Health News

New Debate on Human Test of Stem Cells

April 10, 2008 -- While politicians battle over where to set limits for human embryonic stem cell studies, regulators are mulling where it should set scientific limits on the promising but controversial research.

Despite widespread media coverage, embryonic stem cells and related cells have only been implanted in a handful of human patients. Researchers say some of the experiments have shown early signs of success. Others have been failures because they were ineffective or led to tumors.

Most research is still conducted in Petri dishes and animals like rats and pigs. But with the field on the brink of producing new therapies for humans, how to test those treatments -- and how much risk to tolerate -- remain open questions.

Stem cells' scientific promise lies in their ability to form dozens of different tissues in the body. As these cells divide and grow, they can be coaxed to form heart, lung, brain, or pancreatic cells. That makes them good candidates to engineer new tissues to repair diseases or injuries.

But their potential may also be a curse. Because embryonic stem cells are genetically programmed to easily divide and grow, research shows they also have the propensity to form tumors.

Cancer and Stem Cells

Scientists and regulators now see a narrow path for the research: designing stem cell studies bold enough to find successful treatments without overreaching and causing cancer.

"We are really in uncharted water," said Stanton L. Gerson, MD, a professor of medicine at Case Western Reserve University in Cleveland and a member of an FDA advisory panel on stem cell research that met outside Washington, D.C. on Thursday.

Research in animals has already shown that high doses of stem cells are ideal for guaranteeing enough cells will survive, reproduce, and grow into new tissue once they're in the body. The cells also grow much more readily if they are implanted at a very early stage, before they differentiate.

But many studies also show that higher doses of more primitive cells are the very ones likely to produce tumors.

So experts and regulators are now wrestling with what kinds of safety cushions researchers should show in animals before the FDA lets the experiments proceed in humans in years to come.

Human Testing: Risks vs. Benefits

All medical research is supposed to balance potential risks with benefits. But embryonic stem cell researchers feel their path is especially narrow, given the politically charged atmosphere around their field.

"It would take very few patients suffering [cancer] to really put a significant damper on the field for years to come," says Steven A. Goldman, MD, a stem cell researcher at the University of Rochester and a panel member.

"All it takes is one," says John W. McDonald, MD, PhD, another panel member and director of International Center for Spinal Cord Injury at the Kennedy Krieger Institute. "Something going awry would cost the field a tremendous amount."