Culture de tissus cornéens en boite de Piétri...

[V2F]

Florence nous a communiqué un article paru dans la Montagne :

Une nouvelle technique de greffe de cornée mise au point par une équipe japonaise pourrait éviter les effets indésirables de la transplantation classique, notamment les gonflements dus aux sutures ou le rejet de la cornée greffée. Cet technique prometteuse ne précise pas si elle s'adaptera, un jour ou l'autre, au kératocône (Ndlr)

Le Pr Teruo Okano, de l'Université médicale des femmes de Tokyo, a mis au point une technique consistant à faire pousser une cornée à partir d'une petite quantité de cellules, dans une boîte de Pietri, espace fermé placé dans un incubateur. La cornée obtenue est placée ensuite à température ambiante, retravaillée pour être greffée dans l'oeil, sans le moindre point de suture. La cornée est la tunique antérieure et transparente de l'oeil.

"Nous pouvons fabriquer un nombre illimité de ces cornées pour des transplantations", explique Teruo Okano. "L'opération est simple, elle ne dure que cinq à dix minutes, la nouvelle cornée tient toute seule".

Ce procédé a été expérimenté pour la première fois en décembre 2002. Douze personnes au total ont pu bénéficier de cette greffe.

Au Japon, les essais cliniques sont limités, et la diffusion de cette technique à grande échelle pourrait prendre deux à trois ans, a ajouté le Pr Okano. Si elle était autorisée, elle pourrait aider des dizaines de milliers de personnes partout dans le monde, d'autant que souvent les donneurs manquent et que les listes d'attente sont longues.

On ne sait pas combien de temps ces greffes vont tenir, mais une chose est sûre, les patients se portent tous bien aujourd'hui, souligne le chirurgien.

Le Pr Okano et Koji Nishida, son collaborateur de l'hôpital universitaire d'Osaka, décrit les résultats des essais menés chez l'animal dans le numéro de février de la revue scientifique américaine Transplantation. Ils devraient publier prochainement les résultats des essais menés chez l'homme.

Faire pousser des cellules dans le but de les transplanter n'a rien de nouveau. Les greffes de peau se pratiquent depuis de nombreuses années chez les grands brûlés, et les scientifiques ont récemment fait des progrès dans la mise au point de grandes quantités de cornées et d'autres tissus. Mais fabriquer des cornées en laboratoire était difficile parce que leur culture nécessite une enzyme qui par ailleurs dégrade les protéines nécessaires à la cornée pour se fixer sur l'oeil transplanté.

Cette recherche représente un immense travail, estime Alan Russell, directeur de l'Institut McGowan, de l'Université de médecine régénératrice de Pittsburgh. "Elle permet littéralement aux aveugles de recouvrer la vue".
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Autre article lu sur Internet:

Japanese scientist's lab dish offers doctors tool for restoring sight
Sunday May 23, 2004
By KENJI HALL
Associated Press Writer
TOKYO (AP) Cornea transplants can give sight back to the blind, but they are notoriously tricky: Sutures can cause swelling. The body can reject the tissue. Each transplant requires a large mass of cells taken from a healthy eye.
Now a Japanese surgeon has come up with a method being hailed as a possible solution for all those troubles.
Teruo Okano, at Tokyo Women's Medical University, has developed a procedure allowing doctors to grow an entire cornea from a tiny speck of cells in a petri dish in an incubator, peel it off at room temperature, and place it directly on the eye without a single stitch.
``We can make an unlimited number of corneas for transplants,'' Okano says. ``And the operation is so simple in five to 10 minutes, the new cornea sticks by itself.''
The experimental procedure was first performed on a human in December 2002, and a total of 12 people have undergone it to replace a cornea, which is the transparent tissue that covers the iris and pupil at the front of the eye.
But while limited trials of unapproved techniques are allowed in Japan, approval for large-scale human clinical trials could take months and full approval for medical use is at least two to three years away, Okano said.
If accepted, the procedure could help tens of thousands of patients in the United States and tens of thousands more in other nations like Japan, where donor cadavers are scarce and waiting lists are long. In Japan, doctors say about 20,000 people need a transplant every year but only about 1,800 get one.
So far, Okano's transplants have worked for all 12 patients operated on at Osaka University Hospital in western Japan. It's not clear how long the corneas will last, but the transplants are still working in all of the patients, he said. The strength of vision varies widely from patient to patient.
Okano and his collaborator at Osaka University Hospital, Koji Nishida, described the results of animal studies in the February issue of the U.S. science journal Transplantation. They plan to submit the results of their human trials to an English-language journal soon.
Other scientists give the research high marks.
Alan Russell, director of the McGowan Institute for Regenerative Medicine at the University of Pittsburgh, said corneal cells grown with Okano's method peel away from the dish so easily it is like removing a Post-it note.
The research ``is tremendous work,'' Russell said. ``Literally, it makes the blind see.''
Normally, doctors transplant cornea cells directly from one person's eye to another, taking about half the cells of a donor's limbus, the circle where the clear cornea turns to white.
But Okano's technique might someday replace person-to-person transplants with tissue bioengineering.
Growing cells for transplants is nothing new. Skin grafts have been around for years, and scientists recently have made progress in research designed to mass produce corneas and other tissue.
But making corneas in a lab dish has been difficult because the best way to pull them off the dish is with an enzyme and that often kills the binding proteins the cornea uses to anchor itself when transplanted onto an eye.
Okano solved that problem with a heat-sensitive polymer coating on the petri dish in which a new cornea is grown. At higher temperatures, the cornea sticks to the dish; at room temperature, the cornea can be peeled off without harming its binding proteins. Once transplanted, those proteins allow the cornea to adhere to the surface of the eye.
The method could give doctors a way to grow enough corneas for several patients from one person's minuscule amount of donated tissue, Okano said.
It also could allow patients to act as their own donors, he said. That would reduce the risk of donor rejection, which occurs when the body tries to defend itself against an invasion of foreign cells.
Between December 2002 and this past January, Okano and Nishida recruited 12 patients with damaged epithelial stem cells in the limbus. Such patients comprise about 20 percent of those awaiting cornea transplants.
Okano and Nishida declined to say how the patients lost their sight, saying they would do so in their scientific paper on the human trials. But people who need such transplants mostly have been blinded by disease, burns or contact with caustic chemicals.
Epithelial stem cells constantly generate new cells to cover the body's outer surface and line the inner walls of the mouth, lungs and stomach. In the eye, the stem cells replace dead corneal cells. The cornea can become cloudy or be overrun by capillaries from the white of the eye if those stem cells die.
Okano's team made each test cornea from an area of limbus stem cells about three-hundredths of a square inch the size of a single printed letter in a newspaper.
Once the cornea grew to about a half inch across on top of a doughnut-shaped membrane, it was lifted off the dish with tweezers and placed on the patient's eye, Okano said. The cornea fused with the eye within 10 minutes and the membrane was cut off, he said.
``The adhesive proteins act as a kind of bio-glue,'' Okano said.
Nishida, an ophthalmologist, said all 12 patients, who had been legally blind, could see after the procedure. However, their vision since the operations has varied widely, depending in part on how much sight was impaired before the operation.
The only side-effect was temporary inflammation, and none so far has complained of deteriorating vision or corneal tearing, Nishida said.
Okano said he set up CellSeed Inc. three years ago to market his research and is in talks with two major U.S. drug makers which he declined to identify about seeking regulatory approval in the United States.
CellSeed plans to recruit new donors and build up its own self-renewing supply of corneal cells, he said.On the Net:
CellSeed Inc.: http://www.cellseed.com