First-in-class MKK4 inhibitors enhance liver regeneration and prevent liver failure.

Diminished hepatocyte regeneration is a key feature of acute and chronic liver diseases and after extended liver resections, resulting in the inability to maintain or restore a sufficient functional liver mass. Therapies to restore hepatocyte regeneration are lacking, making liver transplantation the only curative option for end-stage liver disease. Here, we report on the structure-based development and characterization (nuclear magnetic resonance [NMR] spectroscopy) of first-in-class small molecule inhibitors of the dual-specificity kinase MKK4 (MKK4i). MKK4i increased liver regeneration upon hepatectomy in murine and porcine models, allowed for survival of pigs in a lethal 85% hepatectomy model, and showed antisteatotic and antifibrotic effects in liver disease mouse models. A first-in-human phase I trial (European Union Drug Regulating Authorities Clinical Trials [EudraCT] 2021-000193-28) with the clinical candidate HRX215 was conducted and revealed excellent safety and pharmacokinetics. Clinical trials to probe HRX215 for prevention/treatment of liver failure after extensive oncological liver resections or after transplantation of small grafts are warranted.

Biodegradable biliary stents coated with mesenchymal stromal cells in a porcine choledochojejunostomy model.

BACKGROUND AIMS: Roux en y anastomosis is a preferred method of biliary reconstruction in liver transplantation that involves living donors or pediatric patients. However, biliary stricture is a frequent and serious complication, accounting for up to 40% of biliary complications in these patients. Previously, we demonstrated that extraluminal delivery of adipose-derived (AD) mesenchymal stromal cells (MSCs) decreased peri-biliary fibrosis and increased neo-angiogenesis in a porcine model of duct-to-duct biliary anastomosis. In this study, we used a porcine model of Roux en y anastomosis to evaluate the beneficial impact of a novel intraluminal MSC delivery system. METHODS: Nine animals were divided into three groups: no stent (group 1), bare stent (group 2) and stent coated with AD-MSCs (group 3). All animals underwent cholecystectomy with roux en y choledochojejunostomy. Two animals per group were followed for 4 weeks and one animal per group was followed for 8 weeks. Cholangiograms and blood were sampled at baseline and the end of study. Biliary tissue was collected and examined by Masson trichrome staining and immunohistochemical staining for MSC markers (CD34 and CD44) and for neo-angiogenesis (CD31). RESULTS: Two of three animals in group 1 developed an anastomotic site stricture. No strictures were observed in the animals of group 2 or group 3. CD34 and CD44 staining showed that AD-MSCs engrafted successfully at the anastomotic site by intraluminal delivery (group 3). Furthermore, biliary tissue from group 3 showed significantly less fibrosis and increased angiogenesis compared with the other groups. CONCLUSIONS: Intraluminal delivery of AD-MSCs resulted in successful biliary engraftment of AD-MSCs as well as reduced peri-biliary fibrosis and increased neo-angiogenesis.

A non-human primate model of acute liver failure suitable for testing liver support systems.

Acute hepatic failure is associated with high morbidity and mortality for which the only definitive therapy is liver transplantation. Some fraction of those who undergo emergency transplantation have been shown to recover native liver function when transplanted with an auxiliary hepatic graft that leaves part of the native liver intact. Thus, transplantation could have been averted with the development and use of some form of hepatic support. The costs of developing and testing liver support systems could be dramatically reduced by the availability of a reliable large animal model of hepatic failure with a large therapeutic window that allows the assessment of efficacy and timing of intervention. Non-lethal forms of hepatic injury were examined in combination with liver-directed radiation in non-human primates (NHPs) to develop a model of acute hepatic failure that mimics the human condition. Porcine hepatocyte transplantation was then tested as a potential therapy for acute hepatic failure. After liver-directed radiation therapy, delivery of a non-lethal hepatic ischemia-reperfusion injury reliably and rapidly generated liver failure providing conditions that can enable pre-clinical testing of liver support or replacement therapies. Unfortunately, in preliminary studies, low hepatocyte engraftment and over-immune suppression interfered with the ability to assess the efficacy of transplanted porcine hepatocytes in the model. A model of acute liver failure in NHPs was created that recapitulates the pathophysiology and pathology of the clinical condition, does so with reasonably predictable kinetics, and results in 100% mortality. The model allowed preliminary testing of xenogeneic hepatocyte transplantation as a potential therapy.

Fumarylacetoacetate hydrolase gene as a knockout target for hepatic chimerism and donor liver production.

A reliable source of human hepatocytes and transplantable livers is needed. Interspecies embryo complementation, which involves implanting donor human stem cells into early morula/blastocyst stage animal embryos, is an emerging solution to the shortage of transplantable livers. We review proposed mutations in the recipient embryo to disable hepatogenesis, and discuss the advantages of using fumarylacetoacetate hydrolase knockouts and other genetic modifications to disable hepatogenesis. Interspecies blastocyst complementation using porcine recipients for primate donors has been achieved, although percentages of chimerism remain persistently low. Recent investigation into the dynamic transcriptomes of pigs and primates have created new opportunities to intimately match the stage of developing animal embryos with one of the many varieties of human induced pluripotent stem cell. We discuss techniques for decreasing donor cell apoptosis, targeting donor tissue to endodermal structures to avoid neural or germline chimerism, and decreasing the immunogenicity of chimeric organs by generating donor endothelium.

Autologous Adipose Tissue-Derived Mesenchymal Stem Cells Introduced by Biliary Stents or Local Immersion in Porcine Bile Duct Anastomoses.

Biliary complications (strictures and leaks) represent major limitations in living donor liver transplantation. Mesenchymal stem cells (MSCs) are a promising modality to prevent biliary complications because of immunosuppressive and angiogenic properties. Our goal was to evaluate the safety of adipose-derived MSC delivery to biliary anastomoses in a porcine model. Secondary objectives were defining the optimal method of delivery (intraluminal versus extraluminal) and to investigate MSC engraftment, angiogenesis, and fibrosis. Pigs were divided into 3 groups. Animals underwent adipose collection, MSC isolation, and expansion. Two weeks later, animals underwent bile duct transection, reanastomosis, and stent insertion. Group 1 received plastic stents wrapped in unseeded Vicryl mesh. Group 2 received stents wrapped in MSC-seeded mesh. Group 3 received unwrapped stents with the anastomosis immersed in an MSC suspension. Animals were killed 1 month after stent insertion when cholangiograms and biliary tissue were obtained. Serum was collected for liver biochemistries. Tissue was used for hematoxylin-eosin and trichrome staining and immunohistochemistry for MSC markers (CD44 and CD34) and for a marker of neoangiogenesis (CD31). There were no intraoperative complications. One pig died on postoperative day 3 due to acute cholangitis. All others recovered without complications. Cholangiography demonstrated no biliary leaks and minimal luminal narrowing. Surviving animals exhibited no symptoms, abnormal liver biochemistries, or clinically significant biliary stricturing. Group 3 showed significantly greater CD44 and CD34 staining, indicating MSC engraftment. Fibrosis was reduced at the anastomotic site in group 3 based on trichrome stain. CD31 staining of group 3 was more pronounced, supporting enhanced neoangiogenesis. In conclusion, adipose-derived MSCs were safely applied to biliary anastomoses. MSCs were locally engrafted within the bile duct and may have beneficial effects in terms of fibrosis and angiogenesis.

Stem Cell-Related Studies and Stem Cell-Based Therapies in Liver Diseases.

Owing to the increasing worldwide burden of liver diseases, the crucial need for safe and effective interventions for treating end-stage liver failure has been a very productive line of inquiry in the discipline of hepatology for many years. Liver transplantation is recognized as the most effective treatment for end-stage liver disease; however, the shortage of donor organs, high medical costs, and lifelong use of immunosuppressive agents represent major drawbacks and demand exploration for alternative treatments. Stem cell-based therapies have been widely studied in the field of liver diseases and are considered to be among the most promising therapies. Herein, we review recent advances in the application of stem cell-related therapies in liver disease with the aim of providing readers with relevant knowledge in this field and inspiration to spur further inquiry.

Cold storage of porcine hepatocyte spheroids for spheroid bioartificial liver.

BACKGROUND AND AIMS: Cell-based therapies for liver disease such as bioartificial liver rely on a large quantity and high quality of hepatocytes. Cold storage was previously shown to be a better way to preserve the viability and functionality of hepatocytes during transportation rather than freezing, but this was only proved at a lower density of rat hepatocytes spheroids. The purpose of this study was to optimize conditions for cold storage of high density of primary porcine hepatocyte spheroids. METHODS: Porcine hepatocytes were isolated by a three-step perfusion method; hepatocyte spheroids were formed by a 24 hours rocked culture technique. Hepatocyte cell density was 5 × 106 /mL in 1000 mL spheroid forming medium. Spheroids were then maintained in rocked culture at 37°C (control condition) or cold stored at 4°C for 24, 48 or 72 hours in four different cold storage solutions: histidine-tryptophan-ketoglutarate (HTK) alone; HTK + 1 mM deferoxamine (DEF); HTK + 5 mM N-acetyl-L-cysteine (NAC); and HTK + 1 mM DEF + 5 mM NAC. The viability, ammonia clearance, albumin production, gene expression, and functional activity of cytochrome P450 enzymes were measured after recovery from the cold storage. RESULTS: In this study, we observed that cold-induced injury was reduced by the addition of the iron chelator. Viability of HTK + DEF group hepatocyte spheroids was increased compared with other cold storage groups (P < 0.05). Performance metrics of porcine hepatocyte spheroids cold stored for 24 hours were similar to those in control conditions. The hepatocyte spheroids in control conditions started to lose their ability to clear ammonia while production of albumin was still active at 48 and 72 hours (P < 0.05). In contrast, the viability and functionality of hepatocyte spheroids including ammonia clearance and albumin secretion were preserved in HTK + DEF group at both 48- and 72-hour time points (P < 0.05). CONCLUSIONS: The beneficial effects of HTK supplemented with DEF were more obvious after cold storage of high density of porcine hepatocyte spheroids for 72 hours. The porcine hepatocyte spheroids were above the cutoff criteria for use in a spheroid-based bioartificial liver.

Autologous Gene and Cell Therapy Provides Safe and Long-Term Curative Therapy in A Large Pig Model of Hereditary Tyrosinemia Type 1.

Orthotopic liver transplantation remains the only curative therapy for inborn errors of metabolism. Given the tremendous success for primary immunodeficiencies using ex-vivo gene therapy with lentiviral vectors, there is great interest in developing similar curative therapies for metabolic liver diseases. We have previously generated a pig model of hereditary tyrosinemia type 1 (HT1), an autosomal recessive disorder caused by deficiency of fumarylacetoacetate hydrolase (FAH). Using this model, we have demonstrated curative ex-vivo gene and cell therapy using a lentiviral vector to express FAH in autologous hepatocytes. To further evaluate the long-term clinical outcomes of this therapeutic approach, we continued to monitor one of these pigs over the course of three years. The animal continued to thrive off the protective drug NTBC, gaining weight appropriately, and maintaining sexual fecundity for the course of his life. The animal was euthanized 31 months after transplantation to perform a thorough biochemical and histological analysis. Biochemically, liver enzymes and alpha-fetoprotein levels remained normal and abhorrent metabolites specific to HT1 remained corrected. Liver histology showed no evidence of tumorigenicity and Masson's trichrome staining revealed minimal fibrosis and no evidence of cirrhosis. FAH-immunohistochemistry revealed complete repopulation of the liver by transplanted FAH-positive cells. A complete histopathological report on other organs, including kidney, revealed no abnormalities. This study is the first to demonstrate long-term safety and efficacy of hepatocyte-directed gene therapy in a large animal model. We conclude that hepatocyte-directed ex-vivo gene therapy is a rational choice for further exploration as an alternative therapeutic approach to whole organ transplantation for metabolic liver disease, including HT1.

Lentiviral Vector-mediated Gene Therapy of Hepatocytes Ex Vivo for Autologous Transplantation in Swine.

Gene therapy is an ideal choice to cure many inborn errors of metabolism of the liver. Ex-vivo, lentiviral vectors have been used successfully in the treatment of many hematopoietic diseases in humans, as their use offers stable transgene expression due to the vector's ability to integrate into the host genome. This method demonstrates the application of ex vivo gene therapy of hepatocytes to a large animal model of hereditary tyrosinemia type I. This process consists of 1) isolation of primary hepatocytes from the autologous donor/recipient animal, 2) ex vivo gene delivery via hepatocyte transduction with a lentiviral vector, and 3) autologous transplant of corrected hepatocytes via portal vein injection. Success of the method generally relies upon efficient and sterile removal of the liver resection, careful handling of the excised specimen for isolation of viable hepatocytes sufficient for re-engrafting, high-percentage transduction of the isolated cells, and aseptic surgical procedures throughout to prevent infection. Technical failure at any of these steps will result in low yield of viable transduced hepatocytes for autologous transplant or infection of the donor/recipient animal. The pig model of human type 1 hereditary tyrosinemia (HT-1) chosen for this approach is uniquely amenable to such a method, as even a small percentage of engraftment of corrected cells will lead to repopulation of the liver with healthy cells based on a powerful selective advantage over native-diseased hepatocytes. Although this growth selection will not be true for all indications, this approach is a foundation for expansion into other indications and allows for manipulation of this environment to address additional diseases, both within the liver and beyond, while controlling for exposure to viral vector and opportunity for off-target toxicity and tumorigenicity.

Hepatocyte spheroids as an alternative to single cells for transplantation after ex vivo gene therapy in mice and pig models.

BACKGROUND: Autologous hepatocyte transplantation after ex vivo gene therapy is an alternative to liver transplantation for metabolic liver disease. Here we evaluate ex vivo gene therapy followed by transplantation of single-cell or spheroid hepatocytes. METHODS: Pig and mouse hepatocytes were isolated, labeled with zirconium-89 and returned to the liver as single cells or spheroids. Biodistribution was evaluated through positron emission tomography-computed tomography. Fumarylacetoacetate hydrolase-deficient pig hepatocytes were isolated and transduced with a lentiviral vector containing the Fah gene. Animals received portal vein infusion of single-cell or spheroid autologous hepatocytes after ex vivo gene delivery. Portal pressures were measured and ultrasound was used to evaluate for thrombus. Differences in engraftment and expansion of ex vivo corrected single-cell or spheroid hepatocytes were followed through histologic analysis and animals' ability to thrive off 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione. RESULTS: Positron emission tomography-computed tomography imaging showed spheroid hepatocytes with increased heterogeneity in biodistribution as compared with single cells, which spread more uniformly throughout the liver. Animals receiving spheroids experienced higher mean changes in portal pressure than animals receiving single cells (P < .01). Additionally, two animals from the spheroid group developed portal vein thrombi that required systemic anticoagulation. Immunohistochemical analysis of spheroid- and single-cell-transplanted animals showed similar engraftment and expansion rates of fumarylacetoacetate hydrolase-positive hepatocytes in the liver, correlating with similar weight stabilization curves. CONCLUSION: Ex vivo gene correction of autologous hepatocytes in fumarylacetoacetate hydrolase-deficient pigs can be performed using hepatocyte spheroids or single-cell hepatocytes, with spheroids showing a more heterogeneous distribution within the liver and higher risks for portal vein thrombosis and increased portal pressures.

Chronic Phenotype Characterization of a Large-Animal Model of Hereditary Tyrosinemia Type 1.

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease caused by deficiency in fumarylacetoacetate hydrolase, the last enzyme in the tyrosine catabolic pathway. In this study, we investigated whether fumarylacetoacetate hydrolase deficient (FAH-/-) pigs, a novel large-animal model of HT1, develop fibrosis and cirrhosis characteristic of the human disease. FAH-/- pigs were treated with the protective drug 2-(2-nitro-4-trifluoromethylbenzoyl)-1, 3 cyclohexandione (NTBC) at a dose of 1 mg/kg per day initially after birth. After 30 days, they were assigned to one of three groups based on dosing of NTBC. Group 1 received ≥0.2 mg/kg per day, group 2 cycled on/off NTBC (0.05 mg/kg per day × 1 week/0 mg/kg per day × 3 weeks), and group 3 received no NTBC thereafter. Pigs were monitored for features of liver disease. Animals in group 1 continued to have weight gain and biochemical analyses comparable to wild-type pigs. Animals in group 2 had significant cessation of weight gain, abnormal biochemical test results, and various grades of fibrosis and cirrhosis. No evidence of hepatocellular carcinoma was detected. Group 3 animals declined rapidly, with acute liver failure. In conclusion, the FAH-/- pig is a large-animal model of HT1 with clinical characteristics that resemble the human phenotype. Under conditions of low-dose NTBC, FAH-/- pigs developed liver fibrosis and portal hypertension, and thus may serve as a large-animal model of chronic liver disease.

Curative ex vivo liver-directed gene therapy in a pig model of hereditary tyrosinemia type 1.

We tested the hypothesis that ex vivo hepatocyte gene therapy can correct the metabolic disorder in fumarylacetoacetate hydrolase-deficient (Fah(-/-)) pigs, a large animal model of hereditary tyrosinemia type 1 (HT1). Recipient Fah(-/-) pigs underwent partial liver resection and hepatocyte isolation by collagenase digestion. Hepatocytes were transduced with one or both of the lentiviral vectors expressing the therapeutic Fah and the reporter sodium-iodide symporter (Nis) genes under control of the thyroxine-binding globulin promoter. Pigs received autologous transplants of hepatocytes by portal vein infusion. After transplantation, the protective drug 2-(2-nitro-4-trifluoromethylbenzyol)-1,3 cyclohexanedione (NTBC) was withheld from recipient pigs to provide a selective advantage for expansion of corrected FAH(+) cells. Proliferation of transplanted cells, assessed by both immunohistochemistry and noninvasive positron emission tomography imaging of NIS-labeled cells, demonstrated near-complete liver repopulation by gene-corrected cells. Tyrosine and succinylacetone levels improved to within normal range, demonstrating complete correction of tyrosine metabolism. In addition, repopulation of the Fah(-/-) liver with transplanted cells inhibited the onset of severe fibrosis, a characteristic of nontransplanted Fah(-/-) pigs. This study demonstrates correction of disease in a pig model of metabolic liver disease by ex vivo gene therapy. To date, ex vivo gene therapy has only been successful in small animal models. We conclude that further exploration of ex vivo hepatocyte genetic correction is warranted for clinical use.

Noninvasive 3-dimensional imaging of liver regeneration in a mouse model of hereditary tyrosinemia type 1 using the sodium iodide symporter gene.

Cell transplantation is a potential treatment for the many liver disorders that are currently only curable by organ transplantation. However, one of the major limitations of hepatocyte (HC) transplantation is an inability to monitor cells longitudinally after injection. We hypothesized that the thyroidal sodium iodide symporter (NIS) gene could be used to visualize transplanted HCs in a rodent model of inherited liver disease: hereditary tyrosinemia type 1. Wild-type C57Bl/6J mouse HCs were transduced ex vivo with a lentiviral vector containing the mouse Slc5a5 (NIS) gene controlled by the thyroxine-binding globulin promoter. NIS-transduced cells could robustly concentrate radiolabeled iodine in vitro, with lentiviral transduction efficiencies greater than 80% achieved in the presence of dexamethasone. Next, NIS-transduced HCs were transplanted into congenic fumarylacetoacetate hydrolase knockout mice, and this resulted in the prevention of liver failure. NIS-transduced HCs were readily imaged in vivo by single-photon emission computed tomography, and this demonstrated for the first time noninvasive 3-dimensional imaging of regenerating tissue in individual animals over time. We also tested the efficacy of primary HC spheroids engrafted in the liver. With the NIS reporter, robust spheroid engraftment and survival could be detected longitudinally after direct parenchymal injection, and this thereby demonstrated a novel strategy for HC transplantation. This work is the first to demonstrate the efficacy of NIS imaging in the field of HC transplantation. We anticipate that NIS labeling will allow noninvasive and longitudinal identification of HCs and stem cells in future studies related to liver regeneration in small and large preclinical animal models.

Fumarylacetoacetate hydrolase deficient pigs are a novel large animal model of metabolic liver disease.

Hereditary tyrosinemia type I (HT1) is caused by deficiency in fumarylacetoacetate hydrolase (FAH), an enzyme that catalyzes the last step of tyrosine metabolism. The most severe form of the disease presents acutely during infancy, and is characterized by severe liver involvement, most commonly resulting in death if untreated. Generation of FAH(+/-) pigs was previously accomplished by adeno-associated virus-mediated gene knockout in fibroblasts and somatic cell nuclear transfer. Subsequently, these animals were outbred and crossed to produce the first FAH(-/-) pigs. FAH-deficiency produced a lethal defect in utero that was corrected by administration of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione (NTBC) throughout pregnancy. Animals on NTBC were phenotypically normal at birth; however, the animals were euthanized approximately four weeks after withdrawal of NTBC due to clinical decline and physical examination findings of severe liver injury and encephalopathy consistent with acute liver failure. Biochemical and histological analyses, characterized by diffuse and severe hepatocellular damage, confirmed the diagnosis of severe liver injury. FAH(-/-) pigs provide the first genetically engineered large animal model of a metabolic liver disorder. Future applications of FAH(-/-) pigs include discovery research as a large animal model of HT1 and spontaneous acute liver failure, and preclinical testing of the efficacy of liver cell therapies, including transplantation of hepatocytes, liver stem cells, and pluripotent stem cell-derived hepatocytes.

Cold storage of rat hepatocyte spheroids.

Cell-based therapies for liver disease rely on a high-quality supply of hepatocytes and a means for storage during transportation from site of isolation to site of usage. Unfortunately, frozen cryopreservation is associated with unacceptable loss of hepatocyte viability after thawing. The purpose of this study was to optimize conditions for cold storage of rat hepatocyte spheroids without freezing. Rat hepatocytes were isolated by a two-step perfusion method; hepatocyte spheroids were formed during 48 h of rocked culture in serum-free medium (SFM). Spheroids were then maintained in rocked culture at 37 °C (control condition) or cold stored at 4 °C for 24 or 48 h in six different cold storage solutions: SFM alone; SFM + 1 mM deferoxamine (Def); SFM + 1 µM cyclosporin A (CsA); SFM + 1 mM Def + 1 µM CsA, University of Wisconsin (UW) solution alone, UW + 1 mM Def. Performance metrics after cold storage included viability, gene expression, albumin production, and functional activity of cytochrome P450 enzymes and urea cycle proteins. We observed that cold-induced injury was reduced significantly by the addition of the iron chelator (Def) to both SFM and UW solution. Performance metrics (ammonia detoxification, albumin production) of rat hepatocyte spheroids stored in SFM + Def for 24 h were significantly increased from SFM alone and approached those in control conditions, while performance metrics after cold storage in SFM alone or cold storage for 48 h were both significantly reduced. A serum-free medium supplemented with Def allowed hepatocyte spheroids to tolerate 24 h of cold storage with less than 10% loss in viability and functionality. Further research is warranted to optimize a solution for extended cold storage of hepatocyte spheroids.

Serum-free medium and mesenchymal stromal cells enhance functionality and stabilize integrity of rat hepatocyte spheroids.

Long-term culture of hepatocyte spheroids with high ammonia clearance is valuable for therapeutic applications, especially the bioartificial liver. However, the optimal conditions are not well studied. We hypothesized that liver urea cycle enzymes can be induced by high protein diet and maintain on a higher expression level in rat hepatocyte spheroids by serum-free medium (SFM) culture and coculture with mesenchymal stromal cells (MSCs). Rats were feed normal protein diet (NPD) or high protein diet (HPD) for 7 days before liver digestion and isolation of hepatocytes. Hepatocyte spheroids were formed and maintained in a rocked suspension culture with or without MSCs in SFM or 10% serum-containing medium (SCM). Spheroid viability, kinetics of spheroid formation, hepatic functions, gene expression, and biochemical activities of rat hepatocyte spheroids were tested over 14 days of culture. We observed that urea cycle enzymes of hepatocyte spheroids can be induced by high protein diet. SFM and MSCs enhanced ammonia clearance and ureagenesis and stabilized integrity of hepatocyte spheroids compared to control conditions over 14 days. Hepatocytes from high protein diet-fed rats formed spheroids and maintained a high level of ammonia detoxification for over 14 days in a novel SFM. Hepatic functionality and spheroid integrity were further stabilized by coculture of hepatocytes with MSCs in the spheroid microenvironment. These findings have direct application to development of the spheroid reservoir bioartificial liver.

Cell therapies for liver diseases.

Cell therapies, which include bioartificial liver support and hepatocyte transplantation, have emerged as potential treatments for a variety of liver diseases. Acute liver failure, acute-on-chronic liver failure, and inherited metabolic liver diseases are examples of liver diseases that have been successfully treated with cell therapies at centers around the world. Cell therapies also have the potential to be widely applied to other liver diseases, including noninherited liver diseases and liver cancer, and to improve the success of liver transplantation. Here we briefly summarize current concepts of cell therapy for liver diseases.

Cytotoxic immune response to a xenogeneic bioartificial liver.

Prior studies have suggested the possibility of immune-mediated death of xenogeneic hepatocytes in a bioartificial liver (BAL) during hemoperfusion. This study was designed to elucidate how immunity may cause death of xenogeneic hepatocytes in the BAL. Healthy dogs were treated with a BAL containing hollow fiber membranes with large pores (200 nm) or small pores (400 kDa). The immune response of recipient dogs to BAL therapy was monitored over 3 h of treatment. We observed significantly greater loss of viability of hepatocytes in the 200 nm group compared with the 400 kDa group (p < 0.001). Low viability after treatment with the large pore membrane was associated with positive staining for dog IgG, dog IgM, and dog complement on dead hepatocytes. Significant levels of dog antibody were detected in samples of BAL medium from the 200 nm group. These canine antibodies were cytotoxic to porcine hepatocytes. In contrast, medium from the 400 kDa group contained only trace levels of dog IgG and were noncytotoxic. We conclude that antibody-mediated cytotoxicity contributed to the death of hepatocytes during treatment with a xenogeneic BAL. Immune-mediated death of hepatocytes was reduced by increasing selectivity of the BAL membrane.