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MYOBLAST TRANSFER IN THE TREATMENT OF DUCHENNE ’ S MUSCULAR DYSTROPHY

Background. Myoblast transfer has been proposed as a technique to replace dystrophin, the skeletalmuscle protein that is deficient in Duchenne’s muscular dystrophy. Donor myoblasts injected into muscles of affected patients can fuse with host muscle fibers, thus contributing their nuclei, which are potentially capable of replacing deficient gene products. Previous controlled trials involving a single transfer of myoblasts have been unsuccessful. Methods. We injected donor muscle cells once a month for six months to the biceps brachii muscles of one arm of each of 12 boys with Duchenne’s muscular dystrophy. The opposite arms served as sham-injected controls. In each procedure 110 million cells donated by fathers or brothers were transferred. The patients were randomly assigned to receive either cyclosporine or placebo. Strength was measured by quantitative isometric muscle testing. Six months after the final myoblast transfer, the presence of dystrophin was assessed with the use of peptide antibodies specific to the deleted exons of the dystrophin gene. Results. There was no significant difference in muscle strength between arms injected with myoblasts and sham-injected arms. In one patient, 10.3 percent of muscle fibers expressed donor-derived dystrophin after myoblast transfer. Three other patients also had a low level of donor dystrophin ( 1 percent); eight had none. Conclusions. Myoblasts transferred once a month for six months failed to improve strength in patients with Duchenne’s muscular dystrophy. The value of exon-specific peptide antibodies in the interpretation of myoblasttransfer results was demonstrated in a patient with Duchenne’s muscular dystrophy who had a high percentage of donor-derived dystrophin. Specific variables affecting the efficiency of myoblast transfer need to be identified in order to improve upon this technique. (N Engl J Med 1995;333:832-8.) From the Departments of Neurology (J.R.M., J.T.K., A.A.A., W.K., L.S., T.W.P., Z.S., S.B., P.E.M., R.R., A.H.M.B.), Pathology (J.R.M., T.W.P., R.S., L.L.), Medical Biochemistry (A.H.M.B.), Statistics (H.N.), and Molecular Genetics (P.E.M., A.H.M.B.), Ohio State University, Columbus; and the North East Wales Institute, Research Division, Deeside, Clwyd, United Kingdom (G.E.M.). Address reprint requests to Dr. Mendell at the Department of Neurology, Rm. 463, Means Hall, Ohio State University, 1654 Upham Dr., Columbus, OH 43210. Supported by the Muscular Dystrophy Association, the Muscular Dystrophy Group of Great Britain and Northern Ireland, and a grant from the National Institutes of Health (Mo1-RR-00034). D UCHENNE’S muscular dystrophy is an X-linked disorder caused by deficiency of the protein dystrophin. 1,2 In animals, myoblast transfer was shown to be a promising method of dystrophin replacement. 3-5 The technique consists of injecting skeletal muscles with donor cells capable of fusing with host muscle fibers and thus providing the missing gene to replace dystrophin. Encouraging results in murine dystrophies 3-5 led to clinical studies in patients with Duchenne’s muscular dystrophy. 6-10 In one report, donorderived dystrophin transcripts were demonstrated one month after myoblast injection. 6 Other investigators failed to identify donor-derived dystrophin or messenger RNA. 7-10 No improvement in strength was observed in any controlled study of myoblast transfer, 6,7,9 although uncontrolled trials suggested that muscle strength could be increased. 8,10 Immunosuppression to prevent rejection of donor cells was used in two controlled trials 6,7 and one uncontrolled trial. 10 The use of antiinflammatory agents introduces another variable into the interpretation of myoblast transfer, because prednisone 11 and cyclosporine 12 have been reported to improve strength in patients with Duchenne’s muscular dystrophy. This study differs from previous controlled investigations in several ways. First, instead of a one-time transfer, myoblasts were transferred from donor to host muscles once a month for six months. One study had suggested that myoblasts could assume a satellite-cell position and be available for fusion at a subsequent time. 13 Second, dystrophin expression was measured by the use of peptide antibodies specific to the deleted exons of the dystrophin gene. This method allows one to distinguish between dystrophin-positive fibers derived from donor DNA and host fibers that had reverted to normal (“revertant” fibers). 14,15 Third, patients were randomly assigned to receive cyclosporine or placebo, permitting a direct assessment of the need for antirejection drugs and of the effect of cyclosporine on muscle strength.