The world’s first authorized test in people of a therapy derived from human embryonic stem cells has been cleared by the Food and Drug Administration.
The clinical trial could offer the first glimpse of the safety and possible effectiveness of a technology that has been hailed for its vast medical promise but also embroiled in political and ethical controversy.
The trial will test cells developed by the Geron Corporation and the University of California, Irvine in patients with new spinal cord injuries.
The F.D.A. had initially cleared the clinical trial in January 2009. But before any patients could be treated, the agency suspended the trial after cysts were discovered in some rats injected with the cells. Geron had to do another rat study and develop better ways to check cell purity.
On Friday, the company announced that the F.D.A. had lifted the hold. Geron’s shares rose 17 percent, to $5.63.
Embryonic stem cells can turn into any type of cell in the body. Scientists envision one day making replacements for injured or diseased tissues to treat a wide variety of illnesses.
“I think it’s a very important milestone for the whole industry,” Alan Trounson, the president of California’s stem cell agency, said Friday, adding that the hold on the trial had been a cloud over the field. “It’s very important that they get on and treat the patients and demonstrate the safety” of the therapy.
But the cells have been controversial because their creation has involved the destruction of human embryos, though some researchers claim they can now avoid that.
The politics of embryonic stem cell research has shifted from one presidential administration to another, set in sharp relief by religious conservatives who opposed destroying or using human embryos.
President George W. Bush limited federal funding for research to certain colonies, or existing lines of cells. President Obama lifted those restrictions and is gradually approving more lines to qualify for federal funding.
Geron, based in Menlo Park, Calif., turns embryonic stem cells into precursors of neural support cells called oligodendrocytes. The precursor cells would be injected into the spinal cord at the site of the injury.
The hope is that the cells will repair the insulation, known as myelin, around nerve cells, restoring the ability of some nerves to carry signals.
While this is not expected to allow people to rise from their wheelchairs, it may conceivably restore some movement or sensation.
The first trial, a so-called Phase 1 study, will have up to 10 patients and is mainly aimed at testing the safety of the therapy. Years of further testing will be required before the therapy would be proven and ready for widespread use, assuming it works.
Dr. Thomas B. Okarma, the chief executive of Geron, said that the ethical review boards at two of the seven proposed trial sites had already approved the trial, so that it was possible the first patient might be treated in the next few months.
Dr. Okarma would not identify the trial sites, saying the privacy of the patients must be protected from what could be intense interest from the media.
“We can’t let that happen to disrupt the integrity of the trial,” he said in an interview. “The bright lights are going to be on this.”
That concerns some experts, who say that Geron’s therapy does not have that good a chance of working and that a failure or a safety problem could set back the whole field. The biggest safety concern is that if there are any embryonic stem cells left in the mixture that is injected into patients, they could possibly form tumors.
Dr. Okarma said critics had not seen the 28,000 pages of data that Geron had submitted to the F.D.A. “The degree of heavy lifting and turning over every possible stone is not appreciated,” he said.
Patients in the initial trial will have a so-called complete injury, with virtually no chance of spontaneous recovery, Dr. Okarma said. That way, if there is any improvement in their movement or sensation it could be attributed to the treatment.
Another company, Advanced Cell Technology, is trying to win approval from the F.D.A. to test retinal cells derived from human embryonic stem cells as a treatment for Stargardt disease, an eye condition that causes severe vision loss.
In the last few years scientists have become excited about so-called induced pluripotent stem cells as an alternative to embryonic stem cells.
Those cells can be made from an adult skin or blood cells, doing away with the need for human embryos. And if a patient’s own cell could be turned into new tissue it would eliminate the chance the transplanted cells would be rejected by the patient’s immune system. (Geron’s trial will involve temporary use of an immune-suppressing drug.)
Still, some recent laboratory studies have suggested that the induced pluripotent cells might not be quite as versatile as the embryonic cells in turning into different types of tissues.
