For decades, science has been trying to unlock the mysteries of how a single cell becomes a fully formed human being and what goes wrong to cause genetic diseases, miscarriages and infertility.
Now, scientists have created living entities in their labs that resemble human embryos; the results of two new experiments are the most complete such "model embryos" developed to date.
The goal of the experiments is to gain important insights into early human development and find new ways to prevent birth defects and miscarriages and treat fertility problems.
But the research, which was published in two separate papers Wednesday in the journal Nature Portfolio, raises sensitive moral and ethical concerns.
"I'm sure it makes anyone who is morally serious nervous when people start creating structures in a petri dish that are this close to being early human beings," says Dr. Daniel Sulmasy, a bioethicist at Georgetown University.
"They're not quite there yet, and so that's good. But the more they press the envelope, the more nervous I think anybody would get that people are trying to sort of create human beings in a test tube," Sulmasy says.
Crucial periods of embryonic development are hidden inside women's bodies during pregnancies and are therefore inaccessible to study. And conducting experiments on human embryos in the laboratory is difficult and controversial.
"We know a lot about animals like the mice and rats. But not a lot with humans," says Jun Wu, a molecular biologist at the University of Texas Southwestern Medical Center in Dallas, who led one of the two research teams publishing the results of the new experiments. "It is really a black box."
So in recent years, scientists started creating structures that resemble human embryos in the lab by using chemical signals to coax cells into forming themselves into entities that look like very primitive human embryos.
Now, Wu's team and an international team of scientists have gone further than ever before. They created hollow balls of cells that closely resemble embryos at the stage when they usually implant in the womb — known as blastocysts. The new laboratory-made embryo-like entities have been dubbed "blastoids."
"We are very excited," says Jose Polo, a developmental biologist at Australia's Monash University, who led the second experiment. "Now with this technique, we can make hundreds of these structures. So this will allow us to scale up our understanding of very early human development. We think this will be very important."
Some other scientists are hailing the research.
"I would consider this as a major advance in the field," says Jianping Fu, a professor of mechanical engineering at the University of Michigan, Ann Arbor, who co-wrote a commentary accompanying the research. "This is really the first complete model of a human embryo."
"I think that creating embryo-like models is extremely important," agrees Magdalena Zernicka-Goetz, a biology professor at the California Institute of Technology who has done similar research that she's planning to publish.
The blastoids appear to have enough differences from naturally formed embryos to prevent them from ever becoming a viable fetus or baby. But they appear to be very close.
"Which then raises a very interesting question of, at what point does an embryo model become a real embryo," says Insoo Hyun, a bioethicist at Case Western Reserve University and Harvard University.
The two experiments started with different cells to get similar results. Wu's group created his blastoids from human embryonic stem cells and from "induced pluripotent stem cells," which are made from adult cells. Polo's group started with adult skin cells.
"This work is absolutely unnerving for many people because it really challenges our tidy categories of what life is and when life begins. This is what I call the biological-metaphysical time machine," Hyun says.
Hyun agrees the research is very important and could lead to many other advances. But Hyun says it's important to come up with clear guidelines about how scientists can responsibly be permitted to pursue this kind of research.
Hyun favors revising a guideline known as the 14-day rule, which prohibits experiments on human embryos in the lab beyond two weeks of their existence. Hyun says exceptions should be allowed under certain carefully reviewed conditions.
"I think it should be done case by case in an incremental fashion," Hyun says. "I'm not in favor of having a complete free-for-all. I think it should be carefully thought through for exceptional cases here and there."
But others worry about easing the 14-day rule.
That could mean "we could just keep growing these sort-of humans in a test tube and not even considering the fact that they're so close to being human, right?" says Kirstin Matthews, a fellow in science and technology policy at Rice University. "I guess I watch too much sci fi, because I find it really disturbing."
In fact, a team of scientists at Israel's Weizmann Institute of Science figured out how to grow mouse embryos outside the womb — a step toward creating an "artificial womb," according to a report published Wednesday in the journal Nature.
MARY LOUISE KELLY, HOST:
Scientists have created living entities in lab dishes that resemble human embryos more closely than ever before. The goal - gain insights into human early development and find new ways to prevent and treat many medical problems. But the research is raising sensitive moral and ethical concerns. NPR health correspondent Rob Stein has the story.
ROB STEIN, BYLINE: For decades, scientists have been trying to unlock the mysteries of how a single cell becomes a fully formed human being. What goes wrong to cause genetic diseases, miscarriages, infertility? But embryonic development is mostly hidden inside women's bodies during pregnancies, and it's difficult and controversial to study human embryos in the lab. Jun Wu is a molecular biologist at the University of Texas Southwest Medical Center in Dallas.
JUN WU: We know a lot about animals like mice and rats, but not a lot with human early development. (Unintelligible) black box. We really don't know much about human development.
STEIN: So scientists started coaxing human cells in lab dishes to form themselves into what looked like very primitive human embryos. These entities are called embryoids. Now, Wu and another international team of scientists have gone farther than ever before. They have created complex balls of living cells that look a lot like embryos at the stage when they usually implant in the womb to begin developing into babies. Embryos at that stage are called blastocysts, so the scientists call these blastoids (ph). Jose Polo at the Monash University in Australia leads the other team.
JOSE POLO: We are very excited, yes. We are very excited that now, with the technique, we can create hundreds of these structures. So it will allow us to scale up our understanding of very early human development. So we think that this will be very important.
STEIN: Other scientists are hailing the research. Jianping Fu is doing similar experiments at the University of Michigan.
JIANPING FU: I will consider this as a major advance in the field. This is really the first complete model of a human embryo. This is really a major advance.
STEIN: Now, these blastoids aren't quite complete enough to make a baby, and that's not what these scientists are trying to do, but they are getting pretty close.
INSOO HYUN: Which then raises a really interesting question of, at what point as an embryo model become a real embryo?
STEIN: Insoo Hyun a bioethicist at Case Western Reserve University and Harvard. He says these blastoids raise questions about how far scientists should be allowed to go. And he notes these blastoids were made from stem cells and skin cells, no need for sperm or eggs.
HYUN: This work is absolutely unnerving for many people because it really challenges our tidy categories of what life is and when life begins. This is what I call the biological metaphysical time machine.
STEIN: Now, Hyun says this research could be very valuable, so it's important to come up with clear new guidelines so scientists know what's permissible and what's off limits. But Kirstin Matthews, a bioethicist at Rice University, worries about any suggestion of easing restrictions on these kinds of experiments.
KIRSTIN MATTHEWS: Which means that we could just keep growing these sort of humans in a test tube and not even considering the fact that they're so close to being human, right? I guess I watch too much sci-fi, so I find it really disturbing.
STEIN: In fact, another team of scientists in Israel is now reporting that they've figured out how to grow mouse embryos in their lab outside of a uterus, a step toward a so-called artificial womb. Now, the researchers who created these blastoids say they have no intention of doing anything like that. They just want to study their blastoids in the lab for short periods. And current guidelines bar scientists from keeping them alive for more than 14 days. But experiments like these have stirred moves to lift that prohibition.
Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.