Scientists say they have taken a potentially important — and possibly controversial — step toward creating human eggs in a lab dish.
A team of Japanese scientists turned human blood cells into stem cells, which they then transformed into very immature human eggs.
The eggs are far too immature to be fertilized or make a baby. And much more research would be needed to create eggs that could be useful — and safe — for human reproduction.
But the work, reported Thursday in the journal Science, is seen by other scientists as an important development.
"For the first time, scientists have been able to convincingly demonstrate that we are able to make eggs — very immature eggs," says Amanda Clark, a developmental biologist at UCLA who wasn't involved in the research.
The technique might someday help millions of people suffering from infertility because of cancer treatments or other reasons, Clark says.
But the prospect of being able to mass-produce human eggs in labs raises a host of societal and ethical issues.
Theoretically, babies someday could be made from the blood, hair or skin cells of children, grandmothers, even deceased people. "So there are some very weird possibilities emerging," says Ronald Green, a Dartmouth bioethicist.
People could even potentially make babies from cells stolen from unwitting celebrities, such as skin cells left behind on a soda can or follicles from hair clipped at a salon.
"A woman might want to have George Clooney's baby," Green says. "And his hairdresser could start selling his hair follicles online. So we suddenly could see many, many progeny of George Clooney without his consent."
For years, scientists have been trying to make eggs and sperm from stem cells.
In 2012, Mitinori Saitou at Kyoto University and his colleagues reported they produced mature mouse eggs and sperm from stem cells, and used them to breed healthy mouse pups.
But scientists have been stymied in their attempts to get even close to those results for humans. "The field has been stalled for a number of years at this bottleneck," Clark says.
But Saitou and his colleagues kept at it, and they described how they achieved success in their Science paper.
First, the scientists used a well-established method to turn adult human blood cells into induced pluripotent stem cells, which have the ability to become any cell in the body.
But the key, apparently, was putting the induced human pluripotent stem cells into miniature ovaries they created in the lab from mouse embryonic cells.
"They created a tiny little artificial ovary and inside that little reconstituted ovary were these very immature human egg cells. So the entire experiment happened entirely within an incubator within a laboratory," Clark says.
In their paper, the Japanese scientists say the next step will be to try to make mature human eggs and produce human sperm this way.
"It's the beginning of a paradigm change," says Kyle Orwig, a professor in the department of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine.
In addition to helping infertile people, such a development could enable gay couples to have babies with sperm and eggs made from their own skin cells.
But such a possibility would also have much broader implications, say others following the field.
"If we can make human eggs and sperm from skin cells it opens up an enormous number of possibilities for changing how humans reproduce," says Hank Greely, a bioethicist at Stanford who wrote The End of Sex and the Future of Reproduction.
For example, easy access to eggs might mean it would become routine to scan the DNA of embryos before anyone tries to have a baby.
"Doing genetic testing basically on a large chunk of every generation of babies before they even become fetuses — while they're still embryos — and having parents and potentially governments pick and chose which embryos go on to become babies — that has lots of implications," Greely says.