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.

Single-cell atlas of hepatic T cells reveals expansion of liver-resident naive-like CD4+ T cells in primary sclerosing cholangitis.

BACKGROUND & AIMS: Little is known about the composition of intrahepatic immune cells and their contribution to the pathogenesis of primary sclerosing cholangitis (PSC). Herein, we aimed to create an atlas of intrahepatic T cells and thereby perform an in-depth characterization of T cells in inflamed human liver. METHODS: Different single-cell RNA sequencing methods were combined with in silico analyses on intrahepatic and peripheral T cells from patients with PSC (n = 11) and healthy donors (HDs, n = 4). Multi-parameter flow cytometry and functional in vitro experiments were conducted on samples from patients with PSC (n = 24), controls with other liver diseases and HDs. RESULTS: We identified a population of intrahepatic naive-like CD4+ T cells, which was present in all liver diseases tested, but particularly expanded in PSC. This population had a transcriptome and T cell receptor repertoire similar to circulating naive T cells but expressed a set of genes associated with tissue residency. Their periductal location supported the concept of tissue-resident naive-like T cells in livers of patients with PSC. Trajectory inference suggested that these cells had the developmental propensity to acquire a T helper 17 (TH17) polarization state. Functional and chromatin accessibility experiments revealed that circulating naive T cells in patients with PSC were predisposed to polarize towards TH17 cells. CONCLUSION: We report the first atlas of intrahepatic T cells in PSC, which led to the identification of a previously unrecognized population of tissue-resident naive-like T cells in the inflamed human liver and to the finding that naive CD4+ T cells in PSC harbour the propensity to develop into TH17 cells. LAY SUMMARY: The composition of intrahepatic immune cells in primary sclerosing cholangitis (PSC) and their contribution to disease pathogenesis is widely unknown. We analysed intrahepatic T cells and identified a previously uncharacterized population of liver-resident CD4+ T cells which are expanded in the livers of patients with PSC compared to healthy liver tissue and other liver diseases. These cells are likely to contribute to the pathogenesis of PSC and could be targeted in novel therapeutic approaches.

Upregulation of HLA-F expression by BK polyomavirus infection induces immune recognition by KIR3DS1-positive natural killer cells.

BK polyomavirus-associated nephropathy is a common complication after kidney transplantation leading to reduced graft function or loss. The molecular pathogenesis of BK polyomavirus-induced nephropathy is not well understood. A recent study had described a protective effect of the activating natural killer cell receptor KIR3DS1 in BK polyomavirus-associated nephropathy, suggesting a role of NK cells in modulating disease progression. Using an in vitro cell culture model of human BK polyomavirus infection and kidney biopsy samples from patients with BK polyomavirus-associated nephropathy, we observed significantly increased surface expression of the ligand for KIR3DS1, HLA-F, on BK polyomavirus-infected kidney tubular cells. Upregulation of HLA-F expression resulted in significantly increased binding of KIR3DS1 to BK polyomavirus-infected cells and activation of primary KIR3DS-positive natural killer cells. Thus, our data provide a mechanism by which KIR3DS-positive natural killer cells can control BK polyomavirus infection of the kidney, and rationale for exploring HLA-F/KIR3DS1 interactions for immunotherapeutic approaches in BK polyomavirus-associated nephropathy.

Monocytes as Potential Mediators of Pathogen-Induced T-Helper 17 Differentiation in Patients With Primary Sclerosing Cholangitis (PSC).

BACKGROUND AND AIMS: T cells from patients with primary sclerosing cholangitis (PSC) show a prominent interleukin (IL)-17 response upon stimulation with bacteria or fungi, yet the reasons for this dominant T-helper 17 (Th17) response in PSC are not clear. Here, we analyzed the potential role of monocytes in microbial recognition and in skewing the T-cell response toward Th17. APPROACH AND RESULTS: Monocytes and T cells from blood and livers of PSC patients and controls were analyzed ex vivo and in vitro using transwell experiments with cholangiocytes. Cytokine production was measured using flow cytometry, enzyme-linked immunosorbent assay, RNA in situ hybridization, and quantitative real-time PCR. Genetic polymorphisms were obtained from ImmunoChip analysis. Following ex vivo stimulation with phorbol myristate acetate/ionomycin, PSC patients showed significantly increased numbers of IL-17A-producing peripheral blood CD4+ T cells compared to PBC patients and healthy controls, indicating increased Th17 differentiation in vivo. Upon stimulation with microbes, monocytes from PSC patients produced significantly more IL-1ß and IL-6, cytokines known to drive Th17 cell differentiation. Moreover, microbe-activated monocytes induced the secretion of Th17 and monocyte-recruiting chemokines chemokine (C-C motif) ligand (CCL)-20 and CCL-2 in human primary cholangiocytes. In livers of patients with PSC cirrhosis, CD14hiCD16int and CD14loCD16hi monocytes/macrophages were increased compared to alcoholic cirrhosis, and monocytes were found to be located around bile ducts. CONCLUSIONS: PSC patients show increased Th17 differentiation already in vivo. Microbe-stimulated monocytes drive Th17 differentiation in vitro and induce cholangiocytes to produce chemokines mediating recruitment of Th17 cells and more monocytes into portal tracts. Taken together, these results point to a pathogenic role of monocytes in patients with PSC.

HIV-1 induced changes in HLA-C*03 :  04-presented peptide repertoires lead to reduced engagement of inhibitory natural killer cell receptors.

OBJECTIVE: Viral infections influence intracellular peptide repertoires available for presentation by HLA-I. Alterations in HLA-I/peptide complexes can modulate binding of killer immunoglobuline-like receptors (KIRs) and thereby the function of natural killer (NK) cells. Although multiple studies have provided evidence that HLA-I/KIR interactions play a role in HIV-1 disease progression, the consequence of HIV-1 infection for HLA-I/KIR interactions remain largely unknown. DESIGN: We determined changes in HLA-I presented peptides resulting from HIV-1-infection of primary human CD4 T cells and assessed the impact of changes in peptide repertoires on HLA-I/KIR interactions. METHODS: Liquid chromatography-coupled tandem mass spectrometry to identify HLA-I presented peptides, cell-based in-vitro assays to evaluate functional consequences of alterations in immunopeptidome and atomistic molecular dynamics simulations to confirm experimental data. RESULTS: A total of 583 peptides exclusively presented on HIV-1-infected cells were identified, of which only 0.2% represented HIV-1 derived peptides. Focusing on HLA-C*03 : 04/KIR2DL3 interactions, we observed that HLA-C*03 : 04-presented peptides derived from noninfected CD4 T cells mediated stronger binding of inhibitory KIR2DL3 than peptides derived from HIV-1-infected cells. Furthermore, the most abundant peptide presented by HLA-C*03 : 04 on noninfected CD4 T cells (VIYPARISL) mediated the strongest KIR2DL3-binding, while the most abundant peptide presented on HIV-1-infected cells (YAIQATETL) did not mediate KIR2DL3-binding. Molecular dynamics simulations of HLA-C*03 : 04/KIR2DL3 interactions in the context of these two peptides revealed that VIYPARISL significantly enhanced the HLA-C*03 : 04/peptide contact area to KIR2DL3 compared with YAIQATETL. CONCLUSION: These data demonstrate that HIV-1 infection-induced changes in HLA-I-presented peptides can reduce engagement of inhibitory KIRs, providing a mechanism for enhanced activation of NK cells by virus-infected cells.

The Transcription Factor Promyelocytic Leukemia Zinc Finger Protein Is Associated With Expression of Liver-Homing Receptors on Human Blood CD56bright Natural Killer Cells.

The transcription factor promyelocytic leukemia zinc finger protein (PLZF) is involved in the development of natural killer (NK) cells and innate lymphoid cells, including liver-resident NK cells in mice. In human NK cells, the role of PLZF in liver residency is still unknown. Expression of PLZF in matched human peripheral blood- and liver-derived NK cells and the association of PLZF expression with surface molecules and transcription factors relevant for tissue residency were investigated using multiparameter flow cytometry and assessing single-cell messenger RNA (mRNA) levels. Intrahepatic cluster of differentiation (CD)56bright NK cells expressed significantly higher levels of PLZF than peripheral blood CD56bright NK cells, which were predominantly PLZFlo. Expression of PLZF was highest within C-X-C motif chemokine receptor 6 (CXCR6)+CD69+ liver-resident NK cells among intrahepatic CD56bright NK cell populations. Association of PLZF with liver-residency markers was also reflected at mRNA levels. A small PLZFhiCD56bright NK cell population was identified in peripheral blood that also expressed the liver-residency markers CXCR6 and CD69 and shared functional characteristics with liver-resident NK cells. Conclusion: PLZF is implicated as part of a transcriptional network that promotes liver residency of human NK cells. Expression of liver-homing markers on peripheral blood PLZFhiCD56bright NK cells identifies an intermediate population potentially contributing to the maintenance of liver-resident NK cells.

CD49a Expression Identifies a Subset of Intrahepatic Macrophages in Humans.

Macrophages play central roles in inflammatory reactions and initiation of immune responses during infections. More than 80% of total tissue macrophages are described to be located in the liver as liver-resident macrophages, also named Kupffer cells (KCs). While studies in mice have established a central role of liver-resident KCs in regulating liver inflammation, their phenotype and function are not well-characterized in humans. Comparing paired human liver and peripheral blood samples, we observed significant differences in the distribution of macrophage (Mφ) subsets, with lower frequencies of CD14hiCD16lo and higher frequencies of CD14int-hiCD16int Mφ in human livers. Intrahepatic Mφ consisted of diverse subsets with differential expression of CD49a, a liver-residency marker previously described for human and mice NK cells, and VSIG4 and/or MARCO, two recently described human tissue Mφ markers. Furthermore, intrahepatic CD49a+ Mφ expressed significantly higher levels of maturation and activation markers, exhibited higher baseline levels of TNF-α, IL-12, and IL-10 production, but responded less to additional in vitro TLR stimulation. In contrast, intrahepatic CD49a- Mφ were highly responsive to stimulation with TLR ligands, similar to what was observed for CD49a- monocytes (MOs) in peripheral blood. Taken together, these studies identified populations of CD49a+, VSIG4+, and/or MARCO+ Mφ in human livers, and demonstrated that intrahepatic CD49a+ Mφ differed in phenotype and function from intrahepatic CD49a- Mφ as well as from peripheral blood-derived monocytes.

Chronic hepatitis delta virus infection leads to functional impairment and severe loss of MAIT cells.

BACKGROUND & AIMS: Hepatitis delta virus (HDV) infection is the most severe form of viral hepatitis. Although HDV-associated liver disease is considered immune-mediated, adaptive immune responses against HDV are weak. Thus, the role of several other cell-mediated mechanisms such as those driven by mucosa-associated invariant T (MAIT) cells, a group of innate-like T cells highly enriched in the human liver, has not been extensively studied in clinical HDV infection. METHODS: MAIT cells from a sizeable cohort of patients with chronic HDV were analyzed ex vivo and in vitro after stimulation. Results were compared with MAIT cells from hepatitis B virus (HBV) monoinfected patients and healthy controls. RESULTS: Circulating MAIT cells were dramatically decreased in the peripheral blood of HDV-infected patients. Signs of decline were also observed in the liver. In contrast, only a modest decrease of circulating MAIT cells was noted in HBV monoinfection. Unsupervised high-dimensional analysis of residual circulating MAIT cells in chronic HDV infection revealed the appearance of a compound phenotype of CD38hiPD-1hiCD28loCD127loPLZFloEomesloHelioslo cells indicative of activation. Corroborating these results, MAIT cells exhibited a functionally impaired responsiveness. In parallel to MAIT cell loss, HDV-infected patients exhibited signs of monocyte activation and increased levels of proinflammatory cytokines IL-12 and IL-18. In vitro, IL-12 and IL-18 induced an activated MAIT cell phenotype similar to the one observed ex vivo in HDV-infected patients. These cytokines also promoted MAIT cell death, suggesting that they may contribute to MAIT cell activation and subsequent loss during HDV infection. CONCLUSIONS: These results suggest that chronic HDV infection engages the MAIT cell compartment causing activation, functional impairment, and subsequent progressive loss of MAIT cells as the HDV-associated liver disease progresses. LAY SUMMARY: Hepatitis delta virus (HDV) infection is the most severe form of viral hepatitis. We found that in patients with HDV, a subset of innate-like T cells called mucosa-associated invariant T cells (or MAIT cells), which are normally abundant in peripheral blood and the liver, are activated, functionally impaired and severely depleted.

Tissue-resident Eomes+ NK cells are the major innate lymphoid cell population in human infant intestine.

Innate lymphoid cells (ILC), including natural killer (NK) cells, are implicated in host-defense and tissue-growth. However, the composition and kinetics of NK cells in the intestine during the first year of life, when infants are first broadly exposed to exogenous antigens, are still unclear. Here we show that CD103+ NK cells are the major ILC population in the small intestines of infants. When compared to adult intestinal NK cells, infant intestinal NK cells exhibit a robust effector phenotype, characterized by Eomes, perforin and granzyme B expression, and superior degranulation capacity. Absolute intestinal NK cell numbers decrease gradually during the first year of life, coinciding with an influx of intestinal Eomes+ T cells; by contrast, epithelial NKp44+CD69+ NK cells with less cytotoxic capacity persist in adults. In conclusion, NK cells are abundant in infant intestines, where they can provide effector functions while Eomes+ T cell responses mature.

CCL21-expression and accumulation of CCR7+ NK cells in livers of patients with primary sclerosing cholangitis.

The pathogenesis of primary sclerosing cholangitis (PSC), an autoimmune liver disease, remains unknown. The aim of this study was to characterize peripheral blood and intrahepatic NK cells from patients with PSC. Peripheral blood samples from patients with PSC, other autoimmune liver diseases, and from healthy control individuals were used, as well as liver tissues from PSC patients undergoing liver transplantation. Multiparameter flow cytometry showed that peripheral blood NK cells from PSC patients were significantly enriched for CCR7+ and CXCR3+ cells, and CCR7+ but not CXCR3+ cells were also significantly increased within intrahepatic NK cells. PSC patients undergoing liver transplantation furthermore had significantly higher plasma levels of the CCR7-ligand CCL21, and the CXCR3-ligands CXCL10 and CXCL11, and significantly higher levels of CCL21, but not CXCL10, were detected in liver tissues. CCR7+ and CXCR3+ NK cells from PSC patients exhibited significantly higher functional capacity in peripheral blood, but not liver tissues, consistent with chronic activation of these NK cells in the inflamed liver. These data show that PSC is characterized by intrahepatic CCL21 expression and accumulation of CCR7+ NK cells in the inflamed liver tissue.

Human liver-derived CXCR6+ NK cells are predominantly educated through NKG2A and show reduced cytokine production.

NK cells have been implicated to affect the outcome of numerous liver diseases. In particular, members of the killer-cell Ig-like receptor (KIR) family, predominantly expressed by NK cells, have been associated with the outcome of hepatitis C virus infection and clearance of hepatocellular carcinoma. Inhibitory KIRs tune NK cell function through interaction with HLA class I, a process termed education. Nevertheless, the impact of the hepatic environment on NK cell education is incompletely understood. Therefore, we investigated the composition and function of hepatic KIR-expressing NK cells. Matched PBMC and hepatic lymphocytes were isolated from 20 individuals undergoing liver surgery and subsequently phenotypically analyzed for expression of KIRs and markers for tissue residency using flow cytometry. NK cell function was determined by co-culturing NK cells with the target cell line 721.221 and subsequent assessment of CD107a, IFN-γ, and TNF-α expression. Liver-resident CXCR6+ /CD56Bright NK cells lacked KIRs and were predominantly educated through NKG2A, while CXCR6- /CD16+ NK cells expressed KIRs and resembled peripheral blood NK cells. Hepatic NK cells showed lower response rates compared to peripheral blood NK cells; in particular, CXCR6+ NK cells were hyporesponsive to stimulation with target cells. The high proportion of educated NK cells in both subsets indicates the importance of self-inhibitory receptors for the balance between maintenance of self-tolerance and functional readiness. However, the reduced functionality of hepatic NK cells may reflect the impact of the tolerogenic hepatic environment on NK cells irrespective of NK cell education.

Detectable Vesicular Stomatitis Virus (VSV)-Specific Humoral and Cellular Immune Responses Following VSV-Ebola Virus Vaccination in Humans.

In response to the Ebola virus (EBOV) crisis of 2013-2016, a recombinant vesicular stomatitis virus (VSV)-based EBOV vaccine was clinically tested (NCT02283099). A single-dose regimen of VSV-EBOV revealed a safe and immunogenic profile and demonstrated clinical efficacy. While EBOV-specific immune responses to this candidate vaccine have previously been investigated, limited human data on immunity to the VSV vector are available. Within the scope of a phase 1 study, we performed a comprehensive longitudinal analysis of adaptive immune responses to internal VSV proteins following VSV-EBOV immunization. While no preexisting immunity to the vector was observed, more than one-third of subjects developed VSV-specific cytotoxic T-lymphocyte responses and antibodies.

Role of soluble inflammatory mediators and different immune cell populations in early control of symptomatic acute hepatitis C virus infection.

The natural course of acute Hepatitis C Virus (aHCV) infection is highly heterogeneous, and only few biomarkers have been identified to reliably predict the outcome of infection. We analysed a large panel of soluble inflammatory mediators, immune cell frequencies and phenotypes using peripheral blood samples from 26 patients with symptomatic aHCV infection from a controlled randomized clinical trial (ISRCTN88729946, www.isrctn.com). We found that patients with a spontaneous early HCV control demonstrated a distinct expression pattern of various soluble immune mediators including IFNα and IL-16. Immune cell phenotype and frequency differed between patients who cleared the viral infection early (n=13) and those who remained HCV RNA positive after 12 weeks of observation (n=13) with a reduced ratio of CD4+ T cells to NK cells in the non-early clearer. Further, correlation analyses of 50 cytokines and chemokines revealed more positive correlations in between the distinct cytokines, especially for IFNα and IL-16, and between the cytokines and HCV RNA levels in spontaneous early clearer patients. Beyond that, in vitro stimulation of CD4+ T cells with IL-16 reduced the susceptibility of these cells to killing by IFNα-activated NK cells. These data indicate that the immune cell composition and cytokine pattern varies considerably in patients with symptomatic aHCV infection. NK cell-mediated killing of CD4+ T cells might affect early control of HCV infection.

Stable Frequencies of HLA-C*03:04/Peptide-Binding KIR2DL2/3+ Natural Killer Cells Following Vaccination.

Inhibitory KIRs play a central role in regulating NK cell activity. KIR2DL2/3 bind to HLA-C molecules, but the modulation of these interactions by viral infections and presentation of viral epitopes is not well-understood. We investigated whether the frequencies of KIR2DL2/3+ NK cells recognizing HLA-C*03:04/viral peptide complexes were impacted by YFV vaccination or HIV-1 and HCV infection. Ex vivo HLA class I tetramer staining of primary human NK cells derived from YFV-vaccinated individuals, or HIV-1- or HCV-infected individuals revealed that the YFV/HLA-C*03:04-NS2A4-13-tetramer bound to a larger proportion of KIR2DL2/3+ NK cells compared to HIV-1/HLA-C*03:04-Gag296-304- or HCV/HLA-C*03:04-Core136-144-tetramers. The YFV/HLA-C*03:04-NS2A4-13-tetramer also exhibited a stronger avidity to KIR2DL2/3 compared to the other tested tetramers. The proportional frequencies of KIR2DL2/3+ NK cells binding to the three tested HLA-C*03:04 tetramers were identical between YFV-vaccinated individuals or HIV-1- or HCV-infected individuals, and remained stable following YFV vaccination. These data demonstrate consistent hierarchies in the frequency of primary KIR2DL2/3+ NK cells binding HLA-C*03:04/peptide complexes that were determined by the HLA-C-presented peptide and not modulated by the underlying viral infection or vaccination.

Tissue-resident NK cells differ in their expression profile of the nutrient transporters Glut1, CD98 and CD71.

Metabolism is a critical basis for immune cell functionality. It was recently shown that NK cell subsets from peripheral blood modulate their expression of nutrient receptors following cytokine stimulation, demonstrating that NK cells can adjust to changes in metabolic requirements. As nutrient availability in blood and tissues can significantly differ, we examined NK cells isolated from paired blood-liver and blood-spleen samples and compared expression of the nutrient transporters Glut1, CD98 and CD71. CD56bright tissue-resident (CXCR6+) NK cells derived from livers and spleens expressed lower levels of Glut1 but higher levels of the amino acid transporter CD98 following stimulation than CD56bright NK cells from peripheral blood. In line with that, CD56dim NK cells, which constitute the main NK cell population in the peripheral blood, expressed higher levels of Glut1 and lower levels of CD98 and CD71 compared to liver CD56bright NK cells. Our results show that NK cells from peripheral blood differ from liver- and spleen-resident NK cells in the expression profile of nutrient transporters, consistent with a cell-adaptation to the different nutritional environment in these compartments.

Interactions Between KIR3DS1 and HLA-F Activate Natural Killer Cells to Control HCV Replication in Cell Culture.

Killer-cell immunoglobulin-like receptors (KIRs) are transmembrane glycoproteins expressed by natural killer (NK) cells. Binding of KIR3DS1 to its recently discovered ligand, HLA-F, activates NK cells and has been associated with resolution of hepatitis C virus (HCV) infection. We investigated the mechanisms by which KIR3DS1 contributes to the antiviral immune response. Using cell culture systems, mice with humanized livers, and primary liver tissue from HCV-infected individuals, we found that the KIR3DS1 ligand HLA-F is up-regulated on HCV-infected cells, and that interactions between KIR3DS1 and HLA-F contribute to NK cell-mediated control of HCV. Strategies to promote interaction between KIR3DS1 and HLA-F might be developed for treatment of infectious diseases and cancer.

Carcinoembryonic antigen-related cell adhesion molecule 1 controls IL-2-dependent regulatory T-cell induction in immune-mediated hepatitis in mice.

A dysbalance between effector T cells (Tconv) and regulatory T cells (Tregs) and impaired Treg function can cause autoimmune liver disease. Therefore, it is important to identify molecular mechanisms that control Treg homeostasis. Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1; CD66a) is an immune coreceptor with dichotomous roles in T-cell regulation: its short isoform (CEACAM1S) can activate T cells and induce Tregs, whereas its long isoform (CEACAM1L), containing two intracellular immune receptor tyrosine-based inhibitory motifs, can inhibit activated T-cell function. In the liver, CEACAM1 has antifibrotic effects in models of nonalcoholic steatohepatitis. However, its role in immune-mediated hepatitis is unknown. In the mouse model of concanavalin A-induced CD4+ T-cell-dependent liver injury, liver damage was aggravated and persisted in Ceacam1-/- mice. Concomitantly, we observed hyperexpansion of Tconv, but reduction of interleukin (IL)-2 production and hepatic forkhead box protein P3+ (Foxp3+ )CD4+ Treg numbers. CEACAM1-/- CD4+ T cells showed impaired IL-2-mediated signal transducer and activator of transcription 5 (STAT5) phosphorylation, which correlated with a failure of naïve CEACAM1-/- CD4+ T cells to convert into Tregs in vitro. Furthermore, CEACAM1-/- Tregs expressed reduced levels of Foxp3, CD25, and B-cell lymphoma 2. Adoptive transfer experiments demonstrated that hepatic Treg expansion and suppressive activity required CEACAM1 expression on both CD4+ T cells and Tregs. We identified predominant CEACAM1S expression on hepatic CD4+ T cells and Tregs from mice with acute liver injury and expression of both isoforms in liver-derived CD4+ T-cell clones from patients with liver injury. CONCLUSION: Our data suggest that CEACAM1S expression in CD4+ T cells augments IL-2 production and STAT5 phosphorylation leading to enhanced Treg induction and stability, which, ultimately, confers protection from T-cell-mediated liver injury. (Hepatology 2018;68:200-214).

Proliferative capacity exhibited by human liver-resident CD49a+CD25+ NK cells.

The recruitment and retention of Natural Killer (NK) cells in the liver are thought to play an important role during hepatotropic infections and liver cirrhosis. The aims of this study were to determine differences between liver-derived and peripheral blood-derived NK cells in the context of liver inflammation and cirrhosis. We conducted a prospective dual-center cross-sectional study in patients undergoing liver transplantation or tumor-free liver resections, in which both liver tissue and peripheral blood samples were obtained from each consenting study participants. Intrahepatic lymphocytes and PBMCs were stained, fixed and analyzed by flow cytometry. Our results showed that, within cirrhotic liver samples, intrahepatic NK cells were particularly enriched for CD49a+ NK cells when compared to tumor-free liver resection samples. CD49a+ liver-derived NK cells included populations of cells expressing CD25, CD34 and CXCR3. Moreover, CD49a+CD25+ liver-derived NK cells exhibited high proliferative capacity in vitro in response to low doses of IL-2. Our study identified a specific subset of CD49a+CD25+ NK cells in cirrhotic livers bearing functional features of proliferation.

Hobit expression by a subset of human liver-resident CD56bright Natural Killer cells.

Immune responses show a high degree of tissue specificity shaped by factors influencing tissue egress and retention of immune cells. The transcription factor Hobit was recently shown to regulate tissue-residency in mice. Whether Hobit acts in a similar capacity in humans remains unknown. Our aim was to assess the expression and contribution of Hobit to tissue-residency of Natural Killer (NK) cells in the human liver. The human liver was enriched for CD56bright NK cells showing increased expression levels of the transcription factor Hobit. Hobitpos CD56bright NK cells in the liver exhibited high levels of CD49a, CXCR6 and CD69. Hobitpos CD56bright NK cells in the liver furthermore expressed a unique set of transcription factors with higher frequencies and levels of T-bet and Blimp-1 when compared to Hobitneg CD56bright NK cells. Taken together, we show that the transcription factor Hobit identifies a subset of NK cells in human livers that express a distinct set of adhesion molecules and chemokine receptors consistent with tissue residency. These data suggest that Hobit is involved in regulating tissue-residency of human intrahepatic CD56bright NK cells in a subset of NK cells in inflamed livers.

HIV-1-Mediated Downmodulation of HLA-C Impacts Target Cell Recognition and Antiviral Activity of NK Cells.

It was widely accepted that HIV-1 downregulates HLA-A/B to avoid CTL recognition while leaving HLA-C unaltered in order to prevent NK cell activation by engaging inhibitory NK cell receptors, but it was recently observed that most primary isolates of HIV-1 can mediate HLA-C downmodulation. Now we report that HIV-1-mediated downmodulation of HLA-C was associated with reduced binding to its respective inhibitory receptors. Despite this, HLA-C-licensed NK cells displayed reduced antiviral activity compared to their unlicensed counterparts, potentially due to residual binding to the respective inhibitory receptors. Nevertheless, NK cells were able to sense alterations of HLA-C expression demonstrated by increased antiviral activity when exposed to viral strains with differential abilities to downmodulate HLA-C. These results suggest that the capability of HLA-C-licensed NK cells to control HIV-1 replication is determined by the strength of KIR/HLA-C interactions and is thus dependent on both host genetics and the extent of virus-mediated HLA-C downregulation.