Adeno-associated virus-mediated gene transfer to the brain: Duration and modulation of expression

Adeno-associated virus (AAV) is a promising vector for central nervous syst em (CNS) gene transfer, but a number of issues must be addressed if AAV is to be used for widespread delivery throughout the CNS. Our aim was to test the effect of dose, route of delivery, and hydroxyurea treatment on brain e xpression of beta-galactosidase activity after cerebral inoculation with an rAAV-lacZ vector (rAAV-beta-gal). We also wished to test whether an immune response appeared against the vector and the transgene product. We found i n BALB/c mice that beta-Gal expression increased during the first 2 months after inoculation, then decreased slightly by 4 months, and continued out t o 6, 12, and 15 months in single animals. Cerebral injection produced local ized beta-Gal expression that did not diffuse to other regions despite a fi vefold increase in injection volume. Intraventricular injection resulted in negligible transduction. Antibodies to AAV capsid protein and beta-Gal app eared at low levels at 2 and 4 months, but correlated poorly with beta-Gal expression and did not prevent readministration of rAAV-beta-gal. Hydroxyur ea treatment did not result in increased transduction in vivo. We conclude that our study confirms rAAV vectors as having considerable potential for C NS gene transfer; however, several important problems must be addressed if this vector system is to be used for long-term transduction of the entire b rain. Sustained, regulatable expression will be needed if rAAV is to be use d in the treatment of chronic CNS disease. The difficulty in delivering AAV to diverse regions of the brain is an important problem that must be overc ome if these vectors are to be used for anything beyond localized transduct ion.