A day after news broke of a Chinese scientist who claims to have helped make the world's first genome-edited babies, researchers fear the startling announcement will hinder their efforts to safely translate gene-editing technology into treatments..

As scientists gathered for the Second International Summit on Human Gene Editing in Hong Kong today, conversation constantly turned to He Jiankui 's claim – which is yet to be independently verified – to have impregnated a woman with embryos that had been modified to make them resistant to HIV infection. The woman gave birth to healthy twin girls this month, said He, a genome-editing researcher at the Southern University of Science and Technology of China in Shenzhen, in a video posted to YouTube.

The claim prompted s hock and outrage from scientists , who questioned He's justification for carrying out a preliminary and potentially risky procedure in people, without an international scientific consensus about whether and how such an experiment should be conducted. Even He's own university distanced itself from the results. Now scientists are also raising the prospect of a chilling effect on gene-editing.

“I'm worried about a knee jerk reaction that might cause countries still working on regulations to make it unnecessarily hard to do this research,” says Robin Lovell Badge, a developmental biologist at the Francis Crick Institute in London, who is attending the summit that runs from today until 29 November.

Jin Soo Kim, a molecular biologist at Seoul National University and meeting attendee, has been trying to persuade the South Korean government to relax its strict regulations on embryo research . The country does not allow research on embryos, including using gene-editing tools such as CRISPR–Cas9. Now Kim is worried that He's claims will lead to more restrictions in South Korea.

Chinese concerns

Such concerns are particularly acute in China, where scientists are sensitive to the the country's reputation as a wild west of biomedical research. The Genetics Society of China and the Chinese Society for Stem Cell Research issued a joint statement on 27 November saying: “We strongly condemn it for the extreme responsibility, both scientific and ethical.”

The groups' statement also distanced He's work from mainstream science in China. “The experiment conducted by He is an individual activity,” it said. They also call for government investigations.

On 27 November, the Chinese national health commission ordered the Guangdong Health commission, where He's university is located, to investigate. The government of Shenzhen has also announced an investigation into the ethics approval that is claimed on the trial notification posted online.

Rosario Isasi, a legal scholar at the University of Miami in Florida, says scientists in China fear the country has picked up an unfair reputation for being lax with its regulation of scientific research . This latest announcement won’t help, says Isasi, who has been working with the Chinese Academy of Sciences as an international fellow. “For the Chinese this is hurtful and they are tired,” she says. In 2015, a research group in China fired up debate around using gene-editing in human embryos by publishing the first such use of the technology , although in that case the embryos were not implanted.

Paula Cannon, who studies HIV at the University of Southern California in Los Angeles, says the news could also worsen the stigma of having HIV. He's procedure, in her opinion, casts being HIV positive as a condition that is so awful that people need to be genetically modified to overcome merely being susceptible to infection, she says. “The damage he’s done to the field of gene editing, to HIV-positive individuals and their allies, to Chinese scientists. It’s just horrible," she says.

Evidence needed

Other researchers think it is too early to say whether a backlash will affect support for genome-editing research and are eager to hear what He has to say at the meeting tomorrow, when he is scheduled to give a talk.

“The researchers here will be circumspect. They will watch reaction — there's been a lot of negative reaction. A lot will depend on what we learn from He Jiankui,” says meeting attendee Dana Carroll, a biochemist at the University of Utah in Salt Lake City.

Scientists at the meeting have many questions for He. Above all they want to see evidence of his claims, including sequencing data from the parents and twins to show that genome edits were made. They also want evidence that there were no dangerous off-target mutations and to determine whether either of the girls is genetically mosaic — a condition in which populations of cells within an individual have different genomes.

He will also have to explain whether he had proper ethical approval for the work. That He has made so little data available so far, with his announcement confined to the YouTube videos, has frustrated scientists.

When asked what data she hopes to see presented tomorrow, Jennifer Doudna, a biochemist at the University of California, Berkeley, and pioneer of CRISPR–Cas9, says: “Anything!”

Damaging claims Doudna worries that CRISPR could become associated with He’s claims, which could be damaging if the babies turn out not to be healthy.

But she believes that there will remain public support for gene editing of embryos for reproductive purposes. Surveys have shown there are a lot of people open to human germline editing, she says.

The revelations about gene-edited babies have forced Doudna and other scientists to contemplate the need for a detailed set of criteria for responsible 'germline' editing, which involvesembryos, sperm and eggs. Those criteria need to include what level of uncertainty in the editing process is permissible for proceeding with a procedure, she says. “There’s a potentially positive outcome,” she says.

The meeting, which is sponsored by the Academy of Sciences of Hong Kong, the Royal Society of London, the US National Academy of Sciences and the US National Academy of Medicine, released a non-committal statement on He's work today. "We hope that the dialogue at our summit further advances the world’s understanding of the issues surrounding human genome editing," says the statement. "Our goal is to help ensure that human genome editing research be pursued responsibly, for the benefit of all society." The statement also notes He's upcoming talk on 28 November.