Fetal and adult hematopoietic stem cells give rise to distinct T cell lineages in humans

Transcription factors FOXN1 and intrathymic cytokines contribute to dysfunction of TECs during lipopolysaccharide-induced thymic atrophy

Sepsis is a major cause of mortality in neonates, yet understanding of sepsis-associated immune dysregulation in early life remains limited. Sepsis-induced thymus atrophy results in disruption of T cell development, accompanied by the dysfunction of thymic epithelial cells (TECs). Here, we sought to identify molecular mechanisms underlying TECs dysfunction while induced sepsis in neonatal mice and immortalized TECs cell line (iTECs) via lipopolysaccharide (LPS) treatment. We identified that LPS induced a reduction in thymocytes number starting at the double-negative stage of thymocyte development and significantly reduced numbers of naïve T cells and recent thymic emigrants (RTEs). Further we confirmed the alterations of intrathymic cytokines influencing T cell development and functionality through the FOXN1 signaling pathway upon exposure to LPS ex vivo and in vivo. LPS treatment decreased the number of cortical TECs (cTECs) and medullary TECs (mTECs) by enhancing the apoptosis of cTECs and decreasing the proliferation of mTECs. These findings provide valuable insights for further study on the innate and specific immunity in response to neonatal sepsis.

Reframing the paradigm-rethinking placental and fetal immunity

Preterm birth (PTB), defined as delivery before 37 weeks of gestation, is a leading cause of infant mortality worldwide, with nearly 10 % of births in the U.S. being preterm. PTB leads to various complications, including respiratory, neurological, and immunological issues, along with long-term health problems. It also costs the U.S. healthcare system approximately $25 billion annually, impacting families with lost productivity and long-term care needs. Understanding fetal and placental immunity is critical in addressing PTB. The immune system plays a vital role in maternal tolerance to the fetus and fetal immune development. Research into immune cells and signaling within the placenta may help prevent complications leading to PTB. Additionally, the interaction between maternal and fetal immune systems could reveal therapeutic targets to reduce preterm labor. Although animal models, especially mice, have advanced our understanding of fetal immunity, their differences from humans limit their applicability. Human studies, particularly those examining cord blood, had shown that neonatal immune cells are naïve at birth. However closer examination of preterm infants' blood demonstrated that they exhibit memory T cells linked to preterm labor. Building on this discovery, data demonstrates that fetal memory T cells exist in numerous fetal organs including the placenta. As such, research indicates that the fetus actively shapes the immune environment within the placenta. Disruptions in this process may contribute to PTB. Future investigations into fetal trained immunity and how to improve fetal immune responses could enhance neonatal protection. Understanding immune development in utero could lead to interventions that optimize neonatal health and prevent infections.

Divergent populations of HIV-infected naive and memory CD4+ T cell clones in children on antiretroviral therapy

BACKGROUNDNaive cells comprise 90% of the CD4+ T cell population in neonates and exhibit distinct age-specific capacities for proliferation and activation. We hypothesized that HIV-infected naive CD4+ T cell populations in children on long-term antiretroviral therapy (ART) would thus be distinct from infected memory cells.METHODSPeripheral blood naive and memory CD4+ T cells from 8 children with perinatal HIV on ART initiated at age 1.7-17 months were isolated by FACS. DNA was extracted from sorted cells, and HIV proviruses were counted, evaluated for intactness, and subjected to integration site analysis (ISA).RESULTSNaive CD4+ T cells containing HIV proviruses were detected in children with 95% statistical confidence. A median 4.7% of long terminal repeat-containing naive CD4+ T cells also contained HIV genetic elements consistent with intactness. Full-length proviral sequencing confirmed intactness of 1 provirus. In the participant with the greatest degree of naive cell infection, ISA revealed infected expanded cell clones in both naive and memory T cells, with no common HIV integration sites detected between subsets. Divergent integration site profiles reflected differential gene expression patterns of naive and memory T cells.CONCLUSIONThese results demonstrate that HIV persisted in both naive and memory CD4+ T cells that underwent clonal expansion and harbored intact proviruses, and suggest that infected memory T cell clones do not frequently arise from naive cell differentiation in children with perinatal HIV on long-term ART.FUNDINGCenter for Cancer Research, NCI; Office of AIDS Research; NCI FLEX; Children's and Emory Junior Faculty Focused Award.

Prenatal immune origins of brain aging differ by sex

With an increasing aging population and Alzheimer's disease tsunami, it is critical to identify early antecedents of brain aging to target for intervention and prevention. Women and men develop and age differently, thus using a sex differences lens can contribute to identification of early risk biomarkers and resilience. There is growing evidence for fetal antecedents to adult memory impairments, potentially through disruption of maternal prenatal immune pathways. Here, we hypothesized that in utero exposure to maternal pro-inflammatory cytokines will have sex-dependent effects on specific brain circuitry regulating offspring's memory and immune function that will be retained across the lifespan. Using a unique prenatal cohort, we tested this in 204 adult offspring, equally divided by sex, who were exposed/unexposed to an adverse in utero maternal immune environment and followed into early midlife (~age 50). Functional magnetic resonance imaging results showed exposure to pro-inflammatory cytokines in utero (i.e., higher maternal IL-6 and TNF-α levels) was significantly associated with sex differences in brain activity and connectivity underlying memory circuitry and performance and with a hyperimmune state, 50 years later. In contrast, the anti-inflammatory cytokine, IL-10 alone, was not significantly associated with memory circuitry in midlife. Predictive validity of prenatal exposure was underscored by significant associations with age 7 academic achievement, also associated with age 50 memory performance. Results uniquely demonstrated that adverse levels of maternal in utero pro-inflammatory cytokines during a critical period of the sexual differentiation of the brain produced long-lasting effects on immune function and memory circuitry/function from childhood to midlife that were sex-dependent, brain region-specific, and, within women, reproductive stage-dependent.

Th1 differentiation and function are inhibited in neonates following human metapneumovirus infection

Human metapneumovirus (HMPV) is a leading cause of lower respiratory tract infection in children accounting for 7% of acute care visits and hospitalizations. In particular, neonates and infants have worse outcomes with HMPV infection. The neonatal immune system is regulated to favor anti-inflammatory and tolerogenic responses compared to adults, including prior work demonstrating epigenetic factors in neonatal CD4+ T cells promoting Th2 formation rather than antiviral Th1 differentiation. To interrogate the neonatal immune response to HMPV, 4-to-6 day-old mice or adult 6-to-8 week-old mice were infected with HMPV. Neonates had a decreased Th1 population and increased Th2 and regulatory T-cell (Treg) populations compared to adults. Neonatal Th1 function, but not cell number, was restrained by surface PD-1 expression. To assess if neonatal Th1 formation was intrinsically inhibited after HMPV, neonatal and adult CD4s were transferred into immunocompetent or immunodeficient neonates. Both adult and neonatal CD4s demonstrated reduced Th1 differentiation in the immunocompetent neonates, but robust Th1 differentiation in immunodeficient neonates and immunocompetent adults, suggesting an extrinsic mechanism. Loss of neonatal Tregs led to increased Th1 differentiation after HMPV infection. Neonatal Tregs had increased TGF-β production compared to adult Tregs, and disruption of TGF-β signaling increased Th1 induction. These data demonstrate Tregs provide extrinsic regulation of Th1 formation in the context of respiratory viral infections, rather than an intrinsic limitation of neonatal CD4s. Collectively, these findings identify a nuanced neonatal response to respiratory viruses limiting Th1 formation and function.

Insulin-like growth factor 2 as a driving force for exponential expansion and differentiation of the neonatal thymus

Like all organs, the thymus grows in size and function rapidly during development, but this growth comes to a halt after birth. However, the molecular mechanisms behind such a transition in the thymus remain obscure. Using single-cell RNA sequencing (scRNA-seq) of the murine thymic stroma, we identified that major transcriptomic changes occur in the endothelium and mesenchyme across the transition to homeostasis. Differentially expressed gene and intercellular network analyses of temporally resolved scRNA-seq data revealed fibroblast-derived insulin-like growth factor 2 (IGF2) as a candidate driving neonatal thymic expansion. We demonstrated that IGF2 activity promotes a cortical thymic epithelial cell-specific proliferation and is tightly regulated at the thymic growth transition. Bulk RNA-seq of human thymi across the transition also revealed that IGF2 drives thymic expansion, suggesting an evolutionarily conserved role. Our study highlights the role of fibroblast-derived IGF2 in promoting cortical thymic epithelial cell proliferation and differentiation, resulting in early thymic expansion that is followed by downregulation to establish homeostasis.

Accuracy of International Guidelines in Identifying Normal Liver Histology in Chinese Patients With HBeAg-Positive Chronic HBV Infection

We evaluated the diagnostic accuracy of various international guideline criteria for identifying HBeAg-positive chronic HBV infection patients with no significant liver disease. A total of 1108 HBeAg-positive CHB patients were retrospectively enrolled. The guidelines assessed included those from the European Association for the Study of the Liver (EASL) 2017, the American Association for the Study of the Liver Disease (AASLD) 2018, the Asian Pacific Association for the Study of the Liver (APASL) 2015 and the Chinese Society of Hepatology (CSH) 2022. The CSH criteria demonstrated a higher proportion of patients with G0-1 and S0-1 (82.9%) compared to the EASL (75.9%), AASLD (75.3%) and APASL groups (58.8%). Additionally, the CSH criteria exhibited a significantly higher predictive value (AUC 0.782, 95% CI 0.754-0.809) than the EASL (AUC 0.765, 95% CI 0.737-0.793), AASLD (AUC 0.749, 95% CI 0.720-0.778) and APASL (AUC 0.720, 95% CI 0.690-0.750) criteria for identifying G0-1 and S0-1. Adding quantitative HBsAg levels (> 104 IU/mL) to the EASL, AASLD and APASL criteria improved diagnostic performance. Consequently, the CSH guideline thresholds showed higher accuracy in identifying Chinese HBeAg-positive patients with no significant liver disease compared to EASL, AASLD and APASL criteria, emphasising the importance of considering quantitative HBsAg in the evaluation of HBeAg-positive chronic HBV infection.

Mutual Interactions Between Microbiota and the Human Immune System During the First 1000 Days of Life

The development of the human immune system starts during the fetal period in a largely, but probably not completely, sterile environment. During and after birth, the immune system is exposed to an increasingly complex microbiota. The first microbiota encountered during passage through the birth canal colonize the infant gut and induce the tolerance of the immune system. Transplacentally derived maternal IgG as well as IgA from breast milk protect the infant from infections during the first 100 days, during which the immune system further develops and immunological memory is formed. The Weaning and introduction of solid food expose the immune system to novel (food) antigens and allow for other microbiota to colonize. The cells and molecules involved in the mutual and intricate interactions between microbiota and the developing immune system are now beginning to be recognized. These include bacterial components such as polysaccharide A from Bacteroides fragilis, as well as bacterial metabolites such as the short-chain fatty acid butyrate, indole-3-aldehyde, and indole-3-propionic acid. All these, and probably more, bacterial metabolites have specific immunoregulatory functions which shape the development of the human immune system during the first 1000 days of life.

Regulation of HSC development and function by Lin28b

Hematopoietic stem cells (HSCs) provide all kinds of blood cells for life while maintaining self-renewal ability. During development, HSCs are first produced in the mouse embryo around embryonic day (E) 11. At this time, only one or two transplantable HSCs can be detected per embryo. Then, HSCs migrate to the fetal liver, where the number of HSCs rapidly increases, showing enhanced self-renewal ability. After birth, a transition occurs from the rapidly proliferating fetal HSCs to the more slowly dividing adult HSCs, which ends by 3-4 weeks of age. It is known that fetal HSCs express distinct surface markers and transcriptomes and produce a variety of distinct immune cells that are not made by adult HSCs. Accumulating evidence indicates that the ontogeny of the hematopoietic system is driven by a highly conserved and developmentally regulated RNA binding protein known as Lin28b. Lin28b is predominantly expressed in the fetal hematopoietic stem and progenitor cells (HSPCs) and regulates the developmental switch from fetal to adult HSCs. In this review, we will provide an overview of how Lin28b regulates the expansion and differentiation of HSCs in early life. These insights can be taken into consideration when developing ex vivo HSC expansion utilizing such physiological characteristics of HSCs.

Infectious complications and the utility of serum and cellular markers of infections in the setting of allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients are severely immunocompromised and susceptible to bacterial, viral, and fungal infections. Despite improved anti-microbial prophylaxis and preemptive strategies, bacterial bloodstream infections (BSIs) occur frequently in allo-HSCT recipients and are associated with increased morbidity and mortality. Cytomegalovirus (CMV) and Epstein Barr virus (EBV) are the most relevant viruses following allo-HSCT and remain major concerns. Fungal infections, including those caused by Candida and Aspergillus species, are persistent and feared complications.

AREAS COVERED

We aim to provide clinicians caring for allo-HSCT recipients with a comprehensive overview of the risk factors that predispose patients to common bacterial, fungal, and viral infections during the first years post-transplant. The focus is on the value of noninvasive diagnostic biomarkers and serological assays in enhancing the early detection and management of these infections.

EXPERT OPINION

Effective management of infectious complications following allo-HSCT relies on continuous immune recovery monitoring and the implementation of advanced diagnostic methods. Utilizing noninvasive diagnostic methods is crucial for early detection and different intervention strategies. The development and integration of reliable microbiological markers into clinical practice is essential for enhancing patient outcomes and mitigating infection-related risks. Emphasizing diagnostic innovation will be pivotal in advancing patient care post-allo-HSCT.

Humanized Mouse Models for Immuno-Oncology Research: A Review and Implications in Lung Cancer Research

Cancer immunotherapy has brought significant clinical benefits to patients with cancer, including those with lung cancer. Patient-derived tumor xenograft mouse models have become the preferred animal model for translational cancer research and preclinical studies. Given the unmet need for improved predictive models in immuno-oncology, humanized mouse models which are co-engrafted with both human tumors and immune system components have been used to investigate novel immunotherapeutics. These models have similarly been used to predict immune-related adverse events and to develop predictive biomarkers. This review summarizes key concepts related to humanized mouse models. We highlight the various approaches to generate them, factors that are critical to successfully establishing such models, their respective limitations, and considerations in model selection for preclinical lung cancer immuno-oncology research and therapeutic studies.

Dendritic cells in developing and adult zebrafish arise from different origins and display distinct flt3 dependencies

Dendritic cells (DCs) are key cellular components of the immune system and perform crucial functions in innate and acquired immunity. In mammals, it is generally believed that DCs originate exclusively from hematopoietic stem cells (HSCs). Using a temporal-spatial resolved fate-mapping system, here we show that, in zebrafish, DCs arise from two sources: dorsal aorta-born endothelium-derived hematopoietic progenitors (EHPs) and HSCs. The EHP-derived DCs emerge early, predominantly colonizing the developing thymus during larval stages and diminishing by juvenile stages. In contrast, HSC-derived DCs emerge later and can populate different tissues from late larval stages to adulthood. We further document that the EHP- and HSC-derived DCs display different dependencies on Fms-like tyrosine kinase 3 (Flt3), a pivotal receptor tyrosine kinase crucial for DC development in mammals. Our study reveals the presence of two distinct waves of DC development in zebrafish, each with unique origins and developmental controls.

A synthetic review: natural history of amniote reproductive modes in light of comparative evolutionary genomics

There is a current lack of consensus on whether the ancestral parity mode was oviparity (egg-laying) or viviparity (live-birth) in amniotes and particularly in squamates (snakes, lizards, and amphisbaenids). How transitions between parity modes occur at the genomic level has primary importance for how science conceptualises the origin of amniotes, and highly variable parity modes in Squamata. Synthesising literature from medicine, poultry science, reproductive biology, and evolutionary biology, I review the genomics and physiology of five broad processes (here termed the 'Main Five') expected to change during transitions between parity modes: eggshell formation, embryonic retention, placentation, calcium transport, and maternal-fetal immune dynamics. Throughout, I offer alternative perspectives and testable hypotheses regarding proximate causes of parity mode evolution in amniotes and squamates. If viviparity did evolve early in the history of lepidosaurs, I offer the nucleation site hypothesis as a proximate explanation. The framework of this hypothesis can be extended to amniotes to infer their ancestral state. I also provide a mechanism and hypothesis on how squamates may transition from viviparity to oviparity and make predictions about the directionality of transitions in three species. After considering evidence for differing perspectives on amniote origins, I offer a framework that unifies (i) the extended embryonic retention model and (ii) the traditional model which describes the amniote egg as an adaptation to the terrestrial environment. Additionally, this review contextualises the origin of amniotes and parity mode evolution within Medawar's paradigm. Medawar posited that pregnancy could be supported by immunosuppression, inertness, evasion, or immunological barriers. I demonstrate that this does not support gestation or gravidity across most amniotes but may be an adequate paradigm to explain how the first amniote tolerated internal fertilization and delayed egg deposition. In this context, the eggshell can be thought of as an immunological barrier. If serving as a barrier underpins the origin of the amniote eggshell, there should be evidence that oviparous gravidity can be met with a lack of immunological responses in utero. Rare examples of two species that differentially express very few genes during gravidity, suggestive of an absent immunological reaction to oviparous gravidity, are two skinks Lampropholis guichenoti and Lerista bougainvillii. These species may serve as good models for the original amniote egg. Overall, this review grounds itself in the historical literature while offering a modern perspective on the origin of amniotes. I encourage the scientific community to utilise this review as a resource in evolutionary and comparative genomics studies, embrace the complexity of the system, and thoughtfully consider the frameworks proposed.

Shaping immunity: the influence of the maternal gut bacteria on fetal immune development

The development of the fetal immune response is a highly complex process. In the present review, we describe the development of the fetal immune response and the role of the maternal gut bacteria in this process. In contrast to the previous belief that the fetal immune response is inert, it is now thought that the fetal immune response is uniquely tolerant to maternal and allo-antigens, but able to respond to infectious agents, such as bacteria. This is accomplished by the development of T cells toward regulatory T cells rather than toward effector T cells, but also by the presence of functional innate immune cells, such as monocytes and NK cells. Moreover, in fetuses there is different programming of CD8 + T cells and memory T cells toward innate immune cells rather than to adaptive immune cells. The maternal gut bacteria are important in shaping the fetal immune response by producing bacterial products and metabolites that pass the placenta into the fetus and influence development of the fetal immune response. Insight into how and when these products affect the fetal immune response may open new treatment options with pre- or probiotics to affect the maternal gut bacteria and therewith the fetal immune response.

Lifelong partners: Gut microbiota-immune cell interactions from infancy to old age

Our immune system and gut microbiota are intricately coupled from birth, both going through maturation during early life and senescence during aging almost in a synchronized fashion. The symbiotic relationship between the human host and microbiota is critically dependent on a healthy immune system to keep our microbiota in check, while the microbiota provides essential functions to promote the development and fitness of our immune system. The partnership between our immune system and microbiota is particularly important during early life, when microbial ligands and metabolites shape the development of the immune cells and immune tolerance; during aging, having sufficient beneficial gut bacteria is critical for the maintenance of intact mucosal barriers, immune metabolic fitness, and strong immunity against pathogens. The immune system during childhood is programmed, with the support of the microbiota, to develop robust immune tolerance, and limit autoimmunity and metabolic dysregulation, which are prevalent during aging. This review comprehensively explores the mechanistic underpinnings of gut microbiota-immune cell interactions during infancy and old age, with the goal to gain a better understanding of potential strategies to leverage the gut microbiota to combat age-related immune decline.

Preclinical Models for Functional Precision Lung Cancer Research

Patient-centered precision oncology strives to deliver individualized cancer care. In lung cancer, preclinical models and technological innovations have become critical in advancing this approach. Preclinical models enable deeper insights into tumor biology and enhance the selection of appropriate systemic therapies across chemotherapy, targeted therapies, immunotherapies, antibody-drug conjugates, and emerging investigational treatments. While traditional human lung cancer cell lines offer a basic framework for cancer research, they often lack the tumor heterogeneity and intricate tumor-stromal interactions necessary to accurately predict patient-specific clinical outcomes. Patient-derived xenografts (PDXs), however, retain the original tumor's histopathology and genetic features, providing a more reliable model for predicting responses to systemic therapeutics, especially molecularly targeted therapies. For studying immunotherapies and antibody-drug conjugates, humanized PDX mouse models, syngeneic mouse models, and genetically engineered mouse models (GEMMs) are increasingly utilized. Despite their value, these in vivo models are costly, labor-intensive, and time-consuming. Recently, patient-derived lung cancer organoids (LCOs) have emerged as a promising in vitro tool for functional precision oncology studies. These LCOs demonstrate high success rates in growth and maintenance, accurately represent the histology and genomics of the original tumors and exhibit strong correlations with clinical treatment responses. Further supported by advancements in imaging, spatial and single-cell transcriptomics, proteomics, and artificial intelligence, these preclinical models are reshaping the landscape of drug development and functional precision lung cancer research. This integrated approach holds the potential to deliver increasingly accurate, personalized treatment strategies, ultimately enhancing patient outcomes in lung cancer.

Umbilical cord blood T cells can be isolated and enriched by CD62L selection for use in 'off the shelf' chimeric antigen receptor T-cell therapies to widen transplant options

Umbilical cord blood (UCB) T cells exhibit distinct naïve ontogenetic profiles and may be an attractive source of starting cells for the production of chimeric antigen receptor (CAR) T cells. Pre-selection of UCB-T cells on the basis of CD62L expression was investigated as part of a machine-based manufacturing process, incorporating lentiviral transduction, CRISPR- Cas9 editing, T-cell expansion, and depletion of residual TCRαβ T cells. This provided stringent mitigation against the risk of graft-versus-host disease (GvHD), and was combined with simultaneous knockout of CD52 to enable persistence of edited T cells in combination with preparative lymphodepletion using alemtuzumab. Under compliant manufacturing conditions, two cell banks were generated with high levels of CAR19 expression and minimal carriage of TCRαβ T cells. Sufficient cells were cryopreserved in dose-banded aliquots at the end of each campaign to treat dozens of potential recipients. Molecular characterization captured vector integration sites and CRISPR editing signatures, and functional studies, including in vivo potency studies in humanized mice, confirmed anti-leukemic activity comparable to peripheral blood-derived universal CAR19 T cells. Machine manufactured UCB-derived T-cell banks offer an alternative to autologous cell therapies and could help widen access to CAR T cells.

Dynamic regulation of innate lymphoid cell development during ontogeny

The helper-like ILC contains various functional subsets, such as ILC1, ILC2, ILC3 and LTi cells, mediating the immune responses against viruses, parasites, and extracellular bacteria, respectively. Among them, LTi cells are also crucial for the formation of peripheral lymphoid tissues, such as lymph nodes. Our research, along with others', indicates a high proportion of LTi cells in the fetal ILC pool, which significantly decreases after birth. Conversely, the proportion of non-LTi ILCs increases postnatally, corresponding to the need for LTi cells to mediate lymphoid tissue formation during fetal stages and other ILC subsets to combat diverse pathogen infections postnatally. However, the regulatory mechanism for this transition remains unclear. In this study, we observed a preference for fetal ILC progenitors to differentiate into LTi cells, while postnatal bone marrow ILC progenitors preferentially differentiate into non-LTi ILCs. Particularly, this differentiation shift occurs within the first week after birth in mice. Further analysis revealed that adult ILC progenitors exhibit stronger activation of the Notch signaling pathway compared to fetal counterparts, accompanied by elevated Gata3 expression and decreased Rorc expression, leading to a transition from fetal LTi cell-dominant states to adult non-LTi ILC-dominant states. This study suggests that the body can regulate ILC development by modulating the activation level of the Notch signaling pathway, thereby acquiring different ILC subsets to accommodate the varying demands within the body at different developmental stages.

Early-life thymectomy leads to an increase of granzyme-producing γδ T cells in children with congenital heart disease

Congenital heart disease (CHD) is the most common birth defect in newborns, often requiring cardiac surgery with concomitant thymectomy that is known to increase disease susceptibility later in life. Studies of γδ T cells, which are one of the dominant T cells in the early fetal human thymus, are rare. Here, we provide a comprehensive analysis of the γδ T cell compartment via flow cytometry and next-generation sequencing in children and infants with CHD, who underwent cardiac surgery shortly after birth. A perturbation of the γδ T cell repertoire is evident, and Vδ1 T cell numbers are reduced. However, those cells that are present, do retain cytotoxicity. In contrast, GZMA+CD28+CD161hi innate effector Vγ9Vδ2 T cells are found in higher proportions. TCR-seq identifies an increase in TRDJ3+ γδ T cell clones in children with CHD, but not in a confirmatory group of neonates prior to CHD surgery, which overall points to a persistence of fetal-derived effector γδ T cells in children with CHD.

A newborn's perspective on immune responses to food

In this review, we will highlight infants' immune responses to food, emphasizing the unique aspects of early-life immunity and the critical role of breast milk as a food dedicated to infants. Infants are susceptible to inflammatory responses rather than immune tolerance at the mucosal and skin barriers, necessitating strategies to promote oral tolerance that consider this susceptibility. Breast milk provides nutrients for growth and cell metabolism, including immune cells. The content of breast milk, influenced by maternal genetics and environmental exposures, prepares the infant's immune system for the outside world, including solid foods. To do this, breast milk promotes immune system development through antigen-specific and non-antigen-specific immune education by exposing the newborn to food and respiratory allergens and acting on three key targets for food allergy prevention: the gut microbiota, epithelial cells, and immune cells. Building knowledge of how the maternal exposome and human milk composition influence offspring's healthy immune development will lead to recommendations that meet the specific needs of the developing immune system and increase the chances of promoting an appropriate immune response to food in the long term.

Single-cell transcriptomic analysis of the immune microenvironment in pediatric acute leukemia

Relapse and treatment resistance pose significant challenges in the management of pediatric B cell acute lymphoblastic leukemia (B-ALL) and acute myeloid leukemia (AML). The efficacy of immunotherapy in leukemia remains limited due to factors such as the immunosuppressive tumor microenvironment (TME) and lack of suitable immunotherapeutic targets. Thus, an in-depth characterization of the TME in pediatric leukemia is warranted to improve the efficacy of immunotherapy. Here, we used single-cell RNA sequencing (scRNA-seq) to characterize the TME of pediatric B-ALL and AML, focusing specifically on bone-marrow-derived T cells. Moreover, we investigated the transcriptome changes during the initiation, remission, and relapse stages of pediatric AML. Our findings revealed that specific functional expression programs correlated with fluctuations in various T cell subsets, which may be associated with AML progression and relapse. Furthermore, our analysis of cellular communication networks led to the identification of VISTA, CD244, and TIM3 as potential immunotherapeutic targets in pediatric AML. Finally, we detected elevated proportions of γδ T cells and associated functional genes in samples from pediatric patients diagnosed with B-ALL and AML, which could inform the development of novel therapeutic approaches, potentially focusing on γδ T cells.

Against all odds: The road to success in the development of human immune reconstitution mice

The mouse genome has a high degree of homology with the human genome, and its physiological, biochemical, and developmental regulation mechanisms are similar to those of humans; therefore, mice are widely used as experimental animals. However, it is undeniable that interspecies differences between humans and mice can lead to experimental errors. The differences in the immune system have become an important factor limiting current immunological research. The application of immunodeficient mice provides a possible solution to these problems. By transplanting human immune cells or tissues, such as peripheral blood mononuclear cells or hematopoietic stem cells, into immunodeficient mice, a human immune system can be reconstituted in the mouse body, and the engrafted immune cells can elicit human-specific immune responses. Researchers have been actively exploring the development and differentiation conditions of host recipient animals and grafts in order to achieve better immune reconstitution. Through genetic engineering methods, immunodeficient mice can be further modified to provide a favorable developmental and differentiation microenvironment for the grafts. From initially only being able to reconstruct single T lymphocyte lineages, it is now possible to reconstruct lymphoid and myeloid cells, providing important research tools for immunology-related studies. In this review, we compare the differences in immune systems of humans and mice, describe the development history of human immune reconstitution from the perspectives of immunodeficient mice and grafts, and discuss the latest advances in enhancing the efficiency of human immune cell reconstitution, aiming to provide important references for immunological related researches.

Early-life risk factors which govern pro-allergic immunity

Allergic diseases affect up to 40% of the global population with a substantial rise in food allergies, in particular, over the past decades. For the majority of individuals with allergy fundamental programming of a pro-allergic immune system largely occurs in early childhood where it is crucially governed by prenatal genetic and environmental factors, including their interactions. These factors include several genetic aberrations, such as filaggrin loss-of-function mutations, early exposure to respiratory syncytial virus, and various chemicals such as plasticizers, as well as the influence of the gut microbiome and numerous lifestyle circumstances. The effects of such a wide range of factors on allergic responses to an array of potential allergens is complex and the severity of these responses in a clinical setting are subsequently not easy to predict at the present time. However, some parameters which condition a pro-allergic immune response, including severe anaphylaxis, are becoming clearer. This review summarises what we currently know, and don't know, about the factors which influence developing pro-allergic immunity particularly during the early-life perinatal period.

Gene Regulatory Programs that Specify Age-Related Differences during Thymocyte Development

T cell development is fundamental to immune system establishment, yet how this development changes with age remains poorly understood. Here, we construct a transcriptional and epigenetic atlas of T cell developmental programs in neonatal and adult mice, revealing the ontogeny of divergent gene regulatory programs and their link to age-related differences in phenotype and function. Specifically, we identify a gene module that diverges with age from the earliest stages of genesis and includes programs that govern effector response and cell cycle regulation. Moreover, we reveal that neonates possess more accessible chromatin during early thymocyte development, likely establishing poised gene expression programs that manifest later in thymocyte development. Finally, we leverage this atlas, employing a CRISPR-based perturbation approach coupled with single-cell RNA sequencing as a readout to uncover a conserved transcriptional regulator, Zbtb20, that contributes to age-dependent differences in T cell development. Altogether, our study defines transcriptional and epigenetic programs that regulate age-specific differences in T cell development.

Update on Early-Life T Cells: Impact on Oral Rotavirus Vaccines

Rotavirus infection continues to be a significant public health problem in developing countries, despite the availability of several vaccines. The efficacy of oral rotavirus vaccines in young children may be affected by significant immunological differences between individuals in early life and adults. Therefore, understanding the dynamics of early-life systemic and mucosal immune responses and the factors that affect them is essential to improve the current rotavirus vaccines and develop the next generation of mucosal vaccines. This review focuses on the advances in T-cell development during early life in mice and humans, discussing how immune homeostasis and response to pathogens is established in this period compared to adults. Finally, the review explores how this knowledge of early-life T-cell immunity could be utilized to enhance current and novel rotavirus vaccines.

Role of cancer stem cell ecosystem on breast cancer metastasis and related mouse models

Breast cancer metastasis is responsible for most breast cancer-related deaths and is influenced by many factors within the tumor ecosystem, including tumor cells and microenvironment. Breast cancer stem cells (BCSCs) constitute a small population of cancer cells with unique characteristics, including their capacity for self-renewal and differentiation. Studies have shown that BCSCs not only drive tumorigenesis but also play a crucial role in promoting metastasis in breast cancer. The tumor microenvironment (TME), composed of stromal cells, immune cells, blood vessel cells, fibroblasts, and microbes in proximity to cancer cells, is increasingly recognized for its crosstalk with BCSCs and role in BCSC survival, growth, and dissemination, thereby influencing metastatic ability. Hence, a thorough understanding of BCSCs and the TME is critical for unraveling the mechanisms underlying breast cancer metastasis. In this review, we summarize current knowledge on the roles of BCSCs and the TME in breast cancer metastasis, as well as the underlying regulatory mechanisms. Furthermore, we provide an overview of relevant mouse models used to study breast cancer metastasis, as well as treatment strategies and clinical trials addressing BCSC-TME interactions during metastasis. Overall, this study provides valuable insights for the development of effective therapeutic strategies to reduce breast cancer metastasis.

Worming into infancy: Exploring helminth-microbiome interactions in early life

There is rapidly growing awareness of microbiome assembly and function in early-life gut health. Although many factors, such as antibiotic use and highly processed diets, impinge on this process, most research has focused on people residing in high-income countries. However, much of the world's population lives in low- and middle-income countries (LMICs), where, in addition to erratic antibiotic use and suboptimal diets, these groups experience unique challenges. Indeed, many children in LMICs are infected with intestinal helminths. Although helminth infections are strongly associated with diverse developmental co-morbidities and induce profound microbiome changes, few studies have directly examined whether intersecting pathways between these components of the holobiont shape health outcomes in early life. Here, we summarize microbial colonization within the first years of human life, how helminth-mediated changes to the gut microbiome may affect postnatal growth, and why more research on this relationship may improve health across the lifespan.

Early life microbiome influences on development of the mucosal innate immune system

The gut microbiota is well known to possess immunomodulatory capacities, influencing a multitude of cellular signalling pathways to maintain host homeostasis. Although the formation of the immune system initiates before birth in a sterile environment, an emerging body of literature indicates that the neonatal immune system is influenced by a first wave of external stimuli that includes signals from the maternal microbiota. A second wave of stimulus begins after birth and must be tightly regulated during the neonatal period when colonization of the host occurs concomitantly with the maturation of the immune system, requiring a fine adjustment between establishing tolerance towards the commensal microbiota and preserving inflammatory responses against pathogenic invaders. Besides integrating cues from commensal microbes, the neonatal immune system must also regulate responses triggered by other environmental signals, such as dietary antigens, which become more complex with the introduction of solid food during the weaning period. This "window of opportunity" in early life is thought to be crucial for the proper development of the immune system, setting the tone of subsequent immune responses in adulthood and modulating the risk of developing chronic and metabolic inflammatory diseases. Here we review the importance of host-microbiota interactions for the development and maturation of the immune system, particularly in the early-life period, highlighting the known mechanisms involved in such communication. This discussion is focused on recent data demonstrating microbiota-mediated education of innate immune cells and its role in the development of lymphoid tissues.

Cross-individual cancer transmission to children during the gestational and perinatal periods

Cancer transmission may rarely occur between individuals. Besides through allogenic transplantation, cancer transmission via the hemochorial placenta, which is permissive for cell traffic, has been described in a few reports. Three etiologies of transplacental cancer transmission include (1) maternofetal transmission of maternal cancer cells, (2) transmission of gestational choriocarcinoma to the fetus, and (3) transfer of preleukemic cells from one monozygotic twin to the other. Additionally, we recently reported two pediatric cases of lung tumors in which the lung-only distribution of tumors and genomic profiling of both the child's and mother's tumor samples suggested the airway/transbronchial transmission of maternal cervical cancer cells to the child by aspiration at birth. The immune system coordinates the hemostatic balance between effector and regulatory immunity, especially during fetal development. The immunoregulatory properties are shared in both physiological pregnancy-related and pathological cancer-related conditions. Mechanistically, the survival and colonization of transmitted cancer cells within a child are likely attributed to a combination of the child's immune tolerance and the cancer's immune escape. In this review, we summarize the current understanding of gestational/perinatal cancer transmission and discuss the possible mechanism-based immunotherapy for this rare form of pediatric cancer.

The microbiome: an integral player in immune homeostasis and inflammation in the respiratory tract

The last decade of microbiome research has highlighted its fundamental role in systemic immune and metabolic homeostasis. The microbiome plays a prominent role during gestation and into early life, when maternal lifestyle factors shape immune development of the newborn. Breast milk further shapes gut colonization, supporting the development of tolerance to commensal bacteria and harmless antigens while preventing outgrowth of pathogens. Environmental microbial and lifestyle factors that disrupt this process can dysregulate immune homeostasis, predisposing infants to atopic disease and childhood asthma. In health, the low-biomass lung microbiome, together with inhaled environmental microbial constituents, establishes the immunological set point that is necessary to maintain pulmonary immune defense. However, in disease perturbations to immunological and physiological processes allow the upper respiratory tract to act as a reservoir of pathogenic bacteria, which can colonize the diseased lung and cause severe inflammation. Studying these host-microbe interactions in respiratory diseases holds great promise to stratify patients for suitable treatment regimens and biomarker discovery to predict disease progression. Preclinical studies show that commensal gut microbes are in a constant flux of cell division and death, releasing microbial constituents, metabolic by-products, and vesicles that shape the immune system and can protect against respiratory diseases. The next major advances may come from testing and utilizing these microbial factors for clinical benefit and exploiting the predictive power of the microbiome by employing multiomics analysis approaches.

A Metabolic Axis of Immune Intractability

Immune cells in the tumor niche robustly influence disease progression. Remarkably, in cancer, developmental pathways are reenacted. Many parallels between immune regulation of embryonic development and immune regulation of tumor progression can be drawn, with evidence clearly supporting an immune-suppressive microenvironment in both situations. In these ecosystems, metabolic and bioenergetic circuits guide and regulate immune cell differentiation, plasticity, and functional properties of suppressive and inflammatory immune subsets. As such, there is an emerging pattern of intersection across the dynamic process of ontogeny and the ever-evolving tumor neighborhood. In this article, we focus on the convergence of immune programming during ontogeny and in the tumor microenvironment. Exemplifying dysregulation of Hedgehog (Hh) activity, a key player during ontogeny, we highlight a critical convergence of these fields and the metabolic axis of the nutrient sensing hexosamine biosynthetic pathway (HBP) that integrates glucose, glutamine, amino acids, acetyl CoA, and uridine-5'-triphosphate (UTP), culminating in the synthesis of UDP-GlcNAc, a metabolite that functions as a metabolic and bioenergetic sensor. We discuss an emerging pattern of immune regulation, orchestrated by O-GlcNAcylation of key transcriptional regulators, spurring suppressive activity of dysfunctional immune cells in the tumor microenvironment.

Moderate to severe atopic dermatitis in children: focus on systemic Th2 cytokine receptor antagonists and Janus kinase inhibitors

Atopic dermatitis (AD) is a lifelong disease that markedly impairs quality of life. AD is considered a starting point of the "atopic march," which begins at a young age and may progress to systemic allergic diseases. Moreover, it is strongly associated with comorbid allergic and inflammatory diseases including arthritis and inflammatory bowel disease. Understanding the pathogenesis of AD is essential for the development of targeted therapies. Epidermal barrier dysfunction, immune deviation toward a T helper 2 proinflammatory profile, and microbiome dysbiosis play important roles via complex interactions. The systemic involvement of type 2 inflammation, wheather acute or chronic, and whether extrinsic or intrinsic, is evident in any type of AD. Studies on AD endotypes with unique biological mechanisms have been conducted according to clinical phenotypes, such as race or age, but the endotype for each phenotype, or endophenotype, has not yet been clearly identified. Therefore, AD is still being treated according to severity rather than endotype. Infancy-onset and severe AD are known risk factors leading to atopic march. In addition, up to 40% of adult AD are cases of infancy-onset AD that persist into adulthood, and these are often accompanied by other allergic diseases. Therefore, early intervention strategies to identify high-risk infants and young children, repair an impaired skin barrier, and control systemic inflamation may improve long-term outcomes in AD patients. However, to the best of our knowledge, no study has evaluated the effectiveness of early intervention on atopic march using systemic therapy in high-risk infants. This narrative review addresses the latest knowledge of systemic treatment, including Th2 cytokine receptor antagonists and Janus kinase inhibitors, for children with moderate to severe AD that is refractory to topical treatment.

Early-life interactions between the microbiota and immune system: impact on immune system development and atopic disease

Prenatal and early postnatal life represent key periods of immune system development. In addition to genetics and host biology, environment has a large and irreversible role in the immune maturation and health of an infant. One key player in this process is the gut microbiota, a diverse community of microorganisms that colonizes the human intestine. The diet, environment and medical interventions experienced by an infant determine the establishment and progression of the intestinal microbiota, which interacts with and trains the developing immune system. Several chronic immune-mediated diseases have been linked to an altered gut microbiota during early infancy. The recent rise in allergic disease incidence has been explained by the 'hygiene hypothesis', which states that societal changes in developed countries have led to reduced early-life microbial exposures, negatively impacting immunity. Although human cohort studies across the globe have established a correlation between early-life microbiota composition and atopy, mechanistic links and specific host-microorganism interactions are still being uncovered. Here, we detail the progression of immune system and microbiota maturation in early life, highlight the mechanistic links between microbes and the immune system, and summarize the role of early-life host-microorganism interactions in allergic disease development.

Early-life microbiota-immune homeostasis

As the prevalence of allergy and autoimmune disease in industrialized societies continues to rise, improving our understanding of the mechanistic roles behind microbiota-immune homeostasis has become critical for informing therapeutic interventions in cases of dysbiosis. Of particular importance, are alterations to intestinal microbiota occurring within the critical neonatal window, during which the immune system is highly vulnerable to environmental exposures. This review will highlight recent literature concerning mechanisms of early-life microbiota-immune homeostasis as well as discuss the potential for therapeutics in restoring dysbiosis in early life.

Single cell transcriptomics reveals cell type specific features of developmentally regulated responses to lipopolysaccharide between birth and 5 years

Background

Human perinatal life is characterized by a period of extraordinary change during which newborns encounter abundant environmental stimuli and exposure to potential pathogens. To meet such challenges, the neonatal immune system is equipped with unique functional characteristics that adapt to changing conditions as development progresses across the early years of life, but the molecular characteristics of such adaptations remain poorly understood. The application of single cell genomics to birth cohorts provides an opportunity to investigate changes in gene expression programs elicited downstream of innate immune activation across early life at unprecedented resolution.

Methods

In this study, we performed single cell RNA-sequencing of mononuclear cells collected from matched birth cord blood and 5-year peripheral blood samples following stimulation (18hrs) with two well-characterized innate stimuli; lipopolysaccharide (LPS) and Polyinosinic:polycytidylic acid (Poly(I:C)).

Results

We found that the transcriptional response to LPS was constrained at birth and predominantly partitioned into classical proinflammatory gene upregulation primarily by monocytes and Interferon (IFN)-signaling gene upregulation by lymphocytes. Moreover, these responses featured substantial cell-to-cell communication which appeared markedly strengthened between birth and 5 years. In contrast, stimulation with Poly(I:C) induced a robust IFN-signalling response across all cell types identified at birth and 5 years. Analysis of gene regulatory networks revealed IRF1 and STAT1 were key drivers of the LPS-induced IFN-signaling response in lymphocytes with a potential developmental role for IRF7 regulation.

Conclusion

Additionally, we observed distinct activation trajectory endpoints for monocytes derived from LPS-treated cord and 5-year blood, which was not apparent among Poly(I:C)-induced monocytes. Taken together, our findings provide new insight into the gene regulatory landscape of immune cell function between birth and 5 years and point to regulatory mechanisms relevant to future investigation of infection susceptibility in early life.

Bifidobacteria shape antimicrobial T-helper cell responses during infancy and adulthood

Microbial infections early in life are challenging for the unexperienced immune system. The SARS-CoV-2 pandemic again has highlighted that neonatal, infant, child, and adult T-helper(Th)-cells respond differently to infections, and requires further understanding. This study investigates anti-bacterial T-cell responses against Staphylococcus aureus aureus, Staphylococcus epidermidis and Bifidobacterium longum infantis in early stages of life and adults and shows age and pathogen-dependent mechanisms. Beside activation-induced clustering, T-cells stimulated with Staphylococci become Th1-type cells; however, this differentiation is mitigated in Bifidobacterium-stimulated T-cells. Strikingly, prestimulation of T-cells with Bifidobacterium suppresses the activation of Staphylococcus-specific T-helper cells in a cell-cell dependent manner by inducing FoxP3+CD4+ T-cells, increasing IL-10 and galectin-1 secretion and showing a CTLA-4-dependent inhibitory capacity. Furthermore Bifidobacterium dampens Th responses of severely ill COVID-19 patients likely contributing to resolution of harmful overreactions of the immune system. Targeted, age-specific interventions may enhance infection defence, and specific immune features may have potential cross-age utilization.

Immunology of cord blood T-cells favors augmented disease response during clinical pediatric stem cell transplantation for acute leukemia

Allogeneic hematopoietic stem cell transplantation (HSCT) has been an important and efficacious treatment for acute leukemia in children for over 60 years. It works primarily through the graft-vs.-leukemia (GVL) effect, in which donor T-cells and other immune cells act to eliminate residual leukemia. Cord blood is an alternative source of stem cells for transplantation, with distinct biological and immunological characteristics. Retrospective clinical studies report superior relapse rates with cord blood transplantation (CBT), when compared to other stem cell sources, particularly for patients with high-risk leukemia. Xenograft models also support the superiority of cord blood T-cells in eradicating malignancy, when compared to those derived from peripheral blood. Conversely, CBT has historically been associated with an increased risk of transplant-related mortality (TRM) and morbidity, particularly from infection. Here we discuss clinical aspects of CBT, the unique immunology of cord blood T-cells, their role in the GVL effect and future methods to maximize their utility in cellular therapies for leukemia, honing and harnessing their antitumor properties whilst managing the risks of TRM.

Generation of the NeoThy mouse model for human immune system studies

Humanized mouse models, created via transplantation of human hematopoietic tissues into immune-deficient mice, support a number of research applications, including transplantation immunology, virology and oncology studies. As an alternative to the bone marrow, liver, thymus humanized mouse, which uses fetal tissues for generating a chimeric human immune system, the NeoThy humanized mouse uses nonfetal tissue sources. Specifically, the NeoThy model incorporates hematopoietic stem and progenitor cells from umbilical cord blood (UCB) as well as thymus tissue that is typically discarded as medical waste during neonatal cardiac surgeries. Compared with fetal thymus tissue, the abundant quantity of neonatal thymus tissue offers the opportunity to prepare over 1,000 NeoThy mice from an individual thymus donor. Here we describe a protocol for processing of the neonatal tissues (thymus and UCB) and hematopoietic stem and progenitor cell separation, human leukocyte antigen typing and matching of allogenic thymus and UCB tissues, creation of NeoThy mice, assessment of human immune cell reconstitution and all experimental steps from planning and design to data analysis. This entire protocol takes a total of ~19 h to complete, with steps broken up into multiple sessions of 4 h or less that can be paused and completed over multiple days. The protocol can be completed, after practice, by individuals with intermediate laboratory and animal handling skills, enabling researchers to make effective use of this promising in vivo model of human immune function.

Umbilical cord blood derived cellular therapy: advances in clinical development

While cord blood (CB) is primarily utilized in allogeneic hematopoietic cell transplantation (HCT), the development of novel cell therapy products from CB is a growing and developing field. Compared to adult blood, CB is characterized by a higher percentage of hematopoietic stem cells (HSCs) and progenitor cells, less mature immune cells that retain a high capacity of proliferation, and stronger immune tolerance that requires less stringent HLA-matching when used in the allogenic setting. Given that CB is an FDA regulated product and along with its unique cellular composition, CB lends itself as a readily available and safe starting material for the development of off-the-shelf cell therapies. Moreover, non-hematologic cells such as mesenchymal stem cell (MSCs) residing in CB or CB tissue also have potential in regenerative medicine and inflammatory and autoimmune conditions. In this review, we will focus on recent clinical development on CB-derived cellular therapies in the field of oncology, including T-cell therapies such as chimeric antigen receptor (CAR) T-cells, regulatory T-cells, and virus-specific T-cells; NK-cell therapies, such as NK cell engagers and CAR NK-cells; CB-HCT and various modifications; as well as applications of MSCs in HCT.

Shaping immunity for life: Layered development of CD8+ T cells

Historically, the immune system was believed to develop along a linear axis of maturity from fetal life to adulthood. Now, it is clear that distinct layers of immune cells are generated from unique waves of hematopoietic progenitors during different windows of development. This model, known as the layered immune model, has provided a useful framework for understanding why distinct lineages of B cells and γδ T cells arise in succession and display unique functions in adulthood. However, the layered immune model has not been applied to CD8+ T cells, which are still often viewed as a uniform population of cells belonging to the same lineage, with functional differences between cells arising from environmental factors encountered during infection. Recent studies have challenged this idea, demonstrating that not all CD8+ T cells are created equally and that the functions of individual CD8+ T cells in adults are linked to when they were created in the host. In this review, we discuss the accumulating evidence suggesting there are distinct ontogenetic subpopulations of CD8+ T cells and propose that the layered immune model be extended to the CD8+ T cell compartment.

Multiple waves of fetal-derived immune cells constitute adult immune system

It has been over three decades since Drs. Herzenberg and Herzenberg proposed the layered immune system hypothesis, suggesting that different types of stem cells with distinct hematopoietic potential produce specific immune cells. This layering of immune system development is now supported by recent studies showing the presence of fetal-derived immune cells that function in adults. It has been shown that various immune cells arise at different embryonic ages via multiple waves of hematopoiesis from special endothelial cells (ECs), referred to as hemogenic ECs. However, it remains unknown whether these fetal-derived immune cells are produced by hematopoietic stem cells (HSCs) during the fetal to neonatal period. To address this question, many advanced tools have been used, including lineage-tracing mouse models, cellular barcoding techniques, clonal assays, and transplantation assays at the single-cell level. In this review, we will review the history of the search for the origins of HSCs, B-1a progenitors, and mast cells in the mouse embryo. HSCs can produce both B-1a and mast cells within a very limited time window, and this ability declines after embryonic day (E) 14.5. Furthermore, the latest data have revealed that HSC-independent adaptive immune cells exist in adult mice, which implies more complicated developmental pathways of immune cells. We propose revised road maps of immune cell development.

The ins and outs of innate and adaptive type 2 immunity

Type 2 immunity is orchestrated by a canonical group of cytokines primarily produced by innate lymphoid cells, group 2, and their adaptive counterparts, CD4+ helper type 2 cells, and elaborated by myeloid cells and antibodies that accumulate in response. Here, we review the cytokine and cellular circuits that mediate type 2 immunity. Building from insights in cytokine evolution, we propose that innate type 2 immunity evolved to monitor the status of microbe-rich epithelial barriers (outside) and sterile parenchymal borders (inside) to meet the functional demands of local tissue, and, when necessary, to relay information to the adaptive immune system to reinforce demarcating borders to sustain these efforts. Allergic pathology likely results from deviations in local sustaining units caused by alterations imposed by environmental effects during postnatal developmental windows and exacerbated by mutations that increase vulnerabilities. This framework positions T2 immunity as central to sustaining tissue repair and regeneration and provides a context toward understanding allergic disease.

Primitive haematopoiesis in the human placenta gives rise to macrophages with epigenetically silenced HLA-DR

The earliest macrophages are generated during embryonic development from erythro-myeloid progenitors (EMPs) via primitive haematopoiesis. Although this process is thought to be spatially restricted to the yolk sac in the mouse, in humans, it remains poorly understood. Human foetal placental macrophages, or Hofbauer cells (HBC), arise during the primitive haematopoietic wave ~18 days post conception and lack expression of human leukocyte antigen (HLA) class II. Here, we identify a population of placental erythro-myeloid progenitors (PEMPs) in the early human placenta that have conserved features of primitive yolk sac EMPs, including the lack of HLF expression. Using in vitro culture experiments we demonstrate that PEMP generate HBC-like cells lacking HLA-DR expression. We find the absence of HLA-DR in primitive macrophages is mediated via epigenetic silencing of class II transactivator, CIITA, the master regulator of HLA class II gene expression. These findings establish the human placenta as an additional site of primitive haematopoiesis.

PD-1/PD-L1 Control of Antigen-Specifically Activated CD4 T-Cells of Neonates

Newborns are highly susceptible to infections; however, the underlying mechanisms that regulate the anti-microbial T-helper cells shortly after birth remain incompletely understood. To address neonatal antigen-specific human T-cell responses against bacteria, Staphylococcus aureus (S. aureus) was used as a model pathogen and comparatively analyzed in terms of the polyclonal staphylococcal enterotoxin B (SEB) superantigen responses. Here, we report that neonatal CD4 T-cells perform activation-induced events upon S. aureus/APC-encounter including the expression of CD40L and PD-1, as well as the production of Th1 cytokines, concomitant to T-cell proliferation. The application of a multiple regression analysis revealed that the proliferation of neonatal T-helper cells was determined by sex, IL-2 receptor expression and the impact of the PD-1/PD-L1 blockade. Indeed, the treatment of S. aureus-activated neonatal T-helper cells with PD-1 and PD-L1 blocking antibodies revealed the specific regulation of the immediate neonatal T-cell responses with respect to the proliferation and frequencies of IFNγ producers, which resembled in part the response of adults’ memory T-cells. Intriguingly, the generation of multifunctional T-helper cells was regulated by the PD-1/PD-L1 axis exclusively in the neonatal CD4 T-cell lineage. Together, albeit missing memory T-cells in neonates, their unexperienced CD4 T-cells are well adapted to mount immediate and strong anti-bacterial responses that are tightly controlled by the PD-1/PD-L1 axis, thereby resembling the regulation of recalled memory T-cells of adults.

Immune subset-committed proliferating cells populate the human foetal intestine throughout the second trimester of gestation

The intestine represents the largest immune compartment in the human body, yet its development and organisation during human foetal development is largely unknown. Here we show the immune subset composition of this organ during development, by longitudinal spectral flow cytometry analysis of human foetal intestinal samples between 14 and 22 weeks of gestation. At 14 weeks, the foetal intestine is mainly populated by myeloid cells and three distinct CD3-CD7+ ILC, followed by rapid appearance of adaptive CD4+, CD8+ T and B cell subsets. Imaging mass cytometry identifies lymphoid follicles from week 16 onwards in a villus-like structure covered by epithelium and confirms the presence of Ki-67+ cells in situ within all CD3-CD7+ ILC, T, B and myeloid cell subsets. Foetal intestinal lymphoid subsets are capable of spontaneous proliferation in vitro. IL-7 mRNA is detected within both the lamina propria and the epithelium and IL-7 enhances proliferation of several subsets in vitro. Overall, these observations demonstrate the presence of immune subset-committed cells capable of local proliferation in the developing human foetal intestine, likely contributing to the development and growth of organized immune structures throughout most of the 2nd trimester, which might influence microbial colonization upon birth.

Humanized mouse models for immuno-oncology research

Immunotherapy has emerged as a promising treatment paradigm for many malignancies and is transforming the drug development landscape. Although immunotherapeutic agents have demonstrated clinical efficacy, they are associated with variable clinical responses, and substantial gaps remain in our understanding of their mechanisms of action and specific biomarkers of response. Currently, the number of preclinical models that faithfully recapitulate interactions between the human immune system and tumours and enable evaluation of human-specific immunotherapies in vivo is limited. Humanized mice, a term that refers to immunodeficient mice co-engrafted with human tumours and immune components, provide several advantages for immuno-oncology research. In this Review, we discuss the benefits and challenges of the currently available humanized mice, including specific interactions between engrafted human tumours and immune components, the development and survival of human innate immune populations in these mice, and approaches to study mice engrafted with matched patient tumours and immune cells. We highlight the latest advances in the generation of humanized mouse models, with the aim of providing a guide for their application to immuno-oncology studies with potential for clinical translation.

The Role of Immunity in the Pathogenesis of SARS-CoV-2 Infection and in the Protection Generated by COVID-19 Vaccines in Different Age Groups

This study aims to review the available data regarding the central role of immunity in combating SARS-CoV-2 infection and in the generation of protection by vaccination against COVID-19 in different age groups. Physiologically, the immune response and the components involved in it are variable, both functionally and quantitatively, in neonates, infants, children, adolescents, and adults. These immunological differences are mirrored during COVID-19 infection and in the post-vaccination period. The outcome of SARS-CoV-2 infection is greatly dependent on the reaction orchestrated by the immune system. This is clearly obvious in relation to the clinical status of COVID-19 infection, which can be symptomless, mild, moderate, or severe. Even the complications of the disease show a proportional pattern in relation to the immune response. On the contrary, the commonly used anti-COVID-19 vaccines generate protective humoral and cellular immunity. The magnitude of this immunity and the components involved in it are discussed in detail. Furthermore, many of the adverse effects of these vaccines can be explained on the basis of immune reactions against the different components of the vaccines. Regarding the appropriate choice of vaccine for different age groups, many factors have to be considered. This is a cornerstone, particularly in the following age groups: 1 day to 5 years, 6 to 11 years, and 12 to 17 years. Many factors are involved in deciding the route, doses, and schedule of vaccination for children. Another important issue in this dilemma is the hesitancy of families in making the decision about whether to vaccinate their children. Added to these difficulties is the choice by health authorities and governments concerning whether to make children's vaccination compulsory. In this respect, although rare and limited, adverse effects of vaccines in children have been detected, some of which, unfortunately, have been serious or even fatal. However, to achieve comprehensive control over COVID-19 in communities, both children and adults have to be vaccinated, as the former group represents a reservoir for viral transmission. The understanding of the various immunological mechanisms involved in SARS-CoV-2 infection and in the preparation and application of its vaccines has given the sciences a great opportunity to further deepen and expand immunological knowledge. This will hopefully be reflected positively on other diseases through gaining an immunological background that may aid in diagnosis and therapy. Humanity is still in continuous conflict with SARS-CoV-2 infection and will be for a while, but the future is expected to be in favor of the prevention and control of this disease.

TRAINED IMMUNITY: A POTENTIAL APPROACH FOR IMPROVING HOST IMMUNITY IN NEONATAL SEPSIS

ABSTRACT

Sepsis, a dysregulated host immune response to infection, is one of the leading causes of neonatal mortality worldwide. Improved understanding of the perinatal immune system is critical to improve therapies to both term and preterm neonates at increased risk of sepsis. Our narrative outlines the known and unknown aspects of the human immune system through both the immune tolerant in utero period and the rapidly changing antigen-rich period after birth. We will highlight the key differences in innate and adaptive immunity noted through these developmental stages and how the unique immune phenotype in early life contributes to the elevated risk of overwhelming infection and dysregulated immune responses to infection upon exposure to external antigens shortly after birth. Given an initial dependence on neonatal innate immune host responses, we will discuss the concept of innate immune memory, or "trained immunity," and describe several potential immune modulators, which show promise in altering the dysregulated immune response in newborns and improving resilience to sepsis.

Amphibians as a model to study the role of immune cell heterogeneity in host and mycobacterial interactions

Mycobacterial infections represent major concerns for aquatic and terrestrial vertebrates including humans. Although our current knowledge is mostly restricted to Mycobacterium tuberculosis and mammalian host interactions, increasing evidence suggests common features in endo- and ectothermic animals infected with non-tuberculous mycobacteria (NTMs) like those described for M. tuberculosis. Importantly, most of the pathogenic and non-pathogenic NTMs detected in amphibians from wild, farmed, and research facilities represent, in addition to the potential economic loss, a rising concern for human health. Upon mycobacterial infection in mammals, the protective immune responses involving the innate and adaptive immune systems are highly complex and therefore not fully understood. This complexity results from the versatility and resilience of mycobacteria to hostile conditions as well as from the immune cell heterogeneity arising from the distinct developmental origins according with the concept of layered immunity. Similar to the differing responses of neonates versus adults during tuberculosis development, the pathogenesis and inflammatory responses are stage-specific in Xenopus laevis during infection by the NTM M. marinum. That is, both in human fetal and neonatal development and in tadpole development, responses are characterized by hypo-responsiveness and a lower capacity to contain mycobacterial infections. Similar to a mammalian fetus and neonates, T cells and myeloid cells in Xenopus tadpoles and axolotls are different from the adult immune cells. Fetal and amphibian larval T cells, which are characterized by a lower T cell receptor (TCR) repertoire diversity, are biased toward regulatory function, and they have distinct progenitor origins from those of the adult immune cells. Some early developing T cells and likely macrophage subpopulations are conserved in adult anurans and mammals, and therefore, they likely play an important role in the host-pathogen interactions from early stages of development to adulthood. Thus, we propose the use of developing amphibians, which have the advantage of being free-living early in their development, as an alternative and complementary model to study the role of immune cell heterogeneity in host-mycobacteria interactions.