According to multiple studies, one in three pregnancies results in miscarriage, and one in 33 babies that are born will have a birth defect, due to the embryo forming incorrectly in the womb. Studying how the embryo develops can help us find ways to bring these numbers down. In 2022, we will see advances in this research thanks to stem-cell-based, embryo-like structures that can be grown in the lab.
Stem cells offer a powerful way to study the early development of the embryo. They can be grown in the lab in vast numbers and can be pushed toward making a huge assortment of cell types, including brain, blood, bone, and muscle.
Recently, several researchers have found ways to join stem cells together into small 3D balls of cells, which facilitate the creation of tiny embryo-like structures. These are currently rudimentary—the structures can be variable, they are inefficient to create and are unable to develop much further. Next year, we are likely to see improvements, with more advanced embryo-like structures made from stem cells. And we are also likely to see scientists using these models to investigate specific problems, such as how the embryo implants into the uterus, how organs start to develop or how the embryo ensures that cells are in the right positions.
Such research has traditionally been difficult to perform with human embryos. Parents using in vitro fertilization are able to donate their surplus embryos, but regulation (upheld internationally and enshrined in law in the UK) prevents researchers from culturing them beyond 14 days. This makes it impossible to study the progress of the human embryo directly as it changes from a cluster of cells to a structure with the organization of a rudimentary body—when it is between two and four weeks old. The International Society for Stem Cell Research, which represents researchers in this field, has called for a public dialog about whether this limit should be changed. It is proposing that human embryo culture should be extended on a case-by-case basis. How regulatory bodies will respond to this remains to be seen.
In the meantime, stem-cell embryo-like models might mitigate some of the need to use “real” human embryos at all. They will allow researchers to perform precise studies of embryonic development, seeing how they react when a gene is mutated, for example, or when they are exposed to dangerous chemicals. Because they are made from stem cells, they could even be generated by taking blood or skin samples from patients with a birth defect themselves and winding back the clock to an embryo-like state. This could help us figure out how the defect occurred, and perhaps even take steps to reduce the incidence of such disorders in the future.
The development of embryo-like models will raise many new ethical questions. Other than a potential for moving down a slippery slope toward cloning, stem-cell-based embryo models begin to blur the line between what we regard as human or not. Is an early-stage human embryo, when it’s just a small group of 16 cells, more valuable if it comes from the union of sperm and egg? Or is it the same as if it is derived in the lab from stem cells? Should the moral status often applied to human embryos also apply to groups of cells, even in arrangements that might only vaguely mirror elements of actual embryo development?
As we push further toward models that could alleviate the devastating conditions faced at the very start of life, we will also find ourselves challenged as a society to ask big questions, including the fundamental issue of what it means to be human.
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