"Healing
Eyes with Stem Cell Transplants."
by Dan Ullrich
A cornea and external eye disease specialist
at the Medical College of Wisconsin Eye Institute is breaking
new ground in the treatment of eyes damaged by injury or disease
by transplanting stem cells directly onto the cornea. The transplanted
corneal stem cells divide and multiply, replacing missing cells
and warding off a skin-like tissue (the conjunctiva) that in some
cases invades the cornea and covers it like a blanket.
While the new procedure is still in its infancy,
it has shown great promise in managing corneal disease for people
who suffer limited vision or blindness. In the case of Michael
Jent, a maintenance engineer who was severely burned on the job
by the highly caustic chemical sodium hydroxide, the procedure
has restored enough vision in one eye to enable him to walk without
a white cane and even to drive.
"A stem cell is a cell that can go on to
become, basically, a different cell," said E.
Lee Stock, MD, Medical College Professor of Ophthalmology,
who is leading the work in corneal stem cell transplants at the
Eye Institute. "Basic stem cells are embryonal cells that
then go on to become all of the cells of the body."
Stem cells have the remarkable potential to develop
into many different cell types in the body. Serving as a sort
of repair system for the body, they can theoretically divide without
limit to replenish other cells. When a stem cell divides, each
new cell has the potential to either remain a stem cell or become
another type of cell with a more specialized function, such as
a muscle cell, a red blood cell or - in this case - a corneal
cell.
Good Transplant Territory
The cornea itself is a very successful tissue to transplant, consisting
as it does of three clear layers and no blood vessels. As cornea
transplants have become more common and "tried and true,"
and are currently performed without the need to match donor cells
to recipient cells, Dr. Stock and colleagues with expertise in
transplanting other types of stem cells elsewhere in the body
are moving into a new frontier by taking advantage of lessons
learned and the fact that the cornea is such good territory for
stem cell work.
Keeping the cornea clear of conjunctiva, the
mucous membrane that lines the inner surface of the eye and eyelids,
is the essential goal of corneal stem cell transplants.
"If you injure your cornea - for instance
by a sodium hydroxide burn - the cells should start to grow and
bring new corneal cells in," notes Dr. Stock. "However,
if the cells are destroyed, then the conjunctiva will grow over.
Then, instead of having a clear cornea that you can see through,
you have a cornea that is protected but doesn't transmit light.
"What we have to do is to find a new cell
to replace the damaged ones, but it has to be a stem cell or equivalent.
We just take the same cells from a donor and we put them in place
of the cells that have been damaged."
Work in Progress
Corneal stem cell transplants are complicated and must often be
repeated to achieve optimum results for the patient. As the procedure
is refined, and as the quality and quantity of available stem
cells increases, Dr. Stock said, outcomes will improve. Dr. Stock
uses devices and techniques still in development to remove stem
cells from donor corneas and then transplant them to the eyes
of patients.
"In our early transplants we just took a
few pieces and sutured them in place," said Dr. Stock. "We
got it to look more normal, but it still wasn't cornea. What I
started to do was, instead of taking little pieces, used a (specimen)
that looks like a section of a tire that goes around that whole
part of the eye - where the stem cells are - then took out the
abnormal cells and put in the new ones. "
Dr. Stock noted the work of Dr. Ed Holland in
Cincinnati, who has applied stem cells in patients with aniridia.
"Aniridia is a disease where the patient doesn't have an
iris; it's hereditary, but also they don't have normal corneal
stem cells and they get vascularization (abnormal or excessive
formation of blood vessels) of the cornea.
"In aniridia you get a clouded cornea in
addition to all the other problems and you have stem cell deficiency,"
he said. "What Dr. Holland suggested was doing the same thing
as I described but instead of taking a 'tire' he did three halves
to give more cells, and so we switched to that technique."
The number of people who will benefit from corneal
stem cell transplants is not very large as yet, but the difference
the procedure can make in the lives of those candidates can be
profound. "We're averaging one (stem cell transplant) every
month or two," said Dr. Stock. "It's effective to a
certain extent. For instance, in Michael Jent's case it's hard
to judge because he'd probably be totally blind without it. His
vision is not great vision, but for him it's the difference between
being mobile and immobile. The vision isn't as good as we'd like
it to be, but he's happy to be able to get around."
Regarding the present and the promise of corneal
stem cell transplantation, Dr. Stock is pleased with the progress
so far. "On the whole it is successful, despite a lot of
difficulty. I think the future is really great because, first
of all, we collaborate with the stem cell people and they're always
making more inroads. They've been getting better cells, more concentrated
cells, and there are other ways to do this even now - such as
growing the cells in a culture first and then transplanting them.
That's not been proven yet, but has a lot of potential for improving
things even more." |
