Nobel Prize-winning biologist and Caltech President Emeritus David Baltimore is leading the battle against human embryo DNA editing on the heels of an announcement by a Chinese scientist that he had engineered the world’s first gene-edited babies in twin girls who were born in November.

He JianKui, of the Southern University of Science and Technology in Shenzhen, China, claims he modified the embryos with Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR) to make the twins immune to AIDS, according to a story in the Washington Post. His claims have not been verified, the Post reported.

Several news agencies are reporting that JianKui has gone missing since the announcement.

According to the Post, the process was done to stop the children from contracting the HIV virus from their father.

“I don’t think it has been a transparent process,” Baltimore said. “We’ve only found out about it after it’s happened and the children are born. I personally don’t think it was medically necessary.”

Baltimore — who led Caltech from 1997 to 2006 — said the scientist’s claim could be in “violation of international scientific norms.”

Baltimore has contributed key findings to immunology, virology, cancer research, biotechnology and DNA research. He has trained many doctoral students and postdoctoral fellows, several of whom have gone on to notable and distinguished research careers, according to a press release issued by the institute.

He chaired the organizing committee of the Second International Summit on Human Genome Editing in Hong Kong, which opened late last month.

“At this summit we heard an unexpected and deeply disturbing claim that human embryos had been edited and implanted, resulting in a pregnancy and the birth of twins,” the summit committee members said in a joint statement. “Even if the modifications are verified, the procedure was irresponsible and failed to conform with international norms,”

In addition, a group of 122 Chinese scientists issued a statement calling Jiankui’s actions “crazy” and  “a “huge blow to the global reputation and development of Chinese science.” A Chinese medical ethics board is now investigating whether his experiments were in violation of Chinese laws and regulations.

Professor Julian Savulescu of Oxford University called it “monstrous reproductive medicine,” claiming it had “no moral or scientific justification,” because doctors can already successfully prevent fathers from transmitting HIV without genetic engineering.