Cysts stall stem cell trial?

Just over a week after the linkurl:Geron Corporation;http://www.geron.com/ announced that the linkurl:US Food and Drug Administration;http://www.fda.gov/ (FDA) had linkurl:placed a hold on its stem cell trial;http://www.the-scientist.com/blog/display/55898/ aimed at treating patients with spinal cord injury with human embryonic stem cells (hESCs), the company linkurl:revealed a reason:;http://www.geron.com/media/pressview.aspx?id=1188 microscopic cysts.

Human embryonic stem cells Image: Wikimedia commons, Nissim Benvenisty

The cysts had appeared with a "very low frequency" in previous animal experiments of the drug GRNOPC1, but were "non-proliferative, confined to the injury site, and had no adverse effects on the animals," Geron's statement said. In a more recent animal trial, however, the cysts showed up more often, although again, they were small and did not appear to be harmful in any way. In fact, the statement pointed out, cysts are not uncommon in victims of spinal cord injury, developing in the spinal cord scar tissue in up to 50% of patients. "I...