CXCR6 marks a novel subset of T-bet(lo)Eomes(hi) natural killer cells residing in human liver

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Single-cell landscape of functionally cured chronic hepatitis B patients reveals activation of innate and altered CD4-CTL-driven adaptive immunity

BACKGROUND & AIMS

Hepatitis B surface antigen (HBsAg) loss or functional cure (FC) is considered the optimal therapeutic outcome for patients with chronic hepatitis B (CHB). However, the immune-pathological biomarkers and underlying mechanisms of FC remain unclear. In this study we comprehensively interrogate disease-associated cell states identified within intrahepatic tissue and matched PBMCs (peripheral blood mononuclear cells) from patients with CHB or after FC, at the resolution of single cells, to provide novel insights into putative mechanisms underlying FC.

METHODS

We combined single-cell transcriptomics (single-cell RNA sequencing) with multiparametric flow cytometry-based immune phenotyping, and multiplexed immunofluorescence to elucidate the immunopathological cell states associated with CHB vs. FC.

RESULTS

We found that the intrahepatic environment in CHB and FC displays specific cell identities and molecular signatures that are distinct from those found in matched PBMCs. FC is associated with the emergence of an altered adaptive immune response marked by CD4 cytotoxic T lymphocytes, and an activated innate response represented by liver-resident natural killer cells, specific Kupffer cell subtypes and marginated neutrophils. Surprisingly, we found MHC class II-expressing hepatocytes in patients achieving FC, as well as low but persistent levels of covalently closed circular DNA and pregenomic RNA, which may play an important role in FC.

CONCLUSIONS

Our study provides conceptually novel insights into the immuno-pathological control of HBV cure, and opens exciting new avenues for clinical management, biomarker discovery and therapeutic development. We believe that the discoveries from this study, as it relates to the activation of an innate and altered immune response that may facilitate sustained, low-grade inflammation, may have broader implications in the resolution of chronic viral hepatitis.

IMPACT AND IMPLICATIONS

This study dissects the immuno-pathological cell states associated with functionally cured chronic hepatitis B (defined by the loss of HBV surface antigen or HBsAg). We identified the sustained presence of very low viral load, accessory antigen-presenting hepatocytes, adaptive-memory-like natural killer cells, and the emergence of helper CD4 T cells with cytotoxic or effector-like signatures associated with functional cure, suggesting previously unsuspected alterations in the adaptive immune response, as well as a key role for the innate immune response in achieving or maintaining functional cure. Overall, the insights generated from this study may provide new avenues for the development of alternative therapies as well as patient surveillance for better clinical management of chronic hepatitis B.

TLR8 agonist selgantolimod regulates Kupffer cell differentiation status and impairs HBV entry into hepatocytes via an IL-6-dependent mechanism

OBJECTIVE

Achieving HBV cure will require novel combination therapies of direct-acting antivirals and immunomodulatory agents. In this context, the toll-like receptor 8 (TLR8) agonist selgantolimod (SLGN) has been investigated in preclinical models and clinical trials for chronic hepatitis B (CHB). However, little is known regarding its action on immune effectors within the liver. Our aim was to characterise the transcriptomic changes and intercellular communication events induced by SLGN in the hepatic microenvironment.

DESIGN

We identified TLR8-expressing cell types in the human liver using publicly available single-cell RNA-seq data and established a method to isolate Kupffer cells (KCs). We characterised transcriptomic and cytokine KC profiles in response to SLGN. SLGN's indirect effect was evaluated by RNA-seq in hepatocytes treated with SLGN-conditioned media (CM) and quantification of HBV parameters following infection. Pathways mediating SLGN's effect were validated using transcriptomic data from HBV-infected patients.

RESULTS

Hepatic TLR8 expression takes place in the myeloid compartment. SLGN treatment of KCs upregulated monocyte markers (eg, S100A12) and downregulated genes associated with the KC identity (eg, SPIC). Treatment of hepatocytes with SLGN-CM downregulated NTCP and impaired HBV entry. Cotreatment with an interleukin 6-neutralising antibody reverted the HBV entry inhibition.

CONCLUSION

Our transcriptomic characterisation of SLGN sheds light into the programmes regulating KC activation. Furthermore, in addition to its previously described effect on established HBV infection and adaptive immunity, we show that SLGN impairs HBV entry. Altogether, SLGN may contribute through KCs to remodelling the intrahepatic immune microenvironment and may thus represent an important component of future combinations to cure HBV infection.

Tissue-resident memory NK cells: Homing in on local effectors and regulators

Natural killer (NK) cells are the prototype innate effector lymphocyte population that plays an important role in controlling viral infections and tumors. Studies demonstrating that NK cells form long-lived memory populations, akin to those generated by adaptive immune cells, prompted a revaluation of the potential functions of NK cells. Recent data demonstrating that NK cells are recruited from the circulation into tissues where they form long-lived memory-like populations further emphasize that NK cells have properties that mirror those of adaptive immune cells. NK cells that localize in non-lymphoid tissues are heterogeneous, and there is a growing appreciation that immune responses occurring within tissues are subject to tissue-specific regulation. Here we discuss both the immune effector and immunoregulatory functions of NK cells, with a particular emphasis on the role of NK cells within non-lymphoid tissues and how the tissue microenvironment shapes NK cell-dependent outcomes.

Heterogeneity in Liver Cancer Immune Microenvironment: Emerging Single-Cell and Spatial Perspectives

Primary liver cancer is a solid malignancy with a high mortality rate. The success of immunotherapy has shown great promise in improving patient care and highlights a crucial need to understand the complexity of the liver tumor immune microenvironment (TIME). Recent advances in single-cell and spatial omics technologies, coupled with the development of systems biology approaches, are rapidly transforming the landscape of tumor immunology. Here we review the cellular landscape of liver TIME from single-cell and spatial perspectives. We also discuss the cellular interaction networks within the tumor cell community in regulating immune responses. We further highlight the challenges and opportunities with implications for biomarker discovery, patient stratification, and combination immunotherapies.

Decidual leukocytes respond to African lineage Zika virus infection with mild anti-inflammatory changes during acute infection in rhesus macaques

Zika virus (ZIKV) can be vertically transmitted during pregnancy resulting in a range of adverse pregnancy outcomes. The decidua is commonly found to be infected by ZIKV, yet the acute immune response to infection remains understudied in vivo. We hypothesized that in vivo African-lineage ZIKV infection induces a pro-inflammatory response in the decidua. To test this hypothesis, we evaluated the decidua in pregnant rhesus macaques within the first two weeks following infection with an African-lineage ZIKV and compared our findings to gestationally aged-matched controls. Decidual leukocytes were phenotypically evaluated using spectral flow cytometry, and cytokines and chemokines were measured in tissue homogenates from the decidua, placenta, and fetal membranes. The results of this study did not support our hypothesis. Although ZIKV RNA was detected in the decidual tissue samples from all ZIKV infected dams, phenotypic changes in decidual leukocytes and differences in cytokine profiles suggest that the decidua undergoes mild anti-inflammatory changes in response to that infection. Our findings emphasize the immunological state of the gravid uterus as a relatively immune privileged site that prioritizes tolerance of the fetus over mounting a pro-inflammatory response to clear infection.

Are innate lymphoid cells friend or foe in human pregnancy?

Innate lymphoid cells (ILCs) are involved in the innate immune system because they lack specific antigen receptors and lineage markers. ILCs also display phenotypic and characteristic features of adaptive immune cells. Therefore, ILCs are functional in essential interactions between adaptive and innate immunity. ILCs are found in both lymphoid and nonlymphoid tissues and migrate to the area of inflammation during the inflammatory process. ILCs respond to pathogens by producing a variety of cytokines and are involved in the barrier defense of antigens and in many immunological processes such as allergic events. Recent research has shown that ILCs are functional during human pregnancy and have been suggested to be essential for the healthy progression of pregnancy. In this review, we focus on the role of ILCs in human pregnancy by discussing the relationship between ILCs and the pregnancy microenvironment, specifically summarizing the role of ILCs in physiological and pathological pregnancies.

Serum CXCL16: A new predictor of liver inflammation in patients with chronic hepatitis B

The prompt initiation of antiviral therapy is essential in patients with chronic hepatitis B (CHB), especially when severe liver inflammation is detected. However, transcutaneous liver puncture, the gold standard for assessing liver inflammation, is invasive and its widespread application is limited. Therefore, there is an urgent need for more non-invasive markers to predict liver inflammation. In our retrospective cross-sectional study, which included 120 CHB patients and 31 healthy subjects, we observed a significant increase in serum chemokine C-X-C-motif ligand 16 (CXCL16) in CHB patients compared to healthy controls (p < .001). Notably, patients with severe inflammation (Scheuer's grade G ≥ 3, n = 26) exhibited a substantial increase in serum CXCL16 compared to those with non-severe inflammation (Scheuer's grade G < 3, n = 96) [(median, IQR), 0.42 (0.24-0.71) ng/mL vs. 1.01 (0.25-2.09) ng/mL, p < .001]. Furthermore, we developed a predictive model that combined CXCL16 with platelet count (PLT), alanine aminotransferase (ALT) and albumin (ALB) to accurately predict liver inflammation in CHB patients. This model was more effective than ALT alone in predicting liver inflammation (AUC, 0.92 vs. 0.81, p = .015). Additionally, using an HBV-transduced mouse model, we demonstrated that blocking CXCL16 led to a reduction in liver inflammation and impaired infiltration and function of natural killer T (NKT) and natural killer (NK) cells. These findings suggest that CXCL16 is a promising non-invasive biomarker of liver inflammation in CHB patients and may play a role in inducing liver inflammation via a NKT and NK cell pathway.

NKG2A discriminates natural killer cells with a suppressed phenotype in pediatric acute leukemia

Natural killer (NK) cells are important for early tumor immune surveillance. In patients with hematological cancers, NK cells are generally functional deficient and display dysregulations in their receptor repertoires. Acute leukemia is the most common cancer in children, and we here performed a comparative phenotypic profiling of NK cells from B-cell precursor acute lymphoblastic leukemia (BCP-ALL) patients to identify aberrant NK cell phenotypes. NK cell phenotypes, maturation, and function were analyzed in matched bone marrow and blood NK cells from BCP-ALL patients at diagnosis, during treatment, and at end of treatment and compared with age-matched pediatric control subjects. Expression of several markers were skewed in patients, but with large interindividual variations. Undertaking a multiparameter approach, we found that high expression levels of NKG2A was the single predominant marker distinguishing NK cells in BCP-ALL patients compared with healthy control subjects. Moreover, naïve CD57-NKG2A NK cells dominated in BCP-ALL patients at diagnosis. Further, we found dysregulated expression of the activating receptor DNAM-1 in resident bone marrow CXCR6+ NK cells. CXCR6+ NK cells lacking DNAM-1 expressed NKG2A and had a tendency for lower degranulation activity. In conclusion, high expression of NKG2A dominates NK cell phenotypes from pediatric BCP-ALL patients, indicating that NKG2A could be targeted in therapies for this patient group.

High CD49a+ NK cell infiltrate is associated with poor clinical outcomes in Hepatocellular Carcinoma

NK cells infiltrating Hepatocellular Carcinoma (HCC) may express residency markers such as Integrin Subunit Alpha 1 (CD49a) that have been associated with nurturing functions in the decidua, and characterized by the production of angiogenic factors as well as loss of cytotoxicity. CIBERSORT, a computational analysis method for quantifying cell fractions from bulk tissue gene expression profiles, was used to estimate the infiltrating immune cell composition of the tumor microenvironment from gene expression profiles of a large cohort of 225 HCCs in the public GEO database. Decidual-like CD49a+ NK cells, in addition to another 22 immune cell populations, were characterized and thoroughly investigated so that HCC cell heterogeneity in a large cohort of 225 HCCs from the public GEO database could be studied. An inverse correlation of the expression of CD49a+ NK-cells and CD8+ T-cells suggested a negative association with clinical outcomes. This result was confirmed in a further validation cohort of 100 HCC patients from The Cancer Genome Atlas, Liver Hepatocellular Carcinoma (TCGA-LIHC). Cox regression analysis did not identify CD49a+ cells as a variable independently associated with survival. However, a more abundant infiltrate of this subset was present in patients at a more advanced pathological and clinical HCC stage. In conclusion, we found that NK cells, with a decidual-like gene expression profile, are enriched in HCC, and their abundance increases not only in tumor size but also at advanced stages of the disease suggesting that these cells play a role in tumor growth. For this reason, these NK cells may represent a possible new target for immunotherapeutic approaches in HCC.

Comparative transcriptomics of porcine liver-resident CD8αdim, liver CD8αhigh and circulating blood CD8αhigh NK cells reveals an intermediate phenotype of liver CD8αhigh NK cells

Liver-resident NK (lrNK) cells have been studied in humans as well as in mice. Unfortunately, important differences have been observed between murine and human lrNK cells, complicating the extrapolation of data obtained in mice to man. We previously described two NK cell subsets in the porcine liver: A CD8αhigh subset, with a phenotype much like conventional CD8αhigh NK cells found in the peripheral blood, and a specific liver-resident CD8αdim subset which phenotypically strongly resembles human lrNK cells. These data suggest that the pig might be an attractive model for studying lrNK cell biology. In the current study, we used RNA-seq to compare the transcriptome of three porcine NK cell populations: Conventional CD8αhigh NK cells from peripheral blood (cNK cells), CD8αhigh NK cells isolated from the liver, and the liver-specific CD8αdim NK cells. We found that highly expressed transcripts in the CD8αdim lrNK cell population mainly include genes associated with the (adaptive) immune response, whereas transcripts associated with cell migration and extravasation are much less expressed in this subset compared to cNK cells. Overall, our data indicate that CD8αdim lrNK cells show an immature and anti-inflammatory phenotype. Interestingly, we also observed that the CD8αhigh NK cell population that is present in the liver appears to represent a population with an intermediate phenotype. Indeed, while the transcriptome of these cells largely overlaps with that of cNK cells, they also express transcripts associated with liver residency, in particular CXCR6. The current, in-depth characterization of the transcriptome of porcine liver NK cell populations provides a basis to use the pig model for research into liver-resident NK cells.

Protective and pathogenic functions of innate lymphoid cells in transplantation

Innate lymphoid cells (ILCs) are a family of lymphocytes with essential roles in tissue homeostasis and immunity. Along with other tissue-resident immune populations, distinct subsets of ILCs have important roles in either promoting or inhibiting immune tolerance in a variety of contexts, including cancer and autoimmunity. In solid organ and hematopoietic stem cell transplantation, both donor and recipient-derived ILCs could contribute to immune tolerance or rejection, yet understanding of protective or pathogenic functions are only beginning to emerge. In addition to roles in directing or regulating immune responses, ILCs interface with parenchymal cells to support tissue homeostasis and even regeneration. Whether specific ILCs are tissue-protective or enhance ischemia reperfusion injury or fibrosis is of particular interest to the field of transplantation, beyond any roles in limiting or promoting allograft rejection or graft-versus host disease. Within this review, we discuss the current understanding of ILCs functions in promoting immune tolerance and tissue repair at homeostasis and in the context of transplantation and highlight where targeting or harnessing ILCs could have applications in novel transplant therapies.

The histone demethylase Utx controls CD8+ T-cell-dependent antitumor immunity via epigenetic regulation of the effector function

CD8⁺ T cells play a central role in antitumor immune responses. Epigenetic gene regulation is essential to acquire the effector function of CD8⁺ T cells. However, the role of Utx, a demethylase of histone H3K27, in antitumor immunity remains unclear. In this study, we examined the roles of Utx in effector CD8⁺ T-cell differentiation and the antitumor immune response. In a murine tumor-bearing model, an increased tumor size and decreased survival rate were observed in T-cell-specific Utx KO (Utx KO) mice compared with wild-type (WT) mice. The number of CD8⁺ T cells in tumor-infiltrating lymphocytes (TILs) was significantly decreased in Utx KO mice. We found that the acquisition of effector function was delayed and attenuated in Utx KO CD8⁺ T cells. RNA sequencing revealed that the expression of effector signature genes was decreased in Utx KO effector CD8⁺ T cells, while the expression of naïve or memory signature genes was increased. Furthermore, the expression of Cxcr3, which is required for the migration of effector CD8⁺ T cells to tumor sites, was substantially decreased in Utx KO CD8⁺ T cells. These findings suggest that Utx promotes CD8⁺ T-cell-dependent antitumor immune responses partially through epigenetic regulation of the effector function.

Hepatic C-X-C chemokine receptor type 6-expressing innate lymphocytes limit detrimental myeloid hyperactivation in acute liver injury

BACKGROUND

Acute liver failure (ALF) is characterized by rapid clinical deterioration and high mortality. Acetaminophen (APAP or paracetamol) overdose is a leading cause of ALF, resulting in hepatocellular necrosis with subsequent inflammation, inflicting further liver damage. Infiltrating myeloid cells are early drivers of liver inflammation. However, the role of the abundant population of liver-resident innate lymphocytes, which commonly express the chemokine receptor CXCR6, is incompletely understood in ALF.

METHODS

We investigated the role of CXCR6-expressing innate lymphocytes using the model of acute APAP toxicity in mice deficient in CXCR6 (Cxcr6gfp/gfp).

RESULTS

APAP-induced liver injury was strongly aggravated in Cxcr6gfp/gfp mice compared with wild-type counterparts. Immunophenotyping using flow cytometry revealed a reduction in liver CD4+T cells, natural killer (NK) cells, and most prominently, NKT cells, whereas CXCR6 was dispensable for CD8+ T-cell accumulation. CXCR6-deficient mice exhibited excessive neutrophil and inflammatory macrophage infiltration. Intravital microscopy revealed dense cellular clusters of neutrophils in necrotic liver tissue, with higher numbers of clustering neutrophils in Cxcr6gfp/gfp mice. Gene expression analysis linked hyperinflammation in CXCR6 deficiency to increased IL-17 signaling. Although reduced in overall numbers, CXCR6-deficient mice had a shift in NKT cell subsets with increased RORγt-expressing NKT17 cells as a likely source of IL-17. In patients with ALF, we found a prominent accumulation of IL-17-expressing cells. Accordingly, CXCR6-deficient mice lacking IL-17 (Cxcr6gfp/gfpx Il17-/-) had ameliorated liver damage and reduced inflammatory myeloid infiltrates.

CONCLUSIONS

Our study identifies a crucial role of CXCR6-expressing liver innate lymphocytes as orchestrators in acute liver injury containing IL-17-mediated myeloid cell infiltration. Hence, strengthening the CXCR6-axis or downstream inhibition of IL-17 could yield novel therapeutics in ALF.

Control of human cytomegalovirus replication by liver resident natural killer cells

Natural killer cells are considered to be important for control of human cytomegalovirus- a major pathogen in immune suppressed transplant patients. Viral infection promotes the development of an adaptive phenotype in circulating natural killer cells that changes their anti-viral function. In contrast, less is understood how natural killer cells that reside in tissue respond to viral infection. Here we show natural killer cells resident in the liver have an altered phenotype in cytomegalovirus infected individuals and display increased anti-viral activity against multiple viruses in vitro and identify and characterise a subset of natural killer cells responsible for control. Crucially, livers containing natural killer cells with better capacity to control cytomegalovirus replication in vitro are less likely to experience viraemia post-transplant. Taken together, these data suggest that virally induced expansion of tissue resident natural killer cells in the donor organ can reduce the chance of viraemia post-transplant.

The co-inhibitory receptor TIGIT regulates NK cell function and is upregulated in human intrahepatic CD56bright NK cells

The crosstalk between NK cells and their surrounding environment is enabled through activating and inhibitory receptors, which tightly control NK cell activity. The co-inhibitory receptor TIGIT decreases NK cell cytotoxicity and is involved in NK cell exhaustion, but has also been associated with liver regeneration, highlighting that the contribution of human intrahepatic CD56bright NK cells in regulating tissue homeostasis remains incompletely understood. A targeted single-cell mRNA analysis revealed distinct transcriptional differences between matched human peripheral blood and intrahepatic CD56bright NK cells. Multiparameter flow cytometry identified a cluster of intrahepatic NK cells with overlapping high expression of CD56, CD69, CXCR6, TIGIT and CD96. Intrahepatic CD56bright NK cells also expressed significantly higher protein surface levels of TIGIT, and significantly lower levels of DNAM-1 compared to matched peripheral blood CD56bright NK cells. TIGIT+ CD56bright NK cells showed diminished degranulation and TNF-α production following stimulation. Co-incubation of peripheral blood CD56bright NK cells with human hepatoma cells or primary human hepatocyte organoids resulted in migration of NK cells into hepatocyte organoids and upregulation of TIGIT and downregulation of DNAM-1 expression, in line with the phenotype of intrahepatic CD56bright NK cells. Intrahepatic CD56bright NK cells represent a transcriptionally, phenotypically, and functionally distinct population of NK cells that expresses higher levels of TIGIT and lower levels of DNAM-1 than matched peripheral blood CD56bright NK cells. Increased expression of inhibitory receptors by NK cells within the liver environment can contribute to tissue homeostasis and reduction of liver inflammation.

ILC1: Development, maturation, and transcriptional regulation

Type 1 Innate Lymphoid cells (ILC1s) are tissue-resident cells that partake in the regulation of inflammation and homeostasis. A major feature of ILC1s is their ability to rapidly respond after infections. The effector repertoire of ILC1s includes the pro-inflammatory cytokines IFN-γ and TNF-α and cytotoxic mediators such as granzymes, which enable ILC1s to establish immune responses and to directly kill target cells. Recent advances in the characterization of ILC1s have considerably furthered our understanding of ILC1 development and maintenance in tissues. In particular, it has become clear how ILC1s operate independently from conventional natural killer cells, with which they share many characteristics. In this review, we discuss recent developments with regards to the differentiation, polarization, and effector maturation of ILC1s. These processes may underlie the observed heterogeneity in ILC1 populations within and between different tissues. Next, we highlight transcriptional programs that control each of the separate steps in the differentiation of ILC1s. These transcriptional programs are shared with other tissue-resident type-1 lymphocytes, such as tissue-resident memory T cells (T_RM ) and invariant natural killer T cells (iNKT), highlighting that ILC1s utilize networks of transcriptional regulation that are conserved between lymphocyte lineages to respond effectively to tissue-invading pathogens.

Mapping the interplay between NK cells and HIV: therapeutic implications

Although highly effective at durably suppressing plasma HIV-1 viremia, combination antiretroviral therapy (ART) treatment regimens do not eradicate the virus, which persists in long-lived CD4+ T cells. This latent viral reservoir serves as a source of plasma viral rebound following treatment interruption, thus requiring lifelong adherence to ART. Additionally, challenges remain related not only to access to therapy but also to a higher prevalence of comorbidities with an inflammatory etiology in treated HIV-1+ individuals, underscoring the need to explore therapeutic alternatives that achieve sustained virologic remission in the absence of ART. Natural killer (NK) cells are uniquely positioned to positively impact antiviral immunity, in part due to the pleiotropic nature of their effector functions, including the acquisition of memory-like features, and, therefore, hold great promise for transforming HIV-1 therapeutic modalities. In addition to defining the ability of NK cells to contribute to HIV-1 control, this review provides a basic immunologic understanding of the impact of HIV-1 infection and ART on the phenotypic and functional character of NK cells. We further delineate the qualities of "memory" NK cell populations, as well as the impact of HCMV on their induction and subsequent expansion in HIV-1 infection. We conclude by highlighting promising avenues for optimizing NK cell responses to improve HIV-1 control and effect a functional cure, including blockade of inhibitory NK receptors, TLR agonists to promote latency reversal and NK cell activation, CAR NK cells, BiKEs/TriKEs, and the role of HIV-1-specific bNAbs in NK cell-mediated ADCC activity against HIV-1-infected cells.

Single-cell RNA sequencing identifies a population of human liver-type ILC1s

Group 1 innate lymphoid cells (ILCs) comprise a heterogeneous family of cytotoxic natural killer (NK) cells and ILC1s. We identify a population of "liver-type" ILC1s with transcriptional, phenotypic, and functional features distinct from those of conventional and liver-resident NK cells as well as from other previously described human ILC1 subsets. LT-ILC1s are CD49a+CD94+CD200R1+, express the transcription factor T-BET, and do not express the activating receptor NKp80 or the transcription factor EOMES. Similar to NK cells, liver-type ILC1s produce IFN-γ, TNF-α, and GM-CSF; however, liver-type ILC1s also produce IL-2 and lack perforin and granzyme-B. Liver-type ILC1s are expanded in cirrhotic liver tissues, and they can be produced from blood-derived ILC precursors in vitro in the presence of TGF-β1 and liver sinusoidal endothelial cells. Cells with similar signature and function can also be found in tonsil and intestinal tissues. Collectively, our study identifies and classifies a population of human cross-tissue ILC1s.

Human Hematopoietic Stem Cell Engrafted IL-15 Transgenic NSG Mice Support Robust NK Cell Responses and Sustained HIV-1 Infection

Mice reconstituted with human immune systems are instrumental in the investigation of HIV-1 pathogenesis and therapeutics. Natural killer (NK) cells have long been recognized as a key mediator of innate anti-HIV responses. However, established humanized mouse models do not support robust human NK cell development from engrafted human hematopoietic stem cells (HSCs). A major obstacle to human NK cell reconstitution is the lack of human interleukin-15 (IL-15) signaling, as murine IL-15 is a poor stimulator of the human IL-15 receptor. Here, we demonstrate that immunodeficient NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice expressing a transgene encoding human IL-15 (NSG-Tg(IL-15)) have physiological levels of human IL-15 and support long-term engraftment of human NK cells when transplanted with human umbilical-cord-blood-derived HSCs. These Hu-NSG-Tg(IL-15) mice demonstrate robust and long-term reconstitution with human immune cells, but do not develop graft-versus-host disease (GVHD), allowing for long-term studies of human NK cells. Finally, we show that these HSC engrafted mice can sustain HIV-1 infection, resulting in human NK cell responses in HIV-infected mice. We conclude that Hu-NSG-Tg(IL-15) mice are a robust novel model to study NK cell responses to HIV-1.

The scientific basis of combination therapy for chronic hepatitis B functional cure

Functional cure of chronic hepatitis B (CHB) - or hepatitis B surface antigen (HBsAg) loss after 24 weeks off therapy - is now the goal of treatment, but is rarely achieved with current therapy. Understanding the hepatitis B virus (HBV) life cycle and immunological defects that lead to persistence can identify targets for novel therapy. Broadly, treatments fall into three categories: those that reduce viral replication, those that reduce antigen load and immunotherapies. Profound viral suppression alone does not achieve quantitative (q)HBsAg reduction or HBsAg loss. Combining nucleos(t)ide analogues and immunotherapy reduces qHBsAg levels and induces HBsAg loss in some patients, particularly those with low baseline qHBsAg levels. Even agents that are specifically designed to reduce viral antigen load might not be able to achieve sustained HBsAg loss when used alone. Thus, rationale exists for the use of combinations of all three therapy types. Monitoring during therapy is important not just to predict HBsAg loss but also to understand mechanisms of HBsAg loss using viral and immunological biomarkers, and in selected cases intrahepatic sampling. We consider various paths to functional cure of CHB and the need to individualize treatment of this heterogeneous infection until a therapeutic avenue for all patients with CHB is available.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

The immune landscape in hepatitis delta virus infection-Still an open field!

Hepatitis delta virus (HDV) is known to cause the most aggressive and severe form of viral hepatitis, yet it remained under-diagnosed but does require early diagnosis for accurate disease staging. Antibody to HDV (anti-HDV) is the primary screening tool and should be assessed in patients with hepatitis B surface antigen (HBsAg) positivity, as HDV is a satellite RNA virus of hepatitis B. Additionally, the viral load (HDV RNA) should be assessed in those with positive anti-HDV, to differentiate between active infection and resolved hepatitis delta. Data regarding immune responses in HDV are limited but show dysfunctional adaptive and innate immunity. Many studies however fail to distinguish between active and resolved infection. Limited treatments are available for HDV, but promise has been shown with the newly approved Bulevirtide, a first-in-class HBV entry inhibitor. Thus immune response during therapy requires further investigation, along with additional targets for HDV cure.

Prospects for NK-based immunotherapy of chronic HBV infection

Effective and long-term treatment is required for controlling chronic Hepatitis B Virus (HBV) infection. Natural killer (NK) cells are antiviral innate lymphocytes and represent an essential arm of current immunotherapy. In chronic HBV (CHB), NK cells display altered changes in phenotypes and functions, but preserve antiviral activity, especially for cytolytic activity. On the other hand, NK cells might also cause liver injury in the disease. NK -based immunotherapy, including adoptive NK cell therapy and NK -based checkpoint inhibition, could potentially exploit the antiviral aspect of NK cells for controlling CHB infection while preventing liver tissue damage. Here, we review recent progress in NK cell biology under the context of CHB infection, and discuss potential NK -based immunotherapy strategies for the disease.

Immunobiology of the biliary tract system

The biliary tract is a complex tubular organ system spanning from the liver to the duodenum. It is the site of numerous acute and chronic disorders, many of unknown origin, that are often associated with cancer development and for which there are limited treatment options. Cholangiocytes with proinflammatory capacities line the lumen and specialised types of immune cells reside in close proximity. Recent technological breakthroughs now permit spatiotemporal assessments of immune cells within distinct niches and have increased our understanding of immune cell tissue residency. In this review, a comprehensive overview of emerging knowledge on the immunobiology of the biliary tract system is provided, with a particular emphasis on the role of distinct immune cells in biliary disorders.

Single-cell transcriptomics in bone marrow delineates CD56dimGranzymeK+ subset as intermediate stage in NK cell differentiation

Human natural killer (NK) cells in lymphoid tissues can be categorized into three subsets: CD56^brightCD16⁺, CD56^dimCD16⁺ and CD69⁺CXCR6⁺ lymphoid tissue-resident (lt)NK cells. How the three subsets are functionally and developmentally related is currently unknown. Therefore, we performed single-cell RNA sequencing combined with oligonucleotide-conjugated antibodies against CD56, CXCR6, CD117 and CD34 on fresh bone marrow NK cells. A minor CD56^dimGzmK⁺ subset was identified that shared features with CD56^bright and CD56^dimGzmK^- NK cells based on transcriptome, phenotype (NKG2A^highCD16^lowKLRG1^highTIGIT^high) and functional analysis in bone marrow and blood, supportive for an intermediate subset. Pseudotime analysis positioned CD56^bright, CD56^dimGzmK⁺ and CD56^dimGzmK^- cells in one differentiation trajectory, while ltNK cells were developmentally separated. Integrative analysis with bone marrow cells from the Human Cell Atlas did not demonstrate a developmental connection between CD34⁺ progenitor and NK cells, suggesting absence of early NK cell stages in bone marrow. In conclusion, single-cell transcriptomics provide new insights on development and differentiation of human NK cells.

Barcode clonal tracking of tissue-resident immune cells in rhesus macaque highlights distinct clonal distribution pattern of tissue NK cells

Tissue resident (TR) immune cells play important roles in facilitating tissue homeostasis, coordinating immune responses against infections and tumors, and maintaining immunological memory. While studies have shown these cells are distinct phenotypically and functionally from cells found in the peripheral blood (PB), the clonal relationship between these populations across tissues has not been comprehensively studied in primates or humans. We utilized autologous transplantation of rhesus macaque hematopoietic stem and progenitor cells containing high diversity barcodes to track the clonal distribution of T, B, myeloid and natural killer (NK) cell populations across tissues, including liver, spleen, lung, and gastrointestinal (GI) tract, in comparison with PB longitudinally post-transplantation, in particular we focused on NK cells which do not contain endogenous clonal markers and have not been previously studied in this context. T cells demonstrated tissue-specific clonal expansions as expected, both overlapping and distinct from blood T cells. In contrast, B and myeloid cells showed a much more homogeneous clonal pattern across various tissues and the blood. The clonal distribution of TR NK was more heterogenous between individual animals. In some animals, as we have previously reported, we observed large PB clonal expansions in mature CD56-CD16+ NK cells. Notably, we found a separate set of highly expanded PB clones in CD16-CD56- (DN) NK subset that were also contributing to TR NK cells in all tissues examined, both in TR CD56-CD16+ and DN populations but absent in CD56⁺16^- TR NK across all tissues analyzed. Additionally, we observed sets of TR NK clones specific to individual tissues such as lung or GI tract and sets of TR NK clones shared across liver and spleen, distinct from other tissues. Combined with prior functional data that suggests NK memory is restricted to liver or other TR NK cells, these clonally expanded TR NK cells may be of interest for future investigation into NK cell tissue immunological memory, with implications for development of NK based immunotherapies and an understanding of NK memory.

Renal inflamm-aging provokes intra-graft inflammation following experimental kidney transplantation

Donor age is a major risk factor for allograft outcome in kidney transplantation. The underlying cellular mechanisms and the recipient's immune response within an aged allograft have yet not been analyzed. A comprehensive immunophenotyping of naïve and transplanted young versus aged kidneys revealed that naïve aged murine kidneys harbor significantly higher frequencies of effector/memory T cells, whereas regulatory T cells were reduced. Aged kidney-derived CD8⁺ T cells produced more IFNγ than their young counterparts. Senescent renal CD8⁺ T and NK cells upregulated the cytotoxicity receptor NKG2D and the enrichment of memory-like CD49a⁺ CXCR6⁺ NK cells was documented in aged naïve kidneys. In the C57BL/6 to BALB/c kidney transplantation model, recipient-derived T cells infiltrating an aged graft produced significantly more IFNγ, granzyme B and perforin on day 7 post-transplantation, indicating an enhanced inflammatory, cytotoxic response towards the graft. Pre-treatment of aged kidney donors with the senolytic drug ABT-263 changed the recipient-derived effector molecule profile to significantly reduced levels of IFNγ and IL-10 compared to controls. Graft function after ABT-263 pre-treatment was significantly improved 28 days post kidney transplantation. In conclusion, renal senescence also occurs at the immunological level (inflamm-aging) and aged organs provoke an altered recipient-dominated immune response in the graft.

Liver-resident memory T cells: life in lockdown

A subset of memory T cells has been identified in the liver with a tissue-resident profile and the capacity for long-term 'lockdown'. Here we review how they are retained in, and adapted to, the hepatic microenvironment, including its unique anatomical features and metabolic challenges. We describe potential interactions with other local cell types and the need for a better understanding of this complex bidirectional crosstalk. Pathogen or tumour antigen-specific tissue-resident memory T cells (T_RM) can provide rapid frontline immune surveillance; we review the evidence for this in hepatotropic infections of major worldwide importance like hepatitis B and malaria and in liver cancers like hepatocellular carcinoma. Conversely, T_RM can be triggered by pro-inflammatory and metabolic signals to mediate bystander tissue damage, with an emerging role in a number of liver pathologies. We discuss the need for liver sampling to gain a window into these compartmentalised T cells, allowing more accurate disease monitoring and future locally targeted immunotherapies.

Differential Homing Receptor Profiles of Lymphocytes Induced by Attenuated versus Live Plasmodium falciparum Sporozoites

The onset of an adaptive immune response provides the signals required for differentiation of antigen-specific lymphocytes into effector cells and imprinting of these cells for re-circulation to the most appropriate anatomical site (i.e., homing). Lymphocyte homing is governed by the expression of tissue-specific lymphocyte homing receptors that bind to unique tissue-specific ligands on endothelial cells. In this study, a whole-parasite malaria vaccine (radiation-attenuated sporozoites (RAS)) was used as a model system to establish homing receptor signatures induced by the parasite delivered through mosquito bite to provide a benchmark of desirable homing receptors for malaria vaccine developers. This immunization regimen resulted in the priming of antigen-specific B cells and CD8⁺ T cells for homing primarily to the skin and T/B cell compartments of secondary lymphoid organs. Infection with live sporozoites, however, triggers the upregulation of homing receptor for the liver and the skin, demonstrating that there is a difference in the signal provided by attenuated vs. live sporozoites. This is the first report on imprinting of homing routes by Plasmodium sporozoites and, surprisingly, it also points to additional, yet to be identified, signals provided by live parasites that prime lymphocytes for homing to the liver. The data also demonstrate the utility of this method for assessing the potential of vaccine formulations to direct antigen-specific lymphocytes to the most relevant anatomical site, thus potentially impacting vaccine efficacy.

Impaired intratumoral natural killer cell function in head and neck carcinoma

Natural killer (NK) cells are emerging as unique players in the immune response against cancer; however, only limited data are available on tumor infiltrating NK cells in head and neck squamous cell carcinoma (HNSCC), one of the most common cancer. Occurrence of HNSCC is closely related to the immune microenvironment, and immunotherapy is increasingly being applied to this setting. However, the limited success of this type of treatment in this tumor calls for further investigation in the field.

Surgical HNSSC specimens of 32 consecutive patients were mechanically and enzymatically dissociated. Tumor cells were separated from infiltrating cells by short centrifugation and infiltrating NK cells were phenotypically and functionally characterized by multiple antibody staining and flow cytometry. Tumor infiltrating NK cells in HNSCC showed a peculiar phenotype predominantly characterized by increased NKG2A and reduced Siglec-7, NKG2D, NKp30 and CD16 expression. This phenotype was associated with a decreased ability to perform antibody-dependent cellular cytotoxicity (ADCC). However, NK, CD4 and CD8 shared an increment of glucocorticoid-induced tumor necrosis factor-related (GITR) costimulatory receptor which could be exploited for immunotherapy with agonistic anti-GITR antibodies combined with checkpoint inhibitors.

The unique role of innate lymphoid cells in cancer and the hepatic microenvironment

Cancer is a complex disease, and despite incredible progress over the last decade, it remains the leading cause of death worldwide. Liver cancers, including hepatocellular carcinoma (HCC), and liver metastases are distinct from other cancers in that they typically emerge as a consequence of long-term low-grade inflammation. Understanding the mechanisms that underpin inflammation-driven tissue remodeling of the hepatic immune environment is likely to provide new insights into much needed treatments for this devastating disease. Group 1 innate lymphoid cells (ILCs), which include natural killer (NK) cells and ILC1s, are particularly enriched in the liver and thought to contribute to the pathogenesis of a number of liver diseases, including cancer. NK cells are an attractive, but underexplored, therapeutic target in hepatic disease due to their role in immunosurveillance and their ability to recognize and eliminate malignant cells. ILC1s are closely related to and share many phenotypic features with NK cells but are less well studied. Thus, their utility in immunotherapeutic approaches is not yet well understood. Here, we review our current understanding of ILCs in cancer with a particular focus on liver and liver-related diseases.

IL27 Signaling Serves as an Immunologic Checkpoint for Innate Cytotoxic Cells to Promote Hepatocellular Carcinoma

Although inflammatory mechanisms driving hepatocellular carcinoma (HCC) have been proposed, the regulators of anticancer immunity in HCC remain poorly understood. We found that IL27 receptor (IL27R) signaling promotes HCC development in vivo. High IL27EBI3 cytokine or IL27RA expression correlated with poor prognosis for patients with HCC. Loss of IL27R suppressed HCC in vivo in two different models of hepatocarcinogenesis. Mechanistically, IL27R sig-naling within the tumor microenvironment restrains the cytotoxicity of innate cytotoxic lymphocytes. IL27R ablation enhanced their accumulation and activation, whereas depletion or functional impairment of innate cytotoxic cells abrogated the effect of IL27R disruption. Pharmacologic neutralization of IL27 signaling increased infiltration of innate cytotoxic lymphocytes with upregulated cytotoxic molecules and reduced HCC development. Our data reveal an unexpected role of IL27R signaling as an immunologic checkpoint regulating innate cytotoxic lymphocytes and promoting HCC of different etiologies, thus indicating a therapeutic potential for IL27 pathway blockade in HCC.

SIGNIFICANCE

HCC, the most common form of liver cancer, is characterized by a poor survival rate and limited treatment options. The discovery of a novel IL27-dependent mechanism controlling anticancer cytotoxic immune response will pave the road for new treatment options for this devastating disease. This article is highlighted in the In This Issue feature, p. 1825.

NK Cells and Other Cytotoxic Innate Lymphocytes in Colorectal Cancer Progression and Metastasis

Colorectal cancer (CRC) is one of the most common malignancies and leading causes of cancer-related deaths worldwide. Despite its complex pathogenesis and progression, CRC represents a well-fitting example of how the immune contexture can dictate the disease outcome. The presence of cytotoxic lymphocytes, both CD8⁺ T cells and natural killer (NK) cells, represents a relevant prognostic factor in CRC and is associated with a better overall survival. Together with NK cells, other innate lymphocytes, namely, innate lymphoid cells (ILCs), have been found both in biopsies of CRC patients and in murine models of intestinal cancer, playing both pro- and anti-tumor activities. In particular, several type 1 innate lymphoid cells (ILC1) with cytotoxic functions have been recently described, and evidence in mice shows a role for both NK cells and ILC1 in controlling CRC metastasis. In this review, we provide an overview of the features of NK cells and the expanding spectrum of innate lymphocytes with cytotoxic functions. We also comment on both the described and the potential roles these innate lymphocytes can play during the progression of intestinal cancer leading to metastasis. Finally, we discuss recent advances in the molecular mechanisms underlying the functional regulation of cytotoxic innate lymphocytes in CRC.

The transcription factor RUNX2 drives the generation of human NK cells and promotes tissue residency

Natural killer (NK) cells are innate lymphocytes that eliminate virus-infected and cancer cells by cytotoxicity and cytokine secretion. In addition to circulating NK cells, distinct tissue-resident NK subsets have been identified in various organs. Although transcription factors regulating NK cell development and function have been extensively studied in mice, the role of RUNX2 in these processes has not been investigated, neither in mice nor in human. Here, by manipulating RUNX2 expression with either knockdown or overexpression in human haematopoietic stem cell-based NK cell differentiation cultures, combined with transcriptomic and ChIP-sequencing analyses, we established that RUNX2 drives the generation of NK cells, possibly through induction of IL-2Rβ expression in NK progenitor cells. Importantly, RUNX2 promotes tissue residency in human NK cells. Our findings have the potential to improve existing NK cell-based cancer therapies and can impact research fields beyond NK cell biology, since tissue-resident subsets have also been described in other lymphocyte subpopulations.

Human Hepatic CD56bright NK Cells Display a Tissue-Resident Transcriptional Profile and Enhanced Ability to Kill Allogenic CD8+ T Cells

Liver-resident CD56^brightCD16^- natural killer (NK) cells are enriched in the human liver and are phenotypically distinct from their blood counterparts. Although these cells are capable of rapid cytotoxic effector activity, their functional role remains unclear. We hypothesise that they may contribute to immune tolerance in the liver during transplantation. RNA sequencing was carried out on FACS sorted NK cell subpopulations from liver perfusates (n=5) and healthy blood controls (n=5). Liver-resident CD56^brightCD16^+/- NK cells upregulate genes associated with tissue residency. They also upregulate expression of CD160 and LY9, both of which encode immune receptors capable of activating NK cells. Co-expression of CD160 and Ly9 on liver-resident NK cells was validated using flow cytometry. Hepatic NK cell cytotoxicity against allogenic T cells was tested using an in vitro co-culture system of liver perfusate-derived NK cells and blood T cells (n=10-13). In co-culture experiments, hepatic NK cells but not blood NK cells induced significant allogenic T cell death (p=0.0306). Allogenic CD8⁺ T cells were more susceptible to hepatic NK cytotoxicity than CD4⁺ T cells (p<0.0001). Stimulation of hepatic CD56^bright NK cells with an anti-CD160 agonist mAb enhanced this cytotoxic response (p=0.0382). Our results highlight a role for donor liver NK cells in regulating allogenic CD8⁺ T cell activation, which may be important in controlling recipient CD8⁺ T cell-mediated rejection post liver-transplant.

The human liver microenvironment shapes the homing and function of CD4+ T-cell populations

OBJECTIVE

Tissue-resident memory T cells (TRM) are vital immune sentinels that provide protective immunity. While hepatic CD8+ TRM have been well described, little is known about the location, phenotype and function of CD4+ TRM.

DESIGN

We used multiparametric flow cytometry, histological assessment and novel human tissue coculture systems to interrogate the ex vivo phenotype, function and generation of the intrahepatic CD4+ T-cell compartment. We also used leukocytes isolated from human leukocyte antigen (HLA)-disparate liver allografts to assess long-term retention.

RESULTS

Hepatic CD4+ T cells were delineated into three distinct populations based on CD69 expression: CD69-, CD69INT and CD69HI. CD69HICD4+ cells were identified as tissue-resident CD4+ T cells on the basis of their exclusion from the circulation, phenotypical profile (CXCR6+CD49a+S1PR1-PD-1+) and long-term persistence within the pool of donor-derived leukcoocytes in HLA-disparate liver allografts. CD69HICD4+ T cells produced robust type 1 polyfunctional cytokine responses on stimulation. Conversely, CD69INTCD4+ T cells represented a more heterogenous population containing cells with a more activated phenotype, a distinct chemokine receptor profile (CX3CR1+CXCR3+CXCR1+) and a bias towards interleukin-4 production. While CD69INTCD4+ T cells could be found in the circulation and lymph nodes, these cells also formed part of the long-term resident pool, persisting in HLA-mismatched allografts. Notably, frequencies of CD69INTCD4+ T cells correlated with necroinflammatory scores in chronic hepatitis B infection. Finally, we demonstrated that interaction with hepatic epithelia was sufficient to generate CD69INTCD4+ T cells, while additional signals from the liver microenvironment were required to generate liver-resident CD69HICD4+ T cells.

CONCLUSIONS

High and intermediate CD69 expressions mark human hepatic CD4+ TRM and a novel functionally distinct recirculating population, respectively, both shaped by the liver microenvironment to achieve diverse immunosurveillance.

CXCR6+ and NKG2C+ Natural Killer Cells Are Distinct With Unique Phenotypic and Functional Attributes Following Bone Marrow Transplantation

Reactivation of human cytomegalovirus (HCMV) is a life-threatening complication in transplant patients. Natural Killer (NK) cells are the first lymphocyte lineage to reconstitute following an allogeneic hematopoietic stem cell transplant (HSCT). Amongst them, NK cell Group 2 isoform C/Killer cell lectin-like receptor subfamily C, member 2 (NKG2C)-expressing NK cells contribute significantly to patient protection upon HCMV reactivation. NKG2C⁺ NK cells are capable of immunological memory, albeit NK cell memory is not restricted to them. Hepatic C-X-C Motif Chemokine Receptor 6 (CXCR6)-expressing NK cells also mediate memory responses in mice and humans. Small numbers of them circulate and can thus be studied in peripheral blood samples. We hypothesize that NKG2C⁺ and CXCR6⁺ NK cell subsets are distinct. To test our hypothesis, we used multi-parametric flow cytometry to determine the phenotypes and effector functions of CD56^bright vs. CD56^dim and NKG2C⁺ vs. CXCR6⁺ human NK cell subsets in the peripheral blood (PB) of pediatric transplant recipients monthly while monitoring patients for HCMV reactivation. Interestingly, we did not find any NKG2C⁺CXCR6⁺ NK cells in the transplant recipients' peripheral blood, suggesting that NKG2C⁺ and CXCR6⁺ NK cells are distinct. Also, NKG2C-CXCR6- NK cells, rather than NKG2C⁺ NK cells, made up most NK cells post-transplant, even in transplant recipients with HCMV viremia. In contrast to NKG2C⁺ NK cells, CXCR6⁺ NK cells appeared phenotypically less differentiated but were highly proliferative and produced IFN-γ and TNF _α . Our findings contribute to our understanding of post-transplant NK cell development and its implications for human health.

The Functional Diversity of Tissue-Resident Natural Killer Cells Against Infection

For decades, studies of natural killer (NK) cells have focused on those found in peripheral blood (PBNK cells) as the prototype for NK cell biology. Only recently have researchers begun to explore the diversity of tissue-resident NK (tr-NK) cells. While tr-NK cells were initially identified from mice parabiosis and intravascular staining experiments, they can also be identified by tissue retention markers such as CD69, CD103, and others. More importantly, tr-NK cells have distinct functions compared to PBNK cells. Within the liver, there are diverse subsets of tr-NK cells expressing different combinations of tissue-retention markers and transcription factors, the clinical relevance of which are still unclear. Functionally, liver tr-NK are primed with immediate responsiveness to infection and equipped with regulatory mechanisms to prevent liver damage. When decidual NK (dNK) cells were first discovered, they were mainly characterized by their reduced cytotoxicity and functions related to placental development. Recent studies, however, revealed different mechanisms by which dNK cells prevent uterine infections. The lungs are one of the most highly exposed sites for infection due to their role in oxygen exchange. Upon influenza infection, lung tr-NK cells can degranulate and produce more inflammatory cytokines than PBNK cells. Less understood are gut tr-NK cells which were recently characterized in infants and adults for their functional differences. In this mini-review, we aim to provide a brief overview of the most recent discoveries on how several tr-NK cells are implicated in the immune response against infection. This article is protected by copyright. All rights reserved.

Isolation of human intrahepatic leukocytes for phenotypic and functional characterization by flow cytometry

With the growing appreciation of tissue-resident immunity, studying tissue-specific immune cells contributing to both homeostasis and disease is imperative. Here, we provide a protocol for the isolation of human intrahepatic leukocytes (IHL) maximizing viability, purity, and yield. Our protocol is scalable by tissue weight, allowing for reproducible and efficient IHL liberation suitable for functional characterization, cell isolation, and profiling by flow (or mass) cytometry. Furthermore, we provide a "guide" to determine an expected IHL yield per gram of tissue processed. For complete details on the use and execution of this protocol, please refer to Stegmann et al. (2016), Pallett et al. (2017), Easom et al. (2018), Swadling et al. (2020), Pallett et al. (2020), and Zakeri et al. (2022).

Localization Matters: Epigenetic Regulation of Natural Killer Cells in Different Tissue Microenvironments

Natural Killer cells (NK cells) are cytotoxic innate lymphoid cells (ILCs), which play a key role in the early protection against viral infection and cancer. In addition to mounting rapid effector responses, NK cells possess the capacity to generate long-lived memory cells in response to certain stimuli, thus blurring the lines between innate and adaptive immunity and making NK cells an ideal candidate for tumor immunotherapy. NK cell development, activation and memory formation are regulated by epigenetic alterations driven by a complex interplay of external and internal signals. These epigenetic modifications can convey long-lasting functional and phenotypic changes and critically modify their response to stimulation. Here, we review how NK cell functionality and plasticity are regulated at the epigenetic level in different tissue microenvironments and within tumor microenvironments. An in-depth understanding of the epigenetic modifications underlying NK cell functional diversity in different environments is an essential step in the development of NK cell-based cancer therapies.

Signaling Pathways Tuning Innate Lymphoid Cell Response to Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the deadliest cancers worldwide and its incidence continues to rise globally. Various causes can lead to its development such as chronic viral infections causing hepatitis, cirrhosis or nonalcoholic steatohepatitis (NASH). The contribution of immune cells to HCC development and progression has been extensively studied when it comes to adaptive lymphocytes or myeloid populations. However, the role of the innate lymphoid cells (ILCs) is still not well defined. ILCs are a family of lymphocytes comprising five subsets including circulating Natural Killer (NK) cells, ILC1s, ILC2s, ILC3s and lymphocytes tissue-inducer cells (LTi). Mostly located at epithelial surfaces, tissue-resident ILCs and NK cells can rapidly react to environmental changes to mount appropriate immune responses. Here, we provide an overview of their roles and actions in HCC with an emphasis on the importance of diverse signaling pathways (Notch, TGF-β, Wnt/β-catenin…) in the tuning of their response to HCC.

Natural Killer Cells in Hepatic Ischemia-Reperfusion Injury

Ischemia-reperfusion injury can be divided into two phases, including insufficient supply of oxygen and nutrients in the first stage and then organ injury caused by immune inflammation after blood flow recovery. Hepatic ischemia-reperfusion is an important cause of liver injury post-surgery, consisting of partial hepatectomy and liver transplantation, and a central driver of graft dysfunction, which greatly leads to complications and mortality after liver transplantation. Natural killer (NK) cells are the lymphocyte population mainly involved in innate immune response in the human liver. In addition to their well-known role in anti-virus and anti-tumor defense, NK cells are also considered to regulate the pathogenesis of liver ischemia-reperfusion injury under the support of more and more evidence recently. The infiltration of NK cells into the liver exacerbates the hepatic ischemia-reperfusion injury, which could be significantly alleviated after depletion of NK cells. Interestingly, NK cells may contribute to both liver graft rejection and tolerance according to their origins. In this article, we discussed the development of liver NK cells, their role in ischemia-reperfusion injury, and strategies of inhibiting NK cell activation in order to provide potential possibilities for translation application in future clinical practice.

The Human Male Liver Is Predisposed to Inflammation Via Enhanced Myeloid Responses to Inflammatory Triggers

Background & Aim

Men have a higher prevalence of liver disease. Liver myeloid cells can regulate tissue inflammation, which drives progression of liver disease. We hypothesized that sex alters the responsiveness of liver myeloid cells, predisposing men to severe liver inflammation.

Methods

Luminex was done on plasma from Hepatitis B Virus infected patients undergoing nucleoside analogue cessation in 45 male and female patients. We collected immune cells from the sinusoids of uninfected livers of 53 male and female donors. Multiparametric flow cytometry was used to phenotype and characterize immune composition. Isolated monocytes were stimulated with TLR ligands to measure the inflammatory potential and the expression of regulators of TLR signaling.

Results

We confirmed that men experienced more frequent and severe liver damage upon Hepatitis B Virus reactivation, which was associated with inflammatory markers of myeloid activation. No differences were observed in the frequency or phenotype of sinusoidal myeloid cells between male and female livers. However, monocytes from male livers produced more inflammatory cytokines and chemokines in response to TLR stimulation than female monocytes. We investigated negative regulators of TLR signaling and found that TOLLIP was elevated in female liver-derived monocytes

Conclusions

Our data show that enhanced responsiveness of myeloid cells from the male liver predisposes men to inflammation, which was associated with altered expression of negative regulators of TLR signaling.

NK cells limit therapeutic vaccine-induced CD8+T cell immunity in a PD-L1-dependent manner

A better understanding of mechanisms that regulate CD8+T cell responses to therapeutic vaccines is needed to develop approaches to enhance vaccine efficacy for chronic viral infections and cancers. We show here that NK cell depletion enhanced antigen-specific T cell responses to chimp adenoviral vector (ChAdOx) vaccination in a mouse model of chronic HBV infection (CHB). Probing the mechanism underlying this negative regulation, we observed that CHB drove parallel up-regulation of programmed cell death ligand 1 (PD-L1) on liver-resident NK cells and programmed cell death 1 (PD-1) on intrahepatic T cells. PD-L1-expressing liver-resident NK cells suppressed PD-1hiCD8+T cells enriched within the HBV-specific response to therapeutic vaccination. Cytokine activation of NK cells also induced PD-L1, and combining cytokine activation with PD-L1 blockade resulted in conversion of NK cells into efficient helpers that boosted HBV-specific CD8+T cell responses to therapeutic vaccination in mice and to chronic infection in humans. Our findings delineate an immunotherapeutic combination that can boost the response to therapeutic vaccination in CHB and highlight the broader importance of PD-L1-dependent regulation of T cells by cytokine-activated NK cells.

Tissue-Dependent Adaptations and Functions of Innate Lymphoid Cells

Tissue-resident immune cells reside in distinct niches across organs, where they contribute to tissue homeostasis and rapidly respond to perturbations in the local microenvironment. Innate lymphoid cells (ILCs) are a family of innate immune cells that regulate immune and tissue homeostasis. Across anatomical locations throughout the body, ILCs adopt tissue-specific fates, differing from circulating ILC populations. Adaptations of ILCs to microenvironmental changes have been documented in several inflammatory contexts, including obesity, asthma, and inflammatory bowel disease. While our understanding of ILC functions within tissues have predominantly been based on mouse studies, development of advanced single cell platforms to study tissue-resident ILCs in humans and emerging patient-based data is providing new insights into this lymphocyte family. Within this review, we discuss current concepts of ILC fate and function, exploring tissue-specific functions of ILCs and their contribution to health and disease across organ systems.

Review article: emerging insights into the immunopathology, clinical and therapeutic aspects of hepatitis delta virus

BACKGROUND

Hepatitis delta virus (HDV), which causes the most severe form of viral hepatitis, is an obligated hepatitis B (HBV) satellite virus that can either infect naïve subjects simultaneously with HBV (co-infection), or chronically infect HBV carriers (super-infection). An estimated 12 million people are infected by HDV worldwide.

AIMS

To summarise the most relevant aspects of the molecular biology of HDV, and to discuss the latest understanding of the induced pathology, interactions with the immune system, as well as both approved and investigational treatment options.

METHODS

References for this review were identified through searches of PubMed with the terms "HDV" "viral hepatitis" "co-infection" and "super-infection," published between 1980 and October 2021 RESULTS: The limited access to the HDV-infected liver has hampered the investigation of the intrahepatic compartment and our understanding of the mechanisms of HDV pathogenesis. In the absence of standardised and sensitive diagnostic tools, HDV is often underdiagnosed and owing to its strong dependence on host cellular factors, the development of direct antiviral agents has been challenging. New therapeutic agents targeting different steps of the viral cycle have recently been investigated, among which bulevirtide (which was conditionally approved by EMA in July 2020) and lonafarnib; both drugs having received orphan drug designation from both the EMA and FDA.

CONCLUSIONS

The HBV cure programme potentially offers a unique opportunity to enhance HDV treatment strategies. In addition, a more comprehensive analysis of the intrahepatic compartment is mandated to better understand any liver-confined interaction of HDV with the host immune system.

Impaired antibacterial response of liver sinusoidal Vγ9+Vδ2+ T cells in patients with chronic liver disease

OBJECTIVE

The liver acts as a frontline barrier against diverse gut-derived pathogens, and the sinusoid is the primary site of liver immune surveillance. However, little is known about liver sinusoidal immune cells in the context of chronic liver disease (CLD). Here, we investigated the antibacterial capacity of liver sinusoidal γδ T cells in patients with various CLDs.

DESIGN

We analysed the frequency, phenotype and functions of human liver sinusoidal γδ T cells from healthy donors and recipients with CLD, including HBV-related CLD (liver cirrhosis (LC) and/or hepatocellular carcinoma (HCC)), alcoholic LC and LC or HCC of other aetiologies, by flow cytometry and RNA-sequencing using liver perfusates obtained during living donor liver transplantation. We also measured the plasma levels of D-lactate and bacterial endotoxin to evaluate bacterial translocation.

RESULTS

The frequency of liver sinusoidal Vγ9⁺Vδ2⁺ T cells was reduced in patients with CLD. Immunophenotypic and transcriptomic analyses revealed that liver sinusoidal Vγ9⁺Vδ2⁺ T cells from patients with CLD were persistently activated and pro-apoptotic. In addition, liver sinusoidal Vγ9⁺Vδ2⁺ T cells from patients with CLD showed significantly decreased interferon (IFN)-γ production following stimulation with bacterial metabolites and Escherichia coli. The antibacterial IFN-γ response of liver sinusoidal Vγ9⁺Vδ2⁺ T cells significantly correlated with liver function, and inversely correlated with the plasma level of D-lactate in patients with CLD. Repetitive in vitro stimulation with E. coli induced activation, apoptosis and functional impairment of liver sinusoidal Vγ9⁺Vδ2⁺ T cells.

CONCLUSION

Liver sinusoidal Vγ9⁺Vδ2⁺ T cells are functionally impaired in patients with CLD. Bacterial translocation and decreasing liver functions are associated with functional impairment of liver sinusoidal Vγ9⁺Vδ2⁺ T cells.

Scavenger Receptors: Novel Roles in the Pathogenesis of Liver Inflammation and Cancer

The scavenger receptor superfamily represents a highly diverse collection of evolutionarily-conserved receptors which are known to play key roles in host homeostasis, the most prominent of which is the clearance of unwanted endogenous macromolecules, such as oxidized low-density lipoproteins, from the systemic circulation. Members of this family have also been well characterized in their binding and internalization of a vast range of exogenous antigens and, consequently, are generally considered to be pattern recognition receptors, thus contributing to innate immunity. Several studies have implicated scavenger receptors in the pathophysiology of several inflammatory diseases, such as Alzheimer's and atherosclerosis. Hepatic resident cellular populations express a diverse complement of scavenger receptors in keeping with the liver's homeostatic functions, but there is gathering interest in the contribution of these receptors to hepatic inflammation and its complications. Here, we review the expression of scavenger receptors in the liver, their functionality in liver homeostasis, and their role in inflammatory liver disease and cancer.

Phenotypic and Functional Plasticity of CXCR6+ Peripheral Blood NK Cells

Human NK cells are comprised of phenotypic subsets, whose potentially unique functions remain largely unexplored. C-X-C-motif-chemokine-receptor-6 (CXCR6)+ NK cells have been identified as phenotypically immature tissue-resident NK cells in mice and humans. A small fraction of peripheral blood (PB)-NK cells also expresses CXCR6. However, prior reports about their phenotypic and functional plasticity are conflicting. In this study, we isolated, expanded, and phenotypically and functionally evaluated CXCR6+ and CXCR6– PB-NK cells, and contrasted results to bulk liver and spleen NK cells. We found that CXCR6+ and CXCR6– PB-NK cells preserved their distinct phenotypic profiles throughout 14 days of in vitro expansion (“day 14”), after which phenotypically immature CXCR6+ PB-NK cells became functionally equivalent to CXCR6– PB-NK cells. Despite a consistent reduction in CD16 expression and enhanced expression of the transcription factor Eomesodermin (Eomes), day 14 CXCR6+ PB-NK cells had superior antibody-dependent cellular cytotoxicity (ADCC) compared to CXCR6– PB-NK cells. Further, bulk liver NK cells responded to IL-15, but not IL-2 stimulation, with STAT-5 phosphorylation. In contrast, bulk splenic and PB-NK cells robustly responded to both cytokines. Our findings may allow for the selection of superior NK cell subsets for infusion products increasingly used to treat human diseases.