Geneticist He Jiankui says he’s ‘proud’ of his work, as he defends claims of creating world’s first gene-edited babies.

The Chinese scientist who claims to have created the world’s first genetically-edited babies has paused the trial following an international outcry over the highly controversial procedure.

Geneticist He Jiankui, an associate professor at Southern University of Science and Technology in Shenzhen, defended his work on Wednesday in front of a packed biomedical conference in Hong Kong, saying he had successfully altered the DNA of twin girls born to an HIV-positive father.

If his claims prove to be true, it would be a medical first.

“For this case, I feel proud. I feel proudest,” He said when challenged by several peers at the Summit on Human Genome Editing at the University of Hong Kong.

A total of eight volunteer couples – HIV-positive fathers and HIV-negative mothers – had signed up to the clinical trial, with one dropping out before it was halted.

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He said there had been “another potential pregnancy” involving a second couple, but when questioned further agreed it had been a chemical pregnancy – a term referring to a very early miscarriage.

“I must apologise this result was leaked unexpectedly,” he said of the apparent breakthrough.

“The clinical trial was paused due to the current situation,” he added.

The case prompted a heated debate among the scientific community, with many raising concerns over the lack of verified data and the risks of exposing healthy embryos to gene editing.

The procedure is a potential fix for heritable diseases but it is extremely controversial because the changes would be passed down to future generations and could eventually affect the entire gene pool.

The editing of human DNA is banned in some countries, including the United States, and tightly controlled in others.

‘Backward step’

In videos posted online this week, He said he used a gene-editing technology known as CRISPR-Cas9 to alter the embryonic genes of twin girls born this month.

He said gene editing would help protect the girls from infection with HIV, the virus that causes AIDS.

But scientists and the Chinese government have denounced the work and a hospital linked to his research suggested its ethical approval had been forged.

China’s National Health Commission ordered an “immediate investigation” into the case on Monday, the official Xinhua news agency reported, while the Shenzhen hospital meant to have approved the research programme denied its involvement.

But He took to the stage on Wednesday to justify his work and was bombarded with questions as he told the audience that the parents were aware of the potential dangers when they signed up.

“The volunteers were informed of the risk posed by the existence of one potential off-target and they decided to implant,” he said.

Conference moderator Robin Lovell-Badge said the summit organisers were unaware of the story until it broke this week.

Lovell-Badge called He’s trial a “backward step” for the science industry, but described the babies’ birth as “momentous” nonetheless.

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David Baltimore, a Nobel laureate from the California Institute of Technology and a leader of the conference, said He’s work “would still be considered irresponsible” because it did not meet criteria scientists agreed on several years ago before gene editing could be considered.

The case shows “there has been a failure of self-regulation by the scientific community”, Baltimore said, adding that the conference committee would meet and issue a statement on Thursday about the future of the field.

More than 100 scientists, most in China, said in an open letter on Tuesday that the use of CRISPR-Cas9 technology to edit the genes of human embryos was risky, unjustified and harmed the reputation and development of the biomedical community in China. “Pandora’s box has been opened,” they said.

This is not the first time Chinese researchers have experimented with human embryo technology.

Last September, scientists at Sun Yat-sen University used an adapted version of gene-editing to correct a disease-causing mutation in human embryos.