Scientists have made another bold step into the arena of what some say is the future of medicine - stem cells.

Researchers in South Korea report that they have created personalized stem cell lines for 11 patients by taking their own DNA and putting them into donated, unfertilized human eggs.

Using a cloning technique known as a somatic-cell nuclear transfer, the researchers were able to culture stem cells using eggs with the patients' genetic material inside. They say the method could be a way to custom design tissue that could then be used to repair damaged or diseased parts of the human body.

Because the cell lines exactly match the patients' DNA, a personalized stem cell line could potentially circumvent problems with immune reaction, the researchers say.

But it's work that no doubt will re-ignite the debate over whether it's right to use embryonic tissue as medical treatment.

Unlike adult stem cells, embryonic stem cells have the potential to form any cell or tissue in the body. Opponents to embryonic stem cell research say all such work is unethical because human life begins at conception.

But the study's leader, Seoul National University's Woo Suk Hwang, says that while's he's creating embryonic stem cells, he isn't creating embryos.

"There is no fertilization in our process. We use nuclear transfer technology," he told reporters in a telephone briefing. "I can say this result is not an embryo but a 'nuclear transfer construct'."

But the research does raise the spectre of human cloning, because the technique is similar to that used to produce Dolly the sheep in 1996. Cattle, pigs, sheep, cats and other animals have since been cloned using this method as well.

But David Magnus and Mildred Cho of the Stanford University Center for Biomedical Ethics in California dismiss the worries.

"There is no reason ever to believe one of these things could ever become a human being," said Magnus, who with Cho wrote a commentary on the work.

Hwang and colleagues at Seoul National University report in the journal Science that their process is much more efficient than they hoped.

"This study shows that embryonic stem cells can be derived using nuclear transfer from patients with illness ... regardless of sex or age," Hwang said.

Hwang and his team used 185 eggs donated by 18 women. Then, 11 patients, who ranged in age from 2 to 56, donated abdominal skin biopsies.

Nine of the patients had spinal-cord injuries; one had juvenile diabetes; and one had congenital hypogamma-globulinemia, a type of immune-deficiency disease. In most cases, the egg donors were unrelated to the skin donors, but in one case, a woman donated the egg as well as the skin.

The patients' skin was cultured to provide the nuclear material for injection into the eggs. And in each of the 11 cases, new stem-cell lines were created.

Hwang and his team believe cells created in this way could one day be trained to provide tailored tissue and organ transplants to cure numerous illnesses, such as Parkinson's and spinal cord injuries.

The researchers caution that their report is just the first step and that clinical use of the research for regenerative purposes could be years away.

They also note that the stem cells created from DNA from patients with genetic diseases would still contain the genetic coding for that disease.