PARIS: Blind mice have had their sight restored using stem cells transplanted into their damaged retinas, British scientists say.
The feat is being hailed as a breakthrough in stem cell technology, and the announcement comes a day after the Australian Senate voted to legalise research using human embyonic stem cells.
Reported today in the British journal Nature, the work focusses on replenishment of rod-like photoreceptor cells on the retina which detect light and send a signal to the brain via the optic nerve.
Photoreceptors are like the pixels on a TV or computer screen, but many times more plentiful – each eye has over a hundred million light-sensitive cells, equivalent to one hundred such screens.
These vital cells can be destroyed by diseases such as diabetes, age-related macular degeneration and retinitis pigmentosa, leading to irreversible blindness. Millions around the world are affected by these diseases.
Scientists have tried for several years to attack this tragic problem by transplanting stem cells – the versatile immature cells that grow into various tissues of the body. Until now, however, they have met with failure.
Previous research has used stem cells at a very early stage of development, which for some reason have failed to be integrated into the retina. This time the British team took a different tack, trying cells that instead of being very immature have been allowed to grow a little towards becoming photoreceptors.
They used these committed, but not yet fully differentiated cells to restore some vision to mice born with a genetic disease similar to retinitis pigmentosa. The most successful cells were taken from the retinas of baby mice which were between three and five days old, they found.
“We worked on the theory that cells at a later stage of development might have a higher probability of success upon transplantation,” said the team’s co-leader, Robin Ali, a professor of ophthalmology at University College London.
“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.”
Ali admitted he was surprised at how well the experiment had gone. “Remarkably, we found that the mature retina, previously believed to have no capacity for repair, is in fact able to support the development of new functional photoreceptors.”
The next step is to carry out more experiments on rodents to understand how and why this technique works, and whether the transplanted cells are safe and continue to work well over the longer term.
To accomplish the same results in humans, one obvious source would be stem cells taken from embryos, which are the most versatile stem cells of all. But Ali said this might not be necessary.
“Recent research has shown that a population of cells can be found on the margin of the adult retina which have stem cell-like properties – in other words, they are capable of self-renewal,” he explained. “These could be harvested through minor surgery and grown in the lab to become photoreceptor precursors before being re-implanted on the retina.”
One of the most exciting discoveries has to do with timing: the best moment to use the stem cells was after they had stopped dividing, indicating they had reached the desired “precursor” stage.
That breakthrough could have implications for transplanting tissue to people who have suffered nerve-tissue damage from accidents or degenerative disease, said Thomas Reh, a structural biologist at the University of Washington in the U.S.
“It may be that the specific time at which the particular cell is harvested will make all the difference to its potential for integration and functional differentiation following transplantation,” he said in a review of the study, also published in Nature. “Sometimes, timing is everything.”