About Eye Diseases
- Are there stem cell therapies available for eye diseases?
- How close are we? What do we know about eye disease?
- What research is underway?
- Further reading on eye diseases
Are there stem cell therapies available for eye diseases?
To our knowledge, no stem cell therapy has received Health Canada or U.S. Food and Drug Administration approval for treatment of eye diseases at this time. Patients who are researching their options may come across companies with Web sites or materials that say otherwise and offer fee-based stem cell treatments for curing this disease. Many of these claims are not supported by sound scientific evidence and patients considering these therapies are encouraged to review some of the links below before making crucial decisions about their treatment plan.
For the latest developments read our blog entries here.
For more about stem cell clinical trials for eye diseases click here. (for printed version: http://goo.gl/2i14w)
How close are we? What do we know about eye disease?
- Vision loss can result from injuries or diseases that affect many different parts of the eye, including the cornea, retina and optic nerve.
- The cornea is the transparent bulge that covers the coloured iris and black pupil at the centre of the eye. The retina is the crucial light sensing part of the eye, and is made of multiple layers of photoreceptor neurons that relay light information from one to another. The retina exits the eye as the optic nerve which conveys all the visual information to the brain.
- Some eye diseases can be traced to a genetic defect while others come from complications arising from aging or from illnesses such as diabetes.
- Neurodegenerative diseases of the retina progressively affect the visual network that transmits signals to the brain, leading to visual impairment or blindness. Examples include age-related macular degeneration (AMD), retinitis pigmentosa, glaucoma and ischemic retinopathy.
- For some conditions, such as cataracts or corneal scarring, surgery is available to replace the cloudy lens or cornea. In contrast, the prognosis is poor for neurodegenerative diseases such as glaucoma and AMD.
- In all cases, early diagnosis is critical in trying to prevent or slow the onslaught of irreversible eye damage.
How can stem cells play a part?
There is currently no therapy for curing neurodegenerative eye diseases so the idea of transplanting stem cells to regenerate damaged cells holds great appeal. Stem cells have an unparalleled regenerative capacity and the flexibility to grow into hundreds of different types of cells. In theory, this means that they could be harnessed to produce an inexhaustible source of transplantable cells to repair the eye. This would be a tremendous boon in situations such as corneal transplants, where the demand overtakes the availability of donor tissue from cadavers. Other proposed strategies aim to take advantage of the properties of stem cells and their products to protect the many neurons in the eye responsible for vision.
Are there lots of groups working on developing a stem cell therapy?
There are countless research teams around the globe working to develop stem cell therapies for eye diseases. Their common goals are identifying the best stem cell contenders, understanding the environmental cues that can coax them into becoming photoreceptor neurons, and developing the large scale lab methods required for ramping up the cell production. Researchers agree that one of the biggest challenges will be to figure out how get the transplanted cells to make the right links with other neurons in the eye. These connections are an essential part of restoring the transmission of visual information to the brain.
One of the most important research contributions to date has come from Canadian researchers who identified retinal stem cells, first in the mouse and a few years later in humans. This discovery kindled hope in the research community that retinal damage, long considered permanent, might be reversible. The proof of principle for this concept came from experiments with mice and chicks, where transplanted retinal stem cells could integrate and make a variety of retinal cells, especially photoreceptor neurons.
Stem cell research for eye diseases is moving along a number of different routes and some of the successful stops along the way have been translated into early Phase 1 and 2 clinical studies. These are small trials designed to carefully test the safety of using stem cells to replace or protect cells within the eye. The advances to date in both pre-clinical and clinical studies are quite remarkable, and are providing the basis for a realistic future where stem cell therapies will be a viable option for restoring damaged vision.
Japan has approved the world’s first human tests using induced pluripotent stem (iPS) cells to treat age-related macular degeneration. Find out more here.
What research is underway?
Before basic stem cell research can be translated into the clinic for patients, it must first be rigorously tested and validated. For eye diseases, this involves transplanting stem cells and their products into animal models to test if vision can be improved. Stem cells from a wide variety of sources are being considered, both from inside the eye (limbal and retinal stem cells) and outside the eye (embryonic, induced pluripotent stem cells or iPS cells, bone marrow and neural stem cells). One of the challenges researchers are finding is getting the transplanted stem cells to ‘take.’ Some regions of the eye are more hospitable to transplants and successes have come relatively quickly, as in the case of grafting corneal tissue generated from limbal or embryonic stem cells. The retina, on the other hand, is not so welcoming to incoming cells. Researchers are working hard to overcome this by identifying the normal signals within the eye that work on stem cells to promote tissue repair. They are also developing new delivery methods (for example, biodegradable gels seeded with stem cells) that are able to promote more continuous integration of the transplanted cells into the eye.
The road to finding a stem cell therapy for eye diseases is paved with many challenges that will take time to overcome. But the wealth of information generated from labs around the globe is converging to help with the transition from basic research to the clinic. The results are very promising and in time may point to a viable stem cell therapy that accomplishes more than any of the current therapies by supplying an endless source of transplant material to restore vision in patients with injuries and diseases of the eye.
Current research using embryonic stem cells
In nature, the master stem cell is the embryonic stem cell because it can make an entire human being. In 2006, scientists devised a method for turning human embryonic stem cells into the outer layer of the retina, called the RPE. This is the crucial layer that absorbs light. Scientists were able to transplant this layer just under the retina in mouse models of macular degeneration. Improved vision in the mice proved that the transplanted cells were able to rescue damaged photoreceptor neurons. Moving forward, researchers are tweaking protocols and adding factors that guide more precisely the way to making RPE cells. This process involves careful screening of any unwanted cells that could cause tumours. In a landmark trial in 2012, human embryonic stem cell-derived RPE were transplanted into two people with different forms of macular degeneration. The researchers are guarding their excitement, however, because although both patients have shown a degree of improvement in vision, it is still uncertain whether the transplanted stem cells are responsible and if they may yet be rejected.
Current research using limbal stem cells
Limbal stem cells are also being investigated for their ability to regenerate corneal tissue in people whose eyes have been badly burned. Provided that one of the eyes is undamaged, a sample of the patient’s limbal stem cells can be harvested, grown in the laboratory and transplanted back into the patient’s burned eye. A recent trial tested this approach in over 100 patients and the before and after pictures were remarkable: the cloudy corneas scarred by acid burns became clear, transparent corneas. So far, the effects appear to be long-lasting (up to 10 years) and this bodes well for the future of using this therapy to regenerate damaged corneas.
Current research using retinal cells
Technological advances are paving the way for studies with retinal stem cells. An implantable device has been developed that can be loaded with human retinal stem cells, genetically modified to make a factor that protects neurons and supports their survival. The device can be implanted into the back of the eye where it releases a continuous supply of the protective factor. A big advantage of this method is that graft rejection is minimized because the genetically modified cells are trapped in the device and do not come into contact with the immune system. Early clinical trials in patients with various eye diseases have shown that the device is well tolerated and appears to slow the rate of vision loss. Other trials are testing for adverse effects, rejection or shifting from the site of implantation. This method points to a potentially safe way of delivering stem cells that could make protective factors to treat diseases such as glaucoma or AMD.
Further reading on eye diseases
Readers may wish to peruse the recommended sites and articles below for more information about eye disease and the possible applications of stem cells to treat these conditions.
AMD Alliance International (www.amdalliance.org)
The Foundation Fighting Blindness (Canada) (www.ffb.ca)
Foundation Fighting Blindness (www.blindness.org)
The London Project (UK) (www.thelondonproject.org)
National Eye Institute (www.nei.nih.gov)
Vision Action Plan (www.who.int/blindness/Vision2020_report.pdf)