Noninvasive gene targeting to the brain

Gene therapy of the brain is hindered by the presence of the blood–brain barrier (BBB), which prevents the brain uptake of bloodborne gene formulations. Exogenous genes have been expressed in the brain after invasive routes of administration, such as craniotomy or intracarotid arterial infusion of noxious agents causing BBB disruption. The present studies describe the expression of an exogenous gene in brain after noninvasive i.v. administration of a 6- to 7-kb expression plasmid encoding either luciferase or β-galactosidase packaged in the interior of neutral pegylated immunoliposomes. The latter are conjugated with the OX26 mAb to the rat transferrin receptor, which enables targeting of the plasmid DNA to the brain via the endogenous BBB transferrin receptor. Unlike cationic liposomes, this neutral liposome formulation is stable in blood and does not result in selective entrapment in the lung. Luciferase gene expression in the brain peaks at 48 h after a single i.v. administration of 10 μg of plasmid DNA per adult rat, a dose that is 30- to 100-fold lower than that used for gene expression in rodents with cationic liposomes. β-Galactosidase histochemistry demonstrated gene expression throughout the central nervous system, including neurons, choroid plexus epithelium, and the brain microvasculature. In conclusion, widespread gene expression in the brain can be achieved by using a formulation that does not employ viruses or cationic liposomes, but instead uses endogenous receptor-mediated transport pathways at the BBB.