1. ¹Department of Neuroscience, Powell Gene Therapy Center, McKnight Brain Institute, University of Florida College of Medicine, Gainesville, Florida, USA
2. ²Department of Molecular Genetics and Microbiology, Powell Gene Therapy Center, McKnight Brain Institute, University of Florida College of Medicine, Gainesville, Florida, USA

Correspondence: Ronald J. Mandel, Department of Neuroscience, Powell Gene Therapy Center, McKnight Brain Institute, University of Florida College of Medicine, 100 South Newell Drive, Building 59, Room L1-100, Gainesville, Florida 32610, USA. E-mail: rmandel@ufl.edu

Received 27 March 2007; Accepted 27 April 2007; Published online 12 June 2007.

Abstract

In vivo recombinant adeno-associated viral vector (rAAV)-mediated transduction of various tissues including brain has been characterized by slow onset and gradual increase in gene expression before reaching stable long-term protein levels. The early time course of transgene expression has not been quantified using newly available rAAV capsid serotypes. In this experiment, the onset of expression of green fluorescent protein (GFP) after intrastriatal injection of rAAV2-based pseudotyped vectors (rAAV1, rAAV5, and rAAV8 capsids) was quantified. Native GFP fluorescence displayed a delayed onset of expression of at least 7 days for all the pseudotyped rAAV vectors. However, GFP immunohistochemical staining revealed significant transgene expression by 4 days after transduction for all serotypes and stable GFP⁺ neuronal populations mediated by all serotypes within 14 days post transduction at the latest. rAAV2/1 and rAAV2/2 displayed no time-dependent increase of GFP⁺ striatal neurons; reaching maximal striatal cell GFP⁺ counts at 4 days after injection. All serotypes displayed peak transgene expression by 4 weeks post injection where native GFP⁺ neurons were equal to immunostained striatal GFP⁺ neurons. The inflammatory response to these rAAV vectors was present up to 4 weeks after transduction but was not apparent 9 months post injection. Thus, rAAV-mediated transgene expression begins earlier than previously thought.