Newly established human liver cell line: a potential cell source for the bioartificial liver in the future

Reversibly immortalized hepatic progenitor cell line containing double suicide genes

A large number of functional hepatocytes is required for bioartificial liver therapy. Simian virus 40 T-antigen (SV40T) has been previously reported to improve the immortalized proliferation of primary hepatocytes to generate a sufficient number of cells; however, these long-term immortalized hepatocytes may induce further malignant transformation in vivo. In the present study, the SV40T immortalization gene and two suicide genes, herpes simplex virus thymidine kinase (HSV-tk) and cytosine deaminase (CD), were transducted into primary hepatocytes to construct a novel type of Cre/LoxP-mediated reversible immortalized hepatocyte line. Polymerase chain reaction analysis and western blotting confirmed that the SV40T, HSV-tk and CD genes were successfully inserted into hepatic progenitor cells and their expression was controlled by Cre/LoxP recombination. Total removal of SV40T could be achieved via the ganciclovir (GCV)/HSV-tk suicide system. Cells maintained their biosafety in vivo with CD gene expression and 5-fluoro-cytosine (5-FC) induced cell death. Following transplantation into the carbon tetrachloride (CCl₄) model group, the majority of cells had survived after 14 days post-implantation and a number of the cells had transported into the liver parenchyma. When compared with the CCl₄ model group, the transplanted cells repaired the liver biochemical index and pathological structure markedly. Thus, the present study reports a novel reversible immortalized hepatocyte with double suicide genes, which exhibited the cellular phenotype and recovery function of normal liver cells. This method maximally guaranteed the biological safety of immortalized hepatocytes for in vivo application, providing a reliable, safe and ideal cell material for the artificial liver technique.

Establishment and characterization of an immortalized human hepatocyte line for the development of bioartificial liver system

For further research and application of Bioartificial liver systems (BAL), active proliferation capacity and full hepatic functionality of the biomaterials is mandatory. However, there are still no suitable cell lines meeting the requirements for an ideal cell source in BAL development that makes it necessary to explore other sources. Here, we constructed a new cell line derived from well-differentiated hepatocellular carcinoma tissues designated NHBL2. Immunol staining showed that NHBL2 possessed the capacity of synthesizing albumin and CYP2E1 and quantitative analysis showed that the albumin synthesis ability of NHBL2 was comparable to C3A while urea production was highly abundant of NHBL2 compared with that of C3A. Using gene expression microarray analysis, we found that the expression levels of a set of genes encoding Phase I and Phase II metabolizing enzymes as well as many others related to common bioconversion and metabolic processes were significantly higher in NHBL2 cell line than that in C3A. Moreover, functional optimization assay in Matrigel showed obvious improvements of liver-related function level and a low malignance of this cell line. These findings indicated that NHBL2 possessed relatively attractive and full hepatic functionality that might be a potential cell line for BAL development.

Cell sources for in vitro human liver cell culture models

In vitro liver cell culture models are gaining increasing importance in pharmacological and toxicological research. The source of cells used is critical for the relevance and the predictive value of such models. Primary human hepatocytes (PHH) are currently considered to be the gold standard for hepatic in vitro culture models, since they directly reflect the specific metabolism and functionality of the human liver; however, the scarcity and difficult logistics of PHH have driven researchers to explore alternative cell sources, including liver cell lines and pluripotent stem cells. Liver cell lines generated from hepatomas or by genetic manipulation are widely used due to their good availability, but they are generally altered in certain metabolic functions. For the past few years, adult and pluripotent stem cells have been attracting increasing attention, due their ability to proliferate and to differentiate into hepatocyte-like cells in vitro However, controlling the differentiation of these cells is still a challenge. This review gives an overview of the major human cell sources under investigation for in vitro liver cell culture models, including primary human liver cells, liver cell lines, and stem cells. The promises and challenges of different cell types are discussed with a focus on the complex 2D and 3D culture approaches under investigation for improving liver cell functionality in vitro Finally, the specific application options of individual cell sources in pharmacological research or disease modeling are described.

Reversible immortalization of human hepatocytes mediated by retroviral transfer and site-specific recombination

AIM: To establish a method for the reversible immortalization of human hepatocytes, which may offer a good and safe source of hepatocytes for practical applications.

METHODS: We successfully isolated primary human hepatocytes from surgically resected liver tissue taken from a patient with liver hemangiomas. The freshly isolated cells were then immortalized with retroviral vector SSR#69 expressing simian virus 40 large T antigen (SV40T) and hygromycin-resistance genes flanked by paired loxP recombination targets.

RESULTS: The freshly isolated hepatocytes with high viability (85%) were successfully immortalized using retroviral gene transfer of SV40T. SV40T in the immortalized cells was then excised by Cre/loxP site-specific recombination. This cell population exhibited the characteristics of differentiated hepatocytes.

CONCLUSION: We successfully established reversibly immortalized human hepatocytes, which will provide an unlimited supply of cells for practical applications.