Q. What role might human embryonic stem cells play in treating disease?

A. The most publicized clinical goal of stem cell research is often called "regenerative medicine." This strategy would involve nudging stem cells in the cell culture dish to evolve, or differentiate, into the specialized cells that make up each of the body's tissues. If scientists can meet this challenge, then, theoretically:

Beating-heart cells could be transplanted into diseased or damaged heart tissue.

Dopamine-producing brain cells could replenish those destroyed in Parkinson's patients.

Right now, scientists can observe embryonic stem cells in the culture dish differentiate spontaneously into specialized cells. And they've learned that certain chemicals, or growth factors, can drive the cells to specialize randomly.

But scientists can't yet control the direction in which the cells specialize.

They need to figure out how to control this specialization, so that they can prompt a cell to become, say, a liver cell rather than a heart cell. This requires identifying the many genetic steps that lead a cell to evolve one way or another.

UCSF's Matthias Hebrok and Michael German are working to identify the multiple steps that human embryonic stem cells take on their way to becoming pancreatic islet cells. This research involves studying the genes that turn on and off as a stem cell begins to develop. They have identified some of the key steps in the process, but they need to identify many more.

If they succeed, the payoff could be great and relatively quick.

Today, scientists transplant (from cadaver donors) the full pancreas or individual insulin-producing pancreatic islet cells into patients, with some success. This is partly because UCSF scientist Jeffrey Bluestone, who oversees a major international effort to deliver more effective drugs targeting diabetes and other autoimmune diseases, has developed a drug that reduces rejection of transplanted cells.

The number of organs and cells available from donated cadavers is very limited, however. If scientists had access to a large supply of pancreatic islet cells, there is a strong likelihood that transplant therapy would eventually work in patients.

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