Engineered Myeloid Precursors Differentiate into Osteoclasts and Resorb Heterotopic Ossification in Mice

Abstract Heterotopic ossification (HO) is prevalent following orthopedic trauma, traumatic brain and spinal cord injuries, brain, and limb amputations, particularly in combat veterans. HO causes pain, limited mobility and decreased quality of life. Current treatments are limited and have significant complications with high recurrence rates, underscoring the need for improved therapeutic interventions. In this study, we used genetically engineered osteoclasts (OCs) as a cell therapy to treat HO. Inducible, engineered myeloid precursors (iRANK cells) treated with chemical inducer of dimerization (CID) differentiated into TRAP+ multinucleated OCs, expressed functional osteopontin, and resorbed mineralized tissues in vitro. To investigate if iRANK OCs could reduce HO in vivo, HO lesions were induced by injections of BMP-2, and iRANK cells were locally delivered to ectopic bone nodules with concomitant systemic administration of CID. Micro-CT and histology showed that HO lesions were significantly reduced, and more OCs were observed in the cell-treated group compared to the control. Moreover, many OCs were TRAP, MMP9, and GFP-positive indicating that they differentiated from delivered iRANK cells. Thus, our data confirm the ability of engineered myeloid precursors to differentiate into OCs and resorb HO lesions in vivo paving the way for OC delivery as a promising approach for HO treatment.