Characterization of the chick chorioallantoic membrane model as a short-term in vivo system for human skin

We report on the cultivation and characterization of human skin on the chorioallantoic membrane of chicken eggs with the aim of replacing animals in short-term investigations in dermatology. Adult human split-thickness skin was grafted onto the chorioallantoic membrane of 5-day chick embryos. Grafts and surrounding host tissue were examined daily by in vivo stereomicroscopy and in histological sections and were characterized using a panel of monoclonal antibodies. The skin grafts were completely incorporated into the chorioallantoic membrane 2 days after transplantation. A remarkable angiogenesis occurred towards the grafts. Skin tissues revascularized within 2 or 3 days by reperfusion of the existing graft vasculature. Anastomosis of host and graft blood vessels occurred and the transplanted skin was nourished by the host blood supply as indicated by nucleated chick erythrocytes in the skin vessels. The skin grafts on the chorioallantoic membrane preserved an almost entire human phenotype. Besides a fully differentiated human epidermis and dermis containing all the cellular and extracellular constituents such as skin immune cells, capillary vessels composed of human endothelial cells were enclosed by a basement membrane of human origin. The integrin expression pattern formed in human skin transplants 5 days after grafting was identical to that of human skin controls before grafting.