Most cases of sensorineural deafness are caused by degeneration of hair cells. Although stem/progenitor cell therapy is becoming a promising treatment strategy in a variety of organ systems, cell engraftment in the adult mammalian cochlea has not yet been demonstrated. In this study, we generated human otic progenitor cells (hOPCs) from induced pluripotent stem cells (iPSCs) in vitro and identified these cells by the expression of known otic markers. We showed successful cell transplantation of iPSC-derived-hOPCs in an in vivo adult guinea pig model of ototoxicity. The delivered hOPCs migrated throughout the cochlea, engrafted in non-sensory regions, and survived up to 4 weeks post-transplantation. Some of the engrafted hOPCs responded to environmental cues within the cochlear sensory epithelium and displayed molecular features of early sensory differentiation. We confirmed these results with hair cell progenitors derived from Atoh1-GFP mice as donor cells. These mouse otic progenitors transplanted using the same in vivo delivery system migrated into damaged cochlear sensory epithelium and adopted a partial sensory cell fate. This is the first report of the survival and differentiation of hOPCs in ototoxic-injured mature cochlear epithelium, and it should stimulate further research into cell-based therapies for treatment of deafness.

Age-related neurosensory deficit of the inner ear is mostly due to a loss of hair cells (HCs). Development of stem cell-based therapy requires a better understanding of factors and signals that drive stem cells into otic sensory progenitor cells (OSPCs) to replace lost HCs. Human induced pluripotent stem cells (hiPSCs) theoretically represent an unlimited supply for the generation of human OSPCs in vitro. In this study, we developed a monolayer-based differentiation system to generate an enriched population of OSPCs via a stepwise differentiation of hiPSCs. Gene and protein expression analyses revealed the efficient induction of a comprehensive panel of otic/placodal and late otic markers over the course of the differentiation. Furthermore, whole transcriptome analysis confirmed a developmental path of OSPC differentiation from hiPSCs. We found that modulation of WNT and transforming growth factor-β (TGF-β) signaling combined with fibroblast growth factor 3 (FGF3) and FGF10 treatment over a 6-day period drives the expression of early otic/placodal markers followed by late otic sensory markers within 13 days, indicative of a differentiation into embryonic-like HCs. In summary, we report a rapid and efficient strategy to generate an enriched population of OSPCs from hiPSCs, thereby establishing the value of this approach for disease modeling and cell-based therapies of the inner ear.