An overview of the intrathymic intricacies of T cell development

A cell atlas of human thymic development defines T cell repertoire formation

The thymus provides a nurturing environment for the differentiation and selection of T cells, a process orchestrated by their interaction with multiple thymic cell types. We used single-cell RNA sequencing to create a cell census of the human thymus across the life span and to reconstruct T cell differentiation trajectories and T cell receptor (TCR) recombination kinetics. Using this approach, we identified and located in situ CD8αα⁺ T cell populations, thymic fibroblast subtypes, and activated dendritic cell states. In addition, we reveal a bias in TCR recombination and selection, which is attributed to genomic position and the kinetics of lineage commitment. Taken together, our data provide a comprehensive atlas of the human thymus across the life span with new insights into human T cell development.

Existence of reprogrammed lymphoma stem cells in a murine ALCL-like model

While cancer stem cells are well established in certain hematologic and solid malignancies, their existence in T cell lymphoma is unclear and the origin of disease is not fully understood. To examine the existence of lymphoma stem cells, we utilized a mouse model of anaplastic large cell lymphoma. Established NPM-ALK⁺ lymphomas contained heterogeneous cell populations ranging from mature T cells to undifferentiated hematopoietic stem cells. Interestingly, CD4^-/CD8^- double negative (DN) lymphoma cells aberrantly expressed the T cell receptor α/β chain. Serial transplantation of sorted CD4/CD8 and DN lymphoma subpopulations identified lymphoma stem cells within the DN3/DN4 T cell population, whereas all other subpopulations failed to establish serial lymphomas. Moreover, transplanted lymphoma DN3/DN4 T cells were able to differentiate and gave rise to mature lymphoma T cells. Gene expression analyses unmasked stem-cell-like transcriptional regulation of the identified lymphoma stem cell population. Furthermore, these lymphoma stem cells are characterized by low CD30 expression levels, which might contribute to limited long-term therapeutic success in patients treated with anti-CD30-targeted therapies. In summary, our results highlight the existence of a lymphoma stem cell population in a NPM-ALK-driven CD30⁺ mouse model, thereby giving the opportunity to test innovative treatment strategies developed to eradicate the origin of disease.

Chronic virus infection drives CD8 T cell-mediated thymic destruction and impaired negative selection

Chronic infection provokes alterations in inflammatory and suppressive pathways that potentially affect the function and integrity of multiple tissues, impacting both ongoing immune control and restorative immune therapies. Here we demonstrate that chronic lymphocytic choriomeningitis virus infection rapidly triggers severe thymic depletion, mediated by CD8 T cell-intrinsic type I interferon (IFN) and signal transducer and activator of transcription 2 (Stat2) signaling. Occurring temporal to T cell exhaustion, thymic cellularity reconstituted despite ongoing viral replication, with a rapid secondary thymic depletion following immune restoration by anti-programmed death-ligand 1 (PDL1) blockade. Therapeutic hematopoietic stem cell transplant (HSCT) during chronic infection generated new antiviral CD8 T cells, despite sustained virus replication in the thymus, indicating an impairment in negative selection. Consequently, low amounts of high-affinity self-reactive T cells also escaped the thymus following HSCT during chronic infection. Thus, by altering the stringency and partially impairing negative selection, the host generates new virus-specific T cells to replenish the fight against the chronic infection, but also has the potentially dangerous effect of enabling the escape of self-reactive T cells.

Exploration of Cell Development Pathways through High-Dimensional Single Cell Analysis in Trajectory Space

High-dimensional single cell profiling coupled with computational modeling is emerging as a powerful tool to elucidate developmental programs directing cell lineages. We introduce tSpace, an algorithm based on the concept of "trajectory space", in which cells are defined by their distance along nearest neighbor pathways to every other cell in a population. Graphical mapping of cells in trajectory space allows unsupervised reconstruction and exploration of complex developmental sequences. Applied to flow and mass cytometry data, the method faithfully reconstructs thymic T cell development and reveals development and trafficking regulation of tonsillar B cells. Applied to the single cell transcriptome of mouse intestine and C. elegans, the method recapitulates development from intestinal stem cells to specialized epithelial phenotypes more faithfully than existing algorithms and orders C. elegans cells concordantly to the associated embryonic time. tSpace profiling of complex populations is well suited for hypothesis generation in developing cell systems.

Molecular Mechanisms of Notch Signaling in Lymphoid Cell Lineages Development: NF-κB and Beyond

Notch is a ligand-receptor interaction-triggered signaling cascade highly conserved, that influences multiple lineage decisions within the hematopoietic and the immune system. It is a recognized model of intercellular communication that plays an essential role in embryonic as well as in adult immune cell development and homeostasis. Four members belong to the family of Notch receptors (Notch1-4), and each of them plays nonredundant functions at several developmental stages. Canonical and noncanonical pathways of Notch signaling are multifaceted drivers of immune cells biology. In fact, increasing evidence highlighted Notch as an important modulator of immune responses, also in cancer microenvironment. In these contexts, multiple transduction signals, including canonical and alternative NF-κB pathways, play a relevant role. In this chapter, we will first describe the critical role of Notch and NF-κB signals in lymphoid lineages developing in thymus: natural killer T cells, thymocytes, and thymic T regulatory cells. We will address also the role played by ligand expressing cells. Given the importance of Notch/NF-κB cross talk, its role in T-cell leukemia development and progression will be discussed.

Close Quarters Can Be a Good Fit for Stem Cells to Become T Cells

Human pluripotent stem cells (PSCs) could potentially provide a potentially unlimited supply of T cells. In this issue of Cell Stem Cell, Montel-Hagen et al. (2019) take advantage of a three-dimensional mouse stromal cell-based system that combines mesoderm specification with organoid-induced hematopoietic differentiation to enable commitment, selection, and maturation of conventional human T cells.

[Morphology of the thymus and the specific features of its cellular composition in experimental acute and chronic ulcerative colitis]

OBJECTIVE

To investigate morphological changes in the thymus, the subpopulation composition of lymphocytes and its non-lymphoid cells in dextran-induced experimental acute ulcerative colitis and in different periods of chronic ulcerative colitis.

MATERIAL AND METHODS

Acute and chronic ulcerative colitis was simulated in C57BL/6 mice, by replacing drinking water with a 1% aqueous dextran sulfate sodium solution. Thymic changes were morphometrically assessed; the number and absolute area of thymic corpuscles and epithelial cells were calculated; and the subpopulation composition of lymphocytes and thymic stromal cells was determined using flow cytofluorimetry; the Kruskal-Wallis test and the Mann-Whitney test were used to compare the groups.

RESULTS

In acute catarrhal and ulcerative colitis, there was acute accidental thymic involution with devastation of the cortical substance and with a decline in its volume fraction, with an increase in the levels of cells dying through the mechanism of apoptosis, and with a decrease in the absolute number of lymphocytes, T-helper cells, cytotoxic T-cells, regulatory T-lymphocytes, B-lymphocytes, and dendritic cells, with a rise in the index of the area of thymic corpuscles and in the content of late-phase corpuscles among them, and with the appearance of thymic corpuscles as cyst-like cavities. In chronic ulcerative colitis, the cortex was expanded and the area of thymic corpuscles and the count of medullary epithelial cells increased. The cyst-like thymic corpuscles formed clusters, the count of dendritic cells increased in early-stage chronic ulcerative colitis, but the levels of macrophages decreased in both periods of its development.

CONCLUSION

There is acute accidental involution and thymic hyperplasia with an increase in medullary epithelial cells and thymic corpuscles consisting of cytokeratin 19⁺ in the epithelial cells in experimental acute and chronic ulcerative colitis, respectively. The more pronounced epithelial cell response found in end-stage experimental chronic ulcerative colitis reflects the enhanced differentiation of regulatory T-lymphocytes and the larger number of which is observed in peripheral blood and in the focus of inflammation in patients with ulcerative colitis, according to the literature.

Intrathymic adeno-associated virus gene transfer rapidly restores thymic function and long-term persistence of gene-corrected T cells

BACKGROUND

Patients with T-cell immunodeficiencies are generally treated with allogeneic hematopoietic stem cell transplantation, but alternatives are needed for patients without matched donors. An innovative intrathymic gene therapy approach that directly targets the thymus might improve outcomes.

OBJECTIVE

We sought to determine the efficacy of intrathymic adeno-associated virus (AAV) serotypes to transduce thymocyte subsets and correct the T-cell immunodeficiency in a zeta-associated protein of 70 kDa (ZAP-70)-deficient murine model.

METHODS

AAV serotypes were injected intrathymically into wild-type mice, and gene transfer efficiency was monitored. ZAP-70^-/- mice were intrathymically injected with an AAV8 vector harboring the ZAP70 gene. Thymus structure, immunophenotyping, T-cell receptor clonotypes, T-cell function, immune responses to transgenes and autoantibodies, vector copy number, and integration were evaluated.

RESULTS

AAV8, AAV9, and AAV10 serotypes all transduced thymocyte subsets after in situ gene transfer, with transduction of up to 5% of cells. Intrathymic injection of an AAV8-ZAP-70 vector into ZAP-70^-/- mice resulted in a rapid thymocyte differentiation associated with the development of a thymic medulla. Strikingly, medullary thymic epithelial cells expressing the autoimmune regulator were detected within 10 days of gene transfer, correlating with the presence of functional effector and regulatory T-cell subsets with diverse T-cell receptor clonotypes in the periphery. Although thymocyte reconstitution was transient, gene-corrected peripheral T cells harboring approximately 1 AAV genome per cell persisted for more than 40 weeks, and AAV vector integration was detected.

CONCLUSIONS

Intrathymic AAV-transduced progenitors promote a rapid restoration of the thymic architecture, with a single wave of thymopoiesis generating long-term peripheral T-cell function.

Conditional Deletion of the V-ATPase a2-Subunit Disrupts Intrathymic T Cell Development

Proper orchestration of T lymphocyte development is critical, as T cells underlie nearly all responses of the adaptive immune system. Developing thymocytes differentiate in response to environmental cues carried from cell surface receptors to the nucleus, shaping a distinct transcriptional program that defines their developmental outcome. Our recent work has identified a previously undescribed role for the vacuolar ATPase (V-ATPase) in facilitating the development of murine thymocytes progressing toward the CD4⁺ and CD8⁺ αβ T cell lineages. Vav1^Cre recombinase-mediated deletion of the a2 isoform of the V-ATPase (a2V) in mouse hematopoietic cells leads to a specific and profound loss of peripheral CD4⁺ and CD8⁺ αβ T cells. Utilizing T cell-restricted Lck^Cre and CD4^Cre strains, we further traced this deficiency to the thymus and found that a2V plays a cell-intrinsic role throughout intrathymic development. Loss of a2V manifests as a partial obstruction in the double negative stage of T cell development, and later, a near complete failure of positive selection. These data deepen our understanding of the biological mechanisms that orchestrate T cell development and lend credence to the recent focus on V-ATPase as a potential chemotherapeutic target to combat proliferative potential in T cell lymphoblastic leukemias and autoimmune disease.

Blocked O-GlcNAc cycling disrupts mouse hematopoeitic stem cell maintenance and early T cell development

Small numbers of hematopoietic stem cells (HSCs) balance self-renewal and differentiation to produce the diversity and abundance of cell types that make up the blood system. How nutrients are recruited to support this massive differentiation and proliferation process remains largely unknown. The unique metabolism of adult HSCs, which rely on glycolysis and glutaminolysis, suggests a potential role for the post-translational modification O-GlcNAc as a critical nutrient signal in these cells. Glutamine, glucose, and other metabolites drive the hexosamine biosynthetic pathway (HBP) ultimately leading to the O-GlcNAc modification of critical intracellular targets. Here, we used a conditional targeted genetic deletion of the enzyme that removes O-GlcNAc, O-GlcNAcase (OGA), to determine the consequences of blocked O-GlcNAc cycling on HSCs. Oga deletion in mouse HSCs resulted in greatly diminished progenitor pools, impaired stem cell self-renewal and nearly complete loss of competitive repopulation capacity. Further, early T cell specification was particularly sensitive to Oga deletion. Loss of Oga resulted in a doubling of apoptotic cells within the bone marrow and transcriptional deregulation of key genes involved in adult stem cell maintenance and lineage specification. These findings suggest that O-GlcNAc cycling plays a critical role in supporting HSC homeostasis and early thymocyte development.

Matrix Metalloproteases as Influencers of the Cells' Social Media

Matrix metalloproteinases (MMPs) have been studied in the context of cancer due to their ability to increase cell invasion, and were initially thought to facilitate metastasis solely through the degradation of the extracellular matrix (ECM). MMPs have also been investigated in the context of their ECM remodeling activity in several acute and chronic inflammatory diseases. However, after several MMP inhibitors failed in phase III clinical trials, a global reassessment of their biological functions was undertaken, which has revealed multiple unanticipated functions including the processing of chemokines, cytokines, and cell surface receptors. Despite what their name suggests, the matrix aspect of MMPs could contribute to a lesser part of their physiological functions in inflammatory diseases, as originally anticipated. Here, we present examples of MMP substrates implicated in cell signaling, independent of their ECM functions, and discuss the impact for the use of MMP inhibitors.

Sonic Hedgehog Is a Determinant of γδ T-Cell Differentiation in the Thymus

Here we investigate the function of Hedgehog (Hh) signaling in thymic γδ T-cell maturation and subset differentiation. Analysis of Hh mutants showed that Hh signaling promotes γδ T-cell development in the thymus and influences γδ T-cell effector subset distribution. Hh-mediated transcription in thymic γδ cells increased γδ T-cell number, and promoted their maturation and increased the γδNKT subset, whereas inhibition of Hh-mediated transcription reduced the thymic γδ T-cell population and increased expression of many genes that are normally down-regulated during γδ T-cell maturation. These changes were also evident in spleen, where increased Hh signaling increased γδNKT cells, but reduced CD27-CD44+ and Vγ2+ populations. Systemic in vivo pharmacological Smoothened-inhibition reduced γδ T-cell and γδNKT cells in the thymus, and also reduced splenic γδ T-cell and γδNKT populations, indicating that Hh signaling also influences homeostasis of peripheral γδ T-cell populations. Taken together our data indicate that Sonic Hedgehog is an important determinant of γδ T-cell effector subset differentiation.

Identification of an Intronic Regulatory Element Necessary for Tissue-Specific Expression of Foxn1 in Thymic Epithelial Cells

The thymus is critical for the establishment of the adaptive immune system and the development of a diverse T cell repertoire. T cell development depends upon cell-cell interactions with epithelial cells in the thymus. The thymus is composed of two different types of epithelial cells: cortical and medullary epithelial cells. Both of these express and critically depend on the transcription factor Foxn1 Foxn1 is also expressed in the hair follicle, and disruption of Foxn1 function in mice results in severe thymic developmental defects and the hairless (nude) phenotype. Despite its importance, little is known about the direct regulation of Foxn1 expression. In this study, we identify a cis-regulatory element (RE) critical for expression of Foxn1 in mouse thymic epithelial cells but dispensable for expression in hair follicles. Analysis of chromatin accessibility, histone modifications, and sequence conservation identified regions within the first intron of Foxn1 that possessed the characteristics of REs. Systematic knockout of candidate regions lead us to identify a 1.6 kb region that, when deleted, results in a near total disruption of thymus development. Interestingly, Foxn1 expression and function in the hair follicle were unaffected. RNA fluorescent in situ hybridization showed a near complete loss of Foxn1 mRNA expression in the embryonic thymic bud. Our studies have identified a genomic RE with thymic-specific control of Foxn1 gene expression.

ISWI ATPase Smarca5 Regulates Differentiation of Thymocytes Undergoing β-Selection

Development of lymphoid progenitors requires a coordinated regulation of gene expression, DNA replication, and gene rearrangement. Chromatin-remodeling activities directed by SWI/SNF2 superfamily complexes play important roles in these processes. In this study, we used a conditional knockout mouse model to investigate the role of Smarca5, a member of the ISWI subfamily of such complexes, in early lymphocyte development. Smarca5 deficiency results in a developmental block at the DN3 stage of αβ thymocytes and pro-B stage of early B cells at which the rearrangement of Ag receptor loci occurs. It also disturbs the development of committed (CD73⁺) γδ thymocytes. The αβ thymocyte block is accompanied by massive apoptotic depletion of β-selected double-negative DN3 cells and premitotic arrest of CD4/CD8 double-positive cells. Although Smarca5-deficient αβ T cell precursors that survived apoptosis were able to undergo a successful TCRβ rearrangement, they exhibited a highly abnormal mRNA profile, including the persistent expression of CD44 and CD25 markers characteristic of immature cells. We also observed that the p53 pathway became activated in these cells and that a deficiency of p53 partially rescued the defect in thymus cellularity (in contrast to early B cells) of Smarca5-deficient mice. However, the activation of p53 was not primarily responsible for the thymocyte developmental defects observed in the Smarca5 mutants. Our results indicate that Smarca5 plays a key role in the development of thymocytes undergoing β-selection, γδ thymocytes, and also B cell progenitors by regulating the transcription of early differentiation programs.

Hippo Pathway in Mammalian Adaptive Immune System

The Hippo pathway was originally identified as an evolutionarily-conserved signaling mechanism that contributes to the control of organ size. It was then rapidly expanded as a key pathway in the regulation of tissue development, regeneration, and cancer pathogenesis. The increasing amount of evidence in recent years has also connected this pathway to the regulation of innate and adaptive immune responses. Notably, the Hippo pathway has been revealed to play a pivotal role in adaptive immune cell lineages, as represented by the patients with T- and B-cell lymphopenia exhibiting defective expressions of the pathway component. The complex regulatory mechanisms of and by the Hippo pathway have also been evident as alternative signal transductions are employed in some immune cell types. In this review article, we summarize the current understanding of the emerging roles of the Hippo pathway in adaptive immune cell development and differentiation. We also highlight the recent findings concerning the dual functions of the Hippo pathway in autoimmunity and anti-cancer immune responses and discuss the key open questions in the interplay between the Hippo pathway and the mammalian immune system.

The RANKL-RANK Axis: A Bone to Thymus Round Trip

The identification of Receptor activator of nuclear factor kappa B ligand (RANKL) and its cognate receptor Receptor activator of nuclear factor kappa B (RANK) during a search for novel tumor necrosis factor receptor (TNFR) superfamily members has dramatically changed the scenario of bone biology by providing the functional and biochemical proof that RANKL signaling via RANK is the master factor for osteoclastogenesis. In parallel, two independent studies reported the identification of mouse RANKL on activated T cells and of a ligand for osteoprotegerin on a murine bone marrow-derived stromal cell line. After these seminal findings, accumulating data indicated RANKL and RANK not only as essential players for the development and activation of osteoclasts, but also for the correct differentiation of medullary thymic epithelial cells (mTECs) that act as mediators of the central tolerance process by which self-reactive T cells are eliminated while regulatory T cells are generated. In light of the RANKL-RANK multi-task function, an antibody targeting this pathway, denosumab, is now commonly used in the therapy of bone loss diseases including chronic inflammatory bone disorders and osteolytic bone metastases; furthermore, preclinical data support the therapeutic application of denosumab in the framework of a broader spectrum of tumors. Here, we discuss advances in cellular and molecular mechanisms elicited by RANKL-RANK pathway in the bone and thymus, and the extent to which its inhibition or augmentation can be translated in the clinical arena.

Role of arginine deiminase in thymic atrophy during experimental Streptococcus pyogenes infection

Expression of gene of arginine deiminase (AD) allows adaptation of Streptococcus pyogenes to adverse environmental conditions. AD activity can lead to L-arginine deficiency in the host cells' microenvironment. Bioavailability of L-arginine is an important factor regulating the functions of the immune cells in mammals. By introducing a mutation into S pyogenes M46-16, we obtained a strain with inactivated arcA/sagp gene (M49-16 delArcA), deficient in AD. This allowed elucidating the function of AD in pathogenesis of streptococcal infection. The virulence of the parental and mutant strains was examined in a murine model of subcutaneous streptococcal infection. L-arginine concentration in the plasma of mice infected with S pyogenes M49-16 delArcA remained unchanged in course of the entire experiment. At the same time mice infected with S pyogenes M49-16 demonstrated gradual diminution of L-arginine concentration in the blood plasma, which might be due to the activity of streptococcal AD. Mice infected with S pyogenes M49-16 delArcA demonstrated less intensive bacterial growth in the primary foci and less pronounced bacterial dissemination as compared with animals infected with the parental strain S pyogenes M46-16. Similarly, thymus involution, alterations in apoptosis, thymocyte subsets and Treg cells differentiation were less pronounced in mice infected with S pyogenes M49-16 delArcA than in those infected with the parental strain. The results obtained showed that S pyogenes M49-16 delArcA, unable to produce AD, had reduced virulence in comparison with the parental S pyogenes M49-16 strain. AD is an important factor for the realization of the pathogenic potential of streptococci.

Glycans as Key Checkpoints of T Cell Activity and Function

The immune system is highly controlled and fine-tuned by glycosylation, through the addition of a diversity of carbohydrates structures (glycans) to virtually all immune cell receptors. Despite a relative backlog in understanding the importance of glycans in the immune system, due to its inherent complexity, remarkable findings have been highlighting the essential contributions of glycosylation in the regulation of both innate and adaptive immune responses with important implications in the pathogenesis of major diseases such as autoimmunity and cancer. Glycans are implicated in fundamental cellular and molecular processes that regulate both stimulatory and inhibitory immune pathways. Besides being actively involved in pathogen recognition through interaction with glycan-binding proteins (such as C-type lectins), glycans have been also shown to regulate key pathophysiological steps within T cell biology such as T cell development and thymocyte selection; T cell activity and signaling as well as T cell differentiation and proliferation. These effects of glycans in T cells functions highlight their importance as determinants of either self-tolerance or T cell hyper-responsiveness which ultimately might be implicated in the creation of tolerogenic pathways in cancer or loss of immunological tolerance in autoimmunity. This review discusses how specific glycans (with a focus on N-linked glycans) act as regulators of T cell biology and their implications in disease.

Hedgehog Signaling in Cancer: A Prospective Therapeutic Target for Eradicating Cancer Stem Cells

The Hedgehog (Hh) pathway is a signaling cascade that plays a crucial role in many fundamental processes, including embryonic development and tissue homeostasis. Moreover, emerging evidence has suggested that aberrant activation of Hh is associated with neoplastic transformations, malignant tumors, and drug resistance of a multitude of cancers. At the molecular level, it has been shown that Hh signaling drives the progression of cancers by regulating cancer cell proliferation, malignancy, metastasis, and the expansion of cancer stem cells (CSCs). Thus, a comprehensive understanding of Hh signaling during tumorigenesis and development of chemoresistance is necessary in order to identify potential therapeutic strategies to target various human cancers and their relapse. In this review, we discuss the molecular basis of the Hh signaling pathway and its abnormal activation in several types of human cancers. We also highlight the clinical development of Hh signaling inhibitors for cancer therapy as well as CSC-targeted therapy.

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.

Alteration of Bcl11b upon stimulation of both the MAP kinase- and Gsk3-dependent signaling pathways in double-negative thymocytes

B-cell lymphoma/leukemia 11B (Bcl11b) is a transcription factor critical for thymocyte development. We have previously characterized the kinetic post-translational modifications (PTMs) of Bcl11b in double-positive (DP) thymocytes during stimulation of the T cell receptor-activated MAP kinase pathway. However, the PTMs of Bcl11b in thymocytes from other developmental stages in the thymus, primarily double-negative (DN) cells, have not been previously identified. We found that kinetic modifications of Bcl11b in DN cells are somewhat different than the patterns observed in DP cells. Distinct from DP thymocytes, phosphorylation and sumoylation of Bcl11b in DN cells were not oppositely regulated in response to activation of MAP kinase, even though hyper-phosphorylation of Bcl11b coincided with near complete desumoylation. Additionally, prolonged stimulation of the MAP kinase pathway in DN cells, unlike DP thymocytes, did not alter Bcl11b levels of sumoylation or ubiquitinylation, or stability. On the other hand, activation of Wnt-Gsk3-dependent signaling in DN cells resulted in composite dephosphorylation and sumoylation of Bcl11b. Moreover, stimulation of MAP kinase and (or) Wnt signaling pathways differentially affects gene expression of some Bcl11b target and maturation-associated genes. Defining the signaling pathways and regulation of sequence-specific transcription factors by PTMs at various stages of thymopoiesis may improve our understanding of leukemogenesis.

Peroxisome Proliferator-Activated Receptor-δ Supports the Metabolic Requirements of Cell Growth in TCRβ-Selected Thymocytes and Peripheral CD4+ T Cells

During T cell development, progenitor thymocytes undergo a large proliferative burst immediately following successful TCRβ rearrangement, and defects in genes that regulate this proliferation have a profound effect on thymus cellularity and output. Although the signaling pathways that initiate cell cycling and nutrient uptake after TCRβ selection are understood, less is known about the transcriptional programs that regulate the metabolic machinery to promote biomass accumulation during this process. In this article, we report that mice with whole body deficiency in the nuclear receptor peroxisome proliferator-activated receptor-δ (PPARδ^mut) exhibit a reduction in spleen and thymus cellularity, with a decrease in thymocyte cell number starting at the double-negative 4 stage of thymocyte development. Although in vivo DNA synthesis was normal in PPARδ^mut thymocytes, studies in the OP9-delta-like 4 in vitro system of differentiation revealed that PPARδ^mut double-negative 3 cells underwent fewer cell divisions. Naive CD4⁺ T cells from PPARδ^mut mice also exhibited reduced proliferation upon TCR and CD28 stimulation in vitro. Growth defects in PPAR-δ-deficient thymocytes and peripheral CD4⁺ T cells correlated with decreases in extracellular acidification rate, mitochondrial reserve, and expression of a host of genes involved in glycolysis, oxidative phosphorylation, and lipogenesis. By contrast, mice with T cell-restricted deficiency of Ppard starting at the double-positive stage of thymocyte development, although exhibiting defective CD4⁺ T cell growth, possessed a normal T cell compartment, pointing to developmental defects as a cause of peripheral T cell lymphopenia in PPARδ^mut mice. These findings implicate PPAR-δ as a regulator of the metabolic program during thymocyte and T cell growth.

Comprehensively Profiling the Chromatin Architecture of Tissue Restricted Antigen Expression in Thymic Epithelial Cells Over Development

Thymic epithelial cells (TEC) effect crucial roles in thymopoiesis including the control of negative thymocyte selection. This process depends on their capacity to express promiscuously genes encoding tissue-restricted antigens. This competence is accomplished in medullary TEC (mTEC) in part by the presence of the transcriptional facilitator AutoImmune REgulator, AIRE. AIRE-regulated gene transcription is marked by repressive chromatin modifications, including H3K27me3. When during TEC development these chromatin marks are established, however, remains unclear. Here we use a comprehensive ChIP-seq dataset of multiple chromatin modifications in different TEC subtypes to demonstrate that the chromatin landscape is established early in TEC differentiation. Much of the chromatin architecture found in mature mTEC was found to be present already over earlier stages of mTEC lineage differentiation as well as in non-TEC tissues. This was reflected by the fact that a machine learning approach accurately classified genes as AIRE-induced or AIRE-independent both in immature and mature mTEC. Moreover, analysis of TEC specific enhancer elements identified candidate transcription factors likely to be important in mTEC development and function. Our findings indicate that the mature mTEC chromatin landscape is laid down early in mTEC differentiation, and that AIRE is not required for large-scale re-patterning of chromatin in mTEC.

Altered Maturation of Medullary TEC in EphB-Deficient Thymi Is Recovered by RANK Signaling Stimulation

In the present study, the relevance of EphB2 and EphB3 tyrosine kinase receptors for the maturation of medullary thymic epithelial cells (TECs) is analyzed. The absence of both molecules, but particularly that of EphB2, courses with altered maturation of medullary Cld3,4^hiSSEA1⁺ epithelial progenitor cells, mature medulla epithelial cells, defined by the expression of specific cell markers, including UEA1, MHCII, CD40, CD80, and AIRE, and reduced expansion of medullary islets. In vivo assays demonstrate that these changes are a consequence of the absence of EphBs in both TECs and thymocytes. On the other hand, the changes, that remains in the adult thymus, correlated well with reduced proportions of E15.5 Vγ5⁺RANKL⁺ cells in EphB-deficient thymi that could result in decreased stimulation of RANK⁺ medullary TECs to mature, a fact that was confirmed by recovering of proportions of both CD40^hiCD80⁺ and MHCII^hiUEA1⁺ mature medullary TECs of mutant E14.5 alymphoid thymic lobes by agonist anti-RANK antibody treatment. Accordingly, the effects of EphB deficiency on medullary TECs maturation are recovered by RANK stimulation.

Recirculating Th2 cells induce severe thymic dysfunction via IL-4/STAT6 signaling pathway

Thymic involution happened early in life, but a certain ratio of activated CD4⁺ T cells will persistently recirculate into the thymus from the periphery and it have been suggested to be able to inhibit the development of embryonic thymocytes. Our present study was aimed to elucidate the specific mechanism how activated CD4⁺ T cells could influence upon developing thymocytes by using fetal thymic organ culture (FTOC) and kidney capsule transplantation. Our results demonstrated that Th2 cells were found to play a fundamental role in the inhibition of embryonic thymocyte development since a very low concentration of Th2 cells could obviously reduce the total number of thymocytes. And this effect was not tenable in other Th cell type. Notably, IL-4, the major cytokine secreted by Th2 cells, was suggested the key factor playing the inhibition role. In addition to reduced cell population, the proportion of double positive (DP) T cells was also heavily decreased. Furthermore, we demonstrated that it was the downstream effector signal transducer and activator of transcription 6 (STAT6) of IL-4 partially manipulate this inhibition. Together, these findings reveal a novel influence of Th2 cells re-entering the thymus on thymic involution.

Activation of CD4 and CD8 T cell receptors and regulatory T cells in response to human proteins

This study assessed in detail the influence of four different human proteins on the activation of CD4+ and CD8+ T lymphocytes and on the formation of regulatory T cells. Human whole-blood samples were incubated with four different human proteins. The effects of these proteins on the downstream immune-system response, on the expression of extracellular activation markers on and intracellular cytokines in T lymphocytes, and on the number of regulatory T cells (T-reg cells) were investigated via flow cytometry. Incubation with β-actin or glyceraldehyde 3-phosphate dehydrogenase (GAPDH), which are cytoplasmic proteins, increased the expression of both extracellular activation markers (CD69 and HLA-DR) and intracellular cytokines but did not significantly affect the number of T-reg cells. In contrast, incubation with human albumin or insulin, which are serum proteins, reduced both extracellular activation markers and intracellular cytokine expression and subsequently increased the number of T-reg cells. These findings may help to explain the etiological basis of autoimmune diseases.

The kinesin motor protein Kif7 is required for T-cell development and normal MHC expression on thymic epithelial cells (TEC) in the thymus

Kif7 is a ciliary kinesin motor protein that regulates mammalian Hedgehog pathway activation through influencing structure of the primary cilium. Here we show that Kif7 is required for normal T-cell development, despite the fact that T-cells lack primary cilia. Analysis of Kif7-deficient thymus showed that Kif7-deficiency increases the early CD44+CD25+CD4-CD8- thymocyte progenitor population but reduces differentiation to CD4+CD8+ double positive (DP) cell. At the transition from DP to mature T-cell, Kif7-deficiency selectively delayed maturation to the CD8 lineage. Expression of CD5, which correlates with TCR signal strength, was reduced on DP and mature CD4 and CD8 cells, as a result of thymocyte-intrinsic Kif7-deficiency, and Kif7-deficient T-cells from radiation chimeras activated less efficiently when stimulated with anti-CD3 and anti-CD28 in vitro. Kif7-deficient thymocytes showed higher expression of the Hedgehog target gene Ptch1 than WT, but were less sensitive to treatment with recombinant Shh, and Kif7-deficient T-cell development was refractory to neutralisation of endogenous Hh proteins, indicating that Kif7-deficient thymocytes were unable to interpret changes in the Hedgehog signal. In addition, Kif7-deficiency reduced cell-surface MHCII expression on thymic epithelial cells.

Small interference ITGA6 gene targeting in the human thymic epithelium differentially regulates the expression of immunological synapse-related genes

The thymus supports differentiation of T cell precursors. This process requires relocation of developing thymocytes throughout multiple microenvironments of the organ, mainly with thymic epithelial cells (TEC), which control intrathymic T cell differentiation influencing the formation and maintenance of the immunological synapse. In addition to the proteins of the major histocompatibility complex (MHC), this structure is supported by several adhesion molecules. During the process of thymopoiesis, we previously showed that laminin-mediated interactions are involved in the entrance of T-cell precursors into the thymus, as well as migration of differentiating thymocytes within the organ. Using small interference RNA strategy, we knocked-down the ITGA6 gene (which encodes the CD49f integrin α-chain) in cultured human TEC, generating a decrease in the expression of the corresponding CD49f subunit, in addition to modulation in several other genes related to cell adhesion and migration. Thymocyte adhesion to TEC was significantly impaired, comprising both immature and mature thymocyte subsets. Moreover, we found a modulation of the MHC, with a decrease in membrane expression of HLA-ABC, in contrast with increase in the expression of HLA-DR. Interestingly, the knockdown of the B2M gene (encoding the β-2 microglobulin of the HLA-ABC complex) increased CD49f expression levels, thus unraveling the existence of a cross-talk event in the reciprocal control of CD49f and HLA-ABC. Our data suggest that the expression levels of CD49f may be relevant in the general control of MHC expression by TEC and consequently the corresponding synapse with developing thymocytes mediated by the T-cell receptor.

Concise Review: Human Pluripotent Stem Cells to Produce Cell-Based Cancer Immunotherapy

Human pluripotent stem cells (PSCs) provide a promising resource to produce immune cells for adoptive cellular immunotherapy to better treat and potentially cure otherwise lethal cancers. Cytotoxic T cells and natural killer (NK) cells can now be routinely produced from human PSCs. These PSC-derived lymphocytes have phenotype and function similar to primary lymphocytes isolated from peripheral blood. PSC-derived T and NK cells have advantages compared with primary immune cells, as they can be precisely engineered to introduce improved anti-tumor activity and produced in essentially unlimited numbers. Stem Cells 2018;36:134-145.

Notch and T Cell Function - A Complex Tale

Notch drives critical decisions in a multitude of developmental decisions in many invertebrate and vertebrate organisms including flies, worms, fish, mice and humans. Therefore, it is not surprising that Notch family members also play a key role in cell fate choices in the vertebrate immune system. This review highlights the critical function of Notch in the development of mature T lymphocytes from hematopoietic precursors and describes the role of Notch in mature T cell activation, proliferation and differentiation.

Regulation of immunity and inflammation by hypoxia in immunological niches

Immunological niches are focal sites of immune activity that can have varying microenvironmental features. Hypoxia is a feature of physiological and pathological immunological niches. The impact of hypoxia on immunity and inflammation can vary depending on the microenvironment and immune processes occurring in a given niche. In physiological immunological niches, such as the bone marrow, lymphoid tissue, placenta and intestinal mucosa, physiological hypoxia controls innate and adaptive immunity by modulating immune cell proliferation, development and effector function, largely via transcriptional changes driven by hypoxia-inducible factor (HIF). By contrast, in pathological immunological niches, such as tumours and chronically inflamed, infected or ischaemic tissues, pathological hypoxia can drive tissue dysfunction and disease development through immune cell dysregulation. Here, we differentiate between the effects of physiological and pathological hypoxia on immune cells and the consequences for immunity and inflammation in different immunological niches. Furthermore, we discuss the possibility of targeting hypoxia-sensitive pathways in immune cells for the treatment of inflammatory disease.

Chemokine-Mediated Choreography of Thymocyte Development and Selection

As they differentiate, thymocytes encounter spatially restricted cues critical for differentiation and selection of a functional, self-tolerant T cell repertoire. Sequential migration of developing T cells through distinct thymic microenvironments is enforced by the ordered expression of chemokine receptors. Herein, we provide an updated perspective on T cell differentiation through the lens of recent advances that illuminate the dynamics of chemokine-driven thymocyte migration, localization, and interactions with stromal cells. We consider these findings in the context of earlier groundwork exploring the contribution of chemokines to T cell development, recent advances regarding the specificity of chemokine signaling, and novel techniques for evaluating the T cell repertoire. We suggest future research should amalgamate visualization of localized cellular interactions with downstream molecular signals.

Geographic clonal tracking in macaques provides insights into HSPC migration and differentiation

Wu et al. use barcode tracking to uncover prolonged geographic bone marrow segregation of regenerating hematopoietic stem and progenitor cell clones after transplantation and provide evidence for local bone marrow production of T cells.

The geographic distribution of hematopoiesis at a clonal level is of interest in understanding how hematopoietic stem and progenitor cells (HSPCs) and their progeny interact with bone marrow (BM) niches during regeneration. We tagged rhesus macaque autologous HSPCs with genetic barcodes, allowing clonal tracking over time and space after transplantation. We found marked geographic segregation of CD34⁺ HSPCs for at least 6 mo posttransplantation, followed by very gradual clonal mixing at different BM sites over subsequent months to years. Clonal mapping was used to document local production of granulocytes, monocytes, B cells, and CD56⁺ natural killer (NK) cells. In contrast, CD16⁺CD56⁻ NK cells were not produced in the BM, and in fact were clonally distinct from multipotent progenitors producing all other lineages. Most surprisingly, we documented local BM production of CD3⁺ T cells early after transplantation, using both clonal mapping and intravascular versus tissue-resident T cell staining, suggesting a thymus-independent T cell developmental pathway operating during BM regeneration, perhaps before thymic recovery.

NMR-directed design of pre-TCRβ and pMHC molecules implies a distinct geometry for pre-TCR relative to αβTCR recognition of pMHC

The pre-T cell receptor (pre-TCR) guides early thymocytes through maturation processes within the thymus via interaction with self-ligands displayed on thymic epithelial cells. The pre-TCR is a disulfide-linked heterodimer composed of an invariant pre-TCR α (pTα) subunit and a variable β subunit, the latter of which is incorporated into the mature TCR in subsequent developmental progression. This interaction of pre-TCR with peptide-major histocompatibility complex (pMHC) molecules has recently been shown to drive robust pre-TCR signaling and thymocyte maturation. Although the native sequences of β are properly folded and suitable for NMR studies in isolation, a tendency to self-associate rendered binding studies with physiological ligands difficult to interpret. Consequently, to structurally define this critical interaction, we have re-engineered the extracellular regions of β, designated as β-c1, for prokaryotic production to be used in NMR spectroscopy. Given the large size of the full extracellular domain of class I MHC molecules such as H-K^b, we produced a truncated form termed K^b-t harboring properties favorable for NMR measurements. This system has enabled robust measurement of a pre-TCR-pMHC interaction directly analogous to that of TCRαβ-pMHC. Binding surface analysis identified a contact surface comparable in size to that of the TCRαβ-pMHC but potentially with a rather distinct binding orientation. A tilting of the pre-TCRβ when bound to the pMHC ligand recognition surface versus the upright orientation of TCRαβ would alter the direction of force application between pre-TCR and TCR mechanosensors, impacting signal initiation.

An Exploration into the Origins and Pathogenesis of Anaplastic Large Cell Lymphoma, Anaplastic Lymphoma Kinase (ALK)-Positive

T-cell non-Hodgkin lymphoma is a heterogeneous disease ranging from malignancies arising from thymic T cells halted in development, through to mature, circulating peripheral T cells. The latter cases are diagnostically problematic with many entering the category of peripheral T-cell lymphoma, not otherwise specified (PTCL, NOS). Anaplastic large cell lymphoma (ALCL) is one of the exceptions to this whereby aberrant expression of anaplastic lymphoma kinase (ALK) and the distinctive presence of cell surface CD30 places this entity in its own class. Besides the expression of a well-studied oncogenic translocation, ALCL, ALK+ may also have a unique pathogenesis with a thymic origin like T lymphoblastic lymphoma but a peripheral presentation akin to PTCL. This perspective discusses evidence towards the potential origin of ALCL, ALK+, and mechanisms that may give rise to its unique phenotype.

Aberrant Signaling Pathways in T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive disease caused by the malignant transformation of immature progenitors primed towards T-cell development. Clinically, T-ALL patients present with diffuse infiltration of the bone marrow by immature T-cell blasts high blood cell counts, mediastinal involvement, and diffusion to the central nervous system. In the past decade, the genomic landscape of T-ALL has been the target of intense research. The identification of specific genomic alterations has contributed to identify strong oncogenic drivers and signaling pathways regulating leukemia growth. Notwithstanding, T-ALL patients are still treated with high-dose multiagent chemotherapy, potentially exposing these patients to considerable acute and long-term side effects. This review summarizes recent advances in our understanding of the signaling pathways relevant for the pathogenesis of T-ALL and the opportunities offered for targeted therapy.

Apoptotic Diminution of Immature Single and Double Positive Thymocyte Subpopulations Contributes to Thymus Involution During Murine Polymicrobial Sepsis

To generate and maintain functional T-cell receptor diversity, thymocyte development is tightly organized. Errors in this process may have dramatic consequences, provoking, for example, autoimmune diseases. Probably for this reason, the thymus reacts to septic stress with involution, decreasing the numbers of thymocytes. Because it is still unclear which thymocyte subpopulation contributes to thymus involution and whether thymocyte emigration is altered, we were interested to clarify this question in detail. Here, we show, using the cecal ligation and puncture (CLP) mouse model of polymicrobial sepsis, that predominantly immature thymocytes are reduced. The number of immature single positive thymocytes was most marked diminished (CLP: 6.54 × 10 ± 3.79 × 10 vs. sham: 4.54 × 10 ± 7.66 × 10 cells/thymus [24 h], CLP: 2.60 × 10 ± 2.14 × 10 vs. sham: 2.17 × 10 ± 1.90 × 10 cells/thymus [48 h]), and was consequently associated with the highest rate of apoptosis (8.4 [CLP] vs. 2.2% [sham]), the reduction in double positive thymocytes being associated with a smaller apoptotic response (number, CLP: 2.33 × 10 ± 1.38 × 10 vs. sham: 1.07 × 10 ± 2.72 × 10 cells/thymus [24 h], CLP: 2.34 × 10 ± 9.08 × 10 vs. sham: 3.5 × 10 ± 9.62 × 10 cells/thymus [48 h]; apoptosis: 2.5% [CLP] vs. 0.7% [sham]). Analysis of T-cell receptor excision circles revealed that the emigration of mature thymocytes was not inhibited. Real-time qPCR analysis revealed upregulation of pro-apoptotic Bim expression and suggested interference between Notch receptor expression on thymocytes and the respective ligands on thymic stromal cells during CLP-dependent sepsis, which might be responsible for the altered thymocyte viability in CLP-dependent sepsis.

What Happens in the Thymus Does Not Stay in the Thymus: How T Cells Recycle the CD4+-CD8+ Lineage Commitment Transcriptional Circuitry To Control Their Function

MHC-restricted CD4(+) and CD8(+) T cells are at the core of most adaptive immune responses. Although these cells carry distinct functions, they arise from a common precursor during thymic differentiation, in a developmental sequence that matches CD4 and CD8 expression and functional potential with MHC restriction. Although the transcriptional control of CD4(+)-CD8(+) lineage choice in the thymus is now better understood, less was known about what maintains the CD4(+) and CD8(+) lineage integrity of mature T cells. In this review, we discuss the mechanisms that establish in the thymus, and maintain in postthymic cells, the separation of these lineages. We focus on recent studies that address the mechanisms of epigenetic control of Cd4 expression and emphasize how maintaining a transcriptional circuitry nucleated around Thpok and Runx proteins, the key architects of CD4(+)-CD8(+) lineage commitment in the thymus, is critical for CD4(+) T cell helper functions.

Loss of Gαi proteins impairs thymocyte development, disrupts T-cell trafficking, and leads to an expanded population of splenic CD4+PD-1+CXCR5+/- T-cells

Thymocyte and T cell trafficking relies on signals initiated by G-protein coupled receptors. To address the importance of the G-proteins Gα_i2 and Gα_i3 in thymocyte and T cell function, we developed several mouse models. Gα_i2 deficiency in hematopoietic progenitors led to a small thymus, a double negative (DN)1/DN2 thymocyte transition block, and an accumulation of mature single positive (SP) thymocytes. Loss at the double positive (DP) stage of thymocyte development caused an increase in mature cells within the thymus. In both models an abnormal distribution of memory and naïve CD4 T cells occurred, and peripheral CD4 and CD8 T cells had reduced chemoattractant responses. The loss of Gα_i3 had no discernable impact, however the lack of both G-proteins commencing at the DP stage caused a severe T cell phenotype. These mice lacked a thymic medullary region, exhibited thymocyte retention, had a peripheral T cell deficiency, and lacked T cell chemoattractant responses. Yet a noteworthy population of CD4⁺PD-1⁺CXCR5^+/− cells resided in the spleen of these mice likely due to a loss of regulatory T cell function. Our results delineate a role for Gα_i2 in early thymocyte development and for Gα_i2/3 in multiple aspects of T cell biology.

Ghrelin Protects the Thymic Epithelium From Conditioning-Regimen-Induced Damage and Promotes the Restoration of CD4+ T Cells in Mice After Bone Marrow Transplantation

BACKGROUND

The delay in immune reconstitution after hematopoietic stem cell transplantation (HSCT), especially a delay in central immune reconstitution, leads to opportunistic infections and disease relapse after transplantation and affects the long-term outcome of HSCT. This delay is mainly attributable to thymic damage after myeloablative chemotherapy and radiotherapy.

METHODS

We established a model of allogeneic bone marrow transplantation (BMT) in mice and administered ghrelin (GRL) 7 days before the conditioning regimen or the day after BMT to explore the effect of GRL on thymus.

RESULTS

All the GRL-treated mice, especially those administered GRL before the conditioning regimen, exhibited more intact thymic architecture and a more rapid restoration of CD4 T lymphocytes after BMT than those of the corresponding control mice. Moreover, the levels of T cell receptor excision circles were significantly higher in the mice treated with GRL before the conditioning regimen than in the control mice at 28 days after BMT.

CONCLUSIONS

Our findings suggest that GRL may be a novel potential therapeutic approach to protecting the thymic epithelium from conditioning regimen-induced damage and promoting rapid and durable thymic and peripheral CD4 T cell recovery after HSCT.

Thymic homing of activated CD4+ T cells induces degeneration of the thymic epithelium through excessive RANK signaling

Activated T cells have been shown to be able to recirculate into the thymus from the periphery. The present study was aimed to elucidate the functional consequences of thymic homing of activated T cells upon developing thymocytes and thymic epithelial cells (TEC). In the presence of activated T cells, especially CD4⁺ T cells, T cell development was found to be inhibited in thymic organ cultures with markedly reduced cellularity. Thymic transplantation demonstrated that the inhibitory effect was most likely due to a defective microenvironment. As the major component of the thymic stroma, the TEC compartment was severely disturbed after prolonged exposure to the activated T cells. In addition to reduced cell proliferation, TEC differentiation was heavily skewed to the mTEC lineage. Furthermore, we demonstrated that RANKL highly expressed by activated CD4⁺ T cells was primarily responsible for the detrimental effects. Presumably, excessive RANK signaling drove overproduction of mTECs and possibly exhaustion of epithelial progenitors, thereby facilitating the deterioration of the epithelial structures. These findings not only reveal a novel activity of activated T cells re-entering the thymus, but also provide a new perspective for understanding the mechanism underlying thymic involution.

Concomitant Disruption of CD4 and CD8 Genes Facilitates the Development of Double Negative αβ TCR+ Peripheral T Cells That Respond Robustly to Staphylococcal Superantigen

Mature peripheral double negative T (DNT) cells expressing αβ TCR but lacking CD4/CD8 coreceptors play protective as well as pathogenic roles. To better understand their development and functioning in vivo, we concomitantly inactivated CD4 and CD8 genes in mice with intact MHC class I and class II molecules with the hypothesis that this would enable the development of DNT cells. We also envisaged that these DNT cells could be activated by bacterial superantigens in vivo as activation of T cells by superantigens does not require CD4 and CD8 coreceptors. Because HLA class II molecules present superantigens more efficiently than murine MHC class II molecules, CD4 CD8 double knockout (DKO) mice transgenically expressing HLA-DR3 or HLA-DQ8 molecules were generated. Although thymic cellularity was comparable between wild type (WT) and DKO mice, CD3⁺ αβ TCR⁺ thymocytes were significantly reduced in DKO mice, implying defects in thymic-positive selection. Splenic CD3⁺ αβ TCR⁺ cells and Foxp3⁺ T regulatory cells were present in DKO mice but significantly reduced. However, the in vivo inflammatory responses and immunopathology elicited by acute challenge with the staphylococcal superantigen enterotoxin B were comparable between WT and DKO mice. Choric exposure to staphylococcal enterotoxin B precipitated a lupus-like inflammatory disease with characteristic lympho-monocytic infiltration in lungs, livers, and kidneys, along with production of anti-nuclear Abs in DKO mice as in WT mice. Overall, our results suggest that DNT cells can develop efficiently in vivo and chronic exposure to bacterial superantigens may precipitate a lupus-like autoimmune disease through activation of DNT cells.

The NOTCH1-MYC highway toward T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a highly proliferative hematologic malignancy that results from the transformation of immature T-cell progenitors. Aberrant cell growth and proliferation in T-ALL lymphoblasts are sustained by activation of strong oncogenic drivers promoting cell anabolism and cell cycle progression. Oncogenic NOTCH signaling, which is activated in more than 65% of T-ALL patients by activating mutations in the NOTCH1 gene, has emerged as a major regulator of leukemia cell growth and metabolism. T-ALL NOTCH1 mutations result in ligand-independent and sustained NOTCH1-receptor signaling, which translates into activation of a broad transcriptional program dominated by upregulation of genes involved in anabolic pathways. Among these, the MYC oncogene plays a major role in NOTCH1-induced transformation. As result, the oncogenic activity of NOTCH1 in T-ALL is strictly dependent on MYC upregulation, which makes the NOTCH1-MYC regulatory circuit an attractive therapeutic target for the treatment of T-ALL.

Medullary thymic epithelial stem cells: role in thymic epithelial cell maintenance and thymic involution

The thymus consists of two distinct anatomical regions, the cortex and the medulla; medullary thymic epithelial cells (mTECs) play a crucial role in establishing central T-cell tolerance for self-antigens. Although the understanding of mTEC development in thymic organogenesis as well as the regulation of their differentiation and maturation has improved, the mechanisms of postnatal maintenance remain poorly understood. This issue has a central importance in immune homeostasis and physiological thymic involution as well as autoimmune disorders in various clinicopathological settings. Recently, several reports have demonstrated the existence of TEC stem or progenitor cells in the postnatal thymus, which are either bipotent or unipotent. We identified stem cells specified for mTEC-lineage that are generated in the thymic ontogeny and may sustain mTEC regeneration and lifelong central T-cell self-tolerance. This finding suggested that the thymic medulla is maintained autonomously by its own stem cells. Although several issues, including the relationship with other putative TEC stem/progenitors, remain unclear, further examination of mTEC stem cells (mTECSCs) and their regulatory mechanisms may contribute to the understanding of postnatal immune homeostasis. Possible relationships between decline of mTECSC activity and early thymic involution as well as various autoimmune disorders are discussed.

Cellular Adjuvant Properties, Direct Cytotoxicity of Re-differentiated Vα24 Invariant NKT-like Cells from Human Induced Pluripotent Stem Cells

Vα24 invariant natural killer T (iNKT) cells are a subset of T lymphocytes implicated in the regulation of broad immune responses. They recognize lipid antigens presented by CD1d on antigen-presenting cells and induce both innate and adaptive immune responses, which enhance effective immunity against cancer. Conversely, reduced iNKT cell numbers and function have been observed in many patients with cancer. To recover these numbers, we reprogrammed human iNKT cells to pluripotency and then re-differentiated them into regenerated iNKT cells in vitro through an IL-7/IL-15-based optimized cytokine combination. The re-differentiated iNKT cells showed proliferation and IFN-γ production in response to α-galactosylceramide, induced dendritic cell maturation and downstream activation of both cytotoxic T lymphocytes and NK cells, and exhibited NKG2D- and DNAM-1-mediated NK cell-like cytotoxicity against cancer cell lines. The immunological features of re-differentiated iNKT cells and their unlimited availability from induced pluripotent stem cells offer a potentially effective immunotherapy against cancer.

Thymic Nurse Cells Participate in Heterotypic Internalization and Repertoire Selection of Immature Thymocytes; Their Removal from the Thymus of Autoimmune Animals May be Important to Disease Etiology

Thymic nurse cells (TNCs) are specialized epithelial cells that reside in the thymic cortex. The initial report of their discovery in 1980 showed TNCs to contain up to 200 thymocytes within specialized vacuoles in their cytoplasm. Much has been reported since that time to determine the function of this heterotypic internalization event that exists between TNCs and developing thymocytes. In this review, we discuss the literature reported that describes the internalization event and the role TNCs play during T cell development in the thymus as well as why these multicellular complexes may be important in inhibiting the development of autoimmune diseases.

A genome wide transcriptional model of the complex response to pre-TCR signalling during thymocyte differentiation

Developing thymocytes require pre-TCR signalling to differentiate from CD4-CD8- double negative to CD4+CD8+ double positive cell. Here we followed the transcriptional response to pre-TCR signalling in a synchronised population of differentiating double negative thymocytes. This time series analysis revealed a complex transcriptional response, in which thousands of genes were up and down-regulated before changes in cell surface phenotype were detected. Genome-wide measurement of RNA degradation of individual genes showed great heterogeneity in the rate of degradation between different genes. We therefore used time course expression and degradation data and a genome wide transcriptional modelling (GWTM) strategy to model the transcriptional response of genes up-regulated on pre-TCR signal transduction. This analysis revealed five major temporally distinct transcriptional activities that up regulate transcription through time, whereas down-regulation of expression occurred in three waves. Our model thus placed known regulators in a temporal perspective, and in addition identified novel candidate regulators of thymocyte differentiation.