Targeted gene correction in osteopetrotic-induced pluripotent stem cells for the generation of functional osteoclasts

Autosomal recessive osteopetrosis is a human bone disease mainly caused by TCIRG1 gene mutations that prevent osteoclasts resorbing activity, recapitulated by the oc/oc mouse model. Bone marrow transplantation is the only available treatment, limited by the need for a matched donor. The use of induced pluripotent stem cells (iPSCs) as an unlimited source of autologous cells to generate gene corrected osteoclasts might represent a powerful alternative. We generated iPSCs from oc/oc mice, corrected the mutation using a BAC carrying the entire Tcirg1 gene locus as a template for homologous recombination, and induced hematopoietic differentiation. Similarly to physiologic fetal hematopoiesis, iPSC-derived CD41⁺ cells gradually gave rise to CD45⁺ cells, which comprised both mature myeloid cells and high proliferative potential colony-forming cells. Finally, we differentiated the gene corrected iPSC-derived myeloid cells into osteoclasts with rescued bone resorbing activity. These results are promising for a future translation into the human clinical setting.