With the isolation of the gene responsible for cystic fibrosis and the characterization of its protein product (the cystic fibrosis transmembrane conductance regulator - CFTR), attention has focused on possible therapeutic strategies using somatic gene transfer. Although in vitro complementation experiments and studies in rodents have supported the feasibility of this approach, the development of a human model will be important for a number of reasons. First, the ability to transfect or infect human cells with specific vectors is clearly different from other species. Second, toxicity and other possible deleterious effects would best be analyzed in a human rather than rodent model. Third, the anatomy of non-human airway differs from that of human tissue. Specifically rodent airway lacks well-developed submucosal glands, and it would therefore be useful to have a model of intact human bronchus. We have begun the development of such a model by transplanting pieces of human bronchus subcutaneously into severe combined immunodeficiency mice where they maintain a normal human phenotype. We hypothesize that this model will be useful to study the biology of gene transfer into the human airway, and in particular to study the importance of submucosal gland function in cystic fibrosis. The specific aims of this pilot proposal are: 1) To more fully develop and characterize a model of human bronchus transplanted into severe combined immunodeficiency (SCID) mice. This will be accomplished by transplantation of tissue and subsequent timed analysis of the histologic appearance, proliferative characteristics, and expression of differentiation markers (i.e.keratin subtypes) using immunohistochemical techniques. 2) To use this model to evaluate gene transfer techniques Into the human airway Techniques will be developed to optimize the delivery of viral vectors into the transplanted bronchus. Subsequently, studies will analyze the efficiency of expression and the exact anatomic localization of marker genes and CFTR using adenovirus and retroviral vectors. Completion of the experiments proposed in this sect should provide valuable and practical information in the treatment of CF using gene therapy. Specifically, this model will aid in the planning of strategies that optimize delivery of current vectors, as well as providing a system to test new vector or vector delivery systems (i.e. liposome-coated plasmids) as they are developed. One interesting future direction would be transplantation and transfection of bronchi obtained from cystic fibrosis patients undergoing lung transplantation. In these experiments we could actually analyze the mucus secretions in the treated versus non-treated bronchi.