Developmental options and functional plasticity of innate lymphoid cells

A novel type-2 innate lymphoid cell-based immunotherapy for cancer

Cell-based cancer immunotherapy has achieved significant advancements, providing a source of hope for cancer patients. Notwithstanding the considerable progress in cell-based immunotherapy, the persistently low response rates and the exorbitant costs associated with their implementation still present a formidable challenge in clinical settings. In the landscape of cell-based cancer immunotherapies, an uncharted territory involves Type 2 innate lymphoid cells (ILC2s) and interleukin-33 (IL-33) which promotes ILC2 functionality, recognized for their inherent ability to enhance immune responses. Recent discoveries regarding their role in actuating cytolytic T lymphocyte responses, including curbing tumor growth rates and hindering metastasis, have added a new dimension to our understanding of the IL-33/ILC2 axis. These recent insights may hold significant promise for ILC2 cell-based immunotherapy. Nevertheless, the prospect of adoptively transferring ILC2s to confer immune protection against tumors has yet to be investigated. The present study addresses this hypothesis, revealing that ILC2s isolated from the lungs of tumor-bearing mice, and tumor infiltrating ILC2s when adoptively transferred after tumor establishment at a ratio of one ILC2 per sixty tumor cells, leads to an influx of tumor infiltrating CD4+ and CD8+ T lymphocytes as well as tumor infiltrating eosinophils resulting in a remarkable reduction in tumor growth. Moreover, we find that post-adoptive transfer of ILC2s, the number of tumor infiltrating ILC2s is inversely proportional to tumor size. Finally, we find corollaries of the IL-33/ILC2 axis enhancing the infiltration of eosinophils in human prostate carcinomas patients' expressing high levels of IL-33 versus those expressing low levels of IL-33. Our results underscore the heightened efficacy of adoptively transferred ILC2s compared to alternative approaches, revealing an approximately one hundred fifty-fold superiority on a cell-per-cell basis over CAR T-cells in the specific targeting and elimination of tumors within the same experimental model. Overall, this study demonstrates the functional significance of ILC2s in cancer immunosurveillance and provides the proof of concept of the potential utility of ILC2 cell-based cancer immunotherapies.

Role of epigenetics in innate lymphoid cells

Epigenetics plays a crucial role in gene regulation and cell function without changing the DNA sequence. The process of differentiation in eukaryotes during cellular morphogenesis is a paradigm of epigenetic change; stem cells develop into pluripotent cell lines in the embryo, eventually becoming terminally developed cells. Recently, epigenetic changes were shown to play an important role in immune cell development, activation and differentiation, which impacts chromatin remodeling, DNA methylation, post-translational histone modifications and small or lncRNA engagement. Innate lymphoid cells (ILCs) are newly identified immune cells that lack antigen receptors. ILCs differentiate from hematopoietic stem cells via multipotent progenitor stages. In this editorial, the authors discuss the epigenetic regulation of ILC differentiation and function.

Function of Innate Lymphoid Cells in Periodontal Tissue Homeostasis: A Narrative Review

Periodontitis is an irreversible inflammatory response that occurs in periodontal tissues. Given the size and diversity of natural flora in the oral mucosa, host immunity must strike a balance between pathogen identification and a complicated system of tolerance. The innate immune system, which includes innate lymphoid cells (ILCs), certainly plays a crucial role in regulating this homeostasis because pathogens are quickly recognized and responded to. ILCs are a recently discovered category of tissue-resident lymphocytes that lack adaptive antigen receptors. ILCs are found in both lymphoid and non-lymphoid organs and are particularly prevalent at mucosal barrier surfaces, where they control inflammatory response and homeostasis. Recent studies have shown that ILCs are important players in periodontitis; however, the mechanisms that govern the innate immune response in periodontitis still require further investigation. This review focuses on the intricate crosstalk between ILCs and the microenvironment in periodontal tissue homeostasis, with the purpose of regulating or improving immune responses in periodontitis prevention and therapy.

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.

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.

T-BET drives the conversion of human type 3 innate lymphoid cells into functional NK cells

Type 3 innate lymphoid cells (ILC3s) are characterized by RORγt expression and they produce IL-22 upon activation. ILC3s play a role in maintenance of barrier integrity in the intestine. Under inflammatory conditions, the ILC composition of the mucosal tissues is altered due to a high degree of plasticity. It has been extensively demonstrated that both murine and human ILC3s convert into ILC1s to mediate appropriate immune responses. However, plasticity between human ILC3s and NK cells is less well documented. As T-BET and EOMES are key transcription factors in NK cell differentiation, we investigated whether ectopic T-BET or EOMES expression converts human ILC3s into NK cells. ILC3s with ectopic T-BET and EOMES expression downregulate RORγt expression, while T-BET-overexpressing ILC3s additionally upregulate EOMES expression. High E ctopic T-BET expression in ILC3s results in transdifferentiation towards CD94⁺ NK cells, whereas ectopic EOMES overexpression results in dedifferentiation of ILC3s into CD94-CD117^-/low cells but is ineffective in NK cell generation. Dedifferentiating ILC3s from both T-BET and EOMES overexpression cultures upregulate NK cell receptors, perforin and granzyme B. Finally, IL-22 secretion is completely blocked in transdifferentiating ILC3s with both T-BET and EOMES ectopic expression, whereas only T-BET overexpression increases IFN-γ secretion and cytotoxicity. Altogether, these findings demonstrate that human ILC3s can convert into functional NK cells, wherein T-BET, and not EOMES, is the main driver.

Immunological Aspects of Chronic Rhinosinusitis

Chronic rhinosinusitis (CRS) is related to persistent inflammation with a dysfunctional relationship between environmental agents and the host immune system. Disturbances in the functioning of the sinus mucosa lead to common clinical symptoms. The major processes involved in the pathogenesis of CRS include airway epithelial dysfunctions that are influenced by external and host-derived factors which activate multiple immunological mechanisms. The molecular bases for CRS remain unclear, although some factors commonly correspond to the disease: bacterial, fungal and viral infections, comorbidity diseases, genetic dysfunctions, and immunodeficiency. Additionally, air pollution leads increased severity of symptoms. CRS is a heterogeneous group of sinus diseases with different clinical courses and response to treatment. Immunological pathways vary depending on the endotype or genotype of the patient. The recent knowledge expansion into mechanisms underlying the pathogenesis of CRS is leading to a steadily increasing significance of precision medicine in the treatment of CRS. The purpose of this review is to summarize the current state of knowledge regarding the immunological aspects of CRS, which are essential for ensuring more effective treatment strategies.

Interplay Between Liver Type 1 Innate Lymphoid Cells and NK Cells Drives the Development of Alcoholic Steatohepatitis

BACKGROUND & AIMS

Liver contains high frequency of group 1 innate lymphoid cells (ILC), which are composed of comparable number of type 1 ILC (ILC1) and natural killer (NK) cells in steady state. Little is known about whether and how the interaction between ILC1 and NK cells affects the development of alcoholic liver disease.

METHODS

A mouse model of chronic alcohol abuse plus single-binge (Gao-Binge model) was established. The levels of alanine aminotransferase/aspartate aminotransferase, hepatic lipid, and inflammatory cytokines or neutrophils were measured to evaluate the degree of liver injury, steatosis, and inflammation. Flow cytometric analysis, cell depletion, or adoptive transfer were used to interrogate the interaction between ILC1 and NK cells.

RESULTS

Upon chronic alcohol consumption, NK cells, but not ILC1, underwent apoptosis, resulting in ILC1 dominance among group 1 ILC. Interleukin (IL) 17A expression was up-regulated, and increased IL17A was mainly derived from liver ILC1 after chronic alcohol feeding. Either depletion of ILC1 or neutralization of IL17A could significantly attenuate liver steatosis, inflammation, and injury in alcohol-fed mice. In contrast, normalization of the ILC1/NK cells ratio through NK cells transfer or expanding NK cells had a significant hepatoprotection against alcohol-induced steatohepatitis. Furthermore, NK cell-derived interferon gamma exerted a protective function via inhibiting IL17A production by liver ILC1 during alcoholic steatohepatitis.

CONCLUSIONS

This is the first study showing that the interplay between liver ILC1 and NK cells occurs and drives the development of alcoholic steatohepatitis. Our findings support further exploration of liver ILC1 or NK cells as a therapeutic target for the treatment of alcohol-associated liver disease.

Crosstalk between macrophages and innate lymphoid cells (ILCs) in diseases

Innate lymphoid cells (ILCs) and macrophages are tissue-resident cells that play important roles in tissue-immune homeostasis and immune regulation. ILCs are mainly distributed on the barrier surfaces of mammals to ensure immunity or tissue homeostasis following host, microbial, or environmental stimulation. Their complex relationships with different organs enable them to respond quickly to disturbances in environmental conditions and organ homeostasis, such as during infections and tissue damage. Gradually emerging evidence suggests that ILCs also play complex and diverse roles in macrophage development, homeostasis, polarization, inflammation, and viral infection. In turn, macrophages also determine the fate of ILCs to some extent, which indicates that network crossover between these interactions is a key determinant of the immune response. More work is needed to better define the crosstalk of ILCs with macrophages in different tissues and demonstrate how it is affected during inflammation and other diseases. Here, we summarize current research on the functional interactions between ILCs and macrophages and consider the potential therapeutic utility of these interactions for the benefit of human health.

Role of rare immune cells in common variable immunodeficiency

Common variable immunodeficiency disorder (CVID) is a heterogeneous disorder and the most common symptomatic antibody deficiency disease characterized with hypogammaglobulinemia and a broad range of clinical manifestations. Multiple genetic, epigenetic, and immunological defects are involved in the pathogenesis of CVID. These immunological defects include abnormalities in the number and/or function of B lymphocytes, T lymphocytes, and other rare immune cells. Although some immune cells have a relatively lower proportion among total immune subsets in the human body, they could have important roles in the pathogenesis of immunological disorders like CVID. To the best of our knowledge, this is the first review that described the role of rare immune cells in the pathogenesis and clinical presentations of CVID.

Altered Frequencies and Functions of Innate Lymphoid Cells in Melanoma Patients Are Modulated by Immune Checkpoints Inhibitors

Monoclonal antibodies targeting immune checkpoints improved clinical outcome of patients with malignant melanoma. However, the mechanisms are not fully elucidated. Since immune check-point receptors are also expressed by helper innate lymphoid cells (ILCs), we investigated the capability of immune checkpoints inhibitors to modulate ILCs in metastatic melanoma patients as well as melanoma cells effects on ILC functions. Here, we demonstrated that, compared to healthy donors, patients showed a higher frequency of total peripheral ILCs, lower percentages of CD117⁺ ILC2s and CD117⁺ ILCs as well as higher frequencies of CD117^- ILCs. Functionally, melanoma patients also displayed an impaired TNFα secretion by CD117^- ILCs and CD117⁺ ILCs. Nivolumab therapy reduced the frequency of total peripheral ILCs but increased the percentage of CD117^- ILC2s and enhanced the capability of ILC2s and CD117⁺ ILCs to secrete IL-13 and TNFα, respectively. Before Nivolumab therapy, high CCL2 serum levels were associated with longer Overall Survival and Progression Free Survival. After two months of treatment, CD117^- ILC2s frequency as well as serum concentrations of IL-6, CXCL8 and VEGF negatively correlated with both the parameters. Moreover, melanoma cells boosted TNFα production in all ILC subsets and increased the number of IL-13 producing ILC2s in vitro. Our work shows for the first time that PD-1 blockade is able to affect ILCs proportions and functions in melanoma patients and that a specific subpopulation is associated with the therapy response.

Colitis and Colorectal Carcinogenesis: The Focus on Isolated Lymphoid Follicles

Gut-associated lymphoid tissue is one of the most diverse and complex immune compartments in the human body. The subepithelial compartment of the gut consists of immune cells of innate and adaptive immunity, non-hematopoietic mesenchymal cells, and stem cells of different origins, and is organized into secondary (and even tertiary) lymphoid organs, such as Peyer's patches, cryptopatches, and isolated lymphoid follicles. The function of isolated lymphoid follicles is multifaceted; they play a role in the development and regeneration of the large intestine and the maintenance of (immune) homeostasis. Isolated lymphoid follicles are also extensively associated with the epithelium and its conventional and non-conventional immune cells; hence, they can also function as a starting point or maintainer of pathological processes such as inflammatory bowel diseases or colorectal carcinogenesis. These relationships can significantly affect both physiological and pathological processes of the intestines. We aim to provide an overview of the latest knowledge of isolated lymphoid follicles in colonic inflammation and colorectal carcinogenesis. Further studies of these lymphoid organs will likely lead to an extended understanding of how immune responses are initiated and controlled within the large intestine, along with the possibility of creating novel mucosal vaccinations and ways to treat inflammatory bowel disease or colorectal cancer.

Update: Innate Lymphoid Cells in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic and nonspecific intestinal inflammatory condition with high relapse rate. Its pathogenesis has been linked to dysbacteriosis, genetic and environmental factors. In recent years, a new type of lymphocytes, termed innate lymphoid cells, has been described and classified into three subtypes of innate lymphoid cells-group 1, group 2 and group 3. An imbalance among these subsets' interaction with gut microbiome, and other immune cells affects intestinal mucosal homeostasis. Understanding the role of innate lymphoid cells may provide ideas for developing novel and targeted approaches for treatment of IBD.

A mitochondrial STAT3-methionine metabolism axis promotes ILC2-driven allergic lung inflammation

BACKGROUND

Group 2 innate lymphoid cells (ILC2s), the innate counterpart of T helper 2 cells (Th2), play a critical role in type 2 immune responses. However, the molecular regulatory mechanisms of ILC2s are still unclear.

OBJECTIVE

The aim of this study was to explore the importance of signal transducer and activator of transcription 3 (STAT3) to ILC2 function in allergic lung inflammation.

METHODS

Acute and chronic asthma models were established by intranasal administration of the protease allergen papain in Vav^icreStat3^fl/fl, Il5^tdtomato-creStat3^fl/fl, and Rorc^creStat3^fl/fl mice to verify the necessity of functional STAT3 for ILC2 allergic response. The intrinsic role of STAT3 in regulating ILC2 function was examined by generation of bone marrow chimera mice. The underlying mechanism was studied through confocal imaging, metabolomics analysis, and chromatin immunoprecipitation quantitative PCR.

RESULTS

STAT3 is essential for ILC2 effector function and promotes ILC2-driven allergic inflammation in the lung. Mechanistically, the alarmin cytokine interleukin (IL)-33 induces a non-canonical STAT3 phosphorylation at serine 727 in ILC2s, leading to translocation of STAT3 into the mitochondria. Mitochondrial STAT3 further facilitates adenosine triphosphate synthesis to fuel the methionine cycle and generation of S-adenosylmethionine, which supports the epigenetic reprogramming of type 2 cytokines in ILC2s. STAT3 deficiency, inhibition of STAT3 mitochondrial translocation, or blockade of methionine metabolism markedly dampened the ILC2 allergic response and ameliorated allergic lung inflammation.

CONCLUSION

The mitochondrial STAT3-methionine metabolism pathway is a key regulator that shapes ILC2 effector function through epigenetic regulation, and the related proteins or metabolites represent potential therapeutic targets for allergic lung inflammation.

Therapeutic Potential of Innate Lymphoid Cells for Multiple Myeloma Therapy

Innate lymphoid cells (ILCs) are a recently identified family of lymphocyte-like cells lacking a specific antigen receptor. They are part of the innate immune system. They play a key role in tissue homeostasis and also control inflammatory and neoplastic processes. In response to environmental stimuli, ILCs change their phenotype and functions, and influence the activity of other cells in the microenvironment. ILC dysfunction can lead to a wide variety of diseases, including cancer. ILC can be divided into three subgroups: ILC Group 1, comprising NK cells and ILC1; Group 2, including ILC2 alone; and Group 3, containing Lymphoid Tissue inducers (LTi) and ILC3 cells. While Group 1 ILCs mainly exert antitumour activity, Group 2 and Group 3 ILCs are protumorigenic in nature. A growing body of preclinical and clinical data support the role of ILCs in the pathogenesis of multiple myeloma (MM). Therefore, targeting ILCs may be of clinical benefit. In this manuscript, we review the available data on the role of ILCs in MM immunology and therapy.

Clinical and immunological allergy assessment in cancer patients

Cancer is associated with immunodeficiency, while allergies result from immune system hyperactivity mediated by cytokines and immunoglobulins. The purpose of this study was to determine the relationship between immune environment of specific cancers and allergies, emphasizing cytokines related to Th1 and Th2 responses associated with IgE. 80 adults were distributed into two groups: control (n = 20) and cancer (n = 60), distributed in three subgroups (n = 20), head and neck, stomach, and prostate cancers. This study compared Th1 (IL-2) and Th2 (IL-4) parameters, anti-inflammatory, pro-inflammatory, or regulatory profile regarding both IgE levels and reported allergies, by means of clinical manifestations and IgE, IL-1β, IL-2, IL-4, IL-17, and TGF-β serum concentration. Clinically allergies were observed in 50% of the control group and in 20% of the cancer group (p = 0.009). IL-2 cytokine and TGF-β concentrations were higher in the patients with cancer as compared to the control (p < 0.005). However, there were IL-4, IL-17, and IL-1β decreases in the patients with cancer (p < 0.05). No correlation was observed between the cytokines studied and IgE and clinically proven allergies in both investigated groups. There was an inverse association between cancer and clinical allergy manifestations. In head and neck, stomach, and prostate cancers, an immunosuppressive serum tumor environment was predominant. There was no difference in cytokines related to Th1 and Th2 parameters in relation to IgE. No correlation was found between clinically proved allergies and immunity markers related to the same allergens.

Innate Lymphoid Cells in Intestinal Homeostasis and Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a heterogeneous state of chronic intestinal inflammation of unknown cause encompassing Crohn’s disease (CD) and ulcerative colitis (UC). IBD has been linked to genetic and environmental factors, microbiota dysbiosis, exacerbated innate and adaptive immunity and epithelial intestinal barrier dysfunction. IBD is classically associated with gut accumulation of proinflammatory Th1 and Th17 cells accompanied by insufficient Treg numbers and Tr1 immune suppression. Inflammatory T cells guide innate cells to perpetuate a constant hypersensitivity to microbial antigens, tissue injury and chronic intestinal inflammation. Recent studies of intestinal mucosal homeostasis and IBD suggest involvement of innate lymphoid cells (ILCs). These lymphoid-origin cells are innate counterparts of T cells but lack the antigen receptors expressed on B and T cells. ILCs play important roles in the first line of antimicrobial defense and contribute to organ development, tissue protection and regeneration, and mucosal homeostasis by maintaining the balance between antipathogen immunity and commensal tolerance. Intestinal homeostasis requires strict regulation of the quantity and activity of local ILC subpopulations. Recent studies demonstrated that changes to ILCs during IBD contribute to disease development. A better understanding of ILC behavior in gastrointestinal homeostasis and inflammation will provide valuable insights into new approaches to IBD treatment. This review summarizes recent research into ILCs in intestinal homeostasis and the latest advances in the understanding of the role of ILCs in IBD, with particular emphasis on the interaction between microbiota and ILC populations and functions.

The dual function of ILC2: From host protection to pathogenic players in type 2 asthma

Innate lymphoid cells type 2 (ILC2) are considered the innate counterpart of Th2 cells and cooperate with them in host protection against helminths and in the pathogenesis of allergic diseases. ILC2 are characterized by type 2 cytokines production (IL-13, IL-4 and IL-5) and by GATA-3 transcription factor expression. Belonging to innate immune system, ILC2 lack of antigen specific receptor and their activation is controlled mainly by epithelial derived cytokines, such as TSLP, IL-25, and IL-33. ILC2 are located in a strategic position in the airway mucosa and are important to patrol the airways, to recruit other immune system cells and to activate resident cells in response to pathogens injury and/or tissue damage. In the last decade, many studies, in both humans and mice, focused on ILC2, fully investigating their main features such as the development from the precursor, the stimuli for their activation or inhibition, their plasticity, their classification in different subsets, and finally, their pathogenetic role in type 2 immune-mediated disorders. In this review we performed an excursus on phenotypical and functional properties on both human and mouse ILC2, in physiological and pathological conditions (mainly in type 2 asthma), considering this cell subset as target for specific therapeutic strategies.

How Do Uterine Natural Killer and Innate Lymphoid Cells Contribute to Successful Pregnancy?

Innate lymphoid cells (ILCs) are the most abundant immune cells in the uterine mucosa both before and during pregnancy. Circumstantial evidence suggests they play important roles in regulating placental development but exactly how they contribute to the successful outcome of pregnancy is still unclear. Uterine ILCs (uILCs) include subsets of tissue-resident natural killer (NK) cells and ILCs, and until recently the phenotype and functions of uILCs were poorly defined. Determining the specific roles of each subset is intrinsically challenging because of the rapidly changing nature of the tissue both during the menstrual cycle and pregnancy. Single-cell RNA sequencing (scRNAseq) and high dimensional flow and mass cytometry approaches have recently been used to analyse uILC populations in the uterus in both humans and mice. This detailed characterisation has significantly changed our understanding of the heterogeneity within the uILC compartment. It will also enable key clinical questions to be addressed including whether specific uILC subsets are altered in infertility, miscarriage and pregnancy disorders such as foetal growth restriction and pre-eclampsia. Here, we summarise recent advances in our understanding of the phenotypic and functional diversity of uILCs in non-pregnant endometrium and first trimester decidua, and review how these cells may contribute to successful placental development.

Inflammatory status might direct ILC and NK cells to IL-17 expressing ILC3 and NK subsets in Behcet's disease

Innate lymphoid cells (ILCs) are lymphoid cells that have important effector and regulatory functions in innate immunity and tissue remodeling. Uncontrolled activation and proliferation of ILCs can contribute to inflammatory autoimmune diseases. Behcet's disease (BD) is a complex systemic inflammatory disorder of unknown etiology. It has been shown that natural killer (NK) cells may play an immunoregulatory role in BD, however the role of ILCs is unknown. In this study, the levels and functions of ILCs and NK cell subsets in BD patients were investigated. Cell surface and cytotoxic granules (perforin and granzyme) expression of NK cells and ILCs were evaluated and labeled according to whole blood lysing protocol in peripheral blood samples obtained from the patients and healthy subjects. Cytokine levels of NK cells were investigated in stimulated peripheral blood mononuclear cells. All data were analyzed by flow cytometry. Total ILC and ILC3⁺ cells were increased in active BD patients compared to inactive BD patients and healthy subjects. There was no significant difference between the patients and healthy subjects regarding NK cell surface and intracellular molecule expression. Although, an increase in IFN-γ and IL-17, and a decrease in IL-4 levels were observed in CD56^dim NK cell subset of BD patients. Recent studies showed increased neutrophilic infiltration and IL-17 secreting Th17 cells in BD patients. It is known that ILC3⁺cells are similar to Th17 subset regarding their cytokine profile and transcription factor expression patterns. Results of current study may suggest that inflammatory microenvironment in BD patients might direct ILC cells to differentiate into ILC3⁺ subset, and IL-17 released by NK cells might have a role in neutrophilic infiltration.

Role of Aiolos and Ikaros in the Antitumor and Immunomodulatory Activity of IMiDs in Multiple Myeloma: Better to Lose Than to Find Them

The Ikaros zing-finger family transcription factors (IKZF TFs) are important regulators of lymphocyte development and differentiation and are also highly expressed in B cell malignancies, including Multiple Myeloma (MM), where they are required for cancer cell growth and survival. Moreover, IKZF TFs negatively control the functional properties of many immune cells. Thus, the targeting of these proteins has relevant therapeutic implications in cancer. Indeed, accumulating evidence demonstrated that downregulation of Ikaros and Aiolos, two members of the IKZF family, in malignant plasma cells as well as in adaptative and innate lymphocytes, is key for the anti-myeloma activity of Immunomodulatory drugs (IMiDs). This review is focused on IKZF TF-related pathways in MM. In particular, we will address how the depletion of IKZF TFs exerts cytotoxic effects on MM cells, by reducing their survival and proliferation, and concomitantly potentiates the antitumor immune response, thus contributing to therapeutic efficacy of IMiDs, a cornerstone in the treatment of this neoplasia.

Human innate lymphoid cell precursors express CD48 that modulates ILC differentiation through 2B4 signaling

Innate lymphoid cells (ILCs) develop from common lymphoid progenitors (CLPs), which further differentiate into the common ILC progenitor (CILP) that can give rise to both ILCs and natural killer (NK) cells. Murine ILC intermediates have recently been characterized, but the human counterparts and their developmental trajectories have not yet been identified, largely due to the lack of homologous surface receptors in both organisms. Here, we show that human CILPs (CD34+CD117+α4β7+Lin-) acquire CD48 and CD52, which define NK progenitors (NKPs) and ILC precursors (ILCPs). Two distinct NK cell subsets were generated in vitro from CD34+CD117+α4β7+Lin-CD48-CD52+ and CD34+CD117+α4β7+Lin-CD48+CD52+ NKPs, respectively. Independent of NKPs, ILCPs exist in the CD34+CD117+α4β7+Lin-CD48+CD52+ subset and give rise to ILC1s, ILC2s, and NCR+ ILC3s, whereas CD34+CD117+α4β7+Lin-CD48+CD52- ILCPs give rise to a distinct subset of ILC3s that have lymphoid tissue inducer (LTi)-like properties. In addition, CD48-expressing CD34+CD117+α4β7+Lin- precursors give rise to tissue-associated ILCs in vivo. We also observed that the interaction of 2B4 with CD48 induced differentiation of ILC2s, and together, these findings show that expression of CD48 by human ILCPs modulates ILC differentiation.

Helper Innate Lymphoid Cells in Allogenic Hematopoietic Stem Cell Transplantation and Graft Versus Host Disease

Helper Innate Lymphoid Cells (hILCs), including ILC1s, ILC2s, and ILC3s, are mainly localized at the mucosal barriers where they play an important role in tissue regeneration and homeostasis through the secretion of specific sets of cytokines. The recent identification of a circulating ILC precursor able to generate all ILC mature subsets in physiological conditions, suggests that “ILC-poiesis” may be important in the context of hematopoietic stem cell transplantation (HSCT). Indeed, in HSCT the conditioning regimen (chemotherapy and radiotherapy) and Graft vs Host Disease (GvHD) may cause severe damages to mucosal tissues. Therefore, it is conceivable that rapid reconstitution of the hILC compartment may be beneficial in HSCT, by promoting mucosal tissue repair/regeneration and providing protection from opportunistic infections. In this review, we will summarize the evidence for a role of hILCs in allogenic HSCT for the treatment of hematological malignancies in all its steps, from the preparative regimen to the immune reconstitution in the recipient. The protective properties of hILCs at the mucosal barrier interfaces make them an attractive target to exploit in future cellular therapies aimed at improving allogenic HSCT outcome.

Plasticity and regulatory mechanisms of human ILC2 functions

Human group 2 innate lymphoid cells (ILC2) represent the innate counterpart of Th2 cells and cooperate with them in helminths protection and in the pathogenesis of allergic diseases. Some reports described ILC2 plasticity and few studies investigated the cellular and molecular mechanisms regulating human ILC2 functions. The aim of this study is to define how immune deviation and immune regulation control human ILC2-mediated immune response. Human circulating ILC2 were expanded in vitro and then cultured in presence of IL-12 or IL-1β plus IL-23 or co-coltured in presence of circulating CD4+CD25highFoxp3+Treg. IL-12 induces IFN-γ production and upregulation of T-bet mRNA level on human circulating ILC2 whereas IL-1β and IL-23 mediate IL-22 production and upregulation of RORC mRNA level. In all these conditions, GATA-3 mRNA level is not reduced and the typical type 2 cytokines are only partially reduced. Moreover, "modulated" ILC2 have reduced ability to induce IgE producing by B cells. ILC2 proliferation, cytokines production and CD154 expression were inhibited by CD4+CD25highFoxp3+ Treg cells. TGF-β reduced CD154 expression on ILC2 stimulated with IL-25/IL-33. This study defines possible cellular and molecular mechanisms responsible for modulation and inhibition of human ILC2 activity. These results may be useful in the development of strategies aimed to dampen ILC2 function in type-2 mediated diseases.

Selective reconstitution of IFN‑γ gene function in Ncr1+ NK cells is sufficient to control systemic vaccinia virus infection

IFN-γ is an enigmatic cytokine that shows direct anti-viral effects, confers upregulation of MHC-II and other components relevant for antigen presentation, and that adjusts the composition and balance of complex cytokine responses. It is produced during immune responses by innate as well as adaptive immune cells and can critically affect the course and outcome of infectious diseases, autoimmunity, and cancer. To selectively analyze the function of innate immune cell-derived IFN-γ, we generated conditional IFN-γ^OFF mice, in which endogenous IFN-γ expression is disrupted by a loxP flanked gene trap cassette inserted into the first intron of the IFN-γ gene. IFN-γ^OFF mice were intercrossed with Ncr1-Cre or CD4-Cre mice that express Cre mainly in NK cells (IFN-γ^Ncr1-ON mice) or T cells (IFN-γ^CD4-ON mice), respectively. Rosa26RFP reporter mice intercrossed with Ncr1-Cre mice showed selective RFP expression in more than 80% of the NK cells, while upon intercrossing with CD4-Cre mice abundant RFP expression was detected in T cells, but also to a minor extent in other immune cell subsets. Previous studies showed that IFN-γ expression is needed to promote survival of vaccinia virus (VACV) infection. Interestingly, during VACV infection of wild type and IFN-γ^CD4-ON mice two waves of serum IFN-γ were induced that peaked on day 1 and day 3/4 after infection. Similarly, VACV infected IFN-γ^Ncr1-ON mice mounted two waves of IFN-γ responses, of which the first one was moderately and the second one profoundly reduced when compared with WT mice. Furthermore, IFN-γ^Ncr1-ON as well as IFN-γ^CD4-ON mice survived VACV infection, whereas IFN-γ^OFF mice did not. As expected, ex vivo analysis of splenocytes derived from VACV infected IFN-γ^Ncr1-ON mice showed IFN-γ expression in NK cells, but not T cells, whereas IFN-γ^OFF mice showed IFN-γ expression neither in NK cells nor T cells. VACV infected IFN-γ^Ncr1-ON mice mounted normal cytokine responses, restored neutrophil accumulation, and showed normal myeloid cell distribution in blood and spleen. Additionally, in these mice normal MHC-II expression was detected on peripheral macrophages, whereas IFN-γ^OFF mice did not show MHC-II expression on such cells. In conclusion, upon VACV infection Ncr1 positive cells including NK cells mount two waves of early IFN-γ responses that are sufficient to promote the induction of protective anti-viral immunity.

Viral infections induce interferon (IFN) responses that constitute a first line of defense. Type II IFN (IFN-γ) is required for protection against lethal vaccinia virus (VACV) infection. To address the cellular origin of protective IFN-γ responses during VACV infection, we generated IFN-γ^OFF mice, in which the endogenous IFN-γ gene function can be reconstituted in a Cre-dependent manner. IFN-γ^OFF mice were intercrossed with Ncr1-Cre mice that express Cre selectively in Ncr1⁺ innate cell subsests such as NK cells. Surprisingly, VACV infected IFN-γ^Ncr1-ON mice mounted two waves of IFN-γ responses. Reconstitution of innate IFN-γ was sufficient to restore cytokine responses that supported normal myeloid cell distribution and survival upon VACV infection. In conclusion, IFN-γ derived from Ncr1⁺ innate immune cells is sufficient to elicit fully effective immune responses upon VACV infection. Our new mouse model is suitable to further address the role of Ncr1⁺ cell-derived IFN-γ also in other models of infection, as well as of autoimmunity and cancer.

Distinct and shared gene expression for human innate versus adaptive helper lymphoid cells

Innate lymphoid cells (ILCs) are the latest identified innate immune cell family. Given their similarity in transcription factor expression and cytokine secretion profiles, ILCs have been considered as the innate phenocopy of CD4 Th cells. Here, we explored the transcriptome of circulating human ILC subsets as opposed to CD4 Th cell subsets. We describe transcriptomic differences between total ILCs and total CD4 Th cells, as well as between paired innate and adaptive cell subsets (ILC1 vs. Th1; ILC2 vs. Th2; and ILC3 vs. Th17 cells). In particular, we observed differences in expression of genes involved in cell trafficking such as CCR1, CCR6 and CXCR3, innate activation and inhibitory functions, including CD119, 2B4, TIGIT, and CTLA‐4, and neuropeptide receptors, such as VIPR2. Moreover, we report for the first time on distinct expression of long noncoding RNAs (lncRNAs) in innate vs. adaptive cells, arguing for a potential role of lncRNA in shaping human ILC biology. Altogether, our results point for unique, rather than redundant gene organization in ILCs compared to CD4 Th cells, in regard to kinetics, fine‐tuning and spatial organization of the immune response.

Intravenous immunoglobulin therapy enhances suppressive regulatory T cells and decreases innate lymphoid cells in children with immune thrombocytopenia

BACKGROUND

This study aimed to investigate the relationship between CD4⁺ regulatory T cells (Tregs) and innate lymphoid cells (ILCs) in children with primary immune thrombocytopenia (ITP) undergoing high-dose intravenous immunoglobulin (IVIG) therapy.

METHODS

We enrolled a cohort of 30 children with newly diagnosed ITP and 30 healthy controls and collected blood samples for levels of Tregs, ILCs, relevant cytokines, and Treg suppression assay at the diagnosis, two days, four weeks, and one year (only platelet count) after high-dose IVIG treatment. IVIG partial responders was defined by a platelet count less than 100 × 10⁹ /L at 12 months after IVIG treatment.

RESULTS

Children with newly diagnosed ITP exhibited elevated levels of ILC1, ILC2, ILC3, Th17, myeloid dendritic cells (DCs), plasmacytoid DCs, and serum IFN-γ and IL-17A levels, accompanied by a decrease in IL-10-producing Tregs. High-dose IVIG therapy reversed these aberrations. Platelet counts positively correlated with Tregs (rho = 0.72) and negatively correlated with both ILC1 (rho = -0.49) and ILC3 (rho = -0.60) (P < 0.05). Significantly lower Tregs and higher ILC1, ILC3, DCs, and serum IL-17A levels were noted in the partial responders (n = 8) versus responders (n = 22; P < 0.05). We found that Tregs suppressed proliferation of ILCs and CD4⁺ T cells in CD25-depleted peripheral PBMCs and enhanced the apoptosis of CD4⁺ CD45RO⁺ T cells in vitro following IVIG therapy.

CONCLUSIONS

Effective high-dose IVIG therapy for children with newly diagnosed ITP appears to result in the induction of Tregs, which suppresses ILC proliferation in vitro and is associated with platelet response.

Hitting More Birds with a Stone: Impact of TGF-β on ILC Activity in Cancer

Transforming growth factor (TGF)-β is a central immunosuppressive cytokine within tumor microenvironment inhibiting the expansion and function of major cellular components of adaptive and innate immune system. Among them, compelling evidence has demonstrated that TGF-β is a key regulator of natural killer (NK) cells, innate lymphoid cells (ILCs) with a critical role in immunosurveillance against different kinds of cancer cells. A TGF-β rich tumor microenvironment blocks NK cell activity at multiple levels. This immunosuppressive factor exerts direct regulatory effects on NK cells including inhibition of cytokine production, alteration of activating/inhibitory receptor expression, and promotion of the conversion into non cytotoxic group I ILC (ILC1). Concomitantly, TGF-β can render tumor cells less susceptible to NK cell-mediated recognition and lysis. Indeed, accumulating evidence suggest that changes in levels of NKG2D ligands, mainly MICA, as well as an increase of immune checkpoint inhibitors (e.g., PD-L1) and other inhibitory ligands on cancer cells significantly contribute to TGF-β-mediated suppression of NK cell activity. Here, we will take into consideration two major mechanisms underlying the negative regulation of ILC function by TGF-β in cancer. First, we will address how TGF-β impacts the balance of signals governing NK cell activity. Second, we will review recent advances on the role of this cytokine in driving ILC plasticity in cancer. Finally, we will discuss how the development of therapeutic approaches blocking TGF-β may reverse the suppression of host immune surveillance and improve anti-tumor NK cell response in the clinic.

Imbalance of Circulating Innate Lymphoid Cell Subpopulations in Patients With Septic Shock

Background: Septic shock, a major cause of death in critical care, is the clinical translation of a cytokine storm in response to infection. It can be complicated by sepsis-induced immunosuppression, exemplified by blood lymphopenia, an excess of circulating Treg lymphocytes, and decreased HLA-DR expression on circulating monocytes. Such immunosuppression is associated with secondary infections, and higher mortality. The effect of these biological modifications on circulating innate lymphoid cells (ILCs) has been little studied.

Methods: We prospectively enrolled patients with septic shock (Sepsis-3 definition) in the intensive care unit (ICU) of Timone CHU Hospital. ICU controls (trauma, cardiac arrest, neurological dysfunction) were recruited at the same time (NCT03297203). We performed immunophenotyping of adaptive lymphocytes (CD3⁺ T cells, CD19⁺ B cells, CD4⁺CD25⁺FoxP3⁺ Treg lymphocytes), ILCs (CD3⁻CD56⁺ NK cells and helper ILCs – ILC1, ILC2, and ILC3), and monocytes by flow cytometry on fresh blood samples collected between 24 and 72 h after admission.

Results: We investigated adaptive and innate circulating lymphoid cells in the peripheral blood of 18 patients in septic shock, 15 ICU controls, and 30 healthy subjects. As expected, the peripheral blood lymphocytes of all ICU patients showed lymphopenia, which was not specific to sepsis, whereas those of the healthy volunteers did not. Circulating CD3⁺ T cells and CD3⁻CD56⁺ NK cells were mainly concerned. There was a tendency toward fewer Treg lymphocytes and lower HLA-DR expression on monocytes in ICU patients with sepsis. Although the ILC1 count was higher in septic patients than healthy subjects, ILC2, and ILC3 counts were lower in both ICU groups. However, ILC3s within the total ILCs were overrepresented in patients with septic shock. The depression of immune responses has been correlated with the occurrence of secondary infections. We did not find any differences in ILC distribution according to this criterion.

Conclusion: All ICU patients exhibit lymphopenia, regardless of the nature (septic or sterile) of the initial medical condition. Specific distribution of circulating ILCs, with an excess of ILC1, and a lack of ILC3, may characterize septic shock during the first 3 days of the disease.

From Discrete to Continuous Modeling of Lymphocyte Development and Plasticity in Chronic Diseases

The molecular events leading to differentiation, development, and plasticity of lymphoid cells have been subject of intense research due to their key roles in multiple pathologies, such as lymphoproliferative disorders, tumor growth maintenance and chronic diseases. The emergent roles of lymphoid cells and the use of high-throughput technologies have led to an extensive accumulation of experimental data allowing the reconstruction of gene regulatory networks (GRN) by integrating biochemical signals provided by the microenvironment with transcriptional modules of lineage-specific genes. Computational modeling of GRN has been useful for the identification of molecular switches involved in lymphoid specification, prediction of microenvironment-dependent cell plasticity, and analyses of signaling events occurring downstream the activation of antigen recognition receptors. Among most common modeling strategies to analyze the dynamical behavior of GRN, discrete dynamic models are widely used for their capacity to capture molecular interactions when a limited knowledge of kinetic parameters is present. However, they are less powerful when modeling complex systems sensitive to biochemical gradients. To compensate it, discrete models may be transformed into regulatory networks that includes state variables and parameters varying within a continuous range. This approach is based on a system of differential equations dynamics with regulatory interactions described by fuzzy logic propositions. Here, we discuss the applicability of this method on modeling of development and plasticity processes of adaptive lymphocytes, and its potential implications in the study of pathological landscapes associated to chronic diseases.

Characterization of Transcriptional Regulatory Networks that Promote and Restrict Identities and Functions of Intestinal Innate Lymphoid Cells

Innate lymphoid cells (ILCs) promote tissue homeostasis and immune defense but also contribute to inflammatory diseases. ILCs exhibit phenotypic and functional plasticity in response to environmental stimuli, yet the transcriptional regulatory networks (TRNs) that control ILC function are largely unknown. Here, we integrate gene expression and chromatin accessibility data to infer regulatory interactions between transcription factors (TFs) and genes within intestinal type 1, 2, and 3 ILC subsets. We predicted the "core" TFs driving ILC identities, organized TFs into cooperative modules controlling distinct gene programs, and validated roles for c-MAF and BCL6 as regulators affecting type 1 and type 3 ILC lineages. The ILC network revealed alternative-lineage-gene repression, a mechanism that may contribute to reported plasticity between ILC subsets. By connecting TFs to genes, the TRNs suggest means to selectively regulate ILC effector functions, while our network approach is broadly applicable to identifying regulators in other in vivo cell populations.

Deconstructing deployment of the innate immune lymphocyte army for barrier homeostasis and protection

The study of the immune system has shifted from a purely dichotomous separation between the innate and adaptive arms to one that is now highly complex and reshaping our ideas of how steady‐state health is assured. It is now clear that immune cells do not neatly fit into these two streams and immune homeostasis depends on continual dialogue between multiple lineages of the innate (including dendritic cells, innate lymphoid cells, and unconventional lymphocytes) and adaptive (T and B lymphocytes) arms together with a finely tuned synergy between the host and microbes which is essential to ensure immune homeostasis. Innate lymphoid cells are critical players in this new landscape. Here, we discuss recent studies that have elucidated in detail the development of ILCs from their earliest progenitors and examine factors that influence their identification and ability to drive immune homeostasis and long‐term immune protection.

JAK/STAT signaling in regulation of innate lymphoid cells: The gods before the guardians

Immunity to pathogens is ensured through integration of early responses mediated by innate cells and late effector functions taking place after terminal differentiation of adaptive lymphocytes. In this context, innate lymphoid cells (ILCs) and adaptive T cells represent a clear example of how prototypical effector functions, including polarized expression of cytokines and/or cytotoxic activity, can occur with overlapping modalities but different timing. The ability of ILCs to provide early protection relies on their poised epigenetic state, which determines their propensity to quickly respond to cytokines and to activate specific patterns of signal-dependent transcription factors. Cytokines activating the Janus kinases (JAKs) and members of the signal transducer and activator of transcription (STAT) pathway are key regulators of lymphoid development and sustain the processes underlying T-cell activation and differentiation. The role of the JAK/STAT pathway has been recently extended to several aspects of ILC biology. Here, we discuss how JAK/STAT signals affect ILC development and effector functions in the context of immune responses, highlighting the molecular mechanisms involved in regulation of gene expression as well as the potential of targeting the JAK/STAT pathway in inflammatory pathologies.

An Essential Role of Innate Lymphoid Cells in the Pathophysiology of Graft-vs.-Host Disease

Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is the only curative treatment for multiple hematologic malignancies and non-malignant hematological diseases. However, graft-vs.-host disease (GVHD), one of the main complications after allo-HSCT, remains the major reason for morbidity and non-relapse mortality. Emerging evidence has demonstrated that innate lymphoid cells (ILCs) play a non-redundant role in the pathophysiology of GVHD. In this review, we will summarize previously published data regarding the role of ILCs in the pathogenesis of GVHD.

Hide and seek: Plasticity of innate lymphoid cells in cancer

The advance of immunotherapies has revolutionized the treatment of cancer patients. Mostly agents modulating the adaptive immune system are currently used. More recently, attempts to stimulate the innate immune system are being promoted for clinical evaluation. Innate lymphoid cells (ILCs) are a highly plastic population of immune cells crucial for tissue homeostasis and the regulation of immune responses and maybe a promising target to improve current cancer immunotherapies. Although we have made significant progress in understanding ILC biology, their impact on tumor development, progression and therapy is controversial. In this review, we discuss the recent advances of ILC function and plasticity in the context of cancer.

Innate Lymphoid Cells in Protection, Pathology, and Adaptive Immunity During Apicomplexan Infection

Apicomplexans are a diverse and complex group of protozoan pathogens including Toxoplasma gondii, Plasmodium spp., Cryptosporidium spp., Eimeria spp., and Babesia spp. They infect a wide variety of hosts and are a major health threat to humans and other animals. Innate immunity provides early control and also regulates the development of adaptive immune responses important for controlling these pathogens. Innate immune responses also contribute to immunopathology associated with these infections. Natural killer (NK) cells have been for a long time known to be potent first line effector cells in helping control protozoan infection. They provide control by producing IL-12 dependent IFNγ and killing infected cells and parasites via their cytotoxic response. Results from more recent studies indicate that NK cells could provide additional effector functions such as IL-10 and IL-17 and might have diverse roles in immunity to these pathogens. These early studies based their conclusions on the identification of NK cells to be CD3–, CD49b+, NK1.1+, and/or NKp46+ and the common accepted paradigm at that time that NK cells were one of the only lymphoid derived innate immune cells present. New discoveries have lead to major advances in understanding that NK cells are only one of several populations of innate immune cells of lymphoid origin. Common lymphoid progenitor derived innate immune cells are now known as innate lymphoid cells (ILC) and comprise three different groups, group 1, group 2, and group 3 ILC. They are a functionally heterogeneous and plastic cell population and are important effector cells in disease and tissue homeostasis. Very little is known about each of these different types of ILCs in parasitic infection. Therefore, we will review what is known about NK cells in innate immune responses during different protozoan infections. We will discuss what immune responses attributed to NK cells might be reconsidered as ILC1, 2, or 3 population responses. We will then discuss how different ILCs may impact immunopathology and adaptive immune responses to these parasites.

Negative regulation of innate lymphoid cell responses in inflammation and cancer

The immune system employs an array of effector cells to ensure tissue homeostasis and protection against pathogens. Lymphocytes belonging to both the adaptive and innate branches share several functions, comprising the ability to directly kill stressed or transformed cells, and to provide helper responses through specific production of cytokines. These properties are regulated by distinct sets of soluble molecules, receptors, and intracellular factors, which altogether tune the functional output of effector lymphocytes and their final activation state. In contrast to adaptive T cells, innate lymphoid cells (ILCs) do not require antigen receptors and are characterized for their ability to provide rapid immune responses. While the factors underlying functional diversification and the main principles leading to ILC activation have been dissected, our understanding of the mechanisms underlying termination of ILC effector functions is still in its infancy. Herein, we discuss the recent findings describing how ILC responses are turned off in the context of inflammation and cancer.

Airway innate lymphoid cells in the induction and regulation of allergy

The recent discovery of innate lymphoid cells has revolutionized our understanding of the pathogenesis of immune diseases including allergy and asthma. Innate lymphoid cells (ILCs) are a heterogeneous collection of lymphocytes that lack antigen-specificity (non-T, non-B cells) and potently produce characteristic cytokines of T cell subsets (Th1, Th2, Th17). ILCs are divided into group 1 (ILC1s), group 2 (ILC2s), or group 3 (ILC3s). Similar to Th2 cells, ILC2s produce IL-4, IL-5, and IL-13, among others, and are present in increased numbers in samples from patients with many allergic disorders including asthma and chronic rhinosinusitis (CRS). Animal models have identified that ILC2s contribute to eosinophilic tissue infiltration, airway hyperresponsiveness, mucus production, as well as coordinate adaptive immune responses. Finally, recent studies support regulation of ILC2s by neuro-immune mechanisms as well as demonstrate a significant degree of plasticity between ILC subsets that may impact the immune responses in asthma and allergic airway diseases. Here, we review the current literature on ILC2s in human asthma and allergic airway diseases, as well as highlight some recent mechanistic insights into ILC2 function from in vitro studies and in vivo animal models.

Human Innate Lymphoid Cells: Their Functional and Cellular Interactions in Decidua

Innate lymphoid cells (ILC) are developmentally related cell subsets that play a major role in innate defenses against pathogens, in lymphoid organogenesis and in tissue remodeling. The best characterized ILC are natural killer (NK) cells. They are detectable in decidua in the early phases of pregnancy. During the first trimester, NK cells represent up to 50% of decidua lymphocytes. Differently from peripheral blood (PB) NK cells, decidual NK (dNK) cells are poorly cytolytic, and, instead of IFNγ, they release cytokines/chemokines that induce neo-angiogenesis, tissue remodeling, and placentation. dNK interact with resident myeloid cells and participate in the induction of regulatory T cells that play a pivotal role in maintaining an efficient fetal-maternal tolerance. dNK cells may originate from CD34⁺ precursor cells present in situ and/or from immature NK cells already present in endometrial tissue and/or from PB NK cells migrated to decidua. In addition to NK cells, also ILC3 are present in human decidua during the first trimester. Decidual ILC3 include both natural cytotoxic receptor (NCR)⁺ and NCR^- cells, producing respectively IL-8/IL-22/GM-CSF and TNF/IL-17. NCR⁺ILC3 have been shown to establish physical and functional interactions with neutrophils that, in turn, produce factors that are crucial for pregnancy induction/maintenance and for promoting the early inflammatory phase, a fundamental process for a successful pregnancy. While NCR⁺ILC3 display a stable phenotype, most of NCR^-ILC3 may acquire phenotypic and functional features of NCR⁺ILC3. In conclusion, both NK cells and ILC3 are present in human decidua and may establish functional interactions with immune and myeloid cells playing an important role both in innate defenses and in tissue building/remodeling/placentation during the early pregnancy. It is conceivable that altered numbers or function of these cells may play a role in pregnancy failure.

Diversification of human NK cells: Lessons from deep profiling

NK cells are innate lymphocytes with important roles in immunoregulation, immunosurveillance, and cytokine production. Originally defined on the functional basis of their "natural" ability to lyse tumor targets and thought to be a relatively homogeneous group of lymphocytes, NK cells possess a remarkable degree of phenotypic and functional diversity due to the combinatorial expression of an array of activating and inhibitory receptors. Diversification of NK cells is multifaceted: mechanisms of NK cell education that promote self-tolerance result in a heterogeneous repertoire that further diversifies upon encounters with viral pathogens. Here, we review the genetic, developmental, and environmental sources of NK cell diversity with a particular focus on deep profiling and single-cell technologies that will enable a more thorough and accurate dissection of this intricate and poorly understood lymphocyte lineage.

Group 2 innate lymphocytes at the interface between innate and adaptive immunity

Group 2 innate lymphoid cells (ILC2) are innate immune cells that respond rapidly to their environment through soluble inflammatory mediators and cell-to-cell interactions. As tissue-resident sentinels, ILC2 help orchestrate localized type 2 immune responses. These ILC2-driven type 2 responses are now recognized in diverse immune processes, different anatomical locations, and homeostatic or pathological settings. ILC2-derived cytokines and cell surface signaling molecules function as key regulators of innate and adaptive immunity. Conversely, ILC2 are governed by their environment. As such, ILC2 form an important nexus of the immune system and may present an attractive target for immune modulation in disease.

Chemokine regulation of innate lymphoid cell tissue distribution and function

Three groups of innate lymphoid cells (ILCs) can be defined based on transcription factor requirements, cytokine production profiles, and roles in immunity. Given their strategic anatomical location into barrier tissues and the ability to rapidly produce cytokines and to cross-talk with other immune and non-immune cells, ILCs play fundamental functions in tissue homeostasis and regulation of immune responses. Several members of the chemokine family influence ILC tissue localization in the correct microenvironment by regulating their release from the bone marrow as well as their homing and retention in the tissues. In this review, we discuss the recent advances on how chemokine regulation of ILC tissue-positioning and functional interaction with other cells play essential roles in tissue-specific regulation of innate and adaptive immune responses.

Lineage specification in innate lymphocytes

Innate lymphoid cells (ILCs) are immune cells that lack specific antigen receptors but possess similar effector functions as T cells. Concordantly, ILCs express many transcription factors known to be important for T cell effector function. ILCs develop from lymphoid progenitors in fetal liver and adult bone marrow. However, the identification of ILC progenitor (ILCP) and other precursors in peripheral tissues raises the question of whether ILC development might occur at extramedullary sites. We discuss central and local generation in maintaining ILC abundance at peripheral sites.

The Broad Spectrum of Human Natural Killer Cell Diversity

Natural killer (NK) cells provide protection against infectious pathogens and cancer. For decades it has been appreciated that two major NK cell subsets (CD56^bright and CD56^dim) exist in humans and have distinct anatomical localization patterns, phenotypes, and functions in immunity. In light of this traditional NK cell dichotomy, it is now clear that the spectrum of human NK cell diversity is much broader than originally appreciated as a result of variegated surface receptor, intracellular signaling molecule, and transcription factor expression; tissue-specific imprinting; and foreign antigen exposure. The recent discoveries of tissue-resident NK cell developmental intermediates, non-NK innate lymphoid cells, and the capacity for NK cells to adapt and differentiate into long-lived memory cells has added further complexity to this field. Here we review our current understanding of the breadth and generation of human NK cell diversity.

Evolution of Alternative Adaptive Immune Systems in Vertebrates

Adaptive immunity in jawless fishes is based on antigen recognition by three types of variable lymphocyte receptors (VLRs) composed of variable leucine-rich repeats, which are differentially expressed by two T-like lymphocyte lineages and one B-like lymphocyte lineage. The T-like cells express either VLRAs or VLRCs of yet undefined antigen specificity, whereas the VLRB antibodies secreted by B-like cells bind proteinaceous and carbohydrate antigens. The incomplete VLR germline genes are assembled into functional units by a gene conversion-like mechanism that employs flanking variable leucine-rich repeat sequences as templates in association with lineage-specific expression of cytidine deaminases. B-like cells develop in the hematopoietic typhlosole and kidneys, whereas T-like cells develop in the thymoid, a thymus-equivalent region at the gill fold tips. Thus, the dichotomy between T-like and B-like cells and the presence of dedicated lymphopoietic tissues emerge as ancestral vertebrate features, whereas the somatic diversification of structurally distinct antigen receptor genes evolved independently in jawless and jawed vertebrates.