Innate lymphoid cells: A potential link between microbiota and immune responses against cancer

The interplay between innate lymphoid cells and microbiota

Innate lymphoid cells (ILCs) are mainly resident in mucosal tissues such as gastrointestinal tract and respiratory tract, so they are closely linked to the microbiota. ILCs can protect commensals to maintain homeostasis and increase resistance to pathogens. Moreover, ILCs also play an early role in defense against a variety of pathogenic microorganisms including pathogenic bacteria, viruses, fungi and parasites, before the intervention of adaptive immune system. Due to the lack of adaptive antigen receptors expressed on T cells and B cells, ILCs need to use other means to sense the signals of microbiota and play a role in corresponding regulation. In this review, we focus on and summarize three major mechanisms used in the interaction between ILCs and microbiota: the mediation of accessory cells represented by dendritic cells; the metabolic pathways of microbiota or diet; the participation of adaptive immune cells.

Innate lymphoid cells: potential targets for cancer therapeutics

Innate lymphoid cells (ILCs) comprise a number of different subsets, including natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue-inducer (LTi) cells that express receptors and signaling pathways that are highly responsive to continuously changing microenvironmental cues. In this Review, we highlight the key features of innate cells that define their capacity to respond rapidly to different environments, how this ability can drive both tumor protection (limiting tumor development) or, alternatively, tumor progression, promoting tumor dissemination and resistance to immunotherapy. We discuss how understanding the regulation of ILCs that can detect tumor cells early in a response opens the possibility of exploiting this functional plasticity to develop rational therapeutic strategies to bolster adaptive immune responses and improve patient outcomes.

Metabolic features of innate lymphoid cells

Innate and adaptive immune cells are found in distinct tissue niches where they orchestrate immune responses. This requires intrinsic and temporal metabolic adaptability to coordinately activate the immune response cascade. Dysregulation of this program is a key feature of immunosuppression. Direct or indirect metabolic immune cell reprogramming may offer new approaches to modulate immune cells behavior for therapy to overcome dysregulation. In this review, we explored how metabolism regulates lymphocytes beyond the classical T cell subsets. We focus on the innate lymphoid cell (ILC) family, highlighting the distinct metabolic characteristics of these cells, the impact of environmental factors, and the receptors that could alter immune cell functions through manipulation of metabolic pathways to potentially prevent or treat various diseases.

The role of innate lymphoid cells in response to microbes at mucosal surfaces

Innate lymphoid cells (ILCs) are a lymphocyte population that is mostly resident at mucosal surfaces. They help to induce an appropriate immune response to the microbiome at homeostasis. In healthy people, the mucosal immune system works symbiotically with organisms that make up the microbiota. ILCs play a critical role in orchestrating this balance, as they can both influence and in turn be influenced by the microbiome. ILCs also are important regulators of the early response to infections by diverse types of pathogenic microbes at mucosal barriers. Their rapid responses initiate inflammatory programs, production of antimicrobial products and repair processes. This review will focus on the role of ILCs in response to the microbiota and to microbial infections of the lung and intestine.

Gut dysbiosis and multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) and T cell-mediated autoimmune processes are assumed to be involved in its pathogenesis. Recently, accumulating evidence has indicated that commensal bacteria interact with the host immune system and that the alteration of commensal bacteria composition, termed dysbiosis, is associated with various autoimmune diseases including CNS autoimmune diseases. In this review, we introduce recent findings regarding the association between gut microbiota and MS and related diseases and microbiota function in an animal model of MS.

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.

The interaction of intestinal microbiota and innate lymphoid cells in health and disease throughout life

Immunity is shaped by commensal microbiota. From early life onwards, microbes colonize mucosal surfaces of the body and thereby trigger the establishment of immune homeostasis and defense mechanisms. Recent evidence reveals that the family of innate lymphoid cells (ILCs), which are mainly located in mucosal tissues, are essential in the maintenance of barrier functions as well as in the initiation of an appropriate immune response upon pathogenic infection. In this review, we summarize recent insights on the functional interaction of microbiota and ILCs at steady‐state and throughout life. Furthermore, we will discuss the interplay of ILCs and the microbiota in mucosal infections focusing on intestinal immunity.

Progression or suppression: Two sides of the innate lymphoid cells in cancer

Innate lymphoid cells (ILCs) as key players in innate immunity have been shown to be significantly associated with inflammation, lymphoid neogenesis, tissue remodeling, mucosal immunity and lately have been considered a remarkable nominee for either tumor-promoting or tumor-inhibiting functions. This dual role of ILCs, which is driven by intrinsic and extrinsic factors like plasticity of ILCs and the tumor microenvironment, respectively, has aroused interest in ILCs subsets in past decade. So far, numerous studies in the cancer field have revealed ILCs to be key players in the initiation, progression and inhibition of tumors, therefore providing valuable insights into therapeutic approaches to utilize the immune system against cancer. Herein, the most recent achievements regarding ILCs subsets including new classifications, their transcription factors, markers, cytokine release and mechanisms that led to either progression or inhibition of many tumors have been evaluated. Additionally, the available data regarding ILCs in most prevalent cancers and new therapeutic approaches are summarized.

Functions of Group 2 Innate Lymphoid Cells in Tumor Microenvironment

Innate lymphoid cells (ILCs), defined as a heterogeneous population of lymphocytes, have received much attention over recent years. They can be categorized into three subsets according to the expression profiles of transcription factors and differing levels of cytokine production. These cells are widely distributed in human organs and tissues, especially in mucosal tissue. The ILCs are involved in various physiological and pathological processes, including inflammation, worm expulsion, autoimmune disease and tumor progression, many of which have been investigated and clarified in recent studies. In the tumor microenvironment, group 2 innate lymphoid cells (ILC2s) have been proved to be able to either promote or inhibit tumor progression by producing different cytokines, recruiting diverse types of immune cells, expressing immunosuppressive molecules and by regulating the expression of certain inflammatory factors. This review summarizes recent research progress on the immunomodulatory functions of ILC2s in the tumor microenvironment and puts forward some perspectives for future study.