Human alpha beta and gamma delta thymocyte development: TCR gene rearrangements, intracellular TCR beta expression, and gamma delta developmental potential--differences between men and mice

Comparative analysis of primer sets for the assessment of clonality in feline lymphomas

Introduction

Lymphomas are among the most important and common malignant tumors in cats. Differentiating lymphomas from reactive lymphoid proliferations can be challenging, so additional tools such as clonality assessment by PCR are important in diagnosis finding. Several PCR assays have been developed to assess clonality in feline lymphomas. For T-cell lymphomas TRG (T-cell receptor gamma) genes are the preferred target whereas for B-cell lymphomas most primer sets target immunoglobulin heavy chain (IGH) genes. Here we compare commonly used diagnostic primer sets for the assessment of clonality in feline lymphomas under controlled conditions (i.e., identical sample set, PCR setup, amplicon detection system).

Methods

Formalin-fixed and paraffin-embedded samples from 31 feline T-cell lymphomas, 29 B-cell lymphomas, and 11 non-neoplastic controls were analyzed by PCR combined with capillary electrophoresis.

Results and discussion

We show that the combination of the primer sets published by Weiss et al. and Mochizuki et al. provided the best results for T-cell clonality, i.e., correctly assigns most populations as clonal or polyclonal. For B-cell clonality, the combination of the primer sets by Mochizuki et al. and Rout et al. gave the best results when omitting the Kde gene rearrangement due to its low specificity. This study rigorously evaluated various primer sets under uniform experimental conditions to improve accuracy of lymphoma diagnostic and provides a recommendation for achieving the highest diagnostic precision in lymphoma clonality analysis.

Mechanism study of ubiquitination in T cell development and autoimmune disease

T cells play critical role in multiple immune processes including antigen response, tumor immunity, inflammation, self-tolerance maintenance and autoimmune diseases et. Fetal liver or bone marrow-derived thymus-seeding progenitors (TSPs) settle in thymus and undergo T cell-lineage commitment, proliferation, T cell receptor (TCR) rearrangement, and thymic selections driven by microenvironment composed of thymic epithelial cells (TEC), dendritic cells (DC), macrophage and B cells, thus generating T cells with diverse TCR repertoire immunocompetent but not self-reactive. Additionally, some self-reactive thymocytes give rise to Treg with the help of TEC and DC, serving for immune tolerance. The sequential proliferation, cell fate decision, and selection during T cell development and self-tolerance establishment are tightly regulated to ensure the proper immune response without autoimmune reaction. There are remarkable progresses in understanding of the regulatory mechanisms regarding ubiquitination in T cell development and the establishment of self-tolerance in the past few years, which holds great potential for further therapeutic interventions in immune-related diseases.

Tumor reactive γδ T cells contribute to a complete response to PD-1 blockade in a Merkel cell carcinoma patient

Immunotherapies targeting PD-1/PD-L1 are now widely used in the clinic to treat a variety of malignancies. While most of the research on T cell exhaustion and PD-1 blockade has been focused on conventional αβ T cells, the contribution of innate-like T cells such as γδ T cells to anti-PD-1/PD-L1 mediated therapy is limited. Here we show that tumor reactive γδ T cells respond to PD-1 blockade in a Merkel cell carcinoma (MCC) patient experiencing a complete response to therapy. We find clonally expanded γδ T cells in the blood and tumor after pembrolizumab treatment, and this Vγ2Vδ1 clonotype recognizes Merkel cancer cells in a TCR-dependent manner. Notably, the intra-tumoral γδ T cells in the MCC patient are characterized by higher expression of PD-1 and TIGIT, relative to conventional CD4 and CD8 T cells. Our results demonstrate that innate-like T cells could also contribute to an anti-tumor response after PD-1 blockade.

Dendritic Cell-Based Immunity: Screening of Dendritic Cell Subsets in Breast Cancer-Bearing Mice

Background

Breast cancer (BC) is the most devastating disease, particularly the lethal invasive form. It is the most underlying cause of death among women worldwide. The expansion of BC is controlled by a variety of alterations in the tumor cells themselves, in addition to the state of the immune system, which has a direct influence on the tumor microenvironment. Numerous receptors expressed by T-cells interact with ligands on antigen-presenting cells to provide activation signals results in mounting effector anti-tumor T-cell responses. On the other hand, there is a dearth of information about the actual interactions and reactions of T-cells and dendritic cells (DCs) all through the progression of tumor development.

Aim

Immune system response against BC was investigated through tumor induction in mice. The size and volume of the tumor were calculated. Moreover, the phenotypical profile of T-cells and DCs from lymph nodes (LN) and spleens of BC-bearing mice was investigated. In addition, the levels of Transforming growth factor-β, Interferon-gamma (IFN-γ), Interleukin IL-2, IL-10, IL-4, IL-12, and tumor necrosis factor (TNF)-α were determined.

Materials and Methods

MDA231 cells were utilized to induce BC in 30 white BALB/C mice, whereas the other 30 mice acted as healthy controls and were not treated with any cancer-causing agents. The impact of malignancy was evaluated using flow cytometry based on the marking surface molecules, as well as the titer of specific cytokines of the mice's LN culture using the ELISA method. These cytokines included transforming growth factor-β (TGF-β), IFN-γ, IL-2, IL -10, IL -4, IL -12, and TNF-α.

Results

The findings showed that the maturation of DCs was inhibited, followed by an accumulation of immature DCs. These immature DCs increase the release of TGF-β and cytokines like IL-10 and inhibit the release of IFN-γ and IL-12 in the culture supernatant of nodal lymph and spleen suspension of BC-bearing mice compared to control. In addition, there was a low expression of CD80 and CD86 on DCs, which indicates a low maturation process.

Conclusion

According to the findings, the tumor microenvironment may have been responsible for preventing the maturation of DCs. This, in turn, weakened the immune response and facilitated the ability of the tumor to proliferate. Furthermore, the tumor microenvironment increased the number of immature DCs by inhibiting their stimulation by overexpression of TGF-β-produced by regulatory T lymphocytes and stimulation of tumor cells. In addition, the tumor microenvironment stimulated the secretion of cytokines such as IL-10, and CD4 and decreased the secretion of IFN-γ-and IL-12 in tumor-induced mice cultured LN and spleen.

GM-CSF and IL-7 fusion cytokine engineered tumor vaccine generates long-term Th-17 memory cells and increases overall survival in aged syngeneic mouse models of glioblastoma

Age-related immune dysfunctions, such as decreased T-cell output, are closely related to pathologies like cancers and lack of vaccine efficacy among the elderly. Engineered fusokine, GIFT-7, a fusion of interleukin 7 (IL-7) and GM-CSF, can reverse aging-related lymphoid organ atrophy. We generated a GIFT-7 fusokine tumor vaccine and employed it in aged syngeneic mouse models of glioblastoma and found that peripheral vaccination with GIFT-7TVax resulted in thymic regeneration and generated durable long-term antitumor immunity specifically in aged mice. Global cytokine analysis showed increased pro-inflammatory cytokines including IL-1β in the vaccinated group that resulted in hyperactivation of dendritic cells. In addition, GIFT-7 vaccination resulted in increased T-cell trafficking to the brain and robust Th-17 long-term effector memory T-cell formation. TCR-seq analysis showed increased productive frequency among detected rearrangements within the vaccinated group. Overall, our data demonstrate that aging immune system can be therapeutically augmented to generate lasting antitumor immunity.

Identification and Purification of Human T Cell Precursors

During their development, human T cells undergo similar genomic changes and pass through the same developmental checkpoints as developing thymocytes in the mouse. The difference between both species, however, is that some of these developmental stages are characterized by different phenotypic markers, and as a result, evidence emerges that the molecular regulation of human T cell development subtly differs from the mouse (Taghon et al., Curr Top Microbiol Immunol 360:75-97, 2021; Haddad et al., Immunity 24:217-230, 2006; Hao et al., Blood 111:1318-1326, 2008; Taghon and Rothenberg, Semin Immunopathol 30:383-398, 2008). In this chapter, we describe in detail how the different stages of human T cell development can be characterized and isolated using specific surface markers.

Development of γδ T cells in the thymus - A human perspective

γδ T cells are increasingly emerging as crucial immune regulators that can take on innate and adaptive roles in the defence against pathogens. Although they arise within the thymus from the same hematopoietic precursors as conventional αβ T cells, the development of γδ T cells is less well understood. In this review, we focus on summarising the current state of knowledge about the cellular and molecular processes involved in the generation of γδ T cells in human.

Interleukin-7 receptor signaling is crucial for enhancer-dependent TCRδ germline transcription mediated through STAT5 recruitment

γδ T cells play important roles in immune responses by rapidly producing large quantities of cytokines. Recently, γδ T cells have been found to be involved in tissue homeostatic regulation, playing roles in thermogenesis, bone regeneration and synaptic plasticity. Nonetheless, the mechanisms involved in γδ T-cell development, especially the regulation of TCRδ gene transcription, have not yet been clarified. Previous studies have established that NOTCH1 signaling plays an important role in the Tcrg and Tcrd germline transcriptional regulation induced by enhancer activation, which is mediated through the recruitment of RUNX1 and MYB. In addition, interleukin-7 signaling has been shown to be required for Tcrg germline transcription, VγJγ rearrangement and γδ T-lymphocyte generation as well as for promoting T-cell survival. In this study, we discovered that interleukin-7 is required for the activation of enhancer-dependent Tcrd germline transcription during thymocyte development. These results indicate that the activation of both Tcrg and Tcrd enhancers during γδ T-cell development in the thymus depends on the same NOTCH1- and interleukin-7-mediated signaling pathways. Understanding the regulation of the Tcrd enhancer during thymocyte development might lead to a better understanding of the enhancer-dependent mechanisms involved in the genomic instability and chromosomal translocations that cause leukemia.

Transcriptional dynamics and epigenetic regulation of E and ID protein encoding genes during human T cell development

T cells are generated from hematopoietic stem cells through a highly organized developmental process, in which stage-specific molecular events drive maturation towards αβ and γδ T cells. Although many of the mechanisms that control αβ- and γδ-lineage differentiation are shared between human and mouse, important differences have also been observed. Here, we studied the regulatory dynamics of the E and ID protein encoding genes during pediatric human T cell development by evaluating changes in chromatin accessibility, histone modifications and bulk and single cell gene expression. We profiled patterns of ID/E protein activity and identified up- and downstream regulators and targets, respectively. In addition, we compared transcription of E and ID protein encoding genes in human versus mouse to predict both shared and unique activities in these species, and in prenatal versus pediatric human T cell differentiation to identify regulatory changes during development. This analysis showed a putative involvement of TCF3/E2A in the development of γδ T cells. In contrast, in αβ T cell precursors a pivotal pre-TCR-driven population with high ID gene expression and low predicted E protein activity was identified. Finally, in prenatal but not postnatal thymocytes, high HEB/TCF12 levels were found to counteract high ID levels to sustain thymic development. In summary, we uncovered novel insights in the regulation of E and ID proteins on a cross-species and cross-developmental level.

Double-negative T cells: Setting the stage for disease control or progression

Double-negative (DN) T cells are present at relatively low frequencies in human peripheral blood, and are characterized as expressing the alpha-beta or gamma-delta T-cell receptor (TCR), but not the CD4 nor the CD8 co-receptors. Despite their low frequencies, these cells are potent producers of cytokines and, thus, are key orchestrators of immune responses. DN T cells were initially associated with induction of peripheral immunological tolerance and immunomodulatory activities related to disease prevention. However, other studies demonstrated that these cells can also display effector functions associated with pathology development. This apparent contradiction highlighted the heterogeneity of the DN T-cell population. Here, we review phenotypic and functional characteristics of DN T cells, emphasizing their role in human diseases. The need for developing biomarkers to facilitate the translation of studies from animal models to humans will also be discussed. Finally, we will examine DN T cells as promising therapeutic targets to prevent or inhibit human disease development.

Novel clonality assays for T cell lymphoma in cats targeting the T cell receptor beta, T cell receptor delta, and T cell receptor gamma loci

BACKGROUND

T cell clonality assays in veterinary medicine currently target only the T cell receptor gamma (TRG) locus. Existing assays have suboptimal sensitivity because of insufficient primer coverage of all possible rearrangements.

OBJECTIVE

Develop higher sensitivity clonality assays targeting the TRG, delta (TRD), and beta (TRB) loci in cats.

ANIMALS

Cats with histopathologically confirmed lymphoma (n = 89), non-lymphoma (n = 35), and possible hepatic small cell lymphoma (n = 31).

METHODS

Molecular clonality assay development utilizing our recently reported topology and expressed repertoire data of the T cell receptor loci in cats. Determination of clonality status of lymphoma, non lymphoma, and possible hepatic small cell lymphoma samples, and calculation of assay sensitivity and specificity.

RESULTS

The new multiplex TRG assay yielded the highest sensitivity (95.5%). All assays yielded 100% specificity except for the new multiplex TRG assay (97.3%). The combination of the new TRG and TRB assays yielded sensitivity of 98.9% and specificity of 97.0%. The new TRG assay detected clonality in 17/31 possible small cell lymphoma livers, whereas an existing TRG assay detected clonality in 6/31 livers.

CONCLUSIONS AND CLINICAL IMPORTANCE

The assessment of multiple T cell loci compensates for the potential shortcomings of individual assays. Using a combination of molecular clonality assays will increase the overall sensitivity for the diagnosis of T-cell lymphoma in cats, especially intestinal, and hepatic small cell lymphoma. Hepatic small cell lymphomas detected by the new TRG assay utilized rarely expressed V and J genes not recognized by previous assays, likely indicating unique biology of hepatic small cell lymphoma in cats.

Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects

Inborn errors of thymic stromal cell development and function lead to impaired T-cell development resulting in a susceptibility to opportunistic infections and autoimmunity. In their most severe form, congenital athymia, these disorders are life-threatening if left untreated. Athymia is rare and is typically associated with complete DiGeorge syndrome, which has multiple genetic and environmental etiologies. It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects. This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire. Mortality after this treatment usually occurs before immune reconstitution and is mainly associated with infections most often acquired pre-transplantation. In this review, we will discuss the current approaches to the diagnosis and management of thymic stromal cell defects, in particular those resulting in athymia. We will discuss the impact of the expanding implementation of newborn screening for T-cell lymphopenia, in combination with next generation sequencing, as well as the role of novel diagnostic tools distinguishing between hematopoietic and thymic stromal cell defects in facilitating the early consideration for thymus transplantation of an increasing number of patients and disorders. Immune reconstitution after the current treatment is usually incomplete with relatively common inflammatory and autoimmune complications, emphasizing the importance for improving strategies for thymus replacement therapy by optimizing the current use of postnatal thymus tissue and developing new approaches using engineered thymus tissue.

Single-cell insights into the hematopoietic generation of T-lymphocyte precursors in mouse and human

T-Cell development is a major branch of lymphoid development and a key output of hematopoiesis, especially in early life, but the molecular requirements for T-cell potential have remained obscure. Considerable advances have now been made toward solving this problem through single-cell transcriptome studies, interfaced with in vitro differentiation assays that monitor potential efficiently at the single-cell level. This review focuses on a series of recent reports studying mouse and human early T-cell precursors, both in the developing fetus and in stringently purified postnatal samples of intrathymic and prethymic T-lineage precursors. Cross-comparison of results reveals a robustly conserved core program in mouse and human, but with some informative and provocative variations between species and between ontogenic states. Repeated findings are the multipotent progenitor regulatory signature of thymus-seeding cells and the proximity of the T-cell program to dendritic cell programs, especially to plasmacytoid dendritic cells in humans.

Leaving no one behind: tracing every human thymocyte by single-cell RNA-sequencing

The thymus is the primary organ for T-cell development, providing an essential microenvironment consisting of the appropriate cytokine milieu and specialized stromal cells. Thymus-seeding progenitors from circulation immigrate into the thymus and undergo the stepwise T-cell specification, commitment, and selection processes. The transcriptional factors, epigenetic regulators, and signaling pathways involved in the T-cell development have been intensively studied using mouse models. Despite our growing knowledge of T-cell development, major questions remain unanswered regarding the ontogeny and early events of T-cell development at the fetal stage, especially in humans. The recently developed single-cell RNA-sequencing technique provides an ideal tool to investigate the heterogeneity of T-cell precursors and the molecular mechanisms underlying the divergent fates of certain T-cell precursors at the single-cell level. In this review, we aim to summarize the current progress of the study on human thymus organogenesis and thymocyte and thymic epithelial cell development, which is to shed new lights on developing novel strategies for in vitro T-cell regeneration and thymus rejuvenation.

Distinct and temporary-restricted epigenetic mechanisms regulate human αβ and γδ T cell development

The development of TCRαβ and TCRγδ T cells comprises a step-wise process in which regulatory events control differentiation and lineage outcome. To clarify these mechanisms, we employed RNA-sequencing, ATAC-sequencing and ChIPmentation on well-defined thymocyte subsets that represent the continuum of human T cell development. The chromatin accessibility dynamics show clear stage specificity and reveal that human T cell-lineage commitment is marked by GATA3- and BCL11B-dependent closing of PU.1 sites. A temporary increase in H3K27me3 without open chromatin modifications is unique for β-selection, whereas emerging γδ T cells, which originate from common precursors of β-selected cells, show large chromatin accessibility changes due to strong T cell receptor (TCR) signaling. Furthermore, we unravel distinct chromatin landscapes between CD4⁺ and CD8⁺ αβ-lineage cells that support their effector functions and reveal gene-specific mechanisms that define mature T cells. This resource provides a framework for studying gene regulatory mechanisms that drive normal and malignant human T cell development.

Single-Cell RNA Sequencing Resolves Spatiotemporal Development of Pre-thymic Lymphoid Progenitors and Thymus Organogenesis in Human Embryos

Generation of the first T lymphocytes in the human embryo involves the emergence, migration, and thymus seeding of lymphoid progenitors together with concomitant thymus organogenesis, which is the initial step to establish the entire adaptive immune system. However, the cellular and molecular programs regulating this process remain unclear. We constructed a single-cell transcriptional landscape of human early T lymphopoiesis by using cells from multiple hemogenic and hematopoietic sites spanning embryonic and fetal stages. Among heterogenous early thymic progenitors, one subtype shared common features with a subset of lymphoid progenitors in fetal liver that are known as thymus-seeding progenitors. Unbiased bioinformatics analysis identified a distinct type of pre-thymic lymphoid progenitors in the aorta-gonad-mesonephros (AGM) region. In parallel, we investigated thymic epithelial cell development and potential cell-cell interactions during thymus organogenesis. Together, our data provide insights into human early T lymphopoiesis that prospectively direct T lymphocyte regeneration, which might lead to development of clinical applications.

High-throughput targeted long-read single cell sequencing reveals the clonal and transcriptional landscape of lymphocytes

High-throughput single-cell RNA sequencing is a powerful technique but only generates short reads from one end of a cDNA template, limiting the reconstruction of highly diverse sequences such as antigen receptors. To overcome this limitation, we combined targeted capture and long-read sequencing of T-cell-receptor (TCR) and B-cell-receptor (BCR) mRNA transcripts with short-read transcriptome profiling of barcoded single-cell libraries generated by droplet-based partitioning. We show that Repertoire and Gene Expression by Sequencing (RAGE-Seq) can generate accurate full-length antigen receptor sequences at nucleotide resolution, infer B-cell clonal evolution and identify alternatively spliced BCR transcripts. We apply RAGE-Seq to 7138 cells sampled from the primary tumor and draining lymph node of a breast cancer patient to track transcriptome profiles of expanded lymphocyte clones across tissues. Our results demonstrate that RAGE-Seq is a powerful method for tracking the clonal evolution from large numbers of lymphocytes applicable to the study of immunity, autoimmunity and cancer.

Single cell RNA sequencing generates short reads from one end of a template, providing incomplete transcript coverage and limiting identification of diverse sequences such as antigen receptors. Here the authors combine long read nanopore sequencing with short read profiling of barcoded libraries to generate full-length antigen receptor sequences.

A new transcript in the TCRB locus unveils the human ortholog of the mouse pre-Dß1 promoter

Introduction

While most transcripts arising from the human T Cell Receptor locus reflect fully rearranged genes, several germline transcripts have been identified. We describe a new germline transcript arising from the human TCRB locus.

Methods

cDNA sequencing, promoter, and gene expression analyses were used to characterize the new transcript.

Results

The new germline transcript encoded by the human TCRB locus consists of a new exon of 103 bp, which we named TRBX1 (X1), spliced with the first exon of gene segments Cß1 or Cß2. X1 is located upstream of gene segment Dß1 and is therefore deleted from a V‐DJ rearranged TCRB locus. The X1‐Cß transcripts do not appear to code for a protein. We define their transcription start and minimal promoter. These transcripts are found in populations of mature T lymphocytes from blood or tissues and in T cell clones with a monoallelic TCRB rearrangement. In immature thymocytes, they are already detectable in CD1a⁻CD34⁺CD4⁻CD8⁻ cells, therefore before completion of the TCRB rearrangements.

Conclusions

The X1 promoter appears to be the ortholog of the mouse pre‐Dß1 promoter (PDß1). Like PDß1, its activation is regulated by Eß in T cells and might facilitate the TCRB rearrangement process by contributing to the accessibility of the Dß1 locus.

The Role of the Ikaros Family of Transcription Factors in Regulatory T cell Development and Function

Regulatory T (Treg) cells are a subset of immune cells that maintain homeostasis by promoting immune tolerance and suppressing the immune response via a variety of mechanisms such as secreting cytokines, killing reactive immune cells, and inducing anergy. Dysfunction of Treg cells has been implicated in inflammatory diseases such as autoimmunity and transplant rejection. Conversely, too many or hyperresponsive Treg cells has been observed in cancer and chronic infections. Treg cells have proven to be difficult to study as there are no definitive Treg surface markers. Additionally, Tregs can gain pro-inflammatory phenotype depending on stimuli. In this commentary, we discuss the expression and function of members of the Ikaros family of transcription factors during Treg cell development and activation.

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

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

Expression patterns of Ikaros family members during positive selection and lineage commitment of human thymocytes

The Ikaros family of transcription factors is essential for normal T-cell development, but their expression pattern in human thymocytes remains poorly defined. Our goal is to determine how protein levels of Ikaros, Helios and Aiolos change as human thymocytes progress through the positive selection and lineage commitment stages. To accomplish this goal, we used multi-parameter flow cytometry to define the populations in which positive selection and lineage commitment are most likely to occur. After human thymocytes express CD3 and receive positive selection signals, the cells down-regulate expression of CD4 to become transitional single-positive (TSP) CD8⁺ thymocytes. At this stage, there was a transient increase in the Ikaros, Helios and Aiolos protein levels. After the TSP CD8⁺ developmental stage, some thymocytes re-express CD4 and become CD3^hi double-positive thymocytes before down-regulating CD8 to become mature single-positive CD4⁺ thymocytes. Except for regulatory T cells, Helios protein levels declined and Aiolos protein levels transiently increased during CD4⁺ T-cell maturation. For thymocytes progressing toward the CD8⁺ T-cell lineage, TSP CD8⁺ thymocytes increase their expression of CD3 and maintain high levels of Aiolos protein as the cells complete their maturation. In summary, we defined the TSP CD8⁺ developmental stage in human T-cell development and propose that this stage is where CD4/CD8 lineage commitment occurs. Ikaros, Helios and Aiolos each undergo a transient increase in protein levels at the TSP stage before diverging in their expression patterns at later stages.

Phenotypic profile of dendritic and T cells in the lymph node of Balb/C mice with breast cancer submitted to dendritic cells immunotherapy

Breast cancer (BC) is the most common malignant neoplasm and the cause of death by cancer among women worldwide. Its development influenced by various mutations that occur in the tumor cell and by the immune system's status, which has a direct influence on the tumor microenvironment and, consequently, on interactions with non-tumor cells involved in the immunological response. Strategies using dendritic cells (DCs) or antigen-presenting cells (APCs), therapeutic mode, in cancer have been developed for some time. The proper interaction between DCs and T cells upon antigen presentation is of greatest importance for an antitumor immune response activation. Thus, various receptors on the surface of T cells must be able to recognize ligands that are located on the surface of APCs. However, little is known about the real behavior and interaction forms of CDs and T cells after vaccination. Due to the crucial importance of DCs in an effective anti-tumor immune response activation and the search for compliant results in inducing this response by immunotherapies with DCs, the phenotypic profile of DCs and T cells in lymph nodes obtained from female Balb/C mice with breast cancer induced by 4T1 cells and DCs treated with vaccines was investigated. We evaluated through flow cytometry based on the surface and intracellular molecules marking; as well as the presence of cytokines and chemokines, IL-2, IL-4, IL-10, IL-12, IFN-γ, TNF-α and TGF-β in the supernatant of the culture of Balb/C lymph nodes by ELISA. The results show that the vaccination with DCs, in the maturation parameters used in this study, was able to stimulate the secretion of cytokines such as IFN-γ and IL-12 and inhibit the secretion of TGF-β and IL-10 in nodal lymph infiltrates, as well as co-stimulatory activating (CD86) and adhesion molecules in DCs and T cells LFA-1/ICAM-1 and inhibit the secretion of CTLA-4 present in lymph nodes. Facts that led to aTh1 profile polarization, immuno competent in relation to breast cancer. We indirectly evaluated the interaction between DCs and T cells dependent on the vaccination with DCs in tumor draining lymph nodes, in breast cancer in Balb/C mice and we believe that, this way, we will be able to achieve a model vaccine protocol in the future, based on the correct interaction between cells that enable the induction of anti-tumor effective response. Breast cancer (BC) is the most common malignant neoplasm and the cause of death by cancer among women worldwide. Its development influenced by various mutations that occur in the tumor cell and by the immune system's status, which has a direct influence on the tumor microenvironment and, consequently, on interactions with non-tumor cells involved in the immunological response. Strategies using dendritic cells (DCs) or antigen-presenting cells (APCs), therapeutic mode, in cancer have been developed for some time. The proper interaction between DCs and T cells upon antigen presentation is of greatest importance for an antitumor immune response activation. Thus, various receptors on the surface of T cells must be able to recognize ligands that are located on the surface of APCs. However, little is known about the real behavior and interaction forms of DCs and T cells after vaccination. Due to the crucial importance of DCs in an effective anti-tumor immune response activation and the search for compliant results in inducing this response by immunotherapies with DCs, the phenotypic profile of DCs and T cells in lymph nodes obtained from female Balb/C mice with breast cancer induced by 4T1 cells and DCs treated with vaccines was investigated. We evaluated through flow cytometry based on the surface and intracellular molecules marking; as well as the presence of cytokines and chemokines, IL-2, IL-4, IL-10, IL-12, IFN-γ, TNF-α and TGF-β in the supernatant of the culture of Balb/C lymph nodes by ELISA. The results show that the vaccination with DCs, in the maturation parameters used in this study, was able to stimulate the secretion of cytokines such as IFN-γ and IL-12 and inhibit the secretion of TGF-β and IL-10 in nodal lymph infiltrates, as well as co-stimulatory activating (CD86) and adhesion molecules in DCs and T cells LFA-1/ICAM-1 and inhibit the secretion of CTLA-4 present in lymph nodes. Facts that led to aTh1 profile polarization, immuno competent in relation to breast cancer. We indirectly evaluated the interaction between DCs and T cells dependent on the vaccination with DCs in tumor draining lymph nodes, in breast cancer in Balb/C mice and we believe that, this way, we will be able to achieve a model vaccine protocol in the future, based on the correct interaction between cells that enable the induction of anti-tumor effective response.

Clonality Testing in Veterinary Medicine

The accurate distinction of reactive and neoplastic lymphoid proliferations can present challenges. Given the different prognoses and treatment strategies, a correct diagnosis is crucial. Molecular clonality assays assess rearranged lymphocyte antigen receptor gene diversity and can help differentiate reactive from neoplastic lymphoid proliferations. Molecular clonality assays are commonly used to assess atypical, mixed, or mature lymphoid proliferations; small tissue fragments that lack architecture; and fluid samples. In addition, clonality testing can be utilized to track neoplastic clones over time or across anatomic sites. Molecular clonality assays are not stand-alone tests but useful adjuncts that follow clinical, morphologic, and immunophenotypic assessment. Even though clonality testing provides valuable information in a variety of situations, the complexities and pitfalls of this method, as well as its dependency on the experience of the interpreter, are often understated. In addition, a lack of standardized terminology, laboratory practices, and interpretational guidelines hinders the reproducibility of clonality testing across laboratories in veterinary medicine. The objectives of this review are twofold. First, the review is intended to familiarize the diagnostic pathologist or interested clinician with the concepts, potential pitfalls, and limitations of clonality testing. Second, the review strives to provide a basis for future harmonization of clonality testing in veterinary medicine by providing diagnostic guidelines.

Characterization and Isolation of Human T Cell Progenitors

During their development, human T cells undergo similar genomic changes and pass through the same developmental checkpoints as developing thymocytes in the mouse. The difference between both species, however, is that some of these developmental stages are characterized by different phenotypic markers and as a result, evidence emerges that the molecular regulation of human T cell development subtly differs from the mouse [1-4]. In this chapter, we describe in detail how the different stages of human T cell development can be characterized and isolated using specific surface markers.

Generation of multipotent early lymphoid progenitors from human embryonic stem cells

During human embryonic stem cell (ESC) hematopoietic differentiation, the description of the initial steps of lymphopoiesis remains elusive. Using a two-step culture procedure, we identified two original populations of ESC-derived hematopoietic progenitor cells (HPCs) with CD34(+)CD45RA(+)CD7(-) and CD34(+)CD45RA(+)CD7(+) phenotypes. Bulk cultures and limiting dilution assays, culture with MS5 cells in the presence of Notch ligand Delta-like-1 (DL-1), and ex vivo colonization tests using fetal thymic organ cultures showed that although CD34(+)CD45RA(+)CD7(-) HPCs could generate cells of the three lymphoid lineages, their potential was skewed toward the B cell lineages. In contrast, CD34(+)CD45RA(+)CD7(+) HPCs predominantly exhibited a T/natural killer (NK) cell differentiation potential. Furthermore these cells could differentiate equivalently into cells of the granulo-macrophagic lineage and dendritic cells and lacked erythroid potential. Expression profiling of 18 markers by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) revealed that CD34(+)CD45RA(+)CD7(-) and CD34(+)CD45RA(+)CD7(+) HPCs express genes of the lymphoid specification and that CD34(+)CD45RA(+)CD7(-) cells express B-cell-associated genes, while CD34(+)CD45RA(+)CD7(+) HPCs display a T-cell molecular profile. Altogether, these findings indicate that CD34(+)CD45RA(+)CD7(-) and CD34(+)CD45RA(+)CD7(+) HPCs correspond to candidate multipotent early lymphoid progenitors polarized toward either the B or T/NK lineage, respectively. This work should improve our understanding of the early steps of lymphopoiesis from pluripotent stem cells and pave the way for the production of lymphocytes for cell-based immunotherapy and lymphoid development studies.

Developmental gene networks: a triathlon on the course to T cell identity

Cells acquire their ultimate identities by activating combinations of transcription factors that initiate and sustain expression of the appropriate cell type-specific genes. T cell development depends on the progression of progenitor cells through three major phases, each of which is associated with distinct transcription factor ensembles that control the recruitment of these cells to the thymus, their proliferation, lineage commitment and responsiveness to T cell receptor signals, all before the allocation of cells to particular effector programmes. All three phases are essential for proper T cell development, as are the mechanisms that determine the boundaries between each phase. Cells that fail to shut off one set of regulators before the next gene network phase is activated are predisposed to leukaemic transformation.

Broad T-cell receptor repertoire in T-lymphocytes derived from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) have enormous potential for the treatment of inherited and acquired disorders. Recently, antigen-specific T lymphocytes derived from hiPSCs have been reported. However, T lymphocyte populations with broad T cell receptor (TCR) diversity have not been generated. We report that hiPSCs derived from skin biopsy are capable of producing T lymphocyte populations with a broad TCR repertoire. In vitro T cell differentiation follows a similar developmental program as observed in vivo, indicated by sequential expression of CD7, intracellular CD3 and surface CD3. The γδ TCR locus is rearranged first and is followed by rearrangement of the αβ locus. Both γδ and αβ T cells display a diverse TCR repertoire. Upon activation, the cells express CD25, CD69, cytokines (TNF-α, IFN-γ, IL-2) and cytolytic proteins (Perforin and Granzyme-B). These results suggest that most, if not all, mechanisms required to generate functional T cells with a broad TCR repertoire are intact in our in vitro differentiation protocol. These data provide a foundation for production of patient-specific T cells for the treatment of acquired or inherited immune disorders and for cancer immunotherapy.

Challenges and new prospects in hepatosplenic γδ T-cell lymphoma

Peripheral T-cell lymphomas (PTCLs) are a heterogeneous group of lymphoid neoplasms characterized by aggressive clinical behavior and dismal prognosis. Hepatosplenic γδ T-cell lymphoma (γδ-HSTL) is a particular form of PTCL that arises from a small subset of γ/δ T-cell receptor-expressing lymphocytes. γδ-HSTL has a rapidly progressive course and poor outcome due also to its refractoriness to conventional chemotherapy regimens. The very low incidence of γδ-HSTL, along with its propensity to mimic different pathological entities, makes this lymphoma a true diagnostic challenge. In this review, we highlight the biological and clinical features of γδ-HSTL that contribute to making this lymphoma a mostly incurable disease. Moreover, we provide a new insight into the crosstalk between HSTL clones and the bone marrow, liver and spleen vascular microenvironment, in which neoplastic cells reside and proliferate. We further discuss γδ-HSTL associated molecules that might be proposed as potential targets for novel therapeutic approaches.

Intestinal γδ T-cell lymphomas are most frequently of type II enteropathy-associated T-cell type

Enteropathy-associated T-cell lymphoma includes type I cases and distinctive type II cases that, according to 2008 and 2010 World Health Organization descriptions, are T-cell receptor β+. Although T-cell receptor γδ enteropathy-associated T-cell lymphomas are reported, it is unknown if they have distinctive features and if they should be categorized as enteropathy-associated T-cell lymphoma or as a mucocutaneous γδ T-cell lymphoma. To address these questions, the clinicopathologic, immunophenotypic, molecular, and cytogenetic features of 5 γδ-enteropathy-associated T-cell lymphomas were investigated. Only 1 patient had celiac disease and had type I enteropathy-associated T-cell lymphoma, and the others fulfilled the histopathologic criteria for type II enteropathy-associated T-cell lymphoma. All lacked cutaneous involvement. A celiac disease-associated HLA type was found in the patient with CD and one of four others. All were T-cell receptor γ+, T-cell receptor δ+, βF1-, CD3+, CD7+, CD5-, CD4-, and TIA-1+ with variable staining for CD2 (3/5), CD8 (2/5), Granzyme B (1/5), and CD56 (4/5). Fluorescence in situ hybridization demonstrated 9q34 gains in 4 cases, with 9q33-34 gains by single nucleotide polymorphism in 3 of these. Single nucleotide polymorphism analysis also demonstrated gains in 5q34-q35.1/5q35.1 (4/5), 8q24 (3/5), and in 32 other regions in 3 of 5 cases. Vδ1 rearrangements were identified in 4 of 4 cases with documented clonality showing the same clone in normal-appearing distant mucosa (3/3 tested cases). Thus, γδ-enteropathy-associated T-cell lymphomas share many features with other enteropathy-associated T-cell lymphoma and are mostly of type II. Their usual nonactivated cytotoxic phenotype and Vδ1 usage are features unlike many other mucocutaneous γδ T-cell lymphomas but shared with hepatosplenic T-cell lymphoma. These findings support the conclusion that a γδ T-cell origin at extracutaneous sites does not define a specific entity.

Comparison of three humanized mouse models for adoptive T cell transfer

BACKGROUND

Humanized mouse models for adoptive T cell transfer are important for preclinical efficacy and toxicity studies. However, common xenograft models using immunodeficient mice have so far failed to efficiently support the homing of human T cells to secondary lymphoid tissues.

METHODS

We established a new mouse model for the adoptive transfer of genetically-modified (gm) T cells using conditioned BALB/c mice. Conditioning involved cyclophosphamide injections, lethal irradiation and radioprotection with bone marrow from immunodeficient mice. We compared repopulation kinetics and the quality of grafts in these modified Trimera (mT3) mice with immunodeficient BALB/c Rag2(-/-) interleukin (IL)2 receptor gamma (rg) knockout (DKO) and NOD/LtSz-scid IL2rg(-/-) (NSG) recipient mouse strains.

RESULTS

DKO mice showed only marginal engraftment until onset of graft-versus-host disease, whereas mT3 and NSG were repopulated with comparable kinetics. However, T cell repertoire and human cytokine profiles suggest a xenoreactivity-driven gm T cell expansion in mT3 mice, whereas NSG mice were characterized by an initial homeostatic proliferation. Morphological analysis revealed high levels of human gm T cell infiltration in the spleen and liver of all three mouse strains. However, mT3 mice provided the strongest homing of human gm T cells to mucosal sites. Additionally, mT3 mice were the only model with macroscopically visible superficial inguinal lymph nodes. These lymph nodes strongly supported the homing of gm T cells.

CONCLUSIONS

In the present study, we give proof-of-concept that wild-type mice can accept gm T cell grafts while providing secondary lymphoid structures. Despite limitations, mT3 mice are a valid alternative for applications that specifically rely on improved secondary lymphoid structures.

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

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

Notch signaling during human T cell development

Notch signaling is critical during multiple stages of T cell development in both mouse and human. Evidence has emerged in recent years that this pathway might regulate T-lineage differentiation differently between both species. Here, we review our current understanding of how Notch signaling is activated and used during human T cell development. First, we set the stage by describing the developmental steps that make up human T cell development before describing the expression profiles of Notch receptors, ligands, and target genes during this process. To delineate stage-specific roles for Notch signaling during human T cell development, we subsequently try to interpret the functional Notch studies that have been performed in light of these expression profiles and compare this to its suggested role in the mouse.

A novel clonality assay for the assessment of canine T cell proliferations

Polymerase chain reaction (PCR) based clonality assays are an important tool to differentiate neoplastic from reactive lymphocyte populations. A recent description of the canine T cell receptor γ locus identified a large number of formerly unknown genes, and determined the locus topology consisting of 8 cassettes with up to 3 variable (V) genes, 2 joining (J) genes and one constant (C) gene each. Given that these data were not available when existing canine T cell clonality assays were developed, it is likely that they will fail to detect a subset of clonal lymphocyte populations. The objective of this study was to gauge the potential of canine T cell clonality assays to detect all rearranged T cell receptor γ genes and to develop an improved clonality assay. The primer sequences of existing clonality assays were aligned to the reference sequences of all rearranged genes and genes were scored as to the likelihood of being recognized by a primer. All four assays likely recognized subgroup Vγ2 and Vγ6 genes but 3 out of 4 assays were unlikely to detect subgroup Vγ3 and Vγ7 genes. All assays likely recognized Jγx-2 genes, but only two assays were likely to detect most Jγx-1 genes. Two assays had forward primers located as close as four nucleotides to the junctional region. A new multiplex PCR was designed with all primers combined in a single tube. An alternative primer set allowed identification of variable gene usage through gene specific forward primers. The coverage of all rearranged genes facilitated the detection of multiple clonal rearrangements per neoplastic sample. The new assay detected clonal DNA at a concentration of 5% within polyclonal background but detection thresholds were dependent on the gene usage of clonal rearrangements as well as the position of the clonal peak in respect to the polyclonal background. The new multiplex assay recognized 12/12 (100%) of confirmed neoplastic samples as compared to 2/12 (17%) by an existing assay. On a series of 60 diagnostic samples the concordance rate of both assays was 41/60 (68.3%). In 14/60 (23.3%) of the cases, the new multiplex assay yielded a clonal result while the existing assay gave a non-clonal result. In 5/60 (8.3%) of cases, the new assay yielded a non-clonal result while the existing primer set gave a clonal result. These findings suggest that the new multiplex assay has an improved sensitivity over traditional assays and is suited to reduce the rate of false-negative results.

Deep sequencing of the human TCRγ and TCRβ repertoires suggests that TCRβ rearranges after αβ and γδ T cell commitment

T lymphocytes respond to a broad array of pathogens with the combinatorial diversity of the T cell receptor (TCR). This adaptive response is possible because of the unique structure of the TCR, which is composed of two chains, either αβ or γδ, that undergo genetic rearrangement in the thymus. αβ and γδ T cells are functionally distinct within the host but are derived from a common multipotent precursor. The canonical model for T cell lineage commitment assumes that the γ, δ, and β chains rearrange before αβ or γδ T cell commitment. To test the standard model in humans, we used high-throughput sequencing to catalog millions of TCRγ and TCRβ chains from peripheral blood αβ and γδ T cells from three unrelated individuals. Almost all sampled αβ and γδ T cells had rearranged TCRγ sequences. Although sampled αβ T cells had a diverse repertoire of rearranged TCRβ chains, less than 4% of γδ T cells in peripheral blood had a rearranged TCRβ chain. Our data suggest that TCRγ rearranges in all T lymphocytes, consistent with TCRγ rearranging before T cell lineage commitment. However, rearrangement of the TCRβ locus appears to be restricted after T cell precursors commit to the αβ T cell lineage. Indeed, in T cell leukemias and lymphomas, TCRγ is almost always rearranged and TCRβ is only rearranged in a subset of cancers. Because high-throughput sequencing of TCRs is translated into the clinic for monitoring minimal residual for leukemia/lymphoma, our data suggest the sequencing target should be TCRγ.

Notch induces human T-cell receptor γδ+ thymocytes to differentiate along a parallel, highly proliferative and bipotent CD4 CD8 double-positive pathway

In wild-type mice, T-cell receptor (TCR) γδ(+) cells differentiate along a CD4 CD8 double-negative (DN) pathway whereas TCRαβ(+) cells differentiate along the double-positive (DP) pathway. In the human postnatal thymus (PNT), DN, DP and single-positive (SP) TCRγδ(+) populations are present. Here, the precursor-progeny relationship of the various PNT TCRγδ(+) populations was studied and the role of the DP TCRγδ(+) population during T-cell differentiation was elucidated. We demonstrate that human TCRγδ(+) cells differentiate along two pathways downstream from an immature CD1(+) DN TCRγδ(+) precursor: a Notch-independent DN pathway generating mature DN and CD8αα SP TCRγδ(+) cells, and a Notch-dependent, highly proliferative DP pathway generating immature CD4 SP and subsequently DP TCRγδ(+) populations. DP TCRγδ(+) cells are actively rearranging the TCRα locus, and differentiate to TCR(-) DP cells, to CD8αβ SP TCRγδ(+) cells and to TCRαβ(+) cells. Finally, we show that the γδ subset of T-cell acute lymphoblastic leukemias (T-ALL) consists mainly of CD4 SP or DP phenotypes carrying significantly more activating Notch mutations than DN T-ALL. The latter suggests that activating Notch mutations in TCRγδ(+) thymocytes induce proliferation and differentiation along the DP pathway in vivo.

Repertoire development and the control of cytotoxic/effector function in human gammadelta T cells

T cells develop into two major populations distinguished by their T cell receptor (TCR) chains. Cells with the alphabeta TCR generally express CD4 or CD8 lineage markers and mostly fall into helper or cytotoxic/effector subsets. Cells expressing the alternate gammadelta TCR in humans generally do not express lineage markers, do not require MHC for antigen presentation, and recognize nonpeptidic antigens. We are interested in the dominant Vgamma2Vdelta2+ T cell subset in human peripheral blood and the control of effector function in this population. We review the literature on gammadelta T cell generation and repertoire selection, along with recent work on CD56 expression and defining a cytotoxic/effector lineage within the phosphoantigen-reactive Vgamma2Vdelta2 cells. A unique mechanism for MHC-independent repertoire selection is linked to the control of effector function that is vital to the role for gammadelta T cells in tumor surveillance. Better understanding of these mechanisms will improve our ability to exploit this population for tumor immunotherapy.

Involvement of T-cell receptor-beta alterations in the development of otosclerosis linked to OTSC2

Otosclerosis is a common form of hearing loss, characterized by disordered bone remodeling in the otic capsule. Within the otosclerotic foci, several immunocompetent cells and immune-modulating factors can be found. Different etiological theories involving the immune system have been suggested. However, a genetic component is clearly present. In large otosclerosis families, seven autosomal-dominant loci have been found, but none of the disease-causing genes has been identified. This study focused on the exploration of the second otosclerosis locus on chromosome 7q34-36 (OTSC2), holding the T-cell receptor beta locus (TRB locus). A significantly lower T-cell receptor-beta (TCR-beta) mRNA expression and percentage of blood circulating TCR-alphabeta(+) T cells was detected in OTSC2 patients compared with controls and patients with the complex form of the disease. Further analysis illustrated more significant disturbances in specific T-cell subsets, including an increased CD28(null) cell population, suggesting a disturbed T-cell development and ageing in OTSC2 patients. These disturbances could be associated with otosclerotic bone remodeling, given the known effects of immunocompetent cells on bone physiology. These data implicate the TRB locus as the causative gene in the OTSC2 region and represent an important finding in the elucidation of the disease pathology.

A reliable and simplified sj/beta-TREC ratio quantification method for human thymic output measurement

Current techniques to peripherally assess thymic function are: the signal-joint T-cell receptor excision circle (sj-TREC) level measurement and the naive T cell and CD31+ TREC-rich subset determination. However, all of them are indirect approaches and none could be considered a direct recent thymic emigrant (RTE) marker. To overcome their limitations, Dion et al. (2004) described the sj/beta-TREC ratio that allows the peripheral quantification of the double negative to double positive intrathymic proliferation step. Nevertheless, the protocol described is expensive, sample and time-consuming, thus, limiting its usefulness. In this study, we describe a simplified protocol that reduces from 33 to 9 the amount of PCR reaction needed but maintaining the sensitivity and reproducibility of the original technique. In addition, we corroborated the effectiveness of our technique as an accurate thymic output-related marker by correlating the peripheral sj/beta-TREC ratio with a direct measurement of thymic function as the percentage of double positive thymocytes (r=0.601, p<0.001).

Characterization in vitro and engraftment potential in vivo of human progenitor T cells generated from hematopoietic stem cells

T-cell development follows a defined set of stage-specific differentiation steps. However, molecular and cellular events occurring at early stages of human T-cell development remain to be fully elucidated. To address this, human umbilical cord blood (UCB) hematopoietic stem cells (HSCs) were induced to differentiate to the T lineage in OP9-DL1 cocultures. A developmental program involving a sequential and temporally discrete expression of key differentiation markers was revealed. Quantitative clonal analyses demonstrated that CD34(+)CD38(-) and CD34(+)CD38(lo) subsets of UCB contain a similarly high T-lineage progenitor frequency, whereas the frequency in CD34(+)CD38(+/hi) cells was 5-fold lower. Delta-like/Notch-induced signals increased the T-cell progenitor frequency of CD34(+)CD38(-/lo) cells differentiated on OP9-DL1, and 2 distinct progenitor subsets, CD34(+)CD45RA(+)CD7(++)CD5(-)CD1a(-) (proT1) and CD34(+)CD45RA(+)CD7(++)CD5(+)CD1a(-) (proT2), were identified and their thymus engrafting capacity was examined, with proT2 cells showing a 3-fold enhanced reconstituting capacity compared with the proT1 subset. Furthermore, in vitro-generated CD34(+)CD7(++) progenitors effectively engrafted the thymus of immunodeficient mice, which was enhanced by the addition of an IL-7/IL-7 antibody complex. Taken together, the identification of T-progenitor subsets readily generated in vitro may offer important avenues to improve cellular-based immune-reconstitution approaches.

Pathobiology of mature T-cell lymphomas

Mature T- and natural killer (NK)-cell neoplasms are relatively rare forms of leukemia/lymphoma. The diagnosis of these entities is often difficult, necessitating extensive immunophenotypic, molecular, and genetic testing. Despite the accumulating information on the pathobiology of these neoplasms, in many cases the prognosis remains poor. This article presents an updated view of the morphologic, immunophenotypic, genetic, and molecular characteristics of the mature T- and NK-cell neoplasms. For a better understanding of this complex topic, the development of normal T and NK cells is briefly discussed. The presentation of the characteristic features of the neoplasms in the 2008 World Health Organization classification of hematopoietic neoplasms includes advances in the understanding of the pathobiology of each diagnostic category.

Genomic sequence encoding diversity segments of the pig TCR delta chain gene demonstrates productivity of highly diversified repertoire

To better understand the function and diversity of gammadelta T cells, we determined the genomic sequence encoding diversity (D) segments of the porcine TCR delta chain and its upstream regions, because pigs and other artiodactyls have relatively high proportions of gammadelta T cells. The revealed sequence contained 28 variable (V) alpha/delta segments, including 4 TRDV1 and at least 6 Ddelta segments, a much higher number than in humans and mice. All 6 of the Ddelta segments that had canonical recombination signal sequences were functionally utilized in expressed TCR delta chain genes. The multiplicity of Ddelta segments enabled the use of more than 3 Ddelta segments in a single functional TCR delta chain. The increased number of TCR delta segments was acquired by the duplication of the germline sequence, which occurred after the divergence of artiodactyls from primates and rodents. These data demonstrate that the pig is able to generate a highly diversified repertoire of TCR delta chain molecules.

Restoration of adenosine deaminase-deficient human thymocyte development in vitro by inhibition of deoxynucleoside kinases

Mutations in the gene encoding adenosine deaminase (ADA), a purine salvage enzyme, lead to immunodeficiency in humans. Although ADA deficiency has been analyzed in cell culture and murine models, information is lacking concerning its impact on the development of human thymocytes. We have used chimeric human/mouse fetal thymic organ culture to study ADA-deficient human thymocyte development in an "in vivo-like" environment where toxic metabolites accumulate in situ. Inhibition of ADA during human thymocyte development resulted in a severe reduction in cellular expansion as well as impaired differentiation, largely affecting mature thymocyte populations. Thymocyte differentiation was not blocked at a discrete stage; rather, the paucity of mature thymocytes was due to the induction of apoptosis as evidenced by activation of caspases and was accompanied by the accumulation of intracellular dATP. Inhibition of adenosine kinase and deoxycytidine kinase prevented the accumulation of dATP and restored thymocyte differentiation and proliferation. Our work reveals that multiple deoxynucleoside kinases are involved in the phosphorylation of deoxyadenosine when ADA is absent, and suggests an alternate therapeutic strategy for treatment of ADA-deficient patients.

Notch signaling is required for proliferation but not for differentiation at a well-defined beta-selection checkpoint during human T-cell development

Notch signaling is absolutely required for beta-selection during mouse T-cell development, both for differentiation and proliferation. In this report, we investigated whether Notch has an equally important role during human T-cell development. We show that human CD34(+) thymocytes can differentiate into CD4(+)CD8beta(+) double positive (DP) thymocytes in the absence of Notch signaling. While these DP cells phenotypically resemble human beta-selected cells, they lack a T-cell receptor (TCR)-beta chain. Therefore, we characterized the beta-selection checkpoint in human T-cell development, using CD28 as a differential marker at the immature single positive CD4(+)CD3(-)CD8alpha(-) stage. Through intracellular TCR-beta staining and gene expression analysis, we show that CD4(+)CD3(-)CD8alpha(-)CD28(+) thymocytes have passed the beta-selection checkpoint, in contrast to CD4(+)CD3(-)CD8alpha(-)CD28(-) cells. These CD4(+)CD3(-)CD8alpha(-)CD28(+) thymocytes can efficiently differentiate into CD3(+)TCRalphabeta(+) human T cells in the absence of Notch signaling. Importantly, preselection CD4(+)CD3(-)CD8alpha(-)CD28(-) thymocytes can also differentiate into CD3(+)TCRalphabeta(+) human T cells without Notch activation when provided with a rearranged TCR-beta chain. Proliferation of human thymocytes, however, is clearly Notch-dependent. Thus, we have characterized the beta-selection checkpoint during human T-cell development and show that human thymocytes require Notch signaling for proliferation but not for differentiation at this stage of development.

Molecular mechanisms that control mouse and human TCR-alphabeta and TCR-gammadelta T cell development

Following specification of hematopoietic precursor cells into the T cell lineage, several developmental options remain available to the immature thymocytes. The paradigm is that the outcome of the T cell receptor rearrangements and the corresponding T cell receptor signaling events will be predominant to determine the first of these choices: the alphabeta versus gammadelta T cell pathways. Here, we review the thymus-derived environmental signals, the transcriptional mediators, and other molecular mechanisms that are also involved in this decision in both the mouse and human. We discuss the differences in cellular events between the alphabeta and gammadelta developmental pathways and try to correlate these with a corresponding complexity of the molecular mechanisms that support them.

Lack of nonfunctional B-cell receptor rearrangements in a patient with normal B cell numbers despite partial RAG1 deficiency and atypical SCID/Omenn syndrome

INTRODUCTION

A 2.5-month old boy presented with recurrent wheezing, protracted diarrhea, erythrodermia, and failure to thrive.

METHODS AND RESULTS

Laboratory analysis showed lymphocytopenia with severely reduced T-cell numbers but normal numbers of B and NK cells. Serum IgE was increased and the patient had eosinophilia. These presentations are consistent with atypical severe combined immunodeficiency (SCID)/Omenn Syndrome and the diagnosis was confirmed by demonstration of homozygosity for the R841W mutation in the catalytic core of RAG1. Comparison of the patient's immunoglobulin heavy chain rearrangements to those of age-matched controls, cord blood, and adults revealed an almost total lack of nonproductive rearrangements (2.7% versus 14.7%, 27.6%, and 19.8% in the controls, respectively) indicating failure to correct out-of-frame rearrangements by a second rearrangement on the homologous chromosome 14.

CONCLUSION

We hypothesize that the R841W mutation causes a malfunction of RAG1 that has differential outcome on V(D)J recombination in B and T cells, as the patient had normal B cell numbers but suffered severe alpha-beta T-cell immunodeficiency.

The thymus chapter in the life of gut-specific intra epithelial lymphocytes

The intestinal intraepithelial lymphocytes (IEL) represent multi-lineage T cell populations. In addition to a major gammadeltaTCR(+) T cell subset, many IEL express alphabetaTCRs and they can be separated into alphabeta sublineages. Some TCRalphabeta(+)IEL have characteristics in common with conventional TCRalphabeta(+)T cells whereas others share an unconventional phenotype with their TCRgammadelta(+) counterparts. Because the latter are enriched for autoreactive TCRs and can be generated in the absence of a thymus, it has long been postulated that some IEL subsets develop locally in the intestine. Several new data however, indicate that under physiological conditions, IEL require a thymic education that directs lineage commitment and functional differentiation. This review will discuss the contributions of the thymus in shaping the various intestinal IEL sublineages.

Different chromosomal breakpoints impact the level of LMO2 expression in T-ALL

The t(11;14)(p13;q11) is presumed to arise from an erroneous T-cell receptor delta TCRD V(D)J recombination and to result in LMO2 activation. However, the mechanisms underlying this translocation and the resulting LMO2 activation are poorly defined. We performed combined in vivo, ex vivo, and in silico analyses on 9 new t(11;14)(p13;q11)-positive T-cell acute lymphoblastic leukemia (T-ALL) as well as normal thymocytes. Our data support the involvement of 2 distinct t(11;14)(p13;q11) V(D)J-related translocation mechanisms. We provide compelling evidence that removal of a negative regulatory element from the LMO2 locus, rather than juxtaposition to the TCRD enhancer, is the main determinant for LMO2 activation in the majority of t(11;14)(p13;q11) translocations. Furthermore, the position of the LMO2 breakpoints in T-ALL in the light of the occurrence of TCRD-LMO2 translocations in normal thymocytes points to a critical role for the exact breakpoint location in determining LMO2 activation levels and the consequent pressure for T-ALL development.