This proposal links a series of innovative AAV gene therapy experiments in two well-established animal models of alpha-mannosidosis with preclinical toxicology studies to develop a path forward to a first-in-human clinical trial of cerebrospinal fluid (CSF)-delivered gene therapy for this illness. The Kaler lab has treated a mouse model of Menkes disease using CSF-directed AAV5 gene therapy via efficient transduction of choroid plexus epithelia. The choroid plexuses (CP) are highly vascularized structures that project into the ventricles of the brain. The polarized epithelia of the CP produce CSF and secrete a large number of proteins. Lysosomal storage diseases (LSDs) could potentially benefit from a CP-targeted approach because AAV transduction results in sustained episomal transgene expression and CP epithelia have a slow rate of turnover. The Wolfe lab has shown that AAV gene transfer into the brains of animal models of LSDs can mediate substantial but incomplete cellular correction and clinical improvement. The advantage of targeting CSF flow is that it extends throughout the ventricular system to the subarachnoid space, from which molecules ultimately reach the entire brain. Intrathecal delivery of purified recombinant lysosomal enzyme (enzyme replacement therapy, ERT) has been successful in ameliorating some brain pathology in animal models and recently in a human clinical trial. However, a major drawback to this approach is the need for repeated intrathecal injections due to short half- lives of recombinant enzymes. An alternative long-term strategy is to remodel CP epithelial cells with an AAV vector to secrete enzyme of interest. CP epithelia have an extremely slow turnover rate, thus this approach could generate a permanent source of enzyme production for secretion into the CSF and penetration to brain structures. Furthermore, intraventricular injection AAV vectors can deliver the normal gene to some of the parenchymal cells, which can then also secrete normal enzyme into extracellular spaces for delivery to other cells. A two-year NIH Bench-to-Bedside Award (R21 equivalent) supported the initial evaluation of this hypothesis in animal models of alpha-mannosidosis (AMD), a prototypical LSD. This U01 proposal expands that effort with the goal of completing the pre-clinical studies needed to submit a phase I clinical trial IND in 3-4 years. We propose to: 1) Evaluate the relative abilities of different AAV-vector serotypes to support CSF- directed AAV transduction in a mouse model of AMD and test the most promising serotypes in the much larger brain of the AMD cat, with the goal of identifying the vector that is most likely to produce the greatest benefit in human clinica trials; 2) Establish clinical and biochemical features in AMD patients for outcome measures in a future clinical trial; and 3) Perform preclinical toxicology studies in non-human primates and develop regulatory approval for a first-in-human gene therapy trial for AMD. The potential impact on clinical practice in the field of LSD is high since, if the proposed aims are successfully achieved, the largest current barriers to health for patients with AMD and other LSDs with brain disease would be circumvented.