Mitochondrial mass governs the extent of human T cell senescence

T cell exhaustion and senescence for ovarian cancer immunotherapy

Ovarian cancer is a common gynecological malignancy, and its treatment remains challenging. Although ovarian cancer may respond to immunotherapy because of endogenous immunity at the molecular or T cell level, immunotherapy has so far not had the desired effect. The functional status of preexisting T cells is an indispensable determinant of powerful antitumor immunity and immunotherapy. T cell exhaustion and senescence are two crucial states of T cell dysfunction, which share some overlapping phenotypic and functional features, but each status possesses unique molecular and developmental signatures. It has been widely accepted that exhaustion and senescence of T cells are important strategies for cancer cells to evade immunosurveillance and maintain the immunosuppressive microenvironment. Herein, this review summarizes the phenotypic and functional features of exhaust and senescent T cells, and describes the key drivers of the two T cell dysfunctional states in the tumor microenvironment and their functional roles in ovarian cancer. Furthermore, we present a summary of the molecular machinery and signaling pathways governing T cell exhaustion and senescence. Possible strategies that can prevent and/or reverse T cell dysfunction are also explored. An in-depth understanding of exhausted and senescent T cells will provide novel strategies to enhance immunotherapy of ovarian cancer through redirecting tumor-specific T cells away from a dysfunctional developmental trajectory.

Mitochondrial Transplantation Promotes Protective Effector and Memory CD4+ T Cell Response During Mycobacterium Tuberculosis Infection and Diminishes Exhaustion and Senescence in Elderly CD4+ T cells

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), is a major global health concern, particularly affecting those with weakened immune systems, including the elderly. CD4+ T cell response is crucial for immunity against M.tb, but chronic infections and aging can lead to T cell exhaustion and senescence, worsening TB disease. Mitochondrial dysfunction, prevalent in aging and chronic diseases, disrupts cellular metabolism, increases oxidative stress, and impairs T-cell functions. This study investigates the effect of mitochondrial transplantation (mito-transfer) on CD4+ T cell differentiation and function in aged mouse models and human CD4+ T cells from elderly individuals. Mito-transfer in naïve CD4+ T cells is found to promote protective effector and memory T cell generation during M.tb infection in mice. Additionally, it improves elderly human T cell function by increasing mitochondrial mass and altering cytokine production, thereby reducing markers of exhaustion and senescence. These findings suggest mito-transfer as a novel approach to enhance aged CD4+ T cell functionality, potentially benefiting immune responses in the elderly and chronic TB patients. This has broader implications for diseases where mitochondrial dysfunction contributes to T-cell exhaustion and senescence.

Fueling CARs: metabolic strategies to enhance CAR T-cell therapy

CAR T cells are widely applied for relapsed hematological cancer patients. With six approved cell therapies, for Multiple Myeloma and other B-cell malignancies, new insights emerge. Profound evidence shows that patients who fail CAR T-cell therapy have, aside from antigen escape, a more glycolytic and weakened metabolism in their CAR T cells, accompanied by a short lifespan. Recent advances show that CAR T cells can be metabolically engineered towards oxidative phosphorylation, which increases their longevity via epigenetic and phenotypical changes. In this review we elucidate various strategies to rewire their metabolism, including the design of the CAR construct, co-stimulus choice, genetic modifications of metabolic genes, and pharmacological interventions. We discuss their potential to enhance CAR T-cell functioning and persistence through memory imprinting, thereby improving outcomes. Furthermore, we link the pharmacological treatments with their anti-cancer properties in hematological malignancies to ultimately suggest novel combination strategies.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: the biology of a neglected disease

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic, debilitating disease characterised by a wide range of symptoms that severely impact all aspects of life. Despite its significant prevalence, ME/CFS remains one of the most understudied and misunderstood conditions in modern medicine. ME/CFS lacks standardised diagnostic criteria owing to variations in both inclusion and exclusion criteria across different diagnostic guidelines, and furthermore, there are currently no effective treatments available. Moving beyond the traditional fragmented perspectives that have limited our understanding and management of the disease, our analysis of current information on ME/CFS represents a significant paradigm shift by synthesising the disease's multifactorial origins into a cohesive model. We discuss how ME/CFS emerges from an intricate web of genetic vulnerabilities and environmental triggers, notably viral infections, leading to a complex series of pathological responses including immune dysregulation, chronic inflammation, gut dysbiosis, and metabolic disturbances. This comprehensive model not only advances our understanding of ME/CFS's pathophysiology but also opens new avenues for research and potential therapeutic strategies. By integrating these disparate elements, our work emphasises the necessity of a holistic approach to diagnosing, researching, and treating ME/CFS, urging the scientific community to reconsider the disease's complexity and the multifaceted approach required for its study and management.

Cellular senescence, DNA damage, and neuroinflammation in the aging brain

Aging may lead to low-level chronic inflammation that increases the susceptibility to age-related conditions, including memory impairment and progressive loss of brain volume. As brain health is essential to promoting healthspan and lifespan, it is vital to understand age-related changes in the immune system and central nervous system (CNS) that drive normal brain aging. However, the relative importance, mechanistic interrelationships, and hierarchical order of such changes and their impact on normal brain aging remain to be clarified. Here, we synthesize accumulating evidence that age-related DNA damage and cellular senescence in the immune system and CNS contribute to the escalation of neuroinflammation and cognitive decline during normal brain aging. Targeting cellular senescence and immune modulation may provide a logical rationale for developing new treatment options to restore immune homeostasis and counteract age-related brain dysfunction and diseases.

Peripheral CX3CR1+ T cells combined with PD-1 blockade therapy potentiates the anti-tumor efficacy for lung cancer

Identifying tumor-relevant T cell subsets in the peripheral blood (PB) has become a potential strategy for cancer treatment. However, the subset of PB that could be used to treat cancer remains poorly defined. Here, we found that the CX3CR1+ T cell subset in the blood of patients with lung cancer exhibited effector properties and had a higher TCR matching ratio with tumor-infiltrating lymphocytes (TILs) compared to CX3CR1- T cells, as determined by paired single-cell RNA and TCR sequencing. Meanwhile, the anti-tumor activities, effector cytokine production, and mitochondrial function were enhanced in CX3CR1+ T cells both in vitro and in vivo. However, in the co-culture system of H322 cells with T cells, the percentages of apoptotic cells and Fas were substantially higher in CX3CR1+ T cells than those in CX3CR1- T cells. Fas-mediated apoptosis was rescued by treatment with an anti-PD-1 antibody. Accordingly, the combination of adoptive transfer of CX3CR1+ T cells and anti-PD-1 treatment considerably decreased Fas expression and improved the survival of lung xenograft mice. Moreover, an increased frequency of CX3CR1+ T cells in the PB correlated with a better response and prolonged survival of patients with lung cancer who received anti-PD-1 therapy. These findings indicate the promising potential of adoptive transfer of peripheral CX3CR1+ T cells as an individual cancer immunotherapy.

Targeting DNMT3A-mediated oxidative phosphorylation to overcome ibrutinib resistance in mantle cell lymphoma

The use of Bruton tyrosine kinase (BTK) inhibitors such as ibrutinib achieves a remarkable clinical response in mantle cell lymphoma (MCL). Acquired drug resistance, however, is significant and affects long-term survival of MCL patients. Here, we demonstrate that DNA methyltransferase 3A (DNMT3A) is involved in ibrutinib resistance. We find that DNMT3A expression is upregulated upon ibrutinib treatment in ibrutinib-resistant MCL cells. Genetic and pharmacological analyses reveal that DNMT3A mediates ibrutinib resistance independent of its DNA-methylation function. Mechanistically, DNMT3A induces the expression of MYC target genes through interaction with the transcription factors MEF2B and MYC, thus mediating metabolic reprogramming to oxidative phosphorylation (OXPHOS). Targeting DNMT3A with low-dose decitabine inhibits the growth of ibrutinib-resistant lymphoma cells both in vitro and in a patient-derived xenograft mouse model. These findings suggest that targeting DNMT3A-mediated metabolic reprogramming to OXPHOS with decitabine provides a potential therapeutic strategy to overcome ibrutinib resistance in relapsed/refractory MCL.

Immunological factors linked to geographical variation in vaccine responses

Vaccination is one of medicine's greatest achievements; however, its full potential is hampered by considerable variation in efficacy across populations and geographical regions. For example, attenuated malaria vaccines in high-income countries confer almost 100% protection, whereas in low-income regions these same vaccines achieve only 20-50% protection. This trend is also observed for other vaccines, such as bacillus Calmette-Guérin (BCG), rotavirus and yellow fever vaccines, in terms of either immunogenicity or efficacy. Multiple environmental factors affect vaccine responses, including pathogen exposure, microbiota composition and dietary nutrients. However, there has been variable success with interventions that target these individual factors, highlighting the need for a better understanding of their downstream immunological mechanisms to develop new ways of modulating vaccine responses. Here, we review the immunological factors that underlie geographical variation in vaccine responses. Through the identification of causal pathways that link environmental influences to vaccine responsiveness, it might become possible to devise modulatory compounds that can complement vaccines for better outcomes in regions where they are needed most.

Senescent T Cells in Age-Related Diseases

Age-induced alterations in human immunity are often considered deleterious and are referred to as immunosenescence. The immune system monitors the number of senescent cells in the body, while immunosenescence may represent the initiation of systemic aging. Immune cells, particularly T cells, are the most impacted and involved in age-related immune function deterioration, making older individuals more prone to different age-related diseases. T-cell senescence can impact the effectiveness of immunotherapies that rely on the immune system's function, including vaccines and adoptive T-cell therapies. The research and practice of using senescent T cells as therapeutic targets to intervene in age-related diseases are in their nascent stages. Therefore, in this review, we summarize recent related literature to investigate the characteristics of senescent T cells as well as their formation mechanisms, relationship with various aging-related diseases, and means of intervention. The primary objective of this article is to explore the prospects and possibilities of therapeutically targeting senescent T cells, serving as a valuable resource for the development of immunotherapy and treatment of age-related diseases.

Age-related bone diseases: Role of inflammaging

Bone aging is characterized by an imbalance in the physiological and pathological processes of osteogenesis, osteoclastogenesis, adipogenesis, and chondrogenesis, resulting in exacerbated bone loss and the development of age-related bone diseases, including osteoporosis, osteoarthritis, rheumatoid arthritis, and periodontitis. Inflammaging, a novel concept in the field of aging research, pertains to the persistent and gradual escalation of pro-inflammatory reactions during the aging process. This phenomenon is distinguished by its low intensity, systemic nature, absence of symptoms, and potential for management. The mechanisms by which inflammaging contribute to age-related chronic diseases, particularly in the context of age-related bone diseases, remain unclear. The precise manner in which systemic inflammation induces bone aging and consequently contributes to the development of age-related bone diseases has yet to be fully elucidated. This article primarily examines the mechanisms underlying inflammaging and its association with age-related bone diseases, to elucidate the potential mechanisms of inflammaging in age-related bone diseases and offer insights for developing preventive and therapeutic strategies for such conditions.

Mitochondrial Transplantation promotes protective effector and memory CD4+ T cell response during Mycobacterium tuberculosis infection and diminishes exhaustion and senescence in elderly CD4+ T cells

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (M.tb), remains a significant health concern worldwide, especially in populations with weakened or compromised immune systems, such as the elderly. Proper adaptive immune function, particularly a CD4+ T cell response, is central to host immunity against M.tb. Chronic infections, such as M.tb, as well as aging promote T cell exhaustion and senescence, which can impair immune control and promote progression to TB disease. Mitochondrial dysfunction contributes to T cell dysfunction, both in aging and chronic infections and diseases. Mitochondrial perturbations can disrupt cellular metabolism, enhance oxidative stress, and impair T-cell signaling and effector functions. This study examined the impact of mitochondrial transplantation (mito-transfer) on CD4+ T cell differentiation and function using aged mouse models and human CD4+ T cells from elderly individuals. Our study revealed that mito-transfer in naïve CD4+ T cells promoted the generation of protective effector and memory CD4+ T cells during M.tb infection in mice. Further, mito-transfer enhanced the function of elderly human T cells by increasing their mitochondrial mass and modulating cytokine production, which in turn reduced exhaustion and senescence cell markers. Our results suggest that mito-transfer could be a novel strategy to reestablish aged CD4+ T cell function, potentially improving immune responses in the elderly and chronic TB patients, with a broader implication for other diseases where mitochondrial dysfunction is linked to T cell exhaustion and senescence.

Implications of Senescent T Cells for Cancer Immunotherapy

T-cell senescence is thought to result from the age-related loss of the ability to mount effective responses to pathogens and tumor cells. In addition to aging, T-cell senescence is caused by repeated antigenic stimulation and chronic inflammation. Moreover, we demonstrated that T-cell senescence was induced by treatment with DNA-damaging chemotherapeutic agents. The characteristics of therapy-induced senescent T (TIS-T) cells and general senescent T cells are largely similar. Senescent T cells demonstrate an increase in the senescence-associated beta-galactosidase-positive population, cell cycle arrest, secretion of senescence-associated secretory phenotypic factors, and metabolic reprogramming. Furthermore, senescent T cells downregulate the expression of the co-stimulatory molecules CD27 and CD28 and upregulate natural killer cell-related molecules. Moreover, TIS-T cells showed increased PD-1 expression. However, the loss of proliferative capacity and decreased expression of co-stimulatory molecules associated with T-cell senescence cause a decrease in T-cell immunocompetence. In this review, we discuss the characteristics of senescent T-cells, including therapy-induced senescent T cells.

STAT3 modulates CD4+ T mitochondrial dynamics and function in aging

Aging promotes numerous intracellular changes in T cells that impact their effector function. Our data show that aging promotes an increase in the localization of STAT3 to the mitochondria (mitoSTAT3), which promotes changes in mitochondrial dynamics and function and T-cell cytokine production. Mechanistically, mitoSTAT3 increased the activity of aging T-cell mitochondria by increasing complex II. Limiting mitoSTAT3 using a mitochondria-targeted STAT3 inhibitor, Mtcur-1 lowered complex II activity, prevented age-induced changes in mitochondrial dynamics and function, and reduced Th17 inflammation. Exogenous expression of a constitutively phosphorylated form of STAT3 in T cells from young adults mimicked changes in mitochondrial dynamics and function in T cells from older adults and partially recapitulated aging-related cytokine profiles. Our data show the mechanistic link among mitoSTAT3, mitochondrial dynamics, function, and T-cell cytokine production.

Mitochondria pleiotropism in stem cell senescence: Mechanisms and therapeutic approaches

Aging is a complex biological process characterized by a progressive decline in cellular and tissue function, ultimately leading to organismal aging. Stem cells, with their regenerative potential, play a crucial role in maintaining tissue homeostasis and repair throughout an organism's lifespan. Mitochondria, the powerhouses of the cell, have emerged as key players in the aging process, impacting stem cell function and contributing to age-related tissue dysfunction. Here are discuss the mechanisms through which mitochondria influence stem cell fate decisions, including energy production, metabolic regulation, ROS signalling, and epigenetic modifications. Therefore, this review highlights the role of mitochondria in driving stem cell senescence and the subsequent impact on tissue function, leading to overall organismal aging and age-related diseases. Finally, we explore potential anti-aging therapies targeting mitochondrial health and discuss their implications for promoting healthy aging. This comprehensive review sheds light on the critical interplay between mitochondrial function, stem cell senescence, and organismal aging, offering insights into potential strategies for attenuating age-related decline and promoting healthy longevity.

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.

Maladaptive T-Cell Metabolic Fitness in Autoimmune Diseases

Immune surveillance and adaptive immune responses, involving continuously circulating and tissue-resident T-lymphocytes, provide host defense against infectious agents and possible malignant transformation while avoiding autoimmune tissue damage. Activation, migration, and deployment of T-cells to affected tissue sites are crucial for mounting an adaptive immune response. An effective adaptive immune defense depends on the ability of T-cells to dynamically reprogram their metabolic requirements in response to environmental cues. Inability of the T-cells to adapt to specific metabolic demands may skew cells to become either hyporesponsive (creating immunocompromised conditions) or hyperactive (causing autoimmune tissue destruction). Here, we review maladaptive T-cell metabolic fitness that can cause autoimmune diseases and discuss how T-cell metabolic programs can potentially be modulated to achieve therapeutic benefits.

The role of TEMRA cell-mediated immune senescence in the development and treatment of HIV disease

Human Immunodeficiency Virus (HIV) has plagued human society for a long time since its discovery, causing a large number of patients to suffer and costing hundreds of millions of medical services every year. Scientists have found that HIV and antiretroviral therapy accelerate immune aging by inducing mitochondrial dysfunction, and that terminal effector memory T cells (TEMRA cells) are crucial in immune aging. This specific subset of effector memory T cells has terminally differentiated properties and exhibits high cytotoxicity and proinflammatory capacity. We therefore explored and described the interplay between exhaustion features, essential markers, functions, and signaling pathways from previous studies on HIV, antiretroviral therapy, immune senescence, and TEMRA cells. Their remarkable antiviral capacity is then highlighted by elucidating phenotypic changes in TEMRA cells during HIV infection, describing changes in TEMRA cells before, during, and after antiretroviral therapy and other drug treatments. Their critical role in complications and cytomegalovirus (CMV)-HIV superinfection is highlighted. These studies demonstrate that TEMRA cells play a key role in the antiviral response and immune senescence during HIV infection. Finally, we review current therapeutic strategies targeting TEMRA cells that may be clinically beneficial, highlight their potential role in HIV-1 vaccine development, and provide perspectives and predictions for related future applications.

Sub-lethal doses of chemotherapeutic agents induce senescence in T cells and upregulation of PD-1 expression

Cellular senescence is a stable cell cycle arrest, usually in response to internal and/or external stress, including telomere dysfunction, abnormal cellular growth, and DNA damage. Several chemotherapeutic drugs, such as melphalan (MEL) and doxorubicin (DXR), induce cellular senescence in cancer cells. However, it is not clear whether these drugs induce senescence in immune cells. We evaluated the induction of cellular senescence in T cells were derived from human peripheral blood mononuclear cells (PBMNCs) in healthy donors using sub-lethal doses of chemotherapeutic agents. The PBMNCs were kept overnight in RPMI 1640 medium with 2% phytohemagglutinin and 10% fetal bovine serum and then cultured in RPMI 1640 with 20 ng/mL IL-2 and sub-lethal doses of chemotherapeutic drugs (2 μM MEL and 50 nM DXR) for 48 h. Sub-lethal doses of chemotherapeutic agents induced phenotypes associated with senescence, such as the formation of γH2AX nuclear foci, cell proliferation arrest, and induction of senescence-associated beta-galactosidase (SA-β-Gal) activity, (control vs. MEL, DXR; median mean fluorescence intensity (MFI) 1883 (1130-2163) vs. 2233 (1385-2254), 2406.5 (1377-3119), respectively) in T cells. IL6 and SPP1 mRNA, which are senescence-associated secretory phenotype (SASP) factors, were significantly upregulated by sublethal doses of MEL and DXR compared to the control (P = 0.043 and 0.018, respectively). Moreover, sub-lethal doses of chemotherapeutic agents significantly enhanced the expression of programmed death 1 (PD-1) on CD3 + CD4 + and CD3 + CD8 + T cells compared to the control (CD4 + T cells; P = 0.043, 0.043, and 0.043, respectively, CD8 + T cells; P = 0.043, 0.043, and 0.043, respectively). Our results suggest that sub-lethal doses of chemotherapeutic agents induce senescence in T cells and tumor immunosuppression by upregulating PD-1 expression on T cells.

Mitochondrial dysfunctions in T cells: focus on inflammatory bowel disease

Mitochondria has emerged as a critical ruler of metabolic reprogramming in immune responses and inflammation. In the context of colitogenic T cells and IBD, there has been increasing research interest in the metabolic pathways of glycolysis, pyruvate oxidation, and glutaminolysis. These pathways have been shown to play a crucial role in the metabolic reprogramming of colitogenic T cells, leading to increased inflammatory cytokine production and tissue damage. In addition to metabolic reprogramming, mitochondrial dysfunction has also been implicated in the pathogenesis of IBD. Studies have shown that colitogenic T cells exhibit impaired mitochondrial respiration, elevated levels of mROS, alterations in calcium homeostasis, impaired mitochondrial biogenesis, and aberrant mitochondria-associated membrane formation. Here, we discuss our current knowledge of the metabolic reprogramming and mitochondrial dysfunctions in colitogenic T cells, as well as the potential therapeutic applications for treating IBD with evidence from animal experiments.

Cholesterol metabolism in T-cell aging: Accomplices or victims

Aging has a significant impact on the function and metabolism of T cells. Cholesterol, the most important sterol in mammals, is known as the "gold of the body" because it maintains membrane fluidity, rigidity, and signal transduction while also serving as a precursor of oxysterols, bile acids, and steroid hormones. Cholesterol homeostasis is primarily controlled by uptake, biosynthesis, efflux, and regulatory mechanisms. Previous studies have suggested that there are reciprocal interactions between cholesterol metabolism and T lymphocytes. Here, we will summarize the most recent advances in the effects of cholesterol and its derivatives on T-cell aging. We will furthermore discuss interventions that might be used to help older individuals with immune deficiencies or diminishing immune competence.

Mitochondria during T cell aging

Mitochondrial dysfunction is a hallmark of aging that contributes to inflammaging. It is characterized by alterations of the mitochondrial DNA, reduced respiratory capacity, decreased mitochondrial membrane potential and increased reactive oxygen species production. These primary alterations disrupt other interconnected and important mitochondrial-related processes such as metabolism, mitochondrial dynamics and biogenesis, mitophagy, calcium homeostasis or apoptosis. In this review, we gather the current knowledge about the different mitochondrial processes which are altered during aging, with special focus on their contribution to age-associated T cell dysfunction and inflammaging.

Activation of telomerase by TA-65 enhances immunity and reduces inflammation post myocardial infarction

Myocardial infarction (MI) accelerates immune ageing characterised by lymphopenia, expansion of terminally differentiated CD8+ T-lymphocytes (CD8+ TEMRA) and inflammation. Pre-clinical data showed that TA-65, an oral telomerase activator, reduced immune ageing and inflammation after MI. We conducted a double blinded randomised controlled pilot trial evaluating the use of TA-65 to reduce immune cell ageing in patients following MI. Ninety MI patients aged over 65 years were randomised to either TA-65 (16 mg daily) or placebo for 12 months. Peripheral blood leucocytes were analysed by flow cytometry. The pre-defined primary endpoint was the proportion of CD8+ T-lymphocytes which were CD8+ TEMRA after 12 months. Secondary outcomes included high-sensitivity C-reactive protein (hsCRP) levels. Median age of participants was 71 years. Proportions of CD8+ TEMRA did not differ after 12 months between treatment groups. There was a significant increase in mean total lymphocyte count in the TA-65 group after 12 months (estimated treatment effect: + 285 cells/μl (95% CI: 117-452 cells/ μ l, p < 0.004), driven by significant increases from baseline in CD3+, CD4+, and CD8+ T-lymphocytes, B-lymphocytes and natural killer cells. No increase in lymphocyte populations was seen in the placebo group. At 12 months, hsCRP was 62% lower in the TA-65 group compared to placebo (1.1 vs. 2.9 mg/L). Patients in the TA-65 arm experienced significantly fewer adverse events (130 vs. 185, p = 0.002). TA-65 did not alter CD8+ TEMRA but increased all major lymphocyte subsets and reduced hsCRP in elderly patients with MI after 12 months.

Surveying the Metabolic and Dysfunctional Profiles of T Cells and NK Cells in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Millions globally suffer from myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The inflammatory symptoms, illness onset, recorded outbreak events, and physiological variations provide strong indications that ME/CFS, at least sometimes, has an infectious origin, possibly resulting in a chronic unidentified viral infection. Meanwhile, studies exposing generalized metabolic disruptions in ME/CFS have stimulated interest in isolated immune cells with an altered metabolic state. As the metabolism dictates the cellular function, dissecting the biomechanics of dysfunctional immune cells in ME/CFS can uncover states such as exhaustion, senescence, or anergy, providing insights into the consequences of these phenotypes in this disease. Despite the similarities that are seen metabolically between ME/CFS and other chronic viral infections that result in an exhausted immune cell state, immune cell exhaustion has not yet been verified in ME/CFS. This review explores the evidence for immunometabolic dysfunction in ME/CFS T cell and natural killer (NK) cell populations, comparing ME/CFS metabolic and functional features to dysfunctional immune cell states, and positing whether anergy, exhaustion, or senescence could be occurring in distinct immune cell populations in ME/CFS, which is consistent with the hypothesis that ME/CFS is a chronic viral disease. This comprehensive review of the ME/CFS immunometabolic literature identifies CD8+ T cell exhaustion as a probable contender, underscores the need for further investigation into the dysfunctional state of CD4+ T cells and NK cells, and explores the functional implications of molecular findings in these immune-cell types. Comprehending the cause and impact of ME/CFS immune cell dysfunction is critical to understanding the physiological mechanisms of ME/CFS, and developing effective treatments to alleviate the burden of this disabling condition.

Growth hormone remodels the 3D-structure of the mitochondria of inflammatory macrophages and promotes metabolic reprogramming

Introduction

Macrophages are a heterogeneous population of innate immune cells that support tissue homeostasis through their involvement in tissue development and repair, and pathogen defense. Emerging data reveal that metabolism may control macrophage polarization and function and, conversely, phenotypic polarization may drive metabolic reprogramming.

Methods

Here we use biochemical analysis, correlative cryogenic fluorescence microscopy and cryo-focused ion-beam scanning electron microscopy.

Results

We demonstrate that growth hormone (GH) reprograms inflammatory GM-CSF-primed monocyte-derived macrophages (GM-MØ) by functioning as a metabolic modulator. We found that exogenous treatment of GM-MØ with recombinant human GH reduced glycolysis and lactate production to levels similar to those found in anti-inflammatory M-MØ. Moreover, GH treatment of GM-MØ augmented mitochondrial volume and altered mitochondrial dynamics, including the remodeling of the inner membrane to increase the density of cristae.

Conclusions

Our data demonstrate that GH likely serves a modulatory role in the metabolism of inflammatory macrophages and suggest that metabolic reprogramming of macrophages should be considered as a new target to intervene in inflammatory diseases.

The central role of DNA damage in immunosenescence

Ageing is the biggest risk factor for the development of multiple chronic diseases as well as increased infection susceptibility and severity of diseases such as influenza and COVID-19. This increased disease risk is linked to changes in immune function during ageing termed immunosenescence. Age-related loss of immune function, particularly in adaptive responses against pathogens and immunosurveillance against cancer, is accompanied by a paradoxical gain of function of some aspects of immunity such as elevated inflammation and increased incidence of autoimmunity. Of the many factors that contribute to immunosenescence, DNA damage is emerging as a key candidate. In this review, we discuss the evidence supporting the hypothesis that DNA damage may be a central driver of immunosenescence through senescence of both immune cells and cells of non-haematopoietic lineages. We explore why DNA damage accumulates during ageing in a major cell type, T cells, and how this may drive age-related immune dysfunction. We further propose that existing immunosenescence interventions may act, at least in part, by mitigating DNA damage and restoring DNA repair processes (which we term "genoprotection"). As such, we propose additional treatments on the basis of their evidence for genoprotection, and further suggest that this approach may provide a viable therapeutic strategy for improving immunity in older people.

Rotenone-exposure as cytofunctional aging model of human dermal fibroblast prior replicative senescence

Rotenone (Ro), causes superoxide imbalance by inhibiting complex I of the mitochondrial electron transport chain, being able to serve as a model for functional skin aging by inducing cytofunctional changes in dermal fibroblasts prior to proliferative senescence. To test this hypothesis, we conducted an initial protocol to select a concentration of Ro (0.5, 1, 1.5, 2, 2.5, and 3 μM) that would induce the highest levels of the aging marker beta-galactosidase (β-gal) in human dermal HFF-1 fibroblasts after 72 h of culture, as well as a moderate increase in apoptosis and partial G1 arrestment. We evaluated whether the selected concentration (1 μM) differentially modulated oxidative and cytofunctional markers of fibroblasts. Ro 1.0 μM increased β-gal levels and apoptosis frequency, decreased the frequency of S/G2 cells, induced higher levels of oxidative markers, and presented a genotoxic effect. Fibroblasts exposed to Ro showed lower mitochondrial activity, extracellular collagen deposition, and fewer fibroblast cytoplasmic connections than controls. Ro triggered overexpression of the gene associated with aging (MMP-1), downregulation genes of collagen production (COL1A, FGF-2), and cellular growth/regeneration (FGF-7). The 1 μM concentration of Ro could serve as an experimental model for functional aging fibroblasts prior to replicative senescence. It could be used to identify causal aging mechanisms and strategies to delay skin aging events.

Inflammation and aging: signaling pathways and intervention therapies

Aging is characterized by systemic chronic inflammation, which is accompanied by cellular senescence, immunosenescence, organ dysfunction, and age-related diseases. Given the multidimensional complexity of aging, there is an urgent need for a systematic organization of inflammaging through dimensionality reduction. Factors secreted by senescent cells, known as the senescence-associated secretory phenotype (SASP), promote chronic inflammation and can induce senescence in normal cells. At the same time, chronic inflammation accelerates the senescence of immune cells, resulting in weakened immune function and an inability to clear senescent cells and inflammatory factors, which creates a vicious cycle of inflammation and senescence. Persistently elevated inflammation levels in organs such as the bone marrow, liver, and lungs cannot be eliminated in time, leading to organ damage and aging-related diseases. Therefore, inflammation has been recognized as an endogenous factor in aging, and the elimination of inflammation could be a potential strategy for anti-aging. Here we discuss inflammaging at the molecular, cellular, organ, and disease levels, and review current aging models, the implications of cutting-edge single cell technologies, as well as anti-aging strategies. Since preventing and alleviating aging-related diseases and improving the overall quality of life are the ultimate goals of aging research, our review highlights the critical features and potential mechanisms of inflammation and aging, along with the latest developments and future directions in aging research, providing a theoretical foundation for novel and practical anti-aging strategies.

Mitochondrial Dysfunction in CD4+ T Effector Memory RA+ Cells

Human ageing is accompanied by poor responses to infection and decreased vaccine efficacy. While the causes of this can be attributed to defects in the immune system that increase with age, it is unknown whether mitochondrial dysfunction may also contribute to these phenomena. This study aims to assess mitochondrial dysfunction in CD4+ terminal effector memory T cells re-expressing CD45RA (TEMRA) cells and other CD4+ memory T cell subtypes, which are increased in number in the elderly population, with respect to how their metabolic responses to stimulation are altered compared to CD4+ naïve T cells. In this study, we show that CD4+ TEMRA cells exhibit altered mitochondrial dynamics compared to CD4+ naïve cells and CD4+ central and effector memory cells, with a 25% reduction in OPA1 expression. CD4+ TEMRA and memory cells show increased upregulation of Glucose transporter 1 following stimulation and higher levels of mitochondrial mass compared to CD4+ naïve T cells. Additionally, TEMRA cells exhibit a decrease in mitochondrial membrane potential compared to other CD4+ memory cell subsets by up to 50%. By comparing young to aged individuals, more significant mitochondria mass and lower membrane potential were observed in CD4+ TEMRA of young individuals. In conclusion, we suggest that CD4+ TEMRA cells may be impaired with respect to their metabolic response to stimulation, possibly contributing to impaired responses to infection and vaccination.

[Abnormal Activation of T Cells in HIV-1 Infection After Antiretroviral Therapy]

Objective

To investigate the relationship between abnormal activation of T cell subsets in peripheral whole blood and the recovery of immune function in persons infected with HIV-1, and to examine the relationship between the size of the viral reservoir of HIV-1 DNA and T cell subsets.

Methods

HIV-1-infected persons who underwent routine testing between July 2019 and May 2020 were the target population of the study. According to whether, at the time of enrollment, their CD4+ T cells reached 500 cells/μL after antiretroviral therapy (ART), HIV-1-infected persons were divided into two groups, 76 in the deficiency group and 61 in the immune recovery group. In addition, 22 people who were not exposed to HIV-1, and who were tested negative for HIV-1 antibody were selected as the control group. For the three groups of subjects, tests of the T cell subsets were conducted. A total of 77 HIV-1-infected persons, with 44 from the deficiency group and 33 from the recovery group, were examined for HIV-1 DNA reservoir. The deficiency group and the recovery group were followed up 6 months later and the CD4+ T cell test results of 133 blood samples were collected, with 74 from the deficiency group and 59 from the recovery group.

Results

The proportions of activated CD4+ and CD8+ T cells of the deficiency group were higher than those of the recovery group and the control group. The proportions of senescent CD4+ and CD8+ T cells in the deficiency group were comparable to those of the recovery group, which were higher than those of the control group, showing significant differences only in senescent CD8+ T cells, and no significant difference in senescent CD4+ T cells. The deficiency group expressed higher levels of effector memory CD4+ T and CD8+ T cells than the control group did, and the recovery group only expressed a higher level of effect memory CD8+ T cells. Both the deficiency group and the recovery group showed lower levels of central memory CD4+ T and CD8+ T cells than the control group did, and the recovery group had an even lower level of central memory CD4+ T cells than the deficiency group did. The recovery group showed a higher expression level of naïve CD4+ T cells, and the deficiency group and the recovery group had lower expression levels of naïve CD8+ T cells than the control group did. There was no correlation between the size of the viral reservoir of HIV-1 DNA and CD4+ T cell count or the T cell subsets. Activated CD4+ T cells, activated CD8+ T cells, and central memory CD4+ T cells were negatively correlated with the follow-up findings for CD4+ T cells, with r at －0.378, －0.334, and －0.322, respectively ( P<0.05). Naïve CD4+ T cells and naïve CD8+ T cells were positively correlated with the follow-up findings for CD4+ T cell subset, with r at 0.350 and 0.267, respectively ( P<0.05).

Conclusion

HIV-1 infected persons have varying degrees of abnormal immune activation of T cell subsets. The abnormal activation of some T-cell subsets is partly associated with the subsequent recovery of immune functions and the size of the viral reservoir of HIV-1 DNA was not associated with the T cell subsets.

T-cell senescence: A crucial player in autoimmune diseases

Senescent T cells are proliferative disabled lymphocytes that lack antigen-specific responses. The development of T-cell senescence in autoimmune diseases contributes to immunological disorders and disease progression. Senescent T cells lack costimulatory markers with the reduction of T cell receptor repertoire and the uptake of natural killer cell receptors. Senescent T cells exert cytotoxic effects through the expression of perforin, granzymes, tumor necrosis factor, and other molecules without the antigen-presenting process. DNA damage accumulation, telomere damage, and limited DNA repair capacity are important features of senescent T cells. Impaired mitochondrial function and accumulation of reactive oxygen species contribute to T cell senescence. Alleviation of T-cell senescence could provide potential targets for the treatment of autoimmune diseases.

Cellular senescence: all roads lead to mitochondria

Senescence is a multi-functional cell fate, characterized by an irreversible cell-cycle arrest and a pro-inflammatory phenotype, commonly known as the senescence-associated secretory phenotype (SASP). Emerging evidence indicates that accumulation of senescent cells in multiple tissues drives tissue dysfunction and several age-related conditions. This has spurred the academic community and industry to identify new therapeutic interventions targeting this process. Mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence which plays important roles not only in the senescence growth arrest but also in the development of the SASP and resistance to cell-death. Here, we review the evidence that supports a role for mitochondria in the development of senescence and describe the underlying mechanisms. Finally, we propose that a detailed road map of mitochondrial biology in senescence will be crucial to guide the future development of senotherapies.

CD4+ T cells expressing CX3CR1, GPR56, with variable CD57 are associated with cardiometabolic diseases in persons with HIV

Persons with HIV (PWH) on long-term antiretroviral therapy (ART) have a higher incidence and prevalence of cardiometabolic diseases attributed, in part, to persistent inflammation despite viral suppression. In addition to traditional risk factors, immune responses to co-infections such as cytomegalovirus (CMV) may play an unappreciated role in cardiometabolic comorbidities and offer new potential therapeutic targets in a subgroup of individuals. We assessed the relationship of CX3CR1+, GPR56+, and CD57+/- T cells (termed CGC+) with comorbid conditions in a cohort of 134 PWH co-infected with CMV on long-term ART. We found that PWH with cardiometabolic diseases (non-alcoholic fatty liver disease, calcified coronary arteries, or diabetes) had higher circulating CGC+CD4+ T cells compared to metabolically healthy PWH. The traditional risk factor most correlated with CGC+CD4+ T cell frequency was fasting blood glucose, as well as starch/sucrose metabolites. While unstimulated CGC+CD4+ T cells, like other memory T cells, depend on oxidative phosphorylation for energy, they exhibited higher expression of carnitine palmitoyl transferase 1A compared to other CD4+ T cell subsets, suggesting a potentially greater capacity for fatty acid β-oxidation. Lastly, we show that CMV-specific T cells against multiple viral epitopes are predominantly CGC+. Together, this study suggests that among PWH, CGC+ CD4+ T cells are frequently CMV-specific and are associated with diabetes, coronary arterial calcium, and non-alcoholic fatty liver disease. Future studies should assess whether anti-CMV therapies could reduce cardiometabolic disease risk in some individuals.

Inhibition of Klf10 Attenuates Oxidative Stress-Induced Senescence of Chondrocytes via Modulating Mitophagy

Osteoarthritis (OA) is the most prevalent degenerative joint disease in the elderly. Accumulation of evidence has suggested that chondrocyte senescence plays a significant role in OA development. Here, we show that Krüppel-like factor 10 (Klf10), also named TGFβ inducible early gene-1 (TIEG1), is involved in the pathology of chondrocyte senescence. Knocking down the Klf10 in chondrocytes attenuated the tert-butyl hydroperoxide (TBHP)-induced senescence, inhibited generation of reactive oxygen species (ROS), and maintained mitochondrial homeostasis by activating mitophagy. These findings suggested that knocking down Klf10 inhibited senescence-related changes in chondrocytes and improved cartilage homeostasis, indicating that Klf10 may be a therapeutic target for protecting cartilage against OA.

Partners in crime: The feedback loop between metabolic reprogramming and immune checkpoints in the tumor microenvironment

The tumor microenvironment (TME) is a complex and constantly changing cellular system composed of heterogeneous populations of tumor cells and non-transformed stromal cells, such as stem cells, fibroblasts, endothelial cells, pericytes, adipocytes, and innate and adaptive immune cells. Tumor, stromal, and immune cells consume available nutrients to sustain their proliferation and effector functions and, as a result of their metabolism, produce a wide array of by-products that gradually alter the composition of the milieu. The resulting depletion of essential nutrients and enrichment of by-products work together with other features of the hostile TME to inhibit the antitumor functions of immune cells and skew their phenotype to promote tumor progression. This review briefly describes the participation of the innate and adaptive immune cells in recognizing and eliminating tumor cells and how the gradual metabolic changes in the TME alter their antitumor functions. In addition, we discuss the overexpression of the immune checkpoints and their ligands as a result of nutrient deprivation and by-products accumulation, as well as the amplification of the metabolic alterations induced by the immune checkpoints, which creates an immunosuppressive feedback loop in the TME. Finally, the combination of metabolic and immune checkpoint inhibitors as a potential strategy to treat cancer and enhance the outcome of patients is highlighted.

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.

Multiomics and artificial intelligence enabled peripheral blood-based prediction of amnestic mild cognitive impairment

BACKGROUND

Since dementia is preventable with early interventions, biomarkers that assist in diagnosing early stages of dementia, such as mild cognitive impairment (MCI), are urgently needed.

METHODS

Multiomics analysis of amnestic MCI (aMCI) peripheral blood (n = 25) was performed covering the transcriptome, microRNA, proteome, and metabolome. Validation analysis for microRNAs was conducted in an independent cohort (n = 12). Artificial intelligence was used to identify the most important features for predicting aMCI.

FINDINGS

We found that hsa-miR-4455 is the best biomarker in all omics analyses. The diagnostic index taking a ratio of hsa-miR-4455 to hsa-let-7b-3p predicted aMCI patients against healthy subjects with 97% overall accuracy. An integrated review of multiomics data suggested that a subset of T cells and the GCN (general control nonderepressible) pathway are associated with aMCI.

INTERPRETATION

The multiomics approach has enabled aMCI biomarkers with high specificity and illuminated the accompanying changes in peripheral blood. Future large-scale studies are necessary to validate candidate biomarkers for clinical use.

Mitochondrial Impairments in Peripheral Blood Mononuclear Cells of Multiple Sclerosis Patients

Although impaired mitochondrial function has been proposed as a hallmark of multiple sclerosis (MS) disease, few studies focus on the mitochondria of immune cells. We aimed to compare the mitochondrial function of the peripheral blood mononuclear cells (PBMCs) from MS patients with (M+) and without (M-) lipid-specific oligoclonal immunoglobulin M bands (LS-OCMB), and healthydonors (HD). We conducted an exploratory cross-sectional study with 19 untreated MS patients (M+ = 9 and M- = 10) and 17 HDs. Mitochondrial superoxide anion production and mitochondrial mass in PBMCs were assessed without and with phytohemagglutinin by flow cytometry. The PBMCs' mitochondrial function was analyzed using Seahorse technology. Superoxide anion production corrected by the mitochondrial mass was higher in MS patients compared with HDs (p = 0.011). Mitochondrial function from M+ patients showed some impairments compared with M- patients. Without stimulus, we observed higher proton leak (p = 0.041) but lower coupling efficiency (p = 0.041) in M+ patients; and under stimulation, lower metabolic potential ECAR (p = 0.011), and lower stressed OCR/ECAR in the same patients. Exclusively among M+ patients, we described a higher mitochondrial dysfunction in the oldest ones. The mitochondrial impairments found in the PBMCs from MS patients, specifically in M+ patients, could help to better understand the disease's physiopathology.

Immune senescence in multiple myeloma-a role for mitochondrial dysfunction?

Age-related immune dysfunction is primarily mediated by immunosenescence which results in ineffective clearance of infective pathogens, poor vaccine responses and increased susceptibility to multi-morbidities. Immunosenescence-related immunometabolic abnormalities are associated with accelerated aging, an inflammatory immune response (inflammaging) and ultimately frailty syndromes. In addition, several conditions can accelerate the development of immunosenescence, including cancer. This is a bi-directional interaction since inflammaging may create a permissive environment for tumour development. Multiple myeloma (MM) is a mature B-cell malignancy that presents in the older population. MM exemplifies the interaction of age- (Host Response Biology; HRB) and disease-related immunological dysfunction, contributing to the development of a frailty syndrome which impairs the therapeutic impact of recent advances in treatment strategies. Understanding the mechanisms by which accelerated immunological aging is induced and the ways in which a tumour such as MM influences this process is key to overcoming therapeutic barriers. A link between cellular mitochondrial dysfunction and the acquisition of an abnormal immune phenotype has recently been described and has widespread physiological consequence beyond the impact on the immune system. Here we outline our current understanding of normal immune aging, describe the mechanism of immunometabolic dysfunction in accelerating this process, and propose the role these processes are playing in the pathogenesis of MM.

An expanded population of CD8dim T cells with features of mitochondrial dysfunction and senescence is associated with persistent HIV-associated Kaposi’s sarcoma under ART

HIV-associated Kaposi’s sarcoma (KS), which is caused by Kaposi’s sarcoma-associated herpesvirus, usually arises in the context of uncontrolled HIV replication and immunosuppression. However, disease occasionally occurs in individuals with durable HIV viral suppression and CD4 T cell recovery under antiretroviral therapy (ART). The underlying mechanisms associated with this phenomenon are unclear. Suppression of viral infections can be mediated by CD8 T cells, which detect infected cells via their T cell receptor and the CD8 coreceptor. However, CD8 T cells exhibit signs of functional exhaustion in untreated HIV infection that may not be fully reversed under ART. To investigate whether KS under ART was associated with phenotypic and functional perturbations of CD8 T cells, we performed a cross-sectional study comparing HIV-infected individuals with persistent KS under effective ART (HIV+ KS+) to HIV-infected individuals receiving effective ART with no documented history of KS (HIV+ KS^neg). A subset of T cells with low cell surface expression of CD8 (“CD8^dim T cells”) was expanded in HIV+ KS+ compared with HIV+ KS^neg participants. Relative to CD8^bright T cells, CD8^dim T cells exhibited signs of senescence (CD57) and mitochondrial alterations (PGC-1α, MitoTracker) ex vivo. Mitochondrial activity (MitoTracker) was also reduced in proliferating CD8^dim T cells. These findings indicate that an expanded CD8^dim T cell population displaying features of senescence and mitochondrial dysfunction is associated with KS disease under ART. CD8 coreceptor down-modulation may be symptomatic of ongoing disease.

The aging of ER-mitochondria communication: A journey from undifferentiated to aged cells

The complex physiology of eukaryotic cells requires that a variety of subcellular organelles perform unique tasks, even though they form highly dynamic communication networks. In the case of the endoplasmic reticulum (ER) and mitochondria, their functional coupling relies on the physical interaction between their membranes, mediated by domains known as mitochondria-ER contacts (MERCs). MERCs act as shuttles for calcium and lipid transfer between organelles, and for the nucleation of other subcellular processes. Of note, mounting evidence shows that they are heterogeneous structures, which display divergent behaviors depending on the cell type. Furthermore, MERCs are plastic structures that remodel according to intra- and extracellular cues, thereby adjusting the function of both organelles to the cellular needs. In consonance with this notion, the malfunction of MERCs reportedly contributes to the development of several age-related disorders. Here, we integrate current literature to describe how MERCs change, starting from undifferentiated cells, and their transit through specialization, malignant transformation (i.e., dedifferentiation), and aging/senescence. Along this journey, we will review the function of MERCs and their relevance for pivotal cell types, such as stem and cancer cells, cardiac, skeletal, and smooth myocytes, neurons, leukocytes, and hepatocytes, which intervene in the progression of chronic diseases related to age.

Altered Nutrient Uptake Causes Mitochondrial Dysfunction in Senescent CD8+ EMRA T Cells During Type 2 Diabetes

Mitochondrial health and cellular metabolism can heavily influence the onset of senescence in T cells. CD8⁺ EMRA T cells exhibit mitochondrial dysfunction and alterations to oxidative phosphorylation, however, the metabolic properties of senescent CD8⁺ T cells from people living with type 2 diabetes (T2D) are not known. We show here that mitochondria from T2D CD8⁺ T cells had a higher oxidative capacity together with increased levels of mitochondrial reactive oxgen species (mtROS), compared to age-matched control cells. While fatty acid uptake was increased, fatty acid oxidation was impaired in T2D CD8⁺ EMRA T cells, which also showed an accumulation of lipid droplets and decreased AMPK activity. Increasing glucose and fatty acids in healthy CD8⁺ T cells resulted in increased p-p53 expression and a fragmented mitochondrial morphology, similar to that observed in T2D CD8⁺ EMRA T cells. The resulting mitochondrial changes are likely to have a profound effect on T cell function. Consequently, a better understanding of these metabolic abnormalities is crucial as metabolic manipulation of these cells may restore correct T cell function and help reduce the impact of T cell dysfunction in T2D.

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

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

CD8+ T Cell Senescence: Lights and Shadows in Viral Infections, Autoimmune Disorders and Cancer

CD8⁺ T lymphocytes are a heterogeneous class of cells that play a crucial role in the adaptive immune response against pathogens and cancer. During their lifetime, they acquire cytotoxic functions to ensure the clearance of infected or transformed cells and, in addition, they turn into memory lymphocytes, thus providing a long-term protection. During ageing, the thymic involution causes a reduction of circulating T cells and an enrichment of memory cells, partially explaining the lowering of the response towards novel antigens with implications in vaccine efficacy. Moreover, the persistent stimulation by several antigens throughout life favors the switching of CD8⁺ T cells towards a senescent phenotype contributing to a low-grade inflammation that is a major component of several ageing-related diseases. In genetically predisposed young people, an immunological stress caused by viral infections (e.g., HIV, CMV, SARS-CoV-2), autoimmune disorders or tumor microenvironment (TME) could mimic the ageing status with the consequent acceleration of T cell senescence. This, in turn, exacerbates the inflamed conditions with dramatic effects on the clinical progression of the disease. A better characterization of the phenotype as well as the functions of senescent CD8⁺ T cells can be pivotal to prevent age-related diseases, to improve vaccine strategies and, possibly, immunotherapies in autoimmune diseases and cancer.

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

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

Knowns and Unknowns about CAR-T Cell Dysfunction

Simple Summary

The primary issue of adoptive cell therapy is the poor in vivo persistence. In this context, it is necessary to clarify the fundamental mechanisms of T cell dysfunction. Here we review common dysfunctional states, including exhaustion and senescence, and discuss the challenges associated with phenotypical characterization of these T cell subsets. We overview the heterogeneity among exhausted T cells as well as mechanisms by which T cells get reinvigorated by checkpoint inhibitors. We emphasize that some cancers not responding to such treatment may activate distinct T cell dysfunction programs. Finally, we describe the dysfunction-promoting mechanisms specific for CAR-T cells and the ways to mitigate them.

Abstract

Immunotherapy using chimeric antigen receptor (CAR) T cells is a promising option for cancer treatment. However, T cells and CAR-T cells frequently become dysfunctional in cancer, where numerous evasion mechanisms impair antitumor immunity. Cancer frequently exploits intrinsic T cell dysfunction mechanisms that evolved for the purpose of defending against autoimmunity. T cell exhaustion is the most studied type of T cell dysfunction. It is characterized by impaired proliferation and cytokine secretion and is often misdefined solely by the expression of the inhibitory receptors. Another type of dysfunction is T cell senescence, which occurs when T cells permanently arrest their cell cycle and proliferation while retaining cytotoxic capability. The first section of this review provides a broad overview of T cell dysfunctional states, including exhaustion and senescence; the second section is focused on the impact of T cell dysfunction on the CAR-T therapeutic potential. Finally, we discuss the recent efforts to mitigate CAR-T cell exhaustion, with an emphasis on epigenetic and transcriptional modulation.

Mitochondrial Dysfunction Associates With Acute T Lymphocytopenia and Impaired Functionality in COVID-19 Patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection results in rapid T lymphocytopenia and functional impairment of T cells. The underlying mechanism, however, remains incompletely understood. In this study, we focused on characterizing the phenotype and kinetics of T-cell subsets with mitochondrial dysfunction (MD) by multicolor flow cytometry and investigating the association between MD and T-cell functionality. While 73.9% of study subjects displayed clinical lymphocytopenia upon hospital admission, a significant reduction of CD4 or CD8 T-cell frequency was found in all asymptomatic, symptomatic, and convalescent cases. CD4 and CD8 T cells with increased MD were found in both asymptomatic and symptomatic patients within the first week of symptom onset. Lower proportion of memory CD8 T cell with MD was found in severe patients than in mild ones at the stage of disease progression. Critically, the frequency of T cells with MD in symptomatic patients was preferentially associated with CD4 T-cell loss and CD8 T-cell hyperactivation, respectively. Patients bearing effector memory CD4 and CD8 T cells with the phenotype of high MD exhibited poorer T-cell responses upon either phorbol 12-myristate-13-acetate (PMA)/ionomycin or SARS-CoV-2 peptide stimulation than those with low MD. Our findings demonstrated an MD-associated mechanism underlying SARS-CoV-2-induced T lymphocytopenia and functional impairment during the acute phase of infection.

Clinical and epidemiological correlates of low IFN-gamma responses in mitogen tube of QuantiFERON assay in tuberculosis infection screening during the COVID-19 pandemic: A population-based marker of COVID-19 mortality?

Background

The clinical and epidemiological implications of abnormal immune responses in COVID-19 for latent tuberculosis infection (LTBI) screening are unclear.

Methods

We reviewed QuantiFERON TB Gold Plus (QFT-Plus) results (36,709 patients) from July 2016 until October 2021 in Asturias (Spain). We also studied a cohort of ninety hospitalized patients with suspected/confirmed COVID-19 pneumonia and a group of elderly hospitalized patients with COVID-19 who underwent serial QFT-Plus and immune profiling testing.

Results

The indeterminate QFT-Plus results rate went from 1.4% (July 2016 to November 2019) to 4.2% during the COVID-19 pandemic. The evolution of the number of cases with low/very low interferon-gamma (IFN-gamma) response in the mitogen tube paralleled the disease activity and number of deaths during the pandemic waves in our region (from March 2020 to October 2021). The percentages of positive QFT-plus patients did not significantly change before and during the pandemic (13.9% vs. 12.2%). Forty-nine patients from the suspected/confirmed COVID-19 pneumonia cohort (54.4%) had low/very low IFN-gamma response to mitogen, 22 of them (24.4%) had severe and critical pneumonia. None received immunosuppressants prior to testing. Abnormal radiological findings (P = 0.01) but not COVID-19 severity was associated with low mitogen response. Immune profiling showed a reduction of CD8 + T cells and a direct correlation between the number of EMRA CD8 + T-cells and IFN-gamma response to mitogen (P = 0.03).

Conclusion

Low IFN-gamma responses in mitogen tube of QFT-Plus often occur in COVID-19 pneumonia, which is associated with a low number of an effector CD8 + T-cell subset and does not seem to affect LTBI screening; however, this abnormality seems to parallel the dynamics of COVID-19 at the population level and its mortality.

Impact of acute exercise on peripheral blood mononuclear cells nutrient sensing and mitochondrial oxidative capacity in healthy young adults

Regular exercise is associated with changes in peripheral blood mononuclear cell (PBMC) proportions that have enhanced effector functions in young and old adults; however, the effects of acute exercise on PBMC nutrient sensors and metabolic function in active young adults is unknown. To fill this gap, activation status and nutrient-sensing mechanisms of PBMCs isolated from 21 healthy active adults (20-35 yr; 36.5 ± 6.3 V̇O2peak ) were characterized before and after 30 min of moderate-to-vigorous cycling (65%-75% V̇O2peak ). In addition, changes in PBMC mitochondrial respiratory function in response to exercise were assessed using high-resolution respirometry. There was an increase in the number of activated CD69+/CD4 (79% increase) and CD69+/CD8 (166% increase) T-cells in response to the acute bout of exercise, while the nutrient-sensing mechanisms remained unchanged. PBMC mitochondrial respiration did not increase on a cell-per-cell basis, however, mitochondrial oxidative capacity (OXPHOS) increased at the tissue level (18.6 pmol/(s*ml blood) versus 29.3 pmol/(s*ml blood); p < 0.05) in response to acute exercise. Thus, this study shows that acute exercise preferentially mobilizes activated T-cells while concomitantly increasing PBMC mitochondrial oxidative capacity at the tissue level, rather than acutely changing mitochondrial oxidative capacity at the cellular level in young adults.