The Chinese researcher who startled and outraged the scientific world bysaying he had genetically edited a pair of twin girls, on his own and without any official permission, said on Wednesday he was proud of what he had done.

He Jiankui of China’s Southern University of Science and Technology presented some details of his work at a meeting on genome editing in Hong Kong. He said twins, Lulu and Nana, were healthy baby girls and that he thought another woman might be pregnant with a genetically edited embryo.

He said he was working to help people with the human immunodeficiency virus (HIV), but has paused further work for the time being, while defending his methods.”For this specific case, I feel proud,” He told a packed-out audience at the meeting.

“Lulu and Nana were born normal and healthy.”

It was the first the public had seen of any evidence He had done what he said he did — genetically altered two early human embryos, then implanted them into a woman, who carried them to term. He promised to publish his research in a scientific journal.

If it is proven true, it would be the first time a human being had been genetically altered in this way.

The claim both angered and worried other researchers in the field, who said it was dangerous, irresponsible, and unethical.

“It is profoundly unfortunate that the first apparent application of this powerful technique to the human germline has been carried out so irresponsibly,” National Institutes of Health Director Dr. Francis Collinssaid in a blog post.

The meeting was being held to discuss the field of gene editing, which is moving forward slowly and cautiously because of the questions around the work, the risks it poses to the unborn infants who will be the subjects of any experiments, and the questions it raises for society as a whole.

Dr. David Baltimore, a Nobel laureate, leading AIDS researcher and expert in immunology, called He “irresponsible.” Baltimore, who supports a moratorium on human gene editing, said He’s experiment was medically unnecessary. “I don’t think it has been a transparent process. We only found out about it after it happened, so we feel left out,” Baltimore said at the Hong Kong meeting.

“It is impossible to overstate how irresponsible, unethical and dangerous this is at the moment. It will take a thorough investigation to find out exactly what happened and what if any approvals were in place before the experiment began,” stem cell biologist Kathy Niakan of Britain’s Francis Crick Institute said in a statement.

Genome editing is a relatively new scientific technique that can be used to precisely alter the DNA of cells. A process called CRISPR-cas9 is the best-known tool for genome editing, and promises to be an advance on the less precise methods now used to genetically alter cells, which often use a virus to insert new DNA and which can have unexpected results.

Genome editing, as opposed to genetic engineering, is meant to permanently alter the DNA in all of an organism’s cells. Scientists approach it with caution because of the risk of unexpected consequences that could haunt not only the patient, but his or her progeny.

Most countries have laws or regulations either banning experiments on humans outright, or making it very difficult to perform the work.

He circumvented the scientific community’s own self-imposed moratorium on the work. He said he worked outside the labs and procedures of his university, but officials at Southern University of Science and Technology said they were investigating.

Health

Usually, when working on human beings, researchers must get permission from their institutions as well as their governments. In the U.S., the Food and Drug Administration regulates experiments on people. Legitimate scientists also usually publish their work on journals or at conferences, which employ staff to review the methods and processes and usually also ask other known experts in the same field to review the reports before they are published.

He, who had described his work extensively to the Associated Press before the conference, apologized that it had “leaked”. He said he was trying to help people with HIV and was working with a group of well-educated and deeply informed parents, who knew what they were getting into.

He said he genetically altered a gene called CCR5, which is a well-studied stretch of DNA that can make people resistant to infection with HIV. People with certain versions of the CCR5 gene are rarely infected with HIV even when they are exposed to it.

He said the father of the twins was infected with HIV and the mother was not. He aimed to genetically engineer babies that would be resistant to HIV.

He used a common fertility method called Intracytoplasmic sperm injection or ICSI to create embryos in a lab dish and then genetically altered their DNA. One twin has two copies of the desired CCR5 gene while the other has one copy, He said.

He said he had experimented first on mice, then monkeys and finally on human embryos that could not ever develop before he finally tried his method on a viable embryo.

He said he paid for the treatment himself, something Niakan called a conflict of interest. “He’s presentation did nothing to assuage my scientific, moral or ethical concerns about the work,” she said. “The team doesn’t seem to have had adequate training on proper consent processes, and offering vulnerable patients free IVF treatment presents a clear conflict of interest.”

NIH’s Collins said He had “flaunted” international norms.

“Lest there be any doubt, and as we have stated previously, NIH does not support the use of gene-editing technologies in human embryos,” he said.

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