EFFICIENCY AND FUNCTIONAL CONSEQUENCES OF ADENOVIRUS-MEDIATED IN-VIVOGENE-TRANSFER TO NORMAL AND DYSTROPHIC (MDX) MOUSE DIAPHRAGM

The protein dystrophin is absent in muscles of patients with Duchenne muscular dystrophy (DMD) as well as in mdx mice. The mdx mouse diaphra gm closely resembles the human DMD phenotype and should serve as an ap propriate model for future studies of dystrophin gene replacement. In this regard, recombinant adenovirus (AV) holds great promise as a vect or for delivering a functional dystrophin gene to muscle. However, the use of AV is hampered by the development of an immune response agains t transduced cells, resulting in short-lived transgene expression as w ell as possible adverse effects on organ function. In the present stud y, sensitive reporter genes were employed to determine the efficiency and functional consequences of AV-mediated gene transfer to the diaphr agm in both normal and mdx adult mice. One week after direct intramusc ular injection of AV into the diaphragm, the level of transgene expres sion was significantly increased in mdx compared with normal diaphragm s. In addition, small-caliber fibers (< 500 mu m(2)) demonstrated pref erential transduction in both groups of mice, Normal diaphragms receiv ing AV exhibited a substantial reduction in maximal twitch and tetanic force generation, whereas no significant effect on diaphragm contract ility was found in the mdx group at 1 wk after injection. At 1 mo afte r AV administration, however, there was a significant decrease in forc e production by both normal and mdx diaphragms. Immunosuppression with cyclosporine A over 1 mo did not augment the level of transgene expre ssion, but a beneficial effect on diaphragm force-generating capacity was observed in both groups of animals. We conclude the following: (I) short-term transduction of the diaphragm is more efficient in mdx tha n in normal mice; (2) AV leads to reduced force production by the diap hragm, with this effect being more pronounced in normal than in mdx in the early (but not the late) postinjection period; and (3) immunosupp ressive therapy with cyclosporine has a partially protective effect on muscle function after AV administration, which is apparently unrelate d to sparing of transduced fibers from elimination by the host immune system. These findings have important implications for the application of AV-mediated dystrophin gene transfer to the treatment of DMD.