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“This is not the end. It’s not even the beginning of the end. But it is, perhaps, the end of the beginning.” Sir Winston Churchill Immune reconstitution after hematopoietic stem cell transplantation (HSCT) has been well studied in mouse... more
“This is not the end. It’s not even the beginning of the end. But it is, perhaps, the end of the beginning.” Sir Winston Churchill Immune reconstitution after hematopoietic stem cell transplantation (HSCT) has been well studied in mouse and man and the relationship between delayed immune reconstitution and post-transplant morbidity and mortality from infections and relapse has been well documented (1). Whereas erythroid, myeloid and platelet reconstitution occurs in most cases in the first weeks after HSCT and is primarily determined by engraftment of donor HSCs, B cell and especially T cell reconstitution takes much longer and recipients of an allogeneic HSCT can have an impaired T and B cell function even years after their HSCT (2). In recent years a number of strategies to enhance post-transplant immune reconstitution have been developed and successfully tested in preclinical models. These studies in experimental models mark “the end of the beginning” and in this chapter we will discuss the first attempts to introduce these strategies in clinical trials with HSCT recipients.
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T cell development in the thymus requires constant interactions between developing thymocytes and the surrounding resident stromal cells (TSCs). These functional, non-hematopoietic-derived cells are predominantly of epithelial origin and... more
T cell development in the thymus requires constant interactions between developing thymocytes and the surrounding resident stromal cells (TSCs). These functional, non-hematopoietic-derived cells are predominantly of epithelial origin and constitute 1% of total thymus cellularity. Thymic function and naive T cell output are optimal in humans during the early years of life, but decline sharply after the first years of life and further after the onset of puberty, with progressive contraction of functional thymus tissue. The loss of thymic epithelial cells (TECs) eventually results in an altered microenvironment that affects normal T cell development, reducing naive T cell output and contributing to the overall demise of immune functions. Other extrinsic factors that exacerbate the effects of thymic involution include cytoreductive conditioning regimes in the context of cancer treatments and hematopoietic stem cell transplantation (HSCT). In these scenarios, elderly patients are incapable of full immune recovery. With such complications present, we describe herein various preclinical approaches that could lead to potential new treatment strategies to restore thymic function and, more importantly, T-cell mediated immunity following clinically induced damage (Fig. 13.1).
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Although the thymus is a primary lymphoid organ, its function is compromised by an age-induced loss of resident epithelial cells, which results in reduced naïve T cell output. This has important implications for immune recovery in aged... more
Although the thymus is a primary lymphoid organ, its function is compromised by an age-induced loss of resident epithelial cells, which results in reduced naïve T cell output. This has important implications for immune recovery in aged and elderly patients following damage from cytoablative therapies. As thymic architecture plays a crucial role in naïve T cell development, a tissue specific scaffold that provides essential supporting matrix may assist in stem cell-based thymus regeneration to recreate complex organoids. Here we investigate thymus decellularization approaches that preserve major extracellular matrix components and support thymic epithelial cells for the generation of a functional thymic microenvironment with improved T cell output. We also established an in vitro, serum-free culture system that both maintains a progenitor thymic epithelial cell pool and drives their differentiation in the presence of decellularized thymic matrix. This approach enables further dissect...
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The thymus is primarily responsible for T cell production. However, it begins to recede in size and function, from early in life. This decreased generation of naive T cells during normal thymus ageing, or linked with pathology (i.e.... more
The thymus is primarily responsible for T cell production. However, it begins to recede in size and function, from early in life. This decreased generation of naive T cells during normal thymus ageing, or linked with pathology (i.e. chronic inflammation), leads to reduced T cell specificities, peripheral T cell imbalances, and higher susceptibilities to infections. Various clinical strategies for thymus and T cell recovery have been investigated, although no effective clinical treatments for the reconstitution of peripheral T cell diversity in severe immune deficiencies are available. The recent identification of thymic epithelial progenitor cells (TEPC) in the adult thymus will enable investigations into a new generation of therapies focused on regenerating the thymic microenvironment for diverse specificity T cell reconstitution in the elderly. The specific mechanisms underlying TEPC activation are still being investigated. Recent data point to an important role of the intrathymic transforming growth factor-β (TGF-β) circuitry. Although dual actions of this cytokine have been reported in the immune system, TGF-β signaling is transiently activated in hematopoietic stem and progenitor cells during hematopoietic regeneration. This review investigates the current strategies for thymus reactivation to replenish the peripheral T cell repertoire and potentially reverse the age-related inflammatory milieu.
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Most of the steps of lymphopoiesis have been elucidated but contentious issues remain, particularly regarding the identity and function of the earliest lymphoid progenitors that leave the bone marrow and seed the thymus. Hematopoiesis is... more
Most of the steps of lymphopoiesis have been elucidated but contentious issues remain, particularly regarding the identity and function of the earliest lymphoid progenitors that leave the bone marrow and seed the thymus. Hematopoiesis is effectively continuous throughout life, but there is a profound decline in immune function with increasing age, driven by thymus involution and severely curtailed B cell development. A key question is whether defects in bone marrow progenitors, such as reduced differentiation and repopulation potential, are the common denominator. While thymic involution temporally precedes overt HSC functional decline, a logical supposition is that the latter exacerbates the former. This review explores this possible link, and concludes that improving bone marrow function is fundamental to sustained thymic regeneration.
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Presented here is a cell-suspension model for positive selection using thymocytes fromαβ-TCR (H-2Db-restricted) transgenic mice specific to the lymphocytic choriomeningitis virus (LCMV) on a nonselecting MHC background (H-2dor TAP-1 –/–),... more
Presented here is a cell-suspension model for positive selection using thymocytes fromαβ-TCR (H-2Db-restricted) transgenic mice specific to the lymphocytic choriomeningitis virus (LCMV) on a nonselecting MHC background (H-2dor TAP-1 –/–), cocultured with freshly isolated adult thymus stromal cells of the selecting MHC type. The thymic stromal cells alone induced positive selection of functional CD4-CD8+cells whose kinetics and efficiency were enhanced by nominal peptide. Fibroblasts expressing the selecting MHC alone did not induce positive selection; however, together with nonselecting stroma and nominal peptide, there was inefficient positive. These results suggest multiple signaling in positive selection with selection events able to occur on multiple-cell types. The ease with which this model can be manipulated should greatly facilitate the resolution of the mechanisms of positive selection in normal and pathological states.
Research Interests: Immunology, Biology, Medicine, Transgenic Mice, Signal Transduction, and 13 moreHematopoietic Stem Cells, Cell Differentiation, Mice, Animals, Peptides, CD, Positive Selection, Major histocompatibility complex, Stromal Cells, Negative Selection Algorithm, Developmental Immunology, coculture techniques, and Thymus Gland
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Research Interests: Immunology, Transcription Regulation, Transcription Factors, Gene expression, Molecular Mechanics, and 15 moreSignal Transduction, Cell Differentiation, Mice, Immunity, Female, Animals, Male, Peptides, Bone marrow, Transcription Factor, Phosphotyrosine, Stromal Cells, Negative Selection Algorithm, DNA binding proteins, and MHC class I
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ABSTRACT
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Tolerance to tissue-engineering products is a major obstacle hindering the clinical application of this rapidly advancing technology. Manipulation of central tolerance, by establishing thymus chimerism of both donor and host-derived... more
Tolerance to tissue-engineering products is a major obstacle hindering the clinical application of this rapidly advancing technology. Manipulation of central tolerance, by establishing thymus chimerism of both donor and host-derived haemopoietic cells (haemopoietic stem cell transplant--HSCT), should purge any T cells reactive to potential donor organ or tissue transplant. A functional thymus, however, is required to induce chimerism and repopulate the peripheral T cell pool, but age-related thymic atrophy and damage caused by ablative conditioning regimes significantly reduce thymic function and increase incident of infection-dependent morbidity and mortality. Thus rejuvenation of the thymus alongside HSCT may potentiate the use of this strategy in the clinic. In addition, the use of thymic epithelial progenitor cell technology may allow growth of ex vivo thymic tissue for use in clinical situations of immunodeficiency as well as in establishing tolerance to tissue/organ products derived from the same source.
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To determine if temporarily blocking sex steroids prior to stem cell transplantation can increase thymus function and thus enhance the rate of T cell regeneration. This was a pilot study of luteinizing hormone-releasing hormone agonist... more
To determine if temporarily blocking sex steroids prior to stem cell transplantation can increase thymus function and thus enhance the rate of T cell regeneration. This was a pilot study of luteinizing hormone-releasing hormone agonist (LHRH-A) goserelin given 3 weeks prior to allogeneic or autologous hemopoietic stem cell transplantation and administered up to 3 months posttransplantation. Patients (with or without LHRH-A administration) were assessed from 1 week to 12 months posttransplantation for multiple immunologic variables by flow cytometry (particularly naïve T cells), quantitative PCR to assess T-cell receptor excision circle levels (as a correlate of thymus function), CDR3 length analysis to determine the variability of the TCR repertoire, and in vitro assays to determine functional T cell responses. LHRH-A administration prior to stem cell transplantation significantly increased neutrophil and lymphocyte numbers within the first month of posttransplantation. Most importantly, total and naïve CD4(+) T cell regeneration together with T-cell receptor excision circle production, T cell repertoire regeneration, and peripheral T cell function were also significantly enhanced at multiple time points posttransplant. In addition, an increase in disease-free survival (P = 0.04) was seen in the autologous setting. Although LHRH-A administration increased T cell responses in vitro, it did not exacerbate graft-versus-host disease in the allogeneic setting. This study provides an important new approach to the improvement of immune reconstitution in patients undergoing hemopoietic stem cell transplantation and may have generic applications in many T cell-based disorders.
Research Interests: Flow Cytometry, Adolescent, Humans, Female, Male, and 5 moreT lymphocytes, Sex Steroids, Middle Aged, Immune system, and Adult
A major underlying cause for aging of the immune system is the structural and functional atrophy of the thymus, and associated decline in T cell genesis. This loss of naïve T cells reduces adaptive immunity to new stimuli and precipitates... more
A major underlying cause for aging of the immune system is the structural and functional atrophy of the thymus, and associated decline in T cell genesis. This loss of naïve T cells reduces adaptive immunity to new stimuli and precipitates a peripheral bias to memory cells against prior antigens. Whilst multiple mechanisms may contribute to this process, the temporal alliance of thymic decline with puberty has implicated a causative role for sex steroids. Accordingly ablation of sex steroids induces profound thymic rejuvenation. Although the thymus retains some, albeit highly limited, function in healthy adults, this is insufficient for resurrecting the T cell pool following cytoablative treatments such as chemo- and radiation-therapy and AIDS. Increased risk of opportunistic infections and cancer relapse or appearance, are a direct consequence. Temporary sex steroid ablation may thus provide a clinically effective means to regenerate the thymus and immune system in immunodeficiency states.
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A recent paper in PNAS (Swijnenburg et al., 2008) reveals that human embryonic stem cells are not immune privileged. Potential therapeutic use of these cells will thus depend on the development of new strategies to counter foreign graft... more
A recent paper in PNAS (Swijnenburg et al., 2008) reveals that human embryonic stem cells are not immune privileged. Potential therapeutic use of these cells will thus depend on the development of new strategies to counter foreign graft rejection by patient immune systems.
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ABSTRACT The present invention relates generally to novel thymic cellular populations and, more particularly, to novel thymic epithelial cellular populations. Most particular, the present invention is directed to novel thymic epithelial... more
ABSTRACT The present invention relates generally to novel thymic cellular populations and, more particularly, to novel thymic epithelial cellular populations. Most particular, the present invention is directed to novel thymic epithelial progenitor cell populations. The cellular populations of the present invention are useful in a wide range of clinical and research settings including, inter alia, the in vitro or in vivo generation of thymic epithelial cell populations and the therapeutic or prophylactic treatment of a range of conditions via the administration of these cells. Also facilitated is the design of in vitro based screening systems for testing the therapeutic impact and/or toxicity of potential treatment or culture regimes to which thymic epithelial cells may be exposed. In another aspect, the present invention is directed to a method of identifying thymic epithelial cellular subpopulations and, more particularly, thymic epithelial progenitors by screening for the co-expression of markers including MHC Class II, UEA1 and Ly51. This method is useful in a range of applications including, but not limited to, assessing or monitoring for the presence of thymic epithelial cell populations and/or facilitating the isolation of or enrichment for these cellular populations of use in a range of research and clinical applications.
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The intrathymic differentiation events leading to the development and export of mature T cells tolerant to self yet capable of responding to foreign peptide antigen in the context of self-MHC are clearly both dynamic and complex. The... more
The intrathymic differentiation events leading to the development and export of mature T cells tolerant to self yet capable of responding to foreign peptide antigen in the context of self-MHC are clearly both dynamic and complex. The changing phenotype of the developing thymocyte as it migrates through and interacts with the heterogeneous thymic microenvironment and the intracellular signalling events associated with such interactions are being extensively studied, yet many aspects remain poorly defined, such as the precise relationship between stromal cells and thymic selection. Positive and negative selection are crucial events in the development of T cells, leading to a diverse yet non-autoreactive immune system. A breakdown in either of these processes could lead to either a reduced T cell repertoire or the escape into the periphery of autoreactive T cells - both clearly having deleterious consequences for the health of the individual. This review aims to summarise the current status of research in thymic positive selection with emphasis on the role of different cell types and peptides.
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Research Interests: Immunology, Aging, Biology, Immunology of the Gut, Apoptosis, and 15 moreCell Differentiation, Humans, Castration, Animals, Male, Aged, Bone Marrow Transplantation, Atrophy, Gonadotropin Releasing Hormone, Immunophenotyping, Androgen, Cell Proliferation, Blockade, Lymphopoiesis, and Androgen antagonists
Research Interests: Immunology, Biology, Immunology of the Gut, Stem Cell, Medicine, and 15 moreDendritic Cells, Spleen, Mice, Animals, T Cell, Male, The, Haematopoiesis, Immune system, Bone Marrow Transplantation, Interleukin, Hematopoietic Stem Cell Transplantation, Combined Modality Therapy, Thymus Gland, and orchiectomy
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Research Interests: Immunology, Regeneration, Autoimmunity, Immunology of the Gut, Transcription Factors, and 15 moreDexamethasone, Mice, Animals, Immunosuppression, The, Cyclosporine, Thymus, Immune system, Epithelial cells, Stromal Cells, Immune Tolerance, Cyclophosphamide, Immunosuppressive Agents, cytometry, and Thymus Gland
Age-related thymic atrophy plays a significant role in delayed immune reconstitution in older recipients after hemopoietic stem cell transplantations (HSCT). Sex steroid ablation has been shown to reverse thymic atrophy and previously we... more
Age-related thymic atrophy plays a significant role in delayed immune reconstitution in older recipients after hemopoietic stem cell transplantations (HSCT). Sex steroid ablation has been shown to reverse thymic atrophy and previously we have shown that in syngeneic and allogeneic models of HSCT, sex steroid ablation enhances immune reconstitution. Donor-derived HSC numbers, as well as precursor T and B cells are increased in castrated mice following HSCT. These primary changes lead to an increase in both T and B cells in the periphery. The current study examined both the molecular mechanisms behind this enhanced reconstitution and the function of the lymphocytes produced. Bone marrow (BM) and thymic stromal cell (TSCs) populations were analysed using RT-PCR and were tested for the production of growth factors previously implicated in immune reconstitution. Functional studies including proliferation and cytotoxicity assays and intracellular cytokine production showed that on a per c...
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Polymorphisms impacting thymic function may decrease peripheral tolerance and hasten autoimmune disease. The NF-κB transcription factor subunit, RelB, is essential for the development and differentiation of medullary thymic epithelial... more
Polymorphisms impacting thymic function may decrease peripheral tolerance and hasten autoimmune disease. The NF-κB transcription factor subunit, RelB, is essential for the development and differentiation of medullary thymic epithelial cells (mTECs): RelB-deficient mice have reduced thymic cellularity and markedly fewer mTECs, lacking AIRE. The precise mechanism of this mTEC reduction in the absence of RelB is unclear. To address this, we studied mTECs and dendritic cells (DCs), which critically regulate negative selection, and thymic regulatory T-cells (tTreg) in RelB mice, which have spontaneous multiorgan autoimmune disease. RelB thymi were organized, with medullary structures containing AIRE mTECs, DCs, and CD4 thymocytes, but fewer tTreg. Granulocytes infiltrated the RelB thymic cortex, capsule, and medulla, producing inflammatory thymic medullary atrophy, which could be treated by granulocyte depletion or RelB DC immunotherapy, with concomitant recovery of mTEC and tTreg number...
Autologous hematopoietic stem cell transplantation (auto-HSCT) patients experience long-term immunosuppression, which increases susceptibility to infection and relapse rates due to minimal residual disease (MRD). Sex steroid (SS) ablation... more
Autologous hematopoietic stem cell transplantation (auto-HSCT) patients experience long-term immunosuppression, which increases susceptibility to infection and relapse rates due to minimal residual disease (MRD). Sex steroid (SS) ablation is known to reverse age-related thymic atrophy and decline in B-cell production This study used a congenic HSCT mouse model to analyze the effects of SS ablation (through surgical castration) on immune reconstitution and growth factor production following auto-HSCT. Bone marrow (BM) and thymic stromal cell (TSCs) populations were analyzed using RT-PCR and were tested for the production of growth factors previously implicated in immune reconstitution or age-relate immune degeneration Castration increased bone marrow (BM), thymic, and splenic cellularity following auto-HSCT. HSC number and common lymphoid precursor (CLP) frequency and number were increased in castrated mice. B cell precursor numbers were also significantly increased in the BM of these mice. Triple negative, double positive and single positive thymocytes were increased following HSCT and castration, as were thymic dendritic cells and natural killer T (NKT) cells. This enhanced lymphoid reconstitution of the primary immune organs leads to a significant increase in splenic T and B cells 42 days after HSCT. The molecular mechanisms behind the enhanced reconstitution were also studied. TGF-beta1 was decreased in castrated mice compared to sham-castrated controls in TSCs and BM cells. TSC production of IL-6 was also decreased in castrated mice These data suggest that sex steroid ablation significantly enhances lymphopoiesis following auto-HSCT providing a new strategy for posttransplant immune reconstitution.