Transplanted myoblasts can migrate several millimeters to fuse with damaged myofibers in nonhuman primate skeletal muscle.

A major restriction of the intramuscular transplantation of myoblasts is that the grafted cells fuse mostly with myofibers along the injection trajectories. This has been attributed to a "lack of migration ability" of the grafted myoblasts. It has been assumed that grafted myoblasts remain motionless in the sites of delivery and fuse only with myofibers with which they come into contact. In the present study, we analyzed this phenomenon in 17 cynomolgus monkeys. We found that intramuscularly injected myoblasts within 1 hour after their injection are mainly located in the perimysium and not distributed along the injection trajectories. This suggested that the grafted myoblasts later migrate from the perimysium to fuse with myofibers that are damaged by the injections. Therefore, we analyzed whether β-galactosidase-labeled myoblasts injected subcutaneously over skeletal muscles migrate in needle-damaged and nondamaged muscle regions. We observed that grafted myoblasts migrated up to 1cm in depth from the muscle surface into the muscles, although they seemingly fused mainly with damaged myofibers. Our findings suggest that myoblast transplantation is not necessarily restricted bya "lack of migration ability" of the grafted cells but by the fact that myoblasts fuse with regenerating myofibers and not with undamaged myofibers.