With concerns about a worldwide shortage of cornea donors, exacerbated by an increase in corrective surgery, which renders corneas unsuitable for grafting, the results of the project, expected three years from now, are likely to be embraced by surgeons. The method will also reduce the risk of passing on transmissible diseases through surgery.
The development of tissue engineered corneas will also reduce the number of cosmeto-pharmacotoxicity tests carried out on animals. As project co-ordinator David Hulmes explained, the Draize test, carried out on rabbits in order to assess the effect of a chemical on the eye, is currently very widespread. If a desire to decrease animal suffering is not enough to persuade some companies to seek alternatives to animal models, European Union legislation banning the marketing of cosmetic products that have been tested on animals, due to be implemented shortly, should provide a stimulus.
The cornea is comprised of three layers, as Dr. Hulmes explained, the epithelium or outside layer, the endothelium or inside layer, and the stroma, which is in between and makes up the bulk of the cornea. The collagen, which constitutes 16 percent of the cornea, is made of layers of fibres. Within each layer, all fibres are parallel, but from one layer to the next, the direction of the fibres changes so that as one moves from the outside to the inside of the cornea, the fibres are pointing in all directions. This makes the cornea both transparent and biomechanically very rigid, as stated by Dr. Hulmes.
"The idea of the project is to construct the cornea using proteins made in culture", stated Dr. Hulmes. "This will produce human proteins in recombinant form and simulate as closely as possible the natural components." This technique is likely to eradicate the problems inherent to cornea grafting today. Two methods currently exist. One involves using polymers instead of cells to create a synthetic cornea, but this runs a high risk of being rejected by the surrounding tissue. The second involves tissue engineering, but uses a bovine source for the proteins, which introduces the risk of BSE, according to Dr. Hulmes.
The consortium, which involves 14 teams from nine different countries and includes basic scientists, ophthalmologists and small and medium sized enterprises (SMEs), has set itself a number of goals for the next three years.
The first is to carry out trials on a technique, developed by an Italian team involved in the project, for replacing the outside layer of the cornea. The procedure can help to restore sight following corneal burns caused by chemicals. Italian scientists have done this by taking stem cells from the patient's limbus, the area between the white tissue and the cornea, and then creating a sheet, a replica epithelium, which can be put back over the same patient's cornea.
The second goal is to develop a hemi-cornea, which could be used for replacing the outer half of the cornea. "There is a good chance of this working out by the end of the project", stated Dr. Hulmes. The final goal, described by Dr. Hulmes as "more ambitious" is to reconstruct the whole cornea. For this to happen, a suitable stem cell source for the endothelium still needs to be found, however.