Constitutive and regulated expression of processed insulin following in vivo hepatic gene transfer

NeuroD-betacellulin gene therapy induces islet neogenesis in the liver and reverses diabetes in mice

To explore induced islet neogenesis in the liver as a strategy for the treatment of diabetes, we used helper-dependent adenovirus (HDAD) to deliver the pancreatic duodenal homeobox-1 gene (Ipf1; also known as Pdx-1) to streptozotocin (STZ)-treated diabetic mice. HDAD is relatively nontoxic as it is devoid of genes encoding viral protein. Mice treated with HDAD-Ipf1 developed fulminant hepatitis, however, because of the exocrine-differentiating activity of Ipf1. The diabetes of STZ mice was partially reversed by HDAD-mediated transfer of NeuroD (Neurod), a factor downstream of Ipf1, and completely reversed by a combination of Neurod and betacellulin (Btc), without producing hepatitis. Treated mice were healthy and normoglycemic for the duration of the experiment (>120 d). We detected in the liver insulin and other islet-specific transcripts, including proinsulin-processing enzymes, beta-cell-specific glucokinase and sulfonylurea receptor. Immunocytochemistry detected the presence of insulin, glucagon, pancreatic polypeptide and somatostatin-producing cells organized into islet clusters; immuno-electron microscopy showed typical insulin-containing granules. Our data suggest that Neurod-Btc gene therapy is a promising regimen to induce islet neogenesis for the treatment of insulin-dependent diabetes.

Vectors for the treatment of autoimmune disease

Gene therapy has been applied in a variety of experimental models of autoimmunity with some success. In this article, we outline recent developments in gene therapy vectors, discuss advantages and disadvantages of each, and highlight their recent applications in autoimmune models. We also consider progress in vector targeting and components for regulating transgene expression, which will both improve gene therapy safety and empower gene therapy to fullfil its potential as a therapeutic modality. In conclusion, we consider candidate vectors that satisfy requirements for application in the principal therapeutic strategies in which gene therapy will be applied to autoimmune conditions.

Dimerizer-regulated gene expression

Control of gene expression using small molecules is a powerful research tool and has clinical utility in the context of regulated gene therapy. Use of chemical inducers of dimerization, or dimerizers, for this purpose has several advantages, including tight regulation, modularity to facilitate iterative improvements, and assembly from human proteins to minimize immune responses in clinical applications. Recent developments include the use of the rapamycin-based dimerizer system to regulate the expression of endogenous genes, the generation of new chemical dimerizers based on FK506, dexamethasone and methotrexate, and progress towards the clinical use of adeno-associated virus and adenovirus vectors regulated by rapamycin analogs.

Pharmacological regulation of protein expression from adeno-associated viral vectors in the eye

The control, over time and space, of the levels of therapeutic proteins is crucial for successful retinal gene therapy. We tested the ability of adeno-associated viral vectors (AAV) delivered intraocularly to release a secreted protein (erythropoietin (Epo) used as a marker) in the eye, either constitutively or in a pharmacologically regulated manner using the dimerizer-inducible transcriptional regulatory system. Following delivery of a constitutively expressing vector to the intravitreal or subretinal space of nude rats, Epo protein was detected in both the anterior chamber and vitreous fluids. A dual-vector system inducible by the dimerizer rapamycin and expressing Epo was administered into the subretinal space in an attempt to achieve pharmacologic control of trangene expression in the eye. Before induction with rapamycin, the intraocular Epo level was negligible. However, following a systemic administration of rapamycin, Epo was detected in the anterior chamber, peaking on day 3 and returning to baseline 2-3 weeks after withdrawal of the drug. Peak-induced Epo in the anterior chamber was proportional to the dose of rapamycin and was not detected in serum. Similar results were obtained following subretinal administration of the vectors in one nonhuman primate. The rapamycin inducible system promises to be useful for developing gene therapies for inherited retinal degeneration and ocular neovascularization.