Stem Cell Research Heads for a Renaissance

Ten years to the month after James Thomson at the University of Wisconsin announced in the journal Science his discovery of human embryonic stem cells, scientists and officials from the Food and Drug Administration gathered in Washington last week to talk about the prospects of starting the first human clinical trials of the high-profile cells.

At a public meeting hosted by the National Academies, scientists discussed results from the latest animal studies suggesting that the cells, after proper treatments in laboratory dishes, show promise for their ability to rebuild scarred cardiac muscle after a heart attack, replace lost brain cells in Parkinson's disease, and regenerate the parts of the pancreas that go awry in diabetes.  In response, an FDA official urged them to move the research onward but also noted, as gently as she could, that they could still expect to face some significant hurdles before getting a green light to try their fledgling therapies in patients.

The scientists were not taken completely by surprise about the regulatory labyrinth ahead. Most were already well aware of Geron Corp.'s repeated announcements that it was on the verge of starting the world's first human embryonic stem cell-based clinical trial -- announcements that in every case have been followed by less-loudly-trumpeted updates noting that FDA-related delays had set those start dates back. The Menlo Park, Calif.-based company, which wants to inject partially matured embryonic stem cells into the spinal cords of paralyzed people, has conducted tests on nearly 1,000 rodents, filed some 21,000 pages of data to the regulatory agency, and distributed a compelling video showing partially paralyzed mice walking again after getting the cells. But the nearly decade-long road to approval wends onward still.

It may be, one official said, that despite the promise shown in animal studies, patients with partial paralysis or Parkinson's disease are not the ideal first subjects for embryonic stem cell experiments.

Some of the issues that stand between ongoing laboratory experimentation and eventual hospital studies are common to cell therapies of all kinds: How do you know where the cells will go once they are injected? Will they change in some way once they are in the body? How long will the cells live and what happens when they die? Will they stir up a dangerous immune response?

Other concerns are more specific to cells with embryonic origins: Are you sure they will mature into the right kinds of cells once they settle in the body? What are the odds that a few will fail to mature but rather will grow and multiply like tumors? And if there is a chance of that happening -- and since tumors often take a decade or more to form -- are you prepared to follow the patients for the rest of their lives, to watch for cancers or other long-term side effects?

Animal studies to date mostly suggest that cells derived from embryonic stem cells pose very small health risks if cultivated and purified appropriately before injection or infusion into the body. And the evidence for potential benefits continues to grow -- albeit slowly, in part because of constraints on the funding of stem cell experiments (even in animals) under the policy promulgated by President Bush in 2001.

But despite the encouraging evidence to date, the cells are new and different enough that the FDA is opting to play it conservatively. It may be, one official said, that despite the promise shown in animal studies, patients with partial paralysis or Parkinson's disease are not the ideal first subjects for embryonic stem cell experiments. That's because despite their compromised condition, they can in most cases expect to live long and relatively satisfying lives. Instead, suggested FDA investigator Deborah Hursh, researchers may want to choose patients whose ailments portend "very limited life-spans."