Britain's fertility regulator said Wednesday it was loosening rules on screening human embryos to allow couples to conceive a baby in hopes of curing an ailing sibling.
Britain previously permitted embryo screening only to eliminate genetic disorders.
After a months-long review and a meeting Wednesday, the Human Fertilization and Embryology Authority said it would let couples with a sick child test embryos conceived during fertility treatment and pick one to implant in the uterus that matched the older child's tissue type.
Advocates of the change say it will help parents treat desperately ill children. Opponents fear it could lead to creation of "designer babies" for spare parts.
Suzi Leather, head of the fertility board, said the decision would affect very few families. "We're going to look at this on a case-by-case basis, and we believe this should be a treatment of last resort," she said. "However, it will make a very great deal of difference to a small number of people. It will help save the lives of some much-loved children.
"This is a cautionary advance for medical treatment for an existing, very sick sibling. I do not believe this is playing God," she said.
Joe and Julie Fletcher, of County Down in Northern Ireland, toasted the decision with champagne. They hope to have a child whose stem cells will help their son Joshua, 2, who now must have frequent blood transfusions for a rare blood disease.
"It is great news," said Joe Fletcher. "What we need is for them to say 'Yes, you have passed the criteria and can now proceed.' That will come hopefully within a few short weeks and we will start along the road. Tonight's decision opens up the door for us."
Nuala Scarisbrick, a trustee of the anti-abortion group Life, said that while the group sympathized with the parents of sick children, it would be better to find other treatments than to create babies for tissue transplants.
"Human beings should not be created and then tested and discarded, it is eugenics," she said. "It means that we are trying to create perfect people and that is wrong, it's not a healthy thing for a society to do."
She said choosing embryos based on tissue type could open the door to allowing them to be selected for attributes like gender or eye color.
The British Medical Association said it welcomed the decision and did not believe selecting an embryo on the basis of tissue type meant a newborn would not be cherished.
In 2002, the fertility board denied a British couple, Jayson and Michelle Whitaker, permission to conceive a baby whose umbilical cord stem cells would match their first son's tissue type so they could treat his rare blood disorder. The couple went to the United States for the treatment and Michelle Whitaker gave birth to a baby last year.
In December 2001, the fertilization authority had announced that it would, in principle, permit couples to select test-tube embryos whose tissue type matched that of a sick sibling, but only if the couple already qualified for embryo testing to avoid passing on an inherited disease.
Stem cells are found in human embryos, umbilical cords and placentas, and develop into the various types of cells that make up the human body, making them useful for treatments for some diseases.
