Ocular Surface Disorders — Reconstruction of transparent tissues —

With the establishment of human embryonic stem (ES) cell lines, the idea of transplanting stem cells differentiating into blood cells, nerve cells, and muscle cells is gradually being realized. If stem cells established from human ES cells become available, not only transplantation medicine, but also the quality of medicine as a whole would be expected to change. If extracorporeal generation of tissues or organs by means of tissue culture succeeds, it will pave the way for regeneration medicine, in which not only transplantation of cells, but also replacement of whole diseased organs or tissues may become possible. Stem cell transplantation that heralds the beginning of regeneration medicine has been widely applied clinically in the form of blood stem cell transplantation (bone marrow transplantation). In the case of somatic cells, progress has been made in research on stem cells differentiating into epithelial cells, including those of the skin and intestinal mucosa. Recently, the presence of stem cells in corneal epithelial cells of the eye was identified, and transplantation of the corneal epithelial stem cells has been initiated. In the year 2000, the production of epithelial sheets by in vitro incubation of stem cells and its clinical application to transplantation were reported. Another ongoing project attempts to produce each of the three layers comprising the structure of the cornea separately, and to combine these to produce an artificial cornea. Clinical application of reconstruction of transparent tissues based on research on corneal epithelial stem cells is rapidly expanding. In the near future, transplantation of corneas that were regenerated using ES cells or autogenous stem cells may become possible, without the need for dependence on the supply of stem cells from eye banks.