A Chinese scientist who claims to have created the first genetically edited babies in the world has defended his work.
Speaking at the genome summit in Hong Kong, He Jiankui said he was "proud" of changing the genes of twin girls.
Earlier this week, he announced that he had changed embryo DNA to prevent them from contracting HIV. However, his work has not been verified.
Many scientists have condemned the announcement. Such gene editing work is banned in most countries, including China.
Prof He University – South University of Science and Technology in Shenzhen – said that they did not know about the research project and would conduct an investigation. It said Mr He had been on leave without pay since February.
Prof. He stressed the university was not aware, adding he had funded the experiment itself.
He had spoken at the Human Genome Editing Summit at the University of Hong Kong for the first time about his work since the uproar.
He revealed that twin girls – known as "Lulu" and "Nana" – "born normal and healthy", added that there were plans to monitor the twins for the next 18 years.
He explained that eight couples – consisting of HIV-positive fathers and HIV-negative mothers – had voluntarily registered for the trial; one pair then exits.
Prof. He also said that research had been submitted to scientific journals for review, although he did not name the journal.
He also said that "other potential pregnancies" of gene-edited embryos were in the early stages.
But he apologized that his research "leaked suddenly".
"The clinical trial was suspended due to the current situation," he said.
Why is this controversial?
The Crispr gene editing tool that he claims has been used is not new to the scientific world, and was first discovered in 2012.
It works by using "molecular scissors" to change a very specific DNA strand – cut it, replace it or change it.
Gene editing has the potential to help prevent heritable disease by removing or changing encoding that is troublesome in the embryo.
But experts worry that interfering with the embryo genome can cause damage not only to individuals but also future generations who inherit this same change.
Prof. He's claims have recently been widely criticized by other scientists.
Hundreds of Chinese scientists also signed letters on social media condemning the research, saying they were "firm" against it.
"If true, this experiment is terrible. Editing the gene itself is experimental and is still associated with off-target mutations, which are capable of causing genetic problems early and later, including the development of cancer," Julian Savulescu, an ethicist at Oxford University, told the BBC.
"This experiment exposes healthy normal children to the risk of gene editing without the real benefits needed."
Many countries, including the United Kingdom, have laws that prevent the use of genome editing in embryos for reproduction of assistance to humans.
Scientists can conduct gene editing studies on discarded IVF embryos, provided they are destroyed immediately afterwards and are not used to make babies.
Prof He's trial was banned under Chinese law, Deputy Minister of Science and Technology Xu Nanping told state media.
China allows in-vitro human embryonic stem cell research for a maximum period of 14 days, Xu said.