What would you rather lose, your sense of taste or touch? Your sight or your hearing? Thankfully, for most of us the question remains theoretical. We can try to imagine what it would be like to live without our senses, but we always open our eyes and uncover our ears when the game is over.
However, approximately 1 in 2,000 people worldwide don’t have that option. They suffer from conditions called inherited retinal diseases (IRDs). People with IRD are born with a genetic weakness in their eyes. They experience retinal deterioration which ultimately leads to blindness. Up until several years ago, IRD patients had no hope of ever seeing again. However, advances in gene therapy may one day offer a treatment that can slow this form of optical degeneration or prevent it.
What is gene therapy?
Genes are the body’s building instructions that are passed from parent to offspring. They tell the body how to make its building material (lipids, proteins, and carbohydrates) and how the body should function. While much of one’s genetic makeup is fixed at birth, some genes can be changed by environmental factors. When a gene is deliberately changed or replaced to cure a genetic disease, this is referred to as gene therapy. There are three methods to carry out gene therapy:
- Viruses are very good at injecting their genetic material into body cells. However, if the virus’s genetic material is replaced with healthy genes, those genes can be injected into the cell instead. Then, when the cell reproduces, the new cells will also carry the healthy genes. This will stop and reverse the disease harming the body.
- Stem cells are a type of cell that can become any kind of cell. In a lab setting, stem cells will be modified to express a new gene that can fight disease. This new cell will be grown in large numbers and reintroduced to the patient’s body.
- Liposomes are pouches in the body made of fatty material, similar to the cell membrane. Disease-fighting genes can be placed in liposomes and then pass into the cell’s DNA to create a permanent change in cell function.
For many types of genetic diseases, viruses are the most common conduit to transplant healthy genetic material. However, there are many risks in using viruses as vectors. Treatments gone wrong can lead to infections or tumors. They can also trigger an attack response from the immune system. Therefore, researchers have been studying stem cells to find a safer and more reliable replacement for viruses. Regardless of the vector in use, gene therapy is currently in its experimental stages and is not used in mainstream clinical practice.
How can gene therapy be used to cure IRD?
Scientists have made progress in using stem cells to treat IRDs. Stem cells are raised and converted to retinal photoreceptor precursors. Then, they are implanted into the fovea to replace the damaged photoreceptors. Researchers at the Yong Loo Lin School of Medicine have met with some success implanting retinal photoreceptor precursors in cynomolgus monkeys. They surgically implanted 11 monkeys with stem cells derived from humans. Of the 11 implantations, 6 monkeys demonstrated an improvement in retinal ability. While this study didn’t produce perfect results, it does show that stem cells can be successfully implanted into higher-level animals. Previous studies have worked with pigs and rabbits which do not have a fovea. Performing the transplantation with monkeys, who have a similar eye structure to humans, is another step toward creating therapies for humans.
While there is still some way to go before scientists develop a cure for IRDs, every new discovery is a promise for the future. With the help of gene therapy and stem cell research, there may be a time when the blind can open their eyes and see the light, colors, and shapes that have been hiding from them all this time.
Written by Chani Bonner