Gene-edited babies are now closer to becoming a reality. The ethical debate is far from settled

(CNN) — Pioneering gene-editing treatments are already in clinical use, saving lives and easing the pain of devastating genetic diseases. However, the growing number of patients receiving these treatments still run the risk of passing their disease-causing mutations to their children.

Scientific consensus — and the law in 70 countries — has long acknowledged that it’s too dangerous to use the powerful technique for human germline editing, the process of manipulating human embryo DNA to avoid genetic diseases and prevent them from being passed down from one generation to the next.

New research, however, has found that it’s now possible to edit the DNA of human embryos with unprecedented precision, suggesting that human germline editing might be possible in the relatively near future. Scientists, however, have warned that significant obstacles remain before they reach the point where it’s possible to safely edit viable human embryos.

“Six years ago, I thought the use of gene editing in human embryos was a non-starter,” said Amander Clark, a professor of molecular cell and developmental biology at the University of California, Los Angeles, and director of the UCLA Center for Reproductive Science, Health and Education.
“This work restores the possibility that gene editing for therapeutic purposes could be possible with IVF embryos in the future,” Clark, who wasn’t involved in the research, said via email.

Lab research on human embryos, usually donated by in vitro fertilization patients, remains strictly regulated in most countries and is usually only permitted for a period of 14 days after the embryo’s creation. It’s also unclear how supportive public attitudes are toward gene-edited babies; beyond questions of medical safety, skepticism is largely driven by ethical questions around this cutting-edge technology’s potential use in creating so-called “designer babies” whose genes are edited or intentionally selected for desirable traits.

Sharpening a blunt tool

The gene-editing technique known as CRISPR-Cas9 is used in laboratories around the world and has revolutionized scientific research, allowing scientists to edit the genes of living organisms for biotechnology and medical research. In 2020, two of the scientists who devised the technology won the Nobel Prize in chemistry, and in 2023, the US Food and Drug Administration approved the first two gene therapies for sickle cell disease, a debilitating and life-shortening inherited red blood cell disorder that disproportionately affects African Americans.

But, in some respects, CRISPR-Cas9 is a blunt tool. When the technology edits DNA it creates a double strand break at the target site in the helix, and when used to modify human embryos, several studies have shown it to result in large and unintended changes — possibly even the loss of an entire chromosome.

The potential for unknown health effects is one reason why the scientific community condemned the work of Chinese researcher He Jiankui when he revealed in 2018 the existence of two girls who had been born from embryos he said he had modified using CRISPR-Cas9 to make them resistant to HIV. He received a three-year jail sentence in 2019 but has since been released. He did not respond to a request for comment.

Modifying a single letter of DNA

A newer, more precise form of CRISPR, known as base editing, can change a single letter (or base) of DNA at a time.

Base editing was used for the first time in a 2022 clinical trial to modify the immune cells of a UK teenager after doctors exhausted all other options to treat her form of leukemia. Eight other children and two adults have gone on to receive the treatment. And last year, doctors used base editing to treat a baby born with a severe CPS1 deficiency, a rare and dangerous genetic disease.

Now, two new studies have used the technique to edit human embryos in the earliest stages of development, donated for research purposes by individuals who underwent IVF treatment. Both teams found that the precision of the technique reduced the likelihood of unintended chromosomal abnormalities.

Kathy Niakan, a professor of the physiology of reproduction and a director of the Loke Centre for Trophoblast Research at the University of Cambridge, and her team used the technique to better understand how a pivotal gene in human embryo development functioned. They discovered that a gene called NANOG — named for the mythical Celtic Tír na nÓg, or land of the ever young — plays a key role in how the first embryonic cells that ultimately become the fetus and placenta are established. The study was published June 25 in the scientific journal Nature.

Niakan said base editing represented a significant advance on conventional CRISPR-Cas9 because it carries a far lower risk of causing unintended chromosome errors. “Base editing can precisely change a single nucleotide base pair to another in an entire human genome of around 3 billion base pairs — that’s an incredible feat,” she explained.

In a separate study, Dietrich Egli, an associate professor of developmental cell biology at Columbia University, used base editing to insert one of two genetic mutations into newly fertilized eggs. One targeted a gene known as PCSK9 that regulates cholesterol and another targeted HBG, which encodes the fetal form of hemoglobin, a protein that carries oxygen. He chose these two genes because they were well-studied targets in non-heritable gene editing. Egli said a peer-reviewed scientific journal had conditionally accepted the study.

While both studies represent a step toward heritable gene editing, Egli said it is still a long way from use in a clinical setting. Even though base editing doesn’t appear to cause major chromosomal damage, at least two major downsides remain.

Egli, Niakan and their teams found that some of the embryos they edited went on to display what they described as “mosaicism,” when the intended edit doesn’t take effect in all cells. In addition, they both found some “off-target” effects, in which unintended genes were altered. This presents a risk in human embryo editing because that embryo will give rise to every cell in the body.

“This is a long stairway with many different steps and maybe some plateaus in between,” Egli said. “We started at the very bottom and we’ve made a few steps in that direction, but I think we can look at the progress that has been made, and the discussion can be had about the pros and cons of going further.”

Genome editing in human embryos has value, allowing scientists to understand the rules that govern the earliest stages of human life, said Helen O’Neill, an associate professor in reproductive and molecular genetics at the Institute for Women’s Health, University College London. She was not involved in either study.

“It can help us understand why so many embryos in IVF fail to develop, arrest, implant or progress, despite appearing morphologically acceptable,” O’Neill said in statement.

“In the longer term, it may help us think more clearly and compassionately about a very small group of patients with serious inherited conditions for whom preimplantation genetic testing is not enough.”

O’Neill added that the debate around embryo editing is often framed as if the only possible endpoint is designer babies. “That framing misses the actual scientific and clinical value,” she noted.

The concerns around designer babies

Laurie Zoloth, a professor of religion and ethics at the University of Chicago, said the research activated once more the ethical debate about altering human embryos, noting that editing embryos is risk laden and, except for use in scientific research, should therefore remain banned for the time being on the grounds of safety alone. She noted there are already ways to avoid having babies with genetic abnormalities — using genetic screening before conception and during pregnancy, and testing embryos prior to implantation during IVF.

“The problem of mosaicism is not resolved; they don’t really understand the long-term effects of the intervention; and there is no way to do a trial of a pregnancy without, well, an actual pregnancy and a child,” she said in an email.

There are also longer range theological and philosophic issues around “designing” babies to have desirable traits, she added.

“These are even more profound when they seem to be designing babies that in the long distant future would be at lower risk for cardiovascular issues which could be addressed by lifestyle choices and may well be completely treatable by medications in that hypothetical future anyway.”

While it might be defensible to edit embryos to prevent conditions such as Tay-Sachs, a fatal neurological disorder that attacks in the first few months of life, she said there would likely be “slippage between treatment and enhancement,” a situation that could lead to what Zoloth called the “Gattaca problem” after the 1997 film, which imagines a society obsessed with and dictated by genetic perfection.

“Might this road lead us to a future that is even more unfair and unjust with the children of the wealthiest curated, and the children of the poor without resources, unable to compete in a democracy,” she said.

“It is striking that on the one hand we might have the capacity to spend so many resources and attention on altering the genetic code of an embryo to get it precisely in line with what we think is normal or optimal when we cannot figure out how to provide clean, safe and engaging elementary schools for children with well-paid teachers once they are born,” Zoloth added, noting that knowledge of how human genetics affects physical traits and behavior is still very limited.

A newly released survey on public attitudes toward research on human embryos in four countries indicated that a majority of respondents in the UK, the Netherlands and Spain supported the use of genome editing in embryos that would help establish a pregnancy by eliminate a severe or life-threatening condition. However, in Italy that figure was 46%.

Zoloth noted that while bioethicists have a duty to reflect and raise questions, prohibiting science also has its risks.

“We don’t want to prohibit inquiry,” she said. “That is why setting guardrails for new science is important, and protective both of the inquiry and of the society.”

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