Mice with impaired vision had their eyesight restored when light-sensitive photoreceptors were transplanted into their eyes, researchers from University College London Institute of Ophthalmology reported in the journal Nature. The authors believe that transplanting photoreceptors may form the basis for new treatment to help patients with degenerative eye diseases see again. Photoreceptors are light-sensitive nerve cells that line the back of the eye.

The scientists took cells from young healthy mice and injected them into the retinas of adult mice that had no functional rod-photoreceptors. Several human diseases that cause loss of eyesight are due to a loss of photoreceptors; examples include diabetes-related blindness, retinitis pigmentosa, and age-related macular degeneration.

The eye has rods and cones – two types of photoreceptors. In this animal study, progenitor (immature) rod-photoreceptor cells were transplanted. Rod cells are crucial for seeing in the dark; they are very sensitive to light.

Within four to six weeks, the scientists found that the transplanted cells appeared to be working nearly as well as the normal rod-photoreceptor cells; they had formed the connections required to transmit visual data to the brain.

When having to find their way through a dimly lit maze, the mice with the transplanted rod cells fared well, while the untreated ones floundered. Their aim was to seek out a hidden platform.

Team leader, Prof. Robin Ali, said:

“We’ve shown for the first time that transplanted photoreceptor cells can integrate successfully with the existing retinal circuitry and truly improve vision. We’re hopeful that we will soon be able to replicate this success with photoreceptors derived from embryonic stem cells and eventually to develop human trials.

Although there are many more steps before this approach will be available to patients, it could lead to treatments for thousands of people who have lost their sight through degenerative eye disorders. The findings also pave the way for techniques to repair the central nervous system as they demonstrate the brain’s amazing ability to connect with newly transplanted neurons.”

Dr Rachael Pearson said:

“We are now finding ways to improve the efficiency of cone photoreceptor transplantation and to increase the effectiveness of transplantation in very degenerate retina. We will probably need to do both in order to develop effective treatments for patients.”

Dr Rob Buckle, head of regenerative medicine at the Medical Research Council, said:

“This is a landmark study that will inform future research across a wide range of fields including vision research, neuroscience and regenerative medicine. It provides clear evidence of functional recovery in the damaged eye through cell transplantation, providing great encouragement for the development of stem cell therapies to address the many debilitating eye conditions that affect millions worldwide.”

In a recent study, published in the same journal, the team had demonstrated that it is possible to transplant photoreceptor cells in the retina of an adult mouse, as long as they came from a donor mouse at a specific stage of development – before the retina is fully formed.

In this current experiment, they managed to transplant a larger number of cells into the recipient mice, and thus restore their vision.

Written by Christian Nordqvist