The human liver is usually perceived as a non-immunological organ engaged primarily in metabolic, nutrient storage and detoxification activities. However, we now know that the healthy liver is also a site of complex immunological activity mediated by a diverse immune cell repertoire as well as non-hematopoietic cell populations. In the non-diseased liver, metabolic and tissue remodeling functions require elements of inflammation. This inflammation, in combination with regular exposure to dietary and microbial products, creates the potential for excessive immune activation. In this complex microenvironment, the hepatic immune system tolerates harmless molecules while at the same time remaining alert to possible infectious agents, malignant cells or tissue damage. Upon appropriate immune activation to challenge by pathogens or tissue damage, mechanisms to resolve inflammation are essential to maintain liver homeostasis. Failure to clear ‘dangerous' stimuli or regulate appropriately activated immune mechanisms leads to pathological inflammation and disrupted tissue homeostasis characterized by the progressive development of fibrosis, cirrhosis and eventual liver failure. Hepatic inflammatory mechanisms therefore have a spectrum of roles in the healthy adult liver; they are essential to maintain tissue and organ homeostasis and, when dysregulated, are key drivers of the liver pathology associated with chronic infection, autoimmunity and malignancy. In this review, we explore the changing perception of inflammation and inflammatory mediators in normal liver homeostasis and propose targeting of liver-specific immune regulation pathways as a therapeutic approach to treat liver disease.

Colorectal cancer is the third most common malignancy worldwide, with 1.3 million new cases annually. Metastasis to the liver is a leading cause of mortality in these patients. In human liver, metastatic cancer cells must evade populations of liver-resident natural killer (NK) cells with potent cytotoxic capabilities. Here, we investigated how these tumors evade liver NK-cell surveillance. Tissue biopsies were obtained from patients undergoing resection of colorectal liver metastasis (CRLM, n ¼ 18), from the tumor, adjacent tissue, and distal resection margin. The number and phenotype of liver-resident NK cells, at each site, were analyzed by flow cytometry. Tumorconditioned media (TCM) was generated for cytokine and metabolite quantification and used to treat healthy liverresident NK cells, isolated from donor liver perfusate during transplantation. Liver-resident NK cells were significantly depleted from CRLM tumors. Healthy liver-resident NK cells exposed to TCM underwent apoptosis in vitro, associated with elevated lactate. Tumor-infiltrating liver-resident NK cells showed signs of mitochondrial stress, which was recapitulated in vitro by treating liver-resident NK cells with lactic acid. Lactic acid induced apoptosis by decreasing the intracellular pH of NK cells, resulting in mitochondrial dysfunction that could be prevented by blocking mitochondrial ROS accumulation. CRLM tumors produced lactate, thus decreasing the pH of the tumor microenvironment. Liver-resident NK cells migrating toward the tumor were unable to regulate intracellular pH resulting in mitochondrial stress and apoptosis. Targeting CRLM metabolism provides a promising therapeutic approach to restoring local NK-cell activity and preventing tumor growth.

The adult human liver is enriched with natural killer (NK) cells, accounting for 30-50% of hepatic lymphocytes, which include tissue-resident hepatic NK-cell subpopulations, distinct from peripheral blood NK cells. In murine liver, a subset of liver-resident hepatic NK cells have altered expression of the two highly related T-box transcription factors, T-bet and eomesodermin (Eomes). Here, we investigate the heterogeneity of T-bet and Eomes expression in NK cells from healthy adult human liver with a view to identifying humanliver-resident populations. Hepatic NK cells were isolated from donor liver perfusates and biopsies obtained during orthotopic liver transplantation (N = 28). Hepatic CD56 bright NK cells were Eomes hi T-bet lo , a phenotype virtually absent from peripheral blood. These NK cells express the chemokine receptor CXCR6 (chemokine (C-X-C motif) receptor 6), a marker of tissue residency, which is absent from hepatic CD56 dim and blood NK cells. Compared to blood populations, these hepatic CD56 bright NK cells have increased expression of activatory receptors (NKp44, NKp46, and NKG2D). They show reduced ability to produce IFN-γ but enhanced degranulation in response to challenge with target cells. This functionally distinct population of hepatic NK cells constitutes 20-30% of the total hepatic lymphocyte repertoire and represents a tissue-resident immune cell population adapted to the tolerogenic liver microenvironment. Eur. J. Immunol. 2016Immunol. . 46: 2111Immunol. -2120 less cytokines than the CD56 bright population [1,2]. Studies in knockout mice have identified a number of transcription factors essential for the developmental program of NK cells, such as Nfil3, Id2,, as well as the two highly related T-box transcription factors, T-bet and eomesodermin (Eomes) [6,7]. In the bone marrow (BM), T-bet expression is initially repressed, allowing the development of Eomes + NK-cell precursors, with T-bet expression subsequently increased during the final stages of NKcell maturation [6]. While conventional NK cells circulate in the PB, transiting through several organs, significant NK-cell populations also permanently reside in tissues such as the lung, gut, uterus, and liver and may develop there [8]. Among these tissue-resident NK-cell populations, the role of uterine NK cells in successful pregnancy is well described [9]; however, the functions of other heterogeneous tissue-resident NK-cell populations remain largely unknown. Within these tissue microenvironments, it is evident that the developmental, functional, and phenotypic features of NK-cell subsets are poorly characterized compared to their PB counterparts [10]. Keywords: CD56 bright natural killer (NK) cells Human liver Interferon MicroenvironmentThe adult human liver contains a unique and extensive lymphoid repertoire. There is a predominance of innate lymphoid cells including NK cells, NKT cells, mucosal-associated invariant T cells and γδ T cells in the liver, in addition to the presence of conventional CD4 + and CD8 + lymphocytes of ...

Poor myeloid engraftment remains a barrier to experimental use of humanized mice. Focusing primarily on peripheral blood cells, we compared the engraftment profile of NOD-scid-IL2Rγc(-/-) (NSG) mice with that of NSG mice transgenic for human membrane stem cell factor (hu-mSCF mice), NSG mice transgenic for human interleukin (IL)-3, granulocyte-macrophage-colony stimulating factor (GM-CSF), and stem cell factor (SGM3 mice). hu-mSCF and SGM3 mice showed enhanced engraftment of human leukocytes compared to NSG mice, and this was reflected in the number of human neutrophils and monocytes present in these strains. Importantly, discrete classical, intermediate, and nonclassical monocyte populations were identifiable in the blood of NSG and hu-mSCF mice, while the nonclassical population was absent in the blood of SGM3 mice. Granulocyte-colony stimulating factor (GCSF) treatment increased the number of blood monocytes in NSG and hu-mSCF mice, and neutrophils in NSG and SGM3 mice; however, this effect appeared to be at least partially dependent on the stem cell donor used to engraft the mice. Furthermore, GCSF treatment resulted in a preferential expansion of nonclassical monocytes in both NSG and hu-mSCF mice. Human tubulointerstitial CD11c(+) cells were present in the kidneys of hu-mSCF mice, while monocytes and neutrophils were identified in the liver of all strains. Bone marrow-derived macrophages prepared from NSG mice were most effective at phagocytosing polystyrene beads. In conclusion, hu-mSCF mice provide the best environment for the generation of human myeloid cells, with GCSF treatment further enhancing peripheral blood human monocyte cell numbers in this strain.

γδ T cells are a small population of mostly tissue‐resident lymphocytes, with both innate and adaptive properties. These unique features make them particularly attractive candidates for the development of new cellular therapy targeted against tumor development. Nevertheless, γδ T cells may play dual roles in cancer, promoting cancer development on the one hand, while participating in antitumor immunity on the other hand. In mice, γδ T‐cell subsets preferentially produce IL‐17 or IFN‐γ. While antitumor functions of murine γδ T cells can be attributed to IFN‐γ+ γδ T cells, recent studies have implicated IL‐17+ γδ T cells in tumor growth and metastasis. However, in humans, IL‐17‐producing γδ T cells are rare and most studies have attributed a protective role to γδ T cells against cancer. In this review, we will present the current knowledge and most recent findings on γδ T‐cell functions in mouse models of tumor development and human cancers. We will also discuss their potential as cellular immunotherapy against cancer.