Scarless wound repair: a human fetal skin model.

Animal studies demonstrate that the fetus heals cutaneous wounds by reformation of normal tissue architecture without scar formation. We have developed a new model to study human fetal skin wound healing. Grafts of human fetal skin placed onto athymic mice retain the morphologic features of normal development, although they differentiate at an accelerated rate when placed cutaneously compared to subcutaneously. Full-thickness skin grafts from human fetuses at 15 (n = 12), 17 (n = 11), 18 (n = 25), 19 (n = 20) and 22 (n = 13) weeks gestational age were placed onto athymic (nu/nu) mice in 2 locations: (1) cutaneously onto a fascial bed and thereby exposed to air or (2) subcutaneously in a pocket under the murine panniculus carnosus. Linear incisions were made in each graft 7 days after transplantation. Grafts were harvested at 7, 14 and 21 days postwounding and analyzed histologically for scar formation. By hematoxylin & eosin and Mallory's trichrome stains, complete epidermal and dermal graft wound healing without scar formation was demonstrated in the subcutaneous grafts at each gestational age studied. In contrast, scar was seen at all time points in the cutaneous grafts in both the incisional wound and at the interface of the fetal human skin graft and adult mouse skin, regardless of fetal skin gestational age.(ABSTRACT TRUNCATED AT 250 WORDS)