In an on-line publication of the New England Journal of Medicine on June 23, 2010, Paolo Rama and colleagues described a study in which patients who were blind because of “corneal burns,” or burns to the outer surface of the eye, were given back their sight. The technique they used to restore sight to these patients was stem cell transplants.
The transparent covering of the eye, which is call the cornea, transmits light through the surface of the eye to the lens. The cornea contains no blood vessels, and this keeps it clear and transparent. Because the cornea contains no blood vessels, corneal cells are constantly replaced by a stem cell population called limbal stem cells lie at the border between the cornea and the whites of the eye, which is known as the “conjunctiva.” These limbal stem cells divide and spread throughout the cornea until they are sloughed from the cornea by blinking or tear action, only to be replaced by limbal stem cells.
If the cornea is burned by chemicals, sparks, or other insults, damage to the limbus can prevent it from constantly regenerating the cornea. Such burns can cause the cornea to cloud and induce the formation of blood vessels in the cornea. This makes the cornea opaque and prevents it from transmitting light to the lens.
Several papers have shown that transplanting limbal stem cells can rejuvenate the corneal limbus and the cornea too. However, if the cornea and its limbus is damaged, then where can the clinician go for limbal stem cells?
Some papers have describes the use of corneal limbal stem cells from cadavers. These so-called allogeneic limbal stem cell transplants have problems. Finding enough limbal stem cells to transplant is the first problem and the inability of these stem cells transplants to properly integrate into the eyes of the patients are just two of the major ones. Other researchers have tried taking limbal stem cells from the undamaged eye and transplanting them into the damaged eye. While this technique, which is called autogenous limbal stem cell transplants, have a better success rate than the allogeneic limbal stem cells transplants, damaging the good eye to help the blind eye is problematic.
How could physicians get around this problem? The best answer for now seems to be culturing limbal stem cells from patient’s own eyes and growing them in the lab. This provides large quantities of limbal stem cells for transplantations.
In this New England Journal of Medicine article, dozens of people blinded or injured by chemical burns had their sight restored by transplants of stem cells from their own eyes. The limbal stem cells were grown on fibrin and used in transplantations to heal the opaque corneas of these patients. This is another victory for somatic stem cell treatments.