452. Bone Marrow Stem Cells Are Potent Targets for Gene Therapy of Epidermolysis Bullosa, a Genetic Blistering Skin Disease

Abstract

Pluripotency of bone marrow stem cell (BMSC) has been intensively investigated, and promoted new concept, i.e. BMSC-gene therapy, for various genetic diseases to regenerate gene-corrected tissues derived from BMSCs. Despite these intensive studies, the plasticity of BMSCs to the epidermal keratinocytes is still under controversial arguments. The rarity of the BMSCs-derived keratinocytes in vivo has led pessimistic view on the roles of BMSCs for maintenance of the epidermal structures. Here, we investigated our hypothesis that follicular and interfollicular epidermal stem/ progenitor cells may migrate, at least in part, from bone marrow to the engrafted new born mouse skin, which will newly develop abundant follicles and epidermal appendages as well as squamous epithelia under regional severe hypoxic condition. Concretely, the skin sheets of newborn and adult mice were surgically engrafted onto the back of 8 week-old mice with prior transplantation of GFP-transgenic bone marrow cells after lethal dose X-ray irradiation, and examined appearance of GFP-positive epidermal cells in the grafts in various time points. In a week after the skin grafting, dense migration of GFP+ mesenchymal cells appeared in the upper dermis of the newborn skin graft, whereas only sparse GFP+ cells in the adult skin graft were detected. In 2 to 4 weeks after engraftment, various regions of newly generated follicular and interfollicular epidermis were significantly composed of GFP+ keratinocytes, and some regions exhibited full thickness of GFP+ epidermis, suggesting existence of BMSCs-derived epidermal stem cells. Recruitment of the GFP-transgenic BMSCs to the skin graft was further enhanced by transplantation of the type VII collagen gene (COL7A1) null newborn mouse skin, which required rapid proliferation of the epidermal keratinocytes due to frequent detachment of the epidermis from the underlying dermis. The COL7A1 null skin graft exhibited more than 50% occupancy of the follicular and interfollicular epidermis with GFP+ keratinocytes at 4 weeks after engraftment. These data suggest that BMSCs may provide epidermal stem cells in the newborn skin, especially of severe epidermolysis bullosa patients. COL7A1 Gene-collected bone marrow cell transplantation in the blisters of dystrophic epidermolysis bullosa patients, who are suffering from defect of type VII collagen at the cutaneous basement membrane zone, would be potential strategy for effective gene therapy of this intractable genetic blistering skin disease.