For the first time, scientists have used human cells to create structures that mimic the earliest stages of development, which they say will pave the way for more research without having to deal with restrictions on the use of real embryos.
Two articles published Wednesday in the journal Nature describe how two teams of scientists independently created such structures.
They emphasized that their work is for research only, not reproduction, but that it is likely to raise new ethical questions.
“It’s really difficult to study early human development. It’s basically a black box, ”said Jun Wu, a stem cell biologist at the University of Texas, Southwestern Medical Center.
“We believe our model can open this field,” he said, if “you can test your hypothesis without using human embryos.”
Wu’s team used embryonic stem cells, and the second team used reprogrammed skin cells to produce cell balls that resemble one of the earliest stages of human development.
These balls, called blastocysts, form a few days after an egg is fertilized, but before the cells attach to the uterus to become an embryo. To distinguish their models from blastocysts created by fertilization, the researchers refer to structures as “iBlastoids” and “human blastoids.”
“They should not be considered equivalent to a blastocyst, although they are an excellent model for some aspects of biology,” said Jose Polo, an epigeneticist at Monash University in Australia who led the second research team.
Both groups stressed that the structures they made were not the same as naturally occurring embryos, and it is unclear whether they can develop into viable embryos.
“The blastoids are less efficient in terms of generating structures that mimic human embryos in later stages,” said Wu, whose team stopped growing the structure in culture after four days.
Scientists previously generated similar structures from mouse cells in a lab, but this is the first time they have been made from human cells. The new models correspond to about three to 10 days after conception, Wu said. Last year, researchers unveiled structures that model cells 18 to 21 days after fertilization.
Research involving human embryos and blastocysts is currently not eligible for federal funding in the US, and several states outright ban it.
Some scientists are now using blastocysts donated by fertility clinics to research the causes of infertility and congenital diseases. The new work should allow them to conduct such research on a much larger scale, Polo said.
“This ability to operate at scale will revolutionize our understanding of these early stages of human development,” said Polo.
The scientists stressed that their creations were not intended to be used for human reproduction.
“There is no implantation,” said Amander Clark, a stem cell biologist at the University of California, Los Angeles, who co-wrote the paper with Polo. “These structures are not transferred to a uterus or uterine-like structure,” she said. “There is no pregnancy.”
The distinction between blastocysts derived from fertilization and the structures created in a lab may not be that clear, said Shoukhrat Mitalipov, a human embryologist at Oregon Health and Science University who was not involved in the study.
“Both groups show how much they resemble real embryos,” he said. “If they are really as good as embryos, should they be treated like embryos?”
“This brings new ethical issues,” he said. Will they be mated as human embryos? Should there be any restrictions? “
Scientists previously tried to convert lab-generated mouse cell structures into embryos, but failed.
The optimal scenario for research is to “get as close as possible to a real embryo so that you can learn from it, but not an actual embryo, so you don’t get into debates about the moral status of embryos,” said Alta Charo, a professor emeritus. law and bioethics at the University of Wisconsin, who was not involved in the papers.