Exploring the Promise of Transplants to Restore Vision
January 22, 2013 - The Foundation Fighting Blindness funds several research programs working to make sight-restoring transplants a reality. In these programs, scientists are using stem cells to create new photoreceptors for transplant.
When might it be appropriate to use transplant cells? Will they work for people with different types of retinal conditions at different stages of disease? Our hope is that stem cells will provide a sight-restoring treatment for a broad range of people. Recently, two British studies have provided encouragement for that perspective.
We spoke with Dr. Derek van der Kooy (at right) who helped us understand this research news. Dr. van der Kooy's research is currently funded by the Foundation Fighting Blindness, thanks to a generous donation from the Krembil Foundation.
The studies came from the laboratories of two British scientists: Dr. Robin Ali and Dr. Robert MacLaren. In both cases, their studies do not use cells derived from stem cells. Instead they use rod photoreceptors extracted from the eyes of young mice immediately after the rod photoreceptors are born.
“What my lab is trying to do in a culture dish, from adult stem cells, is to make transplantable cells that are as good as these rod photoreceptors,” says Dr. van der Kooy. “This work is wonderful proof-of-principle work, because it demonstrates what is possible with transplanted cells in ideal conditions.”
One of the things that “is possible” is to restore at least some vision to a mouse where all of the vision cells have been completely destroyed. In the MacLaren study, the scientists tested transplants in a type of retinal disease where all of the photoreceptors are destroyed in only a few weeks. This is similar to the very late stages of retinitis pigmentosa and other severe retinal conditions.
“These results are amazing,” says Dr. van der Kooy. There are no original photoreceptors present to guide the new cells, but the transplanted cells are able to create a new layer of the retina, and the majority of the cells actually orient themselves correctly and are able to restore some vision.
“There are interactions between cells in the retina,” says Dr. van der Kooy, “and previous studies have suggested that this can create a toxic environment that might kill off many of the transplanted cells. We have seen this in our own studies. However this research suggests that if we can grow and transplant the cells at exactly the right time, they can survive. It will be possible to restore sight even if all light-sensing cells have been destroyed by disease.”
The second British study, led by Dr. Ali, tested transplants for different conditions. They used transplants of rod photoreceptors to treat mice with six different retinal diseases:
- Four types of retinitis pigmentosa
- One type of Leber congenital amaurosis
- One type of stationary night-blindness
These mouse versions of the diseases are not identical to human types, but the study allowed the scientists to see how transplant cells would react to different types of cell damage and different severity of disease.
The research found that transplants were successful to some degree for all conditions. The transplanted photoreceptors made connections with existing nerve cells and restored vision.
Several different potential barriers to transplants were observed, observations that Dr. van der Kooy says also have been made by other scientists. For example, in some types of less severe retinitis pigmentosa, there may still be a protective membrane around the photoreceptor layer which can interfere with getting photoreceptors to the right place. Certain kinds of scarring and cell changes in a damaged retina may also inhibit transplanted photoreceptors.
Again, all of these barriers appear to be surmountable. Dr. van der Kooy envisions that we will someday do different types of transplants in different situations, eventually involving all three types of cells which can be damaged by retinal disease:
- Retinal pigmented epithelial (RPE) cells, which support and nourish the light sensing photoreceptors
- Cone photoreceptors, responsible for fine central vision
- Rod photoreceptors, responsible for night vision and peripheral vision
A human trial testing transplants of RPE cells is already underway in the United States. Such transplants may help protect and restore vision, but they will not reverse severe vision loss. That will require transplants of photoreceptors as well.
“For macular degeneration, where most of the cells lost are cones, we would transplant cones,” says Dr. van der Kooy, noting that his laboratory is already collaborating with Dr. Gilbert Bernier in Quebec, another Foundation Fighting Blindness funded scientist whose work focuses on cone cells.
“For people in the earlier stages of retinitis pigmentosa, where substantial vision has been lost, but not the fine central vision, we would transplant the rod cells my lab has worked with,” he says. Watch this video, for more about Dr. van der Kooy’s transplant studies.
“Finally for people with severe vision loss, we might transplant all three types of cells, or perhaps sheets combining different cell types.”
These recent British findings provide further evidence of what is possible. Your donations are helping Dr. van der Kooy and others to make these possibilities, a reality.