235. The Fetal Approach: A Novel Therapy for the Treatment of Musculo-Skeletal Disease

Gene therapy for Duchenne muscular dystrophy has so far not been successful because of the difficulty in achieving efficient and permanent gene transfer to the large number of affected muscles and the development of immune reactions against vector and transgenic protein. In addition, the prenatal onset of disease complicates postnatal gene therapy. We have therefore proposed a fetal approach to overcome these barriers. We have applied b-galactosidase expressing EIAV lentiviruses by single or combined injection via different routes to the MF1 mouse fetus on day 15 of gestation and describe substantial gene delivery to the musculature. Highly efficient gene transfer to skeletal muscles, including the diaphragm and intercostal muscles, as well as to cardiac myocytes was observed and gene expression persisted for at least five months after administration of this integrating vector. Using alternative envelope glycoproteins to pseudotype the EIAV vector also appears to provide improved gene targeting not only to muscle fibres but also muscle satellite cells important for muscle regeneration. These findings support the concept of in utero gene delivery for therapeutic and long term prevention/correction of muscular dystrophies and pave the way for a future application in the clinic.