Recombinant adeno-associated virus (rAAV) vectors can mediate long-term stable transduction in various target tissues. However, with rAAV serotype 2 (rAAV2) vectors, liver transduction is confined to only a small portion of hepatocytes even after administration of extremely high vector doses. In order to investigate whether rAAV vectors of other serotypes exhibit similar restricted liver transduction, we performed a dose-response study by injecting mice with ␤-galactosidase-expressing rAAV1 and rAAV8 vectors via the portal vein. The rAAV1 vector showed a blunted dose-response similar to that of rAAV2 at high doses, while the rAAV8 vector dose-response remained unchanged at any dose and ultimately could transduce all the hepatocytes at a dose of 7.2 ؋ 10 12 vector genomes/mouse without toxicity. This indicates that all hepatocytes have the ability to process incoming single-stranded vector genomes into duplex DNA. A single tail vein injection of the rAAV8 vector was as efficient as portal vein injection at any dose. In addition, intravascular administration of the rAAV8 vector at a high dose transduced all the skeletal muscles throughout the body, including the diaphragm, the entire cardiac muscle, and substantial numbers of cells in the pancreas, smooth muscles, and brain. Thus, rAAV8 is a robust vector for gene transfer to the liver and provides a promising research tool for delivering genes to various target organs. In addition, the rAAV8 vector may offer a potential therapeutic agent for various diseases affecting nonhepatic tissues, but great caution is required for vector spillover and tight control of tissue-specific gene expression.

Regulation of gene expression is necessary to avoid possible adverse effects of gene therapy due to excess synthesis of transgene products. To reduce transgene expression, we developed a viral vector-mediated somatic regulation system using inducible Cre recombinase. A recombinant adeno-associated virus (AAV) vector expressing Cre recombinase fused to a mutated ligand-binding domain of the estrogen receptor alpha (CreER(T2)) was delivered along with AAV vectors expressing dopamine-synthesizing enzymes to rats of a Parkinson disease model. Treatment with 4-hydroxytamoxifen, a synthetic estrogen receptor modulator, activated Cre recombinase within the transduced neurons and induced selective excision of the tyrosine hydroxylase (TH) coding sequence flanked by loxP sites, leading to a reduction in transgene-mediated dopamine synthesis. Using this strategy, aromatic L-amino acid decarboxylase (AADC) activity was retained so that l-3,4-dihydroxyphenylalanine (L-dopa), a substrate for AADC, could be converted to dopamine in the striatum and the therapeutic effects of L-dopa preserved, even after reduction of TH expression in the case of dopamine overproduction. Our data demonstrate that viral vector-mediated inducible Cre recombinase can serve as an in vivo molecular switch, allowing spatial and temporal control of transgene expression, thereby potentially increasing the safety of gene therapy.

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DescriptionA 56-year-old woman complained of a three-month history of progressive clumsiness in her left hand. She reported fine hand movements to have become slow and uncoordinated, thus leading to moderate difficulty in dressing and working as a beautician. A neurological examination revealed rigidity in her left limb. No obvious tremors were noted. She was treated with ʟ-dopa (300 mg/day), which provided substantial symptomatic benefits. MRI showed the putamen to have a normal morphology and size, and no areas of any altered signals were observed in the brain parenchyma ( Figure 1A). Positron emission tomography (PET) with an aromatic ʟ-amino acid decarboxylase (AADC) tracer, 6-[ 18 F] fluoro-ʟ-m-tyrosine (FMT) showed a reduced uptake in the posterior part of the right putamen ( Figure 1B). In Parkinson's disease (PD), the activity of AADC in the striatum is reduced to 5%-20% of normal levels before cardinal motor symptoms become apparent [1]. High-resolution FMT-PET images can clearly demonstrate a reduction of the subregional AADC activities, and the lowest FMT uptake values tend to be observed in the posterior part of the putamen contralateral to the more affected limbs, even in the early stage of the disease [2]. This case therefore demonstrated the diagnostic value of using FMT-PET in the diagnosis of mild PD, particularly when encountering patients that do not show any remarkable tremors while at rest. Neurological DisordersOno, et al., J Neurol Disord 2014, 2:6 http://dx