Medical milestone: South Korean scientists have cloned human cells to help treat disease. Find out how, and why it could change the future

Science World, May 10, 2004 by Libby Tucker

Since Dolly the sheep was born in 1996, scientists have produced a virtual zoo of cloned animals: pigs, cows, horses, goats, mice, cats, and even the cattlelike banteng--one of the first endangered species to be cloned. Now, researchers are closer than ever to a human. clone, or an exact genetic copy of a cell or an organism.

Scientists create clones for two very different reasons. Reproductive cloning produces a baby animal that's the genetic twin of an adult. So far, no scientist has pulled off human reproductive cloning--no cloned children have been born. Scientists did create cloned human embryos (unborn animals in the first eight weeks of growth) for the first time in 2001. But the embryos didn't live very long.

Then, this March, biologist Woo Suk Hwang and a research team from Seoul National University in South Korea announced that they had used a microscopic needle to create more than 200 cloned human embryos from adult cells. Hwang's research took the first steps in therapeutic cloning, a process in which stem cells (cells that can become any one of the 200 different cell types present in the human body) are taken from a cloned embryo. The cells are then used to grow replacement tissues that could help treat human ailments such as diabetes, Parkinson's disease (brain disease that impairs movement), and spinal cord injuries.

Thirty of the embryos Hwang created survived in petri dishes for longer than any cloned human embryos have survived before. For this reason, his research may be the closest science has come to producing a human clone. But that doesn't mean you can start planning for your clone. "We are opposed to any attempts toward human reproductive cloning," says Hwang--a view shared by many scientists.

Read on to learn how Hwang's team tweaked the process of sexual reproduction (creation of new life by combining genetic material from a male and a female) to clone human embryos, and how his research may eventually be used to treat deadly or debilitating diseases. Then have a class discussion: Is it right to clone humans?

BACK TO BASICS

You have two sets of chromosomes (DNA, structure that carries genetic information, and protein). One set came from your father's sperm (male sex cell) and one from your mother's oocyte (unfertilized egg). Before fertilization, the egg is stuck in a stage of growth called metaphase II. It still has two sets of DNA--one set too many. To produce a new person, the egg needs sperm. "The egg will just stay [in metaphase II] forever until the sperm comes in," says Jose Cibelli, a biotechnology scientist at Michigan State University.

When a sperm enters the egg, it releases a dose of calcium particles that kick-start the egg. The egg throws its extra set of DNA out in a speck of a cell called the polar body. And DNA from the egg and sperm are united. The fertilized egg cell begins to divide and grow to become a blastocyst (ball of about 100 cells), then an embryo, and finally a fetus (unborn animal eight weeks after fertilization).

WAY TO CLONE!

A clone's DNA comes from only one parent. Some female reptiles and insects can reproduce on their own by parthenogenesis, or when an unfertilized egg in metaphase II begins to divide without sperm. The embryo is identical to the mother--a natural clone. So why not just trigger parthenogenesis to clone a person? Only women could be cloned and as of today no mammals have ever been born this way, says Cibelli.

To clone an adult cell, Hwang and his colleagues used a process very similar to those used to clone other mammals. They first removed the nucleus (area that contains DNA) from an egg cell in metaphase II. Then they took a somatic cell (any cell in the body that is not a reproductive cell--sperm or egg) from a woman and inserted it into the enucleated (nucleus-free) egg (see diagram, p. 12). Every somatic cell holds two sets of DNA.

To trick the egg into "thinking" it was fertilized, the scientists spiked it with calcium. Then the egg began dividing on its own. But instead of letting the ball of cells grow into a fetus, the scientists kept it at the blastocyst stage. At this stage, "[the clone] is tiny, tiny, tiny," says Cibelli. "It's one tenth of a millimeter, or about one third [the size] of the period at the end of a sentence."

Hwang's team made history when they removed the inner cell mass (cells that become the embryo) from the blastocyst and grew the cells in a nutrient-rich petri dish. Most cells in the inner cell mass are stem cells. Hwang used the cells to create a stem cell line, or a group of cells genetically identical to each other that would continue to grow and divide forever. It's the first stem cell line ever created from a cloned human embryo.

MIRACLE CELLS

Stem cells were originally dubbed "miracle cells" by researchers, because of their potential to treat or cure many human diseases (for more on stem cells, see Science World, Nov. 12, 2001). Already, many treatments developed from embryonic and adult stem cells are in the works. Stem cells are, in a sense, unemployed. They have no specific job in the body, so scientists can use chemicals to force the cells to become a cell type that's missing or damaged. The cells are then injected into the diseased person's body.