Importance of the timing between the induction of muscle regeneration and the administration of muscle precursor cells for optimal engraftment: a study in nonhuman primates

Background & Aim Cell therapy is a major strategy for a future treatment of some myopathies. The cell therapy protocol that we developed in nonhuman primates (NHPs) using muscle precursor cells (MPCs) allowed the restoration of the genetically missing protein (dystrophin) with better efficacy than previously in myofibers of patients with Duchenne muscular dystrophy, but needs improvements to obtain a broader cell engraftment. Of the factors analyzed so far in NHPs, only wide muscle regenerationfavored a broader engraftment of MPCs in the myofibers of the recipient.Since muscle regeneration is a dynamic process, we wanted to investigate which is the best timming between the induction of muscle regeneration and the administration of MPCs for an optimal engraftment.To elucidate that, we carried out a study in NHPs. Methods, Results & Conclusion Methods We administrated allogeneic MPCs labeled with s-galactosidase (s-Gal) in muscle regions of 1 cm3in cynomolgus monkeys, using arrays of 25 equidistant microinjections. The sites were treated or not with electroporation (EP) to trigger massive muscle regeneration (3 pulses of 400 V/cm and 5 ms with a delay of 200 ms).MPC were administered immediately after EP, as well as on days 1 to 7 after EP and days 1, 2, 3, 6 and 7 before EP. Tacrolimus was given daily to control rejection. Cell grafted regions were sampled 1 month after MPC administration, snap frozen in liquid nitrogen and sectioned in a cryostat. Muscle cross-sections were stained with hematoxylin and eosin and for histochemical demonstration of s-Gal. The amount of s-Gal+ myofibers was quantified as an indication of engraftment success. Results The amount of s-Gal+ myofibers was significantly increased by a factor of 3.2 ± 1.2 in the muscles in which MPC administration was done immediately after EP, with respect to regions grafted similarly but without EP (p Conclusion According to these data, MPC administration must be concomitant with the induction of muscle regenerationto ensure an increase of MPC engraftment. The MPC administration between days 3 and 7 after muscle regeneration induction can jeopardize the MPC engraftment, while in the rest of the timings the results can be variable.