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Human Cloning: The State of the Science

On Feb. 12, scientists from Hanyang University in South Korea announced they had successfully harvested stem cells from human embryos that they had cloned. Their experiment has reignited the debate over human cloning, raising both scientific and ethical questions. BusinessWeek Correspondent Arlene Weintraub, who has been covering this issue, presents a primer on the science of cloning and the promise and the concerns surrounding this controversial field:

Q: How did the scientists at Hanyang do it?

A: First, they gingerly removed the genetic material from eggs donated by young women. Then they injected the eggs with DNA from nonreproductive cells taken from those same women. Finally, they used chemicals to coax the cells to grow into embryos. The scientists were then able to harvest stem cells from those embryos. After they were placed in Petri dishes, the cells grew and proliferated on their own.

Q: Why are the stem cells from these embryos so promising for medical research?

A: Stem cells taken from embryos are known as "pluripotent" cells. Unlike stem cells from adults, pluripotent cells are undifferentiated, meaning they can eventually grow into virtually any type of tissue, including skin, muscle, or bone. Scientists believe these stem cells might someday be used to treat spinal-cord injuries and diseases such as Parkinson's and diabetes.

It may be possible, for example, to use stem cells to grow normal pancreatic cells, then transplant them into patients with diabetes, so their bodies will be able to make insulin on their own.

Q: What will it take to turn these stem cells into life-saving therapies?

A: Much more research. Scientists are still trying to figure out how to create different types of tissues from pluripotent stem cells. Then they'll have to do studies in animals and humans to determine if tissues grown from stem cells can cure diseases without causing adverse side effects.

Q: How close are we to actually cloning humans?

A: Ethical concerns have prevented most scientists from going so far as to try to create a cloned human. In 2002, Advanced Cell Technology of Worcester, Mass., claimed to have cloned humans, but reported that the embryos died when they had grown to no more than a cluster of six cells.

Some experts believe the technique the South Korean scientists used in this recent experiment could be used to grow viable embryos, which could then be implanted into a woman's womb. But there's no evidence that such a procedure would be safe for the woman and that it would result in a normal human baby.

Q: But efforts to clone animals have succeeded.

A: Yes, some companies are cloning cows and pigs for meat production, although cloned meat has yet to be approved for marketing in the U.S. Scientists have many concerns about the health of cloned animals. Dolly -- the sheep that was the first cloned animal -- died prematurely at the age of six, suffering from arthritis and a lung disease commonly found in sheep twice her age.

In several studies, cloned mice have died long before their normal counterparts and sometimes for reasons that couldn't be determined. Such problems have only fueled the campaigns of anticloning activists, who say cloning is neither ethical nor safe.

Q: What is the status of the U.S. government's efforts to ban cloning?

A: In 2003, the U.S. House of Representatives passed a law banning human cloning, but the bill stalled in the Senate, where a debate erupted over whether or not cloning for medical research should be permitted.

It is allowed at present, but very few companies are doing it because the political outcry and ethical questions surrounding cloning make it very difficult for companies to get such research funded.

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