The treatment of disease by genetic manipulation is emerging as a practical tool in medicine. The goal of this program project is to contribute to the development of gene therapy as a therapeutic modality through the study of model systems. The focus of the project is to use model systems to reveal obstacles and provide solutions to the impediments to gene therapy. Cellular and animal models will be employed to study transfer of potentially therapeutic genes, promote their expression, and measure the effects on a system that is predictive of similar responses in man. While clinical trials are not foreseen as within the scope of the proposal for all four projects the studies proposed in the program are intended to provide substantial information upon which clinical trials will be based. The program seeks through its four interactive projects and four cores to contribute data relevant to the general approach of gene therapy. While diverse in the organ systems studied in the program, the central purpose of the project is single and focused on the methods of gene transfer that may be needed to target and express human genes in different tissues. This goal will be accomplished by a thorough analysis of the vectors developed to transfer a variety of genes and by consideration of the problems of transduction and expression that are peculiar to each model system.