Systematic Analysis of Repeated Gene Delivery into Animal Lungs with a Recombinant Adenovirus Vector

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Abstract
Adenovirus-based vectors are promising candidates for genetic therapy of cystic fibrosis (CF). Because adenoviruses naturally infect airway cells, they grow to very high titers, and the transgenes carried by the adenoviruses are expressed at high levels. In addition, adenoviruses are relatively safe because the disease caused by the wild-type virus is self-limiting. One disadvantage of adenovirual vectors is that the transgene expression would be transient because adenoviruses do not integrate their DNA into the genome of the host cells. Adenoviral gene delivery into the lungs is also complicated by the anatomy of the airways and the defense mechanisms of the recipient. To assess the feasibility of adenovirus-mediated gene therapy for CF, a recombinant adenovirus carrying a lacZ gene was delivered into animal lungs to study the efficiency and cellular distribution of gene transfer, the duration of gene expression, the possible histopathology of the lungs after gene transfer, and the efficacy of repeated administrations of the viral agent. The results of these studies demonstrate that (i) efficient gene transfer into animal lungs can be achieved; (ii) a near-homogenous delivery of the vectors can be achieved by airway instillation, although the pattern of transduction varies among individual animals; (iii) pathological effects are generally mild in CD1 mice; (iv) gene expression is transient; (v) repetitive gene transfer is achievable, but becomes progressively less efficient, and (vi) immune responses are induced against both the viral and transgene products. Recombinant adenoviruses are effective vectors for gene transfer into animal lungs. However, because gene expression is transient, repetitive gene delivery is required for a therapeutic effect in cystic fibrosis (CF) gene therapy. By using a recombinant adenovirus that carries the lacZ gene, we have directly visualized the efficiency and cellular distribution of gene transfer, the duration of gene expression, the efficacy of repeated gene delivery into the lungs of CD-1 mice, and the host immune response after multiple exposures to high doses of the virus. The results of these studies indicate that adenovirus-mediated gene tranasfer into lungs is efficient but transient. Repeated gene transfers are achievable, but are progressively less efficient. Intratracheal delivery of adenoviral vectors induces an antibody response against the viral and transgene products, although a limited inflammatory response was observed in the lungs of CD-1 mice.