A Chinese researcher claims he helped make the world's first genetically edited babies: twin girls whose DNA he says he altered to try to help them resist possible future infection with the AIDS virus.
He Jiankui of Shenzhen revealed it on Monday in Hong Kong to one of the organisers of an international conference on gene editing that begins on Tuesday, and earlier in exclusive interviews with the Associated Press.
There is no independent confirmation of his claim and it has not been published in a journal.
If true, it would be a profound leap of science and ethics. This kind of work is banned in the United States because the DNA changes can pass to future generations and it risks harming other genes.
He says he altered embryos for seven couples during fertility treatments, with one pregnancy resulting thus far.
His goal was not to cure or prevent an inherited disease but to try to bestow a trait few people naturally have: an ability to resist possible future infection with HIV.
"I feel a strong responsibility that it's not just to make a first but also make it an example," he told the AP.
"Society will decide what to do next" in terms of allowing or forbidding such science.
Some scientists strongly condemned the claim.
It's "unconscionable ... an experiment on human beings that is not morally or ethically defensible", said Dr Kiran Musunuru, a University of Pennsylvania gene editing expert and editor of a genetics journal.
"This is far too premature," said Dr Eric Topol, who heads the Scripps Research Translational Institute in California.
"We're dealing with the operating instructions of a human being. It's a big deal."
However, one famed geneticist, Harvard University's George Church, defended attempting gene editing for HIV, which he called "a major and growing public health threat".
Scientists have discovered a relatively easy way to edit DNA. The tool, called CRISPR-cas9, makes it possible to operate on DNA to supply a needed gene or disable one that is causing problems.
It's only recently been tried in adults to treat deadly diseases and the changes are confined to that person.
Editing sperm, eggs or embryos is different - the changes can be inherited. In the US, it's not allowed except for lab research. China outlaws human cloning but not specifically gene editing.
