Liver repopulation by transplanted hepatocytes and risk of hepatocellular carcinoma

BACKGROUND: Transplantation of isolated hepatocytes in rats treated with retrorsine (RS) results in massive repopulation of the host liver. In this study, the long-term fate of hepatocytes transplanted into RS-treated recipients was followed for up to two years. METHODS: Dipeptidyl-peptidase type IV-deficient (DPPIV) Fischer 344 rats were given two injections of RS (30 mg/kg), followed by transplantation of 2 million hepatocytes, isolated from a syngenic, DPPIV donor. RESULTS: Extensive (91+/-7%) liver replacement by transplanted hepatocytes was observed in animals sacrificed 18 months posttransplantation. Similar levels of repopulation persisted at two years (87+/-5%). No evidence of preneoplastic and/or neoplastic evolution of the transplanted cell population was present in the RS-treated and repopulated livers at any time point considered. Furthermore, serum parameters related to hepatocyte function and integrity were in the normal range. In control groups given cell transplantation in the absence of prior treatment with RS, only small clusters of donor-derived, DPPIV hepatocytes were discerned. CONCLUSIONS: These results indicate that liver repopulation in this model is largely stable, persisting for up to two years and allowing for a normal liver function. In addition, no increased risk of neoplastic transformation appears to be associated with the process of liver repopulation for as long as over two thirds of the life span of the recipient animal.     

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.     

Functional characterization of serum-free cultured rat hepatocytes for downstream transplantation applications

Although ex vivo culture of hepatocytes is known to impair functionality, it may still be considered as desirable to propagate or manipulate them in culture prior to transplantation into the host liver. The aim of this study was to clarify whether rat hepatocytes cultured over different periods of time proliferate and retain their hepatocyte-specific functions following transplantation into the recipient liver. Rat hepatocytes were cultured under serum-free conditions in the presence of hepatocyte and epidermal growth factors. Cells derived from wild-type donor livers were transplanted into the livers of CD26-deficient rats. Cell proliferation and the expression of hepatocyte-specific markers were determined before and after transplantation. Cell number increased threefold over a culture period of 10 days. The expression of connexin 32 and phosphoenolpyruvate carboxykinase declined over time, indicating the loss of hepatocyte-specific functions. Hepatocytes cultured over 4 or 7 days and then transplanted proliferated in the host parenchyma. The transplanted cells expressed connexin 32, cytokeratin 18, and phosphoenolpyruvate carboxykinase, indicating the differentiated phenotype. The loss of hepatocyte-specific functions during culture may be restored after transplantation, suggesting that the proper physiological environment is required to maintain the differentiated phenotype.     

p27Kip1 inactivation provides a proliferative advantage to transplanted hepatocytes in DPPIV/Rag2 double knockout mice after repeated host liver injury

Studies were conducted to develop a new DPPIV(-/-)/Rag2(-/-) mouse model for hepatocyte transplantation by allogeneic and xenogeneic cells and to compare the proliferative capacity of p27 null hepatocytes versus normal hepatocytes in this system. Dipeptidyl peptidase IV (DPPIV) gene knockout mice, in which wild-type (wt) DPPIV+ donor hepatocytes can be readily identified by enzyme histochemistry, were bred with Rag2 null mice to prepare immunotolerant DPPIV(-/-)/Rag2(-/-) double knockout mice. DPPIV(-/-)/Rag(-/-) mice were transplanted with wt hepatocytes or p27 null mouse hepatocytes, which show enhanced cell cycle activity due to disruption of the Kip1 cyclin kinase inhibitor gene, and liver repopulation was assessed under nonproliferative versus proliferative experimental conditions. After their initial engraftment, transplanted wt hepatocytes did not proliferate in untreated livers or increase significantly in response to an acute liver regenerative stimulus. p27 null hepatocytes engrafted with the same efficiency as wt hepatocytes, but showed a noticeable, although not statistically significant, increase in proliferation in response to partial hepatectomy or acute CCl4 administration. Repeated treatments with CCl4 substantially increased proliferation and liver repopulation by p27 null hepatocytes but not by wt hepatocytes. These results suggest that p27 gene inactivation does not overcome proliferative restrictions imposed on hepatocytes by the normal liver, but that after repeated episodes of toxic liver injury, the augmented proliferative capacity of p27 null hepatocytes leads to significant liver repopulation compared with wt hepatocytes. These properties of p27-deficient hepatocytes could prove useful as a target for liver repopulation in patients with intermittent or a low level of chronic liver injury.     

Liver tissue engineering utilizing hepatocytes propagated in mouse livers in vivo

Recent advances in tissue engineering technologies have highlighted the ability to create functional liver systems using isolated hepatocytes in vivo. Considering the serious shortage of donor livers that can be used for hepatocyte isolation, it has remained imperative to establish a hepatocyte propagation protocol to provide highly efficient cell recovery allowing for subsequent tissue engineering procedures. Donor primary hepatocytes were isolated from human α-1 antitrypsin (hA1AT) transgenic mice and were transplanted into the recipient liver of urokinase-type plasminogen activator-severe combined immunodeficiency (uPA/SCID) mice. Transplanted donor hepatocytes actively proliferated within the recipient liver of the uPA/SCID mice. At week 8 or later, full repopulation of the uPA/SCID livers with the transplanted hA1AT hepatocytes were confirmed by blood examination and histological assessment. Proliferated hA1AT hepatocytes were recovered from the recipient uPA/SCID mice, and we generated hepatocyte sheets using these recovered hepatocytes for subsequent transplantation into the subcutaneous space of mice. Stable persistency of the subcutaneously engineered liver tissues was confirmed for up to 90 days, which was the length of our present study. These new data demonstrate the feasibility in propagating murine hepatocytes prior to the development of hepatic cells and bioengineered liver systems. The ability to regenerate and expand hepatocytes has potential clinical value whereby procurement of small amounts of tissue could be expanded to sufficient quantities prior to their use in hepatocyte transplantation or other hepatocyte-based therapies.     

Growth ability and repopulation efficiency of transplanted hepatic stem cells, progenitor cells, and mature hepatocytes in retrorsine-treated rat livers

Cell-based therapies as an alternative to liver transplantation have been anticipated for the treatment of potentially fatal liver diseases. Not only mature hepatocytes (MHs) but also hepatic stem/progenitor cells are considered as candidate cell sources. However, whether the stem/progenitor cells have an advantage to engraft and repopulate the recipient liver compared with MHs has not been comprehensively assessed. Therefore, we used Thy1(+) (oval) and CD44(+) (small hepatocytes) cells isolated from GalN-treated rat livers as hepatic stem and progenitor cells, respectively. Cells from dipeptidylpeptidase IV (DPPIV)(+) rat livers were transplanted into DPPIV(-) livers treated with retrorsine following partial hepatectomy. Both stem and progenitor cells could differentiate into hepatocytes in host livers. In addition, the growth of the progenitor cells was faster than that of MHs until days 14. However, their repopulation efficiency in the long term was very low, since the survival period of the progenitor cells was much shorter than that of MHs. Most foci derived from Thy1(+) cells disappeared within 2 months. Many cells expressed senescence-associated β-galactosidase in 33% of CD44-derived foci at day 60, whereas the expression was observed in 13% of MH-derived ones. The short life of the cells may be due to their cellular senescence. On the other hand, the incorporation of sinusoidal endothelial cells into foci and sinusoid formation, which might be correlated to hepatic maturation, was completed faster in MH-derived foci than in CD44-derived ones. The survival of donor cells may have a close relation to not only early integration into hepatic plates but also the differentiated state of the cells at the time of transplantation.     

Transplantation of isolated hepatocytes, is it an alternative for total liver transplantation? On the treatment of hereditary hepatic metabolic diseases

Since 1976, it has been demonstrated in the small animal that isolated hepatocytes transferred into the liver can integrate into the recipient organ, survive and perform differentiated functions. This cell therapy technique can be used to partially correct for hereditary metabolic disorders in animal models of human hereditary metabolic diseases. The first methods used for hepatocytes transplantation involved a mass of hepatocytes that was clearly to limited (about 0.5% and never more than 2%). Integration fo the hepathocytes was limited by poorly understood factors. The vary variable clinicial results in the eight trials performed in the 90s is a clear demonstration. Recent work has helped understand the mechanisms limiting the integration of transplanted hepatocytes in the recipient liver. This led to the concept of repopulation, increasing the percentage of the hepatocyte mass reconstituted during the transplantation. The goal is to give the transplanted hepatocytes a proliferation advantage over he native hepatocytes. Several models have been designed and are currently being evaluated for application in humans. We are not far from new clinical trials with hepatocyte transplantation in humans for the treatment hereditary metabolic diseases. For certain disease, 3 to 5% normally functioning hepatocytes in the recipient liver would be sufficient to achieve a clinically significant effect for the patient.     

A simple and effective method to improve intrasplenic rat hepatocyte transplantation

Transplanted hepatocytes integrate, survive, and express their specific functions in the liver parenchyma. The aim of this study was to determine whether a large number of hepatocytes could move from the spleen to the liver when the cells are injected together with sodium nitroprusside, and if the improved hepatocyte migration may be related with portal vein dilatation. Wistar rats were transplanted in the spleen with fluorescent-labeled hepatocytes alone or together with sodium nitroprusside. At 1, 3, 6, and 24 h after the transplant, the liver from recipient animals was removed and morphometric analyses were performed. Portal and arterial pressures were also measured immediately after intrasplenic injection of a solution of sodium nitroprusside, hepatocytes alone, or hepatocytes plus sodium nitroprusside. Intrasplenically injected sodium nitroprusside produced a transient drop in arterial pressure and a sustained reduction in portal pressure. During hepatocyte transplantation it increased the number of transplanted cells migrating to the liver after 3 h. Sodium nitroprusside simultaneously injected with hepatocytes in the spleen allowed more cells to migrate into the liver of the host animal without risk in animal survival.     

Transplantation of liver organoids in the omentum and kidney

Liver organoids were reconstructed by mouse-immortalized hepatocytes and nonparenchymal cells (sinusoidal endothelial cells and hepatic stellate cells) in a radial-flow bioreactor (RFB). A biodegradable apatite-fiber scaffold (AFS) was used as a scaffold packed in the RFB, which enables three-dimensional cell cultures. The organoids cocultured in the RFB showed a liver-like structure with high-density layers of hepatocytes and the formation of vessel-like structures. A liver organoid consisting of three cocultured cells was transplanted under the kidney capsule (kidney group) or into the omentum (omentum group) using BALB/c nude mice. Transplanted liver organoids survived in the kidney or omentum. The expression of mRNAs of albumin, connexin 26 and 32, hepatocyte nuclear factor 4α, and glucose-6-phosphatase was increased in both groups at 8 weeks after transplantation in comparison to the pretransplant status. Tyrosine aminotransferase appeared only in the omentum group. The results suggested that the functions of liver organoids differed depending on the transplanted site in the recipient animals.     

Hepatocyte transplantation through the hepatic vein: a new route of cell transplantation to the liver

The efficiency of hepatocyte transplantation into the liver varies with the method of administration. This study investigated whether retrograde infusion via the hepatic vein provides a sufficient number of donor cells for the liver. Donor hepatocytes were isolated from dipeptidyl peptidase IV (DPPIV(+)) rats and transplanted into DPPIV(-) rat livers either by antegrade portal vein infusion or retrograde hepatic vein infusion. Hepatocyte engraftment ratios and localization were evaluated by histological DPPIV enzymatic staining at 1 week and 8 weeks after the transplantation. No significant differences in engraftment efficiency were observed at either 1 week or 8 weeks after transplantation by either route. However, the localization of the transplanted hepatocytes differed with the administration route. Portal vein infusion resulted in predominantly periportal engraftment, whereas hepatic vein infusion led to pericentral zone engraftment. Immunohistochemical analysis showed that the transplanted hepatocytes engrafted in the pericentral zone after retrograde infusion displayed intense CYP2E1 staining similar to the surrounding native hepatocytes. CYP2E1 staining was further enhanced by administration of isosafrole, an inducing agent for various cytochrome P450 enzymes, including CYP2E1. This study demonstrates a novel approach of transplanting hepatocytes into the liver through retrograde hepatic vein infusion as the means to target cell implantation to the pericentral zone.     

Liver repopulation after cell transplantation in mice treated with retrorsine and carbon tetrachloride

BACKGROUND: Efficiency of engraftment after liver cell transplantation is less than 1% under conventional conditions. Our aim was to develop a high-efficiency, nonsurgical, no-genetic-advantage mouse model of liver repopulation with transplanted cells. METHODS: Mice were conditioned with nonlethal doses of a cell cycle inhibitor, retrorsine, 70 mg/kg, to irreversibly block proliferation of native hepatocytes. After the drug was eliminated, 2 million freshly isolated beta-galactosidase-labeled liver cells were transplanted into the spleens of C57BL/6J recipient mice. To stimulate donor cell proliferation, three doses of carbon tetrachloride (CCl4), 0.5 ml/kg, were given. Several control groups were studied to evaluate the contribution of each treatment to liver repopulation. RESULTS: Repopulation, as measured by cell isolation from recipient livers 1-7 months after transplantation, was on average 20%. Repopulation was 10% if CCl4 was given only once, between 0.5% and 1% if only retrorsine or CCl4 were used, and 0.05% if no conditioning was used. Phenotypically, whole livers turned blue on exposure to X-gal staining, whereas negative (control) livers remained pale brown. More than 55% of liver repopulation resulted from clusters containing 21 or more cells, some of which contained more than 200 cells, suggesting seven or more rounds of cell division in a subset of transplanted cells. CONCLUSION: This murine study demonstrates high levels of repopulation after liver cell transplantation into nongenetically modified livers, using a cell cycle inhibitor and chemical liver injury to provide transplanted cells a proliferative advantage. Liver repopulation was effected mostly by a small fraction of transplanted cells. Analogous nonsurgical liver cell transplantation strategies, but with clinically applicable drugs, could be devised for the treatment of liver-based metabolic diseases.     

Construction of liver tissue in vivo with preparative partial hepatic irradiation and growth stimulus: investigations of less invasive techniques and progenitor cells

Background

The selective proliferation of transplanted hepatocytes with a growth stimulus, such as partial hepatectomy or hepatocyte growth factor, concomitant with hepatic irradiation (HIR), which can suppress proliferation of host hepatocytes, has been reported. We have conducted experiments that focused on less invasive and clinically applicable techniques and progenitor cells.

Materials and methods

First, dipeptidyl-peptidase IV-F344 or jaundiced Gunn rats underwent partial HIR (only 30% of whole liver) and portal vein branch ligation (PVBL) of one lobe, followed by intrasplenic hepatocyte transplantation at 1 × 10⁷. Second, after partial HIR and PVBL, two types of progenitor cells were transplanted (i.e., small hepatocytes (SHs) or adipose-derived mesenchymal stem cells.

Results

Sixteen weeks after transplantation, the donor cells constituted > 70% of the hepatocytes of the irradiated lobe, showing connexin 32, phosphoenolpyruvate carboxykinase-1, and glycogen storage. Moreover, the serum bilirubin level had decreased significantly in the jaundiced Gunn rats and remained at this level throughout the 24 wk experimental period. The SHs grew more quickly than the hepatocytes. After 8 wk, around 40% of the host hepatocytes had been replaced by transplanted SHs. Although the donor adipose-derived mesenchymal cells were engrafted after 8 wk, their proliferation was not observed.

Conclusions

HIR, combined with PVBL, can be given to a selective liver lobe and is a less-invasive but effective method for proliferation of transplanted hepatocytes. Even a smaller number of SHs can construct liver tissue with their prevailing proliferative ability.     

Regulation of hepatocyte engraftment and proliferation after cytotoxic drug-induced perturbation of the rat liver

BACKGROUND: Perturbations in specific liver cell compartments benefit transplanted cell engraftment and/or proliferation. We analyzed whether cytotoxic drugs interfering with the integrity of genomic DNA or cell division could be useful for liver cell transplantation. METHODS: We used dipeptidyl peptidase IV deficient (DPPIV-) rats as recipients of syngeneic F344 rat hepatocytes. Rats were pretreated with doxorubicin, irinotecan, or vincristine prior to cell transplantation and synergistic liver perturbations were induced by drug administration followed by partial hepatectomy or carbon tetrachloride treatments. Transplanted cells were identified by DPPIV histochemistry and cell engraftment and proliferation were analyzed morphometrically. Perturbations in endothelial, Kupffer cell, and hepatocyte compartments were analyzed by electron microscopy, carbon incorporation, and blood tests, respectively. RESULTS: Cell engraftment was improved in rats treated with doxorubicin but not with irinotecan or vincristine. Doxorubicin disrupted endothelial cells for up to seven days without causing Kupffer cell or hepatocellular toxicity. Neither doxorubicin nor vincristine induced liver repopulation in animals up to three months, including after partial hepatectomy or carbon tetrachloride-induced additional liver injury. CONCLUSIONS: Doxorubicin-induced hepatic endothelial damage enhanced cell engraftment, which should be useful in cell therapy strategies.     

Transplanted fetal cardiomyocytes as cardiac pacemaker.

BACKGROUND: While morphologic integration of transplanted fetal cardiomyocytes into the ventricular myocardium is a well-known fact, no studies have yet shown transplanted cells to coherently contribute to contraction and electrical excitation of the host myocardium. The aim of this study was to prove the hypothesis that by transplanting cardiomyocytes with a higher intrinsic rhythmic rate into the myocardium of the left ventricle, these cells could act as an ectopic pacemaker by functional coupling with host cardiomyocytes. METHODS AND RESULTS: Dissociated fetal canine atrial cardiomyocytes including sinus nodal cells were delivered into the free wall of the left ventricle of adult canine X-linked muscular dystrophy dogs (n=2). These dogs fail to express Dystrophin in both cardiac and skeletal muscle. In the control group (n=2) fetal skin fibroblasts were used for grafting. A total of 3-4 weeks after transplantation the dogs underwent catheter ablation of the atrioventricular node (AV-node) and subsequent electrophysiological mapping studies. Transplanted cells were identified by Dystrophin immunoreactivity, indicating survival and morphological integration in the recipient heart. The expression of Connexin 43 between donor and recipient cells suggested formation of gap junctions between injected and host cardiomyocytes. After catheter ablation of the AV-node, a ventricular escape rhythm emerged driving the pace of the heart and originating from the labeled transplantation site. This effect could not be observed in the control group (n=2). CONCLUSIONS: The results constitute the first observation of phenomena indicating electrical and mechanical coupling between allogeneic donor cardiomyocytes and recipient myocardium in-vivo. Further experiments are necessary to evaluate the technique as a potential therapy for atrioventricular block.     

HVEGF165 increases survival of transplanted hepatocytes within portal radicles: suggested mechanism for early cell engraftment

VEGF is a potent angiogenic factor that promotes hepatocyte growth, increases permeability of blood vessels, and induces vasodilatation, and may accelerate engraftment and function of transplanted hepatocytes. The aim was to study the effect of VEGF on early hepatocyte engraftment. Thirty-two Lewis syngeneic female rats underwent 70% partial hepatectomy. Eighteen received 240 ng VEGF165 and 14 received saline for control. Thereafter, intrasplenic transplantation of 10(7) male hepatocytes was done. Semiquantitative analysis of PCR product of the SRY region of the Y-chromosome was performed. Paraffin-embedded sections were stained for H&E and for PCNA immunostaining. By PCR, male hepatocytes were identified in 8 livers out of 14 VEGF-treated rats at 24-48 h, compared with only 1 liver out of 8 controls. Transplanted cells were seen within portal vessels radicles in 7 out of 14 VEGF-treated rats for as long as 48 h posttransplantation, compared with only one control liver at 24 h. There was no histological sign of cell injury to transplanted or adjacent cells. Two weeks after transplantation male transplanted cells were identified in two out of four rats treated with hVEGF165 and in one out of six rats treated with saline. No transplanted cells were detected within portal tracts 14 days after transplantation. hVEGF165 enhances the presence of transplanted hepatocytes within portal vessels after transplantation. We suggest an additional mechanism for cell engraftment, whereby transplanted hepatocytes first stick to each other in the portal radicles. Later they become included in the liver parenchyma as groups of organized cells in a process stimulated by VEGF.     

Selective repopulation of mice liver after Fas-resistant hepatocyte transplantation

Hepatocyte transplantation has been proposed as a potential therapeutic method to treat irreversible liver failure and inherited hepatic disorders, although transplanted cells do not easily reconstruct the liver tissue under intact conditions. This study was aimed at modulating the recipient liver conditions to promote repopulation of the liver after hepatocyte transplantation. Hepatocytes isolated from male MRL-lpr/lpr (lpr) mice with a mutation of Fas antigen were transplanted in a number of 1 x 10(6) cells in female MRL-+/+ (wild-type mice) by intrasplenic injection. An agonistic anti-Fas antibody (0.15 mg/kg) was administered intravenously 24 h after cell transplantation. We also administrated the antibody at 0.3 mg/kg 1 week after grafting and at 0.6 mg/kg 2 weeks after transplantation. The liver specimens were taken at different time intervals for histological examination. The reconstructed male lpr hepatocytes in the female wild-type mice were determined by a real-time quantitative PCR assay using the primers and probe for the sry gene. The pathologic findings of the recipient livers after treatment with anti-Fas antibody revealed a large number of apoptotic hepatocytes. The grafted lpr hepatocytes were observed to reconstruct as much as 6.9% of the recipient liver in the anti-Fas antibody-treated group 3 months after transplantation. In contrast, we observed the transplanted cells at lower than 0.1% in the nontreated livers. These findings demonstrated that repeated induction of apoptosis in recipient hepatocytes shifts the environment of the liver to a regenerative condition. This method may be useful to promote the reconstruction of transplanted hepatocytes in a recipient liver.     

Amplification of engrafted hepatocytes by preparative manipulation of the host liver

Scarcity of donor livers is a major obstacle to the general application of hepatocytes for the development of bioartificial liver assist devices as well as intracorporeal engraftment of hepatocytes for the treatment of inherited metabolic diseases. The number of hepatocytes that can be transplanted into the liver safely in a single sitting also limits the utility of this procedure. These limitations could be addressed by providing preferential proliferative advantage to the transplanted cells. Studies using transgenic mouse recipients or donors have indicated that massive repopulation of the host liver by engrafted hepatocytes requires that the transplanted cells are subjected to a proliferative stimulus to which the host hepatocytes cannot respond. Prevention of host hepatocyte proliferation has been achieved by treatment with a plant alkaloid, retrorsine. Because retrorsine is carcinogenic, we have evaluated preparative irradiation for this purpose. The proliferative stimulus may consist of the loss of hepatic mass (e.g., partial hepatectomy, reperfusion injury or induction of Fas-mediated apoptosis by gene transfer) or administration of stimulants of hepatocellular mitosis (e.g., growth factors or thyroid hormone). Potential applications of these preparative manipulations of the host liver include the treatment of inherited metabolic disorders by transplantation of allogeneic hepatocytes, hepatocyte-mediated ex vivo gene therapy, rescuing liver cancer patients from radiation-induced liver damage, and expansion of human hepatocytes in animal livers.     

Hepatocyte transplantation

Numerous laboratory studies have shown that hepatocyte transplantation may serve as an alternative to organ transplantation for patients with life-threatening liver disease. Because of the successes of experimental hepatocyte transplantation, institutions have attempted to use this therapy in the clinic for the treatment of a variety of hepatic diseases. Unfortunately, unequivocal evidence of transplanted human hepatocyte function has been obtained in only one patient with Crigler-Najjar syndrome type I, and, even then, the amount of bilirubin-UGT enzyme activity derived from the transplanted cells was not sufficient to eliminate the patient's eventual need for organ transplantation. A roadmap for improving patient outcome following hepatocyte transplantation can be obtained by a re-examination of previous animal research. A better understanding of the factors that allow hepatocyte integration and survival in the liver and spleen is needed to help reduce the need for repeated cell infusions and multiple donors. Although clinical evidence of hepatocyte function can be used to indicate function of transplanted hepatocytes, definitive histologic evidence is difficult to obtain. In order to assess whether rejection is taking place in a timely fashion, a reliable way of detecting donor hepatocytes will be needed. The most important issue affecting transplantation, however, relates to donor availability. Alternatives to the transplantation of allogeneic human hepatocytes include transplantation of hepatocytes derived from fetal, adult or embryonic stem cells, engineered immortalized cells, or hepatocytes derived from other animal species.     

Bipotential properties and proliferation of fetal liver epithelial progenitor cells in mice

The potential of embryonal day 14 (ED) fetal liver epithelial progenitor (FLEP) cells to repopulate the normal and damaged liver was studied throughout a 3-month period in syngeneic mice. In normal liver, FLEP cells proliferated and differentiated into hepatocytes after transplantation, and liver repopulation was moderate (5%-10%) after 3 months. In diethylnitrosamine-treated livers FLEP cells continued to proliferate at 3 months after transplantation; both the number and size of clusters derived from FLEP cells gradually increased throughout time. Transplanted cells proliferated and differentiated into both hepatocytes and bile ducts to produce extensive liver repopulation (30%-50%). This report showed that isolated fetal liver epithelial cells exhibit bipotential properties of stem cells, which can engraft, proliferate, and differentiate into hepatocytes and bile duct epithelial cells with high repopulation capacity in the injured liver.