With biotech companies inching up on clinical trials for human embryonic stem cell-based therapies, the US Food and Drug Administration held a meeting yesterday to discuss scientific issues in properly deriving and characterizing the cells, as well as appropriate clinical trial monitoring.

Three biotechs, Geron Corporation, Advanced Cell Technology, and Novocell presented some of their scientific work on spinal cord injury, vision impairment, and diabetes, respectively, at the meeting. Geron and Advanced Cell Technology are hoping to begin testing therapies of cells derived from human embryonic stem cells sometime this year, according to Bloomberg News. Jane Lebkowski, senior vice president of regenerative medicine at Geron Corporation, told The Scientist she could not comment on whether this was true.

"The science was ready to have this kind of discussion, to make sure clinical trials are safe," Celia Witten, spokesperson for the FDA told a group of reporters after the day-long meeting, though she declined to say whether the agency has yet received any Investigational New Drug applications.

The advisory committee, which was made up of 25 independent scientists and FDA researchers, addressed issues of proper animal studies for preclinical testing and how researchers can control the embryonic stem cells for appropriate differentiation -- that is, so they don't form cancerous teratomas.

"There was a lot discussed in the range of things we're already thinking about," Lebkowski told The Scientist. "And several ideas we've been implementing already." Some of the committee's ideas were rather extreme, she added; some of the large animal model studies in non-human primates or pigs that the committee discussed were not very practical and extremely complicated -- the committee mused aloud whether allograft experiments (for example, pig embryonic stem cells transplanted to pig body) should be conducted before transplanting human embryonic stem cells to different species.

Several committee members noted that guidelines and requirements of human embryonic stem cell-based therapies will vary from disease to disease, and cell product to cell product. However, all the members seemed to agree that a common, standardized assay should be developed to determine the tumorigenicity of a specific cell product.

Kenneth Chein, from Harvard Medical School, noted that transplanting cardiomyocites and other types of differentiated embryonic stem cells has yielded mixed efficacy results so far, requiring that more definitive assays need to be developed for efficacy and safety.

The committee also addressed how researchers and clinicians will be able to control and monitor where the cells go once they are administered. While new technologies such as reporter genes may improve researchers' ability to track transplanted cells, some committee members questioned whether new techniques should be used at the same time as therapeutic embryonic stem cells, which itself is a novel type of therapy.

Some members of the committee said they were uneasy about embryonic stem cell therapies, and the committee discussed the potential of developing failsafe mechanisms in the cell products, like suicide genes. But some noted that such approaches may have their own therapeutic complications and risks.