A team of scientists has successfully restored vision in a monkey by repairing a retinal hole with a patch derived from human stem cells. This significant achievement, detailed in the journal Stem Cell Reports, represents a major step forward in retinal transplant technology.
The retina, a layer of light-sensitive cells at the back of the eye, can suffer damage from various diseases, leading to vision loss and blindness. While some conditions can be treated by moving peripheral retinal tissue to the center, this often results in blind spots in peripheral vision.
The study focused on repairing a macular hole, a rare condition where a hole forms in the center of the retina, specifically in the fovea, which is crucial for central vision and precise focus. These holes often occur when the gel-like substance inside the eye retracts, causing tears. Approximately 90% of such cases can be treated surgically, but 10% of patients still experience blurred vision or blind spots.
Dr. Michiko Mandai, director of the research center at Kobe Eye Hospital in Japan, has been developing miniature retinal versions grown from stem cells for years. These retinal organoids are sheets of light-sensitive cells derived from stem cells capable of developing into any tissue type in the body.
In 2019, Mandai had the opportunity to test these sheets on a monkey with a macular hole, which had been unable to complete visual tasks. The monkey was transferred to Mandai's lab for surgery. The team grew a retinal sheet from human stem cells and applied it to the monkey's eye, similar to patching a torn garment. The transplant was safe and effective, with the monkey's visual performance improving post-surgery. The only complication was mild rejection of the patch after four months, which was resolved with steroid injections to suppress the immune response.
Mandai noted that rejection might be due to the interspecies nature of the transplant, stating that a human-to-human tissue transplant would likely carry a lower risk of immune reaction.
Six months after the operation, researchers removed the monkey's eye for examination and found new visual cells had developed: rods, essential for night vision, and cones, crucial for color perception. However, they could not confirm whether connections had formed between the transplanted cells and the monkey's original cells.
Mandai explained that the improvement in vision for a macular hole comes from restoring the eye's structure and function after closing the hole. It remains unclear if the transplanted cells contribute to visual function, but this may not be necessary, as vision can improve simply by closing the hole.
The Mandai team continues to research using retinal organoids to treat other conditions. Last year, they reported results from a clinical study where these sheets were used on human patients with retinitis pigmentosa, a genetic disease causing progressive vision loss. After two years, the grafts integrated safely into the patients' retinas, and vision loss progressed more slowly than in untreated patients.
The team is also studying the function of transplanted retinal tissue in animals to determine if the grafts can support functional cells.