A DIFFERENTIAL EFFICIENCY OF ADENOVIRUS-MEDIATED IN-VIVO GENE-TRANSFER INTO SKELETAL-MUSCLE CELLS OF DIFFERENT MATURITY

High titre (10(11) - 10(12) pfu/ml) suspensions of autonomously replication-defective type 5 human adenovirus (AV) recombinants with different reporter gene inserts (CMV-Luciferase (Lux), CMV-beta-galactosidase (Lac Z), RSV-Lux and RSV-Lac Z) were injected into intact quadriceps muscles of 1 - 5 day old (Group 1) or 35 - 45 day old (Group 2) normal mice, as well as regenerating adult mouse muscles (Group 3) and 35 day old mdx muscles (Group 4). The expression of the reporter genes was quantitated 10 days and 2 months later. At 10 days postinjection all reporter gene expression was very high in the neonatally injected (Group 1) muscles. In Group 2 muscles the transduction was markedly less. In Group 3 muscles the gene expression was significantly better than in the Group 2 muscles. In adult mdx muscles (Group 4) where spontaneous regeneration is usually present, the results were similar to those in Group 3 animals. At 2 months post-injection in Group 1 animals, the RSV-Lux expression was even higher than at 10 days postinjection. The cell surface density of alpha(v)-integrin-containing molecules including the internalization receptor for AV in Groups 1, 2, 3 and 4 showed a positive correlation with AV transducibility. We conclude that adenovirus vector in high titre (10(10) pfu/ml or above) is capable of efficiently transducing only immature muscle cells but not mature muscle fibers in vivo and this appears to correlate with a higher surface density of the available AV internalization receptor in immature muscle cells and lower level in mature muscle fibers. The results of this study have important relevance to gene therapy of skeletal muscles in such diseases as Duchenne muscular dystrophy (DMD).