Retina Stem Cells May Restore Sight
Stem Cells Harvested in Later Stage of Development Restored Visual Function in Mice
Nov. 8, 2006 - Timing may be everything when it comes to restoring lost
eyesight through stem cell therapy.
In a new study, retina stem cells harvested at a particular stage of
development successfully restored visual function in mice affected by a common
cause of blindness also found in humans, known as photoreceptor loss.
Although earlier attempts at retina transplantation using embryonic stem
cells failed, the researchers say that by using stem cells at a later stage of
development, they were able to repair damaged retinas in the mice.
"We worked on the theory that cells at a later stage of development
might have a higher probability of success upon transplantation" says
researcher Robin Ali of the University College London Institute of
Ophthalmology in a news release.
"And we show here that cells taken from the peak rod genesis stage of
development, when the retina is about to be formed, can be successfully
transplanted and integrate into the adult or degenerating retina," says
Researchers say the findings challenge the assumption that early embryonic
stem cells are the best option for tissue repair and may have implications for
other types of stem cell therapy and transplantation.
Photoreceptor loss is a form of retina damage implicated in many causes of
blindness in humans, from age-related macular
degeneration to diabetes.
This type of blindness has been considered irreversible because the mature
retina was believed to have no ability to repair itself or to support
development of new photoreceptors, which are light-sensing cells.
Previous attempts to generate new photoreceptors using brain and retina stem
cells - cells with the ability to become a number of different types of cells
-- have failed because the stem cells didn't integrate into their new
environment or develop into photoreceptor cells.
In this study, researchers took stem cells at later developmental stages and
transplanted them into adult mice with photoreceptor loss.
Their results suggest there is a particular time window of development for
transplant success in restoring sight to the blind mice.
In the study, cells harvested during this window were able to form new
connections within the mature retina and improve the blind mice's visual
responses to light.
Older May Be Better
In a commentary accompanying the study in the journal Nature,
Thomas A. Reh, of the University of Washington School of Medicine, says the
results provide hope for cell-based treatments of retinal disease.
The study also has implications for transplantation strategies in other
areas of the central nervous system, he says.
The specific time a cell is harvested may make all the difference in stem
cell therapy and transplantation success, Reh says.
Rather than injecting undifferentiated stem cells into damaged tissue, using
precursor cells from a later stage of development -- ones already
"programmed" to become retina or some other type of cell -- may be more
successful, he says.
"These results provide the best evidence so far that cell-replacement
therapy may be possible," writes Reh.
"But there's a catch," he adds. "If this scenario were to be
applied to humans, one would have to obtain newly generated [photoreceptor]
rods from the state of development comparable to postnatal days 3-7 in the
mouse [as in the study].
"This is likely to be in the second trimester [in humans] and is clearly
not feasible," writes Reh. Harvesting such cells would mean taking them
from a fetus or aborted fetus three to six months into a pregnancy.
However, recent research suggests it might be possible to generate such
cells from human embryonic stem cell lines under the right conditions.