Pre-transplant treatments of muscle precursor cells that were reported to improve their engraftment in mice failed to improve it in nonhuman primates

Abstract

Background & Aim Cell therapy is a major strategy for the potential future treatment of some myopathies. The protocol of cell therapy that we developed in nonhuman primates (NHPs) allowed dystrophin restoration with better efficacy than previously in patients with Duchenne muscular dystrophy, but needs improvements to obtain a broader engraftment and dystrophin restoration. Studies in mice reported methods that substantially increased cell engraftment, based onin vitrotreatments and co-injection of the cells with growth factors or other molecules. Since these methods would be easily applicable in the clinic, we wanted to verify them in NHPs, given thatthis animal model is crucial in preclinical research in several areas of medicine before translating protocols to humans. Methods, Results & Conclusion Methods We allotransplanted muscle precursor cells (MPCs) labeled with s-galactosidase (s-Gal) in muscle regions of 1 cm3in cynomolgus monkeys. Tacrolimus was administered daily to control acute rejection. The strategies to improve the MPC engraftment were: in vitro treatment with or without co-injection of the cells with the following molecules: insulin growth factor 1 (IGF-1), basic fibroblast growth factor (bFGF), IGF-1 + bFGF + plasmin, concanavalin A and SB203580 (a p38 MAP kinase inhibitor). One of two cell-grafted regions was treated by electroporation to induce broad myofiber regeneration concomitant to the graft. Cell grafted regions were sampled one month after transplantation, 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. s-Gal+ myofibers were quantified as an indication of engraftment success. Results The only factor that substantially increased the number of s-Gal+ myofibers was the extensive muscle regeneration induced by electroporation. Otherwise, for the same cell graft conditions (injection with or without electroporation) none of the cell treatments increased the amount of s-Gal+ myofibers and therefore the success of the cell graft in terms of genetic complementation. Conclusion Cell treatments reported to increase the MPC engraftment in mice had no incidence in NHPs.The only strategy capable of increasing the cell engraftment in NHPs remained the induction of extensive muscle regeneration concomitant with the cell graft. As in other areas of preclinical research, this study also questions the clinical validity of results reported only in mice.