Liver sinusoidal endothelial cell lectin, LSECtin, negatively regulates hepatic T-cell immune response

Progress and challenges in glypican-3 targeting for hepatocellular carcinoma therapy

INTRODUCTION

Glypican-3 (GPC3) is a cell membrane-anchored heparan sulfate proteoglycan that has recently garnered attention as a cancer antigen owing to its high expression in numerous cancers, particularly hepatocellular carcinoma (HCC), and to limited expression in adult normal tissue.

AREAS COVERED

Here, we propose the potential of GPC3 as a cancer antigen based on our experience with the GPC3 peptide vaccine against HCC, having developed a vaccine that progressed from preclinical studies to first-in-human clinical trials. In this review, we present a summary of the current status and future prospects of immunotherapies targeting GPC3 by focusing on clinical trials; peptide vaccines, mRNA vaccines, antibody therapy, and chimeric antigen receptor/T-cell receptor - T-cell therapy and discuss additional strategies for effectively eliminating HCC through immunotherapy.

EXPERT OPINION

GPC3 is an ideal cancer antigen for HCC immunotherapy. In resectable HCC, immunotherapies that leverage physiological immune surveillance, immune checkpoint inhibitors, and GPC3-target cancer vaccines appear promising in preventing recurrence and could be considered as a prophylactic adjuvant therapy. However, in advanced HCC, clinical trials have not demonstrated sufficient anti-tumor efficacy, in contrast with preclinical studies. Reverse translation, bedside-to-bench research, is crucial to identify the factors that have hindered GPC3 target immunotherapies.

Angiocrine signaling in sinusoidal homeostasis and liver diseases

The hepatic sinusoids are composed of liver sinusoidal endothelial cells (LSECs), which are surrounded by hepatic stellate cells (HSCs) and contain liver-resident macrophages called Kupffer cells, and other patrolling immune cells. All these cells communicate with each other and with hepatocytes to maintain sinusoidal homeostasis and a spectrum of hepatic functions under healthy conditions. Sinusoidal homeostasis is disrupted by metabolites, toxins, viruses, and other pathological factors, leading to liver injury, chronic liver diseases, and cirrhosis. Alterations in hepatic sinusoids are linked to fibrosis progression and portal hypertension. LSECs are crucial regulators of cellular crosstalk within their microenvironment via angiocrine signaling. This review discusses the mechanisms by which angiocrine signaling orchestrates sinusoidal homeostasis, as well as the development of liver diseases. Here, we summarise the crosstalk between LSECs, HSCs, hepatocytes, cholangiocytes, and immune cells in health and disease and comment on potential novel therapeutic methods for treating liver diseases.

Antibody-Decorated Nanoplatform to Reprogram Macrophage and Block Immune Checkpoint LSECtin for Effective Cancer Immunotherapy

Repolarizing tumor-associated macrophages (TAMs) into tumor-inhibiting M1 macrophages has been considered a promising strategy for enhanced cancer immunotherapy. However, several immunosuppressive ligands (e.g., LSECtin) can still be highly expressed on M1 macrophages, inducing unsatisfactory therapeutic outcomes. We herein developed an antibody-decorated nanoplatform composed of PEGylated iron oxide nanoparticles (IONPs) and LSECtin antibody conjugated onto the surface of IONPs via the hydrazone bond for enhanced cancer immunotherapy. After intravenous administration, the tumor microenvironment (TME) pH could trigger the hydrazone bond breakage and induce the disassociation of the nanoplatform into free LSECtin antibodies and IONPs. Consequently, the IONPs could repolarize TAMs into M1 macrophages to remodel immunosuppressive TME and provide an additional anticancer effect via secreting tumoricidal factors (e.g., interlukin-12). Meanwhile, the LSECtin antibody could further block the activity of LSECtin expressed on M1 macrophages and relieve its immunosuppressive effect on CD8+ T cells, ultimately leading to significant inhibition of tumor growth.

Signaling through the nicotinic acetylcholine receptor in the liver protects against the development of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) is the progressive form of liver steatosis, the most common liver disease, and substantially increases the mortality rate. However, limited therapies are currently available to prevent MASH development. Identifying potential pharmacological treatments for the condition has been hampered by its heterogeneous and complex nature. Here, we identified a hepatic nonneuronal cholinergic signaling pathway required for metabolic adaptation to caloric overload. We found that cholinergic receptor nicotinic alpha 2 subunit (CHRNA2) is highly expressed in hepatocytes of mice and humans. Further, CHRNA2 is activated by a subpopulation of local acetylcholine-producing macrophages during MASH development. The activation of CHRNA2 coordinates defensive programs against a broad spectrum of MASH-related pathogenesis, including steatosis, inflammation, and fibrosis. Hepatocyte-specific loss of CHRNA2 signaling accelerates the disease onset in different MASH mouse models. Activation of this pathway via pharmacological inhibition of acetylcholine degradation protects against MASH development. Our study uncovers a hepatic nicotinic cholinergic receptor pathway that constitutes a cell-autonomous self-defense route against prolonged metabolic stress and holds therapeutic potential for combatting human MASH.

Molecular Events in Immune Responses to Sublingual Influenza Vaccine with Hemagglutinin Antigen and Poly(I:C) Adjuvant in Nonhuman Primates, Cynomolgus Macaques

Sublingual vaccines offer the benefits of inducing mucosal immunity to protect against respiratory viruses, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and influenza, while also enabling needle-free self-administration. In a previous study, a sublingual SARS-CoV-2 vaccination was created by combining a recombinafigureCoV-2 spike protein receptor-binding domain antigen with a double strand RNA Poly(I:C) adjuvant. This vaccine was tested on nonhuman primates, Cynomolgus macaques. This study examined the immune and inflammatory responses elicited by the sublingual influenza vaccine containing hemagglutinin (HA) antigen and Poly(I:C) adjuvants, and assessed the safety of this vaccine in nonhuman primates. The Poly(I:C)-adjuvanted sublingual vaccine induced both mucosal and systemic immunities. Specifically, the sublingual vaccine produced HA-specific secretory IgA antibodies in saliva and nasal washings, and HA-specific IgA and IgG were detected in the blood. This vaccine appeared to be safe, as judged from the results of blood tests and plasma C-reactive protein levels. Notably, sublingual vaccination neither increased the production of inflammation-associated cytokines-IFN-alpha, IFN-gamma, and IL-17-in the blood, nor upregulated the gene expression of proinflammatory cytokines-IL12A, IL12B, IFNA1, IFNB1, CD69, and granzyme B-in white blood cells. Moreover, DNA microarray analyses revealed that sublingual vaccination evoked both enhancing and suppressing expression changes in genes associated with immune-related responses in cynomolgus monkeys. Therefore, the sublingual vaccine with the Poly(I:C) adjuvant is safe, and creates a balanced state of enhancing and suppressing the immune-related response.

Cirrhosis-downregulated LSECtin can be retrieved by cytokines, shifts the TLR-induced LSECs secretome and correlates with the hepatic Th response

BACKGROUND AND AIMS

We evaluated tolerogenic C-type lectin LSECtin loss in cirrhosis and its potential regulation by cytokines.

METHODS

Liver tissue from patients with cirrhosis and healthy controls, immortalised and generated LSECtin-CRISPR immortalised LSECs, and murine primary LSECs from the CCl4 model were handled.

RESULTS

LSECtin expression was reduced in liver tissue from cirrhotic patients, and it decreased from compensated to decompensated disease. Increased phosphorylation of MAPK, Akt and NFkB was observed upon LSECtin stimulation in LSEC murine cell line, showing a pattern of inflammatory and chemotactic cytokines either restrained (IL-10, CCL4) or unrestrained (TNF-α, IL-1β, IL-6, CCL2). CD44 attenuated whereas LAG-3 increased all substrates phosphorylation in combination with TLR4 and TLR2 ligands except for NFkB. TNF-α, IL-1 β, IL-6 and CCL2 were restrained by LSECtin crosslinking on TLRs studied. Conversely, IL-10 and CCL4 were upregulated, suggesting a LSECtin-TLRs synergistic effect. Also, LSECtin was significantly induced after IL-13 stimulation or combined with anti-inflammatory cytokines in cirrhotic and immortalised LSECs. Th17 and regulatory T cells were progressively increased in the hepatic tissue from compensated to decompensated patients. A significant inverse correlation was present between gene expression levels of CLEC4G/LSECtin and RORγT and FOXP3 in liver tissues.

CONCLUSION

LSECtin restrains TLR proinflammatory secretome induced on LSECs by interfering immune response control, survival and MAPKs signalling pathways. The cytokine-dependent induction of LSECtin and the association between LSECtin loss and Th17 cell subset expansion in the liver, provides a solid background for exploring LSECtin retrieval as a mechanism to reprogram LSEC homeostatic function hampered during cirrhosis.

Characterization of the Immune Microenvironment and Identification of Biomarkers in Chronic Rhinosinusitis with Nasal Polyps Using Single-Cell RNA Sequencing and Transcriptome Analysis

Purpose

Chronic rhinosinusitis is a prevalent condition in the field of otorhinolaryngology; however, its pathogenesis remains to be elucidated. The immunological defense of the nasal mucosa is significantly influenced by dendritic cells (DCs). We identified specific biological indicators linked to DCs and explored their significance in cases of chronic rhinosinusitis with nasal polyps (CRSwNP).

Patients and Methods

We categorized cells using single-cell RNA (scRNA) sequencing, and combined transcriptome sequencing was used to identify potential candidate genes for CRSwNP. We selected three biomarkers based on two algorithms and performed enrichment and immune correlation analyses. Biomarkers were verified using training and validation sets, receiver operating characteristic curves, immunohistochemistry, and quantitative real-time reverse-transcription PCR (qRT-PCR). Variations in biomarker expression were validated using pseudotime analysis. The networks of competing transcription factor (TF)-mRNA and competing endogenous RNA (ceRNA) were established, and the protein drugs associated with these biomarkers were predicted.

Results

Both scRNA-seq and transcriptome data showed that DCs immune infiltration was higher in the CRSwNP group than in the control group. Three DC-related biomarkers (NR4A1, CLEC4G, and CD163) were identified. In CRSwNP, NR4A1 expression decreased, whereas CLEC4G and CD163 expression increased. All biomarkers were shown to be involved in immunological and metabolic pathways by enrichment analysis. These biomarkers were associated with γδ T cells, effector memory CD4 + T cells, regulatory T cells, and immature DCs. According to pseudotime analysis, NR4A1 and CD163 expression decreased from high to low, whereas CLEC4G expression remained low.

Conclusion

We screened and identified potential DC-associated biomarkers of CRSwNP progression by integrating scRNA-seq with whole transcriptome sequencing. We analyzed the biological pathways in which they were involved, explored their molecular regulatory mechanisms and related drugs, and constructed ceRNA, TF-mRNA, and biomarker-drug networks to identify new CRSwNP treatment targets, laying the groundwork for the clinical management of CRSwNP.

Endothelial and tumor-intrinsic mechanisms of hepatic melanoma metastasis

The treatment of metastatic cutaneous melanoma was fundamentally improved by the discovery and introduction of immune checkpoint inhibitors, such as anti-PD-1 and anti-CTLA-4 antibodies, and targeted therapy with BRAF and MEK inhibition. Unfortunately, many patients suffer a relapse due to resistance mechanisms that in part are mediated by organ-specific metastatic sites. Especially, brain and liver metastases are negative predictive factors for both treatment modalities. There is still high unmet clinical need to prevent and treat spread to these organs. Therefore, experimental research should focus on mechanisms of hepatic melanoma metastasis to better understand this process and to identify therapeutic targets.

Endotheliale und tumor-intrinsische Mechanismen der hepatischen Melanommetastasierung: Endothelial and tumor-intrinsic mechanisms of hepatic melanoma metastasis

Die Behandlung des metastasierten kutanen Melanoms wurde durch die Entdeckung und Zulassung von Immuncheckpoint‐Inhibitoren (ICI) wie Anti‐PD‐1‐ und Anti‐CTLA‐4‐Antikörpern sowie der zielgerichteten Therapie mit BRAF‐ und MEK‐Inhibition grundlegend verbessert. Allerdings entwickeln viele Patienten Rezidive aufgrund von Resistenzmechanismen, die zum Teil durch Metastasierung in bestimmte Organe verursacht werden. Insbesondere Hirn‐ und Lebermetastasen sind negative prädiktive Faktoren für beide Behandlungsmodalitäten. Bislang gibt es nur begrenzte Möglichkeiten, organspezifische Metastasierung aufzuhalten oder zu behandeln. Daher muss sich die experimentelle Forschung unter anderem Mechanismen der hepatischen Metastasierung des Melanoms widmen, um diesen Prozess besser zu verstehen und therapeutische Ziele ausfindig zu machen.

Advancement of anti-LAG-3 in cancer therapy

Immune checkpoint inhibitors have effectively transformed the treatment of many cancers, particularly those highly devastating malignancies. With their widespread popularity, the drawbacks of immune checkpoint inhibitors are also recognized, such as drug resistance and immune-related systematic side effects. Thus, it never stops investigating novel immune checkpoint inhibitors. Lymphocyte Activation Gene-3 (LAG-3) is a well-established co-inhibitory receptor that performs negative regulation on immune responses. Recently, a novel FDA-approved LAG-3 blocking agent, together with nivolumab as a new combinational immunotherapy for metastatic melanoma, brought LAG-3 back into focus. Clinical data suggests that anti-LAG-3 agents can amplify the therapeutic response of other immune checkpoint inhibitors with manageable side effects. In this review, we elucidate the intercellular and intracellular mechanisms of LAG-3, clarify the current understanding of LAG-3 in the tumor microenvironment, identify present LAG-3-associated therapeutic agents, discuss current LAG-3-involving clinical trials, and eventually address future prospects for LAG-3 inhibitors.

Liver metastasis from colorectal cancer: pathogenetic development, immune landscape of the tumour microenvironment and therapeutic approaches

Colorectal cancer liver metastasis (CRLM) is one of the leading causes of death among patients with colorectal cancer (CRC). Although immunotherapy has demonstrated encouraging outcomes in CRC, its benefits are minimal in CRLM. The complex immune landscape of the hepatic tumour microenvironment is essential for the development of a premetastatic niche and for the colonisation and metastasis of CRC cells; thus, an in-depth understanding of these mechanisms can provide effective immunotherapeutic targets for CRLM. This review summarises recent studies on the immune landscape of the tumour microenvironment of CRLM and highlights therapeutic prospects for targeting the suppressive immune microenvironment of CRLM.

Novel inflammatory biomarkers associated with stroke severity: results from a cross-sectional stroke cohort study

BACKGROUND

Stroke is a leading cause of mortality and disability worldwide and its occurrence is expected to increase in the future. Blood biomarkers have proven their usefulness in identification and monitoring of the disease. Stroke severity is a major factor for estimation of prognosis and risk of recurrent events, but knowledge on respective blood biomarkers is still scarce. Stroke pathophysiology comprises a multitude of ischemia-induced inflammatory and immune mediated responses. Therefore, the assessment of an immune-related panel in correlation with stroke severity seems promising.

METHODS

In the present cross-sectional evaluation, a set of 92 blood biomarkers of a standardized immune panel were gathered (median 4.6 days after admission) and related to stroke severity measures, assessed at hospital admission of acute stroke patients. Multivariable logistic regression models were used to determine associations between biomarkers and modified Rankin Scale (mRS), linear regression models were used for associations with National Institute of Health Stroke Scale.

RESULTS

415 patients (mean age 69 years; 41% female) were included for biomarker analysis. C-type lectin domain family 4 member G (CLEC4G; OR = 2.89, 95% CI [1.49; 5.59], p_adj = 0.026, Cytoskeleton-associated protein 4 (CKAP4; OR = 2.38, 95% CI [1.43; 3.98], p_adj = 0.019), and Interleukin-6 (IL-6) (IL6; OR = 1.97, 95% CI [1.49; 2.62], p_adj < 0.001) were positively associated with stroke severity measured by mRS, while Lymphocyte antigen 75 (LY75; OR = 0.37, 95% CI [0.19; 0.73], p_adj = 0.049) and Integrin alpha-11 (ITGA11 OR = 0.24, 95% CI [0.14, 0.40] p_adj < 0.001) were inversely associated. When investigating the relationships with the NIHSS, IL-6 (β = 0.23, 95% CI [0.12, 0.33] p_adj = 0.001) and ITGA11 (β =  - 0.60, 95% CI [- 0.83, - 0.37] p_adj < 0.001) were significantly associated.

CONCLUSIONS

Higher relative concentrations of plasma CLEC4G, CKAP4, and IL-6 were associated with higher stroke severity, whereas LY75 and ITGA11 showed an inverse association. Future research might show a possible use as therapeutic targets and application in individual risk assessments.

Remodeling the hepatic fibrotic microenvironment with emerging nanotherapeutics: a comprehensive review

Liver fibrosis could be the last hope for treating liver cancer and remodeling of the hepatic microenvironment has emerged as a strategy to promote the ablation of liver fibrosis. In recent years, especially with the rapid development of nanomedicine, hepatic microenvironment therapy has been widely researched in studies concerning liver cancer and fibrosis. In this comprehensive review, we summarized recent advances in nano therapy-based remodeling of the hepatic microenvironment. Firstly, we discussed novel strategies for regulatory immune suppression caused by capillarization of liver sinusoidal endothelial cells (LSECs) and macrophage polarization. Furthermore, metabolic reprogramming and extracellular matrix (ECM) deposition are caused by the activation of hepatic stellate cells (HSCs). In addition, recent advances in ROS, hypoxia, and impaired vascular remodeling in the hepatic fibrotic microenvironment due to ECM deposition have also been summarized. Finally, emerging nanotherapeutic approaches based on correlated signals were discussed in this review. We have proposed novel strategies such as engineered nanotherapeutics targeting antigen-presenting cells (APCs) or direct targeting T cells in liver fibrotic immunotherapy to be used in preventing liver fibrosis. In summary, this comprehensive review illustrated the opportunities in drug targeting and nanomedicine, and the current challenges to be addressed.

Immunotolerance in liver transplantation: a primer for the clinician

The use of immunosuppressive medications for solid organ transplantation is associated with cardiovascular, metabolic, and oncologic complications. On the other hand, the development of graft rejection is associated with increased mortality and graft dysfunction. Liver transplant recipients can withdraw from immunosuppression without developing graft injury while preserving an adequate antimicrobial response - a characteristic known as immunotolerance. Immunotolerance can be spontaneously or pharmacologically achieved. Contrary to the classic dogma, clinical studies have elucidated low rates of true spontaneous immunotolerance (no serologic or histological markers of immune injury) among liver transplant recipients. However, clinical, serologic, and tissue biomarkers can aid in selecting patients in whom immunosuppression can be safely withdrawn. For those who failed an immunosuppression withdrawal trial or are at high risk of rejection, pharmacological interventions for immunotolerance induction are under development. In this review, we provide an overview of the mechanisms of immunotolerance, the clinical studies investigating predictors and biomarkers of spontaneous immunotolerance, as well as the potential pharmacological interventions for inducing it.

Evaluation of cutaneous immune response in a controlled human in vivo model of mosquito bites

Mosquito-borne viruses are a growing global threat. Initial viral inoculation occurs in the skin via the mosquito 'bite', eliciting immune responses that shape the establishment of infection and pathogenesis. Here we assess the cutaneous innate and adaptive immune responses to controlled Aedes aegypti feedings in humans living in Aedes-endemic areas. In this single-arm, cross-sectional interventional study (trial registration #NCT04350905), we enroll 30 healthy adult participants aged 18 to 45 years of age from Cambodia between October 2020 and January 2021. We perform 3-mm skin biopsies at baseline as well as 30 min, 4 h, and 48 h after a controlled feeding by uninfected Aedes aegypti mosquitos. The primary endpoints are measurement of changes in early and late innate responses in bitten vs unbitten skin by gene expression profiling, immunophenotyping, and cytokine profiling. The results reveal induction of neutrophil degranulation and recruitment of skin-resident dendritic cells and M2 macrophages. As the immune reaction progresses T cell priming and regulatory pathways are upregulated along with a shift to Th2-driven responses and CD8+ T cell activation. Stimulation of participants' bitten skin cells with Aedes aegypti salivary gland extract results in reduced pro-inflammatory cytokine production. These results identify key immune genes, cell types, and pathways in the human response to mosquito bites and can be leveraged to inform and develop novel therapeutics and vector-targeted vaccine candidates to interfere with vector-mediated disease.

ACE2-Independent Alternative Receptors for SARS-CoV-2

Severe acute respiratory syndrome-related coronavirus (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), is highly contagious and remains a major public health challenge despite the availability of effective vaccines. SARS-CoV-2 enters cells through the binding of its spike receptor-binding domain (RBD) to the human angiotensin-converting enzyme 2 (ACE2) receptor in concert with accessory receptors/molecules that facilitate viral attachment, internalization, and fusion. Although ACE2 plays a critical role in SARS-CoV-2 replication, its expression profiles are not completely associated with infection patterns, immune responses, and clinical manifestations. Additionally, SARS-CoV-2 infects cells that lack ACE2, and the infection is resistant to monoclonal antibodies against spike RBD in vitro, indicating that some human cells possess ACE2-independent alternative receptors, which can mediate SARS-CoV-2 entry. Here, we discuss these alternative receptors and their interactions with SARS-CoV-2 components for ACE2-independent viral entry. These receptors include CD147, AXL, CD209L/L-SIGN/CLEC4M, CD209/DC-SIGN/CLEC4L, CLEC4G/LSECtin, ASGR1/CLEC4H1, LDLRAD3, TMEM30A, and KREMEN1. Most of these receptors are known to be involved in the entry of other viruses and to modulate cellular functions and immune responses. The SARS-CoV-2 omicron variant exhibits altered cell tropism and an associated change in the cell entry pathway, indicating that emerging variants may use alternative receptors to escape the immune pressure against ACE2-dependent viral entry provided by vaccination against RBD. Understanding the role of ACE2-independent alternative receptors in SARS-CoV-2 viral entry and pathogenesis may provide avenues for the prevention of infection by SARS-CoV-2 variants and for the treatment of COVID-19.

Mechanotransduction-induced glycolysis epigenetically regulates a CXCL1-dominant angiocrine signaling program in liver sinusoidal endothelial cells in vitro and in vivo

BACKGROUND & AIMS

Liver sinusoidal endothelial cells (LSECs) are ideally situated to sense stiffness and generate angiocrine programs that potentially regulate liver fibrosis and portal hypertension. We explored how specific focal adhesion (FA) proteins parlay LSEC mechanotransduction into stiffness-induced angiocrine signaling in vitro and in vivo.

METHODS

Primary human and murine LSECs were placed on gels with incremental stiffness (0.2 kPa vs. 32 kPa). Cell response was studied by FA isolation, actin polymerization assay, RNA-sequencing and electron microscopy. Glycolysis was assessed using radioactive tracers. Epigenetic regulation of stiffness-induced genes was analyzed by chromatin-immunoprecipitation (ChIP) analysis of histone activation marks, ChIP sequencing and circularized chromosome conformation capture (4C). Mice with LSEC-selective deletion of glycolytic enzymes (Hk2fl/fl/Cdh5cre-ERT2) or treatment with the glycolysis inhibitor 3PO were studied in portal hypertension (partial ligation of the inferior vena cava, pIVCL) and early liver fibrosis (CCl4) models.

RESULTS

Glycolytic enzymes, particularly phosphofructokinase 1 isoform P (PFKP), are enriched in isolated FAs from LSECs on gels with incremental stiffness. Stiffness resulted in PFKP recruitment to FAs, which paralleled an increase in glycolysis. Glycolysis was associated with expansion of actin dynamics and was attenuated by inhibition of integrin β1. Inhibition of glycolysis attenuated a stiffness-induced CXCL1-dominant angiocrine program. Mechanistically, glycolysis promoted CXCL1 expression through nuclear pore changes and increases in NF-kB translocation. Biochemically, this CXCL1 expression was mediated through spatial re-organization of nuclear chromatin resulting in formation of super-enhancers, histone acetylation and NF-kB interaction with the CXCL1 promoter. Hk2fl/fl/Cdh5cre-ERT2 mice showed attenuated neutrophil infiltration and portal hypertension after pIVCL. 3PO treatment attenuated liver fibrosis in a CCl4 model.

CONCLUSION

Glycolytic enzymes are involved in stiffness-induced angiocrine signaling in LSECs and represent druggable targets in early liver disease.

LAY SUMMARY

Treatment options for liver fibrosis and portal hypertension still represent an unmet need. Herein, we uncovered a novel role for glycolytic enzymes in promoting stiffness-induced angiocrine signaling, which resulted in inflammation, fibrosis and portal hypertension. This work has revealed new targets that could be used in the prevention and treatment of liver fibrosis and portal hypertension.

Carma3 Protects from Liver Injury by Preserving Mitochondrial Integrity in Liver Sinusoidal Endothelial Cells

Carma3 is an intracellular scaffolding protein that can form complex with Bcl10 and Malt1 to mediate G protein–coupled receptor– or growth factor receptor–induced NF-κB activation. However, the in vivo function of Carma3 has remained elusive. Here, by establishing a Con A–induced autoimmune hepatitis model, we show that liver injury is exacerbated in Carma3−/− mice. Surprisingly, we find that the Carma3 expression level is higher in liver sinusoidal endothelial cells (LSECs) than in hepatocytes in the liver. In Carma3−/− mice, Con A treatment induces more LSEC damage, accompanied by severer coagulation. In vitro we find that Carma3 localizes at mitochondria and Con A treatment can trigger more mitochondrial damage and cell death in Carma3-deficient LSECs. Taken together, our data uncover an unrecognized role of Carma3 in maintaining LSEC integrity, and these results may extend novel strategies to prevent liver injury from toxic insults.

Immunological Tolerance in Liver Transplant Recipients: Putative Involvement of Neuroendocrine-Immune Interactions

The transplantation world changed significantly following the introduction of immunosuppressants, with millions of people saved. Several physicians have noted that liver recipients that do not take their medication for different reasons became tolerant regarding kidney, heart, and lung transplantations at higher frequencies. Most studies have attempted to explain this phenomenon through unique immunological mechanisms and the fact that the hepatic environment is continuously exposed to high levels of pathogen-associated molecular patterns (PAMPs) or non-pathogenic microorganism-associated molecular patterns (MAMPs) from commensal flora. These components are highly inflammatory in the periphery but tolerated in the liver as part of the normal components that arrive via the hepatic portal vein. These immunological mechanisms are discussed herein based on current evidence, although we hypothesize the participation of neuroendocrine-immune pathways, which have played a relevant role in autoimmune diseases. Cells found in the liver present receptors for several cytokines, hormones, peptides, and neurotransmitters that would allow for system crosstalk. Furthermore, the liver is innervated by the autonomic system and may, thus, be influenced by the parasympathetic and sympathetic systems. This review therefore seeks to discuss classical immunological hepatic tolerance mechanisms and hypothesizes the possible participation of the neuroendocrine-immune system based on the current literature.

From Anti-HER-2 to Anti-HER-2-CAR-T Cells: An Evolutionary Immunotherapy Approach for Gastric Cancer

Current Therapeutic modalities provide no survival advantage to gastric cancer (GC) patients. Targeting the human epidermal growth factor receptor-2 (HER-2) is a viable therapeutic strategy against advanced HER-2 positive GC. Antibody-drug conjugates, small-molecule tyrosine kinase inhibitors (TKIs), and bispecific antibodies are emerging as novel drug forms that may abrogate the resistance to HER-2-specific drugs and monoclonal antibodies. Chimeric antigen receptor-modified T cells (CAR-T) targeting HER-2 have shown considerable therapeutic potential in GC and other solid tumors. However, due to the high heterogeneity along with the complex tumor microenvironment (TME) of GC that often leads to immune escape, the immunological treatment of GC still faces many challenges. Here, we reviewed and discussed the current progress in the research of anti-HER-2-CAR-T cell immunotherapy against GC.

Clinical implications and mechanism of histopathological growth pattern in colorectal cancer liver metastases

Liver is the most common site of metastases of colorectal cancer, and liver metastases present with distinct histopathological growth patterns (HGPs), including desmoplastic, pushing and replacement HGPs and two rare HGPs. HGP is a miniature of tumor-host reaction and reflects tumor biology and pathological features as well as host immune dynamics. Many studies have revealed the association of HGPs with carcinogenesis, angiogenesis, and clinical outcomes and indicates HGP functions as bond between microscopic characteristics and clinical implications. These findings make HGP a candidate marker in risk stratification and guiding treatment decision-making, and a target of imaging observation for patient screening. Of note, it is crucial to determine the underlying mechanism shaping HGP, for instance, immune infiltration and extracellular matrix remodeling in desmoplastic HGP, and aggressive characteristics and special vascularization in replacement HGP (rHGP). We highlight the importance of aggressive features, vascularization, host immune and organ structure in formation of HGP, hence propose a novel "advance under camouflage" hypothesis to explain the formation of rHGP.

Hepatic lymphatic vascular system in health and disease

In recent years, significant advances have been made in the study of lymphatic vessels with the identification of their specific markers and the development of research tools that have accelerated our understanding of their role in tissue homeostasis and disease pathogenesis in many organs. Compared to other organs, the lymphatic system in the liver is understudied despite its obvious importance for hepatic physiology and pathophysiology. In this review, we describe fundamental aspects of the hepatic lymphatic system and its role in a range of liver-related pathological conditions such as portal hypertension, ascites formation, malignant tumours, liver transplantation, congenital liver diseases, non-alcoholic fatty liver disease, and hepatic encephalopathy. The article concludes with a discussion regarding the modulation of lymphangiogenesis as a potential therapeutic strategy for liver diseases.

The Crosstalk Between Liver Sinusoidal Endothelial Cells and Hepatic Microenvironment in NASH Related Liver Fibrosis

Chronic liver injury can be caused by many factors, including virus infection, alcohol intake, cholestasis and abnormal fat accumulation. Nonalcoholic steatohepatitis (NASH) has become the main cause of liver fibrosis worldwide. Recently, more and more evidences show that hepatic microenvironment is involved in the pathophysiological process of liver fibrosis induced by NASH. Hepatic microenvironment consists of various types of cells and intercellular crosstalk among different cells in the liver sinusoids. Liver sinusoidal endothelial cells (LSECs), as the gatekeeper of liver microenvironment, play an irreplaceable role in the homeostasis and alterations of liver microenvironment. Many recent studies have reported that during the progression of NASH to liver fibrosis, LSECs are involved in various stages mediated by a series of mechanisms. Therefore, here we review the key role of crosstalk between LSECs and hepatic microenvironment in the progression of NASH to liver fibrosis (steatosis, inflammation, and fibrosis), as well as promising therapeutic strategies targeting LSECs.

HBeAg Is Indispensable for Inducing Liver Sinusoidal Endothelial Cell Activation by Hepatitis B Virus

Background and Aims

Liver sinusoidal endothelial cells (LSECs) serve as sentinel cells to detect microbial infection and actively contribute to regulating immune responses for surveillance against intrahepatic pathogens. We recently reported that hepatitis B e antigen (HBeAg) stimulation could induce LSEC maturation and abrogate LSEC-mediated T cell suppression in a TNF-α and IL27 dependent manner. However, it remains unclear how HBeAg deficiency during HBV infection influences LSEC immunoregulation function and intrahepatic HBV-specific CD8 T cell responses.

Methods

The function of LSECs in regulating effector T cell response, intrahepatic HBV-specific CD8 T cell responses and HBV viremia were characterized in both HBeAg-deficient and -competent HBV hydrodynamic injection (HDI) mouse models.

Results

LSECs isolated from HBeAg-deficient HBV HDI mice showed a reduced capacity to promote T cell immunity in vitro compared with those isolated from wild-type HBV HDI mice. HBeAg expression replenishment in HBeAg-deficient HBV HDI mice restored the HBV-induced LSEC maturation, and resulted in potent intrahepatic anti-HBV CD8 T cell responses and efficient control of HBV replication. Moreover, in vivo TNF-α, but not IL27 blockade in HBV HDI mice impaired HBV-specific CD8 T cell immunity and delayed HBV clearance.

Conclusion

Our study underlines that HBeAg is indispensable for HBV-induced LSEC maturation to trigger intrahepatic HBV-specific T cell activation, and provides a new mechanism to elucidate the intrahepatic immune microenvironment regulation upon HBV exposure.

Seven mysteries of LAG-3: a multi-faceted immune receptor of increasing complexity

Despite three decades of research to its name and increasing interest in immunotherapies that target it, LAG-3 remains an elusive co-inhibitory receptor in comparison to the well-established PD-1 and CTLA-4. As such, LAG-3 targeting therapies have yet to achieve the clinical success of therapies targeting other checkpoints. This could, in part, be attributed to the many unanswered questions that remain regarding LAG-3 biology. Of these, we address: (i) the function of the many LAG-3-ligand interactions, (ii) the hurdles that remain to acquire a high-resolution structure of LAG-3, (iii) the under-studied LAG-3 signal transduction mechanism, (iv) the elusive soluble form of LAG-3, (v) the implications of the lack of (significant) phenotype of LAG-3 knockout mice, (vi) the reports of LAG-3 expression on the epithelium, and (vii) the conflicting reports of LAG-3 expression (and potential contributions to pathology) in the brain. These mysteries which surround LAG-3 highlight how the ever-evolving study of its biology continues to reveal ever-increasing complexity in its role as an immune receptor. Importantly, answering the questions which shroud LAG-3 in mystery will allow the maximum therapeutic benefit of LAG-3 targeting immunotherapies in cancer, autoimmunity and beyond.

Gut-liver-axis: Barrier function of liver sinusoidal endothelial cell

Liver diseases are associated with the leaky gut via the gut-liver-axis. Previous studies have paid much attention to the effect of gut barrier damage. Notably, clinical observations and basic research reveal that the gut barrier damage seldom leads to liver injury independently but aggravates pre-existing liver diseases such as non-alcoholic fatty liver disease and drug-induced liver injury. These evidences suggest that there is a hepatic barrier in the gut-liver-axis, protecting the liver against gut-derived pathogenic factors. However, it has never been investigated which type of liver cell plays the role of hepatic barrier. Under physiological conditions, liver sinusoidal endothelial cell (LSEC) can take up and eliminate virus, bacteriophage, microbial products, and metabolic wastes. LSEC also keeps the homeostasis of liver immune environment via tolerance-inducing and anti-inflammatory functions. In contrast, under pathological conditions, the clearance function of LSEC is impaired, and LSEC turns into a pro-inflammatory pattern. Given its anatomical position and physiological functions, LSEC is proposed as the hepatic barrier in the gut-liver-axis. In this review, we aim to further understand the role of LSEC as the hepatic barrier. Future studies are warranted to seek effective treatments to improve LSEC health, which appears to be a promising approach to prevent gut-derived liver injury.

Lymph Node-Targeted Synthetically Glycosylated Antigen Leads to Antigen-Specific Immunological Tolerance

Inverse vaccines that tolerogenically target antigens to antigen-presenting cells (APCs) offer promise in prevention of immunity to allergens and protein drugs and treatment of autoimmunity. We have previously shown that targeting hepatic APCs through intravenous injection of synthetically glycosylated antigen leads to effective induction of antigen-specific immunological tolerance. Here, we demonstrate that targeting these glycoconjugates to lymph node (LN) APCs under homeostatic conditions leads to local and increased accumulation in the LNs compared to unmodified antigen and induces a tolerogenic state both locally and systemically. Subcutaneous administration directs the polymeric glycoconjugate to the draining LN, where the glycoconjugated antigen generates robust antigen-specific CD4+ and CD8+ T cell tolerance and hypo-responsiveness to antigenic challenge via a number of mechanisms, including clonal deletion, anergy of activated T cells, and expansion of regulatory T cells. Lag-3 up-regulation on CD4+ and CD8+ T cells represents an essential mechanism of suppression. Additionally, presentation of antigen released from the glycoconjugate to naïve T cells is mediated mainly by LN-resident CD8+ and CD11b+ dendritic cells. Thus, here we demonstrate that antigen targeting via synthetic glycosylation to impart affinity for APC scavenger receptors generates tolerance when LN dendritic cells are the cellular target.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

SARS-CoV-2 exacerbates proinflammatory responses in myeloid cells through C-type lectin receptors and Tweety family member 2

Despite mounting evidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) engagement with immune cells, most express little, if any, of the canonical receptor of SARS-CoV-2, angiotensin-converting enzyme 2 (ACE2). Here, using a myeloid cell receptor-focused ectopic expression screen, we identified several C-type lectins (DC-SIGN, L-SIGN, LSECtin, ASGR1, and CLEC10A) and Tweety family member 2 (TTYH2) as glycan-dependent binding partners of the SARS-CoV-2 spike. Except for TTYH2, these molecules primarily interacted with spike via regions outside of the receptor-binding domain. Single-cell RNA sequencing analysis of pulmonary cells from individuals with coronavirus disease 2019 (COVID-19) indicated predominant expression of these molecules on myeloid cells. Although these receptors do not support active replication of SARS-CoV-2, their engagement with the virus induced robust proinflammatory responses in myeloid cells that correlated with COVID-19 severity. We also generated a bispecific anti-spike nanobody that not only blocked ACE2-mediated infection but also the myeloid receptor-mediated proinflammatory responses. Our findings suggest that SARS-CoV-2-myeloid receptor interactions promote immune hyperactivation, which represents potential targets for COVID-19 therapy.

Role of liver sinusoidal endothelial cells in liver diseases

Liver sinusoidal endothelial cells (LSECs) form the wall of the hepatic sinusoids. Unlike other capillaries, they lack an organized basement membrane and have cytoplasm that is penetrated by open fenestrae, making the hepatic microvascular endothelium discontinuous. LSECs have essential roles in the maintenance of hepatic homeostasis, including regulation of the vascular tone, inflammation and thrombosis, and they are essential for control of the hepatic immune response. On a background of acute or chronic liver injury, LSECs modify their phenotype and negatively affect neighbouring cells and liver disease pathophysiology. This Review describes the main functions and phenotypic dysregulations of LSECs in liver diseases, specifically in the context of acute injury (ischaemia-reperfusion injury, drug-induced liver injury and bacterial and viral infection), chronic liver disease (metabolism-associated liver disease, alcoholic steatohepatitis and chronic hepatotoxic injury) and hepatocellular carcinoma, and provides a comprehensive update of the role of LSECs as therapeutic targets for liver disease. Finally, we discuss the open questions in the field of LSEC pathobiology and future avenues of research.

The cellular and molecular components involved in pre-metastatic niche formation in colorectal cancer liver metastasis

Introduction: Liver metastasis is the main cause of death in colorectal cancer (CRC). Premetastatic niche (PMN), a favorable microenvironment for cancer cells colonization at the distant organ, plays a pivotal role in CRC liver metastasis (CRCLM). Our understanding of the mechanisms mediating the formation of liver PMN in CRC has been significantly advanced in recent years, there are still many challenges and questions that remain.Areas covered: This review covers cellular and molecular components, and the interaction of theprimary cancer with the resident microenvironment of the distant organ that leads to PMN formation in CRCLM based on the latest literature.Expert Opinion: Various cellular and molecular events are involved in the liver PMN formation in CRC such as bone marrow-derived cells (BMDCs), hepatic stellate cells, Kupffer cells, extracellular matrix, and CRC-derived factors. The formation of the liver PMN depends on a complex interaction of CRC with the liver microenvironment including BMDCs recruitment, vascularization, immunosuppression, inflammatory response, and extracellular matrix remodeling. This review firstly discusses on the cellular and molecular components contributing to the formation of the liver PMN in CRC, so as to provide new ideas for designing effective therapeutic strategies and prognostic markers for CRCLM.

Transcriptomic analysis reveals the molecular mechanisms of rumen wall morphological and functional development induced by different solid diet introduction in a lamb model

Background

This study aimed to elucidate the molecular mechanisms of solid diet introduction initiating the cellular growth and maturation of rumen tissues and characterize the shared and unique biological processes upon different solid diet regimes.

Methods

Twenty-four Hu lambs were randomly allocated to three groups fed following diets: goat milk powder only (M, n = 8), goat milk powder + alfalfa hay (MH, n = 8), and goat milk powder + concentrate starter (MC, n = 8). At 42 days of age, the lambs were slaughtered. Ruminal fluid sample was collected for analysis of concentration of volatile fatty acid (VFA) and microbial crude protein (MCP). The sample of the rumen wall from the ventral sac was collected for analysis of rumen papilla morphology and transcriptomics.

Results

Compared with the M group, MH and MC group had a higher concentration of VFA, MCP, rumen weight, and rumen papilla area. The transcriptomic results of rumen wall showed that there were 312 shared differentially expressed genes (DEGs) between in “MH vs. M” and “MC vs. M”, and 232 or 796 unique DEGs observed in “MH vs. M” or “MC vs. M”, respectively. The shared DEGs were most enriched in VFA absorption and metabolism, such as peroxisome proliferator-activated receptor (PPAR) signaling pathway, butanoate metabolism, and synthesis and degradation of ketone bodies. Additionally, a weighted gene co-expression network analysis identified M16 (2,052 genes) and M18 (579 genes) modules were positively correlated with VFA and rumen wall morphology. The M16 module was mainly related to metabolism pathway, while the M18 module was mainly associated with signaling transport. Moreover, hay specifically depressed expression of genes involved in cytokine production, immune response, and immunocyte activation, and concentrate starter mainly altered nutrient transport and metabolism, especially ion transport, amino acid, and fatty acid metabolism.

Conclusions

The energy production during VFA metabolism may drive the rumen wall development directly. The hay introduction facilitated establishment of immune function, while the concentrate starter enhanced nutrient transport and metabolism, which are important biological processes required for rumen development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00556-4.

Understanding, predicting and achieving liver transplant tolerance: from bench to bedside

In the past 40 years, liver transplantation has evolved from a high-risk procedure to one that offers high success rates for reversal of liver dysfunction and excellent patient and graft survival. The liver is the most tolerogenic of transplanted organs; indeed, immunosuppressive therapy can be completely withdrawn without rejection of the graft in carefully selected, stable long-term liver recipients. However, in other recipients, chronic allograft injury, late graft failure and the adverse effects of anti-rejection therapy remain important obstacles to improved success. The liver has a unique composition of parenchymal and immune cells that regulate innate and adaptive immunity and that can promote antigen-specific tolerance. Although the mechanisms underlying liver transplant tolerance are not well understood, important insights have been gained into how the local microenvironment, hepatic immune cells and specific molecular pathways can promote donor-specific tolerance. These insights provide a basis for the identification of potential clinical biomarkers that might correlate with tolerance or rejection and for the development of novel therapeutic targets. Innovative approaches aimed at promoting immunosuppressive drug minimization or withdrawal include the adoptive transfer of donor-derived or recipient-derived regulatory immune cells to promote liver transplant tolerance. In this Review, we summarize and discuss these developments and their implications for liver transplantation.

Molecular Recognition in C-Type Lectins: The Cases of DC-SIGN, Langerin, MGL, and L-Sectin

Carbohydrates play a pivotal role in intercellular communication processes. In particular, glycan antigens are key for sustaining homeostasis, helping leukocytes to distinguish damaged tissues and invading pathogens from healthy tissues. From a structural perspective, this cross-talk is fairly complex, and multiple membrane proteins guide these recognition processes, including lectins and Toll-like receptors. Since the beginning of this century, lectins have become potential targets for therapeutics for controlling and/or avoiding the progression of pathologies derived from an incorrect immune outcome, including infectious processes, cancer, or autoimmune diseases. Therefore, a detailed knowledge of these receptors is mandatory for the development of specific treatments. In this review, we summarize the current knowledge about four key C-type lectins whose importance has been steadily growing in recent years, focusing in particular on how glycan recognition takes place at the molecular level, but also looking at recent progresses in the quest for therapeutics.

Clinical significance of LSECtin and its association with PVR in non-small-cell lung cancer patients

BACKGROUND

Liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin) is one of the new generation immune checkpoint ligand molecules and plays an important role in the immune environment. Poliovirus receptor (PVR), as another immunosuppression-related molecule, is upregulated in various malignant tumors. However, the clinical value of LSECtin and the correlation of LSECtin with PVR in non-small-cell lung cancer (NSCLC) remain to be elucidated. In this study, a retrospective study was performed to address these issues.

METHODS

This retrospective study included 98 patients with NSCLC. Immunohistochemistry (IHC) was used to detect the expression of LSECtin and PVR in the paraffin-embedded tumor tissue specimens. LSECtin was analyzed for associations with the survival rate and overall survival (OS) of the subjects. The mRNA expression of LSECtin and PVR was assessed using the expression data from The Cancer Genome Atlas (TCGA) database. Clinical characteristics, prognosis, and the expression of LSECtin and PVR were included in the statistical analysis.

RESULTS

High positive rates of LSECtin were found in the patients with NSCLC who were nonsmokers, at advanced stages, or had lung adenocarcinoma. Patients with positive LSECtin expression had a significantly lower survival rate (P=0.008) and shorter OS (P=0.017) than those with negative LSECtin. Significant correlation was found between the LSECtin and PVR expression in the patients with NSCLC (P<0.001).

CONCLUSIONS

The increased expression of LSECtin was related to the poor prognosis of patients with NSCLC after tumor resection and has the potential value for predicting the prognosis of these patients. The positive correlation between LSECtin and PVR in NSCLC provides a theoretical basis for the future combination therapy of immune checkpoints.

Activation of mTORC1 by LSECtin in macrophages directs intestinal repair in inflammatory bowel disease

Damage to intestinal epithelial cells and the induction of cellular apoptosis are characteristics of inflammatory bowel disease. The C-type lectin receptor family member LSECtin promotes apoptotic cell clearance by macrophages and induces the production of anti-inflammatory/tissue growth factors, which direct intestinal repair in experimental colitis. However, the mechanisms by which the phagocytosis of apoptotic cells triggers the pro-repair function of macrophages remain largely undefined. Here, using immunoprecipitation in combination with mass spectrometry to identify LSECtin-interacting proteins, we found that LSECtin interacted with mTOR, exhibiting a role in activating mTORC1. Mechanistically, apoptotic cells enhance the interaction between LSECtin and mTOR, and increase the activation of mTORC1 induced by LSECtin in macrophages. Elevated mTORC1 signaling triggers macrophages to produce anti-inflammatory/tissue growth factors that contribute to the proliferation of epithelial cells and promote the reestablishment of tissue homeostasis. Collectively, our findings suggest that LSECtin-dependent apoptotic cell clearance by macrophages activates mTORC1, and thus contributes to intestinal regeneration and the remission of colitis.

Live Imaging of Innate and Adaptive Immune Responses in the Liver

Immune response in the liver is determined by the spatial organization and cellular dynamics of hepatic immune cells. The liver vasculature accommodates abundant tissue-resident innate immune cells, such as Kupffer cells, natural killer cells, and natural killer T cells, to ensure efficient intravascular immunosurveillance. The fenestrated sinusoids also allow direct contact between circulating T cells and non-canonical antigen-presenting cells, such as hepatocytes, to instruct adaptive immune responses. Distinct cellular behaviors are exploited by liver immune cells to exert proper functions. Intravital imaging enables real-time visualization of individual immune cell in living animals, representing a powerful tool in dissecting the spatiotemporal features of intrahepatic immune cells during steady state and liver diseases. This review summarizes current advances in liver immunology prompted by in vivo imaging, with a particular focus on liver-resident innate immune cells and hepatic T cells.

The tumor microenvironment of colorectal cancer metastases: opportunities in cancer immunotherapy

About a fifth of individuals with colorectal cancer (CRC) present with disease metastasis at the time of diagnosis. While the role of the tumor microenvironment (TME) in governing CRC progression is undeniable, the role of the TME in either establishing or suppressing the formation of distant metastases of CRC is less well established. Despite advances in immunotherapy, many individuals with metastatic CRC do not respond to standard-of-care therapy. Therefore, understanding the role of the TME in establishing distant metastases is essential for developing new immunological agents. Here, we summarize our current understanding of the TME of CRC metastases, describe differences between the TME of primary tumors and their distant metastases, and discuss advances in the design and combinations of immunotherapeutic agents.

Prominent Receptors of Liver Sinusoidal Endothelial Cells in Liver Homeostasis and Disease

Liver sinusoidal endothelial cells (LSECs) are the most abundant non-parenchymal cells lining the sinusoidal capillaries of the hepatic system. LSECs are characterized with numerous fenestrae and lack basement membrane as well as a diaphragm. These unique morphological characteristics of LSECs makes them the most permeable endothelial cells of the mammalian vasculature and aid in regulating flow of macromolecules and small lipid-based structures between sinusoidal blood and parenchymal cells. LSECs have a very high endocytic capacity aided by scavenger receptors (SR), such as SR-A, SR-B (SR-B1 and CD-36), SR-E (Lox-1 and mannose receptors), and SR-H (Stabilins). Other high-affinity receptors for mediating endocytosis include the FcγRIIb, which assist in the antibody-mediated removal of immune complexes. Complemented with intense lysosomal activity, LSECs play a vital role in the uptake and degradation of many blood borne waste macromolecules and small (<280 nm) colloids. Currently, seven Toll-like receptors have been investigated in LSECs, which are involved in the recognition and clearance of pathogen-associated molecular pattern (PAMPs) as well as damage associated molecular pattern (DAMP). Along with other SRs, LSECs play an essential role in maintaining lipid homeostasis with the low-density lipoprotein receptor-related protein-1 (LRP-1), in juxtaposition with hepatocytes. LSECs co-express two surface lectins called L-Specific Intercellular adhesion molecule-3 Grabbing Non-integrin Receptor (L-SIGN) and liver sinusoidal endothelial cell lectin (LSECtin). LSECs also express several adhesion molecules which are involved in the recruitment of leukocytes at the site of inflammation. Here, we review these cell surface receptors as well as other components expressed by LSECs and their functions in the maintenance of liver homeostasis. We further discuss receptor expression and activity and dysregulation associated with the initiation and progression of many liver diseases, such as hepatocellular carcinoma, liver fibrosis, and cirrhosis, alcoholic and non-alcoholic fatty liver diseases and pseudocapillarization with aging.

Histopathological growth patterns correlate with the immunoscore in colorectal cancer liver metastasis patients after hepatectomy

Various scoring systems have been proposed to predict the postoperative prognosis of colorectal liver metastasis (CRLM), including the clinical risk score (CRS), the immunoscore and so on. Recently, histopathological growth patterns (HGPs) have been recognized. However, the correlation between HGPs and the immunoscore, and their prognostic values in patients with CRLM after liver resection remain undetermined. In this study, HGPs were retrospectively evaluated in H&E-stained slides from 166 CRLM patients. The immunoscore was calculated according to the densities of immunostained CD3 + and CD8 + cells. A risk score combining HGPs, the immunoscore and the CRS was defined and divided patients into the low-, medium- and high-risk group. Our results showed that the densities of CD3 + and CD8 + cells were higher in the desmoplastic HGP (dHGP) group than in the non-dHGP group, and the proportion of high immunoscores was also higher in the dHGP group (51.9% vs. 33.0%, respectively, P = 0.020). Patients with the dHGP had significantly longer relapse-free survival (RFS) and overall survival (OS) than those with the non-HGP. The low-risk group showed significantly higher 2-year RFS and 5-year OS rates than the other two groups (RFS: 76.2%, 43.7% and 33.1%, respectively; P < 0.001; OS: 89.7%, 54.4% and 33.3%, respectively; P < 0.001). In conclusion, the dHGP correlates with relatively high immunoscores, predicting a favorable prognosis independent of the immunoscore and CRS. A novel risk score combining HGPs, the immunoscore and the CRS may be used for the stratification of CRLM patients' survival.

The Role of Diverse Liver Cells in Liver Transplantation Tolerance

Liver transplantation is the ideal treatment approach for a variety of end-stage liver diseases. However, life-long, systemic immunosuppressive treatment after transplantation is required to prevent rejection and graft loss, which is associated with severe side effects, although liver allograft is considered more tolerogenic. Therefore, understanding the mechanism underlying the unique immunologically privileged liver organ is valuable for transplantation management and autoimmune disease treatment. The unique hepatic acinus anatomy and a complex cellular network constitute the immunosuppressive hepatic microenvironment, which are responsible for the tolerogenic properties of the liver. The hepatic microenvironment contains a variety of hepatic-resident immobile non-professional antigen-presenting cells, including hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, and hepatic stellate cells, that are insufficient to optimally prime T cells locally and lead to the removal of alloreactive T cells due to the low expression of major histocompatibility complex (MHC) molecules, costimulatory molecules and proinflammatory cytokines but a rather high expression of coinhibitory molecules and anti-inflammatory cytokines. Hepatic dendritic cells (DCs) are generally immature and less immunogenic than splenic DCs and are also ineffective in priming naïve allogeneic T cells via the direct recognition pathway in recipient secondary lymphoid organs. Although natural killer cells and natural killer T cells are reportedly associated with liver tolerance, their roles in liver transplantation are multifaceted and need to be further clarified. Under these circumstances, T cells are prone to clonal deletion, clonal anergy and exhaustion, eventually leading to tolerance. Other proposed liver tolerance mechanisms, such as soluble donor MHC class I molecules, passenger leukocytes theory and a high-load antigen effect, have also been addressed. We herein comprehensively review the current evidence implicating the tolerogenic properties of diverse liver cells in liver transplantation tolerance.

Transplant Tolerance Induction: Insights From the Liver

A comparison of pre-clinical transplant models and of solid organs transplanted in routine clinical practice demonstrates that the liver is most amenable to the development of immunological tolerance. This phenomenon arises in the absence of stringent conditioning regimens that accompany published tolerizing protocols for other organs, particularly the kidney. The unique immunologic properties of the liver have assisted our understanding of the alloimmune response and how it can be manipulated to improve graft function and survival. This review will address important findings following liver transplantation in both animals and humans, and how these have driven the understanding and development of therapeutic immunosuppressive options. We will discuss the liver's unique system of immune and non-immune cells that regulate immunity, yet maintain effective responses to pathogens, as well as mechanisms of liver transplant tolerance in pre-clinical models and humans, including current immunosuppressive drug withdrawal trials and biomarkers of tolerance. In addition, we will address innovative therapeutic strategies, including mesenchymal stem cell, regulatory T cell, and regulatory dendritic cell therapy to promote liver allograft tolerance or minimization of immunosuppression in the clinic.

Liver Sinusoidal Endothelial Cells Contribute to Hepatic Antigen-Presenting Cell Function and Th17 Expansion in Cirrhosis

Hepatic immune function is compromised during cirrhosis. This study investigated the immune features of liver sinusoidal endothelial cells (LSECs) in two experimental models of cirrhosis. Dendritic cells, hepatic macrophages, and LSECs were isolated from carbon tetrachloride and bile duct-ligated rats. Gene expression of innate receptors, bacterial internalization, co-stimulatory molecules induction, and CD4+ T cell activation and differentiation were evaluated. Induced bacterial peritonitis and norfloxacin protocols on cirrhotic rats were also carried out. LSECs demonstrated an active immunosurveillance profile, as shown by transcriptional modulation of different scavenger and cell-adhesion genes, and their contribution to bacterial internalization. LSECs significantly increased their expression of CD40 and CD80 and stimulated CD4+ T cell activation marker CD71 in both models. The pro-inflammatory Th17 subset was expanded in CCl₄-derived LSECs co-cultures. In the bile duct ligation (BDL) model, CD4+ T cell differentiation only occurred under induced bacterial peritonitis conditions. Differentiated pro-inflammatory Th cells by LSECs in both experimental models were significantly reduced with norfloxacin treatment, whereas Foxp3 tolerogenic Th CD4+ cells were expanded. Conclusion: LSECs’ participation in the innate-adaptive immune progression, their ability to stimulate pro-inflammatory CD4+ T cells expansion during liver damage, and their target role in norfloxacin-induced immunomodulation granted a specific competence to this cell population in cirrhosis.

In the presence of Trypanosoma cruzi antigens, activated peripheral T lymphocytes retained in the liver induce a proinflammatory phenotypic and functional shift in intrahepatic T lymphocyte

In secondary lymphoid organs, pathogen‐derived and endogenous danger molecules are recognized by pattern recognition receptors, leading to adaptive proinflammatory immune responses. This conceptual rule does not apply directly to the liver, as hepatic immune cells tolerate gut‐derived bacterial molecules from the flora. Therefore, the recognition of danger and proinflammatory stimuli differs between the periphery and the liver. However, the tolerant nature of the liver must be overcome in the case of infections or cancer, for example. The central paradigm is the basis for danger recognition and the balance between inflammation and tolerance in the liver. Here, we observed functional integration, with activated peripheral T lymphocytes playing a role in the induction of a proinflammatory environment in the liver in the presence of Trypanosoma cruzi antigens. When only parasite extract was orally administered, it led to the up‐regulation of hepatic tolerance markers, but oral treatment plus adoptively transferred activated splenic T lymphocytes led to a proinflammatory response. Moreover, treated/recipient mice showed increased levels of TNF, IFN‐γ, IL‐6, and CCL2 in the liver and increased numbers of effector and/or effector memory T lymphocytes and F4/80⁺ cells. There was a reduction in FoxP3⁺ Treg cells, NKT cells, and γδ T lymphocytes with increased liver damage in the presence of activated peripheral T cells. Our results show that the induction of a proinflammatory liver response against T. cruzi danger molecules is at least partially dependent on cooperation with activated peripheral T cells.

Mechanisms of Immune Tolerance in Liver Transplantation-Crosstalk Between Alloreactive T Cells and Liver Cells With Therapeutic Prospects

Liver transplantation (LTx) is currently the most powerful treatment for end-stage liver disease. Although liver allograft is more tolerogenic compared to other solid organs, the majority of LTx recipients still require long-term immune suppression (IS) to control the undesired alloimmune responses, which can lead to severe side effects. Thus, understanding the mechanism of liver transplant tolerance and crosstalk between immune cells, especially alloreactive T cells and liver cells, can shed light on more specific tolerance induction strategies for future clinical translation. In this review, we focus on alloreactive T cell mediated immune responses and their crosstalk with liver sinusoidal endothelial cells (LSECs), hepatocytes, hepatic stellate cells (HSCs), and cholangiocytes in transplant setting. Liver cells mainly serve as antigen presenting cells (APCs) to T cells, but with low expression of co-stimulatory molecules. Crosstalk between them largely depends on the different expression of adhesion molecules and chemokine receptors. Inflammatory cytokines secreted by immune cells further elaborate this crosstalk and regulate the fate of naïve T cells differentiation within the liver graft. On the other hand, regulatory T cells (Tregs) play an essential role in inducing and keeping immune tolerance in LTx. Tregs based adoptive cell therapy provides an excellent therapeutic option for clinical transplant tolerance induction. However, many questions regarding cell therapy still need to be solved. Here we also address the current clinical trials of adoptive Tregs therapy and other tolerance induction strategies in LTx, together with future challenges for clinical translation from bench to bedside.

Sensitivity of Kupffer cells and liver sinusoidal endothelial cells to ricin toxin and ricin toxin-Ab complexes

Ricin toxin is a plant-derived, ribosome-inactivating protein that is rapidly cleared from circulation by Kupffer cells (KCs) and liver sinusoidal endothelial cells (LSECs)-with fatal consequences. Rather than being inactivated, ricin evades normal degradative pathways and kills both KCs and LSECs with remarkable efficiency. Uptake of ricin by these 2 specialized cell types in the liver occurs by 2 parallel routes: a "lactose-sensitive" pathway mediated by ricin's galactose/N-acetylgalactosamine-specific lectin subunit (RTB), and a "mannose-sensitive" pathway mediated by the mannose receptor (MR; CD206) or other C-type lectins capable of recognizing the mannose-side chains displayed on ricin's A (RTA) and B subunits. In this report, we investigated the capacity of a collection of ricin-specific mouse MAb and camelid single-domain (VH H) antibodies to protect KCs and LSECs from ricin-induced killing. In the case of KCs, individual MAbs against RTA or RTB afforded near complete protection against ricin in ex vivo and in vivo challenge studies. In contrast, individual MAbs or VH Hs afforded little (<40%) or even no protection to LSECs against ricin-induced death. Complete protection of LSECs was only achieved with MAb or VH H cocktails, with the most effective mixtures targeting RTA and RTB simultaneously. Although the exact mechanisms of protection of LSECs remain unknown, evidence indicates that the Ab cocktails exert their effects on the mannose-sensitive uptake pathway without the need for Fcγ receptor involvement. In addition to advancing our understanding of how toxins and small immune complexes are processed by KCs and LSECs, our study has important implications for the development of Ab-based therapies designed to prevent or treat ricin exposure should the toxin be weaponized.

Characterization of a novel anti-human lymphocyte activation gene 3 (LAG-3) antibody for cancer immunotherapy

Lymphocyte activation gene 3 (LAG-3) is expressed on activated T cells, natural killer cells or B cells, and functions to negatively regulate homeostasis of these cells. Anti-LAG-3 antibodies might be useful for antitumor immunotherapy. In this study, we characterized a novel anti-LAG-3 antibody, LBL-007, which was isolated from a human antibody phage display library. LBL-007 was found to specifically bind to human LAG-3 antigen, but not to human CD4 or mouse LAG-3. LBL-007 bound activated T cells and promoted interleukin-2 secretion. LBL-007 internalization efficacy by endocytosis into different cells was better than that of another anti-LAG-3 antibody, relatlimab analog. Moreover, LBL-007 was able to block LAG-3 binding to MHC class II molecules and liver sinusoidal endothelial cell lectin, and block LAG-3-induced downstream signaling. In mice transplanted with colorectal cancer cells, treatment with either anti-PD-1 antibody or LBL-007 (10 mg/kg per mouse twice a week for three weeks) resulted in a significant delay in tumor growth compared with control IgG treatment, and their combination was even more effective. Serum LBL-007 levels were highly stable in monkeys after a single intravenous injection of LBL-007 at 3, 10, or 30 mg/kg. This study demonstrated that the combination of LBL-007 with an anti-PD-1 antibody is a promising antitumor regimen for immunotherapy of solid tumors in future that deserves further study.

Metastasis Organotropism: Redefining the Congenial Soil

Metastasis is the most devastating stage of cancer progression and causes the majority of cancer-related deaths. Clinical observations suggest that most cancers metastasize to specific organs, a process known as "organotropism." Elucidating the underlying mechanisms may help identify targets and treatment strategies to benefit patients. This review summarizes recent findings on tumor-intrinsic properties and their interaction with unique features of host organs, which together determine organ-specific metastatic behaviors. Emerging insights related to the roles of metabolic changes, the immune landscapes of target organs, and variation in epithelial-mesenchymal transitions open avenues for future studies of metastasis organotropism.

LSECtin on tumor-associated macrophages enhances breast cancer stemness via interaction with its receptor BTN3A3

Macrophages have been suggested to contribute to constructing a cancer stem cell (CSC) niche. However, whether and how macrophages regulate the activity of CSCs through juxtacrine signaling are poorly understood. Here we report LSECtin, a transmembrane protein highly expressed on tumor-associated macrophages (TAMs), enhances stemness of breast cancer cells (BCCs). We identified BTN3A3, a B7 family member with previously unknown functions as the receptor for LSECtin on BCCs responsible for stemness-promoting effect of LSECtin. In mice bearing human tumor xenografts, either macrophage-specific ablation of LSECtin or silencing of BTN3A3 in BCCs decreased CSC frequency and tumor growth. Admixture of LSECtin-positive macrophages increased the tumorigenic activity of BCCs dependent on BTN3A3. Disruption of the LSECtin-BTN3A3 axis with BTN3A3-Fc or anti-BTN3A3 mAb has a therapeutic effect on breast cancer. These findings define a juxtacrine signaling mechanism by which TAMs promote cancer stemness. Targeting this axis in the CSC niche may provide potential therapies to breast cancer.