Transfer of the CFTR Gene to the Lung of Nonhuman Primates with E1-Deleted, E2a-Defective Recombinant Adenoviruses: A Preclinical Toxicology Study

Abstract

This paper describes a preclinical toxicology study designed to investigate the biological efficacy and safety profile of second-generation adenovirus for CFTR gene transfer into the baboon lung. This second-generation virus is deleted of E1 and contains a temperature-sensitive mutation in the E2a gene, which encodes a defective DNA-binding protein. Two distinct projects were undertaken. Group A animals received a first-generation adenovirus (i.e., deleted of E1) in an upper lobe at the time a second-generation virus was instilled into the contralateral upper lobe. The goal of study A was to compare the biology of each construct directly and to determine if an immune response to the first-generation virus affected the performance of the second-generation virus. Group B animals received a lacZ second-generation virus in an upper lobe at the same time the CFTR second-generation virus was instilled in the other upper lobe. Necropsies were performed 4 or 21 days after gene transfer and tissues were evaluated for recombinant gene expression and histopathology. Using a second-generation adenovirus, recombinant gene stability was prolonged and associated with a diminished level of perivascular inflammation as compared to first-generation vectors. Markedly diminished levels of hexon protein were present in tissues infected with second-generation as compared to first-generation virus. No evidence of viral shedding was evident. Furthermore, coadministration of first- and second-generation adenovirus did not affect the stability of transgene expression from the second-generation virus. These data suggest that second-generation adenoviral vectors provide an improved gene delivery vehicle, and thus may be useful in gene therapy for cystic fibrosis. Adenovirus-mediated gene therapy of cystic fibrosis (CF) in many animal models has been transient and immunogenic, both undesirable features in the potential treatment of the disease. The development of second-generation adenoviral vectors, in which viral gene production is further crippled, appears to be a step toward overcoming those limitations. This study addresses the clinical and pathological consequences and the biological efficacy of using second-generation adenoviruses for gene therapy of CF lung disease.