Efficient transduction of pancreatic islets by feline immunodeficiency virus vectors1

Highly efficient ex vivo lentiviral transduction of primary human pancreatic exocrine cells

The lack of efficient gene transfer methods into primary human pancreatic exocrine cells hampers studies on the plasticity of these cells and their possible role in beta cell regeneration. Therefore, improved gene transfer protocols are needed. Lentiviral vectors are widely used to drive ectopic gene expression in mammalian cells, including primary human islet cells. Here we aimed to optimize gene transfer into primary human exocrine cells using modified lentiviral vectors or transduction conditions. We evaluated different promoters, viral envelopes, medium composition and transduction adjuvants. Transduction efficiency of a reporter vector was evaluated by fluorescence microscopy and flow cytometry. We show that protamine sulfate-assisted transduction of a VSV-G-pseudotyped vector expressing eGFP under the control of a CMV promoter in a serum-free environment resulted in the best transduction efficiency of exocrine cells, reaching up to 90% of GFP-positive cells 5 days after transduction. Our findings will enable further studies on pancreas (patho)physiology that require gene transfer such as gene overexpression, gene knockdown or lineage tracing studies.

Retrovirally Transferred Genes Inhibit Apoptosis in an Insulin-Secreting Cell Line: Implications for Islet Transplantation

The transplantation of pancreatic islets for the treatment of type I diabetes is hindered by the enormous loss of cells due to early apoptotic events. Genetic engineering of islets with cytoprotective genes is an important strategy aimed to enhance the survival of these cells in the transplant setting. The present study was designed to evaluate and compare the effects of five genes on a cell line derived from insulin-producing β-cells, NIT-1. Cells were transduced using a Maloney murine leukemia virus (MLV) vector coding for yellow fluorescent protein (YFP) and for one of the following antiapoptotic genes: cFLIP, FADD-DN, BcL-2, PI-9, and ICAM-2. These genes were able to protect NIT-1 cells from cytokine-induced apoptosis to varying degrees ranging from no protection to significant protection equivalent to an optimal dose of a chemical caspase inhibitor. The data demonstrate that cFLIP, FADD-DN, and PI-9 are significantly more effective in protecting NIT-1 cells than BcL-2 and ICAM-2. Additionally, the data show that despite its weak in vitro inhibition of caspase-3, PI-9 affords significant protection against TNF-α-induced apoptosis in these cells. These genes may be ideal candidates to augment islet survival following transplantation.

Feline immunodeficiency virus-based lentiviral vectors

Feline immunodeficiency virus (FIV)-based lentiviral vectors are useful for introducing integrated transgenes into nondividing human cells. This article describes the production and use of advanced generation FIV vectors. Key properties are discussed in comparison to other lentiviral vectors. Additional topics include the practical implications of species-specific retroviral restriction factors and the production of nonintegrating FIV vectors.

Overexpression of thioredoxin in islets transduced by a lentiviral vector prolongs graft survival in autoimmune diabetic NOD mice

Abstract

Pancreatic islet transplantation is considered an appropriate treatment to achieve insulin independence in type I diabetic patients. However, islet isolation and transplantation-induced oxidative stress and autoimmune-mediated destruction are still the major obstacles to the long-term survival of graft islets in this potential therapy. To protect islet grafts from inflammatory damage and prolong their survival, we transduced islets with an antioxidative gene thioredoxin (TRX) using a lentiviral vector before transplantation. We hypothesized that the overexpression of TRX in islets would prolong islet graft survival when transplanted into diabetic non-obese diabetic (NOD) mice.

Methods

Islets were isolated from NOD mice and transduced with lentivirus carrying TRX (Lt-TRX) or enhanced green fluorescence protein (Lt-eGFP), respectively. Transduced islets were transplanted under the left kidney capsule of female diabetic NOD mice, and blood glucose concentration was monitored daily after transplantation. The histology of the islet graft was assessed at the end of the study. The protective effect of TRX on islets was investigated.

Results

The lentiviral vector effectively transduced islets without altering the glucose-stimulating insulin-secretory function of islets. Overexpression of TRX in islets reduced hydrogen peroxide-induced cytotoxicity in vitro. After transplantation into diabetic NOD mice, euglycemia was maintained for significantly longer in Lt-TRX-transduced islets than in Lt-eGFP-transduced islets; the mean graft survival was 18 vs. 6.5 days (n = 9 and 10, respectively, p < 0.05).

Conclusion

We successfully transduced the TRX gene into islets and demonstrated that these genetically modified grafts are resistant to inflammatory insult and survived longer in diabetic recipients. Our results further support the concept that the reactive oxygen species (ROS) scavenger and antiapoptotic functions of TRX are critical to islet survival after transplantation.

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.

Human gene therapy vectors derived from feline lentiviruses

Lentiviral vectors are useful for gene transfer to dividing and nondividing cells. Feline immunodeficiency virus (FIV) vectors transduce most human cell types with good efficiency and may have advantages for clinical gene therapy applications. This article reviews significant progress in the development and refinement of FIV vector systems.

The status of gene vectors for the treatment of diabetes

Diabetes mellitus type 1 (DM1) represents one of the most obvious targets for successful treatment by gene transfer. The disease provides targets and methods for therapy that include suppression of autoimmunity, restoration of insulin responsiveness, functional replacement of pancreatic islets, and correction of vascular and nerve damage associated with prolonged hyperglycemia. The pathogenesis of DM1 is well understood and gene sequences are known that would support these various approaches for genetic intervention. However, a key limitation at present is the availability of efficient and reliable methods for delivery and sustained expression of the transferred DNA. Most genetic vectors are derived from viruses, and recent improvements in adenovirus-derived, lentivirus-derived, and adeno-associated virus-derived vectors suggest that these will have successful application to diabetes in the future.

Overcoming the Challenges Now Limiting Islet Transplantation: A Sequential, Integrated Approach

Steady improvements in islet cell processing technology and immunosuppressive protocols have made pancreatic islet transplantation a clinical reality for the treatment of patients with Type 1 diabetes mellitus (T1DM). Recent trials are showing that improved glycemic metabolic control, prevention of severe hypoglycemia, and better quality of life can be reproducibly achieved after transplantation of allogeneic islets in patients with unstable T1DM. Despite these encouraging results, challenges ahead comprise obtaining adequate islet cells for transplant, enhancing islets engraftment, sustaining beta cell mass and function over time, and defining effective immune interventions, among others. In order to overcome the current hurdles to the widespread application of islet transplantation there is a need for implementation of integrated, sequential therapeutic approaches.

Long-term gene expression and metabolic control exerted by lentivirus-transduced pancreatic islets

BACKGROUND

Genetic modification of non-human islets before transplantation may provide means by which they can escape immunity and, thus, be used in a human host. To accomplish this, efficient gene transfer methods are needed. Lentiviral vectors are transgene vehicles capable of stably transducing a variety of primary, post-mitotic cells including islets.

METHODS

We investigated whether lentiviral transduction impaired rat pancreatic islet function long term. Following transduction, the gross morphology, viability and in vitro functionality of islets were evaluated by microscopy, adenylate nucleotide and insulin secretion assays, respectively. Further, in vivo functionality of transduced islets was assessed by transplanting the islets under the kidney capsule of diabetic nude mice.

RESULTS

All transduced islets contained green fluorescent protein (GFP)-positive cells. In single cell suspensions prepared from transduced islets, 33+/-8% (n = 3) of dispersed islet cells were GFP-positive. The ADP/ATP ratio was 0.07+/-0.01 for transduced islets and 0.06+/-0.01 for controls (normal range <0.11). No morphological changes were observed in transduced islets. Further, basal insulin secretion was comparable between the two islet groups. When transduced and non-transduced islets were challenged with insulin secretagogues, they showed similar increases in insulin release. Transduced and non-transduced islets were equally effective in normalizing blood glucose when transplanted into diabetic nude mice. Euglycemia was maintained for 8 weeks until the graft-bearing kidney was removed. Intense green fluorescence was seen in removed islet grafts. Histology revealed preserved islet morphology, with abundant insulin-producing cells, few apoptotic cells and infiltrating leukocytes in both transduced and non-transduced grafts.

CONCLUSIONS

Lentivirus transduction does not affect islet morphology or function. Lentiviral vectors will allow genetic modifications to be performed in islets before transplantation--modifications that can improve engraftment and/or prevent xenograft rejection.

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.

Gene therapy progress and prospects: novel gene therapy approaches for AIDS

Acquired immunodeficiency syndrome (AIDS), caused by human immunodeficiency virus (HIV), kills millions worldwide every year. Vaccines against HIV still seem a distant promise. Pharmaceutical treatments exist, but these are not always effective, and there is increasing prevalence of viral strains with multidrug resistance. Highly active antiretroviral therapy (HAART) consists of inhibitors of viral enzymes (reverse transcriptase (RT) and protease). Gene therapy, first introduced as intracellular immunization, may offer hopes for new treatments to be used alone, or in conjunction with, conventional small molecule drugs. Gene therapy approaches against HIV-1, including suicide genes, RNA-based technology, dominant negative viral proteins, intracellular antibodies, intrakines, and peptides, are the subject of this review.

Pharmacologically Regulated Regeneration of Functional Human Pancreatic Islets

Transplantation of allogeneic islets can correct the metabolic abnormalities of Type I diabetes. Limited availability of donor pancreas tissues restricts the application of this therapeutic modality to a subset of eligible recipients. In an attempt to expand the utility of available donor human pancreas tissue, we developed a method to stimulate the proliferation of insulin-secreting beta-cells within human islets. A lentiviral vector was used to introduce into human islets chimeric signaling receptors that are activated to stimulate cell proliferation through interactions with a small-molecule drug called a chemical inducer of dimerization (CID). In vitro exposure of vector-transduced human islets to the CID expanded the number of cells and increased regulated insulin secretion. Transplantation of the regenerated islets into diabetic immunodeficient mice, followed by in vivo administration of the CID, corrected hyperglycemia. This strategy has the potential to reduce the quantity of human islets required for treatment of patients with Type I diabetes.

Transduction of Human Islets with Pseudotyped Lentiviral Vectors

Type I diabetes is caused by an autoimmune-mediated elimination of insulin-secreting pancreatic islets. Genetic modification of islets offers a powerful molecular tool for improving our understanding of islet biology. Moreover, efficient genetic engineering of islets could allow for evaluation of new strategies aimed at preventing islet destruction. The present study evaluated the ability of a human immunodeficiency virus (HIV)-based lentiviral vector pseudotyped with various viral envelopes to target human islets ex vivo, with the goal of improving efficiency while minimizing toxicity. Transfer of the enhanced green fluorescent protein reporter gene in human islets was first evaluated with an HIV-based vector pseudotyped with the vesicular stomatitis virus (VSV), murine leukemia virus, Ebola, rabies, Mokola, or lymphocytic choriomeningitis virus (LCMV) envelope glycoprotein to optimize transduction efficiency. Results indicated that LCMV-pseudotyped vector transduced insulin-secreting beta cells with the highest efficiency. Moreover, toxicity associated with transduction of islets was found to be lower with LCMV-pseudotyped vector than with VSV-G-pseudotyped vector, the second most efficient vector for islet transduction. Overall, our study describes an improved methodology for achieving safe and efficient gene transfer into cells of human islets.

Optimal modes and targets of gene therapy in transplantation

Genetic modification strategies have the potential to improve outcome following cell/organ transplantation. A unique opportunity in transplantation is that gene therapies need not be restricted to in vivo approaches and that ex vivo genetic modification of cell and/or organs can be of value. Improvements in vector design, production, and delivery should enhance transfection efficiency and optimize gene expression. Herein, we discuss potential modes of gene therapy, focusing on viral, liposome, or naked DNA-based systems for gene delivery. We suggest gene therapy targets taking into consideration the essential constituents of anti-allograft repertory. In addition to strategies that may have salutary effects in mitigating the threat of acute rejection, we suggest genetic strategies for minimizing ischemia/reperfusion injury as well as for the perennial problem of progressive functional loss of the transplanted organ. Data from pre-clinical transplant models support the idea that gene therapy may improve allograft function and survival. We are optimistic that gene therapy will be of clinical value in the near future in the management of recipients of allografts; we believe that genetic strategies would be essential for successful breaching of the formidable challenge of xenotransplantation.

Systemic FIV vector administration: transduction of CNS immune cells and Purkinje neurons

The systemic effects of gene therapy have been previously described in a variety of peripheral organs following intravenous administration or intraperitoneal inoculation of viral vectors, as well as in the brain following intracranial administration. However, limited information is available on the ability of viral vectors to cross the blood-brain barrier and infect cells located within the central nervous system (CNS). We employed a VSV-G pseudotyped FIV(lacZ) vector capable of transducing dividing, growth-arrested, as well as post-mitotic cells with the reporter gene lacZ. Adult mice were injected intraperitoneally with FIV(lacZ), and the expression of beta-galactosidase was studied 5 weeks following treatment in the brain, liver, spleen and kidney by X-gal histochemistry and immunocytochemistry. Interestingly, relatively low doses of FIV(lacZ) administered intraperitoneally lead to beta-galactosidase detection in the brain and cerebellum. The identity of these cells was confirmed by double immunofluorescence, and included CD31-, CD3- and CD11b-positive cells. Fluorescent microspheres co-injected with FIV(lacZ) virus were identified within mononuclear cells in the brain parenchyma, suggesting infiltration of peripheral immune cells in the CNS. Cerebellar Purkinje neurons were also transduced in all adult-injected mice. Our observations indicate that relatively low doses of FIV(lacZ) administered intraperitoneally resulted in the transduction of immune cells in the brain, as well as a specific subset of cerebellar neurons.

Double genetic modification of adenovirus fiber with RGD polylysine motifs significantly enhances gene transfer to isolated human pancreatic islets

BACKGROUND

New strategies for improving durable functional islet mass will be instrumental in facilitating islet transplantation as a cure for type 1 diabetes mellitus. The ability to transfer immunoregulatory or cytoprotective genes into pancreatic islets may enhance survival. Adenoviral vectors (Ad5) have been used widely to deliver therapeutic genes to different tissues. Limitations associated with the use of Ad5 for gene therapy are related to the reliance of the virus on the presence of its primary receptor, the transient nature of the transgene expression, and the immediate inflammatory and immune response elicited by the infection. Because the arginine-glycine-aspartame (RGD) and polylysine (pK7) motifs have been shown to enhance Ad5 infection through an Ad5 receptor-independent pathway, we hypothesized that they could act additively to improve infectivity and reduce toxicity to isolated human pancreatic islets (IHPI).

METHODS

Hand-picked IHPI were infected with nonmodified Ad5, single-modified Ad5 with RGD (Ad5RGD) or pK7 (ad5pK7), and Ad5RGDpK7. Transfection efficiency was evaluated by green fluorescent protein and luciferase expression. Apoptosis was assessed using a quantitative assay, activation of caspase 3 by a colorimetric assay, nuclear factor (NF)-kappaB nuclear translocation using a promoter-luciferase NF-kappaB responsive construct, regulated on activation normal T-cell expressed and secreted (RANTES) by enzyme-linked immunosorbent assay. In vivo functionality was evaluated after transplantation into diabetic nonobese diabetic severe combined immunodeficiency mice.

RESULTS

Compared with unmodified and singly-modified Ad5 vectors, Ad5RGDpK7 demonstrated the highest infectivity. After the infection of IHPI with adenoviral vectors using the minimal dose required to infect greater than 80% of the islet cells (Ad5, 500 viral particles [VP]/cell; Ad5RGD and Ad5pK7, 10 VP/cell; Ad5RGDpK7, 0.1 VP/cell), islets infected with Ad5RGDpK7 presented a significant reduction in apoptosis, NF-kappaB nuclear translocation, RANTES expression, and higher glucose disposal rate; reduced Ad5-driven specific Th1 and antibody response were also observed.

CONCLUSIONS

Ad5RGDpK7 exhibited higher transfection efficiency, allowing a significant reduction in the viral dose required to infect greater than 80% of the islet cells. The reduction in the viral dose was associated with reduced toxicity, inflammation, and immune responses related to Ad5 infection. This strategy may thus be used to successfully modify isolated pancreatic islets.

Lentivirus-mediated transduction of connexin cDNAs shows level- and isoform-specific alterations in insulin secretion of primary pancreatic beta-cells

We have generated novel lentiviral vectors to integrate various connexin cDNAs into primary, non-dividing cells. We have used these vectors to test whether proper control of insulin secretion depends on a specific connexin isoform and/or on its level of expression. We have observed that transduced connexin32, connexin36 and connexin43 were expressed by primary adult beta-cells at membrane interfaces, were packed into typical gap junction plaques and formed functional channels that allowed a variable coupling, depending on the type and level of connexin expressed. The infected cells spontaneously reaggregated into three-dimensional pseudo-islet organs that could be maintained in culture. We have found that pseudo-islets made by cells transduced with either GFP- or connexin43-expressing lentivirus released insulin in response to various secretagogues similarly to controls. By contrast, pseudo-islets made by cells expressing connexin32, a connexin exogenous to pancreatic islets, or over-expressing connexin36, the endogenous islet connexin, featured a marked decrease in the secretory response to glucose. The data show: (1) that lentiviral vectors allow stable modulation of various connexin in primary, non-proliferating cells; (2) that specific connexin isoforms affect insulin secretion differently; and (3) that adequate levels of coupling via connexin36 channels are required for proper beta-cell function.

Cationic lipid and polymer-based gene delivery to human pancreatic islets

Transplantation of pancreatic islets has great potential for treating Type I diabetes. Ex vivo gene therapy may promote re-vascularization or inhibit apoptosis of the islets and promote graft. In this study, we investigated the feasibility of non-viral gene delivery using Enhanced Green Fluorescent Protein (EGFP) and human Vascular Endothelial Growth Factor (hVEGF(165)) expression plasmids as model reporter and therapeutic genes. LipofectAMINE/pDNA and Superfect/pDNA complexes showed high transfection efficiency in rapidly dividing Jurkat cells, but low transfection in non-dividing human islets. LipofectAMINE/pCAGGS-hVEGF transfected islets showed relatively higher levels of hVEGF than in those transfected with LipofectAMINE/pCMS-EGFP complexes or 5% glucose. To exclude endogenously secreted hVEGF, real time RT-PCR experiment was repeated using pCAGGS vector-specific forward primer and hVEGF gene-specific reverse primer. In this case, both non-transfected islets and the islets transfected with LipofectAMINE/pCMS-EGFP complexes showed negligible amplification of hVEGF. On glucose challenge, insulin release from LipofectAMINE/pCAGGS-hVEGF transfected human islets increased from 10.78 +/- 4.56 to 65 +/- 5 ng/ml, suggesting little adverse effect on islet beta cell response to glucose challenge. The low transfection efficiency is due to the islets being a cluster of approximately 1000 non-dividing cells. This underscores the importance of experimentation with the actual human islets.