Identification of a human recent thymic emigrant phenotype

Lymph nodes link sex-biased immune aging to compromised antigen recognition

A diverse naive CD8 T cell repertoire is essential to provide broad protection against infection and cancer. Aging diminishes naive T cells, reducing potential diversity and leading to lymph node contraction. Here, we revealed that this decline occurs earlier in males, resulting in significant sex differences in immunity during middle age. Earlier in life, naive CD8 T cells in males become virtual memory cells prone to premature senescence. Due to androgen-driven thymic atrophy in males, naive CD8 T cells are insufficiently replenished. Therapeutic thymus rejuvenation via testosterone ablation restored naive CD8 T cells in lymph nodes of middle-aged male mice, leading to enhanced tumor recognition. These findings show the crucial role of sex and age on lymph node T cell repertoires and suggest potential strategies to restore immune function in males during aging.

Systematic review and quantitative meta-analysis of age-dependent human T-lymphocyte homeostasis

Objective

To evaluate and quantitatively describe age-dependent homeostasis for a broad range of total T-cells and specific T-lymphocyte subpopulations in healthy human subjects.

Methods

A systematic literature review was performed to identify and collect relevant quantitative information on T-lymphocyte counts in human blood and various organs. Both individual subject and grouped (aggregated) data on T-lymphocyte observations in absolute and relative values were digitized and curated; cell phenotypes, gating strategies for flow cytometry analyses, organs from which observations were obtained, subjects' number and age were also systematically inventoried. Age-dependent homeostasis of each T-lymphocyte subpopulation was evaluated via a weighted average calculation within pre-specified age intervals, using a piece-wise equal-effect meta-analysis methodology.

Results

In total, 124 studies comprising 11722 unique observations from healthy subjects encompassing 20 different T-lymphocyte subpopulations - total CD45+ and CD3+ lymphocytes, as well as specific CD4+ and CD8+ naïve, recent thymic emigrants, activated, effector and various subpopulations of memory T-lymphocytes (total-memory, central-memory, effector-memory, resident-memory) - were systematically collected and included in the final database for a comprehensive analysis. Blood counts of most T-lymphocyte subpopulations demonstrate a decline with age, with a pronounced decrease within the first 10 years of life. Conversely, memory T-lymphocytes display a tendency to increase in older age groups, particularly after ~50 years of age. Notably, an increase in T-lymphocyte numbers is observed in neonates and infants (0 - 1 year of age) towards less differentiated T-lymphocyte subpopulations, while an increase into more differentiated subpopulations emerges later (1 - 5 years of age).

Conclusion

A comprehensive systematic review and meta-analysis of T-lymphocyte age-dependent homeostasis in healthy humans was performed, to evaluate immune T-cell profiles as a function of age and to characterize generalized estimates of T-lymphocyte counts across age groups. Our study introduces a quantitative description of the fundamental parameters characterizing the maintenance and evolution of T-cell subsets with age, based on a comprehensive integration of available organ-specific and systems-level flow cytometry datasets. Overall, it provides the most up-to-date view of physiological T-cell dynamics and its variance and may be used as a consistent reference for gaining further mechanistic understanding of the human immune status in health and disease.

Multidimensional profiling of human T cells reveals high CD38 expression, marking recent thymic emigrants and age-related naive T cell remodeling

Thymic involution is a key factor in human immune aging, leading to reduced thymic output and a decline in recent thymic emigrant (RTE) naive T cells in circulation. Currently, the precise definition of human RTEs and their corresponding cell surface markers lacks clarity. Analysis of single-cell RNA-seq/ATAC-seq data distinguished RTEs by the expression of SOX4, IKZF2, and TOX and CD38 protein, whereby surface CD38hi expression universally identified CD8+ and CD4+ RTEs. We further determined the dynamics of RTEs and mature cells in a cohort of 158 individuals, including age-associated transcriptional reprogramming and shifts in cytokine production. Spectral cytometry profiling revealed two axes of aging common to naive CD8+ and CD4+ T cells: (1) a decrease in CD38++ cells (RTEs) and (2) an increase in CXCR3hi cells. Identification of RTEs enables direct assessment of thymic health. Furthermore, resolving the dynamics of naive T cell remodeling yields insight into vaccination and infection responsiveness throughout aging.

Comprehensive Flow Cytometric, Immunohistologic, and Molecular Assessment of Thymus Function in Rhesus Macaques

The critical importance of the thymus for generating new naive T cells that protect against novel infections and are tolerant to self-antigens has led to a recent revival of interest in monitoring thymic function in species other than humans and mice. Nonhuman primates such as rhesus macaques (Macaca mulatta) provide particularly useful animal models for translational research in immunology. In this study, we tested the performance of a 15-marker multicolor Ab panel for flow cytometric phenotyping of lymphocyte subsets directly from rhesus whole blood, with validation by thymectomy and T cell depletion. Immunohistochemical and multiplex RNA expression analysis of thymus tissue biopsies and molecular assays on PBMCs were used to further validate thymus function. Results identify Ab panels that can accurately classify rhesus naive T cells (CD3+CD45RA+CD197+ or CD3+CD28+CD95-) and recent thymic emigrants (CD8+CD28+CD95-CD103+CD197+) using just 100 µl of whole blood and commercially available fluorescent Abs. An immunohistochemical panel reactive with pan-cytokeratin (CK), CK14, CD3, Ki-67, CCL21, and TdT provides histologic evidence of thymopoiesis from formalin-fixed, paraffin-embedded thymus tissues. Identification of mRNAs characteristic of both functioning thymic epithelial cells and developing thymocytes and/or molecular detection of products of TCR gene rearrangement provide additional complementary methods to evaluate thymopoiesis, without requiring specific Abs. Combinations of multiparameter flow cytometry, immunohistochemistry, multiplex gene expression, and TCR excision circle assays can comprehensively evaluate thymus function in rhesus macaques while requiring only minimal amounts of peripheral blood or biopsied thymus tissue.

Better safe than sorry: Naive T-cell dynamics in healthy ageing

It is well-known that the functioning of the immune system gradually deteriorates with age, and we are increasingly confronted with its consequences as the life expectancy of the human population increases. Changes in the T-cell pool are among the most prominent features of the changing immune system during healthy ageing, and changes in the naive T-cell pool in particular are generally held responsible for its gradual deterioration. These changes in the naive T-cell pool are thought to be due to involution of the thymus. It is commonly believed that the gradual loss of thymic output induces compensatory mechanisms to maintain the number of naive T cells at a relatively constant level, and induces a loss of diversity in the T-cell repertoire. Here we review the studies that support or challenge this widely-held view of immune ageing and discuss the implications for vaccination strategies.

Human circulating and tissue-resident memory CD8+ T cells

Our current knowledge of human memory CD8⁺ T cells is derived largely from studies of the intravascular space. However, emerging data are starting to challenge some of the dogmas based on this work, suggesting that a conceptual revision may be necessary. In this review, we provide a brief history of the field and summarize the biology of circulating and tissue-resident memory CD8⁺ T cells, which are ultimately responsible for effective immune surveillance. We also incorporate recent findings into a biologically integrated model of human memory CD8⁺ T cell differentiation. Finally, we address how future innovative human studies could improve our understanding of anatomically localized CD8⁺ T cells to inform the development of more effective immunotherapies and vaccines, the need for which has been emphasized by the global struggle to contain severe acute respiratory syndrome coronavirus 2.

Generation of T-cell-receptor-negative CD8αβ-positive CAR T cells from T-cell-derived induced pluripotent stem cells

The production of autologous T cells expressing a chimaeric antigen receptor (CAR) is time-consuming, costly and occasionally unsuccessful. T-cell-derived induced pluripotent stem cells (TiPS) are a promising source for the generation of 'off-the-shelf' CAR T cells, but the in vitro differentiation of TiPS often yields T cells with suboptimal features. Here we show that the premature expression of the T-cell receptor (TCR) or a constitutively expressed CAR in TiPS promotes the acquisition of an innate phenotype, which can be averted by disabling the TCR and relying on the CAR to drive differentiation. Delaying CAR expression and calibrating its signalling strength in TiPS enabled the generation of human TCR- CD8αβ+ CAR T cells that perform similarly to CD8αβ+ CAR T cells from peripheral blood, achieving effective tumour control on systemic administration in a mouse model of leukaemia and without causing graft-versus-host disease. Driving T-cell maturation in TiPS in the absence of a TCR by taking advantage of a CAR may facilitate the large-scale development of potent allogeneic CD8αβ+ T cells for a broad range of immunotherapies.

Age-Related Adaptive Immune Changes in Parkinson’s Disease

Ageing is a major risk factor for most neurodegenerative diseases, including Parkinson’s disease (PD). Progressive age-related dysregulation of the immune system is termed immunosenescence and is responsible for the weakened response to novel antigens, increased susceptibility to infections and reduced effectiveness of vaccines seen in the elderly. Immune activation, both within the brain and periphery, is heavily implicated in PD but the role of immunosenescence has not been fully explored. Studies to date provide some evidence for an attenuation in immunosenescence in PD, particularly a reduction in senescent CD8 T lymphocytes in PD cases compared to similarly aged controls. Here, we discuss recent evidence of age-related immune abnormalities in PD with a focus on T cell senescence and explore their potential role in disease pathogenesis and development.

Reframing How Physical Activity Reduces The Incidence of Clinically-Diagnosed Cancers: Appraising Exercise-Induced Immuno-Modulation As An Integral Mechanism

Undertaking a high volume of physical activity is associated with reduced risk of a broad range of clinically diagnosed cancers. These findings, which imply that physical activity induces physiological changes that avert or suppress neoplastic activity, are supported by preclinical intervention studies in rodents demonstrating that structured regular exercise commonly represses tumour growth. In Part 1 of this review, we summarise epidemiology and preclinical evidence linking physical activity or regular structured exercise with reduced cancer risk or tumour growth. Despite abundant evidence that physical activity commonly exerts anti-cancer effects, the mechanism(s)-of-action responsible for these beneficial outcomes is undefined and remains subject to ongoing speculation. In Part 2, we outline why altered immune regulation from physical activity - specifically to T cells - is likely an integral mechanism. We do this by first explaining how physical activity appears to modulate the cancer immunoediting process. In doing so, we highlight that augmented elimination of immunogenic cancer cells predominantly leads to the containment of cancers in a 'precancerous' or 'covert' equilibrium state, thus reducing the incidence of clinically diagnosed cancers among physically active individuals. In seeking to understand how physical activity might augment T cell function to avert cancer outgrowth, in Part 3 we appraise how physical activity affects the determinants of a successful T cell response against immunogenic cancer cells. Using the cancer immunogram as a basis for this evaluation, we assess the effects of physical activity on: (i) general T cell status in blood, (ii) T cell infiltration to tissues, (iii) presence of immune checkpoints associated with T cell exhaustion and anergy, (iv) presence of inflammatory inhibitors of T cells and (v) presence of metabolic inhibitors of T cells. The extent to which physical activity alters these determinants to reduce the risk of clinically diagnosed cancers - and whether physical activity changes these determinants in an interconnected or unrelated manner - is unresolved. Accordingly, we analyse how physical activity might alter each determinant, and we show how these changes may interconnect to explain how physical activity alters T cell regulation to prevent cancer outgrowth.

Salutary effects of moderate but not high intensity aerobic exercise training on the frequency of peripheral T-cells associated with immunosenescence in older women at high risk of breast cancer: a randomized controlled trial

Background

Immunosenescence is described as age-associated changes within the immune system that are responsible for decreased immunity and increased cancer risk. Physically active individuals have fewer ‘senescent’ and more naïve T-cells compared to their sedentary counterparts, but it is not known if exercise training can rejuvenate ‘older looking’ T-cell profiles. We determined the effects of 12-weeks supervised exercise training on the frequency of T-cell subtypes in peripheral blood and their relationships with circulating levels of the muscle-derived cytokines (i.e. ‘myokines’) IL-6, IL-7, IL-15 and osteonectin in older women at high risk of breast cancer. The intervention involved 3 sessions/week of either high intensity interval exercise (HIIT) or moderate intensity continuous exercise (MICT) and were compared to an untrained control (UC) group.

Results

HIIT decreased total granulocytes, CD4+ T-cells, CD4+ naïve T-cells, CD4+ recent thymic emigrants (RTE) and the CD4:CD8 ratio after training, whereas MICT increased total lymphocytes and CD8 effector memory (EM) T-cells. The change in total T-cells, CD4+ naïve T-cells, CD4+ central memory (CM) T-cells and CD4+ RTE was elevated after MICT compared to HIIT. Changes in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \dot{\mathrm{V}}{\mathrm{O}}_{2\max } $$\end{document}V˙O2max after training, regardless of exercise prescription, was inversely related to the change in highly differentiated CD8+ EMRA T-cells and positively related to changes in β2-adrenergic receptor (β2-AR) expression on CM CD4+ and CM CD8+ T-cells. Plasma myokine levels did not change significantly among the groups after training, but individual changes in IL-7 were positively related to changes in the number of β2-AR expressing CD4 naïve T cells in both exercise groups but not controls. Further, CD4 T-cells and CD4 naive T-cells were negatively related to changes in IL-6 and osteonectin after HIIT but not MICT, whereas CD8 EMRA T-cells were inversely related to changes in IL-15 after MICT but not HIIT.

Conclusions

Aerobic exercise training alters the frequency of peripheral T-cells associated with immunosenescence in middle aged/older women at high risk of breast cancer, with HIIT (pro-senescent) and MICT (anti-senescent) evoking divergent effects. Identifying the underlying mechanisms and establishing whether exercise-induced changes in peripheral T-cell numbers can alter the risk of developing breast cancer warrants investigation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00266-z.

Rocaglamide Prolonged Allograft Survival by Inhibiting Differentiation of Th1/Th17 Cells in Cardiac Transplantation

BACKGROUND

Aglaia (Meliaceae) species are used for treating autoimmune disorders and allergic diseases in Asian countries. Rocaglamide, an extract obtained from Aglaia species, exhibits suppressive effect by regulating the T cell subset balance and cytokine network in cancer. However, whether it can be used in organ transplantation is unknown. In this study, we investigated the antirejection effect and mechanism of action of rocaglamide in a mouse cardiac allograft model.

METHODS

Survival studies were performed by administering mice with phosphate-buffered saline (PBS) (n = 6) and rocaglamide (n = 8). Heart grafts were monitored until they stopped beating. After grafting, the mice were sacrificed on day 7 for histological, mixed lymphocyte reaction (MLR), enzyme-linked immunosorbent assay (ELISA), and flow cytometric analyses.

RESULTS

Rocaglamide administration significantly prolonged the median survival of the grafts from 7 to 25 days compared with PBS treatment (P < 0.001). On posttransplantation day 7, the rocaglamide-treated group showed a significant decrease in the percentage of Th1 cells (7.9 ± 0.9% vs. 1.58 ± 0.5%, P < 0.001) in the lymph nodes and spleen (8.0 ± 2.5% vs. 2.4 ± 1.3%, P < 0.05). Rocaglamide treatment also significantly inhibited the production of Th17 cells (6.4 ± 1.0% vs. 1.8 ± 0.4%, P < 0.01) in the lymph nodes and spleen (5.9 ± 0.3% vs. 2.9 ± 0.8%, P < 0.01). Furthermore, the prolonged survival of the grafts was associated with a significant decrease in IFN-γ and IL-17 levels. Our results also showed that NF-AT activation was inhibited by rocaglamide, which also induced p38 and Jun N-terminal kinase (JNK) phosphorylation in Jurkat T cells. Furthermore, by using inhibitors that suppressed p38 and JNK phosphorylation, rocaglamide-mediated reduction in NF-AT protein levels was prevented.

CONCLUSION

We identified a new immunoregulatory property of rocaglamide, wherein it was found to regulate oxidative stress response and reduce inflammatory cell infiltration and organ injury, which have been associated with the inhibition of NF-AT activation in T cells.

How to Reliably Define Human CD8+ T-Cell Subsets: Markers Playing Tricks

In recent years, our understanding about the functional complexity of CD8+ T-cell populations has increased tremendously. The immunology field is now facing challenges to translate these insights into phenotypic definitions that correlate reliably with distinct functional traits. This is key to adequately monitor and understand compound immune responses including vaccination and immunotherapy regimens. Here we will summarize our understanding of the current state in the human CD8+ T-cell subset characterization field. We will address how reliably the currently used cell surface markers are connected to differentiation status and function of particular subsets. By restricting ourselves to CD8+ αβ T cells, we will focus mostly on major histocompatibility complex (MHC) class I-restricted virus- and tumor-specific T cells. This comes with a major advantage as fluorescently labeled peptide-loaded MHC class I multimers have been widely used to identify and characterize these cells.

T lymphocyte senescence is attenuated in Parkinson's disease

Background

Immune involvement is well-described in Parkinson’s disease (PD), including an adaptive T lymphocyte response. Given the increasing prevalence of Parkinson’s disease in older age, age-related dysregulation of T lymphocytes may be relevant in this disorder, and we have previously observed changes in age-associated CD8⁺ T cell subsets in mid-stage PD. This study aimed to further characterise T cell immunosenescence in newly diagnosed PD patients, including shifts in CD4⁺ and CD8⁺ subpopulations, and changes in markers of cellular ageing in CD8⁺ T lymphocytes.

Methods

Peripheral blood mononuclear cells were extracted from the blood of 61 newly diagnosed PD patients and 63 age- and sex-matched controls. Flow cytometric analysis was used for immunophenotyping of CD8⁺ and CD4⁺ lymphocyte subsets, and analysis of recent thymic emigrant cells. Telomere length within CD8⁺ T lymphocytes was assessed, as well as the expression of the telomerase reverse transcriptase enzyme (hTERT), and the cell-ageing markers p16^INK4a and p21^CIP1/Waf1.

Results

The number of CD8⁺ TEMRA T cells was found to be significantly reduced in PD patients compared to controls. The expression of p16^INK4a in CD8⁺ lymphocytes was also lower in patients versus controls. Chronic latent CMV infection was associated with increased senescent CD8⁺ lymphocytes in healthy controls, but this shift was less apparent in PD patients.

Conclusions

Taken together, our data demonstrate a reduction in CD8⁺ T cell replicative senescence which is present at the earliest stages of Parkinson’s disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02287-9.

IgG Immune Complexes Inhibit Naïve T Cell Proliferation and Suppress Effector Function in Cytotoxic T Cells

Elevated levels of circulating immune complexes are associated with autoimmunity and with worse prognoses in cancer. Here, we examined the effects of well-defined, soluble immune complexes (ICs) on human peripheral T cells. We demonstrate that IgG-ICs inhibit the proliferation and differentiation of a subset of naïve T cells but stimulate the division of another naïve-like T cell subset. Phenotypic analysis by multi-parameter flow cytometry and RNA-Seq were used to characterize the inhibited and stimulated T cells revealing that the inhibited subset presented immature features resembling those of recent thymic emigrants and non-activated naïve T cells, whereas the stimulated subset exhibited transcriptional features indicative of a more differentiated, early memory progenitor with a naïve-like phenotype. Furthermore, we show that while IgG1-ICs do not profoundly inhibit the proliferation of memory T cells, IgG1-ICs suppress the production of granzyme-β and perforin in cytotoxic memory T cells. Our findings reveal how ICs can link humoral immunity and T cell function.

FRugally Optimized DNA Octomer (FRODO) qPCR Measurement of HIV and SIV in Human and Nonhuman Primate Samples

Quantitative polymerase chain reactions (qPCRs) are commonly employed to enumerate genes of interest among particular biological samples. Insertion of PCR amplicons into plasmid DNA is a mainstay for creation of known quantities of target sequences to standardize qPCRs. Typically, one amplicon is inserted into one plasmid construct, and the plasmid is then amplified, purified, serially diluted, and quantified to be used to enumerate target sequences in unknown samples. As qPCR is often used to detect multiple amplicons simultaneously, individual qPCR standards are often desired to normalize one to another. Here we report a single plasmid containing eight amplicons, which can be used to quantify several different strains of simian immunodeficiency virus and human immunodeficiency virus, cell number equivalents for humans and nonhuman primates, T cell receptor excision circles, and bacterial 16S DNA. This FRugally Optimized DNA Octomer (FRODO) plasmid was created and standardized to quantify all eight PCR amplicons. © 2021 US Government. Basic Protocol 1: Total genomic DNA extraction from primary cells Basic Protocol 2: Quantitative PCR for viral, bacterial, and cell number equivalents Support Protocol: Purification, quantification, and storage of FRODO standard plasmid DNA.

Characterization of CD31 expression in CD4+ and CD8+T cell subpopulations in chronic untreated HIV infection

BACKGROUND

The platelet endothelial cell adhesion molecule-1 (PECAM-1) or CD31 has been involved in regulation of T-cell tolerance, activation, survival and homing in mice cells. However, there is limited knowledge about the expression pattern and role of this molecule in human T cells, particularly in conditions of chronic immune activation.

OBJECTIVES

We explored CD31 expression in T cell differentiation subsets of individuals with untreated HIV infection and in non-HIV-infected controls. We also assessed phenotypic differences between CD31+ and CD31- subsets in memory and terminally differentiated (TEMRA) CD4+ and CD8 + T cells.

METHODS

Forty-one individuals with untreated HIV infection and 34 non-HIV-infected controls were included in the study. We compared the expression of CD31 in CD4+ and CD8 + T cells across stages of differentiation in the two study groups by flow cytometry. We also analyzed the expression of CD57 (a marker of senescence), Ki67 (a marker of cycling cells), PD-1 (a marker of exhaustion), and CD38/HLA-DR (a marker of immune activation) on memory and TEMRA CD31+ and CD31- T cells.

RESULTS

CD31 expression was significantly higher in CD8 + T cells than in CD4 + T cells, measured as frequency, absolute numbers and median fluorescence intensity (MFI), in both study groups (p < 0.0001 in all cases). Intermediate differentiation subsets of CD4+ and CD8 + T cells expressed higher levels of CD31 in the context of HIV infection (p < 0.001 in all cases). CD31 expression frequency decreased with cellular differentiation of CD4+ and CD8 + T cells in both groups, but this decrease was steeper in individuals without HIV infection (CD4+: p < 0.001 and CD8+: p < 0.0001). As expected, memory and TEMRA CD4+ and CD8 + T cells expressed significantly higher levels of CD57, PD-1, Ki67 and CD38/HLA-DR in HIV-infected compared to non-HIV-infected individuals (p < 0.01 in all cases). CD31 expression was associated with lower activation of memory (but not TEMRA) CD4 + T cells in non-HIV-infected persons, an effect not observed in the HIV-infected group. CD31 expression on memory CD8 + T cells of HIV-infected individuals was associated higher levels of PD-1 (p = 0.0019) and CD38/HLADR (p = 0.0345), and higher PD-1 expression on CD8 + TEMRA (p = 0.0024), an effect not observed in non-HIV-infected individuals.

CONCLUSION

In the context of HIV-associated chronic immune activation, specifically on memory CD8 + T cells, CD31 expression was associated with higher PD-1 and CD38/HLA-DR co-expression, suggesting that CD31 expression may result from an insufficient attempt to contain T cell exhaustion and activation. CD31-targeted therapies may contribute to modulate these cellular responses.

Evaluation of Thymic Output and Regulatory T Cells in Kidney Transplant Recipients with Chronic Antibody-Mediated Rejection

Background

Regulatory T cells (Tregs) and recent thymic emigrants (RTEs) have an essential role in the regulation of allogeneic immune responses. However, their mechanisms of action in chronic antibody-mediated rejection (cAMR) are still unclear. In this study, we aimed to compare Treg and RTE levels between stable graft function (SGF) patients and cAMR subjects after kidney transplantation.

Method

Mononuclear cells (MNs) were separated from peripheral blood, and flow cytometry analysis was performed for detection of CD4⁺ and CD25^high as Treg markers and CD4⁺, CD31⁺, and CD45RA⁺ as RTE immunophenotyping markers.

Result

The level of peripheral Treg cells was significantly lower in cAMR subjects in comparison to stable graft function patients. Moreover, SGF patients who had received cyclosporine A had a higher level of Treg in comparison to the tacrolimus recipients. Nevertheless, the RTE level between SGF and cAMR patients did not show any significant differences.

Conclusion

It seems that Treg cells are significantly associated with transplant outcomes in cAMR patients, and prescribed immunosuppressive drugs can influence the frequency of this crucial subset of T cells. Although these drugs are beneficial and inevitable for allograft maintenance, more investigations are needed to elucidate their complete effects on different immune cell subsets which some of them like Tregs are in favor of transplant tolerance. Besides, the thymic output is seemingly not a beneficial biomarker for predicting cAMR; however, more in vivo and in vitro studies are needed for revealing the precise role of Tregs and RTEs in the transplantation context.

T cell markers recount the course of immunosenescence in healthy individuals and chronic kidney disease

Aging results in substantial changes in almost all cellular subpopulations within the immune system, including functional and phenotypic alterations. T lymphocytes, as the main representative population of cellular immunity, have been extensively studied in terms of modifications and adjustments during aging. Phenotypic alterations are attributed to three main mechanisms; a reduction of naïve T cell population with a shift to more differentiated forms, a subsequent oligoclonal expansion of naïve T cells characterized by repertoire restriction, and replicative insufficiency after repetitive activation. These changes and the subsequent phenotypic disorders are comprised in the term "immunosenescence". Similar changes seem to occur in chronic kidney disease, with T cells of young patients resembling those of healthy older individuals. A broad range of surface markers can be utilized to identify immunosenescent T cells. In this review, we will discuss the most important senescence markers and their potential connection with impaired renal function.

CD103 Deficiency Promotes Autism (ASD) and Attention-Deficit Hyperactivity Disorder (ADHD) Behavioral Spectra and Reduces Age-Related Cognitive Decline

The incidence of autism spectrum disorders (ASD) and attention deficit hyperactivity disorder (ADHD), which frequently co-occur, are both rising. The causes of ASD and ADHD remain elusive, even as both appear to involve perturbation of the gut-brain-immune axis. CD103 is an integrin and E-cadherin receptor most prominently expressed on CD8 T cells that reside in gut, brain, and other tissues. CD103 deficiency is well-known to impair gut immunity and resident T cell function, but it's impact on neurodevelopmental disorders has not been examined. We show here that CD8 T cells influence neural progenitor cell function, and that CD103 modulates this impact both directly and potentially by controlling CD8 levels in brain. CD103 knockout (CD103KO) mice exhibited a variety of behavioral abnormalities, including superior cognitive performance coupled with repetitive behavior, aversion to novelty and social impairment in females, with hyperactivity with delayed learning in males. Brain protein markers in female and male CD103KOs coincided with known aspects of ASD and ADHD in humans, respectively. Surprisingly, CD103 deficiency also decreased age-related cognitive decline in both sexes, albeit by distinct means. Together, our findings reveal a novel role for CD103 in brain developmental function, and identify it as a unique factor linking ASD and ADHD etiology. Our data also introduce a new animal model of combined ASD and ADHD with associated cognitive benefits, and reveal potential therapeutic targets for these disorders and age-related cognitive decline.

T cell regeneration after immunological injury

Following periods of haematopoietic cell stress, such as after chemotherapy, radiotherapy, infection and transplantation, patient outcomes are linked to the degree of immune reconstitution, specifically of T cells. Delayed or defective recovery of the T cell pool has significant clinical consequences, including prolonged immunosuppression, poor vaccine responses and increased risks of infections and malignancies. Thus, strategies that restore thymic function and enhance T cell reconstitution can provide considerable benefit to individuals whose immune system has been decimated in various settings. In this Review, we focus on the causes and consequences of impaired adaptive immunity and discuss therapeutic strategies that can recover immune function, with a particular emphasis on approaches that can promote a diverse repertoire of T cells through de novo T cell formation.

Interleukin-8 as a candidate for thymoma identification and recurrence surveillance

Thymoma is the most common tumor of the anterior mediastinum. Routine imaging methods such as computed tomography or magnetic resonance imaging often lead to misdiagnosis between thymoma and other thymic abnormalities. Therefore, urgently needed is to develop a new diagnostic strategy. Here we identify interleukin-8 (IL-8) as a biomarker for auxiliary diagnosis of thymoma. We find that IL-8 levels in naïve T cells are markedly elevated in patients with thymoma compared to those with other thymic tumors. IL-8 levels in naive T cells are significantly decreased after surgical resection in thymoma patients, and rise again when thymoma recurs. A receiver operating characteristic curve analysis shows that IL-8 evaluation performs well in thymoma identification, with high specificities and sensitivities. We also observe significant clinical relevance between IL-8 levels in naïve T cells and clinicopathological features. In conclusion, our study suggests that IL-8 is a biomarker for thymoma identification and recurrence surveillance.

Inborn Errors of Adaptive Immunity in Down Syndrome

Down syndrome fits an immunophenotype of combined immunodeficiency with immunodysregulation, manifesting with increased susceptibility to infections, autoimmunity, autoinflammatory diseases, and hematologic malignancies. Qualitative and quantitative alterations in innate and adaptive immunity are found in most individuals with Down syndrome. However, there is substantial heterogeneity and no correlation between immunophenotype and clinical presentation. Previously, it was thought that the immunological changes in Down syndrome were caused by precocious aging. We emphasize in this review that the immune system in Down syndrome is intrinsically different from the very beginning. The overexpression of specific genes located on chromosome 21 contributes to immunodeficiency and immunodysregulation, but gene expression differs between genes located on chromosome 21 and depends on tissue and cell type. In addition, trisomy 21 results in gene dysregulation of the whole genome, reflecting the complex nature of this syndrome in comparison to well-known inborn errors of immunity that result from monogenic germline mutations. In this review, we provide an updated overview focusing on inborn errors of adaptive immunity in Down syndrome.

Transcriptome profiling of human thymic CD4+ and CD8+ T cells compared to primary peripheral T cells

Background

The thymus is a highly specialized organ of the immune system where T cell precursors develop and differentiate into self-tolerant CD4+ or CD8+ T cells. No studies to date have investigated how the human transcriptome profiles differ, between T cells still residing in the thymus and T cells in the periphery.

Results

We have performed high-throughput RNA sequencing to characterize the transcriptomes of primary single positive (SP) CD4+ and CD8+ T cells from infant thymic tissue, as well as primary CD4+ and CD8+ T cells from infant and adult peripheral blood, to enable the comparisons across tissues and ages. In addition, we have assessed the expression of candidate genes related to autoimmune diseases in thymic CD4+ and CD8+ T cells. The thymic T cells showed the largest number of uniquely expressed genes, suggesting a more diverse transcription in thymic T cells. Comparing T cells of thymic and blood origin, revealed more differentially expressed genes, than between infant and adult blood. Functional enrichment analysis revealed an over-representation of genes involved in cell cycle and replication in thymic T cells, whereas infant blood T cells were dominated by immune related terms. Comparing adult and infant blood T cells, the former was enriched for inflammatory response, cytokine production and biological adhesion, while upregulated genes in infant blood T cells were associated with cell cycle, cell death and gene expression.

Conclusion

This study provides valuable insight into the transcriptomes of the human primary SP T cells still residing within the thymus, and offers a unique comparison to primary blood derived T cells. Interestingly, the majority of autoimmune disease associated genes were expressed in one or more T cell subset, however ~ 11% of these were not expressed in frequently studied adult peripheral blood.

Generation and Regeneration of Thymic Epithelial Cells

The thymus is unique in its ability to support the maturation of phenotypically and functionally distinct T cell sub-lineages. Through its combined production of MHC-restricted conventional CD4⁺ and CD8⁺, and Foxp3⁺ regulatory T cells, as well as non-conventional CD1d-restricted iNKT cells and invariant γδT cells, the thymus represents an important orchestrator of immune system development and control. It is now clear that thymus function is largely determined by the availability of stromal microenvironments. These specialized areas emerge during thymus organogenesis and are maintained throughout life. They are formed from both epithelial and mesenchymal components, and collectively they support a stepwise program of thymocyte development. Of these stromal cells, cortical, and medullary thymic epithelial cells represent functional components of thymic microenvironments in both the cortex and medulla. Importantly, a key feature of thymus function is that levels of T cell production are not constant throughout life. Here, multiple physiological factors including aging, stress and pregnancy can have either short- or long-term detrimental impact on rates of thymus function. Here, we summarize our current understanding of the development and function of thymic epithelial cells, and relate this to strategies to protect and/or restore thymic epithelial cell function for therapeutic benefit.

Thalidomide with blockade of co-stimulatory molecules prolongs the survival of alloantigen-primed mice with cardiac allografts

Background

Miscellaneous memory cell populations that exist before organ transplantation are crucial barriers to transplantation. In the present study, we used a skin-primed heart transplantation model in mouse to evaluate the abilities of Thalidomide (TD), alone or in combination with co-stimulatory blockade, using monoclonal antibodies (mAbs) against memory T cells and alloantibodies to prolong the second cardiac survival.

Results

In the skin-primed heart transplantation model, TD combined with mAbs significantly prolonged the second cardiac survival, accompanied by inhibition of memory CD8⁺ T cells. This combined treatment enhanced the CD4⁺Foxp3⁺ regulatory T cells ratio in the spleen, restrained the infiltration of lymphocytes into the allograft, and suppressed the allo-response of spleen T cells in the recipient. The levels of allo-antibodies also decreased in the recipient serum. In addition, we detected low levels of the constitutions of the lytic machinery of cytotoxic cells, which cause allograft damage.

Conclusions

Our study indicated a potential synergistic action of TD in combination with with mAbs to suppress the function of memory T cells and increase the survival of second allografts in alloantigen-primed mice.

Thymic activity in immune recovery after allogeneic hematopoietic stem cell transplantation in children

Thymic output was studied prospectively in 52 children who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). Thymic activity was assessed by quantification of recent thymic emigrants (RTE) discriminated from the rest of naive T cells by immunophenotype CD3+/CD4+/CD31+/CD45RA+. Thymic output was analyzed in correlation with the kinetics of immune recovery and in relation to other potential risk factors that may influence thymopoiesis: underlying disease, type of HSCT, source of stem cells, age of recipient and donor, type of conditioning, implemented graft versus host disease (GvHD) prophylaxis, viral reactivations (herpes viruses cytomegalovirus - CMV, Epstein-Barr virus - EBV, adenovirus - ADV, BK virus - BKV), occurrence and grade of both acute and chronic graft versus host disease (aGvHD, cGvHD) and number of transplanted CD34 cells/kg. The absolute count of RTE in peripheral blood was evaluated at 6 time points: before the conditioning and on days +15, +30, +60 , +90 and +180 after HSCT. Occurrence of grade II-IV aGvHD was the most important factor associated with low RTE counts after HSCT. History of malignant disease, and transplantation from matched unrelated donor were risk factors for lower thymic output. We found a weak inverse correlation between the age of the recipient and thymic output on post-HSCT day +180. Source of stem cells, type of conditioning, viral reactivations, occurrence of chronic GvHD, age of the donor and the number of transplanted CD34 cells/kg did not affect thymopoiesis in our study group. These preliminary findings and identification of risk factors for deterioration of thymic activity may in the future help in selecting candidates for thymus rejuvenation strategies.

CXCR3 Identifies Human Naive CD8+ T Cells with Enhanced Effector Differentiation Potential

In mice, the ability of naive T (TN) cells to mount an effector response correlates with TCR sensitivity for self-derived Ags, which can be quantified indirectly by measuring surface expression levels of CD5. Equivalent findings have not been reported previously in humans. We identified two discrete subsets of human CD8+ TN cells, defined by the absence or presence of the chemokine receptor CXCR3. The more abundant CXCR3+ TN cell subset displayed an effector-like transcriptional profile and expressed TCRs with physicochemical characteristics indicative of enhanced interactions with peptide-HLA class I Ags. Moreover, CXCR3+ TN cells frequently produced IL-2 and TNF in response to nonspecific activation directly ex vivo and differentiated readily into Ag-specific effector cells in vitro. Comparative analyses further revealed that human CXCR3+ TN cells were transcriptionally equivalent to murine CXCR3+ TN cells, which expressed high levels of CD5. These findings provide support for the notion that effector differentiation is shaped by heterogeneity in the preimmune repertoire of human CD8+ T cells.

Cell generation dynamics underlying naive T-cell homeostasis in adult humans

Thymic involution and proliferation of naive T cells both contribute to shaping the naive T-cell repertoire as humans age, but a clear understanding of the roles of each throughout a human life span has been difficult to determine. By measuring nuclear bomb test–derived ¹⁴C in genomic DNA, we determined the turnover rates of CD4⁺ and CD8⁺ naive T-cell populations and defined their dynamics in healthy individuals ranging from 20 to 65 years of age. We demonstrate that naive T-cell generation decreases with age because of a combination of declining peripheral division and thymic production during adulthood. Concomitant decline in T-cell loss compensates for decreased generation rates. We investigated putative mechanisms underlying age-related changes in homeostatic regulation of CD4+ naive T-cell turnover, using mass cytometry to profile candidate signaling pathways involved in T-cell activation and proliferation relative to CD31 expression, a marker of thymic proximity for the CD4+ naive T-cell population. We show that basal nuclear factor κB (NF-κB) phosphorylation positively correlated with CD31 expression and thus is decreased in peripherally expanded naive T-cell clones. Functionally, we found that NF-κB signaling was essential for naive T-cell proliferation to the homeostatic growth factor interleukin (IL)-7, and reduced NF-κB phosphorylation in CD4⁺CD31⁻ naive T cells is linked to reduced homeostatic proliferation potential. Our results reveal an age-related decline in naive T-cell turnover as a putative regulator of naive T-cell diversity and identify a molecular pathway that restricts proliferation of peripherally expanded naive T-cell clones that accumulate with age.

Our pool of naive T cells is critical for protection against new infections and cancers. By measuring remnant 14C from 1960s nuclear bomb blasts that has been incorporated into cellular DNA, this study defines the average age of the naive T-cell pool in healthy adults, revealing the slow, regulated turnover of the naive T-cell pool, supporting its maintenance for a human lifetime.

Memory CD4+ T cells are generated in the human fetal intestine

The fetus is thought to be protected from exposure to foreign antigens, yet CD45RO+ T cells reside in the fetal intestine. Here we combined functional assays with mass cytometry, single-cell RNA sequencing and high-throughput T cell antigen receptor (TCR) sequencing to characterize the CD4+ T cell compartment in the human fetal intestine. We identified 22 CD4+ T cell clusters, including naive-like, regulatory-like and memory-like subpopulations, which were confirmed and further characterized at the transcriptional level. Memory-like CD4+ T cells had high expression of Ki-67, indicative of cell division, and CD5, a surrogate marker of TCR avidity, and produced the cytokines IFN-γ and IL-2. Pathway analysis revealed a differentiation trajectory associated with cellular activation and proinflammatory effector functions, and TCR repertoire analysis indicated clonal expansions, distinct repertoire characteristics and interconnections between subpopulations of memory-like CD4+ T cells. Imaging mass cytometry indicated that memory-like CD4+ T cells colocalized with antigen-presenting cells. Collectively, these results provide evidence for the generation of memory-like CD4+ T cells in the human fetal intestine that is consistent with exposure to foreign antigens.

Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood

It is widely accepted that aging is accompanied by remodelling of the immune system including thymic atrophy and increased frequency of senescent T cells, leading to immune compromise. However, physical activity, which influences immunity but declines dramatically with age, is not considered in this literature. We assessed immune profiles in 125 adults (55-79 years) who had maintained a high level of physical activity (cycling) for much of their adult lives, 75 age-matched older adults and 55 young adults not involved in regular exercise. The frequency of naïve T cells and recent thymic emigrants (RTE) were both higher in cyclists compared with inactive elders, and RTE frequency in cyclists was no different to young adults. Compared with their less active counterparts, the cyclists had significantly higher serum levels of the thymoprotective cytokine IL-7 and lower IL-6, which promotes thymic atrophy. Cyclists also showed additional evidence of reduced immunesenescence, namely lower Th17 polarization and higher B regulatory cell frequency than inactive elders. Physical activity did not protect against all aspects of immunesenescence: CD28^-ve CD57^+ve senescent CD8 T-cell frequency did not differ between cyclists and inactive elders. We conclude that many features of immunesenescence may be driven by reduced physical activity with age.

Exploring viral reservoir: The combining approach of cell sorting and droplet digital PCR

Combined antiretroviral therapy (cART) blocks different steps of HIV replication and maintains plasma viral RNA at undetectable levels. The virus can remain in long-living cells and create a reservoir where HIV can restart replicating after cART discontinuation. A persistent viral production triggers and maintains a persistent immune activation, which is a well-known feature of chronic HIV infection, and contributes either to precocious aging, or to the increased incidence of morbidity and mortality of HIV positive patients. The new frontier of the treatment of HIV infection is nowadays eradication of the virus from all host cells and tissues. For this reason, it is crucial to have a clear and precise idea of where the virus hides, and which are the cells that keep it silent. Important efforts have been made to improve the detection of viral reservoirs, and new techniques are now giving the opportunity to characterize viral reservoirs. Among these techniques, a strategic approach based upon cell sorting and droplet digital PCR (ddPCR) is opening new horizons and opportunities of research. This review provides an overview of the methods that combine cell sorting and ddPCR for the quantification of HIV DNA in different cell types, and for the detection of its maintenance.

Alterations in the Thymic Selection Threshold Skew the Self-Reactivity of the TCR Repertoire in Neonates

Neonatal and adult T cells differ in their effector functions. Although it is known that cell-intrinsic differences in mature T cells contribute to this phenomenon, the factors involved remain unclear. Given emerging evidence that the binding strength of a TCR for self-peptide presented by MHC (self-pMHC) impacts T cell function, we sought to determine whether altered thymic selection influences the self-reactivity of the TCR repertoire during ontogeny. We found that conventional and regulatory T cell subsets in the thymus of neonates and young mice expressed higher levels of cell surface CD5, a surrogate marker for TCR avidity for self-pMHC, as compared with their adult counterparts, and this difference in self-reactivity was independent of the germline bias of the neonatal TCR repertoire. The increased binding strength of the TCR repertoire for self-pMHC in neonates was not solely due to reported defects in clonal deletion. Rather, our data suggest that thymic selection is altered in young mice such that thymocytes bearing TCRs with low affinity for self-peptide are not efficiently selected into the neonatal repertoire, and stronger TCR signals accompany both conventional and regulatory T cell selection. Importantly, the distinct levels of T cell self-reactivity reflect physiologically relevant differences based on the preferential expansion of T cells from young mice to fill a lymphopenic environment. Therefore, differences in thymic selection in young versus adult mice skew the TCR repertoire, and the relatively higher self-reactivity of the T cell pool may contribute to the distinct immune responses observed in neonates.

Microvascular Complications in Type 1 Diabetes: A Comparative Analysis of Patients Treated with Autologous Nonmyeloablative Hematopoietic Stem-Cell Transplantation and Conventional Medical Therapy

OBJECTIVE

To explore the impact on microvascular complications, long-term preservation of residual B-cell function and glycemic control of patients with type 1 diabetes treated with autologous nonmyeloablative hematopoietic stem-cell transplantation (AHST) compared with conventional medical therapy (CT).

RESEARCH DESIGN AND METHODS

Cross-sectional data of patients treated with AHST were compared with patients who received conventional therapy from the Brazilian Type 1 Diabetes Study Group, the largest multicenter observational study in type 1 diabetes mellitus in Brazil. Both groups of patients had diabetes for 8 years on average. An assessment comparison was made on the presence of microvascular complications, residual function of B cell, A1c, and insulin dose of the patients.

RESULTS

After a median of 8 years of diagnosis, none of the AHST-treated patients (n = 24) developed microvascular complications, while 21.5% (31/144) had at least one (p < 0.005) complication in the CT group (n = 144). Furthermore, no case of nephropathy was reported in the AHST group, while 13.8% of CT group (p < 0.005) developed nephropathy during the same period. With regard of residual B-cell function, the percentage of individuals with predicted higher C-peptide levels (IDAA1C ≤ 9) was about 10-fold higher in the AHST group compared with CT (75 vs. 8.3%) (p < 0.001) group. Among AHST patients, 54.1% (13/24) had the HbA1c < 7.0 compared with 13.1% in the CT (p < 0.001) group.

CONCLUSION

Patients with newly diagnosed type 1 diabetes treated with AHST presented lower prevalence of microvascular complications, higher residual B-cell function, and better glycemic control compared with the CT group.

Self-reactivity as the necessary cost of maintaining a diverse memory T-cell repertoire

The adaptive immune system is expected to protect the host from infectious agents and malignancies, while avoiding robust activation against self-peptides. However, T cells are notoriously inept at protection whenever the pathogen or tumor is persistent in the body for longer periods of time. While this has been thought of as an adaptation to limit the immunopathology from continued effector T-cell responses, it is also likely an extension of the T cell's intrinsic mechanisms which evolved to tolerate self-peptides. Here we deliberate on how the need to tolerate self-peptides might stem from a paradoxical requirement-the utility of such molecules in maintaining a diverse repertoire of pathogen-specific memory T cells in the body. Understanding the mechanisms underlying this intriguing nexus, therefore, has the potential to reveal therapeutic strategies not only for improving immune responses to chronic infections and tumors but also the long-term efficacy of vaccines aimed at cellular immune responses.

Role of Wnt3a expressed by dendritic cells in the activation of canonical Wnt signaling and generation of memory T cells during primary immune responses

The presence of memory T cells (T_Ms) hinders transplant survival. Dendritic cells (DCs) induce the generation of T_Ms during primary immune responses. However, the specific mechanisms are unclear. In this study, we constructed a Wnt3a-expressing adenovirus and used small interfering RNA (siRNA) targeting Wnt3a to investigate the influence of Wnt3a expression in DCs on the generation of T_Ms during primary immune responses. Our results demonstrated that the Wnt3a expression levels in DCs influenced the generation of T_Ms after 5days in co-culture with naïve T cells through activation of the Wnt canonical pathway. Interleukin-7 secretion levels in supernatants of DC/T_Ns co-cultures showed a similar pattern of Wnt3a expression levels in DCs. These findings provide a better understanding of T_Ms generation mechanisms that might be useful to improve transplant outcomes.

Immune activation is associated with decreased thymic function in asymptomatic, untreated HIV-infected individuals

Background

Reduced thymic function causes poor immunological reconstitution in human immunodeficiency virus (HIV)-positive patients on combined antiretroviral therapy (cART). The association between immune activation and thymic function in asymptomatic HIV-positive treatment-naive individuals has thus far not been investigated.

Aims and objectives

To optimise a five-colour flow cytometric assay for measurement of thymic function by measuring recent thymic emigrants (RTEs) in treatment-naive HIV-infected patients and healthy controls and correlate results with levels of immune activation, CD4 counts and viral load.

Methods

Blood obtained from 53 consenting HIV-positive individuals and 32 controls recruited from HIV prevention and testing clinic in Cape Town, South Africa. RTEs were measured (CD3⁺/CD4⁺/CD45RA⁺/CD31⁺/CD62L⁺) and levels were correlated with CD4 counts of HIV-infected individuals, log viral load and levels of immune activation (CD8⁺/CD38⁺ T-cells).

Results

HIV-infected individuals had reduced frequencies of RTEs when compared to controls (p = 0.0035). Levels of immune activation were inversely correlated with thymic function (p = 0.0403), and the thymic function in HIV-infected individuals showed no significant correlation with CD4 counts (p = 0.31559) and viral load (p = 0.20628).

Conclusions

There was impaired thymic function in HIV-infected individuals, which was associated with increased levels of immune activation. The thymic dysfunction was not associated with CD4 counts and viral load. Immune activation may result in inflammatory damage to the thymus and subsequent thymic dysfunction, and CD4 counts and viral load may not necessarily reflect thymic dysfunction in HIV.

Recent thymic emigrants are tolerized in the absence of inflammation

T cell development requires a period of postthymic maturation. Why this is the case has remained a mystery, particularly given the rigors of intrathymic developmental checkpoints, successfully traversed by only ∼5% of thymocytes. We now show that the first few weeks of T cell residence in the lymphoid periphery define a period of heightened susceptibility to tolerance induction to tissue-restricted antigens (TRAs), the outcome of which depends on the context in which recent thymic emigrants (RTEs) encounter antigen. After encounter with TRAs in the absence of inflammation, RTEs exhibited defects in proliferation, diminished cytokine production, elevated expression of anergy-associated genes, and diminished diabetogenicity. These properties were mirrored in vitro by enhanced RTE susceptibility to regulatory T cell-mediated suppression. In the presence of inflammation, RTEs and mature T cells were, in contrast, equally capable of inducing diabetes, proliferating, and producing cytokines. Thus, recirculating RTEs encounter TRAs during a transitional developmental stage that facilitates tolerance induction, but inflammation converts antigen-exposed, tolerance-prone RTEs into competent effector cells.

Distinctive Leukocyte Subpopulations According to Organ Type in Cynomolgus Macaques

Cynomolgus macaques (CYNO; Macaca fascicularis) are a well-established NHP model used for studies in immunology. To provide reference values on the baseline cell distributions in the hematopoietic and lymphoid organs (HLO) of these animals, we used flow cytometry to analyze the peripheral blood, bone marrow, mesenteric lymph nodes, spleen, and thymus of a cohort of male, adult, research-naïve, Mauritian CYNO. Our findings demonstrate that several cell distribution patterns differ between CYNO and humans. First, the CD4(+):CD8(+) T-cell ratio is lower in CYNO compared with humans. Second, the peripheral blood of CYNO contains a population of CD4(+)CD8(+) T cells. Third, the CD31 level was elevated in all organs studied, suggesting that CD31 may not be an accurate marker of recent thymic emigrants within the CD4(+) T cells of CYNO. Finally the B-cell population is lower in CYNO compared with humans. In summary, although the majority of immune cell populations are similar between cynomolgus macaques and humans, several important differences should be considered when using CYNO in immunologic studies. Our current findings provide valuable information to not only researchers but also veterinarians working with CYNO at research centers, in zoos, or in the wild.

Lymphoid and Myeloid Recovery in Rhesus Macaques Following Total Body X-Irradiation

Recovery from severe immunosuppression requires hematopoietic stem cell reconstitution and effective thymopoiesis to restore a functional immune cell repertoire. Herein, a model of immune cell reconstitution consequent to potentially lethal doses of irradiation is described, which may be valuable in evaluating potential medical countermeasures. Male rhesus macaques were total body irradiated by exposure to 6.00 Gy 250 kVp x-radiation (midline tissue dose, 0.13 Gy min), resulting in an approximate LD10/60 (n = 5/59). Animals received medical management, and hematopoietic and immune cell recovery was assessed (n ≤ 14) through 370 d post exposure. A subset of animals (n ≤ 8) was examined through 700 d. Myeloid recovery was assessed by neutrophil and platelet-related parameters. Lymphoid recovery was assessed by the absolute lymphocyte count and FACS-based phenotyping of B- and T-cell subsets. Recent thymic emigrants were identified by T cell receptor excision circle quantification. Severe neutropenia, lymphopenia, and thrombocytopenia resolved within 30 d. Total CD3+ cells μL required 60 d to reach values 60% of normal, followed by subsequent slow recovery to approximately normal by 180 d post irradiation. Recovery of CD3+4+ and CD3+8+ cell memory and naïve subsets were markedly different. Memory populations were ≥ 100% of normal by day 60, whereas naïve populations were only 57% normal at 180 d and never fully recovered to baseline post irradiation. Total (CD20+) B cells μL were within normal levels by 77 d post exposure. This animal model elucidates the variable T- and B-cell subset recovery kinetics after a potentially lethal dose of total-body irradiation that are dependent on marrow-derived stem and progenitor cell recovery, peripheral homeostatic expansion, and thymopoiesis.

Arsenic trioxide inhibits accelerated allograft rejection mediated by alloreactive CD8(+) memory T cells and prolongs allograft survival time

CD8(+) memory T (Tm) cells are a significant barrier to transplant tolerance induction in alloantigen-primed recipients, and are insensitive to existing clinical immunosuppressants. Here, we studied the inhibition of CD8(+) Tm cells by arsenic trioxide (As2O3) for the first time. Alloantigen-primed CD8(+) Tm cells were transferred to T cell immunodeficient nude mice. The mice were subjected to heart allotransplantation, and treated with As2O3. The transplant survival time was determined, and the inhibitory effects of As2O3 on CD8(+) Tm cell-mediated immune rejection were assessed through serological studies and inspection of the transplanted heart and lymphoid organs. We found that As2O3 treatment prolonged the mean survival time of the graft and reduced the number of CD8(+) Tm cells in the spleen and lymph nodes. The expression of the genes encoding interleukin (IL)-2, and IFN-γ was reduced, while expression of IL-10 and transforming growth factor-β was increased in the transplant. Our findings show that As2O3 treatment inhibits allograft rejection mediated by alloreactive CD8(+) Tm cells in the mouse heart transplantation model.

T cells in the control of organ-specific autoimmunity

Immune tolerance is critical to the avoidance of unwarranted immune responses against self antigens. Multiple, non-redundant checkpoints are in place to prevent such potentially deleterious autoimmune responses while preserving immunity integral to the fight against foreign pathogens. Nevertheless, a large and growing segment of the population is developing autoimmune diseases. Deciphering cellular and molecular pathways of immune tolerance is an important goal, with the expectation that understanding these pathways will lead to new clinical advances in the treatment of these devastating diseases. The vast majority of autoimmune diseases develop as a consequence of complex mechanisms that depend on genetic, epigenetic, molecular, cellular, and environmental elements and result in alterations in many different checkpoints of tolerance and ultimately in the breakdown of immune tolerance. The manifestations of this breakdown are harmful inflammatory responses in peripheral tissues driven by innate immunity and self antigen-specific pathogenic T and B cells. T cells play a central role in the regulation and initiation of these responses. In this Review we summarize our current understanding of the mechanisms involved in these fundamental checkpoints, the pathways that are defective in autoimmune diseases, and the therapeutic strategies being developed with the goal of restoring immune tolerance.

Functional dynamics of Foxp3⁺ regulatory T cells in mice and humans

Forkhead box protein 3 (Foxp3)(+) regulatory T (Treg) cells are critical mediators for the establishment of self-tolerance and immune homeostasis and for the control of pathology in various inflammatory responses. While Foxp3(+) Treg cells often control immune responses in secondary lymphoid tissues, they must also traffic to and persist within non-lymphoid tissues, where they integrate various environmental cues to coordinate and adapt their effector acitvities in these sites. In recent years, our group has made use of several mouse models, including the non-obese diabetic model of type 1 diabetes, to characterize the factors, which impact the homeostasis, function, and reprogramming potential of Foxp3(+) Treg cells in situ. In addition, our recent work shows that Foxp3(+) Treg cells possess distinct post-transcriptional mechanisms of gene regulation, namely mRNA translation, to modulate tissue-specific inflammatory responses. In humans, there is a pressing need for reliable markers of FOXP3(+) Treg cells and their related function in blood and tissue. Experimental progress in our group has enabled us to discover novel markers of FOXP3(+) Treg cell (dys)function and unique gene signatures that discriminate effector and Treg cells, as well as functional and dysfunctional FOXP3(+) Treg cells.

Integrin αEβ7: molecular features and functional significance in the immune system

Alpha E beta 7 (αEβ7) is an α-I domain-containing integrin that is highly expressed by a variety of leukocyte populations at mucosal sites including intraepithelial T cells, dendritic cells, mast cells, and T regulatory cells (Treg). Expression depends largely or solely on transforming growth factor beta (TGF-β) isoforms. The best characterized ligand for αEβ7 is E-cadherin on epithelial cells, though there is evidence of a second ligand in the human system. An exposed acidic residue on the distal aspect of E-cadherin domain 1 interacts with the MIDAS site in the αE α-I domain. By binding to E-cadherin, αEβ7 contributes to mucosal specific retention of leukocytes within epithelia. Studies on αE knockout mice have identified an additional important function for this integrin in allograft rejection and have also indicated that it may have a role in immunoregulation. Recent studies point to a multifaceted role for αEβ7 in regulating both innate and acquired immune responses to foreign antigen.