Retinitis pigmentosa and macular degeneration are two vision crippling conditions that can result in blindness. Researchers with roots in London and Oxford recently found a way to restore vision in those suffering from severe photoreceptor loss using rod stem cell transplants.
The inspiration for trying such a large scale de novo vision restoration was a previous study that showed blind patients still being able to read with direct subretinal stimulation. This meant that those suffering from macular degeneration and such still had all the vision circuitry in tact, but were missing photoreceptors to catch the light.
Retinitis pigmentosa (RP) and macular degeneration (MaD) are two conditions that result in the loss of a large number of photoreceptors, cells that detect light and allow for sight, in the eye. RP affects 1 in 4,000 people in the U.S. as it is mostly acquired through genetics, and MaD affects about 20% of those age 66-85 as it is usually age acquired.
This study involved rd1 mice, which were those who quickly developed severe human RP and lost all rods by three weeks of age. Rods are photoreceptors that make up most of the retina and have high sensitivity to light yielding vision at night. Donor Tg mice were those with green fluorescent protein expressed in their rod precursor cells, so the cells could be tracked when put in the rd1 mice.
After transplanting the donor cells, analysis was done to test longevity and effectiveness in acting as normal rod cells. At week 12, 33% of donor cells had survived in the 12 mouse eyes assayed. 76% ± 18.9% of these cells were found expressing Pde6b and other mature rod-specific markers. This meant the rod precursor cells successfully grew into mature rod cells. Furthermore, bassoon was found being expressed by these cells. This is a protein only expressed by rod cells actively linked to nerves indicating successful linkage to the underlying vision pathway back to the brain. Finally, the pupils were tested for their response to light. Average pupil constriction doubled (76.5 ± 3.9% before transplant to 38.5 ± 4.6% post-transplant) indicating positive light response by donor rod cells.
Researchers found successful transplantation, maturation, and connection of these donor rod cells into the rd1 mice who originally had no rods at all. Although results of this study yielded a small number of complete transplant to connection donor cells, the findings show that it is possible to restore vision to the blind using cell transplants.
Mandeep S. Singh, Peter Charbel Issa, Rachel Butler, Chris Martin, Daniel M. Lipinski, Sumathi Sekaran, Alun R. Barnard, Robert E. MacLaren. Reversal of end-stage retinal degeneration and restoration of visual function by photoreceptor transplantation. PNAS, 2013.