499 A Novel Preclinical Model for Translating an Induced Pluripotent Stem Cell Therapy for the Treatment of Skin Diseases

Induced pluripotent stem cells (iPSCs) hold promise for treating recessive dystrophic epidermolysis bullosa (RDEB). An iPSC-based therapy for RDEB involves multiple steps such as reprogramming, gene correction, iPSC differentiation, and transplantation of genetically corrected iPSC-derived skin cells onto patients. Strong evidence supports the use of epidermal sheets or composite skin grafts as final therapeutic products for the transplantation of genetically corrected iPSC-derived skin cells. However, the generation of epidermal sheets or composite grafts is a lengthy and consequently expensive process. To develop a more straightforward and cost effective skin transplantation approach, we established a novel preclinical model for grafting a human skin cell suspension onto immunocompromised mice that requires low starting cell numbers. The model involves the use of a silicone chamber and sequential transplantation of fibroblasts followed by keratinocytes. Both fibroblasts and keratinocytes are delivered in suspension in a fibrin-based gel formulation. Using this modified assay, we have successfully engrafted as low as 5 x 105 keratinocytes per 1.4 cm2 of wound area. We have also successfully engrafted iPSC-derived keratinocytes. In all cases, the grafted cells formed a multilayered stratified human epidermis. We are currently investigating strategies to deliver genetically corrected RDEB iPSC-derived skin cells, including the cell harvesting and application techniques currently used for Spray-On-Skin™ cells developed by AVITA Medical. This approach will decrease the time to patient application vs. the time and cost it takes to grow epidermal sheets and will potentially simplify iPSC therapies for RDEB and other skin diseases.