1. ¹Department of Neuroscience, University of Florida College of Medicine, Gainesville, Florida, USA
2. ²Powell Gene Therapy Center, McKnight Brain Institute, University of Florida College of Medicine, Gainesville, Florida, USA
3. ³Department of Neurosurgery, University of Florida College of Medicine, Gainesville, Florida, USA
4. ⁴Department of Neurology, University of Wisconsin–Madison, Clinical Science Center, Madison, Wisconsin, USA
5. ⁵Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, Florida, USA

Correspondence: Ronald J. Mandel, Department of Neuroscience, University of Florida College of Medicine, PO Box 100244, Gainesville, Florida 326210-0244, USA. E-mail: rmandel@ufl.edu

Received 22 September 2008; Accepted 25 November 2008; Published online 13 January 2009.

Abstract

Recombinant adeno-associated virus (rAAV) expresses no viral genes after transduction. In addition, because the brain is relatively immunoprivileged, intracranial rAAV transduction may be immunologically benign due to a lack of antigen presentation. However, preexposure to AAV allows neutralizing antibodies (nAbs) to block brain transduction and rAAV readministration in the brain leads to an inflammatory response in the second-injection site. In this study, we replicate our striatal rAAV2/2-GDNF readministration results and extend this effect to a second transgene, green fluorescent protein (GFP). Unlike rAAV2/2-GDNF readministration, striatal rAAV2/2-GFP readministration leads to a loss of transgene in the second site in the absence of detectable circulating nAbs. In order to determine whether the transgene or the AAV2 capsid is the antigenic stimulus in brain for the immune response in the second site, we readministered rAAV2/2-GFP using two different rAAV serotypes (rAAV2/2 followed by rAAV2/5). In this case, there was no striatal inflammation or transgene loss detected in the second-injection site. In addition, striatal readministration of rAAV2/5-GFP also resulted in no detectable immune response. Furthermore, delaying rAAV2/2 striatal readministration to a 11-week interval abrogated the immune response in the second-injection site. Finally, while striatal readministration of rAAV2/2 leads to significant loss of transgene in the second-injection site, this effect is not due to loss of vector genomes as determined by quantitative real-time PCR. We conclude that intracellular processing of AAV capsids after transduction is the immunogenic antigen and capsid serotypes that are processed more quickly than rAAV2/2 are less immunogenic.