Cystic fibrosis (CF) is a common, fatal hereditary disease resulting from mutations of the human cystic fibrosis transmembrane conductance regulator (CFTR) gene in which epithelial cells throughout the body manifest altered regulation of apical membrane chloride secretion. Although the disease affects multiple organs throughout the body, over 90% of patients die of complications of the lung involvement. The feasibility of adenovirus-derived vectors for in vivo delivery of the human CFTR cDNA to treat the pulmonary component of CF is currently being evaluated using in vitro and in vivo approaches. Defining the therapeutic window between biological efficacy and toxicity is an important part of this work. Here we present data regarding the preclinical evaluation of the safety of in vivo delivery of the human CFTR cDNA to the cotton rat airway epithelium using the replication-deficient adenoviral vector Av1Cf2 or a similar vector, Av1LacZ4, expressing the Escherichia coli LacZ gene as a histologic marker. Gene transfer to the respiratory epithelium was efficient, as demonstrated by in situ hybridization and histochemical staining. Administration of these vectors resulted in a mild, transient, dose-dependent cellular inflammatory response similar in character to that seen with adenovirus 5 (Ad5), but far less in intensity, which was not associated with structural lung damage or mortality. Av1Cf2 DNA sequences were easily detected in the lung after pulmonary administration, but could not be demonstrated in organs other than the lung. These preclinical observations suggest that adenovirus-mediated gene transfer to the airway epithelium can be achieved efficiently, but is accompanied by a dose- and time-dependent inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)