The present invention relates to improved compositions and methods for delivering and expressing therapeutic genes in mammals. More particularly, the invention stems from the unexpected discovery that a remarkable, massive and widespread therapeutic gene delivery and expression is obtained in mammals when a therapeutic gene is incorporated in a viral vector and administered both into the CSF and into the blood of the mammal. Such a combined administration leads to a surprising and substantial therapeutic benefit in the mammal as compared to administration in one single site, and further enables the use of reduced doses of the virus. The invention may be used in any mammal, including human subjects, and is particularly suited to treat multi-systemic diseases, such as motor neuron or lysosomal disorders, where widespread expression of a therapeutic gene is desirable.
