Age-related Macular Degeneration: How Stem Cells Restore Vision

Age-related macular degeneration is one of the most common causes of visual loss in people over the age of 60, affecting 30-50 million people worldwide and more than 600,000 in the UK; the numbers are expected to rise with an ageing population. About 90 percent of the cases are dry AMD, which exhibit breakdown or thinning of retinal pigment epithelial layer (RPE) supporting the light sensitive photoreceptor cells. In AMD, the RPE cells stop performing their support functions, resulting in death of rods and cones and loss of central vision.

There is no treatment at present for the dry AMD. People take vitamin supplements, but dry AMD is progressive and over time the central vision worsens. However, there are drugs and surgical techniques that are effective in treating wet AMD. Since there is no cure for wet AMD, but it can be treated by injecting drugs into the eye to stop the growth of the abnormal blood vessels. These injections are needed regularly to preserve vision. Now Macula, a small area about 5.5 millimeters in diameter is responsible for reading, driving and facial recognition. It is a densely packed with photoreceptor cells called rods and cones that react to light and send electrical impulses to the optic nerve and to the brain. Behind the photoreceptors there is retinal pigment epithelium (RPE), which support the rods and cones by delivering nutrients from the bloodstream and removing waste that the rods and cones generate. Now the stem cell research is helping the scientists to understand how the different cell types in the retina function together, exploring ways to replace both rods and cones and the supporting RPE to regain vision.. In fact, eye is a good target for stem cell treatment. Replacing rods and cones is a challenging task, as these cells have to establish connections with nerve fibers that feed signals into the optic nerve and to the brain to interpret. Researchers are actively working on this approach, but ensuring new rods and cones to integrate with nerve fibers alongside the patient’s existing rods and cones is extremely complex process. Wet AMD occurs when abnormal blood vessels appear underneath the macula and is damaged by a deposit of fatty protein. The pioneering treatment is involved implanting an engineered patch of retinal pigments from the epithelium in the retina to replace those that are damaged. In this new approach, researchers took a stem cell - which is a single cell – and reproduced it many times, turning them into a perfect copy of RPE layer and placed onto a patch being inserted under the retina to replace the damaged cells of the patient with due to AMD. The study was published in Nature Biotechnology journal describing how the stem cell therapy can restore sight. Two people received stem cell treatment in Moorefield’s Eye Hospital London. First patient aged 86 with severe wet AMD, after 3 months of the surgery, his eyesight improved and he could read the newspaper. The 2nd patient was a woman in her 60s who also had wet AMD, was operated and monitored for 12 months. She reported improvement for her vision. After the operation she was able to read with her normal reading glasses. The RPE cells don’t need to connect with nerve fibers and to integrate with the existing retinal cells. New RPE cells could replace diseased RPE cells and take on some of their supportive functions. If the transplant is done before rods and cones are lost, new RPE cells may be able to prevent them from dying thus stopping the progression of the disease. RPE cells are also easier to make as a uniform cell type from stem cells, reducing problems associated with the generation of a uniform population of cells for transplantation. Since, it was the first experience of using an engineered tissue successfully, the results have given a real hope to the patients who suffer from AMD and other retinal degenerative disorders that the stem cells replacement therapy may be a reality in the near future. It was only an early clinical trial and the results have shown that the technology is moving in the right direction which represents the real progress in regenerative medicine and open the door to new treatment options for age-related macular degeneration. Moreover, it is a major milestone to cure blindness through implantation of a specially engineered patch of retinal pigment epithelium cells derived from stem cells.

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The results suggest that this new therapeutic approach is safe and provides good visual outcomes enhancing their quality of life. This project was established by a philanthropic donation from an anonymous American donor and the UK Medical Research Council (MRC) under the auspices of London Project to Cure Blindness, University College London (a best place in the world for Ophthalmic research) and Moorefield’s Eye Hospital,London. In Summary, the stem cell researchers are making great progress in their efforts to replace the RPE layer, which they believe will halt or even reverse the vision loss associated with AMD. Some researchers are using induced pluripotent stem (iPS) cells—tissue-specific cells (usually skin cells, but sometimes other tissue cells) those are re-programmed in the lab to behave like embryonic stem cells – to grow rods and cones or RPE cells. Some groups are using human embryonic stem cells while others are exploring RPE-specific stem cells that can be grown from the adult RPE, for example, from eyes donated to eye banks. Researchers are also working to determine that less mature cells have more self-renewal properties and possibly more potential to integrate and repair the rods and cones. Researchers are also exploring different methods to deliver stem cells from human embryo in the lab to be inserted into the diseased eye.

Dr. Jahanzeb Durrani.,(M.S)Ophth
Dr. Madiha Durrani FRCS (Eng)
Prof. M. Yasin Khan Durrani. FRC Ophth
Ph: 2222927/Ext 1255,
ophthalmologyupdate@gmail.com
www.ophthalmologyupdate.com