Six months after giving it the green light, the U.S. Food and Drug Administration has told Geron to put plans for a clinical trial in spinal cord injury on hold. The company has differentiated embryonic stem cells into precursors of cells known as oligodendrocytes, which help keep neurons alive. Geron hopes this cell product could promote healing in people who have recently severed their spinal cords.
In a press release, Geron said that the hold was placed after the company submitted data on animal studies done to support delivery of increased doses of its cell product and on animal studies applying the cell product to other neurodegenerative diseases. (See the story from the San Jose Mercury News; here’s the Nature story when trial won approval)
I asked Evan Snyder, who directs the stem cell program at the Burnham Institute and is not privy to the confidential information, to speculate what might have been in the preclinical data that prompted teh FDA’s action. It’s possible that the FDA just wanted more time to review newly submitted data, he said. Or on the other end of the extreme perhaps some sort of tumour or adverse reaction had been observed in the animals. Most likely, he thought, given that the company is trying to make larger doses of the cells, is that undifferentiated or non-neural cells have been observed in the cell product.
Clinical holds are not unusual particularly for innovative therapies. The FDA issued a clinical hold for NeuralStem in February on a trial in Lou Gehrig’s disease (the company uses neural stem cells derived from fetal cells)
At a large FDA advisory committee meeting in April last year, experts discussed the risks and benefits of products derived from embryonic stem cells. They were particularly concerned about uncontrolled cell growth. Even if the cells are not cancerous, tumours in the contained spaces of the brain and spinal cord could be devastating. Committee members were particularly concerned for diseases that are debilitating but not immediately deadly, since adverse events caused by experimental procedures could mean that people with years to live die early or end up suffering more. Patient advocates protested that they should be allowed to decide whether to take that risk.
See previous posts: Overview of FDA meeting (includes links to transcripts)