Dystrophin expression in muscle following gene transfer with a fully deleted ("gutted"') adenovirus is markedly improved by trans-acting adenoviral gene products

Helper-dependent adenoviruses (HDAd) are Ad vectors lacking all or most vir al genes. They hold great promise for gene therapy of diseases such as Duch enne muscular dystrophy (DMD), because they are less immunogenic than E1/E3 -deleted Ad (first-generation Ad or FGAd) and can carry the full-length (Fl ) dystrophin (dys) cDNA (12 kb). We have compared the transgene expression of a HDAd (HDAdCMVDysFl) and a FGAd (FGAdCMV-dys) in cell culture (HeLa, C2 C12 myotubes) and in the muscle of mdx mice (the mouse model for DMD). Both vectors encoded dystrophin regulated by the same cytomegalovirus (CMV) pro moter. We demonstrate that the amount of dystrophin expressed was significa ntly higher after gene transfer with FGAdCMV-dys compared to HDAdCMVDysFl b oth in vitro and in vivo. However, gene transfer with HDAd-CMVDysFl in the presence of a FGAd resulted in a significant increase of dystrophin express ion indicating that gene products synthesized by the FGAd increase, in tran s, the amount of dystrophin produced. This enhancement occurred in cell cul ture and after gene transfer in the muscle of mdx mice and dystrophic golde n retriever (GRMD) dogs, another animal model for DMD. The E4 region of Ad is required for the enhancement, because no increase of dystrophin expressi on from HDAdCMVDysFl was observed in the presence of an E1/E4-deleted Ad in vitro and in vivo. The characterization of these enhancing gene products f ollowed by their inclusion into an HDAd may be required to produce sufficie nt dystrophin to mitigate the pathology of DMD by HDAd-mediated gene transf er.