Despite the enormous replication potential of the human liver, there are currently no culture systems available that sustain hepatocyte replication and/or function in vitro. We have shown previously that single mouse Lgr5+ liver stem cells can be expanded as epithelial organoids in vitro and can be differentiated into functional hepatocytes in vitro and in vivo. We now describe conditions allowing long-term expansion of adult bile duct-derived bipotent progenitor cells from human liver. The expanded cells are highly stable at the chromosome and structural level, while single base changes occur at very low rates. The cells can readily be converted into functional hepatocytes in vitro and upon transplantation in vivo. Organoids from α1-antitrypsin deficiency and Alagille syndrome patients mirror the in vivo pathology. Clonal long-term expansion of primary adult liver stem cells opens up experimental avenues for disease modeling, toxicology studies, regenerative medicine, and gene therapy.

Tumor organoids derived from the most common subtypes of primary liver cancer recapitulate the histologic and molecular features of the tissues of origin, even after long-term culture. These in vitro models, as well as those for colorectal cancer reported in Crespo et al. in a previous issue, are amenable for drug screening and allow the identification of therapeutic approaches with potential for cancer treatment. Human liver cancer research currently lacks in vitro models that can faithfully recapitulate the pathophysiology of the original tumor. We recently described a novel, near-physiological organoid culture system, wherein primary human healthy liver cells form long-term expanding organoids that retain liver tissue function and genetic stability. Here we extend this culture system to the propagation of primary liver cancer (PLC) organoids from three of the most common PLC subtypes: hepatocellular carcinoma (HCC), cholangiocarcinoma (CC) and combined HCC/CC (CHC) tumors. PLC-derived organoid cultures preserve the histological architecture, gene expression and genomic landscape of the original tumor, allowing for discrimination between different tumor tissues and subtypes, even after long-term expansion in culture in the same medium conditions. Xenograft studies demonstrate that the tumorogenic potential, histological features and metastatic properties of PLC-derived organoids are preserved in vivo. PLC-derived organoids are amenable for biomarker identification and drug-screening testing and led to the identification of the ERK inhibitor SCH772984 as a potential therapeutic agent for primary liver cancer. We thus demonstrate the wide-ranging biomedical utilities of PLC-derived organoid models in furthering the understanding of liver cancer biology and in developing personalized-medicine approaches for the disease.

Recent evidence indicates there is a role for small membrane vesicles, including exosomes, as vehicles for intercellular communication. Exosomes secreted by most cell types can mediate transfer of proteins, mRNAs, and microRNAs, but their role in the transmission of infectious agents is less established. Recent studies have shown that hepatocyte-derived exosomes containing hepatitis C virus (HCV) RNA can activate innate immune cells, but the role of exosomes in the transmission of HCV between hepatocytes remains unknown. In this study, we investigated whether exosomes transfer HCV in the presence of neutralizing antibodies. Purified exosomes isolated from HCV-infected human hepatoma Huh7.5.1 cells were shown to contain full-length viral RNA, viral protein, and particles, as determined by RT-PCR, mass spectrometry, and transmission electron microscopy. Exosomes from HCV-infected cells were capable of transmitting infection to naive human hepatoma Huh7.5.1 cells and establishing a productive infection. Even with subgenomic replicons, lacking structural viral proteins, exosome-mediated transmission of HCV RNA was observed. Treatment with patient-derived IgGs showed a variable degree of neutralization of exosome-mediated infection compared with free virus. In conclusion, this study showed that hepatic exosomes can transmit productive HCV infection in vitro and are partially resistant to antibody neutralization. This discovery sheds light on neutralizing antibodies resistant to HCV transmission by exosomes as a potential immune evasion mechanism.

Chronic hepatitis B virus (HBV) infection is characterized by a weak immune response to HBV. Regulatory T cells (T_reg) can suppress the function of effector T cells and may thus be key players in this impaired immune response. Changes in the functionality or number of T_reg could explain the decreased antiviral response in chronic HBV patients. To investigate the role of T_reg in chronic HBV infection, we compared the proportional frequency and functionality of T_reg in peripheral blood of 50 chronic HBV patients, 23 healthy controls, and 9 individuals with a resolved HBV infection. A higher percentage of T_reg, defined as CD4, CD25, CD45RO, and cytotoxic T‐lymphocyte–associated antigen 4–positive cells, was detected within the population of CD4⁺ cells in peripheral blood of chronic HBV patients compared with healthy controls and individuals with a resolved HBV infection. Accordingly, chronic HBV patients displayed a higher FoxP3 messenger RNA level than healthy controls. Depletion of CD25⁺ cells from peripheral blood mononuclear cells (PBMC) of chronic HBV patients resulted in an enhanced proliferation after stimulation with HBV core antigen. Reconstitution of these depleted PBMC with CD4⁺CD25⁺ T_reg resulted in a dose‐dependent reduction of both HBV‐specific proliferation and interferon γ production. In conclusion, chronic HBV patients harbor an increased percentage of T_reg in peripheral blood compared with controls. T_reg have an immunosuppressive effect on HBV‐specific T helper cells. The presence of HBV‐specific T_reg could contribute to an inadequate immune response against the virus, leading to chronic infection. (HEPATOLOGY 2005;41:771–778.)

The extracellular matrix (ECM) is essential for cell support during homeostasis and plays a critical role in cancer. Although research often concentrates on the tumor’s cellular aspect, attention is growing for the importance of the cancer-associated ECM. Biochemical and physical ECM signals affect tumor formation, invasion, metastasis, and therapy resistance. Examining the tumor microenvironment uncovers intricate ECM dysregulation and interactions with cancer and stromal cells. Anticancer therapies targeting ECM sensors and remodelers, including integrins and matrix metalloproteinases, and ECM-remodeling cells, have seen limited success. This review explores the ECM’s role in cancer and discusses potential therapeutic strategies for cell-ECM interactions.