IMPAIRMENT OF FORCE GENERATION AFTER ADENOVIRUS-MEDIATED GENE-TRANSFER TO MUSCLE IS ALLEVIATED BY ADENOVIRAL GENE INACTIVATION AND HOST CD8(-CELL DEFICIENCY() T)

Recombinant adenovirus vectors (AdV) hold promise as a means of delive ring therapeutic genes to muscle in diseases such as Duchenne muscular dystrophy (DMD). However, we have previously shown that the use of Ad V is hampered by the development of reduced force-generating capacity, which occurs within 1 week and is progressive up to at least 1 month after AdV delivery in immune-competent animals. Determinations of musc le force production provide a sensitive and clinically important measu re of potential adverse effects of AdV-mediated gene transfer on muscl e cell function. In the present study, we investigated the role of AdV -related gene expression and host T lymphocyte responses in the genesi s of muscle dysfunction following AdV injection of muscle. We report t hat UV-irradiation of AdV particles, which reduced AdV transcriptional activity without impairing infectivity (as confirmed by in situ polym erase chain reaction), significantly reversed early (4 days post-injec tion) AdV-induced contractile impairment in immune-competent mice as w ell as in mice lacking effective CD8(+) T cell activity. The superimpo sed additional reduction in force-generating capacity normally found b etween 4 and 30 days post-AdV delivery in immune-competent mice, along with the associated loss of transgene (beta-galactosidase) expression , was largely abrogated by the absence of an intact CD8(+) T lymphocyt e response. Furthermore, short-term administration of a neutralizing a ntibody against CD4(+) T cells significantly prolonged transgene expre ssion and showed a trend toward mitigation of AdV-induced reductions i n force-generating capacity. Cellular infiltration and humoral immune responses against the vector and transgene product were also blunted t o varying degrees in the setting of CD8(+) or CD4(+) T cell deficiency . We conclude that AdV-related gene expression has an early negative ( probably toxic) effect on muscle cell function that is independent of CD8(+) T cell-mediated immunity, In contrast, further progression of c ontractile impairment and the accompanying loss of transgene expressio n from AdV-injected muscle are largely dependent upon the activity of CD8(+) T cells. These results have implications for the design of futu re generation vectors and the potential need for immunosuppressive the rapy after AdV-mediated gene transfer to muscle.