Distinct Roles for CXCR6(+) and CXCR6(-) CD4(+) T Cells in the Pathogenesis of Chronic Colitis

The role of the CXCR6/CXCL16 axis in the pathogenesis of fibrotic disease

CXC chemokine receptor 6 (CXCR6), a seven-transmembrane domain G-protein-coupled receptor, plays a pivotal regulatory role in inflammation and tissue damage through its interaction with CXC chemokine ligand 16 (CXCL16). This axis is implicated in the pathogenesis of various fibrotic diseases and correlates with clinical parameters that indicate disease severity, activity, and prognosis in organ fibrosis, including afflictions of the liver, kidney, lung, cardiovascular system, skin, and intestines. Soluble CXCL16 (sCXCL16) serves as a chemokine, facilitating the migration and recruitment of CXCR6-expressing cells, while membrane-bound CXCL16 (mCXCL16) functions as a transmembrane protein with adhesion properties, facilitating intercellular interactions by binding to CXCR6. The CXCR6/CXCL16 axis is established to regulate the cycle of damage and repair during chronic inflammation, either through modulating immune cell-mediated intercellular communication or by independently influencing fibroblast homing, proliferation, and activation, with each pathway potentially culminating in the onset and progression of fibrotic diseases. However, clinically exploiting the targeting of the CXCR6/CXCL16 axis requires further elucidation of the intricate chemokine interactions within fibrosis pathogenesis. This review explores the biology of CXCR6/CXCL16, its multifaceted effects contributing to fibrosis in various organs, and the prospective clinical implications of these insights.

The CXCL16-CXCR6 axis in glioblastoma modulates T-cell activity in a spatiotemporal context

Introduction

Glioblastoma multiforme (GBM) pathobiology is characterized by its significant induction of immunosuppression within the tumor microenvironment, predominantly mediated by immunosuppressive tumor-associated myeloid cells (TAMCs). Myeloid cells play a pivotal role in shaping the GBM microenvironment and influencing immune responses, with direct interactions with effector immune cells critically impacting these processes.

Methods

Our study investigates the role of the CXCR6/CXCL16 axis in T-cell myeloid interactions within GBM tissues. We examined the surface expression of CXCL16, revealing its limitation to TAMCs, while microglia release CXCL16 as a cytokine. The study explores how these distinct expression patterns affect T-cell engagement, focusing on the consequences for T-cell function within the tumor environment. Additionally, we assessed the significance of CXCR6 expression in T-cell activation and the initial migration to tumor tissues.

Results

Our data demonstrates that CXCL16 surface expression on TAMCs results in predominant T-cell engagement with these cells, leading to impaired T-cell function within the tumor environment. Conversely, our findings highlight the essential role of CXCR6 expression in facilitating T-cell activation and initial migration to tumor tissues. The CXCL16-CXCR6 axis exhibits dualistic characteristics, facilitating the early stages of the T-cell immune response and promoting T-cell infiltration into tumors. However, once inside the tumor, this axis contributes to immunosuppression.

Discussion

The dual nature of the CXCL16-CXCR6 axis underscores its potential as a therapeutic target in GBM. However, our results emphasize the importance of carefully considering the timing and context of intervention. While targeting this axis holds promise in combating GBM, the complex interplay between TAMCs, microglia, and T cells suggests that intervention strategies need to be tailored to optimize the balance between promoting antitumor immunity and preventing immunosuppression within the dynamic tumor microenvironment.

Role of the CXCR6/CXCL16 axis in autoimmune diseases

The C-X-C motif ligand 16, or CXCL16, is a chemokine that belongs to the ELR - CXC subfamily. Its function is to bind to the chemokine receptor CXCR6, which is a G protein-coupled receptor with 7 transmembrane domains. The CXCR6/CXCL16 axis has been linked to the development of numerous autoimmune diseases and is connected to clinical parameters that reflect disease severity, activity, and prognosis in conditions such as multiple sclerosis, autoimmune hepatitis, rheumatoid arthritis, Crohn's disease, and psoriasis. CXCL16 is expressed in various immune cells, such as dendritic cells, monocytes, macrophages, and B cells. During autoimmune diseases, CXCL16 can facilitate the adhesion of immune cells like monocytes, T cells, NKT cells, and others to endothelial cells and dendritic cells. Additionally, sCXCL16 can regulate the migration of CXCR6-expressing leukocytes, which includes CD8⁺ T cells, CD4⁺ T cells, NK cells, constant natural killer T cells, plasma cells, and monocytes. Further investigation is required to comprehend the intricate interactions between chemokines and the pathogenesis of autoimmune diseases. It remains to be seen whether the CXCR6/CXCL16 axis represents a new target for the treatment of these conditions.

CXCR6 expressing T cells: Functions and role in the control of tumors

CXCR6 is a receptor for the chemokine CXCL16, which exists as a membrane or soluble form. CXCR6 is a marker for resident memory T (TRM) cells that plays a role in immunosurveillance through their interaction with epithelial cells. The interaction of CXCR6 with CXCL16 expressed at the membrane of certain subpopulations of intratumor dendritic cells (DC) called DC3, ideally positions these CXCR6+ T cells to receive a proliferation signal from IL-15 also presented by DC3. Mice deficient in cxcr6 or blocking the interaction of CXCR6 with its ligand, experience a poorer control of tumor proliferation by CD8+ T cells, but also by NKT cells especially in the liver. Intranasal vaccination induces CXCL16 production in the lungs and is associated with infiltration by TRM expressing CXCR6, which are then required for the efficacy of anti-tumor vaccination. Therapeutically, the addition of CXCR6 to specific CAR-T cells enhances their intratumoral accumulation and prolongs survival in animal models of pancreatic, ovarian and lung cancer. Finally, CXCR6 is part of immunological signatures that predict response to immunotherapy based on anti-PD-(L)1 in various cancers. In contrast, a protumoral role of CXCR6+T cells has also been reported mainly in Non-alcoholic steatohepatitis (NASH) due to a non-antigen specific mechanism. The targeting and amplification of antigen-specific TRM expressing CXCR6 and its potential use as a biomarker of response to immunotherapy opens new perspectives in cancer treatment.

GPR65 promotes intestinal mucosal Th1 and Th17 cell differentiation and gut inflammation through downregulating NUAK2

G protein-coupled receptor 65 (GPR65), a susceptibility gene for inflammatory bowel diseases (IBD), has been identified to promote Th17 cell pathogenicity and induce T cell apoptosis. However, the potential role of GPR65 in modulating CD4+ T cell immune responses in the pathogenesis of IBD stills not entirely understood. Here, we displayed that GPR65 expression was increased in inflamed intestinal mucosa of IBD patients and positively associated with disease activity. It was expressed in CD4+ T cells and robustly upregulated through the TNF-α-caspase 3/8 signalling pathway. Ectopic expression of GPR65 significantly promoted the differentiation of peripheral blood (PB) CD4+ T cells from IBD patients and HC to Th1 and Th17 cells in vitro. Importantly, conditional knockout of Gpr65 in CD4+ T cells ameliorated trinitrobenzene sulfonic acid (TNBS)-induced acute murine colitis and a chronic colitis in Rag1-/- mice reconstituted with CD45RBhigh CD4+ T cells in vivo, characterised by attenuated Th1 and Th17 cell immune response in colon mucosa and decreased infiltration of CD4+ T cells, neutrophils and macrophages. RNA-seq analysis of Gpr65ΔCD4 and Gpr65flx/flx CD4+ T cells revealed that NUAK family kinase 2 (Nuak2) acts as a functional target of Gpr65 to restrict Th1 and Th17 cell immune response. Mechanistically, GPR65 deficiency promoted NUAK2 expression via the cAMP-PKA-C-Raf-ERK1/2-LKB1-mediated signalling pathway. Consistently, silencing of Nuak2 facilitated the differentiation of Gpr65ΔCD4 and Gpr65flx/flx CD4+ T cells into Th1 and Th17 cells. Therefore, our data point out that GPR65 promotes Th1 and Th17 cell immune response and intestinal mucosal inflammation by suppressing NUAK2 expression, and that targeting GPR65 and NUAK2 in CD4+ T cells may represent a novel therapeutic approach for IBD.

Pathogenic Tconvs promote inflammatory macrophage polarization through GM‐CSF and exacerbate abdominal aortic aneurysm formation

Abdominal aortic aneurysms (AAAs) elicit massive inflammatory leukocyte recruitment to the aorta. CD4⁺ T cells, which include regulatory T cells (Tregs) and conventional T cells (Tconvs), are involved in the progression of AAA. Tregs have been reported to limit AAA formation. However, the function and phenotype of the Tconvs found in AAAs remain poorly understood. We characterized aortic Tconvs by bulk RNA sequencing and discovered that Tconvs in aortic aneurysm highly expressed Cxcr6 and Csf2. Herein, we determined that the CXCR6/CXCL16 signaling axis controlled the recruitment of Tconvs to aortic aneurysms. Deficiency of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), encoded by Csf2, markedly inhibited AAA formation and led to a decrease of inflammatory monocytes, due to a reduction of CCL2 expression. Conversely, the exogenous administration of GM‐CSF exacerbated inflammatory monocyte infiltration by upregulating CCL2 expression, resulting in worsened AAA formation. Mechanistically, GM‐CSF upregulated the expression of interferon regulatory factor 5 to promote M1‐like macrophage differentiation in aortic aneurysms. Importantly, we also demonstrated that the GM‐CSF produced by Tconvs enhanced the polarization of M1‐like macrophages and exacerbated AAA formation. Our findings revealed that GM‐CSF, which was predominantly derived from Tconvs in aortic aneurysms, played a pathogenic role in the progression of AAAs and may represent a potential target for AAA treatment.

Mapping Rora expression in resting and activated CD4+ T cells

The transcription factor Rora has been shown to be important for the development of ILC2 and the regulation of ILC3, macrophages and Treg cells. Here we investigate the role of Rora across CD4+ T cells in general, but with an emphasis on Th2 cells, both in vitro as well as in the context of several in vivo type 2 infection models. We dissect the function of Rora using overexpression and a CD4-conditional Rora-knockout mouse, as well as a RORA-reporter mouse. We establish the importance of Rora in CD4+ T cells for controlling lung inflammation induced by Nippostrongylus brasiliensis infection, and have measured the effect on downstream genes using RNA-seq. Using a systematic stimulation screen of CD4+ T cells, coupled with RNA-seq, we identify upstream regulators of Rora, most importantly IL-33 and CCL7. Our data suggest that Rora is a negative regulator of the immune system, possibly through several downstream pathways, and is under control of the local microenvironment.

Removal of CD276+ cells from haploidentical memory T-cell grafts significantly lowers the risk of GVHD

Detrimental graft-versus-host disease (GVHD) still remains a major cause of death in hematopoietic stem cell transplantation (HSCT). The recently explored depletion of naive cells from mobilized grafts (CD45RA depletion) has shown considerable promise, yet is unable to eliminate the incidence of GVHD. Analysis of CD45RA-depleted haploidentical mixed lymphocytes culture (haplo-MLC) revealed insufficient suppression of alloresponses in the CD4⁺ compartment and identified CD276 as a marker for alloreactive memory Th1 T cells. Conclusively, depleting CD276⁺ cells from CD45RA-depleted haplo-MLC significantly attenuated alloreactivity to recipient cells while increasing antiviral reactivity and maintaining anti-third party reactivity in vitro. To evaluate these findings in vivo, bulk, CD45RA-depleted, or CD45RA/CD276-depleted CD4⁺ T cells from HLA-DR4^negative healthy humans were transplanted into NSG-Ab°DR4 mice, a sensitive human allo-GVHD model. Compellingly, CD45RA/CD276-depleted grafts from HLA-DR4^negative donors or in vivo depletion of CD276⁺ cells after transplant of HLA-DR4^negative memory CD4 T cells significantly delay the onset of GVHD symptoms and significantly alleviate its severity in NSG-Ab°DR4 mice. The clinical courses correlated with diminished Th1-cytokine secretion and downregulated CXCR6 expression of engrafted peripheral T cells. Collectively, mismatched HLA-mediated GVHD can be controlled by depleting recipient-specific CD276⁺ alloreacting T cells from the graft, highlighting its application in haplo-HSCT.

The Role of CXCL16 in the Pathogenesis of Cancer and Other Diseases

CXCL16 is a chemotactic cytokine belonging to the α-chemokine subfamily. It plays a significant role in the progression of cancer, as well as the course of atherosclerosis, renal fibrosis, and non-alcoholic fatty liver disease (NAFLD). Since there has been no review paper discussing the importance of this chemokine in various diseases, we have collected all available knowledge about CXCL16 in this review. In the first part of the paper, we discuss background information about CXCL16 and its receptor, CXCR6. Next, we focus on the importance of CXCL16 in a variety of diseases, with an emphasis on cancer. We discuss the role of CXCL16 in tumor cell proliferation, migration, invasion, and metastasis. Next, we describe the role of CXCL16 in the tumor microenvironment, including involvement in angiogenesis, and its significance in tumor-associated cells (cancer associated fibroblasts (CAF), microglia, tumor-associated macrophages (TAM), tumor-associated neutrophils (TAN), mesenchymal stem cells (MSC), myeloid suppressor cells (MDSC), and regulatory T cells (T_reg)). Finally, we focus on the antitumor properties of CXCL16, which are mainly caused by natural killer T (NKT) cells. At the end of the article, we summarize the importance of CXCL16 in cancer therapy.

Expression of CXC Chemokine Receptors in Acute Ulcerative Colitis: Initial Study from an Animal Model

Background:

Ulcerative colitis (UC) is an inflammatory disease which is characterized by infiltration of inflammatory cells, crypt abscesses, distortion of the mucosal glands, and goblet cell depletion. The existence of neutrophil-rich inflammation in colon tissues of patients with UC is one of the most significant histological features of this disease. Nonetheless, the expression of CXCR chemokine receptors which appear as the main chemical mediators governing the migration of neutrophils into the mucosal tissue of patients with UC has not been well clarified.

Materials and Methods:

In this experimental study, the UC model was induced in Wistar rats by administration of 2 ml 4% acetic acid into the large colon through the rectum. Animals were anesthetized after 48 h; their colon tissue samples were isolated for macroscopic and histopathological examination. The expression of receptor_1-7 of CXC chemokine was assessed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) technique.

Results:

Heavy infiltration of neutrophils, coagulative necrosis, and ulcers were observed in H and E staining, which pathologically proved the UC model. qRT-PCR results indicated that CXCR2 as one of the important ELR⁺ chemokine family receptors bears the highest expression in the UC group (32 fold) than the control group (P ≤ 0.05). In addition, other CXCRs of this group including CXCR1 did not possess any change (P > 0.05). In contrast, RLR negative chemokine family receptors did not show any changes with the normal group.

Conclusion:

The results showed that CXCR2 is the only receptor for CXCL family which was remarkably upregulated in experimental UC and that CXCR2 might play a significant role in the pathogenesis of UC.

SerpinB1 controls encephalitogenic T helper cells in neuroinflammation

SerpinB1, a protease inhibitor and neutrophil survival factor, was recently linked with IL-17-expressing T cells. Here, we show that serpinB1 (Sb1) is dramatically induced in a subset of effector CD4 cells in experimental autoimmune encephalomyelitis (EAE). Despite normal T cell priming, Sb1 ^-/- mice are resistant to EAE with a paucity of T helper (T_H) cells that produce two or more of the cytokines, IFNγ, GM-CSF, and IL-17. These multiple cytokine-producing CD4 cells proliferate extremely rapidly; highly express the cytolytic granule proteins perforin-A, granzyme C (GzmC), and GzmA and surface receptors IL-23R, IL-7Rα, and IL-1R1; and can be identified by the surface marker CXCR6. In Sb1 ^-/- mice, CXCR6⁺ T_H cells are generated but fail to expand due to enhanced granule protease-mediated mitochondrial damage leading to suicidal cell death. Finally, anti-CXCR6 antibody treatment, like Sb1 deletion, dramatically reverts EAE, strongly indicating that the CXCR6⁺ T cells are the drivers of encephalitis.

SIV Coreceptor Specificity in Natural and Non-Natural Host Infection: Implications for Cell Targeting and Differential Outcomes from Infection

Pathogenic HIV-1 infection of humans and SIVmac infection of macaques are the result of zoonotic transfer of primate immunodeficiency viruses from their natural hosts into non-natural host species. Natural host infections do not result in pathogenesis despite high levels of virus replication, and evidence suggests that differences in anatomical location and specific subsets of CD4+ T cells infected may underlie distinct outcomes from infection. The coreceptor CCR5 has long been considered the sole pathway for SIV entry and the key determinant of CD4+ cell targeting, but it has also been known that natural hosts express exceedingly low levels of CCR5 despite maintaining high levels of virus replication. This review details emerging data indicating that in multiple natural host species, CCR5 is dispensable for SIV infection ex vivo and/or in vivo and, contrary to the established dogma, alternative coreceptors, particularly CXCR6, play a central role in infection and cell targeting. Infections of non-natural hosts, however, are characterized by CCR5-exclusive entry. These findings suggest that alternative coreceptor-mediated cell targeting in natural hosts, combined with low CCR5 expression, may direct the virus to distinct populations of cells that are dispensable for immune homeostasis, particularly extralymphoid and more differentiated CD4+ T cells. In contrast, CCR5-mediated entry in non-natural hosts results in targeting of CD4+ T cells that are located in lymphoid tissues, critical for immune homeostasis, or necessary for gut barrier integrity. Thus, fundamental differences in viral entry coreceptor use may be central determinants of infection outcome. These findings redefine the normal SIV/host relationship in natural host species, shed new light on key features linked to zoonotic immunodeficiency virus transfer, and highlight important questions regarding how and why this coreceptor bottleneck occurs and the coevolutionary equilibrium is lost following cross-species transfer that results in AIDS.

CD11c+ Cells Are Gatekeepers for Lymphocyte Trafficking to Infiltrated Islets During Type 1 Diabetes

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease that affects more than 19 million people with incidence increasing rapidly worldwide. For T cells to effectively drive T1D, they must first traffic to the islets and extravasate through the islet vasculature. Understanding the cues that lead to T cell entry into inflamed islets is important because diagnosed T1D patients already have established immune infiltration of their islets. Here we show that CD11c⁺ cells are a key mediator of T cell trafficking to infiltrated islets in non-obese diabetic (NOD) mice. Using intravital 2-photon islet imaging we show that T cell extravasation into the islets is an extended process, with T cells arresting in the islet vasculature in close proximity to perivascular CD11c⁺ cells. Antigen is not required for T cell trafficking to infiltrated islets, but T cell chemokine receptor signaling is necessary. Using RNAseq, we show that islet CD11c⁺ cells express over 20 different chemokines that bind chemokine receptors expressed on islet T cells. One highly expressed chemokine-receptor pair is CXCL16-CXCR6. However, NOD. CXCR6^-/- mice progressed normally to T1D and CXCR6 deficient T cells trafficked normally to the islets. Even with CXCR3 and CXCR6 dual deficiency, T cells trafficked to infiltrated islets. These data reinforce that chemokine receptor signaling is highly redundant for T cell trafficking to inflamed islets. Importantly, depletion of CD11c⁺ cells strongly inhibited T cell trafficking to infiltrated islets of NOD mice. We suggest that targeted depletion of CD11c⁺ cells associated with the islet vasculature may yield a therapeutic target to inhibit T cell trafficking to inflamed islets to prevent progression of T1D.

CXCR6-Mediated Simian Immunodeficiency Virus SIVagmSab Entry into Sabaeus African Green Monkey Lymphocytes Implicates Widespread Use of Non-CCR5 Pathways in Natural Host Infections

African green monkeys (AGM) and sooty mangabeys (SM) are well-studied natural hosts of simian immunodeficiency virus (SIV) that do not progress to AIDS when infected with their species-specific viruses. Natural hosts of SIV express very low levels of the canonical entry coreceptor CCR5, and recent studies have shown that CCR5 is dispensable for SIV infection of SM in vivo and that blocking of CCR5 does not prevent ex vivo infection of peripheral blood mononuclear cells (PBMC) from SM or vervet AGM. In both hosts, CXCR6 is an efficient entry pathway in vitro Here we investigated the use of species-matched CXCR6 and other alternative coreceptors by SIVagmSab, which infects sabaeus AGM. We cloned sabaeus CD4 and 10 candidate coreceptors. Species-matched CXCR6, CCR5, and GPR15 mediated robust entry into transfected cells by pseudotypes carrying SIVagmSab92018ivTF Env, with lower-level entry through GPR1 and APJ. We cloned genetically divergent env genes from the plasma of two wild-infected sabaeus AGM and found similar patterns of coreceptor use. Titration experiments showed that CXCR6 and CCR5 were more efficient than other coreceptors when tested at limiting CD4/coreceptor levels. Finally, blocking of CXCR6 with its ligand CXCL16 significantly inhibited SIVagmSab replication in sabaeus PBMC and had a greater impact than did the CCR5 blocker maraviroc, confirming the use of CXCR6 in primary lymphocyte infection. These data suggest a new paradigm for SIV infection of natural host species, whereby a shared outcome of virus-host coevolution is the use of CXCR6 or other alternative coreceptors for entry, which may direct SIV toward CD4⁺ T cell subsets and anatomical sites that support viral replication without disrupting immune homeostasis and function.

IMPORTANCE

Natural hosts of SIV do not progress to AIDS, in stark contrast to pathogenic human immunodeficiency virus type 1 (HIV-1)-human and SIVmac-macaque infections. Identifying how natural hosts avoid immunodeficiency can elucidate key mechanisms of pathogenesis. It is known that despite high viral loads, natural hosts have a low frequency of CD4⁺ cells expressing the SIV coreceptor CCR5. In this study, we demonstrate the efficient use of the coreceptor CXCR6 by SIVagmSab to infect sabaeus African green monkey lymphocytes. In conjunction with studies of SIVsmm, which infects sooty mangabeys, and SIVagmVer, which infects vervet monkeys, our data suggest a unifying model whereby in natural hosts, in which the CCR5 expression level is low, the use of CXCR6 or other coreceptors to mediate infection may target SIV toward distinct cell populations that are able to support high-level viral replication without causing a loss of CD4⁺ T cell homeostasis and lymphoid tissue damage that lead to AIDS in HIV-1 and SIVmac infections.

Cyclosporine A regulates pro-inflammatory cytokine production in ulcerative colitis

Crohn's disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel diseases (IBD), which are defined as relapsing inflammations of the gastrointestinal tract. Cyclosporine A (CsA) is a potential rescue treatment to avoid colectomy in severe steroid-refractory UC patients. The molecular mechanism of action of CsA in UC is nevertheless still not well understood. The aim of this study was to investigate the effect of CsA on a possible modulation of cytokine production by peripheral blood mononuclear cells (PBMCs) of controls and patients with UC or CD. Upon CsA treatment, analyses of cytokine levels revealed a significant reduction of IL-13 expression in PBMCs from patients with UC, whereas other cytokine expression levels remained unaffected. To address the question whether CsA treatment impinges on the induction of cell death, apoptosis assays were performed using CD4(+) T cells from peripheral blood of patients suffering from either UC or CD. It became clear that CsA treatment resulted in a specific induction of apoptosis in samples from controls and patients with UC but not with CD. Apoptosis induction was not mediated via the mitochondrial apoptosis pathway. The present data support the concept that CsA treatment modulates pro-inflammatory cytokine production and T cell survival in UC via the induction of apoptosis and might therefore help to explain the clinical efficacy of CsA in patients with UC.