Promotion of Wound Healing by Cord Blood Derived Unrestricted Somatic Stem Cells (USSCs) in a Murine Wound Healing Model and Analysis On Their Bio-Distribution by in Vivo Bioluminescent Imaging (BLI)

Background: Delayed healing of skin wounds is a major morbidity. Repeated wounding is characteristic in patients with recessive dystrophic epidermolysis bullosa (RDEB), caused by mutations in COL7A1 gene. Stem cell therapy offers an option in treating this disease (Kiru/Cairo et al. PNAS, 2011). Recently, cord blood (CB) derived pluripotent stem cells, USSCs, have been applied in several animal models of degenerative diseases with beneficial outcomes.

Goal: To determine the potential of USSCs in the treatment of RDEB and its associated wounding phenotype.

Method: CB-USSCs were characterized for genetic and functional properties. Their in vivo functions were evaluated in a murine full-thickness excisional wound healing model and by bioluminescent imaging (BLI), using USSCs modified with a luciferase reporter gene. 

Results: CB-USSCs share several embryonic stem cell properties and could be induced to express hallmark genes of keratinocyte differentiation. USSCs constitutively express Col7A1, supporting their therapeutic potential in the treatment of patients with RDEB.  In the wounding model, a single USSC intradermal injection promoted epithelialization and facilitated formation and remodeling of epidermis, accompanied by a significantly accelerated rate of wound healing on days 6-10 post wounding (F_(1,168)=50.8 p<0.01). In vivo BLI revealed specific migration of USSCs from a distant intradermal injection site toward the wound, as well as following systemic injection. Temporal quantification on the total bioluminescence indicated an overall 59.9% signal loss over 3 days followed by a 95.06% loss at 1 week. The bioluminescence in the area of wound was then maintained at ~0.5-1% level till the end of the experiment (3 month). USSCs express several chemokine receptors that may mediate their migration to the wound, including CXCR4 (for SDF1), CCR7 (for CCL21) and PDGFRα (for HMGB1). In vitro chemotaxis assays indicated that SDF-1 significantly enhanced USSC migration at a concentration of 100ng/ml, while neither CCL21 nor HMGB1 showed significance even at a concentration of 10µg/ml. The effects of such chemokine/receptor interactions on USSC recruitment in vivo are now being investigated. 

Conclusion: These results suggest significant beneficial effects of CB-USSCs on wound healing and raised the possibility of USSC's therapeutic beneifit in the treatment of patients with RDEB.