Transduction of human and mouse pancreatic islet cells using a bicistronic recombinant adeno-associated viral vector

Inducing immune tolerance: a focus on Type 1 diabetes mellitus

Tolerogenic strategies that specifically target diabetogenic immune cells in the absence of complications of immunosuppression are the desired treatment for the prevention or even reversal of Type 1 diabetes (T1D). Antigen (Ag)-based therapies must not only suppress disease-initiating diabetogenic T cells that are already activated, but, more importantly, prevent activation of naive auto-Ag-specific T cells that may become autoreactive through epitope spreading as a result of Ag liberation from damaged islet cells. Therefore, identification of auto-Ags relevant to T1D initiation and progression is critical to the design of effective Ag-specific therapies. Animal models of T1D have been successfully employed to identify potential diabetogenic Ags, and have further facilitated translation of Ag-specific tolerance strategies into human clinical trials. In this review, we highlight important advances using animal models in Ag-specific T1D immunotherapies, and the application of the preclinical findings to human subjects. We provide an up-to-date overview of the strengths and weaknesses of various tolerance-inducing strategies, including infusion of soluble Ags/peptides by various routes of delivery, genetic vaccinations, cell- and inert particle-based tolerogenic approaches, and various other strategies that target distinct tolerance-inducing pathways.

Carbamazepine as a novel small molecule corrector of trafficking-impaired ATP-sensitive potassium channels identified in congenital hyperinsulinism

ATP-sensitive potassium (KATP) channels consisting of sulfonylurea receptor 1 (SUR1) and the potassium channel Kir6.2 play a key role in insulin secretion by coupling metabolic signals to β-cell membrane potential. Mutations in SUR1 and Kir6.2 that impair channel trafficking to the cell surface lead to loss of channel function and congenital hyperinsulinism. We report that carbamazepine, an anticonvulsant, corrects the trafficking defects of mutant KATP channels previously identified in congenital hyperinsulinism. Strikingly, of the 19 SUR1 mutations examined, only those located in the first transmembrane domain of SUR1 responded to the drug. We show that unlike that reported for several other protein misfolding diseases, carbamazepine did not correct KATP channel trafficking defects by activating autophagy; rather, it directly improved the biogenesis efficiency of mutant channels along the secretory pathway. In addition to its effect on channel trafficking, carbamazepine also inhibited KATP channel activity. Upon subsequent removal of carbamazepine, however, the function of rescued channels was recovered. Importantly, combination of the KATP channel opener diazoxide and carbamazepine led to enhanced mutant channel function without carbamazepine washout. The corrector effect of carbamazepine on mutant KATP channels was also demonstrated in rat and human β-cells with an accompanying increase in channel activity. Our findings identify carbamazepine as a novel small molecule corrector that may be used to restore KATP channel expression and function in a subset of congenital hyperinsulinism patients.

Genetic vaccination for re-establishing T-cell tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease resulting in the destruction of the insulin-secreting β cells. Currently, there is no established clinical approach to effectively suppress long-term the diabetogenic response. Genetic-based vaccination offers a general strategy to reestablish β-cell specific tolerance within the T-cell compartment. The transfer of genes encoding β-cell autoantigens, anti-inflammatory cytokines and/or immunomodulatory proteins has proven to be effective at preventing and suppressing the diabetogenic response in animal models of T1D. The current review will discuss genetic approaches to prevent and treat T1D with an emphasis on plasmid DNA- and adeno-associated virus-based vaccines.

Combined vascular endothelial growth factor-A and fibroblast growth factor 4 gene transfer improves wound healing in diabetic mice

BACKGROUND

Impaired wound healing in diabetes is related to decreased production of growth factors. Hence, gene therapy is considered as promising treatment modality. So far, efforts concentrated on single gene therapy with particular emphasis on vascular endothelial growth factor-A (VEGF-A). However, as multiple proteins are involved in this process it is rational to test new approaches. Therefore, the aim of this study was to investigate whether single AAV vector-mediated simultaneous transfer of VEGF-A and fibroblast growth factor 4 (FGF4) coding sequences will improve the wound healing over the effect of VEGF-A in diabetic (db/db) mice.

METHODS

Leptin receptor-deficient db/db mice were randomized to receive intradermal injections of PBS or AAVs carrying β-galactosidase gene (AAV-LacZ), VEGF-A (AAV-VEGF-A), FGF-4 (AAV-FGF4-IRES-GFP) or both therapeutic genes (AAV-FGF4-IRES-VEGF-A). Wound healing kinetics was analyzed until day 21 when all animals were sacrificed for biochemical and histological examination.

RESULTS

Complete wound closure in animals treated with AAV-VEGF-A was achieved earlier (day 19) than in control mice or animals injected with AAV harboring FGF4 (both on day 21). However, the fastest healing was observed in mice injected with bicistronic AAV-FGF4-IRES-VEGF-A vector (day 17). This was paralleled by significantly increased granulation tissue formation, vascularity and dermal matrix deposition. Mechanistically, as shown in vitro, FGF4 stimulated matrix metalloproteinase-9 (MMP-9) and VEGF receptor-1 expression in mouse dermal fibroblasts and when delivered in combination with VEGF-A, enhanced their migration.

CONCLUSION

Combined gene transfer of VEGF-A and FGF4 can improve reparative processes in the wounded skin of diabetic mice better than single agent treatment.

Angiopoiesis and bone regeneration via co-expression of the hVEGF and hBMP genes from an adeno-associated viral vector in vitro and in vivo

AIM

To investigate the therapeutic potential of adeno-associated virus (AAV)-mediated expression of vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP).

METHODS

Four experimental groups were administered the following AAV vector constructs: rAAV-hVEGF(165)-internal ribosome entry site (IRES)-hBMP-7 (AAV-VEGF/BMP), rAAV-hVEGF(165)-GFP (AAV-VEGF), rAAV-hBMP-7-GFP (AAV-BMP), and rAAV-IRES-GFP (AAV-GFP). VEGF(165) and BMP-7 gene expression was detected using RT-PCR. The VEGF(165) and BMP-7 protein expression was determined by Western blotting and ELISA. The rabbit ischemic hind limb model was adopted and rAAV was administered intramuscularly into the ischemic limb.

RESULTS

Rabbit bone marrow-derived mesenchymal stem cells (BMSCs) were cultured and infected with the four viral vectors. The expression of GFP increased from the 7th day of infection and could be detected on the 28th day post-infection. In the AAV-VEGF/BMP group, the levels of VEGF165 and BMP-7 increased with prolonged infection time. The VEGF(165) and BMP-7 secreted from BMSCs in the AAV-VEGF/BMP group enhanced HUVEC tube formation and resulted in a stronger osteogenic ability, respectively. In rabbit ischemic hind limb model, GFP expression increased from the 4th week and could be detected at 8 weeks post-injection. The rAAV vector had superior gene expressing activity. Eight weeks after gene transfer, the mean blood flow was significantly higher in the AAV-VEGF/BMP group. Orthotopic ossification was radiographically evident, and capillary growth and calcium deposits were obvious in this group.

CONCLUSION

AAV-mediated VEGF and BMP gene transfer stimulates angiogenesis and bone regeneration and may be a new therapeutic technique for the treatment of avascular necrosis of the femoral head (ANFH).

Protection of human pancreatic islets using a lentiviral vector expressing two genes: cFLIP and GFP

Pancreatic islet transplantation can provide insulin independence to diabetic patients. However, apoptosis of islets often leads to early graft failure. Genetic engineering with protective gene(s) can improve the viability of these cells. Here we show successful transduction of human islets with a feline immunodeficiency virus (FIV) vector expressing both a cytoprotective (cFLIP) gene and the green fluorescent protein (GFP). Despite using low virus titers to maximize safety, transduced islets expressed both genes, resulting in improved beta-cell metabolic activity and viability. Although only approximately 10% of total islet cells were transduced, the significant viability advantages suggest a "barrier" effect in which protecting the periphery of the islet shields the core. These results provide the first demonstration that a lentiviral vector can express two genes in islets. Furthermore, the engineered islets are resistant to a variety of apoptotic stimuli, suggesting the potential of this approach in enhancing the viability of transplanted cells.

Efficient and persistent transduction of exocrine and endocrine pancreas by adeno-associated virus type 8

Efficient delivery of therapeutic proteins into the pancreas represents a major obstacle to gene therapy of pancreatic disorders. The current study compared the efficiency of recombinant lentivirus and adeno-associated virus (AAV) serotypes 1, 2, 5, 8 vectors delivered by intrapancreatic injection for gene transfer in vivo. Our results indicate that lentivirus and AAV 1, 2, 8 are capable of transducing pancreas with the order of efficiency AAV8 >>AAV1 > AAV2 >/= lentivirus, whereas AAV5 was ineffective. AAV8 resulted in an efficient, persistent (150 days) and dose-dependent transduction in exocrine acinar cells and endocrine islet cells. Pancreatic ducts and blood vessels were also transduced. Extrapancreatic transduction was restricted to liver. Leukocyte infiltration was not observed in pancreas and blood glucose levels were not altered. Thus, AAV8 represents a safe and effective vehicle for therapeutic gene transfer to pancreas in vivo.

Long-Term Monitoring of Transplanted Islets Using Positron Emission Tomography

Islet transplantation can restore glucose homeostasis in those with type 1 diabetes; however, most recipients eventually lose graft function. A noninvasive method to monitor islets following transplantation would enable assessment of their survival and aid the development of therapeutics to prolong graft survival. Here, we show that recombinant lentivirus can be used to engineer human islets to express a positron emission tomography (PET) reporter gene. Following transplantation into mice, transduced islets could be imaged in vivo using microPET and a radiolabeled probe approved by the FDA for clinical use in humans. The magnitude of signal from engineered islets implanted into the axillary cavity reflected the implanted islet mass. Signals from implanted islets decreased by approximately one-half during the first few weeks following transplantation, which may reflect islet cell death shortly after transplantation. Thereafter, the magnitude of signals from the implanted islets remained fairly constant when the recipients were repetitively reimaged over 90 days. Histological analysis of the implants showed healthy islets with PET reporter-expressing cells distributed throughout the islet architecture. These studies suggest that PET imaging of lentivirus-transduced islets could provide a safe and feasible method for long-term monitoring of islet graft survival.

Biological and Biomaterial Approaches for Improved Islet Transplantation

Islet transplantation may be used to treat type I diabetes. Despite tremendous progress in islet isolation, culture, and preservation, the clinical use of this modality of treatment is limited due to post-transplantation challenges to the islets such as the failure to revascularize and immune destruction of the islet graft. In addition, the need for lifelong strong immunosuppressing agents restricts the use of this option to a limited subset of patients, which is further restricted by the unmet need for large numbers of islets. Inadequate islet supply issues are being addressed by regeneration therapy and xenotransplantation. Various strategies are being tried to prevent beta-cell death, including immunoisolation using semipermeable biocompatible polymeric capsules and induction of immune tolerance. Genetic modification of islets promises to complement all these strategies toward the success of islet transplantation. Furthermore, synergistic application of more than one strategy is required for improving the success of islet transplantation. This review will critically address various insights developed in each individual strategy and for multipronged approaches, which will be helpful in achieving better outcomes.

New strategies for cardiovascular gene therapy: regulatable pre-emptive expression of pro-angiogenic and antioxidant genes

Cardiovascular diseases are among the major targets for gene therapy. Initially, clinical experiments of gene transfer of vascular endothelial growth factor (VEGF) improved vascularization and prevented the amputation in patients with critical leg ischemia. However, the majority of trials did not provide conclusive results and therefore further preclinical studies are required. Importantly, data indicate the necessity of regulated expression of angiogenic factors, particularly VEGF, to obtain the therapeutic effect. It is also suggested that the combined delivery of two or more genes may improve the formation of mature vasculature and therefore may be more effective in the amelioration of ischemia. Moreover, experimental approaches in animal models displayed the promise of gene transfer modulating the inflammatory processes and oxidant status of the cells. Particularly, the concept of preemptive gene therapy has been tested, and recent studies have demonstrated that overexpression of heme oxygenase-1 or extracellular superoxide dismutase can prevent heart injury by myocardial infarction induced several weeks after gene instillation. The combination of a preemptive strategy with regulated gene expression, using the vectors in which the therapeutic transgene is driven by exogenously or endogenously controllable promoter, offers another modality. However, we hypothesize that regulatable gene therapy, dependent on the activity of endogenous factors, might be prone to limitations owing to the potential disturbance in the expression of endogenous genes. Here, we demonstrated some indications of these drawbacks. Therefore, the final acceptance of these promising strategies for clinical trials requires careful validation in animal experiments.

Widespread and stable pancreatic gene transfer by adeno-associated virus vectors via different routes

Diabetes is a disease of epidemic proportions and is on the rise worldwide. Gene therapy has been actively pursued but limited by technical hurdles and profound inefficiency of direct gene transfer to the pancreas in vivo. Here, we show that, for the first time, appropriate serotypes of adeno-associated virus (AAV), coupled with a double-stranded vector DNA cassette, enable extensive and long-term in vivo gene transfer in the adult mouse pancreas by three different delivery methods. Intraperitoneal and intravenous delivery of AAV8 effectively transduced exocrine acinar cells as well as endocrine beta-cells, while local pancreatic intraductal delivery of AAV6 showed the best efficiency in the beta-cells among all AAV serotypes tested in this study. Nearly the entire islet population showed gene transfer but with distinct gene transfer efficiency and patterns when different delivery methods and vectors were used. Importantly, localized gene delivery coupled with an insulin promoter allowed extensive yet specific gene expression in the beta-cells. These effective new methods should provide useful tools to study diabetes pathogenesis and gene therapy.

Gene Therapy Progress and Prospects – Vectorology: design and production of expression cassettes in AAV vectors

Adeno-associated virus (AAV) derived vectors are considered highly eligible vehicles for human gene therapy. Not only do they possess many great potential for clinical applications due to their wide range of tissue targets but also their excellent preclinical safety profile makes them particularly suitable candidates for treating serious diseases. Initial clinical trials have yielded encouraging results and prompted further improvements in their design and methods of production. Many studies have been performed to modify the tropism of recombinant (r)AAV by capsid modification. However, the precise control of spatial and temporal gene expression, which may be important in determining the safety and efficacy of gene transfer, lies in a rational choice and a subtle combination of various regulatory genetic elements to be inserted into the expression cassette. Moreover, new strategies based on such genetic sequences open new perspectives for enhancing vector genome persistence, disrupting or reducing pathogenic gene expression and even targeting genes.

Gene therapy for type 1 diabetes

The most intensively studied autoimmune disorder, type 1 diabetes mellitus (DM1), has attracted perhaps the greatest interest for gene-based therapeutic and prophylactic interventions. The final clinical manifestation of this immunologically and genetically complex disease, the absence of insulin, is the major starting point for almost all the gene therapy modalities attempted to date. Insulin replacement by transplantation of islets of Langerhans or surrogate beta cells is the obvious choice, but the allogeneic nature of the transplants activates potent antidonor immunoreactivity necessitating gene and cell-based immunosuppressive strategies as an alternative to the toxic pharmacologic immunosuppressives indicated for classic solid organ transplants. Accumulating knowledge of the cellular mechanisms involved in onset, however, have yielded promising tolerance induction prophylactic approaches using genes and cells. Despite the early successes in a number of animal models, the true test of efficacy in humans remains to be demonstrated.

Efficient gene delivery to human and rodent islets with double-stranded (ds) AAV-based vectors

Transplantation of allogeneic pancreatic islets is an effective approach to treat type 1 diabetes. To bypass the need for systemic administration of immunosuppression drugs following transplantation, approaches to genetically modify allogeneic islets to express anti-inflammatory, immunosuppressive, or antiapoptotic proteins prior to transplantation are being developed. Adeno-associated viral (AAV) based vectors have been used for gene transfer to islets, but the efficiency of functional transduction is low. Recently, double-stranded (ds) or double-copy (dc) based AAV vectors have been developed that allow for more rapid and efficient AAV-mediated transgene expression following transduction. Here we demonstrate that intact human and murine islets can be transduced with dsAAV2-eGFP efficiently compared to single-stranded AAV2-eGFP. Furthermore, our results demonstrate that murine islets transduced with dsAAV2-eGFP have normal islet glucose responsiveness, viability, and islet insulin content. Transplantation of the dsAAV2-eGFP transduced islet restored normal glycemia in diabetic mice without eliciting an immune response. Significant dsAAV2-mediated eGFP expression was observed in the islet grafts for at least 6 months post-transplant. Finally, we demonstrated that dsAAV serotypes 2, 6, and 8 infect human islets efficiently. Taken together, these results suggest that dsAAV based vectors are highly appropriate for gene transfer to islets to facilitate transplantation.

Efficient transduction of vascular endothelial cells with recombinant adeno-associated virus serotype 1 and 5 vectors

Recombinant adeno-associated virus (rAAV) has become an attractive tool for gene therapy because of its ability to transduce both dividing and nondividing cells, elicit a limited immune response, and the capacity for imparting long-term transgene expression. Previous studies have utilized rAAV serotype 2 predominantly and found that transduction of vascular cells is relatively inefficient. The purpose of the present study was to evaluate the transduction efficiency of rAAV serotypes 1 through 5 in human and rat aortic endothelial cells (HAEC and RAEC). rAAV vectors with AAV2 inverted terminal repeats containing the human alpha1-antitrypsin (hAAT) gene were transcapsidated using helper plasmids to provide viral capsids for the AAV1 through 5 serotypes. True type rAAV2 and 5 vectors encoding beta-galactosidase or green fluorescence protein were also studied. Infection with rAAV1 resulted in the most efficient transduction in both HAEC and RAEC compared to other serotypes (p < 0.001) at 7 days posttransduction. Interestingly, expression was increased in cells transduced with rAAV5 to levels surpassing rAAV1 by day 14 and 21. Transduction with rAAV1 was completely inhibited by removal of sialic acid with sialidase, while heparin had no effect. These studies are the first demonstration that sialic acid residues are required for rAAV1 transduction in endothelial cells. Transduction of rat aortic segments ex vivo and in vivo demonstrated significant transgene expression in endothelial and smooth muscle cells with rAAV1 and 5 serotype vectors, in comparison to rAAV2. These results suggest the unique potential of rAAV1 and rAAV5-based vectors for vascular-targeted gene-based therapeutic strategies.

Efficient restricted gene expression in beta cells by lentivirus-mediated gene transfer into pancreatic stem/progenitor cells

AIMS/HYPOTHESIS

Gene transfer into pancreatic beta cells, which produce and secrete insulin, is a promising strategy to protect such cells against autoimmune destruction and also to generate beta cells in mass, thereby providing a novel therapeutic approach to treat diabetic patients. Until recently, exogenous DNA has been directly transferred into mature beta cells with various levels of success. We investigated whether exogenous DNA could be stably transferred into pancreatic stem/progenitor cells, which would subsequently differentiate into mature beta cells expressing the transgene.

METHODS

We designed transplantation and tissue culture procedures to obtain ex vivo models of pancreatic development. We next constructed recombinant lentiviruses expressing enhanced green fluorescent protein (eGFP) under the control of either the rat insulin promoter or a ubiquitous promoter, and performed viral infection of rat embryonic pancreatic tissue.

RESULTS

Embryonic pancreas infected with recombinant lentiviruses resulted in endocrine cell differentiation and restricted cell type expression of the transgene according to the specificity of the promoter used in the viral construct. We next demonstrated that the efficiency of infection could be further improved upon infection of embryonic pancreatic epithelia, followed by their in vitro culture, using conditions that favour endocrine cell differentiation. Under these conditions, endocrine stem/progenitor cells expressing neurogenin 3 are efficiently transduced by recombinant lentiviral vectors. Moreover, when eGFP was placed under the control of the insulin promoter, 70.4% of the developed beta cells were eGFP-expressing cells. All of the eGFP-positive cells were insulin-producing cells.

CONCLUSIONS/INTERPRETATION

We have demonstrated that mature rat pancreatic beta cells can be stably modified by infecting pancreatic stem/progenitor cells that undergo endocrine differentiation.

Adenovirus-based vascular endothelial growth factor gene delivery to human pancreatic islets

Islet transplantation is limited by islet graft failure due to poor revascularization, host immune rejection and nonspecific inflammatory response. Delivery of human vascular endothelial growth factor (hVEGF) gene to the islets is likely to promote islet revascularization and survival. We used a bicistronic adenoviral vector encoding hVEGF and CpG-free allele of green fluorescent protein (Adv-GFP-hVEGF) and introduced into human pancreatic islets by transfection. We found that transfection efficiency and apoptosis were dependent on the multiplicity of infection (MOI). Compared to Adv-GFP transfected and nontransfected islets, the levels of hVEGF secreted from Adv-GFP-hVEGF transfected islets were higher and exhibit a linear relationship between hVEGF expression and MOI (10-5000). Persistent, but low level expression of hVEGF from nontransfected islets was also observed. This may be due to expression of the endogenous hVEGF gene under hypoxic conditions. The levels of DNA fragmentation determined by ELISA of islet lysates were dependent on the MOI of Adv-GFP-hVEGF. On glucose challenge, insulin release from transfected islets was comparable to nontransfected islets. Immunohistochemical staining for hVEGF was very high in Adv-GFP-hVEGF transfected islets. Weak staining was also observed for hCD31 in both transfected and nontransfected islets. These findings suggest that Adv-GFP-hVEGF is a potential candidate for promoting islet revascularization.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

Gene- and cell-based therapeutics for type I diabetes mellitus

Type 1 diabetes mellitus, an autoimmune disorder is an attractive candidate for gene and cell-based therapy. From the use of gene-engineered immune cells to induce hyporesponsiveness to autoantigens to islet and beta cell surrogate transplants expressing immunoregulatory genes to provide a local pocket of immune privilege, these strategies have demonstrated proof of concept to the point where translational studies can be initiated. Nonetheless, along with the proof of concept, a number of important issues have been raised by the choice of vector and expression system as well as the point of intervention; prophylactic or therapeutic. An assessment of the current state of the science and potential leads to the conclusion that some strategies are ready for safety trials while others require varying degrees of technical and conceptual refinement.

Adeno-associated virus transduction of islets with interleukin-4 results in impaired metabolic function in syngeneic marginal islet mass transplantation

Previous studies suggest that therapeutic expression of interleukin (IL)-4 by islet cells improves their efficacy in transplantation models directed at reversing type 1 diabetes. We investigated the effects of introducing IL-4 into islets with recombinant adeno-associated virus (rAAV) on the reversal of hyperglycemia in a syngeneic marginal islet mass transplantation model. C57BL/6 islets were mock-transduced or transduced with rAAV expressing murine IL-4 (rAAV-IL-4) or rAAV expressing green fluorescent protein (rAAV-GFP) before transplantation of a marginal mass into diabetic mice. Normoglycemia was achieved in only 1/7 mice receiving rAAV-IL-4 transduced islets in comparison to 6/6 mock-transduced and 4/6 rAAV-GFP transduced animals. The failure of IL-4 expressing islets was not associated with cellular toxicity of rAAV or impairment of glucose-stimulated insulin release in vitro. Islet expression of IL-4 led to impaired metabolic function in mice receiving a marginal mass of syngeneic islets.