Gene therapy of blindness: simple, effective and non-invasive

Gene therapy offers a simple and effective way to restore vision

LifeSciencesToday based on materials from UC Berkeley: Researchers develop easy and effective therapy to restore sight

Scientists at the University of California at Berkeley (University of California, Berkeley) have developed a simpler and more effective method of delivering genes to eye cells, which can significantly expand the possibilities of gene therapy in restoring vision in patients with blindness caused by both inherited defects, such as retinitis pigmentosa, and age-related degenerative diseases, such as macular degeneration.

The new procedure is distinguished from the treatment methods used today by its speed and surgical noninvasiveness, while at the same time delivering therapeutic genes to hard-to-reach cells throughout the retina is highly effective.

In the last six years, several groups have succeeded in treating patients with one of the rare hereditary eye diseases by injecting a virus carrying a normal gene directly into the retina. Despite the obvious invasiveness of this procedure, doctors are forced to resort to this method of administration, since the virus carrying the normal gene is unable to reach the retinal cells that need to be restored.

"Piercing the retina with a needle and inserting an engineering virus behind the retina is a risky surgical procedure," comments David Schaffer, professor of chemical and biomolecular engineering, director of the Berkeley Stem Cell Center at UC Berkeley. "But doctors have no choice, because none of the viruses capable of delivering genes can go all the way through the back of the eye and reach photoreceptors – light-sensitive cells that need therapeutic genes. Based on 14 years of research, we have created a virus that is simply injected into the vitreous body and delivers genes to a very difficult-to-access population of delicate cells in a surgically non-invasive and safe way. This is a 15-minute procedure, and you will most likely be able to go home on the same day."

Tested on two models of human degenerative eye diseases reproduced in rodents, this engineered virus works much better than the standard strain. In addition, it can penetrate the photoreceptors of the monkey's eye, which is very similar to the human eye.

The cells of the eye successfully absorb the virus carrying the green fluorescent protein gene. The picture clearly shows that the engineered strain of the adenoassociated virus (right) is more effective than its predecessor, the standard virus. The new strain is particularly successful in delivering genes to critical photoreceptors (the upper layer). Photos here and further – newscenter.berkeley.edu

Now Professor Schaffer and his colleagues are establishing cooperation with doctors to find patients who can benefit from this method of gene delivery. In the near future, scientists hope to move on to clinical trials.

Schaffer and John Flannery, professor of molecular and cellular biology and optometry at UC Berkeley, together with their colleagues from the Helen Wills Neuroscience Institute at UC Berkeley and the Flaum Eye Institute at the University of Rochester in New York, published the results of their study in the journal Science Translational Medicine (Dalkara et al., In Vivo-Directed Evolution of a New Adeno-Associated Virus for Therapeutic Outer Retinal Gene Delivery from the Vitreous)

Using a safe virus in gene therapy

Three groups of researchers have successfully restored the vision of more than a dozen patients with a rare disease called Leber congenital amaurosis, which leads to complete loss of vision at a young age. They achieved this by embedding corrective genes in adeno-associated viruses (AAV) and injecting these common but harmless respiratory viruses directly into the retina of the eye. Photoreceptor cells absorbed viruses and, by including a functional gene in their chromosomes, began the synthesis of the most important protein, saving photoreceptors and restoring vision.

Schematic image of an adeno-associated virus showing the proteins of its envelope. Scientists from the University of California at Berkeley changed 10 amino acids in one of the proteins (orange) so that the virus could reach photoreceptors by passing through the layers of the retina.

Unfortunately, this method cannot be applied in most ophthalmic diseases, since the needle often causes retinal detachment, aggravating the situation. However, the standard adenoassociated virus cannot penetrate the tissue to reach photoreceptors and other cells, such as retinal pigment epithelium, that need to be repaired. The retina is about 100,000 times thicker than the diameter of the AAV, which is about 20 nanometers.

Many years ago, Professor Schaffer decided to find a way to modify the adenoassociated virus so that it penetrates into tissues, including the eye and liver, and becomes a vector for delivering genes to certain cells. To date, he has created 100 million variants of AAV, each of which is slightly different from the others by the proteins on its shell. Of these millions, he and his colleagues selected five that effectively penetrate the retina. They then used the best of these five – 7M8 –to transport genes to treat two types of hereditary blindness for which mouse models exist: X-chromosome retinoschisis, affecting only boys and turning their retina into a kind of Swiss cheese, and Leber congenital amaurosis. In all cases, when injected into the vitreous body, a new engineered adenoassociated virus delivered correcting genes to all areas of the retina and restored photoreceptors to almost normal condition.

Scientists have created and injected more than 100 million engineered adenoassociated viruses into the vitreous body of the eye (left). Viruses capable of passing through many layers of retinal cells are used to transfer the correcting gene into cells with a defective gene. To reach these cells, in particular photosensitive photoreceptors and retinal pigment epithelium (RPE) cells, the virus must pass through several layers of cells (right).

When injected into the eye of a normal monkey, this virus penetrates into a certain number of retinal cells, while almost all photoreceptors of a very important field of vision, the so-called fossa, which ordinary viral vectors cannot do at all.

Professor Schaffer suggests that such viruses can be used not only to restore the function of non-functioning genes, but also to knock out genes or stop processes that actively kill retinal cells, which occurs with age-related macular degeneration.

Portal "Eternal youth" http://vechnayamolodost.ru 19.06.2013