Human intrahepatic ILC2 are IL-13positive amphiregulinpositive and their frequency correlates with model of end stage liver disease score

Involvement of Janus kinase-dependent Bcl-xL overexpression in steroid resistance of group 2 innate lymphoid cells in asthma

The mechanisms underlying the development of steroid resistance in asthma remain unclear. To establish whether as well as the mechanisms by which the activation of Janus kinases (JAKs) is involved in the development of steroid resistance in asthma, murine steroid-resistant models of the proliferation of group 2 innate lymphoid cells (ILC2s) in vitro and asthmatic airway inflammation in vivo were analysed. ILC2s in the lungs of BALB/c mice were sorted and then incubated with IL-33, thymic stromal lymphopoietin (TSLP), and/or IL-7 with or without dexamethasone (10 nM), the pan-JAK inhibitor, delgocitinib (1-10 000 nM), and/or the Bcl-xL inhibitor, navitoclax (1-100 nM), followed by the detection of viable and apoptotic cells. The anti-apoptotic factor, Bcl-xL was detected in ILC2s by flow cytometry. As a steroid-resistant asthma model, ovalbumin (OVA)-sensitized BALB/c mice were intratracheally challenged with OVA at a high dose of 500 μg four times. Dexamethasone (1 mg/kg, i.p.), delgocitinib (3-30 mg/kg, p.o.), or navitoclax (30 mg/kg, p.o.) was administered during the challenges. Cellular infiltration into the lungs was analysed by flow cytometry. Airway remodelling was histologically evaluated. The following results were obtained. (1) Cell proliferation concomitant with a decrease in apoptotic cells was induced when ILC2s were cultured with TSLP and/or IL-7, and was potently inhibited by dexamethasone. In contrast, when the culture with TSLP and IL-7 was performed in the presence of IL-33, the proliferative response exhibited steroid resistance. Steroid-resistant ILC2 proliferation was suppressed by delgocitinib in a concentration-dependent manner. (2) The culture with IL-33, TSLP, and IL-7 induced the overexpression of Bcl-xL, which was clearly inhibited by delgocitinib, but not by dexamethasone. When ILC2s were treated with navitoclax, insensitivity to dexamethasone was significantly cancelled. (3) The development of airway remodelling and the infiltration of ILC2s into the lungs in the asthma model were not suppressed by dexamethasone, but were dose-dependently inhibited by delgocitinib. Combination treatment with dexamethasone and either delgocitinib or navitoclax synergistically suppressed these responses. Therefore, JAKs appear to play significant roles in the induction of steroid resistance by up-regulating Bcl-xL in ILC2s. The inhibition of JAKs and Bcl-xL has potential as pharmacotherapy for steroid-resistant asthma, particularly that mediated by ILC2s.

Immunopathogenesis of Primary Biliary Cholangitis, Primary Sclerosing Cholangitis and Autoimmune Hepatitis: Themes and Concepts

Autoimmune liver diseases include primary biliary cholangitis, primary sclerosing cholangitis, and autoimmune hepatitis, a family of chronic immune-mediated disorders that target hepatocytes and cholangiocytes. Treatments remain nonspecific, variably effective, and noncurative, and the need for liver transplantation is disproportionate to their rarity. Development of effective therapies requires better knowledge of pathogenic mechanisms, including the roles of genetic risk, and how the environment and gut dysbiosis cause immune cell dysfunction and aberrant bile acid signaling. This review summarizes key etiologic and pathogenic concepts and themes relevant for clinical practice and how such learning can guide the development of new therapies for people living with autoimmune liver diseases.

Plasticity between type 2 innate lymphoid cell subsets and amphiregulin expression regulates epithelial repair in biliary atresia

BACKGROUND AND AIMS

Although a dysregulated type 1 immune response is integral to the pathogenesis of biliary atresia, studies in both humans and mice have uncovered a type 2 response, primarily driven by type 2 innate lymphoid cells. In nonhepatic tissues, natural type 2 innate lymphoid cell (nILC2s) regulate epithelial proliferation and tissue repair, whereas inflammatory ILC2s (iIlC2s) drive tissue inflammation and injury. The aim of this study is to determine the mechanisms used by type 2 innate lymphoid cell (ILC2) subpopulations to regulate biliary epithelial response to an injury.

APPROACH AND RESULTS

Using Spearman correlation analysis, nILC2 transcripts, but not those of iILC2s, are positively associated with cholangiocyte abundance in biliary atresia patients at the time of diagnosis. nILC2s are identified in the mouse liver through flow cytometry. They undergo expansion and increase amphiregulin production after IL-33 administration. This drives epithelial proliferation dependent on the IL-13/IL-4Rα/STAT6 pathway as determined by decreased nILC2s and reduced epithelial proliferation in knockout strains. The addition of IL-2 promotes inter-lineage plasticity towards a nILC2 phenotype. In experimental biliary atresia induced by rotavirus, this pathway promotes epithelial repair and tissue regeneration. The genetic loss or molecular inhibition of any part of this circuit switches nILC2s to inflammatory type 2 innate lymphoid cell-like, resulting in decreased amphiregulin production, decreased epithelial proliferation, and the full phenotype of experimental biliary atresia.

CONCLUSIONS

These findings identify a key function of the IL-13/IL-4Rα/STAT6 pathway in ILC2 plasticity and an alternate circuit driven by IL-2 to promote nILC2 stability and amphiregulin expression. This pathway induces epithelial homeostasis and repair in experimental biliary atresia.

Identification and characterization of a hepatic IL-13-producing ILC3-like population potentially involved in liver fibrosis

BACKGROUND AND AIMS

Human innate lymphoid cells (ILCs) are critically involved in the modulation of homeostatic and inflammatory processes in various tissues. However, only little is known about the composition of the intrahepatic ILC pool and its potential role in chronic liver disease. Here, we performed a detailed characterization of intrahepatic ILCs in both healthy and fibrotic livers.

APPROACH AND RESULTS

A total of 50 livers (nonfibrotic = 22, and fibrotic = 29) were analyzed and compared with colon and tonsil tissue (each N = 14) and peripheral blood (N = 32). Human intrahepatic ILCs were characterized ex vivo and on stimulation using flow cytometry and single-cell RNA sequencing. ILC differentiation and plasticity were analyzed by both bulk and clonal expansion experiments. Finally, the effects of ILC-derived cytokines on primary human HSteCs were studied. Unexpectedly, we found that an "unconventional" ILC3-like cell represented the major IL-13-producing liver ILC subset. IL-13 + ILC3-like cells were specifically enriched in the human liver, and increased frequencies of this cell type were found in fibrotic livers. ILC3-derived IL-13 production induced upregulation of proinflammatory genes in HSteCs, indicating a potential role in the regulation of hepatic fibrogenesis. Finally, we identified KLRG1-expressing ILC precursors as the potential progenitor of hepatic IL-13 + ILC3-like cells.

CONCLUSIONS

We identified a formerly undescribed subset of IL-13-producing ILC3-like cells that is enriched in the human liver and may be involved in the modulation of chronic liver disease.

Single-cell RNA sequencing identifies a population of human liver-type ILC1s

Group 1 innate lymphoid cells (ILCs) comprise a heterogeneous family of cytotoxic natural killer (NK) cells and ILC1s. We identify a population of "liver-type" ILC1s with transcriptional, phenotypic, and functional features distinct from those of conventional and liver-resident NK cells as well as from other previously described human ILC1 subsets. LT-ILC1s are CD49a+CD94+CD200R1+, express the transcription factor T-BET, and do not express the activating receptor NKp80 or the transcription factor EOMES. Similar to NK cells, liver-type ILC1s produce IFN-γ, TNF-α, and GM-CSF; however, liver-type ILC1s also produce IL-2 and lack perforin and granzyme-B. Liver-type ILC1s are expanded in cirrhotic liver tissues, and they can be produced from blood-derived ILC precursors in vitro in the presence of TGF-β1 and liver sinusoidal endothelial cells. Cells with similar signature and function can also be found in tonsil and intestinal tissues. Collectively, our study identifies and classifies a population of human cross-tissue ILC1s.

Single-cell profiling of human CD127+ innate lymphoid cells reveals diverse immune phenotypes in hepatocellular carcinoma

BACKGROUND AND AIMS

Innate lymphoid cells (ILCs) are tissue-resident lymphocytes that play critical roles in cytokine-mediated regulation of homeostasis and inflammation. However, relationships between their immune phenotypic characteristics and HCC remain largely unexplored.

APPROACH AND RESULTS

We performed single-cell RNA sequencing analysis on sorted hepatic ILC cells from human patients with HCC and validated using flow cytometry, multiplex immunofluorescence staining, and functional experiments. Moreover, we applied selection strategies to enrich ILC populations in HCC samples to investigate the effects of B cells on the immune reaction of inducible T cell costimulator (ICOS)⁺ ILC2 cells. Dysregulation of ILCs was manifested by the changes in cell numbers or subset proportions in HCC. Seven subsets of 3433 ILCs were identified with unique properties, of which ICOS⁺ ILC2a were preferentially enriched in HCC and correlated with poor prognosis. Mechanistically, we report that B cells, particularly resting naïve B cells, have a previously unrecognized function that is involved in inflammatory differentiation of ILC2 cells. B cell-derived ICOSL signaling was responsible for exacerbating inflammation through the increased production of IL-13 in ICOS⁺ ILC2a cells. Heat shock protein 70 (HSP70) genes Heat Shock Protein Family A Member 1A (HSPA1A) and Heat Shock Protein Family A Member 1B (HSPA1B) were highly expressed in ILC2s in late-stage HCC, and targeting to ICOS and its downstream effector HSP70 in ILC2s suppressed tumor growth and remodeled the immunosuppressive tumor microenvironment.

CONCLUSIONS

This in-depth understanding sheds light on B cell-driven innate type 2 inflammation and provides a potential strategy for HCC immunotherapy.

Liver group 2 innate lymphoid cells regulate blood glucose levels through IL-13 signaling and suppression of gluconeogenesis

The liver stores glycogen and releases glucose into the blood upon increased energy demand. Group 2 innate lymphoid cells (ILC2) in adipose and pancreatic tissues are known for their involvement in glucose homeostasis, but the metabolic contribution of liver ILC2s has not been studied in detail. Here we show that liver ILC2s are directly involved in the regulation of blood glucose levels. Mechanistically, interleukin (IL)-33 treatment induces IL-13 production in liver ILC2s, while directly suppressing gluconeogenesis in a specific Hnf4a/G6pc-high primary hepatocyte cluster via Stat3. These hepatocytes significantly interact with liver ILC2s via IL-13/IL-13 receptor signaling. The results of transcriptional complex analysis and GATA3-ChIP-seq, ATAC-seq, and scRNA-seq trajectory analyses establish a positive regulatory role for the transcription factor GATA3 in IL-13 production by liver ILC2s, while AP-1 family members are shown to suppress IL-13 release. Thus, we identify a regulatory role and molecular mechanism by which liver ILC2s contribute to glucose homeostasis.

Besides hepatocytes, resident immune cells of the liver are also contributing to the body’s energy homeostasis. Here authors show that group 2 innate lymphoid cells interact with a specific set of hepatocytes in suppressing gluconeogenesis and regulate blood glucose levels via Interleukin-13 signalling.

Tissue-Dependent Adaptations and Functions of Innate Lymphoid Cells

Tissue-resident immune cells reside in distinct niches across organs, where they contribute to tissue homeostasis and rapidly respond to perturbations in the local microenvironment. Innate lymphoid cells (ILCs) are a family of innate immune cells that regulate immune and tissue homeostasis. Across anatomical locations throughout the body, ILCs adopt tissue-specific fates, differing from circulating ILC populations. Adaptations of ILCs to microenvironmental changes have been documented in several inflammatory contexts, including obesity, asthma, and inflammatory bowel disease. While our understanding of ILC functions within tissues have predominantly been based on mouse studies, development of advanced single cell platforms to study tissue-resident ILCs in humans and emerging patient-based data is providing new insights into this lymphocyte family. Within this review, we discuss current concepts of ILC fate and function, exploring tissue-specific functions of ILCs and their contribution to health and disease across organ systems.

Mucosal immunity in primary sclerosing cholangitis: from the bowel to bile ducts and back again

PURPOSE OF REVIEW

In this article, we provide a contemporary overview on PSC pathogenesis, with a specific focus on the role of mucosal immunity.

RECENT FINDINGS

The extent of enteric dysbiosis in PSC has been extensively quantified, with evidence of reduced bacterial diversity and enrichment of species capable of driving lymphocyte recruitment from the gut to the liver. Integrative pathway-based analysis and metagenomic sequencing indicate a reduction in butyrate-producing species, near absence of bacteria that activate the nuclear bile acid receptor FXR, and depletion of species that regulate the synthesis of vitamin B6 and branched-chain amino acids. Immunotyping of the cellular inflammatory infiltrate has identified a population of intrahepatic naive T cells, with tendency to acquire a Th17 polarisation state, paralleled by heightened responses to pathogen stimulation. Moreover, the search for antigen specificity has revealed the presence of overlapping nucleotide clonotypes across the gut and liver, highlighting the ability to recognize a common pool of epitopes bearing structural similarities across afflicted sites.

SUMMARY

Understanding the complex mechanisms that underpin mucosal immune responses between the liver and gut will help identify new druggable targets in PSC, centring on gut microbial manipulation, bile acid therapies, and restoration of immune homeostasis.

Tissue-Specific Molecular Markers and Heterogeneity in Type 2 Innate Lymphoid Cells

Innate lymphoid cells (ILCs) are the most recently described group of lymphoid subpopulations. These tissue-resident cells display a heterogeneity resembling that observed on different groups of T cells, hence their categorization as cytotoxic NK cells and helper ILCs type 1, 2 and 3. Each one of these groups is highly diverse and expresses different markers in a context-dependent manner. Type 2 innate lymphoid cells (ILC2s) are activated in response to helminth parasites and regulate the immune response. They are involved in the etiology of diseases associated with allergic responses as well as in the maintenance of tissue homeostasis. Markers associated with their identification differ depending on the tissue and model used, making the study and understanding of these cells a cumbersome task. This review compiles evidence for the heterogeneity of ILC2s as well as discussion and analyses of molecular markers associated with their identity, function, tissue-dependent expression, and how these markers contribute to the interaction of ILC2s with specific microenvironments to maintain homeostasis or respond to pathogenic challenges.

Group-2 Innate Lymphoid Cells Promote HCC Progression Through CXCL2-Neutrophil-Induced Immunosuppression

BACKGROUND AND AIMS

Due to their inherent characteristics, the function of group-2 innate lymphoid cells (ILC2s) varies in a context-dependent manner. ILC2s are involved in certain liver diseases; however, their involvement in HCC is unknown. In the present study, we assessed the role of an HCC-derived ILC2 population in tumor progression.

APPROACH AND RESULTS

Through FACS and single-cell RNA sequencing, we discovered that ILC2s were highly enriched in human HCC and correlated significantly with tumor recurrence and worse progression-free survival as well as overall survival in patients. Mass cytometry identified a subset of HCC-derived ILC2s that had lost the expression of killer cell lectin-like receptor subfamily G, member 1 (KLRG1). Distinct from their circulating counterparts, these hepatic ILC2s highly expressed CD69 and an array of tissue resident-related genes. Furthermore, reduction of E-cadherin in tumor cells caused the loss of KLRG1 expression in ILC2s, leading to their increased proliferation and subsequent accumulation in HCC sites. The KLRG1^- ILC2 subset showed elevated production of chemotaxis factors, including C-X-C motif chemokine (C-X-C motif) ligand (CXCL)-2 and CXCL8, which in turn recruited neutrophils to form an immunosuppressive microenvironment, leading to tumor progression. Accordingly, restoring KLRG1 in ILC2s, inhibiting CXCL2 in ILC2s, or depleting neutrophils inhibited tumor progression in a murine HCC model.

CONCLUSIONS

We identified HCC-associated ILC2s as an immune regulatory cell type that promotes tumor development, suggesting that targeting these ILC2s might lead to new treatments for HCC.

Type 2 Innate Lymphoid Cells: Protectors in Type 2 Diabetes

Type 2 innate lymphoid cells (ILC2) are the innate counterparts of Th2 cells and are critically involved in the maintenance of homeostasis in a variety of tissues. Instead of expressing specific antigen receptors, ILC2s respond to external stimuli such as alarmins released from damage. These cells help control the delicate balance of inflammation in adipose tissue, which is a determinant of metabolic outcome. ILC2s play a key role in the pathogenesis of type 2 diabetes mellitus (T2DM) through their protective effects on tissue homeostasis. A variety of crosstalk takes place between resident adipose cells and ILC2s, with each interaction playing a key role in controlling this balance. ILC2 effector function is associated with increased browning of adipose tissue and an anti-inflammatory immune profile. Trafficking and maintenance of ILC2 populations are critical for tissue homeostasis. The metabolic environment and energy source significantly affect the number and function of ILC2s in addition to affecting their interactions with resident cell types. How ILC2s react to changes in the metabolic environment is a clear determinant of the severity of disease. Treating sources of metabolic instability via critical immune cells provides a clear avenue for modulation of systemic homeostasis and new treatments of T2DM.

Natural Killer Cells and Regulatory T Cells Cross Talk in Hepatocellular Carcinoma: Exploring Therapeutic Options for the Next Decade

Despite major advances in immunotherapy, hepatocellular carcinoma (HCC) remains a challenging target. Natural Killer (NK) cells are crucial components of the anti-HCC immune response, which can be manipulated for immunotherapeutic benefit as primary targets, modulators of the tumour microenvironment and in synchronising with tumour antigen specific effector CD8 cells for tumour clearance. Regulatory T cells shape the anti-tumour response from effector T cells via multiple suppressive mechanisms. Future research is needed to address the development of novel NK cell-targeted immunotherapy and on restraining Treg frequency and function in HCC. We have now entered a new era of anti-cancer treatment using checkpoint inhibitor (CPI)-based strategies. Combining GMP-NK cell immunotherapy to enhance the frequency of NK cells with CPI targeting both NK and CD8 T cells to release co-inhibitory receptors and enhance the cells anti-tumour immunity of HCC would be an attractive therapeutic option in the treatment of HCC. These therapeutic approaches should now be complemented by the application of genomic, proteomic and metabolomic approaches to understanding the microenvironment of HCC which, together with deep immune profiling of peripheral blood and HCC tissue before and during treatment, will provide the much-needed personalised medicine approach required to improve clinical outcomes for patients with HCC.

A crosstalk between type 2 innate lymphoid cells and alternative macrophages in lung development and lung diseases (Review)

Type 2 innate lymphoid cells (ILC2s) are important innate immune cells that are involved in type 2 inflammation, in both mice and humans. ILC2s are stimulated by factors, including interleukin (IL)-33 and IL-25, and activated ILC2s secrete several cytokines that mediate type 2 immunity by inducing profound changes in physiology, including activation of alternative (M2) macrophages. M2 macrophages possess immune modulatory, phagocytic, tissue repair and remodeling properties, and can regulate ILC2s under infection. The present review summarizes the role of ILC2s as innate cells and M2 macrophages as anti-inflammatory cells, and discusses current literature on their important biological significance. The present review also highlights how the crosstalk between ILC2s and M2 macrophages contributes to lung development, induces pulmonary parasitic expulsion, exacerbates pulmonary viral and fungal infections and allergic airway diseases, and promotes the development of lung diseases, such as pulmonary fibrosis, chronic obstructive pulmonary disease and carcinoma of the lungs.

Interleukin-13 as a target to alleviate severe coronavirus disease 2019 and restore lung homeostasis

The ongoing coronavirus disease (COVID-19) pandemic urgently requires the availability of interventions that improve outcomes for those with severe disease. Since severe acute respiratory syndrome coronavirus 2 infection is characterized by dysregulated lung mucosae, and that mucosal homeostasis is heavily influenced by interleukin (IL)-13 activity, we explore recent findings indicating that IL-13 production is proportional to disease severity. We propose that excessive IL-13 contributes to the progression of severe/fatal COVID-19 by (1) promoting the recruitment of immune cells that express inflammatory cytokines, causing a cytokine storm that results in widespread destruction of lung tissue, (2) directly facilitating tissue-remodeling that causes airway hyperinflammation and obstruction, and (3) diverting the immune system away from developing high-quality cytotoxic T cells that confer effective anti-viral immunity. These factors may cumulatively result in significant lung distress, multi-organ failure, and death. Here, we suggest repurposing existing IL-13-inhibiting interventions, including antibody therapies routinely used for allergic lung hyperinflammation, as well as viral vector-based approaches, to alleviate disease. Since many of these strategies have previously been shown to be both safe and effective, this could prove to be a highly cost-effective solution.

Relevance for Patients

There remains a desperate need to establish medical interventions that reliably improves outcomes for patients suffering from COVID-19. We explore the role of IL-13 in maintaining homeostasis at the lung mucosae and propose that its dysregulation during viral infection may propagate the hallmarks of severe disease - further exploration may provide a platform for invaluable therapeutics.

Single-cell landscape of the ecosystem in early-relapse hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has high relapse and low 5-year survival rates. Single-cell profiling in relapsed HCC may aid in the design of effective anticancer therapies, including immunotherapies. We profiled the transcriptomes of ∼17,000 cells from 18 primary or early-relapse HCC cases. Early-relapse tumors have reduced levels of regulatory T cells, increased dendritic cells (DCs), and increased infiltrated CD8⁺ T cells, compared with primary tumors, in two independent cohorts. Remarkably, CD8⁺ T cells in recurrent tumors overexpressed KLRB1 (CD161) and displayed an innate-like low cytotoxic state, with low clonal expansion, unlike the classical exhausted state observed in primary HCC. The enrichment of these cells was associated with a worse prognosis. Differential gene expression and interaction analyses revealed potential immune evasion mechanisms in recurrent tumor cells that dampen DC antigen presentation and recruit innate-like CD8⁺ T cells. Our comprehensive picture of the HCC ecosystem provides deeper insights into immune evasion mechanisms associated with tumor relapse.

Age-Related Dynamics of Circulating Innate Lymphoid Cells in an African Population

Innate lymphoid cell (ILC) lineages mirror those of CD4+ T helper cell subsets, producing type 1, 2 and 3 cytokines respectively. Studies in adult human populations have shown contributions of non-cytotoxic ILC to immune regulation or pathogenesis in a wide range of diseases and have prompted investigations of potential functional redundancy between ILC and T helper cell compartments in neonates and children. To investigate the potential for ILC to contribute to immune responses across the human lifespan, we examined the numbers and frequencies of peripheral blood ILC subsets in a cohort of Gambians aged between 5 and 73 years of age. ILC2 were the most abundant peripheral blood ILC subset in this Gambian cohort, while ILC1 were the rarest at all ages. Moreover, the frequency of ILC1s (as a proportion of all lymphocytes) was remarkably stable over the life course whereas ILC3 cell frequencies and absolute numbers declined steadily across the life course and ILC2 frequencies and absolute numbers declined from childhood until the age of approx. 30 years of age. Age-related reductions in ILC2 cell numbers appeared to be partially offset by increasing numbers of total and GATA3+ central memory (CD45RA-CCR7+) CD4+ T cells, although there was also a gradual decline in numbers of total and GATA3+ effector memory (CD45RA-CCR7-) CD4+ T cells. Despite reduced overall abundance of ILC2 cells, we observed a coincident increase in the proportion of CD117+ ILC2, indicating potential for age-related adaptation of these cells in childhood and early adulthood. While both CD117+ and CD117- ILC2 cells produced IL-13, these responses occurred predominantly within CD117- cells. Furthermore, comparison of ILC frequencies between aged-matched Gambian and UK young adults (25–29 years) revealed an overall higher proportion of ILC1 and ILC2, but not ILC3 in Gambians. Thus, these data indicate ongoing age-related changes in ILC2 cells throughout life, which retain the capacity to differentiate into potent type 2 cytokine producing cells, consistent with an ongoing role in immune modulation.

Group 2 Innate Lymphoid Cells: A Double-Edged Sword in Cancer?

Group 2 Innate Lymphoid Cells (ILC2s) belong to the family of helper ILCs which provide host defense against infectious agents, participate in inflammatory responses and mediate lymphoid organogenesis and tissue repair, mainly at the skin and mucosal level. Based on their transcriptional, phenotypic and functional profile, ILC2s mirror the features of the adaptive CD4+ Th2 cell subset, both contributing to the so-called type 2 immune response. Similar to other ILCs, ILC2s are rapidly activated by signals deriving from tissue and/or other tissue-resident immune cells. The biologic activity of ILCs needs to be tightly regulated in order to prevent them from contributing to severe inflammation and damage in several organs. Indeed, ILC2s display both enhancing and regulatory roles in several pathophysiological conditions, including tumors. In this review, we summarize the actual knowledge about ILC2s ability to induce or impair a protective immune response, their pro- or antitumor activity in murine models, human (children and adults) pathologies and the potential strategies to improve cancer immunotherapy by exploiting the features of ILC2s.

Innate Lymphoid Cells in the Malignant Melanoma Microenvironment

Simple Summary

Innate lymphoid cells (ILCs) are the innate counterparts of adaptive immune cells. Emerging data indicate that they are also key players in the progression of multiple tumors. In this review we briefly describe ILCs’ functions in the skin, lungs and liver. Next, we analyze the role of ILCs in primary cutaneous melanoma and in its most frequent and deadly metastases, those in liver and lung. We focus on their dual anti– and pro-tumoral functions, depending on the cross-interactions among them and with the surrounding stromal cells that form the tumor microenvironment (TME) in each organ. Next, we detail the role of extracellular vesicles secreted to the TME by ILCs and melanoma on both cell populations. We conclude that the identification of markers and tools to allow the modulation of individual ILC subsets, in addition to the development of standardized protocols, is essential for addressing the therapeutic modulation of ILCs.

Abstract

The role of innate lymphoid cells (ILCs) in cancer progression has been uncovered in recent years. ILCs are classified as Type 1, Type 2, and Type 3 ILCs, which are characterized by the transcription factors necessary for their development and the cytokines and chemokines they produce. ILCs are a highly heterogeneous cell population, showing both anti– and protumoral properties and capable of adapting their phenotypes and functions depending on the signals they receive from their surrounding environment. ILCs are considered the innate counterparts of the adaptive immune cells during physiological and pathological processes, including cancer, and as such, ILC subsets reflect different types of T cells. In cancer, each ILC subset plays a crucial role, not only in innate immunity but also as regulators of the tumor microenvironment. ILCs’ interplay with other immune and stromal cells in the metastatic microenvironment further dictates and influences this dichotomy, further strengthening the seed-and-soil theory and supporting the formation of more suitable and organ-specific metastatic environments. Here, we review the present knowledge on the different ILC subsets, focusing on their interplay with components of the tumor environment during the development of primary melanoma as well as on metastatic progression to organs, such as the liver or lung.

Foxp3+ Regulatory T Cells Inhibit CCl4-Induced Liver Inflammation and Fibrosis by Regulating Tissue Cellular Immunity

Foxp3+ regulatory T (Treg) cells are pivotal in maintaining immunological self-tolerance and tissue homeostasis; however, it remains unclear how tissue Treg cells respond to liver injury and regulate chronic inflammation, which can cause liver fibrosis. We report here that hepatic Treg cells play a critical role in preventing liver pathology by suppressing inflammatory cellular immunity that can promote liver damage and fibrosis. Chronic liver inflammation induced by injections of carbon tetrachloride (CCl₄) led to preferential expansion of hepatic Treg cells that prevented liver fibrosis. In contrast, depletion of Treg cells in the CCl₄-induced liver fibrosis model exacerbated the severity of liver pathology. Treg depletion unleashed tissue cellular immunity and drove the activation and expansion of the pro-fibrotic IL-4-producing T helper 2 cells, as well as CCR2^high Ly-6C^high inflammatory monocytes/macrophages in the inflamed liver. Although Treg expression of amphiregulin plays a key role in tissue remodeling and repair in various inflammation models, amphiregulin from hepatic Treg cells, the largest producer among liver immune cells, was dispensable for maintaining liver homeostasis and preventing liver fibrosis during CCl₄-induced chronic inflammation. Our results indicate that Treg cells control chronic liver inflammation and fibrosis by regulating the aberrant activation and functions of immune effector cells. Harnessing Treg functions, which effectively regulate tissue cellular immunity, may be a therapeutic strategy for preventing and treating liver fibrosis.

Innate immune cells in cirrhosis

Cirrhosis is a multisystemic disease wherein inflammatory responses originating from advanced liver disease and its sequelae affect distant compartments. Patients with cirrhosis are susceptible to bacterial infections, which may precipitate acute decompensation and acute-on-chronic liver failure, both of which are associated with high short-term mortality. Innate immune cells are an essential first line of defence against pathogens. Activation of liver macrophages (Kupffer cells) and resident mastocytes generate proinflammatory and vaso-permeating mediators that induce accumulation of neutrophils, lymphocytes, eosinophils and monocytes in the liver, and promote tissue damage. During cirrhosis progression, damage- and pathogen-associated molecular patterns activate immune cells and promote development of systemic inflammatory responses which may involve different tissues and compartments. The antibacterial function of circulating neutrophils and monocytes is gradually and severely impaired as cirrhosis worsens, contributing to disease progression. The mechanisms underlying impaired antimicrobial responses are complex and incompletely understood. This review focuses on the continuous and distinct perturbations arising in innate immune cells during cirrhosis, including their impact on disease progression, as well as reviewing potential therapeutic targets.

Group 2 innate lymphoid cells exhibit progressively higher levels of activation during worsening of liver fibrosis

INTRODUCTION

The interleukin-33/interleukin-13 pathway is involved in the immunopathology of liver fibrosis and recently characterized group 2 innate lymphoid cells (ILC2) were identified as profibrotic immune cells in the liver of mouse models. Our aim was to elucidate whether ILC2 might be present in human liver tissue and whether ILC2 contribute to liver fibrosis.

MATERIALS AND METHODS

To identify ILC2 in liver tissue and blood, we purified mononuclear immune cells from needle biopsies, cirrhotic explant specimen, and paired peripheral blood samples. Cell suspensions were incubated with specific markers for ILC2 and analyzed by flow cytometry. The CD69 marker was included to assess the activation level of ILC2. In addition, we determined the IL-33 plasma level.

RESULTS

Results were correlated with the METAVIR fibrotic score of patients enrolled in this study. We detected ILC2 in a higher percentage of CD45⁺ cells in liver tissue than in paired peripheral blood. The number of ILC2 was significantly increased in fibrotic tissue, but only slightly increased in paired peripheral blood. A higher percentage of CD69⁺ ILC2 was observed in fibrotic tissue, and this increase correlates positively with aggravation of liver fibrosis measured by fibrotic METAVIR score. A higher level of plasma IL-33 was only detected in samples obtained from cirrhotic patients.

CONCLUSION

Our study indicates that ILC2 are present in the human liver and are activated in tissue contributing to the immunopathology of human liver fibrosis, independently of the etiology; which might be a potential new therapeutic target.

Mesenchymal stem cell therapy for liver fibrosis/cirrhosis

Liver fibrosis represents a common outcome of most chronic liver diseases. Advanced fibrosis leads to cirrhosis for which no effective treatment is available except liver transplantation. Because of the limitations of liver transplantation, alternative therapeutic strategies are an urgent need to find. Recently, mesenchymal stem cells (MSCs) based therapy has been suggested as an attractive therapeutic option for liver fibrosis and cirrhosis, based on the promising results from preclinical and clinical studies. Although the precise mechanisms of MSC transplantation are still not fully understood, accumulating evidence has indicated that MSCs eliminate the progression of fibrosis due to their immune-modulatory properties. In this review, we summarise the properties of MSCs and their clinical application in the treatment of liver fibrosis and cirrhosis. We also discuss the mechanisms involved in MSC-dependent regulation of immune microenvironment in the context of liver fibrosis and cirrhosis.

Reduction of circulating innate lymphoid cell progenitors results in impaired cytokine production by innate lymphoid cells in patients with lupus nephritis

Background

Innate lymphoid cells (ILCs) play an essential role in maintaining homeostasis; however, they can also cause chronic inflammation and autoimmune disease. This study aimed to identify the role of ILCs in the pathogenesis of lupus nephritis (LN).

Methods

The percentage of ILCs within the peripheral blood mononuclear cell (PBMC) population and urine of patients with LN (n = 16), healthy controls (HC; n = 8), and disease controls (ANCA-associated vasculitis (AAV; n = 6), IgA nephropathy (IgAN; n = 9), and other glomerular diseases (n = 5)) was determined by flow cytometry analysis. In addition, ILCs were sorted and cultured with plasma from LN patients or HC to elucidate whether the reduced population of CD117⁺ ILCs observed in LN was due to changes in the ILC progenitor population.

Results

The percentage of total ILCs and CD117⁺ ILCs in LN was significantly lower than that in HC. The percentage of cytokine-secreting ILCs was also lower in LN; however, when the disease stabilized, cytokine production was restored to levels similar to those in HC. The increase in the number of exhausted ILCs (cells unable to secrete cytokines) correlated positively with disease activity. When CD117⁺ ILCs were cultured with LN plasma, the number of CD117⁺ ILCs fell, but that of other ILC subsets increased.

Conclusions

The percentage of CD117⁺ ILCs and the capacity of ILCs to secrete cytokines fell as LN severity increased, suggesting that an inflammatory environment of LN induces persistent differentiation and exhaustion of ILCs.

Hepatic ILC2 activity is regulated by liver inflammation-induced cytokines and effector CD4+ T cells

In immune-mediated hepatitis, type 2 innate lymphoid cells (ILC2) as well as effector CD4⁺ T cells have been shown to drive disease pathology. However, less is known about mechanisms involved in the regulation of ILC2 function during liver inflammation. We showed that in homeostasis, hepatic ILC2 constituted a very small population with a naive, inactive phenotype. During immune-mediated hepatitis, the cytokines IL-33 and IFNγ were expressed in liver tissue. IL-33 induced strong activation and expression of type 2 cytokines as well as IL-6 by hepatic ILC2 while IFNγ suppressed cytokine production. Interestingly, this inhibitory effect was overcome by IL-33. The phenotype of activated hepatic ILC2 were stable since they did not show functional plasticity in response to liver inflammation-induced cytokines. Moreover, hepatic ILC2 induced a Th2 phenotype in activated CD4⁺ T cells, which increased ILC2-derived cytokine expression via IL-2. In contrast, Th1 cells inhibited survival of ILC2 by production of IFNγ. Thus, hepatic ILC2 function is regulated by IL-33, IL-2, and IFNγ. While IL-33 and IL-2 support hepatic ILC2 activation, their inflammatory activity in immune-mediated hepatitis might be limited by infiltrating IFNγ-expressing Th1 cells.

Helminth infections drive heterogeneity in human type 2 and regulatory cells

Helminth infections induce strong type 2 and regulatory responses, but the degree of heterogeneity of such cells is not well characterized. Using mass cytometry, we profiled these cells in Europeans and Indonesians not exposed to helminths and in Indonesians residing in rural areas infected with soil-transmitted helminths. To assign immune alteration to helminth infection, the profiling was performed before and 1 year after deworming. Very distinct signatures were found in Europeans and Indonesians, showing expanded frequencies of T helper 2 cells, particularly CD161+ cells and ILC2s in helminth-infected Indonesians, which was confirmed functionally through analysis of cytokine-producing cells. Besides ILC2s and CD4+ T cells, CD8+ T cells and γδ T cells in Indonesians produced type 2 cytokines. Regulatory T cells were also expanded in Indonesians, but only those expressing CTLA-4, and some coexpressed CD38, HLA-DR, ICOS, or CD161. CD11c+ B cells were found to be the main IL-10 producers among B cells in Indonesians, a subset that was almost absent in Europeans. A number of the distinct immune profiles were driven by helminths as the profiles reverted after clearance of helminth infections. Moreover, Indonesians with no helminth infections residing in an urban area showed immune profiles that resembled Europeans rather than rural Indonesians, which excludes a major role for ethnicity. Detailed insight into the human type 2 and regulatory networks could provide opportunities to target these cells for more precise interventions.

ILC2s: New Actors in Tumor Immunity

Innate lymphoid cells (ILCs) represent the most recently identified family of innate lymphocytes that act as first responders, maintaining tissue homeostasis and protecting epithelial barriers. In the last few years, group 2 ILCs (ILC2s) have emerged as key regulators in several immunological processes such as asthma and allergy. Whilst ILC2s are currently being evaluated as novel targets for immunotherapy in these diseases, their involvement in tumor immunity has only recently begun to be deciphered. Here, we provide a comprehensive overview of the pleiotropic roles of ILC2s in different tumor settings. Furthermore, we discuss how different therapeutic approaches targeting ILC2s could improve the efficacy of current tumor immunotherapies.

Inhibitors of class I histone deacetylases attenuate thioacetamide-induced liver fibrosis in mice by suppressing hepatic type 2 inflammation

BACKGROUND AND PURPOSE

Chronic liver diseases feature excessive collagen and matrix protein deposition or crosslinking that characterises fibrosis, leads to scar tissue, and disrupts liver functions. There is no effective treatment. This study investigated whether treatment with selective histone deacetylase (HDAC) inhibitors might specifically reduce type 2 inflammation in the injured liver, thereby attenuating fibrogenesis in mice.

EXPERIMENTAL APPROACH

Thioacetamide (TAA) was used to induce hepatic inflammation, fibrosis, and liver damage in female C57BL/6 mice, similar to the clinical features of chronic human liver disease. We used eight inhibitors of different human HDAC enzymes to probe histological (IHC and TUNEL), biochemical and immunological changes (flow cytometry, qPCR, Legendplex, and ELISA) in pathology, fibrosis, hepatic immune cell flux, and inflammatory cytokine expression.

KEY RESULTS

Inhibitors of class I, but not class II, HDAC enzymes potently suppressed chronic hepatic inflammation and fibrosis in mice, attenuating accumulation and activation of IL-33-dependent, but not IL-25-dependent, group 2 innate lymphoid cells (ILC2) and inhibiting type 2 inflammation that drives hepatic stellate cells to secrete excessive collagen and matrix proteins.

CONCLUSIONS AND IMPLICATIONS

The results show that potent and selective inhibitors of class I only HDAC enzymes profoundly inhibit hepatocyte death and type 2 inflammation to prevent TAA-induced liver fibrosis in mice. The specific HDAC enzymes identified here may be key promoters of inflammation in chronic liver fibrosis.

The Roles of Liver-Resident Lymphocytes in Liver Diseases

Tissue-resident lymphocytes usually reside in barrier sites and are involved in innate and adaptive immunity. In recent years, many studies have shown that multiple types of lymphocytes are resident in the liver, including memory CD8⁺ T (T_RM) cells; "unconventional" T cells, such as invariant natural killer T (iNKT) cells, mucosal associated invariant T (MAIT) cells, and γδT cells; innate lymphoid cells (ILCs) such as natural killer (NK) cells and other ILCs. Although diverse types of tissue-resident lymphocytes share similar phenotypes, functional properties, and transcriptional regulation, the unique microenvironment of the liver can reshape their phenotypic and functional characteristics. Liver-resident lymphocytes serve as sentinels and perform immunosurveillance in response to infection and non-infectious insults, and are involved in the maintenance of liver homeostasis. Under the pathological conditions, distinct liver-resident lymphocytes exert protective or pathological effects in the process of various liver diseases. In this review, we highlight the unique properties of liver-resident lymphocytes, and discuss their functional characteristics in different liver diseases.

The role of helper innate lymphoid cells in cancer

Innate lymphoid cells (ILCs) are an emerging family of innate immune cells and have been found to have an important role in infection, inflammation and tissue repair. In particular, recent work has identified significant alterations of ILC responses in tumor patients, suggesting potential roles of ILCs in tumor development. In this paper, we have focused on the basic features of ILCs and their interaction with other immune cells. Importantly, as the role of cytotoxic natural killer cells, assigned to ILC1 family, in cancer has been well established, we have summarized the new findings that showcase the potential role and mechanism of helper ILCs in different tumors. Helper ILCs might promote or inhibit tumor growth and metastasis, which depends on tumor type and ILC subset.

Type 2 Innate Lymphoid Cells in Liver and Gut: From Current Knowledge to Future Perspectives

Innate lymphoid cells (ILCs) represent a heterogeneous population of recently discovered immune cells that mirror the functions of adaptive T lymphocytes. However, ILCs are devoid of specific antigen receptors and cellular activation depends on environmental cytokines, rendering them as early regulators of immune responses. Type 2 innate lymphoid cells (ILC2s) respond to alarmins, such as interleukin-25 and -33 and shape Th2-associated immunity by expressing IL-5 and IL-13 in a GATA3-dependent manner. In addition, ILC2s express the epidermal growth factor-like molecule Amphiregulin thereby promoting regeneration of injured tissue during inflammation. The gut and liver confer nutrient metabolism and bidirectional exchange of products, known as the gut-liver axis. Accordingly, both organs are continuously exposed to a large variety of harmless antigens. This requires avoidance of immunity, which is established by a tolerogenic environment in the gut and liver. However, dysregulations within the one organ are assumed to influence vitality of the other and frequently promote chronic inflammatory settings with poor prognosis. Intensive research within the last years has revealed that ILC2s are involved in acute and chronic inflammatory settings of gut and liver. Here, we highlight the roles of ILC2s in intestinal and hepatic inflammation and discuss a regulatory potential.

ILC2s-Trailblazers in the Host Response Against Intestinal Helminths

Group 2 innate lymphoid cells (ILC2s) were first discovered in experimental studies of intestinal helminth infection—and much of our current knowledge of ILC2 activation and function is based on the use of these models. It is perhaps not surprising therefore that these cells have also been found to play a key role in mediating protection against these large multicellular parasites. ILC2s have been intensively studied over the last decade, and are known to respond quickly and robustly to the presence of helminths—both by increasing in number and producing type 2 cytokines. These mediators function to activate and repair epithelial barriers, to recruit other innate cells such as eosinophils, and to help activate T helper 2 cells. More recent investigations have focused on the mechanisms by which the host senses helminth parasites to activate ILC2s. Such studies have identified novel stromal cell types as being involved in this process—including intestinal tuft cells and enteric neurons, which respond to the presence of helminths and activate ILC2s by producing IL-25 and Neuromedin, respectively. In the current review, we will outline the latest insights into ILC2 activation and discuss the requirement for—or redundancy of—ILC2s in providing protective immunity against intestinal helminth parasites.

Group 2 Innate Lymphoid Cells in Human Respiratory Disorders

Recent studies using animal models have generated profound insight into the functions of various subsets of innate lymphoid cells (ILCs). The group 2 ILC subset (ILC2) has been implicated in tissue homeostasis, defense responses against parasites, tissue repair, and immunopathology associated with type-2 immunity. In addition, progress has also been made in translating these findings from animal studies into a context of human immunity. Importantly, recent observations strongly support a role for ILC2s in several diseases of the human respiratory system. However, many aspects of human ILC2 biology are still unclear, including how these cells develop and which signals control their activity. As a result, the exact role played by ILCs in human health and disease remains poorly understood. Here, we summarize our current understanding of human ILC2 biology and focus on their potential involvement in various human respiratory disorders.

IL-33/ST2 Axis in Organ Fibrosis

Interleukin 33 (IL-33) is highly expressed in barrier sites, acting via the suppression of tumorigenicity 2 receptor (ST2). IL-33/ST2 axis has long been known to play a pivotal role in immunity and cell homeostasis by promoting wound healing and tissue repair. However, it is also involved in the loss of balance between extensive inflammation and tissue regeneration lead to remodeling, the hallmark of fibrosis. The aim of the current review is to critically evaluate the available evidence regarding the role of the IL-33/ST2 axis in organ fibrosis. The role of the axis in tissue remodeling is better understood considering its crucial role reported in organ development and regeneration. Generally, the IL-33/ST2 signaling pathway has mainly anti-inflammatory/anti-proliferative effects; however, chronic tissue injury is responsible for pro-fibrogenetic responses. Regarding pulmonary fibrosis mature IL-33 enhances pro-fibrogenic type 2 cytokine production in an ST2- and macrophage-dependent manner, while full-length IL-33 is also implicated in the pulmonary fibrotic process in an ST2-independent, Th2-independent fashion. In liver fibrosis, evidence indicate that when acute and massive liver damage occurs, the release of IL-33 might act as an activator of tissue-protective mechanisms, while in cases of chronic injury IL-33 plays the role of a hepatic fibrotic factor. IL-33 signaling has also been involved in the pathogenesis of acute and chronic pancreatitis. Moreover, IL-33 could be used as an early marker for ulcer-associated activated fibroblasts and myofibroblast trans-differentiation; thus one cannot rule out its potential role in inflammatory bowel disease-associated fibrosis. Similarly, the upregulation of the IL-33/ST2 axismay contribute to tubular cell injury and fibrosis via epithelial to mesenchymal transition (EMT) of various cell types in the kidneys. Of note, IL-33 exerts a cardioprotective role via ST2 signaling, while soluble ST2 has been demonstrated as a marker of myocardial fibrosis. Finally, IL-33 is a crucial cytokine in skin pathology responsible for abnormal fibroblast proliferation, leukocyte infiltration and morphologic differentiation of human endothelial cells. Overall, emerging data support a novel contribution of the IL-33/ST2 pathway in tissue fibrosis and highlight the significant role of the Th2 pattern of immune response in the pathophysiology of organ fibrosis.

Innate lymphoid cells in organ fibrosis

Innate lymphoid cells (ILCs) are a recently identified family of lymphoid effector cells. ILCs are mainly clustered into 3 groups based on their unique cytokine profiles and transcription factors typically attributed to the subsets of T helper cells. ILCs have a critical role in the mucosal immune response through promptly responding to pathogens and producing large amount of effector cytokines of type 1, 2, or 3 responses. In addition to the role of early immune responses against infections, ILCs, particularly group 2 ILCs (ILC2), have recently gained attention for modulating remodeling and fibrosis especially in the mucosal tissues. Herein, we overview the current knowledge in this area, highlighting roles of ILCs on fibrosis in the mucosal tissues, especially focusing on the gut and lung. We also discuss some new directions for future research by extrapolating from knowledge derived from studies on Th cells.

Linking the gut and liver: crosstalk between regulatory T cells and mucosa-associated invariant T cells

The gut–liver axis is increasingly considered to play a vital part in the progression of chronic inflammatory gut and liver diseases. Hence, a detailed understanding of the local and systemic regulatory mechanisms is crucial to develop novel therapeutic approaches. In this review, we discuss in-depth the roles of regulatory T cells (Tregs) and mucosal-associated invariant T cells (MAITs) within the context of inflammatory bowel disease, primary sclerosing cholangitis, and non-alcoholic steatohepatitis. Tregs are crucial in maintaining peripheral tolerance and preventing autoimmunity. MAIT cells have a unique ability to rapidly recognize microbial metabolites and mount a local immune response and act as a ‘biliary firewall’ at the gut and biliary epithelial barrier. We also outline how current knowledge can be exploited to develop novel therapies to control the propagation of chronic gut- and liver-related inflammatory and autoimmune conditions. We specifically focus on the nature of the Tregs’ cell therapy product and outline an adjunctive role for low-dose IL-2. All in all, it is clear that translational immunology is at crucial crossroads. The success of ongoing clinical trials in cellular therapies for inflammatory gut and liver conditions could revolutionize the treatment of these conditions and the lives of our patients in the coming years.

ILC2s in infectious diseases and organ-specific fibrosis

Type 2 immune responses evolved to provide host protection against parasitic infections and to support the repair of infection-induced tissue injury. However, persistent chronic organ damage can result in dysregulated production of critical type 2 cytokines supporting tissue remodeling and fibrosis development. Recently, group 2 innate lymphoid cells (ILC2s) were newly described as central innate mediators of type 2 responses. In particular, by secretion of the cytokines IL-5, IL-9, and IL-13 and the growth factor amphiregulin in response to the release of tissue-derived alarmins, ILC2s have been shown to substantially contribute to both the dismissal of metazoan parasites and the repair of infection-dependent or sterile tissue damage. Conversely, cytokine production by ILC2s emerged as a driving force for tissue remodeling and excessive fibrosis in several organ systems including the lung, liver, and skin. In this review, we discuss how ILC2s are specifically implicated in the body's immune response to different pathogenic infections and how dysregulated ILC2s may promote organ-specific fibrosis.