A novel strategy for in vivo expansion of transplanted hepatocytes using preparative hepatic irradiation and FasL-induced hepatocellular apoptosis

Hepatocyte Transplantation: Quo Vadis?

Orthotopic liver transplantation (OLT) has been effective in managing end-stage liver disease since the advent of cyclosporine immunosuppression therapy in 1980. The major limitations of OLT are organ supply, monetary cost, and the burden of lifelong immunosuppression. Hepatocyte transplantation, as a substitute for OLT, has been an exciting topic of investigation for several decades. HT is potentially minimally invasive and can serve as a vehicle for delivery of personalized medicine through autologous cell transplant after modification ex vivo. However, 3 major hurdles have prevented large-scale clinical application: (1) availability of transplantable cells; (2) safe and efficient ex vivo gene therapy methods; and (3) engraftment and repopulation efficiency. This review will discuss new sources for transplantable liver cells obtained by lineage reprogramming, clinically acceptable methods of genetic manipulation, and the development of hepatic irradiation-based preparative regimens for enhancing engraftment and repopulation of transplanted hepatocytes. We will also review the results of the first 3 patients with genetic liver disorders who underwent preparative hepatic irradiation before hepatocyte transplantation.

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 × 10(7). 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.

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.

Efficacy and limitation of bone marrow transplantation in the treatment of acute and subacute liver failure in rats

AIM

Recent reports have shown that bone marrow cells (BMC) retain the potential to differentiate into hepatocytes. Thus, the BMC have been recognized as an attractive source for liver regenerative medicine. However, it has not been clarified whether BMC transplantation can be used to treat liver damage in vivo. In the present study, we explored whether BMC possess therapeutic potential to treat acute and/or subacute liver failure.

METHODS

Fulminant hepatic failure (FHF) was induced by 70% hepatectomy with ligation of the right lobe pedicle (24% liver mass), followed by transplantation of BMC into the spleen. Dipeptidyl peptidase IV-positive (DPPIV(+)) BMC were then transplanted into DPPIV-negative (DPPIV(-)) recipients following hepatic irradiation (HIR) in which 70% of the liver was resected and the remnant liver irradiated.

RESULTS

There was no benefit of BMC transplantation towards survival in the FHF model. DPPIV(+) hepatocytes appeared in the liver tissues of the DPPIV(-) HIR model rats, but DPPIV(+) hepatocytes replaced less than 13% of the recipient liver.

CONCLUSION

BMC transplantation may have limitations in the treatment of fulminant or acute liver failure because they do not have sufficient time to develop into functional hepatocytes. Preparative HIR may be beneficial in help to convert the transplanted BMC into host hepatocytes, and provide a survival benefit. Although, However, the precise mechanism warrants further studies.

Hepatic irradiation augments engraftment of donor cells following hepatocyte transplantation

Engraftment of donor hepatocytes is a critical step that determines the success of hepatocyte transplantation. Rapid and efficient integration of donor cells would enable prompt liver repopulation of these cells in response to selective proliferative stimuli offered by a preparative regimen. We have earlier demonstrated that hepatic irradiation (HIR) in combination with a variety of hepatotrophic growth signals, such as partial hepatectomy and hepatocyte growth factor, can be used as a preparative regimen for liver repopulation of transplanted hepatocytes. In this study, we investigated the effects of HIR on engraftment of transplanted dipeptidyl peptidase IV (DPPIV)-positive hepatocytes in congeneic DPPIV-deficient rats. HIR-induced apoptosis of hepatic sinusoidal endothelial cells (SEC) within 6 hours of HIR resulted in dehiscence of the SEC lining in 24 hours. Although there was no change of the number of Kupffer cells after HIR, colloidal carbon clearance decreased 24 hours post HIR, indicating a suppression of phagocytic function. DPPIV+ donor cells were transplanted 24 hours after HIR (0-50 Gy). There was an HIR dose-dependent increase in the donor hepatocyte mass engrafted in the liver parenchyma. The number of viable transplanted hepatocytes present in hepatic sinusoids or integrated in the parenchyma was greater in the HIR-treated group at 3 and 7 days after transplantation compared with the sham controls. Finally, we validated these rodent studies in cynomolgus monkeys, demonstrating that a single 10-Gy dose of HIR was sufficient to enhance engraftment of donor porcine hepatocytes. These data indicate that transient disruption of the SEC barrier and inhibition of the phagocytic function of Kupffer cells by HIR enhances hepatocyte engraftment and the integrated donor cell mass. Thus, preparative HIR could be potentially useful to augment hepatocyte transplantation.

Correction of hyperoxaluria by liver repopulation with hepatocytes in a mouse model of primary hyperoxaluria type-1

BACKGROUND

Primary hyperoxaluria type-1 (PH1) is an autosomal recessive disease characterized by excessive oxalate production by hepatocytes caused by the deficiency of peroxisomal alanine-glyoxylate aminotransferase (AGT) activity. Persistent hyperoxaluria causes nephrocalcinosis and urolithiasis, leading to renal failure, followed by tissue oxalosis with life-threatening complications. Combined liver-kidney transplantation is the only definitive treatment of PH1. Hepatocyte transplantation, which is much less invasive, could have offered an attractive alternative. However, because the AGT-deficient hepatocytes overproduce oxalate, a large fraction of the mutant host hepatocytes must be replaced by AGT-competent cells, which is beyond the capacity of current hepatocyte transplantation procedures. Here, we have evaluated a preparative irradiation-based method of liver repopulation in an Agxt-deleted mouse model of PH1 (Agxt-/-).

MATERIALS AND METHODS

Hepatocytes (10(6) viable cells) isolated from congeneic mice ([ROSA]26 C57BL/6J) expressing Escherichia coli beta-galactosidase were transplanted into Agxt-/- mice by intrasplenic injection. The preparative regimen consisted of X-irradiation of the host liver and mitotic stimulation of the hepatocytes by adenovector-based expression of hepatocyte growth factor.

RESULTS

The procedure resulted in progressive replacement of the mutant host hepatocytes with the AGT-competent hepatocytes, leading to correction of urinary oxalate excretion. Oral ethylene glycol challenge (0.7% for 1 week) resulted in nephrocalcinosis and microlithiasis in untreated Agxt-/- mice, but not in the mice after hepatic repopulation.

CONCLUSION

The results indicate that hepatocyte transplantation after appropriate preparative regimens may permit sufficient repopulation of the liver to ameliorate hyperoxaluria, and therefore should be evaluated further as a potential treatment of PH1.

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

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

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.

Ex vivo lentivirus transduction and immediate transplantation of uncultured hepatocytes for treating hyperbilirubinemic Gunn rat

BACKGROUND

Ex vivo liver gene therapy provides an attractive alternative to orthotopic liver transplantation for the treatment of liver diseases. We previously reported a protocol in which human primary hepatocytes are highly transduced in Suspension with Lentiviral vectors and Immediately Transplanted (SLIT). Here, we evaluated the SLIT approach in Gunn rats, the animal model for Crigler-Najjar syndrome type 1, a defect in bilirubin UDP-glucuronosyltransferase (BUGT).

METHODS

We constructed lentiviral vectors coding for BUGT under control of an ubiquitous promoter. Control vectors contained Green Fluorescent Protein (GFP) under control of the same promoter. Hepatocytes were isolated from jaundiced Gunn rats and transduced in suspension for four hr. After washing, 2x10 hepatocytes were immediately transplanted into syngeneic rats. Bilirubinemia and bile pigments were regularly assessed after cell transplantation. The percentage and presence of transduced hepatocytes was analyzed by immunohistochemistry in GFP-transplanted animals.

RESULTS

In rats receiving BUGT-transduced hepatocytes, bilirubinemia decreased by about 30%. The level of correction remained stable for up to 240 days. Bilirubin glucuronides were present in the bile of treated animals, indicating the metabolic activity of engrafted hepatocytes. In contrast, bilirubinemia in GFP-transplanted rats did not decline but rather increased. GFP-positive hepatocytes amounted to 0.5-1% of the liver, which is in agreement with the number of transplanted and genetically-modified hepatocytes (6x10).

CONCLUSIONS

This work reports the first demonstration of long-term metabolic benefit after rapid transplantation of ex vivo lentivirally tranduced hepatocytes. Therefore, this study demonstrates the therapeutic proof-of-principle and potential of the SLIT approach for treating inherited metabolic liver diseases.

Noninvasive evaluation of liver repopulation by transplanted hepatocytes using 31P MRS imaging in mice

Hepatocyte transplantation (HT) is being explored as a substitute for liver transplantation for the treatment of liver diseases. For the clinical application of HT, a preparative regimen that allows preferential proliferation of transplanted cells in the host liver and a noninvasive method to monitor donor cell engraftment, proliferation, and immune rejection would be useful. We describe an imaging method that employs the creatine kinase (CK) gene as a marker of donor hepatocytes. Creatine kinase is unique among marker genes, because it is normally expressed in brain and muscle tissues and is therefore not immunogenic. Preferential proliferation of transplanted CK-expressing hepatocytes was induced by preparative hepatic irradiation and expression of hepatocyte growth factor using a recombinant adenoviral vector. CK is normally not expressed in mouse liver and its expression by the donor cells led to the production of phosphocreatine in the host liver, permitting (31)P magnetic resonance spectroscopic imaging of liver repopulation by engrafted hepatocytes. In conclusion, this study combined a noninvasive imaging technique to assess donor hepatocyte proliferation with a preparative regimen of partial liver irradiation that allowed regional repopulation of the host liver. Our results provide groundwork for future development of clinical protocols for HT.

Prolonged survival of mice with acute liver failure with transplantation of monkey hepatocytes cultured with an antiapoptotic pentapeptide V5

BACKGROUND

Because hepatocyte transplantation has been considered to be an attractive method to treat acute liver failure (ALF), efficient recovery of hepatocytes and maintenance of differentiated hepatocyte functions is of extreme importance. We here report the usefulness of an antiapoptotic pentapeptide V5, composed of Val-Pro-Met-Leu-Lys, in the monkey hepatocyte cultures.

METHODS

We evaluated albumin production, metabolizing abilities of ammonia, lidocaine, and diazepam of monkey hepatocytes cultured with V5. The protein expression of apoptosis-associated molecules was analyzed using power blot analysis. An unwoven cloth inoculated with V5-treated monkey hepatocytes was transplanted on the surface of the spleen of both SCID mice and Balb/c mice suffering from ALF induced by 90% hepatectomy.

RESULTS

When 100 microM V5 was utilized, ammonia-, lidocaine- and diazepam- metabolizing capacities and albumin production ability were significantly increased in V5-treated monkey hepatocytes. Such hepatocytes showed decreased Annexin V binding and increased the expression of anti-apoptotic and/or cytoprotective molecules, including Ku70, NF-kappaB, IKAP, hILP/XIAP, IkappaB, and CAS. Transplantation of the cloth containing the monkey hepatocytes significantly improved blood levels of glucose and ammonia and encephalopathy score and prolonged the survival of the mice with ALF.

CONCLUSIONS

The present work clearly demonstrates the usefulness of V5 for maintaining the functions of monkey hepatocytes in tissue culture.

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.

Liver repopulation and long-term function of rat small hepatocyte transplantation as an alternative cell source for hepatocyte transplantation

Hepatocyte transplantation (HT) is an attractive therapeutic modality for liver disease as an alternative for liver organ transplantation. Primary fresh hepatocytes (FHs) are the exclusive cell source that has been used for clinical HT. However, the use of FHs is limited due to a shortage of donor cells. Small hepatocytes (SHs) are hepatic progenitor cells and can be isolated not only from rodents but also from humans. SHs can proliferate in vitro and express liver functions, although conventional hepatocytes lose them within a short period after culture. SH functions in vivo have never been studied. We therefore investigated HT using SHs to evaluate cell engraftment and function compared to HT using FHs. The donor cell number in the SH group was smaller than that in the FH group at HT. The cell engraftment in the SH group was smaller in the liver and larger in the spleen than in the FH group. The cell engraftment in the liver increased after HT; however, that in the spleen decreased after HT in both groups. HT using SHs supported the serum albumin level in the NAR experiment as well as that using FH, and albumin mRNA was detectable in the recipients' tissues at 12 weeks after HT. In conclusion, HT using SHs showed hepatic repopulation similar to that using FHs. This suggests that both SHs and FHs can repopulate the liver as if they were hepatic stem cells. In addition, HT using SHs supported liver functions such as albumin correction at the same level as that using FHs. These observations strongly support the idea that SHs could be an alternative to primary FHs as a novel cell source for future HT.

Functional hepatocyte culture and its application to cell therapies

Since Berry and Friend developed methods to isolate hepatocytes from the liver by a collagenase digestion technique in 1969, studies in laboratory animals have demonstrated that hepatocyte transplantation could potentially be used for the treatment of liver failure and inborn errors of liver-based metabolism. Healthy human hepatocytes are an ideal source for hepatocyte transplantation; however, their relative scarcity is one of the major drawbacks, further compounded by the competing demands of liver transplantation. Notably, most of the hepatocytes are isolated from discarded livers that are not suitable for organ transplantation for a variety of reasons, including excessive fat content. Importantly, the hepatocyte isolation procedure itself exerts major stress on hepatocytes by the disruption of cell-to-cell and cell-to-matrix contacts, resulting in hepatocytic apoptosis. Prevention of apoptosis would maximize yield of healthy cells and maintain hepatocyte differentiated function in culture. In this review, we describe methods to prevent apoptosis by utilizing both antiapoptotic molecules and matrices. We also introduce a new type of liver tissue engineering, hepatocyte sheet transplantation, which utilizes unwoven cloth having a cellular adhesive property.

Liver allograft radiotherapy to treat rejection in children: efficacy in orthotopic liver transplantation and long-term safety

BACKGROUND

We studied, retrospectively, the efficacy to control rejection and long-term safety of liver allograft radiotherapy (RT) performed in 14 children. Long-term safety data were collected with the prospect of possible use of RT in liver cell transplantation (LCT).

METHODS

Immune suppression included cyclosporine, azathioprine and prednisone. In case of intractable rejection, low-dose allograft RT was administered daily for 3 days, and short-term efficacy was evaluated by liver enzyme assays and histology. The long-term outcome was compared with that of 122 patients undergone transplantation and who had similar treatment, but no RT.

RESULTS

Survival at 15 years was 71.4% vs 69.7% in the comparison group. In the RT group, rejection control was complete in six of 14 children and partial in two, all being alive and well 14-18 years later. Ten of 14 children had follow-up biopsy. Six children had normal histology and four had mild unspecific fibrosis. The long-term follow-up biopsy in the comparison group showed fibrosis in 42 of 85 children. The incidence of complications was similar in both groups.

CONCLUSIONS

This series shows that, such a RT regimen appeared to be efficient and safe as a rescue treatment for acute rejection. Provided that further investigations in animal models show a certain benefit of low-dose irradiation around LCT, such a regimen could be proposed in human liver cell transplant programmes.

Feasibility of hepatocyte transplantation-based therapies for primary hyperoxalurias

Primary hyperoxalurias (PHs) are diseases caused by overproduction of oxalate by hepatocytes. Most patients with PHs develop nephrocalcinosis and renal failure. Combined liver-kidney transplantation is often used as a definitive treatment of PHs, but because of a large body oxalate load at the time of transplantation, the procedure is not always successful. Because all hepatocytes overproduce oxalate, partial liver replacement procedures, such as auxiliary transplantation of a liver lobe or hepatocyte transplantation are not expected to be useful in this disorder. In this paper we describe novel techniques, based on preparative hepatic irradiation and stimulation of hepatocyte mitosis, through loss of liver mass or administration of hepatic growth factor, which permit transplanted wild-type hepatocytes to massively repopulate the liver, replacing up to 90% of the hepatocytes in recipient mouse livers. Application of this procedure in a recently developed Agxt-gene-deleted mouse model of PH1 resulted in marked amelioration of hyperoxaluria. We propose that further refinement of the different components of this procedure may permit early cell-based therapies of PHs, thereby preventing renal failure and its complications.

Hepatocyte transplantation for total liver repopulation

Hepatocyte transplantation (HT) is an attractive therapeutic alternative to liver transplantation. A number of experiments have shown the feasibility of total liver parenchymal cell replacement by transplanted hepatocytes. In this review, we would like to highlight researches and clinical reports of HT for liver repopulation. Cellular source of clinical HT should be safety. Immortalized cells, hepatic stem cells, and other stem cells have been used for an experimental model for HT. The exact mechanism of the cell engraftment after HT has not been completely understood, although there were some markers to detect and investigate transplanted cells. In order to achieve liver repopulation following HT, a mild hepatic damage may need to facilitate cell engraftment and replace the host liver by transplanted cells. Hormonal factor may use for the same purpose. Despite the results of preclinical studies promising clinical benefits for cell therapy, the clinical experience of HT has been disappointing, except in a few cases. HT may become an alternative for liver transplantation in the future; however, many efforts should made before establishing an effective method for HT and liver replacement therapy.

Liver gene therapy: advances and hurdles

Liver gene therapy is being developed as an alternative to orthotopic liver transplantation, which is the only effective therapy for many liver diseases. The liver has unique features that make it attractive for in vivo and ex vivo gene transfer. In vivo approach is far less invasive than ex vivo approach, although in most cases, host immune response directed against the transgene product and/or vector particles severely impairs the efficiency of gene transfer, and precludes long-term transgene expression after in vivo gene delivery. Ex vivo approach allows for an elective targeting of the hepatocytes, avoiding that the transgene be expressed in professional antigen-presenting, but is faced with the low in vitro proliferative ability of hepatocytes, and to the low in vivo liver repopulating ability of transplanted cells. In some specific situations where immune response was controlled or transplanted cells had a strong growth advantage over host hepatocytes, gene transfer resulted in long-term and complete correction of a liver genetic defect. In this review, we will outline the liver diseases that may benefit from gene therapy, the vector technology under investigation, the advances and the problems to be overcome.