In an experiment that boosts hopes for regenerative medicine, scientists have used stem cells from human embryos to save the sight of lab rats going blind.
The genetically engineered rodents suffered from an eye disease similar to macular degeneration, the leading cause of vision loss in people older than 55. But after receiving injections of retinal tissue generated from human embryonic stem cells, the rodents' vision did not deteriorate and, researchers say, proved to be 100 per cent better than untreated rats.
The work not only represents a new possibility for treating an incurable condition on the rise, but also a strategic bit of ammunition for those fighting for the potential medical value of human embryonic stem cells.
"People are saying this stuff [stem-cell therapies] is decades away and with this we're saying, 'No, we've shown you can do this sooner, with large numbers of cells that are reliable and look to clinical trials,' " said study leader Robert Lanza, who is scientific director at the U.S. biotech firm Advanced Cell Technology. "We rescued the visual function in these rats, rats that would have otherwise gone blind."
Macular degeneration involves the deterioration of retinal tissue crucial for central vision tasks such as reading and driving. Light-sensitive cells in the macula, known as photoreceptors, transmit signals to the brain and losing them can result in blind spots and blurred vision. More than a third of Canadians older than 55 will develop the condition that already affects 30 million people worldwide.
A key challenge for any therapy that would rely on stem cells is being able to produce enough of the tissue needed for a given treatment. But the researchers report in this week's issue of the journal Cloning and Stem Cells that they succeeded in growing 67 good-quality batches of retinal cells from 18 different human embryonic stem-cell lines.
While animal studies are continuing, Dr. Lanza's group is now generating large numbers of particular retinal cells with the hope of applying next year to test them in vision-impaired patients.
"We're in the process of creating these cells under Good Manufacturing Practices and getting ready to supply them for human clinical trials," he said. (Good Manufacturing Practices are regulations set up by the U.S. and Canadian governments for the manufacture of medicines.)
A great gap lies between treating rats and treating people and Dr. Lanza acknowledged certain safety questions must still be answered. For one, rats in this study received the implants not long after birth and it is unclear how well older human eyes would accept new tissues.
There was no evidence of serious side effects or abnormal tissue growths -- a particular concern with any stem-cell therapy because stem cells are prized for their power to multiply indefinitely and mature into the various tissue types that make up the human body. But the rats were followed for only 100 days. Dr. Lanza said ongoing studies are expected to follow the animals for about a year.
Mick Bhatia, scientific director of the Stem Cell and Cancer Research Institute at McMaster University in Hamilton, applauded the work for being one of few that has made the leap of "getting [stem cells] out of the dish and into a living animal."
However, Dr. Bhatia cautioned that the paper does not make clear that there is a real therapy here. He noted that the researchers transplanted only one type of retinal cell, even though they generated various retinal-cell types. He also noted that other research has shown that any cell implanted at an injury site might improve conditions and so it cannot be certain that the benefits reported in this experiment are due specifically to the tissue from embryonic stem cells.
Advanced Cell Technology has often made headlines in the controversial field of embryonic stem-cell research. Last month, the company reported it had found a method to derive stem cells without destroying an embryo -- the key concern of those morally opposed to the work.
