Scientists have developed a method for converting human fibroblast-derived induced pluripotent stem cells (iPSCs) into genetically corrected mesoangioblast-like cells that improved muscle function when subsequently transplanted in mice with limb-girdle muscular dystrophy. The method could feasibly provide a platform for generating enough mesoangioblasts for use as autologous cell therapy in patients with limb-girdle muscular dystrophy 2D (LGMD2D), and possibly other recessive muscular dystrophies, claim the developers at the San Raffaele Scientific Institute in Milan, and University College London (UCL).
The U.K. University’s Giulio Cossu, Ph.D., and Francesco Saverio Tedesco, Ph.D., report their methods and experiments in Science Translational Medicine in a paper titled "Transplantation of Genetically Corrected Human iPSC-Derived Progenitors in Mice with Limb-Girdle Muscular Dystrophy.”
Mesoangioblasts (MABs) are a cell population derived from alkaline phosphatase–positive (AP+) human skeletal musclepericytes, which has been shown to colonize and contribute to the regeneration of dystrophic muscle when administered systemically. However, human MABs have a limited life span, and generating huge quantities of such cells for treating all the skeletal muscles in muscular dystrophy patients isn’t feasible, the authors note. The problem is compound because patients with LGMD2D, for example, produce lower than normal numbers of AP+ pericytes, so collecting and expanding enough MABs for use as autologous therapy becomes even less viable.
As an alternative, the Italian and U.K. researchers developed a protocol that allowed them to derive and genetically correct MABs from patient-derived iPSCs as a means of generating potentially unlimited numbers of myogenic progenitors for autologous therapy. Their approach essentially involved generating iPSCs from the skeletal muscle cells of LGMD2D patients, prompting these cells to differentiate into MABS that could then be expanded in vitro, and transducing the MABs with a lentiviral vector carrying the wild-type human α-sarcoglycan gene (SGCA) under the control of a muscle-specific promotor to correct the gene defect that is responsible for LGMD2D, but ensure it is only expressed in striated muscle.
The resulting iPSC-derived MABs, or HIDEMs (human iPSC-derived MAB-like stem/progenitor cells) resembled human MABs in morphology, AP expression, and proliferative capacity, were genetically stable through multiple passages, and demonstrated equivalent gene-expression profiles.
To test the potential therapeutic value in vivo, the researchers generated a dystrophic and immune-deficient triple mutant mouse model, the SGCA-null/scid/beige mouse. These animals show absence administered either intravenously or directly into the muscle of juvenile SGCA/null/scid/beige mice. Both routes of administration resulted in the engraftment of GFP+ cells in the dystrophic skeletal muscle and the associated generation of clusters of SGCA+ myofibrils.
Engraftment was even more pronounced when the experimental mice were given transplants of murine iPSC-derived MABs (MIDEMs), rather than human-derived cells. Animals treated with MIDEMs either intra-arterially or intramuscularly demonstrated five- to sixfold more SGCA+ fibrils than mice given HIDEMs, and showed a marked reduction in fibrotic-adipose tissue in transplanted muscle. The higher level of MIDEM engraftment was also associated with animals that demonstrated significant improvements in motor capacity using a treatmill test. At four months after treatment tests in addition showed that the titanic force was significantly higher in the tibialis anterior muscles of treated animals than untreated animals, and GFP+ muscle fibers exhibited greater contractile force. Interestingly, the transplanted cells also contributed to replenishing the population of pericytes.
“Although very preliminary, our study suggests that genetically corrected MABs generated from iPSCs derived from the fibroblasts or myoblasts of LGMD2D patients could be useful for autologous transplantation and that this approach might also be applicable for treating other recessive muscular dystrophies,” the authors conclude.
Independent research has separately led to the derivation of myogenic progentiors from human iPSCs, which may have utility in treating localized forms of muscle disorders that can be addressed by direct intramuscular transplantation when there aren’t numerous affected muscles, the investigators add. However, they stress, “the advantage of HIDEMs is that they can be delivered through the arterial circulation and thus are able to reach muscles throughout the body.”