TRANSIENT IMMUNOSUPPRESSION BY FK506 PERMITS A SUSTAINED HIGH-LEVEL DYSTROPHIN EXPRESSION AFTER ADENOVIRUS-MEDIATED DYSTROPHIN MINIGENE TRANSFER TO SKELETAL-MUSCLES OF ADULT DYSTROPHIC (MDX) MICE

Adenovirus (AV)-mediated gene transfer into skeletal muscles of adult immune-competent animals has been limited by the fact that a cell-medi ated immune attack of the host against transduced muscle fibers preven ted efficient long-term transgene expression. More recently, various i mmunomodulating strategies have been shown to improve the longevity of transgene expression after AV-mediated gene transfer. In this study w e treated adult dystrophic (mdx) mice with daily subcutaneous injectio ns of the immunosuppressive drug FK506 (tacrolimus) over 5, 10, 30 and 60 days after AV-mediated dystrophin gene transfer and compared the t ransduction level with saline-injected mds controls. We show that dail y FK506 treatment after AV-mediated dystrophin gene transfer into adul t mdx muscle results in the maintenance of the initial transgene expre ssion for at least 2 months, even when FK506 treatment was discontinue d after 1 month. This is in keeping with the marked reduction of infla mmatory infiltrates and the reduced activation level (inducible nitric oxide synthase) of macrophages in adenoviral recombinant (AVR)-inject ed muscles of FK506-treated animals. Moreover, we find that FK506 effi ciently suppresses the humoral immune response against both the vector proteins and the transgene protein product (dystrophin). Furthermore, we demonstrate thai continuous FK506 treatment over 30 days significa ntly improves the efficiency of gene transfer when the same vector is readministered to an animal which had been transduced 20 days earlier. In conclusion, the data suggest that sensitization by the initial ant igenic load of the AVR application plays a pivotal role in triggering the humoral and cellular immune response of the host, which can be sig nificantly counteracted by relatively short-term immunosuppressive tre atment. These findings have important implications for the design of f uture human trials for gene replacement therapy in Duchenne muscular d ystrophy.