Adult rat liver cells transdifferentiated with lentiviral IPF1 vectors reverse diabetes in mice: an ex vivo gene therapy approach

Therapeutic approaches for Type 1 Diabetes: Promising cell-based approaches to achieve ultimate success

Type 1 Diabetes mellitus (T1DM) is a chronic metabolic disorder characterized by pancreatic β-cells destruction. Despite substantial advances in T1DM treatment, lifelong exogenous insulin administration is the mainstay of treatments, and constant control of glucose levels is still a challenge. Endogenous insulin production by replacing insulin-producing cells is an alternative, but the lack of suitable donors is accounted as one of the main obstacles to its widespread application. The research and trials overview demonstrates that endogenous production of insulin has started to go beyond the deceased-derived to stem cells-derived insulin-producing cells. Several protocols have been developed over the past couple of years for generating insulin-producing cells (IPCs) from various stem cell types and reprogramming fully differentiated cells. A straightforward and quick method for achieving this goal is to investigate and apply the β-cell specific transcription factors as a direct strategy for IPCs generation. In this review, we emphasize the significance of transcription factors in IPCs development from different non-beta cell sources, and pertinent research underlies the marked progress in the methods for generating insulin-producing cells and application for Type 1 Diabetes treatment.

Pancreatic Transdifferentiation Using β-Cell Transcription Factors for Type 1 Diabetes Treatment

Type 1 diabetes is a chronic illness in which the native beta (β)-cell population responsible for insulin release has been the subject of autoimmune destruction. This condition requires patients to frequently measure their blood glucose concentration and administer multiple daily exogenous insulin injections accordingly. Current treatments fail to effectively treat the disease without significant side effects, and this has led to the exploration of different approaches for its treatment. Gene therapy and the use of viral vectors has been explored extensively and has been successful in treating a range of diseases. The use of viral vectors to deliver β-cell transcription factors has been researched in the context of type 1 diabetes to induce the pancreatic transdifferentiation of cells to replace the β-cell population destroyed in patients. Studies have used various combinations of pancreatic and β-cell transcription factors in order to induce pancreatic transdifferentiation and have achieved varying levels of success. This review will outline why pancreatic transcription factors have been utilised and how their application can allow the development of insulin-producing cells from non β-cells and potentially act as a cure for type 1 diabetes.

Temporal analysis of distribution pattern of islet cells and antioxidant enzymes for diabetes onset in postnatal critical development window in rats

AIM

At performing a temporal analysis of the distribution pattern of islet endocrine cells and antioxidant enzymes in diabetic rats during the post-natal critical development window.

MAIN METHODS

The newborns received streptozotocin (STZ) at birth for diabetes induction, and control females received the vehicle. The animals were euthanized at different lifetimes: D5, D10, D15, and D30. Morphological analysis of pancreas and biochemical assays was performed.

KEY FINDINGS

The STZ-induced rats presented irregular shape of islet on D5 and there was an attempt to restore of this shape in other life moment studied. There was an increase progressive in islet area, however they maintained smaller than those of control rats, with lower labeling intensity for insulin, higher for glucagon and somatostatin, lower for SOD-1 was lower in the islets of the STZ-induced animals at all times studied and for GSH-Px in D10 and D30.

SIGNIFICANCE

Although STZ-induced diabetic rats presented compensatory mechanisms to restore the mass of endocrine cells, this was not sufficient since these rats developed the diabetic state. This was confirmed by the oral glucose tolerance test from D30. In addition, the delta (δ)-cells presented ectopic location in islets, indicating a possible relationship for beta (β)-cell mass restoration. There was a response of the pancreas to reduce the hyperglycemia in the first month of life. Furthermore, the cells from the endocrine pancreas of diabetic animals show a decline of antioxidant enzymatic, contributing to the increased susceptibility of cells to hyperglycemia-induced ROS in this postnatal critical development window.

Promoter optimisation of lentiviral vectors for efficient insulin gene expression in canine mesenchymal stromal cells: potential surrogate beta cells

BACKGROUND

The lack of an ideal cell type that can be easily acquired, modified to produce insulin, and re-implanted has been a limitation for ex vivo insulin gene therapy. Canine diabetes is currently treated with human insulin and is a good model for human diabetes. Mesenchymal stromal cells (MSCs) are a promising candidate cell type for gene therapy. In the present study, we optimised insulin production using lentiviral transduced canine MSCs (cMSCs), aiming to evaluate their ability for use as surrogate beta cells.

METHODS

Canine MSCs were derived from bone marrow and validated by measuring the expression of MSC lineage specific markers. Lentivirus vectors encoding the proinsulin gene (with or without a Kozak sequence) under the control of spleen focus forming virus, cytomegalovirus, elongation factor 1α and simian virus 40 promotors were generated and used to transduce primary cMSCs and a hepatocyte cell line. The insulin-producing capacity of transduced primary cMSCs was assessed by measuring the concentration of C-peptide produced.

RESULTS

Primary cMSC could be readily expanded in culture and efficiently transduced using lentiviral vectors encoding proinsulin. Increasing the multiplicity of infection from 3 to 20 led to an increase in C-peptide secretion (from 1700 to 4000 pmol/l). The spleen focus forming virus promoter conferred the strongest transcriptional ability.

CONCLUSIONS

The results of the present study suggest that optimised lentiviral transduction of the insulin gene into primary cMSCs renders these cells capable of secreting insulin over both the short- and long-term, in sufficient quantities in vitro to support their potential use in insulin gene therapy.

Epigenetic Induction of Definitive and Pancreatic Endoderm Cell Fate in Human Fibroblasts

Reprogramming can occur by the introduction of key transcription factors (TFs) as well as by epigenetic changes. We demonstrated that histone deacetylase inhibitor (HDACi) Trichostatin A (TSA) combined with a chromatin remodeling medium (CRM) induced expression of a number of definitive endoderm and early and late pancreatic marker genes. When CRM was omitted, endoderm/pancreatic marker genes were not induced. Furthermore, treatment with DNA methyltransferase inhibitor (DNMTi) 5-azacytidine (5AZA) CRM did not affect gene expression changes, and when 5AZA was combined with TSA, no further increase in gene expression of endoderm, pancreatic endoderm, and endocrine markers was seen over levels induced with TSA alone. Interestingly, TSA-CRM did not affect expression of pluripotency and hepatocyte genes but induced some mesoderm transcripts. Upon removal of TSA-CRM, the endoderm/pancreatic gene expression profile returned to baseline. Our findings underscore the role epigenetic modification in transdifferentiation of one somatic cell into another. However, full reprogramming of fibroblasts to β-cells will require combination of this approach with TF overexpression and/or culture of the partially reprogrammed cells under β-cell specific conditions.

Reprogramming of liver cells into insulin-producing cells

Tissue replacement is a promising direction for the treatment of diabetes, which will become widely available only when islets or insulin-producing cells that will not be rejected by the diabetic recipients are available in unlimited amounts. The present review addresses the research in the field of generating functional insulin-producing cells by transdifferentiation of adult liver cells both in vitro and in vivo. It presents recent knowledge of the mechanisms which underlie the process and assesses the challenges which should be addressed for its efficient implementation as a cell based replacement therapy for diabetics.

PDX1 binds and represses hepatic genes to ensure robust pancreatic commitment in differentiating human embryonic stem cells

Inactivation of the Pancreatic and Duodenal Homeobox 1 (PDX1) gene causes pancreatic agenesis, which places PDX1 high atop the regulatory network controlling development of this indispensable organ. However, little is known about the identity of PDX1 transcriptional targets. We simulated pancreatic development by differentiating human embryonic stem cells (hESCs) into early pancreatic progenitors and subjected this cell population to PDX1 chromatin immunoprecipitation sequencing (ChIP-seq). We identified more than 350 genes bound by PDX1, whose expression was upregulated on day 17 of differentiation. This group included known PDX1 targets and many genes not previously linked to pancreatic development. ChIP-seq also revealed PDX1 occupancy at hepatic genes. We hypothesized that simultaneous PDX1-driven activation of pancreatic and repression of hepatic programs underlie early divergence between pancreas and liver. In HepG2 cells and differentiating hESCs, we found that PDX1 binds and suppresses expression of endogenous liver genes. These findings rebrand PDX1 as a context-dependent transcriptional repressor and activator within the same cell type.

•

Early pancreatic progenitor (ePP) cells are efficiently derived from hESCs

•

High levels of the homeobox transcription factor PDX1 label ePP cells

•

PDX1 binds a battery of foregut/midgut and early pancreatic genes in ePP cells

•

PDX1 binds and represses hepatic genes

Platelet-derived growth factor BB mimics serum-induced dispersal of pancreatic epithelial cell clusters

We showed previously that proliferating human islet-derived de-differentiated cells (DIDs) exhibit many characteristics of mesenchymal stem cells. Dispersed DIDs can be induced by serum deprivation to undergo mesenchymal-to-epithelial transition and aggregate into epithelial cell clusters (ECCs). Conversely, ECCs can be induced to disperse and undergo epithelial-to-mesenchymal transition (EMT) by re-addition of mammalian sera. In this study, we show that platelet-derived growth factor BB (PDGF-BB) mimics and mediates serum-induced ECCs' dispersal accompanied by accumulation of cytoplasmic β-catenin and a decrease in the levels of insulin and glucagon mRNAs. Moreover, we show that PDGF-BB-induced dispersal of ECCs is a more general phenomenon that occurs also with bone marrow mesenchymal stem cells (BM-MSCs) and dermal fibroblasts (DFs). In DIDs, BM-MSCs, and DFs, PDGF decreased the levels of DKK1 mRNA, suggesting involvement of the Wnt signaling pathway. PDGF-BB stimulated a significant increase in S473 phosphorylation of Akt and the PI3K specific inhibitor (PIP828) partially inhibited PDGF-BB-induced ECC dispersal. Lastly, the PDGF-receptor (PDGF-R) antagonist JNJ-10198409 inhibited both PDGF-BB--and serum-induced ECC dispersal. Epidermal growth factor (EGF), which shares most of the PDGF signaling pathway, did not induce dispersal and only weakly stimulated Akt phosphorylation. Our data suggest that PDGF-BB mediates serum-induced DIDs dispersal, correlated with the activation of the PI3K-Akt pathway.

Differentiation of human adipose tissue-derived stem cells into aggregates of insulin-producing cells through the overexpression of pancreatic and duodenal homeobox gene-1

The pancreatic and duodenal homeobox gene 1 (Pdx-1) plays a key role in normal pancreas development and is required for maintaining the normal function of islets. In this study, we examined whether human adipose tissue-derived stem cells (hASCs) could differentiate into insulin-producing cells by exogenously expressed Pdx-1. hASCs were infected with recombinant adenovirus encoding the mouse Pdx-1 gene and differentiated under high-glucose conditions. Insulin transcript levels and the expression of key transcription factors required for pancreatic development including FoxA2, Nkx2.2, and NeuroD were significantly increased by exogenous Pdx-1 overexpression. The expression of Nkx6.1 was found only in Pdx-1-induced hASCs. In addition to transcripts for transcription factors involved in pancreatic development, transcripts for the GLP-1 receptor, glucokinase, and glucose transporter, which are required for maintaining the function of pancreatic β-cells, were observed only in Pdx-1-induced hASCs. Pdx-1-induced hASCs exhibited insulin secretion in response to glucose challenge in vitro. When Pdx-1-induced hASCs were transplanted into streptozotocin (STZ)-induced diabetic mice, they reduced blood glucose levels, although they did not restore normoglycemia. These results demonstrate that the expression of exogenous Pdx-1 is sufficient to induce pancreatic differentiation in vitro but does not induce the fully functional, mature insulin-producing cells that are required for restoring normoglycemia in vivo.

NKX6.1 promotes PDX-1-induced liver to pancreatic β-cells reprogramming

Reprogramming adult mammalian cells is an attractive approach for generating cell-based therapies for degenerative diseases, such as diabetes. Adult human liver cells exhibit a high level of developmental plasticity and have been suggested as a potential source of pancreatic progenitor tissue. An instructive role for dominant pancreatic transcription factors in altering the hepatic developmental fate along the pancreatic lineage and function has been demonstrated. Here we analyze whether transcription factors expressed in mature pancreatic β-cells preferentially activate β-cell lineage differentiation in liver. NKX6.1 is a transcription factor uniquely expressed in β-cells of the adult pancreas, its potential role in reprogramming liver cells to pancreatic lineages has never been analyzed. Our results suggest that NKX6.1 activates immature pancreatic markers such as NGN-3 and ISL-1 but not pancreatic hormones gene expression in human liver cells. We hypothesized that its restricted capacity to activate a wide pancreatic repertoire in liver could be related to its incapacity to activate endogenous PDX-1 expression in liver cells. Indeed, the complementation of NKX6.1 by ectopic PDX-1 expression substantially and specifically promoted insulin expression and glucose regulated processed hormone secretion to a higher extent than that of PDX-1 alone, without increasing the reprogrammed cells. This may suggest a potential role for NKX6.1 in promoting PDX-1 reprogrammed cells maturation along the β-cell-like lineage. By contrast, NKX6.1 repressed PDX-1 induced proglucagon gene expression. The individual and concerted effects of pancreatic transcription factors in adult extra-pancreatic cells, is expected to facilitate developing regenerative medicine approaches for cell replacement therapy in diabetics.

Gene therapy in diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease, whereby auto-reactive cytotoxic T cells target and destroy insulin-secreting β-cells in pancreatic islets leading to insulin deficiency and subsequent hyperglycemia. These individuals require multiple daily insulin injections every day of their life without which they will develop life-threatening diabetic ketoacidosis (DKA) and die. Gene therapy by viral vector and non-viral transduction may be useful techniques to treat T1D as it can be applied from many different angles; such as the suppression of autoreactive T cells to prevent islet destruction (prophylactic) or the replacement of the insulin gene (post-disease). The need for a better method for providing euglycemia arose from insufficient numbers of cadaver islets for transplantation and the immunosuppression required post-transplant. Ectopic expression of insulin or islet modification have been examined, but not perfected. This review examines the various gene transfer methods, gene therapy techniques used to date and promising novel techniques for the maintenance of euglycemia in the treatment of T1D.

Adult cell fate reprogramming: converting liver to pancreas

Regenerative medicine aims at producing new cells for repair or replacement of diseased and damaged tissues. Embryonic and adult stem cells have been suggested as attractive sources of cells for generating the new cells needed. The leading dogma was that adult cells in mammals, once committed to a specific lineage, become "terminally differentiated" and can no longer change their fate. However, in recent years increasing evidence has accumulated demonstrating the remarkable ability of some differentiated cells to be converted into a different cell type via a process termed developmental redirection or adult cells reprogramming. For example, abundant human cell types, such as dermal fibroblasts and adipocytes, could potentially be harvested and converted into other, medically important cell types, such as neurons, cardiomyocytes, or pancreatic beta cells. In this chapter, we describe a method of activating the pancreatic lineage and beta-cells function in adult human liver cells by ectopic expression of pancreatic transcription factors. This approach aims to generate custom-made autologous surrogate beta cells for treatment of diabetes, and possibly bypass both the shortage of cadaveric human donor tissues and the need for life-long immune-suppression.

Distinct regulation of hepatic nuclear factor 1alpha by NKX6.1 in pancreatic beta cells

Hepatic nuclear factor 1alpha (HNF1alpha) is a key regulator of development and function in pancreatic beta cells and is specifically involved in regulation of glycolysis and glucose-stimulated insulin secretion. Abnormal expression of HNF1alpha leads to development of MODY3 (maturity-onset diabetes of the young 3). We report that NK6 homeodomain 1 (NKX6.1) binds to a cis-regulatory element in the HNF1alpha promoter and is a major regulator of this gene in beta cells. We identified an NKX6.1 recognition sequence in the distal region of the HNF1alpha promoter and demonstrated specific binding of NKX6.1 in beta cells by electrophoretic mobility shift and chromatin immunoprecipitation assays. Site-directed mutagenesis of the NKX6.1 core-binding sequence eliminated NKX6.1-mediated activation and substantially decreased activity of the HNF1alpha promoter in beta cells. Overexpression or small interfering RNA-mediated knockdown of the Nkx6.1 gene resulted in increased or diminished HNF1alpha gene expression, respectively, in beta cells. We conclude that NKX6.1 is a novel regulator of HNF1alpha in pancreatic beta cells. This novel regulatory mechanism for HNF1alpha in beta cells may provide new molecular targets for the diagnosis of MODY3.

Conversion of adult pancreatic alpha-cells to beta-cells after extreme beta-cell loss

Pancreatic insulin-producing β-cells have a long lifespan, such that in healthy conditions they replicate little during a lifetime. Nevertheless, they show increased self-duplication upon increased metabolic demand or after injury (i.e. β-cell loss). It is unknown if adult mammals can differentiate (regenerate) new β-cells after extreme, total β-cell loss, as in diabetes. This would imply differentiation from precursors or other heterologous (non β-cell) source. Here we show β-cell regeneration in a transgenic model of diphtheria toxin (DT)-induced acute selective near-total β-cell ablation. If given insulin, the mice survived and displayed β-cell mass augmentation with time. Lineage-tracing to label the glucagon-producing α-cells before β-cell ablation tracked large fractions of regenerated β-cells as deriving from α-cells, revealing a previously disregarded degree of pancreatic cell plasticity. Such inter-endocrine spontaneous adult cell conversion could be harnessed towards methods of producing β-cells for diabetes therapies, either in differentiation settings in vitro or in induced regeneration.

Pdx-1 or Pdx-1-VP16 protein transduction induces beta-cell gene expression in liver-stem WB cells

Background

Pancreatic duodenal homeobox-1 (Pdx-1) or Pdx-1-VP16 gene transfer has been shown to induce in vitro rat liver-stem WB cell conversion into pancreatic endocrine precursor cells. High glucose conditions were necessary for further differentiation into functional insulin-producing cells. Pdx-1 has the ability to permeate different cell types due to an inherent protein transduction domain (PTD). In this study, we evaluated liver-to-pancreas conversion of WB cells following Pdx-1 or Pdx-1-VP16 protein transduction.

Findings

WB cells were grown in high glucose medium containing Pdx-1 or Pdx-1-VP16 recombinant proteins for two weeks. β-like cell commitment was analysed by RT-PCR of pancreatic endocrine genes. We found that WB cells in high glucose culture spontaneously express pancreatic endocrine genes (Pdx-1, Ngn3, Nkx2.2, Kir6.2). Their further differentiation into β-like cells expressing genes related to endocrine pancreas development (Ngn3, NeuroD, Pax4, Nkx2.2, Nkx6.1, Pdx-1) and β-cell function (Glut-2, Kir6.2, insulin) was achieved only in the presence of Pdx-1(-VP16) protein.

Conclusion

These results demonstrate that Pdx-1(-VP16) protein transduction is instrumental for in vitro liver-to-pancreas conversion and is an alternative to gene therapy for β-cell engineering for diabetes cell therapy.

Expression of human insulin gene wrapped with chitosan nanoparticles in NIH3T3 cells and diabetic rats

AIM

To study the expression of human insulin gene wrapped with chitosan nanoparticles in NIH3T3 cells and diabetic rats.

METHODS

pCMV.Ins, an expression plasmid of the human insulin gene, was constructed. In total, 100 microg pCMV.Ins wrapped with chitosan nanoparticles (chitosan-pCMV.Ins) was transfected to NIH3T3 cells and diabetes rats through lavage and coloclysis, respectively. The transfected cells were grown in Dulbecco's modified Eagle's medium, containing G418, for 72 h after transfection. The clones were selected and continued to grow in G418 medium for 24 d. The expression of human insulin was detected by immunohistochemistry. Human insulin in the culture medium of transfected cells was measured. Fasting blood glucose and plasma human insulin of diabetic rats were measured for 5 d after transfection. RT-PCR and Western blotting were performed to confirm the expression of the human insulin gene in diabetic rats.

RESULTS

Approximately 10% of NIH3T3 cells transfected by chitosan-pCMV.Ins expressed human insulin. Human insulin in the culture medium of NIH3T3 cells transfected by chitosan-pCMV.Ins significantly increased compared with that of the control group (P<0.01). Fasting blood glucose levels of the lavage group and the coloclysis group decreased significantly in 5 d (P<0.01) in comparison, while plasma insulin levels were much higher (P<0.01). The human insulin gene mRNA and human insulin were only detected in the lavage and the coloclysis groups.

CONCLUSION

The human insulin gene can be transfected and expressed successfully by chitosan- pCMV.Ins in NIH3T3 cells and diabetes rats, which indicates that chitosan is a promising, non-viral vector for gene expression.

Minimization and withdrawal of steroids in pancreas and islet transplantation

For reducing the corticosteroid (CS)-related side-effects, especially cardiovascular events, CS-sparing protocols have become increasingly common in pancreas transplantation (PT). Lympho-depleting induction antibodies, such as rabbit anti-thymocyte globulin (rATG) or alemtuzumab, have been widely used in successful trials. The results of various CS-sparing protocols combining calcineurin inhibitors (CNI) and mycophenolate or sirolimus, have been mixed for rejection and survival rates. Most of the studies were uncontrolled trials of low-risk patients, therefore the grade of evidence is limited. Large-scale prospective studies with long-term follow up are necessary to assess risks and benefits of CS-sparing regimens in PT before recommending such strategies as standard practice. Islet allo-transplantation for patients with brittle type 1 diabetes mellitus, less invasive and safer procedure than PT, has been attempted since late 1980s, but diabetogenic immunosuppressants at maintenance, mainly CS and high-dose CNI, prevented satisfactory results (10% insulin-independence at 1-year post-transplant). Since 2000, CS-free and CNI-reducing protocols, including more potent induction [daclizumab, OKT3gamma1(ala-ala) anti-CD3 antibody, rATG] and maintenance (sirolimus, mycophenolate) agents, have significantly improved short-term outcomes whereas long-term are still inadequate (from 80% to 20% insulin-independence from 1- to 5-year post-transplant). Main limitations are allo- and autoimmunity, immunosuppression-related islet and systemic toxicity and transplant site unsuitability, which tolerogenic protocols and biotechnological solutions may solve.

Promoting ectopic pancreatic fates: pancreas development and future diabetes therapies

Diabetes is a disease that could be treated more effectively with a better understanding of pancreas development. This review examines the role of master regulator genes driving crucial steps in pancreas development, from foregut specification to differentiation of the five endocrine cell types. The roles of Pdx1, Ptf1a, and Ngn3 are particularly examined as they are both necessary and sufficient for promoting pancreatic cell fates (Pdx1, Ptf1a) and endocrine cell development (Ngn3). The roles of Arx and Pax4 are studied as they compose part of the regulatory mechanism balancing development of different types of endocrine cells within the iselts and promote the development of alpha/PP and beta/delta cell progenitors, respectively. The roles of the aforementioned genes, and the consequences of misexpression of them for functionality of the pancreas, are examined through recent studies in model organisms, particularly Xenopus and zebrafish. Recent developments in cell replacement therapy research are also covered, concentrating on stem cell research (coaxing both adult and embryonic stem cells toward a beta cell fate) and transdifferentiation (generating beta cells from other differentiated cell types).

Conversion of immortal liver progenitor cells into pancreatic endocrine progenitor cells by persistent expression of Pdx-1

The conversion of expandable liver progenitor cells into pancreatic beta cells would provide a renewable cell source for diabetes cell therapy. Previously, we reported the establishment of liver epithelial progenitor cells (LEPCs). In this work, LEPCs were modified into EGFP/Pdx-1 LEPCs, cells with stable expression of both Pdx-1 and EGFP. Unlike previous work, with persistent expression of Pdx-1, EGFP/Pdx-1 LEPCs acquired the phenotype of pancreatic endocrine progenitor cells rather than giving rise to insulin-producing cells directly. EGFP/Pdx-1 LEPCs proliferated vigorously and expressed the crucial transcription factors involved in beta cell development, including Ngn3, NeuroD, Nkx2.2, Nkx6.1, Pax4, Pax6, Isl1, MafA and endogenous Pdx-1, but did not secrete insulin. When cultured in high glucose/low serum medium supplemented with cytokines, EGFP/Pdx-1 LEPCs stopped proliferating and gave rise to functional beta cells without any evidence of exocrine or other islet cell lineage differentiation. When transplanted into diabetic SCID mice, EGFP/Pdx-1 LEPCs ameliorated hyperglycemia by secreting insulin in a glucose regulated manner. Considering the limited availability of beta cells, we propose that our experiments will provide a framework for utilizing the immortal liver progenitor cells as a renewable cell source for the generation of functional pancreatic beta cells.

Nonvirally modified autologous primary hepatocytes correct diabetes and prevent target organ injury in a large preclinical model

BACKGROUND

Current gene- and cell-based therapies have significant limitations which impede widespread clinical application. Taking diabetes mellitus as a paradigm, we have sought to overcome these limitations by ex vivo electrotransfer of a nonviral insulin expression vector into primary hepatocytes followed by immediate autologous reimplantation in a preclinical model of diabetes.

METHODS AND RESULTS

In a single 3-hour procedure, hepatocytes were isolated from a surgically resected liver wedge, electroporated with an insulin expression plasmid ex vivo and reimplanted intraparenchymally under ultrasonic guidance into the liver in each of 10 streptozotocin-induced diabetic Yorkshire pigs. The vector was comprised of a bifunctional, glucose-responsive promoter linked to human insulin cDNA. Ambient glucose concentrations appropriately altered human insulin mRNA expression and C-peptide secretion within minutes in vitro and in vivo. Treated swine showed correction of hyperglycemia, glucose intolerance, dyslipidemia and other metabolic abnormalities for > or = 47 weeks. Metabolic correction correlated significantly with the number of hepatocytes implanted. Importantly, we observed no hypoglycemia even under fasting conditions. Direct intrahepatic implantation of hepatocytes did not alter biochemical indices of liver function or induce abnormal hepatic lobular architecture. About 70% of implanted hepatocytes functionally engrafted, appeared histologically normal, retained vector DNA and expressed human insulin for > or = 47 weeks. Based on structural tissue analyses and transcriptome data, we showed that early correction of diabetes attenuated and even prevented pathological changes in the eye, kidney, liver and aorta.

CONCLUSIONS

We demonstrate that autologous hepatocytes can be efficiently, simply and safely modified by electroporation of a nonviral vector to express, process and secrete insulin durably. This strategy, which achieved significant and sustained therapeutic efficacy in a large preclinical model without adverse effects, warrants consideration for clinical development especially as it could have broader future applications for the treatment of other acquired and inherited diseases for which systemic reconstitution of a specific protein deficiency is critical.

Beta-cell replacement for insulin-dependent diabetes mellitus

Beta-cell replacement is considered the optimal treatment for type 1 diabetes, however, it is hindered by a shortage of human organ donors. Given the difficulty of expanding adult beta cells in vitro, stem/progenitor cells, which can be expanded in tissue culture and induced to differentiate into multiple cell types, represent an attractive source for generation of cells with beta-cell properties. In the absence of well-characterized human pancreas progenitor cells, investigators are exploring the use of embryonic stem cells and stem/progenitor cells from other tissues. Once abundant surrogate beta cells are available, the challenge will be to protect them from recurring autoimmunity.

Genetic modification of cells for transplantation

Progress in gene therapy has produced promising results that translate experimental research into clinical treatment. Gene modification has been extensively employed in cell transplantation. The main barrier is an effective gene delivery system. Several viral vectors were utilized in end-stage differentiated cells. Recently, successful applications were described with adenovirus-associated vectors. As an alternative, embryonic stem cell- and stem cell-like systems were established for generation of tissue-specified gene-modified cells. Owing to the feasibility for genetic manipulations and the self-renewing potency of these cells they can be used in a way enabling large-scale in vitro production. This approach offers the establishment of in vitro cell culture systems that will deliver sufficient amounts of highly purified, immunoautologous cells suitable for application in regenerative medicine. In this review, the current technology of gene delivery systems to cells is recapitulated and the latest developments for cell transplantation are discussed.

Long-term correction of diabetes in rats after lentiviral hepatic insulin gene therapy

AIMS/HYPOTHESIS

Type 1 diabetes results from the autoimmune destruction of pancreatic beta cells. Exogenous insulin therapy cannot achieve precise physiological control of blood glucose concentrations, and debilitating complications develop. Lentiviral vectors are promising tools for liver-directed gene therapy. However, to date, transduction rates in vivo remain low in hepatocytes, without the induction of cell cycling. We investigated long-term transgene expression in quiescent hepatocytes in vitro and determined whether the lentiviral delivery of furin-cleavable insulin to the liver could reverse diabetes in rats.

MATERIALS AND METHODS

To improve transduction efficiency in vitro, we optimised hepatocyte isolation and maintenance protocols and, using an improved surgical delivery method, delivered furin-cleavable insulin alone or empty vector to the livers of streptozotocin-induced diabetic rats by means of a lentiviral vector. Rats were monitored for changes in body weight and blood glucose, and intravenous glucose tolerance tests were performed. Expression of insulin was determined by RT-PCR, immunohistochemistry and electron microscopy.

RESULTS

We achieved long-term transgene expression in quiescent hepatocytes in vitro (87 +/- 1.2% transduction efficiency), with up to 60 +/- 3.2% transduction in vivo. We normalised blood glucose for 500 days-a significantly longer period than previously reported-making this the first successful study using a lentiviral vector. This procedure resulted in the expression of genes encoding several beta cell transcription factors, some pancreatic endocrine transdifferentiation, hepatic insulin storage in granules, and restoration of glucose tolerance. Liver function tests remained normal. Importantly, pancreatic exocrine transdifferentiation did not occur.

CONCLUSIONS/INTERPRETATION

Our data suggest that this regimen may ultimately be employed for the treatment of type 1 diabetes.

Generation of insulin-producing cells from human bone marrow mesenchymal stem cells by genetic manipulation

Beta cell replacement is a promising approach for treatment of type 1 diabetes; however, it is limited by a shortage of pancreas donors. The pluripotent MSC in adult bone marrow (BM) offer an attractive source of stem cells for generation of surrogate beta cells. BM-MSC can be obtained with relative ease from each patient, allowing potential circumvention of allograft rejection. Here, we report a procedure for expansion of BM-MSC in vitro and their differentiation into insulin-producing cells. The pancreatic duodenal homeobox 1 (Pdx1) gene was expressed in BM-MSC from 14 human donors, and the extent of differentiation of these cells toward the beta-cell phenotype was evaluated. RNA and protein analyses documented the activation of expression of all four islet hormones. However, the cells lacked expression of NEUROD1, a key transcription factor in differentiated beta cells. A significant insulin content, as well as glucose-stimulated insulin release, were demonstrated in vitro. Cell transplantation into streptozotocin-diabetic immunodeficient mice resulted in further differentiation, including induction of NEUROD1, and reduction of hyperglycemia. These findings were reproducible in BM-MSC from 9 of 14 donors of both sexes, ages 19-62. These results suggest a therapeutic potential for PDX1-expressing BM-MSC in beta-cell replacement in patients with type 1 diabetes.

Stem cells in the adult pancreas and liver

Stem cells are undifferentiated cells that can self-renew and generate specialized (functional) cell types. The remarkable ability of stem cells to differentiate towards functional cells makes them suitable modalities in cellular therapy (which means treating diseases with the body's own cells). Potential targets for cellular therapy include diabetes and liver failure. However, in order for stem cells to be clinically useful, we must learn to identify them and to regulate their differentiation. We will use the intestine as a classical example of a stem cell compartment, and then examine the evidence for the existence of adult stem cells in two endodermally derived organs: pancreas and liver. We will review the characteristics of the putative stem cells in these tissues and the transcription factors controlling their differentiation towards functional cell types.