Stem cells for liver tissue repair:Current knowledge and perspectives

Stem cells from extra-or intrahepatic sources have been recently characterized and their usefulness for the generation of hepatocyte-like lineages has been demonstrated. Therefore, they are being increasingly considered for future applications in liver cell therapy. In that field, liver cell transplantation is currently regarded as a possible alternative to whole organ transplantation, while stem cells possess theoretical advantages on hepatocytes as they display higher in vitro culture performances and could be used in autologous transplant procedures. However, the current research on the hepatic fate of stem cells is still facing difficulties to demonstrate the acquisition of a full mature hepatocyte phenotype, both in vitro and in vivo. Furthermore, the lack of obvious demonstration of in vivo hepatocyte-like cell functionality remains associated to low repopulation rates obtained after current transplantation procedures. The present review focuses on the current knowledge of the stem cell potential for liver therapy. We discuss the characteristics of the principal cell candidates and the methods to demonstrate their hepatic potential in vitro and in vivo. We finally address the question of the future clinical applications of stem cells for liver tissue repair and the technical aspects that remain to be investigated.

Hepatocyte cryopreservation:Is it time to change the strategy?

Liver cell transplantation presents clinical benefit in patients with inborn errors of metabolism as an alternative,or at least as a bridge,to orthotopic liver transplantation.The success of such a therapeutic approach remains limited by the quality of the transplanted cells.Cryopreservation remains the best option for long-term storage of hepatocytes,providing a permanent and sufficient cell supply.However, isolated adult hepatocytes are poorly resistant to such a process,with a significant alteration both at the morphological and functional levels.Hence,the aim of the current review is to discuss the state of the art regarding widely-used hepatocyte cryopreservation protocols,as well as the assays performed to analyse the post-thawing cell quality both in vitro and in vivo. The majority of studies agree upon the poor quality and efficiency of cryopreserved/thawed hepatocytes as compared to freshly isolated hepatocytes.Intracellular ice formation or exposure to hyperosmotic solutionsremains the main phenomenon of cryopreservation process,and its effects on cell quality and cell death induction will be discussed.The increased knowledge and understanding of the cryopreservation process will lead to research strategies to improve the viability and the quality of the cell suspensions after thawing.Such strategies,such as vitrification,will be discussed with respect to their potential to significantly improve the quality of cell suspensions dedicated to liver cell-based therapies.

Liver cell transplantation for Crigler-Najjar syndrome type Ⅰ: Update and perspectives

Liver cell transplantation is an attractive technique to treat liver-based inborn errors of metabolism. The feasibility and efficacy of the procedure has been demonstrated, leading to medium term partial metabolic control of various diseases. Crigler-Najjar is the paradigm of such diseases in that the host liver is lacking one function with an otherwise normal parenchyma. The patient is at permanent risk for irreversible brain damage. The goal of liver cell transplantation is to reduce serum bilirubin levels within safe limits and to alleviate phototherapy requirements to improve quality of life. Preliminary data on Gunn rats, the rodent model of the disease, were encouraging and have led to successful clinical trials. Herein we report on two additional patients and describe the current limits of the technique in terms of durability of the response as compared to alternative therapeutic procedures. We discuss the future developments of the technique and new emerging perspectives.

Epithelial cells with hepatobiliary phenotype:Is it another stem cell candidate for healthy adult human liver?

AIM:To investigate the presence and role of liver epithelial cells in the healthy human adult liver.METHODS:Fifteen days after human hepatocyte primary culture,epithelial like cells emerged and started proliferating.Cell colonies were isolated and sub-cultured for more than 160 d under specific culture conditions.Cells were analyzed for each passage using immunofluorescence,flow cytometry and reverse transcription-polymerase chain reaction(RT-PCR).RESULTS:Flow cytometry analysis demonstrated that liver epithelial cells expressed common markers for hepatic and stem cells such as CD90,CD44 and CD29 but were negative for CD34 and CD117.Using immunofluorescence we demonstrated that liver epithelial cells expressed not only immature(α-fetoprotein)but also differentiated hepatocyte(albumin and CK-18)and biliary markers(CK-7 and 19),whereas they were negative for OV-6.RT-PCR analysis confirmed immunofluorescence data and revealed that liver epithelial cells did not express mature hepatocyte markers such as CYP2B6,CYP3A4 and tyrosine amino-transferase.Purified liver epithelial cells were transplanted into SCID mice.One month after transplantation,albumin positive cell foci were detected in the recipient mouse parenchyma.CONCLUSION:According to their immature and bipotential phenotype,liver epithelial cells might represent a pool of precursors in the healthy human adult liver other than oval cells.