Rewriting Life

Cell Transplants for Macular Degeneration

A stem-cell startup aims to test neural stem cells for treating two leading causes of blindness.

Rats genetically engineered to lose their sight can be protected from blindness by injections of human neural stem cells, according to research presented at the International Society for Stem Cell Research conference in San Francisco last week. StemCells, a startup in Palo Alto, CA, plans to use the positive results to file for approval from the U.S. Food and Drug Administration to begin human trials. The company is already testing the cells in children with a rare, fatal brain disorder called Batten’s disease.

Reviving the retina: Human neural stem cells injected into the retina of rats that were engineered to go blind form a layer of tissue (purple) between the animals’ photoreceptors (blue) and retinal pigment epithelium (black), which typically nourishes photoreceptors. A startup called StemCells aims to begin human testing of the cells for retinitis pigmentosa and macular degeneration, two degenerative diseases that cause blindness.

The company’s cells are isolated from human fetal tissue and then grown in culture. To determine whether these cells can protect against retinal degeneration, scientists studied rats that were genetically engineered to progressively lose their photoreceptors–cells in the retina that convert light into neural signals. These animals are commonly used to model macular degeneration and retinitis pigmentosa, two major causes of blindness that result from cell loss in the retina. Researchers injected about 100,000 cells into the animals’ eyes when the rats were 21 days old. According to Alexandra Capela, a scientist at StemCells who presented the work, the cells migrate over time, forming a layer between the photoreceptors and a layer of tissue called the retinal pigment epithelium, cells which nourish and support the photoreceptors.

Using electrodes implanted into the visual system, scientists measured the lowest levels of light the rats could detect. They found that the cells protected vision in the part of the retina in which they were implanted. They also tested the animals’ acuity by examining the maximal speed at which they followed a series of moving bars, a natural rat reflex. “The treated animals maintain a high level of visual acuity, while the untreated animals decline steadily,” said Capela.

The implanted cells don’t actually develop into new photoreceptors; in fact, they appear to maintain their undifferentiated state. So it’s not clear how they protect against blindness. “The neuroprotective effect in the rats is interesting, but the mechanism is still pretty obscure,” says Thomas Reh, a neuroscientist at the University of Washington, in Seattle, who was not involved in the study.

Raymond Lund, a scientist at the Casey Eye Institute at Oregon Health Sciences University who collaborated on the study, says the cells “seem to somehow bypass the defect without actually correcting it.” This may be because the cells make growth factors known to keep damaged cells alive, says Lund, who has also tested the cells in a different animal model of blindness. Another hypothesis is that the cells help clear cellular debris that builds up in the retinas of these rats and harms the photoreceptors.

While the cells seem to survive for months in mice, it’s not yet clear how long they will survive in humans, who live much longer lives, or whether they will affect the long-term function of the retina in other ways. For example, they might interfere with the interaction between the photoreceptors and the retinal pigment epithelium, says Reh.

Because the stem-cell treatment doesn’t replace lost cells, it most likely needs to be administered early in the course of a disease. “This would not be something for advanced macular degeneration, where the receptors are already damaged,” says Lund. “We would want to spot patients who are seriously as risk and hopefully slow or stop process of disease.” A number of genetic factors have been identified that boost risk for the disease, and genetic testing is available.

Taken together, retinitis pigmentosa and macular degeneration are the most common causes of blindness in people 40 and older. No treatments yet exist for the most common form of macular degeneration, which accounts for about 90 percent of cases. A number of novel therapies are under development, including drugs, cell transplants, and implanted devices. Advanced Cell Technology, based in Worcester, MA, uses human embryonic stem cells to grow retinal pigment epithelium, often the first cell type to die off in age-related macular degeneration and other eye diseases. The company filed for permission to begin clinical trials of the cells last November.

Tech Obsessive?
Become an Insider to get the story behind the story — and before anyone else.

Subscribe today

Uh oh–you've read all of your free articles for this month.

Insider Premium
$179.95/yr US PRICE

More from Rewriting Life

Reprogramming our bodies to make us healthier.

Want more award-winning journalism? Subscribe to Insider Premium.
  • Insider Premium {! insider.prices.premium !}*

    {! insider.display.menuOptionsLabel !}

    Our award winning magazine, unlimited access to our story archive, special discounts to MIT Technology Review Events, and exclusive content.

    See details+

    What's Included

    Bimonthly magazine delivery and unlimited 24/7 access to MIT Technology Review’s website

    The Download: our daily newsletter of what's important in technology and innovation

    Access to the magazine PDF archive—thousands of articles going back to 1899 at your fingertips

    Special discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

    First Look: exclusive early access to important stories, before they’re available to anyone else

    Insider Conversations: listen in on in-depth calls between our editors and today’s thought leaders

You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.