Bone marrow transplantation in mice leads to a minor population of hepatocytes that can be selectively amplified in vivo

Phase 1-2 pilot clinical trial in patients with decompensated liver cirrhosis treated with bone marrow-derived endothelial progenitor cells

The aim of this nonrandomized, open label, phase 1 clinical trial was to evaluate the safety and the feasibility of the treatment with autologous bone marrow-derived endothelial progenitor cells (EPC) in decompensated liver cirrhosis. In addition, the changes in liver function and hepatic venous pressure gradient (HVPG) and their relation with the characteristics of the cellular product were analyzed. Twelve patients with Child-Pugh ≥8 liver cirrhosis underwent bone marrow harvest for ex vivo differentiation of EPC. The final product was administered through the hepatic artery in a single administration. Patients underwent clinical and radiologic follow-up for 12 months. The phenotype and the ability to produce cytokines and growth factors of the final cellular suspension were analyzed. Eleven patients were treated (feasibility 91%). No treatment-related severe adverse events were observed as consequence of any study procedure or treatment. Model for end-stage liver disease score improved significantly (P 0.042) in the first 90 days after cells administration and 5 of the 9 patients alive at 90 days showed a decreased of HVPG. There was a direct correlation between the expression of acetylated-low density lipoprotein and von Willebrand factor in the cellular product and the improvement in liver function and HVPG. The treatment with EPCs in patients with decompensated liver cirrhosis is safe and feasible and might have therapeutic potential. Patients receiving a higher amount of functionally active EPC showed an improvement of liver function and portal hypertension suggesting that the potential usefulness of these cells for the treatment of liver cirrhosis deserves further evaluation.

The hematopoietic system in the context of regenerative medicine

Hematopoietic stem cells (HSC) represent the prototype stem cell within the body. Since their discovery, HSC have been the focus of intensive research, and have proven invaluable clinically to restore hematopoiesis following inadvertent radiation exposure and following radio/chemotherapy to eliminate hematologic tumors. While they were originally discovered in the bone marrow, HSC can also be isolated from umbilical cord blood and can be "mobilized" peripheral blood, making them readily available in relatively large quantities. While their ability to repopulate the entire hematopoietic system would already guarantee HSC a valuable place in regenerative medicine, the finding that hematopoietic chimerism can induce immunological tolerance to solid organs and correct autoimmune diseases has dramatically broadened their clinical utility. The demonstration that these cells, through a variety of mechanisms, can also promote repair/regeneration of non-hematopoietic tissues as diverse as liver, heart, and brain has further increased their clinical value. The goal of this review is to provide the reader with a brief glimpse into the remarkable potential HSC possess, and to highlight their tremendous value as therapeutics in regenerative medicine.

Could Stem Cell Therapy be the Cure in Liver Cirrhosis?

Over the past five decades, liver cirrhosis has become an increasingly prevalent disease and one that will often require considerable medical intervention. However, current treatment options have demonstrated severe problems that have prompted research to provide a suitable alternative. These treatments are scarcely available, very expensive and present at a huge cost to the patient's quality of life. The introduction of stem cell therapy into liver disease has been heralded as the future of personalized medicine and may be the alternative that the healthcare system desperately seeks. To truly determine the scientific basis surrounding this excitement, a literature search was carried out in January 2013 to determine all the data that was present in this topic area. All articles also underwent full cross-referencing to ensure no data was missed. 11 clinical trials were found to meet this criteria and trials were included in both English and non-English languages. The sporadic nature of the data across the trials, with various methods and stem cell types, made comparisons difficult. The basic trends from the data were positive and the majority deemed the use of stem cells safe and feasible in patients presenting with cirrhotic liver disease. However, there is a clear requirement for more research, not only to determine the most efficacious technique and stem cell type but also to further understand stem cells to enhance progress. There may also be a requirement for a framework that future stem cell trials can be based on, which would allow future data to be comparative and allow valid conclusions to be drawn which may propel this therapy into standard clinical practice.

Prevention of liver fibrosis by intrasplenic injection of high-density cultured bone marrow cells in a rat chronic liver injury model

Endothelial progenitor cells (EPCs) from bone marrow have proven to be functional for the prevention of liver fibrosis in chronic liver injury. However, expansion of EPCs in culture is complicated and expansive. Previously, we have established a simple method that could enrich and expand EPCs by simple seeding bone marrow cells in high density dots. The purpose of this study is to evaluate whether cells derived from high-density (HD) culture of rat bone marrow cells could prevent the liver fibrosis in a chronic liver injury rat model, induced by carbon tetrachloride (CCl₄). Flow cytometric analysis showed that cells from HD culture were enriched for EPCs, expressing high levels of EPC markers. Intrasplenic injection of HD cultured bone marrow cells in the CCl₄-induced liver injury rat showed an enhanced antifibrogenic effect compared with animals treated with cells from regular-density culture. The antifibrogenic effect was demonstrated by biochemical and histological analysis 4 weeks post-transplantation. Furthermore, cells from HD culture likely worked through increasing neovascularization, stimulating liver cell proliferation, and suppressing pro-fibrogenic factor expression. HD culture, which is a simple and cost-effective procedure, could potentially be used to expand bone marrow cells for the treatment of liver fibrosis.

Bone marrow derived stem cells for the treatment of end-stage liver disease

End-stage disease due to liver cirrhosis is an important cause of death worldwide. Cirrhosis results from progressive, extensive fibrosis and impaired hepatocyte regeneration. The only curative treatment is liver transplantation, but due to the several limitations of this procedure, the interest in alternative therapeutic strategies is increasing. In particular, the potential of bone marrow stem cell (BMSC) therapy in cirrhosis has been explored in different trials. In this article, we evaluate the results of 18 prospective clinical trials, and we provide a descriptive overview of recent advances in the research on hepatic regenerative medicine. The main message from the currently available data in the literature is that BMSC therapy is extremely promising in the context of liver cirrhosis. However, its application should be further explored in randomized, controlled trials with large cohorts and long follow-ups.

Suppression of orthotopically implanted hepatocarcinoma in mice by umbilical cord-derived mesenchymal stem cells with sTRAIL gene expression driven by AFP promoter

Mesenchymal stem cells (MSCs) are promising vehicles for delivering therapeutic agents in tumor therapy. Human umbilical cord-derived mesenchymal stem cells (HUMSCs) resemble bone marrow-derived MSCs with respect to hepatic differentiation potential in injured livers in animals, while their hepatic differentiation under the hepatocarcinoma microenvironment is unclear. In this study, HUMSCs were isolated and transduced by lentiviral vectors coding the soluble human tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) gene driven by alpha-fetoprotein (AFP) promoter to investigate the therapeutic effects of these HUMSC against orthotopically implanted hepatocarcinoma in mice. We showed that HUMSCs can be transduced by lentivirus efficiently. HUMSCs developed cuboidal morphology, and expressed AFP and albumin in a two-step protocol. HUMSCs were capable of migrating to hepatocarcinoma in vitro as well as in vivo. In the orthotopical hepatocarcinoma microenvironment, the AFP promoter was activated during the early hepatic differentiation of HUMSCs. After intravenous injected, MSC.AFPILZ-sTRAIL expressed sTRAIL exclusively at the tumor site, and exhibited significant antitumor activity. This effect was stronger when in combination with 5-FU. The treatment was tolerated well in mice. Collectively, our results provide a potential strategy for targeted tumor therapy relying on the use of the tumor tropism and specific differentiation of HUMSCs as vehicles.

Role of stem cells in repair of liver injury: Experimental and clinical benefit of transferred stem cells on liver failure

Although the liver has a high regenerative capacity, as a result of massive hepatocyte death, liver failure occurs. In addition to liver failure, for acute, chronic and hereditary diseases of the liver, cell transplantation therapies can stimulate regeneration or at least ensure sufficient function until liver transplantation can be performed. The lack of donor organs and the risks of rejection have prompted extensive experimental and clinical research in the field of cellular transplantation. Transplantation of cell lineages involved in liver regeneration, including mature hepatocytes, fetal hepatocytes, fetal liver progenitor cells, fetal stem cells, hepatic progenitor cells, hepatic stem cells, mesenchymal stem cells, hematopoietic stem cells, and peripheral blood and umbilical cord blood stem cells, have been found to be beneficial in the treatment of liver failure. In this article, the results of experimental and clinical cell transplantation trials for liver failure are reviewed, with an emphasis on regeneration.

Implication of hepatic stem cells in functional liver repopulation

The liver has an enormous potential to restore the parenchymal tissue loss due to injury. This is accomplished by the proliferation of either the hepatocytes or liver progenitor cells in cases where massive damage prohibits hepatocytes from entering the proliferative response. Under debate is still whether hepatic stem cells are involved in liver tissue maintenance and regeneration or even whether they exist at all. The definition of an adult tissue-resident stem cell comprises basic functional stem cell criteria like the potential of self-renewal, multipotent, i.e. at least bipotent differentiation capacity and serial transplantability featuring the ability of functional tissue repopulation. The relationship between a progenitor and its progeny should exemplify the lineage commitment from the putative stem cell to the differentiated cell. This is mainly assessed by lineage tracing and immunohistochemical identification of markers specific to progenitors and their descendants. Flow cytometry approaches revealed that the liver stem cell population in animals is likely to be heterogeneous giving rise to progeny with different molecular signatures, depending on the stimulus to activate the putative stem cell compartment. The stem cell criteria are met by a variety of cells identified in the fetal and adult liver both under normal and injury conditions. It is the purpose of this review to verify hepatic stem cell candidates in the light of the stem cell definition criteria mentioned. Also from this point of view adult stem cells from non-hepatic tissues such as bone marrow, umbilical cord blood or adipose tissue, have the potential to differentiate into cells featuring functional hepatocyte characteristics. This has great impact because it opens the possibility of generating hepatocyte-like cells from adult stem cells in a sufficient amount and quality for their therapeutical application to treat end-stage liver diseases by stem cell-based hepatocytes in place of whole organ transplantation.

Bone marrow chimeras in the study of experimental stroke

Inflammation is known to contribute to stroke evolution, and poststroke immune responses have been documented to emanate from the brain via microglia. However, circulating immune cells are increasingly recognized to play a significant role as well. Recent work has demonstrated the importance of the peripheral circulation and stroke pathogenesis. Understanding how the peripheral circulation contributes to ischemic brain injury may reveal important therapeutic targets and strategies. The use of bone marrow chimeras can be a useful tool in understanding the relative contributions of brain resident and peripheral inflammatory responses.

Role of bone marrow transplantation for correcting hemophilia A in mice

To better understand cellular basis of hemophilia, cell types capable of producing FVIII need to be identified. We determined whether bone marrow (BM)-derived cells would produce cells capable of synthesizing and releasing FVIII by transplanting healthy mouse BM into hemophilia A mice. To track donor-derived cells, we used genetic reporters. Use of multiple coagulation assays demonstrated whether FVIII produced by discrete cell populations would correct hemophilia A. We found that animals receiving healthy BM cells survived bleeding challenge with correction of hemophilia, although donor BM-derived hepatocytes or endothelial cells were extremely rare, and these cells did not account for therapeutic benefits. By contrast, donor BM-derived mononuclear and mesenchymal stromal cells were more abundant and expressed FVIII mRNA as well as FVIII protein. Moreover, injection of healthy mouse Kupffer cells (liver macrophage/mononuclear cells), which predominantly originate from BM, or of healthy BM-derived mesenchymal stromal cells, protected hemophilia A mice from bleeding challenge with appearance of FVIII in blood. Therefore, BM transplantation corrected hemophilia A through donor-derived mononuclear cells and mesenchymal stromal cells. These insights into FVIII synthesis and production in alternative cell types will advance studies of pathophysiological mechanisms and therapeutic development in hemophilia A.

Therapeutic application of stem cells in gastroenterology: an up-date

Adult stem cells represent the self-renewing progenitors of numerous body tissues, and they are currently classified according to their origin and differentiation ability. In recent years, the research on stem cells has expanded enormously and holds therapeutic promises for many patients suffering from currently disabling diseases. This paper focuses on the possible use of stem cells in the two main clinical settings in gastroenterology, i.e., hepatic and intestinal diseases, which have a strong impact on public health worldwide. Despite encouraging results obtained in both regenerative medicine and immune-mediated conditions, further studies are needed to fully understand the biology of stem cells and carefully assess their putative oncogenic properties. Moreover, the research on stem cells arouses fervent ethical, social and political debate. The Italian Society of Gastroenterology sponsored a workshop on stem cells held in Verona during the XVI Congress of the Federation of Italian Societies of Digestive Diseases (March 6-9, 2010). Here, we report on the issues discussed, including liver and intestinal diseases that may benefit from stem cell therapy, the biology of hepatic and intestinal tissue repair, and stem cell usage in clinical trials.

Liver stem cells

The capacity of hepatocytes and cholangiocytes to contribute to their own maintenance has long been recognized. More recently, studies have indicated the presence of both intra-hepatic and extra-hepatic stem/progenitor cell populations. The intraorgan compartment probably derives primarily from the biliary tree, most particularly the most proximal branches, i.e. the canals of Hering and smallest ductules. The extra-organ compartment is at least in part derived from diverse populations of cells from the bone marrow. These three tiers of liver cell regeneration serve to maintain the normal organ and to regenerate damaged parenchyma in response to a variety of insults. The nature and extent of the insult determines the balance between these stem/progenitor compartments.

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.

Possibility of differentiation of hematopoietic stem cells into liver cells

Bone marrow-derived hematopoietic stem cells have the potential to undergo multilineage differentiation. Recent studies have shown that, in a given microenvironment, hematopoietic stem cells can differentiate into liver cells. However, some researchers hold a dissenting view. This review discusses the possibility of differentiation of hematopoietic stem cells into liver cells.

Administration of granulocyte colony-stimulating factor ameliorates radiation-induced hepatic fibrosis in mice

On the basis of the recent report that granulocyte colony-stimulating factor (G-CSF) treatment significantly improves survival and liver histology among chemically injured mice, we investigated whether G-CSF administration could contribute to faster recovery and promote tissue repair after local liver irradiation. Bone marrow chimeric female C57BL/6 mice were treated with G-CSF at days 7, 14, and 21 after local liver irradiation. We assessed the fibrosis index and the origin of proliferating cells reconstituting the liver at 2 or 5 weeks after radiation challenge. At day 35 after local irradiation, we observed G-CSF treatment to significantly reduce radiation-induced liver damage and collagen deposition. In addition, hepatic hydroxyproline levels and serum fibrosis markers in mice receiving G-CSF administration after radiation challenge were significantly lower compared with those of control mice. More importantly, histological examination suggested that recovery from hepatic damage was much better among the G-CSF-treated mice. Immunofluorescence and fluorescence in situ hybridization analyses revealed that donor cells engrafted into the host liver displayed epithelium-like morphology and expressed albumin, albeit at low frequency. These results suggested that G-CSF treatment initiated endogenous hepatic tissue regeneration in response to radiation injury and ameliorated its fibrogenic effects.

Bone marrow stem cells and liver regeneration

Development of new approaches to treat patients with hepatic diseases that can eliminate the need for liver transplantation is imperative. Use of cell therapy as a means of repopulating the liver has several advantages over whole-organ transplantation because it would be less invasive, less immunogenic, and would allow the use, in some instances, of autologous-derived cells. Stem/progenitor cells that would be ideal for liver repopulation would need to have characteristics such as availability and ease of isolation, the ability to be expanded in vitro, ensuring adequate numbers of cells, susceptibility to modification by viral vector transduction/genetic recombination, to correct any underlying genetic defects, and the ability of restoring liver function following transplantation. Bone marrow-derived stem cells, such as hematopoietic, mesenchymal and endothelial progenitor cells possess some or most of these characteristics, making them ideal candidates for liver regenerative therapies. Here, we will summarize the ability of each of these stem cell populations to give rise to functional hepatic elements that could mediate repair in patients with liver damage/disease.

Rodent models of liver repopulation

The liver has an extraordinary faculty to regenerate. Hepatocytes are highly differentiated cells that, despite a resting G0 state in the normal quiescent liver, can re-enter the cell cycle to reconstitute the organ after an injury. However, the first cell therapy approaches trying to harness this specific characteristic of the hepatocytes came up against the competition with resident hepatocytes in the ability to proliferate. This review will describe the different rodent models that have been developed in the last 15 years to demonstrate the concept of liver repopulation with transplanted cells harbouring a selective advantage over resident hepatocytes. Examples will then be given to show how these models demonstrated the therapeutic efficiency of cell transplantation in specific disorders. The transplantation of human hepatocytes into some of these mouse models led to the creation of humanized livers. These humanized mice provide a powerful tool to study the physiopathology of human hepatotropic pathogens and to develop drugs against them. Finally, emphasis will be placed on the role of these rodent models in the demonstration of the hepatocytic potential of stem cells.

Human progenitor cells with high aldehyde dehydrogenase activity efficiently engraft into damaged liver in a novel model

Human cord blood stem cells (hCBSCs) have been reported to generate hepatocyte-like cells and thus hold promise for repairing damaged liver. However, the frequency of hCBSC-derived hepatocytes varies tremendously between different studies, and it is still controversial as to whether hCBSC-derived cells can transdifferentiate into hepatocytes or simply fuse to recipient hepatocytes. We used the beta-glucuronidase-deficient nonobese diabetic/severe combined immunodeficient/mucopolysaccharidosis type VII (NOD/SCID/MPSVII) mouse model for better identification of engrafted cells. We transplanted lineage-depleted human umbilical cord blood-derived cells with high aldehyde dehydrogenase activity (ALDH(hi)Lin(-)) into irradiated NOD/SCID/MPSVII mice followed by carbon tetrachloride administration to induced liver damage. ALDH(hi)Lin(-) cells were efficiently engrafted in the recipient mouse livers and improved recovery of the mice from toxic insult. The percentage of human cells in these livers ranged between 3% and 14.2% using quantitative real-time polymerase chain reaction. Furthermore, human-originated cells expressing liver-specific alpha1-antitrypsin messenger RNA, albumin and hepatocyte nuclear factor 1 protein were detected in the recipient livers. Interestingly, human versus murine centromeric fluorescent in situ hybridization analysis on the liver sections demonstrated that most human cells were not fused to mouse cells. However, the majority of the human originated albumin-expressing cells also carried mouse genetic material, hence were the product of cell fusion.

CONCLUSION

hCBSCs or their progeny may home to the injured liver and release trophic factors that hasten tissue repair, whereas fusion of these cells with hepatocytes may occur rarely and contribute to a lesser extent to liver repair.

Therapeutic potential of adult bone marrow stem cells in liver disease and delivery approaches

Hematopoietic stem cells (HSCs) and mesenchymal stem cell (MSCs) are two main subtypes of bone marrow stem cells. Extensive studies have been carried out to investigate the therapeutic potential of BMSCs in liver disease. A number of animal and human studies demonstrated that either HSCs or MSCs could be applied to therapeutic purposes in certain liver diseases. The diseased liver may recruit migratory stem cells, particularly from the bone marrow, to generate hepatocyte-like cells either by transdifferentiation or cell fusion. Transplantation of BMSCs has therapeutic effects of restoration of liver mass and function, alleviation of fibrosis and correction of inherited liver diseases. There are still controversial results over the potential effects of BMSCs on liver diseases, and some of the discrepancies are thought to be lied in the differences of experimental protocols, differences in individual research laboratory, and the uncertainties of the techniques employed. Several potential approaches for BMSCs delivery in liver diseases have been proposed in animal studies and human trials. BMSCs can be delivered via intraportal vein, systemic infusion, intraperitoneal, intrahepatic, intrasplenic. The optimal stem cells delivery should be easy to perform, less invasive and traumatic, minimum side effects, and with high cells survival rate. In this review, we focus on the up-to-date evidence of therapeutic effects of BMSCs on liver disease, the characteristics of various delivery approaches, and the considerations for future studies.

Rat bone marrow mesenchymal stem cells differentiate into hepatocyte-like cells in vitro

AIM: To investigate differentiation of rat bone marrow mesenchymal stem cells (MSCs) into hepatocyte-like cells.

METHODS: A total of 24 Wistar rats were randomly divided into 3 groups: normal group, hepatic fibrosis model group and Chinese medicine treatment group. The model of liver fibrosis was induced by subcutaneous injection of CCl₄. After the model was successfully developed, and the rats in Chinese medicine treatment group were fed with Danjin Shugan capsule. At the end of treatment, the rats were killed and the livers were obtained. Histopathological changes were evaluated by hematoxylin and eosin staining. MSCs were isolated by gradient density centrifugation and plastic adherence and then purified. The purified MSCs in each group were cultured with hepatocyte growth factor (HGF) and fibroblast growth factor-4 (FGF-4). The levels of alpha-fetoprotein (AFP) and albumin (Alb) in the supernatant were determined by radioimmunoassay on days 15, 21 and 27. On day 27, the cells were collected for glycogen staining and CK-18 immunocytochemical analysis.

RESULTS: Compared with those in the non-induced MSCs among the three groups, the levels of AFP in the induced-MSCs were higher on days 15, 21, and 27, and reached to the peak value on day 21 (hepatic fibrosis model group: 48.94 ± 0.08 vs 9.90 ± 0.09; Chinese medicine treatment group: 49.86 ± 0.29 vs 8.69 ± 0.62; normal group: 38.65 ± 0.33 vs 9.04 ± 0.11; all P< 0.01). There were significant differences in Alb levels on days 21 and 27 between the induced and non-induced MSCs (1.11 ± 0.08 vs 0.32 ± 0.00, 1.25 ± 0.04 vs 0.32 ± 0.00, 1.06 ± 0.03 vs 0.33 ± 0.00; 1.52 ± 0.02 vs 0.33 ± 0.00, 1.79 ± 0.01 vs 0.31 ± 0.03, 1.63 ± 0.04 vs 0.32 ± 0.01; all P < 0.01), but not on day 15; the peak level of Alb was on day 27. Both glycogen and CK-18 were positive on day 27 in the induced MSCs. According to AFP and Alb levels, the induced effects of Chinese medicine group were superior to those of the other two groups.

CONCLUSION: MSCs can differentiate into hepatocyte-like cells with hepatic phenotype and function in the presence of HGF and FGF-4, which may be used as a kind of cell resources to treat severe hepatic disease. Chinese medicine may optimize the induction of MSCs differentiation in vitro.

Hepatic injury and the kinetics of bone marrow-derived hepatocyte transgene expression

BACKGROUND

Numerous congenital and acquired liver diseases could benefit from a successful hepatic cell therapy strategy. Hepatotypic cells derived from bone marrow have been recognized during liver injury, repair, and regeneration. To study this phenomenon, we compared the effect of several modes of experimental hepatic injury on hepatotypic protein expression in a mouse model after bone marrow transplantation.

METHODS

Male mice transgenic for the liver-specific protein human alpha-1 antitrypsin (hAAT) were used as bone marrow donors. Syngeneic wild-type recipient mice were subjected to 1 of 3 hepatic injuries: (1) sublethal irradiation, (2) injection of a hepatotoxic adenoviral construct, and (3) administration of a hepatotoxic diet. Bone marrow-derived hepatotypic (BMdH) transgene expression was determined by serial serum enzyme-linked immunosorbent assay for hAAT.

RESULTS

In both acute injury models, hAAT expression was detected as early as 1 week, whereas the control group never elicited hAAT expression. The adenovirus-treated group demonstrated transient hAAT level expression lasting up to 2 weeks postinjury, whereas the irradiated group maintained persistent hAAT expression through 4 months. In the chronic injury (hepatotoxin) model, hAAT expression persisted and was noted to increase over time to 200 to 300 ng/mL.

CONCLUSIONS

Irradiation favors long-term establishment of BMdH transgene expression, and chronic injury further promotes this phenomenon.

Critical review of clinical trials of bone marrow stem cells in liver disease

Morbidity and mortality from cirrhosis is increasing rapidly in the Western world. Currently the only effective treatment is liver transplantation, an increasingly limited and expensive resource. Consequently, there has been great hope that stem cells may offer new therapeutic approaches in the management of liver disease. In this review we critically appraise the 11 published clinical studies of bone marrow stem cells in liver disease, and focus on the unresolved issues regarding their role. We outline the different mechanisms by which stem cells may impact on liver disease, as well as highlight the importance of the type of stem cell chosen. There are multiple different stem cell populations that have, in rodent studies, been shown to have differing effects on liver regeneration and fibrogenesis/degradation. Thus, choice of cell should reflect the desired or expected mechanism of action. The importance, and methods, of studying the fate of stem cells infused in clinical studies is emphasized as we seek to translate observations in rodents into the clinical setting. Finally, we discuss which cohorts of patients with liver disease would benefit from stem cell therapy, as well as establish minimum criteria for future clinical trials of stem cells.

Effect of different induction conditions on hepatocyte-like cells induced in vitro by rat bone marrow mesenchymal stem cells

AIM: To study the optimal conditions for in vitro induction and culture of rat bone marrow mesenchymal stem cells (MSCs) in order to provide the theoretical basis for the treatment of severe liver disease patients with MSCs.

METHODS: MSCs were isolated by gradient density centrifugation and plastic adherence and purified. MSCs were induced by different concentrations of FBS and cytokines. Levels of AFP and albumin in the supernatant were measured by radioimmunoassay on days 15, 21 and 27. On day 27, cells were collected. Glycogen store of heoatocytes was determined by periodic acid-Schiff staining and the expression of CK-18 and CK-19 in MSCs were detected by immunocytochemical analysis.

RESULTS: The level of AFP was higher in induced MSCs than in non-induced MSCs on days 15, 21, 27, and reached its highest on day 21. There was no significant difference in albumin levels on day 15, between induced and non-induced MSCs. However, on days 21 and 27, the albumin level was higher in induced MSCs than in non-induced MSCs. Glycogen storage in induced MSCs was observed on day 27 but not in non-induced MSCs. The induced MSCs expressed CK-18 and CK-19 while the non-induced MSCs did not. Multiple factor analysis by ANOVA showed that MSCs should be cultured in Dulbecco's modified Eagle's medium supplemented with 200 mL/L FBS, 20 μg/L hepatocyte growth factor (HGF) and 20 μg/L fibroblast growth factor 4 (FGF-4), which might be the best induction conditions for MSCs.

CONCLUSION: Rat MSCs can differentiate into hepatocyte-like cells with hepatic phenotypes and functions in the presence HGF and/or FGF-4 in vitro. The concentrations of fetal bovine serum, HGF and FGF-4 affect the differentiation of rat MSCs into hepatocyte-like cells. MSCs can be used in the treatment of severe hepatic diseases.

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.

Hepatic parenchymal replacement in mice by transplanted allogeneic hepatocytes is facilitated by bone marrow transplantation and mediated by CD4 cells

The lack of adequate donor organs is a major limitation to the successful widespread use of liver transplantation for numerous human hepatic diseases. A desirable alternative therapeutic option is hepatocyte transplantation (HT), but this approach is similarly restricted by a shortage of donor cells and by immunological barriers. Therefore, in vivo expansion of tolerized transplanted cells is emerging as a novel and clinically relevant potential alternative cellular therapy. Toward this aim, in the present study we established a new mouse model that combines HT with prior bone marrow transplantation (BMT). Donor hepatocytes were derived from human alpha(1)-antitrypsin (hAAT) transgenic mice of the FVB strain. Serial serum enzyme-linked immunosorbent assays for hAAT protein were used to monitor hepatocyte engraftment and expansion. In control recipient mice lacking BMT, we observed long-term yet modest hepatocyte engraftment. In contrast, animals undergoing additional syngeneic BMT prior to HT showed a 3- to 5-fold increase in serum hAAT levels after 24 weeks. Moreover, complete liver repopulation was observed in hepatocyte-transplanted Balb/C mice that had been transplanted with allogeneic FVB-derived bone marrow. These findings were validated by a comparison of hAAT levels between donor and recipient mice and by hAAT-specific immunostaining. Taken together, these findings suggest a synergistic effect of BMT on transplanted hepatocytes for expansion and tolerance induction. Livers of repopulated animals displayed substantial mononuclear infiltrates, consisting predominantly of CD4(+) cells. Blocking the latter prior to HT abrogated proliferation of transplanted hepatocytes, and this implied an essential role played by CD4(+) cells for in vivo hepatocyte selection following allogeneic BMT.

CONCLUSION

The present mouse model provides a versatile platform for investigation of the mechanisms governing HT with direct relevance to the development of clinical strategies for the treatment of human hepatic failure.

Stem cells, cell transplantation and liver repopulation

Liver transplantation is currently the only therapeutic option for patients with end-stage chronic liver disease and for severe acute liver failure. Because of limited donor availability, attention has been focused on the possibility to restore liver mass and function through cell transplantation. Stem cells are a promising source for liver repopulation after cell transplantation, but whether or not the adult mammalian liver contains hepatic stem cells is highly controversial. Part of the problem is that proliferation of mature adult hepatocytes is sufficient to regenerate the liver after two-thirds partial hepatectomy or acute toxic liver injury and participation of stem cells is not required. However, under conditions in which hepatocyte proliferation is blocked, undifferentiated epithelial cells in the periportal areas, called "oval cells", proliferate, differentiate into hepatocytes and restore liver mass. These cells are referred to as facultative liver stem cells, but they do not repopulate the normal liver after their transplantation. In contrast, epithelial cells isolated from the early fetal liver can effectively repopulate the normal liver, but they are already traversing the hepatic lineage and may not be true stem cells. Mesenchymal stem cells and embryonic stem cells can be induced to differentiate along the hepatic lineage in culture, but at present these cells are inefficient in repopulating the liver. This review will characterize these various cell types and compare the properties of these cells and the conditions under which they do or do not repopulate the liver following their transplantation.

Improvement of the survival rate by fetal liver cell transplantation in a mice lethal liver failure model

BACKGROUND

The use of cell transplantation as an alternative therapy for orthotopic liver transplantation has been widely anticipated due to a chronic donor shortage. We previously reported the method used to enrich hepatic progenitor cells (HPCs) forming cell aggregations. In this study, we transplanted HPCs into the liver injury model mice to determine whether HPC transplantation may improve the liver dysfunction.

METHODS

We obtained donor cells from E13.5 fetal livers of green fluorescent protein (GFP) transgenic mice. We transplanted GFP-positive fetal liver cells into the transgenic mice which express diphtheria toxin (DT) receptors under the control of an albumin enhancer/promoter. Subsequently, we induced selective liver injury to recipient mice by DT administration. We then evaluated the engraftment of the transplanted cells and their effect on survivorship.

RESULTS

The low dose of DT induced sublethal liver injury and the high dose of DT was lethal to the liver injury model mice. The transplanted GFP-positive cells were engrafted into the recipient livers and expressed albumin, resembling mature hepatocytes. They continued to proliferate, forming clusters. The survival rate at 25 days after transplantation of the cell-transplanted group (8 of 20; 40.0%) was improved significantly (P=0.0047) in comparison to that of the sham-operated group (0 of 20; 0%).

CONCLUSIONS

The transplanted cells were engrafted and repopulated the liver of recipient mice, resulting in the improvement of the survival rate of the liver injury model mice. We therefore propose that HPCs are a desirable cell source for cell transplantation.

Stem cells as a treatment for chronic liver disease and diabetes

Advances in stem cell biology and the discovery of pluripotent stem cells have made the prospect of cell therapy and tissue regeneration a clinical reality. Cell therapies hold great promise to repair, restore, replace or regenerate affected organs and may perform better than any pharmacological or mechanical device. There is an accumulating body of evidence supporting the contribution of adult stem cells, in particular those of bone marrow origin, to liver and pancreatic islet cell regeneration. In this review, we will focus on the cell therapy for the diseased liver and pancreas by adult haematopoietic stem cells, as well as their possible contribution and application to tissue regeneration. Furthermore, recent progress in the generation, culture and targeted differentiation of human haematopoietic stem cells to hepatic and pancreatic lineages will be discussed. We will also explore the possibility that stem cell technology may lead to the development of clinical modalities for human liver disease and diabetes.

Characterization of the Potential Subpopulation of Bone Marrow Cells Involved in the Repair of Injured Liver Tissue

In vitro and in vivo studies have shown that bone marrow (BM) stem cells can differentiate into hepatocytes. However, it is not known whether such a differentiation event occurs during normal liver regeneration process. We investigated the role of endogenous BM cells in liver regeneration following acute injury and phenotypically characterized them. We showed that Lin(-)Sca-1(+) cells proliferate in the BM and subsequently mobilize in the peripheral blood in response to liver injury by CCl(4) or an injury simulating condition. In vitro studies confirmed that the damaged liver tissue was capable of inducing migration of a distinct population of BM cells, phenotypically characterized as Lin(-)CXCR4(+)OSMRbeta(+), which can differentiate into albumin and cytoketarin-18 expressing cells. In order to study the migration of BM cells to the regenerating liver, the hematopoietic system was reconstituted with green fluorescent protein (GFP)(+) BM cells by intra-bone marrow transplantation prior to liver damage. The BM-derived cells were found to express hepatocyte-specific genes and proteins in the regenerating liver. Quantitative polymerase chain reaction analysis for a recipient specific gene (sry) in sorted GFP(+)Alb(+) donor cells suggested that fusion was a rare event in this experimental model. In conclusion, we first demonstrated the potential phenotype of BM cells involved in regeneration of liver from acute injury, primarily by the process of direct differentiation. Disclosure of potential conflicts of interest is found at the end of this article.

Cytokine mobilization of bone marrow cells and pancreatic lesion do not improve streptozotocin-induced diabetes in mice by transdifferentiation of bone marrow cells into insulin-producing cells

OBJECTIVE

Transdifferentiation of bone marrow cells (BMC) into insulin-producing cells might provide a new cellular therapy for type I diabetes, but its existence is controversial. Our aim was to determine if those cells could transdifferentiate, even at low frequency, into insulin-producing cells, in testing optimized experimental conditions.

METHODS

We grafted mice with total BMC, genetically labeled either ubiquitarily, or with a marker conditionally expressed under the control of the insulin beta-cell specific promoter. We treated some of the recipients with an agent toxic to beta-cells (streptozotocin) and with cytokines stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF).

RESULTS

The contribution of grafted cells could be detected neither for natural turnover (n=6), nor for beta-cell regeneration after pancreatic lesion (n=7), 90 days post-transplantation. Cytokine mobilization of BMC in the blood stream, reported to favor their transdifferentiation into cardiac and neural cells, had never been tested before for beta-cell generation. Here, we showed that injection of SCF and G-CSF did not lead to a detectable level of transdifferentiation (n=7).

CONCLUSIONS

We conclude that BMC cannot spontaneously transdifferentiate into insulin-producing cells in vivo, even after beta-cell lesion and mobilization induced by cytokines. Interestingly, however, treatment by cytokines may have beneficial indirect effects on STZ-induced hyperglycaemia.

Jekyll and Hyde: evolving perspectives on the function and potential of the adult liver progenitor (oval) cell

The liver progenitor cell (LPC) has enormous potential for use in cell therapy to treat liver disease. Since liver regenerates readily from pre-existing hepatocytes, a role for LPCs and, indeed, their existence have been questioned. Research during the last decade has established that LPCs are an important alternative source of cells for liver regeneration. Their utility for cell therapy lies in their ability to generate both hepatocytes and cholangiocytes. However, they are observed in liver diseases that often lead to cancer and there is experimental evidence that implicates LPCs as the source of tumours. This article provides a brief history of the studies that established the functional importance of LPCs in liver disease. It focuses on mouse models that have led to the identification of factors that regulate LPC growth and differentiation and discusses LPCs derived from different sources. Recent promising results from both in vitro and vivo studies suggest that LPCs could be useful for cell therapy. In the context of liver disease, LPCs may indeed be the cell of the future and understandably "our favourite cell".

Liver repopulation trial using bone marrow cells in a retrorsine-induced chronic hepatocellular injury model

OBJECTIVES

The aim of this study was to determine the potential of bone marrow derived cells to participate in liver repopulation. In this model, the injected cells had a "selective growth advantage" compared to the native hepatocytes whose proliferation was blocked by retrorsine.

METHODS

Total bone marrow cells were isolated from male Fisher 344 rats not deficient in dipeptidyl peptidase activity (F344, DPP IV+). The animals were given an injection of retrorsine and were divided in 2 groups: 1/group R (N=13): female F344 rats received 4.106 male cells at day 0 (labeled by chromosome Y). 2/group RH (N=19): Male F344 DPP IV- rats received 4.106 male DPP IV+ cells after hepatectomy at day 0 (labelled by DPP IV activity).

RESULTS

Group R: no male cell was detected by PCR at day 14, 28, 56 and 84. Group RH: isolated DPP IV+ transplanted cells were observed at days 14 and 28 in the periportal areas. Later, these cells were no longer visible. Liver regeneration occurred by proliferation of small clusters of hepatocytes.

CONCLUSIONS

In this experimental model the capacity of transplanted bone marrow cells to repopulate the liver was tested against the same capacity of native liver stem cells. Liver regeneration occurred via native liver cells seen as small hepatocytes. In this model the small hepatocytes may be considered as hepatic stem cells.

L’apoptose hépatique

Apoptosis or programmed cell death occurs in the liver as in other organs. In the normal state it is not a frequent mode of hepatic cell destruction. Morphological and biochemical characteristics of liver cell apoptosis do not differ from what is observed in other cells. The Fas receptor pathway, a frequent hepatic apoptotic pathway among various others, involves intra-cellular signals amplified by mitochondria. Although hepatic apoptosis may occur by following several others pathways, Fas, which is abundantly expressed in the plasma membrane of hepatocytes, is very often involved in hepatocyte demise during B or C viral hepatitis irrespective of their clinical form, alcoholic hepatitis, cholestasis due to accumulation of hepatic biliary salts, or certain types of drug-induced hepatitis. Fas is also probably responsible for the death of biliary cells in primary biliary cirrhosis. In contrast one of the causes of resistance to apoptosis of hepatic cancerous cells could be related to an alteration of the Fas receptor. This is why much experimental work is presently performed to achieve inhibition of the Fas receptor either at the mRNA level or at the level of Fas-inductible proteolytic enzymes called caspases. One perspective is a specific treatment of apoptosis as an adjuvant treatment of liver diseases.

Immune-mediated hepatitis drives low-level fusion between hepatocytes and adult bone marrow cells

BACKGROUND/AIMS

The role of adult bone marrow-derived cells (BMC) in hepatic regeneration is controversial. Both transdifferentiation of BMC as well as fusion with hepatocytes have been suggested in toxin-based and genetic selection models.

METHODS

We have developed a transgenic mouse model of immune-mediated hepatitis to clarify the role of BMC in liver regeneration following injury mediated by T cells.

RESULTS

Repeated adoptive transfer of transgenic T cells into bone marrow chimeras resulted in multiple waves of hepatitis. Hepatocytes derived from donor bone marrow were identified using a self-protein that does not interfere with hepatocyte function and proliferation in recipient animals. Some cells contained one recipient nucleus and another independent donor bone marrow-derived nucleus, suggesting that cellular fusion plays some role in liver repair after immune hepatitis. However, despite pronounced infiltration by myeloid cells, the frequency of fusion was extremely low.

CONCLUSIONS

This study provides a unique, clinically relevant model in which fusion hepatocytes can be purified and characterized by the expression of donor MHC antigen. It demonstrates that although fusion between BMC and hepatocytes occurs under conditions of inflammation that correspond to human disease, its frequency needs to be increased to be of any therapeutic value.

Cell competition leads to a high level of normal liver reconstitution by transplanted fetal liver stem/progenitor cells

BACKGROUND & AIMS

A critical property of stem cells is their ability to repopulate an organ or tissue under nonselective conditions. The aims of this study were to determine whether we could obtain reproducible, high levels of liver repopulation by transplanted fetal liver stem/progenitor cells in normal adult liver and the mechanism by which liver replacement occurred.

METHODS

Wild-type (dipeptidyl peptidase IV [DPPIV(+)]) embryonic day (ED) 14 fetal liver cells underwent transplantation into DPPIV(-) mutant F344 rats to follow the fate and differentiation of transplanted cells. To determine the mechanism for repopulation, proliferation and apoptosis of transplanted and host liver cells were also followed.

RESULTS

Transplanted ED 14 fetal liver cells proliferated continuously for 6 months, differentiated into mature hepatocytes, and replaced 23.5% of total liver mass. The progeny of transplanted cells were morphologically and functionally indistinguishable from host hepatocytes and expressed unique liver-specific genes commensurate with their location in the hepatic lobule. Repopulation was based on greater proliferative activity of transplanted cells and reduced apoptosis of their progeny compared with host hepatocytes, coupled with increased apoptosis of host hepatocytes immediately adjacent to transplanted cells. This process, referred to as cell-cell competition, has been described previously in Drosophila during wing development.

CONCLUSIONS

We show for the first time that cell-cell competition, a developmental paradigm, can be used to replace functional organ tissue in an adult mammalian species under nonselective conditions and may serve as a strategy for tissue reconstitution in a wide variety of metabolic and other disorders involving the liver, as well as other organs.

Engraftment of Bone Marrow-Derived Epithelial Cells

Discoveries of the ability of bone marrow-derived cells (BMDCs) to differentiate into nonhematopoietic cells have opened up a new field of inquiry in adult stem cell plasticity. There are far more questions than there are answers to date. We and others have investigated whether differentiation occurs in response to tissue damage, what the underlying mechanisms might be, and whether this plasticity may be useful clinically. BMDC have been shown to differentiate into mature-appearing epithelial cells in the lung, liver, gastrointestinal tract, skin, buccal mucosa, and kidney. The mechanism(s) by which cells transition to these nonhematopoietic phenotypes is not yet clear, but possibilities include cell-to-cell fusion, direct differentiation of a nonhematopoietic precursor cell from the BM, and transdifferentiation of a BM cell that had previously been committed to a different phenotype. Data obtained to date support the first two possibilities, and there are no data proving that transdifferentiation is responsible for the engraftment of marrow-derived epithelial cells. Theoretically, the engraftment of marrow-derived cells as nonhematopoietic cell types could be used in either the autologous or the allogeneic setting to restore functional epithelial cells to a diseased organ. For example, a marrow-derived cell that has been transduced to express a specific transgene can continue to express this transgene after it engrafts as a nonhematopoietic epithelial cell in the lung. Analyses of the kinetics of this engraftment suggest that it can be increased within days to weeks following certain types of injury, depending on the tissue examined. Most reports of adult stem cell plasticity show relatively low frequencies of marrow-derived nonhematopoietic cells, on the order of 1 in 10(3) to 1 in 10(4) epithelial cells in many organs being marrow derived. This frequency is likely to be too low to be of therapeutic relevance. Therefore, future efforts will need to be focused on enhancing levels of engraftment.

Liver repopulation: a new concept of hepatocyte transplantation

Hepatocyte transplantation has been recognized as an alternative strategy for organ transplantation because the supply of donor livers is limited. However, in conventional hepatocyte transplantation, only 1%-10% of the liver replaced with transplanted hepatocytes. Recently a novel concept termed "liver repopulation" has been established, where the whole recipient liver can be replaced by a small number of donor hepatocytes. To induce liver repopulation, growth advantage of the donor hepatocytes against the host liver seems to be required according to the data of previous studies. Additionally, various cell sources, including bone marrow cells and other stem cells, could potentially be used as donor cells for liver repopulation. In this article, we discuss recent progress and future perspectives of this emerging technology.

Transplantation of Undifferentiated, Bone Marrow‐Derived Stem Cells

Stem cell research has known an enormous development, and cellular transplantation holds great promise for regenerative medicine. However, some aspects, such as the mechanisms underlying stem cell plasticity (cell fusion vs true transdifferentiation) and the functional improvement after stem cell transplantation, are highly debated. Furthermore, the great variability in methodology used by several groups, sometimes leads to confusing, contradicting results. In this chapter, we review a number of studies in this area with an eye on possible technical and other difficulties in interpretation of the obtained results.

Promotion effect of Zuoguiwan on bone marrow cells' forming into liver cells in mice

AIM: To observe the influence of nourishing kidney (using Zuoguiwan) on the formation of liver cells from bone marrow cells.

METHODS: The female BALB/c mice were randomly divided into kidney nourishing group (KN, treated by Zuoguiwan), Qi-Xue restorative group (QXR, treated by Bazhentang) and control group (NC, treated by normal saline). After whole body irradiation with 9.0 Gy 60Co γ-rays, the female mice were injected via the tail vein with bone marrow cells from homogenic male mice to establish bone marrow transplantation model. Zuoguiwan, Bazhentang and normal saline intragatrically given to the corresponding group at the same dose [7 g/(kg•d)] after bone marrow transplantation. The mice were sacrificed to obtain liver tissues at 2, 4, and 6 mo. Fluorescence in situ hybridization (FISH) for Chromosome Y (Sry) and albumin mRNA was used to detect liver cells derived from male bone marrow, and then the rate of positive cells was calculated.

RESULTS: The positive rates of liver cells in KN, QXR and NC group were all increased with the time increase after bone marrow transplantation. The positive rate in KN group at 6 mo was markedly elevated (18.25±3.36% vs 4.00±1.73%, 4.80±1.30%, P < 0.01). Furthermore, the positive rate in NK group was significantly higher than that in QXR group (2 mo: 4.00±1.73% vs 1.20±0.45%, P < 0.01; 4 mo: 4.80±1.30% vs 1.40±0.55%, P < 0.01; 18.25±3.36% vs 7.20±1.33%, P < 0.01) and NC group (2 mo: 4.00±1.73% vs 1.00±0.61%, P < 0.01; 6 mo: 18.25±3.36% vs 9.25±1.31%, P < 0.01) at the same time point.

CONCLUSION: Zuoguiwan can promote bone marrow cells' forming into liver cells in mice.

Hepatocyte differentiation from embryonic stem cells and umbilical cord blood cells

With the development of regeneration medicine, many researchers have attempted hepatic differentiation from nonhepatic-origin cell sources. The differentiation of embryonic stem (ES) cells into hepatocyte-like cells has been reported in several papers. Mouse ES cells have shown a potential to develop into hepatocyte-like cells in vitro on the basis of hepatic gene expression after adding several growth factors. We transplanted cultured embryoid body (EB) cells (male) into female mice. A liver specimen of the recipient was examined by immunohistochemical staining for albumin and fluorescence in situ hybridization for the Y chromosome after transplantation. Both Y chromosome- and albumin-positive cells were recognized in the recipient female liver, and were considered to be hepatocyte-like cells derived from ES cells containing the Y chromosome. Many groups, including ourselves, have studied hepatocyte-like cell differentiation from umbilical cord blood cells (UBCs). We cultured nucleated cells isolated from UBCs. Using immunostaining, ALB-positive and CK-19-positive cells were recognized in the culture. Dual staining of ALB and CK-19 demonstrated that ALB was coexpressed with CK-19, suggesting the existence of hepatic progenitors. In this review, we consider recent studies of the differentiation of hepatocytes from nonhepatic origins, especially ES cells and umbilical cord blood.

In vivo formation of unstable heterokaryons after liver damage and hematopoietic stem cell/progenitor transplantation

Following reports of lineage plasticity in human hematopoietic stem cells (HSCs), we investigated the potential of human cord blood HSC-enriched cells to create hepatocytes in hosts after inducing liver damage. Carbon tetrachloride induces severe liver damage and subsequent repair via mitosis of resident hepatocytes. It additionally leads to a threefold increase in homing of human mononuclear cells to bone marrow and liver and subsequently to a substantial enhancement of bone marrow engraftment. Eight weeks after liver damage and infusion of an enhanced green fluorescent protein (eGFP) lentivirus-transduced human HSC-enriched cell population, we observed eGFP-positive cells with clear hepatocyte morphology in the livers of animals. These eGFP-positive cells co-expressed human albumin, and reverse-transcription polymerase chain reaction (PCR) analysis demonstrated the presence of human albumin and alpha-anti-trypsin mRNA. However, two antibodies against human mitochondria and human nuclei failed to mark eGFP-positive hepatocyte-like cells but did give clear staining of donor-derived hematopoietic cells. Subsequent fluorescent in situ hybridization (FISH) analysis revealed the presence of mouse Y chromosome in eGFP-positive hepatocyte-like cells. To resolve this discrepancy, we performed single-cell PCR analysis of microdissected eGFP-positive hepatocyte-like cells and found that they contained mostly mouse and little human genomic material. FISH analysis highlighting the centromeres of all human chromosomes revealed only few human chromosomes in these cells. From these results, we conclude that similar to their murine counterparts, human hematopoietic cells have the potential to fuse with resident host hepatocytes. Because no selective pressure is applied to retain the human genomic material, it is gradually lost over time, leading to a variable phenotype of the chimeric cells and making their detection difficult.

Experimental models of acute and chronic liver failure in nude mice to study hepatocyte transplantation

Although hepatocyte transplantation is a promising therapy for acute liver failure in human, there is still a lack of animal models suffering from hepatic injury in which the benefits of hepatocyte transplantation could be evaluated solely, without the bias caused by immunosuppression. As a consequence, the aim of the study was first to develop reproducible models of partial hepatectomy and of thioacetamide (TA)- or Jo2-induced acute liver failure in nude mice. Chronic liver disease was also investigated by repeated injections of sublethal doses of thioacetamide. Survival rates, routine histologic observations, alanin aminotransferase sera content, Ki67, and caspase 3 immunodetection were investigated both after 40% partial hepatectomy and after toxic-induced damages. Liver injuries were more severe and/or precocious in nude mice than in Balb/c mice for a given treatment with a maximum of acute injury obtained 24 h after single toxic injection, and were found to be transitory and reversible within 10 days. Toxics induced apoptosis followed by necrosis, confirming recent published data. Onset of fibrosis leading to reproducible chronic cirrhosis in nude mice correlated with increasing number of Ki67-positive cells, indicating that high levels of cell proliferation occurred. Chronic cirrhosis progressively reversed to fibrosis when the treatment ceased. Preliminary results demonstrated that engrafted xenogeneic hepatocytes could be detected in the host liver by anti-MHC class I immunohistochemistry. Fractions enriched in 2n or 4n hepatocytes by cell sorting using a flow cytometer were equivalent to the unpurified fraction in terms of engraftment in control nude mice or in nude mice subjected to PH. However, in mice suffering from liver injury 24 h after Jo2 or TA treatment, the engraftment of 2n hepatocytes was about twice that of an unpurified hepatocyte population or of a population enriched in 4n hepatocytes.