TCR and Notch signaling in CD4 and CD8 T-cell development

Transcriptomic profiling of thymic dysregulation and viral tropism after neonatal roseolovirus infection

Introduction

Herpesviruses, including the roseoloviruses, have been linked to autoimmune disease. The ubiquitous and chronic nature of these infections have made it difficult to establish a causal relationship between acute infection and subsequent development of autoimmunity. We have shown that murine roseolovirus (MRV), which is highly related to human roseoloviruses, induces thymic atrophy and disruption of central tolerance after neonatal infection. Moreover, neonatal MRV infection results in development of autoimmunity in adult mice, long after resolution of acute infection. This suggests that MRV induces durable immune dysregulation.

Methods

In the current studies, we utilized single-cell RNA sequencing (scRNAseq) to study the tropism of MRV in the thymus and determine cellular processes in the thymus that were disrupted by neonatal MRV infection. We then utilized tropism data to establish a cell culture system.

Results

Herein, we describe how MRV alters the thymic transcriptome during acute neonatal infection. We found that MRV infection resulted in major shifts in inflammatory, differentiation and cell cycle pathways in the infected thymus. We also observed shifts in the relative number of specific cell populations. Moreover, utilizing expression of late viral transcripts as a proxy of viral replication, we identified the cellular tropism of MRV in the thymus. This approach demonstrated that double negative, double positive, and CD4 single positive thymocytes, as well as medullary thymic epithelial cells were infected by MRV in vivo. Finally, by applying pseudotime analysis to viral transcripts, which we refer to as "pseudokinetics," we identified viral gene transcription patterns associated with specific cell types and infection status. We utilized this information to establish the first cell culture systems susceptible to MRV infection in vitro.

Conclusion

Our research provides the first complete picture of roseolovirus tropism in the thymus after neonatal infection. Additionally, we identified major transcriptomic alterations in cell populations in the thymus during acute neonatal MRV infection. These studies offer important insight into the early events that occur after neonatal MRV infection that disrupt central tolerance and promote autoimmune disease.

Prognostic value of CD8+T cells related genes and exhaustion regulation of Notch signaling pathway in hepatocellular carcinoma

Immunotherapy has emerged as the primary treatment modality for patients with advanced Hepatocellular carcinoma (HCC). However, its clinical efficacy remains limited, benefiting only a subset of patients, while most exhibit immune tolerance and face a grim prognosis. The infiltration of immune cells plays a pivotal role in tumor initiation and progression. In this study, we conducted an analysis of immune cell infiltration patterns in HCC patients and observed a substantial proportion of CD8+T cells. Leveraging the weighted gene co-expression network analysis (WGCNA), we identified 235 genes associated with CD8+T cell and constructed a risk prediction model. In this model, HCC patients were stratified into a high-risk and low-risk group. Patients in the high-risk group exhibited a lower survival rate, predominantly presented with intermediate to advanced stages of cancer, displayed compromised immune function, showed limited responsiveness to immunotherapy, and demonstrated elevated expression levels of the Notch signaling pathway. Further examination of clinical samples demonstrated an upregulation of the Notch1+CD8+T cell exhaustion phenotype accompanied by impaired cytotoxicity and cytokine secretion functions that worsened with increasing Notch activation levels. Our study not only presents a prognostic model but also highlights the crucial involvement of the Notch pathway in CD8+T cell exhaustion-a potential target for future immunotherapeutic interventions.

New insights into the stemness of adoptively transferred T cells by γc family cytokines

T cell-based adoptive cell therapy (ACT) has exhibited excellent antitumoral efficacy exemplified by the clinical breakthrough of chimeric antigen receptor therapy (CAR-T) in hematologic malignancies. It relies on the pool of functional T cells to retain the developmental potential to serially kill targeted cells. However, failure in the continuous supply and persistence of functional T cells has been recognized as a critical barrier to sustainable responses. Conferring stemness on infused T cells, yielding stem cell-like memory T cells (TSCM) characterized by constant self-renewal and multilineage differentiation similar to pluripotent stem cells, is indeed necessary and promising for enhancing T cell function and sustaining antitumor immunity. Therefore, it is crucial to identify TSCM cell induction regulators and acquire more TSCM cells as resource cells during production and after infusion to improve antitumoral efficacy. Recently, four common cytokine receptor γ chain (γc) family cytokines, encompassing interleukin-2 (IL-2), IL-7, IL-15, and IL-21, have been widely used in the development of long-lived adoptively transferred TSCM in vitro. However, challenges, including their non-specific toxicities and off-target effects, have led to substantial efforts for the development of engineered versions to unleash their full potential in the induction and maintenance of T cell stemness in ACT. In this review, we summarize the roles of the four γc family cytokines in the orchestration of adoptively transferred T cell stemness, introduce their engineered versions that modulate TSCM cell formation and demonstrate the potential of their various combinations. Video Abstract.

Characteristics and clustering analysis of peripheral blood lymphocyte subsets in children with systemic lupus erythematosus complicated with clinical infection

OBJECTIVES

Clinical infection is a common complication in children with systemic lupus erythematosus (SLE). However, few studies have investigated immune alterations in children with SLE complicated with clinical infection. We assessed lymphocyte subsets in children with SLE to explore the possibility of clinical infection.

METHODS

We retrospectively analyzed the proportion of peripheral lymphocyte subsets in 140 children with SLE. Children with SLE were classified into different clusters according to the proportion of peripheral blood lymphocyte subsets: (CD3 + /CD4 + T cell, CD3 + /CD8 + T cell, CD3 + /CD4 + /CD8 + T cell, CD3 + /CD4-/CD8- T cell, CD19 + B cell, and CD3-/CD16 + /CD56 + NK cell). Differences in the proportion of lymphoid subsets, infection rates, and systemic lupus erythematosus disease activity index (SLEDAI) scores were compared between clusters. In addition, we grouped the subjects according to the presence or absence of infection. Proportions of lymphoid subsets, demographic variables, clinical presentation, and other laboratory variables were compared between the infected and uninfected groups. Finally, the diagnostic ability of lymphocyte subset ratios to distinguish secondary infection in children with SLE was predicted using an ROC curve.

RESULTS

Cluster C2 had a higher proportion of B cells than Cluster C1, while Cluster C1 had a lower proportion of NK cells, CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells. Infection rates and SLEDAI scores were higher in Cluster C2 than in Cluster C1. The infected children had a higher proportion of B cells and a lower proportion of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells. There were no significant differences in lymphoid subsets between children in Cluster C2 and the infected groups. The area under the ROC curve of B lymphocytes in predicting SLE children with infection was 0.842. The area under the ROC curve was 0.855 when a combination of B cells, NK cells, CD4 + T cells, and CD8 + T cells was used to predict the outcome of coinfection.

CONCLUSIONS

A high percentage of B cells and a low percentage of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, CD3 + /CD4 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells may be associated with infection in children with SLE. B cells was used to predict the outcome of coinfection in children with SLE. Key Points • A high percentage of B cells and a low percentage of CD3 + T cells, CD3 + /CD4 + T cells, CD3 + /CD8 + T cells, CD3 + /CD4 + /CD8 + T cells, and CD3 + /CD4-/CD8- T cells may be associated with infection in children with SLE • B cells was used to predict the outcome of coinfection in children with SLE.

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

Critical Role of Notch-1 in Mechanistic Target of Rapamycin Hyperactivity and Vascular Inflammation in Patients With Takayasu Arteritis

OBJECTIVE

Takayasu arteritis (TA) is a major type of large vessel vasculitis characterized by progressive inflammation in vascular layers. In our recent study we identified a central role of mechanistic target of rapamycin (mTOR) hyperactivity in proinflammatory T cell differentiation in TA. This study was undertaken to explore potential mechanisms underpinning T cell-intrinsic mTOR hyperactivity and vascular inflammation in TA, with a focus on Notch-1.

METHODS

Notch-1 expression and activity was determined according to Notch-1, activated Notch-1, and HES-1 levels. We detected mTOR activity with intracellular expression of phosphorylated ribosomal protein S6. Differentiation of proinflammatory T cells was analyzed by detecting Th1 and Th17 lineage-determining transcription factors. The function of Notch-1 was evaluated using γ-secretase inhibitor DAPT and gene knockdown using a short hairpin RNA (shRNA) strategy. We performed our translational study using humanized NSG mouse chimeras in which human vasculitis was induced using immune cells from TA patients.

RESULTS

CD4+ T cells from TA patients exerted Notch-1^high , leading to mTOR hyperactivity and spontaneous maldifferentiation of Th1 cells and Th17 cells. Blockade of Notch-1 using DAPT and Notch-1 shRNA efficiently abrogated mTOR complex 1 (mTORC1) activation and proinflammatory T cell differentiation. Mechanistically, Notch-1 promoted mTOR expression, interacted with mTOR, and was associated with lysosomal localization of mTOR. Accordingly, systemic administration of DAPT and CD4+ T cell-specific gene knockdown of Notch-1 could alleviate vascular inflammation in humanized TA chimeras.

CONCLUSION

Expression of Notch-1 is elevated in CD4+ T cells from TA patients, resulting in mTORC1 hyperactivity and proinflammatory T cell differentiation. Targeting Notch-1 is a promising therapeutic strategy for the clinical management of TA.

Notch1 deficiency alters the migratory behavior of developing T cells and calcium signaling in the thymus of medaka

The differentiation of T cells from lymphoid progenitors in the thymus follows sequential developmental stages that constantly require interaction with thymic epithelial cells. Several distinct aspects of early T cell development depend on the activation of Notch receptors on thymocytes, while the selection of thymocytes at later stages are believed to be Notch independent. Using reverse genetic approaches and whole-thymus live imaging in an in vivo teleost model, the medaka, we report that Notch1 signals is required for proliferation and specification of developing T cells as well as involved in their selection in the thymus. We reveal that Notch1 controls the migratory behavior of thymocytes through controlling the chemokine receptor Ccr9b and thereby influence the T cell receptor (TCR) activation. Hence, we propose that, in lower vertebrates, the function of Notch signaling extends to all stages of T cell development, except when thymocytes undergo TCRβ rearrangement.

Rebuilding the hematopoietic stem cell niche: Recent developments and future prospects

Hematopoietic stem cells (HSCs) have proven their clinical relevance in stem cell transplantation to cure patients with hematological disorders. Key to their regenerative potential is their natural microenvironment - their niche - in the bone marrow (BM). Developments in the field of biomaterials enable the recreation of such environments with increasing preciseness in the laboratory. Such artificial niches help to gain a fundamental understanding of the biophysical and biochemical processes underlying the interaction of HSCs with the materials in their environment and the disturbance of this interplay during diseases affecting the BM. Artificial niches also have the potential to multiply HSCs in vitro, to enable the targeted differentiation of HSCs into mature blood cells or to serve as drug-testing platforms. In this review, we will introduce the importance of artificial niches followed by the biology and biophysics of the natural archetype. We will outline how 2D biomaterials can be used to dissect the complexity of the natural niche into individual parameters for fundamental research and how 3D systems evolved from them. We will present commonly used biomaterials for HSC research and their applications. Finally, we will highlight two areas in the field of HSC research, which just started to unlock the possibilities provided by novel biomaterials, in vitro blood production and studying the pathophysiology of the niche in vitro. With these contents, the review aims to give a broad overview of the different biomaterials applied for HSC research and to discuss their potentials, challenges and future directions in the field. STATEMENT OF SIGNIFICANCE: Hematopoietic stem cells (HSCs) are multipotent cells responsible for maintaining the turnover of all blood cells. They are routinely applied to treat patients with hematological diseases. This high clinical relevance explains the necessity of multiplication or differentiation of HSCs in the laboratory, which is hampered by the missing natural microenvironment - the so called niche. Biomaterials offer the possibility to mimic the niche and thus overcome this hurdle. The review introduces the HSC niche in the bone marrow and discusses the utility of biomaterials in creating artificial niches. It outlines how 2D systems evolved into sophisticated 3D platforms, which opened the gateway to applications such as, expansion of clinically relevant HSCs, in vitro blood production, studying niche pathologies and drug testing.

Content and location of lymphocyte subpopulations with markers CD4+, CD8+ and CD20+ in the esophageal tonsil of chickens and the Meckel diverticulum of ducks

Immune formations of birds' digestive organs, including the esophageal tonsil and Meckel’s diverticulum, protect the body from foreign antigens that enter the body with food and water and play an important role in maintaining the genetic constancy of its internal environment. This unique property of the immune system is formed during ontogenesis and is associated with maintaining the selection of lymphocyte clones that are able to respond to foreign antigens and carry out a specific immune response of two types: humoral and cellular. This article presents the results of a study of T- and B-lymphocyte subpopulations of the esophageal tonsil of Shever 579 cross chickens at the age of 25, 180 and 300 days, the Meckel diverticulum of the Blagovarsky cross ducks at the age of 30, 150 and 180 days. Immunohistochemical and statistical research methods were used to determine the localization and quantitative parameters of cell populations of lymphocytes (CD4+, CD8+, CD20+) using monoclonal antibodies and the DAKO EnVision FLEX+ imaging system (Dako Cytomation, Denmark). Separate subpopulations of T-lymphocytes (CD4+ - helpers, CD8+ -cytotoxic / T-suppressors) and mature B-lymphocytes (CD20+) were found in the esophageal tonsil and Meckel diverticulum of birds. Their presence confirms that antigen-independent proliferation and differentiation of lymphocytes into effector cells occur in the immune formations of the digestive system. The lymphoid tissue of these formations is represented mainly by a well-defined diffuse form and nodules with light centers (secondary). In the esophageal tonsil of chickens, these structures are located in the tunica mucosa and tela submucosa, and in the Meckel diverticulum of ducks – also in the tunica muscularis. The content of lymphocytes with these markers predominates in diffuse lymphoid tissue compared to that in secondary lymphoid nodules. In the diffuse lymphoid tissue of the esophageal tonsil, lymphocytes are located mainly near the adenomeres and excretory ducts of the esophageal glands, blood vessels, and under the surface epithelium, and in Meckel’s diverticulum – around the crypts, in their epithelium and in the epithelium of the villi. They are also found in the light centers of lymphoid nodules and on their periphery. The indices of the content of lymphocytes with the indicated markers in the esophageal tonsil and Meckel diverticulum which we determined were associated with age characteristics of the poultry in the postnatal period of ontogenesis. According to our observations, the content of CD20+ lymphocytes was the highest, while the populations of CD4+ and CD8+ lymphocytes were much smaller. This indicates an increase in the activity and predominance of the humoral immunity over the cellular one. The content of CD20+ lymphocytes was highest in birds at the age of 180 days, that is, during their sexual maturity. The data presented in the work can be used by morphologists researching the organs of the immune system, immunologists, poultry specialists involved in breeding, using and raising poultry and in educational work.

Immunological memory in teleost fish

Immunological memory can be regarded as the key aspect of adaptive immunity, i.e. a specific response to first contact with an antigen, which in mammals is determined by the properties of T, B and NK cells. Re-exposure to the same antigen results in a more rapid response of the activated specific cells, which have a unique property that is the immunological memory acquired upon first contact with the antigen. Such a state of immune activity is also to be understood as related to "altered behavior of the immune system" due to genetic alterations, presumably maintained independently of the antigen. It also indicates a possible alternative mechanism of maintaining the immune state at a low level of the immune response, "directed" by an antigen or dependent on an antigen, associated with repeated exposure to the same antigen from time to time, as well as the concept of innate immune memory, associated with epigenetic reprogramming of myeloid cells, i.e. macrophages and NK cells. Studies on Teleostei have provided evidence for the presence of immunological memory determined by T and B cells and a secondary response stronger than the primary response. Research has also demonstrated that in these animals macrophages and NK-like cells (similar to mammalian NK cells) are able to respond when re-exposed to the same antigen. Regardless of previous reports on immunological memory in teleost fish, many reactions and mechanisms related to this ability require further investigation. The very nature of immunological memory and the activity of cells involved in this process, in particular macrophages and NK-like cells, need to be explained. This paper presents problems associated with adaptive and innate immune memory in teleost fish and characteristics of cells associated with this ability.

NSrp70 is a lymphocyte-essential splicing factor that controls thymocyte development

Alternative pre-mRNA splicing is a critical step to generate multiple transcripts, thereby dramatically enlarging the proteomic diversity. Thus, a common feature of most alternative splicing factor knockout models is lethality. However, little is known about lineage-specific alternative splicing regulators in a physiological setting. Here, we report that NSrp70 is selectively expressed in developing thymocytes, highest at the double-positive (DP) stage. Global splicing and transcriptional profiling revealed that NSrp70 regulates the cell cycle and survival of thymocytes by controlling the alternative processing of various RNA splicing factors, including the oncogenic splicing factor SRSF1. A conditional-knockout of Nsrp1 (NSrp70-cKO) using CD4Cre developed severe defects in T cell maturation to single-positive thymocytes, due to insufficient T cell receptor (TCR) signaling and uncontrolled cell growth and death. Mice displayed severe peripheral lymphopenia and could not optimally control tumor growth. This study establishes a model to address the function of lymphoid-lineage-specific alternative splicing factor NSrp70 in a thymic T cell developmental pathway.

Analysis of the Efficacy and Mechanism of Action of Xuebijing Injection on ARDS Using Meta-Analysis and Network Pharmacology

Objective

Acute respiratory distress syndrome (ARDS) is defined as the acute onset of noncardiogenic edema and subsequent gas-exchange impairment due to a severe inflammatory process known as cytokine storm. Xuebijing injection (hereinafter referred to as Xuebijing) is a patent drug that was used to treat ARDS or severe pneumonia (SP) in China. However, its efficacy and mechanism of actions remain unclear. In this study, we used meta-analysis and network pharmacology to assess these traits of Xuebijing.

Methods

We searched PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), and Wanfang databases for randomized controlled trials (RCTs) that evaluated Xuebijing therapy for ARDS or SP. The outcomes were total mortality, intensive care unit (ICU) stay time, and TNF-α and IL-6 levels. We performed a meta-analysis using RevMan 5.3 software. The putative targets, top 10 proteins, and possible pathway of Xuebinjing on ARDS were analyzed by network pharmacology. TNF-α and IL-6 were further docked with the six main active components of Xuebinjing using AutoDock 4.2.6 and PyMol 1.5.0.3 software.

Results

Fifteen RCTs involving 2778 patients (13 ARDS and 2 SP) were included. Compared with the control, Xuebijing treatment significantly reduced the mortality rate (risk ratio, 0.64 (95% credible interval (CrI), 0.54-0.77)), reduced the ICU stay time (mean difference (MD), -4.51 (95% CrI, -4.97--4.06)), reduced the TNF-α ((MD), -1.23 (95% CrI, -1.38--1.08)) and IL-6 ((MD), -1.15 (95% CrI, -1.52--0.78)) levels. The 56 putative targets, top 10 proteins (MAPK1 (mitogen-activated protein kinase 1), MAPK8 (mitogen-activated protein kinase 8), RELA (transcription factor p65), NFKB1 (nuclear factor NF-kappa-B p105 subunit), JUN (transcription factor AP-1), SRC (proto-oncogene tyrosine-protein kinase), TNF (tumor necrosis factor), HRAS (GTPase HRas), IL6 (interleukin-6), and APP (amyloid-beta A4 protein)), and possible pathways (Ret tyrosine kinase, IL2-mediated signaling events, CD4+/CD8+ T cell-related TCR signaling, p75(NTR)-mediated signaling, CXCR4-mediated signaling events, LPA receptor-mediated events, IL12-mediated signaling events, FAS (CD95) signaling pathway, and immune system) of Xuebinjing's action on ARDS were obtained. The molecular docking results showed that all the six components of Xuebinjing docked with TNF-α, and two components docked with IL-6 got the binding energies lower than -5.

Conclusion

Our results recommended Xuebijing treatment for patients with ARDS. Xuebijing has therapeutic effects on ARDS patients partly by regulating the immune cell/cytokine pathways and thus inhibiting the cytokine storm. TNF-α is the cytokine both directly and indirectly inhibited by Xuebijing, and IL-6 is the cytokine mainly indirectly inhibited by Xuebijing.

Elucidating the Functional Roles of Helper and Cytotoxic T Cells in the Cell-Mediated Immune Responses of Olive Flounder (Paralichthys olivaceus)

In higher vertebrates, helper and cytotoxic T cells, referred to as CD4 and CD8 T lymphocytes, respectively, are mainly associated with adaptive immunity. The adaptive immune system in teleosts involves T cells equivalent to those found in mammals. We previously generated monoclonal antibodies (mAbs) against olive flounder (Paralichthys olivaceus) CD4 T cells, CD4-1 and CD4-2, and used these to describe the olive flounder’s CD4 Tcell response during a viral infection. In the present study, we successfully produced mAbs against CD8 T lymphocytes and their specificities were confirmed using immuno-blotting, immunofluorescence staining, flow cytometry analysis andreverse transcription polymerase chain reaction (RT-PCR). The results showed that these mAbs are specific for CD8 T lymphocytes. We also investigated variations in CD4 and CD8 T cells populations, and analyzed the expression of immune-related genes expressed by these cells in fish infected with nervous necrosis virus or immunized with thymus dependent and independent antigens. We found that both CD4 and CD8 T lymphocyte populations significantly increased in these fish and Th1-related genes were up-regulated compared to the control group. Collectively, these findings suggest that the CD4 and CD8 T lymphocytes in olive flounder are similar to the helper and cytotoxic T cells found in mammals, and Th1 and cytotoxic immune responses are primarily involved in the early adaptive immune response against extracellular antigens.

Preclinical efficacy of humanized, non–FcγR-binding anti-CD3 antibodies in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy that accounts for ∼20% of ALL cases. Intensive chemotherapy regimens result in cure rates >85% in children and <50% in adults, warranting a search of novel therapeutic strategies. Although immune-based therapies have tremendously improved the treatment of B-ALL and other B-cell malignancies, they are not yet available for T-ALL. We report here that humanized, non–Fcγ receptor (FcγR)–binding monoclonal antibodies (mAbs) to CD3 have antileukemic properties in xenograft (PDX) models of CD3+ T-ALL, resulting in prolonged host survival. We also report that these antibodies cooperate with chemotherapy to enhance antileukemic effects and host survival. Because these antibodies show only minor, manageable adverse effects in humans, they offer a new therapeutic option for the treatment of T-ALL. Our results also show that the antileukemic properties of anti-CD3 mAbs are largely independent of FcγR-mediated pathways in T-ALL PDXs.

T Cells in Fish

Cartilaginous and bony fish are the most primitive vertebrates with a thymus, and possess T cells equivalent to those in mammals. There are a number of studies in fish demonstrating that the thymus is the essential organ for development of T lymphocytes from early thymocyte progenitors to functionally competent T cells. A high number of T cells in the intestine and gills has been reported in several fish species. Involvement of CD4⁺ and CD8α⁺ T cells in allograft rejection and graft-versus-host reaction (GVHR) has been demonstrated using monoclonal antibodies. Conservation of CD4⁺ helper T cell functions among teleost fishes has been suggested in a number studies employing mixed leukocyte culture (MLC) and hapten/carrier effect. Alloantigen- and virus-specific cytotoxicity has also been demonstrated in ginbuna and rainbow trout. Furthermore, the important role of cell-mediated immunity rather than humoral immunity has been reported in the protection against intracellular bacterial infection. Recently, the direct antibacterial activity of CD8α⁺, CD4⁺ T-cells and sIgM⁺ cells in fish has been reported. In this review, we summarize the recent progress in T cell research focusing on the tissue distribution and function of fish T cells.

Generation of functional, antigen-specific CD8+ human T cells from cord blood stem cells using exogenous Notch and tetramer-TCR signaling

In vitro differentiation of mouse and human stem cells into early T cells has been successfully demonstrated using artificial Notch signaling systems. However, generation of mature, antigen-specific, functional T cells, directly from human stem cells has remained elusive, except when using stromal coculture of stem cells retrovirally transfected with antigen-specific T cell receptors (TCRs). Here we show that human umbilical cord blood (UCB)-derived CD34+CD38-/low hematopoietic stem cells can be successfully differentiated into functional, antigen-specific cytotoxic CD8+ T cells without direct stromal coculture or retroviral TCR transfection. Surface-immobilized Notch ligands (DLL1) and stromal cell conditioned medium successfully induced the development of CD1a+CD7+ and CD4+CD8+ early T cells. These cells, upon continued culture with cytomegalovirus (CMV) or influenza-A virus M1 (GIL) epitope-loaded human leukocyte antigen (HLA)-A*0201 tetramers, resulted in the generation of a polyclonal population of CMV-specific or GIL-specific CD8+ T cells, respectively. Upon further activation with antigen-loaded target cells, these antigen-specific, stem cell-derived T cells exhibited cytolytic functionality, specifically CD107a surface mobilization, interferon gamma (IFNg) production, and Granzyme B secretion. Such scalable, in vitro generation of functional, antigen-specific T cells from human stem cells could eventually provide a readily available cell source for adoptive transfer immunotherapies and also allow better understanding of human T cell development.

A novel T cell subset with trans-rearranged Vγ-Cβ TCRs shows Vβ expression is dispensable for lineage choice and MHC restriction

αβ T cells, which express the α-β TCR heterodimer, express CD4 or CD8 coreceptors on cells that are MHC class I or MHC class II dependent. In contrast, γδ T cells do not express CD4 or CD8 and develop independently of MHC interaction. The factors that determine αβ and γδ lineage choice are not fully understood, and the determinants of MHC restriction of TCR specificity have been controversial. In this study we have identified a naturally occurring population of T cells expressing Vγ-Cβ receptor chains on the cell surface, the products of genomic trans-rearrangement between the Vγ2 gene and a variety of Dβ or Jβ genes, in place of an intact TCRβ-chain and in association with TCRα. Identification of this population allowed an analysis of the role of TCR variable regions in determining T cell lineage choice and MHC restriction. We found that Vγ2(+)Cβ(+) cells are positive for either CD4 or CD8 and are selected in an MHC class II- or MHC class I-dependent manner, respectively, thus following the differentiation pathway of αβ and not γδ cells and demonstrating that Vβ V region sequences are not required for selection of an MHC-restricted repertoire.

Cellular and molecular requirements for the selection of in vitro-generated CD8 T cells reveal a role for Notch

Differentiation of CD8 single-positive (SP) T cells is predicated by the ability of lymphocyte progenitors to integrate multiple signaling cues provided by the thymic microenvironment. In the thymus and the OP9-DL1 system for T cell development, Notch signals are required for progenitors to commit to the T cell lineage and necessary for their progression to the CD4(+)CD8(+) double-positive (DP) stage of T cell development. However, it remains unclear whether Notch is a prerequisite for the differentiation of DP cells to the CD8 SP stage of development. In this study, we demonstrate that Notch receptor-ligand interactions allow for efficient differentiation and selection of conventional CD8 T cells from bone marrow-derived hematopoietic stem cells. However, bone marrow-derived hematopoietic stem cells isolated from Itk(-/-)Rlk(-/-) mice gave rise to T cells with decreased IFN-γ production, but gained the ability to produce IL-17. We further reveal that positive and negative selection in vitro are constrained by peptide-MHC class I expressed on OP9 cells. Finally, using an MHC class I-restricted TCR-transgenic model, we show that the commitment of DP precursors to the CD8 T cell lineage is dependent on Notch signaling. Our findings further establish the requirement for Notch receptor-ligand interactions throughout T cell differentiation, including the final step of CD8 SP selection.

Differential gene expression profiles of PPP2R5C-siRNA-treated malignant T cells

Recently, alterations in the expression pattern of PPP2R5C associated with malignant transformation have been characterized, and PPP2R5C overexpression was demonstrated in leukemias. To confirm the role of PPP2R5C in proliferation and its molecular mechanism, three PPP2R5C-siRNAs and a scrambled nonsilencing siRNA control were used to treat Molt-4 and Jurkat T cells. After nucleofection, PPP2R5C expression and biological consequences based on a highly efficient and specific PPP2R5C-siRNA were demonstrated by qRT-PCR, CCK-8 assay, Annexin V/PI, and flow cytometry. The global gene expression profile of PPP2R5C-siRNA-treated Jurkat T cells was established. A significant reduction in the PPP2R5C mRNA level was observed at 24 to 72 h in Molt-4 and Jurkat T cells with all of the PPP2R5C-siRNAs. The proliferation rate of Molt-4 and Jurkat T cells transfected with different PPP2R5C-siRNAs was significantly decreased at 72 h compared with the control (p<0.05). However, the transfected cells did not show a significant increase in Annexin V/PI-positive cells (apoptosis). The highly efficient PPP2R5C-siRNA2 was used to treat Jurkat T cells for gene expression profile analysis. In total, 439 genes were upregulated, and 524 genes were downregulated at least twofold in PPP2R5C-siRNA-treated Jurkat T cells. Changes in signaling pathway genes closely related to the TCR, Wnt, calcium, MAPK, and p53 signaling pathways were observed. In conclusion, the suppression of PPP2R5C by RNA interference could effectively inhibit the proliferation of leukemic T cells, the PPP2R5C-siRNA treatment altered gene expression profiles, and the differential expression of the glycogen synthase kinase 3 beta (GSK-3β), ataxia telangiectasia mutated (ATM), and Mdm2 p53 binding protein homolog (MDM2) genes may play an important role in the effects of PPP2R5C knockdown in Jurkat T cells.

Interpreting Stress Responses during Routine Toxicity Studies

Stress often occurs during toxicity studies. The perception of sensory stimuli as stressful primarily results in catecholamine release and activation of the hypothalamic–pituitary–adrenal (HPA) axis to increase serum glucocorticoid concentrations. Downstream effects of these neuroendocrine signals may include decreased total body weights or body weight gain; food consumption and activity; altered organ weights (e.g., thymus, spleen, adrenal); lymphocyte depletion in thymus and spleen; altered circulating leukocyte counts (e.g., increased neutrophils with decreased lymphocytes and eosinophils); and altered reproductive functions. Typically, only some of these findings occur in a given study. Stress responses should be interpreted as secondary (indirect) rather than primary (direct) test article–related findings. Determining whether effects are the result of stress requires a weight-of-evidence approach. The evaluation and interpretation of routinely collected data (standard in-life, clinical pathology, and anatomic pathology endpoints) are appropriate and generally sufficient to assess whether or not changes are secondary to stress. The impact of possible stress-induced effects on data interpretation can partially be mitigated by toxicity study designs that use appropriate control groups (e.g., cohorts treated with vehicle and subjected to the same procedures as those dosed with test article), housing that minimizes isolation and offers environmental enrichment, and experimental procedures that minimize stress and sampling and analytical bias.

This article is a comprehensive overview of the biological aspects of the stress response, beginning with a Summary (Section 1) and an Introduction (Section 2) that describes the historical and conventional methods used to characterize acute and chronic stress responses. These sections are followed by reviews of the primary systems and parameters that regulate and/or are influenced by stress, with an emphasis on parameters evaluated in toxicity studies: In-life Procedures (Section 3), Nervous System (Section 4), Endocrine System (Section 5), Reproductive System (Section 6), Clinical Pathology (Section 7), and Immune System (Section 8). The paper concludes (Section 9) with a brief discussion on Minimizing Stress-Related Effects (9.1.), and a final section explaining why Parameters routinely measured are appropriate for assessing the role of stress in toxicology studies (9.2.).

Thymic epithelial requirement for γδ T cell development revealed in the cell ablation transgenic system with TSCOT promoter

In order to investigate the role of thymic epithelial cell (TEC) subsets during T-cell development, we established a new transgenic system, enabling inducible cell-specific ablation as well as marking the TEC subsets using bicistronic bacterial nitroreductase and EGFP genes. Two different lengths of the TSCOT promoter in transgenic mice, named 3.1T-NE and 9.1T-NE, drive EGFP expression into TECs. In adult life, EGFP expression was located in the medulla with a smaller 3.1 kb TSCOT promoter, while it was maintained in the cortex with a 9.1 kb promoter, suggesting putative TEC specific as well as compartment specific cis elements within two promoters. Nitroreductase induced cell death was specific without bystander killing upon the treatment of prodrugs such as nitrofurantoin and metronidazol. The degree of cell death was dependent on the dose of the prodrug in the cell and the fetal thymic organ cultures (FTOCs). Fetal thymic stromal populations were analyzed based on the expression levels of EpCAM, MHCII, CDR1 and/or UEA-1. EGFP expression patterns varied among subsets indicating the differential TSCOT promoter activity in each TEC subset. Prodrug treatment in FTOCs reduced the numbers of total and subsets of thymocytes. A CD4(+)CD8(+) double positive cell population was highly susceptible in both transgenic lines. Surprisingly, there was a distinct reduction in γδ T cell population only in the 9.1T-NE thymus, indicating that they require a NTREGFP expressing TEC population. Therefore, these results support a division of labor within TEC subsets for the αβ and γδ lineage specification.

Restoration of electric footshock-induced immunosuppression in mice by Gynostemma pentaphyllum components

The immunomodulatory effects of the ethanol extract of Gynostemma pentaphyllum (GP-EX) were examined in electric footshock (EFS)-stressed mice. The mice were orally administered various doses of GP-EX for 7 days before exposure to EFS (duration: 3 min, interval: 10 s, intensity: 2 mA) once a day from day 8 for 14 days with continuous daily feeding of GP-EX. Oral administration of GP-EX to mice prevented EFS stress-induced immunosuppression as determined by the lymphoid organ (thymus and spleen) weight and cellularity. In addition, oral administration of GP-EX restored EFS-suppressed functional properties of mature lymphocytes in terms of concanavalin A-induced proliferation of splenocytes and lipopolysaccharide-induced cytokine production (TNF-α, IL-1β). Furthermore, we found that mice that were orally administered with GP-EX generated much more potent ovalbumin-specific cytotoxic T lymphocyte responses upon intravenous ovalbumin injection compared to the untreated controls. These results demonstrate that oral administration of the ethanol extract of Gynostemma pentaphyllum could increase host defense in immunocompromised situations such as stress-induced immunosuppression.

On becoming a T cell, a convergence of factors kick it up a Notch along the way

The thymus is seeded by bone marrow-derived progenitors, which undergo a series of differentiation and proliferation events in order to generate functional T lymphocytes. The Notch signaling pathway, together with multiple transcription factors, act in concert to commit progenitors to a T-lineage fate, extinguishing non-T cell potential, inducing thymocyte differentiation and supporting proliferation and survival along the way to becoming a mature T cell. This review focuses on recent evidence regarding the complex interplay between the Notch pathway and other key transcription factors at specific lineage-decision points during the program of T cell development.

The expression of CD8α discriminates distinct T cell subsets in teleost fish

CD8, belonging to the TCR complex, is the main marker molecule of CTLs. Although CD8 genes have been detected in many fish species, the analysis of teleost CD8+ cells has been limited because of the lack of antibodies. Using newly established mAbs against rainbow trout CD8α, we found high ratios of CD8α+ cells in trout thymus, gill and intestine, but relatively low abundance in pronephros, spleen and blood. Accordingly, tissue sections revealed many CD8α+ cells in thymus, numerous intra- and subepithelial CD8α+ cells in intestine and gill and few scattered CD8α+ cells in spleen and pronephros. In secondary lymphoid tissues, CD8α+ lymphocytes, which did not react with anti-thrombocyte or anti-IgM mAbs, expressed CD8α, CD8β and TCRα, while Ig and CD4 transcripts were found in CD8α⁻ lymphocytes. In contrast, considerable CD4 expression in CD8α+ thymocytes suggests the presence of double-positive early T cells. Highly expressed TCRγ, LAG3 and CTLA4 in CD8α+ lymphocytes imply that they constitute a heterogeneous population different from found in non-mucosal tissues. PHA stimulation resulted in an up-regulation of CTL effector genes (perforin, granulysin and IFN-γ) in CD8α+ pronephrocytes, while both Th1 (IFN-γ) and Th2 (IL-4/13A) cytokines were up-regulated in CD8α⁻ pronephrocytes. Although the basic characteristics of CD8α+ lymphocytes seem similar in teleost and mammals, features such as the low proportion of teleost CD8α+ lymphocytes in blood and their high abundance in respiratory tissue reveal a unique dynamics and distribution.

Conservation of characteristics and functions of CD4 positive lymphocytes in a teleost fish

The presence of helper and cytotoxic T cells in fish has been suggested, although T cell subsets have yet to be identified at the cellular level. In order to investigate the functions of CD4 and CD8α positive T cells we attempted to produce and characterize monoclonal antibodies (mAbs) against teleost CD4 and CD8α. Here we report the successful production of mAbs against CD4 and CD8α in clonal ginbuna crucian carp Carassius auratus langsdorfii and the function of CD4 positive T cells. In this study we demonstrate the presence of teleost CD4- and CD8α-positive T cell subsets with morphology, tissue distribution and gene expression similar to those of mammalian CD4- and CD8-positive T lymphocytes. Using mAbs we found that CD4/CD8 double positive T cells are only present in the thymus, suggesting that it is the site of T cell development. We further demonstrated in vitro proliferation of CD4 positive T cells by allogeneic combination of mixed leukocyte culture and antigen-specific proliferation of CD4 positive T cells after in vitro sensitization with OVA. In our previous study we showed that CD8α-positive lymphocytes are the primary cell type showing specific cytotoxicity against allogeneic targets. Collectively, these findings suggest that CD4 and CD8α positive T cells in ginbuna are equivalent to helper and cytotoxic T lymphocytes (CTL) in mammals, respectively. This is the first report to show the characteristics and functions of CD4 positive T cells in fish and these findings shed light into the evolutionary origins and primordial functions of helper T cells.

Acute endotoxin-induced thymic atrophy is characterized by intrathymic inflammatory and wound healing responses

Background

Productive thymopoiesis is essential for a robust and healthy immune system. Thymus unfortunately is acutely sensitive to stress resulting in involution and decreased T cell production. Thymic involution is a complication of many clinical settings, including infection, malnutrition, starvation, and irradiation or immunosuppressive therapies. Systemic rises in glucocorticoids and inflammatory cytokines are known to contribute to thymic atrophy. Little is known, however, about intrathymic mechanisms that may actively contribute to thymus atrophy or initiate thymic recovery following stress events.

Methodology/Principal Findings

Phenotypic, histologic and transcriptome/pathway analysis of murine thymic tissue during the early stages of endotoxemia-induced thymic involution was performed to identify putative mechanisms that drive thymic involution during stress. Thymus atrophy in this murine model was confirmed by down-regulation of genes involved in T cell development, cell activation, and cell cycle progression, correlating with observed phenotypic and histologic thymus involution. Significant gene changes support the hypothesis that multiple key intrathymic pathways are differentially activated during stress-induced thymic involution. These included direct activation of thymus tissue by LPS through TLR signaling, local expression of inflammatory cytokines, inhibition of T cell signaling, and induction of wound healing/tissue remodeling.

Conclusions/Significance

Taken together, these observations demonstrated that in addition to the classic systemic response, a direct intrathymic response to endotoxin challenge concurrently contributes to thymic involution during endotoxemia. These findings are a substantial advancement over current understanding of thymus response to stress and may lead to the development of novel therapeutic approaches to ameliorate immune deficiency associated with stress events.

Itk derived signals regulate the expression of Th-POK and controls the development of CD4 T cells

T cell development is critically dependent on both the environment and signals delivered by the T cell Receptor (TCR). The Tec family kinase Itk has been suggested to be an amplifier of signals emanating from the TCR and the loss of Itk partially affects most stages of thymopoiesis. Loss of Itk also differentially affects the development of conventional vs. non-conventional or innate memory phenotype T cells. Here, we examine whether these lineage choices are affected by a combination of TCR affinity and Itk by analyzing mice lacking Itk and carrying two TCR transgenes with differing affinities, OT-II and DO11.10. Our results show that developing thymocytes receive a gradient of signals, DO11.10>OT-II>DO11.10/Itk(-/-)>OT-II/Itk(-/-). We also show that the development of CD4(+) T cells is controlled by TCR signaling via Itk, which regulates the expression of the transcription factor, Th-POK, an enforcement factor for CD4 commitment. This results in a reduction in CD4(+) T cell development, and an increase in the development of MHC class II restricted TCR transgenic CD8(+) T cells that resemble non-conventional or innate memory phenotype CD8 T cells. This alteration accompanies increased expression of Runx3 and its target genes Eomesodermin, Granzyme B and Perforin in Itk null OT-II CD4(+) thymocytes. All together, these data suggest that Itk plays an important role in CD4/CD8 commitment by regulating signal thresholds for the lineage commitment. Our data also suggest that the lower level of TCR signaling that occurs with a low affinity TCR in the absence of Itk can redirect some MHC class II restricted CD4(+) T cell to class II-restricted CD8(+) innate memory phenotype T cells.

LKB1 is essential for the proliferation of T-cell progenitors and mature peripheral T cells

The serine/threonine kinase LKB1 has a conserved role in Drosophila and nematodes to co-ordinate cell metabolism. During T lymphocyte development in the thymus, progenitors need to synchronize increased metabolism with the onset of proliferation and differentiation to ensure that they can meet the energy requirements for development. The present study explores the role of LKB1 in this process and shows that loss of LKB1 prevents thymocyte differentiation and the production of peripheral T lymphocytes. We find that LKB1 is required for several key metabolic processes in T-cell progenitors. For example, LKB1 controls expression of CD98, a key subunit of the L-system aa transporter and is also required for the pre-TCR to induce and sustain the regulated phosphorylation of the ribosomal S6 subunit, a key regulator of protein synthesis. In the absence of LKB1 TCR-beta-selected thymocytes failed to proliferate and did not survive. LBK1 was also required for survival and proliferation of peripheral T cells. These data thus reveal a conserved and essential role for LKB1 in the proliferative responses of both thymocytes and mature T cells.

NK-like homeodomain proteins activate NOTCH3-signaling in leukemic T-cells

Background

Homeodomain proteins control fundamental cellular processes in development and in cancer if deregulated. Three members of the NK-like subfamily of homeobox genes (NKLs), TLX1, TLX3 and NKX2-5, are implicated in T-cell acute lymphoblastic leukemia (T-ALL). They are activated by particular chromosomal aberrations. However, their precise function in leukemogenesis is still unclear. Here we screened further NKLs in 24 T-ALL cell lines and identified the common expression of MSX2. The subsequent aim of this study was to analyze the role of MSX2 in T-cell differentiation which may be disturbed by oncogenic NKLs.

Methods

Specific gene activity was examined by quantitative real-time PCR, and globally by expression profiling. Proteins were analyzed by western blot, immuno-cytology and immuno-precipitation. For overexpression studies cell lines were transduced by lentiviruses.

Results

Quantification of MSX2 mRNA in primary hematopoietic cells demonstrated higher levels in CD34+ stem cells as compared to peripheral blood cells and mature CD3+ T-cells. Furthermore, analysis of MSX2 expression levels in T-cell lines after treatment with core thymic factors confirmed their involvement in regulation. These results indicated that MSX2 represents an hematopoietic NKL family member which is downregulated during T-cell development and may functionally substituted by oncogenic NKLs. For functional analysis JURKAT cells were lentivirally transduced, overexpressing either MSX2 or oncogenic TLX1 and NKX2-5, respectively. These cells displayed transcriptional activation of NOTCH3-signaling, including NOTCH3 and HEY1 as analyzed by gene expression profiling and quantitative RT-PCR, and consistently attenuated sensitivity to gamma-secretase inhibitor as analyzed by MTT-assays. Furthermore, in addition to MSX2, both TLX1 and NKX2-5 proteins interacted with NOTCH-pathway repressors, SPEN/MINT/SHARP and TLE1/GRG1, representing a potential mechanism for (de)regulation. Finally, elevated expression of NOTCH3 and HEY1 was detected in primary TLX1/3 positive T-ALL cells corresponding to the cell line data.

Conclusion

Identification and analysis of MSX2 in hematopoietic cells implicates a modulatory role via NOTCH3-signaling in early T-cell differentiation. Our data suggest that reduction of NOTCH3-signaling by physiological downregulation of MSX2 expression during T-cell development is abrogated by ectopic expression of oncogenic NKLs, substituting MSX2 function.

Cutting Edge: Ikaros null thymocytes mature into the CD4 lineage with reduced TCR signal: A study using CD3{zeta} immunoreceptor tyrosine-based activation motif transgenic mice

Positive selection is a critical T cell developmental checkpoint that is driven by TCR signals. Enhanced positive selection toward the CD4 lineage occurs in the absence of Ikaros. One explanation for this phenotype is that Ikaros establishes the TCR signaling threshold that must be overcome for positive selection to occur. In the current study, this possibility is explored through the use of CD3zeta ITAM transgenic mice that express a CD3 zeta-chain with zero, one, or three ITAMs and an MHC class II (DO11.10)- or MHC class I (H-Y)-restricted TCR transgene. Using this system, we demonstrate that in the absence of Ikaros, thymocytes are able to mature into the CD4 lineage with reduced TCR signaling potential compared with that required to drive the maturation of wild-type thymocytes. We also demonstrate that maturation into the CD8 lineage is enhanced under conditions of reduced TCR signaling potential in the absence of Ikaros.

CD27 is a thymic determinant of the balance between interferon-gamma- and interleukin 17-producing gammadelta T cell subsets

The production of cytokines such as interferon-gamma and interleukin 17 by alphabeta and gammadelta T cells influences the outcome of immune responses. Here we show that most gammadelta T lymphocytes expressed the tumor necrosis factor receptor family member CD27 and secreted interferon-gamma, whereas interleukin 17 production was restricted to CD27(-) gammadelta T cells. In contrast to the apparent plasticity of alphabeta T cells, the cytokine profiles of these distinct gammadelta T cell subsets were essentially stable, even during infection. These phenotypes were established during thymic development, when CD27 functions as a regulator of the differentiation of gammadelta T cells at least in part by inducing expression of the lymphotoxin-beta receptor and genes associated with trans-conditioning and interferon-gamma production. Thus, the cytokine profiles of peripheral gammadelta T cells are predetermined mainly by a mechanism involving CD27.

Cbl enforces an SLP76-dependent signaling pathway for T cell differentiation

A signaling pathway involving ZAP-70, LAT, and SLP76 has been regarded as essential for receptor-driven T cell development and activation. Consistent with this model, mice deficient in SLP76 have a complete block at the double negative 3 stage of T cell development. Recently, however, it has been reported that inactivation of Cbl, a ubiquitin-protein isopeptide ligase, partially rescues T cell development in SLP76-deficient mice. To probe the influence of Cbl on domain-specific SLP76 functions, we reconstituted SLP76^-/- Cbl^-/- mice with Slp76 transgenes bearing mutations in each of three functional domains of SLP76 as follows: Y3F, in which the amino-terminal tyrosine residues of SLP76 were mutated, eliminating sites of SLP76 interaction with Vav, Nck, and Itk; Δ20, in which 20 amino acids in the proline-rich region of SLP76 were deleted, removing a binding site for Gads; and RK, in which arginine 448 of SLP76 was replaced by lysine, abolishing function of the Src homology 2 domain. Although each of these transgenes has been shown to partially rescue T cell development in SLP76^-/- mice, we report here that Cbl inactivation completely reverses the severe double negative 3 developmental block that occurs in SLP76-deficient mice expressing the Y3F transgene (Y3F mice) and partially rescues the defect in positive selection in T cell receptor transgenic Y3F mice, but in contrast fails to rescue thymic development of SLP76-deficient mice expressing the Δ20 or RK transgene. Rescue in SLP76^-/-Cbl^-/-Y3F double-positive thymocytes is associated with enhanced tyrosine phosphorylation of signaling molecules, including Lck, Vav, PLC-γ1, and ERKs, but not Itk, in response to T cell receptor stimulation. Thus, our data demonstrate that Cbl suppresses activation of a bypass signaling pathway and thereby enforces SLP76 dependence of early T cell development.

ICAT expression disrupts beta-catenin-TCF interactions and impairs survival of thymocytes and activated mature T cells

T cell factor (TCF) family of transcription factors and beta-catenin critically regulate T cell development as demonstrated by the deletion of the tcf gene, which results in a block early in development that becomes complete in mice bearing tcf/lef double deletion. However, the role of beta-catenin, a major TCF cofactor, remains controversial. To directly address this, we have generated transgenic mice expressing Inhibitor of beta-catenin and TCF (ICAT), a naturally occurring inhibitor that specifically disrupts TCF and beta-catenin interactions. In this report, we demonstrate that disrupting the interaction of beta-catenin with TCF renders adult thymocytes and activated T cells highly susceptible to apoptosis. In contrast to previously reported observations during fetal thymocyte development, these data show that in adult mice, survival and not differentiation of thymocytes, depends on transcription by TCF and beta-catenin. Indeed, we demonstrate that expression of ICAT impedes thymocyte survival by reducing the expression of Bcl(xL) in thymocytes below a critical threshold. Survival of activated mature T cells was also impaired due to diminished expression of activation-induced Bcl(xL). Accordingly, expression of transgenic Bcl-2 rescued activated ICAT-Tg CD4 T cells from apoptosis. Thus, disruption of TCF-beta-catenin interactions specifically impairs the survival of thymocytes and activated T cells.

Notch signaling in CD4 and CD8 T cell development

Because Notch often acts in concert with other signaling pathways, it is able to regulate a diverse set of biological processes in a cell-context dependent manner. In lymphocytes, Notch is essential for specifying the T cell fate and for promoting early stages of T cell differentiation. At later stages of development, Notch signaling is proposed to direct CD4 versus CD8 T lineage commitment. This hypothesis has been challenged by recent studies of conditional Presenilin-deficient mice showing that Notch promotes the selection and maturation of CD4 and CD8 T cells by potentiating TCR signal transduction in immature thymocytes. While similar conclusions have not been reported with conditional mutation of other downstream mediators of Notch activation, it appears that functional inhibition may not have been achieved at a comparable stage of development and/or analogous issues have not been addressed. The differences also question whether in thymocytes Notch signals only through the canonical pathway. Further study of conditional mutants, signaling intermediates, and transcriptional regulators are needed to elucidate how Notch facilitates TCR signaling in generating mature T cells.

A deletion mutation of the protein tyrosine phosphatase kappa (Ptprk) gene is responsible for T-helper immunodeficiency (thid) in the LEC rat

Bone marrow (BM)-derived T-cell progenitors differentiate into CD4 or CD8 single-positive (SP) cells in the thymus. We have previously reported that a single autosomal mutation, thid, causes a defect in the maturation of CD4 SP thymocytes and an abnormality of peripheral helper T cells in the LEC rat. In this study we attempted to identify a gene responsible for the thid mutation. We first performed genetic linkage analysis and mapped the thid locus between Myb and D1Rat392 on Chr 1. In this region we found an approximately 380-kb deletion from intron 3 of the Ptprk gene, which encodes a receptor-like protein tyrosine phosphatase type kappa (RPTPkappa) to intron 1 of the RGD1560849 predicted gene in the LEC rat genome. Reconstitution with syngenic BM cells transduced Ptprk but not the RGD1560849 predicted gene rescued development of CD4 SP cells in the LEC rat thymus. It is confirmed by this result that the Ptprk gene is responsible for the thid mutation in the LEC rat. Our results further suggest that RPTPkappa plays a critical role in the development of CD4 SP cells in the thymus.

Presenilins regulate alphabeta T cell development by modulating TCR signaling

TCRαβ signaling is crucial for the maturation of CD4 and CD8 T cells, but the role of the Notch signaling pathway in this process is poorly understood. Genes encoding Presenilin (PS) 1/2 were deleted to prevent activation of the multiple Notch receptors expressed by developing thymocytes. PS1/2 knockout thymocyte precursors inefficiently generate CD4 T cells, a phenotype that is most pronounced when thymocytes bear a single major histocompatibility complex (MHC) class II–restricted T cell receptor (TCR). Diminished T cell production correlated with evidence of impaired TCR signaling, and could be rescued by manipulations that enhance MHC recognition. Although Notch appears to directly regulate binary fate decisions in many systems, these findings suggest a model in which PS-dependent Notch signaling influences positive selection and the development of αβ T cells by modifying TCR signal transduction.

Cell lineage regulators in B and T cell development

This special issue highlights a pivotal set of regulatory molecules that have emerged as central controllers of cell-type identity in the immune system. Each in its own way has been considered as a kind of 'master' regulator of a particular cell fate choice, but the actual modes of action of these factors vary widely. The comparison among them sheds light on the different ways that an essential regulatory input can affect cellular identity.

Notch-induced T cell development requires phosphoinositide-dependent kinase 1

Phosphoinositide-dependent kinase l (PDK1) phosphorylates and activates multiple AGC serine kinases, including protein kinase B (PKB), p70Ribosomal S6 kinase (S6K) and p90Ribosomal S6 kinase (RSK). PDK1 is required for thymocyte differentiation and proliferation, and herein, we explore the molecular basis for these essential functions of PDK1 in T lymphocyte development. A key finding is that PDK1 is required for the expression of key nutrient receptors in T cell progenitors: CD71 the transferrin receptor and CD98 a subunit of L-amino acid transporters. PDK1 is also essential for Notch-mediated trophic and proliferative responses in thymocytes. A PDK1 mutant PDK1 L155E, which supports activation of PKB but no other AGC kinases, can restore CD71 and CD98 expression in pre-T cells and restore thymocyte differentiation. However, PDK1 L155E is insufficient for thymocyte proliferation. The role of PDK1 in thymus development thus extends beyond its ability to regulate PKB. In addition, PDK1 phosphorylation of AGC kinases such as S6K and RSK is also necessary for thymocyte development.