Direct evidence for thymic function in adult humans

eHealth mindfulness-based music therapy for patients undergoing allogeneic hematopoietic stem cell transplantation: A pilot randomized controlled trial protocol

BACKGROUND

Allogeneic stem cell transplantation (allo-SCT) is the preferred therapy for patients with high-risk or relapsed hematologic malignancies, but may be complicated by psychological distress (e.g., depression, anxiety) and symptom burden (e.g., fatigue, pain). Mindfulness-based music therapy (MBMT), a relatively novel integrative medicine intervention that draws from mindfulness and music therapy principles, has shown promise in improving psychosocial outcomes and symptom burden in cancer patients. We outline an eHealth-based MBMT (eMBMT) intervention protocol examining: (1) feasibility, acceptability, and intended effects of eMBMT in improving HRQOL, symptom burden, and clinical markers of disease activity (e.g., infections), and (2) the extent to which eMBMT music therapy component-associated improvements in HRQOL, symptom burden, and disease activity are mediated by improvements in psychosocial and physiological (e.g., systemic inflammation, immune recovery) adaptation.

METHODS

Participants (n = 60) with a hematologic malignancy undergoing allo-SCT will be randomized to receive eMBMT or an eHealth-based mindfulness meditation (eMM) intervention. eMBMT includes eight 60-min sessions facilitated by a music therapist focusing on mindfulness and music therapy. eMM includes eight 60-min self-led MM practices.

RESULTS

Feasibility, acceptability, HRQOL, symptom burden, disease activity, and mediation effects of psychosocial and physiological adaptation will be assessed at baseline, pre-infusion, and post-engraftment with blood collection at baseline and post-engraftment.

CONCLUSION

The current pilot RCT is the first eMBMT intervention to address the HRQOL and symptom burden of patients who are undergoing allo-SCT. Results will inform a fully powered RCT to establish preliminary efficacy of eMBMT on improvements in HRQOL, symptom burden, and disease activity.

Thymic Hyperplasia and COVID-19 Pulmonary Sequelae: A Bicentric CT-Based Follow-Up Study

This study aimed to investigate the role of the thymus in influencing long-term outcomes of COVID-19 by comparing the thymic appearance in patients with and without COVID-19 pulmonary sequelae at chest computed tomography (CT). A total of 102 adult patients previously hospitalized for COVID-19 underwent a follow-up chest CT three months after discharge. Pulmonary sequelae and thymic appearance were independently assessed by two experienced radiologists. The thymus was detectable in 55/102 patients (54%), with only 7/55 (13%) having any kind of pulmonary sequelae, compared to 33 out of 47 (70%, p < 0.001) in patients without thymic visibility, as confirmed in age-stratified analysis and at logistic regression analysis, where thymic involution had a 9.3 odds ratio (95% CI 3.0–28.2, p < 0.001) for the development of pulmonary sequelae. These results support the hypothesis that thymic reactivation plays a protective role against adverse long-term outcomes of COVID-19.

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.

Different Properties of Involuted Thymus upon Nutritional Deficiency in Young and Aged Mice

Immune suppression in elderly individuals is one of the most important hygienic problems in aged societies. The primary immune organ thymus is histologically and functionally reduced by aging, which is known as thymic involution. The thymus is also involuted by nutritional deficiency, which frequently occurs in elderly individuals. However, there is no information on the thymic changes caused by nutritional deficiency with aging. Therefore, this study was conducted to examine the histological and molecular responses of the thymus to nutritional deficiency in young and aged mice. The thymic size was significantly smaller in 16- or 18-week-old aged mice than in 7-week-old young mice. Dietary restriction for 48 h reduced the thymic size in young mice, but not in aged mice. Immunostaining with anti-keratin 5 antibody revealed that the integrity of the corticomedullary boundary was maintained in the aged thymus, whereas dietary restriction induced its disorganization in both young and aged thymus. The numbers of immunoglobulin G (IgG)-positive cells were increased upon dietary restriction in aged, but not in young, thymus. Dietary restriction, but not aging, upregulated the mRNA levels of T-helper 2 (Th2)-related Il5, Il6, and Il10, whereas aging increased that of Th1-related interferon-γ (Ifng). The dietary restriction-induced upregulation of prostanoid-synthesizing enzymes was clearly observed in the young thymus but attenuated in the aged thymus. Thus, nutritional deficiency and aging cause an involuted thymus with different properties. Moreover, the thymus in aged mice does not show further reduction in size by nutritional deficiency but still responds differently compared with that in young mice.

Multi-omic analyses in immune cell development with lessons learned from T cell development

Traditionally, flow cytometry has been the preferred method to characterize immune cells at the single-cell level. Flow cytometry is used in immunology mostly to measure the expression of identifying markers on the cell surface, but-with good antibodies-can also be used to assess the expression of intracellular proteins. The advent of single-cell RNA-sequencing has paved the road to study immune development at an unprecedented resolution. Single-cell RNA-sequencing studies have not only allowed us to efficiently chart the make-up of heterogeneous tissues, including their most rare cell populations, it also increasingly contributes to our understanding how different omics modalities interplay at a single cell resolution. Particularly for investigating the immune system, this means that these single-cell techniques can be integrated to combine and correlate RNA and protein data at the single-cell level. While RNA data usually reveals a large heterogeneity of a given population identified solely by a combination of surface protein markers, the integration of different omics modalities at a single cell resolution is expected to greatly contribute to our understanding of the immune system.

Recovery of lymphocyte subpopulations is incomplete in the long-term setting in pediatric solid tumor survivors

BACKGROUND

Childhood cancer survivors (CCSs) may have comorbidities including a long-term abnormality in the immune system. Immune reconstitution in CCSs after treatment for acute leukemia has been reported previously, while analyses of immune reconstitution in CCSs with solid tumors have been limited.

METHODS

Childhood cancer survivors who received chemotherapy for solid tumors and who visited University of Tsukuba Hospital between November 2019 and March 2021 were included the study. Peripheral blood was collected for flow cytometry analysis.

RESULTS

Forty-nine samples from 35 CCSs (18 male, 17 female) were included in the study. High-dose chemotherapy and cerebral spinal irradiation were conducted in 14 CCSs (40%) and in five CCSs (14%), respectively. The median time between the completion of chemotherapy and the collection of the present samples was 15.0 months (range, 0-286 months). The total lymphocyte count, B cells, and CD8-positive T cells recovered to the normal range of controls (NR-CTLs) in 0 (0%), four (66.7%), and four (66.7%) of six samples at 0-3 months after the completion of chemotherapy, and in three (60%), four (80%), and three (60%) of five samples at 3-12 months after the completion of chemotherapy, respectively. Meanwhile, CD4-positive T cells remained lower than NR-CTLs in 0 (0%) of six samples, one (20%) of five samples, and seven (63.7%) of 11 samples at 0-3, 3-12 and 12-60 months after the completion of chemotherapy, respectively.

CONCLUSIONS

Recovery to the NR-CTLs was rapidly achieved in B cells and CD8-positive T cells, while the recovery was slower and incomplete in CD4-positive T cells. Careful observation of infection in long-term follow-up clinics is needed.

Protective reactive thymus hyperplasia in COVID-19 acute respiratory distress syndrome

Background

Patients with COVID-19 (COVID) may develop acute respiratory distress syndrome with or without sepsis, coagulopathy and visceral damage. While chest CT scans are routinely performed in the initial assessment of patients with severe pulmonary forms, thymus involvement and reactivation have not been investigated so far.

Methods

In this observational study, we systematically scored the enlargement of the thymus and the lung involvement, using CT scans, in all adult patients admitted to the ICU for COVID or any other cause (control group) at one centre between March and April 2020. Initial biological investigations included nasal detection of SARS-CoV-2 ribonucleic acid by polymerase chain reaction (PCR). In a subgroup of 24 patients with different degrees of pulmonary involvement and thymus hypertrophy, plasma cytokine concentrations were measured and the export of mature T cells from the thymus was estimated simultaneously by PCR quantification of T cell receptor excision circles (TRECs).

Results

Eighty-seven patients were studied: 50 COVID patients and 37 controls. Non-atrophic or enlarged thymus was more commonly observed in COVID patients than in controls (66% vs. 24%, p < 0.0001). Thymus enlargement in COVID patients was associated with more extensive lung injury score on CT scans (4 [3–5] vs. 2 [1.5–4], p = 0.01), but a lower mortality rate (8.6% vs. 41.2%, p < 0.001). Other factors associated with mortality were age, lymphopaenia, high CRP and co-morbidities. COVID patients had higher concentrations of IL-7 (6.00 [3.72–9.25] vs. 2.17 [1.76–4.4] pg/mL; p = 0.04) and higher thymic production of new lymphocytes (sj/βTREC ratio = 2.88 [1.98–4.51] vs. 0.23 [0.15–0.60]; p = 0.004). Thymic production was also correlated with the CT scan thymic score (r = 0.38, p = 0.03) and inversely correlated with the number of lymphocytes (r = 0.56, p = 0.007).

Conclusion

In COVID patients, thymus enlargement was frequent and associated with increased T lymphocyte production, which appears to be a beneficial adaptation to virus-induced lymphopaenia. The lack of thymic activity/reactivation in older SARS-CoV-2 infected patients could contribute to a worse prognosis.

Radiotherapy-Related Lymphopenia Affects Overall Survival in Patients With Lung Cancer

INTRODUCTION

Lymphopenia after radiotherapy has an adverse effect on the patient's outcome. However, the relationship between radiotherapy dose delivery and lymphopenia is not fully understood. This work used image-based data mining to identify anatomical regions where the received dose is correlated with severe lymphopenia.

METHODS

A total of 901 patients with lung cancer were analyzed. A Cox model was used to assess prognostic factors of overall survival (OS). Two matched groups were defined-patients with lymphopenia of grade 3 or higher and patients without lymphopenia of grade 3-based on tumor volume, baseline lymphocytes, and prescribed dose. Then, data mining was used to identify regions where dose correlates significantly with lymphopenia of grade 3 or higher. For this, dose matrices were aligned using registration of the computed tomography images to one reference patient. Mean dose distributions were obtained for the two groups, and organs of significance were detected. Dosimetric parameters from the identified organs that had the highest correlation with lymphocytes at nadir were selected. Multivariable analysis was conducted for lymphopenia of grade 3 or higher on the full lung cohort, and the model was tested on 305 patients with esophageal cancer.

RESULTS

Adjusted Cox regression revealed that lymphopenia of grade 3 or higher is an independent factor of OS. The anatomical regions identified were the heart, lung, and thoracic vertebrae. Dosimetric parameters for lymphopenia included thoracic vertebrae V20, mean lung dose, and mean heart dose, which were further validated in the esophageal cancer cohort.

CONCLUSIONS

We report that severe lymphopenia during radiotherapy is a poor prognostic factor for OS in patients with lung cancer and could be mitigated by minimizing thoracic vertebrae V20, mean lung dose, and mean heart dose to limit the irradiation of stem cells and blood pool.

[Vascular Remodeling Induced by Biological Stresses]

The thymus is a vital organ for functional immune systems, and is the site of T cell development, which plays a central role in cellular immune defenses. Unlike other major organs, the thymus is highly dynamic in size and structure. It shrinks immediately upon bacterial infection, aging, pregnancy, mental stress, nutritional deficiency, and more. The reduction in size and function of the thymus during such biological events is called thymic involution or thymic atrophy; thymic involution is a particularly important issue because dysfunctional T cell immunity increases the risks of tumorigenesis and infectious diseases. However, the molecular mechanisms underlying thymic involution remain obscure. Our recent study indicated that blood vessels are remodeled during thymic involution that occurs upon aging, estradiol-treatment, or nutritional deficiency. We also found that prostanoid synthesis is induced during thymic involution. Treatment with non-steroidal anti-inflammatory drugs (NSAIDs), aspirin or etodolac, at least partially inhibited thymic involution-induced remodeling of the blood vessels, suggesting that prostanoids are involved in blood vessel remodeling. Our results revealed the potential role of blood vessel remodeling during thymic involution, which can lead to biological stress-induced immunosenescence.

Radiotherapy-related lymphopenia in patients with advanced non-small cell lung cancer receiving palliative radiotherapy

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Risk of grade 3 lymphopenia increased with RT dose to the soft tissue and trabecular bone.

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High baseline CRP/Albumin was negatively associated with overall survival.

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Risk of lymphopenia may decrease by limiting irradiation field in palliative RT.

Background

Lymphopenia during radiotherapy (RT) may have an adverse effect on treatment outcome. The aim of this study is to investigate associations between lymphopenia and RT parameters in patients with advanced lung cancer. Moreover, to investigate the prognostic role of lymphopenia, blood protein levels, and treatment and patient-related factors.

Material and Methods

Sixty-two advanced stage non-small cell lung cancer (NSCLC) patients were retrospectively analyzed. Blood counts were available prior to, during, and after RT (3Gyx10). For each patient, a thoracic volume of interest (VOI) –including thoracic soft tissue and trabecular bone– was obtained by applying a CT window of −500 to 1200 HU in the planning CT. Dose parameters from thoracic VOI and other regions including lungs and vertebrae were calculated. Association between risk of lymphopenia ≥ G3 (lymphocytes at nadir according to CTCAE v4.0) and therapeutic parameters was investigated using Logistic regression. Relationships between overall survival (OS) and RT dose parameters, baseline blood counts and protein levels, and clinical factors were evaluated using Log-rank and Cox models.

Result

Mean thoracic RT dose (odds ratio [OR] 1.67; p = 0.04), baseline lymphocytes (OR 0.65; p = 0.01), and corticosteroids use (OR 6.07; p = 0.02) were significantly associated with increased risk of lymphopenia ≥ G3 in multivariable analysis. Worse OS was associated with high mean thoracic RT dose, high CRP/Albumin, large tumor volume and corticosteroids use (p < 0.05, univariate analysis), but not with lymphopenia ≥ G3. CRP/Albumin ratio > 0.12 (hazard ratio [HR] 2.28, p = 0.03) and corticosteroid use (HR 2.52, p = 0.01) were independently associated with worse OS.

Conclusion

High thoracic RT dose gave a higher risk of lymphopenia ≥ G3; hence limiting dose volume to the thorax may be valuable in preventing severe lymphopenia for patients receiving palliative fractionated RT. Still, lymphopenia ≥ G3 was not associated with worse OS. however, high baseline CRP/Albumin was associated with poorer OS and may carry important information as a prognostic factor of OS in advanced NSCLC receiving palliative RT.

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.

Incomplete functional T-cell reconstitution in immunological non-responders at one year after initiation of antiretroviral therapy possibly predisposes them to infectious diseases

BACKGROUND

Immunological non-responders (INR) represent a unique category of HIV-infected patients on antiretroviral therapy. These patients have suppressed viremia but a suboptimal increase in CD4 cell count, which might have opposing effects on functional immune reconstitution. Hence, the extent of immune reconstitution in INR patients was investigated in order to determine their susceptibility to opportunistic infections.

METHODS

Twenty-three INR patients (CD4 increase <50 cells/mm³, viral load <40 copies/ml), 40 age-, sex-, and baseline CD4 count-matched responders (CD4 increase >100 cells/mm³, viral load <40 copies/ml), and 18 treatment failures defined as per the national guidelines were enrolled at 1year of antiretroviral therapy. The following examinations were performed: haemogram, phenotypic characterization by flow cytometry, and assessment of functional immune status by ELISPOT and intracellular cytokine assays.

RESULTS

A higher percentage of INR patients had clinically symptomatic infections than the responders. CD8⁺ activation and innate immune parameters, including the absolute neutrophil count and natural killer (NK) cell frequency and functionality, were restored in the INR patients. They had significantly higher non-HIV antigen-specific T-cell responses and activated CD4⁺ cells, but significantly compromised T-cell functionality, as assessed after anti-CD3 stimulation, and lower CD31⁺ and CD62L⁺CD4⁺ cells.

CONCLUSIONS

INR patients showed lower thymic output, incomplete functional T-cell reconstitution, higher responses to HIV co-pathogens, and higher symptomatic events, indicating the need for close monitoring and intervention strategies to overcome their continuing immunocompromised status.

Aging, Immunity, and Neuroinflammation: The Modulatory Potential of Nutrition

Aging influences an organism’s entire physiology, affecting functions at the molecular, cellular, and systemic levels and increasing susceptibility to many major chronic diseases. The changes in the immune system that accompany human aging are very complex and are generally referred to as immunosenescence. The factors and mechanisms of immunosenescence are multiple and include, among others, defects in the bone marrow, thymic involution, and intrinsic defects in the formation, maturation, homeostasis, and migration of peripheral lymphocytes. Aging affects both the innate and adaptive arms of the immune system. The process of aging is commonly accompanied by low-grade inflammation thought to contribute to neuroinflammation and to many age-related diseases. Numerous attempts to define the role of chronic inflammation in aging have implicated chronic oxidative stress, mitochondrial damage, immunosenescence, epigenetic modifications, and other phenomena. Several lifestyle strategies, such as intervening to provide an adequate diet and physical and mental activity, have been shown to result in improved immune and neuroprotective functions, a decrease in oxidative stress and inflammation, and a potential increase in individual longevity. The studies published thus far describe a critical role for nutrition in maintaining the immune response of the aged, but they also indicate the need for a more in-depth, holistic approach to determining the optimal nutritional and behavioral strategies that would maintain immune and other physiological systems in elderly people. In this chapter, we focus first on the age-related changes of the immune system. Further, we discuss possible deleterious influences of immunosenescence and low-grade inflammation (inflammaging) on neurodegenerative processes in the normally aging brain. Finally, we consider our current understanding of the modulatory potential of nutrition that may mediate anti-inflammatory effects and thus positively affect immunity and the aging brain.

Single-Cell Analysis Identifies Thymic Maturation Delay in Growth-Restricted Neonatal Mice

Fetal growth restriction (FGR) causes a wide variety of defects in the neonate which can lead to increased risk of heart disease, diabetes, anxiety and other disorders later in life. However, the effect of FGR on the immune system, is poorly understood. We used a well-characterized mouse model of FGR in which placental Igf-2 production is lost due to deletion of the placental specific Igf-2 P₀ promotor. The thymi in such animals were reduced in mass with a ~70% reduction in cellularity. We used single cell RNA sequencing (Drop-Seq) to analyze 7,264 thymus cells collected at postnatal day 6. We identified considerable heterogeneity among the Cd8/Cd4 double positive cells with one subcluster showing marked upregulation of transcripts encoding a sub-set of proteins that contribute to the surface of the ribosome. The cells from the FGR animals were underrepresented in this cluster. Furthermore, the distribution of cells from the FGR animals was skewed with a higher proportion of immature double negative cells and fewer mature T-cells. Cell cycle regulator transcripts also varied across clusters. The T-cell deficit in FGR mice persisted into adulthood, even when body and organ weights approached normal levels due to catch-up growth. This finding complements the altered immunity found in growth restricted human infants. This reduction in T-cellularity may have implications for adult immunity, adding to the list of adult conditions in which the in utero environment is a contributory factor.

Superior immune reconstitution using Treg-expanded donor cells versus PTCy treatment in preclinical HSCT models

Posttransplant cyclophosphamide (PTCy) has been found to be effective in ameliorating acute graft-versus-host disease (GVHD) in patients following allogeneic hematopoietic stem cell transplantation (aHSCT). Adoptive transfer of high numbers of donor Tregs in experimental aHSCT has shown promise as a therapeutic modality for GVHD regulation. We recently described a strategy for in vivo Treg expansion targeting two receptors: TNFRSF25 and CD25. To date, there have been no direct comparisons between the use of PTCy and Tregs regarding outcome and immune reconstitution within identical groups of transplanted mice. Here, we assessed these two strategies and found both decreased clinical GVHD and improved survival long term. However, recipients transplanted with Treg-expanded donor cells (TrED) exhibited less weight loss early after HSCT. Additionally, TrED recipients demonstrated less thymic damage, significantly more recent thymic emigrants, and more rapid lymphoid engraftment. Three months after HSCT, PTCy-treated and TrED recipients showed tolerance to F1 skin allografts and comparable immune function. Overall, TrED was found superior to PTCy with regard to weight loss early after transplant and initial lymphoid engraftment. Based on these findings, we speculate that morbidity and mortality after transplant could be diminished following TrED transplant into aHSCT recipients, and, therefore, that TrED could provide a promising clinical strategy for GVHD prophylaxis.

The Great Recession and Immune Function

The Great Recession precipitated unprecedented home foreclosures increases, but documentation of related neighborhood changes and population health is scant. Using the Detroit Neighborhood Health Study (N = 277), we examined associations between neighborhood-level recession indicators and thymic function, a life course immunological health indicator. In covariate-adjusted multilevel models, each 10 percentage point increase in abandoned home prevalence and 1 percentage point increase in 2009 home foreclosures was associated with 1.7-year and 3.3-year increases in thymic aging, respectively. Associations attenuated after adjustment for neighborhood-level social cohesion, suggesting community ties may buffer recession-related immune aging. Effects of neighborhood stressors were strongest in middle-income households, supporting theory of excess vulnerability in this group. Future research should assess whether ongoing foreclosure and blight reduction efforts improve health for residents of recession impacted neighborhoods.

Combination central tolerance and peripheral checkpoint blockade unleashes antimelanoma immunity

Blockade of immune checkpoint proteins (e.g., CTLA-4, PD-1) improves overall survival in advanced melanoma; however, therapeutic benefit is limited to only a subset of patients. Because checkpoint blockade acts by "removing the brakes" on effector T cells, the efficacy of checkpoint blockade may be constrained by the limited pool of melanoma-reactive T cells in the periphery. In the thymus, autoimmune regulator (Aire) promotes deletion of T cells reactive against self-antigens that are also expressed by tumors. Thus, while protecting against autoimmunity, Aire also limits the generation of melanoma-reactive T cells. Here, we show that Aire deficiency in mice expands the pool of CD4+ T cells capable of melanoma cell eradication and has additive effects with anti-CTLA-4 antibody in slowing melanoma tumor growth and increasing survival. Moreover, pharmacologic blockade of central T cell tolerance and peripheral checkpoint blockade in combination enhanced antimelanoma immunity in a synergistic manner. In melanoma patients treated with anti-CTLA-4 antibody, clinical response to therapy was associated with a human Aire polymorphism. Together, these findings suggest that Aire-mediated central tolerance constrains the efficacy of peripheral checkpoint inhibition and point to simultaneous blockade of Aire and checkpoint inhibitors as a novel strategy to enhance antimelanoma immunity.

Pre-transplantation thymic function is associated with the risk of acute graft versus host disease and cytomegalovirus viremia after allogeneic hematopoietic stem cell transplantation

OBJECTIVES

To analyze the kinetics of T-cell subsets and thymic function reconstitution after allogeneic hematopoietic stem cell transplantation (AHSCT); to determine whether sjTREC (signal joint TCR rearrangement excision circle) and CD31-positive recent thymic emigrant (CD31 + RTE) are correlated with acute graft versus host disease (aGVHD) or CMV (cytomegalovirus) viremia after AHSCT.

METHODS

Forty-nine patients who underwent AHSCT in our institution were prospectively enrolled. Periphery blood samples were collected before conditioning and at 1, 2, 3 months after AHSCT. T-cell subsets were analyzed with flow cytometry. Genomic DNA was purified from peripheral blood mononuclear cells (PBMCs), and sjTREC was quantified by real-time PCR. Impact of sjTREC and CD31 + RTE on aGVHD and CMV viremia was evaluated by univariate and multivariate Cox regression analyses.

RESULTS

The analyzed T-cell subsets and sjTREC of patients before AHSCT were all significantly lower than those of healthy donors (p < 0.05). sjTREC and CD31 + RTE were remarkably decreased in 3 months after AHSCT (p < 0.05). Patients with lower pre-transplantation sjTREC and CD31 + RTE level had higher incidence of CMV viremia after AHSCT (p < 0.05). sjTREC/10⁶ PBMCs was negatively correlated with aGVHD (p = 0.024).

CONCLUSION

Thymic function was impaired before transplantation, and was consistently decreased in 3 months after AHSCT. Patients who had lower pre-transplantation sjTREC level were at high risk of aGVHD and CMV viremia after AHSCT, low pre-transplantation CD31 + RTE was correlated with CMV viremia after AHSCT.

John L, Sams CF, Mehta SK, Crucian BE, Pierson DL, Komanduri KV. Decreases in thymopoiesis of astronauts returning from space flight

Following the advent of molecular assays that measure T cell receptor excision circles (TRECs) present in recent thymic emigrants, it has been conclusively shown that thymopoiesis persists in most adults, but that functional output decreases with age, influencing the maintenance of a diverse and functional T cell receptor (TCR) repertoire. Space flight has been shown to result in a variety of phenotypic and functional changes in human T cells and in the reactivation of latent viruses. While space flight has been shown to influence thymic architecture in rodents, thymopoiesis has not previously been assessed in astronauts. Here, we assessed thymopoiesis longitudinally over a 1-year period prior to and after long-term space flight (median duration, 184 days) in 16 astronauts. While preflight assessments of thymopoiesis remained quite stable in individual astronauts, we detected significant suppression of thymopoiesis in all subjects upon return from space flight. We also found significant increases in urine and plasma levels of endogenous glucocorticoids coincident with the suppression of thymopoiesis. The glucocorticoid induction and thymopoiesis suppression were transient, and they normalized shortly after return to Earth. This is the first report to our knowledge to prospectively demonstrate a significant change in thymopoiesis in healthy individuals in association with a defined physiologic emotional and physical stress event. These results suggest that suppression of thymopoiesis has the potential to influence the maintenance of the TCR repertoire during extended space travel. Further studies of thymopoiesis and endogenous glucocorticoids in other stress states, including illness, are warranted.

Population Distributions of Thymic Function in Adults: Variation by Sociodemographic Characteristics and Health Status

The thymus is critical for mounting an effective immune response and maintaining health. However, epidemiologic studies characterizing thymic function in the population setting are lacking. Using data from 263 adults in the Detroit Neighborhood Health Study, we examined thymic function as measured by the number of signal joint T-cell receptor excision circles (sjTREC) and assessed associations with established indicators of physiological health. Overall, increasing age and male gender were significantly associated with reduced thymic function. Adjusting for covariates, individuals with elevated levels of the pro-inflammatory biomarkers C-reactive protein (β: -0.50 [95% CI: -0.82, -0.18] for moderate elevation, β: -0.29 [95% CI: -0.59, 0.00] for high elevation) and interleukin-6 (β: -0.60 [95% CI: -0.92, -0.28] for moderate elevation, β: -0.43 [95% CI: -0.77, -0.08] for severe elevation) also had lower thymic function. Compared to individuals with a BMI < 25, individuals who were overweight (β: 0.36 [95% CI: 0.07, 0.64]) or obese (β: 0.27 [95% CI: -0.03, 0.56]) had higher thymic function. Differences by self-rated health were not statistically significant. Our findings underscore demographic- and health-related gradients in thymic function among adult residents of Detroit, suggesting thymic function may be an important biomarker of health status in adults at the population level.

As we age: Does slippage of quality control in the immune system lead to collateral damage?

The vertebrate adaptive immune system is remarkable for its possession of a very broad range of antigen receptors imbuing the system with exquisite specificity, in addition to the phagocytic and inflammatory cells of the innate system shared with invertebrates. This system requires strict control both at the level of the generation the cells carrying these receptors and at the level of their activation and effector function mediation in order to avoid autoimmunity and mitigate immune pathology. Thus, quality control checkpoints are built into the system at multiple nodes in the response, relying on clonal selection and regulatory networks to maximize pathogen-directed effects and minimize collateral tissue damage. However, these checkpoints are compromised with age, resulting in poorer immune control manifesting as tissue-damaging autoimmune and inflammatory phenomena which can cause widespread systemic disease, paradoxically compounding the problems associated with increased susceptibility to infectious disease and possibly cancer in the elderly. Better understanding the reasons for slippage of immune control will pave the way for developing rational strategies for interventions to maintain appropriate immunity while reducing immunopathology.

Population doublings of murine CD4(+) memory T cells during continuous antigen stimulation in vivo

We investigated the expansion rate of CD4(+) memory T cells using a newly developed in vivo system. Neonatal thymectomy abrogates the subsequent production of T cells and induces autoimmune gastritis (AIG) by the activation of CD4(+) T cells; this disease was transferred into athymic nude mice through the inoculation of splenic CD4(+) memory T cells. The transferred CD4(+) T cells increased logarithmically in number during the first 2months in the spleen of the recipients. The serial transfer of these splenocytes at two-month intervals revealed that the numbers of the AIG-transferable generations were inversely correlated with the age of the first AIG donors. The duration of the AIG-promoting capacity of CD4(+) T cells under continuous antigenic stimulation in vivo was approximately equivalent-one and a half years. These results indicate that there exists an intrinsic population doubling limit in memory CD4(+) T cells similar to that of self-renewing naïve ones.

Pre-birth world and the development of the immune system: mum's diet affects our adult health: new insight on how the diet during pregnancy permanently influences offspring health and immune fitness

Secondary lymphoid organs form in utero through an inherited and well-established developmental program. However, maternal non-heritable features can have a major impact on the gene expression of the embryo, hence influencing the future health of the offspring. Recently, maternal retinoids were shown to regulate the formation of immune structures, shedding light on the role of maternal nutrition in the genetic signature of emergent immune cells. Here we highlight evidence showing how the maternal diet influences the establishment of the immune system, and we also discuss how unbalanced maternal diets may set the response to infection and vaccination in the progeny.

Diversity and clonal selection in the human T-cell repertoire

T-cell receptor (TCR) diversity, a prerequisite for immune system recognition of the universe of foreign antigens, is generated in the first two decades of life in the thymus and then persists to an unknown extent through life via homeostatic proliferation of naïve T cells. We have used next-generation sequencing and nonparametric statistical analysis to estimate a lower bound for the total number of different TCR beta (TCRB) sequences in human repertoires. We arrived at surprisingly high minimal estimates of 100 million unique TCRB sequences in naïve CD4 and CD8 T-cell repertoires of young adults. Naïve repertoire richness modestly declined two- to fivefold in healthy elderly. Repertoire richness contraction with age was even less pronounced for memory CD4 and CD8 T cells. In contrast, age had a major impact on the inequality of clonal sizes, as estimated by a modified Gini-Simpson index clonality score. In particular, large naïve T-cell clones that were distinct from memory clones were found in the repertoires of elderly individuals, indicating uneven homeostatic proliferation without development of a memory cell phenotype. Our results suggest that a highly diverse repertoire is maintained despite thymic involution; however, peripheral fitness selection of T cells leads to repertoire perturbations that can influence the immune response in the elderly.

Mechanisms shaping the naïve T cell repertoire in the elderly - thymic involution or peripheral homeostatic proliferation?

The ability of the human immune system to repel infections is drastically diminished with age. Elderly individuals are more susceptible to new threats and are less able to control endogenous infections. The thymus, which is the sole source of new T cells, has been proposed as a target for regenerative efforts to improve immune competence, as thymic activity is dramatically reduced after puberty. In this review, we review the role of the thymus in the maintenance of T cell homeostasis throughout life and contrast the differences in mice and humans. We propose that in humans, lack of thymic T cell generation does not explain a decline in T cell receptor diversity nor would thymic rejuvenation restore diversity. Initial studies using next generation sequencing are beginning to establish lower boundaries of T cell receptor diversity. With increasing sequencing depth and the development of new statistical models, we are now in the position to test this model and to assess the impact of age on T cell diversity and clonality.

The past, present, and future of immune repertoire biology - the rise of next-generation repertoire analysis

T and B cell repertoires are collections of lymphocytes, each characterized by its antigen-specific receptor. We review here classical technologies and analysis strategies developed to assess immunoglobulin (IG) and T cell receptor (TR) repertoire diversity, and describe recent advances in the field. First, we describe the broad range of available methodological tools developed in the past decades, each of which answering different questions and showing complementarity for progressive identification of the level of repertoire alterations: global overview of the diversity by flow cytometry, IG repertoire descriptions at the protein level for the identification of IG reactivities, IG/TR CDR3 spectratyping strategies, and related molecular quantification or dynamics of T/B cell differentiation. Additionally, we introduce the recent technological advances in molecular biology tools allowing deeper analysis of IG/TR diversity by next-generation sequencing (NGS), offering systematic and comprehensive sequencing of IG/TR transcripts in a short amount of time. NGS provides several angles of analysis such as clonotype frequency, CDR3 diversity, CDR3 sequence analysis, V allele identification with a quantitative dimension, therefore requiring high-throughput analysis tools development. In this line, we discuss the recent efforts made for nomenclature standardization and ontology development. We then present the variety of available statistical analysis and modeling approaches developed with regards to the various levels of diversity analysis, and reveal the increasing sophistication of those modeling approaches. To conclude, we provide some examples of recent mathematical modeling strategies and perspectives that illustrate the active rise of a "next-generation" of repertoire analysis.

Molecular mechanisms involved in the aging of the T-cell immune response

T-lymphocytes play a central role in the effector and regulatory mechanisms of the adaptive immune response. Upon exiting the thymus they begin to undergo a series of phenotypic and functional changes that continue throughout the lifetime and being most pronounced in the elderly. The reason postulated for this is that the dynamic processes of repeated interaction with cognate antigens lead to multiple division cycles involving a high degree of cell differentiation, senescence, restriction of the T-cell receptor (TCR) repertoire, and cell cycle arrest. This cell cycle arrest is associated with the loss of telomere sequences from the ends of chromosomes. Telomere length is reduced at each cell cycle, and critically short telomeres recruit components of the DNA repair machinery and trigger replicative senescence or apoptosis. Repetitively stimulated T-cells become refractory to telomerase induction, suffer telomere erosion and enter replicative senescence. The latter is characterized by the accumulation of highly differentiated T-cells with new acquired functional capabilities, which can be caused by aberrant expression of genes normally suppressed by epigenetic mechanisms in CD4+ or CD8+ T-cells. Age-dependent demethylation and overexpression of genes normally suppressed by DNA methylation have been demonstrated in senescent subsets of T-lymphocytes. Thus, T-cells, principally CD4+CD28^null T-cells, aberrantly express genes, including those of the KIR gene family and cytotoxic proteins such as perforin, and overexpress CD70, IFN-γ, LFA-1 and others. In summary, owing to a lifetime of exposure to and proliferation against a variety of pathogens, highly differentiated T-cells suffer molecular modifications that alter their cellular homeostasis mechanisms.

Naive T-cells in myelodysplastic syndrome display intrinsic human telomerase reverse transcriptase (hTERT) deficiency

Telomeres are specialized structures providing chromosome integrity during cellular division along with protection against premature senescence and apoptosis. Accelerated telomere attrition in patients with myelodysplastic syndrome (MDS) occurs by an undefined mechanism. Although the MDS clone originates within the myeloid compartment, T-lymphocytes display repertoire contraction and loss of naive T-cells. The replicative lifespan of T-cells is stringently regulated by telomerase activity. In MDS cases, we show that purified CD3+ T-cells have significantly shorter telomere length and reduced proliferative capacity upon stimulation compared with controls. To understand the mechanism, telomerase enzymatic activity and telomerase reverse transcriptase (hTERT), gene expression were compared in MDS cases (n=35) and healthy controls (n=42) within different T-cell compartments. Telomerase activity is greatest in naive T-cells illustrating the importance of telomere repair in homeostatic repertoire regulation. Compared with healthy controls, MDS cases had lower telomerase induction (P<0.0001) that correlated with significantly lower hTERT mRNA (P<0.0001), independent of age and disease stratification. hTERT mRNA deficiency affected naive but not memory T-cells, and telomere erosion in MDS occurred without evidence of an hTERT-promoter mutation, copy number variation or deletion. Telomerase insufficiency may undermine homeostatic control within the hematopoietic compartment and promote a change in the T-cell repertoire in MDS.

Presentation of neuroendocrine self in the thymus: a necessity for integrated evolution of the immune and neuroendocrine systems

During evolution, from ancestor thymoids scattered in gill baskets of the lamprey, the first unique thymus appeared in jawed cartilaginous fishes around 450-500 millions years ago, concomitantly or shortly after the emergence of recombinase-dependent adaptive immunity. The major biological function of the thymus is to generate a diverse repertoire of T cell receptors that are self tolerant. The thymus achieves this role by using two complementary and intimately associated mechanisms: apoptotic deletion of T cell clones bearing a TCR with high affinity for self-antigens presented by MHC proteins on thymic epithelial cells (TECs) and dendritic cells (DCs); and generation of self-antigen-specific natural regulatory T (nT(reg)) cells. Moreover, the escape from thymic central self-tolerance plays a primary role in the development of autoimmune diseases that are a significant burden for the quality of life and health-care cost. Our new knowledge in thymus physiology and physiopathology is currently translated into innovative therapeutic strategies against these devastating chronic diseases.

Mechanisms involved in CD4 cell gains in HIV-infected patients switched to raltegravir

BACKGROUND

CD4 gains in HIV patients on HAART result from release of T cells recently migrated from the thymus, redistribution from lymphoid tissues, proliferation in the periphery and/or reduced apoptosis. The relative contribution of each mechanism in CD4 restoration in patients with suppressed viremia switching antiretrovirals is unclear.

METHODS

HIV patients with undetectable viremia on HAART were identified at our clinic. A subset switched to raltegravir was compared with another group that kept therapy unmodified. Naive and memory CD4 T-cells were measured by flow cytometry using CD45RA and CD27, respectively. Activation was examined using CD38 and recent thymic emigrants using CD31. Apoptosis was analyzed measuring soluble tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL).

RESULTS

Thirty-seven patients were examined, 19 switched to raltegravir and 18 controls, after a median of 26 months of suppressed viremia. At 6 months, mean CD4 cell counts significantly increased in raltegravir patients from 322 to 448 cells/μl (P = 0.026) but not in controls (from 312 to 330 cells/μl; P  = 0.813). No significant changes were recognized in activation or CD31 expression in any group. In raltegravir patients, however, the proportion of naive CD4 T cells significantly increased (P = 0.014) as well as CD38 expression in these cells (P = 0.036). A positive correlation was found between CD38 and CD31 expression in naive CD4 T cells (R  = 0.51, P < 0.001). TRAIL and FasL did not decline significantly in any group.

CONCLUSION

HIV patients with prolonged undetectable viremia on HAART experience more pronounced CD4 gains after raltegravir switching than keeping the same regimen. An increased production of naive CD4 T cells largely explains this effect.

CD8+ T-cell reconstitution in recipients of umbilical cord blood transplantation and characteristics associated with leukemic relapse

Recipients of umbilical cord blood (UCB) transplantation (UCBT) face a high risk of morbidity and mortality related to opportunistic infections (OI) and leukemic relapse. To understand the molecular basis of these UCBT-related complications, the characteristics of UCB-derived antigen-specific CD8+ T cells were examined in a group of pediatric UCBT recipients. Compared with the UCB graft inoculum and the late post-UCBT period (12-36 months), declining clonal diversity of UCB-derived CD8+ T cells specific for the Melan-A26-35 A27L peptide and high frequencies of PD-1-expressing CD8+ T cells were observed in the first 3 months after UCBT, a period during which OIs are most frequent. The CD8+ T-cell compartment predominantly comprised CD45RA+ CCR7− terminally differentiated effector-memory T cells until 6 months after UCBT, at which time the polyfunctionality of antigen-specific CD8+ T cells was reestablished. Finally, the frequency of PD-1+ CD8+ T cells was significantly higher in subjects who subsequently experienced leukemic relapse. This study informs the biologic properties of UCB-derived CD8+ T cells and provides a rationale for the characteristics of UCBT in terms of immune reconstitution and OI. These results also suggest that the elevated frequency of PD-1+ CD8+ T cells could be associated with leukemic relapse in pediatric UCBT recipients.

Cocaine reduces thymic endocrine function: another mechanism for accelerated HIV disease progression

Thymulin is a thymic peptide important for the maturation and differentiation of immature thymocytes, which have been found to be depressed in patients with low-level CD4(+) cell recovery despite viral control. Substance use is associated with faster progression of HIV disease, which has been ascribed to poor adherence to antiretroviral medication. Recent findings of an association between cocaine use and decline in CD4(+) cell counts independent of antiretroviral adherence indicate alternative mechanisms for disease progression. We evaluated the relationship between thymulin activity, CD4(+) and CD8(+) cell counts and the CD4(+)/CD8(+) ratio, and the covariate effects of substance use cross-sectionally in 80 HIV(+) active substance users and over 12 months in 40 participants. Thymulin activity was analyzed in plasma using a modification of the sheep rosette bioassay. Thymulin activity was negatively associated with cocaine use (β = -0.908,95% CI: -1.704, -0.112; p = 0.026). Compared to those who do not use cocaine, cocaine users were 37% less likely to have detectable thymulin activity (RR = 0.634, 95% CI: 0.406, 0.989 p = 0.045) and were 75 times more likely to show a decrease in thymulin activity (OR = 74.7, 95% CI: 1.59, 3519.74; p = 0.028) over time. CD4(+) cell count was positively associated with thymulin activity (β = 0.127, 95% CI: 0.048,0.205; p = 0.002), detectable thymulin activity was 2.32 times more likely in those with a CD4 cell count ≥200 cells/μl (RR = 2.324, 95% CI: 1.196, 4.513, p = 0.013), and those with an increase in CD4 cell counts were more likely to show an increase in thymulin activity (OR = 1.02, 95% CI: 1.00, 1.034; p = 0.041) over time. Thymulin activity is predictive of HIV disease progression and is depressed in cocaine users independent of antiretroviral treatment (ART) and HIV viral load. Understanding the mechanisms for accelerated HIV disease progression provides opportunities to find alternative strategies to counteract immunosuppression.

Thymic plasmacytoid dendritic cells are susceptible to productive HIV-1 infection and efficiently transfer R5 HIV-1 to thymocytes in vitro

Background

HIV-1 infection of the thymus contributes to the defective regeneration and loss of CD4⁺ T cells in HIV-1-infected individuals. As thymic dendritic cells (DC) are permissive to infection by HIV-1, we examined the ability of thymic DC to enhance infection of thymocytes which may contribute to the overall depletion of CD4⁺ T cells. We compared productive infection in isolated human thymic and blood CD11c⁺ myeloid DC (mDC) and CD123⁺ plasmacytoid DC (pDC) using enhanced green fluorescent protein (EGFP) CCR5 (R5)-tropic NL(AD8) and CXCR4 (X4)-tropic NL4-3 HIV-1 reporter viruses. Transfer of productive HIV-1 infection from thymic mDC and pDC was determined by culturing these DC subsets either alone or with sorted thymocytes.

Results

Productive infection was observed in both thymic pDC and mDC following exposure to R5 HIV-1 and X4 HIV-1. Thymic pDC were more frequently productively infected by both R5 and X4 HIV-1 than thymic mDC (p = 0.03; n = 6). Thymic pDC efficiently transferred productive R5 HIV-1 infection to both CD3^hi (p = 0.01; mean fold increase of 6.5; n = 6) and CD3^lo thymocytes (mean fold increase of 1.6; n = 2). In comparison, transfer of productive infection by thymic mDC was not observed for either X4 or R5 HIV-1.

Conclusions

The capacity of thymic pDC to efficiently transfer R5 HIV-1 to both mature and immature thymocytes that are otherwise refractory to R5 virus may represent a pathway to early infection and impaired production of thymocytes and CD4⁺ T cells in HIV-1-infected individuals.

Long-term restoration of the human T-cell compartment after thymectomy during infancy: a role for thymic regeneration?

Thymectomy during early childhood is generally thought to have serious consequences for the establishment of the T-cell compartment. In the present study, we investigated the composition of the T-cell pool in the first 3 decades after thymectomy during infancy due to cardiac surgery. In the first 5 years after thymectomy, naive and total CD4(+) and CD8(+) T-cell numbers in the blood and T-cell receptor excision circle (TREC) levels in CD4(+) T cells were significantly lower than in healthy age-matched controls. In the first years after thymectomy, plasma IL-7 levels were significantly elevated and peripheral T-cell proliferation levels were increased by ∼ 2-fold. From 5 years after thymectomy onward, naive CD4(+) and CD8(+) T-cell counts and TRECs were within the normal range. Because TREC levels are expected to decline continuously in the absence of thymic output, we investigated whether normalization of the naive T-cell pool could be due to regeneration of thymic tissue. In the majority of individuals who had been thymectomized during infancy, thymic tissue could indeed be identified on magnetic resonance imaging scans. Whereas thymectomy has severe effects on the establishment of the naive T-cell compartment during early childhood, our data suggest that functional regrowth of thymic tissue can limit its effects in subsequent years.

Frequency analysis of TRBV subfamily sjTRECs to characterize T-cell reconstitution in acute leukemia patients after allogeneic hematopoietic stem cell transplantation

Background

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) leads to a prolonged state of immunodeficiency and requires reconstitution of normal T-cell immunity. Signal joint T-cell receptor excision DNA circles (sjTRECs) are markers of developmental proximity to the thymus that have been used to evaluate thymic function related to T-cell immune reconstitution after HSCT. To assess the proliferative history in different T-cell receptor beta variable region (TRBV) subfamilies of T cells after HSCT, expansion of TRBV subfamily-naive T cells was determined by analysis of a series of TRBV-BD1 sjTRECs.

Methods

sjTRECs levels were detected by real-time quantitative polymerase chain reaction (PCR) in peripheral blood mononuclear cells (PBMCs) from 43 Chinese acute leukemia patients who underwent allo-HSCT. Twenty-three TRBV-BD1 sjTRECs were amplified by semi-nested PCR. Sixteen age-matched healthy volunteers served as normal controls.

Results

sjTRECs levels were low or undetectable in the first 6 weeks after allo-HSCT and increased after 8 weeks post HSCT; however, sjTRECs levels at week 20 post-HSCT were still less than normal controls. Frequencies of TRBV subfamily sjTRECs in PBMCs from recipients at week 8 post-HSCT (29.17 ± 20.97%) or at week 16 post-HSCT (38.33 ± 9.03%) were significantly lower than those in donors (47.92 ± 13.82%) or recipients at pre-HSCT (45.83 ± 14.03%). However, frequencies of TRBV subfamily sjTRECs in recipients at week 30 post-HSCT (42.71 ± 21.62%) were similar to those in donors and recipients at pre-HSCT. sjTRECs levels in donors had a positive linear correlation with sjTRECs levels in recipients within 8-12 weeks post-HSCT. Patients with acute graft-versus-host disease (GVHD) or chronic GVHD had profoundly reduced TRECs levels during the first year post-HSCT. Frequencies of BV22-BD1 sjTRECs and BV23-BD1 sjTRECs in patients with GVHD were significantly lower than those in recipients at pre-HSCT, and the frequencies of BV22-BD1 sjTRECs in patients with GVHD were significantly lower than those in donors.

Conclusions

Reconstitution of thymic output function resulted in a period of immunodeficiency, with low or undetectable TRECs after transplantation, although fludarabine-based dose-reduced conditioning regimens were used. GVHD could affect reconstitution of thymic output function and reduce sjTRECs levels and frequencies of TRBV-BD1 sjTRECs. Low frequency of BV22-BD1 and BV23-BD1 sjTRECs might be associated with GVHD.

Thymopoietic and bone marrow response to murine Pneumocystis pneumonia

CD4(+) T cells play a key role in host defense against Pneumocystis infection. To define the role of naïve CD4(+) T cell production through the thymopoietic response in host defense against Pneumocystis infection, Pneumocystis murina infection in the lung was induced in adult male C57BL/6 mice with and without prior thymectomy. Pneumocystis infection caused a significant increase in the number of CCR9(+) multipotent progenitor (MPP) cells in the bone marrow and peripheral circulation, an increase in populations of earliest thymic progenitors (ETPs) and double negative (DN) thymocytes in the thymus, and recruitment of naïve and total CD4(+) T cells into the alveolar space. The level of murine signal joint T cell receptor excision circles (msjTRECs) in spleen CD4(+) cells was increased at 5 weeks post-Pneumocystis infection. In thymectomized mice, the numbers of naïve, central memory, and total CD4(+) T cells in all tissues examined were markedly reduced following Pneumocystis infection. This deficiency of naïve and central memory CD4(+) T cells was associated with delayed pulmonary clearance of Pneumocystis. Extracts of Pneumocystis resulted in an increase in the number of CCR9(+) MPPs in the cultured bone marrow cells. Stimulation of cultured bone marrow cells with ligands to Toll-like receptor 2 ([TLR-2] zymosan) and TLR-9 (ODN M362) each caused a similar increase in CCR9(+) MPP cells via activation of the Jun N-terminal protein kinase (JNK) pathway. These results demonstrate that enhanced production of naïve CD4(+) T lymphocytes through the thymopoietic response and enhanced delivery of lymphopoietic precursors from the bone marrow play an important role in host defense against Pneumocystis infection.

Introduction: knowledge is survival-the mission of the immune system and its stochastic simulations

In this introduction the timeliness and interest of dedicating an issue of Autoimmunity to mostly "discrete" models is motivated by highlighting number of circumstances, observations encounters, that all have favored the rise of a family of agent based simulations of the Immune System. Franco Celada was among the first experimentalists to accept the challenge of interdisciplinarity and create a computational Immune System. He thinks that discrete models are especially useful in handling hypotheses: initiating them, representing their consequences, and revealing their plusses and minuses. He is sure that "looking at" the immune machinery as a cognitive system is useful both to the intuitive understanding and the creative development of models.

Immunoendocrinology of the thymus in Chagas disease

During immune response to infectious agents, the host develops an inflammatory response which could fail to eliminate the pathogen or may become dysregulated. In this case, the ongoing response acquires a new status and turns out to be detrimental. The same elements taking part in the establishment and regulation of the inflammatory response (cytokines, chemokines, regulatory T cells and counteracting compounds like glucocorticoids) may also mediate harmful effects. Thymic disturbances seen during Trypanosoma cruzi (T. cruzi) infection fit well with this conceptual framework. After infection, this organ suffers a severe atrophy due to apoptosis-induced thymocyte exhaustion, mainly affecting the immature double-positive (DP) CD4+CD8+ population. Thymus cellularity depletion, which occurs in the absence of main immunological mediators involved in anti-T. cruzi defense, seems to be linked to a systemic cytokine/hormonal imbalance, involving a dysregulated increase in Tumor Necrosis Factor alpha (TNF-α) and corticosterone hormone levels. Additionally, we have found an anomalous exit of potentially autoimmune DP cells to the periphery, in parallel to a shrinkage in the compartment of natural regulatory T cells. In this context, our data clearly point to the view that the thymus is a target organ of T. cruzi infection. Preserved thymus may be essential for the development of an effective immune response against T. cruzi, but this organ is severely affected by a dysregulated circuit of proinflammatory cytokines and glucocorticoids. Also, the alterations observed in the DP population might have potential implications for the autoimmune component of human Chagas disease.

Immune reconstitution in children following chemotherapy for haematological malignancies: a long-term follow-up

Modern intensive chemotherapy for childhood haematological malignancies has led to high cure rates, but has detrimental effects on the immune system. There is little knowledge concerning long-term recovery of the adaptive immune system. Here we studied the long-term reconstitution of the adaptive immune system in 31 children treated for haematological malignancies between July 2000 and October 2006. We performed detailed phenotypical and functional analyses of the various B and T cell subpopulations until 5 years after chemotherapy. We show that recovery of newly-developed transitional B cells and naive B and T cells occurred rapidly, within months, whereas recovery of the different memory B and T cell subpopulations was slower and incomplete, even after 5 years post-chemotherapy. The speed of B and T cell recovery was age-independent, despite a significant contribution of the thymus to T cell recovery. Plasmablast B cell levels remained above normal and immunoglobulin levels normalised within 1 week. Functional T cell responses were normal, even within the first year post-chemotherapy. This study shows that after intensive chemotherapy for haematological malignancies in children, numbers of several memory B and T cell subpopulations were decreased on the long term, while functional T cell responses were not compromised.

Lymphocyte homeostasis and the antitumor immune response

Lymphocyte homeostasis is regulated by proliferation of antigen-responsive T-cells in the peripheral circulation and their apoptosis. Patients with cancer have altered lymphocyte homeostasis. Spontaneous apoptosis of circulating CD8(+) antigen-responding effector T-cells contributes to rapid lymphocyte turnover and depressed absolute numbers of T-cell subsets observed in patients with cancer. A rapid transit of naive CD8(+) T-cells to the expanded memory pool and enhanced apoptosis of antitumor effector T-cells in the peripheral circulation of patients with cancer are partly responsible for this rapid lymphocyte turnover. Future strategies for restoration of normal lymphocyte homeostasis in cancer will involve therapies with survival cytokines and factors selected for extending survival of antitumor effector cells and establishing long-term immunologic memory.

Insulin-like growth factor-I regulation of immune function: a potential therapeutic target in autoimmune diseases?

This topically limited review explores the relationship between the immune system and insulin-like growth factors (IGF-I and IGF-II) and the proteins through which they act, including IGF-I receptor (IGF-IR) and the IGF-I binding proteins. The IGF/IGF-IR pathway plays important and diverse roles in tissue development and function. It regulates cell cycle progression, apoptosis, and the translation of proteins. Many of the consequences ascribed to IGF-IR activation result from its association with several accessory proteins that are either identical or closely related to those involved in insulin receptor signaling. Relatively recent awareness that IGF-I and IGF-IR regulate immune function has cast this pathway in an unexpected light; it may represent an important switch governing the quality and amplitude of immune responses. IGF-I/IGF-IR signaling may also participate in the pathogenesis of autoimmune diseases, although its relationship with these processes seems complex and relatively unexplored. On the one hand, IGF-I seems to protect experimental animals from developing insulin-deficient diabetes mellitus. In contrast, activating antibodies directed at IGF-IR have been detected in patients with Graves' disease, where the receptor is overexpressed by multiple cell types. The frequency of IGF-IR+ B and T cells is substantially increased in patients with that disease. Potential involvement of IGF-I and IGF-IR in the pathogenesis of autoimmune diseases suggests that this pathway might constitute an attractive therapeutic target. IGF-IR has been targeted in efforts directed toward drug development for cancer, employing both small-molecule and monoclonal antibody approaches. These have been generally well-tolerated. Recognizing the broader role of IGF-IR in regulating both normal and pathological immune responses may offer important opportunities for therapeutic intervention in several allied diseases that have proven particularly difficult to treat.

Decreased level of recent thymic emigrants in CD4+ and CD8+T cells from CML patients

BACKGROUND

T-cell immunodeficiency is a common feature in cancer patients, which may relate to initiation and development of tumor. Based on our previous finding, to further characterize the immune status, T cell proliferative history was analyzed in CD4+ and CD8+ T cells from chronic myeloid leukemia (CML) patients.

METHODS

Quantitative analysis of deltaRec-psiJalpha signal joint T cell receptor excision circles (sjTRECs) was performed in PBMCs, CD3+, CD4+ and CD8+T cells by real-time PCR, and the analysis of 23 TRBV-D1 sjTRECs was performed by semi-nested PCR. Forty eight CML cases in chronic phase (CML-CP) were selected for this study and 17 healthy individuals served as controls.

RESULTS

The levels of deltaRec-psiJalpha sjTRECs in PBMCs, CD3+, CD4+, and CD8+ T cells were significantly decreased in CML patients, compared with control groups. Moreover, the numbers of detectable TRBV subfamily sjTRECs, as well as the frequency of particular TRBV-BD1 sjTRECs in patients with CML were significantly lower than those from healthy individuals.

CONCLUSIONS

We observed decreased levels of recent thymic emigrants in CD4+ and CD8+ T cells that may underlay the persistent immunodeficiency in CML patients.

Cord blood transplantation: evolving strategies to improve engraftment and immune reconstitution

PURPOSE OF REVIEW

For many patients with relapsed or high-risk hematologic malignancies, allogeneic stem cell transplantation offers the best hope for cure. For patients lacking a suitable family or unrelated donor, umbilical cord blood provides a promising alternative graft source. Dramatic advances in cord blood transplantation (CBT) have been made in the past 2 decades, leading to a rapid expansion of CBT programs worldwide.

RECENT FINDINGS

Promising new strategies, including double CBT and ex-vivo graft engineering, have improved myeloid and platelet engraftment rates and kinetics. However, delayed immune reconstitution and associated infectious morbidity and mortality remain a significant challenge, especially in adult CBT recipients. In adults, both impaired recipient thymopoiesis and the lack of transferred memory cells contribute to delayed T cell recovery, resulting in an increased risk of opportunistic infections.

SUMMARY

Novel clinical approaches in CBT have improved outcomes, especially those associated with delays in myeloid and platelet engraftment. However, delayed immune reconstitution remains a great challenge. Novel strategies, including graft engineering approaches capable of improving T cell recovery, and pharmacologic interventions capable of preserving thymopoiesis and facilitating the recovery of a diverse functional T cell repertoire are being pursued; these approaches have great potential to further improve outcomes after CBT.

Thymectomy in early childhood: a model for premature T cell immunosenescence?

The thymus is the main source of recent thymic emigrants (RTE) and naïve T cells. The aging of the immune system (immunosenescence) is characterized by loss of thymic function, decreased numbers of RTE, peripheral proliferation of mature T cells, and oligoclonal expansions of specific T cell subpopulations. As shown in several studies, thymectomized patients demonstrate signs of premature immunosenescence reminiscent of aged people, such as decreased proportions of naïve T cells and RTE, a compensatory increase of mature T cell subpopulations with increased proliferation rates, restriction of the T cell receptor repertoire, and a delayed response to new antigens and vaccinations. This review demonstrates that, despite some limitations, childhood thymectomy may serve as an useful model for premature immunosenescence, mimicking changes expected after physiological thymus involution in the elderly. Thus, it may prove an insightful tool for obtaining better understanding of human naïve T cell development, thymic function, and maintenance of the naïve T cell pool.