Gene and Cell Therapy for Multigenic Human Diseases

Diabetes mellitus is simply characterized by abnormally high blood glucose levels (hyperglycemia) in patients. There are two most common forms of diabetes in which diminished production of insulin is observed in Type 1 while Type 2 displays impaired insulin response as a result of beta cell dysfunction.

Nonetheless, both lead to hyperglycemia, excessive urine production, compensatory thirst, increased fluid intake, blurred vision, unexplained weight loss, lethargy, and changes in energy metabolism. Increased hepatic glucose production, diminished insulin secretion, and impaired insulin action are the hallmarks of Type 2 Diabetes.

Gene Altered Islets in Transplantation:

Diabetes is the third most common disease and the fourth leading cause of death in North America. At present, the main treatment modality for patients with type 1 diabetes (T1D) is insulin injection.Islet Transplantation

Although this approach protects patients from nephropathy, neuropathy, and retinopathy, it does ot prevent the recurrence of hypoglycemic events, seizures, and coma. Furthermore, insulin administration cannot completely compensate for the physiologic loss of insulin secretion.

The best option for a cure from this chronic disease is pancreas transplantation, which can dramatically prolong and improve quality of life; however, this means of treatment remains controversial because of the less favorable outcome due to major surgery and need for long-term immunosuppression. As an alternative, pancreatic islet transplantation may be a better therapeutic option because it avoids the complications associated with whole- organ transplant surgery or the need for lifelong enzyme injections.

Even though intrahepatic islet transplantation has been a promising approach for the treatment of patients with T1D, the success of this approach is limited by the high frequency of nonfunctioning grafts and secondary graft failure leading to the majority of patients needing to resume the administration of insulin within 5 years. Thus, the use of gene-altered islets has been suggested as a viable option to increase the success rate in islet transplantation.

BACKGROUND: To increase the success rate in xenogeneic islet transplantation, proper assessment of graft mass is required following transplantation. For this reason, we aimed to develop a suitable fluorescence imaging system to monitor islet xenograft survival in diabetic mice.

METHODS: Adenovirus vector encoding enhanced green fluorescent protein-transduced rat pancreatic islets were transplanted under the renal capsule of streptozotocin-induced diabetic mice and the fluorescence signal was quantified over time using a cooled charge-coupled device. Non-fasting blood glucose levels were recorded during the same period. Insulin release from transduced and control islets was detected via enzyme-linked immunosorbent assay.

RESULTS: Adenovirus vector encoding enhanced green fluorescent protein infection did not alter the function or survival of pancreatic islets post transduction. A direct correlation was found between the number of islets (250-750) transplanted under the kidney capsule and the blood glucose recovery.

CONCLUSIONS: Fluorescence imaging appears to be a useful tool for quantitative assessment of islet cell viability post transplantation and could permit earlier detection of graft rejection.

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Type 1 diabetes (T1D), characterized by permanent destruction of insulin-producing beta cells, is lethal unless conventional exogenous insulin therapy or whole-organ transplantation is employed. Although pancreatic islet transplantation is a safer and less invasive method compared with whole-organ transplant surgery, its treatment efficacy has been limited by islet graft malfunction and graft failure. Thus, ex vivo genetic engineering of beta cells is necessary to prolong islet graft survival.

For this reason, a novel gene therapy approach involving adenovirus-mediated TRAIL gene delivery into pancreatic islets was tested to determine whether this approach would defy autoreactive T cell assault in streptozotocin (STZ)-induced diabetic rats. To test this, genetically modified rat pancreatic islets were transplanted under the kidney capsule of STZ-induced diabetic rats, and diabetic status (blood sugar and body weight) was monitored after islet transplantation.

STZ-induced diabetic rats carrying Ad5hTRAIL-infected islets experienced prolonged normoglycemia compared with animals grafted with mock-infected or AdCMVLacZ-infected islets. In addition, severe insulitis was detected in animals trans- planted with mock-infected or AdCMVLacZ-infected islets, whereas the severity of insulitis was reduced in animals engrafted with Ad5hTRAIL-infected islets.

Thus, TRAIL overexpression in pancreatic islets extends allograft survival and function, leading to a therapeutic benefit in STZ-induced diabetic rats.

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Objectives: Type 1 diabetes (T1D) has been characterized by the T cell-mediated destruction of pancreatic beta cells. Although various members of the tumor necrosis factor (TNF) family, such as Fas ligand or TNF, have recently been implicated in the development of T1D, the lack of TNF-related apoptosis-inducing ligand (TRAIL) expression or function facilitates the onset of T1D. Thus, the goal of the present study was to investigate the expression profiles of TRAIL and its receptors in human pancreas.

Methods: Pancreata of 31 patients were analyzed by immunohistochemistry using antibodies developed against TRAIL and its receptors. Apoptosis was confirmed by Annexin V fluorescein isothiocyanate binding and terminal deoxynucleotidyl transferase mediated 2'-deoxyuridine 5'-triphosphate nick end labeling assays.

Results: Acinar cells displayed high levels of TRAIL and death receptor 4, but only low levels of death receptor 5. In contrast, only TRAIL and TRAIL decoy receptors (DcR1, DcR2) were detected in ductal cells. Similarly, Langerhans islets expressed only TRAIL and TRAIL decoy receptor. High levels of TRAIL expression in pancreas correlated with increased number of apoptotic cells.

Conclusions: Although the expression of TRAIL decoy receptors might be necessary for defense from TRAIL-induced apoptosis, high levels of TRAIL may provide protection for Langerhans islets from the immunological attack of cytotoxic T cells.

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Novel Gene Therapy Approaches for Patients with Type 2 Diabetes

Type 2 diabetes (T2D) is characterized by chronic insulin resistance and a progressive decline in beta cell function. Although rigorous glucose control can reduce morbidity and mortality associated with diabetes, it is very difficult if not impossible to achieve optimal, long-term glycemic control in many treated patients. Since beta cell mass and function inevitably decline in T2D, the failure of therapy is not uncommon due to the progressive nature of the disease.

GLP-1Despite the use of oral anti-hyperglycemic agents and intensification of oral regimens, exogenous insulin administration is almost unavoidable as a final outcome.

Increased apoptosis but not the defect in new islet formation or beta cell replication is blamed for the decrease in beta cell mass observed in T2D patients.

Thus therapeutic approaches designed to protect islet cells from apoptosis could be a significant value in the management of T2D because of its potential to reverse not just palliate glycemia.

The ideal beta cell preserving agent is expected to decrease beta cell apoptosis, increase beta cell replication and islet neogenesis.

Accordingly incretin-based therapies (Glucagon-like peptide-1 (GLP-1) agonists, exenatide) with the potential to overcome the limitations of traditional treatments, which are typically associated with weight gain and increased hypoglycemia are a relatively new option for the treatment of patients with T2D. Major beneficial effects of exenatide are attributed to potentiating glucose-stimulated insulin secretion, suppression of glucagon secretion and slowing of gastric emptying.

Despite these advantages, clinical use of exenatide has been associated with increased risk for pancreatitis and high frequency of gastrointestinal disturbances, with 30-45% of treated patients experiencing one or more episodes of nausea, vomiting, or diarrhea. One of the relevant scientific projects conducted in the Center is given below as an example. For more information about the projects conducted in the Center please Click to get more info.

Vasoactive Intestinal Peptide as a Therapeutic Agent

Rationale

Apart from GLP-1, an islet endocrine neuro-peptide known as vasoactive intestinal peptide (VIP) robustly stimulates post-prandial insulin secretion. Because of its broad spectrum of biologic functions such as acting as a potent anti-inflammatory factor, inhibiting Th1 responses, and promoting immune tolerance by inducing Treg cells, VIP has emerged as a promising tool for the treatment of autoimmune/inflammatory diseases.

Despite these advantages, there are several obstacles to translating VIP-based treatment into viable clinical therapies. VIP is very unstable and extremely sensitive to the peptidases present in most tissues. This necessitates multiple injections of high doses of the peptide to achieve a sustained therapeutic effect. However, gene based therapeutic strategies enable continuous and/or regulated synthesis of therapeutic molecules inside the target tissues for prolonged period of time.

Hence, a novel gene therapy strategy is designed to express human VIP specifically in pancreatic islet cells driven by human insulin promoter to test whether such an approach would be beneficial in the setting of T2D.

Gene Delivery Vehicle

Lentiviral vectors were chosen for gene delivery since it has been described as the most powerful of all integrative vector systems and is one of the most efficient vectors for in vivo application.

Knowing that the latest generation of lentiviral vectors is one of the safest and most efficient tools for stable gene transfer, this vector system will be directly applicable for clinical testing if successful results are obtained in the experimental animal models of T2D.

Animal Model

Fat fed/STZ diabetic rodents, developed by combination of diet-induced insulin resistance and relatively low-dose streptozotocin (STZ) provide a novel animal model for diet induced type 2 diabetes. In these animals, insulin resistance is generated by feeding diets enriched in fat. Subsequently, hyperglycemia is induced by injection with a low dose of STZ.

Thus, these fat-fed/STZ-treated rats simulate natural disease progression and metabolic characteristics typical of individuals at increased risk of developing T2D because of insulin resistance and obesity. High fat diet/low dose STZ induced animal model will be instrumental in testing the therapeutic efficacy of islet specific gene expression of VIP on beta cell failure and islet cell loss.

Conclusions:

T2D evolved from a disease with no effective pharmacological treatment in the previous century to a disease with a variety of options available for its management in the 21st century. Despite this progress, we are still faced with the new challenge of a diabetes pandemic of gigantic scale. Hence, identification of novel therapeutic interventions such as gene therapy to prevent progressive beta-cell failure is of paramount importance.

Type 1 Diabetes

Type 1 Diabetes

When a person's own immune system gradually attacks and destroys the cells in the pancreas that produce insulin that's when Type 1 Diabetes occurs.

Insulin production drops down gradually, it eventually comes to a stop completely. This is why patients requires daily insulin injections.

Type 1 Genetics

Genetics of T1D

Type 1 diabetes is caused by a combination of genetic and non-genetic (or environmental) risk factors.

It is estimated that about 88% of the risk of type 1 diabetes is based on genetic risk factors while non-genetic factors (such as virus exposure) account for 12%.

Type 2 Diabetes

Type 2 Diabetes

T2DM is a complex heterogeneous group of metabolic disorders including hyperglycemia and impaired insulin action and/or insulin secretion.

Pathogenesis of T2DM includes a defect in insulin-mediated glucose uptake in muscle, a dysfunction of the pancreatic beta-cells, a disruption of secretory function of adipocytes, and an impaired insulin action in liver.