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Cellular Therapy for Liver Disease

      Abstract

      Regenerative medicine is energizing and empowering basic science and has the potential to dramatically transform health care in the future. Given the remarkable intrinsic regenerative properties of the liver, as well as widespread adoption of regenerative strategies for liver disease (eg, liver transplant, partial hepatectomy, living donor transplant), hepatology has always been at the forefront of clinical regenerative medicine. However, an expanding pool of patients awaiting liver transplant, a limited pool of donor organs, and finite applicability of the current surgical approaches have created a need for more refined and widely available regenerative medicine strategies. Although cell-based therapies have been used extensively for hematologic malignant diseases and other conditions, the potential application of cellular therapy for acute and chronic liver diseases has only more recently been explored. New understanding of the mechanisms of liver regeneration and repair, including activation of local stem/progenitor cells and contributions from circulating bone marrow–derived stem cells, provide the theoretical underpinnings for the rational use of cell-based therapies in clinical trials. In this review, we dissect the scientific rationale for various modalities of cell therapy for liver diseases being explored in animal models and review those tested in human clinical trials. We also attempt to clarify some of the important ongoing questions that need to be addressed in order to bring these powerful therapies to clinical translation. Discussions will cover transplant of hepatocytes and liver stem/progenitor cells as well as infusion or stimulation of bone marrow–derived stem cells. We also highlight tremendous scientific advances on the horizon, including the potential use of induced pluripotent stem cells and their derivatives as individualized regenerative therapy for liver disease.

      Abbreviations and Acronyms:

      CP (Child-Pugh), ESLD (end-stage liver disease), GC-SF (granulocyte colony-stimulating factor), HLC (hepatocytelike cell), HSC (hematopoietic stem cell), iPSC (induced pluripotent stem cell), LSPC (liver stem/progenitor cell), MELD (model for end-stage liver disease), MSC (mesenchymal stem cell)
      CME Activity
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      Learning Objectives: On completion of this article, you should be able to (1) recognize the historical use of regenerative medicine technologies in liver disease, (2) summarize the clinical trials to date in cell therapy for liver disease, and (3) differentiate the various sources of cell therapy for liver disease.
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      In their editorial and administrative roles, William L. Lanier, Jr, MD, Terry L. Jopke, Kimberly D. Sankey, and Nicki M. Smith, MPA, have control of the content of this program but have no relevant financial relationship(s) with industry.
      The authors report no competing interests.
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      We are now living in a golden age of regenerative and individualized medicine in which sweeping scientific advances are poised to fundamentally alter the way we approach health and disease, as well as the delivery of medical therapies. In this new era, there is a growing armamentarium of therapeutic options that may benefit patients with acute or chronic liver disease. For the past 30 years, many patients with end-stage liver disease (ESLD) have benefitted from liver transplant as a treatment option. As a regenerative medicine option designed to “replace” a failing liver, liver transplant has transformed the care of patients with liver disease and the practice of hepatology. However, due in part to epidemic levels of chronic hepatitis C virus infection and nonalcoholic fatty liver disease, the applicability of this lifesaving procedure has now become more limited because of a mismatch between the number of patients awaiting liver transplant and the availability of suitable donor organs. Thus, the fatality rate of patients on the waiting list for liver transplant can be as high as 20%, depending on the severity of the underlying hepatic disease and the availability of organ donors in a specific United Network for Organ Sharing region.
      • Dienstag J.L.
      • Cosimi A.B.
      Liver transplantation—a vision realized.
      The remarkable innate ability of the liver to regenerate and the advent of living donor liver transplant have partially addressed the shortage of organs for transplant. In this way, transplant hepatology has always been at the forefront of clinical regenerative medicine. However, the limited applicability of current surgical paradigms has continued to stimulate extensive research into other approaches in the realm of liver regenerative medicine,
      • Terzic A.
      • Nelson T.J.
      Regenerative medicine primer.
      • Matteson E.L.
      • Terzic A.
      Introduction to the Symposium on Regenerative Medicine.
      including the enticing and seemingly limitless potential of cell-based therapies.
      In this review, we focus on the potential role of various modalities of cellular therapy as a means to “repair” or “regenerate” a failing liver or to augment native liver regeneration after hepatectomy or living donor liver transplant. We begin with discussions of hepatocyte and liver stem/progenitor cell (LSPC) transplant. Thereafter, we review the use of circulating or bone marrow–derived stem cell therapies for chronic liver disease, including a review of the clinical trials to date. We conclude with a discussion of the future of cell-based therapy in hepatology, including the astonishing diagnostic and therapeutic potential of induced pluripotent stem cells (iPSCs) and their derivatives in liver disease. We will not address artificial and bioartificial liver support devices, which are outside the scope of the current review and have been reviewed in detail elsewhere.
      • McKenzie T.J.
      • Lillegard J.B.
      • Nyberg S.L.
      Artificial and bioartificial liver support.

      Hepatocyte Transplant

      Initial attempts at cellular therapy for liver disease consisted of using primary hepatocytes infused via the portal vein to patients with ESLD or certain genetic and metabolic liver disorders.
      • Dhawan A.
      • Puppi J.
      • Hughes R.D.
      • Mitry R.R.
      Human hepatocyte transplantation: current experience and future challenges.
      • Weber A.
      • Groyer-Picard M.T.
      • Franco D.
      • Dagher I.
      Hepatocyte transplantation in animal models.
      • Ito M.
      • Nagata H.
      • Miyakawa S.
      • Fox I.J.
      Review of hepatocyte transplantation.
      • Fox I.J.
      • Roy-Chowdhury J.
      Hepatocyte transplantation.
      • Fox I.J.
      • Chowdhury J.R.
      Hepatocyte transplantation.
      • Horslen S.P.
      • McCowan T.C.
      • Goertzen T.C.
      • et al.
      Isolated hepatocyte transplantation in an infant with a severe urea cycle disorder.
      • Strom S.C.
      • Chowdhury J.R.
      • Fox I.J.
      Hepatocyte transplantation for the treatment of human disease.
      • Fox I.J.
      • Chowdhury J.R.
      • Kaufman S.S.
      • et al.
      Treatment of the Crigler-Najjar syndrome type I with hepatocyte transplantation.
      Various reports have indicated a beneficial effect. However, the observed improvements in liver function are rather modest and of uncertain duration. The hepatocytes are typically harvested from livers that are not deemed to be suitable for liver transplant, but these cells are limited in number, variable in quality, and not able to be expanded in vitro. The ability of hepatocytes to effectively repopulate a diseased liver appears to be limited to a select group of disorders that allow a growth advantage to the transplanted cells (such as hereditary tyrosinemia, Wilson disease, or progressive familial intrahepatic cholestasis).
      • Rountree C.B.
      • Mishra L.
      • Willenbring H.
      Stem cells in liver diseases and cancer: recent advances on the path to new therapies.
      Furthermore, these procedures continue to require immunosuppression, and there has been insufficient experience to define the amount and duration of immunosuppression needed in this setting. Lastly, how long these hepatocytes will be viable and the nature of their interaction with native hepatocytes remain unclear. All these factors have conspired against making primary hepatocyte transplant a current option for patients with ESLD or metabolic/genetic disorders. There is a growing body of literature seeking alternative sources of abundant, high-quality hepatocytes for transplant in patients with acute liver failure, chronic liver disease, and during regeneration after large hepatic resections.
      • Yu Y.
      • Fisher J.E.
      • Lillegard J.B.
      • Rodysill B.
      • Amiot B.
      • Nyberg S.L.
      Cell therapies for liver diseases.
      • Duncan A.W.
      • Dorrell C.
      • Grompe M.
      Stem cells and liver regeneration.
      Several approaches are in development, including hepatocytes derived from cell lines, xenotransplant of animal-derived hepatocytes, and even in vivo expansion of human hepatocytes in fumarylacetoacetate hydrolase-deficient animal incubators.
      • Chistiakov D.A.
      Liver regenerative medicine: advances and challenges.
      • Forbes S.J.
      • Newsome P.N.
      New horizons for stem cell therapy in liver disease.
      • Fisher J.E.
      • Lillegard J.B.
      • McKenzie T.J.
      • Rodysill B.R.
      • Wettstein P.J.
      • Nyberg S.L.
      In utero transplanted human hepatocytes allow postnatal engraftment of human hepatocytes in pigs.
      Although these approaches are promising, further basic science advances will be needed before these methods can be translated to human studies.

      Liver Stem/Progenitor Cells

      Liver stem/progenitor cells (also known as oval cells in rodents) are thought to represent tissue-specific, bipotential precursors to liver parenchymal cells. When hepatocyte replication is impaired or overwhelmed, the LSPCs residing in the terminal bile ductules (canals of Hering) are activated to proliferate and differentiate. Numerous studies have investigated the activation of the liver stem cell compartment in various forms of chronic liver disease,
      • Lanthier N.
      • Rubbia-Brandt L.
      • Spahr L.
      Liver progenitor cells and therapeutic potential of stem cells in human chronic liver diseases.
      including chronic viral hepatitis,
      • Libbrecht L.
      • Desmet V.
      • Van Damme B.
      • Roskams T.
      Deep intralobular extension of human hepatic 'progenitor cells' correlates with parenchymal inflammation in chronic viral hepatitis: can 'progenitor cells' migrate?.
      • Wu N.
      • Liu F.
      • Ma H.
      • et al.
      HBV infection involving in hepatic progenitor cells expansion in HBV-infected end-stage liver disease.
      • Clouston A.D.
      • Powell E.E.
      • Walsh M.J.
      • Richardson M.M.
      • Demetris A.J.
      • Jonsson J.R.
      Fibrosis correlates with a ductular reaction in hepatitis C: roles of impaired replication, progenitor cells and steatosis.
      • Lowes K.N.
      • Brennan B.A.
      • Yeoh G.C.
      • Olynyk J.K.
      Oval cell numbers in human chronic liver diseases are directly related to disease severity.
      alcoholic liver disease,
      • Lowes K.N.
      • Brennan B.A.
      • Yeoh G.C.
      • Olynyk J.K.
      Oval cell numbers in human chronic liver diseases are directly related to disease severity.
      • Sancho-Bru P.
      • Altamirano J.
      • Rodrigo-Torres D.
      • et al.
      Liver progenitor cell markers correlate with liver damage and predict short-term mortality in patients with alcoholic hepatitis.
      and fatty liver disease.
      • Richardson M.M.
      • Jonsson J.R.
      • Powell E.E.
      • et al.
      Progressive fibrosis in nonalcoholic steatohepatitis: association with altered regeneration and a ductular reaction.
      • Chiba M.
      • Sasaki M.
      • Kitamura S.
      • Ikeda H.
      • Sato Y.
      • Nakanuma Y.
      Participation of bile ductular cells in the pathological progression of non-alcoholic fatty liver disease.
      Although they are considered to have the ability to become hepatocytes or cholangiocytes, the true ability of LSPCs to transdifferentiate into mature hepatocytes and the extent to which this process might contribute to liver regeneration and repair in various disease states are not entirely clear. Nonetheless, methods to isolate and characterize liver-specific stem cells have been developed in fetal and adult rodent models.
      • Oertel M.
      Fetal liver cell transplantation as a potential alternative to whole liver transplantation?.
      • Takana M.
      • Miyajima A.
      Identification and isolation of adult liver stem/progenitor cells.
      • Guo J.
      • Li J.
      • Lu Y.
      • et al.
      A novel technique for hepatic progenitor cell isolation from normal adult rat livers.
      • Sahin M.B.
      • Schwartz R.E.
      • Buckley S.M.
      • et al.
      Isolation and characterization of a novel population of progenitor cells from unmanipulated rat liver.
      • Aravalli R.N.
      • Behnan Sahin M.
      • Cressman E.N.
      • Steer C.J.
      Establishment and characterization of a unique 1 microm diameter liver-derived progenitor cell line.
      Furthermore, bipotential mouse embryonic liver cell lines have been developed that retain the ability to undergo morphogenesis into hepatocytes or cholangiocytes in vitro.
      • Strick-Marchand H.
      • Weiss M.C.
      Inducible differentiation and morphogenesis of bipotential liver cell lines from wild-type mouse embryos.
      • Akkari L.
      • Haouzi D.
      • Binamé F.
      • et al.
      Cell shape and TGF-beta signaling define the choice of lineage during in vitro differentiation of mouse primary hepatic precursors.
      Directed differentiation techniques have also allowed generation of hepatic progenitor cells from human embryonic stem cells.
      • Zhao D.
      • Chen S.
      • Cai J.
      • et al.
      Derivation and characterization of hepatic progenitor cells from human embryonic stem cells.
      Transplant of LSPCs from various sources has been accomplished via intrasplenic injection or infusion into a peripheral vein or the portal vein, with the idea that they may augment the impaired regeneration seen in the setting of chronic liver disease and promote reverse remodeling of fibrosis.
      • Yovchev M.I.
      • Dabeva M.D.
      • Oertel M.
      Isolation, characterization, and transplantation of adult liver progenitor cells.
      Engraftment and repopulation have been observed, even in the setting of fibrosis,
      • Oertel M.
      Fetal liver cell transplantation as a potential alternative to whole liver transplantation?.

      Yovchev MI, Xue Y, Shafritz DA, Locker J, Oertel M. Repopulation of the fibrotic/cirrhotic rat liver by transplanted hepatic stem/progenitor cells and mature hepatocytes [published online ahead of print July 10, 2013]. Hepatology. http://dx.doi.org/10.1002/hep.26615.

      but generally, a regenerative stimulus such as partial hepatectomy or retrorsine injection is required for optimal engraftment. Although some studies suggest reduced fibrosis after LSPC transplant,

      Yovchev MI, Xue Y, Shafritz DA, Locker J, Oertel M. Repopulation of the fibrotic/cirrhotic rat liver by transplanted hepatic stem/progenitor cells and mature hepatocytes [published online ahead of print July 10, 2013]. Hepatology. http://dx.doi.org/10.1002/hep.26615.

      there have also been descriptions of a severe fibrogenic response that is, in fact, driven by the activation of the hepatic progenitor compartment.
      • Kuramitsu K.
      • Sverdlov D.Y.
      • Liu S.B.
      • et al.
      Failure of fibrotic liver regeneration in mice is linked to a severe fibrogenic response driven by hepatic progenitor cell activation.
      Furthermore, as in hepatocyte transplant, adult LSPCs are available only in limited numbers, and there are ethical constraints on the use of human fetal LSPCs. Thus, caution and additional study will be needed to clarify the therapeutic potential of LSPCs.

      Circulating Stem Cells

      Several publications have provided evidence suggesting that bone marrow–derived stem cells are mobilized after hepatic resection (ie, partial hepatectomy), inflammatory hepatic disease, or ischemic injury.
      • Cho K.A.
      • Woo S.Y.
      • Seoh J.Y.
      • Han H.S.
      • Ryu K.H.
      Mesenchymal stem cells restore CCl4-induced liver injury by an antioxidative process.
      • Petersen B.E.
      • Bowen W.C.
      • Patrene K.D.
      • et al.
      Bone marrow as a potential source of hepatic oval cells.
      • Oh S.H.
      • Witek R.P.
      • Bae S.H.
      • et al.
      Bone marrow-derived hepatic oval cells differentiate into hepatocytes in 2-acetylaminofluorene/partial hepatectomy-induced liver regeneration.
      • Thomas J.A.
      • Pope C.
      • Wojtacha D.
      • et al.
      Macrophage therapy for murine liver fibrosis recruits host effector cells improving fibrosis, regeneration, and function.
      Circulating bone marrow–derived stem cells consist of 2 major types of adult stem cells: hematopoietic stem cells (HSCs), which are CD34 and CD133 positive, and mesenchymal stem cells (MSCs) that lack a well-defined surface antigen expression pattern and can also be found in adipose tissue.
      • Seki A.
      • Sakai Y.
      • Komura T.
      • et al.
      Adipose tissue-derived stem cells as a regenerative therapy for a mouse steatohepatitis-induced cirrhosis model.
      True pluripotent stem cells present in bone marrow are estimated to be less than 0.1% of CD133+ cells. The migration of these stem cells appears to be mediated by a chemoattractant, such as stromal cell–derived factor 1.
      • Jin S.Z.
      • Meng X.W.
      • Han M.Z.
      • Sun X.
      • Sun L.Y.
      • Liu B.R.
      Stromal cell derived factor-1 enhances bone marrow mononuclear cell migration in mice with acute liver failure.
      Subsequently, the secretion of interleukin 8, matrix metalloproteinase 9, hepatocyte growth factor, and stem cell factors facilitates homing and engraftment of MSCs
      • Li C.
      • Kong Y.
      • Wang H.
      • et al.
      Homing of bone marrow mesenchymal stem cells mediated by sphingosine 1-phosphate contributes to liver fibrosis.
      • Chen Y.
      • Xiang L.X.
      • Shao J.Z.
      • et al.
      Recruitment of endogenous bone marrow mesenchymal stem cells towards injured liver.
      in the liver.
      The underlying mechanisms of the beneficial effect observed after the infusion of HSCs and MSCs have not been well characterized. Transdifferentiation into hepatocytes, stimulation of native hepatocyte proliferation, an antifibrotic effect, immunomodulatory effects, and cell plasticity are all possible mechanisms involved in this beneficial effect. Initially, several investigators postulated that the mobilized bone marrow–derived stem cells were able to transdifferentiate into hepatocytes. Other interpretations for their beneficial effects have attributed them to fusion of adult stem cells with local hepatocytes
      • Wang X.
      • Willenbring H.
      • Akkari Y.
      • et al.
      Cell fusion is the principal source of bone-marrow-derived hepatocytes.
      or a paracrine proliferative effect on native hepatocytes.
      • Alison M.R.
      • Islam S.
      • Lim S.
      Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly.
      Another postulated mechanism of action is an ability to remodel fibrosis.
      • Zhao D.C.
      • Lei J.X.
      • Chen R.
      • et al.
      Bone marrow-derived mesenchymal stem cells protect against experimental liver fibrosis in rats.
      Specifically, endogenous hepatocytes in cirrhosis have been reported to have a decreased proliferative capacity. Stem cell therapy may initially exert a beneficial effect by the expression of matrix metalloproteinase 9 to decrease fibrosis. As fibrosis diminishes, local hepatocytes in a cirrhotic liver may regain their ability to proliferate.
      Houlihan and Newsome
      • Houlihan D.D.
      • Newsome P.N.
      Critical review of clinical trials of bone marrow stem cells in liver disease.
      have recently described some potential adverse events associated with this type of cell therapy in patients with liver diseases. Hepatic stellate cells and myofibroblasts may derive from bone marrow stem cells.
      • Yang L.
      • Chang N.
      • Liu X.
      • et al.
      Bone marrow-derived mesenchymal stem cells differentiate to hepatic myofibroblasts by transforming growth factor-β1 via sphingosine kinase/sphingosine 1-phosphate (S1P)/S1P receptor axis.
      These observations raise the possibility that cell therapies may have the potential to enhance, not diminish, hepatic fibrosis. It has also been pointed out that MSCs can undergo malignant transformation.
      • Wu X.Z.
      • Chen D.
      Origin of hepatocellular carcinoma: role of stem cells.
      The approaches utilized in the preparation of bone marrow–derived stem cells for clinical use have included infusion of collected autologous stem cells and mobilization of bone marrow stem cells by the administration of granulocyte colony-stimulating factor (GC-SF).

      Clinical Trials With MSCs

      The initial 2 reported pilot studies
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Mohyeddin-Bonab M.
      • et al.
      Phase 1 trial of autologous bone marrow mesenchymal stem cell transplantation in patients with decompensated liver cirrhosis.
      • Kharaziha P.
      • Hellström P.M.
      • Noorinayer B.
      • et al.
      Improvement of liver function in liver cirrhosis patients after autologous mesenchymal stem cell injection: a phase I-II clinical trial.
      included a total of 12 patients and suggested a beneficial effect after the infusion of an autologous MSC preparation (Table 1). The authors described improvement of the model for end-stage liver disease (MELD) score, quality of life (by 36-Item Short-Form Health Survey measurement), and serum albumin levels and decreasing prothrombin time. Subsequently, there have been 4 randomized controlled trials performed; 3 of them
      • Amer M.E.
      • El-Sayed S.Z.
      • El-Kheir W.A.
      • et al.
      Clinical and laboratory evaluation of patients with end-stage liver cell failure injected with bone marrow-derived hepatocyte-like cells.
      • Peng L.
      • Xie D.Y.
      • Lin B.L.
      • et al.
      Autologous bone marrow mesenchymal stem cell transplantation in liver failure patients caused by hepatitis B: short-term and long-term outcomes.
      • Zhang Z.
      • Lin H.
      • Shi M.
      • et al.
      Human umbilical cord mesenchymal stem cells improve liver function and ascites in decompensated liver cirrhosis patients.
      reported beneficial effects associated with MSCs, characterized by less ascites, decreased MELD score, increased serum albumin level, and decreased total bilirubin level. There was no observed improvement in patient survival during the time of observation. Another randomized controlled trial
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Bagheri M.
      • et al.
      Randomized placebo-controlled trial of mesenchymal stem cell transplantation in decompensated cirrhosis.
      did not show any significant improvement between the treatment and control groups.
      These trials utilized different doses of MSCs and different routes of administration. Amer et al
      • Amer M.E.
      • El-Sayed S.Z.
      • El-Kheir W.A.
      • et al.
      Clinical and laboratory evaluation of patients with end-stage liver cell failure injected with bone marrow-derived hepatocyte-like cells.
      administered an average of 2 × 107 “hepatic lineage–committed” cells in a 5-mL cell suspension that was injected intrasplenically or intrahepatically with ultrasonographic guidance. Peng et al
      • Peng L.
      • Xie D.Y.
      • Lin B.L.
      • et al.
      Autologous bone marrow mesenchymal stem cell transplantation in liver failure patients caused by hepatitis B: short-term and long-term outcomes.
      did not provide the exact number of cells that were injected into the hepatic artery. Zhang et al
      • Zhang Z.
      • Lin H.
      • Shi M.
      • et al.
      Human umbilical cord mesenchymal stem cells improve liver function and ascites in decompensated liver cirrhosis patients.
      administered 0.5 × 106 cells/kg intravenously every 4 weeks three times. Mohamadnejad et al
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Bagheri M.
      • et al.
      Randomized placebo-controlled trial of mesenchymal stem cell transplantation in decompensated cirrhosis.
      administered one median dose of 1.95 × 108 cells intravenously. This variability of protocols precludes a comprehensive comparison among these trials and the ability to draw conclusions in terms of a preferred dose and route of administration.
      Mohamadnejad et al,
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Bagheri M.
      • et al.
      Randomized placebo-controlled trial of mesenchymal stem cell transplantation in decompensated cirrhosis.
      who have pioneered the use MSCs in compensated or early decompensated cirrhosis, recently reported a randomized placebo-controlled trial in decompensated cirrhosis. They studied 27 patients, 15 of whom were randomized to MSCs. At the end of the trial, they found that Child-Pugh-Turcotte (CPT) score, MELD score, serum albumin level, international normalized ratio, and serum aminotransferase level were not different between the groups. Thus, they were unable to document a beneficial effect of MSC therapy administered via a peripheral vein. They suggested that as a next step, repeated infusion of MSCs via the hepatic artery or portal vein should be evaluated in the setting of a randomized placebo-controlled trial.

      Clinical Trials With Autologous Bone Marrow–Derived Stem Cells

      Autologous bone marrow stem cells have been evaluated in 10 studies; 6 of them (Table 2) utilized unsorted bone marrow–derived mononuclear cells.
      • Lyra A.C.
      • Soares M.B.
      • da Silva L.F.
      • et al.
      Feasibility and safety of autologous bone marrow mononuclear cell transplantation in patients with advanced chronic liver disease.
      • Terai S.
      • Ishikawa T.
      • Omori K.
      • et al.
      Improved liver function in patients with liver cirrhosis after autologous bone marrow cell infusion therapy.
      • Kim J.K.
      • Park Y.N.
      • Kim J.S.
      • et al.
      Autologous bone marrow infusion activates the progenitor cell compartment in patients with advanced liver cirrhosis.
      • Saito T.
      • Okumoto K.
      • Haga H.
      • et al.
      Potential therapeutic application of intravenous autologous bone marrow infusion in patients with alcoholic liver cirrhosis.
      • Lyra A.C.
      • Soares M.B.
      • da Silva L.F.
      • et al.
      Infusion of autologous bone marrow mononuclear cells through hepatic artery results in a short-term improvement of liver function in patients with chronic liver disease: a pilot randomized controlled study.
      • Spahr L.
      • Chalandon Y.
      • Terraz S.
      • et al.
      Autologous bone marrow mononuclear cell transplantation in patients with decompensated alcoholic liver disease: a randomized controlled trial.
      The clinical conditions treated with this approach included cirrhosis associated with hepatitis C virus or hepatitis B virus, alcoholic liver disease, primary sclerosing cholangitis, drug-induced acute liver failure, cryptogenic cirrhosis, and decompensated cirrhosis. The end points utilized to assess the efficacy of cellular therapy included CPT score, quality of life, and improvement in albumin, bilirubin, and aminotransferase levels and prothrombin time. Most of the patients had improvement in the measured parameters. One patient died of sepsis, and one patient had development of hepatorenal syndrome that led to discontinuation of the trial.
      • Pai M.
      • Zacharoulis D.
      • Milicevic M.N.
      • et al.
      Autologous infusion of expanded mobilized adult bone marrow-derived CD34+ cells into patients with alcoholic liver cirrhosis.
      Three of the studies were randomized controlled trials, 2 of which revealed efficacy
      • Saito T.
      • Okumoto K.
      • Haga H.
      • et al.
      Potential therapeutic application of intravenous autologous bone marrow infusion in patients with alcoholic liver cirrhosis.
      • Lyra A.C.
      • Soares M.B.
      • da Silva L.F.
      • et al.
      Infusion of autologous bone marrow mononuclear cells through hepatic artery results in a short-term improvement of liver function in patients with chronic liver disease: a pilot randomized controlled study.
      and one that did not.
      • Spahr L.
      • Chalandon Y.
      • Terraz S.
      • et al.
      Autologous bone marrow mononuclear cell transplantation in patients with decompensated alcoholic liver disease: a randomized controlled trial.
      Table 1Trials of Mesenchymal Stem Cell Transplant in Patients With Chronic Liver Diseases
      ReferenceCell therapyDose, routeNo. of patientsType of studyResults
      Amer et al,
      • Amer M.E.
      • El-Sayed S.Z.
      • El-Kheir W.A.
      • et al.
      Clinical and laboratory evaluation of patients with end-stage liver cell failure injected with bone marrow-derived hepatocyte-like cells.
      2011
      BM-MSC (bone marrow– derived hepatocytes)Single dose, intrahepatic, intrasplenic10 Intrahepatic

      10 Intrasplenic

      20 Controls
      Controlled trialLess ascites/edema, increased albumin
      Zhang et al,
      • Zhang Z.
      • Lin H.
      • Shi M.
      • et al.
      Human umbilical cord mesenchymal stem cells improve liver function and ascites in decompensated liver cirrhosis patients.
      2012
      UC-MSCMultiple doses, peripheral vein30 Treatment

      15 Controls
      Randomized controlled trialLess ascites, decreased MELD
      Mohamadnejad et al,
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Mohyeddin-Bonab M.
      • et al.
      Phase 1 trial of autologous bone marrow mesenchymal stem cell transplantation in patients with decompensated liver cirrhosis.
      2007
      BM-MSCSingle dose, peripheral vein4Uncontrolled trialDecreased MELD in 2 of 4 patients
      Kharaziha et al,
      • Kharaziha P.
      • Hellström P.M.
      • Noorinayer B.
      • et al.
      Improvement of liver function in liver cirrhosis patients after autologous mesenchymal stem cell injection: a phase I-II clinical trial.
      2009
      BM-MSCSingle dose, portal vein8Uncontrolled trialDecreased MELD
      Peng et al,
      • Peng L.
      • Xie D.Y.
      • Lin B.L.
      • et al.
      Autologous bone marrow mesenchymal stem cell transplantation in liver failure patients caused by hepatitis B: short-term and long-term outcomes.
      2011
      BM-MSCSingle dose, hepatic artery53 Treatment

      105 Controls
      Randomized controlled trialDecreased T Bil, improved INR and MELD score
      Mohamadnejad et al,
      • Mohamadnejad M.
      • Alimoghaddam K.
      • Bagheri M.
      • et al.
      Randomized placebo-controlled trial of mesenchymal stem cell transplantation in decompensated cirrhosis.
      2013
      BM-MSCSingle dose, peripheral vein15 Treatment

      12 Placebo
      Randomized controlled trialNo differences between the groups
      BM-MSC = bone marrow–derived mesenchymal stem cells; INR = international normalized ratio; MELD = model of end-stage liver disease; T Bil = total bilirubin; UC-MSC = umbilical cord-derived mesenchymal stem cell.
      Table 2Trials of Unsorted Bone Marrow–Derived Mononuclear Cell Transplant in Patients With Chronic Liver Diseases
      ReferenceCell therapyDose, routeNo. of patientsType of studyResults
      Lyran et al,
      • Lyra A.C.
      • Soares M.B.
      • da Silva L.F.
      • et al.
      Feasibility and safety of autologous bone marrow mononuclear cell transplantation in patients with advanced chronic liver disease.
      2007
      BM-MNCSingle dose, hepatic artery10Uncontrolled trialDecreased T Bil and INR, increased serum albumin
      Terai et al,
      • Terai S.
      • Ishikawa T.
      • Omori K.
      • et al.
      Improved liver function in patients with liver cirrhosis after autologous bone marrow cell infusion therapy.
      2006
      BM-MNCSingle dose, peripheral vein9Uncontrolled trialImproved serum albumin, total protein, CP score
      Kim et al,
      • Kim J.K.
      • Park Y.N.
      • Kim J.S.
      • et al.
      Autologous bone marrow infusion activates the progenitor cell compartment in patients with advanced liver cirrhosis.
      2010
      BM-MNCSingle dose, peripheral vein10Uncontrolled trialLess ascites, improved CP scores, increased liver volume
      Saito et al,
      • Saito T.
      • Okumoto K.
      • Haga H.
      • et al.
      Potential therapeutic application of intravenous autologous bone marrow infusion in patients with alcoholic liver cirrhosis.
      2011
      BM-MNCSingle dose, peripheral vein5 Treatment

      5 Controls
      Randomized controlled trialImproved CP scores and INR, higher serum albumin and total protein
      Lyra et al,
      • Lyra A.C.
      • Soares M.B.
      • da Silva L.F.
      • et al.
      Infusion of autologous bone marrow mononuclear cells through hepatic artery results in a short-term improvement of liver function in patients with chronic liver disease: a pilot randomized controlled study.
      2010
      BM-MNCSingle dose, hepatic artery15 Treatment

      15 Controls
      Randomized controlled trialImproved serum albumin and CP score
      Spahr et al,
      • Spahr L.
      • Chalandon Y.
      • Terraz S.
      • et al.
      Autologous bone marrow mononuclear cell transplantation in patients with decompensated alcoholic liver disease: a randomized controlled trial.
      2013
      BM-MNC + GC-SFSingle dose, hepatic artery28 Treatment

      30 Controls
      Randomized controlled trialNo significant differences between study groups
      BM-MNC = bone marrow–derived mononuclear cells; CP = Child-Pugh; GC-SF = granulocyte colony-stimulating factor; INR = international normalized ratio; T Bil = total bilirubin.
      Spahr et al
      • Spahr L.
      • Chalandon Y.
      • Terraz S.
      • et al.
      Autologous bone marrow mononuclear cell transplantation in patients with decompensated alcoholic liver disease: a randomized controlled trial.
      recently reported a randomized trial in 58 patients with decompensated alcoholic liver disease. Thirty patients were randomized to standard medical care alone, and 28 patients received a combination of GC-SF injections and autologous bone marrow mononuclear cell transplant. Their primary end point was a decrease of 3 or more points in the MELD score. They found no significant differences between the groups; the MELD score improved in 64% of the patients who received GC-SF and autologous bone marrow mononuclear cell transplant vs 53% among those randomized to standard medical care. As possible explanations for the lack of therapeutic effect, they pointed out that they were not able to document an expansion of the hepatic progenitor cell compartment in a 4-week liver biopsy sample, and about 31% of the patients had an alcohol relapse during therapy. They attributed the lack of a response to therapy by hepatocytes to the presence of concomitant cirrhosis.
      Sorted HSCs, specifically CD34+ cells, have been used in 4 pilot studies
      • Pai M.
      • Zacharoulis D.
      • Milicevic M.N.
      • et al.
      Autologous infusion of expanded mobilized adult bone marrow-derived CD34+ cells into patients with alcoholic liver cirrhosis.
      • Gordon M.Y.
      • Levicar N.
      • Pai M.
      • et al.
      Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor.
      • Mohamadnejad M.
      • Namiri M.
      • Bagheri M.
      • et al.
      Phase 1 human trial of autologous bone marrow-hematopoietic stem cell transplantation in patients with decompensated cirrhosis.
      • Levicar N.
      • Pai M.
      • Habib N.A.
      • et al.
      Long-term clinical results of autologous infusion of mobilized adult bone marrow derived CD34+ cells in patients with chronic liver disease.
      in patients with chronic liver diseases (Table 3). These uncontrolled studies showed improvement of liver test results and CP scores.
      Table 3Trials of Sorted Hematopoietic Stem Cell Transplant in Patients With Chronic Liver Diseases
      ReferenceCell therapyDose, routeNo. of patientsType of studyResults
      Gordan et al,
      • Gordon M.Y.
      • Levicar N.
      • Pai M.
      • et al.
      Characterization and clinical application of human CD34+ stem/progenitor cell populations mobilized into the blood by granulocyte colony-stimulating factor.
      2006
      CD34+Single dose, portal vein or hepatic artery5Uncontrolled trialSerum albumin improved, T Bil improved
      Mohamadnejad et al,
      • Mohamadnejad M.
      • Namiri M.
      • Bagheri M.
      • et al.
      Phase 1 human trial of autologous bone marrow-hematopoietic stem cell transplantation in patients with decompensated cirrhosis.
      2007
      CD34+Single dose, hepatic artery4Uncontrolled trialSerum albumin, INR, T Bil improved
      Pai et al,
      • Pai M.
      • Zacharoulis D.
      • Milicevic M.N.
      • et al.
      Autologous infusion of expanded mobilized adult bone marrow-derived CD34+ cells into patients with alcoholic liver cirrhosis.
      2008
      CD34+Single dose, hepatic artery9Uncontrolled trialCP score improved, T Bil decreased
      Levicar et al,
      • Levicar N.
      • Pai M.
      • Habib N.A.
      • et al.
      Long-term clinical results of autologous infusion of mobilized adult bone marrow derived CD34+ cells in patients with chronic liver disease.
      2008
      CD34+Single dose, hepatic artery5Uncontrolled trialImproved T Bil
      CP = Child-Pugh; INR = international normalized ratio; T Bil = total bilirubin.

      Clinical Trials With GC-SF

      There was one controlled trial with CD133+ cells in a different clinical setting in which cell therapy was used as a mechanism to increase liver volume growth before partial hepatectomy in patients with hepatic metastatic disease.
      • Fürst G.
      • Schulte am Esch J.
      • Poll L.W.
      • et al.
      Portal vein embolization and autologous CD133+ bone marrow stem cells for liver regeneration: initial experience.
      Another approach has been to use GC-SF injection to increase the production of HSCs. There have been 7 studies utilizing GC-SF
      • Yannaki E.
      • Anagnostopoulos A.
      • Kapetanos D.
      • et al.
      Lasting amelioration in the clinical course of decompensated alcoholic cirrhosis with boost infusions of mobilized peripheral blood stem cells.
      • Gaia S.
      • Smedile A.
      • Omedè P.
      • et al.
      Feasibility and safety of G-CSF administration to induce bone marrow-derived cells mobilization in patients with end stage liver disease.
      • Yan L.
      • Han Y.
      • Wang J.
      • Liu J.
      • Hong L.
      • Fan D.
      Peripheral blood monocytes from patients with HBV related decompensated liver cirrhosis can differentiate into functional hepatocytes.
      • Gasbarrini A.
      • Rapaccini G.L.
      • Rutella S.
      • et al.
      Rescue therapy by portal infusion of autologous stem cells in a case of drug-induced hepatitis.
      • Khan A.A.
      • Parveen N.
      • Mahaboob V.S.
      • et al.
      Safety and efficacy of autologous bone marrow stem cell transplantation through hepatic artery for the treatment of chronic liver failure: a preliminary study.
      • Han Y.
      • Yan L.
      • Han G.
      • et al.
      Controlled trials in hepatitis B virus-related decompensate liver cirrhosis: peripheral blood monocyte transplant versus granulocyte-colony-stimulating factor mobilization therapy.
      • Garg V.
      • Garg H.
      • Khan A.
      • et al.
      Granulocyte colony-stimulating factor mobilizes CD34(+) cells and improves survival of patients with acute-on-chronic liver failure.
      (Table 4), although one of them was a case report of a patient with drug-induced acute liver failure
      • Gasbarrini A.
      • Rapaccini G.L.
      • Rutella S.
      • et al.
      Rescue therapy by portal infusion of autologous stem cells in a case of drug-induced hepatitis.
      (not included in Table 4). Two of the studies
      • Han Y.
      • Yan L.
      • Han G.
      • et al.
      Controlled trials in hepatitis B virus-related decompensate liver cirrhosis: peripheral blood monocyte transplant versus granulocyte-colony-stimulating factor mobilization therapy.
      • Garg V.
      • Garg H.
      • Khan A.
      • et al.
      Granulocyte colony-stimulating factor mobilizes CD34(+) cells and improves survival of patients with acute-on-chronic liver failure.
      were randomized controlled studies, both of which reported efficacy; however, they differed in terms of patient population studied and dose administered.
      Table 4Trials of GC-SF–Mobilized Hematopoietic Stem Cell Transplant in Patients With Chronic Liver Diseases
      ReferenceCell therapyDose, routeNo. of patientsType of studyResults
      Yannaki et al,
      • Yannaki E.
      • Anagnostopoulos A.
      • Kapetanos D.
      • et al.
      Lasting amelioration in the clinical course of decompensated alcoholic cirrhosis with boost infusions of mobilized peripheral blood stem cells.
      2006
      GC-SF/PBMNCSingle dose, hepatic artery2Uncontrolled trialCP score improved, MELD score improved
      Gaia et al,
      • Gaia S.
      • Smedile A.
      • Omedè P.
      • et al.
      Feasibility and safety of G-CSF administration to induce bone marrow-derived cells mobilization in patients with end stage liver disease.
      2006
      GC-SFMultiple doses of GC-SF8Uncontrolled trialFeasibility, safety study
      Yan et al,
      • Yan L.
      • Han Y.
      • Wang J.
      • Liu J.
      • Hong L.
      • Fan D.
      Peripheral blood monocytes from patients with HBV related decompensated liver cirrhosis can differentiate into functional hepatocytes.
      2007
      GC-SF/HGFUnclear2Uncontrolled trialPBMNCs were transformed in hepatocyte-like cells
      Khan et al,
      • Khan A.A.
      • Parveen N.
      • Mahaboob V.S.
      • et al.
      Safety and efficacy of autologous bone marrow stem cell transplantation through hepatic artery for the treatment of chronic liver failure: a preliminary study.
      2007
      GC-SF/CD34+Single dose, hepatic artery4Uncontrolled trialImproved serum albumin, T Bil, ALT
      Han et al,
      • Han Y.
      • Yan L.
      • Han G.
      • et al.
      Controlled trials in hepatitis B virus-related decompensate liver cirrhosis: peripheral blood monocyte transplant versus granulocyte-colony-stimulating factor mobilization therapy.
      2008
      GC-SF/PBMNCSingle dose, hepatic artery20 GC-SF plus PBMNC infusion 20 GC-SFRandomized controlled trialGC-SF plus PBMNC group had better liver test results
      Garg et al,
      • Garg V.
      • Garg H.
      • Khan A.
      • et al.
      Granulocyte colony-stimulating factor mobilizes CD34(+) cells and improves survival of patients with acute-on-chronic liver failure.
      2012
      GC-SFMultiple doses23 Treatment 24 PlaceboRandomized, blinded, controlled trialImproved MELD score, better patient survival
      ALT = alanine aminotransferase; CP = Child-Pugh; GC-SF = granulocyte colony-stimulating factor; HGF = hepatocyte growth factor; MELD = model of end-stage liver disease; PBMNC = peripheral blood mononuclear cells; T Bil = total bilirubin.
      Garg et al
      • Garg V.
      • Garg H.
      • Khan A.
      • et al.
      Granulocyte colony-stimulating factor mobilizes CD34(+) cells and improves survival of patients with acute-on-chronic liver failure.
      evaluated GC-SF therapy in the setting of acute-on-chronic liver failure. Forty-seven consecutive patients with acute-on-chronic liver failure were randomized to receive 12 doses of GC-SF (5 μg/kg subcutaneously) or placebo. Of the 23 patients who received GC-SF therapy, 16 (69.6%) survived, compared with 7 (29.2%) of 24 patients who received placebo. Actuarial survival at 60 days was 66% vs 26% (P=.001). There was also significant improvement in CPT scores, MELD scores, and Sequential Organ Failure Assessment scores associated with GC-SF therapy. The authors also observed a lower incidence of hepatorenal syndrome, hepatic encephalopathy, or sepsis in the GC-SF therapy group. They also reported a significant increase of the CD34+ cell population in the liver associated with GC-SF therapy.
      In these pilot studies, as well as randomized trials, there were no unexpected serious adverse events that could be attributed to cell therapy. Worsening hepatic fibrosis and a possible increased risk of hepatocellular carcinoma associated with stem cell therapy should be monitored for a longer period of time in future trials.
      The preliminary results obtained with various modalities of adult stem cell therapy in patients with ESLD are promising. It is difficult to reach a definite conclusion on its utility in the setting of cirrhosis. Future clinical trials should standardize the cell preparations utilized. Thus far, investigators have used bone marrow–derived mononuclear cells, bone marrow MSCs, bone marrow HSCs, peripheral blood mononuclear cells from GC-SF–mobilized peripheral blood, CD34+ cells, and CD133+ cells, which makes comparison among studies quite challenging. The period of administration has also been variable; it ranges from one infusion to multiple infusions in variable periods of time.
      These cell therapies have been administered to patients with different underlying etiologies and variable degrees of compensation. The mechanism of action of cell therapies may differ among different etiologies and degrees of decompensation.

      iPSCs and the Future of Cell Therapies in Hepatology

      There is a growing body of evidence from experimental models of liver injury supporting the use of hepatocytes derived from embryonic stem cells.
      • Shafritz D.A.
      • Oertel M.
      Model systems and experimental conditions that lead to effective repopulation of the liver by transplanted cells.
      • Woo D.H.
      • Kim S.K.
      • Lim H.J.
      • et al.
      Direct and indirect contribution of human embryonic stem cell-derived hepatocyte-like cells to liver repair in mice.
      However, ethical barriers limit the widespread use of embryonic stem cell technology. Recently, however, the Nobel Prize–winning discovery of the pluripotency factors
      • Takahashi K.
      • Yamanaka S.
      Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.
      has revealed remarkable cellular plasticity in cells previously dogmatically considered to be “terminally differentiated.” Conceptually based on somatic cell nuclear transfer technology,
      • Gurdon J.B.
      • Elsdale T.R.
      • Fischberg M.
      Sexually mature individuals of Xenopus laevis from the transplantation of single somatic nuclei.
      it is now possible to generate iPSCs from virtually any tissue in the human body and to then recapitulate developmental biology in vitro to generate diverse cellular phenotypes.
      • Rashid S.T.
      • Alexander G.J.
      Induced pluripotent stem cells: from Nobel Prizes to clinical applications.
      To accomplish this, cells from a patient or an experimental animal model (typically skin fibroblasts obtained via a skin biopsy) are expanded in culture and subjected to “reprogramming” by enforced expression of a limited number of pluripotency factors (eg, Oct 3/4, Sox2, Klf4, and c-Myc), which collectively revert the somatic cells back to a pluripotent state (Figure 1).
      Figure thumbnail gr1
      Figure 1Derivation and use of induced pluripotent stem cells (iPSCs) for liver diseases. HLCs = hepatocytelike cells.
      On the basis of known developmental biology of the liver, several groups have developed methods for generating hepatocytelike cells (HLCs) from iPSCs via stepwise differentiation strategies through definitive endoderm, hepatic specification, and hepatocyte maturation.

      Si-Tayeb K, Noto FK, Nagaoka M, et al. Highly efficient generation of human hepatocyte-like cells from induced pluripotent stem cells [published correction appears in Hepatology. 2010;51(3):1094]. Hepatology. 2010;51(1):297-305.

      • Sancho-Bru P.
      • Roelandt P.
      • Narain N.
      • et al.
      Directed differentiation of murine-induced pluripotent stem cells to functional hepatocyte-like cells.
      • Yu Y.
      • Liu H.
      • Ikeda Y.
      • et al.
      Hepatocyte-like cells differentiated from human induced pluripotent stem cells: relevance to cellular therapies.
      • Chen Y.F.
      • Tseng C.Y.
      • Wang H.W.
      • Kuo H.C.
      • Yang V.W.
      • Lee O.K.
      Rapid generation of mature hepatocyte-like cells from human induced pluripotent stem cells by an efficient three-step protocol.
      • Aravalli R.N.
      • Cressman E.N.
      • Steer C.J.
      Hepatic differentiation of porcine induced pluripotent stem cells in vitro.
      Direct differentiation from fibroblasts to either hepatocytes or bipotent hepatic cells using defined factors (without a pluripotent intermediate) have also been described.
      • Yu B.
      • He Z.Y.
      • You P.
      • et al.
      Reprogramming fibroblasts into bipotential hepatic stem cells by defined factors.
      • Huang P.
      • He Z.
      • Ji S.
      • et al.
      Induction of functional hepatocyte-like cells from mouse fibroblasts by defined factors.
      The HLCs generated in this fashion express hepatocyte proteins (eg, albumin) and share synthetic (urea) and metabolic (cytochrome P-450) features of mature hepatocytes.
      • Yu Y.
      • Fisher J.E.
      • Lillegard J.B.
      • Rodysill B.
      • Amiot B.
      • Nyberg S.L.
      Cell therapies for liver diseases.
      These remarkable advances are paralleled by an astounding array of genetic information from large-scale sequencing efforts as well as improved methods for seamless genetic engineering.
      • Liu J.Z.
      • Hov J.R.
      • Folseraas T.
      • et al.
      UK-PSCSC Consortium; International IBD Genetics Consortium; International PSC Study Group
      Dense genotyping of immune-related disease regions identifies nine new risk loci for primary sclerosing cholangitis.
      • Campbell J.M.
      • Hartjes K.A.
      • Nelson T.J.
      • Xu X.
      • Ekker S.C.
      New and TALENted genome engineering toolbox.
      The incredible potential of these regenerative medicine technologies spans all of modern medicine and has been embraced as a strategic priority at the national level and among many academic institutions. Multiple groups have reported the ability to generate mature hepatic cell types from adult cells, to genetically modify them in culture, and to transplant and engraft these cells within the liver in vivo.
      • Choi S.M.
      • Kim Y.
      • Liu H.
      • Chaudhari P.
      • Ye Z.
      • Jang Y.Y.
      Liver engraftment potential of hepatic cells derived from patient-specific induced pluripotent stem cells.
      The stunning corollary is that mature liver cells derived from patient-specific iPSCs could potentially be a limitless source of high-quality, individualized liver cells that can be (1) studied in vitro as a patient-specific model of liver disease, (2) treated in vitro to test putative therapeutic compounds, (3) genetically modified to correct underlying disease-causing defects, and (4) transplanted (without the need for immunosuppression) as individualized, cell-based, regenerative therapies for hepatic disorders.
      • Subba Rao M.
      • Sasikala M.
      • Nageshwar Reddy D.
      Thinking outside the liver: induced pluripotent stem cells for hepatic applications.
      Indeed, HLCs originating from iPSCs have been used successfully to model several inherited metabolic liver disorders, including α1-antitrypsin deficiency, familial hypercholesterolemia, and hereditary tyrosinemia, among others.
      • Rashid S.T.
      • Corbineau S.
      • Hannan N.
      • et al.
      Modeling inherited metabolic disorders of the liver using human induced pluripotent stem cells.
      The iPSC-derived HLCs have also produced beneficial effects in experimental models of both liver injury and partial hepatectomy.
      • Espejel S.
      • Roll G.R.
      • McLaughlin K.J.
      • et al.
      Induced pluripotent stem cell-derived hepatocytes have the functional and proliferative capabilities needed for liver regeneration in mice.
      Despite these promising advances, head-to-head comparisons of mature hepatocytes and iPSC-derived HLCs do continue to yield some notable differences in gene expression (eg, α-fetoprotein) and functionality, both in vitro
      • Yu Y.
      • Liu H.
      • Ikeda Y.
      • et al.
      Hepatocyte-like cells differentiated from human induced pluripotent stem cells: relevance to cellular therapies.
      and in vivo.
      • Takebe T.
      • Sekine K.
      • Enomura M.
      • et al.
      Vascularized and functional human liver from an iPSC-derived organ bud transplant.
      These differences indicate that additional improvements may be needed before clinical application of these cell types can be considered. Additional study will also be needed to assuage theoretical concerns about tumorigenicity, teratoma formation, epigenetic memory of reprogrammed cells, and the unknown effects of potential stray genetic changes left over from the reprogramming process.
      It may be possible to generate other liver cell types using iPSC technology as well, such as cholangiocytes, endothelial cells, and stellate cells, in order to modify chronic biliary disease, liver angiogenesis, and hepatic fibrogenesis. Indeed, cholangiocytic elements derived from both embryonic stem cells
      • Jin L.F.
      • Ji S.H.
      • Yang J.F.
      • Ji W.Z.
      Notch signalling dependent differentiation of cholangiocyte-like cells from rhesus monkey embryonic stem cells.
      and iPSCs
      • Nakamura N.
      • Saeki K.
      • Mitsumoto M.
      • et al.
      Feeder-free and serum-free production of hepatocytes, cholangiocytes, and their proliferating progenitors from human pluripotent stem cells: application to liver-specific functional and cytotoxic assays.
      • Yanagida A.
      • Ito K.
      • Chikada H.
      • Nakauchi H.
      • Kamiya A.
      An in vitro expansion system for generation of human iPS cell-derived hepatic progenitor-like cells exhibiting a bipotent differentiation potential.
      have been reported. Mature and functional iPSC-derived cholangiocytelike cells would be an important advancement given the complexities of incorporating biliary elements into organ buds or bioartificial organs.
      • Takebe T.
      • Sekine K.
      • Enomura M.
      • et al.
      Vascularized and functional human liver from an iPSC-derived organ bud transplant.
      • Sanal M.G.
      Future of liver transplantation: non-human primates for patient-specific organs from induced pluripotent stem cells.
      The concept of cholangiocyte transplant for repopulation or repair of a diseased biliary system is conceptually appealing given the clinical access offered by endoscopic retrograde cholangiopancreatography. Such technology could be revolutionary for patients with chronic biliary disorders such as primary sclerosing cholangitis, primary biliary cirrhosis, or ischemic cholangiopathy after transplant, all of which are essentially untreatable at this time without whole-organ transplant.
      Numerous therapeutic modalities for cell-based therapy are being investigated for the treatment of liver disease (Figure 2), including cell transplant (hepatocytes, LSPCs, or HLCs), autologous transfer of circulating or bone marrow–derived stem cells, and stimulation of native stem cell compartments (ie, GC-SF).
      Figure thumbnail gr2
      Figure 2Various modalities of cell-based therapies for liver diseases. GC-SF= granulocyte colony-stimulating factor; +/− = with or without.

      Conclusion

      Over the past several years, there have been remarkable advancements in liver regenerative medicine including numerous promising observations at the basic science and translational levels. As a result, it appears that we are now on the cusp of new paradigms for the management of chronic liver disease including cell-based therapies. The field is ripe for ongoing basic science advancements as well as standardized and carefully designed clinical trials to bridge the final knowledge gaps and make these new therapies a reality for patients with ESLD.

      Supplemental Online Material

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