Deep phenotyping of Tregs identifies an immune signature for idiopathic aplastic anemia and predicts response to treatment

Aplastic anaemia: Current concepts in diagnosis and management

Aplastic anaemia is a rare, previously fatal condition with a significantly improved survival rate owing to advances in understanding of the pathophysiology and improved treatment strategies including haematopoietic stem cell transplantation. Although a rare condition, aplastic anaemia continues to present a high burden for affected patients, their families and the health system due to the prolonged course of disease often associated with high morbidity and the uncertainty regarding clinical outcome. Modern molecular and genetic techniques including next-generation sequencing have contributed to a better understanding of this heterogeneous group of conditions, albeit at a cost of increased complexity of clinical decision-making regarding prognosis and choice of treatment for individual patients. Here we present a concise and comprehensive review of aplastic anaemia and closely related conditions based on extensive literature review and long-standing clinical experience. The review takes the reader across the complex pathophysiology consisting of three main causative mechanisms of bone marrow destruction resulting in aplastic anaemia: direct injury, immune mediated and bone marrow failure related including inherited and clonal disorders. A comprehensive diagnostic algorithm is presented and an up-to-date therapeutic approach to acquired immune aplastic anaemia, the most represented type of aplastic anaemia, is described. Overall, the aim of the review is to provide paediatricians with an update of this rare, heterogeneous and continuously evolving condition.

Suppressive Characteristics of Umbilical Cord Blood-derived Regulatory T Cells After Ex Vivo Expansion on Autologous and Allogeneic T Effectors and Various Lymphoblastic Cells

The third-party umbilical cord blood (UCB)-derived regulatory T cells (Treg) are an alternative to donor-derived Treg as cellular therapy of graft-versus-host disease following hematopoietic stem cell transplantation. However, their suppressive characteristics against autologous and allogeneic T effector cells (Teff) have rarely been documented. The exact role of UCB-Treg in hematologic malignancies is also uncertain. Here, we investigated the direct effects of UCB-Treg on the proliferation of autologous Teff, as compared with allogeneic Teff, and also determined cellular fates of lymphoblasts after UCB-Treg co-culture. UCB-Treg were isolated from 8 UCB samples using 2-step immunomagnetic bead sorting. After 10-day ex vivo expansion, up to 60-fold increase in cell number with 76.7%±4.9% of CD4CD25CD127FoxP UCB-Treg was obtained. Further characterization showed that ex vivo-expanded UCB-Treg contained a higher proportion of CD95CD45RACCR4Treg-B subpopulation compared with the CD95CD45RACCR4Treg-A subpopulation (13.0%±4.8% vs. 0.8%±0.7%; P<0.05), along with the detecting of substantial amounts of secretory IL-10 (57.7±17.8 pg/mL) and TGF-β1 (196.5±29.7 pg/mL) in culture supernatants. After 4 days co-culture with UCB-Treg (at the ratio of 1:1), the proliferation of autologous and allogeneic Teff was decreased comparably (43.6%±17.5% vs. 37.6±17.7%; P=0.437). Suppression was independent of HLA-A, B, and DRB1 compatibility between UCB-Treg and Teff. UCB-Treg co-culture with various lymphoblasts showed proliferative suppression of Jurkat T lymphoblasts (45.4%±20.5% at the ratio of 1:1), but not Namalwa and Raji B lymphoblasts. All lymphoblasts had no significant cell apoptosis or death after co-culture. In conclusion, the ex vivo-expanded UCB-Treg had no difference in autologous and allogeneic Teff suppression. UCB-Treg therapy in patients with graft-versus-host disease who have a primary disease of T-cell leukemia may have additional benefits in the prevention of relapsed disease.

The Migratory Properties and Numbers of T Regulatory Cell Subsets in Circulation Are Differentially Influenced by Season and Are Associated With Vitamin D Status

The control of peripheral immune responses by FOXP3⁺ T regulatory (Treg) cells is essential for immune tolerance. However, at any given time, Treg frequencies in whole blood can vary more than fivefold between individuals. An understanding of factors that influence Treg numbers and migration within and between individuals would be a powerful tool for cellular therapies that utilize the immunomodulatory properties of Tregs to control pathology associated with inflammation. We sought to understand how season could influence Treg numbers and phenotype by monitoring the proportion of natural thymus-derived Tregs (nTregs) defined as (CD3⁺CD4⁺CD25⁺FOXP3⁺CD127^–/low) cells as a proportion of CD4⁺ T cells and compared these to all FOXP3⁺ Tregs (allTregs, CD3⁺CD25⁺FOXP3⁺CD127^–/low). We were able to determine changes within individuals during 1 year suggesting an influence of season on nTreg frequencies. We found that, between individuals at any given time, nTreg/CD4⁺ T cells ranged from 1.8% in February to 8.8% in the summer where median nTreg/CD4 in January and February was 2.4% (range 3.75–1.76) and in July and August was 4.5% (range 8.81–3.17) p = 0.025. Importantly we were able to monitor individual nTreg frequencies throughout the year in donors that started the year with high or low nTregs. Some nTreg variation could be attributed to vitamin D status where normal linear regression estimated that an absolute increase in nTreg/CD4⁺ by 0.11% could be expected with 10 nmol increase in serum 25 (OH) vitamin D3 (p = 0.005, 95% CI: 0.03–0.19). We assessed migration markers on Tregs for the skin and/or gut. Here cutaneous lymphocyte associated antigen (CLA⁺) expression on CD25⁺FOXP3⁺CD4⁺/CD4⁺ was compared with the same population expressing the gut associated integrin, β7. Gut tropic CD25⁺FOXP3⁺β7⁺Tregs/CD4⁺ had similar dynamics to nTreg/CD4⁺. Conversely, CD25⁺FOXP3⁺CLA⁺Tregs/CD4⁺ showed no association with vitamin D status. Important for cellular therapies requiring isolation of Tregs, the absolute number of β7⁺CD4⁺CD25⁺FOXP3⁺Tregs was positively associated with 25(OH)vitamin D3 (R² = 0.0208, r = 0.184, p = 0.021) whereas the absolute numbers of CLA⁺CD4⁺CD25⁺FOXP3⁺Tregs in the periphery were not influenced by vitamin D status. These baseline observations provide new opportunities to utilize seasonal variables that influence Treg numbers and their migratory potential in patients or donors.

Advances in the role of helper T cells in autoimmune diseases

Autoimmune diseases are primary immune diseases in which autoreactive antibodies or sensitized lymphocytes destroy and damage tissue and cellular components, resulting in tissue damage and organ dysfunction. Helper T cells may be involved in the pathogenesis of autoimmune diseases under certain conditions. This review summarizes recent research on the role of helper T cells in autoimmune diseases from two aspects, helper T cell-mediated production of autoantibodies by B cells and helper T cell-induced activation of abnormal lymphocytes, and provides ideas for the treatment of autoimmune diseases. The abnormal expression of helper T cells promotes the differentiation of B cells that produce autoantibodies, which leads to the development of different diseases. Among them, abnormal expression of Th2 cells and T follicular helper cells is more likely to cause antibody-mediated autoimmune diseases. In addition, abnormal activation of helper T cells also mediates autoimmune diseases through the production of abnormal cytokines and chemokines. Helper T cells play an essential role in the pathogenesis of autoimmune diseases, and a full understanding of their role in autoimmune diseases is helpful for providing ideas for the treatment of autoimmune diseases.

Deficit of circulating CD19+ CD24hi CD38hi regulatory B cells in severe aplastic anaemia

Immune aplastic anaemia (AA) is caused by cytotoxic T lymphocytes (CTLs) that destroy haematopoietic stem and progenitor cells. Enhanced type 1 T helper (Th1) responses and reduced regulatory T cells (Tregs) are involved in the immune pathophysiology. CD24^hiCD38^hi regulatory B cells (Bregs) suppress CTLs and Th1 responses, and induce Tregs via interleukin 10 (IL‐10). We investigated circulating B‐cell subpopulations, including CD24^hiCD38^hi Bregs, as well as total B cells, CD4⁺ T cells, CD8⁺ T cells and natural killer cells in 104 untreated patients with severe and very severe AA, aged ≥18 years. All patients were treated with standard immunosuppressive therapy (IST) plus eltrombopag. CD24^hiCD38^hi Bregs were markedly reduced in patients with AA compared to healthy individuals, especially in very severe AA, but residual Bregs remained functional, capable of producing IL‐10; total B‐cell counts and the other B‐cell subpopulations were similar to those of healthy individuals. CD24^hiCD38^hi Bregs did not correlate with responses to IST, and they recovered to levels present in healthy individuals after therapy. Mature naïve B‐cell counts were unexpectedly associated with IST response. Markedly reduced CD24^hiCD38^hi Bregs, especially in very severe AA, with recovery after IST suggest Breg deficits may contribute to the pathophysiology of immune AA.

Treatment of Severe Aplastic Anemia with Porcine Anti-Human Lymphocyte Globulin

Aplastic anemia (AA) is a bone marrow failure syndrome characterized by pancytopenia. Decreased numbers of hematopoietic stem cells and impaired bone marrow microenvironment caused by abnormal immune function describe the major pathogenesis of AA. Hematopoietic stem cell transplantation and immunesuppressive therapy are the first-line treatments for AA. Porcine anti-lymphocyte globulin (p-ALG) is a new product developed in China. Several studies have shown that p-ALG exhibited good therapeutic effects in AA.

Regulatory T cells in solid organ transplantation

The induction of graft tolerance remains the holy grail of transplantation. This is important as chronic allograft dysfunction and the side effects of immunosuppression regimens place a major burden on the lives of transplant patients and their healthcare systems. This has mandated the need to understand the immunobiology of graft rejection and identify novel therapeutics. Regulatory T (Treg) cells play an important role in modulating pro-inflammatory microenvironments and maintaining tissue homeostasis. However, there are fundamental unanswered questions regarding Treg cell immunobiology. These cells are a heterogeneous entity with functionally diverse roles. Moreover, the adoption of novel deeper immunophenotyping and genomic sequencing technologies has identified this phenotype and function to be more complex than expected. Hence, a comprehensive understanding of Treg cell heterogeneity is needed to safely and effectively exploit their therapeutic potential. From a clinical perspective, the recent decade has seen different clinical teams commence and complete first-in-man clinical trials utilising Treg cells as an adoptive cellular therapy. In this review, we discuss these trials from a translational perspective with an important focus on safety. Finally, we identify crucial knowledge gaps for future study.

Integrating the "Immunome" in the Stratification of Myelodysplastic Syndromes and Future Clinical Trial Design

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis and often include a dysregulation and dysfunction of the immune system. In the context of population aging, MDS incidence is set to increase substantially, with exponential increases in health care costs, given the limited and expensive treatment options for these patients. Treatment selection is mainly based on calculated risk categories according to a Revised International Prognostic Scoring System (IPSS-R). However, although IPSS-R is an excellent predictor of disease progression, it is an ineffective predictor of response to disease-modifying therapies. Redressing these unmet needs, the "immunome" is a key, multifaceted component in the initiation and overall response against malignant cells in MDS, and the current omission of immune status monitoring may in part explain the insufficiencies of current prognostic stratification methods. Nevertheless, integrating these and other recent molecular advances into clinical practice proves difficult. This review highlights the complexity of immune dysregulation in MDS pathophysiology and the fine balance between smoldering inflammation, adaptive immunity, and somatic mutations in promoting or suppressing malignant clones. We review the existing knowledge and discuss how state-of-the-art immune monitoring strategies could potentially permit novel patient substratification, thereby empowering practical predictions of response to treatment in MDS. We propose novel multicenter studies, which are needed to achieve this goal.

Pitfalls in the characterization of circulating and tissue-resident human γδ T cells

Dissection of the role and function of human γδ T cells and their heterogeneous subsets in cancer, inflammation, and auto-immune diseases is a growing and dynamic research field of increasing interest to the scientific community. Therefore, harmonization and standardization of techniques for the characterization of peripheral and tissue-resident γδ T cells is crucial to facilitate comparability between published and emerging research. The application of commercially available reagents to classify γδ T cells, in particular the combination of multiple Abs, is not always trouble-free, posing major demands on researchers entering this field. Occasionally, even entire γδ T cell subsets may remain undetected when certain Abs are combined in flow cytometric analysis with multicolor Ab panels, or might be lost during cell isolation procedures. Here, based on the recent literature and our own experience, we provide an overview of methods commonly employed for the phenotypic and functional characterization of human γδ T cells including advanced polychromatic flow cytometry, mass cytometry, immunohistochemistry, and magnetic cell isolation. We highlight potential pitfalls and discuss how to circumvent these obstacles.

Idiopathic Aplastic Anemia in Children and Adults: Diagnosis, Treatments, and Management - A Review

Aplastic Anemia (AA) is also known as idiopathic aplastic anemia (IAA) and the production of new blood cells ceases in AA, which leads to an abnormal hematological syndrome such as pancytopenia and suppression of hypo-cellular bone marrow. The pathophysiology of AA in most cases is immune-mediated and is stimulated by type 1 cytotoxic T cells. Reliable early diagnostic tests of IAA are not yet available, therefore most of the cases are identified in advanced stages. Recently, abnormal immune response and hematopoietic cell deficiencies are defined genetically, such as in target cells of telomere repair gene mutations and by the dysregulation of T-cell activation pathways. Importantly, anti-thymocyte globulins and cyclosporine-associated immunosuppression are successful treatments for restoring blood cell production in most of the cases, however, clonal hematologic diseases remain challenging. In the current review, we have discussed the common practices in the treatment, pathophysiology, diagnosis, and management of AA.

Controlled Human Malaria Infection in Semi-Immune Kenyan Adults (CHMI-SIKA): a study protocol to investigate in vivo Plasmodium falciparum malaria parasite growth in the context of pre-existing immunity

Malaria remains a major public health burden despite approval for implementation of a partially effective pre-erythrocytic malaria vaccine. There is an urgent need to accelerate development of a more effective multi-stage vaccine. Adults in malaria endemic areas may have substantial immunity provided by responses to the blood stages of malaria parasites, but field trials conducted on several blood-stage vaccines have not shown high levels of efficacy.  We will use the controlled human malaria infection (CHMI) models with malaria-exposed volunteers to identify correlations between immune responses and parasite growth rates in vivo.  Immune responses more strongly associated with control of parasite growth should be prioritized to accelerate malaria vaccine development. We aim to recruit up to 200 healthy adult volunteers from areas of differing malaria transmission in Kenya, and after confirming their health status through clinical examination and routine haematology and biochemistry, we will comprehensively characterize immunity to malaria using >100 blood-stage antigens. We will administer 3,200 aseptic, purified, cryopreserved Plasmodium falciparum sporozoites (PfSPZ Challenge) by direct venous inoculation. Serial quantitative polymerase chain reaction to measure parasite growth rate in vivo will be undertaken. Clinical and laboratory monitoring will be undertaken to ensure volunteer safety. In addition, we will also explore the perceptions and experiences of volunteers and other stakeholders in participating in a malaria volunteer infection study. Serum, plasma, peripheral blood mononuclear cells and whole blood will be stored to allow a comprehensive assessment of adaptive and innate host immunity. We will use CHMI in semi-immune adult volunteers to relate parasite growth outcomes with antibody responses and other markers of host immunity. Registration: ClinicalTrials.gov identifier NCT02739763.

STAT3 and STAT5 Targeting for Simultaneous Management of Melanoma and Autoimmune Diseases

Melanoma is a skin cancer which can become metastatic, drug-refractory, and lethal if managed late or inappropriately. An increasing number of melanoma patients exhibits autoimmune diseases, either as pre-existing conditions or as sequelae of immune-based anti-melanoma therapies, which complicate patient management and raise the need for more personalized treatments. STAT3 and/or STAT5 cascades are commonly activated during melanoma progression and mediate the metastatic effects of key oncogenic factors. Deactivation of these cascades enhances antitumor-immune responses, is efficient against metastatic melanoma in the preclinical setting and emerges as a promising targeting strategy, especially for patients resistant to immunotherapies. In the light of the recent realization that cancer and autoimmune diseases share common mechanisms of immune dysregulation, we suggest that the systemic delivery of STAT3 or STAT5 inhibitors could simultaneously target both, melanoma and associated autoimmune diseases, thereby decreasing the overall disease burden and improving quality of life of this patient subpopulation. Herein, we review the recent advances of STAT3 and STAT5 targeting in melanoma, explore which autoimmune diseases are causatively linked to STAT3 and/or STAT5 signaling, and propose that these patients may particularly benefit from treatment with STAT3/STAT5 inhibitors.

Activity of eltrombopag in severe aplastic anemia

Since the approval of horse antithymocyte globulin (ATG) decades ago, there was a long hiatus in therapies with activity in severe aplastic anemia (SAA). This scenario changed in 2014 when eltrombopag, a thrombopoietin receptor agonist, was approved for SAA after an insufficient response to initial immunosuppressive therapy (IST). The basis for this approval was the observation of single-agent activity of eltrombopag in this patient population, where 40% to 50% recovered blood counts at times involving >1 lineage. The achievement of transfusion independence confirmed the clinical benefit of this approach. Increase in marrow cellularity and CD34+ cells suggested a recovery to a more functioning bone marrow. Further in its development, eltrombopag was associated with standard horse ATG plus cyclosporine in first line, producing increases in overall (at about 90%) and complete response rates (at about 40%) and leading to transfusion independence and excellent survival. Interestingly, best results were observed when all drugs were started simultaneously. The cumulative incidence of clonal cytogenetic abnormalities to date has compared favorably with the vast experience with IST alone in SAA. Longer follow-up will help in define these long-term risks. In this review, the development of eltrombopag in SAA will be discussed.

Management of aplastic anemia after failure of frontline immunosuppression

Introduction: About 60% of aplastic anemia (AA) patients are in need of further treatment after frontline standard immunosuppressive therapy (IST). This along with the prolonged survival of AA subjects who do not respond to or relapse after this treatment makes management of these patients a rising and very challenging issue. Areas covered: Literature research, carried out from the most commonly used databases, included the following keywords: aplastic anemia, immunosuppressive treatment, antithymocyte globuline, ciclosporine A, refractory aplastic anemia, relapsing aplastic anemia, hematopoietic stem cell transplantation including haploidentical and cord blood transplantations thrombopoietin mimetics, supportive treatment, chelation and infections. Studies on the treatment of aplastic anemia with different levels of evidence were included. Top level of evidence studies (metanalyses and randomized prospective controlled trials) were a minority because severe AA, particularly in the subset of patients who fail upfront IST, is an extremely rare disease. Guidelines from National Societies and review articles were also included. Expert opinion: The most commonly used treatments after failure of upfront immunosuppression are hematopoietic stem cell transplantation, a second course of immunosuppression and thrombopoietin mimetics alone or in combination with immunosuppression. Other potential options are alemtuzumab, androgens, oral cyclosporine A in monotherapy. Not many comparative studies exist to clearly establish the superiority of one over another strategy. Therefore, the choice of the best treatment for these patients should rely on major driving factors like patient's age and comorbidities, availability of a matched unrelated donor, donor's characteristics and drug-availability.

Thrombomodulin-expressing monocytes are associated with low-risk features in myelodysplastic syndromes and dampen excessive immune activation

The bone marrow of patients with low-risk myelodysplastic syndromes (MDS) is often an inflammatory environment and associated with an active cellular immune response. An active immune response generally contributes to antitumor responses and may prevent disease progression. However, chronic immune stimulation can also induce cell stress, DNA damage and contribute to the pathogenesis of MDS. The protective mechanisms against excessive immune activation are therefore an important aspect of the pathophysiology of MDS and characterizing them may help us to better understand the fine balance between protective and destabilizing inflammation in lower-risk disease. In this study we investigated the role of thrombomodulin (CD141/BDCA-3) expression, a molecule with anti-inflammatory properties, on monocytes in the bone marrow and peripheral blood of MDS patients in different risk groups. Patient-derived classical monocytes showed high expression levels of thrombomodulin, whereas monocytes from healthy donors hardly expressed any thrombomodulin. The presence of thrombomodulin on monocytes from MDS patients correlated with lower-risk disease groups and better overall and leukemia-free survival. Using multidimensional mass cytometry, in an in-vitro setting, we showed that thrombomodulin-positive monocytes could polarize naïve T cells toward cell clusters which are closer to T helper type 2 and T regulatory cell phenotypes and less likely to contribute to effective immune surveillance. In conclusion, the expression of thrombomodulin on classical monocytes is a favorable and early prognostic marker in patients with low-risk MDS and may represent a new mechanism in the protection against disproportionate immune activation.

The Case for Upfront HLA-Matched Unrelated Donor Hematopoietic Stem Cell Transplantation as a Curative Option for Adult Acquired Severe Aplastic Anemia

The improved success of HLA-matched unrelated donor (MUD) hematopoietic stem cell transplantation (HSCT) for severe aplastic anemia (SAA) in recent decades has had an impact on the indications for and timing of this treatment modality. In the absence of a matched sibling donor (MSD), historically MUD HSCT was reserved as an option after failure to respond to at least 2 courses of immunosuppressive therapy (IST) in adults with SAA, but with improved outcomes over time, it is now considered following failure to respond to 1 course of IST. Recent national and international studies and guidelines now recommend upfront MUD HSCT as an option for children for whom an MUD is readily available, because outcomes are similar to those for MSD HSCT. Fludarabine-based conditioning and the use of in vivo T cell depletion with antithymocyte globulin or alemtuzumab has been associated with a reported overall survival (OS) of >85% in adult patients undergoing MUD HSCT. However, the recent introduction of eltrombopag for patients with SAA has transformed the treatment landscape, and there is currently much interest in its use with IST as upfront treatment, which showed a high response rate in an early-phase study. The risks of HSCT, especially graft-versus-host disease (GVHD), need to be carefully balanced against the concerns of IST, namely relapse and later clonal evolution to myelodysplastic syndrome (MDS)/acute myelogenous leukemia (AML). In the absence of a current prospective randomized trial comparing these 2 approaches, in this review we examine the evidence supporting consideration of early MUD HSCT in adults with SAA who would have been considered for MSD HSCT but who lack a MSD and for whom an MUD is readily available, especially using an irradiation-free conditioning regimen, with a low risk of GVHD, as another treatment option. This option may be offered to patients to provide them with an informed choice, with the aim of curing disease rather than achieving freedom from disease, relapse-free survival, or OS. Furthermore, understanding the immune signature for the response to IST and the immunologic responses to somatic mutations and clonal progression to MDS/AML may help define the future indications for upfront HSCT and a more precise medical approach to therapy.

Functional Phenotypic Diversity of Regulatory T Cells Remaining in Inflamed Skin

Regulatory T cells (Tregs) migrate between lymphoid and peripheral tissues for maintaining immune homeostasis. Tissue-specific function and functional heterogeneity of Tregs have been suggested, however, correlation between them and inter-tissue movement remain unknown. We used a contact hypersensitivity model of mice expressing a photoconvertible protein for tracking migratory cells. After marking cells in skin, we purified Tregs exhibiting a different migration pattern [Tregs recruiting to or remaining in the skin and emigrating from the skin to draining lymph nodes (dLNs) within half a day] and examined single-cell gene and protein expression profiles. Correlation and unsupervised clustering analyses revealed that Tregs in both skin and dLNs comprised two subpopulations, one highly expressing Nrp1 with variable CD25, Granzyme B, and/or CTLA-4 expression and another with 3 subsets strongly expressing CD25, Granzyme B, or CTLA-4 together with CD39. Characteristic subsets of Tregs remaining in the skin displayed higher CD25 and CD39 expression and lower Granzyme B and CTLA-4 expression compared with Tregs migrating to the skin. In addition, CCR5 expression in Tregs in skin was positively and negatively correlated with CD39 and Nrp-1 expression, respectively. To assess the predictive value of these data for immunotherapy, we blocked CCR5 signaling and found modest downregulation of CD39 and modest upregulation of Nrp1 expression in skin Tregs. Our data reveal a high functional diversity of Tregs in skin that is strongly related to trafficking behavior, particularly skin retention. Modulation of tissue-specific trafficking and function is a promising clinical strategy against autoimmune, infectious, and neoplastic diseases.

Mass Cytometry Identifies Distinct Subsets of Regulatory T Cells and Natural Killer Cells Associated With High Risk for Type 1 Diabetes

Type 1 diabetes (T1D) is characterized by autoimmune destruction of insulin producing β-cells. The time from onset of islet autoimmunity to manifest clinical disease can vary widely in length, and it is fairly uncharacterized both clinically and immunologically. In the current study, peripheral blood mononuclear cells from autoantibody-positive children with high risk for T1D, and from age-matched healthy individuals, were analyzed by mass cytometry using a panel of 32 antibodies. Surface markers were chosen to identify multiple cell types including T, B, NK, monocytes, and DC, and antibodies specific for identification of differentiation, activation and functional markers were also included in the panel. By applying dimensional reduction and computational unsupervised clustering approaches, we delineated in an unbiased fashion 132 phenotypically distinct subsets within the major immune cell populations. We were able to identify an effector memory Treg subset expressing HLA-DR, CCR4, CCR6, CXCR3, and GATA3 that was increased in the high-risk group. In addition, two subsets of NK cells defined by CD16⁺ CD8⁺ CXCR3⁺ and CD16⁺ CD8⁺ CXCR3⁺ CD11c⁺ were also higher in the same subjects. High-risk individuals did not show impaired glucose tolerance at the time of sampling, suggesting that the changes observed were not the result of metabolic imbalance, and might be potential biomarkers predictive of T1D.

Roles of regulatory T cells in the pathogenesis of pediatric aplastic anemia

The pathogenesis of aplastic anemia (AA) in children is not clear. This study was conducted to investigate the changes in the proportion and function of regulatory T cells (Tregs) in pediatric AA. The proportion of Tregs, mRNA levels of transcription factors, and concentrations of cytokines were measured by flow cytometry, reverse transcription-PCR, and enzyme-linked immunosorbent assay, respectively. Tregs were co-cultured with effector T cells (Teff) to evaluate the function of Tregs. The proportion of Tregs after immunosuppressive therapy (IST) in pediatric AA was monitored dynamically. Compared to the control, the proportions of Tregs in peripheral blood and bone marrow lymphocytes of the untreated AA group were lower (1.31% ± 0.73% vs. 3.16% ± 0.92%, 1.49% ± 0.81% vs. 3.06% ± 0.82%, respectively, p < 0.001). The mRNA levels of FOXP3 and STAT3 in the AA group were lower (p = 0.014; p < 0.001). However, the mRNA levels of T-BET did not significantly differ between groups. The concentration of interferon-γ and interleukin-17 in the AA group were higher (p = 0.004; p = 0.003), whereas the concentration of TGF-β decreased (p = 0.044). The immunosuppressive function of Tregs was impaired in the AA group. After IST, the proportion of Tregs was significantly lower than that in the control. The proportion of Tregs at the time of diagnosis in the nonresponsive group was lower than that in the responsive group, but the difference was not significant. Treg levels were significantly decreased and were functionally impaired at the time of diagnosis of pediatric AA. However, there was no significant change in Tregs at the resolution of AA.

Activity of eltrombopag in severe aplastic anemia

Since the approval of horse antithymocyte globulin (ATG) decades ago, there was a long hiatus in therapies with activity in severe aplastic anemia (SAA). This scenario changed in 2014 when eltrombopag, a thrombopoietin receptor agonist, was approved for SAA after an insufficient response to initial immunosuppressive therapy (IST). The basis for this approval was the observation of single-agent activity of eltrombopag in this patient population, where 40% to 50% recovered blood counts at times involving >1 lineage. The achievement of transfusion independence confirmed the clinical benefit of this approach. Increase in marrow cellularity and CD34+ cells suggested a recovery to a more functioning bone marrow. Further in its development, eltrombopag was associated with standard horse ATG plus cyclosporine in first line, producing increases in overall (at about 90%) and complete response rates (at about 40%) and leading to transfusion independence and excellent survival. Interestingly, best results were observed when all drugs were started simultaneously. The cumulative incidence of clonal cytogenetic abnormalities to date has compared favorably with the vast experience with IST alone in SAA. Longer follow-up will help in define these long-term risks. In this review, the development of eltrombopag in SAA will be discussed.

Computational Immune Monitoring Reveals Abnormal Double-Negative T Cells Present across Human Tumor Types

Advances in single-cell biology have enabled measurements of >40 protein features on millions of immune cells within clinical samples. However, the data analysis steps following cell population identification are susceptible to bias, time-consuming, and challenging to compare across studies. Here, an ensemble of unsupervised tools was developed to evaluate four essential types of immune cell information, incorporate changes over time, and address diverse immune monitoring challenges. The four complementary properties characterized were (i) systemic plasticity, (ii) change in population abundance, (iii) change in signature population features, and (iv) novelty of cellular phenotype. Three systems immune monitoring studies were selected to challenge this ensemble approach. In serial biopsies of melanoma tumors undergoing targeted therapy, the ensemble approach revealed enrichment of double-negative (DN) T cells. Melanoma tumor-resident DN T cells were abnormal and phenotypically distinct from those found in nonmalignant lymphoid tissues, but similar to those found in glioblastoma and renal cell carcinoma. Overall, ensemble systems immune monitoring provided a robust, quantitative view of changes in both the system and cell subsets, allowed for transparent review by human experts, and revealed abnormal immune cells present across multiple human tumor types.

Human retinoic acid-regulated CD161+ regulatory T cells support wound repair in intestinal mucosa

Repair of tissue damaged during inflammatory processes is key to the return of local homeostasis and restoration of epithelial integrity. Here we describe CD161⁺ regulatory T (T_reg) cells as a distinct, highly suppressive population of T_reg cells that mediate wound healing. These T_reg cells were enriched in intestinal lamina propria, particularly in Crohn's disease. CD161⁺ T_reg cells had an all-trans retinoic acid (ATRA)-regulated gene signature, and CD161 expression on T_reg cells was induced by ATRA, which directly regulated the CD161 gene. CD161 was co-stimulatory, and ligation with the T cell antigen receptor induced cytokines that accelerated the wound healing of intestinal epithelial cells. We identified a transcription-factor network, including BACH2, RORγt, FOSL2, AP-1 and RUNX1, that controlled expression of the wound-healing program, and found a CD161⁺ T_reg cell signature in Crohn's disease mucosa associated with reduced inflammation. These findings identify CD161⁺ T_reg cells as a population involved in controlling the balance between inflammation and epithelial barrier healing in the gut.

Aplastic anemia: Etiology, molecular pathogenesis, and emerging concepts

Aplastic anemia (AA) is rare disorder of bone marrow failure which if severe and not appropriately treated is highly fatal. AA is characterized by morphologic marrow features, namely hypocellularity, and resultant peripheral cytopenias. The molecular pathogenesis of AA is not fully understood, and a uniform process may not be the culprit across all cases. An antigen-driven and likely autoimmune dysregulated T-cell homeostasis is implicated in the hematopoietic stem cell injury which ultimately founds the pathologic features of the disease. Defective telomerase function and repair may also play a role in some cases as evidenced by recurring mutations in related telomerase complex genes such as TERT and TERC. In addition, recurring mutations in BCOR/BCORL, PIGA, DNMT3A, and ASXL1 as well as cytogenetic abnormalities, namely monosomy 7, trisomy 8, and uniparental disomy of the 6p arm seem to be intimately related to AA pathogenesis. The increased incidence of late clonal disease has also provided clues to accurately describe plausible predispositions to the development of AA. The emergence of newer genomic sequencing and other techniques is incrementally improving the understanding of the pathogenic mechanisms of AA, the detection of the disease, and ultimately offers the potential to improve patient outcomes. In this comprehensive review, we discuss the current understanding of the immunobiology, molecular pathogenesis, and future directions of such for AA.

Immune-Phenotyping and Transcriptomic Profiling of Peripheral Blood Mononuclear Cells From Patients With Breast Cancer: Identification of a 3 Gene Signature Which Predicts Relapse of Triple Negative Breast Cancer

Background: Interactions between the immune system and tumors are highly reciprocal in nature, leading to speculation that tumor recurrence or therapeutic resistance could be influenced or predicted by immune events that manifest locally, but can be detected systemically.

Methods: Multi-parameter flow cytometry was used to examine the percentage and phenotype of natural killer (NK) cells, myeloid-derived suppressor cells (MDSCs), monocyte subsets and regulatory T (Treg) cells in the peripheral blood of of 85 patients with breast cancer (50 of whom were assessed before and after one cycle of anthracycline-based chemotherapy), and 23 controls. Transcriptomic profiles of peripheral blood mononuclear cells (PBMCs) in 23 patients were generated using a NanoString gene profiling platform.

Results: An increased percentage of immunosuppressive cells such as granulocytic MDSCs, intermediate CD14⁺⁺CD16⁺ monocytes and CD127^negCD25^highFoxP3⁺ Treg cells was observed in patients with breast cancer, especially patients with stage 3 and 4 disease, regardless of ER status. Following neoadjuvant chemotherapy, B cell numbers decreased significantly, whereas monocyte numbers increased. Although chemotherapy had no effect on the percentage of Treg, MDSC and NK cells, the expression of inhibitory receptors CD85j, LIAR and NKG2A and activating receptors NKp30 and NKp44 on NK cells increased, concomitant with a decreased expression of NKp46 and DNAM-1 activating receptors. Transcriptomic profiling revealed a distinct group of 3 patients in the triple negative breast cancer (TNBC) cohort who expressed high levels of mRNA encoding genes predominantly involved in inflammation. The analysis of a large transcriptomic dataset derived from the tumors of patients with TNBC revealed that the expression of CD163, CXCR4, THBS1 predicted relapse-free survival.

Conclusions: The peripheral blood immunome of patients with breast cancer is influenced by the presence and stage of cancer, but not by molecular subtypes. Furthermore, immune profiling coupled with transcriptomic analyses of peripheral blood cells may identify patients with TNBC that are at risk of relapse after chemotherapy.

Somatic Mutations in Aplastic Anemia

Aplastic anemia (AA) is an immune-mediated disorder that overlaps closely with clonal disorders, such as myelodysplastic syndrome and paroxysmal nocturnal hemoglobinuria (PNH). PIGA mutations in PNH clones and functional loss of HLA, including structural HLA mutations, likely represent immune escape clones and correlate with response to immunosuppressive therapy (IST). Somatic mutations typical for myeloid malignancies and age-related clonal hematopoiesis are detected in a proportion of AA patients, but their significance is unclear and seems to depend on whether patients are tested at diagnosis or after IST, patient age and ethnicity, and the methodology of molecular testing used.

Cell Therapy in Organ Transplantation: Our Experience on the Clinical Translation of Regulatory T Cells

Solid organ transplantation is the treatment of choice for patients with end-stage organ dysfunction. Despite improvements in short-term outcome, long-term outcome is suboptimal due to the increased morbidity and mortality associated with the toxicity of immunosuppressive regimens and chronic rejection (1–5). As such, the attention of the transplant community has focused on the development of novel therapeutic strategies to achieve allograft tolerance, a state whereby the immune system of the recipient can be re-educated to accept the allograft, averting the need for long-term immunosuppression. Indeed, reports of “operational” tolerance, whereby the recipient is off all immunosuppressive drugs and maintaining good graft function, is well documented in the literature for both liver and kidney transplantations (6–8). However, this phenomenon is rare and in the setting of liver transplantation has been shown to occur late after transplantation, with the majority of patients maintained on life-long immunosupression to prevent allograft rejection (9). As such, significant research has focused on immune regulation in the context of organ transplantation with regulatory T cells (Tregs) identified as cells holding considerable promise in this endeavor. This review will provide a brief introduction to human Tregs, their phenotypic and functional characterization and focuses on our experience to date at the clinical translation of Treg immunotherapy in the setting of solid organ transplantation.

Danazol increases T regulatory cells in patients with aplastic anemia

OBJECTIVES

Danazol is an attenuated androgen and is used in the treatment of aplastic anemia (AA) in resource constraint settings. We chose to study the role of CD4+ CD25^high CD127^low FoxP3+ T regulatory cells (T-regs) in the pathophysiology of AA and their response to treatment with Danazol alone or in combination with immunosuppressive treatment (IST).

METHODS

T-regs' percentages of 25 acquired idiopathic AA patients and 25 healthy controls who completed study protocol were analyzed by performing multicolor flowcytometry on peripheral blood samples.

RESULTS

More than one-third (36%) of AA patients in our study received Danazol as monotherapy, whereas less than a third (32%) each received standard doses of IST with equine Anti Thymocyte Globulin (ATG) and Cyclosporine combination, or Cyclosporine and Danazol combination, respectively. Results showed that all AA patients had a significantly lower percentage of T-regs at the time of diagnosis when compared to healthy controls (p < 0.0001), implicating their role in the pathophysiology. On treatment, all 25 patients showed a significant rise in the percentage of T-regs when compared to baseline (p < 0.0001).

DISCUSSION

The rise in T-regs' percentage was higher in patients treated with Danazol alone when compared to standard IST (ATG with Cyclosporine), or Cyclosporine with Danazol combinations (p = 0.585).

CONCLUSION

We conclude that Danazol also leads to increase in T-regs in acquired idiopathic AA.

α1-Antitrypsin infusion for treatment of steroid-resistant acute graft-versus-host disease

Corticosteroid resistance after acute graft-versus-host disease (SR-aGVHD) results in high morbidity and mortality after allogeneic hematopoietic cell transplantation. Current immunosuppressive therapies for SR-aGVHD provide marginal effectiveness because of poor response or excessive toxicity, primarily from infection. α₁-Antitrypsin (AAT), a naturally abundant serine protease inhibitor, is capable of suppressing experimental GVHD by downmodulating inflammation and increasing ratios of regulatory (T_reg) to effector T cells (T_effs). In this prospective multicenter clinical study, we sought to determine the safety and response rate of AAT administration in SR-aGVHD. Forty patients with a median age of 59 years received intravenous AAT twice weekly for 4 weeks as first-line treatment of SR-aGVHD. The primary end point was overall response rate (ORR), the proportion of patients with SR-aGVHD in complete (CR) or partial response by day 28 without addition of further immunosuppression. Treatment was well tolerated without drug-related adverse events. A significant increase in serum levels of AAT was observed after treatment. The ORR and CR rates by day 28 were 65% and 35%, respectively, and included responses in all aGVHD target organs. At day 60, responses were sustained in 73% of patients without intervening immunosuppression. Infectious mortality was 10% at 6 months and 2.5% within 30 days of last AAT infusion. Consistent with preclinical data, correlative samples showed an increase in ratio of activated T_regs to T_effs after AAT treatment. These data suggest that AAT is safe and may be potentially efficacious in treating SR-aGVHD. This trial was registered at www.clinicaltrials.gov as #NCT01700036.

Discovery of human cell selective effector molecules using single cell multiplexed activity metabolomics

Discovering bioactive metabolites within a metabolome is challenging because there is generally little foreknowledge of metabolite molecular and cell-targeting activities. Here, single-cell response profiles and primary human tissue comprise a response platform used to discover novel microbial metabolites with cell-type-selective effector properties in untargeted metabolomic inventories. Metabolites display diverse effector mechanisms, including targeting protein synthesis, cell cycle status, DNA damage repair, necrosis, apoptosis, or phosphoprotein signaling. Arrayed metabolites are tested against acute myeloid leukemia patient bone marrow and molecules that specifically targeted blast cells or nonleukemic immune cell subsets within the same tissue biopsy are revealed. Cell-targeting polyketides are identified in extracts from biosynthetically prolific bacteria, including a previously unreported leukemia blast-targeting anthracycline and a polyene macrolactam that alternates between targeting blasts or nonmalignant cells by way of light-triggered photochemical isomerization. High-resolution cell profiling with mass cytometry confirms response mechanisms and is used to validate initial observations.

Identity and Diversity of Human Peripheral Th and T Regulatory Cells Defined by Single-Cell Mass Cytometry

Human CD3⁺CD4⁺ Th cells, FOXP3⁺ T regulatory (Treg) cells, and T regulatory type 1 (Tr1) cells are essential for ensuring peripheral immune response and tolerance, but the diversity of Th, Treg, and Tr1 cell subsets has not been fully characterized. Independent functional characterization of human Th1, Th2, Th17, T follicular helper (Tfh), Treg, and Tr1 cells has helped to define unique surface molecules, transcription factors, and signaling profiles for each subset. However, the adequacy of these markers to recapitulate the whole CD3⁺CD4⁺ T cell compartment remains questionable. In this study, we examined CD3⁺CD4⁺ T cell populations by single-cell mass cytometry. We characterize the CD3⁺CD4⁺ Th, Treg, and Tr1 cell populations simultaneously across 23 memory T cell-associated surface and intracellular molecules. High-dimensional analysis identified several new subsets, in addition to the already defined CD3⁺CD4⁺ Th, Treg, and Tr1 cell populations, for a total of 11 Th cell, 4 Treg, and 1 Tr1 cell subsets. Some of these subsets share markers previously thought to be selective for Treg, Th1, Th2, Th17, and Tfh cells, including CD194 (CCR4)⁺FOXP3⁺ Treg and CD183 (CXCR3)⁺T-bet⁺ Th17 cell subsets. Unsupervised clustering displayed a phenotypic organization of CD3⁺CD4⁺ T cells that confirmed their diversity but showed interrelation between the different subsets, including similarity between Th1-Th2-Tfh cell populations and Th17 cells, as well as similarity of Th2 cells with Treg cells. In conclusion, the use of single-cell mass cytometry provides a systems-level characterization of CD3⁺CD4⁺ T cells in healthy human blood, which represents an important baseline reference to investigate abnormalities of different subsets in immune-mediated pathologies.

Forkhead-Box-P3 Gene Transfer in Human CD4+ T Conventional Cells for the Generation of Stable and Efficient Regulatory T Cells, Suitable for Immune Modulatory Therapy

The development of novel approaches to control immune responses to self- and allogenic tissues/organs represents an ambitious goal for the management of autoimmune diseases and in transplantation. Regulatory T cells (Tregs) are recognized as key players in the maintenance of peripheral tolerance in physiological and pathological conditions, and Treg-based cell therapies to restore tolerance in T cell-mediated disorders have been designed. However, several hurdles, including insufficient number of Tregs, their stability, and their antigen specificity, have challenged Tregs clinical applicability. In the past decade, the ability to engineer T cells has proven a powerful tool to redirect specificity and function of different cell types for specific therapeutic purposes. By using lentivirus-mediated gene transfer of the thymic-derived Treg transcription factor forkhead-box-P3 (FOXP3) in conventional CD4⁺ T cells, we converted effector T cells into Treg-like cells, endowed with potent in vitro and in vivo suppressive activity. The resulting CD4^FOXP3 T-cell population displays stable phenotype and suppressive function. We showed that this strategy restores Treg function in T lymphocytes from patients carrying mutations in FOXP3 [immune-dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX)], in whom CD4^FOXP3 T cell could be used as therapeutics to control autoimmunity. Here, we will discuss the potential advantages of using CD4^FOXP3 T cells for in vivo application in inflammatory diseases, where tissue inflammation may undermine the function of natural Tregs. These findings pave the way for the use of engineered Tregs not only in IPEX syndrome but also in autoimmune disorders of different origin and in the context of stem cell and organ transplantation.

Deep Immune Profiling of an Arginine-Enriched Nutritional Intervention in Patients Undergoing Surgery

Application of high-content immune profiling technologies has enormous potential to advance medicine. Whether these technologies reveal pertinent biology when implemented in interventional clinical trials is an important question. The beneficial effects of preoperative arginine-enriched dietary supplements (AES) are highly context specific, as they reduce infection rates in elective surgery, but possibly increase morbidity in critically ill patients. This study combined single-cell mass cytometry with the multiplex analysis of relevant plasma cytokines to comprehensively profile the immune-modifying effects of this much-debated intervention in patients undergoing surgery. An elastic net algorithm applied to the high-dimensional mass cytometry dataset identified a cross-validated model consisting of 20 interrelated immune features that separated patients assigned to AES from controls. The model revealed wide-ranging effects of AES on innate and adaptive immune compartments. Notably, AES increased STAT1 and STAT3 signaling responses in lymphoid cell subsets after surgery, consistent with enhanced adaptive mechanisms that may protect against postsurgical infection. Unexpectedly, AES also increased ERK and P38 MAPK signaling responses in monocytic myeloid-derived suppressor cells, which was paired with their pronounced expansion. These results provide novel mechanistic arguments as to why AES may exert context-specific beneficial or adverse effects in patients with critical illness. This study lays out an analytical framework to distill high-dimensional datasets gathered in an interventional clinical trial into a fairly simple model that converges with known biology and provides insight into novel and clinically relevant cellular mechanisms.

Rapamycin is highly effective in murine models of immune-mediated bone marrow failure

Acquired aplastic anemia, the prototypical bone marrow failure disease, is characterized by pancytopenia and marrow hypoplasia. Most aplastic anemia patients respond to immunosuppressive therapy, usually with anti-thymocyte globulin and cyclosporine, but some relapse on cyclosporine withdrawal or require long-term administration of cyclosporine to maintain blood counts. In this study, we tested efficacy of rapamycin as a new or alternative treatment in mouse models of immune-mediated bone marrow failure. Rapamycin ameliorated pancytopenia, improved bone marrow cellularity, and extended animal survival in a manner comparable to the standard dose of cyclosporine. Rapamycin effectively reduced Th1 inflammatory cytokines interferon-γ and tumor necrosis factor-α, increased the Th2 cytokine interleukin-10, stimulated expansion of functional regulatory T cells, eliminated effector CD8⁺ T cells (notably T cells specific to target cells bearing minor histocompatibility antigen H60), and preserved hematopoietic stem and progenitor cells. Rapamycin, but not cyclosporine, reduced the proportion of memory and effector T cells and maintained a pool of naïve T cells. Cyclosporine increased cytoplasmic nuclear factor of activated T-cells-1 following T-cell receptor stimulation, whereas rapamycin suppressed phosphorylation of two key signaling molecules in the mammalian target of rapamycin pathway, S6 kinase and protein kinase B. In summary, rapamycin was an effective therapy in mouse models of immune-mediated bone marrow failure, acting through different mechanisms to cyclosporine. Its specific expansion of regulatory T cells and elimination of clonogenic CD8⁺ effectors support its potential clinical utility in the treatment of aplastic anemia.

Regulatory T cells: tolerance induction in solid organ transplantation

The concept of regulatory T cell (T_reg ) therapy in transplantation is now a reality. Significant advances in science and technology have enabled us to isolate human T_regs , expand them to clinically relevant numbers and infuse them into human transplant recipients. With several Phase I/II trials under way investigating T_reg safety and efficacy it is now more crucial than ever to understand their complex biology. However, our journey is by no means complete; results from these trials will undoubtedly provoke both further knowledge and enquiry which, alongside evolving science, will continue to drive the optimization of T_reg therapy in the pursuit of transplantation tolerance. In this review we will summarize current knowledge of T_reg biology, explore novel technologies in the setting of T_reg immunotherapy and address key prerequisites surrounding the clinical application of T_regs in transplantation.

Preparing Viable Single Cells from Human Tissue and Tumors for Cytomic Analysis

Mass cytometry is a single-cell biology technique that samples >500 cells per second, measures >35 features per cell, and is sensitive across a dynamic range of >104 relative intensity units per feature. This combination of technical assets has powered a series of recent cytomic studies where investigators used mass cytometry to measure protein and phospho-protein expression in millions of cells, characterize rare cell types in healthy and diseased tissues, and reveal novel, unexpected cells. However, these advances largely occurred in studies of blood, lymphoid tissues, and bone marrow, since the cells in these tissues are readily obtained in single-cell suspensions. This unit establishes a primer for single-cell analysis of solid tumors and tissues, and has been tested with mass cytometry. The cells obtained from these protocols can be fixed for study, cryopreserved for long-term storage, or perturbed ex vivo to dissect responses to stimuli and inhibitors. © 2017 by John Wiley & Sons, Inc.