Implanted neurons fuse with pre-existing brain wiring in the lab

Among the many hurdles to be cleared before human embryonic stem cells can achieve their therapeutic potential is determining whether or not transplanted cells can functionally integrate into target organs or tissues.

Writing in the Proceedings of the National Academy of Sciences (PNAS) , a team of Wisconsin scientists reports, in a study funded by the US National Institutes of Health, that neurons, forged in the lab from blank slate human embryonic stem cells and implanted into the brains of mice, can successfully fuse with the brain's wiring, and both send and receive signals.

Neurons are specialized, impulse conducting cells that are the most elementary functional unit of the central nervous system. The 100 billion or so neurons in the human brain are constantly sending and receiving the signals that govern everything from walking and talking to thinking. The work represents a crucial step toward deploying customized cells to repair damaged or diseased brains, the most complex human organ.

"The big question was can these cells integrate in a functional way," says Jason P. Weick, the lead author of the new study and a staff scientist at the University of Wisconsin-Madison's Waisman Center. "We show for the first time that these transplanted cells can both listen and talk to surrounding neurons of the adult brain."

The Wisconsin team tested the ability of their lab grown neurons to integrate into the brain's circuitry by transplanting the cells into the adult mouse hippocampus, a well-studied region of the brain that plays a key role in processing memory and spatial navigation. The capacity of the cells to integrate was observed in live tissue taken from the animals that received the cell transplants.

Weick and colleagues also reported that the human neurons adopted the rhythmic firing behavior of many brain cells talking to one another in unison. And, perhaps more importantly, that the human cells could modify the way the neural network behaved.

A critical tool that allowed the UW group to answer this question was a new technology known as optogenetics, where light, instead of electric current, is used to stimulate the activity of the neurons.

"Previously, we've been limited in how efficiently we could stimulate transplanted cells. Now we have a tool that allows us to specifically stimulate only the transplanted human cells, and lots of them at once in a non-invasive way," says Weick.

Weick explains that the capacity to modulate the implanted cells was a necessary step in determining the function of implanted cells because previous technologies were too imprecise and unreliable to accurately determine what transplanted neurons were doing.

Embryonic stem cells, and the closely related induced pluripotent stem cells can give rise to all of the 220 types of tissues in the human body, and have been directed in the lab to become many types of cells, including brain cells.

The appeal of human embryonic stem cells and induced pluripotent cells is the potential to manufacture limitless supplies of healthy, specialized cells to replace diseased or damaged cells. Brain disorders such as Parkinson's disease and amyotrophic lateral sclerosis, more widely known as Lou Gehrig's disease, are conditions that scientists think may be alleviated by using healthy lab grown cells to replace faulty ones. Multiple studies over the past decade have shown that both embryonic stem cells and induced cells can alleviate deficits of these disorders in animal models.

The new study opens the door to the potential for clinicians to deploy light-based stimulation technology to manipulate transplanted tissue and cells. "The marriage between stem cells and optogenetics has the potential to assist in the treatment of a number of debilitating neurodegenerative disorders," notes Su-Chun Zhang, a UW-Madison professor of neuroscience and an author of the new PNAS report. "You can imagine that if the transplanted cells don't behave as they should, you could use this system to modulate them using light."

Source

Editorial note: Outcome from this research will have a major role to play in retinal diseases, since retina is considered to be a part of the brain, and most stem cell treatments have not been successful due to issues with connectivity of the newly formed retinal cells derived from stem cells, with the functional ones that preexist in the retina. 

New treatments for Age-related Macular Degeneration and Stargardt's disease

Elderly people losing their vision from age-related macular degeneration might one day have a treatment option that requires fewer injections into the eye than the standard drug now used.

In testing, an experimental drug being developed by Regeneron Pharmaceuticals, when injected every eight weeks, proved as effective as the standard treatment, Lucentis from Genentech, which was injected every four weeks. The findings are from two clinical trials that Regeneron is expected to announce on Monday.

In a separate development, Advanced Cell Technology is expected to announce Monday that it has won regulatory approval to test a therapy derived from human embryonic stem cells in people with Stargardt’s macular dystrophy, another retina disease.

It is only the second trial of a therapy derived from human embryonic stem cells to be cleared by the Food and Drug Administration. The first involves a treatment for spinal cord injury developed by Geron.

Age-related macular degeneration is the leading cause of blindness in the elderly. Lucentis can restore a person’s ability to drive and read, in some cases.

But the drug works best when given every four weeks, which can be inconvenient for patients and doctors. Doctors often give Lucentis less frequently, but even if that regimen produces good results, patients must still get checkups every month to make sure their vision is not deteriorating.

Regeneron’s drug, which is called VEGF Trap-Eye, “gives us the opportunity to not have to see them monthly,” said Dr. Jeffrey Heier of Boston, an investigator in one of the trials and a consultant to Regeneron. That would be “very meaningful to patients and their families,” he said.

Regeneron and its partner, Bayer, said they planned to apply for approval of the drug in the first half of 2011.

The two similar trials involved a total of 2,457 patients who were randomly chosen to receive either Lucentis every four weeks or VEGF Trap-Eye either every four weeks or every eight weeks. In the eight-week arm, the first three doses were given every four weeks.

After a year, roughly 95 percent of the patients in all the arms of the trial maintained their vision, meaning their ability to read an eye chart declined by no more than 15 letters, or three lines.

VEGF Trap-Eye was also “noninferior” to Lucentis in terms of the average change in vision after one year. Lucentis recipients had a mean gain of 8.1 letters and 9.4 letters in the two trials. Those getting Regeneron’s drug every eight weeks had gains of 7.9 letters and 8.9 letters. Regeneron said the two drugs were equally safe.

Both VEGF Trap-Eye and Lucentis block a protein called vascular endothelial growth factor that causes blood vessels to grow and leak into the eye.

VEGF Trap-Eye could become the first big product for Regeneron, which was founded in 1988 and is based in Tarrytown, N.Y. It sells one drug for a rare disease and has garnered hundreds of millions of dollars from licensing deals with big pharmaceutical companies.

Regeneron’s drug is likely to face competition from off-label use of Genentech’s cancer drug Avastin. When used in the eye, Avastin costs about $50 a dose, compared with about $2,000 for Lucentis. Still, even with such low-priced competition, Lucentis has sales exceeding $2 billion globally.

Meanwhile, Advanced Cell Technology, of Marlborough, Mass., said it would test its stem cell therapy on 12 adults with severe vision loss caused by Stargardt’s, an inherited disease.

The company has turned human embryonic stem cells into retinal pigment epithelial cells, which will be surgically implanted into the eye. The hope is that the implanted cells will replace those injured by the disease.

Human embryonic stem cells are controversial because their creation usually entails the destruction of human embryos, although Advanced Cell Technology is working on a technique to avoid that.

Embryonic cells can also form tumors if injected into the body. Dr. Robert Lanza, chief scientist at Advanced Cell, said the company had to prove to the F.D.A. that its retinal cells contained virtually no residual embryonic stem cells. It took a year for the company to get clearance for the trial from the F.D.A.

It is likely to be several years before such a treatment can reach the market, if it works. Still, even starting the trial could be a boost to Advanced Cell, which often makes headlines but has struggled to raise money. Its shares closed at 5 cents on Friday.

Dr. Peter J. Francis, an associate professor at the Oregon Health and Science University, which will be a site for the trial, says the eye is a good place to test stem cell therapy because it is accessible. Also, he said, there is less chance of rejection of the implanted cells because the eye is shielded somewhat from the body’s immune system.

There is no treatment for Stargardt’s, which affects more than 25,000 people in the United States (and about 1 lakh people in India). The disease is usually diagnosed during childhood and it causes a loss of central vision, though not usually peripheral vision.

From the New York Times

Note from Retina India:
Retina India is creating registries or databases of patients with macular degeneration and Stargardt's disease. If you, or someone you know has the above diseases, or any other retinal disease, please write to info@retinaindia.org to be included in the database. Retina India also runs Connect Programs, which allow patients and family members interested in one particular diseases (e.g. Stargardt Connect) to connect with each other, which allows them to discuss and resolve their problems.