Defects In T-cell Development Research Articles

Crucial Roles of SATB1 in Regulation of Thymocyte Migration after Positive Selection.

Double-positive thymocytes that have passed positive selection migrate from the cortex to the medulla, where negative selection and the development of thymic regulatory T cells (tTregs) take place. Medullary thymic epithelial cells (mTECs) play important roles in these selections, and their differentiation and maintenance depend on interaction with positively selected CD4+ single-positive cells. Therefore, migration and differentiation after positive selection must be coordinated to establish immune tolerance. However, the regulatory mechanisms of these processes are not fully understood. SATB1 is a genome organizer highly expressed in double-positive thymocytes, and SATB1 deletion causes various defects in T-cell development, including impaired positive and negative selection and tTreg differentiation. Here, we show that SATB1 is critical for temporally coordinated thymocyte trafficking after positive selection in mice. Satb1 knockout (ΔSatb1) led to precocious thymic egress caused by augmented S1pr1 upregulation in positively selected thymocytes, accompanied by lower induction of Ccr7, Tnfsf11, and Cd40lg. Altered thymocyte trafficking and functionality affected the differentiation of mTECs and, in turn, tTreg differentiation. Thus, SATB1 is required to establish immune tolerance, at least in part, by ensuring timely thymic egress and mTEC differentiation.

HIV-1LAI Nef blocks the development of hematopoietic stem/progenitor cells into T lymphoid cells.

Objective:Despite successful antiviral therapy, the recovery of CD4+ T cells may not be complete in certain HIV-1-infected individuals. In our previous work with humanized mice infected with CXCR4-tropic HIV-1LAI (LAI), viral protein Nef was found the major factor determining rapid loss of both CD4+ T cells and CD4+CD8+ thymocytes but its effect on early T-cell development is unknown. The objective of this study is to investigate the influence of LAI Nef on the development of hematopoietic stem/progenitor cells (HSPCs) into T lymphoid cells.Design:HSPC-OP9-DL1 cell co-culture and humanized mouse model was used to investigate the objective of our study in vitro and in vivo. RNA-seq was exploited to study the change of gene expression signature after nef expression in HSPCs.Results:Nef expression in HSPCs was found to block their development into T lymphoid cells both in vitro and in the mice reconstituted with nef-expressing HSPCs derived from human cord blood. More surprisingly, in humanized mice nef expression preferentially suppressed the production of CD4+ T cells. This developmental defect was not the result of CD34+ cell loss. RNA-seq analysis revealed that Nef affected the expression of 176 genes in HSPCs, including those involved in tumor necrosis factor, Toll-like receptor, and nucleotide-binding oligomerization domain-like receptor signaling pathways that are important for hematopoietic cell development.Conclusion:Our results demonstrate that Nef compromises the development of HSPCs into T lymphoid cells, especially CD4+ T cells. This observation suggests that therapeutics targeting Nef may correct HIV-1-associated hematopoietic abnormalities, especially defects in T-cell development.

SR-BI (Scavenger Receptor Class B Type 1) Is Critical in Maintaining Normal T-Cell Development and Enhancing Thymic Regeneration.

Objective- Continuous T-cell production from thymus is essential in replenishing naïve T-cell pool and maintaining optimal T-cell functions. However, the underlying mechanisms regulating the T-cell development in thymus remains largely unknown. Approach and Results- We identified SR-BI (scavenger receptor class B type 1), an HDL (high-density lipoprotein) receptor, as a novel modulator in T-cell development. We found that SR-BI deficiency in mice led to reduced thymus size and decreased T-cell production, which was accompanied by narrowed peripheral naïve T-cell pool. Further investigation revealed that SR-BI deficiency impaired progenitor thymic homing, causing a dramatic reduction in the percentage of earliest thymic progenitors, but did not affect other downstream T-cell developmental steps inside the thymus. As a result of the impaired progenitor thymic homing, SR-BI-deficient mice displayed delayed thymic regeneration postirradiation. Using a variety of experimental approaches, we revealed that the impaired T-cell development in SR-BI-deficient mice was not caused by hematopoietic SR-BI deficiency or SR-BI deficiency-induced hypercholesterolemia, but mainly attributed to the SR-BI deficiency in adrenal glands, as adrenal-specific SR-BI-deficient mice exhibited similar defects in T-cell development and thymic regeneration with SR-BI-deficient mice. Conclusions- This study demonstrates that SR-BI deficiency impaired T-cell development and delayed thymic regeneration by affecting progenitor thymic homing in mice, elucidating a previously unrecognized link between SR-BI and adaptive immunity.

Partial defects of T-cell development associated with poor T-cell function

For many years, severe combined immune deficiency diseases, which are characterized by virtual lack of circulating T cells and severe predisposition to infections since early in life, have been considered the prototypic forms of genetic defects of T-cell development. More recently, advances in genome sequencing have allowed identification of a growing number of gene defects that cause severe but incomplete defects in T-cell development, function, or both. Along with recurrent and severe infections, especially cutaneous viral infections, the clinical phenotype of these conditions is characterized by prominent immune dysregulation.

Thymus microenvironment in human primary immunodeficiency diseases

Severe combined immunodeficiencies represent a heterogeneous group of genetic disorders affecting genes of both early and late steps in lymphocytes development, a process tightly controlled by thymic epithelial cells. Detailed analysis of thymic morphology aids to the assessment of the severity of the immune disorder and may be critical to the understanding of the role of the genetic defects in the pathophysiology of these diseases. In this review, we highlight recent advancements in the characterization of the thymic microenvironment in primary immunodeficiencies. Crosstalk between thymocytes and thymic epithelial cells is essential to preserve thymic architecture and function, and therefore to promote T-cell maturation and development of self-tolerance. Early severe defects in T-cell development result in profound abnormalities of thymic epithelial cells differentiation with loss of AIRE expression and severe reduction of thymic dendritic and T-regulatory cells. Differently, later defects in T-cell development that are permissive for normal thymocytes development allow cortico-medullary differentiation with partially preserved AIRE expression and dendritic/T-regulatory cells distribution. Hypomorphic mutations in the same genes partially permissive to T-cell development may result in a more complex phenotype with immunodysreactivity and peculiar thymic alterations. Although the molecular and genetic bases of primary immunodeficiencies directly aid to both diagnosis and management of the patients, the detailed analysis of thymic morphology critically contributes to unveil the pathophysiology of these diseases.

SUMO Conjugation to the Matrix Attachment Region-binding Protein, Special AT-rich Sequence-binding Protein-1 (SATB1), Targets SATB1 to Promyelocytic Nuclear Bodies Where It Undergoes Caspase Cleavage

SATB1 (special AT-rich sequence-binding protein-1) provides a key link between DNA loop organization, chromatin modification/remodeling, and association of transcription factors at matrix attachment regions (MARs). To investigate the role of SATB1 in cellular events, we performed a yeast two-hybrid screen that identified SUMO-1, Ubc9, and protein inhibitor of activated STAT (PIAS) family members as SATB1 interaction partners. These proteins, working in concert, enhanced SUMO conjugation to lysine-744 of SATB1. Overexpression of SUMO or PIAS in Jurkat cells, which express high levels of endogenous SATB1, exhibited enhanced caspase cleavage of this MAR-associating protein. Sumoylation-deficient SATB1 (SATB1(K744R)) failed to display the characteristic caspase cleavage pattern; however, fusion of SUMO in-frame to SATB1(K744R) restored cleavage. A SUMO-independent interaction of inactive caspase-6 and SATB1 was noted. A subset of total cellular SATB1 localized into promyelocytic leukemia nuclear bodies where enhanced SATB1 cleavage was detected subsequent to caspase activation. These results reveal a novel sumoylation-directed caspase cleavage of this key regulatory molecule. The role of regulated proteolysis of SATB1 may be to control transcription in immune cells during normal cell functions or to assist in efficient and rapid clearance of nonfunctional or potentially damaging immune cells.

A Human Lymphoid Progenitor Capable of Circulating and Seeding the Thymus.

Identification of a thymus-seeding progenitor originating from human bone marrow constitutes a key milestone in understanding and correcting defects in T-cell development. Here, we report the characterization of a novel human bone marrow lymphoid-restricted subpopulation which is part of the lineage-negative CD34+CD10+ progenitor population and which can be distinguished from B-cell-committed precursors by the absence of CD24 expression. We demonstrated that these Lin-CD34+CD10+CD24- progenitors lack myeloid and erythroid potential but can generate B, T and NK lymphocytes following culture on MS5 or OP9-hDelta1 stroma. The gene expression profile of this population, analyzed by a multiplex RT-PCR assay, revealed co-expression of RAG1, TdT, PAX5, CD3ε and IL-7Rα. These progenitors are not only present in the bone marrow but also in the blood throughout life, suggesting an ability to circulate. Moreover we showed that the Lin-CD34+CD10+CD24- cells also correspond to the most immature population of the thymus which gives rise to Lin-CD34+CD7+ T-cell precursors. Taken as a whole these findings unravel for the first time the existence of a postnatal lymphoid-restricted population which is capable of migrating from the bone marrow to the thymus.

Impaired chemokine-induced migration during T-cell development in the absence of Jak 3.

The arrival of bone marrow T-cell progenitors to the thymus, and the directed migration of thymocytes, are thought to be regulated by the expression of chemokines and their receptors. Recent data has shown that the Jak/Stat signalling pathway is involved in chemokine receptor signalling. We have investigated the role of Jak 3 in chemokine-mediated signalling in the thymus using Jak 3(-/-) mice. These mice show defects in T-cell development, as well as in peripheral T-cell function, resulting in a hypoplastic thymus and an altered T-cell homeostasis. Here we demonstrate, for the first time, that bone marrow progenitors and thymocytes from Jak 3(-/-) mice have decreased chemotactic responses to CXCL12 and CCL25. We also show that Jak 3 is involved in signalling through CCR9 and CXCR4, and that specific inhibition of Jak 3 in wild-type progenitors and thymocytes decreases their chemotactic responses towards CCL25 and CXCL12. Finally, quantitative reverse transcription-polymerase chain reaction analysis showed that thymocytes from Jak 3(-/-) mice express similar levels of CXCR4 and CCR9 compared to wild-type mice. Altogether, deficient CCL25- and CXCL12-induced migration could result in a homing defect of T-cell progenitors to the thymus, as well as in a deficient thymocyte migration through the thymic stroma. Our results strongly suggest that the absence of Jak 3 affects T-cell development, not only through an impaired interleukin-7 receptor (IL-7R)-mediated signalling, but also through impaired chemokine-mediated responses, which are crucial for thymocyte migration and differentiation.

Tumor associated macrophages (TAM) and microvasculature in cartilage tumors

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit the function of cyclooxygenases, COX-1 and COX-2, which catalyze the first step in the synthesis of inflammatory mediators (PGE2). We sought to understand the roles of cyclooxygenases and NSAIDs in T-cell development. Our data show no significant defects in T-cell development in fetal thymic organ cultures of mice disrupted in both or either COX genes or in mice disrupted in either EP-1 or EP-2 receptor genes. On the other hand, NSAIDs reproducibly caused thymocyte developmental defects. However, the specific effects of the COX-2 inhibitors were not correlated with their potency for inhibition of COX-2 activity. We focused on the NS-398 COX-2 inhibitor and showed that its effects could not be reversed by exogenous PGE2. Furthermore, NS-398 was inhibitory even when its target, COX-2, was absent. These data show that the T-cell developmental effects of NS-398 are COX-2 and PGE2 independent.

The COX-2 Inhibitor NS-398 Causes T-Cell Developmental Disruptions Independent of COX-2 Enzyme Inhibition

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit the function of cyclooxygenases, COX-1 and COX-2, which catalyze the first step in the synthesis of inflammatory mediators (PGE2). We sought to understand the roles of cyclooxygenases and NSAIDs in T-cell development. Our data show no significant defects in T-cell development in fetal thymic organ cultures of mice disrupted in both or either COX genes or in mice disrupted in either EP-1 or EP-2 receptor genes. On the other hand, NSAIDs reproducibly caused thymocyte developmental defects. However, the specific effects of the COX-2 inhibitors were not correlated with their potency for inhibition of COX-2 activity. We focused on the NS-398 COX-2 inhibitor and showed that its effects could not be reversed by exogenous PGE2. Furthermore, NS-398 was inhibitory even when its target, COX-2, was absent. These data show that the T-cell developmental effects of NS-398 are COX-2 and PGE2 independent.

The MAR-binding protein SATB1 orchestrates temporal and spatial expression of multiple genes during T-cell development

SATB1 is expressed primarily in thymocytes and can act as a transcriptional repressor. SATB1 binds in vivo to the matrix attachment regions (MARs) of DNA, which are implicated in the loop domain organization of chromatin. The role of MAR-binding proteins in specific cell lineages is unknown. We generated SATB1-null mice to determine how SATB1 functions in the T-cell lineage. SATB1-null mice are small in size, have disproportionately small thymi and spleens, and die at 3 weeks of age. At the cellular level, multiple defects in T-cell development were observed. Immature CD3(-)CD4(-)CD8(-) triple negative (TN) thymocytes were greatly reduced in number, and thymocyte development was blocked mainly at the DP stage. The few peripheral CD4(+) single positive (SP) cells underwent apoptosis and failed to proliferate in response to activating stimuli. At the molecular level, among 589 genes examined, at least 2% of genes including a proto-oncogene, cytokine receptor genes, and apoptosis-related genes were derepressed at inappropriate stages of T-cell development in SATB1-null mice. For example, IL-2Ralpha and IL-7Ralpha genes were ectopically transcribed in CD4(+)CD8(+) double positive (DP) thymocytes. SATB1 appears to orchestrate the temporal and spatial expression of genes during T-cell development, thereby ensuring the proper development of this lineage. Our data provide the first evidence that MAR-binding proteins can act as global regulators of cell function in specific cell lineages.