A researcher who has been met with widespread criticism after claiming to have used CRISPR-Cas9 gene-editing technology to alter the embryonic genes of twin girls born earlier this month in China defended the work on Wednesday. "For this case, I feel proud," He Jiankui remarked at the Human Genome Editing Summit, adding that using technology to help people with genetic diseases is "compassion."

According to He, an associate professor at Southern University of Science and Technology in Shenzhen, the two babies have been born with an edited CCR5 gene in the hope that the genetic modification will protect them from HIV infection. One child has both copies of the CCR5 gene disabled, while the second has only one copy affected. "They need this protection since a vaccine is not available," He said, noting that the study "has been submitted to a scientific journal for review." He added that he would monitor the two newborns for the next 18 years and hoped they would support continued monitoring thereafter.

On Wednesday, He also disclosed that "another potential pregnancy" of a gene-edited embryo was in its early stages and needs more time to be monitored to see if it will last. The study initially enrolled eight couples, with one dropping out, with the inclusion criteria requiring the father to be HIV positive and the mother to be HIV negative. He suggested that all the participants had a "good education background" and went through two rounds of discussions with him and his team.

The study is now on hold as China's National Health Commission has ordered local officials in Guangdong province to investigate He's actions, while Southern University of Science and Technology said that it would launch a probe as it was unaware of the project. Indeed, He confirmed that the university did not know of the study, which was self-funded. Meanwhile, Shenzhen Harmonicare Medical, which was linked to He's project in China's clinical trial registry, distanced itself from the work, suggesting that its ethical approval had been forged and "no relevant meeting of the medical ethics committee of the hospital in fact took place."

News of the research has been criticised globally, with David Baltimore, a leader of the Human Genome Editing Summit, commenting "I think he acted irresponsibly," adding "I personally don't think it was medically necessary." Baltimore said the work shows "there has been a failure of self-regulation by the scientific community."

In response to the claims, the Chinese Society for Cell Biology (CSCB) said that scientists in the country previously "reached a clear consensus that any clinical application of gene editing for reproductive purpose should be strictly forbidden in China." The CSCB noted that "it is uncertain whether knocking out CCR5 would ensure the health of the baby," adding "loss of CCR5 function in Chinese genetic background has never been proven to be safe, and the potential negative effect is almost impossible to predict."

The CSCB also said that "from an ethical perspective, knocking out CCR5 gene from a genetically normal zygote would not provide much benefit because the baby could have been kept from being exposed to HIV infection. There is no sound reason to perform this editing."