Endothelial cell transplantation and growth behavior of the human corneal endothelium

Background: The human corneal endothelium has a limited proliferative capacity in vivo. Until now it has only been possible to replace damaged endothelium by transplantation of a donor cornea. After establishing methods for the isolation and in vitro cultivation of human corneal endothelial cells, transplantation of these cells my be an alternative therapeutic option. Materials and methods: In this review methods for the in vitro cultivation of human corneal endothelial cells and their transplantation on the Descemet membrane of donor corneas are described. Results: In vitro proliferation of human adult corneal endothelial cells was achieved by the development of defined cell culture conditions, including supplementation of culture medium with specified growth factors and substances. Dependent on the culture conditions, as well as independent of them, in vitro cultured endothelial cells showed phenotypic changes and different proliferative behavior. Thus, molecular biological examinations revealed a different expression pattern of growth factor receptors in fibroblast-like endothelial cells (dedifferentiated) compared to typical endothelial cells (differentiated). Moreover, the proliferative capacity of the cells differed, dependent on their corneal location. Cells isolated from the peripheral part of donor corneas have a higher proliferative capacity than cells obtained from the central part. The propagation of corneal endothelial cells in vitro offered the possibility of their transplantation on donor corneas in an in vitro model. After transplantation, these cells formed a monolayer whose morphology and cell density depended on the differentiation of the cells. DNA synthesis was predominantly detectable in cells of the corneal periphery. Conclusions: Our findings are the basis of the following hypothesis: the periphery of the cornea represents a regenerative zone of the corneal endothelium. The fact that early after transplantation corneal endothelial cells form a monolayer on the natural extracellular matrix (ECM), which shows contact inhibition, suggests that inhibitory factors are released by the Descemet membrane that influence the proliferation of the cells. Further studies on the regulation of the proliferation and differentiation of human corneal endothelial cells in vitro and after transplantation might offer the possibility to establish a selective procedure for the treatment of corneal endothelial cell loss in the near future.