LACK OF MYOBLASTS MIGRATION BETWEEN TRANSPLANTED AND HOST MUSCLES OF MDX AND NORMAL MICE

Extensor digitorum longus muscles of normal mice (C57BL/10ScSn hereaft er called C57) were orthotopically transplanted into dystrophin-defici ent mice (mdx) and reciprocally, mdx Extensor digitorum longus muscles were transplanted into C57 mice. After an initial phase of degenerati on, transplanted muscles regenerate nearly completely, as evaluated fr om the maximum isometric force of muscles isolated 60 days after the s urgery. In other similar experiments, instead of isolating the grafted muscles, we excised the antero-external muscles of the leg, including the grafted muscle. Cryostat cross-sections at three levels along the muscles were immunostained with an anti-dystrophin antibody. No muscl e cells of dystrophin-deficient muscles grafted into normal mice took the antibody except a few 'revertant' fibres, while all the muscle cel ls of the normal host were immunostained. Reciprocally, all the muscle s cells of normal grafts were stained, whilst no antibody stained the cells of the surrounding muscles of the dystrophin-deficient host. The se experiments show that very few if any of the myoblasts or muscle pr ecursor cells, active during the regeneration of grafted muscle, migra te into the adjacent muscles. These results could be explained by the absence, in our work, of injuries of the grafted and adjacent host mus cles epimysium and the absence of extensive inflammatory reactions. Th is lack of myoblast mobility suggest that when myoblast transfer is ap plied to muscle therapy, it will be necessary to inject myoblasts with in each muscle to obtain an efficient treatment.