Producing eggs and sperm from stem cells has long been a science goal.
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 stumped 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,” commented Amander Clark, a developmental biologist at UCLA.
But Saitou and his colleagues kept at it, and they reported their achieved success in the journal Science.
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.
However, the work 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 Clark.
The technique might someday help millions of people suffering from infertility because of cancer treatments or other reasons, she explains.
But the possibility of being able to mass-produce human eggs presents an array 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.
“A woman might want to have George Clooney’s baby,” Green elaborates. “And his hairdresser could start selling his hair follicles online. So we suddenly could see many, many progeny of George Clooney without his consent.”
The revolutionary discovery was founded using 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 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,” explained Clark.
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 children with sperm and eggs made from their own skin cells.
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 choose which embryos go on to become babies — that has lots of implications,” Greely says.
