The fetal liver counterpart of adult common lymphoid progenitors gives rise to all lymphoid lineages, CD45+CD4+CD3- cells, as well as macrophages

Early life imprinting of intestinal immune tolerance and tissue homeostasis

Besides its canonical role in protecting the host from pathogens, the immune system plays an arguably equally important role in maintaining tissue homeostasis. Within barrier tissues that interface with the external microenvironment, induction of immune tolerance to innocuous antigens, such as commensal, dietary, and environmental antigens, is key to establishing immune homeostasis. The early postnatal period represents a critical window of opportunity in which parallel development of the tissue, immune cells, and microbiota allows for reciprocal regulation that shapes the long-term immunological tone of the tissue and subsequent risk of immune-mediated diseases. During early infancy, the immune system appears to sacrifice pro-inflammatory functions, prioritizing the establishment of tissue tolerance. In this review, we discuss mechanisms underlying early life windows for intestinal tolerance with a focus on newly identified RORγt+ antigen-presenting cells-Thetis cells-and highlight the role of the intestinal microenvironment in shaping intestinal immune system development and tolerance.

Tertiary lymphoid structures in autoimmune diseases

Tertiary lymphoid structures (TLSs) are organized lymphoid-like aggregations in non-lymphoid tissues. Tissues with chronic and persistent inflammation infiltration may drive and form ectopic germinal center-like structures, which are very common in autoimmune diseases, chronic infections, and tumor microenvironments. However, the mechanisms governing the formation of TLSs are still being explored. At present, it is not clear whether the formation of TLSs is associated with local uncontrolled immune inflammatory responses. While TLSs suggest a good prognosis in tumors, the opposite is true in autoimmune diseases. This review article will discuss the current views on initiating and maintaining TLSs and the potential therapeutic target in autoimmune diseases.

Natural killer cells and their exosomes in viral infections and related therapeutic approaches: where are we?

Innate immunity is the first line of the host immune system to fight against infections. Natural killer cells are the innate immunity lymphocytes responsible for fighting against virus-infected and cancerous cells. They have various mechanisms to suppress viral infections. On the other hand, viruses have evolved to utilize different ways to evade NK cell-mediated responses. Viruses can balance the response by regulating the cytokine release pattern and changing the proportion of activating and inhibitory receptors on the surface of NK cells. Exosomes are a subtype of extracellular vesicles that are involved in intercellular communication. Most cell populations can release these nano-sized vesicles, and it was shown that these vesicles produce identical outcomes to the originating cell from which they are released. In recent years, the role of NK cell-derived exosomes in various diseases including viral infections has been highlighted, drawing attention to utilizing the therapeutic potential of these nanoparticles. In this article, the role of NK cells in various viral infections and the mechanisms used by viruses to evade these important immune system cells are initially examined. Subsequently, the role of NK cell exosomes in controlling various viral infections is discussed. Finally, the current position of these cells in the treatment of viral infections and the therapeutic potential of their exosomes are reviewed. Video Abstract.

Transcription factor TCF-1 regulates the functions, but not the development, of lymphoid tissue inducer subsets in different tissues

Lymphoid tissue inducer (LTi) cells, a subset of innate lymphoid cells (ILCs), play an essential role in the formation of secondary lymphoid tissues. However, the regulation of the development and functions of this ILC subset is still elusive. In this study, we report that the transcription factor T cell factor 1 (TCF-1), just as GATA3, is indispensable for the development of non-LTi ILC subsets. While LTi cells are still present in TCF-1-deficient mice, the organogenesis of Peyer's patches (PPs), but not of lymph nodes, is impaired in these mice. LTi cells from different tissues have distinct gene expression patterns, and TCF-1 regulates the expression of lymphotoxin specifically in PP LTi cells. Mechanistically, TCF-1 may directly and/or indirectly regulate Lta, including through promoting the expression of GATA3. Thus, the TCF-1-GATA3 axis, which plays an important role during T cell development, also critically regulates the development of non-LTi cells and tissue-specific functions of LTi cells.

A local subset of mesenchymal cells expressing the transcription factor Osr1 orchestrates lymph node initiation

During development, lymph node (LN) initiation is coordinated by lymphoid tissue organizer (LTo) cells that attract lymphoid tissue inducer (LTi) cells at strategic positions within the embryo. The identity and function of LTo cells during the initial attraction of LTi cells remain poorly understood. Using lineage tracing, we demonstrated that a subset of Osr1-expressing cells was mesenchymal LTo progenitors. By investigating the heterogeneity of Osr1+ cells, we uncovered distinct mesenchymal LTo signatures at diverse anatomical locations, identifying a common progenitor of mesenchymal LTos and LN-associated adipose tissue. Osr1 was essential for LN initiation, driving the commitment of mesenchymal LTo cells independent of neural retinoic acid, and for LN-associated lymphatic vasculature assembly. The combined action of chemokines CXCL13 and CCL21 was required for LN initiation. Our results redefine the role and identity of mesenchymal organizer cells and unify current views by proposing a model of cooperative cell function in LN initiation.

Controversial role of ILC3s in intestinal diseases: A novelty perspective on immunotherapy

ILC3s have been identified as crucial immune regulators that play a role in maintaining host homeostasis and modulating the antitumor response. Emerging evidence supports the idea that LTi cells play an important role in initiating lymphoid tissue development, while other ILC3s can promote host defense and orchestrate adaptive immunity, mainly through the secretion of specific cytokines and crosstalk with other immune cells or tissues. Additionally, dysregulation of ILC3-mediated overexpression of cytokines, changes in subset abundance, and conversion toward other ILC subsets are closely linked with the occurrence of tumors and inflammatory diseases. Regulation of ILC3 cytokines, ILC conversion and LTi-induced TLSs may be a novel strategy for treating tumors and intestinal or extraintestinal inflammatory diseases. Herein, we discuss the development of ILCs, the biology of ILC3s, ILC plasticity, the correlation of ILC3s and adaptive immunity, crosstalk with the intestinal microenvironment, controversial roles of ILC3s in intestinal diseases and potential applications for treatment.

Cell autonomous expression of BCL6 is required to maintain lineage identity of mouse CCR6+ ILC3s

Innate lymphoid cells (ILC) are similar to T helper (Th) cells in expression of cytokines and transcription factors. For example, RORγt is the lineage-specific transcription factor for both ILC3 and Th17 cells. However, the ILC counterpart for BCL6-expressing T follicular helper (Tfh) cells has not been defined. Here, we report that in the ILC compartment, BCL6 is selectively co-expressed with not only CXCR5 but also RORγt and CCR6 in ILC3 from multiple tissues. BCL6-deficient ILC3 produces enhanced levels of IL-17A and IL-22. More importantly, phenotypic and single-cell ATAC-seq analysis show that absence of BCL6 in mature ILC3 increases the numbers of ILC1 and transitional cells co-expressing ILC3 and ILC1 marker genes. A lineage-tracing experiment further reveals BCL6+ ILC3 to ILC1 trans-differentiation under steady state. Finally, microbiota promote BCL6 expression in colonic CCR6+ ILC3 and thus reinforce their stability. Collectively, our data have demonstrated that CCR6+ ILC3 have both Th17 and Tfh programs and that BCL6 expression in these cells functions to maintain their lineage identity.

Embryonic ILC-poiesis across tissues

The family of innate lymphoid cells (ILCs), consisting of Group 1 ILCs (natural killer cells and ILC1), ILC2, and ILC3, are critical effectors of innate immunity, inflammation, and homeostasis post-natally, but also exert essential functions before birth. Recent studies during critical developmental periods in the embryo have hinted at complex waves of tissue colonization, and highlighted the breadth of multipotent and committed ILC progenitors from both classic fetal hematopoietic organs such as the liver, as well as tissue sites such as the lung, thymus, and intestine. Assessment of the mechanisms driving cell fate and function of the ILC family in the embryo will be vital to the understanding ILC biology throughout fetal life and beyond.

Embryonic and neonatal waves generate distinct populations of hepatic ILC1s

Group 1 innate lymphoid cells (ILCs) comprising circulating natural killer (cNK) cells and tissue-resident ILC1s are critical for host defense against pathogens and tumors. Despite a growing understanding of their role in homeostasis and disease, the ontogeny of group 1 ILCs remains largely unknown. Here, we used fate mapping and single-cell transcriptomics to comprehensively investigate the origin and turnover of murine group 1 ILCs. Whereas cNK cells are continuously replaced throughout life, we uncovered tissue-dependent development and turnover of ILC1s. A first wave of ILC1s emerges during embryogenesis in the liver and transiently colonizes fetal tissues. After birth, a second wave quickly replaces ILC1s in most tissues apart from the liver, where they layer with embryonic ILC1s, persist until adulthood, and undergo a specific developmental program. Whereas embryonically derived ILC1s give rise to a cytotoxic subset, the neonatal wave establishes the full spectrum of ILC1s. Our findings uncover key ontogenic features of murine group 1 ILCs and their association with cellular identities and functions.

Organoids capture tissue-specific innate lymphoid cell development in mice and humans

Organoid-based models of murine and human innate lymphoid cell precursor (ILCP) maturation are presented. First, murine intestinal and pulmonary organoids are harnessed to demonstrate that the epithelial niche is sufficient to drive tissue-specific maturation of all innate lymphoid cell (ILC) groups in parallel, without requiring subset-specific cytokine supplementation. Then, more complex human induced pluripotent stem cell (hiPSC)-based gut and lung organoid models are used to demonstrate that human epithelial cells recapitulate maturation of ILC from a stringent systemic human ILCP population, but only when the organoid-associated stromal cells are depleted. These systems offer versatile and reductionist models to dissect the impact of environmental and mucosal niche cues on ILC maturation. In the future, these could provide insight into how ILC activity and development might become dysregulated in chronic inflammatory diseases.

The Acute Hepatic NF-κB-Mediated Proinflammatory Response to Endotoxemia Is Attenuated in Intrauterine Growth-Restricted Newborn Mice

Intrauterine growth restriction (IUGR) is a relevant predictor for higher rates of neonatal sepsis worldwide and is associated with an impaired neonatal immunity and lower immune cell counts. During the perinatal period, the liver is a key immunological organ responsible for the nuclear factor kappa B (NF-κB)-mediated innate immune response to inflammatory stimuli, but whether this role is affected by IUGR is unknown. Herein, we hypothesized that the newborn liver adapts to calorie-restriction IUGR by inducing changes in the NF-κB signaling transcriptome, leading to an attenuated acute proinflammatory response to intraperitoneal lipopolysaccharide (LPS). We first assessed the hepatic gene expression of key NF-κB factors in the IUGR and normally grown (NG) newborn mice. Real-time quantitative PCR (RT-qPCR) analysis revealed an upregulation of both IκB proteins genes (Nfkbia and Nfkbib) and the NF-κB subunit Nfkb1 in IUGR vs. NG. We next measured the LPS-induced hepatic expression of acute proinflammatory genes (Ccl3, Cxcl1, Il1b, Il6, and Tnf) and observed that the IUGR liver produced an attenuated acute proinflammatory cytokine gene response (Il1b and Tnf) to LPS in IUGR vs. unexposed (CTR). Consistent with these results, LPS-exposed hepatic tumor necrosis factor alpha (TNF-α) protein concentrations were lower in IUGR vs. LPS-exposed NG and did not differ from IUGR CTR. Sex differences at the transcriptome level were observed in the IUGR male vs. female. Our results demonstrate that IUGR induces key modifications in the NF-κB transcriptomic machinery in the newborn that compromised the acute proinflammatory cytokine gene and protein response to LPS. Our results bring novel insights in understanding how the IUGR newborn is immunocompromised due to fundamental changes in NF-κB key factors.

In utero inflammatory challenge induces an early activation of the hepatic innate immune response in late gestation fetal sheep

Chorioamnionitis is associated with inflammatory end-organ damage in the fetus. Tissues in direct contact with amniotic fluid drive a pro-inflammatory response and contribute to this injury. However, due to a lack of direct contact with the amniotic fluid, the liver contribution to this response has not been fully characterized. Given its role as an immunologic organ, we hypothesized that the fetal liver would demonstrate an early innate immune response to an in utero inflammatory challenge. Fetal sheep (131 ± 1 d gestation) demonstrated metabolic acidosis and high cortisol and norepinephrine values within 5 h of exposure to intra-amniotic LPS. Likewise, expression of pro-inflammatory cytokines increased significantly at 1 and 5 h of exposure. This was associated with NF-κB activation, by inhibitory protein IκBα degradation, and nuclear translocation of NF-κB subunits (p65/p50). Corroborating these findings, LPS exposure significantly increased pro-inflammatory innate immune gene expression in fetal sheep hepatic macrophages in vitro. Thus, an in utero inflammatory challenge induces an early hepatic innate immune response with systemic metabolic and stress responses. Within the fetal liver, hepatic macrophages respond robustly to LPS exposure. Our results demonstrate that the fetal hepatic innate immune response must be considered when developing therapeutic approaches to attenuate end-organ injury associated with in utero inflammation.

Maturation of the Acute Hepatic TLR4/NF-κB Mediated Innate Immune Response Is p65 Dependent in Mice

Compared to adults, neonates are at increased risk of infection. There is a growing recognition that dynamic qualitative and quantitative differences in immunity over development contribute to these observations. The liver plays a key role as an immunologic organ, but whether its contribution to the acute innate immune response changes over lifetime is unknown. We hypothesized that the liver would activate a developmentally-regulated acute innate immune response to intraperitoneal lipopolysaccharide (LPS). We first assessed the hepatic expression and activity of the NF-κB, a key regulator of the innate immune response, at different developmental ages (p0, p3, p7, p35, and adult). Ontogeny of the NF-κB subunits (p65/p50) revealed a reduction in Rela (p65) and Nfkb1 (p105, precursor to p50) gene expression (p0) and p65 subunit protein levels (p0 and p3) vs. older ages. The acute hepatic innate immune response to LPS was associated by the degradation of the NF-κB inhibitory proteins (IκBα and IκBβ), and nuclear translocation of the NF-κB subunit p50 in all ages, whereas nuclear translocation of the NF-κB subunit p65 was only observed in the p35 and adult mouse. Consistent with these findings, we detected NF-κB subunit p65 nuclear staining exclusively in the LPS-exposed adult liver compared with p7 mouse. We next interrogated the LPS-induced hepatic expression of pro-inflammatory genes (Tnf, Icam1, Ccl3, and Traf1), and observed a gradually increase in gene expression starting from p0. Confirming our results, hepatic NF-κB subunit p65 nuclear translocation was associated with up-regulation of the Icam1 gene in the adult, and was not detected in the p7 mouse. Thus, an inflammatory challenge induces an NF-κB-mediated hepatic innate immune response activation across all developmental ages, but nuclear translocation of the NF-κB subunit p65 and associated induction of pro-inflammatory genes occurred only after the first month of life. Our results demonstrate that the LPS-induced hepatic innate immune response is developmentally regulated by the NF-κB subunit p65 in the mouse.

New Molecular Insights into Immune Cell Development

During development innate lymphoid cells and specialized lymphocyte subsets colonize peripheral tissues, where they contribute to organogenesis and later constitute the first line of protection while maintaining tissue homeostasis. A few of these subsets are produced only during embryonic development and remain in the tissues throughout life. They are generated through a unique developmental program initiated in lympho-myeloid-primed progenitors, which lose myeloid and B cell potential. They either differentiate into innate lymphoid cells or migrate to the thymus to give rise to embryonic T cell receptor-invariant T cells. At later developmental stages, adaptive T lymphocytes are derived from lympho-myeloid progenitors that colonize the thymus, while lymphoid progenitors become specialized in the production of B cells. This sequence of events highlights the requirement for stratification in the establishment of immune functions that determine efficient seeding of peripheral tissues by a limited number of cells.

Hematopoietic Stem Cells and Their Roles in Tissue Regeneration

Hematopoietic stem cells (HSCs) are regarded as one of essential cell sources for treating regenerative diseases. Among many stem cells, the feasibility of using adult-derived hematopoietic stem cells in therapeutic approaches is very diverse, and is unarguably regarded as an important cell source in stem cell biology. So far, many investigators are exploring HSCs and modified HSCs for use in clinical and basic science. In the present review, we briefly summarized HSCs and their application in pathophysiologic conditions, including non-hematopoietic tissue regeneration as well as blood disorders. HSCs and HSCs-derived progenitors are promising cell sources in regenerative medicine and their contributions can be properly applied to treat pathophysiologic conditions. Among many adult stem cells, HSCs are a powerful tool to treat patients with diseases such as hematologic malignancies and liver disease. Since HSCs can be differentiated into diverse progenitors including endothelial progenitors, they may be useful for constructing strategies for effective therapy.

Chemokines and other mediators in the development and functional organization of lymph nodes

Secondary lymphoid organs like lymph nodes (LNs) are the main inductive sites for adaptive immune responses. Lymphocytes are constantly entering LNs, scanning the environment for their cognate antigen and get replenished by incoming cells after a certain period of time. As only a minor percentage of lymphocytes recognizes cognate antigen, this mechanism of permanent recirculation ensures fast and effective immune responses when necessary. Thus, homing, positioning, and activation as well as egress require precise regulation within LNs. In this review we discuss the mediators, including chemokines, cytokines, growth factors, and others that are involved in the formation of the LN anlage and subsequent functional organization of LNs. We highlight very recent findings in the fields of LN development, steady-state migration in LNs, and the intranodal processes during an adaptive immune response.

9-O-acetyl sialic acid levels identify committed progenitors of plasmacytoid dendritic cells

The origins of plasmacytoid dendritic cells (pDCs) have long been controversial and progenitors exclusively committed to this lineage have not been described. We show here that the fate of hematopoietic progenitors is determined in part by their surface levels of 9-O-acetyl sialic acid. Pro-pDCs were identified as lineage negative 9-O-acetyl sialic acid low progenitors that lack myeloid and lymphoid potential but differentiate into pre-pDCs. The latter cells are also lineage negative, 9-O-acetyl sialic acid low cells but are exclusively committed to the pDC lineage. Levels of 9-O-acetyl sialic acid provide a distinct way to define progenitors and thus facilitate the study of hematopoietic differentiation.

The influence of space and time on the establishment of B cell identity

During embryonic development multiple waves of hematopoietic progenitors with distinct lineage potential are differentially regulated in time and space. Consistent with this view, some specialized lymphocytes emerge during a limited time-window in embryogenesis and migrate to the tissues where they contribute to organogenesis and to tissue homeostasis. These cells are not constantly produced by bone marrow derived hematopoietic stem cells but are maintained in tissues and self-renew throughout life. These particular cell subsets are produced from lymphoid restricted progenitors only found in the first days of fetal liver hematopoietic activity. Growing evidence of the heterogeneity and layered organization of the hematopoietic system is leading to a common view that some lymphocyte subsets are functionally different because they follow distinct developmental programs and emerge from distinct waves of lymphoid progenitors. However, understanding the influence of developmental origin and the relative contribution of local microenvironment on the development of these specialized lymphocyte subsets needs further analysis. In this review, we discuss how different pathways followed by developing B cells during ontogeny may contribute to the diverse functions.

The lymphoid-associated interleukin 7 receptor (IL7R) regulates tissue-resident macrophage development

The discovery of a fetal origin for tissue-resident macrophages (trMacs) has inspired an intense search for the mechanisms underlying their development. Here, we performed in vivo lineage tracing of cells with an expression history of IL7Rα, a marker exclusively associated with the lymphoid lineage in adult hematopoiesis. Surprisingly, we found that Il7r-Cre labeled fetal-derived, adult trMacs. Labeling was almost complete in some tissues and partial in others. The putative progenitors of trMacs, yolk sac (YS) erythromyeloid progenitors, did not express IL7R, and YS hematopoiesis was unperturbed in IL7R-deficient mice. In contrast, tracking of IL7Rα message levels, surface expression, and Il7r-Cre-mediated labeling across fetal development revealed dynamic regulation of Il7r mRNA expression and rapid upregulation of IL7Rα surface protein upon transition from monocyte to macrophage within fetal tissues. Fetal monocyte differentiation in vitro produced IL7R⁺ macrophages, supporting a direct progenitor-progeny relationship. Additionally, blockade of IL7R function during late gestation specifically impaired the establishment of fetal-derived trMacs in vivo These data provide evidence for a distinct function of IL7Rα in fetal myelopoiesis and identify IL7R as a novel regulator of trMac development.

Type 2 innate lymphoid cells in the induction and resolution of tissue inflammation

Type 2 immunity against pathogens is tightly regulated to ensure appropriate inflammatory responses that clear infection and prevent excessive tissue damage. Recent research has shown that type 2 innate lymphoid cells (ILC2s) contribute to steady-state tissue integrity and exert tissue-specific functions. However, upon exposure to inflammatory stimuli, they also initiate and amplify type 2 inflammation by inducing mucus production, eosinophilia, and Th2 differentiation. In this review, we discuss the regulation of ILC2 activation by transcription factors and metabolic pathways, as well as by extrinsic signals such as cytokines, lipid mediators, hormones, and neuropeptides. We also review recent discoveries about ILC2 plasticity and heterogeneity in different tissues, as revealed partly through single-cell RNA sequencing of transcriptional responses to various stimuli. Understanding the tissue-specific pathways that regulate ILC2 diversity and function is a critical step in the development of potential therapies for allergic diseases.

Contribution of LTi and TH17 cells to B cell aggregate formation in the central nervous system in a mouse model of multiple sclerosis

Background

In a subgroup of patients suffering from progressive multiple sclerosis (MS), which is an inflammation-mediated neurodegenerative disease of the central nervous system (CNS), B cell aggregates were discovered within the meninges. Occurrence of these structures was associated with a more severe disease course and cortical histopathology. We have developed the B cell-dependent MP4-induced experimental autoimmune encephalomyelitis (EAE) as a mouse model to mimic this trait of the human disease. The aim of this study was to determine a potential role of lymphoid tissue inducer (LTi) and T_H17 cells in the process of B cell aggregate formation in the MP4 model.

Methods

We performed flow cytometry of cerebellar and splenic tissue of MP4-immunized mice in the acute and chronic stage of the disease to analyze the presence of CD3⁻CD5⁻CD4⁺RORγt⁺ LTi and CD3⁺CD5⁺CD4⁺RORγt⁺ T_H17 cells. Myelin oligodendrocyte glycoprotein (MOG):35–55-induced EAE was used as B cell-independent control model. We further determined the gene expression profile of B cell aggregates using laser capture microdissection, followed by RNA sequencing.

Results

While we were able to detect LTi cells in the embryonic spleen and adult intestine, which served as positive controls, there was no evidence for the existence of such a population in acute or chronic EAE in neither of the two models. Yet, we detected CD3⁻CD5⁻CD4⁻RORγt⁺ innate lymphoid cells (ILCs) and T_H17 cells in the CNS, the latter especially in the chronic stage of MP4-induced EAE. Moreover, we observed a unique gene signature in CNS B cell aggregates compared to draining lymph nodes of MP4-immunized mice and to cerebellum as well as draining lymph nodes of mice with MOG:35–55-induced EAE.

Conclusion

The absence of LTi cells in the cerebellum suggests that other cells might take over the function as an initiator of lymphoid tissue formation in the CNS. Overall, the development of ectopic lymphoid organs is a complex process based on an interplay between several molecules and signals. Here, we propose some potential candidates, which might be involved in the formation of B cell aggregates in the CNS of MP4-immunized mice.

Innate Lymphoid Cells in the Maternal and Fetal Compartments

Pregnancy success is orchestrated by the complex balance between the maternal and fetal immune systems. Herein, we summarize the potential role of innate lymphoid cells (ILCs) in the maternal and fetal compartments. We reviewed published literature describing different ILC subsets [ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTi) cells] in the uterus, decidua, fetal tissues [liver, secondary lymphoid organs (SLO), intestine, and lung] and amniotic cavity. ILC1s, ILC2s, and ILC3s are present in the murine uterus prior to and during pregnancy but have only been detected in the non-pregnant endometrium in humans. Specifically, ILC2s reside in the murine uterus from mid-pregnancy to term, ILC1s increase throughout gestation, and ILC3s remain constant. Yet, LTi cells have only been detected in the non-pregnant murine uterus. In the human decidua, ILC1s, ILC3s, and LTi-like cells are more abundant during early gestation, whereas ILC2s increase at the end of pregnancy. Decidual ILC1s were also detected during mid-gestation in mice. Interestingly, functional decidual ILC2s and ILC3s increased in women who underwent spontaneous preterm labor, indicating the involvement of such cells in this pregnancy complication. Fetal ILCs exist in the liver, SLO, intestine, lung, and amniotic cavity. The fetal liver is thought to be the source of ILC progenitors since the differentiation of these cells from hematopoietic stem cells occurs at this site, and mature ILC subsets can be found in this compartment as well. The interaction between LTi cells and specialized stromal cells is important during the formation of SLO. Mature ILCs are found at the mucosal surfaces of the lung and intestine, from where they can extravasate into the amniotic cavity. Amniotic fluid ILCs express high levels of RORγt, CD161, and CD103, hallmarks of ILC3s. Such cells are more abundant in the second trimester than later in gestation. Although amniotic fluid ILC3s produce IL-17A and TNFα, indicating their functionality, their numbers in patients with intra-amniotic infection/inflammation remain unchanged compared to those without this pregnancy complication. Collectively, these findings suggest that maternal (uterine and decidual) ILCs play central roles in both the initiation and maintenance of pregnancy, and fetal ILCs participate in the development of immunity.

Multiple roles of lymphatic vessels in peripheral lymph node development

This work shows how blood and lymphatic vessels contribute to lymph node organogenesis. Both vessel types transport lymphoid tissue inducer cells, while lymphatics also generate interstitial flow, important for mechanical stromal activation and further lymph node expansion.

The mammalian lymphatic system consists of strategically located lymph nodes (LNs) embedded into a lymphatic vascular network. Mechanisms underlying development of this highly organized system are not fully understood. Using high-resolution imaging, we show that lymphoid tissue inducer (LTi) cells initially transmigrate from veins at LN development sites using gaps in venous mural coverage. This process is independent of lymphatic vasculature, but lymphatic vessels are indispensable for the transport of LTi cells that egress from blood capillaries elsewhere and serve as an essential LN expansion reservoir. At later stages, lymphatic collecting vessels ensure efficient LTi cell transport and formation of the LN capsule and subcapsular sinus. Perinodal lymphatics also promote local interstitial flow, which cooperates with lymphotoxin-β signaling to amplify stromal CXCL13 production and thereby promote LTi cell retention. Our data unify previous models of LN development by showing that lymphatics intervene at multiple points to assist LN expansion and identify a new role for mechanical forces in LN development.

The immunophenotype of amniotic fluid leukocytes in normal and complicated pregnancies

PROBLEM

The immune cellular composition of amniotic fluid is poorly understood. Herein, we determined: 1) the immunophenotype of amniotic fluid immune cells during the second and third trimester in the absence of intra-amniotic infection/inflammation; 2) whether amniotic fluid T cells and ILCs display different phenotypical characteristics to that of peripheral cells; and 3) whether the amniotic fluid immune cells are altered in women with intra-amniotic infection/inflammation.

METHOD OF STUDY

Amniotic fluid samples (n = 57) were collected from 15 to 40 weeks of gestation in women without intra-amniotic infection/inflammation. Samples from women with intra-amniotic infection/inflammation were also included (n = 9). Peripheral blood mononuclear cells from healthy adults were used as controls (n = 3). Immunophenotyping was performed using flow cytometry.

RESULTS

In the absence of intra-amniotic infection/inflammation, the amniotic fluid contained several immune cell populations between 15 and 40 weeks. Among these immune cells: (i) T cells and ILCs were greater than B cells and natural killer (NK) cells between 15 and 30 weeks; (ii) T cells were most abundant between 15 and 30 weeks; (iii) ILCs were most abundant between 15 and 20 weeks; (iv) B cells were scarce between 15 and 20 weeks; yet, they increased and were constant after 20 weeks; (v) NK cells were greater between 15 and 30 weeks than at term; (vi) ILCs expressed high levels of RORγt, CD161, and CD103 (ie, group 3 ILCs); (vii) T cells expressed high levels of RORγt; (viii) neutrophils increased as gestation progressed; and (ix) monocytes/macrophages emerged after 20 weeks and remained constant until term. All of the amniotic fluid immune cells, except ILCs, were increased in the presence of intra-amniotic infection/inflammation.

CONCLUSION

The amniotic fluid harbors a diverse immune cellular composition during normal and complicated pregnancies.

Lymphoid tissue inducer-A divergent member of the ILC family

Innate lymphoid cells (ILCs) that are capable of producing effector cytokines reminiscent of CD4⁺ T helper (Th) cells during infections and tissue inflammations have drawn much attention in the immunology field in recent years. Within the ILCs, the lymphoid tissue inducer (LTi) cells that play a critical role in lymphoid organogenesis were identified long before the establishment of the ILC concept. LTi cells, developed and functioning mainly at the fetal stage, and LTi-like cells, presumably generated during the adulthood, are regarded as a subset of type 3 ILCs (ILC3s) because they express the ILC3 lineage-defining transcription factor RORγt, and like other ILC3s, can produce an ILC3 signature cytokine IL-22 and initiate protective immune responses against extracellular bacteria. However, LTi/LTi-like cells have a unique gene expression pattern, and they develop from a progenitor that is distinct from the progenitor of all other ILCs and the progenitor of conventional natural killer (cNK) cells. There are also several other unique features of LTi/LTi-like cells comparing to non-LTi ILC3s. In addition to their classical function in lymphoid organogenesis, LTi/LTi-like cells also have specialized functions in association with the adaptive immune system, which include their effects on T and B cell development, activation and function. In this review, we summarize these specific features of LTi/LTi-like cells and propose that these cells should be considered as a separated innate lymphoid lineage in parallel with other non-LTi ILCs and cNK cells.

The influence of developmental timing on B cell diversity

The adult adaptive immune system is comprised of a wide spectrum of lymphocyte subsets with distinct antigen receptor repertoire profiles, effector functions, turnover times and anatomical locations, acting in concert to provide optimal host protection and self-regulation. While some lymphocyte populations are replenished by bone marrow hematopoietic stem cells (HSCs) through adulthood, others emerge during a limited window of time during fetal and postnatal life and sustain through self-replenishment. Despite fundamental implications in immune regeneration, early life immunity and leukemogenesis, the impact of developmental timing on lymphocyte output remains an under explored frontier in immunology. In this review, we spotlight recent insights into the developmental changes in B cell output in mice and explore how several age specific cellular and molecular factors may shape the formation of a diverse adaptive immune system.

Tertiary Lymphoid Structures in Cancer: Drivers of Antitumor Immunity, Immunosuppression, or Bystander Sentinels in Disease?

Secondary lymphoid organs are integral to initiation and execution of adaptive immune responses. These organs provide a setting for interactions between antigen-specific lymphocytes and antigen-presenting cells recruited from local infected or inflamed tissues. Secondary lymphoid organs develop as a part of a genetically preprogrammed process during embryogenesis. However, organogenesis of secondary lymphoid tissues can also be recapitulated in adulthood during de novo lymphoid neogenesis of tertiary lymphoid structures (TLSs). These ectopic lymphoid-like structures form in the inflamed tissues afflicted by various pathological conditions, including cancer, autoimmunity, infection, or allograft rejection. Studies are beginning to shed light on the function of such structures in different disease settings, raising important questions regarding their contribution to progression or resolution of disease. Data show an association between the tumor-associated TLSs and a favorable prognosis in various types of human cancer, attracting the speculation that TLSs support effective local antitumor immune responses. However, definitive evidence for the role for TLSs in fostering immune responses in vivo are lacking, with current data remaining largely correlative by nature. In fact, some more recent studies have even demonstrated an immunosuppressive, tumor-promoting role for cancer-associated TLSs. In this review, we will discuss what is known about the development of cancer-associated TLSs and the current understanding of their potential role in the antitumor immune response.

Asynchronous lineage priming determines commitment to T cell and B cell lineages in fetal liver

The molecular events that initiate lymphoid-lineage specification remain unidentified because the stages of differentiation during which lineage commitment occurs are difficult to characterize. We isolated fetal liver progenitor cells undergoing restriction of their differentiation potential toward the T cell-innate lymphoid cell lineage or the B cell lineage. Transcripts that defined the molecular signatures of these two subsets were sequentially upregulated in lympho-myeloid precursor cells and in common lymphoid progenitor cells, respectively, and this preceded lineage restriction; this indicates that T cell-versus-B cell commitment is not a binary fate 'decision'. The T cell-bias and B cell-bias transcriptional programs were frequently co-expressed in common lymphoid progenitor cells and were segregated in subsets biased toward T cell differentiation or B cell differentiation, after interleukin 7 (IL-7) signaling that controlled the number of progenitor cells engaging in T cell differentiation versus B cell differentiation.

The transcription factor Gli3 promotes B cell development in fetal liver through repression of Shh

Solanki et al. show that stromal activity of the transcription factor Gli3 is required for B cell development in the fetal liver. Gli3 functions to repress Shh expression, and Shh signals to developing B cells to regulate their development at multiple developmental stages.

Before birth, B cells develop in the fetal liver (FL). In this study, we show that Gli3 activity in the FL stroma is required for B cell development. In the Gli3-deficient FL, B cell development was reduced at multiple stages, whereas the Sonic hedgehog (Hh [Shh])–deficient FL showed increased B cell development, and Gli3 functioned to repress Shh transcription. Use of a transgenic Hh-reporter mouse showed that Shh signals directly to developing B cells and that Hh pathway activation was increased in developing B cells from Gli3-deficient FLs. RNA sequencing confirmed that Hh-mediated transcription is increased in B-lineage cells from Gli3-deficient FL and showed that these cells expressed reduced levels of B-lineage transcription factors and B cell receptor (BCR)/pre-BCR–signaling genes. Expression of the master regulators of B cell development Ebf1 and Pax5 was reduced in developing B cells from Gli3-deficient FL but increased in Shh-deficient FL, and in vitro Shh treatment or neutralization reduced or increased their expression, respectively.

Extending and Applying Spartan to Perform Temporal Sensitivity Analyses for Predicting Changes in Influential Biological Pathways in Computational Models

Through integrating real time imaging, computational modelling, and statistical analysis approaches, previous work has suggested that the induction of and response to cell adhesion factors is the key initiating pathway in early lymphoid tissue development, in contrast to the previously accepted view that the process is triggered by chemokine mediated cell recruitment. These model derived hypotheses were developed using spartan, an open-source sensitivity analysis toolkit designed to establish and understand the relationship between a computational model and the biological system that model captures. Here, we extend the functionality available in spartan to permit the production of statistical analyses that contrast the behavior exhibited by a computational model at various simulated time-points, enabling a temporal analysis that could suggest whether the influence of biological mechanisms changes over time. We exemplify this extended functionality by using the computational model of lymphoid tissue development as a time-lapse tool. By generating results at twelve- hour intervals, we show how the extensions to spartan have been used to suggest that lymphoid tissue development could be biphasic, and predict the time-point when a switch in the influence of biological mechanisms might occur.

Isolation and Flow Cytometry Analysis of Innate Lymphoid Cells from the Intestinal Lamina Propria

The intestinal mucosa constitutes the biggest surface area of the body. It is constantly challenged by bacteria, commensal and pathogenic, protozoa, and food-derived irritants. In order to maintain homeostasis, a complex network of signaling circuits has evolved that includes contributions of immune cells. In recent years a subset of lymphocytes, which belong to the innate immune system, has caught particular attention. These so-called innate lymphoid cells (ILC) reside within the lamina propria of the small and large intestines and rapidly respond to environmental challenges. They provide immunity to various types of infections but may also contribute to organ homeostasis as they produce factors acting on epithelial cells thereby enhancing barrier integrity. Here, we describe how these cells can be isolated from their environment and provide an in-depth protocol how to visualize the various ILC subsets by flow cytometry.

Fetal Lymphoid Progenitors Become Restricted to B-1 Fates Coincident with IL-7Rα Expression

B-1 cells represent a sub-fraction of B lymphocytes that participate in T cell-independent antibody production and contribute to innate immunity. While the production of B-1 cells is favored during the fetal waves of lymphopoiesis, it has been unclear when and how that differentiation option is specified. To clarify this, lymphoid and hematopoietic progenitors of fetal liver (FL) and adult bone marrow (ABM) were examined for the B cell differentiation potential. Mouse common lymphoid progenitors (CLPs) and more primitive KSL fraction of FL and ABM were transferred to SCID mice and donor-derived B cell subsets were analyzed 4 weeks later. CLPs were also cultured on ST2 stromal cells for 6 days prior to transplantation. While Lin^- IL-7Rα⁺ CLPs from ABM differentiated to B-1, B-2 and marginal zone B (MZB) cells, equivalent cells from d15 FL differentiated mostly to B-1a cells. We found that fetal CLPs had less ability to colonize the bone marrow than adult CLPs. However, the fetal/adult difference was already present when progenitors were cultured in an identical condition before transplantation. More primitive KSL fraction of FL could generate the same broad spectrum of B cells typical of adults, including splenic MZB cells. In conclusion, we argue that FL and ABM-CLPs are intrinsically different regarding B-1/B-2 fates and the difference is acquired just before or coincident with the acquisition of IL-7Rα expression.

Circulating innate lymphoid cells are unchanged in response to DAC HYP therapy

Innate lymphoid cells (ILCs) play an important role in immunity, inflammation, and tissue remodeling and their dysregulation is implicated in autoimmune and inflammatory disorders. We analyzed the impact of daclizumab, a humanized monoclonal anti-CD25 antibody, on circulating natural killer (NK) cells and ILCs in a cohort of multiple sclerosis patients. An increase in CD56(bright) NK cells and CD56(hi)CD16(intermediate) transitional NK cells was observed. No significant change in total ILCs or major ILC subpopulations was observed. These results refine our understanding of the impact of daclizumab on innate lymphoid cell populations.

Exploring the multifaceted nature of the common lymphoid progenitor compartment

While the common lymphoid progenitor compartment was originally thought to be a rather homogenous cell population, it has become increasingly clear that this compartment is highly heterogeneous both with regard to phenotypic and functional features. The exploration of this cellular complexity has generated novel molecular insights into regulatory events in lymphoid lineage restriction and provided support for the idea that multiple lineage restriction events occur at this developmental stage. Furthermore, the identification of multiple lineage-restricted progenitors with mixed lineage potential challenges a strictly hierarchical model for lymphoid development. Instead we propose a model based on competence windows during which cell fates are established through the action of lineage determining factors.

Flt3 Ligand Regulates the Development of Innate Lymphoid Cells in Fetal and Adult Mice

Flt3 ligand (Flt3L) promotes survival of lymphoid progenitors in the bone marrow and differentiation of dendritic cells (DCs), but its role in regulating innate lymphoid cells (ILCs) during fetal and adult life is not understood. By using Flt3L knockout and transgenic mice, we demonstrate that Flt3L controls ILC numbers by regulating the pool of α4β7(-) and α4β7(+) lymphoid tissue inducer cell progenitors in the fetal liver and common lymphoid progenitors in the bone marrow. Deletion of flt3l severely reduced the number of fetal liver progenitors and lymphoid tissue inducer cells in the neonatal intestine, resulting in impaired development of Peyer's patches. In the adult intestine, NK cells and group 2 and 3 ILCs were severely reduced. This effect occurred independently of DCs as ILC numbers were normal in mice in which DCs were constitutively deleted. Finally, we could show that administration of Flt3L increased the number of NKp46(-) group 3 ILCs in wild-type and even in Il7(-/-) mice, which generally have reduced numbers of ILCs. Taken together, Flt3L significantly contributes to ILC and Peyer's patches development by targeting lymphoid progenitor cells during fetal and adult life.

Single-Cell Gene Expression Analyses Reveal Heterogeneous Responsiveness of Fetal Innate Lymphoid Progenitors to Notch Signaling

T and innate lymphoid cells (ILCs) share some aspects of their developmental programs. However, although Notch signaling is strictly required for T cell development, it is dispensable for fetal ILC development. Constitutive activation of Notch signaling, at the common lymphoid progenitor stage, drives T cell development and abrogates ILC development by preventing Id2 expression. By combining single-cell transcriptomics and clonal culture strategies, we characterize two heterogeneous α4β7-expressing lymphoid progenitor compartments. αLP1 (Flt3(+)) still retains T cell potential and comprises the global ILC progenitor, while αLP2 (Flt3(-)) consists of ILC precursors that are primed toward the different ILC lineages. Only a subset of αLP2 precursors is sensitive to Notch signaling required for their proliferation. Our study identifies, in a refined manner, the diversity of transitional stages of ILC development, their transcriptional signatures, and their differential dependence on Notch signaling.

Interleukin-22 Signaling in the Regulation of Intestinal Health and Disease

Interleukin (IL)-22 is a member of the IL-10 family of cytokines that has been extensively studied since its discovery in 2000. This review article aims to describe the cellular sources and signaling pathways of this cytokine as well as the functions of IL-22 in the intestine. In addition, this article describes the roles of IL-22 in the pathogenesis of several gastrointestinal diseases, including inhibition of inflammation and barrier defense against pathogens within the intestine. Since many of the functions of IL-22 in the intestine are incompletely understood, this review is meant to assess our current understanding of the roles of IL-22 and provide new opportunities for inquiry to improve human intestinal health and disease.

Differentiation and function of group 3 innate lymphoid cells, from embryo to adult

Group 3 innate lymphoid cells (ILC3) represent a heterogeneous population of cells that share the nuclear hormone receptor RORγt (retinoic acid receptor-related orphan receptor γt) as a master regulator for differentiation and function. ILC3 can be divided into two major subsets based on the cell surface expression of the natural cytotoxicity receptor (NCR), NKp46. A subset of NCR(-) ILC3 includes the previously known lymphoid-tissue inducer cells that are essential for the embryonic formation of peripheral lymph nodes and Peyer's patches. After birth, the NCR(-) and NCR(+) ILC3 contribute to the maintenance of health but also to inflammation in mucosal tissues. This review will describe the differentiation pathways of ILC3, their involvement in the development of the adaptive immune system and their role in the establishment and maintenance of gut immunity.

Central Role of Core Binding Factor β2 in Mucosa-Associated Lymphoid Tissue Organogenesis in Mouse

Mucosa-associated lymphoid tissue (MALT) is a group of secondary and organized lymphoid tissue that develops at different mucosal surfaces. Peyer's patches (PPs), nasopharynx-associated lymphoid tissue (NALT), and tear duct-associated lymphoid tissue (TALT) are representative MALT in the small intestine, nasal cavity, and lacrimal sac, respectively. A recent study has shown that transcriptional regulators of core binding factor (Cbf) β2 and promotor-1-transcribed Runt-related transcription factor 1 (P1-Runx1) are required for the differentiation of CD3-CD4+CD45+ lymphoid tissue inducer (LTi) cells, which initiate and trigger the developmental program of PPs, but the involvement of this pathway in NALT and TALT development remains to be elucidated. Here we report that Cbfβ2 plays an essential role in NALT and TALT development by regulating LTi cell trafficking to the NALT and TALT anlagens. Cbfβ2 was expressed in LTi cells in all three types of MALT examined. Indeed, similar to the previous finding for PPs, we found that Cbfβ2-/- mice lacked NALT and TALT lymphoid structures. However, in contrast to PPs, NALT and TALT developed normally in the absence of P1-Runx1 or other Runx family members such as Runx2 and Runx3. LTi cells for NALT and TALT differentiated normally but did not accumulate in the respective lymphoid tissue anlagens in Cbfβ2-/- mice. These findings demonstrate that Cbfβ2 is a central regulator of the MALT developmental program, but the dependency of Runx proteins on the lymphoid tissue development would differ among PPs, NALT, and TALT.

Using argument notation to engineer biological simulations with increased confidence

The application of computational and mathematical modelling to explore the mechanics of biological systems is becoming prevalent. To significantly impact biological research, notably in developing novel therapeutics, it is critical that the model adequately represents the captured system. Confidence in adopting in silico approaches can be improved by applying a structured argumentation approach, alongside model development and results analysis. We propose an approach based on argumentation from safety-critical systems engineering, where a system is subjected to a stringent analysis of compliance against identified criteria. We show its use in examining the biological information upon which a model is based, identifying model strengths, highlighting areas requiring additional biological experimentation and providing documentation to support model publication. We demonstrate our use of structured argumentation in the development of a model of lymphoid tissue formation, specifically Peyer's Patches. The argumentation structure is captured using Artoo (www.york.ac.uk/ycil/software/artoo), our Web-based tool for constructing fitness-for-purpose arguments, using a notation based on the safety-critical goal structuring notation. We show how argumentation helps in making the design and structured analysis of a model transparent, capturing the reasoning behind the inclusion or exclusion of each biological feature and recording assumptions, as well as pointing to evidence supporting model-derived conclusions.

Transcription factors controlling innate lymphoid cell fate decisions

The mucosal epithelium is in direct contact with symbiotic and pathogenic microorganisms. Therefore, the mucosal surface is the principal portal of entry for invading pathogens and immune cells accumulated in the intestine to prevent infections. In addition to these conventional immune system functions, it has become clear that immune cells during steady-state continuously integrate microbial and nutrient-derived signals from the environment to support organ homeostasis. A major role in both processes is played by a recently discovered group of lymphocytes referred to as innate lymphoid cells (ILCs) Innate lymphoid cells (ILCs) that are specifically enriched at mucosal surfaces but are rather rare in secondary lymphoid organs. In analogy to the dichotomy between CD8 and CD4 T cells, we propose to classify ILCs into interleukin-7 receptor α-negative cytotoxic ILCs and IL-7Rα(+) helper-like ILCs. Dysregulated immune responses triggered by the various ILC subsets have been linked to inflammatory diseases such as inflammatory bowel disease, atopic dermatitis and airway hyperresponsiveness. Here, we will review recent progress in determining the transcriptional and developmental programs that control ILC fate decisions.

Utilising a simulation platform to understand the effect of domain model assumptions

Computational and mathematical modelling approaches are increasingly being adopted in attempts to further our understanding of complex biological systems. This approach can be subjected to strong criticism as substantial aspects of the biological system being captured are not currently known, meaning assumptions need to be made that could have a critical impact on simulation response. We have utilised the CoSMoS process in the development of an agent-based simulation of the formation of Peyer's patches (PP), gut-associated lymphoid organs that have a key role in the initiation of adaptive immune responses to infection. Although the use of genetic tools, imaging technologies and ex vivo culture systems has provided significant insight into the cellular components and associated pathways involved in PP development, interesting questions remain that cannot be addressed using these approaches, and as such well justified assumptions have been introduced into our model to counter this. Here we focus not on the development of the model itself, but instead demonstrate how the resultant simulation can be used to assess how these assumptions impact the simulation response. For example, we consider the impact of our assumption that the migration rate of lymphoid tissue cells into the gut remains constant throughout PP development. We demonstrate that an analysis of the assumptions made in the construction of the domain model may either increase confidence in the model as a representation of the biological system it captures, or may suggest areas where further biological experimentation is required.

Geminin deletion increases the number of fetal hematopoietic stem cells by affecting the expression of key transcription factors

Balancing stem cell self-renewal and initiation of lineage specification programs is essential for the development and homeostasis of the hematopoietic system. We have specifically ablated geminin in the developing murine hematopoietic system and observed profound defects in the generation of mature blood cells, leading to embryonic lethality. Hematopoietic stem cells (HSCs) accumulated in the fetal liver following geminin ablation, while committed progenitors were reduced. Genome-wide transcriptome analysis identified key HSC transcription factors as being upregulated upon geminin deletion, revealing a gene network linked with geminin that controls fetal hematopoiesis. In order to obtain mechanistic insight into the ability of geminin to regulate transcription, we examined Hoxa9 as an example of a key gene in definitive hematopoiesis. We demonstrate that in human K562 cells geminin is associated with HOXA9 regulatory elements and its absence increases HOXA9 transcription similarly to that observed in vivo. Moreover, silencing geminin reduced recruitment of the PRC2 component SUZ12 to the HOXA9 locus and resulted in an increase in RNA polymerase II recruitment and H3K4 trimethylation (H3K4me3), whereas the repressive marks H3K9me3 and H3K27me3 were reduced. The chromatin landscape was also modified at the regulatory regions of HOXA10 and GATA1. K562 cells showed a reduced ability to differentiate to erythrocytes and megakaryocytes upon geminin silencing. Our data suggest that geminin is indispensable for fetal hematopoiesis and regulates the generation of a physiological pool of stem and progenitor cells in the fetal hematopoietic system.

Interleukin-22: immunobiology and pathology

Interleukin-22 (IL-22) is a recently described IL-10 family cytokine that is produced by T helper (Th) 17 cells, γδ T cells, NKT cells, and newly described innate lymphoid cells (ILCs). Knowledge of IL-22 biology has evolved rapidly since its discovery in 2000, and a role for IL-22 has been identified in numerous tissues, including the intestines, lung, liver, kidney, thymus, pancreas, and skin. IL-22 primarily targets nonhematopoietic epithelial and stromal cells, where it can promote proliferation and play a role in tissue regeneration. In addition, IL-22 regulates host defense at barrier surfaces. However, IL-22 has also been linked to several conditions involving inflammatory tissue pathology. In this review, we assess the current understanding of this cytokine, including its physiologic and pathologic effects on epithelial cell function.

Thymopentin enhances the generation of T-cell lineage derived from human embryonic stem cells in vitro

Thymopentin is a group of biologically active peptide secreted mainly by the epithelial cells of thymic cortex and medulla. Whether it promotes T cells production from human embryonic stem cells(hESCs) in vitro remains an elusive issue. In the present study, we develop a novel strategy that enhances T-cell lineage differentiation of hESCs in collagen matrix culture by sequential cytokine cocktails treatment combined with thymopentin stimulation. We observed that approximately 30.75% cells expressed CD34 on day 14 of the cultures and expressed the surface markers of erythroid, lymphoid and myeloid lineages. The results of colony assays and gene expressions by RT-PCR analysis also demonstrated that hematopoietic progenitor cells (HPCs) derived from hESCs were capable of multi-lineage differentiation. Further study revealed that culturing with thymopentin treatment, the CD34(+)CD45RA(+)CD7(+) cells sorted from HPCs expressed T-cell-related genes, IKAROS, DNTT, TCRγ and TCRβ, and T-cell surface markers, CD3, cytoplasmic CD3, CD5, CD27, TCRγδ, CD4 and CD8. The differentiated cells produced the cytokines including IFN-γ, IL-2 and TNF-α in response to stimulation, providing the evidence for T-cell function of these cells. In conclusion, thymopentin enhances T-cell lineage differentiation from hESCs in vitro by mimicking thymus peptide environment in vivo.

Human RORγt(+)CD34(+) cells are lineage-specified progenitors of group 3 RORγt(+) innate lymphoid cells

Group 3 innate lymphoid cells (ILC3s) are defined by the expression of the transcription factor RORγt, which is selectively required for their development. The lineage-specified progenitors of ILC3s and their site of development after birth remain undefined. Here we identified a population of human CD34(+) hematopoietic progenitor cells (HPCs) that express RORγt and share a distinct transcriptional signature with ILC3s. RORγt(+)CD34(+) HPCs were located in tonsils and intestinal lamina propria (LP) and selectively differentiated toward ILC3s. In contrast, RORγt(-)CD34(+) HPCs could differentiate to become either ILC3s or natural killer (NK) cells, with differentiation toward ILC3 lineage determined by stem cell factor (SCF) and aryl hydrocarbon receptor (AhR) signaling. Thus, we demonstrate that in humans RORγt(+)CD34(+) cells are lineage-specified progenitors of IL-22(+) ILC3s and propose that tonsils and intestinal LP, which are enriched both in committed precursors and mature ILC3s, might represent preferential sites of ILC3 lineage differentiation.

Human natural killer cells: origin, receptors, function, and clinical applications

Natural killer (NK) cells are important effectors playing a relevant role in innate immunity, primarily in tumor surveillance and in defenses against viruses. Human NK cells recognize HLA class I molecules through surface receptors (KIR and NKG2A) that inhibit NK cell function and kill target cells that have lost (or underexpress) HLA class I molecules as it occurs in tumors or virus-infected cells. NK cell activation is mediated by an array of activating receptors and co-receptors that recognize ligands expressed primarily on tumors or virus-infected cells. In vivo anti-tumor NK cell activity may be suppressed by tumor or tumor-associated cells. Alloreactive NK cells (i.e. those that are not inhibited by the HLA class I alleles of the patient) derived from HSC of haploidentical donors play a major role in the cure of high-risk leukemia, by killing leukemia blasts and patient's DC, thus preventing tumor relapses and graft-versus-host disease. The expression of the HLA-C2-specific activating KIR2DS1 may also contribute to NK alloreactivity in patients expressing C2 alleles. A clear correlation has been proven between the size of the alloreactive NK cell population and the clinical outcome. Recently, haplo-HSCT has been further improved with the direct infusion, together with HSC, of donor-derived, mature alloreactive NK cells and TCRγδ(+) T cells - both contributing to a prompt anti-leukemia effect together with an efficient defense against pathogens during the 6- to 8-week interval required for the generation of alloreactive NK cells from HSC.

DOCK8 regulates protective immunity by controlling the function and survival of RORγt+ ILCs

Retinoic acid receptor-related orphan receptor-γt-positive (RORγt(+)) innate lymphoid cells (ILCs) produce interleukin (IL)-22 and IL-17, which are critical for protective immunity against enteric pathogens. The molecular mechanism underlying the development and survival of RORγt(+) ILCs is not thoroughly understood. Here, we show that Dedicator of cytokinesis 8 (DOCK8), a scaffolding protein involved in cytoskeletal rearrangement and cell migration, is essential for the protective immunity against Citrobacter rodentium. A comparative RNA sequencing-based analysis reveals an impaired induction of antimicrobial peptides in the colon of DOCK8-deficient mice, which correlates with high susceptibility to infection and a very low number of IL-22-producing RORγt(+) ILCs in their GI tract. Furthermore, DOCK8-deficient RORγt(+) ILCs are less responsive to IL-7 mediated signalling, more prone to apoptosis and produce less IL-22 due to a defect in IL-23-mediated STAT3 phosphorylation. Our studies reveal an unsuspected role of DOCK8 for the function, generation and survival of RORγt(+) ILCs.