Scientists announced the creation of the first synthetic human embryos using stem cells and without donor sperm and eggs, according to the English newspaper The Guardian .
The study was presented at the annual meeting of the International Society for Stem Cell Research in Boston (USA), not without controversy over its ethical and legal implications.
The authors of the work maintain that these model embryos, similar to those found in the early phases of human development, could be "crucial for investigating genetic disorders and the causes of spontaneous abortions."
They clarified that they were designed to lack an autonomous brain and heart, so they could not develop during pregnancy even if they were implanted. And they added that the mouse embryos created with the same technique a year ago and implanted in females did not reach term in any case.
As explained by Professor Magdalena Żernicka-Goetz, from the University of Cambridge and the California Institute of Technology, the models were generated by reprogramming embryonic stem cells. This allows them to work on a step of gestation, gastrulation, in which the cells of each organ begin to differentiate. The legal limit for the development of embryos in the laboratory is 14 days, and this process begins at the third week of gestation.
According to The Guardian publication , there is no short-term prospect of synthetic embryos being used clinically. It would be illegal to implant them in a patient’s uterus, and it is not yet clear whether these structures have the potential to continue maturing beyond the early stages of development.
The motivation for the work is to understand the "black box" period, which scientists call the period of 14 days in which it is legal to grow embryos in the laboratory.
Robin Lovell-Badge, head of stem cell biology and developmental genetics at the Francis Crick Institute in London, said: "The idea is that if you actually model normal human embryonic development using stem cells, you can gain a wealth of information about how we start development, what can go wrong, without having to use early embryos for research.”
Previously, Żernicka-Goetz’s team and a rival group at the Weizmann Institute in Israel had shown that mouse stem cells could be encouraged to self-assemble into early embryo-like structures with an intestinal tract, the beginnings of a brain and a beating heart Since then, a race has been underway to translate this work into human models, and several teams have been able to replicate the early stages of development.
Full details of the latest work, from the Cambridge-Caltech lab, have not yet been published in a scientific journal. But during the lecture, Żernicka-Goetz described growing the embryos to a stage just beyond the equivalent of 14 days of development for a natural embryo.
The model structures, each grown from a single embryonic stem cell, reached the beginning of a developmental milestone known as gastrulation, when the embryo transitions from a continuous sheet of cells to forming distinct cell lines and establishing the basic axes of the body. At this stage, the embryo does not yet have a beating heart, intestine or early brain, but the model showed the presence of primordial cells that are the precursor cells of the egg and sperm.
“Our human model is the first three-lineage human embryo model that specifies amnion and germ cells, egg and sperm precursor cells,” Żernicka-Goetz had stated in a previous interview with The Guardian . “It is beautiful and created entirely from embryonic stem cells,” she added.
The development showed that science has advanced faster in this field than the law, so scientists in the UK and elsewhere are now aiming to draw up voluntary guidelines governing work with synthetic embryos. “If the whole intention is for these models to look very similar to normal embryos, then in some ways they should be treated the same way,” Lovell-Badge said. “Currently in the legislation they are not. People are worried about this,” she added.
There is also an important unanswered question about whether these structures, in theory, have the potential to become a living creature. “That is very difficult to answer. It’s going to be difficult to know if there’s an intrinsic problem with them or if it’s just technical,” Lovell-Badge said. And he emphasized that this unknown potential makes the need for stronger legislation urgent.
In parallel with the case of embryos in mice, in April, researchers in China created synthetic embryos from monkey cells and implanted them in the uteruses of adult monkeys, some of which showed the first signs of pregnancy, but none continued to develop beyond of a few days. Scientists say it is unclear whether the barrier to more advanced development is merely technical or has a more fundamental biological cause.
