Hepatic immune regulation by stromal cells

Liver metastases across cancer types sharing tumor environment immunotolerance can impede immune response therapy and immune monitoring

BACKGROUND

Hepatic immune tolerance might contribute to the development of therapeutic resistance to immunotherapy. However, addressing this issue is challenging since the efficacy of immunotherapy in the context of liver metastasis (LM) remains poorly studied. Here, we aimed to establish an LM common immune feature (LMCIF) score to quantify the characteristics of LM immunotolerance across cancer types for assisting clinical disease management.

METHODS

Large-scale clinical data were collected to identify the prognosis of LM. Multi-omics datasets of metastatic cancers with LM special immune-related pathways (LMSIPs) from the Molecular Signatures Database (MSigDB)were used to obtain an LMCIF cluster. Based on differential expression genes (DEGs), a novel LMCIF score for the LMCIF cluster was constructed. In addition, multi-omics, and immunohistochemistry (IHC) data from the public and in-house cohorts were used to explore the features of LM, and LMCIF score.

RESULTS

Patients with LM had a worse prognosis and significantly lower infiltration of immune cells than patients with metastasis to other organs when analyzed with combined clinical and RNA sequencing data. After extracting the LMCIF cluster from 373 samples by utilizing 29 LMSIPs and validating them in a microarray cohort, an LMCIF score was established to confirm the role of the immunosuppressive environment as a contributor to the poor prognosis of LM across cancer types. Moreover, this LMCIF score could be used to predict the immune response of cancer patients undergoing immunotherapy. Finally, we identified that the majority of the 31 LMCIF genes exhibited a negative correlation with TME cells in LM patients, one of them, KRT19, which possessed the strongest positive correlation with LMCIF score, was confirmed to have an immunosuppressive effect through IHC analysis.

CONCLUSIONS

Our results suggest that LM across cancer types share similar immunological profiles that induce immunotolerance and escape from immune monitoring. The novel LMCIF score represents a common liver metastasis immune cluster for predicting immunotherapy response, the results of which might benefit clinical disease management.

The double roles of T cell-mediated immune response in the progression of MASLD

Metabolic dysfunction-associated steatotic liver disease(MASLD), formerly known as non-alcoholic fatty liver disease(NAFLD), has become a major cause of chronic liver disease and a significant risk factor for hepatocellular carcinoma, which poses a huge burden on global public health and economy. MASLD includes steatotic liver disease, steatohepatitis, and cirrhosis, and the latter two cause great harm to human health and life, even complicated with liver cancer. Immunologic mechanism plays a major role in promoting its development into hepatitis and cirrhosis. Now more and more evidences show that T cells play an important role in the progression of MASLD. In this review, we discuss the double roles of T cells in MASLD from the perspective of T cell response pathways, as well as new evidences regarding the possible application of immunomodulatory therapy in MASH.

Consumption of Antioxidant-Rich “Cerrado” Cashew Pseudofruit Affects Hepatic Gene Expression in Obese C57BL/6J High Fat-Fed Mice

The pseudofruit of A. othonianum Rizzini, “Cerrado” cashew pulp, has been described as rich in flavonoids, phenolic compounds, and vitamin C. The objective of this work was to evaluate the beneficial health effects seen with the addition of “Cerrado” cashew pulp (CP) to an obesogenic high fat diet provided to C57BL/6J male mice. In week 9, the HF-fed group had a significantly higher baseline glucose concentration than the LF- or HF+CP-fed groups. In RNAseq analysis, 4669 of 5520 genes were found to be differentially expressed. Among the genes most upregulated with the ingestion of the CP compared to HF were Ph1da1, SLc6a9, Clec4f, and Ica1 which are related to glucose homeostasis; Mt2 that may be involved steroid biosynthetic process; and Ciart which has a role in the regulation of circadian rhythm. Although “Cerrado” CP intake did not cause changes in the food intake or body weight of fed mice with HF diet, carbohydrate metabolism appeared to be improved based on the observed changes in gene expression.

Extrahepatic factors in hepatic immune regulation

The liver is a site of complex immune activity. The hepatic immune system tolerates harmless immunogenic loads in homeostasis status, shelters liver function, while maintaining vigilance against possible infectious agents or tissue damage and providing immune surveillance at the same time. Activation of the hepatic immunity is initiated by a diverse repertoire of hepatic resident immune cells as well as non-hematopoietic cells, which can sense “danger signals” and trigger robust immune response. Factors that mediate the regulation of hepatic immunity are elicited not only in liver, but also in other organs, given the dual blood supply of the liver via both portal vein blood and arterial blood. Emerging evidence indicates that inter-organ crosstalk between the liver and other organs such as spleen, gut, lung, adipose tissue, and brain is involved in the pathogenesis of liver diseases. In this review, we present the features of hepatic immune regulation, with particular attention to the correlation with factors from extrahepatic organ. We describe the mechanisms by which other organs establish an immune association with the liver and then modulate the hepatic immune response. We discuss their roles and distinct mechanisms in liver homeostasis and pathological conditions from the cellular and molecular perspective, highlighting their potential for liver disease intervention. Moreover, we review the available animal models and methods for revealing the regulatory mechanisms of these extrahepatic factors. With the increasing understanding of the mechanisms by which extrahepatic factors regulate liver immunity, we believe that this will provide promising targets for liver disease therapy.

Hepatic Stellate Cell: A Double-Edged Sword in the Liver

Hepatic stellate cells (HSCs) are located in the space of Disse, between liver sinusoidal endothelia cells (LSECs) and hepatocytes. They have surprised and excited hepatologists for their biological characteristics. Under physiological quiescent conditions, HSCs are the major vitamin A-storing cells of the liver, playing crucial roles in the liver development, regeneration, and tissue homeostasis. Upon injury-induced activation, HSCs convert to a pro-fibrotic state, producing the excessive extracellular matrix (ECM) and promoting angiogenesis in the liver fibrogenesis. Activated HSCs significantly contribute to liver fibrosis progression and inactivated HSCs are key to liver fibrosis regression. In this review, we summarize the comprehensive understanding of HSCs features, including their roles in normal liver and liver fibrosis in hopes of advancing the development of emerging diagnosis and treatment for hepatic fibrosis.

Perivascular stromal cells: Directors of tissue immune niches

Perivascular niches are specialized microenvironments where stromal and immune cells interact with vasculature to monitor tissue status. Adventitial perivascular niches surround larger blood vessels and other boundary sites, supporting collections of immune cells, stromal cells, lymphatics, and neurons. Adventitial fibroblasts (AFs), a subtype of mesenchymal stromal cell, are the dominant constituents in adventitial spaces, regulating vascular integrity while organizing the accumulation and activation of a variety of interacting immune cells. In contrast, pericytes are stromal mural cells that support microvascular capillaries and surround organ-specific parenchymal cells. Here, we outline the unique immune and non-immune composition of perivascular tissue immune niches, with an emphasis on the heterogeneity and immunoregulatory functions of AFs and pericytes across diverse organs. We will discuss how perivascular stromal cells contribute to the regulation of innate and adaptive immune responses and integrate immunological signals to impact tissue health and disease.

Hallmarks of postoperative liver regeneration: An updated insight on the regulatory mechanisms

Performance and advances in liver surgery makes remarkable progress of the understanding of liver regeneration. Liver regeneration after liver resection has been widely researched, and the underlying mechanism mostly concerns proliferation of hepatocytes and the influence by inflammation through activation of Kupffer cells and the other parenchymal cells, the second regenerative pathway by hepatic progenitor cells (HPCs), inducing angiogenesis, remodeling of a extracellular matrix (ECM), and termination mechanisms. New clinical surgeries and the updated multiomics analysis are exploiting the remarkable progress, especially in immune regulation and metabolic process of two emerging hallmarks. This review briefly represents a systemic outline of eight hallmarks, including hepatocyte proliferation, contribution of hepatic progenitor cells, inducing angiogenesis, reprogramming of the extracellular matrix, apoptosis and termination of proliferation, inflammation, immune and metabolic regulation, which are set as organizing characteristics of postoperative liver regeneration and future directions of refining treatment targets.

Pathogenetic Mechanisms of T Cell Dysfunction in Chronic HBV Infection and Related Therapeutic Approaches

A great effort of research has been devoted in the last few years to developing new anti-HBV therapies of finite duration that also provide effective sustained control of virus replication and antigen production. Among the potential therapeutic strategies, immune-modulation represents a promising option to cure HBV infection and the adaptive immune response is a rational target for novel therapeutic interventions, in consideration of the key role played by T cells in the control of virus infections. HBV-specific T cells are severely dysfunctional in chronic HBV infection as a result of several inhibitory mechanisms which are simultaneously active within the chronically inflamed liver. Indeed, the liver is a tolerogenic organ harboring different non-parenchymal cell populations which can serve as antigen presenting cells (APC) but are poorly efficient in effector T cell priming, with propensity to induce T cell tolerance rather than T cell activation, because of a poor expression of co-stimulatory molecules, up-regulation of the co-inhibitory ligands PD-L1 and PD-L2 upon IFN stimulation, and production of immune regulatory cytokines, such as IL10 and TGF-β. They include resident dendritic cells (DCs), comprising myeloid and plasmacytoid DCs, liver sinusoidal endothelial cells (LSECs), Kupffer cells (KCs), hepatic stellate cells (HSCs) as well as the hepatocytes themselves. Additional regulatory mechanisms which contribute to T cell attrition in the chronically infected liver are the high levels of soluble mediators, such as arginase, indoleamine 2,3-dioxygenase (IDO) and suppressive cytokines, the up-regulation of inhibitory checkpoint receptor/ligand pairs, the expansion of regulatory cells, such as CD4+FOXp3+ Treg cells, myeloid-derived suppressor cells and NK cells. This review will deal with the interactions between immune cells and liver environment discussing the different mechanisms which contribute to T cell dysfunction in chronic hepatitis B, some of which are specifically activated in HBV infection and others which are instead common to chronic inflammatory liver diseases in general. Therapeutic interventions targeting dysregulated pathways and cellular functions will be also delineated.

Carcinogenesis and Metastasis in Liver: Cell Physiological Basis

Hepatocellular carcinoma (HCC) incidence is rising. This paper summarises the current state of knowledge and recent discoveries in the cellular and physiological mechanisms leading to the development of liver cancer, especially HCC, and liver metastases. After reviewing normal hepatic cytoarchitecture and immunological characteristics, the paper addresses the pathophysiological factors that cause liver damage and predispose to neoplasia. Particular attention is given to chronic liver diseases, metabolic syndrome and the impact of altered gut microbiota, disrupted circadian rhythm and psychological stress. Improved knowledge of the multifactorial aetiology of HCC has important implications for the prevention and treatment of this cancer and of liver metastases in general.

Activated hepatic stellate cells regulate MDSC migration through the SDF-1/CXCR4 axis in an orthotopic mouse model of hepatocellular carcinoma

Hepatic stellate cells (HSCs) are important stromal cells and pivotal mediators involved in the pathogenesis and immunosuppression of hepatocellular carcinoma (HCC). The liver has been demonstrated to be a site for accumulation of tumor-induced myeloid-derived suppressor cells (MDSCs). We previously reported that HSCs induced an increase in the number of MDSCs in HCC. However, how MDSCs are recruited in HCC remains largely unclear. In the present study, we found that HSC-conditioned medium (HSC-CM) induced bone marrow-derived cell and splenocyte migration, especially MDSC migration. Using chemokine-neutralizing antibodies and chemokine receptor inhibitors, we found that HSCs promoted MDSC migration through the SDF-1/CXCR4 axis. Subsequently, we used an orthotopic mouse liver tumor model to determine how HSCs mediated MDSC migration to HCC in vivo. The in vivo results indicated that pretreatment of MDSCs with a CXCR4 inhibitor or injection with SDF-1-knocked down HSCs inhibited MDSC migration to the spleen and liver of the tumor-bearing mice. Together, our findings indicate a central role for HSCs in MDSC migration mediated by the SDF-1/CXCR4 axis, thus revealing a potentially effective approach for modulating the tumor microenvironment by targeting HSCs in HCC.

Senescent cell clearance by the immune system: Emerging therapeutic opportunities

Senescent cells (SCs) arise from normal cells in multiple organs due to inflammatory, metabolic, DNA damage, or tissue damage signals. SCs are non-proliferating but metabolically active cells that can secrete a range of pro-inflammatory and proteolytic factors as part of the senescence-associated secretory phenotype (SASP). Senescent cell anti-apoptotic pathways (SCAPs) protect SCs from their own pro-apoptotic SASP. SCs can chemo-attract immune cells and are usually cleared by these immune cells. During aging and in multiple chronic diseases, SCs can accumulate in dysfunctional tissues. SCs can impede innate and adaptive immune responses. Whether immune system loss of capacity to clear SCs promotes immune system dysfunction, or conversely whether immune dysfunction permits SC accumulation, are important issues that are not yet fully resolved. SCs may be able to assume distinct states that interact differentially with immune cells, thereby promoting or inhibiting SC clearance, establishing a chronically pro-senescent and pro-inflammatory environment, leading to modulation of the SASP by the immune cells recruited and activated by the SASP. Therapies that enhance immune cell-mediated clearance of SCs could provide a lever for reducing SC burden. Such therapies could include vaccines, small molecule immunomodulators, or other approaches. Senolytics, drugs that selectively eliminate SCs by transiently disabling their SCAPs, may prove to alleviate immune dysfunction in older individuals and thereby accelerate immune-mediated clearance of SCs. The more that can be understood about the interplay between SCs and the immune system, the faster new interventions may be developed to delay, prevent, or treat age-related dysfunction and the multiple senescence-associated chronic diseases and disorders.

Dendritic cells, T cells and lymphatics: dialogues in migration and beyond

Immune cells continuously recirculate through lymph vessels en route from peripheral tissues to the blood. Leuyte trafficking into and within lymph vessels is mediated by an interply with lymphatic endothelial cells (LECs). However, lymphatic vessels are much more than mere conduits for fluid and immune cell transport. Data accumulating during past several years indicate that LECs support T cell survival, induce tolerance to self-antigens, inhibit exaggerated T cell proliferation during immune response and maintain T cell memory. Reciprocally, leukocytes impact LEC biology: lymphatic vessel permeability depends on DCs while lymphocytes regulate LEC proliferation during inflammation. Altogether, these novel results provide important insights on intimate connections between LECs and leukocytes that contribute to the understanding of immune responses.

A short field guide to fibroblast function in immunity

Fibroblasts in secondary lymphoid organs, or fibroblastic reticular cells (FRC), are gate-keepers of immune responses. Here, we frame how these cells regulate immune responses via a three-part scheme in which FRC can setup, support or suppress immune responses. We also review how fibroblasts from non-lymphoid tissues influence immunity and highlight how they resemble and differ from FRC. Overall, we aim to focus attention on the emerging roles of lymphoid tissue and non-lymphoid tissue fibroblasts in control of innate and adaptive immunity.

Mechanisms of liver-induced tolerance

PURPOSE OF REVIEW

To highlight the results of the ongoing research on the mechanisms of liver-induced tolerance focusing on results from the last year.

RECENT FINDINGS

The liver is exposed to a massive antigenic burden of dietary and commensal products from the gastrointestinal tract via portal vein, most of which are necessary for survival. To prevent the immune system from destroying these foreign yet beneficial elements, the liver has developed unique mechanisms to suppress immune responses. It is thought that these mechanisms of acquired tolerance may also underlie the spontaneous acceptance of liver allografts observed after transplantation in many species. The fact that isolated hepatocyte transplants are acutely rejected, suggests that nonparenchymal liver cells play a critical role in spontaneous liver allograft acceptance. IFN-γ, a key inflammatory cytokine produced by T effector (Tef) cells, is paradoxically compulsory for spontaneous liver allograft acceptance. Analysis of IFN-γ signaling points to liver mesenchymal nonparenchymal liver cell that eliminate infiltrating Tef cells via expression of B7-H1, IL-10, and tumor growth factor-β, as well as the enhancement of Tregs and MDSCs. Thus, liver mesenchymal cells are thought to promote tolerance by eliminating alloreactive Tef cells and enhancing suppressor cells (T and B).

SUMMARY

The research during last year offered some key insights into the mechanisms of liver-induced tolerance. Through interactions with activated T cells and B cells via IFN-γ/B7-H1 pathways, liver mesenchymal cells have been shown to be critical components of liver-specific tolerance induction.

The Liver at the Nexus of Host-Microbial Interactions

The liver receives blood from the intestine, from the spleen, and directly from the heart and holds a vital position in vertebrate physiology. It plays a role in intermediary metabolism, bile secretion, maintaining blood sterility, serum homeostasis, xenobiotic detoxification, and immunological activity. This article provides our perspective on the liver as a nexus in establishing and maintaining host microbial mutualism. We discuss the role of the liver not only in sanitizing the blood stream from penetrant live microbes, but also in metabolizing xenobiotics that are synthesized or modified by intestinal microbes, and how microbiota modify the signaling potential of bile acids. The combination of bile acids as hormones and the metabolic control from pervasive effects of other absorbed microbial molecules powerfully shape hepatic metabolism. In addition, intestinal microbial metabolites can be sensed by liver-resident immune cells, which may disturb liver homeostasis, leading to fibrosis and liver cancer.

Hepatic stroma-educated regulatory DCs suppress CD8+ T cell proliferation in mice

Liver dendritic cells (DCs) display immunosuppressive activities and inhibit the CD4⁺ T cell response. The present study assessed whether and how liver DCs suppress CD8⁺ T cells. We found that bone marrow-derived mature DCs incubated with liver stromal cells were characterized by a longer life span, reduced CD11c, IA/IE, CD80, CD86, and CD40 expression, and increased CD11b expression. These unique liver stromal cell-educated mature DCs (LSed-DCs) stimulated CD8⁺ T cells to express CD25 and CD69, but inhibited their proliferation. CD8⁺ T cell suppression depended on soluble factors released by LSed-DCs, but not cell-cell contact. Compared with mature DCs, LSed-DCs produced more nitric oxide and IL-10. Addition of a nitric oxide synthase inhibitor, PBIT, but not an IL-10-blocking mAb, reversed LSed-DC inhibition of CD8⁺ T cell proliferation. We also found that LSed-DCs reduced CD8⁺ T cell-mediated liver damage in a mouse model of autoimmune hepatitis. These results demonstrate that the liver stroma induces mature DCs to differentiate into regulatory DCs that suppress CD8⁺ T cell proliferation, and thus contribute to liver tolerance.

The role of immune mechanisms in alcoholic and nonalcoholic steatohepatitis: a 2015 update

So far, innate immune mechanisms have been recognized as the main responsible for the evolution of both alcoholic steatohepatitis (ASH) and nonalcoholic steatohepatitis (NASH). However, increasing evidence points toward the possible role of adaptive immune responses, as an additional factor in promoting hepatic inflammation in steatohepatitis. In this article, we discuss recent data involving circulating antibodies and lymphocyte-mediated responses in sustaining the progression of ASH and NASH to fibrosis, as well as the possible mechanisms implicated in favoring the onset of adaptive immunity in the setting of steatohepatitis.

High glucose regulates LN expression in human liver sinusoidal endothelial cells through ROS/integrin αvβ3 pathway

Diabetes mellitus can cause a wide variety of vascular complications and is one of the major risk factors for Non Alcoholic Fatty Liver Disease (NAFLD). The present study was designed investigate the expression of laminin (LN) in human liver sinusoidal endothelial cells (HLSECs) induced by high glucose and the role of reactive oxygen species (ROS) and integrin αvβ3 in the regulation of LN expression. HLSECs were cultured and treated with media containing 25 mM glucose in the presence or absence of N-acetylcysteine (NAC) or clone LM609. The level of intracellular ROS of HLSECs was measured with 2',7' dichloro-fluorescein diacetate (DCFH-DA) probe. Expression of integrin αvβ3 was measured using RT-PCR and Western blot. Expression of LN was testified by immunofluorescence assay. Compared with that in control group, ROS level and the expression of integrin αvβ3 and LN increased in high glucose group. Compared with that in high glucose group, antioxidant NAC inhibited the expression of integrin αvβ3, NAC and the anti-body for blocking integrin αvβ3 (clone LM609) down-regulated the expression of LN. However, the above parameters did not differ between control and mannitol groups. High glucose up-regulates expression of LN in HLSECs through ROS/integrin αvβ3 pathway.

Organ-specific differences in achieving tolerance

PURPOSE OF REVIEW

When it comes to tolerance induction, kidney allografts behave differently from heart allografts that behave differently from lung allografts. Here, we examine how and why different organ allografts respond differently to the same tolerance induction protocol.

RECENT FINDINGS

Allograft tolerance has been achieved in experimental and clinical kidney transplantation. Inducing tolerance in experimental recipients of heart and lung allografts has, however, proven to be more challenging. New protocols being developed in nonhuman primates based on mixed chimerism and cotransplantation of tolerogenic organs may provide mechanistic insights to help overcome these challenges.

SUMMARY

Tolerance induction protocols that are successful in patients transplanted with 'tolerance-prone' organs such as kidneys and livers will most likely not succeed in recipients of 'tolerance-resistant' organs such as hearts and lungs. Separate clinical trials using more robust tolerance protocols will be required to achieve tolerance in heart and lung recipients.