Scientists in Japan have used human blood to successfully create immature human egg cells in a lab for the first time, according to new research published Thursday in Science. The work is a major breakthrough in stem cell research and may lead the way to babies that can be created in a lab using the body tissues or blood of their relatives.

Mitinori Saitou, a biologist at Kyoto University who contributed to this pioneering research, managed to produce mouse eggs and sperm from stem cells back in 2012 and used them to breed healthy baby mice. It was the first time that eggs were created from embryonic stem cells.

This image shows the growth of egg cells in an artificial, lab-grown ovary from 7 days to 77 days. Image: Science

When Saitou and his colleagues first produced artificial mouse egg cells, these were grown to maturity inside a simulated mouse ovary constructed from the tissue of fetal mice. Since this tissue would be next to impossible to obtain from humans, the researchers had to figure out a different way of creating an artificial ovary.

To produce immature human eggs, Saitou and his colleagues used human blood cells to create induced pluripotent stem cells, which are notable for their ability to become any type of cell. These cells were then injected into tiny, artificial ovaries that were grown in the lab using embryonic cells derived from mice.

The eggs produced by Saitou and his colleagues are far too immature to be fertilized, much less grow into a human child. Still, they open the door for babies made from the genetic material of relatives, dead or alive. They could also provide a way for infertile people or same-sex partners to produce a child made from their own DNA.

The next step, according to the researchers, is to apply a similar process to the production of human sperm and to create egg cells that are mature enough to be fertilized. This will not only require a lot more research, but creating viable human eggs in a lab is also sure to be incredibly controversial.

For example, it could open the door for cloning people who may not have given their consent. As Ronald Green, a bioethicist at Dartmouth, pointed out to NPR, “a woman might want to have George Clooney’s baby and his hairdresser could start selling his hair follicles online. So we suddenly could see many, many progeny of George Clooney without his consent.” Moreover, many scientists worry that the human reproduction process is not fully understood and that lab-grown egg cells could lead to babies with very serious genetic diseases.