In vitro differentiated adult human liver progenitor cells display mature hepatic metabolic functions: a potential tool for in vitro pharmacotoxicological testing

Senescence and senotherapies in biliary atresia and biliary cirrhosis

BACKGROUND

Premature senescence occurs in adult hepatobiliary diseases and worsens the prognosis through deleterious liver remodeling and hepatic dysfunction. Senescence might also arises in biliary atresia (BA), the first cause of pediatric liver transplantation. Since alternatives to transplantation are needed, our aim was to investigate premature senescence in BA and to assess senotherapies in a preclinical model of biliary cirrhosis.

METHODS

BA liver tissues were prospectively obtained at hepatoportoenterostomy (n=5) and liver transplantation (n=30) and compared to controls (n=10). Senescence was investigated through spatial whole transcriptome analysis, SA-β-gal activity, p16 and p21 expression, γ-H2AX and senescence-associated secretory phenotype (SASP). Human allogenic liver-derived progenitor cells (HALPC) or dasatinib and quercetin (D+Q) were administrated to two-month-old Wistar rats after bile duct ligation (BDL).

RESULTS

Advanced premature senescence was evidenced in BA livers from early stage and continued to progress until liver transplantation. Senescence and SASP were predominant in cholangiocytes, but also present in surrounding hepatocytes. HALPC but not D+Q reduced the early marker of senescence p21 in BDL rats and improved biliary injury (serum γGT and Sox9 expression) and hepatocytes mass loss (Hnf4a).

CONCLUSIONS

BA livers displayed advanced cellular senescence at diagnosis that continued to progress until liver transplantation. HALPC reduced early senescence and improved liver disease in a preclinical model of BA, providing encouraging preliminary results regarding the use of senotherapies in pediatric biliary cirrhosis.

Human Allogeneic Liver-Derived Progenitor Cells Significantly Improve NAFLD Activity Score and Fibrosis in Late-Stage NASH Animal Model

Accumulated experimental and clinical evidence supports the development of human allogeneic liver-derived progenitor cells (HALPCs) to treat fibro-inflammatory liver diseases. The aim of the present study was to evaluate their therapeutic effect in a non-alcoholic steatohepatitis (NASH)-STAM mouse model. The immune signaling characteristics of HALPCs were first assessed in vitro. Upon inflammation treatment, HALPCs secreted large amounts of potent bioactive prostaglandin E2 and indoleamine 2,3-dioxygenase, which significantly reduced CD4⁺ T-lymphocyte proliferation and secretion of proinflammatory cytokines. In vivo, HALPCs were intravenously administered as single or triple shots (of a dose of 12.5 × 10⁶ cells/kg BW) in STAM mice. Transplantation of HALPCs was associated with a significant decrease in the NAFLD activity score at an early stage and in both inflammation and hepatocyte ballooning scores in late-stage NASH. Sirius red staining analyses revealed decreased collagen deposition in the pericentral region at both stages of NASH. Altogether, these findings showed the anti-inflammatory and anti-fibrotic features of HALPCs in an in vivo NASH model, which suggests their potential to reverse the progression of this chronic fibro-inflammatory disease.

Human Liver Stem Cell Transplantation Alleviates Liver Fibrosis in a Rat Model of CCl4-Induced Liver Fibrosis

Background and Objectives

Mesenchymal stem cells (MSCs) elicit therapeutic effects against liver fibrosis in animal models. Human liver stem cells (HLSCs) are cells isolated from human liver tissue that have mesenchymal morphology and express MSC markers. HLSCs also possess intrahepatic stem cell properties. We introduce a rat model of liver fibrosis and trans-portal transplantation of HLSC to demonstrate alleviation of liver fibrosis.

Methods and Results

Liver fibrosis was induced by intraperitoneal injection of Carbon tetrachloride (CCl₄). Sprague Dawley rats underwent simultaneous partial hepatectomy of the left hepatic lobe and HLSC transplantation via the portal vein. Gross appearance of the liver observed following CCl₄ injection showed cholestasis and surface nodularity. Sirius red staining revealed deposition of collagen fibers in the extracellular matrix (ECM). Following HLSC transplantation, human albumin secreting cells were detected by immunohistochemistry in liver specimens. Quantitative measurements of fibrosis area stained by Sirius red were compared between baseline and post-HLSC transplant (1×10⁷ cells) following 10 weeks of CCl₄ treatment liver specimens. Fibrosis area (p<0.05), serum markers of liver inflammation and fibrosis (AST, ALT levels and APRI, p<0.05) significantly decreased from baseline after HLSC transplantation. RNA expression in liver tissues revealed significant decrease in tissue inhibitor of matrix metalloproteinase 1 (TIMP1), TIMP2 expression and increase in hepatocyte growth factor expression following HLSC transplantation (p<0.05).

Conclusions

HLSC transplantation effectively reduced the area of liver fibrosis with increased expression of factors promoting ECM degradation. These findings suggest the potential therapeutic role of HLSCs in various liver diseases presenting with liver fibrosis.

Human Liver Stem Cells: A Liver-Derived Mesenchymal Stromal Cell-Like Population With Pro-regenerative Properties

Human liver stem cells (HLSCs) were described for the first time in 2006 as a new stem cell population derived from healthy human livers. Like mesenchymal stromal cells, HLSCs exhibit multipotent and immunomodulatory properties. HLSCs can differentiate into several lineages under defined in vitro conditions, such as mature hepatocytes, osteocytes, endothelial cells, and islet-like cell organoids. Over the years, HLSCs have been shown to contribute to tissue repair and regeneration in different in vivo models, leading to more than five granted patents and over 15 peer reviewed scientific articles elucidating their potential therapeutic role in various experimental pathologies. In addition, HLSCs have recently completed a Phase 1 study evaluating their safety post intrahepatic injection in infants with inherited neonatal onset hyperammonemia. Even though a lot of progress has been made in understanding HLSCs over the past years, some important questions regarding the mechanisms of action remain to be elucidated. Among the mechanisms of interaction of HLSCs with their environment, a paracrine interface has emerged involving extracellular vesicles (EVs) as vehicles for transferring active biological materials. In our group, the EVs derived from HLSCs have been studied in vitro as well as in vivo. Our attention has mainly been focused on understanding the in vivo ability of HLSC–derived EVs as modulators of tissue regeneration, inflammation, fibrosis, and tumor growth. This review article aims to discuss in detail the role of HLSCs and HLSC-EVs in these processes and their possible future therapeutic applications.

Inflammation Differentially Modulates the Biological Features of Adult Derived Human Liver Stem/Progenitor Cells

The progression of mesenchymal stem cell-based therapy from concept to cure closely depends on the optimization of conditions that allow a better survival and favor the cells to achieve efficient liver regeneration. We have previously demonstrated that adult-derived human liver stem/progenitor cells (ADHLSC) display significant features that support their clinical development. The current work aims at studying the impact of a sustained pro-inflammatory environment on the principal biological features of ADHLSC in vitro. METHODS: ADHLSC from passages 4–7 were exposed to a cocktail of inflammatory cytokines for 24 h and 9 days and subsequently analyzed for their viability, expression, and secretion profiles by using flow cytometry, RT-qPCR, and antibody array assay. The impact of inflammation on the hepatocytic differentiation potential of ADHLSC was also evaluated. RESULTS: ADHLSC treated with a pro-inflammatory cocktail displayed significant decrease of cell yield at both times of treatment while cell mortality was observed at 9 days post-priming. After 24 h, no significant changes in the immuno-phenotype of ADHLSC expression profile could be noticed while after 9 days, the expression profile of relevant markers has changed both in the basal conditions and after inflammation treatment. Inflammation cocktail enhanced the release of IL-6, IL-8, CCL5, monocyte-chemo-attractant protein-2 and 3, CXCL1/GRO, and CXCL5/ENA78. Furthermore, while IP-10 secretion was increased after 24 h priming, granulocyte macrophage colony-stimulating factor enhanced secretion was noticed after 9 days treatment. Finally, priming of ADHLSC did not affect their potential to differentiate into hepatocyte-like cells. CONCLUSION: These results indicate that ADHLSCs are highly sensitive to inflammation and respond to such signals by adjusting their gene and protein expression. Accordingly, monitoring the inflammatory status of patients at the time of cell transplantation, will certainly help in enhancing ADHLSC safety and efficiency.

Glucose and lipid metabolism screening models of hepatocyte spheroids after culture with injectable fiber fragments

With the rise of obesity, diabetes, and other metabolic diseases, in vitro hepatic cell and tissue models play an essential role in the identification of active pharmaceutical ingredients. Up to now, three-dimensional (3D) culture models have rarely focused on hepatic glucose and lipid metabolism. In addition, primary human liver cells suffer from limited availability and interdonor difference for establishing reproducible models. Thus, in the current study, the most available human liver cancer cell line (HepG2) and primary hepatocytes from rats (rPH) were proposed to construct 3D spheroids using injectable fiber fragments with galactose grafts (gSF) as the substrate. rPH and HepG2 spheroids show strong cell-cell and cell-fiber fragment interactions to promote the cell viability, albumin, and urea syntheses. Compared with HepG2 spheroids, rPH spheroids indicate stronger glucose metabolism abilities in terms of glucose consumption, intracellular glycogen content, gluconeogenesis rate, and sensitivity to glucose modulator hormones like insulin and glucagon. On the other hand, HepG2 spheroids display strong lipid metabolism abilities in producing significantly higher levels of total cholesterol and triglyceride. Compared with those without fiber fragments, the gSF-supported 3D culture establishes effective models for in vitro glucose (rPH spheroids) and lipid metabolisms (HepG2 spheroids). The screening models are confirmed from the respective enzyme activities and gene expressions and show significantly higher sensitivity and clinically related responses to hypoglycemic and lipid-lowering drugs. Thus, the culture configuration demonstrates a predictable in vitro platform for defining glucose and lipid metabolism profiles and screening therapeutic agents for metabolism disorders like diabetes and obesity.

A Hepatic Scaffold from Decellularized Liver Tissue: Food for Thought

Allogeneic liver transplantation is still deemed the gold standard solution for end-stage organ failure; however, donor organ shortages have led to extended waiting lists for organ transplants. In order to overcome the lack of donors, the development of new therapeutic options is mandatory. In the last several years, organ bioengineering has been extensively explored to provide transplantable tissues or whole organs with the final goal of creating a three-dimensional growth microenvironment mimicking the native structure. It has been frequently reported that an extracellular matrix-based scaffold offers a structural support and important biological molecules that could help cellular proliferation during the recellularization process. The aim of the present review is to underline the recent developments in cell-on-scaffold technology for liver bioengineering, taking into account: (1) biological and synthetic scaffolds; (2) animal and human tissue decellularization; (3) scaffold recellularization; (4) 3D bioprinting; and (5) organoid technology. Future possible clinical applications in regenerative medicine for liver tissue engineering and for drug testing were underlined and dissected.

Mesenchymal Stem Cells in the Adult Human Liver: Hype or Hope?

Chronic liver diseases constitute a significant economic, social, and biomedical burden. Among commonly adopted approaches, only organ transplantation can radically help patients with end-stage liver pathologies. Cell therapy with hepatocytes as a treatment for chronic liver disease has demonstrated promising results. However, quality human hepatocytes are in short supply. Stem/progenitor cells capable of differentiating into functionally active hepatocytes provide an attractive alternative approach to cell therapy for liver diseases, as well as to liver-tissue engineering, drug screening, and basic research. The application of methods generally used to isolate mesenchymal stem cells (MSCs) and maintain them in culture to human liver tissue provides cells, designated here as liver MSCs. They have much in common with MSCs from other tissues, but differ in two aspects-expression of a range of hepatocyte-specific genes and, possibly, inherent commitment to hepatogenic differentiation. The aim of this review is to analyze data regarding liver MSCs, probably another type of liver stem/progenitor cells different from hepatic stellate cells or so-called hepatic progenitor cells. The review presents an analysis of the phenotypic characteristics of liver MSCs, their differentiation and therapeutic potential, methods for isolating these cells from human liver, and discusses issues of their origin and heterogeneity. Human liver MSCs are a fascinating object of fundamental research with a potential for important practical applications.

Human Hepatocytes and Differentiated Adult-Derived Human Liver Stem/Progenitor Cells Display In Vitro Immunosuppressive Properties Mediated, at Least in Part, through the Nonclassical HLA Class I Molecule HLA-G

One of the main challenges in liver cell therapy (LCT) is the induction of a tolerogenic microenvironment to promote graft acceptance in the recipient. Little is known about the immunomodulatory potential of the hepatic cells used in liver cell therapy. In this work, we wanted to evaluate the immunosuppressive properties of human hepatocytes and adult-derived human liver stem/progenitor cells (ADHLSCs), as well as the potential involvement of the immunomodulatory molecule HLA-G. We demonstrated that both cell types were capable of inhibiting the proliferative response of PBMCs to an allogenic stimulus and that the immune inhibitory potential of ADHLSCs, although lower than that of hepatocytes, increased after hepatogenic differentiation. We demonstrated that liver cells express HLA-G and that the immune inhibition pattern was clearly associated to its expression. Interestingly, HLA-G expression increased after the third step of differentiation, wherein oncostatin M (OSM) was added. A 48 hr treatment with OSM was sufficient to induce HLA-G expression in ADHLSCs and result in immune inhibition. Surprisingly, blocking HLA-G partially reversed the immune inhibition mediated by hepatocytes and differentiated ADHLSCs, but not that of undifferentiated ADHLSCs, suggesting that additional immune inhibitory mechanisms may be used by these cells. In conclusion, we demonstrated that both hepatocytes and ADHLSCs present immunomodulatory properties mediated, at least in part, through HLA-G, which can be upregulated following hepatogenic differentiation or liver cell pretreatment with OSM. These observations open up new perspectives for the induction of tolerance following LCT and for potential therapeutic applications of these liver cells.

Hepatic progenitors of the fetal liver: Interactions with hematopoietic stem cells

The aim of this review is to summarize and give an overview on the findings of signaling between hepatic and hematopoietic progenitors of the liver. To date, there are not many findings published in the field, and the aim of this review is to cover all current publications in this area. The liver is the main site of hematopoiesis during fetal development. However, little is known about how hepatic and other non-hematopoietic progenitors potentially influence hematopoiesis and vice versa. The concurrent peaks of hepatic and hematopoietic progenitor proliferation during development indicate interactions that could possibly be mediated through cell-cell contact, extracellular matrices, cytokines and growth factors, or other signaling molecules. For example, hepatic progenitors, such as hepatic stem cells and hepatoblasts, possess characteristic surface markers that can be cleaved, giving rise to fragments of various lengths. A surface molecule of hepatoblasts has been demonstrated to play an essential role in hematopoiesis. Particularly, these effects on hematopoiesis were distinct, depending on whether it was membrane-bound or cleaved. In this review, the various hepatic and hematopoietic progenitor cell types are concisely described, and the current findings of their potential interactions are summarized.

Cytokinome of adult-derived human liver stem/progenitor cells: immunological and inflammatory features

Background

Being non-immunogenic and capable of achieving major metabolic liver functions, adult-derived human liver stem/progenitor cells (ADHLSCs) are of special interest in the field of liver cell therapy. The cytokine repertoire of engrafted cells may have critical impacts on the immune response balance, particularly during cell transplantation.

Methods

In this work, we analyzed the cytokinome of ADHLSCs during hepatogenic differentiation (HD) following stimulation with a mixture of inflammatory cytokines (I) in vitro and compared it to that of mature hepatocytes.

Results

Independent of their hepatic state, ADHLSCs showed no constitutive expression of pro-inflammatory cytokines, which were significantly induced by inflammation (IL-1β, IL-6, IL-8, TNFα, CCL5, IL-12a, IL-12b, IL-23p19, IL-27p28 and EBI-3). IL1-RA and IDO-1, as immunoregulatory cytokines, were highly induced in undifferentiated ADHLSCs, whereas TGF-β was downregulated by both hepatic and inflammatory events. Interestingly, TDO-1 was exclusively expressed in ADHLSCs after hepatic differentiation and enhanced by inflammatory cytokines. Compared to mature hepatocytes, hepatic-differentiated ADHLSCs showed significantly different cytokine expression patterns.

Conclusions

By establishing the cytokinome of ADHLSCs and highlighting their immunological and inflammatory features, we can enhance our knowledge about the safety and efficiency of the transplantation strategy.

Hepatocyte transplantation and advancements in alternative cell sources for liver-based regenerative medicine

Human hepatocyte transplantation has been actively perused as an alternative to liver replacement for acute liver failure and liver-based metabolic defects. Current challenges in this field include a limited cell source, reduced cell viability following cryopreservation and poor engraftment of cells into the recipient liver with consequent limited life span. As a result, alternative stem cell sources such as pluripotent stem cells, fibroblasts, hepatic progenitor cells, amniotic epithelial cells and mesenchymal stem/stromal cells (MSCs) can be used to generate induced hepatocyte like cells (HLC) with each technique exhibiting advantages and disadvantages. HLCs may have comparable function to primary human hepatocytes and could offer patient-specific treatment. However, long-term functionality of transplanted HLCs and the potential oncogenic risks of using stem cells have yet to be established. The immunomodulatory effects of MSCs are promising, and multiple clinical trials are investigating their effect in cirrhosis and acute liver failure. Here, we review the current status of hepatocyte transplantation, alternative cell sources to primary human hepatocytes and their potential in liver regeneration. We also describe recent clinical trials using hepatocytes derived from stem cells and their role in improving the phenotype of several liver diseases.

Biodistribution of Liver-Derived Mesenchymal Stem Cells After Peripheral Injection in a Hemophilia A Patient

BACKGROUND

With the exception of liver transplantation, there is no cure for hemophilia, which is currently managed by preemptive replacement therapy. Liver-derived stem cells are in clinical development for inborn and acquired liver diseases and could represent a curative treatment for hemophilia A. The liver is a major factor VIII (FVIII) synthesis site, and mesenchymal stem cells have been shown to control joint bleeding in animal models of hemophilia. Adult-derived human liver stem cells (ADHLSCs) have mesenchymal characteristics and have been shown able to engraft in and repopulate both animal and human livers. Thus, the objectives were to evaluate the potency of ADHLSCs to control bleeding in a hemophilia A patient and assess the biodistribution of the cells after intravenous injection.

METHODS

A patient suffering from hemophilia A was injected with repeated doses of ADHLSCs via a peripheral vein (35 million In-oxine-labeled cells, followed by 125 million cells the next day, and 3 infusions of 250 million cells every 2 weeks thereafter; total infusion period, 50 days).

RESULTS

After cell therapy, we found a temporary (15 weeks) decrease in the patient's FVIII requirements and severe bleeding complications, despite a lack of increase in circulating FVIII. The cells were safely administered to the patient via a peripheral vein. Biodistribution analysis revealed an initial temporary entrapment of the cells in the lungs, followed by homing to the liver and to a joint afflicted with hemarthrosis.

CONCLUSION

These results suggest the potential use of ADHLSCs in the treatment of hemophilia A.

Human liver mesenchymal stem/progenitor cells inhibit hepatic stellate cell activation: in vitro and in vivo evaluation

Background

Progressive liver fibrosis leads to cirrhosis and end-stage liver disease. This disease is a consequence of strong interactions between matrix-producing hepatic stellate cells (HSCs) and resident and infiltrating immune cell populations. Accumulated experimental evidence supports the involvement of adult-derived human liver mesenchymal stem/progenitor cells (ADHLSCs) in liver regeneration. The aim of the present study was to evaluate the influence of ADHLSCs on HSCs, both in vitro and in vivo.

Methods

Activated human HSCs were co-cultured with ADHLSCs or ADHLSC-conditioned culture medium. The characteristics of the activated human HSCs were assessed by microscopy and biochemical assays, whereas proliferation was analyzed using flow cytometry and immunocytochemistry. The secretion profile of activated HSCs was evaluated by ELISA and Luminex. ADHLSCs were transplanted into a juvenile rat model of fibrosis established after co-administration of phenobarbital and CCl₄.

Results

When co-cultured with ADHLSCs or conditioned medium, the proliferation of HSCs was inhibited, beginning at 24 h and for up to 7 days. The HSCs were blocked in G0/G1 phase, and showed decreased Ki-67 positivity. Pro-collagen I production was reduced, while secretion of HGF, IL-6, MMP1, and MMP2 was enhanced. Neutralization of HGF partially blocked the inhibitory effect of ADHLSCs on the proliferation and secretion profile of HSCs. Repeated intrahepatic transplantation of cryopreserved/thawed ADHLSCs without immunosuppression inhibited the expression of markers of liver fibrosis in 6 out of 11 rats, as compared to their expression in the vehicle-transplanted group.

Conclusions

These data provide evidence for a direct inhibitory effect of ADHLSCs on activated HSCs, which supports their development for the treatment of liver fibrosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0575-5) contains supplementary material, which is available to authorized users.

Immunoprofiling of Adult-Derived Human Liver Stem/Progenitor Cells: Impact of Hepatogenic Differentiation and Inflammation

Adult-derived human liver stem/progenitor cells (ADHLSCs) are, nowadays, developed as therapeutic medicinal product for the treatment of liver defects. In this study, the impact of hepatogenic differentiation and inflammation priming on the ADHLSCs' immune profile was assessed in vitro and compared to that of mature hepatocytes. The constitutive immunological profile of ADHLSCs was greatly different from that of hepatocytes. Differences in the expression of the stromal markers CD90 and CD105, adhesion molecules CD44 and CD49e, immunoregulatory molecules CD73 and HO-1, and NK ligands CD112 and CD155 were noted. While they globally preserved their immunological profile in comparison to undifferentiated counterparts, differentiated ADHLSCs showed a significant downregulation of CD200 expression as in hepatocytes. This was mainly induced by signals issued from EGF and OSM. On the other hand, the impact of inflammation was quite similar for all studied cell populations with an increased expression level of CD54 and CD106 and induction of that of CD40 and CD274. In conclusion, our immune profiling study suggests CD200 as a key factor in regulating the immunobiology of differentiated ADHLSCs. A better understanding of the molecular and physiological events related to such marker could help in designing the optimal conditions for an efficient therapeutic use of ADHLSCs.

Comprehensive Screening of Cell Surface Markers Expressed by Adult-Derived Human Liver Stem/Progenitor Cells Harvested at Passage 5: Potential Implications for Engraftment

Mesenchymal stromal cells (MSCs) are known to have potential therapeutic benefits for a number of diseases. However, many studies report low engraftment levels, regardless of the target organ. One possible explanation could be that MSCs do not express the necessary receptors for engraftment. Indeed, MSCs appear to use a similar mechanism to leukocytes to engraft into injured organs, relying on various receptors for rolling, firm adhesion, and transmigration. In this study, we conducted an extensive surface molecule screening of adult-derived human liver stem/progenitor cells (ADHLSC) in an attempt to shed some light on this subject. We observed that ADHLSCs lack expression of most of the costimulatory molecules tested. Furthermore, study of the adhesion molecule profile of ADHLSCs revealed that they do not express selectin ligands or LFA-1 which are, respectively, involved in the rolling process and the firm adhesion. In addition, ADHLSCs slightly express VLA-4 and lose expression of CXCR4 altogether on their surface during culture expansion. However, ADHLSCs express all the integrin couples and matrix metalloproteinases needed to bind and integrate the extracellular matrix once the endothelial barrier is crossed. Collectively, these results suggest that binding to the endothelium may be the critical weak point in the engraftment process.

β-cell replacement sources for type 1 diabetes: a focus on pancreatic ductal cells

Thorough research on the capacity of human islet transplantation to cure type 1 diabetes led to the achievement of 3- to 5-year-long insulin independence in nearly half of transplanted patients. Yet, translation of this technique to clinical routine is limited by organ shortage and the need for long-term immunosuppression, restricting its use to adults with unstable disease. The production of new bona fide β cells in vitro was thus investigated and finally achieved with human pluripotent stem cells (PSCs). Besides ethical concerns about the use of human embryos, studies are now evaluating the possibility of circumventing the spontaneous tumor formation associated with transplantation of PSCs. These issues fueled the search for cell candidates for β-cell engineering with safe profiles for clinical translation. In vivo studies revealed the regeneration capacity of the exocrine pancreas after injury that depends at least partially on facultative progenitors in the ductal compartment. These stimulated subpopulations of pancreatic ductal cells (PDCs) underwent β-cell transdifferentiation through reactivation of embryonic signaling pathways. In vitro models for expansion and differentiation of purified PDCs toward insulin-producing cells were described using cocktails of growth factors, extracellular-matrix proteins and transcription factor overexpression. In this review, we will describe the latest findings in pancreatic β-cell mass regeneration due to adult ductal progenitor cells. We will further describe recent advances in human PDC transdifferentiation to insulin-producing cells with potential for clinical translational studies.

Liver-derived human mesenchymal stem cells: a novel therapeutic source for liver diseases

Mesenchymal stem cells (MSCs) represent an attractive cell type for research and therapy due to their ability to proliferate, differentiate, modulate immune reactions, and secrete trophic factors. MSCs exist in a multitude of tissues, including bone marrow, umbilical cord, and adipose tissues. Moreover, MSCs have recently been isolated from the liver. Compared with other MSC types, liver-derived human MSCs (LHMSCs) possess general morphologies, immune functions, and differentiation capacities. Interestingly, LHMCSs produce higher levels of pro-angiogenic, anti-inflammatory, and anti-apoptotic cytokines than those of bone marrow-derived MSCs. Thus, these cells may be a promising therapeutic source for liver diseases. This paper summarizes the biological characteristics of LHMSCs and their potential benefits and risks for the treatment of liver diseases.

Hepatocytic Differentiation Potential of Human Fetal Liver Mesenchymal Stem Cells: In Vitro and In Vivo Evaluation

In line with the search of effective stem cell population that would progress liver cell therapy and because the rate and differentiation potential of mesenchymal stem cells (MSC) decreases with age, the current study investigates the hepatogenic differentiation potential of human fetal liver MSCs (FL-MSCs). After isolation from 11-12 gestational weeks' human fetal livers, FL-MSCs were shown to express characteristic markers such as CD73, CD90, and CD146 and to display adipocytic and osteoblastic differentiation potential. Thereafter, we explored their hepatocytic differentiation potential using the hepatogenic protocol applied for adult human liver mesenchymal cells. FL-MSCs differentiated in this way displayed significant features of hepatocyte-like cells as demonstrated in vitro by the upregulated expression of specific hepatocytic markers and the induction of metabolic functions including CYP3A4 activity, indocyanine green uptake/release, and glucose 6-phosphatase activity. Following transplantation, naive and differentiated FL-MSC were engrafted into the hepatic parenchyma of newborn immunodeficient mice and differentiated in situ. Hence, FL-MSCs appeared to be interesting candidates to investigate the liver development at the mesenchymal compartment level. Standardization of their isolation, expansion, and differentiation may also support their use for liver cell-based therapy development.

Role of Stem Cells Transplantation in Tissue Regeneration After Acute or Chronic Acetaminophen Induced Liver Injury

PURPOSE

Acetaminophen-induced liver injury (APAP) is recognized as a frequent etiologic factor responsible for hepatic damage in the developed world. Management remains still elusive as treatment options are limited and their results are inconclusive. Consequently new strategies are explored at the experimental level. Mesenchymal stem cells (MSCs) present a promising modality as they can promote liver regeneration (LG) and compensate acute liver injury (ALI).

MATERIALS AND METHODS

Our research was focused on articles related to drug-induced liver injury, mechanisms of liver regeneration (LG) after Acute Liver Injury (ALI) and recent experimental protocols of Mesenchymal Stem Cells (MSCs) transplantation after chemical insult. All these studies are cited on Pubmed and MedLine.

RESULTS

This review has three distinct sections. First recent developments in ALI pathogenesis are presented. The second section covers cellular pathways and histological findings relevant to liver regeneration. The final chapter analyzes MSCs transplantation protocols after ALI and interrelation between liver regeneration and hepatic differentiation of MSCs.

CONCLUSION

Adipose tissue stem cells (ADSCs) and (MSCs) transplantation represents a promising modality in severe ALI management although many aspects remain to be clarified.

Turning Regenerative Medicine Breakthrough Ideas and Innovations into Commercial Products

The TERMIS-Europe (EU) Industry committee intended to address the two main critical issues in the clinical/commercial translation of Advanced Therapeutic Medicine Products (ATMP): (1) entrepreneurial exploitation of breakthrough ideas and innovations, and (2) regulatory market approval. Since January 2012, more than 12,000 publications related to regenerative medicine and tissue engineering have been accepted for publications, reflecting the intense academic research activity in this field. The TERMIS-EU 2014 Industry Symposium provided a reflection on the management of innovation and technological breakthroughs in biotechnology first proposed to contextualize the key development milestones and constraints of allocation of financial resources, in the development life-cycle of radical innovation projects. This was illustrated with the biofuels story, sharing similarities with regenerative medicine. The transition was then ensured by an overview of the key identified challenges facing the commercialization of cell therapy products as ATMP examples. Real cases and testimonies were then provided by a palette of medical technologies and regenerative medicine companies from their commercial development of cell and gene therapy products. Although the commercial development of ATMP is still at the proof-of-concept stage due to technology risks, changing policies, changing markets, and management changes, the sector is highly dynamic with a number of explored therapeutic approaches, developed by using a large diversity of business models, both proposed by the experience, pitfalls, and successes of regenerative medicine pioneers, and adapted to the constraint resource allocation and environment in radical innovation projects.

Adult human hepatocytes promote CD4(+) T-cell hyporesponsiveness via interleukin-10-producing allogeneic dendritic cells

The success of liver cell therapy remains closely dependent on how well the infused cells can be accepted after transplantation and is directly related to their degree of immunogenicity. In this study, we investigated the in vitro immunogenic properties of isolated human hepatocytes (hHeps) and adult-derived human liver progenitor cells (ADHLPCs), an alternative cell candidate for liver cell transplantation (LCT). The constitutive expression of immune markers was first analyzed on these liver-derived cells by flow cytometry. Human liver-derived cells were then cocultured with allogeneic human adult peripheral blood mononuclear cells (PBMCs), and the resulting activation and proliferation of PBMCs was evaluated, as well as the cytokine levels in the coculture supernatant. The effect of liver-derived cells on monocyte-derived dendritic cell (MoDC) properties was further analyzed in a secondary coculture with naive CD4(+) T-cells. We report that hHeps and ADHLPCs expressed human leukocyte antigen (HLA) class I and Fas but did not express HLA-DR, Fas ligand, and costimulatory molecules. hHeps and ADHLPCs did not induce T-cell activation or proliferation. Moreover, hHeps induced a cell contact-dependent production of interleukin (IL)-10 that was not observed with ADHLPCs. The IL-10 was produced by a myeloid DC subset characterized by an incomplete mature state. Furthermore, hHep-primed MoDCs induced an antigen-independent hyporesponsiveness of naive CD4(+) T lymphocytes that was partially reversed by blocking IL-10, whereas nonprimed MoDCs (i.e., those cultured alone) did not. hHeps and ADHLPCs present a low immunogenic phenotype in vitro. Allogeneic hHeps, but not ADHLPCs, promote a cell contact-dependent production of IL-10 by myeloid DCs, which induces naive CD4(+) T-cells antigen-independent hyporesponsiveness.

Use of mesenchymal stem cells to treat liver fibrosis: Current situation and future prospects

Progressive liver fibrosis is a major health issue for which no effective treatment is available, leading to cirrhosis and orthotopic liver transplantation. However, organ shortage is a reality. Hence, there is an urgent need to find alternative therapeutic strategies. Cell-based therapy using mesenchymal stem cells (MSCs) may represent an attractive therapeutic option, based on their immunomodulatory properties, their potential to differentiate into hepatocytes, allowing the replacement of damaged hepatocytes, their potential to promote residual hepatocytes regeneration and their capacity to inhibit hepatic stellate cell activation or induce their apoptosis, particularly via paracrine mechanisms. The current review will highlight recent findings regarding the input of MSC-based therapy for the treatment of liver fibrosis, from in vitro studies to pre-clinical and clinical trials. Several studies have shown the ability of MSCs to reduce liver fibrosis and improve liver function. However, despite these promising results, some limitations need to be considered. Future prospects will also be discussed in this review.

Adult human liver mesenchymal progenitor cells express phenylalanine hydroxylase

Phenylketonuria (PKU) is one of the most prevalent inherited metabolic diseases and is accountable for a severe encephalopathy by progressive intoxication of the brain by phenylalanine. This results from an ineffective L-phenylalanine hydroxylase enzyme (PAH) due to a mutated phenylalanine hydroxylase (PAH) gene. Neonatal screening programs allow an early dietetic treatment with restrictive phenylalanine intake. This diet prevents most of the neuropsychological disabilities but remains challenging for lifelong compliance. Adult-derived human liver progenitor cells (ADHLPC) are a pool of precursors that can differentiate into hepatocytes. We aim to study PAH expression and PAH activity in a differenciated ADHLPC. ADHLPC were isolated from human hepatocyte primary culture of two different donors and differenciated under specific culture conditions. We demonstrated the high expression of PAH and a large increase of PAH activity in differenciated LPC. The age of the donor, the cellular viability after liver digestion and cryopreservation affects PAH activity. ADHLPC might therefore be considered as a suitable source for cell therapy in PKU.

Human liver stem/progenitor cells decrease serum bilirubin in hyperbilirubinemic Gunn rat

AIM: To test the ability of adult-derived human liver stem/progenitor cells (ADHLSC) from large scale cultures to conjugate bilirubin in vitro and in bilirubin conjugation deficient rat.

METHODS: ADHLSC from large scale cultures were tested for their phenotype and for their capacity to conjugate bilirubin in vitro after hepatogenic differentiation. In vivo, Gunn rats [uridine diphosphate-glucuronosyltransferase 1A1 (UGT1A1) deficient animal] were injected with ADHLSC and cryopreserved hepatocytes (positive control). Two, 4, 13 and 27 wk post-transplantation, transplanted Gunn rat bilirubin serum levels were determined by high performance liquid chromatography. Human transplanted cell engraftment was assessed 27 wk post-transplantation using immunohistochemistry and RTqPCR.

RESULTS: Large scale culture conditions do not modify ADHLSC phenotype, ADHLSC were able to specifically conjugate bilirubin. ADHLSC were intraportally injected into Gunn rats and blood UCB was measured at different times post-transplantation, infused-Gunn rats exhibited a metabolic effect 3 mo post-transplantation and maintained over a 6 mo period. ADHLSC engraftment into Gunn rat’s liver was demonstrated by RTqPCR and immunohistochemistry against albumin and UGT1A1.

CONCLUSION: ADHLSC from large scale cultures are efficient in conjugating bilirubin in vitro and in restoring a deficient metabolic function (reducing bilirubin level) in hyperbilirubinemic rats.

Treating inborn errors of liver metabolism with stem cells: current clinical development

Advanced therapies including stem cells are currently a major biotechnological development. Adult liver stem cells can differentiate into hepatocyte like cells and be infused in the recipient's liver to bring a missing metabolic function. These cells can be produced in large quantities in vitro. Allogeneic stem cells are required to treat genetic diseases, and this approach allows to use one single source of tissue to treat different diseases and many recipients. Mesenchymal stem cells can in addition play an immunomodulatory and anti-inflammatory role and possibly prevent the accumulation of fibrous tissue in the liver. From a regulatory point of view, stem cells are considered as medicinal products, and must undergo a pharmaceutical development that goes beyond the research and proof-of-concept phases. Here, we review the track followed from the first hepatocyte transplantation in 2000 to the next generation product issued from stem cell technology, and the start of EMA approved clinical trials to evaluate the safety and potency of liver stem cells for the treatment of inborn errors of the liver metabolism.

Gene expression profiling and secretome analysis differentiate adult-derived human liver stem/progenitor cells and human hepatic stellate cells

Adult-derived human liver stem/progenitor cells (ADHLSC) are obtained after primary culture of the liver parenchymal fraction. The cells are of fibroblastic morphology and exhibit a hepato-mesenchymal phenotype. Hepatic stellate cells (HSC) derived from the liver non-parenchymal fraction, present a comparable morphology as ADHLSC. Because both ADHLSC and HSC are described as liver stem/progenitor cells, we strived to extensively compare both cell populations at different levels and to propose tools demonstrating their singularity.

ADHLSC and HSC were isolated from the liver of four different donors, expanded in vitro and followed from passage 5 until passage 11. Cell characterization was performed using immunocytochemistry, western blotting, flow cytometry, and gene microarray analyses. The secretion profile of the cells was evaluated using Elisa and multiplex Luminex assays.

Both cell types expressed α-smooth muscle actin, vimentin, fibronectin, CD73 and CD90 in accordance with their mesenchymal origin. Microarray analysis revealed significant differences in gene expression profiles. HSC present high expression levels of neuronal markers as well as cytokeratins. Such differences were confirmed using immunocytochemistry and western blotting assays. Furthermore, both cell types displayed distinct secretion profiles as ADHLSC highly secreted cytokines of therapeutic and immuno-modulatory importance, like HGF, interferon-γ and IL-10.

Our study demonstrates that ADHLSC and HSC are distinct liver fibroblastic cell populations exhibiting significant different expression and secretion profiles.

Biodistribution of adult derived human liver stem cells following intraportal infusion in a 17-year-old patient with glycogenosis type 1A

INTRODUCTION

Current treatment of inherited liver inborn errors of metabolism in children consists in appropriate diet and drugs and, for unstable patients, final orthotopic liver transplantation. Unfortunately, liver transplantation remains not easily available because of organ shortage and imposes inherent risks and lifelong immunosuppressive therapy. Therefore alternative treatments are required. Hepatocytes transplantation and its limitations led to consider innovative alternative such as transplantation of adult derived human liver stem cells (ADLHSC). These cells present high proliferative capacity, good resistance to cryopreservation and ability to differentiate into hepatocyte-like cells displaying mature hepatocyte functions.

AIM

Biodistribution of ADHLSC had never been assessed after infusion through the portal vein in patients. This information is required to determine the safety of the method.

METHODS

ADHLSC were efficiently labelled with 111-Indium DTPA radiotracer and SPECT imaging was used for the acquisition of whole body imaging to document short term biodistribution of ADHLSC.

RESULTS

Following infusion through the portal vein, ADHLSC diffused homogenously throughout the liver and remained strictly within the targeted organ. Images were acquired until 5 days after infusion. At that time, no signal was observed in any other organs except the liver. Urinary excretion of 111-Indium DTPA was also monitored.

CONCLUSION

For the first time, we documented the short term biodistribution of ADHLSC within the liver after infusion through the portal vein.

Pluripotent stem cell-derived hepatocyte-like cells

Liver disease is an important clinical problem, impacting over 30 million Americans and over 600 million people worldwide. It is the 12th leading cause of death in the United States and the 16th worldwide. Due to a paucity of donor organs, several thousand Americans die yearly while waiting for liver transplantation. Unfortunately, alternative tissue sources such as fetal hepatocytes and hepatic cell lines are unreliable, difficult to reproduce, and do not fully recapitulate hepatocyte phenotype and functions. As a consequence, alternative cell sources that do not have these limitations have been sought. Human embryonic stem (hES) cell- and induced pluripotent stem (iPS) cell-derived hepatocyte-like cells may enable cell based therapeutics, the study of the mechanisms of human disease and human development, and provide a platform for screening the efficacy and toxicity of pharmaceuticals. iPS cells can be differentiated in a step-wise fashion with high efficiency and reproducibility into hepatocyte-like cells that exhibit morphologic and phenotypic characteristics of hepatocytes. In addition, iPS-derived hepatocyte-like cells (iHLCs) possess some functional hepatic activity as they secrete urea, alpha-1-antitrypsin, and albumin. However, the combined phenotypic and functional traits exhibited by iHLCs resemble a relatively immature hepatic phenotype that more closely resembles that of fetal hepatocytes rather than adult hepatocytes. Specifically, iHLCs express fetal markers such as alpha-fetoprotein and lack key mature hepatocyte functions, as reflected by drastically reduced activity (~0.1%) of important detoxification enzymes (i.e. CYP2A6, CYP3A4). These key differences between iHLCs and primary adult human hepatocytes have limited the use of stem cells as a renewable source of functional adult hepatocytes for in vitro and in vivo applications. Unfortunately, the developmental pathways that control hepatocyte maturation from a fetal into an adult hepatocyte are poorly understood, which has hampered the field in its efforts to induce further maturation of iPS-derived hepatic lineage cells. This review analyzes recent developments in the derivation of hepatocyte-like cells, and proposes important points to consider and assays to perform during their characterization. In the future, we envision that iHLCs will be used as in vitro models of human disease, and in the longer term, provide an alternative cell source for drug testing and clinical therapy.

Liver engraftment and repopulation by in vitro expanded adult derived human liver stem cells in a child with ornithine carbamoyltransferase deficiency

A 3-year-old girl suffering from ornithine carbamoyltransferase (OTC) deficiency was poorly equilibrated under conventional diet and scavenger treatment. Following unsuccessful cryopreserved hepatocyte transplantation, she received two infusions of Adult Derived Human Liver Stem/Progenitor Cells (ADHLSCs) expanded in vitro under GMP settings, the quantity being equivalent to 0.75% of her calculated liver mass. Using FISH immunostaining for the Y chromosome, the initial biopsy did not detect any male nuclei in the recipient liver. Two liver biopsies taken 100 days after ADHLSC transplantation showed 3% and 5% of male donor cells in the recipient liver, thus suggesting repopulation by donor cells. Although limited follow-up did not allow us to draw conclusions on long-term improvement, these results provide a promising proof of concept that this therapy is feasible in an OTC patient.

Human Liver Progenitor Cells for Liver Repair

Because of their high proliferative capacity, resistance to cryopreservation, and ability to differentiate into hepatocyte-like cells, stem and progenitor cells have recently emerged as attractive cell sources for liver cell therapy, a technique used as an alternative to orthotopic liver transplantation in the treatment of various hepatic ailments ranging from metabolic disorders to end-stage liver disease. Although stem and progenitor cells have been isolated from various tissues, obtaining them from the liver could be an advantage for the treatment of hepatic disorders. However, the techniques available to isolate these stem/progenitor cells are numerous and give rise to cell populations with different morphological and functional characteristics. In addition, there is currently no established consensus on the tests that need to be performed to ensure the quality and safety of these cells when used clinically. The purpose of this review is to describe the different types of liver stem/progenitor cells currently reported in the literature, discuss their suitability and limitations in terms of clinical applications, and examine how the culture and transplantation techniques can potentially be improved to achieve a better clinical outcome.

Adult human liver mesenchymal stem/progenitor cells participate in mouse liver regeneration after hepatectomy

The advances in stem cell science have promoted research on their use in liver regenerative medicine. Beyond the demonstration of their ability to display metabolic functions in vitro, candidate cells should demonstrate achievable in situ differentiation and ability to participate to liver repopulation. In this work, we studied the in vivo behavior of adult liver mesenchymal stem/progenitor cells (ADHLSCs) after transplantation into immunodeficient mice. The kinetics of engraftment and in situ hepatogenic differentiation were analyzed. Response of transplanted ADHLSCs to regenerative stimulus was also evaluated. Nondifferentiated ADHLSCs were intrasplenically transplanted into SCID mice. Efficiency of transplantation was evaluated at the level of engraftment and in situ differentiation using immunohistochemistry, in situ hybridization, and RT-PCR. After bromodeoxyuridine (BrdU) implantation, proliferation of transplanted ADHLSCs in response to 20% hepatectomy was assessed using immunohistochemistry. We demonstrated that ADHLSC engraftment in the SCID mouse liver was low but remained stable up to 60 days posttransplantation, when albumin (ALB) immunopositive ADHLSCs were still detected and organized as clusters. Coexpression of ornithine transcarbamylase (OTC) demonstrated ADHLSC in situ differentiation mostly near the hepatic portal vein. After 20% hepatectomy on 1 month transplanted mice, the percentage of BrdU and human ALB immunopositive ADHLSCs increased from 3 to 28 days post-BrdU implantation to reach 31.3 ± 5.4% of the total analyzed human cells. In the current study, we demonstrate that transplanted ADHLSCs are able to differentiate in the non preconditioned SCID mouse liver mainly in the periportal area. In response to partial hepatectomy, integrated ADHLSCs proliferate and participate to recipient mouse liver regeneration.

Hepatocyte Transplantation Using the Domino Concept in a Child with Tetrabiopterin Nonresponsive Phenylketonuria

Phenylketonuria is a metabolic disease caused by phenylalanine hydroxylase deficiency. Treatment is based on a strict natural protein-restricted diet that is associated with the risk of malnutrition and severe psychosocial burden. Oral administration of tetrahydrobiopterin can increase residual enzyme activity, but most patients with severe clinical phenotypes are nonresponders. We performed liver cell transplantation in a 6-year-old boy with severe tetrahydrobiopterin nonresponsive phenylketonuria who failed to comply with diet prescriptions. The transplanted hepatocytes were obtained in part from an explanted glycogen storage type 1b liver. Following two infusions, blood phenylalanine levels returned within the therapeutic target while the phenylalanine half-life assessed by loading tests decreased from 43 to 19 h. However, 3 months later, blood phenylalanine concentrations increased and the phenylalanine intake had to be reduced. Cell-based therapy is a promising therapeutic option in phenylketonuria, and the domino concept may solve the issue of cell sources for hepatocyte transplantation.

"Drugs on oxygen": an update and perspective on the role of cytochrome P450 testing in pharmacology

Low hit rates for lead compounds and high attrition remain a major problem for drug development. The reasons for compound failure range from poor pharmacokinetics to toxic metabolites and adverse drug interactions; all of which are frequently mediated by cytochrome P450-dependent monooxygenases (CYPs). However, despite some 30 years of assay development and refinement, CYP metabolism remains a critical issue during drug development. While current testing strategies succeed in characterizing single substance toxicity, they are challenged by practical issues such as assay standardization or complex scenarios such as multidrug usage. This editorial summarizes where we stand and highlights the major challenges we face with CYPs in drug development today. The article also tries to spell out the future direction of CYP testing. The latter will depend on the extended inclusion of polypharmacy into testing strategies, as well as on our capability to make use of upcoming complex in vitro test systems and their inclusion into tiered testing strategies.

Bivalirudin in combination with heparin to control mesenchymal cell procoagulant activity

Islet and hepatocyte transplantation are associated with tissue factor-dependent activation of coagulation which elicits instant blood mediated inflammatory reaction, thereby contributing to a low rate of engraftment. The aim of this study was i) to evaluate the procoagulant activity of human adult liver-derived mesenchymal progenitor cells (hALPCs), ii) to compare it to other mesenchymal cells of extra-hepatic (bone marrow mesenchymal stem cells and skin fibroblasts) or liver origin (liver myofibroblasts), and iii) to determine the ways this activity could be modulated. Using a whole blood coagulation test (thromboelastometry), we demonstrated that all analyzed cell types exhibit procoagulant activity. The hALPCs pronounced procoagulant activity was associated with an increased tissue factor and a decreased tissue factor pathway inhibitor expression as compared with hepatocytes. At therapeutic doses, the procoagulant effect of hALPCs was inhibited by neither antithrombin activators nor direct factor Xa inhibitor or direct thrombin inhibitors individually. However, concomitant administration of an antithrombin activator or direct factor Xa inhibitor and direct thrombin inhibitor proved to be a particularly effective combination for controlling the procoagulant effects of hALPCs both in vitro and in vivo. The results suggest that this dual antithrombotic therapy should also improve the efficacy of cell transplantation in humans.

Hepato-biliary profile of potential candidate liver progenitor cells from healthy rat liver

AIM: To evaluate the presence of progenitor cells in healthy adult rat liver displaying the equivalent advanced hepatogenic profile as that obtained in human.

METHODS: Rat fibroblastic-like liver derived cells (rFLDC) were obtained from collagenase-isolated liver cell suspensions and characterized and their phenotype profile determined using flow cytometry, immunocytochemistry, reverse transcription polymerase chain reaction and functional assays.

RESULTS: rFLDC exhibit fibroblastoid morphology, express mesenchymal (CD73, CD90, vimentin, α-smooth muscle actin), hepatocyte (UGT1A1, CK8) and biliary (CK19) markers. Moreover, these cells are able to store glycogen, and have glucose 6 phosphatase activity, but not UGT1A1 activity. Under the hepatogenic differentiation protocol, rFLDC display an up-regulation of hepatocyte markers expression (albumin, tryptophan 2,3-dioxygenase, G6Pase) correlated to a down-regulation of the expression of the biliary marker CK19.

CONCLUSION: Advanced hepatic features observed in human liver progenitor cells could not be demonstrated in rFLDC. However, we demonstrated the presence of an original rodent hepato-biliary cell type.

Adult-derived human liver progenitor cells in long-term culture maintain appropriate gatekeeper mechanisms against transformation

The use of human liver progenitor cells in the development of clinical cell therapy depends on their constant availability and unaltered properties during culture. The present study investigates the effects of long-term in vitro culture on the specific characteristics of these cells and on their genetic stability. Adult-derived human liver progenitor cells (ADHLPCs) were isolated from 12 donors and cultured until senescence and cell death. Cells were analyzed at different time points for their phenotype stability and differentiation potential. In addition, growth characteristics, chromosomal karyotype, telomere maintenance mechanisms, and activity of cell cycle-related genes were studied. Finally, their in vivo tumorigenicity was investigated in a xenograft assay. The long-term culture of ADHLPCs revealed a variable proliferation capacity. Cells maintained their original phenotype and acquired hepatocyte-like metabolic functions after differentiation. Eight of the 12 cell populations grew fast (doubling time of 6.3 days) during a limited time period (mean, 116.2 days), and mainly presented normal cytogenetic features. The four other cell cultures presented an early decline in growth potential (doubling time of 28.6 days) and premature senescence. Chromosomal alterations were detected in three of four cultures at passage 6. Cytogenetic anomalies were not correlated with tumorigenic potential in vitro or in vivo, and expression of cell cycle-related genes was appropriately upregulated, inducing senescence. Although chromosomal anomalies may occur in long-term cell cultures, neither transformation nor alteration of their characteristics was noted during in vitro expansion. All ADHLPCs reached senescence and growth arrest. Presenescent ADHLPCs might therefore be considered as a suitable source for liver-based cell therapy.

Decrease of global methylation improves significantly hepatic differentiation of Ad-MSCs: possible future application for urea detoxification

Hepatocyte transplantation is considered to be an alternative to orthotopic liver transplantation. Cells can be used to bridge patients waiting for a donor organ, decrease mortality in acute liver failure, and support metabolic liver diseases. The limited availability of primary human hepatocytes for such applications has led to the generation of alternative hepatocyte-like cells from various adult stem or precursor cells. The aim of this study was to generate hepatocyte-like cells from adipose-derived mesenchymal stem cells (Ad-MSCs) for clinical applications, which are available "off the shelf." Epigenetic changes in hepatocyte-like cells were induced by 5-azacytidine, which, in combination with other supplements, leads to significantly improved metabolic and enzymatic activities compared to nontreated cells. Cells with sufficient hepatic features were generated with a four-step protocol: 5-azacytidine (step 1); epidermal growth factor (step 2); fibroblast growth factor-4, dexamethasone, insulin-transferrin-sodium-selenite, and nicotinamide (step 3); and hepatocyte growth factor, dexamethasone, insulin-transferrin-sodium-selenite, and nicotinamide (step 4). Generated differentiated cells had higher phase I (CYP1A1/2, CYP2E1, CYP2B6, CYP3A4) and phase II activities compared to the undifferentiated cells. A strong expression of CYP3A7 and a weak expression of 3A4, as well as the important detoxification markers α-fetoprotein and albumin, could also be detected at the mRNA level. Importantly, urea metabolism (basal, NH4-stimulated, NH4- and ornithine-stimulated) was comparable to freshly isolated human hepatocytes, and unlike cryopreserved human hepatocytes, this activity was maintained after 6 months of cryopreservation. These findings suggest that these cells may be suitable for clinical application, especially for treatment of urea cycle disorders.

Improving the techniques for human hepatocyte transplantation: report from a consensus meeting in London

On September 6 and 7, 2009 a meeting was held in London to identify and discuss what are perceived to be current roadblocks to effective hepatocyte transplantation as it is currently practiced in the clinics and, where possible, to offer suggestions to overcome the blocks and improve the outcomes for this cellular therapy. Present were representatives of most of the active clinical hepatocyte transplant programs along with other scientists who have contributed substantial basic research to this field. Over the 2-day sessions based on the experience of the participants, numerous roadblocks or challenges were identified, including the source of cells for the transplants and problems with tracking cells following transplantation. Much of the discussion was focused on methods to improve engraftment and proliferation of donor cells posttransplantation. The group concluded that, for now, parenchymal hepatocytes isolated from donor livers remain the best cell source for transplantation. It was reported that investigations with other cell sources, including stem cells, were at the preclinical and early clinical stages. Numerous methods to modulate the immune reaction and vascular changes that accompany hepatocyte transplantation were proposed. It was agreed that, to obtain sufficient levels of repopulation of liver with donor cells in patients with metabolic liver disease, some form of liver preconditioning would likely be required to enhance the engraftment and/or proliferation of donor cells. It was reported that clinical protocols for preconditioning by hepatic irradiation, portal vein embolization, and surgical resection had been developed and that clinical studies using these protocols would be initiated in the near future. Participants concluded that sharing information between the groups, including standard information concerning the quality and function of the transplanted cells prior to transplantation, clinical information on outcomes, and standard preconditioning protocols, would help move the field forward and was encouraged.

From hepatocytes to stem and progenitor cells for liver regenerative medicine: advances and clinical perspectives

The parenchymal liver cell is a unique fully functional metabolic unit that can be used for liver regenerative medicine to restore function of the diseased organ; the aim of the procedure is to prevent progression of end-stage disease. The alternative, orthotopic liver transplantation, is highly intrusive, irreversible and limited by general organ shortage. Mature liver cell - hepatocyte - transplantation has been shown to have short- to medium-term efficacy for correction of miscellaneous inborn errors of metabolism. However, although proof of concept has been established, the procedure has not yet achieved full success, due to limited durability of functional benefit. Hepatocyte procurement is also restricted by organ shortage, and their storage is difficult due to poor tolerance of cryopreservation. Alternative cell sources are therefore needed for development and wider accessibility of cell-based liver regenerative medicine. Besides safety, the main challenge for these alternative cells is to acquire similar levels of functionality once implanted into the target organ. In this respect, liver derived progenitor cells may have some advantages over stem cells derived from other tissues.