Scientists have cloned human embryos for the first time using eggs matured in a laboratory — a technique that may help cloning (search) become a viable option for growing patients' own replacement tissue to treat diseases.

The experiment, outlined Monday at the annual conference of the European Society of Human Reproduction and Embryology (search), brings the Belgians to the forefront of human cloning aimed at producing stem cells that are a genetic match for injured or sick patients.

The goal of such therapeutic cloning is not to create babies but to extract stem cells (search), which are created in the earliest days after conception and give rise to the human body. Scientists hope to use the cells as replacement parts for diseased and injured organs. Cells taken from cloned embryos would be a genetic match and theoretically avoid transplant rejection problems.

Some experts have said cloning may not become a practical approach for creating tailor-made stem cells because it requires huge numbers of eggs. There aren't enough mature eggs left over from infertility treatments to meet that need, which means scores of women would have to be willing to donate them.

Until now, scientists have only used mature eggs to create cloned embryos, but if immature eggs work too, the egg supply problem may be significantly eased, said Josiane Van der Elst, who conducted the research at Ghent University in Belgium.

About 10 percent of eggs retrieved from women during infertility treatment are immature. Scientists have matured eggs in a lab before and have reported pregnancies from such eggs, but that is rare and immature eggs are usually discarded.

"As a concept, the idea is great, but unfortunately I think the real capability is limited," said Dr. Gianpiero Palermo, an embryology expert who was not connected with the research.

"Immature eggs, when matured in the lab and injected with sperm, produce very limited numbers of embryos already. When you do cloning, you get even less," said Palermo, director of assisted fertilization and andrology at Cornell University.

In the Belgian experiment, the scientists were able to produce seven cloned embryos from the immature eggs. However, the embryos only developed for four days, not long enough for stem cells to be extracted.

Palermo said that was probably because the eggs were not as good quality as mature eggs would have been.

Van der Elst said her team is continuing to perfect the approach and hopes to produce embryos that can yield stem cells.

"It's certainly a contribution ... a step forward," Palermo said. "It might ease egg supply to some extent, but I don't think dramatically."

The Belgian group is the third to report having cloned human embryos.

South Korean scientists last year were the first to clone a human embryo. Last month, the same group achieved another major advance, creating cloned embryos from nine patients and extracting stem cells from them.

British researchers announced last month that they, too, had cloned a human embryo.

The legal status of cloning varies widely across the world, and most countries have no laws or regulation in place. It is prohibited in Switzerland and Italy, while Belgium, Singapore and Japan have regulations allowing it for medical research.

Australia has a moratorium on the technique until lawmakers decide what to do. In the United States, federal government money cannot be used for cloning projects, but there are no restrictions on privately funded research.