An Overview of Corneal Stem Cell Transplantation

PracticeUpdate: You were one of the first groups to use stem cell transplantation for corneal disease. Can you give us a brief overview and history of stem cell transplantation for limbal stem cell deficiency?

Dr. Watson: Limbal stem cell deficiency treatment with transplantation really began with taking large pieces of the limbus, and these were from the fellow eye or a donor eye and placing them on the cornea that needed the stem cell replacements. But this really put the fellow eye at risk, and for donor tissue it wasn't always successful. People then moved to using smaller and smaller samples of limbal tissue to transplant to the eye that needed the stem cells. Then it was discovered that you could actually culture cells and then transfer cells alone rather than pieces of tissue to the ocular surface. Then it's also been discovered that you can actually use very small pieces of limbus from a fellow eye and these can be scattered on the ocular surface and function as stem cell transplants. And that procedure's called SLET. We're now at the stage where there's some exciting discoveries, where people are looking at new types of cells as cell sources for the limbal stem cells and new types of tissues for transplantation or carriers and scaffolds. We're looking to optimize outcomes for the future.

PracticeUpdate: Other than limbal stem cell deficiency, is there any other condition that might warrant corneal stem cell transplant?

Dr. Watson: Corneal scarring is currently a cause of permanent corneal blindness that affects all ages, and the world health organization has identified corneal scarring as a priority disease. And so this is a disease that we need treatments for and stem cells have been looked at it a way of treating the corneal scarring. This is a different type of stem cell to the limbal epithelial stem cell, it's a mesenchymal stem cell, and researchers have looked at injecting these cells into the corneal stroma. Another area that might benefit from stem cells is corneal ectasias. If tissue could be inserted containing stem cells, it may also correct the loss of tissue. Lastly, endothelial cells are now showing promise. I've recently read a paper looking at the five-year outcomes from 11 patients, where, in Japan, endothelial cells were injected into the anterior chamber in patients with corneal edema and the long-term results showed good outcomes with corneal clearing and vision.

PracticeUpdate: Of the many causes of limbal stem cell deficiency, are there some etiologies that are more amenable to treatment by corneal stem cells?

Dr. Watson: Limbal stem cell deficiency can arise from a number of causes. Unfortunately, the most common cause is a chemical injury, and this tends to occur in a young, working-age population. Now it can also follow severe diseases such as Stevens-Johnson syndrome and ocular cicatricial pemphigoid. The conditions that do better are those where there's not ongoing inflammation and destruction on the ocular surface. But generally, no matter what the cause, the limbal stem cell deficiency clinically presents the same. And so there is equal hope from a variety of conditions that have caused the deficiency, but studies have shown that the more scarring there is on the oculus surface and ongoing inflammation, the poorer the outcomes.