Impaired thymic expression of tissue-restricted antigens licenses the de novo generation of autoreactive CD4+ T cells in acute GVHD

PRMT5: splicing up tolerance

Expression of tissue-restricted antigens (TRAs) within the thymus is critical for the establishment of self-tolerance; however, exact mechanisms regulating the expression of TRAs has proven more complex than previously appreciated. In this issue of the JCI, Muro et al. identify a central role for protein arginine methyltransferase 5 (PRMT5) in posttranscriptional regulation of TRAs and thereby central tolerance. Using conditional KO mice, the authors showed that thymic deficiency of Prmt5 predisposed mice to developing autoimmune diseases while enhancing antitumor efficacy. These studies provide insight into the role of PRMT5 in shaping the T cell repertoire with implications for the development of therapies.

Population pharmacokinetics of cyclosporine A in hematopoietic stem cell transplant recipients: A systematic review

Cyclosporine A (CsA) is the prevalent immunosuppressive drug for preventing and treating graft-versus-host disease after hematopoietic stem cell transplantation (HSCT) in both children and adults. Population pharmacokinetic studies have identified covariates, owing to their large between-subject variability, facilitating individualized therapy. However, no review has summarized CsA's population pharmacokinetics post-HSCT. This systematic review aims to synthesize population pharmacokinetic studies of CsA therapy in HSCT recipients and explore influencing covariates. Thirteen studies, comprising five involving children, one involving both children and adults and seven involving adults, were included. The median apparent clearance in children surpassed that in adults, influenced notably by hematocrit level and body. While liver function impacted clearance, the effect was insignificant. Co-administration with cytochrome P450 enzyme inhibitors (e.g., fluconazole or itraconazole) decreased drug clearance, whereas inducers (e.g., rifampicin or rifapentine) increased it. Area under the curve analysis is recommended over trough concentration-based monitoring for HSCT recipients on CsA. In cases of insufficient trough concentration, additional sampling points are recommended for improved area under the curve estimation. Further studies are needed to evaluate the optimal sampling points required for the area under the curve estimation in CsA therapy post-HSCT.

Associations between acute and chronic graft-versus-host disease

ABSTRACT

Chronic graft-versus-host disease (GVHD) is 1 of the major complications after allogeneic hematopoietic cell transplantation (allo-HCT). Although various risk factors for chronic GVHD have been reported, limited data are available regarding the impact of acute GVHD on chronic GVHD. We examined the association between acute and chronic GVHD using a Japanese registry data set. The landmark point was set at day 100 after allo-HCT, and patients who died or relapsed before the landmark point were excluded. In total, 14 618 and 6135 patients who underwent allo-HCT with bone marrow or peripheral blood (BM/PB) and with umbilical cord blood (UCB), respectively, were analyzed. In the BM/PB cohort, the risk for chronic GVHD that requires systemic steroids increased with each increase in acute GVHD grade from 0 to 2 (grade 0 vs 1 [hazard ratio (HR), 1.32; 95% confidence interval (CI), 1.19-1.46; P < .001]; grade 1 vs 2 [HR, 1.41; 95% CI, 1.28-1.56; P < .001]), but the risk was similar between acute GVHD grade 2 and grade 3 to 4 (HR, 1.02; 95% CI, 0.91-1.15; P = 1.0). These findings were confirmed in the UCB cohort. We further observed that the risk for severe chronic GVHD increased with each increment in the grade of acute GVHD, even between acute GVHD grade 2 and grade 3 to (grade 2 vs 3-4: HR, 1.70; 95% CI, 1.12-2.58; P = .025). In conclusion, the preceding profiles of acute GVHD should help to stratify the risk for chronic GVHD and its severity, which might be useful for the development of risk-adopted preemptive strategies for chronic GVHD.

How does ocular graft-versus-host disease fit under the dry eye umbrella? A review

Graft-versus-host disease (GVHD) is a systemic disease that can affect multiple organs as a consequence of an allogeneic haematopoietic stem cell transplant. One organ system that is often affected in GVHD is the eyes. Ocular GVHD (oGVHD) may involve various structures within the eye including the lacrimal glands, eyelids, conjunctiva, cornea, and nasolacrimal ducts, and is a source of morbidity in patients with GVHD. Common presenting features of GVHD overlap with dry eye disease (DED), including decreased tear production, epithelial disruption, and Meibomian gland dysfunction (MGD). In this review, we aim to compare oGVHD and DED to better understand the similarities and differences between the conditions, with a focus on pathophysiology, risk factors, clinical features, and treatments.

Primary and secondary defects of the thymus

The thymus is the primary site of T-cell development, enabling generation, and selection of a diverse repertoire of T cells that recognize non-self, whilst remaining tolerant to self- antigens. Severe congenital disorders of thymic development (athymia) can be fatal if left untreated due to infections, and thymic tissue implantation is the only cure. While newborn screening for severe combined immune deficiency has allowed improved detection at birth of congenital athymia, thymic disorders acquired later in life are still underrecognized and assessing the quality of thymic function in such conditions remains a challenge. The thymus is sensitive to injury elicited from a variety of endogenous and exogenous factors, and its self-renewal capacity decreases with age. Secondary and age-related forms of thymic dysfunction may lead to an increased risk of infections, malignancy, and autoimmunity. Promising results have been obtained in preclinical models and clinical trials upon administration of soluble factors promoting thymic regeneration, but to date no therapy is approved for clinical use. In this review we provide a background on thymus development, function, and age-related involution. We discuss disease mechanisms, diagnostic, and therapeutic approaches for primary and secondary thymic defects.

Allogeneic stem cell transplant recipients surviving at least 2 years without relapse: outcome and risk factors

Outcomes of 2-year survivours undergoing allo-haematopoietic stem cell transplantation at Oslo University Hospital were retrospectively assessed with the objectives of identification of risk factors for late death as possible means for precautionary measures and interventions to improve long-term survival. 421 patients with haematological malignancy, transplanted between 2005 and 2019, alive and free of disease after 2 years were included with data reported from The OUS-HSCT registry. Median follow-up was 6.2 years (2.016.1), and 232 patients (55%) were observed for minimum 5 years. The probability of being alive 5 and 10 years after HSCT was 86% and 76%. Primary risk factors for late death included initial diagnosis of age ≥ 60 years, chronic lymphocytic leukaemia (CLL), previous blood stream- or invasive fungal infection (BSI, IFI), and chronic graft-versus-host disease (cGVHD). Transplant-related mortality (TRM) and relapse at 5 years were 9.0% and 7.7%, respectively. Two factors were associated with the latter: cytomegalovirus (CMV) seronegative donor and CLL. Compared with the age- and gender-matched Norwegian general population, life expectancy was lower for each disease, except for CML. The prospect for the long-term survival is good for 2-year survivors of the allogeneic hematopoietic stem cell transplantation. However, life expectancy remains inferior to the age- and gender-matched general population. Optimising prophylaxis and treatment for chronic GVHD, BSI and IFI are needed along with the improved adherence to guidelines for early detection of secondary malignancies. Measures to improve immune reconstitution, possibly the microbiota, and the use of CMV seropositive donors regardless of recipient sero-status may be warranted and should be addressed in further studies.

Chronic graft-versus-host disease. Part I: Epidemiology, pathogenesis, and clinical manifestations

Chronic graft-versus-host disease is a major complication of allogeneic hematopoietic cell transplantation and a leading cause of long-term morbidity, nonrelapse mortality, and impaired health-related quality of life. The skin is commonly affected and presents heterogeneously, making the role of dermatologists critical in both diagnosis and treatment. In addition, new clinical classification and grading schemes inform treatment algorithms, which now include 3 U.S. Food and Drug Administration-approved therapies, and evolving transplant techniques are changing disease epidemiology. Part I reviews the epidemiology, pathogenesis, clinical manifestations, and diagnosis of chronic graft-versus-host disease. Part II discusses disease grading and therapeutic management.

Aryl hydrocarbon receptor regulates IL-22 receptor expression on thymic epithelial cell and accelerates thymus regeneration

Improving regeneration of damaged thymus is important for reconstituting T-cell immunity. Interleukin-22 (IL-22) was proved to improve thymus regeneration through recovering thymic epithelial cells (TECs). The IL-22 receptor IL-22RA1 is crucial for mediating IL-22 functions. Mechanism that regulates IL-22RA1 expression is unknown. Through using TECs-conditional knockout mice, we found aryl hydrocarbon receptor (AHR) is important for thymus regeneration, because Foxn1-cre-mediated AHR knockout (AhrKO) significantly blocks recovery of thymus cells. Giving mice the AHR inhibitor CH-223191 or the AHR agonist FICZ blocks or accelerates thymus regeneration, respectively. AhrKO-mediated blockade of thymus regeneration could not be rescued by giving exogenous IL-22. Mechanistically, AhrKO mice shows decreased IL-22RA1 expression. In the murine TECs cell line mTEC1 cells, targeting AHR shows an impact on IL-22RA1 mRNA levels. Using chromatin immunoprecipitation and luciferase reporter assays, we find AHR co-operates with STAT3, binds the promotor region of IL-22RA1 gene and transcriptionally increases IL-22RA1 expression in mTEC1 cells. Foxn1-cre-mediated IL-22RA1 knockout (Il22ra1KO) blocks thymus regeneration after irradiation. Furthermore, targeting AHR or IL-22RA1 has significant impacts on severity of murine chronic graft-versus-host disease (cGVHD), which is an autoimmune-like complication following allogeneic hematopoietic cell transplantation. Giving FICZ decreases cGVHD, whereas Il22ra1KO exacerbates cGVHD. The impacts on cGVHD are associated with thymus regeneration and T-cell immune reconstitution. In conclusion, we report an unrecognized function of TECs-expressed AHR in thymus regeneration and AHR transcriptionally regulates IL-22RA1 expression, which have implications for improving thymus regeneration and controlling cGVHD.

Mesenchymal stromal cells ameliorate chronic GVHD by boosting thymic regeneration in a CCR9-dependent manner in mice

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Mature donor T cells within the graft contribute to severe damage of thymic epithelial cells (TECs), which are known as key mediators in the continuum of acute GVHD (aGVHD) and cGVHD pathology. Mesenchymal stromal cells (MSCs) are reportedly effective in the prevention and treatment of cGVHD. In our previous pilot clinical trial in patients with refractory aGVHD, the incidence and severity of cGVHD were decreased, along with an increase in levels of blood signal joint T-cell receptor excision DNA circles after MSCs treatment, which indicated an improvement in thymus function of patients with GVHD, but the mechanisms leading to these effects remain unknown. Here, we show in a murine GVHD model that MSCs promoted the quantity and maturity of TECs as well as elevated the proportion of Aire-positive medullary TECs, improving both CD4+CD8+ double-positive thymocytes and thymic regulatory T cells, balancing the CD4:CD8 ratio in the blood. In addition, CCL25-CCR9 signaling axis was found to play an important role in guiding MSC homing to the thymus. These studies reveal mechanisms through which MSCs ameliorate cGVHD by boosting thymic regeneration and offer innovative strategies for improving thymus function in patients with GVHD.

The potential role of the thymus in immunotherapies for acute myeloid leukemia

Understanding the factors which shape T-lymphocyte immunity is critical for the development and application of future immunotherapeutic strategies in treating hematological malignancies. The thymus, a specialized central lymphoid organ, plays important roles in generating a diverse T lymphocyte repertoire during the infantile and juvenile stages of humans. However, age-associated thymic involution and diseases or treatment associated injury result in a decline in its continuous role in the maintenance of T cell-mediated anti-tumor/virus immunity. Acute myeloid leukemia (AML) is an aggressive hematologic malignancy that mainly affects older adults, and the disease's progression is known to consist of an impaired immune surveillance including a reduction in naïve T cell output, a restriction in T cell receptor repertoire, and an increase in frequencies of regulatory T cells. As one of the most successful immunotherapies thus far developed for malignancy, T-cell-based adoptive cell therapies could be essential for the development of a durable effective treatment to eliminate residue leukemic cells (blasts) and prevent AML relapse. Thus, a detailed cellular and molecular landscape of how the adult thymus functions within the context of the AML microenvironment will provide new insights into both the immune-related pathogenesis and the regeneration of a functional immune system against leukemia in AML patients. Herein, we review the available evidence supporting the potential correlation between thymic dysfunction and T-lymphocyte impairment with the ontogeny of AML (II-VI). We then discuss how the thymus could impact current and future therapeutic approaches in AML (VII). Finally, we review various strategies to rejuvenate thymic function to improve the precision and efficacy of cancer immunotherapy (VIII).

T-Cell Progenitors As A New Immunotherapy to Bypass Hurdles of Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of preference for numerous malignant and non-malignant hemopathies. The outcome of this approach is significantly hampered by not only graft-versus-host disease (GvHD), but also infections and relapses that may occur because of persistent T-cell immunodeficiency following transplantation. Reconstitution of a functional T-cell repertoire can take more than 1 year. Thus, the major challenge in the management of allogeneic HSCT relies on the possibility of shortening the window of immune deficiency through the acceleration of T-cell recovery, with diverse, self-tolerant, and naïve T cells resulting from de novo thymopoiesis from the donor cells. In this context, adoptive transfer of cell populations that can give rise to mature T cells faster than HSCs while maintaining a safety profile compatible with clinical use is of major interest. In this review, we summarize current advances in the characterization of thymus seeding progenitors, and their ex vivo generated counterparts, T-cell progenitors. Transplantation of the latter has been identified as a worthwhile approach to shorten the period of immune deficiency in patients following allogeneic HSCT, and to fulfill the clinical objective of reducing morbimortality due to infections and relapses. We further discuss current opportunities for T-cell progenitor-based therapy manufacturing, including iPSC cell sources and off-the-shelf strategies. These opportunities will be analyzed in the light of results from ongoing clinical studies involving T-cell progenitors.

Activation of the zinc-sensing receptor GPR39 promotes T-cell reconstitution after hematopoietic cell transplant in mice

Prolonged lymphopenia represents a major clinical problem after cytoreductive therapies such as chemotherapy and the conditioning required for hematopoietic stem cell transplant (HCT), contributing to the risk of infections and malignant relapse. Restoration of T-cell immunity depends on tissue regeneration in the thymus, the primary site of T-cell development, although the capacity of the thymus to repair itself diminishes over its lifespan. However, although boosting thymic function and T-cell reconstitution is of considerable clinical importance, there are currently no approved therapies for treating lymphopenia. Here we found that zinc (Zn) is critically important for both normal T-cell development and repair after acute damage. Accumulated Zn in thymocytes during development was released into the extracellular milieu after HCT conditioning, where it triggered regeneration by stimulating endothelial cell production of BMP4 via the cell surface receptor GPR39. Dietary supplementation of Zn was sufficient to promote thymic function in a mouse model of allogeneic HCT, including enhancing the number of recent thymic emigrants in circulation although direct targeting of GPR39 with a small molecule agonist enhanced thymic function without the need for prior Zn accumulation in thymocytes. Together, these findings not only define an important pathway underlying tissue regeneration but also offer an innovative preclinical approach to treat lymphopenia in HCT recipients.

Towards a Better Understanding of the Atypical Features of Chronic Graft-Versus-Host Disease: A Report from the 2020 National Institutes of Health Consensus Project Task Force

Alloreactive and autoimmune responses after allogeneic hematopoietic cell transplantation can occur in non-classical chronic graft-versus-host disease (chronic GVHD) tissues and organ systems or manifest in atypical ways in classical organs commonly affected by chronic GVHD. The National Institutes of Health (NIH) consensus projects were developed to improve understanding and classification of the clinical features and diagnostic criteria for chronic GVHD. While still speculative whether atypical manifestations are entirely due to chronic GVHD, these manifestations remain poorly captured by the current NIH consensus project criteria. Examples include chronic GVHD impacting the hematopoietic system as immune mediated cytopenias, endothelial dysfunction, or as atypical features in the musculoskeletal system, central and peripheral nervous system, kidneys, and serous membranes. These purported chronic GVHD features may contribute significantly to patient morbidity and mortality. Most of the atypical chronic GVHD features have received little study, particularly within multi-institutional and prospective studies, limiting our understanding of their frequency, pathogenesis, and relation to chronic GVHD. This NIH consensus project task force report provides an update on what is known and not known about the atypical manifestations of chronic GVHD, while outlining a research framework for future studies to be undertaken within the next three to seven years. We also provide provisional diagnostic criteria for each atypical manifestation, along with practical investigation strategies for clinicians managing patients with atypical chronic GVHD features.

Thymus Degeneration and Regeneration

The immune system’s ability to resist the invasion of foreign pathogens and the tolerance to self-antigens are primarily centered on the efficient functions of the various subsets of T lymphocytes. As the primary organ of thymopoiesis, the thymus performs a crucial role in generating a self-tolerant but diverse repertoire of T cell receptors and peripheral T cell pool, with the capacity to recognize a wide variety of antigens and for the surveillance of malignancies. However, cells in the thymus are fragile and sensitive to changes in the external environment and acute insults such as infections, chemo- and radiation-therapy, resulting in thymic injury and degeneration. Though the thymus has the capacity to self-regenerate, it is often insufficient to reconstitute an intact thymic function. Thymic dysfunction leads to an increased risk of opportunistic infections, tumor relapse, autoimmunity, and adverse clinical outcome. Thus, exploiting the mechanism of thymic regeneration would provide new therapeutic options for these settings. This review summarizes the thymus’s development, factors causing thymic injury, and the strategies for improving thymus regeneration.

Non-classical manifestations of acute GVHD

Acute graft-versus-host disease (GVHD) is a major life-threatening complication after allogeneic hematopoietic cell transplantation (allo-HCT). The classical target organs of acute GVHD include the intestines, liver, and skin. The damage of these organs is relatively easy to detect for the clinician as diarrhea, increased bilirubin, and rash. However, there is increasing evidence that also other organs, where the acute damage is less apparent or more difficult to distinguish from drug toxicity, such as the central nervous system, the lungs, the ovaries and testis, the thymus, the bone marrow and the kidney, can be target organs of acute GVHD. Here, we review current evidence for non-classical manifestations of acute GVHD in rodent models and in patients and discuss them in the context of novel emerging therapies for GVHD. A better understanding of the involvement of the non-classical GVHD target organs may help to improve patient outcomes after allo-HCT.

Current Concepts and Advances in Graft-Versus-Host Disease Immunology

Worldwide, each year over 30,000 patients undergo an allogeneic hema-topoietic stem cell transplantation with the intent to cure high-risk hematologic malignancy, immunodeficiency, metabolic disease, or a life-threatening bone marrow failure syndrome. Despite substantial advances in donor selection and conditioning regimens and greater availability of allograft sources, transplant recipients still endure the morbidity and mortality of graft-versus-host disease (GVHD). Herein, we identify key aspects of acute and chronic GVHD pathophysiology, including host/donor cell effectors, gut dysbiosis, immune system and cytokine imbalance, and the interface between inflammation and tissue fibrosis. In particular, we also summarize the translational application of this heightened understanding of immune dysregulation in the design of novel therapies to prevent and treat GVHD.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: I. The 2020 Etiology and Prevention Working Group Report

Preventing chronic graft-versus-host disease (GVHD) remains challenging because the unique cellular and molecular pathways that incite chronic GVHD are poorly understood. One major point of intervention for potential prevention of chronic GVHD occurs at the time of transplantation when acute donor anti-recipient immune responses first set the events in motion that result in chronic GVHD. After transplantation, additional insults causing tissue injury can incite aberrant immune responses and loss of tolerance, further contributing to chronic GVHD. Points of intervention are actively being identified so that chronic GVHD initiation pathways can be targeted without affecting immune function. The major objective in the field is to continue basic studies and to translate what is learned about etiopathology to develop targeted prevention strategies that decrease the risk of morbid chronic GVHD without increasing the risks of cancer relapse or infection. Development of strategies to predict the risk of developing debilitating or deadly chronic GVHD is a high research priority. This working group recommends further interrogation into the mechanisms underpinning chronic GVHD development, and we highlight considerations for future trial design in prevention trials.

Dynamics of thymus function and T cell receptor repertoire breadth in health and disease

T cell recognition of unknown antigens relies on the tremendous diversity of the T cell receptor (TCR) repertoire; generation of which can only occur in the thymus. TCR repertoire breadth is thus critical for not only coordinating the adaptive response against pathogens but also for mounting a response against malignancies. However, thymic function is exquisitely sensitive to negative stimuli, which can come in the form of acute insult, such as that caused by stress, infection, or common cancer therapies; or chronic damage such as the progressive decline in thymic function with age. Whether it be prolonged T cell deficiency after hematopoietic cell transplantation (HCT) or constriction in the breadth of the peripheral TCR repertoire with age; these insults result in poor adaptive immune responses. In this review, we will discuss the importance of thymic function for generation of the TCR repertoire and how acute and chronic thymic damage influences immune health. We will also discuss methods that are used to measure thymic function in patients and strategies that have been developed to boost thymic function.

Monogenic Immune Diseases Provide Insights Into the Mechanisms and Treatment of Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (GvHD) has become a leading cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HSCT) and can burden patients with devastating and lifelong health effects. Our understanding of the pathogenic mechanisms underlying chronic GvHD remains incomplete and this lack of understanding is reflected by lack of clear therapeutic approaches to steroid refractory disease. Observations predominantly from mouse models and human correlative studies currently support a three phase model for the initiation and development of chronic GvHD: 1) early inflammation and tissue damage triggers the innate immune system. This leads to inflammatory cytokine/chemokine patterns that recruit effector immune cell populations; 2) chronic inflammation causes the loss of central and peripheral tolerance mechanisms leading to emergence of pathogenic B and T cell populations that promote autoimmune and alloimmune reactions; 3) the dysregulated immunity causes altered macrophage polarization, aberrant tissue repair leading to scarring and end organ fibrosis. This model has led to the evaluation of many new therapies aimed at limiting inflammation, targeting dysregulated signaling pathways and restoring tolerance mechanisms. However, chronic GvHD is a multisystem disease with complex clinical phenotypes and it remains unclear as to which cluster of patients will respond best to specific therapeutic strategies. However, it is possible to gain novel insights from immune-related monogenic diseases. These diseases either share common clinical manifestations, replicate steps from the three phase chronic GvHD model or serve as surrogates for perfectly targeted drugs being investigated in chronic GvHD therapy. In this review, we will summarize the evidence from these monogenic immune related diseases that provide insight into pathogenic pathways in chronic GvHD, rationales for current therapies and novel directions for future drug discovery.

Thymic origins of autoimmunity-lessons from inborn errors of immunity

During their intrathymic development, nascent T cells are empowered to protect against pathogens and to be operative for a life-long acceptance of self. While autoreactive effector T (Teff) cell progenitors are eliminated by clonal deletion, the intrathymic mechanisms by which thymic regulatory T cell (tTreg) progenitors maintain specificity for self-antigens but escape deletion to exert their regulatory functions are less well understood. Both tTreg and Teff development and selection result from finely coordinated interactions between their clonotypic T cell receptors (TCR) and peptide/MHC complexes expressed by antigen-presenting cells, such as thymic epithelial cells and thymic dendritic cells. tTreg function is dependent on expression of the FOXP3 transcription factor, and induction of FOXP3 gene expression by tTreg occurs during their thymic development, particularly within the thymic medulla. While initial expression of FOXP3 is downstream of TCR activation, constitutive expression is fixed by interactions with various transcription factors that are regulated by other extracellular signals like TCR and cytokines, leading to epigenetic modification of the FOXP3 gene. Most of the understanding of the molecular events underlying tTreg generation is based on studies of murine models, whereas gaining similar insight in the human system has been very challenging. In this review, we will elucidate how inborn errors of immunity illuminate the critical non-redundant roles of certain molecules during tTreg development, shedding light on how their abnormal development and function cause well-defined diseases that manifest with autoimmunity alone or are associated with states of immune deficiency and autoinflammation.

Dynamic of plasma IL-22 level is an indicator of thymic output after allogeneic hematopoietic cell transplantation

AIMS

Interleukin-22 (IL-22) promotes thymus recovery and improves T-cell recovery in preclinical allogeneic hematopoietic cell transplant models. However, the correlation between IL-22 and thymus recovery is unknown in human transplant.

MATERIALS AND METHODS

In this study, plasma IL-22 levels of transplanted humans were analyzed peri-transplant. Thymic output was assessed by detecting blood signal joint T-cell receptor excision circles (TRECs). Flow cytometry was applied to measure T-cell subsets.

KEY FINDINGS

Plasma IL-22 level positively correlated with blood TRECs level at days 14 and 28 posttransplant. Multiple linear regression analysis showed plasma IL-22 level, occurrence of acute graft-versus-host disease (aGVHD) and age were significantly associated with blood TRECs level at day 28 after allotransplant. An increase of plasma IL-22 level during day 14 and day 28 correlated with faster recovery of blood TRECs and naïve T-cell levels in allotransplant recipients. Recipients with high TRECs levels at day 28 had lower incidence of aGVHD comparing with those who with low TRECs levels according to a median split of their TRECs levels, an effect also seen in the high IL-22 level and low IL-22 level cohorts. Other factors such as age and infection had impacts on plasma IL-22 level in allotransplants.

SIGNIFICANCE

Our findings suggest that dynamic change of plasma IL-22 level is an indicator of thymic output and occurrence of aGVHD. Monitoring plasma IL-22 level might help to assess recovery of thymus function in human allotransplants.

The role of the thymus in allogeneic bone marrow transplantation and the recovery of the peripheral T-cell compartment

As the thymus represents the primary site of T-cell development, optimal thymic function is of paramount importance for the successful reconstitution of the adaptive immunity after allogeneic hematopoietic stem cell transplantation. Thymus involutes as part of the aging process and several factors, including previous chemotherapy treatments, conditioning regimen used in preparation to the allograft, occurrence of graft-versus-host disease, and steroid therapy that impair the integrity of the thymus, thus affecting its role in supporting T-cell neogenesis. Although the pathways governing its regeneration are still poorly understood, the thymus has a remarkable capacity to recover its function after damage. Measurement of both recent thymic emigrants and T-cell receptor excision circles is valuable tools to assess thymic output and gain insights on its function. In this review, we will extensively discuss available data on factors regulating thymic function after allogeneic hematopoietic stem cell transplantation, as well as the strategies and therapeutic approaches under investigation to promote thymic reconstitution and accelerate immune recovery in transplanted patients, including the use of cytokines, sex-steroid ablation, precursor T-cells, and thymus bioengineering. Although none of them is routinely used in the clinic, these approaches have the potential to enhance thymic function and immune recovery, not only in patients given an allograft but also in other conditions characterized by immune deficiencies related to a defective function of the thymus.

Graft-versus-host disease reduces lymph node display of tissue-restricted self-antigens and promotes autoimmunity

Acute graft-versus-host disease (GVHD) is initially triggered by alloreactive T cells, which damage peripheral tissues and lymphoid organs. Subsequent transition to chronic GVHD involves the emergence of autoimmunity, although the underlying mechanisms driving this process are unclear. Here, we tested the hypothesis that acute GVHD blocks peripheral tolerance of autoreactive T cells by impairing lymph node (LN) display of peripheral tissue–restricted antigens (PTAs). At the initiation of GVHD, LN fibroblastic reticular cells (FRCs) rapidly reduced expression of genes regulated by DEAF1, an autoimmune regulator-like transcription factor required for intranodal expression of PTAs. Subsequently, GVHD led to the selective elimination of the FRC population, and blocked the repair pathways required for its regeneration. We used a transgenic mouse model to show that the loss of presentation of an intestinal PTA by FRCs during GVHD resulted in the activation of autoaggressive T cells and gut injury. Finally, we show that FRCs normally expressed a unique PTA gene signature that was highly enriched for genes expressed in the target organs affected by chronic GVHD. In conclusion, acute GVHD damages and prevents repair of the FRC network, thus disabling an essential platform for purging autoreactive T cells from the repertoire.

Outcome of Non-hematological Autoimmunity After Hematopoietic Cell Transplantation in Children with Primary Immunodeficiency

PURPOSE

Knowledge of post-hematopoietic cell transplantation (HCT) non-hematological autoimmune disease (AD) is far from satisfactory.

METHOD

This multicenter retrospective study focuses on incidence, risk factors, and outcomes of post-HCT AD in 596 children with primary immunodeficiency (PID) who were transplanted from 2009 to 2018.

RESULTS

The indications of HCT were severe combined immunodeficiency (SCID, n = 158, 27%) and non-SCID PID (n = 438, 73%). The median age at HCT was 2.3 years (range, 0.04 to 18.3 years). The 5-year overall survival for the entire cohort was 79% (95% cumulative incidence (CIN), 74-83%). The median follow-up of surviving patients was 4.3 years (0.08 to 14.7 years). The CIN of post-HCT AD was 3% (2-5%) at 1 year post-HCT, 7% (5-11%) at 5 years post-HCT, and 11% (7-17%) at 8 years post-HCT. The median onset of post-HCT AD was 2.2 years (0.12 to 9.6 years). Autoimmune thyroid disorder (n = 19, 62%) was the most common post-HCT AD, followed by neuromuscular disorders (n = 7, 22%) and rheumatological manifestations (n = 5, 16%). All patients but one required treatment for post-HCT AD. After multivariate analysis, age at transplant (p = 0.01) and T cell-depleted graft (p < 0.001) were significant predictors of post-HCT AD. None of the T cell-depleted graft recipients developed post-HCT AD. Patients with a lower CD3+ count at 6 months post-HCT had a significant higher incidence of post-HCT AD compared to disease controls. Graft-versus-host disease, viral infection, and donor chimerism had no association with post-HCT AD.

CONCLUSION

Post-HCT AD occurred in 11% at 8 years post-HCT and its occurrence was associated with older age at HCT and unmanipulated graft.

T cell regeneration after immunological injury

Following periods of haematopoietic cell stress, such as after chemotherapy, radiotherapy, infection and transplantation, patient outcomes are linked to the degree of immune reconstitution, specifically of T cells. Delayed or defective recovery of the T cell pool has significant clinical consequences, including prolonged immunosuppression, poor vaccine responses and increased risks of infections and malignancies. Thus, strategies that restore thymic function and enhance T cell reconstitution can provide considerable benefit to individuals whose immune system has been decimated in various settings. In this Review, we focus on the causes and consequences of impaired adaptive immunity and discuss therapeutic strategies that can recover immune function, with a particular emphasis on approaches that can promote a diverse repertoire of T cells through de novo T cell formation.

When the Damage Is Done: Injury and Repair in Thymus Function

Even though the thymus is exquisitely sensitive to acute insults like infection, shock, or common cancer therapies such as cytoreductive chemo- or radiation-therapy, it also has a remarkable capacity for repair. This phenomenon of endogenous thymic regeneration has been known for longer even than its primary function to generate T cells, however, the underlying mechanisms controlling the process have been largely unstudied. Although there is likely continual thymic involution and regeneration in response to stress and infection in otherwise healthy people, acute and profound thymic damage such as that caused by common cancer cytoreductive therapies or the conditioning regimes as part of hematopoietic cell transplantation (HCT), leads to prolonged T cell deficiency; precipitating high morbidity and mortality from opportunistic infections and may even facilitate cancer relapse. Furthermore, this capacity for regeneration declines with age as a function of thymic involution; which even at steady state leads to reduced capacity to respond to new pathogens, vaccines, and immunotherapy. Consequently, there is a real clinical need for strategies that can boost thymic function and enhance T cell immunity. One approach to the development of such therapies is to exploit the processes of endogenous thymic regeneration into novel pharmacologic strategies to boost T cell reconstitution in clinical settings of immune depletion such as HCT. In this review, we will highlight recent work that has revealed the mechanisms by which the thymus is capable of repairing itself and how this knowledge is being used to develop novel therapies to boost immune function.

H60: A Unique Murine Hematopoietic Cell-Restricted Minor Histocompatibility Antigen for Graft-versus-Leukemia Effect

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important treatment for many types of hematological malignancies. Matching of donor and recipient for the major histocompatibility complex (MHC) improves the HSCT reconstitution, but donor-derived T cells reactive to non-MHC encoded minor histocompatibility antigens (MiHAs) can induce graft-versus-host disease (GVHD) while also being needed for graft-versus-leukemia (GVL) effects. MiHAs are allelically variant self-peptides presented conventionally on MHC molecules, but are alloantigenic in transplantation settings. Immunodominant MiHAs are most strongly associated with GVHD and GVL. There is need for mouse paradigms to understand these contradictory effects. H60 is a highly immunodominant mouse MiHA with hematopoietic cell-restricted expression. Immunodominance of H60 is tightly associated with its allelic nature (presence vs. absence of the transcripts), and the qualitative (TCR diversity) and quantitative (frequency) traits of the reactive T cells. The identity as a hematopoietic cell-restricted antigen (HRA) of H60 assists the appearance of the immunodominace in allo-HSCT circumstances, and generation of GVL effects without induction of serious GVHD after adoptive T cell transfer. Also it allows the low avidity T cells to escape thymic negative selection and exert GVL effect in the periphery, which is a previously unevaluated finding related to HRAs. In this review, we describe the molecular features and immunobiology in detail through which H60 selectively exerts its potent GVL effect. We further describe how lessons learned can be extrapolated to human allo-HCST.

One-two punch injury to tolerance mechanisms in graft-versus-host disease

Chronic graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic cell transplantation that resembles autoimmunity, with unclear pathogenesis and few effective therapeutic options. In this issue of the JCI, Dertschnig et al. used mouse models to investigate the basis of T cell autoreactivity following GVHD. Notably, GVHD caused irreversible damage to a population of tolerogenic stromal cells that display peripheral tissue-restricted antigens in lymph nodes, which impaired their capacity to purge and suppress autoreactive T cells. Together with damage to central tolerance mechanisms in the thymus, these findings outline a critical one-two punch injury that profoundly disrupts immune tolerance in this devastating disease.

Long-term outcomes of ruxolitinib therapy in steroid-refractory graft-versus-host disease in children and adults

Acute and chronic steroid-refractory graft-versus-host disease (srGVHD) is a life-threatening complication of allogeneic stem cell transplantation. There are a number of reports on case series describing efficacy of ruxolitinib in both acute and chronic srGVHD. We conducted a prospective study (NCT02997280) in 75 patients with srGVHD (32 acute, 43 chronic, 41 adults, and 34 children). Patients with chronic GVHD had severe disease in 83% of cases, and acute GVHD patients had grade III-IV disease in 66% of cases. The overall response rate (ORR) was 75% (95% CI 57-89%) in acute GVHD and 81% (95% CI 67-92%) in chronic. Overall survival was 59% (95% CI 49-74%) in acute group and 85% (95% CI 70-93%). The major risk factors for lower survival were grade III-IV gastrointestinal involvement (29% vs 93%, p = 0.0001) in acute form and high disease risk score in chronic (65% vs 90%, p = 0.038). Toxicity was predominantly hematologic with 79% and 44% of grade III-IV neutropenia in acute and chronic groups, respectively. There was no difference between adults and children in terms of ORR (p = 0.31, p = 0.35), survival (p = 0.44, p = 0.12) and toxicity (p > 0.93). The study demonstrated that ruxolitinib is an effective option in acute and chronic srGVHD and can be used both in adults and children.

IL-22 Accelerates Thymus Regeneration via Stat3/Mcl-1 and Decreases Chronic Graft-versus-Host Disease in Mice after Allotransplants

High-dose chemotherapy and/or radiation given before an allogeneic hematopoietic cell transplantation severely damage thymic epithelial cells (TECs), resulting in poor post-transplant immune recovery. IL-22 mediates recovery of TECs via a proregenerative effect, but the precise mechanism by which this occurs is unknown. In this study, we found IL-22 improved thymus recovery after damage from irradiation in association with increased number of TECs. This effect was blocked by ruxolitinib, a JAK1/JAK2 inhibitor. IL-22 increased the number of TECs via a Stat3-dependent signaling in the mTEC1 murine thymic epithelial cell line. This, in turn, upregulated transcription of myeloid cell leukemia sequence 1 (Mcl1), resulting in increased number of TECs. Similar effects were seen in irradiated mice given IL-22. Defects in IL-22 resulted in delayed thymus recovery in irradiated mice and had an impact on levels of thymus function-related genes such as Foxn1, Aire, and Kgf. In mice, post-transplant use of IL-22 improved repair of TECs, increased the numbers of thymus T cells, increased the intrathymic levels of Aire, and increased the proportion of natural regulatory T cells, resulting in decreased severity of chronic graft-versus-host disease (GVHD). Our data highlight the critical role of the IL-22/Stat3/Mcl-1 pathway in the regeneration of TECs after damage from irradiation in mice and highlight circumstances where normalizing thymus T cell function with IL-22 decreases GVHD after allotransplants.

Keratinocyte growth factor impairs human thymic recovery from lymphopenia

BACKGROUND

The lymphocyte-depleting antibody alemtuzumab is a highly effective treatment of relapsing-remitting multiple sclerosis (RRMS); however 50% of patients develop novel autoimmunity post-treatment. Most at risk are individuals who reconstitute their T-cell pool by proliferating residual cells, rather than producing new T-cells in the thymus; raising the possibility that autoimmunity might be prevented by increasing thymopoiesis. Keratinocyte growth factor (palifermin) promotes thymopoiesis in non-human primates.

METHODS

Following a dose-tolerability sub-study, individuals with RRMS (duration ≤10 years; expanded disability status scale ≤5·0; with ≥2 relapses in the previous 2 years) were randomised to placebo or 180mcg/kg/day palifermin, given for 3 days immediately prior to and after each cycle of alemtuzumab, with repeat doses at M1 and M3. The interim primary endpoint was naïve CD4+ T-cell count at M6. Exploratory endpoints included: number of recent thymic-emigrants (RTEs) and signal-joint T-cell receptor excision circles (sjTRECs)/mL of blood. The trial primary endpoint was incidence of autoimmunity at M30.

FINDINGS

At M6, individuals receiving palifermin had fewer naïve CD4+T-cells (2.229x107/L vs. 7.733x107/L; p=0.007), RTEs (16% vs. 34%) and sjTRECs/mL (1100 vs. 3396), leading to protocol-defined termination of recruitment. No difference was observed in the rate of autoimmunity between the two groupsConclusion: In contrast to animal studies, palifermin reduced thymopoiesis in our patients. These results offer a note of caution to those using palifermin to promote thymopoiesis in other settings, particularly in the oncology/haematology setting where alemtuzumab is often used as part of the conditioning regime.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01712945Funding: MRC and Moulton Charitable Foundation.

Donor T-cell-derived interleukin-22 promotes thymus regeneration and alleviates chronic graft-versus-host disease in murine allogeneic hematopoietic cell transplant

Defect of thymus results in poor posttransplant immune recovery and dysfunction of immune tolerance after allogeneic hematopoietic cell transplants (allo-HCT). Improving thymus regeneration represents a potential strategy to accelerate recovery of T-cell immunity. IL-22 was reported to mediate thymus regeneration after injury. In this study, we found donor T-cell is a major source of IL-22 in allotransplant recipient. Through applying IL-22 knock out (IL-22KO) mice in allo-HCT, we found donor T-cell derived IL-22 promotes thymus regeneration in association with increased level of intra-thymic IL-22. IL-22KO T-cell-transplanted recipients show deficient thymus recovery which is reversed by injection of exogenous IL-22. T-cell derived IL-22 promotes proliferation of thymic epithelial cells (TECs) in vitro. In addition, donor T-cell derived IL-22 increases expression level of Aire in the thymus and decreases skin chronic graft-versus-host disease (GVHD). Furthermore, short-term use of exogenous IL-22 posttransplant accelerates recovery of thymus without increasing severity of acute GVHD. Our data indicate that cross-talk between T-cell and TECs is an important mechanism to mediate reconstitution of T-cell immunity after allo-HCT.

[The role of IL-22 in T cell reconstitution after thymus damage induced by ionizing radiation]

Objective: To explore the levels of IL-22 in thymus damaged by γ-ray total body irradiation (TBI), and to study the role of IL-22 in T cell reconstitution after thymic injury induced by TBI. Methods: To induce thymic injury, mice were treated by sub-lethal TBI. Levels of intra-thymic and circulatory IL-22 were detected by using ELISA assay. Untreated mice were used as control. After receiving sub-lethal TBI, mice were intraperitoneally injected with PBS or recombinant mouse IL-22, which were marked as TBI+PBS or TBI+IL-22, respectively. Mice were monitored for counts of total thymic cells and circulatory white blood cells. Flow cytometry was applied to analyze percentages of thymic epithelial cells (TEC), thymocyte subsets and circulatory T cells. Real-time PCR assay was applied to analyze the mRNA expression levels of Foxn1, Ccl25, Aire and Dll4 in thymus. Results: ①Sub-lethal TBI treated mice expressed higher levels of intra-thymic and circulatory IL-22, compared with untreated ones (all P<0.05). ②After injection of recombinant IL-22, TBI+IL-22 mice had higher levels of intra-thymic IL-22 than TBI+PBS mice (all P<0.05). ③On day 14 after irradiation, real-time PCR assay showed that TBI+IL-22 mice had higher mRNA levels of Foxn1, Ccl25, Aire and Dll4 in thymus compared with TBI+PBS ones. Meanwhile, the TBI+IL-22 mice had higher counts of total thymic cells[(5.93±3.19)×10(6)/ml vs (1.42±0.46)×10(6)/ml, t=3.128, P=0.033] and circulatory white blood cells[(3.08±0.94)×10(6)/ml vs (1.43±0.30)×10(6)/ml, t=3.730, P=0.015] than those of TBI+PBS mice. Flow cytometry analysis indicated that TBI+IL-22 mice had higher counts of TEC and thymocytes than TBI+PBS mice on day 14 after irradiation (all P<0.05). On days 7 and 14 after irradiation, TBI+IL-22 mice had higher counts of circulatory white blood cells and T cells than TBI+PBS mice (all P<0.05). Conclusion: Sub-lethal TBI induces upregulation of intra-thymic IL-22, and injecting of recombinant IL-22 increases level of IL-22 in thymus. Injecting of recombinant IL-22 improves recovery of TEC and increases numbers of thymocyte subsets and circulatory T cell after thymic injury.

Sociodemographic and psychological determinants of influenza vaccine intention among recipients of autologous and allogeneic haematopoietic stem cell transplant: a cross-sectional survey of UK transplant recipients using a modified health belief model

OBJECTIVES

Studies exploring vaccination rates among haematopoietic stem cell transplant (HSCT) recipients have focused on physician factors that limit uptake. Understanding the patient factors that determine vaccination intention is crucial to delivering a successful vaccination programme. Using a modified health belief model (mHBM), we conducted a cross-sectional survey with the objective of exploring the sociodemographic and psychological factors that determined autologous and allogeneic HSCT recipients' intention to receive the seasonal inactivated influenza vaccine (SIIV) during the 2015-2016 influenza season.

SETTING

The setting of our study was three tertiary level, UK National Health Service (NHS) autologous and allogeneic HSCT centres.

PARTICIPANTS

Eligible patients were aged 16 years or over and recipients of autologous or allogeneic HSCT for any disease indication, with no absolute contraindication to receiving the SIIV during the next influenza season, and having not received the SIIV since transplant. 93 participants from 3 UK NHS HSCT centres completed an anonymous study-specific questionnaire. 78.5% were recipients of allogeneic and 21.5% autologous HSCT.

RESULTS

23.7% of participants expressed low intent to receive the SIIV. Patients aged over 65 (OR 0.02, 95% CI 0.01 to 0.57, p=0.02) and those who had not received the SIIV prior to HSCT (OR 0.04, 95% CI 0.02 to 0.56, p=0.02) were less likely to have high intent. A multivariate logistic regression model incorporating constructs of the mHBM was statistically significant (p<0.001) and explained 74.7% of variation in SIIV intention. More patients felt that a recommendation from their HSCT team than their general practitioner would prompt them to receive the SIIV, and this was most pronounced in those who had low intent.

CONCLUSIONS

The mHBM may provide a useful structure for addressing low vaccine intent among HSCT recipients and further interventional studies are warranted. We would encourage HSCT and general practitioners to discuss SIIV intention as a routine part of care.

Restoring T Cell Homeostasis After Allogeneic Stem Cell Transplantation; Principal Limitations and Future Challenges

For several leukemia patients, allogeneic stem cell transplantation (allogeneic-SCT) is the unique therapeutic modality that could potentially cure their disease. Despite significant progress made in clinical management of allogeneic-SCT, acute graft-versus-host disease (aGVHD) and infectious complications remain the second and third cause of death after disease recurrence. Clinical options to restore immunocompetence after allogeneic-SCT are very limited as studies have raised awareness about the safety with regards to graft-versus-host disease (GVHD). Preclinical works are now focusing on strategies to improve thymic functions and to restore the peripheral niche that have been damaged by alloreactive T cells. In this mini review, we will provide a brief overview about the adverse effects of GVHD on the thymus and the peripheral niche and the resulting negative outcome on peripheral T cell homeostasis. Finally, we will discuss the potential relevance of coordinating our studies on thymic rejuvenation and improvement of the peripheral lymphoid niche to achieve optimal T cell regeneration in GVHD patients.

Aire Disruption Influences the Medullary Thymic Epithelial Cell Transcriptome and Interaction With Thymocytes

The function of medullary thymic epithelial cells (mTECs) is associated with thymocyte adhesion, which is crucial for the negative selection of autoreactive thymocytes in the thymus. This process represents the root of central tolerance of self-components and prevents the onset of autoimmune diseases. Since thymic epithelia correspond to an important target of donor T cells during the onset of chronic graft-vs-host-disease, mTEC-thymocyte adhesion may have implications for alloimmunity. The Aire and Fezf2 genes function as transcriptome controllers in mTECs. The central question of this study is whether there is a mutual relationship between mTEC-thymocyte adhesion and the control of the mTEC transcriptome and whether Aire is involved in this process. Here, we show that in vitro mTEC-thymocyte adhesion causes transcriptome changes in mTECs and upregulates the transcriptional expression of Aire and Fezf2, as well as cell adhesion-related genes such as Cd80 or Tcf7, among others. Crispr-Cas9-mediated Aire gene disruption demonstrated that this gene plays a role in the process of mTEC-thymocyte adhesion. Consistent with the nuclear localization signal (NLS) encoded by Aire exon 3, which was targeted, we demonstrate that Aire KO-/- mTECs impair AIRE protein localization in the nucleus. Consequently, the loss of function of Aire reduced the ability of these cells to adhere to thymocytes. Their transcriptomes differed from their wild-type Aire+/+ counterparts, even during thymocyte adhesion. A set of mRNA isoforms that encode proteins involved in cell adhesion were also modulated during this process. This demonstrates that both thymocyte interactions and Aire influence transcriptome profiling of mTEC cells.

Twenty Years of AIRE

About two decades ago, cloning of the autoimmune regulator (AIRE) gene materialized one of the most important actors on the scene of self-tolerance. Thymic transcription of genes encoding tissue-specific antigens (ts-ags) is activated by AIRE protein and embodies the essence of thymic self-representation. Pathogenic AIRE variants cause the autoimmune polyglandular syndrome type 1, which is a rare and complex disease that is gaining attention in research on autoimmunity. The animal models of disease, although not identically reproducing the human picture, supply fundamental information on mechanisms and extent of AIRE action: thanks to its multidomain structure, AIRE localizes to chromatin enclosing the target genes, binds to histones, and offers an anchorage to multimolecular complexes involved in initiation and post-initiation events of gene transcription. In addition, AIRE enhances mRNA diversity by favoring alternative mRNA splicing. Once synthesized, ts-ags are presented to, and cause deletion of the self-reactive thymocyte clones. However, AIRE function is not restricted to the activation of gene transcription. AIRE would control presentation and transfer of self-antigens for thymic cellular interplay: such mechanism is aimed at increasing the likelihood of engagement of the thymocytes that carry the corresponding T-cell receptors. Another fundamental role of AIRE in promoting self-tolerance is related to the development of thymocyte anergy, as thymic self-representation shapes at the same time the repertoire of regulatory T cells. Finally, AIRE seems to replicate its action in the secondary lymphoid organs, albeit the cell lineage detaining such property has not been fully characterized. Delineation of AIRE functions adds interesting data to the knowledge of the mechanisms of self-tolerance and introduces exciting perspectives of therapeutic interventions against the related diseases.

B-cell targeting in chronic graft-versus-host disease

Over the last decade, our understanding of the pathophysiology of chronic graft-versus-host disease (cGVHD) has improved considerably. In this spotlight, we discuss emerging insights into the pathophysiology of cGVHD with a focus on B cells. First, we summarize supporting evidence derived from mouse and human studies. Next, novel cGVHD therapy approaches that target B cells will be covered to provide treating physicians with an overview of the rationale behind the emerging armamentarium against cGVHD.

Escape from thymic deletion and anti-leukemic effects of T cells specific for hematopoietic cell-restricted antigen

Whether hematopoietic cell-restricted distribution of antigens affects the degree of thymic negative selection has not been investigated in detail. Here, we show that T cells specific for hematopoietic cell-restricted antigens (HRA) are not completely deleted in the thymus, using the mouse minor histocompatibility antigen H60, the expression of which is restricted to hematopoietic cells. As a result, low avidity T cells escape from thymic deletion. This incomplete thymic deletion occurs to the T cells developing de novo in the thymus of H60-positive recipients in H60-mismatched bone marrow transplantation (BMT). H60-specific thymic deletion escapee CD8⁺ T cells exhibit effector differentiation potentials in the periphery and contribute to graft-versus-leukemia effects in the recipients of H60-mismatched BMT, regressing H60⁺ hematological tumors. These results provide information essential for understanding thymic negative selection and developing a strategy to treat hematological tumors.

Insights into immune tolerance from AIRE deficiency

AIRE is a well-established master regulator of central tolerance. It plays an essential role in driving expression of tissue-specific antigens in the thymus and shaping the development of positively selected T-cells. Humans and mice with compromised or absent AIRE function have markedly variable phenotypes that include a range of autoimmune manifestations. Recent evidence suggests that this variability stems from cooperation of autoimmune susceptibilities involving both central and peripheral tolerance checkpoints. Here we discuss the broadening understanding of the factors that influence Aire expression, modify AIRE function, and the impact and intersection of AIRE with peripheral immunity. This rapidly expanding body of knowledge will force a reexamination of the definition and clinical management of APS-1 patients as well as provide a foundation for the development of immunomodulatory strategies targeting central tolerance.

Immune Reconstitution after Allogeneic Hematopoietic Stem Cell Transplantation: Time To T Up the Thymus

The success of allogeneic hematopoietic stem cell transplantation, a key treatment for many disorders, is intertwined with T cell immune reconstitution. The thymus plays a key role post allogeneic hematopoietic stem cell transplantation in the generation of a broad but self-tolerant T cell repertoire, but it is exquisitely sensitive to a range of insults during the transplant period, including conditioning regimens, corticosteroids, infections, and graft-versus-host disease. Although endogenous thymic repair is possible it is often suboptimal, and there is a need to develop exogenous strategies to help regenerate the thymus. Therapies currently in clinical trials in the transplant setting include keratinocyte growth factor, cytokines (IL-7 and IL-22), and hormonal modulation including sex steroid inhibition and growth hormone administration. Such regenerative strategies may ultimately enable the thymus to play as prominent a role after transplant as it once did in early childhood, allowing a more complete restoration of the T cell compartment.

T-cell receptor αβ+ and CD19+ cell-depleted haploidentical and mismatched hematopoietic stem cell transplantation in primary immune deficiency

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (HSCT) is used as a therapeutic approach for primary immunodeficiencies (PIDs). The best outcomes have been achieved with HLA-matched donors, but when a matched donor is not available, a haploidentical or mismatched unrelated donor (mMUD) can be useful. Various strategies are used to mitigate the risk of graft-versus-host disease (GvHD) and rejection associated with such transplants.

OBJECTIVE

We sought to evaluate the outcomes of haploidentical or mMUD HSCT after depleting GvHD-causing T-cell receptor (TCR) αβ CD3⁺ cells from the graft.

METHODS

CD3⁺TCRαβ⁺/CD19⁺ depleted grafts were given in conditioned (except 3) children with PIDs. Treosulfan (busulfan in 1 patient), fludarabine, thiotepa, and anti-thymocyte globulin or alemtuzumab conditioning were used in 77% of cases, and all but 4 received GvHD prophylaxis.

RESULTS

Twenty-five patients with 12 types of PIDs received 26 HSCTs. Three underwent transplantation for refractory GvHD that developed after the first cord transplantation. At a median follow-up of 20.8 months (range, 5 month-3.3 years), 21 of 25 patients survived and were cured of underlying immunodeficiency. Overall and event-free survival at 3 years were 83.9% and 80.4%, respectively. Cumulative incidence of grade II to IV acute GvHD was 22% ± 8.7%. No case of visceral or chronic GvHD was seen. Cumulative incidences of graft failure, cytomegalovirus, and/or adenoviral infections and transplant-related mortality at 1 year were 4.2% ± 4.1%, 58.8% ± 9.8%, and 16.1% ± 7.4%, respectively. Patients undergoing transplantation with systemic viral infections had poor survival in comparison with those with absent or resolved infections (33.3% vs 100%).

CONCLUSION

CD3⁺TCRαβ⁺ and CD19⁺ cell-depleted haploidentical or mMUD HSCT is a practical and viable alternative for children with a range of PIDs.

Proinflammatory Dual Receptor T Cells in Chronic Graft-versus-Host Disease

Defective post-transplantation thymopoiesis is associated with chronic graft-versus-host disease (GVHD), a multiorgan pathology affecting up to 80% of patients after allogeneic hematopoietic stem cell transplantation (HSCT). Previous work demonstrated that the subset of T cells expressing 2 T cell receptors (TCRs) is predisposed to alloreactivity, driving selective and disproportionate activity in acute GVHD in both mouse models and HSCT patients. Here we investigate a potential role for this pathogenic T cell subset in chronic GVHD (cGVHD). HSCT patients with cGVHD demonstrated increased numbers of dual TCR cells in circulation. These dual receptor cells had an activated phenotype, indicating an active role in cGVHD. Notably, single-cell RNA sequencing identified the increased dual TCR cells in cGVHD as predominantly expressing Tbet, indicative of a proinflammatory phenotype. These results identify dual TCR cells as specific mediators of pathogenic inflammation underlying cGVHD and highlight Tbet-driven T cell function as a potential pathway for potential therapeutic targeting.

Pre-transplantation thymic function is associated with the risk of acute graft versus host disease and cytomegalovirus viremia after allogeneic hematopoietic stem cell transplantation

OBJECTIVES

To analyze the kinetics of T-cell subsets and thymic function reconstitution after allogeneic hematopoietic stem cell transplantation (AHSCT); to determine whether sjTREC (signal joint TCR rearrangement excision circle) and CD31-positive recent thymic emigrant (CD31 + RTE) are correlated with acute graft versus host disease (aGVHD) or CMV (cytomegalovirus) viremia after AHSCT.

METHODS

Forty-nine patients who underwent AHSCT in our institution were prospectively enrolled. Periphery blood samples were collected before conditioning and at 1, 2, 3 months after AHSCT. T-cell subsets were analyzed with flow cytometry. Genomic DNA was purified from peripheral blood mononuclear cells (PBMCs), and sjTREC was quantified by real-time PCR. Impact of sjTREC and CD31 + RTE on aGVHD and CMV viremia was evaluated by univariate and multivariate Cox regression analyses.

RESULTS

The analyzed T-cell subsets and sjTREC of patients before AHSCT were all significantly lower than those of healthy donors (p < 0.05). sjTREC and CD31 + RTE were remarkably decreased in 3 months after AHSCT (p < 0.05). Patients with lower pre-transplantation sjTREC and CD31 + RTE level had higher incidence of CMV viremia after AHSCT (p < 0.05). sjTREC/10⁶ PBMCs was negatively correlated with aGVHD (p = 0.024).

CONCLUSION

Thymic function was impaired before transplantation, and was consistently decreased in 3 months after AHSCT. Patients who had lower pre-transplantation sjTREC level were at high risk of aGVHD and CMV viremia after AHSCT, low pre-transplantation CD31 + RTE was correlated with CMV viremia after AHSCT.

Treatment of Pediatric Acute Graft-versus-Host Disease-Lessons from Primary Immunodeficiency?

Allogeneic hematopoietic stem cell transplant (HSCT) is used to treat increasing numbers of malignant and non-malignant disorders. Despite significant advances in improved human leukocyte antigens-typing techniques, less toxic conditioning regimens and better supportive care, resulting in improved clinical outcomes, acute graft-versus-host disease (aGvHD) continues to be a major obstacle and, although it principally involves the skin, gastrointestinal tract, and liver, the thymus is also a primary target. An important aim following HSCT is to achieve complete and durable immunoreconstitution with a diverse T-cell receptor (TCR) repertoire to recognize a broad range of pathogens providing adequate long-term adaptive T-lymphocyte immunity, essential to reduce the risk of infection, disease relapse, and secondary malignancies. Reconstitution of adaptive T-lymphocyte immunity is a lengthy and complex process which requires a functioning and structurally intact thymus responsible for the production of new naïve T-lymphocytes with a broad TCR repertoire. Damage to the thymic microenvironment, secondary to aGvHD and the effect of corticosteroid treatment, disturbs normal signaling required for thymocyte development, resulting in impaired T-lymphopoiesis and reduced thymic export. Primary immunodeficiencies, in which failure of central or peripheral tolerance is a major feature, because of intrinsic defects in hematopoietic stem cells leading to abnormal T-lymphocyte development, or defects in thymic stroma, can give insights into critical processes important for recovery from aGvHD. Extracorporeal photopheresis is a potential alternative therapy for aGvHD, which acts in an immunomodulatory fashion, through the generation of regulatory T-lymphocytes (Tregs), alteration of cytokine patterns and modulation of dendritic cells. Promoting normal central and peripheral immune tolerance, with selective downregulation of immune stimulation, could reduce aGvHD, and enable a reduction in other immunosuppression, facilitating thymic recovery, restoration of normal T-lymphocyte ontogeny, and complete immunoreconstitution with improved clinical outcome as the ability to fight infections improves and risk of secondary malignancy or relapse diminishes.

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

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

Graft versus self (GvS) against T-cell autoantigens is a mechanism of graft-host interaction

Graft-versus-host disease (GVHD) represents the major nonrelapse complication of allogeneic hematopoietic cell transplantation. Although rare, the CNS and the eye can be affected. In this study, manifestation in the retina as part of the CNS and T-cell epitopes recognized by the allogeneic T cells were evaluated. In 2 of 6 patients with posttransplantation retina diseases and 6 of 22 patients without ocular symptoms, antigen-specific T-cell responses against retina-specific epitopes were observed. No genetic differences between donor and recipient could be identified indicating T-cell activation against self-antigens (graft versus self). Transplantation of a preexisting immunity and cross-reactivity with ubiquitous epitopes was excluded in family donors and healthy individuals. In summary, an immunological reaction against retina cells represents a mechanism of graft-versus-host interaction following hematopoietic cell transplantation.

Chronic graft-versus-host disease: biological insights from preclinical and clinical studies

With the increasing use of mismatched, unrelated, and granulocyte colony-stimulating factor-mobilized peripheral blood stem cell donor grafts and successful treatment of older recipients, chronic graft-versus-host disease (cGVHD) has emerged as the major cause of nonrelapse mortality and morbidity. cGVHD is characterized by lichenoid changes and fibrosis that affects a multitude of tissues, compromising organ function. Beyond steroids, effective treatment options are limited. Thus, new strategies to both prevent and treat disease are urgently required. Over the last 5 years, our understanding of cGVHD pathogenesis and basic biology, born out of a combination of mouse models and correlative clinical studies, has radically improved. We now understand that cGVHD is initiated by naive T cells, differentiating predominantly within highly inflammatory T-helper 17/T-cytotoxic 17 and T-follicular helper paradigms with consequent thymic damage and impaired donor antigen presentation in the periphery. This leads to aberrant T- and B-cell activation and differentiation, which cooperate to generate antibody-secreting cells that cause the deposition of antibodies to polymorphic recipient antigens (ie, alloantibody) or nonpolymorphic antigens common to both recipient and donor (ie, autoantibody). It is now clear that alloantibody can, in concert with colony-stimulating factor 1 (CSF-1)-dependent donor macrophages, induce a transforming growth factor β-high environment locally within target tissue that results in scleroderma and bronchiolitis obliterans, diagnostic features of cGVHD. These findings have yielded a raft of potential new therapeutics, centered on naive T-cell depletion, interleukin-17/21 inhibition, kinase inhibition, regulatory T-cell restoration, and CSF-1 inhibition. This new understanding of cGVHD finally gives hope that effective therapies are imminent for this devastating transplant complication.