Combined injection of rAAV with mannitol enhances gene expression in the rat brain

Recombinant adeno-associated viruses (rAAV) are highly efficient vectors fo r gene transfer into the central nervous system (CNS). However, a major hur dle for gene delivery to the mammalian brain is to achieve high-level trans duction in target cells beyond the immediate injection site. Therefore, in addition to improvements in expression cassettes and viral titers, optimal injection parameters need to be defined. Here, we show that previous studie s of somatic cell gene transfer to the mammalian brain have used suboptimal injection parameters, with even the lowest reported perfusion rates still excessively fast. Moreover, we evaluated the effect of local administration of mannitol to further enhance transgene expression and vector spread. Ult raslow microperfusion of rAAV, i.e., <33 nl/min, resulted in significantly higher gene expression and less injury of surrounding tissue than the previ ously reported rates of 100 nl/min or faster. Co-infusion of mannitol facil itated gene transfer to neurons, increasing both the total number and the d istribution of transduced cells by 200-300%. Gene transfer studies in the C NS using rAAV should use very slow infusion rates and combined injection wi th mannitol to maximize transduction efficiency and spread.