Scientists are one step closer to curing blindness, after they carried out the first successful transplant of light-sensitive photoreceptor cells from a synthetic retina that was grown from embryonic stem cells.
Researchers from University College London (UCL) and Moorfields Eye Hospital in the UK, transplanted the photoreceptor cells in to night-blind mice and found that the cells developed normally.
The cells integrated into the existing retina in the mice and formed the required nerve connections that transmit visual information to the brain.
The study, published in the journal Nature Biotechnology, shows embryonic stem cells could potentially be used to provide an "unlimited supply of healthy photoreceptors for retinal cell transplantations to treat blindness in humans."
The need for photoreceptor transplantations
Photoreceptors are light-sensitive nerve cells found in the retina of the eye. There are two types of photoreceptors - rods and cones.
The cones provide the eye's color sensitivity. The rods are not sensitive to color, but are more sensitive to light than the cones and are particularly important for providing the ability to see in the dark.
Researchers say this study is one more step towards treating blindness.
According to researchers, the loss of photoreceptors in the eye is a leading cause of sight loss in degenerative eye diseases such as retinitis pigmentosa, diabetes-related blindness and age-related macular degeneration.
Last year, the team conducted research that involved transplanting photoreceptors into mice suffering from retinal degeneration, using cells taken from healthy mice with normal sight.
However, the researchers say that this method of transplantation would "not be practical for the thousands of patients in need of treatment."
Back then, the researchers said: "We are hopeful that we will soon be able to replicate this success with photoreceptors derived from embryonic stem cells and eventually to develop human trials."
Professor Robin Ali, of the Institute of Ophthalmology at UCL and Moorfields Eye Hospital, told Medical News Today:
"Much of this work has been done in mice in the past. Photoreceptor precursor cells taken from the developing mouse retina and pumped into adult mice shows that this can be effective in restoring vision for the mice that lack vision. This really gave the framework for our translation program. To make it practical, we needed to find a cell source from which we can get these photoreceptor precursors."
"We have been working on trying to find ways of repairing the retina by transplanting photoreceptor cells, and we have demonstrated proof of concept of that development. They are not stem cells, they are not fully mature photoreceptor cells, but they are immature photoreceptor cells."
How was the synthetic retina grown?
The researchers say the new technique was developed using 3D culture and differentiation of mouse embryonic stem cells, a method recently developed in Japan.
Retinal precursor cells were grown using the 3D culture method and they were closely compared to normally developed cells, with the researchers noting different stages of development.
The researchers also carried out tests to ensure that the genes being expressed by the two types of cells were "biologically equivalent" to each other.
From this, the scientists were able to grow the synthetic retinas "in a dish" which contain all the nerve cells need to provide sight.
Prof. Ali explains:
"What we have been able to do is build on work of a Japanese group from a study a couple of years ago, in order to make a synthetic retina from embryonic stem cells. We have adapted that and we have shown for the first time that we can use embryonic stem cells to make a retina in a dish."
No more "three blind mice"
The researchers injected around 200,00 of the artificially grown cells into the retinas of the night-blind mice.
Professor Ali and his research team completed the first successful photoreceptor transplant using cells grown from a synthetic retina. Photo credit: UCL/MRC.
The study reports that three weeks after transplantation, the cells from the synthetic retina had "moved and integrated" within the the mice retina and began to look like "normal mature rod cells," which continued to be present after six weeks.
The researchers add that nerve connections (synapses) developed, meaning that the transplanted cells had the ability to connect with the existing connections within the retina.
Prof. Ali adds:
"This now means we have a cell source. This has all been done with mouse embryonic stem cells, but if we do it with human embryonic stem cells then we can do this for the first time using an embryonic stem cell source."
"That means we have got room to think about a human trial and repeat all this using human embryonic stem cells, and investigate whether we can repair the retina in conditions in which blindness is caused by loss of photoreceptor cells ."
Prof. Ali says that it will be a few years before this research will be used within a human trial, but the team have already started working with human embryonic stem cells.
"There are a number of ways that we can use this research to develop ways of treating blindness through gene therapy and artificial retinas. This is a very exciting approach because it has the ability to restore vision in patients who have very little vision, and the main cause of this in the developing world is loss of photoreceptors. Currently there is no treatment for that."