Successful myoblast transplantation in primates depends on appropriate cell delivery and induction of regeneration in the host muscle

Myoblast transplantation (MT) may be a potential treatment for severe reces sive hereditary myopathies. The limited results of MT in clinical trials le d us to improve this technique in monkeys, an animal model phylogenetically similar to humans. Three Macaca mulata monkeys were used as donors and six as receivers for MT. Myoblasts were grown in culture from muscle biopsies of adult monkeys and infected with a retroviral vector encoding the LacZ ge ne. Different numbers of cells (i.e., 4 x 10(6), 8 x 10(6), and 24 x 10(6) cells) were transplanted into different muscles and 8 x 106 cells (resuspen ded in a notexin solution) were injected in one muscle of four monkeys. For these transplantations, the cell suspension (in a volume of about 100 mu l ) was injected at 35 sites less than 1 mm apart. Two Other monkeys received 100 x 106 myoblasts resuspended in 1 mi of HBSS or 1 mi of notexin. For th ese two monkeys, the myoblasts were injected at 200-250 sites within a smal l portion of the muscle. All monkeys were immunosuppressed with daily injec tions of FK506. Four weeks after MT, the transplanted muscle portions mere biopsied and the presence of beta-galactosidase-positive (beta-Gal+) muscle fibers was investigated. The number of beta-Gal+ fibers was 822 +/- 150 (s ite grafted with 4 x 106 cells), 1253 +/- 515 (8 x 10(6) cells), 1084 +/- 2 78 (24 x 10(6)), and 2852 +/- 1211 (notexin). In the monkeys grafted with 1 00 x 10(6) myoblasts, the number of beta-Gal+ fibers was 4850 (site without notexin) and 9600 (site with notexin). We demonstrated that a precise mech anical distribution of myoblasts into the tissue improves substantially MT in primates. The presence of notexin with the transplanted cells further in creased the success of their transplanta tion. These are the best results o btained either with MT or gene therapy in primates and they encourage the p ossibility to human MT trials. (C) 1999 Academic Press.