Delineation of Natural Killer Cell Differentiation from Myeloid Progenitors in Human

Efficient generation of human NOTCH ligand-expressing haemogenic endothelial cells as infrastructure for in vitro haematopoiesis and lymphopoiesis

Arterial endothelial cells (AECs) are the founder cells for intraembryonic haematopoiesis. Here, we report a method for the efficient generation of human haemogenic DLL4+ AECs from pluripotent stem cells (PSC). Time-series single-cell RNA-sequencing reveals the dynamic evolution of haematopoiesis and lymphopoiesis, generating cell types with counterparts present in early human embryos, including stages marked by the pre-haematopoietic stem cell genes MECOM/EVI1, MLLT3 and SPINK2. DLL4+ AECs robustly support lymphoid differentiation, without the requirement for exogenous NOTCH ligands. Using this system, we find IL7 acts as a morphogenic factor determining the fate choice between the T and innate lymphoid lineages and also plays a role in regulating the relative expression level of RAG1. Moreover, we document a developmental pathway by which human RAG1+ lymphoid precursors give rise to the natural killer cell lineage. Our study describes an efficient method for producing lymphoid progenitors, providing insights into their endothelial and haematopoietic ontogeny, and establishing a platform to investigate the development of the human blood system.

Myeloid/natural killer (NK) cell precursor acute leukemia as a distinct leukemia type

Myeloid/natural killer (NK) cell precursor acute leukemia (MNKPL) has been described on the basis of its unique immunophenotype and clinical phenotype. However, there is no consensus on the characteristics for identifying this disease type because of its rarity and lack of defined distinctive molecular characteristics. In this study, multiomics analysis revealed that MNKPL is distinct from acute myeloid leukemia, T cell acute lymphoblastic leukemia, and mixed-phenotype acute leukemia (MPAL), and NOTCH1 and RUNX3 activation and BCL11B down-regulation are hallmarks of MNKPL. Although NK cells have been classically considered to be lymphoid lineage-derived, the results of our single-cell analysis using MNKPL cells suggest that NK cells and myeloid cells share common progenitor cells. Treatment outcomes for MNKPL are unsatisfactory, even when hematopoietic cell transplantation is performed. Multiomics analysis and in vitro drug sensitivity assays revealed increased sensitivity to l-asparaginase and reduced levels of asparagine synthetase (ASNS), supporting the clinically observed effectiveness of l-asparaginase.

Humanized CD36 (hCD36) mouse model supports the preclinical evaluation of therapeutic candidates targeting CD36

CD36 (also known as scavenger receptor B2) is a multifunctional receptor that mediates lipid uptake, advanced oxidation protein products, and immunological recognition, and has roles in lipid accumulation, apoptosis, as well as in metastatic colonization in cancer. CD36 is involved in tumor immunity, metastatic invasion, and therapy resistance through various molecular mechanisms. Targeting CD36 has emerged as an effective strategy for tumor immunotherapy. In this study, we have successfully generated a novel hCD36 mouse (Unless otherwise stated, hCD36 mouse below refer to homozygous hCD36 mouse) strain where the sequences encoding the extracellular domains of the mouse Cd36 gene were replaced with the corresponding human sequences. The results showed that the hCD36 mice only expressed human CD36, and the proportion of each lymphocyte was not significantly changed compared with wild-type mice. Furthermore, CD36 monoclonal antibody could significantly inhibit tumor growth after treatment. Therefore, the hCD36 mouse represent a validated preclinical mouse model for the evaluation of tumor immunotherapy targeting CD36.

Potential Applications and Perspectives of Humanized Mouse Models

As medical and pharmacological technology advances, new and complex modalities of disease treatment that are more personalized and targeted are being developed. Often these modalities must be validated in the presence of critical components of the human biological system. Given the incongruencies between murine and human biology, as well as the human-tropism of certain drugs and pathogens, the selection of animal models that accurately recapitulate the intricacies of the human biological system becomes more salient for disease modeling and preclinical testing. Immunodeficient mice engrafted with functional human tissues (so-called humanized mice), which allow for the study of physiologically relevant disease mechanisms, have thus become an integral aspect of biomedical research. This review discusses the recent advancements and applications of humanized mouse models on human immune system and liver humanization in modeling human diseases, as well as how they can facilitate translational medicine.

Glucocorticoids inhibit human hematopoietic stem cell differentiation toward a common ILC precursor

BACKGROUND

Innate lymphoid cells (ILCs) comprise cytotoxic natural killer (NK) cells and helper ILCs (hILCs). Human hILC development is less characterized as compared with that of NK cells, although all ILCs are developmentally related. It has been reported that the immunosuppressive drugs glucocorticoids (GCs) regulate ILC function, but whether they control ILC differentiation from hematopoietic stem cells (HSCs) is unknown.

OBJECTIVES

This study sought to analyze the effect of GCs on ILC development from HSCs.

METHODS

This study exploited an in vitro system to generate and expand from peripheral blood HSCs a multipotent CD56⁺ ILC precursor able to differentiate into NK cells, ILC1s, and ILC3s. We also analyzed ex vivo, at different time points, the peripheral blood of recipients of allogeneic HSC transplantation who were or were not treated with GCs and compared ILC subset reconstitution.

RESULTS

Invitro, GCs favor the generation of NK cells from myeloid precursors, while they strongly impair lymphoid development. In support of these data, recipients of HSC transplantation who had been treated with GCs display a lower number of circulating hILCs, including the ILC precursor (ILCP) previously identified as a systemic substrate for tissue ILC differentiation.

CONCLUSIONS

GCs impair the development of the CD117⁺ ILCP from CD34⁺ HSCs, while they do not affect the further steps of ILCP differentiation toward NK cells and hILC subsets. This reflects an association of GC treatment with a marked reduction of circulating hILCs in the recipients of HSC transplantation.

Inhibition of BCL9 Modulates the Cellular Landscape of Tumor-Associated Macrophages in the Tumor Immune Microenvironment of Colorectal Cancer

Tumor-associated macrophages (TAMs) are an indispensable part of the tumor microenvironment (TME), and they likely play a negative rather than positive role in cancer treatment. However, the cellular landscape and transcriptional profile regulation of TAMs in the case of tumor gene inactivation or chemical interference remains unclear. The B-cell lymphoma 9/B-cell lymphoma 9-like (BCL9/BCL9L) is a critical transcription co-factor of β-catenin. Suppression of Bcl9 inhibits tumor growth in mouse models of colorectal cancer (CRC). Here, we studied the TAMs of CRC by single-cell sequencing. Bcl9 depletion caused macrophage polarization inhibition from M0 to M2 and changed the CRC TME, which further interferes with the inflammation of M0 and M1. The transcription factor regulating these processes may be related to the Wnt signaling pathway from multiple levels. Furthermore, we also found that the cells delineated from monocyte to NK-like non-functioning cells were significantly different in the BCL9-deprived population. Combining these data, we proposed a TAM-to-NK score to evaluate the dynamic balance in TME of monocyte/TAM cells and NK-like non-functioning cells in The Cancer Genome Atlas (TCGA) clinical samples to verify the clinical significance. We demonstrated that the cell type balance and transcription differences of TAMs regulated by BCL9-driven Wnt signaling affected immune surveillance and inflammation of cancer, ultimately affecting patients' prognosis. We thereby highlighted the potential of targeting Wnt signaling pathway through cancer immunotherapy.

Single-cell transcriptional profiling reveals the heterogeneity in embryonal rhabdomyosarcoma

ABSTRACT

Rhabdomyosarcoma is the most common soft tissue sarcoma in children, and embryonal rhabdomyosarcoma is the most typical type of rhabdomyosarcoma. The heterogeneity, etiology, and origin of embryonal rhabdomyosarcoma remain unknown.After obtaining the gene expression data of every cell in the tumor tissue by single-cell RNA sequencing, we used the Seurat package in R studio for quality control, analysis, and exploration of the data. All cells are divided into tumor cells and non-tumor cells, and we chose tumor cells by marker genes. Then, we repeated the process to cluster the tumor cells and divided the subgroups by their differentially expressed genes and gene ontology/Kyoto Encyclopedia of Genes and Genomes analysis. Additionally, Monocle 2 was used for pseudo-time analysis to obtain the evolution trajectory of cells in tumor tissues.Tumor cells were divided into 5 subgroups according to their functions, which were characterized by high proliferation, sensing and adaptation to oxygen availability, enhanced epigenetic modification, enhanced nucleoside phosphonic acid metabolism, and ossification. Evolution trajectory of cells in tumor tissues is obtained.We used pseudo-time analysis to distinguish between mesenchymal stem cells and fibroblasts, proved that embryonal rhabdomyosarcoma in the pelvic originated from skeletal muscle progenitor cells, showed the evolutionary trajectory of embryonal rhabdomyosarcoma, and improved the method of evaluating the degree of malignancy of embryonal rhabdomyosarcoma.

Human NK cells, their receptors and function

NK cells are cytotoxic components of innate lymphoid cells (ILC) that provide a first line of defense against viral infections and contribute to control tumor growth and metastasis. Their function is finely regulated by an array of HLA-specific and non-HLA-specific inhibitory and activating receptors which allow to discriminate between healthy and altered cells. Human NK cells gained a major attention in recent years because of the important progresses in understanding their biology and of some promising data in tumor therapy. In this review, we will outline well-established issues of human NK cells and discuss some of the open questions, debates, and recent advances regarding their origin, differentiation, and tissue distribution. Newly defined NK cell specializations, including the impact of inhibitory checkpoints on their function, their crosstalk with other cell types, and the remarkable adaptive features acquired in response to certain virus infections will also be discussed.

Potently Cytotoxic Natural Killer Cells Initially Emerge from Erythro-Myeloid Progenitors during Mammalian Development

Natural killer (NK) cells are a critical component of the innate immune system. However, their ontogenic origin has remained unclear. Here, we report that NK cell potential first arises from Hoxaneg/low Kit+CD41+CD16/32+ hematopoietic-stem-cell (HSC)-independent erythro-myeloid progenitors (EMPs) present in the murine yolk sac. EMP-derived NK cells and primary fetal NK cells, unlike their adult counterparts, exhibit robust degranulation in response to stimulation. Parallel studies using human pluripotent stem cells (hPSCs) revealed that HOXAneg/low CD34+ progenitors give rise to NK cells that, similar to murine EMP-derived NK cells, harbor a potent cytotoxic degranulation bias. In contrast, hPSC-derived HOXA+ CD34+ progenitors, as well as human cord blood CD34+ cells, give rise to NK cells that exhibit an attenuated degranulation response but robustly produce inflammatory cytokines. Collectively, our studies identify an extra-embryonic origin of potently cytotoxic NK cells, suggesting that ontogenic origin is a relevant factor in designing hPSC-derived adoptive immunotherapies.

Differentiation of c-Kit+ CD24+ natural killer cells into myeloid cells in a GATA-2-dependent manner

Myeloid progenitor cells have generally been considered the predominant source of myeloid cells under steady-state conditions. Here we show that NK cells contributed to a myeloid cell lineage pool in naïve and tumor-bearing mice. Using fate tracing of NKp46⁺ cells, we found that myeloid cells could be derived from NK cells. Notably, among mature CD11b⁺ CD27⁺ NK cells, c-Kit⁺ CD24⁺ NK cells were capable of differentiating into a range of myeloid lineages in vitro and produced neutrophils and monocytes in vivo. The differentiation was completely inhibited by NK-stimulating cytokines. In addition to the potential for differentiation into myeloid cells, c-Kit⁺ CD24⁺ NK cells retained NK cell phenotypes and effector functions. Mechanistically, GATA-2 was necessary for the differentiation of c-Kit⁺ CD24⁺ NK cells. Therefore, we discovered that GATA-2-dependent differentiation of c-Kit⁺ CD24⁺ NK cells contributes to myeloid cell development and identified a novel pathway for myeloid lineage commitment under physiological conditions.

Human NK Cell Development: One Road or Many?

CD3⁻CD56⁺ NK cells develop from CD34⁺ hematopoietic progenitors (HPCs) in vivo, and this process can be recapitulated in vitro. The prevailing model is that human NK cell development occurs along a continuum whereby common lymphocyte progenitors (CLPs) gradually downregulate CD34 and upregulate CD56. Acquisition of CD94 marks commitment to the CD56^bright stage, and CD56^bright NK cells subsequently differentiate into CD56^dim NK cells that upregulate CD16 and killer immunoglobulin-like receptors (KIR). Support for this linear model comes from analyses of cell populations in secondary lymphoid tissues and in vitro studies of NK cell development from HPCs. However, several lines of evidence challenge this linear model and suggest a more branched model whereby different precursor populations may independently develop into distinct subsets of mature NK cells. A more definitive understanding of human NK cell development is needed to inform in vitro differentiation strategies designed to generate NK cells for immunotherapy. In this review, we summarize current evidence supporting the linear and branched models of human NK cell development and the challenges associated with reaching definitive conclusions.

Humanized Mouse Models for the Study of Hepatitis C and Host Interactions

Hepatitis C virus (HCV) infection is commonly attributed as a major cause of chronic hepatotropic diseases, such as, steatosis, cirrhosis and hepatocellular carcinoma. As HCV infects only humans and primates, its narrow host tropism hampers in vivo studies of HCV-mammalian host interactions and the development of effective therapeutics and vaccines. In this context, we will focus our discussion on humanized mice in HCV research. Here, these humanized mice are defined as animal models that encompass either only human hepatocytes or both human liver and immune cells. Aspects related to immunopathogenesis, anti-viral interventions, drug testing and perspectives of these models for future HCV research will be discussed.

Enterovirus A71 Infection Activates Human Immune Responses and Induces Pathological Changes in Humanized Mice

Since the discovery of enterovirus A71 (EV-A71) half a century ago, it has been recognized as the cause of large-scale outbreaks of hand-foot-and-mouth disease worldwide, particularly in the Asia-Pacific region, causing great concern for public health and economic burdens. Detailed mechanisms on the modulation of immune responses after EV-A71 infection have not been fully known, and the lack of appropriate models hinders the development of promising vaccines and drugs. In the present study, NOD-scid IL2Rγ^-/- (NSG) mice with a human immune system (humanized mice) at the age of 4 weeks were found to be susceptible to a human isolate of EV-A71 infection. After infection, humanized mice displayed limb weakness, which is similar to the clinical features found in some of the EV-A71-infected patients. Histopathological examination indicated the presence of vacuolation, gliosis, or meningomyelitis in brain stem and spinal cord, which were accompanied by high viral loads detected in these organs. The numbers of activated human CD4⁺ and CD8⁺ T cells were upregulated after EV-A71 infection, and EV-A71-specific human T cell responses were found. Furthermore, the secretion of several proinflammatory cytokines, such as human gamma interferon (IFN-γ), interleukin-8 (IL-8), and IL-17A, was elevated in the EV-A71-infected humanized mice. Taken together, our results suggested that the humanized mouse model permits insights into the human immune responses and the pathogenesis of EV-A71 infection, which may provide a platform for the evaluation of anti-EV-A71 drug candidates in the future.IMPORTANCE Despite causing self-limited hand-food-and-mouth disease in younger children, EV-A71 is consistently associated with severe forms of neurological complications and pulmonary edema. Nevertheless, only limited vaccines and drugs have been developed over the years, which is possibly due to a lack of models that can more accurately recapitulate human specificity, since human is the only natural host for wild-type EV-A71 infection. Our humanized mouse model not only mimics histological symptoms in patients but also allows us to investigate the function of the human immune system during infection. It was found that human T cell responses were activated, accompanied by an increase in the production of proinflammatory cytokines in EV-A71-infected humanized mice, which might contribute to the exacerbation of disease pathogenesis. Collectively, this model allows us to delineate the modulation of human immune responses during EV-A71 infection and may provide a platform to evaluate anti-EV-A71 drug candidates in the future.

Murine HSCs contribute actively to native hematopoiesis but with reduced differentiation capacity upon aging

A hallmark of adult hematopoiesis is the continuous replacement of blood cells with limited lifespans. While active hematopoietic stem cell (HSC) contribution to multilineage hematopoiesis is the foundation of clinical HSC transplantation, recent reports have questioned the physiological contribution of HSCs to normal/steady-state adult hematopoiesis. Here, we use inducible lineage tracing from genetically marked adult HSCs and reveal robust HSC-derived multilineage hematopoiesis. This commences via defined progenitor cells, but varies substantially in between different hematopoietic lineages. By contrast, adult HSC contribution to hematopoietic cells with proposed fetal origins is neglible. Finally, we establish that the HSC contribution to multilineage hematopoiesis declines with increasing age. Therefore, while HSCs are active contributors to native adult hematopoiesis, it appears that the numerical increase of HSCs is a physiologically relevant compensatory mechanism to account for their reduced differentiation capacity with age.

As far as we know, all adult blood cells derive from blood stem cells that are located in the bone marrow. These stem cells can produce red blood cells, white blood cells and platelets – the cells fragments that form blood clots to stop bleeding. They can also regenerate, producing more stem cells to support future blood cell production. But, our understanding of the system may be incomplete.

The easiest way to study blood cell production is to watch what happens after a bone marrow transplant. Before a transplant, powerful chemotherapy kills the existing stem cells. This forces the transplanted stem cells to restore the whole system from scratch, allowing scientists to study blood cell production in fine detail. But completely replacing the bone marrow puts major stress on the body, and this may alter the way that the stem cells behave. To understand how adult stem cells keep the blood ticking over on a day-to-day basis, experiments also need to look at healthy animals.

Säwén et al. now describe a method to follow bone marrow stem cells as they produce blood cells in adult mice. The technique, known as lineage tracing, leaves an indelible mark, a red glow, on the stem cells. The cells pass this mark on every time they divide, leaving a lasting trace in every blood cell that they produce. Tracking the red-glowing cells over time reveals which types of blood cells the stem cells make as well as provides estimates on the timing and extent of these processes.

It has previously been suggested that a few types of specialist blood cells, like brain-specific immune cells, originate from cells other than adult blood stem cells. As expected, the adult stem cells did not produce such cells. But, just as seen in transplant experiments, the stem cells were able to produce all the other major blood cell types. They made platelets at the fastest rate, followed by certain types of white blood cells and red blood cells. As the mice got older, the stem cells started to slow down, producing fewer blood cells each. To compensate, the number of stem cells increased, helping to keep blood cell numbers up.

This alternative approach to studying blood stem cells shows how the system behaves in a more natural environment. Away from the stresses of transplant, the technique revealed that blood stem cells are not immune to aging. In the future, understanding more about the system in its natural state could lead to ways to boost blood stem cells as we get older.

Application of small molecule CHIR99021 leads to the loss of hemangioblast progenitor and increased hematopoiesis of human pluripotent stem cells

Improving our understanding of the intricacies of hematopoietic specification of induced or embryonic human pluripotent stem cells is beneficial for many areas of research and translational medicine. Currently, it is not clear whether, during human pluripotent stem cells hematopoietic differentiation in vitro, the maturation of definitive progenitors proceeds through a primitive progenitor (hemangioblast) intermediate or if it develops independently. The objective of this study was to investigate the early stages of hematopoietic specification of pluripotent stem cells in vitro. By implementing an adherent culture, serum-free differentiation system that utilizes a small molecule, CHIR99021, to induce human pluripotent stem cells toward various hematopoietic lineages, we established that, compared with the OP9 coculture hematopoietic induction system, the application of CHIR99021 alters the early steps of hematopoiesis such as hemangioblasts, angiogenic hematopoietic progenitors, and hemogenic endothelium. Importantly, it is associated with the loss of hemangioblast progenitors, loss of CD43⁺ (primitive hematopoietic marker) expression, and predominant development of blast-forming unit erythroid colonies in semisolid medium. These data support the hypothesis that the divergence of primitive and definitive programs during human pluripotent stem cells differentiation precedes the hemangioblast stage. Furthermore, we have shown that the inhibition of primitive hematopoiesis is associated with an increase in hematopoietic potential, which is a fruitful finding due to the growing need for lymphoid and myeloid cells in translational applications.

Humanized Mice as Unique Tools for Human-Specific Studies

With an increasing human population, medical research is pushed to progress into an era of precision therapy. Humanized mice are at the very heart of this new forefront where it is acutely required to decipher human-specific disease pathogenesis and test an array of novel therapeutics. In this review, “humanized” mice are defined as immunodeficient mouse engrafted with functional human biological systems. Over the past decade, researchers have been conscientiously making improvements on the development of humanized mice as a model to closely recapitulate disease pathogenesis and drug mechanisms in humans. Currently, literature is rife with descriptions of novel and innovative humanized mouse models that hold a significant promise to become a panacea for drug innovations to treat and control conditions such as infectious disease and cancer. This review will focus on the background of humanized mice, diseases, and human-specific therapeutics tested on this platform as well as solutions to improve humanized mice for future clinical use.

Technical Improvement and Application of Hydrodynamic Gene Delivery in Study of Liver Diseases

Development of an safe and efficient in vivo gene delivery method is indispensable for molecular biology research and the progress in the following gene therapy. Over the past few years, hydrodynamic gene delivery (HGD) with naked DNA has drawn increasing interest in both research and potential clinic applications due to its high efficiency and low risk in triggering immune responses and carcinogenesis in comparison to viral vectors. This method, involving intravenous injection (i.v.) of massive DNA in a short duration, gives a transient but high in vivo gene expression especially in the liver of small animals. In addition to DNA, it has also been shown to deliver other substance such as RNA, proteins, synthetic small compounds and even viruses in vivo. Given its ability to robustly mimic in vivo hepatitis B virus (HBV) production in liver, HGD has become a fundamental and important technology on HBV studies in our group and many other groups. Recently, there have been interesting reports about the applications and further improvement of this technology in other liver research. Here, we review the principle, safety, current application and development of hydrodynamic delivery in liver disease studies, and discuss its future prospects, clinical potential and challenges.

IL-6/Stat3-Dependent Induction of a Distinct, Obesity-Associated NK Cell Subpopulation Deteriorates Energy and Glucose Homeostasis

Natural killer (NK) cells contribute to the development of obesity-associated insulin resistance. We demonstrate that in mice obesity promotes expansion of a distinct, interleukin-6 receptor (IL6R)a-expressing NK subpopulation, which also expresses a number of other myeloid lineage genes such as the colony-stimulating factor 1 receptor (Csf1r). Selective ablation of this Csf1r-expressing NK cell population prevents obesity and insulin resistance. Moreover, conditional inactivation of IL6Ra or Stat3 in NK cells limits obesity-associated formation of these myeloid signature NK cells, protecting from obesity, insulin resistance, and obesity-associated inflammation. Also in humans IL6Ra⁺ NK cells increase in obesity and correlate with markers of systemic low-grade inflammation, and their gene expression profile overlaps with characteristic gene sets of NK cells in obese mice. Collectively, we demonstrate that obesity-associated inflammation and metabolic disturbances depend on interleukin-6/Stat3-dependent formation of a distinct NK population, which may provide a target for the treatment of obesity, metaflammation-associated pathologies, and diabetes.

CD36 receptor regulates malaria-induced immune responses primarily at early blood stage infection contributing to parasitemia control and resistance to mortality

In malaria, CD36 plays several roles, including mediating parasite sequestration to host organs, phagocytic clearance of parasites, and regulation of immunity. Although the functions of CD36 in parasite sequestration and phagocytosis have been clearly defined, less is known about its role in malaria immunity. Here, to understand the function of CD36 in malaria immunity, we studied parasite growth, innate and adaptive immune responses, and host survival in WT and Cd36^-/- mice infected with a non-lethal strain of Plasmodium yoelii Compared with Cd36^-/- mice, WT mice had lower parasitemias and were resistant to death. At early but not at later stages of infection, WT mice had higher circulatory proinflammatory cytokines and lower anti-inflammatory cytokines than Cd36^-/- mice. WT mice showed higher frequencies of proinflammatory cytokine-producing and lower frequencies of anti-inflammatory cytokine-producing dendritic cells (DCs) and natural killer cells than Cd36^-/- mice. Cytokines produced by co-cultures of DCs from infected mice and ovalbumin-specific, MHC class II-restricted α/β (OT-II) T cells reflected CD36-dependent DC function. WT mice also showed increased Th1 and reduced Th2 responses compared with Cd36^-/- mice, mainly at early stages of infection. Furthermore, in infected WT mice, macrophages and neutrophils expressed higher levels of phagocytic receptors and showed enhanced phagocytosis of parasite-infected erythrocytes than those in Cd36^-/- mice in an IFN-γ-dependent manner. However, there were no differences in malaria-induced humoral responses between WT and Cd36^-/- mice. Overall, the results show that CD36 plays a significant role in controlling parasite burden by contributing to proinflammatory cytokine responses by DCs and natural killer cells, Th1 development, phagocytic receptor expression, and phagocytic activity.

Hypoxia inducible factors are dispensable for myeloid cell migration into the inflamed mouse eye

Hypoxia inducible factors (HIFs) are ubiquitously expressed transcription factors important for cell homeostasis during dynamic oxygen levels. Myeloid specific HIFs are crucial for aspects of myeloid cell function, including their ability to migrate into inflamed tissues during autoimmune disease. This contrasts with the concept that accumulation of myeloid cells at ischemic and hypoxic sites results from a lack of chemotactic responsiveness. Here we seek to address the role of HIFs in myeloid trafficking during inflammation in a mouse model of human uveitis. We show using mice with myeloid-specific Cre-deletion of HIFs that myeloid HIFs are dispensable for leukocyte migration into the inflamed eye. Myeloid-specific deletion of Hif1a, Epas1, or both together, had no impact on the number of myeloid cells migrating into the eye. Additionally, stabilization of HIF pathways via deletion of Vhl in myeloid cells had no impact on myeloid trafficking into the inflamed eye. Finally, we chemically induce hypoxemia via hemolytic anemia resulting in HIF stabilization within circulating leukocytes to demonstrate the dispensable role of HIFs in myeloid cell migration into the inflamed eye. These data suggest, contrary to previous reports, that HIF pathways in myeloid cells during inflammation and hypoxia are dispensable for myeloid cell tissue trafficking.

Signal transducer and activator of transcription 3 (Stat3) regulates host defense and protects mice against herpes simplex virus-1 (HSV-1) infection

Signal transducer and activator of transcription 3 (STAT3) mediates cellular responses to multiple cytokines, governs gene expression, and regulates the development and activation of immune cells. STAT3 also modulates reactivation of latent herpes simplex virus-1 (HSV-1) in ganglia. However, it is unclear how STAT3 regulates the innate immune response during the early phase of HSV-1 lytic infection. Many cell types critical for the innate immunity are derived from the myeloid lineage. Therefore, in this study, we used myeloid-specific Stat3 knockout mice to investigate the role of STAT3 in the innate immune response against HSV-1. Our results demonstrate that Stat3 knockout bone marrow-derived macrophages (BMMs) expressed decreased levels of interferon-α (IFN-α) and interferon-stimulated genes (ISGs) upon HSV-1 infection. In vivo, knockout mice were more susceptible to HSV-1, as marked by higher viral loads and more significant weight loss. Splenic expression of IFN-α and ISGs was reduced in the absence of STAT3, indicating that STAT3 is required for optimal type I interferon response to HSV-1. Expression of TNF-α and IL-12, cytokines that have been shown to limit HSV-1 replication and pathogenesis, was also significantly lower in knockout mice. Interestingly, Stat3 knockout mice failed to expand the CD8⁺ conventional DC (cDC) population upon HSV-1 infection, and this was accompanied by impaired NK and CD8 T cell activation. Collectively, our data demonstrate that myeloid-specific Stat3 deletion causes defects in multiple aspects of the immune system and that STAT3 has a protective role at the early stage of systemic HSV-1 infection.

Human CD56bright NK Cells: An Update

Human NK cells can be subdivided into various subsets based on the relative expression of CD16 and CD56. In particular, CD56(bright)CD16(-/dim) NK cells are the focus of interest. They are considered efficient cytokine producers endowed with immunoregulatory properties, but they can also become cytotoxic upon appropriate activation. These cells were shown to play a role in different disease states, such as cancer, autoimmunity, neuroinflammation, and infection. Although their phenotype and functional properties are well known and have been extensively studied, their lineage relationship with other NK cell subsets is not fully defined, nor is their precise hematopoietic origin. In this article, we summarize recent studies about CD56(bright) NK cells in health and disease and briefly discuss the current controversies surrounding them.