Ex vivo transduced liver progenitor cells as a platform for gene therapy in mice

Noninvasive in-vivo tracing and imaging of transplanted stem cells for liver regeneration

Terminal liver disease is a major cause of death globally. The only ultimate therapeutic approach is orthotopic liver transplant. Because of the innate defects of organ transplantation, stem cell-based therapy has emerged as an effective alternative, based on the capacity of stem cells for multilineage differentiation and their homing to injured sites. However, the disease etiology, cell type, timing of cellular graft, therapeutic dose, delivery route, and choice of endpoints have varied between studies, leading to different, even divergent, results. In-vivo cell imaging could therefore help us better understand the fate and behaviors of stem cells to optimize cell-based therapy for liver regeneration. The primary imaging techniques in preclinical or clinical studies have consisted of optical imaging, magnetic resonance imaging, radionuclide imaging, reporter gene imaging, and Y chromosome-based fluorescence in-situ hybridization imaging. More attention has been focused on developing new or modified imaging methods for longitudinal and high-efficiency tracing. Herein, we provide a descriptive overview of imaging modalities and discuss recent advances in the field of molecular imaging of intrahepatic stem cell grafts.

Therapeutic Potential of Bone Marrow-Derived Mesenchymal Stem Cells on Experimental Liver Injury Induced by Schistosoma mansoni: A Histological Study

Background and Objectives

Bone marrow derived mesenchymal stem cells (BM-MSCs) have been proposed as effective treatment of many diseases owing to their unique ability to differentiate into other cell types in vivo. Schistosoma mansoni (S. mansoni) infection is characterized by hepatic granuloma formation around schistosome eggs at acute stage of infection, followed by hepatic fibrosis at chronic and advanced stages. Whether BM-MSCs have an ameliorative effect on hepatic tissue injury caused by S. mansoni infection or not, was inspected in the current study.

Materials and Results

Female Swiss Albino mice were divided into a control group and an experimental group. Half of control animals served as donors for bone marrow stem cells, and the other half was used to collect liver samples. Experimental group was injected with circariae of S. mansoni, and then subdivided into three subgroups; Subgroup B1, sacrificed after eight weeks of infection without treatment, subgroup B2, received BM-MSCs at the eighth week and sacrificed four weeks later, and subgroup B3, was untreated till the twelfth week of infection. Histological examination of liver samples showed the formation of granulomas and liver fibrosis which were extensive in subgroup B3. However, treated subgroup illustrated improvement of liver histology, signs of hepatocytes regeneration, and possible contribution of oval cell in the process of hepatic and biliary regeneration.

Conclusion

BM-MSCs decreased liver fibrosis and contributed to an increase in oval cells, generation of new hepatocytes and/or to the improvement of resident hepatocytes in S. mansoni infected mice.

Challenges and Prospects for Alpha-1 Antitrypsin Deficiency Gene Therapy

Alpha-1 antitrypsin (AAT) is a protease inhibitor belonging to the serpin family. A number of identified mutations in the SERPINA1 gene encoding this protein result in alpha-1 antitrypsin deficiency (AATD). A decrease in AAT serum concentration or reduced biological activity causes considerable risk of chronic respiratory and liver disorders. As a monogenic disease, AATD appears to be an attractive target for gene therapy, particularly for patients with pulmonary dysfunction, where augmentation of functional AAT levels in plasma might slow down respiratory disease development. The short AAT coding sequence and its activity in the extracellular matrix would enable an increase in systemic serum AAT production by cellular secretion. In vitro and in vivo experimental AAT gene transfer with gamma-retroviral, lentiviral, adenoviral, and adeno-associated viral (AAV) vectors has resulted in enhanced AAT serum levels and a promising safety profile. Human clinical trials using intramuscular viral transfer with AAV1 and AAV2 vectors of the AAT gene demonstrated its safety, but did not achieve a protective level of AAT >11 μM in serum. This review provides an in-depth critical analysis of current progress in AATD gene therapy based on viral gene transfer. The factors affecting transgene expression levels, such as site of administration, dose and type of vector, and activity of the immune system, are discussed further as crucial variables for optimizing the clinical effectiveness of gene therapy in AATD subjects.

Progress in research of hepatic stem cells

Liver disease is a rising cause of mortality and morbidity, and treatment options remain limited. Liver transplantation is curative but limited by donor organ availability, operative risk and long-term complications. There is currently a clear need for new therapies for liver disease, and it is possible that hepatic stem cell (HSC) therapy represents an exciting new therapeutic option. HSCs are undifferentiated cells with the unique ability to self-renew and potentially provide a source of human hepatocytes for regeneration of the injured liver. Evidence from pre-clinical studies is encouraging, but conclusive evidence that this translates into humans remains lacking. Further studies of the mechanisms responsible for the beneficial effects of HSC therapy are needed.

Hepatic stem cell niches

Stem cell niches are special microenvironments that maintain stem cells and control their behavior to ensure tissue homeostasis and regeneration throughout life. The liver has a high regenerative capacity that involves stem/progenitor cells when the proliferation of hepatocytes is impaired. In recent years progress has been made in the identification of potential hepatic stem cell niches. There is evidence that hepatic progenitor cells can originate from niches in the canals of Hering; in addition, the space of Disse may also serve as a stem cell niche during fetal hematopoiesis and constitute a niche for stellate cells in adults.

Cell and gene therapy for genetic diseases: inherited disorders affecting the lung and those mimicking sudden infant death syndrome

Some of the first human gene therapy trials targeted diseases of the lung and provided important information that will continue to help shape future trials. Here we describe both cell and gene therapies for lung diseases such as cystic fibrosis and alpha-1 antitrypsin disorder as well as fatty acid oxidation disorders that mimic sudden infant death syndrome (SIDS). Human clinical gene therapy trials for cystic fibrosis and alpha-1 antitrypsin have been performed using a variety of vectors including adenovirus, adeno-associated virus, and nonviral vectors. No human clinical gene therapy trials have been performed for disorders of fatty acid oxidation; however, important proof-of-principle studies have been completed for multiple fatty acid oxidation disorders. Important achievements have been made and have yet to come for cell and gene therapies for disorders of the lung and those mimicking SIDS.

In situ labeling and magnetic resonance imaging of transplanted human hepatic stem cells

PURPOSE

The purpose is to address the problem in magnetic resonance imaging (MRI) of contrast agent dilution.

PROCEDURES

In situ magnetic labeling of cells and MRI were used to assess distribution and growth of human hepatic stem cells (hHpSCs) transplanted into severe combined immunodeficiency (SCID)/non-obese diabetic (NOD) mice. It was done with commercially available magnetic microbeads coupled to an antibody to a surface antigen, epithelial cell adhesion molecule (EpCAM), uniquely expressed in the liver by hepatic progenitors.

RESULTS

We validated the microbead connection to cells and related MRI data to optical microscopy observations in order to develop a means to quantitatively estimate cell numbers in the aggregates detected. Cell counts of hHpSCs at different times post-transplantation revealed quantifiable evidence of cell engraftment and expansion.

CONCLUSIONS

This magnetic labeling methodology can be used with any antibody coupled to a magnetic particle to target any surface antigen that distinguishes transplanted cells from host cells, thus facilitating studies that define methods and strategies for clinical cell therapy programs.

Model systems and experimental conditions that lead to effective repopulation of the liver by transplanted cells

In recent years, there has been substantial progress in transplanting cells into the liver with the ultimate goal of restoring liver mass and function in both inherited and acquired liver diseases. The basis for considering that this might be feasible is that the liver is a highly regenerative organ. After massive liver injury or surgical removal of two-thirds or more of the liver tissue, the organ can restore its mass with completely normal morphologic structure and function. It has also been found under highly selective conditions that transplanted hepatocytes can fully repopulate the liver and cure a metabolic disorder or deficiency state. Fetal liver cells can also substantially repopulate the normal liver, and it is hoped in the future that effective repopulation will be achievable with cultured cells or cell lines, pluripotent stem cells from other somatic tissues, embryonic stem cells, or induced pluripotent stem cells, which can now be generated in vitro by a variety of methods. The purpose of this review is to present the major systems that have been used for liver repopulation, the variables involved in obtaining successful repopulation and what has been achieved in these various systems to date with different cell types.

Ex vivo transduction and transplantation of bone marrow cells for liver gene delivery of alpha1-antitrypsin

Adult stem cell-based gene therapy holds several unique advantages including avoidance of germline or other undesirable cell transductions. We have previously shown that liver progenitor (oval) cells can be used as a platform for liver gene delivery of human alpha1-antitrypsin (hAAT). However, this cell source cannot be used in humans for autologous transplantation. In the present study, we tested the feasibility of bone marrow (BM) cell-based liver gene delivery of hAAT. In vitro studies showed that BM cells can be transduced by lentiviral vector (Lenti-CB-hAAT) and recombinant adeno-associated viral vectors (rAAV1-CB-hAAT, and rAAV8-CB-hAAT). Transplantation studies showed that transplanted BM cells homed into liver, differentiated into hepatocytes and expressed hAAT in the liver. Importantly, we showed that transplantation of rAAV8-CB-hAAT vector-transduced BM cells resulted in sustained levels of hAAT in the systemic circulation of recipient mice. These results demonstrated that rAAV vector-mediated BM cell-based liver gene therapy is feasible for the treatment of AAT deficiency and implies a novel therapy for the treatment of liver diseases.

Distinct immune responses to transgene products from rAAV1 and rAAV8 vectors

Recently developed serotypes of recombinant adeno-associated virus (rAAV) vectors have significantly enhanced the use of rAAV vectors for gene therapy. However, host immune responses to the transgene products from different serotypes remain uncharacterized. In the present study, we evaluated the differential immune responses to the transgene products from rAAV1 and rAAV8 vectors. In non-obese diabetic (NOD) mice, which have a hypersensitive immunity, rAAV serotype 1 vector (rAAV1-hAAT) induced high levels of both humoral and cellular responses, while rAAV8-hAAT did not. In vitro studies showed that rAAV1, but not rAAV8 vector transduced dendritic cells (DCs) efficiently. In vivo studies indicated that vector transduction of DCs was essential for the immune responses; while the presence of a transgene product (or foreign gene product produced by host cells) was not immunogenic. Intriguingly, preimmunization with rAAV8-hAAT vector or with serum of hAAT transgenic NOD mouse induced immune tolerance to rAAV1-hAAT injection. These results demonstrate the immunogenic differences of rAAV1 and rAAV8 and imply tremendous potential for these vectors in different applications, where an immune response to transgene is to be either elicited or avoided.

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.

Analysis of adeno-associated virus progenitor cell transduction in mouse lung

Although recombinant adeno-associated virus (rAAV) has been widely used in lung gene therapy approaches, it remains unclear to what extent commonly used AAV serotypes transduce adult progenitors in the lung. In this study, we evaluated the life span and proliferative capacity of rAAV1-, 2-, and 5-transduced airway cells in mouse lung, using a LacZ-CRE reporter transgenic model and Cre-expressing rAAV. In this model, the expression of CRE recombinase led to permanent genetic marking of transduced cells and their descendants with LacZ. To investigate whether the rAAV-transduced cells included airway progenitors, we injured the airways of rAAV-infected mice with Naphthalene, while simultaneously labeling with 5-bromodeoxyuridine (BrdU) to identify slow-cycling progenitor/stem cells that entered the cell cycle and retained label. Both rAAV5 and rAAV1 vectors were capable of transducing a subset of long-lived Clara cells and alveolar type II (ATII) cells that retained nucleotide label and proliferated following lung injury. Importantly, rAAV1 and 5 appeared to preferentially transduce conducting airway epithelial progenitors that had the capacity to clonally expand, both in culture and in vivo following lung injury. These studies suggest that rAAV may be a useful vector for gene targeting of airway stem/progenitor cells.

Stem cells, cell transplantation and liver repopulation

Liver transplantation is currently the only therapeutic option for patients with end-stage chronic liver disease and for severe acute liver failure. Because of limited donor availability, attention has been focused on the possibility to restore liver mass and function through cell transplantation. Stem cells are a promising source for liver repopulation after cell transplantation, but whether or not the adult mammalian liver contains hepatic stem cells is highly controversial. Part of the problem is that proliferation of mature adult hepatocytes is sufficient to regenerate the liver after two-thirds partial hepatectomy or acute toxic liver injury and participation of stem cells is not required. However, under conditions in which hepatocyte proliferation is blocked, undifferentiated epithelial cells in the periportal areas, called "oval cells", proliferate, differentiate into hepatocytes and restore liver mass. These cells are referred to as facultative liver stem cells, but they do not repopulate the normal liver after their transplantation. In contrast, epithelial cells isolated from the early fetal liver can effectively repopulate the normal liver, but they are already traversing the hepatic lineage and may not be true stem cells. Mesenchymal stem cells and embryonic stem cells can be induced to differentiate along the hepatic lineage in culture, but at present these cells are inefficient in repopulating the liver. This review will characterize these various cell types and compare the properties of these cells and the conditions under which they do or do not repopulate the liver following their transplantation.

Selective tropism of liver stem cells to hepatocellular carcinoma in vivo

AIM: To investigate the selective tropism of liver stem cells to hepatocellular carcinoma (HCC) in an animal model and its feasibility as a vector to deliver therapeutic genes for targeted therapy of HCC.

METHODS: WB-F344, a kind of rat liver stem cell, was infected with recombinant virus to establish a cell line with stable, high-level expressing enhanced green fluorescent protein (EGFP). An animal model of HCC in Wistar rats was established by implanting HCC cells (CBRH7919) combined with an immunosuppressive drug. EGFP labeled liver stem cells were injected into caudal veins of the animals and distribution was observed at different time points after injection. SDF-1 and c-kit expression in non-tumor liver and tumor tissue were analysed by immunohistochemistry for the relationshiop between the expression and migration of liver stem cells. Furthermore, hepatic stem cells were injected via the portal vein, hepatic artery, caudal vein, or directly into the pericancerous liver tissue, respectively, and effects on migration, localization, and proliferation of the hepatic stem cells within the tumor tissue were observed and analyzed.

RESULTS: Recombinant adenovirus could deliver the EGFP gene to hepatic stem cells. A new stem cell line, named WB-EGFP, was established that stably expressed EGFP. WB-EGFP cells still showed selective tropism towards HCC and EGFP expression was stable in vivo. According to immunohistochemistry results, SDF-1 may not be related to the mechanisms of tropism of hepatic stem cells. Different application sites affected the distribution of liver stem cells. Injection via the portal vein was superior with regard to selective migration, localization, and proliferation of the hepatic stem cells within the tumor tissue.

CONCLUSION: Liver stem cells have the biological behavior of selective migration to HCC in vivo and they could localize and proliferate within HCC tissue stably expressing the target gene. Liver stem cells are a potential tool for a targeted gene therapy of HCC.

Detection and characterization of hepatic engraftment of embryonic stem derived cells by fluorescent stereomicroscopy

BACKGROUND

Embryonic stem (ES) cells have been investigated as a potential replacement therapy for failed organs, such as the liver. However, detection of hepatic engraftment from candidate stem cells has been difficult due to low engraftment efficiency. Previous detection methods required that the graft be processed by molecular and/or immunohistochemical techniques, limiting further functional studies. This study evaluated the use of three-dimensional fluorescent stereomicroscopy for gross detection of ES cell derived hepatic engraftment.

MATERIAL AND METHODS

Murine ES cells expressing the enhanced green fluorescence protein (EGFP) underwent directed endodermal lineage differentiation. Three days after two thirds partial hepatectomy, cells were injected into the liver parenchyma, and livers were harvested at 10 to 20 d and examined by fluorescence stereomicroscopy with a GFP2 long pass filter (100447084; Leica Microsystems AG, Wetzlar, Germany). The sensitivity and reliability of the test was evaluated using quantitative polymerase chain reaction (q-PCR) to assay for the presence of EGFP mRNA in the tissue.

RESULTS

Fluorescent microscopy detected EGFP-positive cells engrafted with normal histology in 5 of 11 specimens. EGFP mRNA was confirmed in all five specimens by q-PCR. Only one of the 11 specimens was negative by fluorescence stereomicroscopy and positive by q-PCR, P < 0.02, Fisher's exact test.

CONCLUSION

Utilization of three-dimensional stereomicroscopy with a GFP2 long pass filter is a powerful and fast screening tool for GFP-ES derived hepatic engraftment.

Recombinant AAV2 transduction of primitive human hematopoietic stem cells capable of serial engraftment in immune-deficient mice

A recombinant AAV2 (rAAV2) vector encoding antisense RNA to HIV-1 transactivating region (TAR) was evaluated for transduction of human cord blood CD34+CD38- hematopoietic stem cells (HSC) capable of serial engraftment in nonobese diabetic (NOD)/severe combined immunodeficient (SCID) mice. Results revealed long-term multilineage marking in primary and secondary recipients, and significantly, an enrichment of transduced cells in secondary hosts, indicating efficient transduction of multipotential self-renewing HSC. These results were confirmed by the persistence of rAAV marking of clonogenic progenitors in serial analyses of recipient marrow. Upon HIV-1 challenge, the macrophage progeny of transduced CD34+ cells expressed antisense RNA and exhibited sustained and significant inhibition of virus replication as compared with controls in every donor tested, without selective pressure. This study represents a clear in vivo demonstration of efficient rAAV2 transduction of human HSC.