Leading genomic scientists from around the world called for an immediate halt to any clinical use of gene editing in human embryos and sharply reprimanded a Chinese researcher who conducted an experiment that he says produced the world’s first genetically edited babies.

The statement came at the conclusion of the Second International Summit on Human Genome Editing in Hong Kong. Later, the Chinese government said it had suspended and launched a probe into the clinical project run by researcher He Jiankui in southern China.

The announcements from the leading scientific body and Chinese authorities capped a dramatic week for the genomics world starting when He made the stunning revelation that a mother had given birth to Lulu and Nana, twin girls whose genes had been edited to make them resistant to HIV.

Hours after the summit closed Thursday, a high-ranking Chinese official told a state broadcaster He’s project has been suspended amid a government investigation. The official did not indicate whether He was charged with any crimes.

“It’s flagrantly violated our national regulations and flagrantly broken the scientific world’s ethical bottom line,” Xu Nanping, vice minister of science and technology, told CCTV in an interview. “It’s shocking, unacceptable, and we firmly oppose it.”

The summit organizers were similarly critical in a highly anticipated consensus statement issued on the event’s last day.

“At this summit we heard an unexpected and deeply disturbing claim that human embryos had been edited and implanted, resulting in a pregnancy and the birth of twins,” said the summit’s organizing committee, which called for independent verification of He’s claims that have so far not been published in a peer-reviewed journal.

“Even if the modifications are verified, the procedure was irresponsible and failed to conform with international norms,” the organizers said in the summit’s consensus statement that is expected to set the tone and direction for the fast-changing field.

 The committee, representing leading researchers from the United States, Britain, China and five other countries, did not call for an outright ban on gene editing that could be inherited.

Instead, it acknowledged that the field was moving toward a future where the procedures would be widely studied in clinical trials and that researchers needed a rigorous framework to set ethical standards and guidelines. But in the meantime, the panel called for a halt.

“The organizing committee concludes that the scientific understanding and technical requirements for clinical practice remain too uncertain and the risks too great to permit clinical trials of germline editing at this time,” the closing statement said.

He’s work was widely criticized this week by peer researchers and ethicists as a rogue demonstration of a gene-editing tool called CRISPR-Cas9, which has opened up a world of possibilities in biomedical research in recent years. Proponents foresee a time when lethal genetic diseases with no treatments could be eradicated, while critics fear the technology might be used for casual genetic enhancements, to tweak traits such as intelligence or height.

But until this week, such debates were largely theoretical, because no one was known to have established a pregnancy from a genetically edited human embryo. He’s claimed experiment was an urgent reminder that discussions about how to responsibly use a technology that could reshape the health and character of future generations might not be enough. 

“The need for development of binding international consensus on setting limits for this kind of research . . . has never been more apparent. Without such limits, the world will face the serious risk of a deluge of similarly ill-considered and unethical projects,” Francis Collins, director of the National Institutes of Health, said in a statement. “Should such epic scientific misadventures proceed, a technology with enormous promise for prevention and treatment of disease will be overshadowed by justifiable public outrage, fear, and disgust.”

Many countries outlaw such experiments, and in the United States, using genetically altered human embryos for reproductive purposes is effectively banned by law. 

After word of He’s project first leaked through news reports, scientists criticized the effort as irresponsible and premature. Investigations were opened into He’s work by China’s Southern University of Science and Technology. He appeared before a packed audience in person and online to defend his work at the summit on Wednesday, but the presentation was far from convincing to experts.

Summit organizers concluded that the “flaws” of He’s work “include an inadequate medical indication, a poorly designed study protocol, a failure to meet ethical standards for protecting the welfare of research subjects, and a lack of transparency in the development, review and conduct of the clinical procedures,” they said.

Outside scientists and ethicists slammed the experiment for being medically unnecessary, because the babies wouldn’t have been born infected with HIV; transmission can be prevented with existing, low-risk interventions. They questioned whether the effort had even succeeded at its own goal of making both girls immune to HIV after seeing He’s data. And they warned the research had not ruled out potentially harmful unintended effects that could afflict the twins and now spread through the human lineage if they have children.

“Having listened to Dr. He, I can only conclude that this was misguided, premature, unnecessary and largely useless,” said R. Alta Charo, a bioethicist at the University of Wisconsin at Madison.

For years, leading scientists have avoided advocating for a ban on gene-editing technology for human reproduction, instead favoring a cautionary approach that such research should not proceed until certain conditions are met.

At the last meeting of the summit in 2015, scientists concluded by saying that it would be “irresponsible” to proceed until the safety concerns had been thoroughly vetted and a societal consensus had developed. But a report two years later by the National Academies of Sciences, Engineering and Medicine said that genome edits that could be inherited “might be permitted” if, for example, there were transparency and an unmet need, among other criteria. A report this summer by the Nuffield Council on Bioethics in Britain concluded that gene editing to influence future generations “could be ethically acceptable in some circumstances.”

Those recommendations suggested the technology could be useful, which may have emboldened He. When he presented his research on Wednesday, he said he was “proud” of his work.

“My original thinking was based on the survey of the United States . . . or the British ethics statement or the Chinese study that gave us the signal that the majority of the public is supporting the use of human genome editing for treatment, including HIV prevention,” He said.

Matthew Porteus, a pediatric stem cell scientist at Stanford University, said that in February, He told Porteus about his animal studies and an open trial in humans.

“I told him that it was irresponsible and reckless to proceed for many reasons and that he needed to discuss his plans with senior authorities in China before proceeding any further,” Porteus said. 

Several scientists said a ban would be premature, but they added that the technology was not ready to be used. Others said a clear message needed to be sent.

“My sense would be, given the circumstances, that anything short of a call for moratorium would be insufficient,” said Paul Knoepfler, a stem cell biologist at the University of California at Davis. “Almost anyone could try this.”

Shih reported from Hong Kong.