A Chinese researcher's attempt to immunise babies against HIV by editing their DNA has failed, scientists say.
Instead his tinkering created unintended mutations.
He Jiankui used technology known as CRISPR-Cas9 to alter the embryonic genes of twin girls born in October 2018. He intended to create a mutation known as CCR5, which would protect them against HIV, the virus which causes AIDS.
But the research - released this week for the first time- shows he failed, scientists say.
"The claim they have reproduced the prevalent CCR5 variant is a blatant misrepresentation of the actual data and can only be described by one term: a deliberate falsehood," said Fyodor Urnov, a genome-editing scientist at the University of California Berkeley.
"The study shows that the research team instead failed to reproduce the prevalent CCR5 variant."
They managed to edit the right genome, but the mutations are wrong. Dr Urnov says it's unclear what effects they'll have.
"The statement that embryo editing will help millions is equal parts delusional and outrageous."
Another said even if it worked, it would take 20 or 30 years to have an effect on HIV rates - by which time we'd have better ways of fighting the condition.
The scientists, quoted in MIT Technology Review, say the couple might only have taken part in the experiment to access fertility treatment for free. The father is HIV-positive, but the gene editing would have had no effect on his children's HIV status as there are already effective techniques to stop it being passed on.
After news of Jiankui's experiment broke, scientists around the world - including in New Zealand - called for a moratorium on further editing of human DNA.
"The case has avoided dealing with ethics properly, and made some gene edits that don't make a lot of sense from either a scientific, a medical or an ethical point of view," Peter Dearden from Genomics Aotearoa said in March.
Jiankui was reprimanded by the Chinese Academy of Science for his research, which called it a "gross violation of both the Chinese regulations and the consensus reached by the international science community".