Recombinant adenovirus deleted of all viral genes for gene therapy of cystic fibrosis

Abstract

Recombinant adenoviruses are being developed for gene therapy of inherited disorders such as cystic fibrosis because they efficiently transduce recombinant genes into nondividing cells in vivo. First generation recombinant adenoviruses, rendered defective by deletion of sequences spanning E1a and E1b, express low levels of early and late viral genes that activate destructive cellular immune responses. Current strategies for improving recombinant adenoviruses attempt to inactivate other essential genes through deletion and growth in new packaging cell lines or incorporation of temperature sensitive mutations which allow propagation of the virus in available packaging cell lines at permissive temperatures. We describe in this report a new type of recombinant adenovirus that is deleted of all viral open reading frames. This recombinant (called ΔrAd), which contains only the essential cis elements (i.e., ITRs and contiguous packaging sequence), is propagated in 293 cells in the presence of E1-deleted helper virus. Concatamers of the monomeric vector genome were passaged and capable of transduction. The ΔrAd genome is packaged into virions that sediment at a lower density than the helper virus in cesium gradients forming the basis for a purification protocol. A fully deleted recombinant adenovirus that expresses human cystic fibrosis transmembrane conductance regulator was produced and used to transduce human airway epithelial cells derived from a cystic fibrosis patient. Packaging and propagation of a fully deleted adenovirus is an important step toward the development of a safer vector. Improved production and purification strategies need to be developed before this new vector system can be evaluated in vivo.