C-C chemokine receptor type 7 (CCR7) regulates hepatic CD8 + T cell homeostasis and response to acute liver injury.

BACKGROUND AND AIMS: Acute liver failure (ALF) is a rare but life-threatening condition, and DILI, particularly acetaminophen toxicity, is the leading cause of ALF. Innate immune mechanisms further perpetuate liver injury, while the role of the adaptive immune system in DILI-related ALF is unclear. APPROACH AND RESULTS: We analyzed liver tissue from 2 independent patient cohorts with ALF and identified hepatic T cell infiltration as a prominent feature in human ALF. CD8 + T cells were characterized by zonation toward necrotic regions and an activated gene expression signature. In murine acetaminophen-induced liver injury, intravital microscopy revealed zonation of CD8 + but not CD4 + T cells at necrotic areas. Gene expression analysis exposed upregulated C-C chemokine receptor 7 (CCR7) and its ligand CCL21 in the liver as well as a broadly activated phenotype of hepatic CD8 + T cells. In 2 mouse models of ALF, Ccr7-/- mice had significantly aggravated early-phase liver damage. Functionally, CCR7 was not involved in the recruitment of CD8 + T cells, but regulated their activation profile potentially through egress to lymphatics. Ccr7-/- CD8 + T cells were characterized by elevated expression of activation, effector, and exhaustion profiles. Adoptive transfer revealed preferential homing of CCR7-deficient CD8 + T cells to the liver, and depletion of CD8 + T cells attenuated liver damage in mice. CONCLUSIONS: Our study demonstrates the involvement of the adaptive immune system in ALF in humans and mice. We identify the CCR7-CCL21 axis as an important regulatory pathway, providing downstream protection against T cell-mediated liver injury.

CCL2 chemokine inhibition primes the tumor vasculature for improved nanomedicine delivery and efficacy.

Blood vessel functionality is crucial for efficient tumor-targeted drug delivery. Heterogeneous distribution and perfusion of angiogenic blood vessels contribute to suboptimal accumulation of (nano-) therapeutics in tumors and metastases. To attenuate pathological angiogenesis, an L-RNA aptamer inhibiting the CC motif chemokine ligand 2 (CCL2) was administered to mice bearing orthotopic 4T1 triple-negative breast cancer tumors. The effect of CCL2 inhibition on tumor blood vessel functionality and tumor-targeted drug delivery was evaluated via multimodal and multiscale optical imaging, employing fluorophore-labeled polymeric (10 nm) and liposomal (100 nm) nanocarriers. Anti-CCL2 treatment induced a dose-dependent anti-angiogenic effect, reflected by a decreased relative blood volume, increased blood vessel maturity and functionality, and reduced macrophage infiltration, accompanied by a shift in the polarization of tumor-associated macrophages (TAM) towards a less M2-like and more M1-like phenotype. In line with this, CCL2 inhibitor treatment improved the delivery of polymers and liposomes to tumors, and enhanced the antitumor efficacy of free and liposomal doxorubicin. Together, these findings demonstrate that blocking the CCL2-CCR2 axis modulates TAM infiltration and polarization, resulting in vascular normalization and improved tumor-targeted drug delivery.

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.

Liver fibrosis affects the targeting properties of drug delivery systems to macrophage subsets in vivo.

Myeloid immune cells promote inflammation and fibrosis in chronic liver diseases. Drug delivery systems, such as polymers, liposomes and microbubbles, efficiently target myeloid cells in healthy liver, but their targeting properties in hepatic fibrosis remain elusive. We therefore studied the biodistribution of three intravenously injected carrier material, i.e. 10 nm poly(N-(2-hydroxypropyl)methacrylamide) polymers, 100 nm PEGylated liposomes and 2000 nm poly(butyl cyanoacrylate) microbubbles, in two fibrosis models in immunocompetent mice. While whole-body imaging confirmed preferential hepatic uptake even after induction of liver fibrosis, flow cytometry and immunofluorescence analysis revealed markedly decreased carrier uptake by liver macrophage subsets in fibrosis, particularly for microbubbles and polymers. Importantly, carrier uptake co-localized with immune infiltrates in fibrotic livers, corroborating the intrinsic ability of the carriers to target myeloid cells in areas of inflammation. Of the tested carrier systems liposomes had the highest uptake efficiency among hepatic myeloid cells, but the lowest specificity for cellular subsets. Hepatic fibrosis affected carrier uptake in liver and partially in spleen, but not in other tissues (blood, bone marrow, lung, kidney). In conclusion, while drug carrier systems target distinct myeloid cell populations in diseased and healthy livers, hepatic fibrosis profoundly affects their targeting efficiency, supporting the need to adapt nanomedicine-based approaches in chronic liver disease.

Targeting and Modulation of Liver Myeloid Immune Cells by Hard-Shell Microbubbles.

Poly n-butylcyanoacrylate (PBCA)-based hard-shell microbubbles (MB) have manifold biomedical applications, including targeted drug delivery or contrast agents for ultrasound (US)-based liver imaging. MB and their fragments accumulate in phagocytes, especially in the liver, but it is unclear if MB affect the function of these immune cells. We herein show that human primary monocytes internalize different PBCA-MB by phagocytosis, which transiently inhibits monocyte migration in vertical chemotaxis assays and renders monocytes susceptible to cytotoxic effects of MB during US-guided destruction. Conversely, human macrophage viability and function, including cytokine release and polarization, remain unaffected after MB uptake. After i.v. injection in mice, MB predominantly accumulate in liver, especially in hepatic phagocytes (monocytes and Kupffer cells). Despite efficiently targeting myeloid immune cells in liver, MB or MB after US-elicited burst do not cause overt hepatotoxicity or inflammation. Furthermore, MB application with or without US-guided burst does not aggravate the course of experimental liver injury in mice or the inflammatory response to liver injury in vivo. In conclusion, PBCA-MB have immunomodulatory effects on primary human myeloid cells in vitro, but do not provoke hepatotoxicity, inflammation or altered response to liver injury in vivo, suggesting the safety of these MB for diagnostic and therapeutic purposes.

Long term intravital multiphoton microscopy imaging of immune cells in healthy and diseased liver using CXCR6.Gfp reporter mice.

Liver inflammation as a response to injury is a highly dynamic process involving the infiltration of distinct subtypes of leukocytes including monocytes, neutrophils, T cell subsets, B cells, natural killer (NK) and NKT cells. Intravital microscopy of the liver for monitoring immune cell migration is particularly challenging due to the high requirements regarding sample preparation and fixation, optical resolution and long-term animal survival. Yet, the dynamics of inflammatory processes as well as cellular interaction studies could provide critical information to better understand the initiation, progression and regression of inflammatory liver disease. Therefore, a highly sensitive and reliable method was established to study migration and cell-cell-interactions of different immune cells in mouse liver over long periods (about 6 hr) by intravital two-photon laser scanning microscopy (TPLSM) in combination with intensive care monitoring. The method provided includes a gentle preparation and stable fixation of the liver with minimal perturbation of the organ; long term intravital imaging using multicolor multiphoton microscopy with virtually no photobleaching or phototoxic effects over a time period of up to 6 hr, allowing tracking of specific leukocyte subsets; and stable imaging conditions due to extensive monitoring of mouse vital parameters and stabilization of circulation, temperature and gas exchange. To investigate lymphocyte migration upon liver inflammation CXCR6.gfp knock-in mice were subjected to intravital liver imaging under baseline conditions and after acute and chronic liver damage induced by intraperitoneal injection(s) of carbon tetrachloride (CCl4). CXCR6 is a chemokine receptor expressed on lymphocytes, mainly on Natural Killer T (NKT)-, Natural Killer (NK)- and subsets of T lymphocytes such as CD4 T cells but also mucosal associated invariant (MAIT) T cells1. Following the migratory pattern and positioning of CXCR6.gfp+ immune cells allowed a detailed insight into their altered behavior upon liver injury and therefore their potential involvement in disease progression.

Liver inflammation abrogates immunological tolerance induced by Kupffer cells.

UNLABELLED: The liver is essential for inducing immunological tolerance toward harmless antigens to maintain immune system homeostasis. However, the precise cellular mechanisms of tolerance induction against particle-bound antigens, the role of the local hepatic microenvironment, and implications for therapeutic targets in immune-mediated diseases are currently unclear. In order to elucidate cellular mechanisms of tolerance induction in healthy and injured liver, we developed a novel in vivo system combining the systemic delivery of low-dose peptide antigens coupled to inert particles, immunological readouts, and sophisticated intravital multiphoton microscopy-based imaging of liver in mice. We show that liver resident macrophages, Kupffer cells (KCs), but not hepatic monocyte-derived macrophages or dendritic cells (DCs), are the central cellular scavenger for circulating particle-associated antigens in homeostasis. KC-associated antigen presentation induces CD4 T-cell arrest, expansion of naturally occurring Foxp3(+) CD25(+) interleukin-10-producing antigen-specific regulatory T cells (Tregs) and tolerogenic immunity. Particle-associated tolerance induction in the liver protected mice from kidney inflammation in T-cell-mediated glomerulonephritis, indicating therapeutic potential of targeting KC for immune-mediated extrahepatic disorders. Liver inflammation in two independent experimental models of chronic liver injury and fibrosis abrogated tolerance induction and led to an immunogenic reprogramming of antigen-specific CD4 T cells. In injured liver, infiltrating monocyte-derived macrophages largely augment the hepatic phagocyte compartment, resulting in antigen redistribution between myeloid cell populations and, simultaneously, KCs lose signature markers of their tolerogenic phenotype. CONCLUSIONS: Hepatic induction of tissue-protective immunological tolerance against particulate antigens is dependent on KCs as well as on a noninflamed liver microenvironment, thereby providing mechanistic explanations for the clinical observation of immune dysfunction and tolerance break in patients with advanced liver diseases.

Chemokine receptor CXCR6-dependent hepatic NK T Cell accumulation promotes inflammation and liver fibrosis.

Chronic liver injury characteristically results in hepatic inflammation, which represents a prerequisite for organ fibrosis. Although NKT cells are abundantly present in liver and involved in hepatic inflammation, molecular mechanisms of their recruitment in liver fibrosis remained elusive. We hypothesized that chemokine receptor CXCR6 and its ligand CXCL16 control NKT cell migration and functionality in liver fibrosis. In patients with chronic liver diseases (n = 58), CXCR6 and CXCL16 expression was intrahepatically upregulated compared with controls. In murine liver, Cxcl16 was strongly expressed by endothelium and macrophages, whereas lymphocyte populations (NKT, NK, CD4 T, CD8 T cells) expressed CXCR6. Intravital two-photon microscopy imaging of Cxcr6(+/gfp) and Cxcr6(gfp/gfp) mice and chemotaxis studies in vitro revealed that CXCR6 specifically controls hepatic NKT cell accumulation during the early response upon experimental liver damage. Hepatic invariant NKT cells expressed distinct proinflammatory cytokines including IFN-γ and IL-4 upon injury. CXCR6-deficient mice were protected from liver fibrosis progression in two independent experimental models. Macrophage infiltration and protein levels of inflammatory cytokines IFN-γ, TNF-α, and IL-4 were also reduced in fibrotic livers of Cxcr6(-/-) mice, corroborating that hepatic NKT cells provide essential cytokine signals perpetuating hepatic inflammation and fibrogenesis. Adoptive transfer of NKT cells, but not CD4 T cells, isolated from wild type livers restored hepatic fibrosis in Cxcr6(-/-) mice upon experimental steatohepatitis. Our results demonstrate that hepatic NKT cells accumulate CXCR6-dependent early upon injury, thereby accentuating the inflammatory response in the liver and promoting hepatic fibrogenesis. Interfering with CXCR6/CXCL16 might therefore bear therapeutic potential in liver fibrosis.