What is mirror life? Experts are raising red flags
Mirror cells would likely be immune to viruses and unrecognisable to the human immune system
"Mirror life" refers to hypothetical living cells built entirely from molecular components that are the mirror image of those found in all known organisms on Earth.
In chemistry, this property is called chirality — a term derived from the Greek word for "hand". Just as left and right hands are mirror images that cannot be superimposed, biological molecules also exist in left- and right-handed forms.
"Most major biological molecules, including all proteins, DNA and RNA, point in one direction or another. In other words, they are chiral, or handed," according to excerpts from The Ecological Risks of Mirror Life.
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All known natural life uses L (left-handed) amino acids in proteins and D (right-handed) sugars in DNA and RNA. In contrast, mirror life would use D proteins and L sugars — effectively a reversed version of biology as we know it.
"This so-called mirror life – living cells made from building blocks with an opposite chirality to those that make up natural life – could have very similar properties to natural living cells," the paper said.
Why are researchers pursuing "mirrored life"?
The idea of creating mirror life has attracted scientists seeking to answer fundamental biological questions and to pioneer new applications in medicine and biotechnology.
"Mirror bacteria in particular had the potential to be a useful basic research tool – possibly allowing scientists to study a new tree of life for the first time and solve many problems in bioengineering and biomedicine," one analysis found.
Because mirror molecules do not interact with ordinary biological systems, they could be used to make drugs that are more stable inside the body. "Mirror molecules are inert chemicals with tremendous benefits," said Michael Kay, a professor of biochemistry at the University of Utah. Such "molecular invisibility" allows drugs to circulate longer without being degraded by enzymes or the immune system.
Researchers also see potential in industrial biotechnology, where mirrored microbes could resist natural viruses or toxins, reducing contamination and enabling new forms of biomanufacturing.
Growing concerns among scientists
Despite its scientific promise, concern has deepened over what might happen if self-replicating mirror cells were ever created and escaped containment.
"As I learned more about the immunology and ecology of mirror life, however, I became aware of the potential environmental and health consequences of this technology," said one synthetic biologist and bioengineer, the implied author of The Ecological Risks of Mirror Life. "I and a group of researchers in immunology, ecology, biosafety and security – including some who used to actively work on mirror life – conducted a thorough analysis of possible concerns regarding the creation of mirror life."
Over the course of 2023 and 2024, those ad hoc discussions evolved into a working group of 38 scientists, including Kate Adamala. In December 2024, the group published a high-profile article in Science titled "Confronting Risks of Mirror Life," which summarised the findings of a detailed 300-page report compiled by the same group.
The Science report concluded that "the potential benefits of engineering mirror life are not worth the risk". The risks, they said, stem from the fact that mirror organisms would be invisible to natural life's defences.
"If mirror cells were released into the environment, they would likely be able to quickly proliferate without much restriction," the report said. "It would be much worse news to the rest of the ecosystem, because mirror bacteria might hog all the nutrients and spread uncontrollably."
David Relman, professor of microbiology and immunology at Stanford University and one of the group's contributors, warned: "There is the possibility that, with admittedly a great deal of work, we could create something which could grow inexorably, spread across the planet and displace or kill many, many forms of life, including us, the animals around us, the plants around us, and even some of the microbes."
"Existential risk"
Relman described mirror life as "the first plausible existential risk" he had encountered in a long scientific career. "We scientists … think about whether we should, not whether we could," he said.
"Mirror life would likely be resistant to viruses," one analysis found. "Mirror cells likely wouldn't pass the first step of that screen: it would not induce an immune response because the immune system would not be able to recognise or bind to mirror cell antigens."
Kate Adamala, a synthetic biologist who initially supported the research, said, "It was never one light bulb moment. It was kind of a slow boiling over a few months." As she and others examined the potential consequences, "The more we looked, the more we were certain, and more people were coming on board to this idea that there actually is no safe way to make a mirror cell."
Even containment measures may not be sufficient. "Consequently, one should see the elephant in the petri dish: mirror life could be unstoppable if released to the natural world," said Faouzi Braza, a senior biotechnology officer.
John Glass, a professor at the J. Craig Venter Institute, reflected on the moral dimension: "It made me wonder if the thing, the work that I have been doing for years, could be enabling, one day, the mirror bacteria-based Armageddon that we fear."
Although researchers estimate that fully self-replicating mirror cells remain decades away, the ethical debate has already begun. "Pretty much everyone agrees that we should not make a living mirror cell," said Adamala. "That's the baseline but below that people have a lot of different ideas where should we stop the research."
The Science article and its accompanying report concluded, "No matter how we looked at it, straight up or in the mirror, the conclusions were clear: The potential benefits of engineering mirror life are not worth the risk."
As one summary put it: "This is mirror life: a biological world, where the most fundamental rules of biology lose their anchor and the familiar unravels into fascinating weirdness."
