A stem cell-based transplantation approach that restores vision in blind mice moves closer to being tested in patients with end-stage retinal degeneration, according to a study published January 10 in Stem Cell Reports. The researchers showed that retinal tissue derived from mouse induced pluripotent stem cells (iPSCs) established connections with neighboring cells and responded to light stimulation after transplantation into the host retina, restoring visual function in half of mice with end-stage retinal degeneration.
End-stage retinal degeneration is a leading cause of irreversible vision loss and blindness in older individuals. Typically, patients with conditions such as retinitis pigmentosa and age-related macular degeneration lose vision as a result of damage to the outer nuclear layer of light-sensitive photoreceptor cells in the eye. There is no cure for end-stage retinal degeneration, and currently available therapies are limited in their ability to stop the progression of vision loss.
One strategy to restore vision in patients who are blind from outer retinal degeneration is cell replacement. Toward that goal, Takahashi and her team recently showed that stem cell-derived retinal tissues could develop to form structured outer nuclear layers consisting of mature photoreceptors when transplanted into animals with end-stage retinal degeneration. But until now, it was not clear whether transplantation of these cells could restore visual function.
In the new study, Takahashi and first author Michiko Mandai of the RIKEN Center for Developmental Biology set out to address that question. To do so, they first genetically reprogrammed skin cells taken from adult mice to an embryonic stem cell-like state, and then converted these iPSCs into retinal tissue. When transplanted into mice with end-stage retinal degeneration, the iPSC-derived retinal tissue developed to form photoreceptors that established direct contact with neighboring cells in the retina.
“We showed the establishment of host-graft synapses in a direct and confirmative way,” Mandai says. “No one has really shown transplanted stem cell-derived retinal cells responding to light in a straightforward approach as presented in this study, and we collected data to support that the signal is transmitted to host cells that send signals to the brain.”
Remarkably, this treatment strategy restored vision in nearly half of the mice with end-stage retinal degeneration. When these mice were placed in a box consisting of two chambers that independently delivered electric shocks on the floor, they were able to use a light warning signal to avoid the shocks by moving into the other chamber. “We showed that visual function could be restored to some degree by transplantation of the iPSC-derived retina,” Mandai says. “This means that those who have lost light perception may be able to see a spot or a broader field of light again.”
To make the findings more applicable to patients, the researchers are currently testing the ability of human iPSC-derived retinal tissue to restore visual function in animals with end-stage retinal degeneration. If these experiments are successful, they will then test the safety of this protocol in part by assessing how the host retina responds to the graft. At the same time, they will continue to search for ways to increase the ability of graft photoreceptors to integrate with the host retinal tissue, with the ultimate goal of moving to clinical trials in humans.
“It is still a developing-stage therapy, and one cannot expect to restore practical vision at the moment,” Takahashi cautions. “We will start from the stage of seeing a light or large figure, but hope to restore more substantial vision in the future.”
- With this new development we are finally able to use CRISPR to edit regular adult cells, giving hope to treat formally incurable diseases.
- Healing the blind is only the beginning for this technology. The scientists are also looking into treating muscular dystrophy, hemophilia and cystic fibrosis.
Gene editing techniques like CRISPR Cas9, while revolutionary and game-changing, have their limitations. One of this is the inability to target stable, non-dividng cells in the eyes, brain, heart, kidneys and liver.
But a new study published in Nature is changing that. Researchers from the Salk Institute have demonstrated the ability to edit the DNA of cells that do not divide or modify their DNA, partially restoring sight in mice born with genetic defects.
Their study involved targeting NHEJ, a DNA-repair cellular pathway present in most cells. Damaged DNA is repaired by rejoining the original strand ends. The researchers set to work modifying the NHEJ pathway to accommodate the CRISPR Cas9 gene editing technique.
They used a custom insertion package called HITI (homology-independent targeted integration) to deliver genetic instructions to the target. All this allowed the researchers to place DNA in cells not previously responsive to CRISPR, making them candidates for gene editing.
To test their method, they decided to cure mice’s retinitis pigmentosa. This is an inherited disorder caused by a faulty gene that makes retinal cells die off. One of these faulty genes is Mertk. So the scientists inserted a replacement Mertk in 3-week old partially blind mice. At the 8 week mark, the rodents showed signs of responsiveness to light.
If proven and perfected, the procedure could usher in a new milestone in genetic engineering. Previous gene editing efforts focused on embryonic stem cells, since they have the propensity to divide a lot. With these, genetic aberrations in a regular adult could be corrected.
The researchers are already at work improving the method. They want to increase the efficacy rate from a mere 5% of cells responding to something closer to 100%.
The company wants to look into gene therapies for muscular dystrophy, hemophilia and cystic fibrosis. They estimate that the product could begin human clinical trials in one to five years.
It’s the most common cause of blindness in the Western world and there is no cure.
At least not yet.
Age-related Macular Degeneration (AMD) affects around 15 million people in the U.S. alone, and globally up to 30 million. For most victims, vitamins and pain relief are the best treatment available.
But Professor Pete Coffey of University College London is pioneering a new therapy that could stop the disease in its tracks, and restore vision to the blind, through the London Project to Cure Blindness.
Discovery could save the sight of 30 million people
Discovery could save the sight of 30 million people 01:44
AMD kills the eye’s Retinal Pigment Epithelium (RPE), a layer of cells that support and nourish the eye’s vision center, the macula, which then also gradually dies. Victims experience a black spot in their vision that grows outward, while they lose the ability to read and recognize familiar faces.
Coffey has spent the past eight years creating and refining his treatment to restore vision and on August 11, 2015, the first patient received it.
The landmark operation
The patient was a 60-year-old woman suffering with a severe form of AMD. Blood vessels at the back of her eyes had burst, flooding the retina and rapidly destroying her vision.
Surgeons at Moorfields Eye Hospital in London implanted a thin layer of cells behind the retina of each eye on a polyester patch just three millimeters wide. They used stem cells due to their ability to become many other cell types in the body. In this case, they had been cultivated as RPE cells to replace the patient’s diminished stock.
We had the cells in the dish and they would do whatever we wanted
Prof. Pete Coffey, University College London
“Recovery is possible … there is a window when you can put the cells in and recover the patient’s vision,” says Coffey. He hopes for patients to get their lives back. “I would hope they can recognize their families again,” he says.
But six months on from the landmark operation, the award-winning ophthalmologist is hesitant to declare victory.
“We are assessing her vision — we need more information to make conclusions,” says Coffey. “I’m pleasantly surprised the cells are surviving to this stage given how nasty (bloody) the environment was.”
Nine more patients will go under the knife during this trial. If it proves successful, Coffey hopes the procedure can become as routine as cataract surgery — ending the suffering of millions.
“My deeply cherished ambition is to make this therapy readily available for anyone suffering with AMD,” he says.
First steps as a student
As a psychology undergraduate in the early 1980s, Coffey was inspired by the work of a research group in Sweden led by Professor Anders Bjorklund, which was exploring cell transplant therapies in the brain to treat Parkinson’s disease.
Coffey followed the group’s work avidly, but wondered why these radical new therapies were being applied to an organ as complex as the brain.
“Why not look at system we know a lot about, and can test easily?” he thought.
The eye was the obvious choice for Coffey, for its accessibility, relative ease of monitoring, and the “immune privilege” that makes it less likely to reject transplant material than other parts of the body.
Within the eye, he targeted RPE cells, as their function appeared less complex than that of other cells involved in the progression of the disease.
From 1998, Coffey began to develop his therapies for the RPE, drawing on a recent advance that was then spreading excitement throughout the field of regenerative medicine: stem cells.
Coffey enjoyed early success. He was initially able to repair the vision of several patients by transplanting healthy cells from other parts of their eye into diseased areas and his work was praised by peers in the field.
However, a lack of funding threatened to curtail his progress, and by 2006 it had become almost impossible to continue. “That was the most difficult period,” Coffey reflects. “The project could have finished there.”
But it didn’t.
Coffey received a surprise call from an anonymous U.S. philanthropist offering a no-strings donation of $5.6 million.
Coffey seized the opportunity, and made an ambitious commitment — to fast-track a stem cell therapy for AMD in human trials within five years, a process that might otherwise have taken 20.
The London Project to Cure Blindness was born.
The first step was to assemble an inter-disciplinary A-team of scientists, engineers and clinicians, including vitreoretinal surgeon Lyndon De Cruz, who would eventually conduct the landmark procedure.
The team moved swiftly through the phases: They selected human embryo cells as their source, after rejecting those of cadavers’, demonstrated the procedure using animals and manufactured the cells to clinical standards for use in humans.
“That was the most confidence-boosting part of the project,” recalls Coffey. “We had the cells in the dish and they would do whatever we wanted — eat rubbish, produce chemicals, handle stress — whatever we threw at the cells, they passed.”
Wearing many hats
As the Project entered unchartered territory, innovation was a constant requirement. New surgical tools were invented, technology from the Hubble telescope was adapted as an imaging tool, and multiple designs were explored and rejected for the membrane that would carry the stem cells into the eye.
“The membrane was the scariest bit — I’m not a bioengineer,” says Coffey. “I had to get off my specialist area.”
But Coffey had to wear many hats — none more alien than that of political lobbyist. After the 2010 general election it was feared that research funding could be cut, so Coffey invited government officials on a tour of his lab. He was relieved to be spared in their spending review.
Progress continued and Coffey’s therapy finally reached trial in 2015 — three years later than planned.
A thriving landscape
The landscape today for eye-related stem cell therapy is teeming with innovation — and competition. Groups in the United States, Japan, and Israel are testing RPE replacement treatments with a range of cell sources and delivery methods, including a new type of stem cell that had arrived on the scene, known as Induced Pluripotent Stem (iPS) cells.
Using stem cells to cure blindness
9 photos: Using stem cells to cure blindness
In 2012, John B. Gurdon and Shinya Yamanaka won the Nobel Prize for Medicine for their discovery and development of iPS cells, which allow almost any cell in the body to be reprogrammed into a stem cell. Using these as a source would lower the risk of immune-system rejection as the patient’s own cells can be used, and this also sidesteps ethical objections to the use of embryos.
The first iPS cell trials with humans were on RPE cells, at the Riken Center in Japan. However, this highlighted a key risk of the practice, as the trial was discontinued after causing abnormal growth in one subject.
Looking out for hurdles
Coffey believes there are two major health concerns with this form of cell therapy. “You don’t want cells to proliferate — this is often defined as a tumor,” he says. “You also don’t want cells wandering off elsewhere in the body (such as) your heart or lungs.”
But he is convinced that the eye should remain the vanguard of stem research, and Deborah Sweet, editor of Cell journal, agrees.
“The eye has advanced more than most areas,” she says, adding that Coffey’s work is “one of the first examples of stem application and I’m excited to see it.”
Dr. Sally Temple, president of the International Society for Stem Cell Research, believes Coffey’s therapy can enable further breakthroughs. “If RPE replacement works, this will help pave the way for replacement of other retinal cells, and other central nervous system cells.”
However, Temple adds a note of caution over the current trial. “A permanent patch such as polyester forms a barrier. If the RPE cells die (this) could cause the overlying retina to die.”
The future will have a cure … and more
Following his recent successes, Coffey is already pursuing new horizons. He is globalizing his AMD therapy through an affiliate in California, and running offshoot project the “Bank of Disease,” targeting new treatments for a range of blindness-causing conditions, such as the inherited conditions Retinitis Pigmentosa and Stargardt’s Disease that also result from damage within the retina.
The scientist is also looking even further ahead, predicting that it will become possible to regenerate cells in the body itself — without need of transplants.
“I always keep sight of the future,” says Coffey.
Thanks to his work, millions of people could keep theirs.
Photo credit: gun4hire
Humans need light for a variety of reasons. Beyond allowing us to perceive our environment with sight, light also activates activity in the brain. A recent study has unexpectedly shown that even individuals who are completely blind are influenced by the presence of light. The presence or absence of light controls many bodily functions, including heart rate, attentiveness, mood, and reflexes. The study will be published in an upcoming edition of Journal of Cognitive Neuroscience. The work is a collaboration between a research team at the University of Montreal and the Brigham and Women’s Hospital in Boston.
The experiment was performed by exposing people who are completely blind to a blue light. The light was turned on and off and the participants were asked whether the light was on or off. The participants were shown to have a non-conscious response to the light, despite not being able to see it. There were more positive identifications made than could be explained by chance alone, though the awareness was non-conscious. This light perception comes from ganglion cells in the retina, which are different from the rod and cone cells that process light for sight.
Next, researchers tested if attentiveness was affected by the presence of light. For this activity, participants had to match sounds with lights on or off. Even though the participants could not visualize the light, they showed an increased attentiveness when light was shining into their eyes.
Finally, the test participants completed a brain scan with functional MRI (fMRI) to measure alertness, memory, and cognition recognition while performing tasks of matching sounds. Across the board, the tasks were completed more efficiently when light was present.
Because of these results, the researchers are speculating that light perception is part of the default mode network. This is the name for the brain activity that occurs non-consciously in the background, while other tasks take priority. They speculate that the ability to perceive light even without actively converting it into images is done to continually pay attention to and monitor the environment. If this is correct, it might help explain why cognitive performance is improved in the presence of light.
A team of researchers, led by University of Kentucky ophthalmologist Dr. Jayakrishna Ambati, has discovered a molecular mechanism implicated in geographic atrophy, the major cause of untreatable blindness in the industrialized world. Their article, “DICER1 Deficit Induces Alu RNA Toxicity in Age-Related Macular Degeneration,” was published online by the journal Nature on February 6, 2011.
Concurrent with this discovery, Ambati’s laboratory developed two promising therapies for the prevention of the condition. This study also elaborates, for the first time, a disease-causing role for a large section of the human genome once regarded as non-coding “junk DNA.”
Geographic atrophy, a condition causing the death of cells in the retina, occurs in the later stages of the “dry type” of macular degeneration, a disease affecting some 10 million older Americans and causing blindness in over 1 million. There is currently no effective treatment for geographic atrophy, as its cause is unknown.
Ambati’s team discovered that an accumulation of a toxic type of RNA, called Alu RNA, causes retinal cells to die in patients with geographic atrophy. In a healthy eye, a “Dicer” enzyme degrades the Alu RNA particles.
“We discovered that in patients with geographic atrophy, there is a dramatic reduction of the Dicer enzyme in the retina,” said Ambati, professor and vice chair of the Department of Ophthalmology and Visual Sciences and the Dr. E. Vernon and Eloise C. Smith Endowed Chair in Macular Degeneration Research at the UK College of Medicine. “When the levels of Dicer decline, the control system is short-circuited and too much Alu RNA accumulates. This leads to death of the retina.”
Alu elements make up a surprisingly large portion—about 11 percent by weight—of the human genome, comprising more than 1 million sequences. However, their function has been unknown, so they have been called “junk” DNA or part of the “dark” genome. The discovery of Alu’s toxicity and its control by Dicer should prove of great interest to other researchers in the biological sciences, Ambati says.
Ambati’s team developed two potential therapies aimed at preventing geographic atrophy and demonstrated the efficacy of both approaches using laboratory models. The first involves increasing Dicer levels in the retina by “over-expressing” the enzyme. The second involves blocking Alu RNA using an “anti-sense” drug that binds and degrades this toxic substance. UK has filed patent applications for both technologies, and Ambati’s group is preparing to start clinical trials by the end of this year.
Response from the scientific community has been enthusiastic.
“These findings provide important new clues on the biological basis of geographic atrophy and may provide avenues for intervention through preventing toxic accumulation of abnormal RNA products,” said Dr. Paul Sieving, director of the National Eye Institute.
“Ambati’s latest research provides important mechanistic insights in geographic atrophy, and identification of this novel pathway may result in new therapeutic targets for a major cause of blindness,” said Dr. Napoleone Ferrara, a member of the National Academy of Sciences and Lasker-DeBakey awardee who is a researcher at Genentech.
This work has “widespread implications” for future study, said Dr. Stephen J. Ryan, president of the Doheny Eye Institute and member of the Institute of Medicine.
“The authors have opened an important line of research with real possibilities for future therapeutic intervention for patients with geographic atrophy,” Ryan said.