Trans-Complementation of E1-Deleted Adenovirus: A New Vector to Reduce the Possibility of Codissemination of Wild-Type and Recombinant Adenoviruses

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Abstract
Treatment of cystic fibrosis by gene therapy will require the development of vectors capable of efficient and safe transfer of a functional cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to airway epithelia. To achieve this goal, replication-deficient (E1¯) adenoviruses (Ad) are promising vectors. We have previously demonstrated efficient CFTR gene delivery to the airways of cotton rats and rhesus monkeys using a replication-deficient adenovirus, Ad-CFTR. Here, we have investigated an important safety issue, the interaction between the vector and wild-type virus which can provide the missing E1 function in trans. We show that Ad5 can mobilize the defective Ad-CFTR genome in vitro and in cotton rats. However, the extent of the complementation in vivo by wild-type virus is limited because no additional spreading or shedding of Ad-CFTR to trachea, lungs, and stools is elicited. To attenuate Ad-CFTR further, a mutation was introduced in the cis-acting regulatory sequences that control the encapsidation of the viral genome. We demonstrate that when cells are coinfected with wild-type virus and the new attenuated vector, the viral DNA containing the natural encapsidation sequences is preferentially packaged, leading to a rapid dilution of the recombinant virus. Adenovirus-mediated gene transfer to the lung is a promising technology for gene therapy of cystic fibrosis. In vivo use of recombinant replication-defective viral vectors raises the issue of possible interaction between the vector and wild-type virus. This article reports that currently used E1-deleted adenovirus vectors can be trans-complemented by wild-type adenovirus in vitro and in vivo. The authors describe a new attenuated adenoviral vector that is less efficiently mobilized by wild-type adenovirus.