The spread of transgene expression at the site of gene construct injection

Seven 2-day-old golden retriever pups were given focal intramuscular injections of a first generation adenovirus-dystrophin minigene construct and adenovirus-beta-galactosidase construct as a 2:1 mixture into the left anterior tibial muscle. The spread of transgene expression within the anterior tibial muscle was compared with the spread of methylene blue dye after identical injection into the contralateral muscle. Transgene expression 5-7 days after intramuscular injection was shown to extend between 5.8 and 11.6 mm along the biopsied muscle length (range of biopsy lengths 11.1-12.2 mm). The level of transgene expression at 2-2.5-mm intervals from the site of injection was significantly related to the distance from the site of injection (dystrophin, P = 0.009; beta-galactosidase, P = 0.015). The spread of methylene blue dye within the anterior tibial muscle < or =24 h after identical intramuscular injection demonstrated a similar pattern to the transgene expression, with dye staining measured between 5.5 and 8.5 mm along the muscle sample length (range of biopsy lengths 5.6-15.6 mm). The greatest transgene expression and dye staining was measured 2-2.5 mm proximal to the site of injection with a maximum of 23% of muscle fibers expressing the dystrophin transgene, 95.2% expressing the beta-galactosidase transgene, and 98% of the tissue section stained with methylene blue dye. These results suggest transgene expression after focal intramuscular injection is relatively localized around the site of injection. Further research is required to develop techniques that will provide transgene expression throughout the length and breadth of a muscle.