ILC1: Development, maturation, and transcriptional regulation

Type 1 Innate Lymphoid cells (ILC1s) are tissue-resident cells that partake in the regulation of inflammation and homeostasis. A major feature of ILC1s is their ability to rapidly respond after infections. The effector repertoire of ILC1s includes the pro-inflammatory cytokines IFN-γ and TNF-α and cytotoxic mediators such as granzymes, which enable ILC1s to establish immune responses and to directly kill target cells. Recent advances in the characterization of ILC1s have considerably furthered our understanding of ILC1 development and maintenance in tissues. In particular, it has become clear how ILC1s operate independently from conventional natural killer cells, with which they share many characteristics. In this review, we discuss recent developments with regards to the differentiation, polarization, and effector maturation of ILC1s. These processes may underlie the observed heterogeneity in ILC1 populations within and between different tissues. Next, we highlight transcriptional programs that control each of the separate steps in the differentiation of ILC1s. These transcriptional programs are shared with other tissue-resident type-1 lymphocytes, such as tissue-resident memory T cells (T_RM ) and invariant natural killer T cells (iNKT), highlighting that ILC1s utilize networks of transcriptional regulation that are conserved between lymphocyte lineages to respond effectively to tissue-invading pathogens.

HIF-PHD inhibitor regulates the function of group2 innate lymphoid cells and polarization of M2 macrophages

Hypoxia-inducible factor-prolyl hydroxylase (HIF-PHD) inhibitors are therapeutic agents for renal anemia that work through HIF2-mediated upregulation of erythropoietin (EPO) and have also been reported to suppress renal fibrosis. Group 2 innate lymphoid cells (ILC2s) have been proven to be involved in the pathogenesis of fibrosis in various organs, including the kidney. However, the relationship between the HIF pathway, renal fibrosis, and kidney ILC2s remains unclear. In the present study, we found that HIF activation by HIF-PHD inhibitors suppressed type 2 cytokine production from kidney ILC2s. The enhanced HIF pathway downregulated the IL-33 receptor ST2L on ILC2s, and phosphorylation of downstream p38 MAPK was attenuated. M2 macrophages that promote renal fibrosis were polarized by ILC2 supernatants, but reduced cytokine production from ILC2s treated with HIF-PHD inhibitors suppressed this polarization. Our findings suggest that HIF-PHD inhibitors are potential therapeutic agents for renal fibrosis that are mediated by the alteration of ILC2 function.

OMIP-086: Full spectrum flow cytometry for high-dimensional immunophenotyping of mouse innate lymphoid cells

This 25-parameter, 22-color full spectrum flow cytometry panel was designed and optimized for the comprehensive enumeration and functional characterization of innate lymphoid cell (ILC) subsets in mouse tissues. The panel presented here allows the discrimination of ILC progenitors (ILCP), ILC1, ILC2, NCR+ ILC3, NCR- ILC3, CCR6+ lymphoid tissue-inducer (LTi)-like ILC3 and mature natural killer (NK) cell populations. Further characterization of ILC and NK cell functional profiles in response to stimulation is provided by the inclusion of subset-specific cytokine markers, and proliferation markers. Development and optimization of this panel was performed on freshly isolated cells from adult BALB/c lungs and small intestine lamina propria, and ex vivo stimulation with phorbol 12-myrisate 13-acetate, ionomycin, and pro-ILC activating cytokines.

Human natural killer cells: Form, function, and development

Human natural killer (NK) cells are innate lymphoid cells that mediate important effector functions in the control of viral infection and malignancy. Their ability to distinguish "self" from "nonself" and lyse virally infected and tumorigenic cells through germline-encoded receptors makes them important players in maintaining human health and a powerful tool for immunotherapeutic applications and fighting disease. This review introduces our current understanding of NK cell biology, including key facets of NK cell differentiation and the acquisition and execution of NK cell effector function. Further, it addresses the clinical relevance of NK cells in both primary immunodeficiency and immunotherapy. It is intended to provide an up-to-date and comprehensive overview of this important and interesting innate immune effector cell subset.

Regulation of Notch Signaling Pathway to Innate Lymphoid Cells in Patients with Acute Myocardial Infarction

The Notch signaling pathway is an important regulator in fate decisions and immune responses of innate lymphoid cells (ILCs). However, the function of Notch signaling in ILCs in acute coronary syndrome is still not fully elucidated. Thirty-one unstable angina pectoris (UAP) patients, 21 acute myocardial infarction (AMI) patients, and 20 controls were included in this study. Peripheral blood mononuclear cells (PBMCs) were isolated. The mRNA expression levels of Notch receptors and ligands were measured by real-time PCR, while ILC subsets were measured by flow cytometry. Lin^- cells were purified and stimulated with γ-secretase inhibitor (GSI). ILC subsets, transcription factors, and secreted cytokines were assessed. Notch receptor and ligand mRNA levels were elevated in PBMCs and peripheral lin^- cells from AMI patients. There was no significant difference in total lin^-CD45⁺CD161⁺CD127⁺ ILC frequency among three groups. The CRTH2^-CD117^- ILC1 subset was down-regulated, while the CRTH2⁺ ILC2 subset was up-regulated in AMI patients. The CRTH2^-CD117⁺ ILC3 subpopulation was comparable among the three groups. ILC1% was negatively correlated with Notch1 and Notch2 in AMI patients. Inhibition of Notch signaling pathway by GSI induced elevations in ILC1 frequency, T-bet mRNA expression, and interferon-γ secretion and reduced ILC2 frequency, GATA3 mRNA levels, and interleukin-5/interleukin-13 production by lin^- cells from AMI patients. The current data indicated that activation of Notch signaling pathway might contribute to ILC1-to-ILC2 shift in peripheral blood in AMI patients.

Helper Innate Lymphoid Cells-Unappreciated Players in Melanoma Therapy

Immune checkpoint inhibitors (ICIs) and targeted therapy have dramatically changed the outcome of metastatic melanoma patients. Although immune checkpoints were developed based on the biology of adaptive T cells, they have subsequently been shown to be expressed by other subsets of immune cells. Similarly, the immunomodulatory properties of targeted therapy have been studied primarily with respect to T lymphocytes, but other subsets of immune cells could be affected. Innate lymphoid cells (ILCs) are considered the innate counterpart of T lymphocytes and include cytotoxic natural killer cells, as well as three helper subsets, ILC1, ILC2 and ILC3. Thanks to their tissue distribution and their ability to respond rapidly to environmental stimuli, ILCs play a central role in shaping immunity. While the role of NK cells in melanoma physiopathology and therapy is well established, little is known about the other helper ILC subsets. In this review, we summarize recent findings on the ability of the melanoma TME to influence the phenotype and functional plasticity of helper ILCs and highlight how this subset may in turn shape the TME. We also discuss changes in the melanoma TME induced by targeted therapy that could affect helper ILC functions, the expression of immune checkpoints on this subset and how their inhibition by ICIs may modulate helper ILC function and contribute to therapeutic efficacy.

CPHEN-15: Comprehensive phenotyping of human peripheral blood helper-ILCs by flow cytometry

Innate lymphoid cells (ILCs) comprise cytotoxic NK cells and helper-ILCs, which are further divided in ILC1, ILC2, and ILC3. Helper-ILCs mirror the effector functions of helper T-cell subsets and contribute to host immune defense, tissue homeostasis and repair through cytokine secretion. Although they are mainly tissue-resident, helper ILCs are also found in the peripheral blood (PB). In the human setting, it may be needed to analyze circulating helper ILCs to compare pathological to physiological conditions. In this review, we provide simple guidelines and a list of markers useful to study human PB helper ILCs phenotype and function by flow cytometry.

Layered origins of lymphoid tissue inducer cells

The Innate Lymphoid Cell (ILC) family is a relatively recently described immune cell family involved in innate immune responses and tissue homeostasis. Lymphoid Tissue Inducer (LTi) cells are part of the type 3 (ILC3) family. The ILC3 family is the main ILC population within the embryo, in which the LTi cells are critically associated with embryonic lymph node formation. Recent studies have shown more insights in ILC origin and residency from local embryonic and tissue resident precursors. Embryonic LTi cells originating from a different hemogenic endothelial source were shown to be replaced by HSC derived progenitors in adult. This review will discuss the layered origin of the ILC3 family with an emphasis on the LTi cell lineage.

Mechanical bacterial lysate enhances antimicrobial barrier mechanisms in human airway epithelial cells

Polyvalent mechanical bacterial lysate is effective in the prevention of respiratory tract infections, although its mechanism of action is not entirely elucidated. Because epithelial cells constitute the frontline defense against infections, we investigated the molecular mechanisms of innate response exerted by bronchial epithelial cells in the presence of polyvalent mechanical bacterial lysate. By using primary human bronchial epithelial cells, we observed that polyvalent mechanical bacterial lysate was able to increase the expression of cellular adhesion molecules such as ICAM-1 and E-cadherin, as well as the expression of amphiregulin, a growth factor able to support human bronchial epithelial cell proliferation. Remarkably, polyvalent mechanical bacterial lysate promoted in human bronchial epithelial cells the de novo expression of human β-defensin-2, a major antimicrobial peptide, conferring them a direct antimicrobial activity. Moreover, polyvalent mechanical bacterial lysate-stimulated human bronchial epithelial cells provided signals for increased IL-22 production by innate lymphoid cells via IL-23, which could further contribute to the release of antimicrobial peptides by epithelial cells. In agreement with these in vitro data, the concentration of both IL-23 and antimicrobial peptides (human β-defensin-2 and LL-37) increased in the saliva of healthy volunteers after sublingual administration of polyvalent mechanical bacterial lysate. Altogether, these results indicate that polyvalent mechanical bacterial lysate administration might support mucosal barrier integrity and promote mechanisms of antimicrobial activity in airway epithelial cells.

Increased Serum Levels of Tumor Necrosis Factor-like Ligand 1A in Atopic Dermatitis

Atopic dermatitis (AD) is a common chronic skin disease with pruritus, affecting 5-20% of the population in developed countries. Though its cause varies from genetic polymorphisms to the environmental factors, the T-helper (Th) 2 inflammation is one of the main characteristic pathoses. TNF superfamily ligand A (TL1A) is a recently discovered cytokine, which is released by various immune cells and reported to have an ability to stimulate Th1, Th2, and Th17 responses. Its association was investigated in chronic inflammatory disease, such as rheumatoid arthritis, inflammatory bowel disease, and psoriasis. However, its role on AD is unclear. To elucidate the association of TL1A in AD, we measured the serum TL1A levels in AD patients and healthy controls and performed the immunohistochemistry of TL1A. The result showed that the serum TL1A levels were higher in AD patients than healthy controls, and they positively correlated with the serum immunoglobulin E levels, serum Lactate dehydrogenase, and the number of eosinophils in peripheral blood. The immunohistochemistry of TL1A also showed TL1A expression in epithelium of AD samples. Because previous studies indicate TL1A has a certain role as an inflammation enhancer in Th2 and/or Th17 polarized disease, TL1A in AD may also has a role as an inflammation generator.

Differential Regulation of Innate Lymphoid Cells in Human and Murine Oral Squamous Cell Carcinoma

Oral squamous cell carcinomas (OSCC) remain a major healthcare burden in Asian countries. In Pakistan alone, it is the most common cancer in males and second only to breast cancer in females. Alarmingly, treatment options for OSCC remain limited. With this context, investigations made to explore the inflammatory milieu of OSCC become highly relevant, with the hope of practicing immunotherapeutic approaches to address this highly prevalent tumor. We investigated the newly identified innate lymphoid cells (ILCs) and associated cytokines in well-defined human oral squamous cell carcinoma (OSCC) as well as in a 7,12-dimethylbenz[a]anthracene (DMBA)-induced murine model of OSCC using flow cytometry and quantitative real-time polymerase chain reaction (qPCR). We further went on to explore molecular circuitry involved in OSCC by developing a murine model of OSCC and using an α-Thy1 antibody to inhibit ILCs. Amongst the ILCs that we found in human OSCC, ILC3 (23%) was the most abundant, followed by ILC2 (17%) and ILC1 (1%). Mice were divided into four groups: DMBA (n = 33), DMBA+antibody (Ab) (n = 30), acetone (n = 5), and control (n = 5). In murine OSCC tissues, ILC1 and ILC3 were down-infiltrated, while ILC2 remained unchanged compared to controls. Interestingly, compared to the controls (DMBA group), mice treated with the α-Thy1 antibody showed fewer numbers of large tumors, and a larger percentage of these mice were tumor-free at this study's end point. We present novel data on the differential expansion/downsizing of ILCs in OSCC, which provides a pivotal basis to dive deeper into molecular circuitry and the OSCC tumor niche to devise novel diagnostic, therapeutic, and prognostic strategies to prevent/treat oral cancers.

The Maresin 1-LGR6 axis decreases respiratory syncytial virus-induced lung inflammation

The resolution of infection is an active process with specific molecular and cellular mechanisms that temper inflammation and enhance pathogen clearance. Here, the specialized pro-resolving mediator (SPM) Maresin 1 (MaR1) inhibited respiratory syncytial virus (RSV)-induced inflammation. inlerleukin-13 production from type 2 innate lymphoid cells (ILC) and CD4 T helper type 2 cells was decreased by exogenous MaR1. In addition, MaR1 increased amphiregulin production and decreased RSV viral transcripts to promote resolution. MaR1 also promoted interferon-β production in mouse lung tissues and also in pediatric lung slices. MaR1 significantly inhibited the RSV-triggered aberrant inflammatory phenotype in FoxP3-expressing Tregs. The receptor for MaR1, leucine-rich repeat-containing G protein-coupled receptor 6 (LGR6), was constitutively expressed on Tregs. Following RSV infection, mice lacking Lgr6 had exacerbated type 2 immune responses with an increased viral burden and blunted responses to MaR1. Together, these findings have uncovered a multi-pronged protective signaling axis for MaR1-Lgr6, improving Tregs's suppressive function and upregulating host antiviral genes resulting in decreased viral burden and pathogen-mediated inflammation, ultimately promoting restoration of airway mucosal homeostasis.

Differential regulation of lineage-determining transcription factor expression in innate lymphoid cell and adaptive T helper cell subsets

CD4 T helper (Th) cell subsets, including Th1, Th2 and Th17 cells, and their innate counterparts innate lymphoid cell (ILC) subsets consisting of ILC1s, ILC2s and ILC3s, display similar effector cytokine-producing capabilities during pro-inflammatory immune responses. These lymphoid cell subsets utilize the same set of lineage-determining transcription factors (LDTFs) for their differentiation, development and functions. The distinct ontogeny and developmental niches between Th cells and ILCs indicate that they may adopt different external signals for the induction of LDTF during lineage commitment. Increasing evidence demonstrates that many conserved cis-regulatory elements at the gene loci of LDTFs are often preferentially utilized for the induction of LDTF expression during Th cell differentiation and ILC development at different stages. In this review, we discuss the functions of lineage-related cis-regulatory elements in inducing T-bet, GATA3 or RORγt expression based on the genetic evidence provided in recent publications. We also review and compare the upstream signals involved in LDTF induction in Th cells and ILCs both in vitro and in vivo. Finally, we discuss the possible mechanisms and physiological importance of regulating LDTF dynamic expression during ILC development and activation.

Tissue specific imprinting on innate lymphoid cells during homeostasis and disease process revealed by integrative inference of single-cell transcriptomics

Introduction

Innate lymphoid cells (ILCs) are key components of the immune system, yet the similarity and distinction of the properties across tissues under homeostasis, inflammation and tumor process remain elusive.

Methods

Here we performed integrative inference of ILCs to reveal their transcriptional profiles and heterogeneity from single-cell genomics. We collected a large number of ILCs from human six different tissues which can represent unique immune niches (circulation, lymphoid tissue, normal and inflamed mucosa, tumor microenvironment), to systematically address the transcriptional imprinting.

Results

ILCs are profoundly imprinted by their organ of residence, and tissue-specific distinctions are apparent under pathological conditions. In the hepatocellular carcinoma microenvironment, we identified intermediate c-kit⁺ ILC2 population, and lin^-CD127^- NK-like cells that expressed markers of cytotoxicity including CCL5 and IFNG. Additionally, CD127⁺CD94⁺ ILC1s were preferentially enriched in inflamed ileum from patients with Crohn's disease.

Discussion

These analyses depicted a comprehensive characterization of ILC anatomical distribution and subset heterogeneity, and provided a base line for future temporal or spatial studies focused on tissue-specific ILC-mediated immunity.

Single-cell mass cytometry on peripheral cells in Myasthenia Gravis identifies dysregulation of innate immune cells

Myasthenia Gravis (MG) is a neurological autoimmune disease characterized by disabling muscle weaknesses due to anti-acetylcholine receptor (AChR) autoantibodies. To gain insight into immune dysregulation underlying early-onset AChR⁺ MG, we performed an in-depth analysis of peripheral mononuclear blood cells (PBMCs) using mass cytometry. PBMCs from 24 AChR⁺ MG patients without thymoma and 16 controls were stained with a panel of 37 antibodies. Using both unsupervised and supervised approaches, we observed a decrease in monocytes, for all subpopulations: classical, intermediate, and non-classical monocytes. In contrast, an increase in innate lymphoid cells 2 (ILC2s) and CD27^- γδ T cells was observed. We further investigated the dysregulations affecting monocytes and γδ T cells in MG. We analyzed CD27^- γδ T cells in PBMCs and thymic cells from AChR⁺ MG patients. We detected the increase in CD27^- γδ T cells in thymic cells of MG patients suggesting that the inflammatory thymic environment might affect γδ T cell differentiation. To better understand changes that might affect monocytes, we analyzed RNA sequencing data from CD14⁺ PBMCs and showed a global decrease activity of monocytes in MG patients. Next, by flow cytometry, we especially confirmed the decrease affecting non-classical monocytes. In MG, as for other B-cell mediated autoimmune diseases, dysregulations are well known for adaptive immune cells, such as B and T cells. Here, using single-cell mass cytometry, we unraveled unexpected dysregulations for innate immune cells. If these cells are known to be crucial for host defense, our results demonstrated that they could also be involved in autoimmunity.

Application of ATAC-seq in tumor-specific T cell exhaustion

Researches show that chronic viral infection and persistent antigen and/or inflammatory signal exposure in cancer causes the functional status of T cells to be altered, mainly by major changes in the epigenetic and metabolic environment, which then leads to T cell exhaustion. The discovery of the immune checkpoint pathway is an important milestone in understanding and reversing T cell exhaustion. Antibodies targeting these pathways have shown superior ability to reverse T cell exhaustion. However, there are still some limitations in immune checkpoint blocking therapy, such as the short-term nature of therapeutic effects and high individual heterogeneity. Assay for transposase-accessible chromatin with sequencing(ATAC-seq) is a method used to analyze the accessibility of whole-genome chromatin. It uses hyperactive Tn5 transposase to assess chromatin accessibility. Recently, a growing number of studies have reported that ATAC-seq can be used to characterize the dynamic changes of epigenetics in the process of T cell exhaustion. It has been determined that immune checkpoint blocking can only temporarily restore the function of exhausted T cells because of an irreversible change in the epigenetics of exhausted T cells. In this study, we review the latest developments, which provide a clearer molecular understanding of T cell exhaustion, reveal potential new therapeutic targets for persistent viral infection and cancer, and provide new insights for designing effective immunotherapy for treating cancer and chronic infection.

Circulating extracellular particles from severe COVID-19 patients show altered profiling and innate lymphoid cell-modulating ability

Introduction

Extracellular vesicles (EVs) and particles (EPs) represent reliable biomarkers for disease detection. Their role in the inflammatory microenvironment of severe COVID-19 patients is not well determined. Here, we characterized the immunophenotype, the lipidomic cargo and the functional activity of circulating EPs from severe COVID-19 patients (Co-19-EPs) and healthy controls (HC-EPs) correlating the data with the clinical parameters including the partial pressure of oxygen to fraction of inspired oxygen ratio (PaO2/FiO2) and the sequential organ failure assessment (SOFA) score.

Methods

Peripheral blood (PB) was collected from COVID-19 patients (n=10) and HC (n=10). EPs were purified from platelet-poor plasma by size exclusion chromatography (SEC) and ultrafiltration. Plasma cytokines and EPs were characterized by multiplex bead-based assay. Quantitative lipidomic profiling of EPs was performed by liquid chromatography/mass spectrometry combined with quadrupole time-of-flight (LC/MS Q-TOF). Innate lymphoid cells (ILC) were characterized by flow cytometry after co-cultures with HC-EPs or Co-19-EPs.

Results

We observed that EPs from severe COVID-19 patients: 1) display an altered surface signature as assessed by multiplex protein analysis; 2) are characterized by distinct lipidomic profiling; 3) show correlations between lipidomic profiling and disease aggressiveness scores; 4) fail to dampen type 2 innate lymphoid cells (ILC2) cytokine secretion. As a consequence, ILC2 from severe COVID-19 patients show a more activated phenotype due to the presence of Co-19-EPs.

Discussion

In summary, these data highlight that abnormal circulating EPs promote ILC2-driven inflammatory signals in severe COVID-19 patients and support further exploration to unravel the role of EPs (and EVs) in COVID-19 pathogenesis.

FXR mediates ILC-intrinsic responses to intestinal inflammation

The pleiotropic actions of the Farnesoid X Receptor (FXR) are required for gut health, and reciprocally, reduced intestinal FXR signaling is seen in inflammatory bowel diseases (IBDs). Here, we show that activation of FXR selectively in the intestine is protective in inflammation-driven models of IBD. Prophylactic activation of FXR restored homeostatic levels of pro-inflammatory cytokines, most notably IL17. Importantly, these changes were attributed to FXR regulation of innate lymphoid cells (ILCs), with both the inflammation-driven increases in ILCs, and ILC3s in particular, and the induction of Il17a and Il17f  in ILC3s blocked by FXR activation. Moreover, a population of ILC precursor-like cells increased with treatment, implicating FXR in the maturation/differentiation of ILC precursors. These findings identify FXR as an intrinsic regulator of intestinal ILCs and a potential therapeutic target in inflammatory intestinal diseases.

Maturation and specialization of group 2 innate lymphoid cells through the lung-gut axis

Innate lymphoid cells (ILC) are abundant in mucosal tissues. They serve critical functions in anti-pathogen response and tissue homeostasis. However, the heterogenous composition of ILCs in mucosal sites and their various maturation trajectories are less well known. In this study, we characterize ILC types and functions from both the lung and the small intestine, and identify their tissue-specific markers. We find that ILC2s residing in the lung express CCR2, whereas intestinal ILC2s express CCR4. Through the use of CCR2 and CCR4 reporter mice, we show that ILC2s undergo translocation via the lung-gut axis upon IL-33 treatment. This trajectory of ILC2s is also observed at the postnatal stage. Allergen-induced activation of lung ILC2s affects the homeostasis of gut ILC2s. Together, our findings implicate that ILCs display tissue-specific features in both the lung and gut, and ILC2s mature along the lung-gut axis in particular homeostatic and inflammatory conditions.

Identification of aceNKPs, a committed common progenitor population of the ILC1 and NK cell continuum

The development of innate lymphoid cell (ILC) transcription factor reporter mice has shown a previously unexpected complexity in ILC hematopoiesis. Using novel polychromic mice to achieve higher phenotypic resolution, we have characterized bone marrow progenitors that are committed to the group 1 ILC lineage. These common ILC1/NK cell progenitors (ILC1/NKP), which we call "aceNKPs", are defined as lineage-Id2+IL-7Rα+CD25-α4β7-NKG2A/C/E+Bcl11b-. In vitro, aceNKPs differentiate into group 1 ILCs, including NK-like cells that express Eomes without the requirement for IL-15, and produce IFN-γ and perforin upon IL-15 stimulation. Following reconstitution of Rag2-/-Il2rg-/- hosts, aceNKPs give rise to a spectrum of mature ILC1/NK cells (regardless of their tissue location) that cannot be clearly segregated into the traditional ILC1 and NK subsets, suggesting that group 1 ILCs constitute a dynamic continuum of ILCs that can develop from a common progenitor. In addition, aceNKP-derived ILC1/NK cells effectively ameliorate tumor burden in a model of lung metastasis, where they acquired a cytotoxic NK cell phenotype. Our results identify the primary ILC1/NK progenitor that lacks ILC2 or ILC3 potential and is strictly committed to ILC1/NK cell production irrespective of tissue homing.

Neonatal development of intestinal neuroimmune interactions

Interactions between the enteric nervous system (ENS), immune system, and gut microbiota regulate intestinal homeostasis in adults, but their development and role(s) in early life are relatively underexplored. In early life, these interactions are dynamic, because the mucosal immune system, microbiota, and the ENS are developing and influencing each other. Moreover, disrupting gut microbiota and gut immune system development, and potentially ENS development, by early-life antibiotic exposure increases the risk of diseases affecting the gut. Here, we review the development of the ENS and immune/epithelial cells, and identify potential critical periods for their interactions and development. We also highlight knowledge gaps that, when addressed, may help promote intestinal homeostasis, including in the settings of early-life antibiotic exposure.

Mass cytometry reveals cladribine-induced resets among innate lymphoid cells in multiple sclerosis

Here we present a comprehensive mass cytometry analysis of peripheral innate lymphoid cell (ILC) subsets in relapsing/remitting MS (RRMS) patients prior to and after onset of cladribine tablets (CladT). ILC analysis was conducted on CyTOF data from peripheral blood mononuclear cells (PBMC) of MS patients before, 2 and 6 months after onset of CladT, and non-MS controls. Dimensionality reduction was used for immunophenotyping ILC subsets. CladT reduced all ILC subsets, except for CD56bright NK cells and ILC2. Furthermore, CD38+ NK cell and CCR6+ ILC3 were excluded from CladT-induced immune cell reductions. Post-CladT replenishment by immature ILC was noted by increased CD5+ ILC1 proportions at 2 months, and boosted CD38-CD56bright NK cell numbers at 6 months. CladT induce immune cell depletion among ILC but exclude CD56bright NK cells and ILC2 subsets, as well as CD38+ NK cell and CCR6+ ILC3 immunophenotypes. Post-CladT ILC expansions indicate ILC reconstitution towards a more tolerant immune system phenotype.

SLC7A8 is a key amino acids supplier for the metabolic programs that sustain homeostasis and activation of type 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2) are innate counterparts of T helper 2 (Th2) cells that maintain tissue homeostasis and respond to injuries through rapid interleukin (IL)-5 and IL-13 secretion. ILC2s depend on availability of arginine and branched-chain amino acids for sustaining cellular fitness, proliferation, and cytokine secretion in both steady state and upon activation. However, the contribution of amino acid transporters to ILC2 functions is not known. Here, we found that ILC2s selectively express Slc7a8, encoding a transporter for arginine and large amino acids. Slc7a8 was expressed in ILC2s in a tissue-specific manner in steady state and was further increased upon activation. Genetic ablation of Slc7a8 in lymphocytes reduced the frequency of ILC2s, suppressed IL-5 and IL-13 production upon stimulation, and impaired type 2 immune responses to helminth infection. Consistent with this, Slc7a8-deficient ILC2s also failed to induce cytokine production and recruit eosinophils in a model of allergic lung inflammation. Mechanistically, reduced amino acid availability due to Slc7a8 deficiency led to compromised mitochondrial oxidative phosphorylation, as well as impaired activation of mammalian target of rapamycin and c-Myc signaling pathways. These findings identify Slc7a8 as a key supplier of amino acids for the metabolic programs underpinning fitness and activation of ILC2s.