Liver-resident Natural Killer Cells Research Articles

Identification of a Porcine Liver EomeshighT-betlow NK Cell Subset That Resembles Human Liver Resident NK Cells.

Natural killer (NK) cells are cells of the innate immunity and play an important role in the defense against viral infections and cancer, but also contribute to shaping adaptive immune responses. Long-lived tissue-resident NK cells have been described in man and mouse, particularly in the liver, contributing to the idea that the functional palette of NK cells may be broader than originally thought, and may include memory-like responses and maintaining tissue homeostasis. Remarkably, liver resident (lr)NK cells in man and mouse show substantial species-specific differences, in particular reverse expression patterns of the T-box transcription factors Eomesodermin (Eomes) and T-bet (EomeshighT-betlow in man and vice versa in mouse). In pig, compared to blood NK cells which are CD3−CD8αhigh cells, the porcine liver contains an abundant additional CD3−CD8αdim NK cell subpopulation. In the current study, we show that this porcine CD3−CD8αdim liver NK population is highly similar to its human lrNK counterpart and therefore different from mouse lrNK cells. Like human lrNK cells, this porcine NK cell population shows an EomeshighT-betlow expression pattern. In addition, like its human counterpart, the porcine liver NK population is CD49e− and CXCR6+. Furthermore, the porcine EomeshighT-betlow liver NK cell population is able to produce IFN-γ upon IL-2/12/18 stimulation but lacks the ability to kill K562 or pseudorabies virus-infected target cells, although limited degranulation could be observed upon incubation with K562 cells or upon CD16 crosslinking. All together, these results show that porcine EomeshighT-betlow NK cells in the liver strongly resemble human lrNK cells, and therefore indicate that the pig may represent a unique model to study the function of these lrNK cells in health and disease.

Everolimus enhances TRAIL-mediated anti-tumor activity of liver resident natural killer cells in mice.

In transplantation, innate immunity plays a pivotal role in immunosurveillance and host defence against microbes and neoplastic cells. Liver-resident NK cells express TNF-related apoptosis-inducing ligand (TRAIL), which distinguishes them from conventional NK cells. In this study, we investigated the impact of mTOR inhibition on liver-resident NK cells in comparison with that on splenic NK cells in a mouse model. In mice that received everolimus (EVR) for 7days (range: 0.0125-0.25mg/kg/day), the proportion of splenic NK cells was unchanged, whereas the number of liver NK cells including TRAIL+ NK subpopulation increased for all doses of EVR. Consistently, liver-resident NK cells from the EVR-treated mice displayed enhanced cytotoxicity against TRAIL-sensitive neoplastic cells. EVR treatment inhibited the transition of the immature subset of liver NK cells to a mature state. The negative regulator of NK cells FoxO1 was activated as a consequence of impaired mTORC2-dependent AKT phosphorylation. Activated FoxO1 both reduced T-bet expression and induced TRAIL expression, thereby inhibiting NK cell maturation and promoting the antitumour activity of the immature subset of liver NK cells in response to EVR treatment. These findings indicate that EVR treatment enhances the antitumour activity of immature liver-resident NK cells through TRAIL upregulation.

Echinococcus multilocularis inoculation induces NK cell functional decrease through high expression of NKG2A in C57BL/6 mice

BackgroundAlveolar echinococcosis (AE) is caused by the larval stage of Echinococcus multilocularis (E. multilocularis), and considered as public health issue. Parasite-host immune interaction is pivotal during infection. As a subset of innate lymphoid cells, NK cells are known to play an important role during virus, bacteria, intra/extracellular parasitic infections and tumor progression. However, the possible role of NK cells in E. multilocularis infection in both human and murine is little known. Herein, the functional alteration of hepatic NK cells and their related molecules in E. multilocularis infected mice were studied.Methods2000 protoscoleces (PSCs) were injected to C57BL/6 mice via the portal vein to establish secondary E. multilocularis infection. NK cells population and their related molecules (CD69, Ly49D, Ly49G2, Ly49H, Ly49I, NKG2A, NKG2D, granzyme B, IFN-γ, TNF-α) were assessed by using fluorescence-activated cell sorter (FACS) techniques and qRT-PCR. NK cell depletion was performed for further understanding the possible function of NK cells during infection.ResultsThe total frequencies of NK cells and NK-derived IFN-γ production were significantly reduced at designated time points (2, 4, 12 weeks). The liver resident (CD49a+DX5−) NK cells are decreased at 4 weeks after inoculation and which is significantly lower than in control mice. Moreover, in vivo antibody-mediated NK cell depletion increased parasitic load and decreased peri-parasitic fibrosis. Expression of the inhibitory receptor NKG2A was negatively related to NK- derived IFN-γ secretion.ConclusionsOur study showed down regulates of NK cells and upper regulates of NKG2A expression on NK cells during E. multilocularis infection. Reduction of NK cell frequencies and increased NKG2A might result in low cytotoxic activity through decreased IFN-γ secretion in E. multilocularis infection. This result might be helpful to restore NK cell related immunity against E. multilocularis infection to treat alveolar echinococcosis.

Liver-Derived TGF-β Maintains the EomeshiTbetlo Phenotype of Liver Resident Natural Killer Cells

The adult human liver hosts a complex repertoire of liver resident and transient natural killer (NK) cell populations with diverse phenotypes and functions. Liver resident NK cells are CD56bright NK cells defined by a unique expression profile of transcription factors and cell surface markers (EomeshiTbetloTIGIT+CD69+CXCR6+CD49e−). Despite extensive characterization of the phenotype of liver resident NK cells, it remains unclear how factors within the liver microenvironment induce and maintain this unique phenotype. In this study, we have explored the factors regulating the phenotype of liver resident NK cells. Isolation of healthy liver resident NK cells from donor liver perfusate and in vitro culture results in the gradual loss of the characteristic Tbetlo phenotype, with the cells increasing Tbet expression significantly at day 7. This phenotypic loss could be halted through the dose-dependent addition of liver conditioned media (LCM), generated from the ex vivo culture of liver biopsies from healthy organ donors. TGF-β, but not IL-10, replicated the Tbet suppressive effects of LCM in both liver resident and peripheral blood NK cells. Furthermore, blocking TGF-β receptor signaling using the inhibitor SB431542, reversed the effect of LCM treatment on liver resident NK cells, causing the loss of tissue resident Eomeshi Tbetlo phenotype. Our findings identify liver-derived TGF-β as an important component of the liver microenvironment, which acts to regulate and maintain the phenotype of liver resident NK cells.

CD8+ T Cells Promote Maturation of Liver-Resident NK Cells Through the CD70-CD27 axis.

Liver-resident natural killer (LrNK) cells are a unique subset of NK cells that are distinct from conventional NK cells. However, little is known about the mechanisms by which LrNK cells mature. In this study, we discovered that LrNK cells exhibit a relatively immature phenotype and impaired cytotoxic capacity in the absence of CD8+ T cells. The provision of CD8+ T cells to Cd8-/- or Rag1-/- mice led to the restoration of LrNK cell maturation. Furthermore, co-culture with CD8+ T cells induced immature CD27+ LrNK cells to convert into mature CD27- LrNK cells, whereas blocking the interaction of CD70 and CD27 abrogated the ability of CD8+ T cells to promote the maturation of LrNK cells. Conclusion: Our findings indicate that CD8+ T cells promote the maturation of LrNK cells through the CD70-CD27 axis, and therefore highlight a previously unknown mechanism responsible for the mediation of LrNK cell maturation.

Cytotoxicity of Human Hepatic Intrasinusoidal CD56bright Natural Killer Cells against Hepatocellular Carcinoma Cells.

Hepatic intrasinusoidal (HI) natural killer (NK) cells from liver perfusate have unique features that are similar to those of liver-resident NK cells. Previously, we have reported that HI CD56bright NK cells effectively degranulate against SNU398 hepatocellular carcinoma (HCC) cells. Thus, the aim of this study was to further investigate the phenotype and function of HI NK cells. We found that HI CD56bright NK cells degranulated much less to Huh7 cells. HI CD56bright NK cells expressed NKG2D, NKp46, TNF-related apoptosis-inducing ligand (TRAIL), and FAS ligand (FASL) at higher levels than CD56dim cells. SNU398 cells expressed more NKG2D ligands and FAS and less PD-L1 than Huh7 cells. Blockade of NKG2D, TRAIL, and FASL significantly reduced the cytotoxicity of HI NK cells against SNU398 cells, but blockade of PD-L1 did not lead to any significant change. However, HI NK cells produced IFN-γ well in response to Huh7 cells. In conclusion, the cytotoxicity of HI CD56bright NK cells was attributed to the expression of NKG2D, TRAIL, and FASL. The results suggest the possible use of HI NK cells for cancer immunotherapy and prescreening of HCC cells to help identify the most effective NK cell therapy recipients.

Liver-resident NK cells suppress autoimmune cholangitis and limit the proliferation of CD4+ T cells.

Liver-resident NK cells are distinct from conventional NK cells and play an important role in the maintenance of liver homeostasis. How liver-resident NK cells participate in autoimmune cholangitis remains unclear. Here, we extensively investigated the impact of NK cells in the pathogenesis of autoimmune cholangitis utilizing the well-established dnTGFβRII cholangitis model, NK cell-deficient (Nfil3-/-) mice, adoptive transfer and in vivo antibody-mediated NK cell depletion. Our data demonstrated that disease progression was associated with a significantly reduced frequency of hepatic NK cells. Depletion of NK cells resulted in exacerbated autoimmune cholangitis in dnTGFβRII mice. We further confirmed that the DX5-CD11chi liver-resident NK cell subset colocalized with CD4+ T cells and inhibited CD4+ T cell proliferation. Gene expression microarray analysis demonstrated that liver-resident NK cells had a distinct gene expression pattern consisting of the increased expression of genes involved in negative regulatory functions in the context of the inflammatory microenvironment.

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.

Lactate-Mediated Acidification of Tumor Microenvironment Induces Apoptosis of Liver-Resident NK Cells in Colorectal Liver Metastasis.

Colorectal cancer is the third most common malignancy worldwide, with 1.3 million new cases annually. Metastasis to the liver is a leading cause of mortality in these patients. In human liver, metastatic cancer cells must evade populations of liver-resident natural killer (NK) cells with potent cytotoxic capabilities. Here, we investigated how these tumors evade liver NK-cell surveillance. Tissue biopsies were obtained from patients undergoing resection of colorectal liver metastasis (CRLM, n = 18), from the tumor, adjacent tissue, and distal resection margin. The number and phenotype of liver-resident NK cells, at each site, were analyzed by flow cytometry. Tumor-conditioned media (TCM) was generated for cytokine and metabolite quantification and used to treat healthy liver-resident NK cells, isolated from donor liver perfusate during transplantation. Liver-resident NK cells were significantly depleted from CRLM tumors. Healthy liver-resident NK cells exposed to TCM underwent apoptosis in vitro, associated with elevated lactate. Tumor-infiltrating liver-resident NK cells showed signs of mitochondrial stress, which was recapitulated in vitro by treating liver-resident NK cells with lactic acid. Lactic acid induced apoptosis by decreasing the intracellular pH of NK cells, resulting in mitochondrial dysfunction that could be prevented by blocking mitochondrial ROS accumulation. CRLM tumors produced lactate, thus decreasing the pH of the tumor microenvironment. Liver-resident NK cells migrating toward the tumor were unable to regulate intracellular pH resulting in mitochondrial stress and apoptosis. Targeting CRLM metabolism provides a promising therapeutic approach to restoring local NK-cell activity and preventing tumor growth.

Liver-Resident NK Cells Control Antiviral Activity of Hepatic T Cells via the PD-1-PD-L1 Axis

The tolerogenic microenvironment of the liver is associated with impaired hepatic Tcell function. Here, weexamined the contribution of liver-resident naturalkiller (LrNK) cells, a prominent hepatic NK cell compartment, to Tcell antiviral responses in the liver. The number of virus-specific Tcells increased in LrNK-cell-deficient mice during both acute and chronic lymphocytic choriomeningitis virus infection. Upon infection with adenovirus, hepatic Tcells from these mice produced more cytokines, which was accompanied by reduced viral loads. Transfer of LrNK cells into LrNK-cell-deficient or wild-type mice inhibited hepatic Tcell function, resulting in impaired viral clearance, whereas transfer of conventional NK cells promoted Tcell antiviral responses. LrNK-cell-mediated inhibition of Tcell function was dependent on the PD-1-PD-L1 axis. Our findings reveal a role forLrNK cells in the regulation of Tcell immunity and provide insight into the mechanisms of immune tolerance in the liver.

Fine needle aspirates comprehensively sample intrahepatic immunity.

ObjectiveIn order to refine new therapeutic strategies in the pipeline for HBV cure, evaluation of virological and immunological changes compartmentalised at the site of infection will be required. We therefore investigated if liver fine needle aspirates (FNAs) could comprehensively sample the local immune landscape in parallel with viable hepatocytes.DesignMatched blood, liver biopsy and FNAs from 28 patients with HBV and 15 without viral infection were analysed using 16-colour multiparameter flow cytometry.ResultsThe proportion of CD4 T, CD8 T, Mucosal Associated Invariant T cell (MAIT), Natural Killer (NK) and B cells identified by FNA correlated with that in liver biopsies from the same donors. Populations of Programmed Death-1 (PD-1)hiCD39hi tissue-resident memory CD8 T cells (CD69+CD103+) and liver-resident NK cells (CXCR6+T-betloEomeshi), were identified by both FNA and liver biopsy, and not seen in the blood. Crucially, HBV-specific T cells could be identified by FNAs at similar frequencies to biopsies and enriched compared with blood. FNAs could simultaneously identify populations of myeloid cells and live hepatocytes expressing albumin, Scavenger Receptor class B type 1 (SR-B1), Programmed Death-Ligand 1 (PD-L1), whereas hepatocytes were poorly viable after the processing required for liver biopsies.ConclusionWe demonstrate for the first time that FNAs identify a range of intrahepatic immune cells including locally resident sentinel HBV-specific T cells and NK cells, together with PD-L1-expressing hepatocytes. In addition, we provide a scoring tool to estimate the extent to which an individual FNA has reliably sampled intrahepatic populations rather than contaminating blood. The broad profiling achieved by this less invasive, rapid technique makes it suitable for longitudinal monitoring of the liver to optimise new therapies for HBV.

Memory formation and long-term maintenance of IL-7R\u03b1+ 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.

Hepatic irradiation persistently eliminates liver resident NK cells

Hepatic irradiation for the treatment of hepatobiliary malignancies often indirectly damages liver tissue and promotes the development of liver fibrosis. However, little is known concerning the effects of hepatic irradiation on the liver immune system, including natural killer (NK) cells. The aim of this study was therefore to investigate how hepatic irradiation influences the functions and characteristics of liver resident NK cells. An established murine hepatic irradiation model was used to examine the specific effects of hepatic irradiation on immune cell populations and metastasis. This analysis demonstrated that hepatic irradiation decreased the number of liver resident NK cells (DX5–TRAIL+), but did not affect the total NK number or proportions of NK cells in the liver or spleen. This effect was correlated with the hepatic irradiation dose. Surprisingly, the liver resident NK population had not recovered by two months after hepatic irradiation. We also found that hepatic irradiation limited the cytotoxic effects of liver-derived lymphocytes against a mouse hepatoma cell line and promoted hepatic metastases in an in vivo model, although adoptive transfer of activated NK cells could alleviate metastatic growth. Finally, we demonstrated that hepatic irradiation disrupted the development of liver-resident NK cells, even after the adoptive transfer of precursor cells from the bone marrow, liver, and spleen, suggesting that irradiation had altered the developmental environment of the liver. In summary, our data demonstrated that hepatic irradiation abolished the DX5–TRAIL+ liver-resident NK cell population and dampened antitumor activities in the liver for at least two months. Additionally, hepatic irradiation prevented differentiation of precursor cells into liver-resident NK cells.

IL-15 Overcomes Hepatocellular Carcinoma-Induced NK Cell Dysfunction.

NK cells have potent antitumor capacity. They are enriched in the human liver, with a large subset specialized for tissue-residence. The potential for liver-resident versus liver-infiltrating NK cells to populate, and exert antitumor functions in, human liver tumors has not been studied. We examined liver-resident and liver-infiltrating NK cells directly ex vivo from human hepatocellular carcinomas (HCCs) and liver colorectal (CRC) metastases, compared with matched uninvolved liver tissue. We found that NK cells were highly prevalent in both HCC and liver CRC metastases, although at lower frequencies than unaffected liver. Up to 79% of intratumoral NK cells had the CXCR6+CD69+ liver-resident phenotype. Direct ex vivo staining showed that liver-resident NK cells had increased NKG2D expression compared to their non-resident counterparts, but both subsets had NKG2D downregulation within liver tumors compared to uninvolved liver. Proliferation of intratumoral NK cells (identified by Ki67) was selectively impaired in those with the most marked NKG2D downregulation. Human liver tumor NK cells were functionally impaired, with reduced capacity for cytotoxicity and production of cytokines, even when compared to the hypo-functional tissue-resident NK cells in unaffected liver. Coculture of human liver NK cells with the human hepatoma cell line PLC/PRF/5, or with autologous HCC, recapitulated the defects observed in NK cells extracted from tumors, with downmodulation of NKG2D, cytokine production, and target cell cytotoxicity. Transwells and conditioned media confirmed a requirement for cell contact with PLC/PRF/5 to impose NK cell inhibition. IL-15 was able to recover antitumor functionality in NK cells inhibited by in vitro exposure to HCC cell lines or extracted directly from HCC. In summary, our data suggest that the impaired antitumor function of local NK cells reflects a combination of the tolerogenic features inherent to liver-resident NK cells together with additional contact-dependent inhibition imposed by HCC itself. The demonstration that IL-15 can recover hepatic NK cell function following tumor exposure supports its inclusion in immunotherapy strategies.

Transcription Factor TX Is Required for Liver-resident NK cells development

Abstract Hepatic NK cells are heterogeneous populations, consisting of DX5+CD49a− NK cells and CD49a+DX5− NK cells. CD49a+DX5− NK cells, also termed “tissue-resident NK (trNK) cells”, are distinct from DX5+CD49a− conventional NK (cNK) cells and possess unique hallmarks. Recent study shows that trNK cell differentiation is programmed by transcription factor T-bet, instead of Eomes, which is critical for cNK cell development. T-bet is highly expressed by both trNK and cNK cells, its deficiency leads to dramatic reduction of trNK cell and terminal mature cNK cells, suggesting a non-specific role of T-bet in the development of NK cell subsets. To find a transcription factor that potentially impacts trNK cell development in a specific manner, we analyzed differentially expressed transcription factor genes between liver trNK and cNK cells by microarrays. We found that the transcription factor TX is expressed on liver trNK cells at much higher levels than on cNK cells. In order to figure out whether TX has an effect on liver trNK cells, we overexpressed TX on HSCs, and transferred the cells into lethally irradiated mice. Surprisingly, the frequency and number of liver trNK cells increased in TX-overexpressed mice. Then, we knocked down TX expression on HSCs, and transferred the cells to lethally irradiated mice. Although the frequency of liver trNK cells was invariant, the number decreased significantly. Therefore, these results suggest that the transcription factor TX affects liver trNK cells development, and the underlying mechanisms await further investigation.

Intrahepatic recruitment of cytotoxic NK cells contributes to autoimmune hepatitis progression

Autoimmune hepatitis (AIH) is a chronic autoimmune disease with the primary focus on autoreactive Th1-mediated response and cytotoxic T cells reaction. The contribution of natural killer cells (NK cells) to AIH remains poorly understood. In this project, we revealed that the frequency of peripheral NK cells, more accurately CD56dimNK subset, was reduced in AIH patients. The reduction of CD56dimNK was negatively correlated with disease progression. In experimental autoimmune hepatitis (EAH), hepatic accumulation of NK cells is observed along with a decrease of NK cells in the periphery. In addition, infiltrated NK cells are almost conventional CXCR3− NK cells, the counterpart of CD56dimNK cells in the human. Furthermore, conventional CXCR3-NK cells of infiltration and liver resident NK cells are activated progressively at active phase. Therefore, recruitment of cytotoxic NK cells into the liver, but not liver resident NK cells expansion, may partly account for AIH progression.

Hepatectomy leads to loss of TRAIL-expressing liver NK cells via downregulation of the CXCL9-CXCR3 axis in mice.

Liver-resident natural killer (NK) cells express TNF-related apoptosis-inducing ligand (TRAIL), a critical molecule for NK cell-mediated tumor cell killing. We previously reported that TRAIL expression in liver NK cells decreases markedly after hepatectomy; however, the mechanism underlying this drastic alteration remains unknown. In this study, we assessed the role of chemokine signaling in liver-resident NK cells during the perioperative period of hepatectomy. The expression levels of various chemokine receptors on liver-resident NK cells and their associations with TRAIL expression were analyzed by flow cytometry. The expression of various intrahepatic chemokines/cytokines was analyzed after 70% hepatectomy in mice by quantitative RT-PCR and flow cytometry. We further investigated whether polyinosinic—polycytidylic acid (poly I:C)-induced NK cell activation could ameliorate TRAIL expression in the liver after 70% hepatectomy in CXCR3-/- and wild-type mice. TRAIL+ NK cells strongly and exclusively expressed CXCR3, and the expression of its ligand CXCL9 was significantly decreased in the liver after hepatectomy. The kinetics of hepatic CXCL9 expression resembled the changes in hepatic TRAIL+ NK cells after hepatectomy. Among liver-resident mononuclear cells, CXCL9 was predominantly secreted by macrophages in response to interferon-γ stimulation. Although the administration of poly I:C, an inducer of interferon-γ, increased hepatic CXCL9 levels in both CXCR3-/- and wild-type mice even after hepatectomy, only wild-type mice exhibited the recovery of TRAIL expression on NK cells. Partial hepatectomy remarkably reduced the proportion of TRAIL-expressing NK cells in the liver via the downregulation of the CXCL9–CXCR3 axis in mice. These findings extend our knowledge of the factors contributing to hepatocellular carcinoma recurrence after hepatectomy.

Liver-resident NK cells and their potential functions.

Natural killer (NK) cells represent a heterogeneous population of innate lymphocytes with phenotypically and functionally distinct subsets. In particular, recent studies have identified a unique subset of NK cells residing within the liver that are maintained as tissue-resident cells, confer antigen-specific memory responses and exhibit different phenotypical and developmental characteristics compared with conventional NK (cNK) cells. These findings have encouraged researchers to uncover tissue-resident NK cells at other sites, and detailed analyses have revealed that these tissue-resident NK cells share many similarities with liver-resident NK cells and tissue-resident memory T cells. Here, we present a brief historical perspective on the discovery of liver-resident NK cells and discuss their relationship to cNK cells and other emerging NK cell subsets and their potential functions.Cellular &Molecular Immunology advance online publication, 18 September 2017; doi:10.1038/cmi.2017.72.

Natural Killer Cells in Liver Disease.

AbstractNatural killer (NK) cells comprise one of the most abundant immune cell populations in human liver and the nature and functions of these cells have been a focus of recent interest. Here, we consider the possible roles of NK cells in diverse liver diseases, concentrating on data from patient studies. NK cells can be protective, killing virally infected and cancerous cells in the liver and limiting fibrosis by eliminating hepatic stellate cells. However, they can also be deleterious, contributing to pathology in viral hepatitis by killing hepatocytes and downregulating virus-specific T-cell responses. It has recently emerged that a large fraction of hepatic NK cells constitute a distinct liver-resident subset and we highlight the need to distinguish between circulating and liver-resident NK cells in future studies. There is also a need for further investigation into how NK cells are influenced by the liver microenvironment and what scope there is to harness their immunotherapeutic potential.

Human intrahepatic CD69\u2009+\u2009CD8+ T cells have a tissue resident memory T cell phenotype with reduced cytolytic capacity

Tissue resident memory T cells (TRM) have been identified in various tissues, however human liver TRM to date remain unidentified. TRM can be recognized by CD69 and/or CD103 expression and may play a role in the pathology of chronic hepatitis B (CHB) and hepatitis C virus infection (CHC). Liver and paired blood mononuclear cells from 17 patients (including 4 CHB and 6 CHC patients) were isolated and CD8+ T cells were comprehensively analysed by flowcytometry, immunohistochemistry and qPCR. The majority of intrahepatic CD8+ T cells expressed CD69, a marker used to identify TRM, of which a subset co-expressed CD103. CD69 + CD8+ T cells expressed low levels of S1PR1 and KLF2 and a large proportion (>90%) was CXCR6+, resembling liver TRM in mice and liver resident NK cells in human. Cytotoxic proteins were only expressed in a small fraction of liver CD69 + CD8+ T cells in patients without viral hepatitis, however, in livers from CHB patients more CD69 + CD8+ T cells were granzyme B+. In CHC patients, less intrahepatic CD69 + CD8+ T cells were Hobit+ as compared to CHB and control patients. Intrahepatic CD69 + CD8+ T cells likely TRM which have a reduced cytolytic potential. In patients with chronic viral hepatitis TRM have a distinct phenotype.