Identification of two major types of age-associated CD8 clonal expansions with highly divergent properties

Immune ageing at single-cell resolution

Ageing leads to profound alterations in the immune system and increases susceptibility to some chronic, infectious and autoimmune diseases. In recent years, widespread application of single-cell techniques has enabled substantial progress in our understanding of the ageing immune system. These comprehensive approaches have expanded and detailed the current views of ageing and immunity. Here we review a body of recent studies that explored how the immune system ages using unbiased profiling techniques at single-cell resolution. Specifically, we discuss an emergent understanding of age-related alterations in innate and adaptive immune cell populations, antigen receptor repertoires and immune cell-supporting microenvironments of the peripheral tissues. Focusing on the results obtained in mice and humans, we describe the multidimensional data that align with established concepts of immune ageing as well as novel insights emerging from these studies. We further discuss outstanding questions in the field and highlight techniques that will advance our understanding of immune ageing in the future.

OMIP-079: Cell cycle of CD4+ and CD8+ naïve/memory T cell subsets, and of Treg cells from mouse spleen

A multicolor flow cytometry panel was designed and optimized to define the following nine mouse T cell subsets: Treg (CD3⁺ CD4⁺ CD8⁻ FoxP3⁺), CD4⁺ T naïve (CD3⁺ CD4⁺ CD8⁻FoxP3⁻ CD44^int/low CD62L⁺), CD4⁺ T central memory (CD3⁺ CD4⁺ CD8⁻ FoxP3⁻ CD44^high CD62L⁺), CD4⁺ T effector memory (CD3⁺ CD4⁺ CD8⁻ FoxP3⁻ CD44^high CD62L⁻), CD4⁺ T EMRA (CD3⁺ CD4⁺ CD8⁻ FoxP3⁻ CD44^int/low CD62L⁻), CD8⁺ T naïve (CD3⁺ CD8⁺ CD4⁻ CD44^int/low CD62L⁺), CD8⁺ T central memory (CD3⁺ CD8⁺ CD4⁻ CD44^high CD62L⁺), CD8⁺ T effector memory (CD3⁺ CD8⁺ CD4⁻ CD44^high CD62L⁻), and CD8⁺ T EMRA (CD3⁺ CD8⁺ CD4⁻ CD44^int/low CD62L⁻). In each T cell subset, a dual staining for Ki‐67 expression and DNA content was employed to distinguish the following cell cycle phases: G₀ (Ki67⁻, with 2n DNA), G₁ (Ki67⁺, with 2n DNA), and S‐G₂/M (Ki67⁺, with 2n < DNA ≤ 4n). This panel was established for the analysis of mouse (C57BL/6J) spleen.

Age-Related Changes in Thymic Central Tolerance

Thymic epithelial cells (TECs) and hematopoietic antigen presenting cells (HAPCs) in the thymus microenvironment provide essential signals to self-reactive thymocytes that induce either negative selection or generation of regulatory T cells (Treg), both of which are required to establish and maintain central tolerance throughout life. HAPCs and TECs are comprised of multiple subsets that play distinct and overlapping roles in central tolerance. Changes that occur in the composition and function of TEC and HAPC subsets across the lifespan have potential consequences for central tolerance. In keeping with this possibility, there are age-associated changes in the cellular composition and function of T cells and Treg. This review summarizes changes in T cell and Treg function during the perinatal to adult transition and in the course of normal aging, and relates these changes to age-associated alterations in thymic HAPC and TEC subsets.

T-cell senescence accelerates angiotensin II-induced target organ damage

AIMS

Aging is a risk factor for cardiovascular diseases and adaptive immunity has been implicated in angiotensin (Ang) II-induced target organ dysfunction. Herein, we sought to determine the role of T-cell senescence in Ang II-induced target organ impairment and to explore the underlying mechanisms.

METHODS AND RESULTS

Flow cytometric analysis revealed that T cell derived from aged mice exhibited immunosenescence. Adoptive transfer of aged T cells to immunodeficient RAG1 KO mice accelerates Ang II-induced cardiovascular and renal fibrosis compared with young T-cell transfer. Aged T cells also promote inflammatory factor expression and superoxide production in these target organs. In vivo and in vitro studies revealed that Ang II promotes interferon-gamma (IFN-γ) production in the aged T cells comparing to young T cells. Importantly, transfer of senescent T cell that IFN-γ KO mitigates the impairment. Aged T-cell-conditioned medium stimulates inflammatory factor expression and oxidative stress in Ang II-treated renal epithelial cells compared with young T cells, and these effects of aged T-cell-conditioned medium are blunted after IFN-γ-neutralizing antibody pre-treatment.

CONCLUSION

These results provide a significant insight into the contribution of senescent T cells to Ang II-induced cardiovascular dysfunction and provide an attractive possibility that targeting T cell specifically might be a potential strategy to treat elderly hypertensive patients with end-organ dysfunction.

Comprehensive Profiling of an Aging Immune System Reveals Clonal GZMK+ CD8+ T Cells as Conserved Hallmark of Inflammaging

Systematic understanding of immune aging on a whole-body scale is currently lacking. We characterized age-associated alterations in immune cells across multiple mouse organs using single-cell RNA and antigen receptor sequencing and flow cytometry-based validation. We defined organ-specific and common immune alterations and identified a subpopulation of age-associated granzyme K (GZMK)-expressing CD8⁺ T (Taa) cells that are distinct from T effector memory (Tem) cells. Taa cells were highly clonal, had specific epigenetic and transcriptional signatures, developed in response to an aged host environment, and expressed markers of exhaustion and tissue homing. Activated Taa cells were the primary source of GZMK, which enhanced inflammatory functions of non-immune cells. In humans, proportions of the circulating GZMK⁺CD8⁺ T cell population that shares transcriptional and epigenetic signatures with mouse Taa cells increased during healthy aging. These results identify GZMK⁺ Taa cells as a potential target to address age-associated dysfunctions of the immune system.

Neutrophil: A New Player in Metastatic Cancers

The interaction between cancer cells and immune cells is important for the cancer development. However, much attention has been given to T cells and macrophages. Being the most abundant leukocytes in the blood, the functions of neutrophils in cancer have been underdetermined. They have long been considered an “audience” in the development of cancer. However, emerging evidence indicate that neutrophils are a heterogeneous population with plasticity, and subpopulation of neutrophils (such as low density neutrophils, polymorphonuclear-myeloid-derived suppressor cells) are actively involved in cancer growth and metastasis. Here, we review the current understanding of the role of neutrophils in cancer development, with a specific focus on their pro-metastatic functions. We also discuss the potential and challenges of neutrophils as therapeutic targets. A better understanding the role of neutrophils in cancer will discover new mechanisms of metastasis and develop new immunotherapies by targeting neutrophils.

Functional recreation of age-related CD8 T cells in young mice identifies drivers of aging- and human-specific tissue pathology

Mitigating effects of aging on human health remains elusive because aging impacts multiple systems simultaneously, and because experimental animals exhibit critical aging differences relative to humans. Separation of aging into discrete processes may identify targetable drivers of pathology, particularly when applied to human-specific features. Gradual homeostatic expansion of CD8 T cells dominantly alters their function in aging humans but not in mice. Injecting T cells into athymic mice induces rapid homeostatic expansion, but its relevance to aging remains uncertain. We hypothesized that homeostatic expansion of T cells injected into T-deficient hosts models physiologically relevant CD8 T cell aging in young mice, and aimed to analyze age-related T cell phenotype and tissue pathology in such animals. Indeed, we found that such injection conferred uniform age-related phenotype, genotype, and function to mouse CD8 T cells, heightened age-associated tissue pathology in young athymic hosts, and humanized amyloidosis after brain injury in secondary wild-type recipients. This validates a model conferring a human-specific aging feature to mice that identifies targetable drivers of tissue pathology. Similar examination of independent aging features should promote systematic understanding of aging and identify additional targets to mitigate its effects on human health.

Similar but different: virtual memory CD8 T cells as a memory-like cell population

Immunological memory is a phenomenon where the immune system can respond more rapidly to pathogens and immunological challenges that it has previously encountered. It is defined by several key hallmarks. After an initial encounter, immune cells (1) expand and (2) differentiate to form memory cell populations. Memory cells are (3) long-lived and (4) facilitate more rapid immune responses to subsequent infection because of (i) an increase in cell number, (ii) a decrease in the signaling threshold required for entry into cell cycle or effector function and (iii) localization of cells to tissue sites for surveillance. Classically, immunological memory has been antigen specific but it is becoming apparent that mechanisms of immunological memory can be co-opted by innate or antigen-inexperienced immune cells to generate heterogeneity in immune responses. One such cell is the virtual memory CD8 T (T_VM ) cell, which is a semi-differentiated but antigen-naïve CD8 T-cell population. This review will summarize current knowledge of how T_VM cells are generated, their memory-like hallmarks, how they are maintained during steady state, infection and aging, and propose a model to integrate key signaling pathways during their generation.

Characterization of age-associated exhausted CD8⁺ T cells defined by increased expression of Tim-3 and PD-1

Aging is accompanied by altered T‐cell responses that result in susceptibility to various diseases. Previous findings on the increased expression of inhibitory receptors, such as programmed cell death protein 1 (PD‐1), in the T cells of aged mice emphasize the importance of investigations into the relationship between T‐cell exhaustion and aging‐associated immune dysfunction. In this study, we demonstrate that T‐cell immunoglobulin mucin domain‐3 (Tim‐3), another exhaustion marker, is up‐regulated on aged T cells, especially CD8⁺ T cells. Tim‐3‐expressing cells also produced PD‐1, but Tim‐3⁺PD‐1⁺CD8⁺ T cells had a distinct phenotype that included the expression of CD44 and CD62L, from Tim‐3⁻PD‐1⁺ cells. Tim‐3⁺PD‐1⁺CD8⁺ T cells showed more evident properties associated with exhaustion than Tim‐3⁻PD‐1⁺CD8⁺ T cells: an exhaustion‐related marker expression profile, proliferative defects following homeostatic or TCR stimulation, and altered production of cytokines. Interestingly, these cells produced a high level of IL‐10 and induced normal CD8⁺ T cells to produce IL‐10, which might contribute to immune dysregulation in aged mice. The generation of Tim‐3‐expressing CD8⁺ T cells in aged mice seems to be mediated by encounters with antigens but not by specific infection, based on their high expression of CD49d and their unbiased TCR Vβ usage. In conclusion, we found that a CD8⁺ T‐cell population with age‐associated exhaustion was distinguishable by its expression of Tim‐3. These results provide clues for understanding the alterations that occur in T‐cell populations with age and for improving dysfunctions related to the aging of the immune system.

Truncated form of TGF-βRII, but not its absence, induces memory CD8+ T cell expansion and lymphoproliferative disorder in mice

Inflammatory and anti-inflammatory cytokines play an important role in the generation of effector and memory CD8(+) T cells. We used two different models, transgenic expression of truncated (dominant negative) form of TGF-βRII (dnTGFβRII) and Cre-mediated deletion of the floxed TGF-βRII to examine the role of TGF-β signaling in the formation, function, and homeostatic proliferation of memory CD8(+) T cells. Blocking TGF-β signaling in effector CD8(+) T cells using both of these models demonstrated a role for TGF-β in regulating the number of short-lived effector cells but did not alter memory CD8(+) T cell formation and their function upon Listeria monocytogenes infection in mice. Interestingly, however, a massive lymphoproliferative disorder and cellular transformation were observed in Ag-experienced and homeostatically generated memory CD8(+) T cells only in cells that express the dnTGFβRII and not in cells with a complete deletion of TGF-βRII. Furthermore, the development of transformed memory CD8(+) T cells expressing dnTGFβRII was IL-7- and IL-15-independent, and MHC class I was not required for their proliferation. We show that transgenic expression of the dnTGFβRII, rather than the absence of TGF-βRII-mediated signaling, is responsible for dysregulated expansion of memory CD8(+) T cells. This study uncovers a previously unrecognized dominant function of the dnTGFβRII in CD8(+) T cell proliferation and cellular transformation, which is caused by a mechanism that is different from the absence of TGF-β signaling. These results should be considered during both basic and translational studies where there is a desire to block TGF-β signaling in CD8(+) T cells.

Intrinsic defects in CD8 T cells with aging contribute to impaired primary antiviral responses

Aging is associated with altered immune responses, particularly with a diminished CD8 T cell response. Although both intrinsic and extrinsic factors are hypothesized to impact this decreased T cell response, the direct evidence of an intrinsic deficiency in virus-specific CD8 T cells is limited. In this study, a TCR transgenic (Tg) P14 mouse model was utilized to compare the activation and proliferation of the Tg CD8 T cells of young and aged P14 mice upon stimulation with antigen or infection with virus. The proliferation of purified Tg CD8 T cells of aged mice was significantly lower than that of young mice when cultured in vitro with both the LCMV specific peptide and antigen presenting cells from young wild type mice. In addition, expression of the activation markers, CD69, CD25, and CD44, was delayed on Tg T cells of aged mice after stimulation. Importantly, while adoptive transfer of purified Tg CD8 T cells of young or aged mice into young wild type mice resulted in expansion of the Tg CD8 T cells of both ages after LCMV infection, the expansion of the Tg T cells from aged mice was significantly decreased compared with that of the Tg T cells from young mice. However, while the number of IFN-γ secreting Tg CD8 T cells from aged mice was significantly decreased compared to that of young mice, the percentages of Tg CD8 T cells producing IFN-γ were similar in young and aged mice, demonstrating that proliferation, but not function, of the Tg CD8 T cells of aged mice was impaired. Importantly, chronological age alone was not sufficient to predict an altered proliferative response; rather, expression of high levels of CD44 on CD8 T cells of aged mice reflected a decreased proliferative response. These results reveal that alterations intrinsic to CD8 T cells can contribute to the age-associated defects in the primary CD8 T cell response during viral infection.

Causes, consequences, and reversal of immune system aging

The effects of aging on the immune system are manifest at multiple levels that include reduced production of B and T cells in bone marrow and thymus and diminished function of mature lymphocytes in secondary lymphoid tissues. As a result, elderly individuals do not respond to immune challenge as robustly as the young. An important goal of aging research is to define the cellular changes that occur in the immune system and the molecular events that underlie them. Considerable progress has been made in this regard, and this information has provided the rationale for clinical trials to rejuvenate the aging immune system.

Increased T-bet is associated with senescence of influenza virus-specific CD8 T cells in aged humans

Aged individuals have increased morbidity and mortality following influenza and other viral infections, despite previous exposure or vaccination. Mouse and human studies suggest increased senescence and/or exhaustion of influenza virus-specific CD8 T cells with advanced age. However, neither the relationship between senescence and exhaustion nor the underlying transcriptional pathways leading to decreased function of influenza virus-specific cellular immunity in elderly humans are well-defined. Here, we demonstrate that increased percentages of CD8 T cells from aged individuals express CD57 and KLRG1, along with PD-1 and other inhibitory receptors, markers of senescence, or exhaustion, respectively. Expression of T-box transcription factors, T-bet and Eomes, were also increased in CD8 T cells from aged subjects and correlated closely with expression of CD57 and KLRG1. Influenza virus-specific CD8 T cells from aged individuals exhibited decreased functionality with corresponding increases in CD57, KLRG1, and T-bet, a molecular regulator of terminal differentiation. However, in contrast to total CD8 T cells, influenza virus-specific CD8 T cells had altered expression of inhibitory receptors, including lower PD-1, in aged compared with young subjects. Thus, our data suggest a prominent role for senescence and/or terminal differentiation for influenza virus-specific CD8 T cells in elderly subjects.

Kidney transplantation and the ageing immune system

The world population is rapidly growing and ageing at a pace that is projected to continue for at least three decades. This shift towards an older populace has invariably increased the number of individuals with diseases related to ageing, such as chronic kidney disease. The increase in chronic kidney disease is associated with a growing number of elderly patients receiving kidney transplants. Understanding how the immune system changes with increasing age will help to define the risks of rejection and infection in the elderly population and will focus attention on the need for individualized immunosuppression for patients in this age group. This Review addresses what is currently known about ageing and the immune system, highlighting age-related changes that affect the outcome of transplantation in elderly individuals. The need for new strategies to improve outcomes in this growing population of elderly renal transplant recipients is also emphasized.

Defective CD8 T cell responses in aged mice are due to quantitative and qualitative changes in virus-specific precursors

Aging is associated with suboptimal CD8 T cell responses to viral infections. It is not clear whether these poor responses are due to environmental influences or quantitative and qualitative changes in the pool of responding CD8 T cells. Our studies demonstrated several deleterious age-related changes in the pool of Ag-specific CD8 T cells that respond to infection. The majority of CD8 T cells from uninfected aged mice was CD44(Hi) and had increased expression of inhibitory receptors including PD1, LAG3, 2B4, and CD160. These aged CD44(Hi) CD8 T cells were transcriptionally similar to exhausted CD8 T cells found during chronic infections. In addition, the number of virus-specific precursors in aged mice prior to infection was decreased up to 10-fold, and many of these Ag-specific precursors had high expression of CD44 and PD1. Finally, TCR transgenic studies demonstrated that the CD44(Hi) Ag-specific CD8 T cells from unimmunized aged and young mice were qualitatively inferior compared with CD44(Lo) CD8 T cells from aged or young donors. Thus, a decrease in precursor frequency as well as qualitative changes of CD8 T cells during aging are directly related to impaired immunity.

TCR-dependent transformation of mature memory phenotype T cells in mice

A fundamental goal in cancer research is the identification of the cell types and signaling pathways capable of initiating and sustaining tumor growth, as this has the potential to reveal therapeutic targets. Stem and progenitor cells have been implicated in the genesis of select lymphoid malignancies. However, the identity of the cells in which mature lymphoid neoplasms are initiated remains unclear. Here, we investigate the origin of peripheral T cell lymphomas using mice in which Snf5, a chromatin remodelling-complex subunit with tumor suppressor activity, could be conditionally inactivated in developing T cells. In this model of mature peripheral T cell lymphomas, the cell of origin was a mature CD44hiCD122loCD8⁺ T cell that resembled a subset of memory cells that has capacity for self-renewal and robust expansion, features shared with stem cells. Further analysis showed that Snf5 loss led to activation of a Myc-driven signaling network and stem cell transcriptional program. Finally, lymphomagenesis and lymphoma proliferation depended upon TCR signaling, establishing what we believe to be a new paradigm for lymphoid malignancy growth. These findings suggest that the self-renewal and robust proliferative capacities of memory T cells are associated with vulnerability to oncogenic transformation. Our findings further suggest that agents that impinge upon TCR signaling may represent an effective therapeutic modality for this class of lethal human cancers.

Persistent viral infections and immune aging

Immunosenescence comprises a set of dynamic changes occurring to both, the innate as well as the adaptive immune system that accompany human aging and result in complex manifestations of still poorly defined deficiencies in the elderly population. One of the most prominent alterations during aging is the continuous involution of the thymus gland which is almost complete by the age of 50. Consequently, the output of naïve T cells is greatly diminished in elderly individuals which puts pressure on homeostatic forces to maintain a steady T cell pool for most of adulthood. In a great proportion of the human population, this fragile balance is challenged by persistent viral infections, especially Cytomegalovirus (CMV), that oblige certain T cell clones to monoclonally expand repeatedly over a lifetime which then occupy space within the T cell pool. Eventually, these inflated memory T cell clones become exhausted and their extensive accumulation accelerates the age-dependent decline of the diversity of the T cell pool. As a consequence, infectious diseases are more frequent and severe in elderly persons and immunological protection following vaccination is reduced. This review therefore aims to shed light on how various types of persistent viral infections, especially CMV, influence the aging of the immune system and highlight potential measures to prevent the age-related decline in immune function.

The narrowing of the CD8 T cell repertoire in old age

Immune function declines progressively with age, resulting in increased susceptibility of the elderly to infection and impaired responses to vaccines. A diverse repertoire of T cells is essential for a vigorous immune response, and an important manifestation of immune aging is the progressive loss of repertoire diversity, predominantly among CD8 T cells in both mice and humans. Importantly, perturbations in the peripheral T cell repertoire, including reduction of the CD4:CD8 ratio and cytomegalovirus-driven T cell clonal expansions, make a major contribution to the 'immune risk phenotype' defined for humans, which predicts two-year mortality in very old individuals.

Nonmalignant clonal expansions of memory CD8+ T cells that arise with age vary in their capacity to mount recall responses to infection

Immune responsiveness declines with age in part due to the development of CD8(+) T cell clonal expansions (TCEs) that can dominate the peripheral T cell pool. Although some TCEs arise due to persistent Ag stimulation from chronic infections, others arise in the apparent absence of chronic infection. We have recently shown that this latter class of TCEs can arise over time from the memory CD8(+) T cell pool established by an acute viral infection. Unlike TCEs driven by chronic infections, these age-related TCEs do not display the phenotypic and in vitro functional characteristics of exhausted cells. However, the rate at which these age-related TCEs develop from the memory CD8(+) T cell pool, as well as their ability to mount a recall response to secondary pathogen challenge in vivo, is not known. In this study, we analyzed large cohorts of mice over time for the development of TCE following Sendai virus infection and found a progressive increase in the appearance of TCEs, such that most mice showed evidence of TCE within the memory T cell pool by 2 y postinfection. Using a dual adoptive transfer approach to address the recall potential of virus-specific TCEs, we also demonstrate that most TCEs examined are poorly responsive to a secondary infection. Therefore, we provide evidence that the development of TCE is a common occurrence due to the progressive dysregulation of the virus-specific memory T cell pool with age, but many TCEs are profoundly defective in their ability to mediate recall responses.

Loss of naive T cells and repertoire constriction predict poor response to vaccination in old primates

Aging is usually accompanied by diminished immune protection upon infection or vaccination. Although aging results in well-characterized changes in the T cell compartment of long-lived, outbred, and pathogen-exposed organisms, their relevance for primary Ag responses remain unclear. Therefore, it remains unclear whether and to what extent the loss of naive T cells, their partial replacement by oligoclonal memory populations, and the consequent constriction of TCR repertoire limit the Ag responses in aging primates. We show in this study that aging rhesus monkeys (Macaca mulatta) exhibit poor CD8 T cell and B cell responses in the blood and poor CD8 responses in the lungs upon vaccination with the modified vaccinia strain Ankara. The function of APCs appeared to be maintained in aging monkeys, suggesting that the poor response was likely intrinsic to lymphocytes. We found that the loss of naive CD4 and CD8 T cells, and the appearance of persisting T cell clonal expansions predicted poor CD8 responses in individual monkeys. There was strong correlation between early CD8 responses in the transitory CD28+ CD62L- CD8+ T cell compartment and the peak Ab titers upon boost in individual animals, as well as a correlation of both parameters of immune response to the frequency of naive CD8+ T cells in old but not in adult monkeys. Therefore, our results argue that T cell repertoire constriction and naive cell loss have prognostic value for global immune function in aging primates.

Workshop on immunizations in older adults: identifying future research agendas

Goals for immunization in older adults may differ from those in young adults and children, in whom complete prevention of disease is the objective. Often, reduced hospitalization and death but also averting exacerbation of underlying chronic illness, functional decline, and frailty are important goals in the older age group. Because of the effect of age on dendritic cell function, T cell-mediated immune suppression, reduced proliferative capacity of T cells, and other immune responses, the efficacy of vaccines often wanes with advanced age. This article summarizes the discussion and proceedings of a workshop organized by the Association of Specialty Professors, the Infectious Diseases Society of America, the American Geriatrics Society, the National Institute on Aging, and the National Institute of Allergy and Infectious Diseases. Leading researchers and clinicians in the fields of immunology, epidemiology, infectious diseases, geriatrics, and gerontology reviewed the current status of vaccines in older adults, identified knowledge gaps, and suggest priority areas for future research. The goal of the workshop was to identify what is known about immunizations (efficacy, effect, and current schedule) in older adults and to recommend priorities for future research. Investigation in the areas identified has the potential to enhance understanding of the immune process in aging individuals, inform vaccine development, and lead to more-effective strategies to reduce the risk of vaccine-preventable illness in older adults.

Cell-intrinsic defects in the proliferative response of antiviral memory CD8 T cells in aged mice upon secondary infection

Although previous studies have demonstrated delayed viral clearance and blunted effector T cell responses in aged mice during infection, memory CD8 T cells and especially secondary responses have received less attention. In this study, we show that modest differences in the number of memory CD8 T cells formed in aged versus young animals were associated with altered memory CD8 T cell differentiation. Aged immune mice had increased morbidity and mortality upon secondary viral challenge, suggesting changes in T cell immunity. Indeed, virus-specific memory CD8 T cells from aged mice showed substantially reduced proliferative expansion upon secondary infection using multiple challenge models. In addition, this defect in recall capacity of aged memory CD8 T cells was cell-intrinsic and persisted upon adoptive transfer into young mice. Thus, the poor proliferative potential of memory T cells and altered memory CD8 T cell differentiation could underlie age-related defects in antiviral immunity.

Diversity in T cell memory: an embarrassment of riches

The adaptive immune response meets the needs of the organism to generate effector cells capable of controlling pathogens but also leads to production of memory cells, which mediate more effective protection during rechallenge. In this review, we focus on the generation, maintenance, and function of memory T cells, with a special emphasis on the increasing evidence for great diversity among functional memory T cell subsets.

CCR6: a biomarker for Alzheimer's-like disease in a triple transgenic mouse model

The inflammatory status of the brain in patients as well as animal models of Alzheimer's disease (AD) has been extensively studied. Accumulation of activated microglia producing tumor necrosis factor-α and monocyte chemotactic protein-1 contribute to the pathology of the disease. However, little is known about the changes in the spleen and associated peripheral immunity that might contribute to AD pathology. The goal of this study was to characterize phenotypic and functional changes in spleen, blood and brain cell populations that contribute to development of an AD-like disease in a triple transgenic (3xTg-AD) mouse model. The 3xTg-AD mice had increased percentages of brain Gr-1+ granulocytes, dendritic cells and macrophages, spleen and blood derived CD8+Ly6C+ memory T cells and CCR6+ B cells, as well as increased levels of secreted interleukin-6. Brain tissue from older 12 month old symptomatic 3xTg-AD female mice exhibited highly elevated mRNA expression of CCR6 compared to wild-type mice. Importantly, this pronounced increase in expression of CCR6 was also detected in brain and spleen tissue from pre-symptomatic 5--6 month old 3xTg-AD females and males. Our data demonstrate increased expression of CCR6 in the brain and peripheral immune organs of both pre-symptomatic and symptomatic 3xTg-AD mice, strongly suggesting an ongoing inflammatory process that precedes onset of clinical AD-like disease.

Adoptively transferred effector cells derived from naive rather than central memory CD8+ T cells mediate superior antitumor immunity

Effector cells derived from central memory CD8(+) T cells were reported to engraft and survive better than those derived from effector memory populations, suggesting that they are superior for use in adoptive immunotherapy studies. However, previous studies did not evaluate the relative efficacy of effector cells derived from naïve T cells. We sought to investigate the efficacy of tumor-specific effector cells derived from naïve or central memory T-cell subsets using transgenic or retrovirally transduced T cells engineered to express a tumor-specific T-cell receptor. We found that naïve, rather than central memory T cells, gave rise to an effector population that mediated superior antitumor immunity upon adoptive transfer. Effector cells developed from naïve T cells lost the expression of CD62L more rapidly than those derived from central memory T cells, but did not acquire the expression of KLRG-1, a marker for terminal differentiation and replicative senescence. Consistent with this KLRG-1(-) phenotype, naïve-derived cells were capable of a greater proliferative burst and had enhanced cytokine production after adoptive transfer. These results indicate that insertion of genes that confer antitumor specificity into naïve rather than central memory CD8(+) T cells may allow superior efficacy upon adoptive transfer.

Immunosenescence: what does it mean to health outcomes in older adults?

The most profound consequences of immune senescence with respect to human health are the increased susceptibility to infectious diseases and decreased vaccine efficacy. Changes in both innate and adaptive immune function converge in the reduced response to vaccination and protection against infection and related diseases. The decline in thymic output of naïve T cells diminishes responses to novel antigens, such as West Nile Virus, while clonal expansions leading to defects in the T cell repertoire are associated with blunted responses of memory T cells to conserved epitopes of the influenza virus. Recent studies on how immunologic mechanisms of protection change during aging have led to novel strategies for improving vaccine responsiveness and outcomes of infectious diseases in older adults.

Effects of aging on T cell function

Immunosenescence influences many components of the immune system. Most importantly, profound changes in T cell function are evident in older individuals. The impact of aging on specific T cell subsets has been difficult to examine, but recent advances in murine model systems and new insights into T cell function have allowed for the more precise examination of how T cell responses change with aging. Importantly, recent studies have shown that age-related enhancement of both Th17 generation and regulatory T cell function may contribute to significant changes in immune function. In this review, we summarize the current views on how aging influences the factors that impact T cell function and how this can affect the immune response to infections, vaccinations, and tumors.

STAT6 deletion converts the Th2 inflammatory pathology afflicting Lat(Y136F) mice into a lymphoproliferative disorder involving Th1 and CD8 effector T cells

Mutant mice in which tyrosine 136 of linker for activation of T cells (LAT) was replaced with a phenylalanine (Lat(Y136F) mice) develop a lymphoproliferative disorder involving polyclonal CD4 effector T cells that produce massive amounts of IL-4 and trigger severe Th2 inflammation. Naive CD4 T cells can themselves produce IL-4 and thereby initiate a self-reinforcing positive regulatory loop that involves the STAT6 transcription factor and leads to Th2 polarization. We determined the functional outcome that results when Lat(Y136F) T cells differentiate in the absence of such STAT6-dependent regulatory loop. The lack of STAT6 had no effect on the timing and magnitude of the lymphoproliferative disorder. However, in Lat(Y136F) mice deprived of STAT6, the expanding CD4 T cell population was dominated by Th1 effector cells that triggered B cell proliferation, elevated IgG2a and IgG2b levels as well as the production of autoantibodies. In contrast to Lat(Y136F) mice that showed no CD8 T cell expansion, the CD8 T cells present in Lat(Y136F) mice deprived of STAT6 massively expanded and acquired effector potential. Therefore, the lack of STAT6 is sufficient to convert the Th2 lymphoproliferative disorder that characterizes Lat(Y136F) mice into a lymphoproliferative disorder that is dominated by Th1 and CD8 effector T cells. The possibility to dispose of a pair of mice that differs by a single gene and develops in the absence of deliberate immunization large numbers of Th cells with almost reciprocal polarization should facilitate the identification of genes involved in the control of normal and pathological Th cell differentiation.