CD8αβ+ γδ T Cells: A Novel T Cell Subset with a Potential Role in Inflammatory Bowel Disease

Innate Lymphoid Cells in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is a complex chronic inflammatory condition of the human gut of unknown causes. Traditionally, dysregulated adaptive immune responses are thought to play a major role; however, accumulating evidence suggests that innate immunity also contributes to this process. Innate lymphoid cells (ILCs) are recently identified important components of innate immunity. They have critical roles in immunity, tissue development and remodeling. Numerous researchers have linked ILCs to the pathogenesis of IBD. In this review, we describe recent progress in our understanding about the phenotype and function alterations of ILCs as well as its interactions with other key mucosal cells in the gut of IBD patients. A better delineation of the ILCs' behavior in the human intestine will contribute to our understanding of ILCs biology and provide valuable insights for potential therapeutic target selection for IBD patients.

Checkpoint Blockade Rescues the Repressive Effect of Histone Deacetylases Inhibitors on γδ T Cell Function

Histone deacetylases (HDAC) are one of the key epigenetic modifiers that control chromatin accessibility and gene expression. Their role in tumorigenesis is well established and HDAC inhibitors have emerged as an effective treatment modality. HDAC inhibitors have been investigated for their specific antitumor activities and also clinically evaluated in treatment of various malignancies. In the present study, we have investigated the effect of HDAC inhibitors on the effector functions of human γδ T cells. HDAC inhibitors inhibit the antigen-specific proliferative response of γδ T cells and cell cycle progression. In antigen-activated γδ T cells, the expression of transcription factors (Eomes and Tbet) and effector molecules (perforin and granzyme B) were decreased upon treatment with HDAC inhibitors. Treatment with HDAC inhibitors attenuated the antitumor cytotoxic potential of γδ T cells, which correlated with the enhanced expression of immune checkpoints programmed death-1 (PD-1) and programmed death ligand-1 in γδ T cells. Interestingly, PD-1 blockade improves the antitumor effector functions of HDAC inhibitor-treated γδ T cells, which is reflected in the increased expression of Granzyme B and Lamp-1. This study provides a rationale for designing HDAC inhibitor and immune check point blockade as a combinatorial treatment modality for cancer.

γδ T Cells: Crosstalk Between Microbiota, Chronic Inflammation, and Colorectal Cancer

Increasing evidence suggests that intestinal microbiota dysbiosis and chronic inflammation contribute to colorectal cancer (CRC) development. γδ T cells represent a major innate immune cell population in the intestinal epithelium that is involved in the maintenance of gut homeostasis, inflammation regulation, and carcinogenesis. The important contributions of γδ T cells are (i) to perform a protective role in the context of barrier damage and pathogenic microorganism translocation; (ii) to exert either pro- or anti-inflammatory effects at different inflammatory stages; and (iii) to boost the crosstalk between immune cells and tumor microenvironment, inducing a cascade of suppressive immune responses. Understanding the crucial role of γδ T cells would enable us to manipulate these cells during the CRC sequence and improve the efficacy of tumor therapy.

The role of the common gamma-chain family cytokines in γδ T cell-based anti-cancer immunotherapy

Cytokines of the common gamma-chain receptor family, comprising interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are vital with respect to organizing and sustaining healthy immune cell functions. Supporting the anti-cancer immune response, these cytokines inspire great interest for their use as vaccine adjuvants and cancer immunotherapies. It is against this background that gamma delta (γδ) T cells, as special-force soldiers and natural contributors of the tumor immunosurveillance, also received a lot of attention the last decade. As γδ T cell-based cancer trials are coming of age, this present review focusses on the effects of the different cytokines of the common gamma-chain receptor family on γδ T cells with respect to boosting γδ T cells as a therapeutic target in cancer immunotherapy. This review also gathers data that IL-15 in particular exhibits key features for augmenting the anti-tumor activity of effector killer γδ T cells whilst overcoming the myriad of immune escape mechanisms used by cancer cells.

Intestinal Barrier Interactions with Specialized CD8 T Cells

The trillions of microorganisms that reside in the gastrointestinal tract, essential for nutrient absorption, are kept under control by a single cell barrier and large amounts of immune cells. Intestinal epithelial cells (IECs) are critical in establishing an environment supporting microbial colonization and immunological tolerance. A large population of CD8⁺ T cells is in direct and constant contact with the IECs and the intraepithelial lymphocytes (IELs). Due to their location, at the interphase of the intestinal lumen and external environment and the host tissues, they seem ideally positioned to balance immune tolerance and protection to preserve the fragile intestinal barrier from invasion as well as immunopathology. IELs are a heterogeneous population, with a large innate-like contribution of unknown specificity, intercalated with antigen-specific tissue-resident memory T cells. In this review, we provide a comprehensive overview of IEL physiology and how they interact with the IECs and contribute to immune surveillance to preserve intestinal homeostasis and host-microbial relationships.

Gammadelta T Cells in Crohn's Disease: A New Player in the Disease Pathogenesis?

Crohn's disease [CD] is a chronic relapsing systemic disease affecting the gastrointestinal tract. An altered immune response to commensal intestinal bacteria takes place in genetically predisposed individuals, resulting in chronic inflammation in the gut. Several alterations in the innate immunity mechanisms have been described in recent years. Thus, the study of the immunological aspects of CD, specifically the role of lymphocytes, is a key element for understanding the pathogenesis of the disease.Gammadelta T cells [γδ T cells] constitute only a small proportion of the lymphocytes that circulate in the blood and peripheral organs and they are present mainly in the epithelia, where they can constitute up to 40% of intraepithelial lymphocytes [IEL] in the intestinal mucosa. Due to their lack of major histocompatibility complex [MHC] restriction and their unique plasticity and immune-regulating properties, they are considered key cells in the first line of defence against infections and in wound healing in the gut. Although there is growing experimental and clinical evidence of their implication in inflammatory bowel disease [IBD], including CD, their clinical relevance is still unclear.In this review, we address the possible involvement of γδ T cells in the pathogenesis of CD, reviewing their role against infections and in inflammation and the current evidence suggesting their implication in CD, offering a novel potential target for immunotherapy in IBD.

γδ T Cells and B Cells

γδ T cells constitute the third arm of a tripartite adaptive immune system in jawed vertebrates, besides αβ T cells and B cells. Like the other two lymphocyte-types, they express diverse antigen receptors, capable of specific ligand recognition. Functionally, γδ T cells represent a system of differentiated subsets, sometimes engaged in cross-regulation, which ultimately determines their effect on other components of the immune system, including B cells and antibodies. γδ T cells are capable of providing help to B cells in antibody production. More recently it became clear that γδ T cells influence B cell differentiation during the peripheral stages of B cell development, control levels of circulating immunoglobulin (all subclasses), and affect production of autoantibodies. Because of this relationship between γδ T cells and B cells, the extensive variation of γδ T cells among human individuals might be expected to modulate their humoral responsiveness.