Race is on to use embryonic stem cells in humans

TISSUE grown from human embryonic stem cells, the most prized, and most controversial, cells ever grown in a lab, could at last make it into the human body.

After a decade of scientific and political wrangling, several therapies are now edging towards human trials. Which will be first?

A decade ago the medical possibilities seemed limitless. Human embryonic stem cells are unique in their ability to grow into all 200 types of human tissue. The idea was to create a range of hESC lines and to implant into people tissues and organs derived from the lines that best matched their existing tissue to prevent immune rejection.

A big hurdle came in 2001 in the US when then-president George Bush restricted federally funded researchers to working on just a dozen or so hESC lines, to please those who object to hESC research on religious or ethical grounds. Research continued in other rich countries, however, and President Barack Obama has now overturned the Bush restrictions.

But another challenge looms: stem cells' prized versatility makes their behaviour in the body unpredictable. This has led regulatory bodies like the US Food and Drug Administration (FDA) to view tissue created from hESCs with extreme caution. If a few hESCs fail to differentiate into the desired tissue they may move away from the target site and disrupt other bodily processes or turn cancerous.

Back in January, it looked likely that biotech firm Geron of Menlo Park, California, would be first to implant hESC-derived neural cells into the human body when it won FDA approval to treat people with spinal cord injuries. But the trial is now on hold after cysts formed in some treated animals.

Now, although Geron says it hopes to implant its neural cells into people by September 2010, it could be pipped to the post. Last week, Advanced Cell Technology of Worcester, Massachusetts, applied to the FDA for permission to treat a rare inherited eye condition with cells grown from hESCs.

ACT chief scientific officer Robert Lanza cites several reasons why these cells might raise fewer safety concerns than Geron's therapy (see opposite), as does a French team planning to apply next year to treat people who have burns with layers of human skin made from hESCs. Treatments for diabetes and heart disease are also on the horizon.