Researchers led by developmental biologist Kathy Niakan at the University of Cambridge have used base editing in human embryos to learn more about human embryonic development. By deactivating a gene called NANOG, the group shows the gene is required for proper cell differentiation at this early stage in development (Nature 2026, DOI: 10.1038/s41586-026-10792-1). The study is the first demonstration of base editing in human embryos for the purpose of understanding human embryonic development.
“We know very little about how the very first cell types that emerge in a human embryo become specialized in their fate and function, and which genes are fundamentally required for this process,” Niakan said on a call with journalists. But this new work has “revealed the role of a master gene,” she added.
Only 3 weeks ago, the scientific community erupted with a mixture of praise and alarm when a group led by Dieter Egli at Columbia University reported the first use of base editing in human embryos. That study showed the gene-editing technique could accurately correct a pair of disease-causing mutations in the human embryonic genome but with significant consequences that prove the technique isn’t ready for use in in vitro fertilization (IVF) in the clinic.
Niakan’s work, in part, corroborates some of Egli’s findings. Both studies show that some base-edited embryos are mosaic, where not all cells carry the gene edit, and that there are unintended bystander mutations near the editing site. The new study also demonstrates that base editing is an improvement over CRISPR-Cas9 for embryonic editing; in 2017 Niakan published a paper showing that using CRISPR in human embryos can cause the loss of entire chromosomes (Nature, DOI: 10.1038/nature24033). Base editing, which creates precise single-nucleotide substitutions in DNA without inducing destructive double-strand breaks, did not result in any mutations of that nature.
Unlike the work from Egli’s group, the NANOG knockout study doesn’t carry with it the implication that these embryos would ever be implanted and developed in a human. NANOG is essential to embryonic development—without the gene, some early embryonic cells fail to establish pluripotency, which is the ability to differentiate into the myriads of cell types we have in our bodies.
Instead, the NANOG knockout study shows how the gene works differently between mice and humans.
A 7-day-old embryo, called a blastocyst, has roughly 200 cells. About 20 of those cells are epiblast progenitor cells, which are precursors to the fetus and enriched with NANOG proteins, and two other small subsets of progenitor cells develop into the yolk sac and placenta. When researchers knock out NANOG in mice, it disrupts the development of epiblast progenitor cells and yolk sac progenitor cells, but in humans the yolk sac progenitor cells seem to develop normally.
This difference shows that model organisms aren’t a perfect substitute for learning about human embryonic development, Niakan said.
Differences in opinion about base editing in IVF
Both Egli and Niakan claim their work is meant to help improve the success rate of IVF, which can be a lengthy and grueling process with no guarantee of success. But Niakan said that “it would be really unethical” to use base editing during the IVF process at the moment.
Instead, Niakan hopes that a better understanding of embryonic development improves IVF by “developing better ways to maintain and grow the embryos, so we can improve rates of blastocyst development or selection for implantation” and to “establish rational optimized techniques for stem cell research and regenerative medicine.”
She also said that work like hers has “important implications for stem cell biology” and ;may help to understand some causes of pregnancy loss and miscarriage.
But not all agree the ends justify the means.
C&EN reached out to David Barrett, CEO of the American Society of Gene and Cell Therapy (ASGCT), to ask if he thought this work was an acceptable use of human embryonic gene editing. He replied by email, saying no. ASGCT, in collaboration with other organizations, called for a 10-year moratorium on heritable human genome editing (Cytotherapy 2025, DOI: 10.1016/j.jcyt.2025.05.007). Barrett says, “This work, while nonclinical in nature, does not comport with the moratorium. . . . It is not merely a question of scientific feasibility. We have not developed a reasonable understanding of societal impact, scientific and safety standards, or ethical and global oversight.”
R. Alta Charo, an emerita professor of bioethics at the University of Wisconsin–Madison and an independent consultant on bioethics for the biotech industry, has a different view. She says Niakan’s work “is important research for understanding basic embryonic development, regardless of what its clinical use might be down the road.” And she adds that “the reason we’re able to see this kind of work done in England is because they don’t have the same level of restriction on funding for this kind of work.”
In the US, research using human embryos is subject to a patchwork of regulation. The biggest barrier is that no federal funding can be used to support a project that results in the destruction of human embryos.
In the UK, research into human embryos is regulated by the Human Fertilisation and Embryology Authority (HFEA). Niakan worked with the HFEA to review and revise the project before it got approval. Patient groups and members of the public also helped the research team develop informed-consent documents—all the embryos used in the study were donated by people who were informed of the nature of the project.
