importantly, human lacrimal glands (age range 55-81 years) also showed the presence of CD4⁺Foxp3⁺ cells. Further studies are needed to propose potential molecular targets to avoid immune-mediated lacrimal gland dysfunction with aging.

How to Slow down the Ticking Clock: Age-Associated Epigenetic Alterations and Related Interventions to Extend Life Span

Epigenetic alterations pose one major hallmark of organismal aging. Here, we provide an overview on recent findings describing the epigenetic changes that arise during aging and in related maladies such as neurodegeneration and cancer. Specifically, we focus on alterations of histone modifications and DNA methylation and illustrate the link with metabolic pathways. Age-related epigenetic, transcriptional and metabolic deregulations are highly interconnected, which renders dissociating cause and effect complicated. However, growing amounts of evidence support the notion that aging is not only accompanied by epigenetic alterations, but also at least in part induced by those. DNA methylation clocks emerged as a tool to objectively determine biological aging and turned out as a valuable source in search of factors positively and negatively impacting human life span. Moreover, specific epigenetic signatures can be used as biomarkers for age-associated disorders or even as targets for therapeutic approaches, as will be covered in this review. Finally, we summarize recent potential intervention strategies that target epigenetic mechanisms to extend healthy life span and provide an outlook on future developments in the field of longevity research.