Stuart Hunter

Biliary epithelium and liver B cells exposed to bacteria activate intrahepatic MAIT cells through MR1

Background & Aims Mucosal-Associated Invariant T (MAIT) cells are innate-like T cells characterised by the invariant TCR-chain, Vα7.2-Jα33, and are restricted by MR1, which presents bacterial vitamin B metabolites. They are important for antibacterial immunity at mucosal sites; however, detailed characteristics of liver-infiltrating MAIT (LI-MAIT) and their role in biliary immune surveillance remain unexplored. Methods The phenotype and intrahepatic localisation of human LI-MAIT cells was examined in diseased and normal livers. MAIT cell activation in response to E. coli-exposed macrophages, biliary epithelial cells (BEC) and liver B cells was assessed with/without anti-MR1. Results Intrahepatic MAIT cells predominantly localised to bile ducts in the portal tracts. Consistent with this distribution, they expressed biliary tropic chemokine receptors CCR6, CXCR6, and integrin αEβ7. LI-MAIT cells were also present in the hepatic sinusoids and possessed tissue-homing chemokine receptor CXCR3 and integrins LFA-1 and VLA-4, suggesting their recruitment via hepatic sinusoids. LI-MAIT cells were enriched in the parenchyma of acute liver failure livers compared to chronic diseased livers. LI-MAIT cells had an activated, effector memory phenotype, expressed α4β7 and receptors for IL-12, IL-18, and IL-23. Importantly, in response to E. coli-exposed macrophages, liver B cells and BEC, MAIT cells upregulated IFN-γ and CD40 Ligand and degranulated in an MR1-dependent, cytokine-independent manner. In addition, diseased liver MAIT cells expressed T-bet and RORγt and the cytokines IFN-γ, TNF-α, and IL-17. Conclusions Our findings provide the first evidence of an immune surveillance effector response for MAIT cells towards BEC in human liver; thus they could be manipulated for treatment of biliary disease in the future.

Neuroblastoma arginase activity creates an immunosuppressive microenvironment that impairs autologous and engineered immunity

Neuroblastoma is the most common extracranial solid tumor of childhood, and survival remains poor for patients with advanced disease. Novel immune therapies are currently in development, but clinical outcomes have not matched preclinical results. Here, we describe key mechanisms in which neuroblastoma inhibits the immune response. We show that murine and human neuroblastoma tumor cells suppress T-cell proliferation through increased arginase activity. Arginase II is the predominant isoform expressed and creates an arginine-deplete local and systemic microenvironment. Neuroblastoma arginase activity results in inhibition of myeloid cell activation and suppression of bone marrow CD34(+) progenitor proliferation. Finally, we demonstrate that the arginase activity of neuroblastoma impairs NY-ESO-1-specific T-cell receptor and GD2-specific chimeric antigen receptor-engineered T-cell proliferation and cytotoxicity. High arginase II expression correlates with poor survival for patients with neuroblastoma. The results support the hypothesis that neuroblastoma creates an arginase-dependent immunosuppressive microenvironment in both the tumor and blood that leads to impaired immunosurveillance and suboptimal efficacy of immunotherapeutic approaches.

Clonal selection in the human Vδ1 T cell repertoire indicates γδ TCR-dependent adaptive immune surveillance

γδ T cells are considered to be innate-like lymphocytes that respond rapidly to stress without clonal selection and differentiation. Here we use next-generation sequencing to probe how this paradigm relates to human Vδ2neg T cells, implicated in responses to viral infection and cancer. The prevalent Vδ1 T cell receptor (TCR) repertoire is private and initially unfocused in cord blood, typically becoming strongly focused on a few high-frequency clonotypes by adulthood. Clonal expansions have differentiated from a naive to effector phenotype associated with CD27 downregulation, retaining proliferative capacity and TCR sensitivity, displaying increased cytotoxic markers and altered homing capabilities, and remaining relatively stable over time. Contrastingly, Vδ2+ T cells express semi-invariant TCRs, which are present at birth and shared between individuals. Human Vδ1+ T cells have therefore evolved a distinct biology from the Vδ2+ subset, involving a central, personalized role for the γδ TCR in directing a highly adaptive yet unconventional form of immune surveillance.

Human intrahepatic regulatory T cells are functional, require IL‐2 from effector cells for survival, and are susceptible to Fas ligand‐mediated apoptosis

Regulatory T cells (Treg) suppress T effector cell proliferation and maintain immune homeostasis. Autoimmune liver diseases persist despite high frequencies of Treg in the liver, suggesting that the local hepatic microenvironment might affect Treg stability, survival, and function. We hypothesized that interactions between Treg and endothelial cells during recruitment and then with epithelial cells within the liver affect Treg stability, survival, and function. To model this, we explored the function of Treg after migration through human hepatic sinusoidal‐endothelium (postendothelial migrated Treg [PEM Treg]) and the effect of subsequent interactions with cholangiocytes and local proinflammatory cytokines on survival and stability of Treg. Our findings suggest that the intrahepatic microenvironment is highly enriched with proinflammatory cytokines but deficient in the Treg survival cytokine interleukin (IL)‐2. Migration through endothelium into a model mimicking the inflamed liver microenvironment did not affect Treg stability; however, functional capacity was reduced. Furthermore, the addition of exogenous IL‐2 enhanced PEM Treg phosphorylated STAT5 signaling compared with PEMCD8. CD4 and CD8 T cells are the main source of IL‐2 in the inflamed liver. Liver‐infiltrating Treg reside close to bile ducts and coculture with cholangiocytes or their supernatants induced preferential apoptosis of Treg compared with CD8 effector cells. Treg from diseased livers expressed high levels of CD95, and their apoptosis was inhibited by IL‐2 or blockade of CD95. Conclusion: Recruitment through endothelium does not impair Treg stability, but a proinflammatory microenvironment deficient in IL‐2 leads to impaired function and increased susceptibility of Treg to epithelial cell‐induced Fas‐mediated apoptosis. These results provide a mechanism to explain Treg dysfunction in inflamed tissues and suggest that IL‐2 supplementation, particularly if used in conjunction with Treg therapy, could restore immune homeostasis in inflammatory and autoimmune liver disease. (Hepatology 2016;64:138–150)

A disease-linked ULBP6 polymorphism inhibits NKG2D-mediated target cell killing by enhancing the stability of NKG2D ligand binding

A disease-associated variant of an activating ligand engages receptors so strongly that it impairs NK cell–mediated killing. Distracting natural killer cells Natural killer (NK) cells target virally infected and transformed cells for cytolysis. When sufficient activating receptors on the NK cell surface, such as NKG2D, are engaged by ligands on the target cell, such as ULBP proteins, the NK cell kills the target. Polymorphisms within ULBP-encoding genes are associated with immune dysfunction. Zuo et al. found that the affinity of a commonly occurring ULBP6 variant for NKG2D was greater than that of the wild-type protein, which impaired NK cell activation. A soluble form of this protein variant bound so tightly to NKG2D that it suppressed receptor activation and target cell killing in response to other NKG2D ligands. Together, these data suggest that targeting NK cell–ligand interactions may provide therapies to modulate the strength of immune responses. NKG2D (natural killer group 2, member D) is an activating receptor found on the surface of immune cells, including natural killer (NK) cells, which regulates innate and adaptive immunity through recognition of the stress-induced ligands ULBP1 (UL16 binding protein 1) to ULBP6 and MICA/B. Similar to class I human leukocyte antigen (HLA), these NKG2D ligands have a major histocompatibility complex–like fold and exhibit pronounced polymorphism, which influences human disease susceptibility. However, whereas class I HLA polymorphisms occur predominantly in the α1α2 groove and affect antigen binding, the effects of most NKG2D ligand polymorphisms are unclear. We studied the molecular and functional consequences of the two major alleles of ULBP6, the most polymorphic ULBP gene, which are associated with autoimmunity and relapse after stem cell transplantation. Surface plasmon resonance and crystallography studies revealed that the arginine-to-leucine polymorphism within ULBP0602 affected the NKG2D-ULBP6 interaction by generating an energetic hotspot. This resulted in an NKG2D-ULBP0602 affinity of 15.5 nM, which is 10- to 1000-fold greater than the affinities of other ULBP-NKG2D interactions and limited NKG2D-mediated activation. In addition, soluble ULBP0602 exhibited high-affinity competitive binding for NKG2D and partially suppressed NKG2D-mediated activation of NK cells by other NKG2D ligands. These effects resulted in a decrease in a range of NKG2D-mediated effector functions. Our results reveal that ULBP polymorphisms affect the strength of human lymphocyte responses to cellular stress signals and may offer opportunities for therapeutic intervention.

The human Vδ2 + T-cell compartment comprises distinct innate-like Vγ9 + and adaptive Vγ9 - subsets

Vδ2+ T cells form the predominant human γδ T-cell population in peripheral blood and mediate T-cell receptor (TCR)-dependent anti-microbial and anti-tumour immunity. Here we show that the Vδ2+ compartment comprises both innate-like and adaptive subsets. Vγ9+ Vδ2+ T cells display semi-invariant TCR repertoires, featuring public Vγ9 TCR sequences equivalent in cord and adult blood. By contrast, we also identify a separate, Vγ9− Vδ2+ T-cell subset that typically has a CD27hiCCR7+CD28+IL-7Rα+ naive-like phenotype and a diverse TCR repertoire, however in response to viral infection, undergoes clonal expansion and differentiation to a CD27loCD45RA+CX3CR1+granzymeA/B+ effector phenotype. Consistent with a function in solid tissue immunosurveillance, we detect human intrahepatic Vγ9− Vδ2+ T cells featuring dominant clonal expansions and an effector phenotype. These findings redefine human γδ T-cell subsets by delineating the Vδ2+ T-cell compartment into innate-like (Vγ9+) and adaptive (Vγ9−) subsets, which have distinct functions in microbial immunosurveillance.Human Vδ2+ γδ T cells are thought to be an innate-like T-cell population. Here the authors show the Vδ2+ compartment contains both innate-like Vγ9+ and an adaptive Vγ9- subset that undergoes clonal expansion during viral infection and can infiltrate liver tissue.

Human liver infiltrating γδ T cells are composed of clonally expanded circulating and tissue-resident populations

Graphical abstract

Recasting Human Vδ1 Lymphocytes in an Adaptive Role

γδ T cells are unconventional lymphocytes commonly described as ‘innate-like’ in function, which can respond in both a T cell receptor (TCR)-independent and also major histocompatibility complex (MHC)-unrestricted TCR-dependent manner. While the relative importance of TCR recognition had remained unclear, recent studies revealed that human Vδ1 T cells display unexpected parallels with adaptive αβ T cells. Vδ1 T cells undergo profound and highly focussed clonal expansion from an initially diverse and private TCR repertoire, most likely in response to specific immune challenges. Concomitantly, they differentiate from a Vδ1 T cell naïve (Tnaïve) to a Vδ1 T cell effector (Teffector) phenotype, marked by the downregulation of lymphoid homing receptors and upregulation of peripheral homing receptors and effector markers. This suggests that an adaptive paradigm applies to Vδ1 T cells, likely involving TCR-dependent but MHC-unrestricted responses to microbial and non-microbial challenges.

Vδ2+ T cells – two subsets for the price of one

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OC-029 Phenotype of Human Intrahepatic Innate Lymphoid Cell Subsets in Heatlh and Disease

Introduction Innate lymphoid cells (ILCs) involve in the initiation, regulation and resolution of inflammation. Although the role of ILCs in murine liver fibrosis and biliary proliferation has been reported, the phenotypic characteristics and functional role of these cells in human liver disease remains undefined. We explored the detailed phenotype of human intrahepatic ILCs to gain insight on their function. Methods Liver infiltrating lymphocytes from normal liver tissue, autoimmune liver diseases (AILD), alcoholic liver disease (ALD) and non-alcoholic steatohepatitis (NASH) explants were phenotyped with flow cytometry. Results Total intrahepatic ILC (CD3− lineage− CD45− CD127+ ) comprised 1% (IQR 0.4–1.7%) of the CD3− CD45+ population in normal liver and 0.4% for ALD/NASH and autoimmune livers. The ILC1 subset constituted the majority of intrahepatic ILC and its frequency is higher in normal liver compared to diseased livers (85% vs. 67%) (p < 0.05). In contrast, CD161+CRTH2+ ILC2 subset and ILC3 subset frequency are higher in diseased livers compared to normal livers. Interestingly, frequency of ILC3 is significantly higher in ALD compared to normal liver (p < 0.01). Intrahepatic ILC subsets are in activated and tissue resident state (CD69 75–90%). All subsets expressed the liver tissue homing chemokine receptor, CXCR3. Expression frequency is highest on diseased ILC1 (AILD 50%, ALD/NASH 56%,) compared to ILC2 (AILD 24%; ALD/NASH 15%) and ILC3 (AILD 38%, ALD/NASH 28%). Biliary tropic receptor CCR6 was expressed more highly by ILC subsets in diseased compared to normal livers. The fibronectin receptor, VLA5 and laminin receptor VLA6 were both highly expressed on all intrahepatic ILC subsets (60–90% and 55–80% respectively). In terms of the cytokine receptors expressed, on all ILC subsets, IL-6R was near undetectable (2%) and low expressions of ST2 (3–6%), IL-25R (2–5%) and IL-23R (2–7%) were detected. In contrast there was almost ubiquitous expression of IL18Ralpha. CD25 was also very highly expressed. Of note, CD25 was significantly higher in ILC1 and ILC3 subsets from normal compared to AILD (p < 0.01) livers (40% vs. 80%; 66% vs. 93%) while intrahepatic ILC2 and ILC3 subsets in diseased states highly expressed CD25 (>90%). Of likely functional importance, intrahepatic ILC1 expressed IFN-γ (40%) while ILC2 expressed IL-13 (20–50%) in diseased states. Conclusion We report for the first time the presence of all three ILC subsets within the human liver immune cell infiltrates. CXCR3+ IFN-γ expressing ILC1 subset is enriched in both normal and inflamed diseased livers. Higher frequencies of CCR6+ VLA5+ VLA6+ IL-13 expressing ILC2 are observed in diseased livers suggesting that this subset may play a role in biliary pathology and peri-biliary fibrosis. Disclosure of Interest None Declared