Formation of human hepatocytes by human hematopoietic stem cells in sheep

The Efficiency of Stem Cells (SCs) Differentiation into Functional Hepatocytes for Treating Liver Disorders: A Systematic Review

Stem cells provided new opportunity to treat various diseases, including liver disorders. Stem cells are unspecialized cells, stimulating influential research interest be indebted to their multipotent self-renewal capacity and differentiation characteristics into several specialized cell types. Many factors contribute to their differentiation into different cell types such as insulin producing cells, osteoblast, and hepatocytes. Accordingly, wide range methods and materials have been used to transform stem cells into hepatocytes, but effectiveness of differentiation is different and depends on several factors such as cell-to-cell adhesion, cell-to-cell contact, and cell biological change. Search was done in PubMed, Scopus, and WOS to evaluate results of studies about stem cells differentiation for higher efficacy. Among more than 28000 papers, 51 studies were considered eligible for more evaluations. Results indicated that most studies were performed on mesenchymal stem cells compared with other types. Acute liver failure was the most investigated liver disorder, and tissue engineering was the most investigated differentiation methods. Also, functional parameters were the most evaluated parameters in assessing differentiation efficacy. We summarize recent advances in increasing efficiency of stem cells differentiation using varied materials, since promising results of this review, further studies are needed to assess efficiency and safety of these cells transplantation in some liver disease treatment.

Liver Regeneration by Hematopoietic Stem Cells: Have We Reached the End of the Road?

The liver is the organ with the highest regenerative capacity in the human body. However, various insults, including viral infections, alcohol or drug abuse, and metabolic overload, may cause chronic inflammation and fibrosis, leading to irreversible liver dysfunction. Despite advances in surgery and pharmacological treatments, liver diseases remain a leading cause of death worldwide. To address the shortage of donor liver organs for orthotopic liver transplantation, cell therapy in liver disease has emerged as a promising regenerative treatment. Sources include primary hepatocytes or functional hepatocytes generated from the reprogramming of induced pluripotent stem cells (iPSC). Different types of stem cells have also been employed for transplantation to trigger regeneration, including hematopoietic stem cells (HSCs), mesenchymal stromal cells (MSCs), endothelial progenitor cells (EPCs) as well as adult and fetal liver progenitor cells. HSCs, usually defined by the expression of CD34 and CD133, and MSCs, defined by the expression of CD105, CD73, and CD90, are attractive sources due to their autologous nature, ease of isolation and cryopreservation. The present review focuses on the use of bone marrow HSCs for liver regeneration, presenting evidence for an ongoing crosstalk between the hematopoietic and the hepatic system. This relationship commences during embryogenesis when the fetal liver emerges as the crossroads between the two systems converging the presence of different origins of cells (mesoderm and endoderm) in the same organ. Ample evidence indicates that the fetal liver supports the maturation and expansion of HSCs during development but also later on in life. Moreover, the fact that the adult liver remains one of the few sites for extramedullary hematopoiesis—albeit pathological—suggests that this relationship between the two systems is ongoing. Can, however, the hematopoietic system offer similar support to the liver? The majority of clinical studies using hematopoietic cell transplantation in patients with liver disease report favourable observations. The underlying mechanism—whether paracrine, fusion or transdifferentiation or a combination of the three—remains to be confirmed.

Human-Immune-System (HIS) humanized mouse model (DRAGA: HLA-A2.HLA-DR4.Rag1KO.IL-2RγcKO.NOD) for COVID-19

We report a Human Immune System (HIS)-humanized mouse model ("DRAGA": HLA-A2.HLA-DR4.Rag1KO.IL-2 RγcKO.NOD) for COVID-19 research. DRAGA mice express transgenically HLA-class I and class-II molecules in the mouse thymus to promote human T cell development and human B cell Ig-class switching. When infused with human hematopoietic stem cells from cord blood reconstitute a functional human immune system, as well as human epi/endothelial cells in lung and upper respiratory airways expressing the human ACE2 receptor for SARS-CoV-2. The DRAGA mice were able to sustain SARS-CoV-2 infection for at least 25 days. Infected mice showed replicating virus in the lungs, deteriorating clinical condition, and human-like lung immunopathology including human lymphocyte infiltrates, microthrombi and pulmonary sequelae. Among the intra-alveolar and peri-bronchiolar lymphocyte infiltrates, human lung-resident (CD103⁺) CD8⁺ and CD4⁺ T cells were sequestered in epithelial (CD326⁺) lung niches and secreted granzyme B and perforin, suggesting anti-viral cytotoxic activity. Infected mice also mounted human IgG antibody responses to SARS-CoV-2 viral proteins. Hence, HIS-DRAGA mice showed unique advantages as a surrogate in vivo human model for studying SARS-CoV-2 immunopathological mechanisms and testing the safety and efficacy of candidate vaccines and therapeutics.

Platelets Boost Recruitment of CD133+ Bone Marrow Stem Cells to Endothelium and the Rodent Liver-The Role of P-Selectin/PSGL-1 Interactions

We previously demonstrated that clinical administration of mobilized CD133⁺ bone marrow stem cells (BMSC) accelerates hepatic regeneration. Here, we investigated the potential of platelets to modulate CD133⁺BMSC homing to hepatic endothelial cells and sequestration to warm ischemic livers. Modulatory effects of platelets on the adhesion of CD133⁺BMSC to human and mouse liver-sinusoidal- and micro- endothelial cells (EC) respectively were evaluated in in vitro co-culture systems. CD133⁺BMSC adhesion to all types of EC were increased in the presence of platelets under shear stress. This platelet effect was mostly diminished by antagonization of P-selectin and its ligand P-Selectin-Glyco-Ligand-1 (PSGL-1). Inhibition of PECAM-1 as well as SDF-1 receptor CXCR4 had no such effect. In a model of the isolated reperfused rat liver subsequent to warm ischemia, the co-infusion of platelets augmented CD133⁺BMSC homing to the injured liver with heightened transmigration towards the extra sinusoidal space when compared to perfusion conditions without platelets. Extravascular co-localization of CD133⁺BMSC with hepatocytes was confirmed by confocal microscopy. We demonstrated an enhancing effect of platelets on CD133⁺BMSC homing to and transmigrating along hepatic EC putatively depending on PSGL-1 and P-selectin. Our insights suggest a new mechanism of platelets to augment stem cell dependent hepatic repair.

Establishment of the Dual Humanized TK-NOG Mouse Model for HIV-associated Liver Pathogenesis

Despite the increased life expectancy of patients infected with human immunodeficiency virus-1 (HIV-1), liver disease has emerged as a common cause of their morbidity. The liver immunopathology caused by HIV-1 remains elusive. Small xenograft animal models with human hepatocytes and human immune system can recapitulate the human biology of the disease's pathogenesis. Herein, a protocol is described to establish a dual humanized mouse model through human hepatocytes and CD34⁺ hematopoietic stem/progenitor cells (HSPCs) transplantation, to study liver immunopathology as observed in HIV-infected patients. To achieve dual reconstitution, male TK-NOG (NOD.Cg-Prkdc^scid Il2rg^tm1Sug Tg(Alb-TK)7-2/ShiJic) mice are intraperitoneally injected with ganciclovir (GCV) doses to eliminate mouse transgenic liver cells, and with treosulfan for nonmyeloablative conditioning, both of which facilitate human hepatocyte (HEP) engraftment and human immune system (HIS) development. Human albumin (ALB) levels are evaluated for liver engraftment, and the presence of human immune cells in blood detected by flow cytometry confirms the establishment of human immune system. The model developed using the protocol described here resembles multiple components of liver damage from HIV-1 infection. Its establishment could prove to be essential for studies of hepatitis virus co-infection and for the evaluation of antiviral and antiretroviral drugs.

Mesenchymal stem cells to treat type 1 diabetes

What is clear is we are in the era of the stem cell and its potential in ameliorating human disease. Our perspective is generated from an in vivo model in a large animal that offers significant advantages (complete transplantation tolerance, large size and long life span). This review is an effort to meld our preclinical observations with others for the reader and to outline potential avenues to improve the present outlook for patients with diabetes. This effort exams the history or background of stem cell research in the laboratory and the clinic, types of stem cells, pluripotency or lack thereof based on a variety of pre-clinical investigations attempting endocrine pancreas recovery using stem cell transplantation. The focus is on the use of hematopoietic and mesenchymal stem cells. This review will also examine recent clinical experience following stem cell transplantation in patients with type 1 diabetes.

Exposure of the Bone Marrow Microenvironment to Simulated Solar and Galactic Cosmic Radiation Induces Biological Bystander Effects on Human Hematopoiesis

The stem cell compartment of the hematopoietic system constitutes one of the most radiosensitive tissues of the body and leukemias represent one of the most frequent radiogenic cancers with short latency periods. As such, leukemias may pose a particular threat to astronauts during prolonged space missions. Control of hematopoiesis is tightly governed by a specialized bone marrow (BM) microenvironment/niche. As such, any environmental insult that damages cells of this niche would be expected to produce pronounced effects on the types and functionality of hematopoietic/immune cells generated. We recently reported that direct exposure of human hematopoietic stem cells (HSC) to simulated solar energetic particle (SEP) and galactic cosmic ray (GCR) radiation dramatically altered the differentiative potential of these cells, and that simulated GCR exposures can directly induce DNA damage and mutations within human HSC, which led to leukemic transformation when these cells repopulated murine recipients. In this study, we performed the first in-depth examination to define changes that occur in mesenchymal stem cells present in the human BM niche following exposure to accelerated protons and iron ions and assess the impact these changes have upon human hematopoiesis. Our data provide compelling evidence that simulated SEP/GCR exposures can also contribute to defective hematopoiesis/immunity through so-called "biological bystander effects" by damaging the stromal cells that comprise the human marrow microenvironment, thereby altering their ability to support normal hematopoiesis.

Human hepatocyte depletion in the presence of HIV-1 infection in dual reconstituted humanized mice

Human immunodeficiency virus type 1 (HIV-1) infection impairs liver function, and liver diseases have become a leading cause of morbidity in infected patients. The immunopathology of liver damage caused by HIV-1 remains unclear. We used chimeric mice dually reconstituted with a human immune system and hepatocytes to address the relevance of the model to pathobiology questions related to human hepatocyte survival in the presence of systemic infection. TK-NOG males were transplanted with mismatched human hematopoietic stem/progenitor cells and hepatocytes, human albumin concentration and the presence of human immune cells in blood were monitored for hepatocytes and immune reconstitution, and mice were infected with HIV-1. HIV-1-infected animals showed a decline in human albumin concentration with a significant reduction in percentage of human hepatocytes compared to uninfected mice. The decrease in human albumin levels correlated with a decline in CD4+ cells in the liver and with an increase in HIV-1 viral load. HIV-1 infection elicited proinflammatory response in the immunological milieu of the liver in HIV-infected mice compared to uninfected animals, as determined by upregulation of IL23, CXCL10 and multiple toll-like receptor expression. The inflammatory reaction associated with HIV-1 infection in vivo could contribute to the depletion and dysfunction of hepatocytes. The dual reconstituted TK-NOG mouse model is a feasible platform to investigate hepatocyte-related HIV-1 immunopathogenesis.This article has an associated First Person interview with the first author of the paper.

Interleukin-10 secreted by mesenchymal stem cells attenuates acute liver failure through inhibiting pyroptosis

AIM

Recently, the benefit of mesenchymal stem cells (MSCs) as a cell-based therapy for acute liver failure (ALF) has gained much attention, although the mechanism of action of MSCs in the treatment of ALF remains elusive. Pyroptosis is a novel form of programmed cell death with an intense inflammatory response. The aim of the present study was to explore the soluble cytokines secreted by MSCs and their therapeutic effects through inhibiting pyroptosis in ALF.

METHODS

Mesenchymal stem cells obtained from C57BL/6 mice were isolated and cultured according to an established protocol. The MSCs were transplanted into mice with D-galactosamine (D-Gal)-induced ALF. Liver function, survival rate, histology, and inflammatory factors were determined. Exogenous recombinant rat interleukin (IL)-10, ShIL-RNA, and MCC950 (NLRP3 inhibitor) were given to the mice to explore the therapeutic mechanism of MSCs. Statistical analyses were carried out with spss version 19.0, and all data were analyzed by independent-samples t-test.

RESULTS

Injection of IL-10 or MSC transplantation ameliorated D-Gal-induced increase in alanine aminotransferase, aspartate aminotransferase, total bilirubin, NH3, and inflammatory cytokines. Blockage of IL-10 confirmed the therapeutic significance of this cytokine.

CONCLUSION

Pyroptosis was inhibited after IL-10 infusion and inhibition of NLRP3 by MCC950 reversed liver dysfunction.

Interleukin-10 Contributes to Therapeutic Effect of Mesenchymal Stem Cells for Acute Liver Failure via Signal Transducer and Activator of Transcription 3 Signaling Pathway

Background:

Mesenchymal stem cells (MSCs) transplantation has been proven to have therapeutic potential for acute liver failure (ALF). However, the mechanism remains controversial. Recently, modulation of inflammation by MSCs has been regarded as a crucial mechanism. The aim of the present study was to explore the soluble cytokines secreted by MSCs and their therapeutic effects in ALF.

Methods:

MSCs isolated from Sprague-Dawley rats were identified by fluorescence-activated cell sorting analysis. Conditioned medium derived from MSCs (MSCs-CM) was collected and analyzed by a cytokine microarray. MSCs and MSCs-CM were transplanted into rats with D-galactosamine-induced ALF. Liver function, survival rate, histology, and inflammatory factors were determined. Exogenous recombinant rat interleukin (IL)-10, anti-rat IL-10 antibody, and AG490 (signal transducer and activator of transcription 3 [STAT3] signaling pathway inhibitor) were administered to explore the therapeutic mechanism of MSCs-CM. Statistical analysis was performed with SPSS version 19.0, and all data were analyzed by the independent-sample t-test.

Results:

There are statistical differences of the survival curve between ALF+MSCs group and ALF+Dulbecco's modified Eagle's medium (DMEM) group, as well as ALF+MSCs-CM group and ALF+DMEM group (all P < 0.05). Serum alanine aminotransferase (ALT) level in the ALF+MSCs and ALF+MSCs-CM groups was lower than that in the ALF+DMEM group (865.53±52.80 vs. 1709.75±372.12 U/L and 964.72±414.59 vs. 1709.75±372.12 U/L, respectively, all P < 0.05); meanwhile, serum aspartate aminotransferase (AST) level in the ALF+MSCs and ALF+MSCs-CM groups was lower than that in the ALF+DMEM group (2440.83±511.94 vs. 4234.35±807.30 U/L and 2739.83±587.33 vs. 4234.35±807.30 U/L, respectively, all P < 0.05). Furthermore, MSCs or MSCs-CM treatment significantly reduced serum interferon-γ (IFN-γ), IL-1β, IL-6 levels and increased serum IL-10 level compared with DMEM (all P < 0.05). Proteome profile analysis of MSCs-CM indicated the presence of anti-inflammatory factors and IL-10 was the most distinct. Blocking of IL-10 confirmed the therapeutic significance of this cytokine. Phosphorylated STAT3 was upregulated after IL-10 infusion and inhibition of STAT3 by AG490 reversed the therapeutic effect of IL-10.

Conclusions:

The factors released by MSCs, especially IL-10, have the potential for therapeutic recovery of ALF, and the STAT3 signaling pathway may mediate the anti-inflammatory effect of IL-10.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

Mesenchymal stem cell therapy for cirrhosis: Present and future perspectives

Cirrhosis occurs as a result of various chronic liver injuries, which may be caused by viral infections, alcohol abuse and the administration of drugs and chemicals. Recently, bone marrow cells (BMCs), hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) have been used for developing treatments for cirrhosis. Clinical trials have investigated the therapeutic potential of BMCs, HSCs and MSCs for the treatment of cirrhosis based on their potential to differentiate into hepatocytes. Although the therapeutic mechanisms of BMC, HSC and MSC treatments are still not fully characterized, the evidence thus far has indicated that the potential therapeutic mechanisms of MSCs are clearer than those of BMCs or HSCs with respect to liver regenerative medicine. MSCs suppress inflammatory responses, reduce hepatocyte apoptosis, increase hepatocyte regeneration, reverse liver fibrosis and enhance liver functionality. This paper summarizes the clinical studies that have used BMCs, HSCs and MSCs in patients with liver failure or cirrhosis. We also present the potential therapeutic mechanisms of BMCs, HSCs and MSCs for the improvement of liver function.

The hematopoietic system in the context of regenerative medicine

Hematopoietic stem cells (HSC) represent the prototype stem cell within the body. Since their discovery, HSC have been the focus of intensive research, and have proven invaluable clinically to restore hematopoiesis following inadvertent radiation exposure and following radio/chemotherapy to eliminate hematologic tumors. While they were originally discovered in the bone marrow, HSC can also be isolated from umbilical cord blood and can be "mobilized" peripheral blood, making them readily available in relatively large quantities. While their ability to repopulate the entire hematopoietic system would already guarantee HSC a valuable place in regenerative medicine, the finding that hematopoietic chimerism can induce immunological tolerance to solid organs and correct autoimmune diseases has dramatically broadened their clinical utility. The demonstration that these cells, through a variety of mechanisms, can also promote repair/regeneration of non-hematopoietic tissues as diverse as liver, heart, and brain has further increased their clinical value. The goal of this review is to provide the reader with a brief glimpse into the remarkable potential HSC possess, and to highlight their tremendous value as therapeutics in regenerative medicine.

Targeted migration of mesenchymal stem cells modified with CXCR4 to acute failing liver improves liver regeneration

AIM: To improve the colonization rate of transplanted mesenchymal stem cells (MSCs) in the liver and effect of MSC transplantation for acute liver failure (ALF).

METHODS: MSC was modified with the chemokine CXC receptor 4 (CXCR4) gene (CXCR4-MSC) or not (Null-MSC) through lentiviral transduction. The characteristics of CXCR4-MSCs and Null-MSCs were determined by real-time quantitative polymerase chain reaction, Western blotting and flow cytometry. CXCR4-MSCs and Null-MSCs were infused intravenously 24 h after administration of CCl₄ in nude mice. The distribution of the MSCs, survival rates, liver function, hepatocyte regeneration and growth factors of the recipient mice were analyzed.

RESULTS: In vitro, CXCR4-MSCs showed better migration capability toward stromal cell-derived factor-1α and a protective effect against thioacetamide in hepatocytes. In vivo imaging showed that CXCR4-MSCs migrated to the liver in larger numbers than Null-MSCs 1 and 5 d after ALF. Higher colonization led to a longer lifetime and better liver function. Either CXCR4-MSCs or Null-MSCs exhibited a paracrine effect through secreting hepatocyte growth factor and vascular endothelial growth factor. Immunohistochemical analysis of Ki-67 showed increased cell proliferation in the damaged liver of CXCR4-MSC-treated animals.

CONCLUSION: Genetically modified MSCs expressing CXCR4 showed greater colonization and conferred better functional recovery in damaged liver.

Bone Marrow Derived Kit-positive Cells Colonize the Gut but Fail to Restore Pacemaker Function in Intestines Lacking Interstitial Cells of Cajal

Background/Aims

Several motility disorders are associated with disruption of interstitial cells of Cajal (ICC), which provide important functions, such as pacemaker activity, mediation of neural inputs and responses to stretch in the gastrointestinal (GI) tract. Restoration of ICC networks may be therapeutic for GI motor disorders. Recent reports have suggested that Kit⁺ cells can be restored to the GI tract via bone marrow (BM) transplantation. We tested whether BM derived cells can lead to generation of functional activity in intestines naturally lacking ICC.

Methods

BM cells from Kit^+/copGFP mice, in which ICC are labeled with a green fluorescent protein, were transplanted into W/W^V intestines, lacking ICC. After 12 weeks the presence of ICC was analyzed by immunohistochemistry and functional analysis of electrical behavior and contractile properties.

Results

After 12 weeks copGFP⁺ BM derived cells were found within the myenteric region of intestines from W/W^V mice, typically populated by ICC. Kit⁺ cells failed to develop interconnections typical of ICC in the myenteric plexus. The presence of Kit⁺ cells was verified with Western analysis. BM cells failed to populate the region of the deep muscular plexus where normal ICC density, associated with the deep muscular plexus, is found in W/W^V mice. Engraftment of Kit⁺-BM cells resulted in the development of unitary potentials in transplanted muscles, but slow wave activity failed to develop. Motility analysis showed that intestinal movements in transplanted animals were abnormal and similar to untransplanted W/W^V intestines.

Conclusions

BM derived Kit⁺ cells colonized the gut after BM transplantation, however these cells failed to develop the morphology and function of mature ICC.

Genetically modified mesenchymal stem cells overexpressing CXCR4 show increased colonization ability and confer better liver regeneration in mice

AIM: To explore whether mesenchymal stem cells (MSCs) overexpressing CXCR4 show increased colonization ability and confer better liver regeneration in mice.

METHODS: MSCs were modified with CXCR4 gene (CXCR4-MSCs) or not (Null-MSCs) through lentiviral transduction. The characteristics of CXCR4-MSCs and Null-MSCs were determined by RT-PCR and flow cytometry. CXCR4-MSCs and Null-MSCs were infused intravenously 24 h after administration of CCl4 in nude mice. The concentration of SDF-1α in the damaged liver was detected by ELISA. Transwell migration assays were carried out to evaluate the migration ability of MSCs toward SDF-1α. The distribution of the stem cells, their survival rates, liver function, histopathology and hepatocyte regeneration were analyzed.

RESULTS: Transfected MSCs overexpressed CXCR4 at both gene and protein levels. In vitro, CXCR4-MSCs showed better migration capability toward SDF-1α. In vivo imaging showed that CXCR4-MSCs migrated to the liver in greater numbers than Null-MSCs 5 d after intravenous infusion in mice with acute liver failure (ALF). Higher colonization led to a longer lifetime and better liver function. Immunohistochemistry analysis of Ki-67 showed increased cell proliferation in the damaged liver of CXCR4-MSC-treated animals.

CONCLUSION: Genetically modified MSCs expressing CXCR4 show greater colonization ability and confer better functional recovery of the damaged liver.

Stem cells in liver regeneration and their potential clinical applications

Stem cells constitute a population of "primitive cells" with the ability to divide indefinitely and give rise to specialized cells under special conditions. Because of these two characteristics they have received particular attention in recent decades. These cells are the primarily responsible factors for the regeneration of tissues and organs and for the healing of lesions, a feature that makes them a central key in the development of cell-based medicine, called Regenerative Medicine. The idea of wound and organ repair and body regeneration is as old as the mankind, reflecting the human desire for inhibiting aging and immortality and it is first described in the ancient Greek myth of Prometheus. It is of interest that the myth refers to liver, an organ with remarkable regenerative ability after loss of mass and function caused by liver injury or surgical resection. Over the last decade there has been an important progress in understanding liver physiology and the mechanisms underlying hepatic development and regeneration. As liver transplantation, despite its difficulties, remains the only effective therapy for advanced liver disease so far, scientific interest has nowadays been orientated towards Regenerative Medicine and the use of stem cells to repair damaged liver. This review is focused on the available literature concerning the role of stem cells in liver regeneration. It summarizes the results of studies concerning endogenous liver regeneration and stem cell experimental protocols. Moreover, this review discusses the clinical studies that have been conducted in humans so far.

HGF and SDF-1-mediated mobilization of CD133+ BMSC for hepatic regeneration following extensive liver resection

BACKGROUND

The molecular mechanisms of haematopoietic stem cells (HSC) mobilization and homing to the liver after partial hepatectomy (PH) remain largely unexplored.

METHODS

Functional liver volume loss and regain was determined by computerized tomography (CT) volumetry in 30 patients following PH. Peripheral HSC mobilization was investigated by fluorescence-activated cell sorting (FACS) analyses and cytokine enzyme-linked immunosorbent assay assays. Migration of purified HSC towards hepatic growth factor (HGF) and stroma-derived factor-1 (SDF-1) gradients was tested in vitro. Mice after 70% PH were examined for HSC mobilization by FACS and cytokine mRNA expression in the liver. FACS-sorted HSC were administered after PH and hepatocyte proliferation was evaluated by immunohistochemical staining for Ki67.

RESULTS

Impaired liver function was noted after extended hepatic resection when compared to smaller resections. Patients with large liver resections were characterized by significantly higher levels of peripheral HSC which were positively correlated with the extent of resected liver volume and its regain after 3 weeks. Increased plasma levels of HGF, SDF-1 and insulin like growth factor (IGF-1) were evident within the first 6 hours post resection. Migration assays of human HSC in vitro showed a specific target-demonstrated migration towards recombinant HGF and SDF-1 gradients in a concentration and specific receptor (c-Met and CXCR4) dependent manner. The evaluation of peripheral human alpha foetoprotein expression demonstrated pronounced stemness following increased CD133(+) HSC in the course of liver regeneration following PH. Our human data were further validated in a murine model of PH and furthermore demonstrated increased hepatocyte proliferation subsequent to CD133(+) HSC treatment.

CONCLUSION

HGF and SDF-1 are required for effective HSC mobilization and homing to the liver after hepatic resection. These findings have significant implications for potential therapeutic strategies targeting chemotactant modulation and stem cell mobilization for liver protection and regeneration.

Role of stem cells in repair of liver injury: Experimental and clinical benefit of transferred stem cells on liver failure

Although the liver has a high regenerative capacity, as a result of massive hepatocyte death, liver failure occurs. In addition to liver failure, for acute, chronic and hereditary diseases of the liver, cell transplantation therapies can stimulate regeneration or at least ensure sufficient function until liver transplantation can be performed. The lack of donor organs and the risks of rejection have prompted extensive experimental and clinical research in the field of cellular transplantation. Transplantation of cell lineages involved in liver regeneration, including mature hepatocytes, fetal hepatocytes, fetal liver progenitor cells, fetal stem cells, hepatic progenitor cells, hepatic stem cells, mesenchymal stem cells, hematopoietic stem cells, and peripheral blood and umbilical cord blood stem cells, have been found to be beneficial in the treatment of liver failure. In this article, the results of experimental and clinical cell transplantation trials for liver failure are reviewed, with an emphasis on regeneration.

In utero transplantation: Disparate ramifications

In utero stem cell transplantation, which promises treatment for a host of genetic disorders early in gestation before disease effect stems from Ray Owen’s seminal observation that self-tolerance, is acquired during gestation. To date, in utero transplantation (IUT) has proved useful in characterizing the hematopoietic stem cell. Recent observations support its use as an in vivo method to further understanding of self-tolerance. Preclinical development continues for its application as a treatment for childhood hematolymphoid diseases. In addition, IUT may offer therapeutic options in the treatment of diabetes among other diseases. Thus IUT serves as a technique or system important in both a basic and applied format. This review summarizes these findings.

Perspective on liver regeneration by bone marrow-derived stem cells-a scientific realization or a paradox

Bone marrow (BM)-derived stem cells are reported to have cellular plasticity, which provoked many investigators to use of these cells in the regeneration of nonhematopoietic tissues. However, adult stem cell plasticity contradicts our classic understanding on progressive restriction of the developmental potential of a cell type. Many alternate mechanisms have been proposed to explain this phenomenon; the working hypotheses for elucidating the cellular plasticity of BM-derived stem cells are on the basis of direct differentiation and/or fusion between donor and recipient cells. This review dissects the different outcomes of the investigations on liver regeneration, which were performed with the use of BM-derived stem cells in experimental animals, and reveals some critical factors to explain cellular plasticity. It has been hypothesized that the competent BM-derived stem/progenitor cells, under the influence of liver-regenerating cues, can directly differentiate into hepatic cells. This differentiation takes place as a result of genetic reprogramming, which may be possible in the chemically induced acute liver injury model or at the stage of fetal liver development. Cellular plasticity emerges as an important phenomenon in cell-based therapies for the treatment of many liver diseases in which tissue regeneration is necessary.

EphB2 isolates a human marrow stromal cell subpopulation with enhanced ability to contribute to the resident intestinal cellular pool

To identify human bone marrow stromal cell (BMSC) subsets with enhanced ability to engraft/contribute to the resident intestinal cellular pool, we transplanted clonally derived BMSCs into fetal sheep. Analysis at 75 d post-transplantation showed 2 of the 6 clones engrafting the intestine at 4- to 5-fold higher levels (5.03±0.089 and 5.04±0.15%, respectively) than the other clones (P<0.01), correlating with the percentage of donor-derived Musashi-1(+) (12.01-14.17 vs. 1.2-3.8%; P<0.01) or leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5)(+) cells within the intestinal stem cell (ISC) region. Phenotypic and transcriptome analysis determined that the clones with enhanced intestinal contribution expressed high levels of Ephrin type B receptor 2 (EphB2). Intestinal explants demonstrated proliferation of the engrafted cells and ability to generate crypt-like structures in vitro still expressing EphB2. Additional transplants based on BMSC EphB2 expression demonstrated that, at 7 d post-transplant, the EphB2(high) BMSCs engrafted in the ISC region at levels of 2.1 ± 0.2%, while control EphB2(low) BMSCs engrafted at 0.3 ± 0.1% (P<0.01). Therefore we identified a marker for isolating and culturing an expandable subpopulation of BMSCs with enhanced intestinal homing and contribution to the ISC region.

Donor chimera model for tolerance induction in transplantation

Tolerance induction is the basis of a successful transplantation with the goal being the re-establishment of homeostasis after transplantation. Non-autograft transplantation disrupts this maintenance drastically which would be avoided by administration of a novel procedure. At present, the blood group antigens and the genotypes of the donor and recipient are cross-matched before transplantation combined with a drug regimen that confers general immunosuppression. But the 'specific' unresponsiveness of the recipient to the donor organ, implied by 'tolerance', is not achieved in this process. This article introduces the 'donor chimera model' via the concept of the 'closed transplantation loop' approach for tolerance induction which seeks to limit the use of immunosuppressive therapy after transplantation.

Liver bioengineering: Current status and future perspectives

The present review aims to illustrate the strategies that are being implemented to regenerate or bioengineer livers for clinical purposes. There are two general pathways to liver bioengineering and regeneration. The first consists of creating a supporting scaffold, either synthetically or by decellularization of human or animal organs, and seeding cells on the scaffold, where they will mature either in bioreactors or in vivo. This strategy seems to offer the quickest route to clinical translation, as demonstrated by the development of liver organoids from rodent livers which were repopulated with organ specific cells of animal and/or human origin. Liver bioengineering has potential for transplantation and for toxicity testing during preclinical drug development. The second possibility is to induce liver regeneration of dead or resected tissue by manipulating cell pathways. In fact, it is well known that the liver has peculiar regenerative potential which allows hepatocyte hyperplasia after amputation of liver volume. Infusion of autologous bone marrow cells, which aids in liver regeneration, into patients was shown to be safe and to improve their clinical condition, but the specific cells responsible for liver regeneration have not yet been determined and the underlying mechanisms remain largely unknown. A complete understanding of the cell pathways and dynamics and of the functioning of liver stem cell niche is necessary for the clinical translation of regenerative medicine strategies. As well, it will be crucial to elucidate the mechanisms through which cells interact with the extracellular matrix, and how this latter supports and drives cell fate.

Implication of hepatic stem cells in functional liver repopulation

The liver has an enormous potential to restore the parenchymal tissue loss due to injury. This is accomplished by the proliferation of either the hepatocytes or liver progenitor cells in cases where massive damage prohibits hepatocytes from entering the proliferative response. Under debate is still whether hepatic stem cells are involved in liver tissue maintenance and regeneration or even whether they exist at all. The definition of an adult tissue-resident stem cell comprises basic functional stem cell criteria like the potential of self-renewal, multipotent, i.e. at least bipotent differentiation capacity and serial transplantability featuring the ability of functional tissue repopulation. The relationship between a progenitor and its progeny should exemplify the lineage commitment from the putative stem cell to the differentiated cell. This is mainly assessed by lineage tracing and immunohistochemical identification of markers specific to progenitors and their descendants. Flow cytometry approaches revealed that the liver stem cell population in animals is likely to be heterogeneous giving rise to progeny with different molecular signatures, depending on the stimulus to activate the putative stem cell compartment. The stem cell criteria are met by a variety of cells identified in the fetal and adult liver both under normal and injury conditions. It is the purpose of this review to verify hepatic stem cell candidates in the light of the stem cell definition criteria mentioned. Also from this point of view adult stem cells from non-hepatic tissues such as bone marrow, umbilical cord blood or adipose tissue, have the potential to differentiate into cells featuring functional hepatocyte characteristics. This has great impact because it opens the possibility of generating hepatocyte-like cells from adult stem cells in a sufficient amount and quality for their therapeutical application to treat end-stage liver diseases by stem cell-based hepatocytes in place of whole organ transplantation.

Distinct contribution of human cord blood-derived endothelial colony forming cells to liver and gut in a fetal sheep model

Although the vasculogenic potential of circulating and cord blood (CB)-derived endothelial colony-forming cells (ECFC) has been demonstrated in vitro and in vivo, little is known about the inherent biologic ability of these cells to home to different organs and contribute to tissue-specific cell populations. Here we used a fetal sheep model of in utero transplantation to investigate and compare the intrinsic ability of human CB-derived ECFC to migrate to the liver and to the intestine, and to define ECFC's intrinsic ability to integrate and contribute to the cytoarchitecture of these same organs. ECFCs were transplanted by an intraperitoneal or intrahepatic route (IH) into fetal sheep at concentrations ranging from 1.1-2.6 × 10(6) cells/fetus. Recipients were evaluated at 85 days posttransplant for donor (human) cells using flow cytometry and confocal microscopy. We found that, regardless of the route of injection, and despite the IH delivery of ECFC, the overall liver engraftment was low, but a significant percentage of cells were located in the perivascular regions and retained the expression of hallmark endothelial makers. By contrast, ECFC migrated preferentially to the intestinal crypt region and contributed significantly to the myofibroblast population. Furthermore, ECFC expressing CD133 and CD117 lodged in areas where endogenous cells expressed those same phenotypes.

CONCLUSION

ECFC inherently constitute a potential source of cells for the treatment of intestinal diseases, but strategies to increase the numbers of ECFC persisting within the hepatic parenchyma are needed in order to enhance ECFC therapeutic potential for this organ.

Stem cell therapy: a novel & futuristic treatment modality for disaster injuries

Stem cell therapy hold the potential to meet the demand for transplant cells/tissues needed for treating damages resulting from both natural and man-made disasters. Pluripotency makes embryonic stem cells and induced pluripotent stem cells ideal for use, but their teratogenic character is a major hindrance. Therapeutic benefits of bone marrow transplantation are well known but characterizing the potentialities of haematopoietic and mesenchymal cells is essential. Haematopoietic stem cells (HSCs) have been used for treating both haematopoietic and non-haematopoietic disorders. Ease of isolation, in vitro expansion, and hypoimmunogenecity have brought mesenchymal stem cells (MSCs) into limelight. Though differentiation of MSCs into tissue-specific cells has been reported, differentiation-independent mechanisms seem to play a more significant role in tissue repair which need to be addressed further. The safety and feasibility of MSCs have been demonstrated in clinical trials, and their use in combination with HSC for radiation injury treatment seems to have extended benefit. Therefore, using stem cells for treatment of disaster injuries along with the conventional medical practice would likely accelerate the repair process and improve the quality of life of the victim.

Infusion of CD133+ bone marrow-derived stem cells after selective portal vein embolization enhances functional hepatic reserves after extended right hepatectomy: a retrospective single-center study

OBJECTIVE

This study was designed to evaluate the clinical outcome of patients undergoing portal vein embolization (PVE) and autologous CD133 bone marrow-derived stem cell (CD133+ BMSC) application before extended right hepatectomy.

BACKGROUND

We have previously shown that portal venous infusion of CD133+ BMSCs substantially increases hepatic proliferation, when compared with PVE alone.

METHODS

: Among 40 consecutive patients with a median follow-up of 28 months (7.4-57.2) scheduled for extended right hepatectomy, we compared a preconditioned group with PVE and CD133+ BMSC cotreatment (PVE+SC group, n = 11) and a group pretreated only with PVE (PVE group, n = 11). Functional and overall outcomes after extended right hepatectomy were evaluated. Patients without presurgical treatment served as controls (n = 18).

RESULTS

In preconditioned patients, mean hepatic growth of segments II/III 14 days after PVE in the PVE+SC group was significantly higher (138.66 mL ± 66.29) when compared with that of PVE group patients (62.95 mL ± 40.03; P = 0.004). There were no significant differences among all 3 groups regarding general and oncological characteristics and functional parameters on postoperative day (POD) 7. Lack of hepatic preconditioning, extrahepatic extension of resection, and postoperative complications were of negative prognostic value, using univariate analysis (P < 0.05). In multivariate analysis, freedom from postoperative major complications (P = 0.012), coagulation status on POD 7 (international normalized ratio < 1.4; P = 0.027), and presurgical expansion of the future liver remnant volume (P = 0.048) were positively associated with overall survival. Post hoc analysis revealed a better survival for the PVE+SC group (P = 0.028) compared with the PVE group (P = 0.094) and compared with controls.

CONCLUSION

Promising data from this survival analysis suggest that PVE, together with CD133+ BMSC pretreatment, could positively impact overall outcomes after extended right hepatectomy.

Simultaneous injection of autologous mononuclear cells with TACE in HCC patients; preliminary study

BACKGROUND

The discovery of the pluripotent stem cells made the prospect of cell therapy and tissue regeneration a clinical reality, especially with the evidence of contribution of the stem cells of bone marrow origin in hepatic regeneration. Infusion of bone marrow stem cells before trans-arterial chemoembolization may help to increase liver volume and consequently increase hepatic reserve in patients with HCC, and this may improve the outcome of this procedure.

MATERIALS AND METHODS

Four Child B class patients with unresectable hepatocellular carcinoma treated by transarterial chemoembolization were injected with autologous bone marrow mononuclear layer containing stem cell in the hepatic artery feeding the contralateral lobe of the liver in the same session, follow-up of the patients was done by doing liver profile and CT liver volumetry before the surgery and 3 months later.

RESULTS

We observed that patients receiving stem cell therapy simultaneously with TACE had shown a significant improvement in biological and volumetric parameters of liver function compared to those historically reported of patients receiving TACE only who usually shows deterioration of liver parameters.

CONCLUSION

BMC infusion into the hepatic artery synchronized with TACE for patients with chronic liver disease complicated with HCC is safe, feasible, and demonstrated an improvement in both biological and radiological volumetric parameters.

[Therapeutic possibilities of stem cells in the treatment of liver diseases]

Cell therapy and the use of stem cells in the treatment of liver diseases is still in the research phase. Nevertheless, the diversity of stem cells in terms of their origin, characteristics and potential for differentiation provides a wide spectrum of possibilities for the treatment of liver diseases. The present article describes the main types of stem cells and their potential for the treatment of liver diseases, as well as the main therapeutic strategies that are currently being explored for the treatment of these diseases through cell therapy. In addition, the main preclinical and clinical studies suggesting that stem cells could become an effective therapeutic alternative in distinct liver diseases are discussed.

Alveolar epithelial cell therapy with human cord blood-derived hematopoietic progenitor cells

The role of umbilical cord blood (CB)-derived stem cell therapy in neonatal lung injury remains undetermined. We investigated the capacity of human CB-derived CD34(+) hematopoietic progenitor cells to regenerate injured alveolar epithelium in newborn mice. Double-transgenic mice with doxycycline (Dox)-dependent lung-specific Fas ligand (FasL) overexpression, treated with Dox between embryonal day 15 and postnatal day 3, served as a model of neonatal lung injury. Single-transgenic non-Dox-responsive littermates were controls. CD34(+) cells (1 × 10(5) to 5 × 10(5)) were administered at postnatal day 5 by intranasal inoculation. Engraftment, respiratory epithelial differentiation, proliferation, and cell fusion were studied at 8 weeks after inoculation. Engrafted cells were readily detected in all recipients and showed a higher incidence of surfactant immunoreactivity and proliferative activity in FasL-overexpressing animals compared with non-FasL-injured littermates. Cord blood-derived cells surrounding surfactant-immunoreactive type II-like cells frequently showed a transitional phenotype between type II and type I cells and/or type I cell-specific podoplanin immunoreactivity. Lack of nuclear colocalization of human and murine genomic material suggested the absence of fusion. In conclusion, human CB-derived CD34(+) cells are capable of long-term pulmonary engraftment, replication, clonal expansion, and reconstitution of injured respiratory epithelium by fusion-independent mechanisms. Cord blood-derived surfactant-positive epithelial cells appear to act as progenitors of the distal respiratory unit, analogous to resident type II cells. Graft proliferation and alveolar epithelial differentiation are promoted by lung injury.

Identification and isolation from either adult human bone marrow or G-CSF-mobilized peripheral blood of CD34(+)/CD133(+)/CXCR4(+)/ Lin(-)CD45(-) cells, featuring morphological, molecular, and phenotypic characteristics of very small embryonic-like (VSEL) stem cells

OBJECTIVE

Recently, we demonstrated that normal human bone marrow (hBM)-derived CD34(+) cells, released into the peripheral blood after granulocyte colony-stimulating factor mobilization, contain cell subpopulations committed along endothelial and cardiac differentiation pathways. These subpopulations could play a key role in the regeneration of post-ischemic myocardial lesion after their direct intracardiac delivery. We hypothesized that these relevant cells might be issued from very small embryonic-like stem cells deposited in the BM during ontogenesis and reside lifelong in the adult BM, and that they could be mobilized into peripheral blood by granulocyte colony-stimulating factor.

MATERIALS AND METHODS

Samples of normal hBM and leukapheresis products harvested from cancer patients after granulocyte colony-stimulating factor mobilization were analyzed and sorted by multiparameter flow cytometry strategy. Immunofluorescence and reverse transcription quantitative polymerase chain reaction assays were performed to analyze the expression of typical pluripotent stem cells markers.

RESULTS

A population of CD34(+)/CD133(+)/CXCR4(+)/Lin(-) CD45(-) immature cells was first isolated from the hBM or from leukapheresis products. Among this population, very small (2-5 μm) cells expressing Oct-4, Nanog, and stage-specific embryonic antigen-4 at protein and messenger RNA levels were identified.

CONCLUSIONS

Our study supports the hypothesis that very small embryonic-like stem cells constitute a "mobile" pool of primitive/pluripotent stem cells that could be released from the BM into the peripheral blood under the influence of various physiological or pathological stimuli. In order to fully support that hBM- and leukapheresis product-derived very small embryonic-like stem cells are actually pluripotent, we are currently testing their ability to differentiate in vitro into cells from all three germ layers.

Human stem cell research and regenerative medicine--present and future

INTRODUCTION

Stem cells are cells with the ability to grow and differentiate into more than 200 cell types.

SOURCES OF DATA

We review here the characteristics and potential of human embryonic stem cells (hESCs), induced pluripotent stem cells (iPSCs) and adult stem cells (ASCs).

AREAS OF AGREEMENT

The differentiation ability of all stem cell types could be stimulated to obtain specialized cells that represent renewable sources of functional cells useful for cell-based therapy.

AREAS OF CONTROVERSY

The proof of functional differentiated cells needs to be investigated in more detail using both in vitro and in vivo assays including animal disease models and clinical studies.

GROWING POINTS

Much progress has been made in the ASCs-based therapies. Meanwhile hESCs and iPSCs have dramatically emerged as novel approaches to understand pathogenesis of different diseases.

AREAS TIMELY FOR DEVELOPING RESEARCH

A number of new strategies become very important in regenerative medicine. However, we discuss the limitations of stem cells and latest development in the reprogramming research.

Multiorgan engraftment of human somatic cells in swine foetuses after intra-blastocyst transplantation

Adult human stem cells, mainly from hematopoietic lineage, have been injected into developing pre-immune animal foetuses, and xenogenic engraftment of liver and other organs has been reported. We isolated a rare cell population from adult human liver, fat and skin. Colonies with few cells became visible as early as 2-3 days, and a fully formed colony took 10-14 days to form. These colonies were named as liver-derived cell lines (LDCs), fat-derived cell lines (FDCs) and skin-derived cell lines (SDCs). All these cells express few pluripotency markers like Klf4, c-myc and Sox2. Pig blastocysts were injected with LDCs, FDCs and SDCs and transferred to recipient pigs. We achieved an overall pregnancy rate of 71.4% at day 35. The foetuses were analysed for human cell chimerism in liver, kidney and heart both by RT-PCR and real-time PCR using primers specific to human and pig mitochondrial DNA. The percentage of foetuses showing chimerism was 17.4% (4/23), 12.5% (2/16) and 11.1% (1/9) for LDCs, FDCs and SDCs, respectively. Of these, 42.9% (three out of seven) showed chimerism in liver and 71.4% (five out of seven) showed kidney chimerism. However, we did not detect any chimerism in the heart. The level of chimerism varied and was in the range of one human cell per one hundred thousand to one million pig cells.

Bone marrow stem cells and liver regeneration

Development of new approaches to treat patients with hepatic diseases that can eliminate the need for liver transplantation is imperative. Use of cell therapy as a means of repopulating the liver has several advantages over whole-organ transplantation because it would be less invasive, less immunogenic, and would allow the use, in some instances, of autologous-derived cells. Stem/progenitor cells that would be ideal for liver repopulation would need to have characteristics such as availability and ease of isolation, the ability to be expanded in vitro, ensuring adequate numbers of cells, susceptibility to modification by viral vector transduction/genetic recombination, to correct any underlying genetic defects, and the ability of restoring liver function following transplantation. Bone marrow-derived stem cells, such as hematopoietic, mesenchymal and endothelial progenitor cells possess some or most of these characteristics, making them ideal candidates for liver regenerative therapies. Here, we will summarize the ability of each of these stem cell populations to give rise to functional hepatic elements that could mediate repair in patients with liver damage/disease.

In vivo generation of beta-cell-like cells from CD34(+) cells differentiated from human embryonic stem cells

OBJECTIVE

CD34(+) cells, present within the bone marrow, have previously been shown to possess pancreatic endocrine potential. Based on this observation, we explored the capacity of CD34(+) cells derived in culture from the differentiation of human embryonic stem cells (hESC), for their in vivo pancreatic endocrine capacity.

MATERIALS AND METHODS

Sheep were transplanted with hESC-derived CD34(+) cells, as well as nonsorted differentiated cultures. Transplantations were carried out with in utero intraperitoneal injections prior to development of the immune system in the fetus so that tolerance toward foreign antigens was acquired during gestation and persisted in the adult.

RESULTS

All cell populations that were tested demonstrated human cellular activity and long-term presence up to 5 years. However, the in vivo beta-cell-like activity achieved from the transplantation of the sorted CD34(+) cell population was not augmented by transplanting the entire cell population from which the CD34(+) cells were isolated. Human DNA and insulin messenger RNA were detected in sheep pancreases. An average of 1.51 ng/mL human C-peptide was detected in serum from eight animals transplanted with differentiated cell populations and assayed up to 55 months posttransplantation. Transplantation of as few as 23,500 cells resulted in long-term sustainable beta-cell-like activity. Teratomas were absent in the transplanted animals.

CONCLUSION

Our data suggest that hESC-derived CD34(+) cells have a potential for long-term in vivo endocrine cellular activity that could prove useful in regenerative medicine. Because the same cell population has previously been shown to contain hematopoietic potential, it could be used for the induction of immunological tolerance and bone marrow chimerism prior to cellular therapy for diabetes.

Bone marrow stem cells and the liver: are they relevant?

The contribution of bone marrow stem cell responses to liver homeostasis, injury and malignancy is discussed in this review. Pluripotent stem cells or their more committed progenitor progeny are essential to tissue development, regeneration and repair and are widely implicated in the pathogenesis of malignancy. Stem cell responses to injury are the focus of intense research efforts in the hope of future therapeutic manipulation. Stem cells occur within tissues, such as the liver, or arise from extrahepatic sites, in particular, the bone marrow. As the largest reservoir of stem cells in the adult, the bone marrow has been implicated in the stem cell response associated with liver injury. However, in liver injury, the relative contribution of bone marrow stem cells compared to intrahepatic progenitor responses is poorly characterized. Intrahepatic progenitor responses have been recently reviewed elsewhere. In this review, we have summarized liver-specific extrahepatic stem cell responses originating from the bone marrow. The physiological relevance of bone marrow stem cell responses to adult liver homeostasis, injury and malignancy is discussed with emphasis on mechanisms of bone marrow stem cell recruitment to sites of liver injury and its contribution to intrahepatic malignancy.

Phenotypic changes of human cells in human-rat liver during partial hepatectomy-induced regeneration

AIM: To examine the human hepatic parenchymal and stromal components in rat liver and the phenotypic changes of human cells in liver of human-rat chimera (HRC) generated by in utero transplantation of human cells during partial hepatectomy (PHx)-induced liver regeneration.

METHODS: Human hepatic parenchymal and stromal components and phenotypic changes of human cells during liver regeneration were examined by flow cytometry, in situ hybridization and immunohistochemistry.

RESULTS: ISH analysis demonstrated human Alu-positive cells in hepatic parenchyma and stroma of recipient liver. Functional human hepatocytes generated in this model potentially constituted human hepatic functional units with the presence of donor-derived human endothelial and biliary duct cells in host liver. Alpha fetoprotein (AFP)⁺, CD34⁺ and CD45⁺ cells were observed in the chimeric liver on day 10 after PHx-induced liver regeneration and then disappeared in PHx group, but not in non-PHx group, suggesting that dynamic phenotypic changes of human cells expressing AFP, CD34 and CD45 cells may occur during the chimeric liver regeneration. Additionally, immunostaining for human proliferating cell nuclear antigen (PCNA) showed that the number of PCNA-positive cells in the chimeric liver of PHx group was markedly increased, as compared to that of control group, indicating that donor-derived human cells are actively proliferated during PHx-induced regeneration of HRC liver.

CONCLUSION: HRC liver provides a tool for investigating human liver regeneration in a humanized animal model.

Cell therapy for the diseased liver: from stem cell biology to novel models for hepatotropic human pathogens

It has long been known that hepatocytes possess the potential to replicate through many cell generations because regeneration can be achieved in rodents after serial two-thirds hepatectomy. It has taken considerable time and effort to harness this potential, with liver regeneration models involving hepatocyte transplantation developing over the past 15 years. This review will describe the experiments that have established the models and methodology for liver repopulation, and the use of cells other than adult hepatocytes in liver repopulation, including hepatic cell lines and hematopoietic, cord blood, hepatic and embryonic stem cells. Emphasis will be placed on the characteristics of the models and how they can influence the outcome of the experiments. Finally, an account of the development of murine models that are competent to accept human hepatocytes is provided. In these models, liver deficiencies are induced in immunodeficient mice, where healthy human cells have a selective advantage. These mice with humanized livers provide a powerful new experimental tool for the study of human hepatotropic pathogens.

Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly

The worldwide shortage of donor livers to transplant end stage liver disease patients has prompted the search for alternative cell therapies for intractable liver diseases, such as acute liver failure, cirrhosis and hepatocellular carcinoma (HCC). Under normal circumstances the liver undergoes a low rate of hepatocyte 'wear and tear' renewal, but can mount a brisk regenerative response to the acute loss of two-thirds or more of the parenchymal mass. A body of evidence favours placement of a stem cell niche in the periportal regions, although the identity of such stem cells in rodents and man is far from clear. In animal models of liver disease, adopting strategies to provide a selective advantage for transplanted hepatocytes has proved highly effective in repopulating recipient livers, but the poor success of today's hepatocyte transplants can be attributed to the lack of a clinically applicable procedure to force a similar repopulation of the human liver. The activation of bipotential hepatic progenitor cells (HPCs) is clearly vital for survival in many cases of acute liver failure, and the signals that promote such reactions are being elucidated. Bone marrow cells (BMCs) make, at best, a trivial contribution to hepatocyte replacement after damage, but other BMCs contribute to the hepatic collagen-producing cell population, resulting in fibrotic disease; paradoxically, BMC transplantation may help alleviate established fibrotic disease. HCC may have its origins in either hepatocytes or HPCs, and HCCs, like other solid tumours appear to be sustained by a minority population of cancer stem cells.

Fate and effects of adult bone marrow cells in lungs of normoxic and hyperoxic newborn mice

Cell-based therapy in adult lung injury models is associated with highly variable donor cell engraftment and epithelial reconstitution. The role of marrow-derived cell therapy in neonatal lung injury is largely unknown. In this study, we determined the fate and effects of adult bone marrow cells in a model of neonatal lung injury. Wild-type mice placed in a normoxic or hyperoxic (95% O(2)) environment received bone marrow cells from animals expressing green fluorescent protein (GFP) at Postnatal Day (P)5. Controls received vehicle buffer. Lungs were analyzed between Post-Transplantation (TPX) Day 2 and Week 8. The volume of GFP-immunoreactive donor cells, monitored by stereologic volumetry, remained constant between Post-TPX Weeks 1 and 8 and was similar in normoxic and hyperoxia-exposed recipients. Virtually all marrow-derived cells showed colocalization of GFP and the pan-macrophage marker, F4/80, by double immunofluorescence studies. Epithelial transdifferentiation was not seen. Marrow cell administration had adverse effects on somatic growth and alveolarization in normoxic mice, while no effects were discerned in hyperoxia-exposed recipients. Reexposure of marrow-treated animals to hyperoxia at P66 resulted in significant expansion of the donor-derived macrophage population. In conclusion, intranasal administration of unfractionated bone marrow cells to newborn mice does not achieve epithelial reconstitution, but establishes persistent alveolar macrophage chimerism. The predominantly adverse effects of marrow treatment in newborn lungs are likely due to macrophage-associated paracrine effects. While this model and route of cell therapy may not achieve epithelial reconstitution, the role of selected stem cell populations and/or alternate routes of administration for cell-based therapy in injured newborn lungs deserve further investigation.

Hematopoietic progenitors from early murine fetal liver possess hepatic differentiation potential

Bipotential hepatoblasts differentiate into hepatocytes and cholangiocytes during liver development. It is believed that hepatoblasts originate from endodermal tissue. Here, we provide evidence for the presence of hepatic progenitor cells in the hematopoietic compartment at an early stage of liver development. Flow cytometric analysis showed that at early stages of liver development, approximately 13% of CD45(+) cells express Delta-like protein-1, a marker of hepatoblasts. Furthermore, reverse transcriptase-PCR data suggest that many hepatic genes are expressed in these cells. Cell culture experiments confirmed the hepatic differentiation potential of these cells with the loss of the CD45 marker. We observed that both hematopoietic activity in Delta-like protein-1(+) cells and hepatic activity in CD45(+) cells were high at embryonic day 10.5 and declined thereafter. Clonal analysis revealed that the hematopoietic fraction of fetal liver cells at embryonic day 10.5 gave rise to both hepatic and hematopoietic colonies. The above results suggest a common source of these two functionally distinct cell lineages. In utero transplantation experiments confirmed these results, as green fluorescent protein-expressing CD45(+) cells at the same stage of development yielded functional hepatocytes and hematopoietic reconstitution. Since these cells were unable to differentiate into cytokeratin-19-expressing cholangiocytes, we distinguished them from hepatoblasts. This preliminary study provides hope to correct many liver diseases during prenatal development via transplantation of fetal liver hematopoietic cells.

A population of serum deprivation-induced bone marrow stem cells (SD-BMSC) expresses marker typical for embryonic and neural stem cells

The bone marrow represents an easy accessible source of adult stem cells suitable for various cell based therapies. Several studies in recent years suggested the existence of pluripotent stem cells within bone marrow stem cells (BMSC) expressing marker proteins of both embryonic and tissue committed stem cells. These subpopulations were referred to as MAPC, MIAMI and VSEL-cells. Here we describe SD-BMSC (serumdeprivation-induced BMSC) which are induced as a distinct subpopulation after complete serumdeprivation. SD-BMSC are generated from small-sized nestin-positive BMSC (S-BMSC) organized as round-shaped cells in the top layer of BMSC-cultures. The generation of SD-BMSC is caused by a selective proliferation of S-BMSC and accompanied by changes in both morphology and gene expression. SD-BMSC up-regulate not only markers typical for neural stem cells like nestin and GFAP, but also proteins characteristic for embryonic cells like Oct4 and SOX2. We hypothesize, that SD-BMSC like MAPC, MIAMI and VSEL-cells represent derivatives from a single pluripotent stem cell fraction within BMSC exhibiting characteristics of embryonic and tissue committed stem cells. The complete removal of serum might offer a simple way to specifically enrich this fraction of pluripotent embryonic like stem cells in BMSC cultures.

In vivo Differentiation Potential of Mesenchymal Stem Cells: Prenatal and Postnatal Model Systems

SUMMARY: Most of our knowledge of mesenchymal stem cell (MSC) biology is derived from in vitro systems that are often highly contrived to favor culture expansion or specific differentiation events. However, any conclusions drawn from in vitro studies regarding MSC differentiation capacity, immune properties, or therapeutic potential must be validated by in vivo studies to ultimately be meaningful. At the present time, there are relatively few in vivo studies demonstrating differentiation and functional integration of MSCs into host tissues after transplantation. There is a need for in vivo model systems to assay MSC biology and to move potential therapeutic strategies forward. Here, we review prenatal model systems as potentially advantageous for the in vivo characterization of MSCs, and we critically review the results of in vivo studies of MSC transplantation in prenatal and postnatal model systems with an emphasis on proven engraftment and differentiation.