Preclinical studies of pluripotent stem cell-derived myogenic progenitors in non-human primates

Summary Muscular dystrophies are genetically and clinically heterogeneous disorders characterized by progressive weakness and degeneration of the skeletal muscles that control movement. The most common, Duchenne Muscular Dystrophy (DMD), is caused by genetic and biochemical defects of the dystrophin-glycoprotein complex (DGC). These alterations lead to cell membrane damage and death of muscle cells, resulting in chronic tissue degeneration and impaired muscle contractility. Although no effective treatment is available at present, one attractive therapeutic approach is to use cell-based therapies to promote muscle regeneration. There has been tremendous excitement for the therapeutic potential of induced pluripotent stem (iPS) cells in treating genetic diseases since these cells have virtually unlimited proliferation potential, and can differentiate into all cell types. We have pioneered a method to generate engraftable skeletal myogenic progenitors from pluripotent stem cells through conditional expression of Pax3 or Pax7. This approach results in highly efficient generation of therapeutic myogenic progenitors, which when transplanted into dystrophic mice locally or systemically produce large quantities of functional skeletal muscle tissue that incorporates normally into the host muscle. Importantly, a fraction of transplanted cells remains mononuclear, and displays key features of skeletal muscle stem cells, including satellite cell localization, response to re-injury, and contribution to muscle regeneration in secondary transplantation assays. Based on these encouraging findings, we have begun the manufacturing of these cells under cGMP compatible conditions and performed preclinical studies in murine recipients. The results from these studies are promising but before moving this therapy towards clinical translation, it would be ideal to assess scalability, delivery, distribution, safety, and engraftment in larger animal models. Therefore, here we propose preclinical studies to investigate these parameters using non-human primates (NHP) as recipients. It will also be critical to understand the impact of HLA mismatch on muscle engraftment, and NHP represent the ideal system to properly address this question. The transplantation of NHP iPS cell-derived myogenic progenitors into NHP recipients will provide critical knowledge for understanding tolerance in the allogeneic setting. This aspect, which has important implications for regenerative medicine, has been mostly overlooked in the pluripotent stem cell field. These are all critical prerequisites to advance this therapy towards successful clinical translation.