Treatment of Duchenne muscular dystrophy with myoblasts expressing dystrophin and treated to block myostatin signaling

A method of increasing the mass of a muscle tissue or treating Duchenne Muscular Dystrophy (DMD) in a subject suffering from DMD, said method comprising implanting into said muscle tissue of said subject a myoblast, said myoblast being autologous or allogeneic to said subject and comprising a nucleic acid encoding an active dystrophin polypeptide operably linked to a promoter, said myoblast having been subjected to a treatment or modification prior to implantation to inhibit myostatin activity or myostatin ActRIIB receptor activity in said myoblast, whereby said muscle tissue mass is increased or said DMD is treated in said subject.