DESCRIPTION: The focus of this study is the in vivo delivery of expression plasmids to produce glucocerebrosidase to treat Gaucher disease. Current efforts at gene therapy for hematopoietic disorders such as Gaucher disease have primarily focused on the use of retroviral vectors targeted to hematopoietic stem cells, which would then result in expression in mature monocyte that are produced. This approach has been greatly limited by the inability to transduce a significant fraction of hematopoietic stem cells. Therefore, the approach proposed in this proposal represents a completely different direction which would not have limitation of retroviral vector targeting to stem cells. Systemic delivery of plasmids complexed to cationic lipids may be able to introduce the GC gene into macrophages throughout the RE system and express GC enzyme in a way that it will be properly localized in the cell. The key questions which will need to be addressed are: 1) the percentages of relevant cells that can be transduced, 2) the quantitative level of expression achieved in appropriate target cells, 3) the duration of expression, 4) any toxic effects from introduction of plasmid/lipid complexes into the bloodstream or from ectopic expression of GC, and 5) the ability to repeat the procedure if expression is transient. The study has three specific aims: 1. Maximize the amount and duration of human glucocerebrosidase gene expression in blood monocytes and tissue macrophages of mice after cationic liposome-mediated in vivo gene delivery. 2. Target the delivery and expression of the glucocerebrosidase gene to monocytes and macrophages in animals, using ligand-based and/or promoter-based targeting. 3. Identify and minimize treatment-related systemic toxicity. The overall goal is to develop safe and effective methods for targeted delivery and expression of the human glucocerebrosidase gene in vivo. This is an essential step toward successful gene therapy for Gaucher disease.