Clinical strategies to enhance thymic recovery after allogeneic hematopoietic stem cell transplantation

Intravital two-photon microscopy of the native mouse thymus

The thymus, a key organ in the adaptive immune system, is sensitive to a variety of insults including cytotoxic preconditioning, which leads to atrophy, compression of the blood vascular system, and alterations in hemodynamics. Although the thymus has innate regenerative capabilities, the production of T cells relies on the trafficking of lymphoid progenitors from the bone marrow through the altered thymic blood vascular system. Our understanding of thymic blood vascular hemodynamics is limited due to technical challenges associated with accessing the native thymus in live mice. To overcome this challenge, we developed an intravital two-photon imaging method to visualize the native thymus in vivo and investigated functional changes to the vascular system following sublethal irradiation. We quantified blood flow velocity and shear rate in cortical blood vessels and identified a subtle but significant increase in vessel leakage and diameter ~24 hrs post-sublethal irradiation. Ex vivo whole organ imaging of optically cleared thymus lobes confirmed a disruption of the thymus vascular structure, resulting in an increase in blood vessel diameter and vessel area, and concurrent thymic atrophy. This novel two-photon intravital imaging method enables a new paradigm for directly investigating the thymic microenvironment in vivo.

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.

Inflammation, Infiltration, and Evasion-Tumor Promotion in the Aging Breast

Breast cancer is a significant cause of morbidity and mortality in women, with over two million new cases reported worldwide each year, the majority of which occur in post-menopausal women. Despite advances in early detection and treatment, approximately one-third of patients diagnosed with breast cancer will develop metastatic disease. The pathogenesis and progression of breast cancer are influenced by a variety of biological and social risk factors, including age, ethnicity, pregnancy status, diet, and genomic alterations. Recent advancements in breast cancer research have focused on harnessing the power of the patient's adaptive and innate immune systems for diagnostic and therapeutic purposes. The breast immune microenvironment plays a critical role in regulating tissue homeostasis and resistance to tumorigenesis. In this review, we explore the dynamic changes in the breast immune microenvironment that occur with age, how these changes impact breast cancer development and progression, and how targeted therapeutic interventions that leverage the immune system can be used to improve patient outcomes. Our review emphasizes the importance of understanding the complex interplay between aging, the immune system, and breast cancer, and highlights the potential of immune-based therapies in the fight against this devastating disease.

Gamma delta T-cell reconstitution after allogeneic HCT: A platform for cell therapy

Allogeneic Hematopoietic stem cell transplantation (allo-HCT) is a curative platform for several hematological diseases. Despite its therapeutic benefits, the profound immunodeficiency associated with the transplant procedure remains a major challenge that renders patients vulnerable to several complications. Today, It is well established that a rapid and efficient immune reconstitution, particularly of the T cell compartment is pivotal to both a short-term and a long-term favorable outcome. T cells expressing a TCR heterodimer comprised of gamma (γ) and delta (δ) chains have received particular attention in allo-HCT setting, as a large body of evidence has indicated that γδ T cells can exert favorable potent anti-tumor effects without inducing severe graft versus host disease (GVHD). However, despite their potential role in allo-HCT, studies investigating their detailed reconstitution in patients after allo-HCT are scarce. In this review we aim to shed lights on the current literature and understanding of γδ T cell reconstitution kinetics as well as the different transplant-related factors that may influence γδ reconstitution in allo-HCT. Furthermore, we will present data from available reports supporting a role of γδ cells and their subsets in patient outcome. Finally, we discuss the current and future strategies to develop γδ cell-based therapies to exploit the full immunotherapeutic potential of γδ cells in HCT setting.

A Proposed Link Between Acute Thymic Involution and Late Adverse Effects of Chemotherapy

Epidemiologic data suggest that cancer survivors tend to develop a protuberant number of adverse late effects, including second primary malignancies (SPM), as a result of cytotoxic chemotherapy. Besides the genotoxic potential of these drugs that directly inflict mutational burden on genomic DNA, the precise mechanisms contributing to SPM development are poorly understood. Cancer is nowadays perceived as a complex process that goes beyond the concept of genetic disease and includes tumor cell interactions with complex stromal and immune cell microenvironments. The cancer immunoediting theory offers an explanation for the development of nascent neoplastic cells. Briefly, the theory suggests that newly emerging tumor cells are mostly eliminated by an effective tissue immunosurveillance, but certain tumor variants may occasionally escape innate and adaptive mechanisms of immunological destruction, entering an equilibrium phase, where immunologic tumor cell death "equals" new tumor cell birth. Subsequent microenvironmental pressures and accumulation of helpful mutations in certain variants may lead to escape from the equilibrium phase, and eventually cause an overt neoplasm. Cancer immunoediting functions as a dedicated sentinel under the auspice of a highly competent immune system. This perspective offers the fresh insight that chemotherapy-induced thymic involution, which is characterized by the extensive obliteration of the sensitive thymic epithelial cell (TEC) compartment, can cause long-term defects in thymopoiesis and in establishment of diverse T cell receptor repertoires and peripheral T cell pools of cancer survivors. Such delayed recovery of T cell adaptive immunity may result in prolonged hijacking of the cancer immunoediting mechanisms, and lead to development of persistent and mortal infections, inflammatory disorders, organ-specific autoimmunity lesions, and SPMs. Acknowledging that chemotherapy-induced thymic involution is a potential risk factor for the emergence of SPM demarcates new avenues for the rationalized development of pharmacologic interventions to promote thymic regeneration in patients receiving cytoreductive chemotherapies.

Thymic Microenvironment: Interactions Between Innate Immune Cells and Developing Thymocytes

The thymus is a crucial organ for the development of T cells. T cell progenitors first migrate from the bone marrow into the thymus. During the journey to become a mature T cell, progenitors require interactions with many different cell types within the thymic microenvironment, such as stromal cells, which include epithelial, mesenchymal and other non-T-lineage immune cells. There are two crucial decision steps that are required for generating mature T cells: positive and negative selection. Each of these two processes needs to be performed efficiently to produce functional MHC-restricted T cells, while simultaneously restricting the production of auto-reactive T cells. In each step, there are various cell types that are required for the process to be carried out suitably, such as scavengers to clean up apoptotic thymocytes that fail positive or negative selection, and antigen presenting cells to display self-antigens during positive and negative selection. In this review, we will focus on thymic non-T-lineage immune cells, particularly dendritic cells and macrophages, and the role they play in positive and negative selection. We will also examine recent advances in the understanding of their participation in thymus homeostasis and T cell development. This review will provide a perspective on how the thymic microenvironment contributes to thymocyte differentiation and T cell maturation.

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.

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.

Effect of graft-versus-host disease on outcomes after pediatric single cord blood transplantation

The effect of GVHD on transplant outcomes after unrelated cord blood transplantation (UCBT) is not yet fully understood. Pediatric patients aged 0-15 years with acute leukemia or myelodysplastic syndrome who underwent their first UCBT (n = 740) were selected from the Japanese registry. Fifty percent of the patients received a UCB unit containing more than 5.0 × 10⁷/kg total nucleated cells. The occurrence of grade III-IV acute GVHD was associated with a higher risk of non-relapse mortality (NRM, hazard ratio [HR] 4.07, P < 0.001) compared with no acute GVHD. Grade I-II acute GVHD was not associated with NRM. The occurrence of grade I-II or grade III-IV acute GVHD was not associated with a relapse risk. These findings showed that grade I-II acute GVHD carried no survival benefit and grade III-IV acute GVHD had an adverse effect (HR 1.68, P = 0.007). The occurrence of limited chronic GVHD was associated with a low risk of overall mortality (HR 0.60, P = 0.045). Severe acute GVHD should be prevented because of its association with high overall mortality and NRM in pediatric single UCBT. Mild acute GVHD provides no overall benefit. Mild chronic GVHD may be beneficial for survival.

Clinical significance of T cell receptor excision circle (TREC) quantitation after allogenic HSCT

Background

Hematopoietic stem cell transplantation (HSCT) is a well-established treatment modality for a variety of diseases. Immune reconstitution is an important event that determines outcomes. The immune recovery of T cells relies on peripheral expansion of mature graft cells, followed by differentiation of donor-derived hematopoietic stem cells. The formation of new T cells occurs in the thymus and as a byproduct, T cell receptor excision circles (TRECs) are released. Detection of TRECs by PCR is a reliable method for estimating the amount of newly formed T cells in the circulation and, indirectly, for estimating thymic function. The aim of this study was to determine the role of TREC quantitation in predicting outcomes of human leucocyte antigen (HLA) identical allogenic HSCT.

Methods

The study was conducted on 100 patients receiving allogenic HSCT from an HLA identical sibling. TREC quantification was done by real time PCR using a standard curve.

Results

TREC levels were inversely related to age (P=0.005) and were significantly lower in patients with malignant diseases than in those with benign diseases (P=0.038). TREC levels could predict relapse as an outcome but not graft versus host disease (GvHD) and infections.

Conclusion

Age and nature of disease determine the TREC levels, which are related to relapse.

Use of Growth Factors and Other Cytokines for Treatment of Injuries During a Radiation Public Health Emergency

Due to the threat of a radiological or nuclear incident that could impact citizens, the U.S. Department of Health and Human Services tasked the National Institute of Allergy and Infectious Diseases (NIAID) with identifying and funding early- to mid-stage medical countermeasure (MCM) development to treat radiation-induced injuries. Given that the body's natural response to radiation exposure includes production of growth factors and cytokines, and that the only drugs approved by the U.S. Food and Drug Administration to treat acute radiation syndrome are growth factors targeting either the granulocyte (Neupogen^® or Neulasta^®) or granulocyte and macrophage (Leukine^®) hematopoietic cell lineages, there is interest in understanding the role that these factors play in responding to and/or ameliorating radiation damage. Furthermore, in an environment where resources are scarce, such as what might be expected during a radiation public health emergency, availability of growth factor or other treatments may be limited. For these reasons, the NIAID partnered with the Radiation Injury Treatment Network (RITN), whose membership includes medical centers with expertise in the management of bone marrow failure, to explore the use of growth factors and other cytokines as MCMs to mitigate/treat radiation injuries. A workshop was convened that included government, industry and academic subject matter experts, with presentations covering the anticipated concept of operations during a mass casualty incident including triage and treatment, growth factors under development for a radiation indication, and how the practice of medicine can inform other potential approaches, as well as considerations for administration of these products to diverse civilian populations. This report reviews the information presented, and provides an overview of the discussions from a guided breakout session.

Profiling analysis of 17β-estradiol-regulated lncRNAs in mouse thymic epithelial cells

Thymus is the primary organ for T cell differentiation and maturation. Many studies have demonstrated that estrogen plays a crucial role in thymic epithelial cell (TEC) proliferation during thymic involution. LncRNAs are involved in various biological processes; however, estrogen-mediated lncRNA expression in TECs has not been yet reported. To address this question, the mouse medullary thymic epithelial cell line 1 (MTEC1) was treated with 17β-estradiol (E2). By using CCK8 assay and flow cytometry, we found that E2 was able to inhibit viability and proliferation of MTEC1 cells. The expression profiles of lncRNAs in MTEC1 cells with or without E2 treatment were then measured by RNA-Seq, and a total of 962 lncRNAs and 2,469 mRNAs were shown to be differentially expressed. The reliability of RNA-Seq was confirmed by quantitative RT-PCR. Correlation analysis was conducted to investigate the potential function of lncRNAs. According to gene ontology (GO) analysis, differentially expressed lncRNAs were mainly related to cell proliferation, cell cycle and cell apoptosis. KEGG pathway analysis indicated that these lncRNAs were associated with several pathways, namely immunological activity, metabolism and cytokine-cytokine receptor interaction. In conclusion, our study provided a novel direction for studying the relationship between lncRNAs and E2 in the thymus.

The Transcription Factor Hif-1 Enhances the Radio-Resistance of Mouse MSCs

Mesenchymal stromal cells (MSCs) are multipotent progenitors supporting bone marrow hematopoiesis. MSCs have an efficient DNA damage response (DDR) and are consequently relatively radio-resistant cells. Therefore, MSCs are key to hematopoietic reconstitution following total body irradiation (TBI) and bone marrow transplantation (BMT). The bone marrow niche is hypoxic and via the heterodimeric transcription factor Hypoxia-inducible factor-1 (Hif-1), hypoxia enhances the DDR. Using gene knock-down, we have previously shown that the Hif-1α subunit of Hif-1 is involved in mouse MSC radio-resistance, however its exact mechanism of action remains unknown. In order to dissect the involvement of Hif-1α in the DDR, we used CRISPR/Cas9 technology to generate a stable mutant of the mouse MSC cell line MS5 lacking Hif-1α expression. Herein, we show that it is the whole Hif-1 transcription factor, and not only the Hif-1α subunit, that modulates the DDR of mouse MSCs. This effect is dependent upon the presence of a Hif-1α protein capable of binding to both DNA and its heterodimeric partner Arnt (Hif-1β). Detailed transcriptomic and proteomic analysis of Hif1a KO MS5 cells leads us to conclude that Hif-1α may be acting indirectly on the DNA repair process. These findings have important implications for the modulation of MSC radio-resistance in the context of BMT and cancer.

T cell progenitor therapy-facilitated thymopoiesis depends upon thymic input and continued thymic microenvironment interaction

Infusion of in vitro-derived T cell progenitor (proT) therapy with hematopoietic stem cell transplant aids the recovery of the thymus damaged by total body irradiation. To understand the interaction between proTs and the thymic microenvironment, WT mice were lethally irradiated and given T cell-deficient (Rag1-/-) marrow with WT in vitro-generated proTs, limiting mature T cell development to infused proTs. ProTs within the host thymus led to a significant increase in thymic epithelial cells (TECs) by day 21 after transplant, increasing actively cycling TECs. Upon thymus egress (day 28), proT TEC effects were lost, suggesting that continued signaling from proTs is required to sustain TEC cycling and cellularity. Thymocytes increased significantly by day 21, followed by a significant improvement in mature T cell numbers in the periphery by day 35. This protective surge was temporary, receding by day 60. Double-negative 2 (DN2) proTs selectively increased thymocyte number, while DN3 proTs preferentially increased TECs and T cells in the spleen that persisted at day 60. These findings highlight the importance of the interaction between proTs and TECs in the proliferation and survival of TECs and that the maturation stage of proTs has unique effects on thymopoiesis and peripheral T cell recovery.

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.

Lymphotoxin β Receptor Controls T Cell Progenitor Entry to the Thymus

The recruitment of lymphoid progenitors to the thymus is essential to sustain T cell production throughout life. Importantly, it also limits T lineage regeneration following bone marrow transplantation, and so contributes to the secondary immunodeficiency that is caused by delayed immune reconstitution. Despite this significance, the mechanisms that control thymus colonization are poorly understood. In this study, we show that in both the steady-state and after bone marrow transplant, lymphotoxin β receptor (LTβR) controls entry of T cell progenitors to the thymus. We show that this requirement maps to thymic stroma, further underlining the key importance of this TNFR superfamily member in regulation of thymic microenvironments. Importantly, analysis of the requirement for LTβR in relationship to known regulators of thymus seeding suggests that it acts independently of its regulation of thymus-homing chemokines. Rather, we show that LTβR differentially regulates intrathymic expression of adhesion molecules known to play a role in T cell progenitor entry to the thymus. Finally, Ab-mediated in vivo LTβR stimulation following bone marrow transplant enhances initial thymus recovery and boosts donor-derived T cell numbers, which correlates with increased adhesion molecule expression by thymic stroma. Collectively, we reveal a novel link between LTβR and thymic stromal cells in thymus colonization, and highlight its potential as an immunotherapeutic target to boost T cell reconstitution after transplantation.

LTβR controls thymic portal endothelial cells for haematopoietic progenitor cell homing and T-cell regeneration

Continuous thymic homing of haematopoietic progenitor cells (HPCs) via the blood is critical for normal T-cell development. However, the nature and the differentiation programme of specialized thymic endothelial cells (ECs) controlling this process remain poorly understood. Here using conditional gene-deficient mice, we find that lymphotoxin beta receptor (LTβR) directly controls thymic ECs to guide HPC homing. Interestingly, T-cell deficiency or conditional ablation of T-cell-engaged LTβR signalling results in a defect in thymic HPC homing, suggesting the feedback regulation of thymic progenitor homing by thymic products. Furthermore, we identify and characterize a special thymic portal EC population with features that guide HPC homing. LTβR is essential for the differentiation and homeostasis of these thymic portal ECs. Finally, we show that LTβR is required for T-cell regeneration on irradiation-induced thymic injury. Together, these results uncover a cellular and molecular pathway that governs thymic EC differentiation for HPC homing.

Lymphoid progenitors migrate from the bone marrow into the thymus to give rise to T and NK cell lineages. Here the authors characterize a lymphotoxin receptor beta-dependent population of thymic endothelial cells that guide lymphoid progenitor homing in the thymus.

The functional relationship between hematopoietic stem cells and developing T lymphocytes

In contrast to all other blood and immune cells, T lymphocytes do not develop in the bone marrow (BM), but in the specialized microenvironment provided by the thymus. Similar to the other lineages, however, all T cells arise from multipotent hematopoietic stem cells (HSCs) that reside in the BM. Not all HSCs give rise to T cells; but how many and what kind of developmental checkpoints are located along this intricate differentiation path is the subject of intense research. Traditionally, this process has been studied almost exclusively using mouse cells, but recent advances in immunodeficient mouse models, high-speed cell sorting, lentiviral transduction protocols, and deep sequencing techniques have allowed these questions to be addressed using human cells. Here we review the process of thymic seeding by BM-derived cells and T cell commitment in humans, discussing recent insights into the clonal composition of the thymus and the definition of developmental checkpoints, on the basis of insights from human severe combined immunodeficiency patients.

Strategies to accelerate immune recovery after allogeneic hematopoietic stem cell transplantation

The interplay existing between immune reconstitution and patient outcome has been extensively demonstrated in allogeneic hematopoietic stem cell transplantation. One of the leading causes of infection-related mortality is the slow recovery of T-cell immunity due to the conditioning regimen and/or age-related thymus damage, poor naïve T-cell output, and restricted T-cell receptor (TCR) repertoires. With the aim of improving posttransplantation immune reconstitution, several immunotherapy approaches have been explored. Donor leukocyte infusions are widely used to accelerate immune recovery, but they carry the risk of provoking graft-versus-host disease. This review will focus on sophisticated strategies of thymus function-recovery, adoptive infusion of donor-derived, allodepleted T cells, T-cell lines/clones specific for life-threatening pathogens, regulatory T cells, and of T cells transduced with suicide genes.

High Disease-Free Survival with Enhanced Protection against Relapse after Double-Unit Cord Blood Transplantation When Compared with T Cell-Depleted Unrelated Donor Transplantation in Patients with Acute Leukemia and Chronic Myelogenous Leukemia

Double-unit cord blood (DCB) grafts are a rapidly available stem cell source for adults with high-risk leukemias. However, how disease-free survival (DFS) after DCB transplantation (DCBT) compares to that of unrelated donor transplantation (URDT) is not fully established. We analyzed 166 allograft recipients (66 8/8 HLA-matched URDT, 45 7/8 HLA-matched URDT, and 55 DCBT) ages 16 to 60 years with high-risk acute leukemia or chronic myelogenous leukemia (CML). URDT and DCBT recipients were similar except DCBT recipients were more likely to have lower weight and non-European ancestry and to receive intermediate-intensity conditioning. All URDT recipients received a CD34(+) cell-selected (T cell-depleted) graft. Overall, differences between the 3-year transplantation-related mortality were not significant (8/8 URDT, 18%; 7/8 URDT, 39%; and DCBT, 24%; P = .108), whereas the 3-year relapse risk was decreased after DCBT (8/8 URDT, 23%; 7/8 URDT, 20%; and DCBT 9%, P = .037). Three-year DFS was 57% in 8/8 URDT, 41% in 7/8 URDT, and 68% in DCBT recipients (P = .068), and the 3-year DFS in DCBT recipients was higher than that of 7/8 URDT recipients (P = .021). In multivariate analysis in acute leukemia patients, factors adversely associated with DFS were female gender (hazard ratio [HR], 1.68; P = .031), diagnosis of acute lymphoblastic leukemia (HR, 2.09; P = .004), and 7/8 T cell-depleted URDT (HR, 1.91; P = .037). High DFS can be achieved in adults with acute leukemia and CML with low relapse rates after DCBT. Our findings support performing DCBT in adults in preference to HLA-mismatched T cell-depleted URDT and suggest DCBT is a readily available alternative to T cell-depleted 8/8 URDT, especially in patients requiring urgent transplantation.

A Tale from TGF-β Superfamily for Thymus Ontogeny and Function

Multiple signaling pathways control every aspect of cell behavior, organ formation, and tissue homeostasis throughout the lifespan of any individual. This review takes an ontogenetic view focused on the large superfamily of TGF-β/bone morphogenetic protein ligands to address thymus morphogenesis and function in T cell differentiation. Recent findings on a role of GDF11 for reversing aging-related phenotypes are also discussed.

CD4+ T cells in aged or thymectomized recipients of allogeneic stem cell transplantations

Background

CD4+CD25highFOXP3+ regulatory T (Treg) cells, which include thymus-derived and peripherally induced cells, play a central role in immune regulation, and are therefore crucial to prevent graft-versus-host disease (GVHD). The increasing use of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for elderly patients with thymus regression, and our case of allo-HSCT shortly after total thymectomy, raised questions about the activity of thymus-derived Treg cells and peripherally induced Treg cells, which are otherwise indistinguishable.

Results

We found that despite pre-transplant thymectomy or older age, both naïve and effector Treg cells, as well as naïve and effector conventional T cells, proliferated in allo-HSCT recipients. Higher proportions of total Treg cells 1 month post allo-HSCT, and naïve Treg cells 1 year post allo-HSCT, appeared in patients achieving complete chimera without developing significant chronic GVHD, including our thymectomized patient, compared with patients who developed chronic GVHD.

Conclusions

Treg cells that modulate human allogeneic immunity may arise peripherally as well as in the thymus of allo-HSCT recipients.