A major international summit on gene editing opened Tuesday in Hong Kong under the shadow of a recent scandal: Researcher He Jiankui claimed Monday to have edited genes in embryos to make them resistant to HIV, causing uproar from the international scientific and academic communities.

Feng Zhang, one of the founders of the CRISPR Cas9 technology used in He’s experiment and a professor at MIT, told Caixin that DNA editing has a long way to go before being used in embryos.

“Fundamentally, I don’t think genome editing is ready to be applied in embryos for implantation purposes. There are still technical hurdles we have to solve,” he said.

He also expressed outrage that the babies had been exposed to unnecessary risks. “There is a standard protocol for treating the mother who is not HIV-positive,” Zhang said. “Given that you already have an established and safe procedure, to expose the child to this level of risk is completely unnecessary and irresponsible.”

Zhang also issued a statement Monday calling for a moratorium on genetic editing of human embryos until comprehensive safety measures were introduced.