Liver-resident NK cells and their potential functions

Lung-resident CD3-NK1.1+CD69+CD103+ Cells Play an Important Role in Bacillus Calmette-Guérin Vaccine-Induced Protective Immunity against Mycobacterium tuberculosis Infection

Tissue-resident immune cells play important roles in local tissue homeostasis and infection control. There is no information on the functional role of lung-resident CD3-NK1.1+CD69+CD103+ cells in intranasal Bacillus Calmette-Guérin (BCG)-vaccinated and/or Mycobacterium tuberculosis (Mtb)-infected mice. Therefore, we phenotypically and functionally characterized these cells in mice vaccinated intranasally with BCG. We found that intranasal BCG vaccination increased CD3-NK1.1+ cells with a tissue-resident phenotype (CD69+CD103+) in the lungs during the first 7 d after BCG vaccination. Three months post-BCG vaccination, Mtb infection induced the expansion of CD3-NK1.1+CD69+CD103+ (lung-resident) cells in the lung. Adoptive transfer of lung-resident CD3-NK1.1+CD69+CD103+ cells from the lungs of BCG-vaccinated mice to Mtb-infected naive mice resulted in a lower bacterial burden and reduced inflammation in the lungs. Our findings demonstrated that intranasal BCG vaccination induces the expansion of CD3-NK1.1+CD69+CD103+ (lung-resident) cells to provide protection against Mtb infection.

Tissue damage from chronic liver injury inhibits peripheral NK cell abundance and proinflammatory function

One of the difficulties in the treatment of hepatocellular carcinoma is that it is impossible to eliminate the inhibitory effect of the tumor microenvironment on immune response. Therefore, it is particularly important to understand the formation process of the tumor microenvironment. Chronic inflammation is the core factor of cancer occurrence and the leading stage of inflammation-cancer transformation, and the natural killer cell subsets play an important role in it. Our study confirmed that in the stage of chronic liver injury, the local immunosuppressive microenvironment of the liver (i.e. the damaged microenvironment) has been formed, but this inhibitory effect is only for peripheral natural killer cells and has no effect on tissue-resident natural killer subsets. The markers of damage microenvironment are the same as those of tumor microenvironment.

Cancer immunity by tissue-resident type 1 innate lymphoid cells and killer innate-like T cells

Cancer progression can be restrained by tumor-infiltrating lymphocytes in a process termed cancer immunosurveillance. Based on how lymphocytes are activated and recruited to the tumor tissue, cancer immunity is either pre-wired, in which innate lymphocytes and innate-like T cells are directly recruited to and activated in tumors following their differentiation in primary lymphoid organs; or priming-dependent, in which conventional adaptive T cells are first primed by cognate antigens in secondary lymphoid organs before homing to and reactivated in tumors. While priming-dependent cancer immunity has been a focus of cancer immunology research for decades, in part due to historical preconception of cancer theory and tumor model choice as well as clinical success of conventional adaptive T cell-directed therapeutic programs, recent studies have revealed that pre-wired cancer immunity mediated by tissue-resident type 1 innate lymphoid cells (ILC1s) and killer innate-like T cells (ILTCKs) is an integral component of the cancer immunosurveillance process. Herein we review the distinct ontogenies and cancer-sensing mechanisms of ILC1s and ILTCKs in murine genetic cancer models as well as the conspicuously conserved responses in human malignancies. How ILC1s and ILTCKs may be targeted to broaden the scope of cancer immunotherapy beyond conventional adaptive T cells is also discussed.

Immunoprotection of cellular transplants for autoimmune type 1 diabetes through local drug delivery

Type 1 diabetes mellitus (T1DM) is an autoimmune condition that results in the destruction of insulin-secreting β cells of the islets of Langerhans. Allogeneic islet transplantation could be a successful treatment for T1DM; however, it is limited by the need for effective, permanent immunosuppression to prevent graft rejection. Upon transplantation, islets are rejected through non-specific, alloantigen specific, and recurring autoimmune pathways. Immunosuppressive agents used for islet transplantation are generally successful in inhibiting alloantigen rejection, but they are suboptimal in hindering non-specific and autoimmune pathways. In this review, we summarize the challenges with cellular immunological rejection and therapeutics used for islet transplantation. We highlight agents that target these three immune rejection pathways and how to package them for controlled, local delivery via biomaterials. Exploring macro-, micro-, and nano-scale immunomodulatory biomaterial platforms, we summarize their advantages, challenges, and future directions. We hypothesize that understanding their key features will help identify effective platforms to prevent islet graft rejection. Outcomes can further be translated to other cellular therapies beyond T1DM.

Single-cell transcriptome analysis of aging mouse liver

Aging has a great impact on the liver, which causes a loss of physiological integrity and an increase in susceptibility to injury, but many of the underlying molecular and cellular processes remain unclear. Here, we performed a comprehensive single-cell transcriptional profiling of the liver during aging. Our data showed that aging affected the cellular composition of the liver. The increase in inflammatory cells including neutrophils and monocyte-derived macrophages, as well as in inflammatory cytokines, could indicate an inflammatory tissue microenvironment in aged livers. Moreover, aging drove a distinct transcriptional course in each cell type. The commonly significant up-regulated genes were S100a8, S100a9, and RNA-binding motif protein 3 across all cell types. Aging-related pathways such as biosynthesis, metabolism, and oxidative stress were up-regulated in aged livers. Additionally, key ligand-receptor pairs for intercellular communication, primarily linked to macrophage migration inhibitory factor, transforming growth factor-β, and complement signaling, were also elevated. Furthermore, hepatic stellate cells (HSCs) serve as the prominent hub for intrahepatic signaling. HSCs acquired an "activated" phenotype, which may be involved in the increased intrahepatic vascular tone and fibrosis with aging. Liver sinusoidal endothelial cells derived from aged livers were pseudocapillarized and procontractile, and exhibited down-regulation of genes involved in vascular development and homeostasis. Moreover, the aging-related changes in cellular composition and gene expression were reversed by caloric restriction. Collectively, the present study suggests liver aging is linked to a significant liver sinusoidal deregulation and a moderate pro-inflammatory state, providing a potential concept for understanding the mechanism of liver aging.

Single-cell dynamics of liver development in postnatal pigs

The postnatal development of the liver, an essential organ for metabolism and immunity, remains poorly characterized at the single-cell resolution. Here, we generated single-nucleus and single-cell transcriptomes of 84,824 pig liver cells at four postnatal time points: day 30, 42, 150, and 730. We uncovered 23 cell types, including three rare cell types: plasmacytoid dendritic cells, CAVIN3+IGF2+ endothelial cells, and EBF1+ fibroblasts. The latter two were verified by multiplex immunohistochemistry. Trajectory and gene regulatory analyses revealed 33 genes that encode transcription factors associated with hepatocyte development and function, including NFIL3 involved in regulating hepatic metabolism. We characterized the spatiotemporal heterogeneity of liver endothelial cells, identified and validated leucine zipper protein 2 (LUZP2) as a novel adult liver sinusoidal endothelial cell-specific transcription factor. Lymphoid cells (NK and T cells) governed the immune system of the pig liver since day 30. Furthermore, we identified a cluster of tissue-resident NK cells, which displayed virus defense functions, maintained proliferative features at day 730, and manifested a higher conservative transcription factor expression pattern in humans than in mouse liver. Our study presents the most comprehensive postnatal liver development single-cell atlas and demonstrates the metabolic and immune changes across the four age stages.

Sirtuin 2 up-regulation suppresses the anti-tumour activity of exhausted natural killer cells in mesenteric lymph nodes in murine colorectal carcinoma

Natural killer (NK) cells inhibit colorectal carcinoma (CRC) initiation and progression through their tumoricidal activity. However, cumulative evidence suggests that NK cells become functionally exhausted in patients with CRC. To deepen the understanding of the mechanisms underlying CRC-associated NK cell exhaustion, we explored the expression and effect of Sirtuin 2 (Sirt2) in mesenteric lymph node (mLN) NK cells in a murine colitis-associated CRC model. Sirt2 was remarkably up-regulated in mLN NK cells after CRC induction. Particularly, Sirt2 was increased in mLN NK cells expressing high T cell immunoglobulin and mucin domain-3 (TIM3), high lymphocyte activation protein-3 (LAG3), high programmed death-1 (PD-1), high T cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT), high NK group 2 member A (NKG2A), but low tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), low interferon-gamma and low granzyme B. In addition, Sirt2 was also increased in NK cells after induction of exhaustion in vitro. Lentivirus-mediated Sirt2 silencing did not affect the acute activation and cytotoxicity of non-exhausted NK cells. However, Sirt2 silencing partially restored the expression of interferon-gamma, granzyme B and CD107a in exhausted NK cells. Meanwhile, Sirt2 silencing down-regulated TIM3, LAG3, TIGIT and NKG2A while up-regulated TRAIL on exhausted NK cells. Consequently, Sirt2 silencing restored the cytotoxicity of exhausted NK cells. Moreover, Sirt2 silencing partially ameliorates the defects in glycolysis and mitochondrial respiration of exhausted NK cells, as evidenced by increases in glycolytic capacity, glycolytic reserve, basal respiration, maximal respiration and spare respiration capacity. Accordingly, Sirt2 negatively regulates the tumoricidal activity of exhausted NK cells in CRC.

Environmental eustress promotes liver regeneration through the sympathetic regulation of type 1 innate lymphoid cells to increase IL-22 in mice

BACKGROUND AND AIMS

The liver has the unique ability of regeneration, which is extremely important for restoring homeostasis after liver injury. Although clinical observations have revealed an association between psychological stress and the liver, whether stress has a causal influence on the liver regeneration remains markedly less defined.

APPROACH AND RESULTS

Rearing rodents in an enriched environment (EE) can induce eustress or positive psychological stress. Herein, EE-induced eustress was found to significantly enhance the ability of liver regeneration after partial hepatectomy or carbon tetrachloride-induced liver injury based on the more rapid restoration of liver/body weight ratio and the significantly increased number of proliferating hepatocytes in EE mice. Mechanistically, the cytokine array revealed that IL-22 was markedly increased in the regenerating liver in response to EE. Blockade of IL-22 signaling abrogated the enhanced liver regeneration induced by EE. Group 1 innate lymphoid cells (ILCs), including type 1 ILCs (ILC1s), have been identified as the major sources of IL-22 in the regenerating liver. EE housing led to a rapid accumulation of hepatic ILC1s after partial hepatectomy and the EE-induced enhancement of liver regeneration and elevation of IL-22 was nearly eliminated in ILC1-deficient Tbx21-/- mice. Chemical sympathectomy or blockade of β-adrenergic signaling also abolished the effect of EE on ILC1s and attenuated the enhanced liver regeneration of EE-housed mice.

CONCLUSION

The study findings support the brain-liver axis and suggest that environment-induced eustress promotes liver regeneration through the sympathetic nerve/ILC1/IL-22 axis.

The Important Roles of Natural Killer Cells in Liver Fibrosis

Liver fibrosis accompanies the development of various chronic liver diseases and promotes their progression. It is characterized by the abnormal accumulation of extracellular matrix proteins (ECM) and impaired ECM degradation. Activated hepatic stellate cells (HSCs) are the major cellular source of ECM-producing myofibroblasts. If liver fibrosis is uncontrolled, it may lead to cirrhosis and even liver cancer, primarily hepatocellular carcinoma (HCC). Natural killer (NK) cells are a key component of innate immunity and have miscellaneous roles in liver health and disease. Accumulating evidence shows that NK cells play dual roles in the development and progression of liver fibrosis, including profibrotic and anti-fibrotic functions. Regulating NK cells can suppress the activation of HSCs and improve their cytotoxicity against activated HSCs or myofibroblasts to reverse liver fibrosis. Cells such as regulatory T cells (Tregs) and molecules such as prostaglandin E receptor 3 (EP3) can regulate the cytotoxic function of NK cells. In addition, treatments such as alcohol dehydrogenase 3 (ADH3) inhibitors, microRNAs, natural killer group 2, member D (NKG2D) activators, and natural products can enhance NK cell function to inhibit liver fibrosis. In this review, we summarized the cellular and molecular factors that affect the interaction of NK cells with HSCs, as well as the treatments that regulate NK cell function against liver fibrosis. Despite a lot of information about NK cells and their interaction with HSCs, our current knowledge is still insufficient to explain the complex crosstalk between these cells and hepatocytes, liver sinusoidal endothelial cells, Kupffer cells, B cells, and T cells, as well as thrombocytes, regarding the development and progression of liver fibrosis.

Early life gut microbiota sustains liver-resident natural killer cells maturation via the butyrate-IL-18 axis

Liver-resident natural killer cells, a unique lymphocyte subset in liver, develop locally and play multifaceted immunological roles. However, the mechanisms for the maintenance of liver-resident natural killer cell homeostasis remain unclear. Here we show that early-life antibiotic treatment blunt functional maturation of liver-resident natural killer cells even at adulthood, which is dependent on the durative microbiota dysbiosis. Mechanistically, early-life antibiotic treatment significantly decreases butyrate level in liver, and subsequently led to defective liver-resident natural killer cell maturation in a cell-extrinsic manner. Specifically, loss of butyrate impairs IL-18 production in Kupffer cells and hepatocytes through acting on the receptor GPR109A. Disrupted IL-18/IL-18R signaling in turn suppresses the mitochondrial activity and the functional maturation of liver-resident natural killer cells. Strikingly, dietary supplementation of experimentally or clinically used Clostridium butyricum restores the impaired liver-resident natural killer cell maturation and function induced by early-life antibiotic treatment. Our findings collectively unmask a regulatory network of gut-liver axis, highlighting the importance of the early-life microbiota in the development of tissue-resident immune cells.

Single-cell RNA sequencing reveals intrahepatic and peripheral immune characteristics related to disease phases in HBV-infected patients

OBJECTIVE

A comprehensive immune landscape for HBV infection is pivotal to achieve HBV cure.

DESIGN

We performed single-cell RNA sequencing of 2 43 000 cells from 46 paired liver and blood samples of 23 individuals, including six immune tolerant, 5 immune active (IA), 3 acute recovery (AR), 3 chronic resolved and 6 HBV-free healthy controls (HCs). Flow cytometry and histological assays were applied in a second HBV cohort for validation.

RESULTS

Both IA and AR were characterised by high levels of intrahepatic exhausted CD8+ T (Tex) cells. In IA, Tex cells were mainly derived from liver-resident GZMK+ effector memory T cells and self-expansion. By contrast, peripheral CX3CR1+ effector T cells and GZMK+ effector memory T cells were the main source of Tex cells in AR. In IA but not AR, significant cell-cell interactions were observed between Tex cells and regulatory CD4+ T cells, as well as between Tex and FCGR3A+ macrophages. Such interactions were potentially mediated through human leukocyte antigen class I molecules together with their receptors CANX and LILRBs, respectively, contributing to the dysfunction of antiviral immune responses. By contrast, CX3CR1+GNLY+ central memory CD8+ T cells were concurrently expanded in both liver and blood of AR, providing a potential surrogate marker for viral resolution. In clinic, intrahepatic Tex cells were positively correlated with serum alanine aminotransferase levels and histological grading scores.

CONCLUSION

Our study dissects the coordinated immune responses for different HBV infection phases and provides a rich resource for fully understanding immunopathogenesis and developing effective therapeutic strategies.

Killer Cell Immunoglobulin-like Receptors (KIR) and Human Leucocyte Antigen C (HLA-C) Increase the Risk of Long-Term Chronic Liver Graft Rejection

Chronic liver rejection (CR) represents a complex clinical situation because many patients do not respond to increased immunosuppression. Killer cell immunoglobulin-like receptors/Class I Human Leukocyte Antigens (KIR/HLA-I) interactions allow for predicting Natural Killer (NK) cell alloreactivity and influence the acute rejection of liver allograft. However, its meaning in CR liver graft remains controversial. KIR and HLA genotypes were studied in 513 liver transplants using sequence-specific oligonucleotides (PCR-SSO) methods. KIRs, human leucocyte antigen C (HLA-C) genotypes, KIR gene mismatches, and the KIR/HLA-ligand were analyzed and compared in overall transplants with CR (n = 35) and no-chronic rejection (NCR = 478). Activating KIR (aKIR) genes in recipients (rKIR2DS2⁺ and rKIR2DS3⁺) increased CR compared with NCR groups (p = 0.013 and p = 0.038). The inhibitory KIR (iKIR) genes in recipients rKIR2DL2⁺ significantly increased the CR rate compared with their absence (9.1% vs. 3.7%, p = 0.020). KIR2DL3 significantly increases CR (13.1% vs. 5.2%; p = 0.008). There was no influence on NCR. CR was observed in HLA-I mismatches (MM). The absence of donor (d) HLA-C2 ligand (dC2⁻) ligand increases CR concerning their presence (13.1% vs. 5.6%; p = 0.018). A significant increase of CR was observed in rKIR2DL3⁺/dC1⁻ (p = 0.015), rKIR2DS4/dC1⁻ (p = 0.014) and rKIR2DL3⁺/rKIR2DS4⁺/dC1⁻ (p = 0.006). Long-term patient survival was significantly lower in rKIR2DS1⁺rKIR2DS4⁺/dC1⁻ at 5–10 years post-transplant. This study shows the influence of rKIR/dHLA-C combinations and aKIR gene-gene mismatches in increasing CR and KIR2DS1⁺/C1-ligands and the influence of KIR2DS4⁺/C1-ligands in long-term graft survival.

Recruited and Tissue-Resident Natural Killer Cells in the Lung During Infection and Cancer

Natural killer (NK) cells are an important component of the innate immune system, and have a key role in host defense against infection and in tumor surveillance. Tumors and viruses employ remarkably similar strategies to avoid recognition and killing by NK cells and so much can be learnt by comparing NK cells in these disparate diseases. The lung is a unique tissue environment and immune cells in this organ, including NK cells, exist in a hypofunctional state to prevent activation against innocuous stimuli. Upon infection, rapid NK cell infiltration into the lung occurs, the amplitude of which is determined by the extent of inflammation and damage. Activated NK cells kill infected cells and produce pro-inflammatory cytokines and chemokines to recruit cells of the adaptive immune system. More recent evidence has shown that NK cells also play an additional role in resolution of inflammation. In lung cancer however, NK cell recruitment is impaired and those that are present have reduced functionality. The majority of lung NK cells are circulatory, however recently a small population of tissue-resident lung NK cells has been described. The specific role of this subset is yet to be determined, but they show similarity to resident memory T cell subsets. Whether resident or recruited, NK cells are important in the control of pulmonary infections, but equally, can drive excessive inflammation if not regulated. In this review we discuss how NK cells are recruited, controlled and retained in the specific environment of the lung in health and disease. Understanding these mechanisms in the context of infection may provide opportunities to promote NK cell recruitment and function in the lung tumor setting.

Effects of acute endurance exercise and exhaustive exercise on innate immune signals induced by mtDNA

Objective: Numerous studies have shown that mitochondrial DNA (mtDNA) can trigger innate immune signaling, and exercise can induce mitochondrial stress. Therefore, this study is aimed at investigating the influence of different types of acute exercise on the innate immune signaling triggered by mtDNA.

Methods: Male C57BL/6 mice ( n = 18) were randomly and equally divided into three groups. They were control group, acute moderate-intensity endurance exercise group (AMIE), and 3-day exhaustive exercise group (EE) respectively. Mice were sacrificed immediately after exercise. The spleen, liver, and blood were taken for analysis.

Results: The amount of mtDNA in the liver cytoplasm and plasma was significantly decreased after AMIE ( p < .05). However, the amount of mtDNA in plasma was increased after EE (p < .05). The mRNA expression of TFAM, and most TLR9 and cGAS/STING signaling pathway-related genes in the liver and spleen was markedly elevated, whereas the expression of those genes in leukocytes was reduced after AMIE. Furthermore, AMIE significantly decreased the protein expression of NLRP3 inflammasome in the liver ( p < .05) and STING in spleen ( p < .01). Also, AMIE and EE caused a drop in circulating IFN-β levels ( p < .05).

Conclusion: A single bout of moderate-intensity exercise reduces mtDNA-induced innate immune signaling and suppresses inflammatory responses by decreasing hepatic cytoplasmic and circulating mtDNA. However, repeated bouts of exhaustive exercise stimulate innate immune signaling by increasing levels of circulating mtDNA.

Immune cell profile and immune-related gene expression of obese peripheral blood and liver tissue

Obesity is associated with changes in immune cell subpopulations. However, tissue and blood obesity-responsive immune phenotypic pathways have not been contrasted. Here, the local niche immune cell population and gene expression in fatty liver is compared to peripheral blood of obese individuals. The Cibersort algorithm enumerated increased fractions of memory CD4+ T lymphocytes and reductions in natural killer and memory B cells in obese liver tissue and obese blood, with similar reductions found in nonalcoholic fatty liver disease tissue. Gene expression analysis identified inflammatory immune signatures of regulatory CD4+ T cells with inferred Th1, Th17, Th2, or Treg phenotypes that differed between liver and blood. Our study suggests that the local tissue-specific immune phenotype in the liver differs from the obese peripheral circulation, with the latter reflective of multisystemic persistent inflammation that is characteristic of obesity.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

T Cell Subsets and Natural Killer Cells in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by hepatic accumulation of excess lipids. T cells are commonly classified into various subsets based on their surface markers including T cell receptors, type of antigen presentation and pathophysiological functions. Several studies have implicated various T cell subsets and natural killer (NK) cells in the progression of NAFLD. While NK cells are mainly components of the innate hepatic immune system, the majority of T cell subsets can be part of both the adaptive and innate systems. Several studies have reported that various stages of NAFLD are accompanied by the accumulation of distinct T cell subsets and NK cells with different functions and phenotypes observed usually resulting in proinflammatory effects. More importantly, the overall stimulation of the intrahepatic T cell subsets is directly influenced by the homeostasis of the gut microbiota. Similarly, NK cells have been found to accumulate in the liver in response to pathogens and tumors. In this review, we discussed the nature and pathophysiological roles of T cell subsets including γδ T cells, NKT cells, Mucosal-associated invariant T (MAIT) cells as well as NK cells in NAFLD.

Identification of liver-specific CD24+ invariant NK T cells with low granzyme B production and high proliferative capacity

Invariant NK T (iNKT) cells are innate-like lymphocytes that can recognize the lipid Ag presented by MHC I like molecule CD1d. Distinct tissue distribution of iNKT cells subsets implies a contribution of these subsets to their related tissue regional immunity. iNKT cells are enriched in liver, an organ with unique immunological properties. Whether liver-specific iNKT cells exist and dedicate to the liver immunity remains elusive. Here, a liver-specific CD24⁺ iNKT subset is shown. Hepatic CD24⁺ iNKT cells show higher levels of proliferation, glucose metabolism, and mTOR activity comparing to CD24^- iNKT cells. Although CD24⁺ iNKT cells and CD24^- iNKT cells in the liver produce similar amounts of cytokines, the hepatic CD24⁺ iNKT cells exhibit lower granzyme B production. These liver-specific CD24⁺ iNKT cells are derived from thymus and differentiate into CD24⁺ iNKT in the liver microenvironment. Moreover, liver microenvironment induces the formation of CD24⁺ conventional T cells as well, and these cells exhibit higher proliferation ability but lower granzyme B production in comparison with CD24^- T cells. The results propose that liver microenvironment might induce the generation of liver-specific iNKT subset that might play an important role in maintaining liver homeostasis.

Innate-like Lymphocytes and Innate Lymphoid Cells in Asthma

Asthma is a chronic pulmonary disease, highly associated with immune disorders. The typical symptoms of asthma include airway hyperresponsiveness (AHR), airway remodeling, mucus overproduction, and airflow limitation. The etiology of asthma is multifactorial and affected by genetic and environmental factors. Increasing trends toward dysbiosis, smoking, stress, air pollution, and a western lifestyle may account for the increasing incidence of asthma. Based on the presence or absence of eosinophilic inflammation, asthma is mainly divided into T helper 2 (Th2) and non-Th2 asthma. Th2 asthma is mediated by allergen-specific Th2 cells, and eosinophils activated by Th2 cells via the secretion of interleukin (IL)-4, IL-5, and IL-13. Different from Th2 asthma, non-Th2 asthma shows little eosinophilic inflammation, resists to corticosteroid treatment, and occurs mainly in severe asthmatic patients. Previous studies of asthma primarily focused on the function of Th2 cells, but, with the discovery of non-Th2 asthma and the involvement of innate lymphoid cells (ILCs) in the pathogenesis of asthma, tissue-resident innate immune cells in the lung have become the focus of attention in asthma research. Currently, innate-like lymphocytes (ILLs) and ILCs as important components of the innate immune system in mucosal tissues are reportedly involved in the pathogenesis of or protection against both Th2 and non-Th2 asthma. These findings of the functions of different subsets of ILLs and ILCs may provide clues for the treatment of asthma.

Natural Killer Cell Integrins and Their Functions in Tissue Residency

Integrins are transmembrane receptors associated with adhesion and migration and are often highly differentially expressed receptors amongst natural killer cell subsets in microenvironments. Tissue resident natural killer cells are frequently defined by their differential integrin expression compared to other NK cell subsets, and integrins can further localize tissue resident NK cells to tissue microenvironments. As such, integrins play important roles in both the phenotypic and functional identity of NK cell subsets. Here we review the expression of integrin subtypes on NK cells and NK cell subsets with the goal of better understanding how integrin selection can dictate tissue residency and mediate function from the nanoscale to the tissue environment.

Role of Natural Killer Cells in Uveal Melanoma

Simple Summary

Metastatic Uveal Melanoma (MUM) is a lethal malignancy with no durable treatment available to date. A vast majority of patients with MUM present with liver metastasis. The liver harbors metastatic disease with an apparent lack of a cytotoxic T cell response. It is becoming evident that MUM is not an immunologically silent malignancy and the investigation of non-T cell anti-tumor immunity is warranted. In this review, we highlight the relevance of Natural Killer (NK) cells in the biology and treatment of MUM. Potent anti-NK cell immunosuppression employed by uveal melanoma alludes to its vulnerability to NK cell cytotoxicity. On the contrary, micro-metastasis in the liver survive for several years within close vicinity of a plethora of circulating and liver-resident NK cells. This review provides unique perspectives into the potential role of NK cells in control or progression of uveal melanoma.

Abstract

Uveal melanoma has a high mortality rate following metastasis to the liver. Despite advances in systemic immune therapy, treatment of metastatic uveal melanoma (MUM) has failed to achieve long term durable responses. Barriers to success with immune therapy include the immune regulatory nature of uveal melanoma as well as the immune tolerant environment of the liver. To adequately harness the anti-tumor potential of the immune system, non-T cell-based approaches need to be explored. Natural Killer (NK) cells possess potent ability to target tumor cells via innate and adaptive responses. In this review, we discuss evidence that highlights the role of NK cell surveillance and targeting of uveal melanoma. We also discuss the repertoire of intra-hepatic NK cells. The human liver has a vast and diverse lymphoid population and NK cells comprise 50% of the hepatic lymphocytes. Hepatic NK cells share a common niche with uveal melanoma micro-metastasis within the liver sinusoids. It is, therefore, crucial to understand and investigate the role of intra-hepatic NK cells in the control or progression of MUM.

Protective Vaccination Reshapes Hepatic Response to Blood-Stage Malaria of Genes Preferentially Expressed by NK Cells

The role of natural killer (NK) cells in the liver as first-line post infectionem (p.i.) effectors against blood-stage malaria and their responsiveness to protective vaccination is poorly understood. Here, we investigate the effect of vaccination on NK cell-associated genes induced in the liver by blood-stage malaria of Plasmodium chabaudi. Female Balb/c mice were vaccinated at weeks 3 and 1 before being infected with 10⁶P. chabaudi-parasitized erythrocytes. Genes preferentially expressed by NK cells were investigated in livers of vaccination-protected and non-protected mice on days 0, 1, 4, 8, and 11 p.i. using microarrays, qRT-PCR, and chromosome landscape analysis. Blood-stage malaria induces expression of specific genes in the liver at different phases of infection, i.e., Itga1 in expanding liver-resident NK (lrNK) cells, Itga2 in immigrating conventional NK (cNK) cells; Eomes and Tbx21 encoding transcription factors; Ncr1, Tnfsf10, Prf1, Gzma, Gzmb, Gzmc, Gzmm, and Gzmk encoding cytolytic effectors; natural killer gene complex (NKC)-localized genes encoding the NK cell receptors KLRG1, KLRK1, KLRAs1, 2, 5, 7, KLRD1, KLRC1, KLRC3, as well as the three receptors KLRB1A, KLRB1C, KLRB1F and their potential ligands CLEC2D and CLEC2I. Vaccination enhances this malaria-induced expression of genes, but impairs Gzmm expression, accelerates decline of Tnfsf10 and Clec2d expression, whereas it accelerates increased expression of Clec2i, taking a very similar time course as that of genes encoding plasma membrane proteins of erythroblasts, whose malaria-induced extramedullary generation in the liver is known to be accelerated by vaccination. Collectively, vaccination reshapes the response of the liver NK cell compartment to blood-stage malaria. Particularly, the malaria-induced expansion of lrNK cells peaking on day 4 p.i. is highly significantly (p < 0.0001) reduced by enhanced immigration of peripheral cNK cells, and KLRB1F:CLEC2I interactions between NK cells and erythroid cells facilitate extramedullary erythroblastosis in the liver, thus critically contributing to vaccination-induced survival of otherwise lethal blood-stage malaria of P. chabaudi.

Role of Innate Immunity in Pediatric Post-transplant Idiopathic Liver Fibrosis

Pediatric post-transplant idiopathic liver fibrosis is an unexplained graft fibrosis that occurs in symptom-free children without acute rejection and surgical complications. Despite a lack of consensus on the subject, the development of pediatric post-transplant idiopathic liver fibrosis is believed to be the result of multiple potential factors, including ischemia-reperfusion injury, allogeneic acute and chronic rejection, viral hepatitis recurrence, opportunistic infection, and drug-induced liver damage. Among them, there is growing evidence that innate immunity may also have a unique role in this progression. This study reviews the features of pediatric post-transplant idiopathic liver fibrosis and discusses current studies illustrating the potential mechanisms of liver allograft tolerance induced by intrahepatic innate immunity, the role of components including Toll-like receptors (TLRs), interferons (IFN), dendritic cells (DC), natural killer cells (NK cells), NKT cells, neutrophils, and Kupffer cells, as well as their possibly relevant role in the development of pediatric post-transplant idiopathic liver fibrosis.

Hepatic NK cells attenuate fibrosis progression of non-alcoholic steatohepatitis in dependent of CXCL10-mediated recruitment

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is a major cause of chronic liver disease. The precise role of NK cells in the progression of NASH has yet to be elucidated.

METHODS

Using methionine- and choline-deficient diets (MCD)-induced NASH model, the role of NK cells was identified in WT mice compared with conventional NK cell-deficient Nfil3^-/- mice.

RESULTS

After 8 weeks of MCD treatment, NASH was induced as shown by the significant macrovesicular steatosis, necro-inflammation and fibrosis in the liver of WT B6 mice. In MCD-treated WT B6 mice, the number of NK cells was markedly increased in the liver, but decreased in the spleen. Intrahepatic NK cells exhibited high levels of activation, as evidenced by the expression of CD107a and cytokine production of IFN-γ, TGF-β and IL-10. Lower expression levels of Ki67 indicated a reduction in the proliferation of intrahepatic NK cells after MCD treatment. Increased expression of CXCL10 in the liver early after MCD treatment led to the increased recruitment of CXCR3⁺ NK cells into the liver. The MCD-treated Nfil3^-/- mice showed similar levels of TG and macrovesicular steatosis, thus more inflammatory infiltration and increased collagen deposition in the liver. Furthermore, the depletion of NK cells during MCD-induced NASH caused a significant increase in the infiltration of monocyte-derived macrophages (MoMFs) particularly Ly6C^lo subsets towards M2.

CONCLUSIONS

Intrahepatic NK cells, recruited through CXCL10-CXCR3 interaction, play a protective role against the fibrosis progression in NASH, which provide us with a better understanding of the immunopathogenesis of NASH.

Anterior gradient 2-derived peptide upregulates major histocompatibility complex class I-related chains A/B in hepatocellular carcinoma cells

AIMS

Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality worldwide. Decrease in NKG2D ligand levels and exhaustion of NK cells in HCC patients are major causes of immune escape, high recurrence, poor prognosis, and low overall survival. Enhancing the susceptibility of HCC to NK cells by upregulating NKG2DLs on tumor cells is an effective treatment strategy. This study aimed to identify the effect of the Anterior gradient 2 (AGR2)-derived peptide P1, which was reported to bind to HLA-A*0201 as an epitope, on both the expression of major histocompatibility complex class I-related chains A/B (MICA/B) on HCC cells and the cytotoxicity of NK cells.

MAIN METHODS

The effect of P1 on MICA/B expression on HCC cells was determined by qRT-PCR, western blotting, and flow cytometry analysis. HCC cells were pre-treated with various pathway inhibitors to identify the molecular pathways associated with P1 treatment. The cytotoxicity of NK cells toward HCC was investigated by LDH cytotoxicity assay. The tumor-suppression effect of P1 was determined in vivo using a NOD/SCID mice HCC model.

KEY FINDINGS

P1 significantly increased MICA/B expression on HCC cells, thereby enhancing their susceptibility to the cytotoxicity of NK cells in vitro and in vivo. Further, p38 MAPK cell signaling pathway inhibitor SB203580 significantly attenuated the effects of P1 in vivo and in vitro.

SIGNIFICANCE

P1 upregulates MICA and MICB expression on HCC cells, thereby promoting their recognition and elimination by NK cells, which makes P1 an attractive novel immunotherapy agent.

NK cells induce hepatic ER stress to promote insulin resistance in obesity through osteopontin production

High-fat diet (HFD) induced hepatic endoplasmic reticulum (ER) stress drives insulin resistance (IR) and steatosis. NK cells in adipose tissue play an important role in the pathogenesis of IR in obesity. Whether NK cells in the liver can induce hepatic ER stress and thus promote IR in obesity is still unknown. We demonstrate that HFD-fed mice display elevated production of proinflammatory cytokine osteopontin (OPN) in hepatic NK cells, especially in CD49a⁺ DX5^- tissue-resident NK (trNK) cells. Obesity-induced ER stress, IR, and steatosis in the liver are ameliorated by ablating NK cells with neutralizing antibody in HFD-fed mice. OPN treatment enhances the expression of ER stress markers, including p-PERK, p-eIF2, ATF4, and CHOP in both murine liver tissues and HL-7702, a human liver cell line. Pretreatment of HL-7702 cells with OPN promotes hyperactivation of JNK and subsequent decrease of tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1), resulting in impaired insulin signaling, which can be reversed by inhibiting ER stress. Collectively, we demonstrate that hepatic NK cells induce obesity-induced hepatic ER stress, and IR through OPN production.

Liver-Mediated Adaptive Immune Tolerance

The liver is an immunologically tolerant organ that is uniquely equipped to limit hypersensitivity to food-derived antigens and bacterial products through the portal vein and can feasibly accept liver allografts. The adaptive immune response is a major branch of the immune system that induces organ/tissue-localized and systematic responses against pathogens and tumors while promoting self-tolerance. Persistent infection of the liver with a virus or other pathogen typically results in tolerance, which is a key feature of the liver. The liver's immunosuppressive microenvironment means that hepatic adaptive immune cells become readily tolerogenic, promoting the death of effector cells and the “education” of regulatory cells. The above mechanisms may result in the clonal deletion, exhaustion, or inhibition of peripheral T cells, which are key players in the adaptive immune response. These tolerance mechanisms are believed to be responsible for almost all liver diseases. However, optimal protective adaptive immune responses may be achieved through checkpoint immunotherapy and the modulation of hepatic innate immune cells in the host. In this review, we focus on the mechanisms involved in hepatic adaptive immune tolerance, the liver diseases caused thereby, and the therapeutic strategies needed to overcome this tolerance.

Landscape and Dynamics of Single Immune Cells in Hepatocellular Carcinoma

The immune microenvironment of hepatocellular carcinoma (HCC) is poorly characterized. Combining two single-cell RNA sequencing technologies, we produced transcriptomes of CD45+ immune cells for HCC patients from five immune-relevant sites: tumor, adjacent liver, hepatic lymph node (LN), blood, and ascites. A cluster of LAMP3+ dendritic cells (DCs) appeared to be the mature form of conventional DCs and possessed the potential to migrate from tumors to LNs. LAMP3+ DCs also expressed diverse immune-relevant ligands and exhibited potential to regulate multiple subtypes of lymphocytes. Of the macrophages in tumors that exhibited distinct transcriptional states, tumor-associated macrophages (TAMs) were associated with poor prognosis, and we established the inflammatory role of SLC40A1 and GPNMB in these cells. Further, myeloid and lymphoid cells in ascites were predominantly linked to tumor and blood origins, respectively. The dynamic properties of diverse CD45+ cell types revealed by this study add new dimensions to the immune landscape of HCC.

HBV-Induced Immune Imbalance in the Development of HCC

Chronic hepatitis B virus (HBV) infection is one of the high-risk factors for human HCC. Despite the integration of virus DNA and the oncoprotein HBx, chronic necroinflammation and hepatocellular regeneration account for hepatocarcinogenesis. As a non-cytopathic virus, HBV is extensively recognized to mediate chronic liver damage through abnormal immune attack. However, the mechanisms driving HBV infection to HCC are poorly understood. During chronic HBV infection in humans, the adaptive immunity changes from immune tolerance to progressive immune activation, inactivation, reactivation and exhaustion, all of which may be the immune pathogenic factors for the development of HCC. Recently, the immunopathogenic mechanisms were described in mouse HBV-induced HCC models, which is absolutely dependent on the presence of HBV-specific T cell response and NK cell-derived IFN-γ, findings which are consistent with the observations from CHB and HCC patients. In this review, we summarize recent research progression on the HBV-specific CD8⁺ T cells, and also CD4⁺ T cells, B cells and non-specific immune cells and molecules underlying chronic HBV infection and eventual HCC development to demonstrate the pathogenesis of HBV-induced immune imbalance. Based on the progression, we discussed the potential of immune-based therapies and their challenges in the treatment of HBV-related HCC, including the checkpoint inhibition, genetically modified T cell transfer, therapeutic vaccines and metabolic modulation.

The Roles of Liver-Resident Lymphocytes in Liver Diseases

Tissue-resident lymphocytes usually reside in barrier sites and are involved in innate and adaptive immunity. In recent years, many studies have shown that multiple types of lymphocytes are resident in the liver, including memory CD8⁺ T (T_RM) cells; "unconventional" T cells, such as invariant natural killer T (iNKT) cells, mucosal associated invariant T (MAIT) cells, and γδT cells; innate lymphoid cells (ILCs) such as natural killer (NK) cells and other ILCs. Although diverse types of tissue-resident lymphocytes share similar phenotypes, functional properties, and transcriptional regulation, the unique microenvironment of the liver can reshape their phenotypic and functional characteristics. Liver-resident lymphocytes serve as sentinels and perform immunosurveillance in response to infection and non-infectious insults, and are involved in the maintenance of liver homeostasis. Under the pathological conditions, distinct liver-resident lymphocytes exert protective or pathological effects in the process of various liver diseases. In this review, we highlight the unique properties of liver-resident lymphocytes, and discuss their functional characteristics in different liver diseases.

Accumulation of Tumor-Infiltrating CD49a+ NK Cells Correlates with Poor Prognosis for Human Hepatocellular Carcinoma

The discovery of CD49a⁺ liver-resident natural killer (NK) cells in mice alters our view of NK cells and provides another opportunity to study NK cells. Although evidence has suggested roles for NK cells in liver diseases, whether and how CD49a⁺ NK cells contribute to liver diseases remain unclear. In this study, we observed that accumulation of CD49a⁺ tissue-resident NK cells in human hepatocellular carcinoma (HCC) was higher than in peritumoral tissues. We studied the exhausted and regulatory phenotypes of CD49a⁺ tissue-resident NK cells by analysis of protein and mRNA. The proportion of CD49a⁺ NK cells was positively correlated to the proportion of NK cells expressing inhibitory receptors. In addition, CD49a⁺ NK cells expressed more of checkpoint molecules PD-1, CD96, and TIGIT. Transcriptomic analysis implicated CD49a⁺ tissue-resident NK cells in the negative regulation of immune responses. Comparison of murine and human CD49a⁺ NK cells revealed their distinct characteristics and functions. Finally, accumulation of tissue-resident CD49a⁺ NK cells in liver tumor was correlated to deteriorating disease condition and poor prognosis. Our findings show that CD49a⁺ NK cells accumulate in liver tumor and suggest a role for CD49a⁺ NK cells in the negative regulation of immune responses and the development of HCC.

Tissue-resident memory-like ILCs: innate counterparts of TRM cells

Innate lymphoid cells (ILCs) are defined as lymphocytes that lack RAG recombinase and do not express diverse antigen receptors; however, recent studies have revealed the adaptive features of ILCs. Mouse cytomegalovirus (MCMV)- and cytokine-induced memory natural killer (NK) cells circulate in the blood and are referred to as conventional memory NK cells. In contrast, virus- and hapten-induced memory NK cells, hapten-induced memory ILC1s, and cytokine-induced memory-like ILC2s exhibit long-term residency in the liver or lung, and are referred to as tissue-resident memory ILCs. Considering their similar migration patterns and memory potential, tissue-resident memory ILCs could be regarded as innate counterparts of resident memory T (T_RM) cells. Both tissue-resident memory ILCs and T_RM cells share common characteristics in terms of dynamics, phenotype, and molecular regulation. The emergence of ILC memory expands the basic biology of ILCs and prompts us to re-examine their functions in disease progression. This review discusses the evidence supporting tissue-resident memory NK cells and other memory ILC subsets, compares them with T_RM cells, and highlights key unsolved questions in this emerging field.

Human CD96 Correlates to Natural Killer Cell Exhaustion and Predicts the Prognosis of Human Hepatocellular Carcinoma

Immune checkpoint blockade has become a promising therapeutic approach to reverse immune cell exhaustion. Coinhibitory CD96 and T-cell immunoglobulin and ITIM domain (TIGIT), together with costimulatory CD226, bind to common ligand CD155. The balancing between three receptors fine-tunes immune responses against tumors. In this study, we investigated the expression of CD96, TIGIT, and CD226 in 55 fresh human hepatocellular carcinoma (HCC) samples, 236 paraffin-embedded HCC samples, and 20 normal human livers. The cumulative percentage, absolute count, and mean fluorescence intensity (MFI) of CD96⁺ NK cells are significantly increased in the intratumoral tissues of HCC and break the balance between three receptors. Human CD96⁺ NK cells are functionally exhausted with impaired interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) production, high gene expression of interleukin (IL)-10 and transforming growth factor-beta 1 (TGF-β1), and low gene expression of T-bet, IL-15, perforin, and granzyme B. In addition, blocking CD96-CD155 interaction specifically increases lysis of HepG2 cells by NK cells. HCC patients with a high level of CD96 or CD155 expression within tumor are strongly associated with deteriorating disease condition and shorter disease-free survival (DFS) and overall survival times. Patients with a higher cumulative percentage of CD96⁺ NK cells within tumor also exhibit shorter DFS. High plasma level of TGF-β1 in HCC patients up-regulates CD96 expression and dynamically shifts the balance between CD96, TIGIT, and CD226 in NK cells. Blocking TGF-β1 specifically restores normal CD96 expression and reverses the dysfunction of NK cells. Conclusion: These findings indicate that human intratumoral CD96⁺ NK cells are functionally exhausted and patients with higher intratumoral CD96 expression exhibit poorer clinical outcomes. Blocking CD96-CD155 interaction or TGF-β1 restores NK cell immunity against tumors by reversing NK cell exhaustion, suggesting a possible therapeutic role of CD96 in fighting liver cancer.

Natural Killer Cells in the Lungs

The lungs, a special site that is frequently challenged by tumors, pathogens and other environmental insults, are populated by large numbers of innate immune cells. Among these, natural killer (NK) cells are gaining increasing attention. Recent studies have revealed that NK cells are heterogeneous populations consisting of distinct subpopulations with diverse characteristics, some of which are determined by their local tissue microenvironment. Most current information about NK cells comes from studies of NK cells from the peripheral blood of humans and NK cells from the spleen and bone marrow of mice. However, the functions and phenotypes of lung NK cells differ from those of NK cells in other tissues. Here, we provide an overview of human and mouse lung NK cells in the context of homeostasis, pathogenic infections, asthma, chronic obstructive pulmonary disease (COPD) and lung cancer, mainly focusing on their phenotype, function, frequency, and their potential role in pathogenesis or immune defense. A comprehensive understanding of the biology of NK cells in the lungs will aid the development of NK cell-based immunotherapies for the treatment of lung diseases.

Natural killer cells involved in tumour immune escape of hepatocellular carcinomar

Natural killer cells are the first line of host immune surveillance and play major roles in the defence against infection and tumours. Hepatic NK cells exhibit unique phenotypic and functional characteristics compared to circulating and spleen NK cells, such as higher levels of cytolytic activity and cytotoxicity mediators against tumour cells. However, the activities of NK cells may be reversed during tumour progression. Recent studies demonstrated that hepatic NK cells were exhausted in hepatocellular carcinoma (HCC) and exhibited impaired cytolytic activity and decreased production of effector cytokines. The present review discusses current knowledge on the role of exhausted NK cells in promoting HCC development and the mechanisms contributing to tumour immune escape, including an imbalance of activating and inhibitory receptors on NK cells, abnormal receptor-ligand interaction, and cross-talk with immune cells and other stromal cells in the tumour environment. We provide a fundamental basis for further study of innate immunity in tumour progression and serve the purpose of exploring new HCC treatment strategies.

CD24 targeting bi-specific antibody that simultaneously stimulates NKG2D enhances the efficacy of cancer immunotherapy

PURPOSE

Bi-specific antibody (BsAb) is an emerging novel format of antibody. We aimed to develop the natural killer (NK) cell receptor NK group 2, member D (NKG2D)-mediated, immune surveillance system. In this system, the NKG2D ligand MHC class I-related chain A (MICA) was fused with BsAb, which targeted a cluster of differentiation 24 (CD24), a tumor-initiating cell marker that is over-expressed on hepatocellular carcinoma (HCC).

METHODS

The Homo MICA extracellular domains (hMICA) were fused to the end of the heavy chain of cG7 with the flexible pentapeptide (Gly-Gly-Gly-Gly-Ser; G4S), which formed the cG7-MICA that was further identified using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting (WB). The targeting specificity was characterized using the Surface Plasmon Resonance (SPR) technology and a flow cytometry assay. Furthermore, the design of BsAb cG7-MICA that targeted CD24 and NKG2D was proven to enhance antibody-dependent, cell-mediated cytotoxicity (ADCC) in vitro by the CytoTox 96 Nonradioactive Cytotoxicity assay. Degranulation and a cytokine production assay of NK cells demonstrated that NK cells were activated effectively by cG7-MICA. Further, in HCC-bearing nude mice, the anti-tumor effects of cG7-MICA combined with sorafenib were verified again.

RESULTS

We purified cG7-MICA successfully, and it has a high affinity. In vivo, cG7-MICA recruited NK cells to the tumor site and improved the anti-tumor efficacy of sorafenib. cG7-MICA also activated NK cells to release interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α), and it increased the CD107a expression on the surface of the NK cells in vitro.

CONCLUSION

NK cells play a major role in the natural, innate immune system, and they have the function of identifying and killing target cells. cG7-MICA remodels the function of MICA molecules to activate NK cells, which provides a possible strategy for HCC-targeting immunotherapy.

Natural Killer Cell-Derived Interferon-Gamma Promotes Hepatocellular Carcinoma Through the Epithelial Cell Adhesion Molecule-Epithelial-to-Mesenchymal Transition Axis in Hepatitis B Virus Transgenic Mice

Hepatitis B virus (HBV) is a major risk factor for development of hepatocellular carcinoma (HCC), at least partially due to dysfunctional anti-HBV adaptive immunity; however, the role of innate immune response to HBV in this process is not well understood. In this study, low-dose polyinosinic:polycytidylic acid (poly [I:C]), a natural killer (NK) cell activator (3 μg/g body weight, twice/week for 8 weeks), induced HCC in HBV transgenic (HBs-Tg) mice, with an incidence of 100% after 6 months, while HBs-Tg mice without treatment only had HCC with an incidence of 16.7%. In HBs-Tg mice, poly (I:C) induced liver inflammation with markedly increased infiltrating lymphocytes, along with the concurrently increased apoptosis and proliferation of hepatocytes, leading to the accelerated epithelial-to-mesenchymal transition (EMT) of hepatocytes shown by increased expression of the typical transcriptional factors (Slug, Twist, and mothers against decapentaplegic-interacting protein 1) and phenotypic proteins (vimentin and chemokine [C-X-C motif] receptor 4). The EMT and tumorigenesis in this model depended on the presence of NK cells because depletion of these cells significantly reduced the HCC rate to 28.6%. Further, intrahepatic NK cells highly expressed interferon-gamma (IFN-γ), anti-IFN-γ neutralizing monoclonal antibody might obviously alleviate the hepatitis, and hepatocyte-specific IFN-γ overexpression promoted HCC. Moreover, IFN-γ deficiency in HBs-Tg mice prevented HCC occurring, though hepatic NK cells existed and could be activated, suggesting the critical role of IFN-γ in NK cell-mediated tumorigenesis. In an in vitro experiment, IFN-γ up-regulated epithelial cell adhesion molecule (EpCAM) expression through phosphorylated signal transducer and activator of transcription (p-STAT1) pathway, which was followed by EMT, and p-STAT1 inhibitor might absolutely abolish the expression of EpCAM and EMT in HBV surface antigen-positive hepatocytes. Conclusion: This work demonstrates that NK cell-derived IFN-γ promotes HCC through the EpCAM-EMT axis in HBs-Tg mice, revealing the importance of innate immunity in pathogenesis of HBV-associated HCC.

γδT Cells Suppress Liver Fibrosis via Strong Cytolysis and Enhanced NK Cell-Mediated Cytotoxicity Against Hepatic Stellate Cells

Liver fibrosis is the excessive accumulation of extracellular matrix proteins, resulting from maladaptive wound healing responses to chronic liver injury. γδT cells are important in chronic liver injury pathogenesis and subsequent liver fibrosis; however, their role and underlying mechanisms are not fully understood. The present study aims to assess whether γδT cells contribute to liver fibrosis regression. Using a carbon tetrachloride (CCl₄)-induced murine model of liver fibrosis in wild-type (WT) and γδT cell deficient (TCRδ^−/−) mice, we demonstrated that γδT cells protected against liver fibrosis and exhibited strong cytotoxicity against activated hepatic stellate cells (HSCs). Further study show that chronic liver inflammation promoted hepatic γδT cells to express NKp46, which contribute to the direct killing of activated HSCs by γδT cells. Moreover, we identified that an IFNγ-producing γδT cell subset (γδT1) cells exhibited stronger cytotoxicity against activated HSCs than the IL-17-producing subset (γδT17) cells upon chronic liver injury. In addition, γδT cells promoted the anti-fibrotic ability of conventional natural killer (cNK) cells and liver-resident NK (lrNK) cells by enhancing their cytotoxicity against activated HSCs. The cell crosstalk between γδT and NK cells was shown to depend partly on co-stimulatory receptor 4-1BB (CD137) engagement. In conclusion, our data confirmed the protective effects of γδT cells, especially the γδT1 subset, by directly killing activated HSCs and increasing NK cell-mediated cytotoxicity against activated HSCs in CCl₄-induced liver fibrosis, which suggest valuable therapeutic targets to treat liver fibrosis.

Innate lymphoid cell memory

Innate lymphoid cells (ILCs), including natural killer (NK) cells, ILC1s, ILC2s, ILC3s, and lymphoid tissue inducer (LTi) cells, comprise the first line of innate immune defense against pathogens and tumors. Over the past decade, accumulating evidence has demonstrated immunological memory in ILC subsets: for example, NK cells recall haptens, viruses, and cytokines; ILC1s recall haptens; and ILC2s recall cytokines. Although the development and functions of ILCs mirror those of T-cell subsets, ILC and T-cell memory exhibit both common characteristics and specific properties. Encouragingly, ILC memory has been found to confer benefits in long-term tumor control and vaccination, providing insight for novel memory ILC-based tumor immunotherapy and vaccine-development strategies. In this review, we discuss the evidence supporting ILC memory and present a comprehensive framework of the ILC memory system.

Tissue-resident lymphocytes: from adaptive to innate immunity

Efficient immune responses against invading pathogens often involve coordination between cells from both the innate and adaptive immune systems. For multiple decades, it has been believed that CD8⁺ memory T cells and natural killer (NK) cells constantly and uniformly recirculate. Only recently was the existence of noncirculating memory T and NK cells that remain resident in the peripheral tissues, termed tissue-resident memory T (T_RM) cells and tissue-resident NK (trNK) cells, observed in various organs owing to improved techniques. T_RM cells populate a wide range of peripheral organs, including the skin, sensory ganglia, gut, lungs, brain, salivary glands, female reproductive tract, and others. Recent findings have demonstrated the existence of T_RM in the secondary lymphoid organs (SLOs) as well, leading to revision of the classic theory that they exist only in peripheral organs. trNK cells have been identified in the uterus, skin, kidney, adipose tissue, and salivary glands. These tissue-resident lymphocytes do not recirculate in the blood or lymphatic system and often adopt a unique phenotype that is distinct from those of circulating immune cells. In this review, we will discuss the recent findings on the tissue residency of both innate and adaptive lymphocytes, with a particular focus on CD8⁺ memory T cells, and describe some advances regarding unconventional T cells (invariant NKT cells, mucosal-associated invariant T cells (MAIT), and γδ T cells) and the emerging family of trNK cells. Specifically, we will focus on the phenotypes and functions of these subsets and discuss their implications in anti-viral and anti-tumor immunity.

Natural Killer Cell Dysfunction in Hepatocellular Carcinoma: Pathogenesis and Clinical Implications

Hepatocellular carcinoma (HCC) is currently the third leading cause of malignancy-related mortalities worldwide. Natural killer (NK) cells are involved in the critical role of first line immunological defense against cancer development. Defects in NK cell functions are recognized as important mechanisms for immune evasion of tumor cells. NK cell function appears to be attenuated in HCC, and many previous reports suggested that NK cells play a critical role in controlling HCC, suggesting that boosting the activity of dysfunctional NK cells can enhance tumor cell killing. However, the detailed mechanisms of NK cell dysfunction in tumor microenvironment of HCC remain largely unknown. A better understanding of the mechanisms of NK cell dysfunction in HCC will help in the NK cell-mediated eradication of cancer cells and prolong patient survival. In this review, we describe the various mechanisms underlying human NK cell dysfunction in HCC. Further, we summarize current advances in the approaches to enhance endogenous NK cell function and in adoptive NK cell therapies, to cure this difficult-to-treat cancer.

Memory formation and long-term maintenance of IL-7Rα+ ILC1s via a lymph node-liver axis

Natural killer (NK) cells are reported to have immunological memory, with CD49a⁺ liver-resident NK cells shown to confer hapten-specific memory responses, but how this memory is induced or maintained is unclear. Here we show that memory type I innate lymphoid cells (ILC1s), which express IL-7Rα, are generated in the lymph nodes (LNs) and require IL-7R signaling to maintain their longevity in the liver. Hapten sensitization initiates CXCR3-dependent recruitment of IL-7Rα⁺ ILC1s into skin-draining LNs, where they are primed and acquire hapten-specific memory potential. Memory IL-7Rα⁺ ILC1s then exit draining LNs and are preferentially recruited, via CXCR6, to reside in the liver. Moreover, long-term blockade of IL-7R signaling significantly reduces ILC1-mediated memory responses. Thus, our results identify a memory IL-7Rα⁺ ILC1 population and reveal a LN-liver axis that is essential for ILC1 memory generation and long-term maintenance.

Natural killer cells may respond better on second antigen encounters, but how this memory is induced or maintained in vivo is not clear. Here the authors show that memory NK cells expressing interleukin-7 (IL-7) receptor are induced in the lymph nodes but later recruited to liver for long term, IL-7 dependent survival and memory maintenance.

NK cells in liver homeostasis and viral hepatitis

As an important member of the innate immune system, natural killer (NK) cells are well known for their rapid and efficient immune responses against infectious agents and tumors. NK cells are widely distributed throughout the body and are particularly enriched within the liver, where they display unique phenotypic and functional properties, playing important roles in various liver diseases. Herein, we present an overview of liver NK cell properties with regard to phenotype, function, and subset composition at steady state, and we also summarize the complex reciprocal interactions between liver NK cells and other cell types within the local environment of the liver. We also provide an overview of recent advances demonstrating the roles of NK cells in viral hepatitis, including a discussion of NK cell altered states and their beneficial versus harmful effects during hepatitis B virus and hepatitis C virus infection.

Cytokine-Based Generation of CD49a+Eomes-/+ Natural Killer Cell Subsets

Recent studies have identified CD49a⁺Eomes⁻ and CD49a⁺Eomes⁺ subsets of tissue-resident NK (trNK) cells in different organs of the mouse. However, the characteristics of CD49a⁺Eomes^−/+ NK cell development and the regulation of Eomes expression in NK cells remain unclear. Here, we established an in vitro cytokine-based feeder-free system in which bone marrow progenitor cells differentiate into CD49a⁺ NK cells. IL-15 was identified as being the key cytokine in this system that supported the development and maintenance of CD49a⁺ NK cells. The CD49a⁺ NK cells generated were Eomes⁻CD49b⁻ and shared the same phenotype as hepatic trNK cells. IL-4 induced the expression of Eomes in generated NK cells and converted them into CD49a⁺Eomes⁺ cells, which were phenotypically and functionally similar to uterine trNK cells. Moreover, the IL-4/STAT6 axis was identified as being important in the generation of CD49a⁺Eomes⁺ induced NK cells. Collectively, these studies describe an approach to generate CD49a⁺Eomes^−/+ subsets of NK cells and demonstrate important roles for IL-15 and IL-4 in the differentiation of these cells. These findings have potential for developmental research underlying the generation of different subsets of NK cells and the application of adoptive NK cell transfer therapies.

Reduced CD160 Expression Contributes to Impaired NK-cell Function and Poor Clinical Outcomes in Patients with HCC

: We previously reported that deficiencies in natural killer (NK)-cell number and function play an important role in the progression of hepatocellular carcinoma (HCC). However, the mechanisms underlying this phenomenon remain obscure. In this study, we analyzed the expression of CD160 on intrahepatic NK cells by evaluating peritumoral and intratumoral tissues of 279 patients with HCC and 20 healthy livers. We observed reduced expression of CD160 on intratumoral NK cells, and patients with lower CD160 cell densities within tumors exhibited worse disease and a higher recurrence rate. High-resolution microarray and gene set enrichment analysis of flow cytometry-sorted primary intrahepatic CD160⁺ and CD160^- NK cells of healthy livers indicated that human CD160⁺ NK cells exhibited functional activation, high IFNγ production, and NK-mediated immunity. In addition, global transcriptomic analysis of sorted peritumoral and intratumoral CD160⁺ NK cells revealed that intratumoral CD160⁺ NK cells are more exhausted than peritumoral CD160⁺ NK cells and produce less IFNγ. High levels of TGFβ1 interfered with production of IFNγ by CD160⁺ NK cells, blocking of which specifically restored IFNγ production in CD160⁺ NK cells to normal levels. These findings indicate that reduced numbers of CD160⁺ NK cells, together with the functional impairment of CD160⁺ NK cells by TGFβ1, contribute to tumor immune escape. In addition, restoring the expression of CD160 and blocking TGFβ1 appear a promising therapeutic strategy against liver cancer. SIGNIFICANCE: These findings show that reduced number and function of CD160⁺ NK cells in the tumor microenvironment contributes to immune escape of HCC; blocking TGFβ1 restores IFNγ production of CD160⁺ NK cells.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/23/6581/F1.large.jpg.

Humanized mice reveal an essential role for human hepatocytes in the development of the liver immune system

The liver is an immunological organ with a distinct immune cell profile. Although the composition and function of liver immune cells have been widely investigated, the mechanisms regulating the development and homeostasis of the specialized immune system, especially in humans, remain largely unknown. Herein, we address this question in humanized mice (hu-mice) that were constructed by transplantation of human fetal thymus and CD34+ hematopoietic stem/progenitor cells in immunodeficient mice with or without autologous human hepatocyte engraftment. Although the levels of human immune cell reconstitution in peripheral blood and spleen were comparable between hu-mice with and without human hepatocyte engraftment, the former group showed that human immune cell reconstitution in the liver was significantly improved. Notably, human immune cells, including Kupffer cells, dendritic cells and natural killer cells, were shown to be closely colocalized with human hepatocytes in the liver. Human hepatocytes engrafted in the mouse liver were found to produce IL-3, IL-15, GM-CSF, M-CSF, MCP-1, CXCL-1 and CXCL-10, which are known to be important for immune cell development, differentiation, tissue migration and retention, and have no or poor cross-reaction between humans and mice. Furthermore, human hepatocytes were able to support human immune cell survival and expansion in an in vitro co-culture assay. This study demonstrates an essential role for hepatocytes in the development and maintenance of the liver immune cell profile. The hu-mouse model with human autologous immune cell and hepatocyte reconstitution has potential for use in studies of the pathogenesis of liver immune disorders such as hepatotropic virus infections.