Cellular therapy for liver disease

Exploiting in silico modelling to enhance translation of liver cell therapies from bench to bedside

Cell therapies are emerging as promising treatments for a range of liver diseases but translational bottlenecks still remain including: securing and assessing the safe and effective delivery of cells to the disease site; ensuring successful cell engraftment and function; and preventing immunogenic responses. Here we highlight three therapies, each utilising a different cell type, at different stages in their clinical translation journey: transplantation of multipotent mesenchymal stromal/signalling cells, hepatocytes and macrophages. To overcome bottlenecks impeding clinical progression, we advocate for wider use of mechanistic in silico modelling approaches. We discuss how in silico approaches, alongside complementary experimental approaches, can enhance our understanding of the mechanisms underlying successful cell delivery and engraftment. Furthermore, such combined theoretical-experimental approaches can be exploited to develop novel therapies, address safety and efficacy challenges, bridge the gap between in vitro and in vivo model systems, and compensate for the inherent differences between animal model systems and humans. We also highlight how in silico model development can result in fewer and more targeted in vivo experiments, thereby reducing preclinical costs and experimental animal numbers and potentially accelerating translation to the clinic. The development of biologically-accurate in silico models that capture the mechanisms underpinning the behaviour of these complex systems must be reinforced by quantitative methods to assess cell survival post-transplant, and we argue that non-invasive in vivo imaging strategies should be routinely integrated into transplant studies.

A Novel Approach to Orthotopic Hepatocyte Transplantation Engineered With Liver Hydrogel for Fibrotic Livers, Enhancing Cell-Cell Interaction and Angiogenesis

Hepatocyte transplantation (HCT) is a potential bridging therapy or an alternative to liver transplantation. Conventionally, single-cell hepatocytes are injected via the portal vein. This strategy, however, has yet to overcome poor cell engraftment and function. Therefore, we developed an orthotopic HCT method using a liver-derived extracellular matrix (L-ECM) gel. PXB cells (flesh mature human hepatocytes) were dispersed into the hydrogel solution in vitro, and the gel solution was immediately gelated in 37°C incubators to investigate the affinity between mature human hepatocyte and the L-ECM gel. During the 3-day cultivation in hepatocyte medium, PXB cells formed cell aggregates via cell-cell interactions. Quantitative analysis revealed human albumin production in culture supernatants. For the in vivo assay, PXB cells were encapsulated in the L-ECM gel and transplanted between the liver lobes of normal rats. Pathologically, the L-ECM gel was localized at the transplant site and retained PXB cells. Cell survival and hepatic function marker expression were verified in another rat model wherein thioacetamide was administered to induce liver fibrosis. Moreover, cell-cell interactions and angiogenesis were enhanced in the L-ECM gel compared with that in the collagen gel. Our results indicate that L-ECM gels can help engraft transplanted hepatocytes and express hepatic function as a scaffold for cell transplantation.

Isolation, culture, and delivery considerations for the use of mesenchymal stem cells in potential therapies for acute liver failure

Acute liver failure (ALF) is a high-mortality syndrome for which liver transplantation is considered the only effective treatment option. A shortage of donor organs, high costs and surgical complications associated with immune rejection constrain the therapeutic effects of liver transplantation. Recently, mesenchymal stem cell (MSC) therapy was recognized as an alternative strategy for liver transplantation. Bone marrow mesenchymal stem cells (BMSCs) have been used in clinical trials of several liver diseases due to their ease of acquisition, strong proliferation ability, multipotent differentiation, homing to the lesion site, low immunogenicity and anti-inflammatory and antifibrotic effects. In this review, we comprehensively summarized the harvest and culture expansion strategies for BMSCs, the development of animal models of ALF of different aetiologies, the critical mechanisms of BMSC therapy for ALF and the challenge of clinical application.

Organoids and regenerative hepatology

The burden of liver diseases is increasing worldwide, with liver transplantation remaining the only treatment option for end-stage liver disease. Regenerative medicine holds great potential as a therapeutic alternative, aiming to repair or replace damaged liver tissue with healthy functional cells. The properties of the cells used are critical for the efficacy of this approach. The advent of liver organoids has not only offered new insights into human physiology and pathophysiology, but also provided an optimal source of cells for regenerative medicine and translational applications. Here, we discuss various historical aspects of 3D organoid culture, how it has been applied to the hepatobiliary system, and how organoid technology intersects with the emerging global field of liver regenerative medicine. We outline the hepatocyte, cholangiocyte, and nonparenchymal organoids systems available and discuss their advantages and limitations for regenerative medicine as well as future directions.

Extracellular vesicles derived from mesenchymal stem/stromal cells: The regenerative impact in liver diseases

Liver dysfunctions are classified into acute and chronic diseases, which comprise a heterogeneous group of pathological features and a high mortality rate. Liver transplantation remains the gold-standard therapy for most liver diseases, with concomitant limitations related to donor organ shortage and lifelong immunosuppressive therapy. A concept in liver therapy intends to overcome these limitations based on the secreted extracellular vesicles (EVs; microvesicles and exosomes) by mesenchymal stem/stromal cells (MSCs). A significant number of studies have shown that factors released by MSCs could induce liver repair and ameliorate systemic inflammation through paracrine effects. It is well known that this paracrine action is based not only on the secretion of cytokines and growth factors but also on EVs, which regulate pathways associated with inflammation, hepatic fibrosis, integrin-linked protein kinase signaling, and apoptosis. Herein, we extensively discuss the differential effects of MSC-EVs on different liver diseases and on cellular and animal models and address the complex molecular mechanisms involved in the therapeutic potential of EVs. In addition, we cover the crucial information regarding the type of molecules contained in MSC-EVs that can be effective in the context of liver diseases. In conclusion, outcomes on MSC-EV-mediated therapy are expected to lead to an innovative, cell-free, noninvasive, less immunogenic, and nontoxic alternative strategy for liver treatment and to provide important mechanistic information on the reparative function of liver cells.

Role of Immune Cells in Biliary Repair

The biliary system is comprised of cholangiocytes and plays an important role in maintaining liver function. Under normal conditions, cholangiocytes remain in the stationary phase and maintain a very low turnover rate. However, the robust biliary repair is initiated in disease conditions, and different repair mechanisms can be activated depending on the pathological changes. During biliary disease, immune cells including monocytes, lymphocytes, neutrophils, and mast cells are recruited to the liver. The cellular interactions between cholangiocytes and these recruited immune cells as well as hepatic resident immune cells, including Kupffer cells, determine disease outcomes. However, the role of immune cells in the initiation, regulation, and suspension of biliary repair remains elusive. The cellular processes of cholangiocyte proliferation, progenitor cell differentiation, and hepatocyte-cholangiocyte transdifferentiation during biliary diseases are reviewed to manifest the underlying mechanism of biliary repair. Furthermore, the potential role of immune cells in crucial biliary repair mechanisms is highlighted. The mechanisms of biliary repair in immune-mediated cholangiopathies, inherited cholangiopathies, obstructive cholangiopathies, and cholangiocarcinoma are also summarized. Additionally, novel techniques that could clarify the underlying mechanisms of biliary repair are displayed. Collectively, this review aims to deepen the understanding of the mechanisms of biliary repair and contributes potential novel therapeutic methods for treating biliary diseases.

Routes of Stem Cell Administration

Stem cells are very promising for the treatment of a plethora of human diseases. Numerous clinical studies have been conducted to assess the safety and efficacy of various stem cell types. Factors that ensure successful therapeutic outcomes in patients are cell-based parameters such as source, viability, and number, as well as frequency and timing of intervention and disease stage. Stem cell administration routes should be appropriately chosen as these can affect homing and engraftment of the cells and hence reduce therapeutic effects, or compromise safety, resulting in serious adverse events. In this chapter, we will describe the use of stem cells in organ repair and regeneration, in particular, the liver and the available routes of cell delivery in the clinic for end-stage liver diseases. Factors affecting homing and engraftment of stem cells for each administration route will be discussed.

A narrative review of liver regeneration-from models to molecular basis

Objective

To elucidate the characteristics of different liver regeneration animal models, understand the activation signals and mechanisms related to liver regeneration, and obtain a more comprehensive conception of the entire liver regeneration process.

Background

Liver regeneration is one of the most enigmatic and fascinating phenomena of the human organism. Despite suffering significant injuries, the liver still can continue to perform its complex functions through the regeneration system. Although advanced topics on liver regeneration have been proposed; unfortunately, complete regeneration of the liver has not been achieved until now. Therefore, increasing understanding of the liver regenerative process can help improve our treatment of liver failure. It will provide a new sight for the treatment of patients with liver injury in the clinic.

Methods

Literatures on liver regeneration animal models and involved basic research on molecular mechanisms were retrieved to analyze the characteristics of different models and those related to molecular basis.

Conclusions

The process of liver regeneration is complex and intricate, consisting of various and interactive pathways. There is sufficient evidence to demonstrate that liver regeneration is similar between humans and rodents. At the same time, many of the same cytokines, growth factors, and signaling pathways are relevant. There are many gaps in our current knowledge. Understanding of this knowledge will provide more supportive clinical treatment strategies, including small-scale liver transplantation and high-quality regenerative process after surgical resection, and offer possible targets to treat the dysregulation of regeneration that occurs in chronic hepatic diseases and tumors. Current research work, such as the use of animal models as in vivo vectors for high-quality human hepatocytes, represents a unique and significant cutting edge in the field of liver regeneration.

Cell therapy strategies for COVID-19: Current approaches and potential applications

Coronavirus disease 2019 (COVID-19) continues to burden society worldwide. Despite most patients having a mild course, severe presentations have limited treatment options. COVID-19 manifestations extend beyond the lungs and may affect the cardiovascular, nervous, and other organ systems. Current treatments are nonspecific and do not address potential long-term consequences such as pulmonary fibrosis, demyelination, and ischemic organ damage. Cell therapies offer great potential in treating severe COVID-19 presentations due to their customizability and regenerative function. This review summarizes COVID-19 pathogenesis, respective areas where cell therapies have potential, and the ongoing 89 cell therapy trials in COVID-19 as of 1 January 2021.

Preclinical Application of Reduced Manipulated Processing Strategy to Collect Transplantable Hepatocytes: A Pilot and Feasibility Study

Background: The complex isolation and purification process of hepatocytes for transplantation is labor intensive and with great contamination risk. Here, as a pilot and feasibility study, we examined in vitro and in vivo hepatocyte isolation feasibility and cell function of Cell Saver^® Elite^®, an intraoperative blood-cell-recovery system. Methods: Rat and pig liver cells were collected using this system and then cultured in vitro, and their hepatocyte-specific enzymes were characterized. We then transplanted the hepatocytes in an established acute liver–injured (retrorsine+D-galactosamine-treated) rat model for engraftment. Recipient rats were sacrificed 1, 2, and 4 weeks after transplantation, followed by donor-cell identification and histological, serologic, and immunohistopathological examination. To demonstrate this Cell Saver^® strategy is workable in the first place, traditional (classical) strategy, in our study, behaved as certainty during the cell manufacturing process for monitoring quality assurance throughout the course, from the start of cell isolation to post-transplantation. Results: We noted that in situ collagenase perfusion was followed by filtration, centrifugation, and collection in the Cell Saver^® until the process ended. Most (>85%) isolated cells were hepatocytes (>80% viability) freshly demonstrating hepatocyte nuclear factor 4α and carbamoyl-phosphate synthase 1 (a key enzyme in the urea cycle), and proliferating through intercellular contact in culture, with expression of albumin and CYP3A4. After hepatocyte transplantation in dipeptidyl peptidase IV (−/−) rat liver, wild-type donor hepatocytes engrafted and repopulated progressively in 4 weeks with liver functional improvement. Proliferating donor hepatocyte–native biliary ductular cell interaction was identified. Post-transplantation global liver functional recovery after Cell Saver and traditional methods was comparable. Conclusions: Cell Saver^® requires reduced manual manipulation for isolating transplantable hepatocytes.

The effect of emodin on liver disease -- comprehensive advances in molecular mechanisms

Liver injury could be caused by a variety of causes, including alcohol, drug poisoning, autoimmune overreaction, etc. In the period of liver injury, hepatic stellate cells (HSCs) will be activated and produce excessive extracellular matrix (ECM). If injury cannot be suppressed, liver injury will develop into fibrosis, even cirrhosis and liver cancer. It is reported that some monomer components extracted from traditional Chinese medicine have better effects on protecting liver. Emodin, an anthraquinone compound extracted from the traditional Chinese medicine RHEI RADIX ET RHIZOMA, has anti-inflammatory, antioxidant, liver protection and anti-cancer effects, and can prevent liver injury induced by a variety of factors. By searching literatures related to the liver protection of emodin in PUBMED, SINOMED, EBM and CNKI databases, it was found that emodin could inhibit the production and promote the secretion of bile acids, and have a protective effect on intrahepatic cholestasis. Also, emodin reduce collagen synthesis and anti-hepatic fibrosis by inhibiting oxidative stress, TGF-β/Smad pathway and HSCs proliferation, and promoting apoptosis of HSCs. Emodin can also regulate lipid metabolism and regulate the synthesis and oxidation of lipids and cholesterol to protect the nonalcoholic fatty liver. Besides, emodin can induce the apoptosis of hepatocellular carcinoma cells by acting on the death receptor pathway and mitochondrial apoptosis pathway, thus inhibiting the development of hepatocellular carcinoma. Moreover, emodin can modulate immunity and improve immune rejection in liver transplantation animals. In conclusion, emodin has a good effect on liver protection, but further experimental data are needed to verify it.

Role of Granulocyte Colony-stimulating Factor Therapy in Cirrhosis, 'Inside Any Deep Asking Is the Answering'

Liver cirrhosis progresses through multiple clinical stages which culminate in either death or liver transplantation. Availability of organs, timely listing and prompt receipt of donor-livers pose difficulties in improving transplant-listed and transplant outcomes. In this regard, regenerative therapies, particularly with granulocyte colony-stimulating factor (GCSF), has become a lucrative option for improving transplant-free survival. However, the literature is confusing with regards to patient selection and real outcomes. In this exhaustive review, we describe the basics of liver fibrosis and cirrhosis through novel insights from a therapeutic point of view, discuss preclinical studies on GCSF in advanced liver disease to improve on clinical utility, shed light on the pertinent literature of GCSF in advanced cirrhosis, and provide astute inputs on growth factor therapy in decompensated cirrhosis.

New Perspectives in Liver Transplantation: From Regeneration to Bioengineering

Advanced liver diseases have very high morbidity and mortality due to associated complications, and liver transplantation represents the only current therapeutic option. However, due to worldwide donor shortages, new alternative approaches are mandatory for such patients. Regenerative medicine could be the more appropriate answer to this need. Advances in knowledge of physiology of liver regeneration, stem cells, and 3D scaffolds for tissue engineering have accelerated the race towards efficient therapies for liver failure. In this review, we propose an update on liver regeneration, cell-based regenerative medicine and bioengineering alternatives to liver transplantation.

Fetal liver stem cell transplantation for liver diseases

Stem cell transplantation exhibited a promising lifesaving therapy for various end-stage liver diseases and could serve as a salvaging bridge until curative methods can be performed. In past decades, mature hepatocytes, liver progenitor cells, mesenchymal stem cells and induced pluripotent stem cells have been practiced in above settings. However, long-term survival rates and continuous proliferation ability of these cells in vivo are unsatisfactory, whereas, fetal liver stem cells (FLSCs), given their unique superiority, may be the best candidate for stem cell transplantation technique. Recent studies have revealed that FLSCs could be used as an attractive genetic therapy or regenerative treatments for inherited metabolic or other hepatic disorders. In this study, we reviewed current status and advancements of FLSCs-based treatment.

Senescence suppressed proliferation of host hepatocytes is precondition for liver repopulation

In the fumarylacetoacetate hydrolase deficient (Fah^-/-) mouse, massive liver repopulation can be easily obtained after transplanted hepatocytes. Understanding the mechanisms of complete liver repopulation in Fah^-/- mice will be useful for future clinical application. Here, we found that the endogenous hepatocytes in liver of Fah^-/- mice undertook senescence during the time of tyrosinemia symptoms. Increase of senescent hepatocytes in Fah^-/- mice provided proliferative advantage to the transplanted hepatocytes. Importantly, senescent hepatocytes upregulated the expression of extracellular matrix enzyme, contributing to degradation of extracellular matrix components and weakness of cell adhesion and connection. The liver exhibiting a loose architecture provided the space for the engraftment and expansion of transplanted hepatocytes. These findings underscore the underlying mechanisms of completed liver repopulation in Fah^-/- mice. Senescence followed by loose hepatic parenchyma is a preconditioning for liver repopulation, which would be a promising strategy to achieve therapeutic liver repopulation in clinical settings.

A small molecule Hedgehog agonist HhAg1.5 mediated reprogramming breaks the quiescence of noninjured liver stem cells for rescuing liver failure

Liver is the second most transplanted organ according to United network for organ sharing. Due to shortage of compatible donors, surgical difficulties, immunological hindrance, and high postoperative cost, stem cell therapy is an attractive substitute of liver transplant for millions of patients suffering from hepatic failure. Due to several technical limitations such as viral integration, inefficient differentiation, and adult phenotypes and epigenetic memory of fibroblasts, induced pluripotent stem cells, mesenchymal stem cells, or induced hepatocyte may not present a great clinical substitute for liver transplant. We pioneered a novel technology for robust expansion of quiescent liver stem cells (LSCs) from mice via utilizing of Hedgehog agonist HhAg1.5 for 3 weeks. These expanded LSCs retained stem-like properties after multiple passaging and differentiated to hepatocytes and cholangiocytes. Grafting of ex vivo expanded LSCs in Fah^-/- Rag2^-/- Il2rg^-/- knockout mice, significantly increased life span compared to control group (P < 0.001). Thus in this study, we provide a promising viable substitute for primary hepatocytes for regenerative medicine and for life-threatening metabolic liver diseases.

Treatment of AECHB and Severe Hepatitis (Liver Failure)

This chapter describes the general treatment and immune principles and internal management for AECHB and HBV ACLF, including ICU monitoring, general supportive medications/nutrition/nursing, immune therapy, artificial liver supportive systems, hepatocyte/stem cell, and liver transplant, management for special populations, frequently clinical complications and the utilization of Chinese traditional medicines.

Early clinical indicators of severe hepatitis B include acratia, gastrointestinal symptoms, a daily increase in serum bilirubin >1 mg/dL, toxic intestinal paralysis, bleeding tendency and mild mind anomaly or character change, and the presence of other diseases inducing severe hepatitis. Laboratory indicators include T-Bil, PTA, cholinesterase, pre-albumin and albumin. The roles of immune indicators (such as IL-6, TNF-α, and fgl2), gene polymorphisms, HBV genotypes, and gene mutations as early clinical indicators.

Intensive Care Unit monitor patients with severe hepatitis include intracranial pressure, infection, blood dynamics, respiratory function, renal function, blood coagulation function, nutritional status and blood purification process. Nursing care should not only include routine care, but psychological and special care (complications).

Nutrition support and nursing care should be maintained throughout treatment for severe hepatitis. Common methods of evaluating nutritional status include direct human body measurement, creatinine height index (CHI) and subject global assessment of nutrition (SGA). Malnourished patients should receive enteral or parenteral nutrition support.

Immune therapies for severe hepatitis include promoting hepatocyte regeneration (e.g. with glucagon, hepatocyte growth factor and prostaglandin E1), glucocorticoid suppressive therapy, and targeting molecular blocking. Corticosteroid treatment should be early and sufficient, and adverse drug reactions monitored. Treatments currently being investigated are those targeting Toll-like receptors, NK cell/NK cell receptors, macrophage/immune coagulation system, CTLA-4/PD-1 and stem cell transplantation.

In addition to conventional drugs and radioiodine, corticosteroids and artificial liver treatment can also be considered for severe hepatitis patients with hyperthyreosis. Patients with gestational severe hepatitis require preventive therapy for fetal growth restriction, and it is necessary to choose the timing and method of fetal delivery. For patients with both diabetes and severe hepatitis, insulin is preferred to oral antidiabetic agents to control blood glucose concentration. Liver toxicity of corticosteroids and immune suppressors should be monitored during treatment for severe hepatitis in patients with connective tissue diseases including SLE, RA and sicca syndrome. Patient with connective tissue diseases should preferably be started after the antiviral treatment with nucleos(t)ide analogues.

An artificial liver can improve patients’ liver function; remove endotoxins, blood ammonia and other toxins; correct amino acid metabolism and coagulation disorders; and reverse internal environment imbalances. Non-bioartificial livers are suitable for patients with early and middle stage severe hepatitis; for late-stage patients waiting for liver transplantation; and for transplanted patients with rejection reaction or transplant failure. The type of artificial liver should be determined by each patient’s condition and previous treatment purpose, and patients should be closely monitored for adverse reactions and complications. Bio- and hybrid artificial livers are still under development.

MELD score is the international standard for choosing liver transplantation. Surgical methods mainly include the in situ classic type and the piggyback type; transplantation includes no liver prophase, no liver phase or new liver phase. Preoperative preparation, management of intraoperative and postoperative complications and postoperative long-term treatment are keys to success.

Severe hepatitis belongs to the categories of “acute jaundice”, “scourge jaundice”, and “hot liver” in traditional Chinese medicine. Treatment methods include Chinese traditional medicines, acupuncture and acupoint injection, external application of drugs, umbilical compress therapy, drip, blow nose therapy, earpins, and clysis. Dietary care is also an important part of traditional Chinese medicine treatment.

Prognosis, Prevention and Research Prospects of Progression to Severe Hepatitis B (Liver Failure)

This chapter describes the factors involved in the disease prognosis, parameters of outcome evaluations, principles and techniques for progression prevention. In last section, the future perspectives in both basic and clinical investigations towards unmet medical needs in AECHB and HBV ACLF are discussed.

Factors affecting the prognosis of patients with severe hepatitis B include those related to the virus (including viral load, HBeAg expression, and gene mutation), patient age, co-morbidity, TBil, INR, serum Cr, and the host genetic background. Indicators associated with patient prognosis include TBil, total cholesterol, albumin and prealbumin, hepatic encephalopathy, kidney damage, alpha-fetoprotein and vitamin D binding protein, blood sodium level, virus HBeAg expression and genotype, and blood glucose.

In addition to TBil, INR, hepatic encephalopathy, Cr level and AFP as indicators for prognosis of severe hepatitis, some other parameters such as clinical signs, symptoms, serum levels of total cholesterol and albumin and natrium, and coagulation factors are all valuable in assessment. The roles of cell apoptosis, liver regeneration and immunological parameters in assessing patient prognosis are under study. Prognostic evaluating systems include MELD score, MELD-Na score, iMELD score, KCI and CTP score.

Prevention of severe hepatitis B should be started in asymptomatic patients. Close observation, sufficient rest, adequate nutrition, meticulous nursing and psychological care, preventing and removing exacerbating factors, treating concomitant diseases, reasonable antiviral and comprehensive therapies are helpful to prevent CHB patients from developing to severe hepatitis. For patients who already have severe hepatitis B, the prevention and management of complications is important for lowering mortality rate.

New research directions in acute-on-chronic liver failure include: (1) Additional well controlled studies using present or new liver systems are warranted. Other approaches include the use of granulocyte colony stimulating factor to treat infections as well as the potential of use of stem cells to restore immune integrity and enhance liver regeneration. (2) Using new cell lines and animal models to understand the molecular biology of HBV, the immune response and to develop novel therapies. (3) Development of new anti-HBV strategies, e.g. silencing or remove cccDNA, enhancing immunologic clearance of HBV infection, inhibiting virus entry or HBc expression and using CRISP to disrupt cccDNA.

Delphinidin protects β2m-/Thy1+ bone marrow-derived hepatocyte stem cells against TGF-β1-induced oxidative stress and apoptosis through the PI3K/Akt pathway in vitro

β2m-/Thy1+ bone marrow-derived hepatocyte stem cells (BDHSCs) have a potential to be applied for cellular treatment in liver cirrhosis. However, the resultant tissue regeneration is restricted by transplanted cells' death. The accumulation of transforming growth factor beta 1 (TGF-β1) in liver fibrosis local microenvironment may play an essential role in the rapid cell death of implanted β2m-/Thy1+ BDHSCs. The main mechanism of poor survival of the target stem cells is still unknown. Delphinidin, an anthocyanidin, has potent antioxidant and anti-inflammatory activities. However, whether this bio-active ingredient can substantially contribute to β2m-/Thy1+ BDHSCs' protection from TGF-β1 induced apoptosis in vitro remains to be elucidated. In the present research, we determined whether delphinidin pretreatment can improve the survival of β2m-/Thy1+ BDHSCs during exposure to TGF-β1 and elucidated its underlying mechanisms. By using TGF-β1, we induced the apoptosis of β2m-/Thy1+ BDHSCs and assessed the apoptotic rates up to 24 h by flow cytometry. β2m-/Thy1+ BDHSC proliferation was gauged using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl- 2H-tetrazolium bromide (MTT) assay. The expression grades of Bcl-2, Akt, caspase-3, and Bax were observed through Western blot analysis. We found that delphinidin can significantly impede TGF-β1-induced apoptosis dose-dependently, scavenge reactive oxygen species (ROS), and inhibit the discharge of caspase-3 in β2m-/Thy1+ BDHSCs. We also demonstrated that delphinidin can activate the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway. The suppression of ROS and succeeding apoptosis was achieved by pretreatment with LY294002, a PI3K/Akt pathway inhibitor. In summary, our findings revealed that delphinidin can protect β2m-/Thy1+ BDHSCs from apoptosis and ROS-dependent oxidative stress induced by the TGF-β1 via PI3K/Akt signaling pathway. On the basis of these data, delphinidin can be regarded as a promising anti-apoptotic agent for enhancing β2m-/Thy1+ BDHSC survival during cell transplantation in liver cirrhosis patients.

Endothelial cell fitness dictates the source of regenerating liver vasculature

Employing a broad array of genetic lineage–tracing protocols including parabiotic pairs, Singhal et al. reveal that the fitness of liver endothelial cells (ECs) determines whether resident ECs or bone marrow–derived mononuclear cells will be adopted for vascular regeneration.

Neoangiogenesis plays a key role in diverse pathophysiological conditions, including liver regeneration. Yet, the source of new endothelial cells (ECs) remains elusive. By analyzing the regeneration of the liver vasculature in irradiation-based myeloablative and nonmyeloablative bone marrow transplantation mouse models, we discovered that neoangiogenesis in livers with intact endothelium was solely mediated by proliferation of resident ECs. However, following irradiation-induced EC damage, bone marrow–derived mononuclear cells were recruited and incorporated into the vasculature. Further experiments with direct bone marrow infusion or granulocyte colony–stimulating factor (G-CSF)–mediated progenitor cell mobilization, which resembles clinically relevant stem cell therapy, demonstrated that bone marrow–derived cells did not contribute to the regeneration of liver vasculature after two-thirds partial hepatectomy (PHx). Taken together, the data reconcile many of the discrepancies in the literature and highlight that the cellular source of regenerating endothelium depends on the fitness of the residual vasculature.

Progress in mesenchymal stem cell-based therapy for acute liver failure

Acute liver failure is a life-threatening clinical syndrome characterized by rapid development of hepatocellular necrosis leading to high mortality and resource costs. Numerous treatment strategies for acute liver failure simply prevent complications and decelerate disease progression. The only curative treatment for acute liver failure is liver transplantation, but there are many restrictions on the application of liver transplantation. In recent years, a growing number of studies have shown that stem cells can effectively treat acute liver failure. Several types of stem cells have been used to study liver diseases; mesenchymal stem cells are most commonly used because they are easy to obtain and present no ethical problems. The aims of this article are to review the current knowledge regarding therapeutic mechanisms of mesenchymal stem cells in acute liver failure, to discuss recent advancements in preclinical and clinical studies in the treatment of mesenchymal stem cells, and to summarize the methodological improvement of mesenchymal stem cell transplantation in treating liver failure.

Beneficial effects of naringenin in liver diseases: Molecular mechanisms

Liver diseases are caused by different etiological agents, mainly alcohol consumption, viruses, drug intoxication or malnutrition. Frequently, liver diseases are initiated by oxidative stress and inflammation that lead to the excessive production of extracellular matrix (ECM), followed by a progression to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). It has been reported that some natural products display hepatoprotective properties. Naringenin is a flavonoid with antioxidant, antifibrogenic, anti-inflammatory and anticancer properties that is capable of preventing liver damage caused by different agents. The main protective effects of naringenin in liver diseases are the inhibition of oxidative stress, transforming growth factor (TGF-β) pathway and the prevention of the transdifferentiation of hepatic stellate cells (HSC), leading to decreased collagen synthesis. Other effects include the inhibition of the mitogen activated protein kinase (MAPK), toll-like receptor (TLR) and TGF-β non-canonical pathways, the inhibition of which further results in a strong reduction in ECM synthesis and deposition. In addition, naringenin has shown beneficial effects on nonalcoholic fatty liver disease (NAFLD) through the regulation of lipid metabolism, modulating the synthesis and oxidation of lipids and cholesterol. Moreover, naringenin protects from HCC, since it inhibits growth factors such as TGF-β and vascular endothelial growth factor (VEGF), inducing apoptosis and regulating MAPK pathways. Naringenin is safe and acts by targeting multiple proteins. However, it possesses low bioavailability and high intestinal metabolism. In this regard, formulations, such as nanoparticles or liposomes, have been developed to improve naringenin bioavailability. We conclude that naringenin should be considered in the future as an important candidate in the treatment of different liver diseases.

Hepatic Parenchymal Injury in Crigler-Najjar Type I

BACKGROUND

Crigler-Najjar syndrome type I (CNI) arises from biallelic variants of UGT1A1 that abrogate uridine diphosphate glucuronosyltransferase (UGT1A1) activity resulting in unconjugated hyperbilirubinemia. Historically, liver parenchyma in CNI was considered structurally and histologically normal. Recent review of CNI liver explants revealed fibrosis. Our aim was to investigate the association between hepatic histology and disease phenotype in CNI.

METHODS

We extracted data from the medical record at the time of liver transplant from 22 patients with CNI at the Children's Hospital of Pittsburgh, and reviewed explant histology. Continuous data were normally distributed, are presented as mean (±1 SD), and analyzed using two-tailed Student t-test. Categorical data were analyzed using the Chi-square test.

RESULTS

Both alanine transaminase (ALT; mean 87.4 IU/L) and aspartate transaminase (AST; mean 54.6 IU/L) were elevated. Nine (41%) of 22 explants had significant fibrosis. Pericentral (n = 5), periportal (n = 2), and mixed (n = 2) patterns of fibrosis occurred. A significant difference in mean age of subjects with fibrotic versus non-fibrotic livers (16.1 years vs 10.5 years; P = 0.02) was seen. There were no indices of synthetic liver dysfunction or portal hypertension. Neither a history of gallstone disease nor excess weight appeared to contribute to the development of fibrosis.

CONCLUSIONS

For the first time, we report a 41% prevalence of clinically silent, yet histologically significant fibrosis among subjects with Crigler-Najjar type 1. Risk for fibrosis appears to accrue with time, indicating that earlier intervention may be prudent whenever considering alternative treatments such as hepatocyte transplant, auxiliary liver transplant, or viral gene therapy.

Highly efficient and expedited hepatic differentiation from human pluripotent stem cells by pure small-molecule cocktails

Background

The advent of human-induced pluripotent stem cells holds great promise for producing ample individualized hepatocytes. Although previous efforts have succeeded in generating hepatocytes from human pluripotent stem cells in vitro by viral-based expression of transcription factors and/or addition of growth factors during the differentiation process, the safety issue of viral transduction and high cost of cytokines would hinder the downstream applications. Recently, the use of small molecules has emerged as a powerful tool to induce cell fate transition for their superior stability, safety, cell permeability, and cost-effectiveness.

Methods

In the present study, we established a novel efficient hepatocyte differentiation strategy of human pluripotent stem cells with pure small-molecule cocktails. This method induced hepatocyte differentiation in a stepwise manner, including definitive endoderm differentiation, hepatic specification, and hepatocyte maturation within only 13 days.

Results

The differentiated hepatic-like cells were morphologically similar to hepatocytes derived from growth factor-based methods and primary hepatocytes. These cells not only expressed specific hepatic markers at the transcriptional and protein levels, but also possessed main liver functions such as albumin production, glycogen storage, cytochrome P450 activity, and indocyanine green uptake and release.

Conclusions

Highly efficient and expedited hepatic differentiation from human pluripotent stem cells could be achieved by our present novel, pure, small-molecule cocktails strategy, which provides a cost-effective platform for in vitro studies of the molecular mechanisms of human liver development and holds significant potential for future clinical applications.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0794-4) contains supplementary material, which is available to authorized users.

Proceedings of the signature series event of the international society for cellular therapy: "Advancements in cellular therapies and regenerative medicine in digestive diseases," London, United Kingdom, May 3, 2017

A summary of the First Signature Series Event, "Advancements in Cellular Therapies and Regenerative Medicine for Digestive Diseases," held on May 3, 2017, in London, United Kingdom, is presented. Twelve speakers from three continents covered major topics in the areas of cellular therapy and regenerative medicine applied to liver and gastrointestinal medicine as well as to diabetes mellitus. Highlights from their presentations, together with an overview of the global impact of digestive diseases and a proposal for a shared online collection and data-monitoring platform tool, are included in this proceedings. Although growing evidence demonstrate the feasibility and safety of exploiting cell-based technologies for the treatment of digestive diseases, regulatory and methodological obstacles will need to be overcome before the successful implementation in the clinic of these novel attractive therapeutic strategies.

Insulin-like growth factor 2 is a key mitogen driving liver repopulation in mice

Hepatocyte transplantation holds great promise as an alternative to orthotopic organ transplantation in the treatment of liver diseases. However, obtaining clinically meaningful levels of liver repopulation has not been achieved because the mechanisms regulating hepatocyte proliferation in recipient livers have not yet been well characterized. In the mouse model of Hereditary Tyrosinemia Type I, the fumarylacetoacetate hydrolase-deficient (Fah^−/−) mouse, we found gradually increasing expression level of insulin-like growth factor 2 (IGF2) in the hepatocytes of host livers. Similarly, high levels of IGF2 were found in the livers of patients with deficient FAH activity. Recombinant IGF2 directly promotes proliferation of primary hepatocytes in vitro. Inhibition on IGF2 expression through the interruption of PI3K/Akt and MAPK pathways significantly reduced the level of liver repopulation in Fah^−/− mice. Interestingly, treatment with IGF2 before hepatocyte transplantation generally improved the amount of liver repopulation seen in various mice models of liver injury. Altogether, these findings underscore the underlying mechanisms of therapeutic liver repopulation in Fah^−/− mice, and indicate that IGF2 is a potential hepatocyte mitogen for liver cell transplantation therapies.

Historical Perspectives and Advances in Mesenchymal Stem Cell Research for the Treatment of Liver Diseases

Liver transplantation is the only effective therapy for patients with decompensated cirrhosis and fulminant liver failure. However, due to a shortage of donor livers and complications associated with immune suppression, there is an urgent need for new therapeutic strategies for patients with end-stage liver diseases. Given their unique function in self-renewal and differentiation potential, stem cells might be used to regenerate damaged liver tissue. Recent studies have shown that stem cell-based therapies can improve liver function in a mouse model of hepatic failure. Moreover, acellular liver scaffolds seeded with hepatocytes produced functional bioengineered livers for organ transplantation in preclinical studies. The therapeutic potential of stem cells or their differentiated progenies will depend on their capacity to differentiate into mature and functional cell types after transplantation. It will also be important to devise methods to overcome their genomic instability, immune reactivity, and tumorigenic potential. We review directions and advances in the use of mesenchymal stem cells and their derived hepatocytes for liver regeneration. We also discuss the potential applications of hepatocytes derived from human pluripotent stem cells and challenges to using these cells in treating end-stage liver disease.

Bioengineering considerations in liver regenerative medicine

Background

Liver disease contributes significantly to global disease burden and is associated with rising incidence and escalating costs. It is likely that innovative approaches, arising from the emerging field of liver regenerative medicine, will counter these trends.

Main body

Liver regenerative medicine is a rapidly expanding field based on a rich history of basic investigations into the nature of liver structure, physiology, development, regeneration, and function. With a bioengineering perspective, we discuss all major subfields within liver regenerative medicine, focusing on the history, seminal publications, recent progress within these fields, and commercialization efforts. The areas reviewed include fundamental aspects of liver transplantation, liver regeneration, primary hepatocyte cell culture, bioartificial liver, hepatocyte transplantation and liver cell therapies, mouse liver repopulation, adult liver stem cell/progenitor cells, pluripotent stem cells, hepatic microdevices, and decellularized liver grafts.

Conclusion

These studies highlight the creative directions of liver regenerative medicine, the collective efforts of scientists, engineers, and doctors, and the bright outlook for a wide range of approaches and applications which will impact patients with liver disease.

Periodic acid‑Schiff staining method for function detection of liver cells is affected by 2% horse serum in induction medium

Developing a thorough understanding of experimental methods of hepatic differentiation in hepatic progenitor cells (HPCs) should expand the knowledge of hepatocyte induction in vitro and may help to develop cell transplantation therapies for the clinical usage of HPCs in liver diseases. A previous induction method effectively induced differentiation and metabolic abilities in HPCs. Periodic acid-Schiff (PAS) staining is used to identify glycogen synthesis and hepatocyte function; however, this method failed to detect induced hepatocytes. The present study aimed to investigate the possible factors affecting the previous confusing results of PAS staining. Removal of single induction factors, including dexamethasone, hepatic growth factor and fibroblast growth factor 4 from the induction media did not restore PAS staining, whereas replacement of 2% horse serum (HS) with 10% fetal bovine serum (FBS) significantly increased the number of PAS positive cells. Following 12 days of basal induction, replacing the induction medium with media containing 10% FBS for 12–72 h significantly improved PAS staining, but did not influence indocyanine green uptake. Furthermore, incubation in induction medium with 10% FBS following 12 days of normal induction did not affect the expression of hepatic markers and mature function of HPCs. Therefore, the present study suggested that 2% HS in the induction medium did not affect the hepatic function of induced cells, but did affect glycogen storage, whereas replacement of medium with 10% FBS in advance of PAS staining may restore the failure of PAS staining in low serum concentrations of induced hepatocytes.

Clinical Application of Pluripotent Stem Cells: An Alternative Cell-Based Therapy for Treating Liver Diseases?

The worldwide shortage of donor livers for organ and hepatocyte transplantation has prompted the search for alternative therapies for intractable liver diseases. Cell-based therapy is envisaged as a useful therapeutic option to recover and stabilize the lost metabolic function for acute liver failure, end-stage and congenital liver diseases, or for those patients who are not considered eligible for organ transplantation. In recent years, research to identify alternative and reliable cell sources for transplantation that can be derived by reproducible methods has been encouraged. Human pluripotent stem cells (PSCs), which comprise both embryonic and induced PSCs, may offer many advantages as an alternative to hepatocytes for liver cell therapy. Their capacity for expansion, hepatic differentiation and self-renewal make them a promising source of unlimited numbers of hepatocyte-like cells for treating and repairing damaged livers. Immunogenicity and tumorigenicity of human PSCs remain the bottleneck for successful clinical application. However, recent advances made to develop disease-corrected hepatocyte-like cells from patients' human-induced PSCs by gene editing have opened up many potential gateways for the autologous treatment of hereditary liver diseases, which may likely reduce the risk of rejection and the need for lifelong immunosuppression. Well-defined methods to reduce the expression of oncogenic genes in induced PSCs, including protocols for their complete and safe hepatic differentiation, should be established to minimize the tumorigenicity of transplanted cells. On top of this, such new strategies are currently being rigorously tested and validated in preclinical studies before they can be safely transferred to clinical practice with patients.

Regenerative Medicine and the Biliary Tree

Despite decades of basic research, biliary diseases remain prevalent, highly morbid, and notoriously difficult to treat. We have, however, dramatically increased our understanding of biliary developmental biology, cholangiocyte pathophysiology, and the endogenous mechanisms of biliary regeneration and repair. All of this complex and rapidly evolving knowledge coincides with an explosion of new technological advances in the area of regenerative medicine. New breakthroughs such as induced pluripotent stem cells and organoid culture are increasingly being applied to the biliary system; it is only a matter of time until new regenerative therapeutics for the cholangiopathies are unveiled. In this review, the authors integrate what is known about biliary development, regeneration, and repair, and link these conceptual advances to the technological breakthroughs that are collectively driving the emergence of a new global field in biliary regenerative medicine.

Cellular Mechanisms of Liver Regeneration and Cell-Based Therapies of Liver Diseases

The emerging field of regenerative medicine offers innovative methods of cell therapy and tissue/organ engineering as a novel approach to liver disease treatment. The ultimate scientific foundation of both cell therapy of liver diseases and liver tissue and organ engineering is delivered by the in-depth studies of the cellular and molecular mechanisms of liver regeneration. The cellular mechanisms of the homeostatic and injury-induced liver regeneration are unique. Restoration of the mass of liver parenchyma is achieved by compensatory hypertrophy and hyperplasia of the differentiated parenchymal cells, hepatocytes, while expansion and differentiation of the resident stem/progenitor cells play a minor or negligible role. Participation of blood-borne cells of the bone marrow origin in liver parenchyma regeneration has been proven but does not exceed 1-2% of newly formed hepatocytes. Liver regeneration is activated spontaneously after injury and can be further stimulated by cell therapy with hepatocytes, hematopoietic stem cells, or mesenchymal stem cells. Further studies aimed at improving the outcomes of cell therapy of liver diseases are underway. In case of liver failure, transplantation of engineered liver can become the best option in the foreseeable future. Engineering of a transplantable liver or its major part is an enormous challenge, but rapid progress in induced pluripotency, tissue engineering, and bioprinting research shows that it may be doable.

Transplantation of Thy1+ Cells Accelerates Liver Regeneration by Enhancing the Growth of Small Hepatocyte-Like Progenitor Cells via IL17RB Signaling

Small hepatocyte-like progenitor cells (SHPCs) transiently form clusters in rat livers treated with retrorsine (Ret)/70% partial hepatectomy (PH). When Thy1⁺ cells isolated from d-galactosamine-treated rat livers were transplanted into the livers of Ret/PH-treated rats, the mass of the recipient liver transiently increased during the first 30 days after transplantation, suggesting that liver regeneration was enhanced. Here we addressed how Thy1⁺ cell transplantation stimulates liver regeneration. We found that the number and size of SHPC clusters increased in the liver at 14 days after transplantation. GeneChip analysis revealed that interleukin 17 receptor b (IL17rb) expression significantly increased in SHPCs from livers transplanted with Thy1⁺ cells. We subsequently searched for ligand-expressing cells and found that sinusoidal endothelial cells (SECs) and Kupffer cells expressed Il17b and Il25, respectively. Moreover, extracellular vesicles (EVs) separated from the conditioned medium of Thy1⁺ cell culture induced IL17b and IL25 expression in SECs and Kupffer cells, respectively. Furthermore, EVs enhanced IL17rb expression in small hepatocytes (SHs), which are hepatocytic progenitor cells; in culture, IL17B stimulated the growth of SHs. These results suggest that Thy1-EVs coordinate IL17RB signaling to enhance liver regeneration by targeting SECs, Kupffer cells, and SHPCs. Indeed, the administration of Thy1-EVs increased the number and size of SHPC clusters in Ret/PH-treated rat livers. Sixty days post-transplantation, most expanded SHPCs entered cellular senescence, and the enlarged liver returned to its normal size. In conclusion, Thy1⁺ cell transplantation enhanced liver regeneration by promoting the proliferation of intrinsic hepatic progenitor cells via IL17RB signaling. Stem Cells 2017;35:920-931.

A Prospective, Single-Blind, Placebo-Controlled Trial of Bone Marrow Aspirate Concentrate for Knee Osteoarthritis

BACKGROUND

Bone marrow aspirate concentrate (BMAC) is increasingly used as a regenerative therapy for musculoskeletal pathological conditions despite limited evidence-based support.

HYPOTHESIS

BMAC will prove feasible, safe, and efficacious for the treatment of pain due to mild to moderate degenerative joint disease of the knee.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

In this prospective, single-blind, placebo-controlled trial, 25 patients with bilateral knee pain from bilateral osteoarthritis were randomized to receive BMAC into one knee and saline placebo into the other. Fifty-two milliliters of bone marrow was aspirated from the iliac crests and concentrated in an automated centrifuge. The resulting BMAC was combined with platelet-poor plasma for an injection into the arthritic knee and was compared with a saline injection into the contralateral knee, thereby utilizing each patient as his or her own control. Safety outcomes, pain relief, and function as measured by Osteoarthritis Research Society International (OARSI) measures and the visual analog scale (VAS) score were tracked initially at 1 week, 3 months, and 6 months after the procedure.

RESULTS

There were no serious adverse events from the BMAC procedure. OARSI Intermittent and Constant Osteoarthritis Pain and VAS pain scores in both knees decreased significantly from baseline at 1 week, 3 months, and 6 months ( P ≤ .019 for all). Pain relief, although dramatic, did not differ significantly between treated knees ( P > .09 for all).

CONCLUSION

Early results show that BMAC is safe to use and is a reliable and viable cellular product. Study patients experienced a similar relief of pain in both BMAC- and saline-treated arthritic knees. Further study is required to determine the mechanisms of action, duration of efficacy, optimal frequency of treatments, and regenerative potential. Registration: ClinicalTrials.gov record 12-004459.

Biliary fibrosis drives liver repopulation and phenotype transition of transplanted hepatocytes

BACKGROUND & AIMS

Current research focuses on developing alternative strategies to restore decreased liver mass prior to the onset of end-stage liver disease. Cell engraftment/repopulation requires regeneration in normal liver, but we have shown that severe liver injury stimulates repopulation without partial hepatectomy (PH). We have now investigated whether a less severe injury, secondary biliary fibrosis, would drive engraftment/repopulation of ectopically transplanted mature hepatocytes.

METHODS

Ductular proliferation and progressive fibrosis in dipeptidyl-peptidase IV (DPPIV)(-) F344 rats was induced by common bile duct ligation (BDL). Purified DPPIV(+)/green fluorescent protein (GFP)(+) hepatocytes were infused without PH into the spleen of BDL rats and compared to rats without BDL.

RESULTS

Within one week, transplanted hepatocytes were detected in hepatic portal areas and at the periphery of expanding portal regions. DPPIV(+)/GFP(+) repopulating cell clusters of different sizes were observed in BDL rats but not untreated normal recipients. Surprisingly, some engrafted hepatocytes formed CK-19/claudin-7 expressing epithelial cells resembling cholangiocytes within repopulating clusters. In addition, substantial numbers of hepatocytes engrafted at the intrasplenic injection site assembled into multicellular groups. These also showed biliary "transdifferentiation" in the majority of intrasplenic injection sites of rats that received BDL but not in untreated recipients. PCR array analysis showed upregulation of osteopontin (SPP1). Cell culture studies demonstrated increased Itgβ4, HNF1β, HNF6, Sox-9, and CK-19 mRNA expression in hepatocytes incubated with osteopontin, suggesting that this secreted protein promotes dedifferentiation of hepatocytes.

CONCLUSIONS

Our studies show that biliary fibrosis stimulates liver repopulation by ectopically transplanted hepatocytes and also stimulates hepatocyte transition towards a biliary epithelial phenotype.

Cell therapy in chronic liver disease

PURPOSE OF REVIEW

To date, the only curative treatment for end-stage liver disease is liver transplantation, which is limited by the shortage of available organs. Cell therapy, in the form of cell transplantation or cell-based extracorporeal support devices, may in the future offer an alternative to transplantation, or at least provide liver function support as a bridging therapy until surgery may be performed. The purpose of this review is to highlight the most recent advances made in the field of cell therapy and regenerative medicine for the treatment of chronic liver disease.

RECENT FINDINGS

After hepatocyte transplantation, long-term engraftment in the liver and spleen may be achieved, which can be stimulated through preconditioning, multiple infusions, and inflammatory response blockade. Mesenchymal stem cells are promising candidates for cell transplantation, as they have been shown to reduce liver fibrosis and support endogenous regeneration. Adipose tissue-derived stem cells are also being tested in this setting, because of their ready availability. Bioartificial liver devices are being built that allow for effective preservation of hepatocytes, and one such device has recently demonstrated survival benefit in a porcine model of liver failure.

SUMMARY

Cell transplantation of primary hepatocytes or stem cell-derived hepatocyte-like cells for the treatment of chronic liver disease holds promise. Bioartificial liver systems may in the future be able to bridge acute-on-chronic liver failure patients to liver transplantation.

Immunological aspects of liver cell transplantation

Within the field of regenerative medicine, the liver is of major interest for adoption of regenerative strategies due to its well-known and unique regenerative capacity. Whereas therapeutic strategies such as liver resection and orthotopic liver transplantation (OLT) can be considered standards of care for the treatment of a variety of liver diseases, the concept of liver cell transplantation (LCTx) still awaits clinical breakthrough. Success of LCTx is hampered by insufficient engraftment/long-term acceptance of cellular allografts mainly due to rejection of transplanted cells. This is in contrast to the results achieved for OLT where long-term graft survival is observed on a regular basis and, hence, the liver has been deemed an immune-privileged organ. Immune responses induced by isolated hepatocytes apparently differ considerably from those observed following transplantation of solid organs and, thus, LCTx requires refined immunological strategies to improve its clinical outcome. In addition, clinical usage of LCTx but also related basic research efforts are hindered by the limited availability of high quality liver cells, strongly emphasizing the need for alternative cell sources. This review focuses on the various immunological aspects of LCTx summarizing data available not only for hepatocyte transplantation but also for transplantation of non-parenchymal liver cells and liver stem cells.

Repair of liver mediated by adult mouse liver neuro-glia antigen 2-positive progenitor cell transplantation in a mouse model of cirrhosis

NG2-expressing cells are a population of periportal vascular stem/progenitors (MLpvNG2(+) cells) that were isolated from healthy adult mouse liver by using a "Percoll-Plate-Wait" procedure. We demonstrated that isolated cells are able to restore liver function after transplantation into a cirrhotic liver, and co-localized with the pericyte marker (immunohistochemistry: PDGFR-β) and CK19. Cells were positive for: stem cell (Sca-1, CD133, Dlk) and liver stem cell markers (EpCAM, CD14, CD24, CD49f); and negative for: hematopoietic (CD34, CD45) and endothelial markers (CD31, vWf, von Willebrand factor). Cells were transplanted (1 × 10(6) cells) in mice with diethylnitrosamine-induced cirrhosis at week 6. Cells showed increased hepatic associated gene expression of alpha-fetoprotein (AFP), Albumin (Alb), Glucose-6-phosphatase (G6Pc), SRY (sex determining region Y)-box 9 (Sox9), hepatic nuclear factors (HNF1a, HNF1β, HNF3β, HNF4α, HNF6, Epithelial cell adhesion molecule (EpCAM), Leucine-rich repeated-containing G-protein coupled receptor 5-positive (Lgr5) and Tyrosine aminotransferase (TAT). Cells showed decreased fibrogenesis, hepatic stellate cell infiltration, Kupffer cells and inflammatory cytokines. Liver function markers improved. In a cirrhotic liver environment, cells could differentiate into hepatic lineages. In addition, grafted MLpvNG2(+) cells could mobilize endogenous stem/progenitors to participate in liver repair. These results suggest that MLpvNG2(+) cells may be novel adult liver progenitors that participate in liver regeneration.

Decellularized Liver Extracellular Matrix as Promising Tools for Transplantable Bioengineered Liver Promotes Hepatic Lineage Commitments of Induced Pluripotent Stem Cells

Liver transplantation is the last resort for liver failure patients. However, due to the shortage of donor organs, bioengineered liver generated from decellularized whole liver scaffolds and induced pluripotent stem cell (iPSC)-derived hepatocytes (iPSC-Heps) is being studied as an alternative approach to treat liver disease. Nevertheless, there has been no report on both the interaction of iPSC-Heps with a liver extracellular matrix (ECM) and the analysis of recellularized iPSC-Heps into the whole liver scaffolds. In this study, we produced porcine iPSC-Heps, which strongly expressed the hepatic markers α-fetoprotein and albumin and exhibited hepatic functionalities, including glycogen storage, lipid accumulation, low-density lipoprotein uptake, and indocyanine green metabolism. Supplementation of ECM from porcine decellularized liver containing liver-derived growth factors stimulated the albumin expression of porcine iPSC-Heps during differentiation procedures. The iPSC-Heps were reseeded into decellularized liver scaffolds, and the recellularized liver was cultured using a continuous perfusion system. The recellularized liver scaffolds were transplanted into rats for a short term, and the grafts expressed hepatocyte markers and did not rupture. These results provide a foundation for development of bioengineered liver using stem cell and decellularized scaffolds.

Blockade of cell adhesion molecules enhances cell engraftment in a murine model of liver cell transplantation

AIM

OLT is the best alternative for patients with end-stage liver diseases. However, as the need for organs surpasses donor availability, alternatives to OLT are required. LCT could be a useful option versus OLT in several patients even though its low cell-engraftment hampers its efficiency. Endothelial cell barrier is the main obstacle for the implantation of cells into the parenchyma. Our study has focused on the modification of the endothelial barrier with monoclonal antibodies against adhesion molecules in order to increase cell engraftment in a mouse model of liver cell transplantation.

METHODS

Anti-mouse CD54 and anti-mouse CD61 antibodies were administered intrasplenically to healthy mice within 60 min prior to stem cell transplantation. Animals were sacrificed either short term at 2h or middle term seven days after transplantation. Immunohistochemical techniques to detect alkaline phosphatase activity were used to identify the transplanted cells within the liver parenchyma.

RESULTS

Anti-CD54 and anti-CD61 administration increases vascular patency and cell engraftment. This represents a 32% and 45% increase, respectively, of engrafted cells compared to the control (p<0.05).

CONCLUSION

Modification of the vascular wall with monoclonal antibodies against endothelial adhesion molecules before cell transplantation enhances cell engraftment into the mouse liver.

Regenerative Medicine Build-Out

Regenerative technologies strive to boost innate repair processes and restitute normative impact. Deployment of regenerative principles into practice is poised to usher in a new era in health care, driving radical innovation in patient management to address the needs of an aging population challenged by escalating chronic diseases. There is urgency to design, execute, and validate viable paradigms for translating and implementing the science of regenerative medicine into tangible health benefits that provide value to stakeholders. A regenerative medicine model of care would entail scalable production and standardized application of clinical grade biotherapies supported by comprehensive supply chain capabilities that integrate sourcing and manufacturing with care delivery. Mayo Clinic has rolled out a blueprint for discovery, translation, and application of regenerative medicine therapies for accelerated adoption into the standard of care. To establish regenerative medical and surgical service lines, the Mayo Clinic model incorporates patient access, enabling platforms and delivery. Access is coordinated through a designated portal, the Regenerative Medicine Consult Service, serving to facilitate patient/provider education, procurement of biomaterials, referral to specialty services, and/or regenerative interventions, often in clinical trials. Platforms include the Regenerative Medicine Biotrust and Good Manufacturing Practice facilities for manufacture of clinical grade products for cell-based, acellular, and/or biomaterial applications. Care delivery leverages dedicated interventional suites for provision of regenerative services. Performance is tracked using a scorecard system to inform decision making. The Mayo Clinic roadmap exemplifies an integrated organization in the discovery, development, and delivery of regenerative medicine within a growing community of practice at the core of modern health care.

SIGNIFICANCE

Regenerative medicine is at the vanguard of health care poised to offer solutions for many of today's incurable diseases. Accordingly, there is a pressing need to develop, deploy, and demonstrate a viable framework for rollout of a regenerative medicine model of care. Translation of regenerative medicine principles into practice is feasible, yet clinical validity and utility must be established to ensure approval and adoption. Standardized and scaled-up regenerative products and services across medical and surgical specialties must in turn achieve a value-added proposition, advancing intended outcome beyond current management strategies.

Hepatic differentiation of porcine embryonic stem cells for translational research of hepatocyte transplantation

Porcine embryonic stem cells (ES) are considered attractive preclinical research tools for human liver diseases. Although several studies previously reported generation of porcine ES, none of these studies has described hepatic differentiation from porcine ES. The aim of this study was to generate hepatocytes from porcine ES and analyze their characteristics. We optimized conditions for definitive endoderm induction and developed a 4-step hepatic differentiation protocol. A brief serum-free condition with activin A efficiently induced definitive endoderm differentiation from porcine ES. The porcine ES-derived hepatocyte-like cells highly expressed hepatic markers including albumin and α-fetoprotein, and displayed liver characteristics such as glycogen storage, lipid production, and low-density lipoprotein uptake. For the first time, we describe a highly efficient protocol for hepatic differentiation from porcine ES. Our findings provide valuable information for translational liver research using porcine models, including hepatic regeneration and transplant studies, drug screening, and toxicology.

Murine Sca1(+)Lin(-) bone marrow contains an endodermal precursor population that differentiates into hepatocytes

The direct differentiation of hepatocytes from bone marrow cells remains controversial. Several mechanisms, including transdifferentiation and cell fusion, have been proposed for this phenomenon, although direct visualization of the process and the underlying mechanisms have not been reported. In this study, we established an efficient in vitro culture method for differentiation of functioning hepatocytes from murine lineage-negative bone marrow cells. These cells reduced liver damage and incorporated into hepatic parenchyma in two independent hepatic injury models. Our simple and efficient in vitro protocol for endodermal precursor cell survival and expansion enabled us to identify these cells as existing in Sca1⁺ subpopulations of lineage-negative bone marrow cells. The endodermal precursor cells followed a sequential developmental pathway that included endodermal cells and hepatocyte precursor cells, which indicates that lineage-negative bone marrow cells contain more diverse multipotent stem cells than considered previously. The presence of equivalent endodermal precursor populations in human bone marrow would facilitate the development of these cells into an effective treatment modality for chronic liver diseases.

Development and characterization of human-induced pluripotent stem cell-derived cholangiocytes

Cholangiocytes are the target of a heterogeneous group of liver diseases known as the cholangiopathies. An evolving understanding of the mechanisms driving biliary development provides the theoretical underpinnings for rational development of induced pluripotent stem cell (iPSC)-derived cholangiocytes (iDCs). Therefore, the aims of this study were to develop an approach to generate iDCs and to fully characterize the cells in vitro and in vivo. Human iPSC lines were generated by forced expression of the Yamanaka pluripotency factors. We then pursued a stepwise differentiation strategy toward iDCs, using precise temporal exposure to key biliary morphogens, and we characterized the cells, using a variety of morphologic, molecular, cell biologic, functional, and in vivo approaches. Morphology shows a stepwise phenotypic change toward an epithelial monolayer. Molecular analysis during differentiation shows appropriate enrichment in markers of iPSC, definitive endoderm, hepatic specification, hepatic progenitors, and ultimately cholangiocytes. Immunostaining, western blotting, and flow cytometry demonstrate enrichment of multiple functionally relevant biliary proteins. RNA sequencing reveals that the transcriptome moves progressively toward that of human cholangiocytes. iDCs generate intracellular calcium signaling in response to ATP, form intact primary cilia, and self-assemble into duct-like structures in three-dimensional culture. In vivo, the cells engraft within mouse liver, following retrograde intrabiliary infusion. In summary, we have developed a novel approach to generate mature cholangiocytes from iPSCs. In addition to providing a model of biliary differentiation, iDCs represent a platform for in vitro disease modeling, pharmacologic testing, and individualized, cell-based, regenerative therapies for the cholangiopathies.

Magnetic cell labeling of primary and stem cell-derived pig hepatocytes for MRI-based cell tracking of hepatocyte transplantation

Pig hepatocytes are an important investigational tool for optimizing hepatocyte transplantation schemes in both allogeneic and xenogeneic transplant scenarios. MRI can be used to serially monitor the transplanted cells, but only if the hepatocytes can be labeled with a magnetic particle. In this work, we describe culture conditions for magnetic cell labeling of cells from two different pig hepatocyte cell sources; primary pig hepatocytes (ppHEP) and stem cell-derived hepatocytes (PICM-19FF). The magnetic particle is a micron-sized iron oxide particle (MPIO) that has been extensively studied for magnetic cell labeling for MRI-based cell tracking. ppHEP could endocytose MPIO with labeling percentages as high as 70%, achieving iron content as high as ~55 pg/cell, with >75% viability. PICM-19FF had labeling >97%, achieving iron content ~38 pg/cell, with viability >99%. Extensive morphological and functional assays indicated that magnetic cell labeling was benign to the cells. The results encourage the use of MRI-based cell tracking for the development and clinical use of hepatocyte transplantation methodologies. Further, these results generally highlight the importance of functional cell assays in the evaluation of contrast agent biocompatibility.

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.

Cell therapy for liver disease: From liver transplantation to cell factory

Work over several decades has laid solid foundations for the advancement of liver cell therapy. To date liver cell therapy in people has taken the form of hepatocyte transplantation for metabolic disorders with a hepatic basis, and for acute or chronic liver failure. Although clinical trials using various types of autologous cells have been implemented to promote liver regeneration or reduce liver fibrosis, clear evidence of therapeutic benefits have so far been lacking. Cell types that have shown efficacy in preclinical models include hepatocytes, liver sinusoidal endothelial cells, mesenchymal stem cells, endothelial progenitor cells, and macrophages. However, positive results in animal models have not always translated through to successful clinical therapies and more realistic preclinical models need to be developed. Studies defining the optimal repopulation by transplanted cells, including routes of cell transplantation, superior engraftment and proliferation of transplanted cells, as well as optimal immunosuppression regimens are required. Tissue engineering approaches to transplant cells in extrahepatic locations have also been proposed. The derivation of hepatocytes from pluripotent or reprogrammed cells raises hope that donor organ and cell shortages could be overcome in the future. Critical hurdles to be overcome include the production of hepatocytes from pluripotent cells with equal functional capacity to primary hepatocytes and long-term phenotypic stability in vivo.