Age-related changes in the cellular composition of the thymus in children

An integrative mechanistic model of thymocyte dynamics

Background

The thymus plays a central role in shaping human immune function. A mechanistic, quantitative description of immune cell dynamics and thymic output under homeostatic conditions and various patho-physiological scenarios are of particular interest in drug development applications, e.g., in the identification of potential therapeutic targets and selection of lead drug candidates against infectious diseases.

Methods

We here developed an integrative mathematical model of thymocyte dynamics in human. It incorporates mechanistic features of thymocyte homeostasis as well as spatial constraints of the thymus and considerations of age-dependent involution. All model parameter estimates were obtained based on published physiological data of thymocyte dynamics and thymus properties in mouse and human. We performed model sensitivity analyses to reveal potential therapeutic targets through an identification of processes critically affecting thymic function; we further explored differences in thymic function across healthy subjects, multiple sclerosis patients, and patients on fingolimod treatment.

Results

We found thymic function to be most impacted by the egress, proliferation, differentiation and death rates of those thymocytes which are most differentiated. Model predictions also showed that the clinically observed decrease in relapse risk with age, in multiple sclerosis patients who would have discontinued fingolimod therapy, can be explained mechanistically by decreased thymic output with age. Moreover, we quantified the effects of fingolimod treatment duration on thymic output.

Conclusions

In summary, the proposed model accurately describes, in mechanistic terms, thymic output as a function of age. It may be further used to perform predictive simulations of clinically relevant scenarios which combine specific patho-physiological conditions and pharmacological interventions of interest.

Thymic Atrophy and Immune Dysregulation in Infants with Complex Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect, and up to 50% of infants with CHD require cardiovascular surgery early in life. Current clinical practice often involves thymus resection during cardiac surgery, detrimentally affecting T-cell immunity. However, epidemiological data indicate that CHD patients face an elevated risk for infections and immune-mediated diseases, independent of thymectomy. Hence, we examined whether the cardiac defect impacts thymus function in individuals with CHD. We investigated thymocyte development in 58 infants categorized by CHD complexity. To assess the relationship between CHD complexity and thymic function, we analyzed T-cell development, thymic output, and biomarkers linked to cardiac defects, stress, or inflammation. Patients with highly complex CHD exhibit thymic atrophy, resulting in low frequencies of recent thymic emigrants in peripheral blood, even prior to thymectomy. Elevated plasma cortisol levels were detected in all CHD patients, while high NT-proBNP and IL-6 levels were associated with thymic atrophy. Our findings reveal an association between complex CHD and thymic atrophy, resulting in reduced thymic output. Consequently, thymus preservation during cardiovascular surgery could significantly enhance immune function and the long-term health of CHD patients.

Molecular Determinants of the Early Life Immune Response to COVID-19 Infection and Immunization

Clinical manifestations from primary COVID infection in children are generally less severe as compared to adults, and severe pediatric cases occur predominantly in children with underlying medical conditions. However, despite the lower incidence of disease severity, the burden of COVID-19 in children is not negligible. Throughout the course of the pandemic, the case incidence in children has substantially increased, with estimated cumulative rates of SARS-CoV-2 infection and COVID-19 symptomatic illness in children comparable to those in adults. Vaccination is a key approach to enhance immunogenicity and protection against SARS-CoV-2. Although the immune system of children is functionally distinct from that of other age groups, vaccine development specific for the pediatric population has mostly been limited to dose-titration of formulations that were developed primarily for adults. In this review, we summarize the literature pertaining to age-specific differences in COVID-19 pathogenesis and clinical manifestation. In addition, we review molecular distinctions in how the early life immune system responds to infection and vaccination. Finally, we discuss recent advances in development of pediatric COVID-19 vaccines and provide future directions for basic and translational research in this area.

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.

Single-cell immune profiling reveals thymus-seeding populations, T cell commitment, and multilineage development in the human thymus

T cell development in the mouse thymus has been studied extensively, but less is known regarding T cell development in the human thymus. We used a combination of single-cell techniques and functional assays to perform deep immune profiling of human T cell development, focusing on the initial stages of prelineage commitment. We identified three thymus-seeding progenitor populations that also have counterparts in the bone marrow. In addition, we found that the human thymus physiologically supports the development of monocytes, dendritic cells, and NK cells, as well as limited development of B cells. These results are an important step toward monitoring and guiding regenerative therapies in patients after hematopoietic stem cell transplantation.

Thymic B Cells as a New Player in the Type 1 Diabetes Response

Type 1 diabetes (T1d) results from a sustained autoreactive T and B cell response towards insulin-producing β cells in the islets of Langerhans. The autoreactive nature of the condition has led to many investigations addressing the genetic or cellular changes in primary lymphoid tissues that impairs central tolerance- a key process in the deletion of autoreactive T and B cells during their development. For T cells, these studies have largely focused on medullary thymic epithelial cells (mTECs) critical for the effective negative selection of autoreactive T cells in the thymus. Recently, a new cellular player that impacts positively or negatively on the deletion of autoreactive T cells during their development has come to light, thymic B cells. Normally a small population within the thymus of mouse and man, thymic B cells expand in T1d as well as other autoimmune conditions, reside in thymic ectopic germinal centres and secrete autoantibodies that bind selective mTECs precipitating mTEC death. In this review we will discuss the ontogeny, characteristics and functionality of thymic B cells in healthy and autoimmune settings. Furthermore, we explore how in silico approaches may help decipher the complex cellular interplay of thymic B cells with other cells within the thymic microenvironment leading to new avenues for therapeutic intervention.

Immunopathological Changes in SARS-CoV-2 Critical and Non-critical Pneumonia Patients: A Systematic Review to Determine the Cause of Co-infection

The ongoing COVID-19 pandemic originating from Wuhan, China is causing major fatalities across the world. Viral pneumonia is commonly observed in COVID-19 pandemic. The number of deaths caused by viral pneumonia is mainly due to secondary bacterial or fungal infection. The immunopathology of SARS-CoV-2 viral pneumonia is poorly understood with reference to human clinical data collected from patients infected by virus and secondary bacterial or fungal infection occurring simultaneously. The co-infection inside the lungs caused by pneumonia has direct impact on the changing lymphocyte and neutrophil counts. Understanding the attribution of these two immunological cells triggered by cytokines level change is of great importance to identify the progression of pneumonia from non-severe to severe state in hospitalized patients. This review elaborates the cytokines imbalance observed in SARS-CoV-1 (2003 epidemic), SARS-CoV-2 (2019 pandemic) viral pneumonia and community acquired pneumonia (CAP), respectively, in patients to determine the potential reason of co-infection. In this review the epidemiology, virology, clinical symptoms, and immunopathology of SARS-CoV-2 pneumonia are narrated. The immune activation during SARS-CoV-1 pneumonia, bacterial, and fungal pneumonia is discussed. Here it is further analyzed with the available literatures to predict the potential internal medicines, prognosis and monitoring suggesting better treatment strategy for SARS-CoV-2 pneumonia patients.

Hyperdense Thymic Atrophy After Chemotherapy in Pediatric Patients With Extrathoracic Malignancies

OBJECTIVE

The aim of the study was to evaluate computed tomography (CT) imaging findings of hyperdense thymic atrophy after chemotherapy in pediatric patients with extrathoracic malignancies.

METHODS

Seventy-eight pediatric patients with extrathoracic malignancies, who developed thymic atrophy after chemotherapy, were included in this study. All patients underwent CT imaging before and after chemotherapy. We retrospectively reviewed the CT images. Hyperdense thymic atrophy was defined as thymic atrophy with high CT attenuation (≥80 HU).

RESULTS

Hyperdense thymic atrophy after chemotherapy was observed in 7 (9%) of 78 patients. Age (4.3 ± 2.4 vs 8.4 ± 5.4 years, P < 0.01), thymic CT attenuation before chemotherapy (70.4 ± 18.8 vs 55.2 ± 11.9 HU, P < 0.01), reduction rate in thymic area (0.76 ± 0.06 vs 0.60 ± 0.22, P < 0.01), and thymic CT attenuation change (30.3 ± 15.2 vs -16.8 ± 24.0 HU, P < 0.01) were significantly different between patients with and without hyperdense thymic atrophy after chemotherapy. Thymic CT attenuation after chemotherapy (61.2 ± 23.8 vs 33.8 ± 30.1 HU, P < 0.01) and thymic CT attenuation change (-1.3 ± 21.2 vs -19.3 ± 27.9 HU, P < 0.01) were significantly different between patients 5 years or younger (n = 29) and 6 years or older (n = 49).

CONCLUSIONS

Hyperdense thymic atrophy after chemotherapy was observed in 9% of pediatric patients with extrathoracic malignancies. It was associated with younger age, greater thymic CT attenuation before chemotherapy, larger reduction rate in thymic area, and greater thymic CT attenuation change.

Conventional and Computational Flow Cytometry Analyses Reveal Sustained Human Intrathymic T Cell Development From Birth Until Puberty

The thymus is the organ where subsets of mature T cells are generated which subsequently egress to function as central mediators in the immune system. While continuously generating T cells even into adulthood, the thymus does undergo involution during life. This is characterized by an initial rapid decrease in thymic cellularity during early life and by a second age-dependent decline in adulthood. The thymic cellularity of neonates remains low during the first month after birth and the tissue reaches a maximum in cellularity at 6 months of age. In order to study the effect that this first phase of thymic involution has on thymic immune subset frequencies, we performed multi-color flow cytometry on thymic samples collected from birth to 14 years of age. In consideration of the inherent limitations posed by conventional flow cytometry analysis, we established a novel computational analysis pipeline that is adapted from single-cell transcriptome sequencing data analysis. This allowed us to overcome technical effects by batch correction, analyze multiple samples simultaneously, limit computational cost by subsampling, and to rely on KNN-graphs for graph-based clustering. As a result, we successfully identified rare, distinct and gradually developing immune subsets within the human thymus tissues. Although the thymus undergoes early involution from infanthood onwards, our data suggests that this does not affect human T-cell development as we did not observe significant alterations in the proportions of T-lineage developmental intermediates from birth to puberty. Thus, in addition to providing an interesting novel strategy to analyze conventional flow cytometry data for the thymus, our work shows that the early phase of human thymic involution mainly limits the overall T cell output since no obvious changes in thymocyte subsets could be observed.

Evolution of pathologic T-cell subsets in patients with atopic dermatitis from infancy to adulthood

BACKGROUND

The circulating immune phenotype was defined in adults and young children with early atopic dermatitis (AD), but chronologic changes in the blood of infants and children with AD through adolescence have not been explored.

OBJECTIVE

We sought to compare immune activation and cytokine polarization in the blood of 0- to 5-year-old (n = 39), 6- to 11-year-old (n = 26), 12- to 17-year-old (n = 21) and 18-year-old or older (n = 43) patients with AD versus age-matched control subjects.

METHODS

Flow cytometry was used to measure IFN-γ, IL-9, IL-13, IL-17, and IL-22 cytokine levels in CD4⁺/CD8⁺ T cells, with inducible costimulator molecule and HLA-DR defining midterm and long-term T-cell activation, respectively, within skin-homing/cutaneous lymphocyte antigen (CLA)⁺ versus systemic/CLA^- T cells. Unsupervised clustering differentiated patients based on their blood biomarker frequencies.

RESULTS

Although CLA⁺ T_H1 frequencies were significantly lower in infants with AD versus all older patients (P < .01), frequencies of CLA⁺ T_H2 T cells were similarly expanded across all AD age groups compared with control subjects (P < .05). After infancy, CLA^- T_H2 frequencies were increased in patients with AD in all age groups, suggesting systemic immune activation with disease chronicity. IL-22 frequencies serially increased from normal levels in infants to highly significant levels in adolescents and adults compared with levels in respective control subjects (P < .01). Unsupervised clustering aligned the AD profiles along an age-related spectrum from infancy to adulthood (eg, inducible costimulator molecule and IL-22).

CONCLUSIONS

The adult AD phenotype is achieved only in adulthood. Unique cytokine signatures characterizing individual pediatric endotypes might require age-specific therapies. Future longitudinal studies, comparing the profile of patients with cleared versus persistent pediatric AD, might define age-specific changes that predict AD clearance.

Temporal expression patterns of the melatoninergic system in the human thymus of children

OBJECTIVES

To obtain greater knowledge of the extra-pineal sources of melatonin during development, the amount of indolamine and the expression levels of the last two enzymes involved in its biosynthesis, Arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT), were analyzed in the human thymus from children from three different age groups (from days to years). The melatonin membrane and nuclear receptor expression levels also were studied.

METHODS

Quantitative reverse transcriptase PCR and western blot were performed to investigate the receptor and enzyme expression levels. The results were examined and correlated with the ages of the thymuses.

RESULTS

We found high levels of indolamine in the thymuses of newborns (younger than 1 month), which decreased during development; thymuses from the months (from 2 to 11 months) and years (from 1 to 12 years) groups showed lower levels. A similar decline was also observed in the mRNA of the AANAT enzyme and the expression levels of melatonin receptors. However, ASMT expression was exactly the opposite, with low levels in the newborn group and higher levels in the years group. Our results show that the thymic synthesis of melatonin occurs very early in childhood. Additionally, this is the first report that is focused on melatonin receptors expression in the human thymus.

CONCLUSION

Considering the limited melatonin synthesis performed by the newborn pineal gland, we suggest that the high levels of melatonin found in human thymus in this experimental group arise from synthesis in the tissue itself, which could be contributing to the immune efficiency at the thymic level.

[Thymic B cells: not simple bystanders of T cell lymphopoiesis]

The thymus is the central site for the differentiation and selection of T cells. It has been known for decades that B lymphocytes reside in the thymus, but little attention has been paid to this unique population. Thymic B cells are mainly located in the medulla and at the cortico-medullary junction. They develop intrathymically, do not recirculate and harbor a distinct phenotype in comparison to peripheral B cells. Furthermore, because of their activated phenotype and their precise histological localization, they have been suspected to play a role in the selection of self-reactive T cells. But it is only during this last decade that murine and human studies have highlighted their functions, such as antigen-presenting cells shaping the T cell repertoire. These works have demonstrated the major role of thymic B cells in the immune system.

Loss of CD44dim Expression from Early Progenitor Cells Marks T-Cell Lineage Commitment in the Human Thymus

Human T-cell development is less well studied than its murine counterpart due to the lack of genetic tools and the difficulty of obtaining cells and tissues. Here, we report the transcriptional landscape of 11 immature, consecutive human T-cell developmental stages. The changes in gene expression of cultured stem cells on OP9-DL1 match those of ex vivo isolated murine and human thymocytes. These analyses led us to define evolutionary conserved gene signatures that represent pre- and post-αβ T-cell commitment stages. We found that loss of dim expression of CD44 marks human T-cell commitment in early CD7⁺CD5⁺CD45^dim cells, before the acquisition of CD1a surface expression. The CD44⁻CD1a⁻ post-committed thymocytes have initiated in frame T-cell receptor rearrangements that are accompanied by loss of capacity to differentiate toward myeloid, B- and NK-lineages, unlike uncommitted CD44^dimCD1a⁻ thymocytes. Therefore, loss of CD44 represents a previously unrecognized human thymocyte stage that defines the earliest committed T-cell population in the thymus.

Ikaros, Helios, and Aiolos protein levels increase in human thymocytes after β selection

In human T cell development, the mechanisms that regulate cell fate decisions after TCRβ expression remain unclear. We defined the stages of T cell development that flank TCRβ expression and found distinct patterns of human T cell development. In half the subjects, T cell development progressed from the CD4(-)CD8(-) double-negative stage to the CD4(+)CD8(+) double-positive (DP) stage through an immature single-positive (ISP) CD4(+) intermediate. However, in some patients, CD4 and CD8 were expressed simultaneously and the ISP population was small. In each group of patients, CD3(-) ISP and DP thymocytes were subdivided into ISP1, ISP2, DP1, DP2, DP3, DP4, and DP5 developmental stages according to their expression of CD28, CD44, CD1a, CD7, CD45RO, and CD38. The ISP2, DP2, and DP3 thymocyte populations proliferated more robustly than ISP1 and DP1 and expressed markers consistent with TCRβ expression. After the DP3 stage, proliferation returned to baseline levels. We then analyzed protein levels of Ikaros, Helios, and Aiolos, the three Ikaros family members most abundantly expressed in human thymocytes. Ikaros and Helios expression increased transiently at the ISP2, DP2, and DP3 populations. Aiolos expression also increased at the ISP2, DP2, and DP3 stages, but its expression remained elevated throughout the DP4 and DP5 stages. In summary, we propose a model of human T cell development that reflects the asynchronous nature of TCRβ expression and we define the subpopulations of thymocytes that are highly proliferative and express Ikaros family members.

Visualizing Human Hematopoietic Stem Cell Trafficking In Vivo Using a Zebrafish Xenograft Model

Zebrafish is gaining increased popularity as a model organism to study stem cell biology. It also is widely used as model system to visualize human leukemic stem cells. However, xenotransplantation of primary human stem/progenitor cells has not been described. Here, we use casper pigmentation mutant fish that are transparent crossed to fli-GFP transgenic fish as recipients of red labeled human CD34(+) cells. We have investigated various conditions and protocols with the aim to monitor and visualize the fate of transplanted human CD34(+) cells. We here report successful use of casper mutant zebrafish embryos for the direct monitoring of human hematopoietic stem cell transplantation, differentiation, and trafficking in vivo.

The functional relationship between hematopoietic stem cells and developing T lymphocytes

In contrast to all other blood and immune cells, T lymphocytes do not develop in the bone marrow (BM), but in the specialized microenvironment provided by the thymus. Similar to the other lineages, however, all T cells arise from multipotent hematopoietic stem cells (HSCs) that reside in the BM. Not all HSCs give rise to T cells; but how many and what kind of developmental checkpoints are located along this intricate differentiation path is the subject of intense research. Traditionally, this process has been studied almost exclusively using mouse cells, but recent advances in immunodeficient mouse models, high-speed cell sorting, lentiviral transduction protocols, and deep sequencing techniques have allowed these questions to be addressed using human cells. Here we review the process of thymic seeding by BM-derived cells and T cell commitment in humans, discussing recent insights into the clonal composition of the thymus and the definition of developmental checkpoints, on the basis of insights from human severe combined immunodeficiency patients.

Development of a diverse human T-cell repertoire despite stringent restriction of hematopoietic clonality in the thymus

The fate and numbers of hematopoietic stem cells (HSC) and their progeny that seed the thymus constitute a fundamental question with important clinical implications. HSC transplantation is often complicated by limited T-cell reconstitution, especially when HSC from umbilical cord blood are used. Attempts to improve immune reconstitution have until now been unsuccessful, underscoring the need for better insight into thymic reconstitution. Here we made use of the NOD-SCID-IL-2Rγ(-/-) xenograft model and lentiviral cellular barcoding of human HSCs to study T-cell development in the thymus at a clonal level. Barcoded HSCs showed robust (>80% human chimerism) and reproducible myeloid and lymphoid engraftment, with T cells arising 12 wk after transplantation. A very limited number of HSC clones (<10) repopulated the xenografted thymus, with further restriction of the number of clones during subsequent development. Nevertheless, T-cell receptor rearrangements were polyclonal and showed a diverse repertoire, demonstrating that a multitude of T-lymphocyte clones can develop from a single HSC clone. Our data imply that intrathymic clonal fitness is important during T-cell development. As a consequence, immune incompetence after HSC transplantation is not related to the transplantation of limited numbers of HSC but to intrathymic events.

Identification of checkpoints in human T-cell development using severe combined immunodeficiency stem cells

BACKGROUND

Severe combined immunodeficiency (SCID) represents congenital disorders characterized by a deficiency of T cells caused by arrested development in the thymus. Yet the nature of these developmental blocks has remained elusive because of the difficulty of taking thymic biopsy specimens from affected children.

OBJECTIVE

We sought to identify the stages of arrest in human T-cell development caused by various major types of SCID.

METHODS

We performed transplantation of SCID CD34(+) bone marrow stem/progenitor cells into an optimized NSG xenograft mouse model, followed by detailed phenotypic and molecular characterization using flow cytometry, immunoglobulin and T-cell receptor spectratyping, and deep sequencing of immunoglobulin heavy chain (IGH) and T-cell receptor δ (TRD) loci.

RESULTS

Arrests in T-cell development caused by mutations in IL-7 receptor α (IL7RA) and IL-2 receptor γ (IL2RG) were observed at the most immature thymocytes much earlier than expected based on gene expression profiling of human thymocyte subsets and studies with corresponding mouse mutants. T-cell receptor rearrangements were functionally required at the CD4(-)CD8(-)CD7(+)CD5(+) stage given the developmental block and extent of rearrangements in mice transplanted with Artemis-SCID cells. The xenograft model used is not informative for adenosine deaminase-SCID, whereas hypomorphic mutations lead to less severe arrests in development.

CONCLUSION

Transplanting CD34(+) stem cells from patients with SCID into a xenograft mouse model provides previously unattainable insight into human T-cell development and functionally identifies the arrest in thymic development caused by several SCID mutations.

Early pediatric atopic dermatitis shows only a cutaneous lymphocyte antigen (CLA)(+) TH2/TH1 cell imbalance, whereas adults acquire CLA(+) TH22/TC22 cell subsets

BACKGROUND

Identifying differences and similarities between cutaneous lymphocyte antigen (CLA)(+) polarized T-cell subsets in children versus adults with atopic dermatitis (AD) is critical for directing new treatments toward children.

OBJECTIVE

We sought to compare activation markers and frequencies of skin-homing (CLA(+)) versus systemic (CLA(-)) "polar" CD4 and CD8 T-cell subsets in patients with early pediatric AD, adults with AD, and control subjects.

METHODS

Flow cytometry was used to measure CD69/inducible costimulator/HLA-DR frequency in memory cell subsets, as well as IFN-γ, IL-13, IL-9, IL-17, and IL-22 cytokines, defining TH1/cytotoxic T (TC) 1, TH2/TC2, TH9/TC9, TH17/TC17, and TH22/TC22 populations in CD4 and CD8 cells, respectively. We compared peripheral blood from 19 children less than 5 years old and 42 adults with well-characterized moderate-to-severe AD, as well as age-matched control subjects (17 children and 25 adults).

RESULTS

Selective inducible costimulator activation (P < .001) was seen in children. CLA(+) TH2 T cells were markedly expanded in both children and adults with AD compared with those in control subjects, but decreases in CLA(+) TH1 T-cell numbers were greater in children with AD (17% vs 7.4%, P = .007). Unlike in adults, no imbalances were detected in CLA(-) T cells from pediatric patients with AD nor were there altered frequencies of TH22 T cells within the CLA(+) or CLA(-) compartments. Adults with AD had increased frequencies of IL-22-producing CD4 and CD8 T cells within the skin-homing population, compared with controls (9.5% vs 4.5% and 8.6% vs 2.4%, respectively; P < .001), as well as increased HLA-DR activation (P < .01).

CONCLUSIONS

These data suggest that TH2 activation within skin-homing T cells might drive AD in children and that reduced counterregulation by TH1 T cells might contribute to excess TH2 activation. TH22 "spreading" of AD is not seen in young children and might be influenced by immune development, disease chronicity, or recurrent skin infections.

The co-stimulatory effects of MyD88-dependent Toll-like receptor signaling on activation of murine γδ T cells

γδ T cells express several different toll-like receptor (TLR)s. The role of MyD88- dependent TLR signaling in TCR activation of murine γδ T cells is incompletely defined. Here, we report that Pam3CSK4 (PAM, TLR2 agonist) and CL097 (TLR7 agonist), but not lipopolysaccharide (TLR4 agonist), increased CD69 expression and Th1-type cytokine production upon anti-CD3 stimulation of γδ T cells from young adult mice (6-to 10-week-old). However, these agonists alone did not induce γδ T cell activation. Additionally, we noted that neither PAM nor CL097 synergized with anti-CD3 in inducing CD69 expression on γδ T cells of aged mice (21-to 22-month-old). Compared to young γδ T cells, PAM and CL097 increased Th-1 type cytokine production with a lower magnitude from anti-CD3- stimulated, aged γδ T cells. Vγ1⁺ and Vγ4⁺ cells are two subpopulations of splenic γδ T cells. PAM had similar effects in anti-CD3-activated control and Vγ4⁺ subset- depleted γδ T cells; whereas CL097 induced more IFN-γ production from Vγ4⁺ subset-depleted γδ T cells than from the control group. Finally, we studied the role of MyD88-dependent TLRs in γδ T cell activation during West Nile virus (WNV) infection. γδ T cell, in particular, Vγ1⁺ subset expansion was significantly reduced in both MyD88- and TLR7- deficient mice. Treatment with TLR7 agonist induced more Vγ1⁺ cell expansion in wild-type mice during WNV infection. In summary, these results suggest that MyD88-dependent TLRs provide co-stimulatory signals during TCR activation of γδ T cells and these have differential effects on distinct subsets.

Bayesian immunological model development from the literature: example investigation of recent thymic emigrants

Bayesian estimation techniques offer a systematic and quantitative approach for synthesizing data drawn from the literature to model immunological systems. As detailed here, the practitioner begins with a theoretical model and then sequentially draws information from source data sets and/or published findings to inform estimation of model parameters. Options are available to weigh these various sources of information differentially per objective measures of their corresponding scientific strengths. This approach is illustrated in depth through a carefully worked example for a model of decline in T-cell receptor excision circle content of peripheral T cells during development and aging. Estimates from this model indicate that 21 years of age is plausible for the developmental timing of mean age of onset of decline in T-cell receptor excision circle content of peripheral T cells.

Sustained Engraftment of Cryopreserved Human Bone Marrow CD34(+) Cells in Young Adult NSG Mice

Hematopoietic stem cells (HSCs) are defined by their ability to repopulate the bone marrow of myeloablative conditioned and/or (lethally) irradiated recipients. To study the repopulating potential of human HSCs, murine models have been developed that rely on the use of immunodeficient mice that allow engraftment of human cells. The NSG xenograft model has emerged as the current standard for this purpose allowing for engraftment and study of human T cells. Here, we describe adaptations to the original NSG xenograft model that can be readily implemented. These adaptations encompass use of adult mice instead of newborns and a short ex vivo culture. This protocol results in robust and reproducible high levels of lympho-myeloid engraftment. Immunization of recipient mice with relevant antigen resulted in specific antibody formation, showing that both T cells and B cells were functional. In addition, bone marrow cells from primary recipients exhibited repopulating ability following transplantation into secondary recipients. Similar results were obtained with cryopreserved human bone marrow samples, thus circumventing the need for fresh cells and allowing the use of patient derived bio-bank samples. Our findings have implications for use of this model in fundamental stem cell research, immunological studies in vivo and preclinical evaluations for HSC transplantation, expansion, and genetic modification.

Role of cognitive parameters in dengue hemorrhagic fever and dengue shock syndrome

Dengue is becoming recognized as one of the most important vector-borne human diseases. It is predominant in tropical and subtropical zones but its geographical distribution is progressively expanding, making it an escalating global health problem of today. Dengue presents with spectrum of clinical manifestations, ranging from asymptomatic, undifferentiated mild fever, dengue fever (DF), to dengue hemorrhagic fever (DHF) with or without shock (DSS), a life-threatening illness characterized by plasma leakage due to increased vascular permeability. Currently, there are no antiviral modalities or vaccines available to treat and prevent dengue. Supportive care with close monitoring is the standard clinical practice. The mechanisms leading to DHF/DSS remains poorly understood. Multiple factors have been attributed to the pathological mechanism, but only a couple of these hypotheses are popular in scientific circles. The current discussion focuses on underappreciated factors, temperature, natural IgM, and endotoxin, which may be critical components playing roles in dengue pathogenesis.

Alternative splicing and differential expression of the islet autoantigen IGRP between pancreas and thymus contributes to immunogenicity of pancreatic islets but not diabetogenicity in humans

AIMS/HYPOTHESIS

Thymic expression of self-antigens during T-lymphocyte development is believed to be crucial for preventing autoimmunity. It has been suggested that G6PC2, the gene encoding islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP), is differentially spliced between pancreatic beta cells and the thymus. This may contribute to incomplete elimination of IGRP-specific T lymphocytes in the thymus, predisposing individuals to type 1 diabetes. We tested whether specific splice variation in islets vs thymus correlates with loss of tolerance to IGRP in type 1 diabetes.

METHODS

Expression of G6PC2 splice variants was compared among thymus, purified medullary thymic epithelial cells and pancreatic islets by RT-PCR. Differential immunogenicity of IGRP splice variants was tested in patients and healthy individuals for autoantibodies and specific cytotoxic T lymphocytes using radiobinding assays and HLA class I multimers, respectively.

RESULTS

Previously reported G6PC2 splice variants, including full-length G6PC2, were confirmed, albeit that they occurred in both pancreas and thymus, rather than islets alone. Yet, their expression levels were profoundly greater in islets than in thymus. Moreover, three novel G6PC2 variants were discovered that occur in islets only, leading to protein truncations, frame shifts and neo-sequences prone to immunogenicity. However, autoantibodies to novel or known IGRP splice variants did not differ between patients and healthy individuals, and similar frequencies of IGRP-specific cytotoxic T lymphocytes could be detected in both patients with type 1 diabetes and healthy individuals.

CONCLUSIONS/INTERPRETATION

We propose that post-transcriptional variation of tissue-specific self-proteins may affect negative thymic selection, although this need not necessarily lead to disease.

Human neonatal naive CD4+ T cells have enhanced activation-dependent signaling regulated by the microRNA miR-181a

Compared with older children and adults, human neonates have reduced and delayed CD4(+) T cell immunity to certain pathogens, but the mechanisms for these developmental differences in immune function remain poorly understood. We investigated the hypothesis that impaired human neonatal CD4(+) T cell immunity was due to reduced signaling by naive CD4(+) T cells following engagement of the αβ-TCR/CD3 complex and CD28. Surprisingly, calcium flux following engagement of CD3 was significantly higher in neonatal naive CD4(+) T cells from umbilical cord blood (CB) compared with naive CD4(+) T cells from adult peripheral blood. Enhanced calcium flux was also observed in adult CD4(+) recent thymic emigrants. Neonatal naive CD4(+) T cells also had higher activation-induced Erk phosphorylation. The microRNA miR-181a, which enhances activation-induced calcium flux in murine thymocytes, was expressed at significantly higher levels in CB naive CD4(+) T cells compared with adult cells. Overexpression of miR-181a in adult naive CD4(+) T cells increased activation-induced calcium flux, implying that the increased miR-181a levels of CB naive CD4(+) T cells contributed to their enhanced signaling. In contrast, AP-1-dependent transcription, which is downstream of Erk and required for full T cell activation, was decreased in CB naive CD4(+) T cells compared with adult cells. Thus, CB naive CD4(+) T cells have enhanced activation-dependent calcium flux, indicative of the retention of a thymocyte-like phenotype. Enhanced calcium signaling and Erk phosphorylation are decoupled from downstream AP-1-dependent transcription, which is reduced and likely contributes to limitations of human fetal and neonatal CD4(+) T cell immunity.

Differential requirements for Wnt and Notch signaling in hematopoietic versus thymic niches

All blood cells are derived from multipotent stem cells, the so-called hematopoietic stem cells (HSCs), that in adults reside in the bone marrow. Most types of blood cells also develop there, with the notable exception of T lymphocytes that develop in the thymus. For both HSCs and developing T cells, interactions with the surrounding microenvironment are critical in regulating maintenance, differentiation, apoptosis, and proliferation. Such specialized regulatory microenvironments are referred to as niches and provide both soluble factors as well as cell-cell interactions between niche component cells and blood cells. Two pathways that are critical for early T cell development in the thymic niche are Wnt and Notch signaling. These signals also play important but controversial roles in the HSC niche. Here, we review the differences and similarities between the thymic and hematopoietic niches, with particular focus on Wnt and Notch signals, as well as the latest insights into regulation of these developmentally important pathways.

Adoptive transfer of macrophages from adult mice reduces mortality in mice infected with human enterovirus 71

Human enterovirus 71 (EV71) causes hand, foot and mouth disease in children under 6 years of age, and the neurological complications of this virus can lead to death. Until now, no vaccines or drugs have been available for the clinical control of this epidemic. Macrophages can engulf pathogens and mediate a series of host immune responses that play a role in the defence against infectious diseases. Using immunohistochemistry, we observed the localizations of virus in muscle tissues of EV71-infected mice. The macrophages isolated from the adult mice could kill the virus gradually in vitro, as shown using quantitative real-time PCR (qRT-PCR) and virus titration. Co-localisation of lysosomes and virus within macrophages suggested that the lysosomes were possibly responsible for the phagocytosis of EV71. Activation of the macrophages in the peritoneal cavity of mice four days pre-infection reduced the mortality of mice upon lethal EV71 infection. The adoptive transfer of macrophages from adult mice inhibited virus replication in the muscle tissues of infected mice, and this was followed by a relief of symptoms and a significant reduction of mortality, which suggested that the adoptive transfer of macrophages from adult humans represents a potential strategy to treat EV71-infected patients.

Combined TCRG and TCRA TREC analysis reveals increased peripheral T-lymphocyte but constant intra-thymic proliferative history upon ageing

T-cell receptor (TCR) repertoire diversity, thymic output, clonal size and peripheral T-lymphocyte numbers largely depend on intra-thymic and post-thymic T-lymphocyte proliferation. However, quantitative insight into thymocyte and T-lymphocyte proliferation is still lacking. We developed a new TCRG-based TCR excision circle (TREC) assay, the Vγ-Jγ TREC assay, which we used together with an adjusted δREC-ψJα TREC assay to quantify the proliferative history of human thymocyte and T-lymphocyte subpopulations from children and adults. This revealed that thymocytes undergo ∼6-8 intra-thymic cell divisions from the double negative (DN) 3 developmental stage onwards, which appeared independent of age. Thus thymocyte proliferation after the DN3 developmental stages is stable and therefore not contributing to the reduced thymic output upon ageing. Cord blood naive T lymphocytes had already undergone ∼2-3 post-thymic cell divisions, which increased to ∼6-7 cell divisions in naive T lymphocytes of middle-aged adults, indicating the importance of homeostatic naive T-lymphocyte proliferation from a young age onwards in the maintenance of peripheral T-lymphocyte numbers. In conclusion, our data provide quantitative insight into the proliferative history of thymocyte and T-lymphocyte subpopulations and alterations herein upon ageing. This novel TREC assay approach could prove valuable in immune status monitoring in a variety of conditions.

Developmental allometry and paediatric malaria

WHO estimates that 80% of mortality due to malaria occurs among infants and young children. Though it has long been established that malaria disproportionately affects children under age five, our understanding of the underlying biological mechanisms for this distribution remains incomplete. Many studies use age as an indicator of exposure, but age may affect malaria burden independently of previous exposure. Not only does the severity of malaria infection change with age, but the clinical manifestation of disease does as well: younger children are more likely to suffer severe anaemia, while older children are more likely to develop cerebral malaria. Intensity of transmission and acquired immunity are important determinants of this age variation, but age differences remain consistent over varying transmission levels. Thus, age differences in clinical presentation may involve inherent age-related factors as well as still-undiscovered facets of acquired immunity, perhaps including the rates at which relevant aspects of immunity are acquired. The concept of "allometry" - the relative growth of a part in relation to that of an entire organism or to a standard - has not previously been applied in the context of malaria infection. However, because malaria affects a number of organs and cells, including the liver, red blood cells, white blood cells, and spleen, which may intrinsically develop at rates partly independent of each other and of a child's overall size, developmental allometry may influence the course and consequences of malaria infection. Here, scattered items of evidence have been collected from a variety of disciplines, aiming to suggest possible research paths for investigating exposure-independent age differences affecting clinical outcomes of malaria infection.

Influence of surgical and chemical orchidectomy on weight and distribution of AChE-nerve fibres in thymuses of adult rats

The thymus is a crossroad between the immune and neuroendocrine systems. As such, it is innervated by acetylcholinesterase (AChE)-positive fibres of the vagus, the recurrent laryngeal and the phrenic nerves. It is well know, that the innervations density of the thymus increases with age. In our study, adult rats were orchidectomized (surgically and chemically by the application of a luteinizing hormone-releasing hormone). The density of AChE-positive nerve fibres in thymuses, as well as the weight of thymuses was examined. The authors found that both surgical and chemical orchidectomy result in macroscopic and microscopic regeneration of the atrophied thymuses. In regenerated rat’s thymuses after orchidectomy the density of AChE-positive nerve fibres was markedly higher in comparison with the control animals. The distribution, as well as the density of AChE-positive nerve fibres in regenerated thymuses after orchidectomy evokes the images of its innervations like in young animals before age-related involution. The authors also found a markedly higher weight of thymuses of orchidectomized rats in comparison with the control groups. In recent study the authors proved that after 8 weeks surgical orchidectomy leads to the regeneration of thymic AChE-positive innervation and chemical orchidectomy by administration of luteinizing hormone-releasing hormone after 4 weeks of adult rats.

Discovery of new microRNAs by small RNAome deep sequencing in childhood acute lymphoblastic leukemia

MicroRNAs (miRNAs) relevant to acute lymphoblastic leukemia (ALL) in children are hypothesized to be largely unknown as most miRNAs have been identified in non-leukemic tissues. In order to discover these miRNAs, we applied high-throughput sequencing to pooled fractions of leukemic cells obtained from 89 pediatric cases covering seven well-defined genetic types of ALL and normal hematopoietic cells. This resulted into 78 million small RNA reads representing 554 known, 28 novel and 431 candidate novel miR genes. In all, 153 known, 16 novel and 170 candidate novel mature miRNAs and miRNA-star strands were only expressed in ALL, whereas 140 known, 2 novel and 82 candidate novel mature miRNAs and miRNA-star strands were unique to normal hematopoietic cells. Stem-loop reverse transcriptase (RT)-quantitative PCR analyses confirmed the differential expression of selected mature miRNAs in ALL types and normal cells. Expression of 14 new miRNAs inversely correlated with expression of predicted target genes (-0.49 ≤ Spearman's correlation coefficients (Rs)≤ -0.27, P ≤ 0.05); among others, low levels of novel sol-miR-23 associated with high levels of its predicted (antiapoptotic) target BCL2 (B-cell lymphoma 2) in precursor B-ALL (Rs -0.36, P = 0.007). The identification of >1000 miR genes expressed in different types of ALL forms a comprehensive repository for further functional studies that address the role of miRNAs in the biology of ALL.

NOTCH and phosphatidylinositide 3-kinase/phosphatase and tensin homolog deleted on chromosome ten/AKT/mammalian target of rapamycin (mTOR) signaling in T-cell development and T-cell acute lymphoblastic leukemia

Activating mutations in NOTCH1 consitute the most prominent genetic abnormality in T-cell acute lymphoblastic leukemia (T-ALL). However, most T-ALL cell lines with NOTCH1 mutations are resistant to treatment with γ-secretase inhibitors (GSIs). The spotlight is now shifting to the phosphatidylinositide 3-kinase (PI3K)/phosphatase and tensin homolog deleted on chromosome ten (PTEN)/AKT/mammalian target of rapamycin (mTOR) pathway as another key potential target. These two signaling routes are deregulated in many types of cancer. In this review we discuss these two pathways with respect to their signaling mechanisms, functions during T-cell development, and their mutual roles in the development of T-ALL.

Protein tyrosine kinase 7: a novel surface marker for human recent thymic emigrants with potential clinical utility

Recent thymic emigrants (RTEs) are antigenically naive T cells that have recently completed intrathymic maturation and have emigrated from the thymus to the periphery. RTEs are clinically and immunologically important as they are essential for maintaining peripheral T cells in sufficient numbers in order to recognize, by their αβT-cell receptors (TCRs), a diverse array of foreign peptide antigens. However, RTE frequency and function has been poorly understood because of a lack of surface markers to distinguish them from older non-RTE naive T cells. This review summarizes the biology of the intrathymic generation and function of RTEs, including the recent identification of protein tyrosine kinase 7 (PTK7) as a novel marker for human RTEs of the CD4 (helper) T-cell lineage. PTK7+ RTEs in adults have a reduced capacity for activation-induced proliferation and cytokine production (interleukin-2 and interferon-γ) than older PTK7- naive CD4 T cells. Importantly, this immaturity in CD4 RTE effector function may contribute to the reduced adaptive immune responses observed in situations in which CD4 RTEs predominate, including the fetus, neonate and young infant, and following immune reconstitution, such as post-hematopoietic stem cell transplant. The ability to identify viable CD4+ RTEs based on PTK7 surface staining may be particularly useful in the infant for better defining the impact of nutritional and environmental factors on thymic output, peripheral T-cell function and adaptive immune responses to vaccination and infection.

Lymphocytopenia as a marker for pandemic influenza A/H1N1 2009 virus infection in children

Lymphocytopenia has been reported in adults with pandemic influenza A/H1N1 2009 infection, but data in children are inconclusive. Data from 76 children presented with flu-like symptoms between July and November 2009 and tested for pandemic influenza A/H1N1 2009 virus and white blood cell (WBC) counts were analyzed. Samples from 37 (48.7%) children resulted in a positive PCR assay for pandemic influenza A/H1N1 2009 virus. When comparing data from these children with data from 39 (51.3%) children with uncomplicated flu-like illness and negative PCR assay for pandemic influenza A/H1N1 2009 virus, no difference in disease duration, median age, red blood cell count, hemoglobin concentration, C reactive protein concentration, and absolute neutrophil count was observed, whereas significant differences were apparent when considering WBC count, relative and absolute lymphocyte count, absolute lymphocyte count z-score, and platelet count. Receiver operating characteristic curve analysis revealed that the best absolute lymphocyte count and absolute lymphocyte count z-score cut-points that simultaneously maximized sensitivity and specificity were 2,256 cells/µl and -0.89, respectively, sensitivity being 0.81 (95% CI: 0.68-0.94), specificity 0.87 (95% CI: 0.77-0.98), positive predictive value 0.85 (95% CI: 0.74-0.97), and negative predictive value 0.83 (95% CI: 0.71-0.94). In conclusion, lymphocytopenia is a marker for influenza A/H1N1 2009 virus infection in children. Absolute lymphocyte count <2,556 cells/µl or absolute lymphocyte count z-score < -0.89 may be useful cut-offs to discriminate against children at higher risk of infection during epidemics. Considering that the pandemic virus is highly likely to continue to circulate in the coming winter season, these findings provide direct and practical implications for the near future.

MicroRNA characterize genetic diversity and drug resistance in pediatric acute lymphoblastic leukemia

BACKGROUND

MicroRNA regulate the activity of protein-coding genes including those involved in hematopoietic cancers. The aim of the current study was to explore which microRNA are unique for seven different subtypes of pediatric acute lymphoblastic leukemia.

DESIGN AND METHODS

Expression levels of 397 microRNA (including novel microRNA) were measured by quantitative real-time polymerase chain reaction in 81 cases of pediatric leukemia and 17 normal hematopoietic control cases.

RESULTS

All major subtypes of acute lymphoblastic leukemia, i.e. T-cell, MLL-rearranged, TEL-AML1-positive, E2A-PBX1-positive and hyperdiploid acute lymphoblastic leukemia, with the exception of BCR-ABL-positive and 'B-other' acute lymphoblastic leukemias (defined as precursor B-cell acute lymphoblastic leukemia not carrying the foregoing cytogenetic aberrations), were found to have unique microRNA-signatures that differed from each other and from those of healthy hematopoietic cells. Strikingly, the microRNA signature of TEL-AML1-positive and hyperdiploid cases partly overlapped, which may suggest a common underlying biology. Moreover, aberrant down-regulation of let-7b (~70-fold) in MLL-rearranged acute lymphoblastic leukemia was linked to up-regulation of oncoprotein c-Myc (P(FDR)<0.0001). Resistance to vincristine and daunorubicin was characterized by an approximately 20-fold up-regulation of miR-125b, miR-99a and miR-100 (P(FDR)≤0.002). No discriminative microRNA were found for prednisolone response and only one microRNA was linked to resistance to L-asparaginase. A combined expression profile based on 14 microRNA that were individually associated with prognosis, was highly predictive of clinical outcome in pediatric acute lymphoblastic leukemia (5-year disease-free survival of 89.4%±7% versus 60.8±12%, P=0.001).

CONCLUSIONS

Genetic subtypes and drug-resistant leukemic cells display characteristic microRNA signatures in pediatric acute lymphoblastic leukemia. Functional studies of discriminative and prognostically important microRNA may provide new insights into the biology of pediatric acute lymphoblastic leukemia.

Novel insights into the development of T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) results from malignant transformation of immature cells of the T-cell lineage. T-ALL is a heterogeneous disease both clinically and genetically. It is generally accepted that T-ALL cells are the malignant counterpart of normally developing T cells in the thymus (thymocytes). Recent data using genome-wide gene expression profiling and assessment of the rearrangement status of the T-cell receptor loci confirm this notion. T-ALL cells differ from normal thymocytes in the overexpression of oncogenes that arise either from chromosomal translocations or via other mechanisms. In addition, signaling pathways that control the very first stages of thymocyte development (of note, the Notch and Wnt pathways) are involved in development of T-ALL in mice and humans when constitutively expressed. In particular, the activating mutations in the Notch pathways are believed to occur in a large proportion of human T-ALL. These findings on genetic events open up new therapeutic possibilities.

Association among size of thymus, anthropometric dimensions and number of lymphocytes in peripheral blood in newborns from Slovakia

AIMS

Thymus is the central lymphatic organ in humans with important endocrine function that is involved in maturation of immunocompetent T-lymphocytes. In our study we investigated the relationship among thymus size and the anthropometric dimensions as well as between thymus size and the number of lymphocytes in peripheral blood in full-term newborns.

METHODS

The examined group consisted of 212 full-term newborns from the region of Southern Slovakia. We examined birth weight, birth body length, head circumference and chest circumference. Thymus size was estimated by ultrasonography and it was expressed as Thymic Index. The number of lymphocytes in peripheral blood was determined from the number of total leukocytes and from the leukogram.

RESULTS

We have found a statistically significant positive correlation among thymus size and the body dimensions of newborns. The highest correlation with thymus size was found for birth weight (r = 0.409; P < 0.001) followed by birth body length (r = 0.368; P < 0.001), head circumference (r = 0.365; P < 0.001) and chest circumference (r = 0.340; P < 0.001). We have proven also a statistically significant positive correlation between the number of lymphocytes in peripheral blood and thymus size (r = 0.208; P = 0.039).

CONCLUSION

Our results confirmed the findings of other authors about a close relationship of Thymic Index and basic body parameters in newborns.

Quantifying thymic export: combining models of naive T cell proliferation and TCR excision circle dynamics gives an explicit measure of thymic output

Understanding T cell homeostasis requires knowledge of the export rate of new T cells from the thymus, a rate that has been surprisingly difficult to estimate. TCR excision circle (TREC) content has been used as a proxy for thymic export, but this quantity is influenced by cell division and loss of naive T cells and is not a direct measure of thymic export. We present in this study a method for quantifying thymic export in humans by combining two simple mathematical models. One uses Ki67 data to calculate the rate of peripheral naive T cell production, whereas the other tracks the dynamics of TRECs. Combining these models allows the contributions of the thymus and cell division to the daily production rate of T cells to be disentangled. The method is illustrated with published data on Ki67 expression and TRECs within naive CD4+ T cells in healthy individuals. We obtain a quantitative estimate for thymic export as a function of age from birth to 20 years. The export rate of T cells from the thymus follows three distinct phases, as follows: an increase from birth to a peak at 1 year, followed by rapid involution until approximately 8 years, and then a more gradual decline until 20 years. The rate of involution shown by our model is compatible with independent estimates of thymic function predicted by thymic epithelial space. Our method allows nonintrusive estimation of thymic output on an individual basis and may provide a means of assessing the role of the thymus in diseases such as HIV.

Human CD4+ T cell recent thymic emigrants are identified by protein tyrosine kinase 7 and have reduced immune function

CD4⁺ recent thymic emigrants (RTEs) comprise a clinically and immunologically important T cell population that indicates thymic output and that is essential for maintaining a diverse αβ–T cell receptor (TCR) repertoire of the naive CD4⁺ T cell compartment. However, their frequency and function are poorly understood because no known surface markers distinguish them from older non-RTE naive CD4⁺ T cells. We demonstrate that protein tyrosine kinase 7 (PTK7) is a novel marker for human CD4⁺ RTEs. Consistent with their recent thymic origin, human PTK7⁺ RTEs contained higher levels of signal joint TCR gene excision circles and were more responsive to interleukin (IL)-7 compared with PTK7⁻ naive CD4⁺ T cells, and rapidly decreased after complete thymectomy. Importantly, CD4⁺ RTEs proliferated less and produced less IL-2 and interferon-γ than PTK7⁻ naive CD4⁺ T cells after αβ-TCR/CD3 and CD28 engagement. This immaturity in CD4⁺ RTE effector function may contribute to the reduced CD4⁺ T cell immunity observed in contexts in which CD4⁺ RTEs predominate, such as in the fetus and neonate or after immune reconstitution. The ability to identify viable CD4⁺ RTEs by PTK7 staining should be useful for monitoring thymic output in both healthy individuals and in patients with genetic or acquired CD4⁺ T cell immunodeficiencies.

Efficient intrathymic gene transfer following in situ administration of a rAAV serotype 8 vector in mice and nonhuman primates

The thymus is the primary site of T-cell development and plays a key role in the induction of self-tolerance. We previously showed that the intrathymic (i.t.) injection of a transgene-expressing lentiviral vector (LV) in mice can result in the correction of a T cell-specific genetic defect. Nevertheless, the efficiency of thymocyte transduction did not exceed 0.1-0.3% and we were unable to detect any thymus transduction in macaques. As such, we initiated studies to assess the capacity of recombinant adeno-associated virus (rAAV) vectors to transduce murine and primate thymic cells. In vivo administration of AAV serotype 2-derived single-stranded AAV (ssAAV) and self-complementary AAV (scAAV) vectors pseudotyped with capsid proteins of serotypes 1, 2, 4, 5, and 8 demonstrated that murine thymus transduction was significantly enhanced by scAAV2/8. Transgene expression was detected in 5% of thymocytes and, notably, transduced cells represented 1% of peripheral T lymphocytes. Moreover, i.t. administration of scAAV2/8 particles in macaques, by endoscopic-mediated guidance, resulted in significant gene transfer. Thus, in healthy animals, where thymic gene transfer does not provide a selective advantage, scAAV2/8 is a unique tool promoting the in situ transduction of thymocytes with the subsequent export of gene-modified lymphocytes to the periphery.

IL-7 activates the phosphatidylinositol 3-kinase/AKT pathway in normal human thymocytes but not normal human B cell precursors

IL-7 signaling culminates in different biological outcomes in distinct lymphoid populations, but knowledge of the biochemical signaling pathways in normal lymphoid populations is incomplete. We analyzed CD127/IL-7Ralpha expression and function in normal (nontransformed) human thymocytes, and human CD19(+) B-lineage cells purified from xenogeneic cord blood stem cell/MS-5 murine stromal cell cultures, to further clarify the role of IL-7 in human B cell development. IL-7 stimulation of CD34(+) immature thymocytes led to phosphorylation (p-) of STAT5, ERK1/2, AKT, and glycogen synthase kinase-3 beta, and increased AKT enzymatic activity. In contrast, IL-7 stimulation of CD34(-) thymocytes (that included CD4(+)/CD8(+) double-positive, and CD4(+) and CD8(+) single-positive cells) only induced p-STAT5. IL-7 stimulation of CD19(+) cells led to robust induction of p-STAT5, but minimal induction of p-ERK1/2 and p-glycogen synthase kinase-3 beta. However, CD19(+) cells expressed endogenous p-ERK1/2, and when rested for several hours following removal from MS-5 underwent de-phosphorylation of ERK1/2. IL-7 stimulation of rested CD19(+) cells resulted in robust induction of p-ERK1/2, but no induction of AKT enzymatic activity. The use of a specific JAK3 antagonist demonstrated that all IL-7 signaling pathways in CD34(+) thymocytes and CD19(+) B-lineage cells were JAK3-dependent. We conclude that human CD34(+) thymocytes and CD19(+) B-lineage cells exhibit similarities in activation of STAT5 and ERK1/2, but differences in activation of the PI3K/AKT pathway. The different induction of PI3K/AKT may at least partially explain the different requirements for IL-7 during human T and B cell development.

WNT signalling in the immune system: WNT is spreading its wings

WNT proteins are secreted morphogens that are required for basic developmental processes, such as cell-fate specification, progenitor-cell proliferation and the control of asymmetric cell division, in many different species and organs. In blood and immune cells, WNT signalling controls the proliferation of progenitor cells and might also affect the cell-fate decisions of stem cells. Recent studies indicate that WNT proteins also regulate effector T-cell development, regulatory T-cell activation and dendritic-cell maturation. WNT signalling seems to function as a universal mechanism in leukocytes to establish a pool of undifferentiated cells for further selection, effector-cell maturation and terminal differentiation. WNT signalling is therefore subject to strict molecular control, and dysregulated WNT signalling is implicated in the development of haematological malignancies.

Role of two distinct gammadelta T cell subsets during West Nile virus infection

gammadelta T cells respond rapidly following West Nile virus (WNV) infection, limiting viremia and invasion of the central nervous system and thereby protecting the host from lethal encephalitis. Here, we investigated the role of two major subpopulations of peripheral gammadelta T cells, Vgamma1(+) and Vgamma4(+) cells, in host immunity against WNV infection. We found initially that aged mice were more susceptible to WNV infection than young mice. Following WNV challenge, Vgamma1(+) cells in young mice expanded significantly whereas Vgamma4(+) cells expanded modestly. In contrast, aged mice exhibited a slower and reduced response of Vgamma1(+) cells but maintained a higher content of Vgamma4(+) cells. Vgamma1(+) cells were the major gammadelta subset producing IFN-gamma during WNV infection. Mice depleted of Vgamma1(+) cells had an enhanced viremia and higher mortality to WNV encephalitis. Vgamma4(+) cells had a higher potential for producing tumor necrosis factor-alpha (TNF-alpha), a cytokine known to be involved in blood-brain barrier compromise and WNV entry into the brain. Depletion of Vgamma4(+) cells reduced TNF-alpha level in the periphery, accompanied by a decreased viral load in the brain and a lower mortality to WN encephalitis. These results suggest that Vgamma1(+) and Vgamma4(+) cells play distinct roles in protection and pathogenesis during WNV infection.

Detection of age-related changes in thoracic structure and function by computed tomography, magnetic resonance imaging, and positron emission tomography

It is useful to understand the normal changes in structure and function in the thorax that occur with age. Thus, we present the following quantitative preliminary data obtained from retrospective quantitative analysis of computed tomography (CT) and positron emission tomography (PET) examinations in subjects 0 to 90 years of age: Mean lung standard uptake values were found to significantly increase with increasing age and with increasing body mass index (BMI). Mean lung attenuation was seen to statistically significantly decrease with increasing age in subjects who had a CT scan, had a nonsignificant tendency to decrease with increasing age in subjects with a PET/CT scan, had a nonsignificant tendency to increase with increasing BMI, and was seen to significantly increase with increasing mean lung standard uptake values. Mean lung volumes were not noted to significantly change with increasing age in adult subjects whether or not they were normalized to the craniocaudal thoracic lengths, although mean lung volumes significantly increased with increasing age in pediatric subjects. Mean lung volumes had a nonsignificant tendency to decrease with increasing BMI, although normalized mean lung volumes significantly decreased with increasing BMI. Lung metabolic volumetric products were not noted to significantly change with increasing BMI or with increasing age. In this work, we also review the literature regarding normal structural and functional changes in the thorax with age.

Investigation of post-weaning changes in immunological parameters in male rats

Normal post-weaning changes in immunological parameters were investigated in male Crl:CD(SD) rats (n=7) for matching of ages with children (referential data). The animals received a single intravenous administration of keyhole limpet hemocyanin (KLH) 3mg/kg on day 1 and were euthanized on day 7 at 5, 7, 9, and 11 weeks of age. Furthermore, to investigate age-dependent differences in susceptibility to cyclophosphamide immunotoxicity, the animals were given oral cyclophosphamide 5mg/kgday from days 1 to 8 and intravenous KLH on day 3, and were euthanized on day 9 at the above ages. As a result, the post-weaning development pattern of a continuous increase until 9 weeks of age, followed by a mild decrease at 11 weeks of age, was commonly observed in white blood cell counts and all of its differential counts in peripheral blood, spleen weight, and total cell, CD3+, CD4+, CD8+ and CD45RA+ cell counts in the spleen. This pattern is similar to the development pattern of peripheral blood cell counts in infants, which mostly peaks at 6-12 months of age. Cyclophosphamide decreased almost all of peripheral blood cell counts and lymphocyte subset counts in the thymus and spleen at all ages, to similar degrees. However, decreases in serum anti-KLH IgM and IgG levels were greatest at 9 weeks of age. In conclusion, 9 (immunization at 8) weeks of age in rats was shown to be the most susceptible timing for cyclophosphamide immunotoxicity, likely corresponding to 6-12 months of age in infants.