Showing series of slides, he quickly described what he said about the three-year work with mice, monkeys, and then human embryos. He used editing technology, Crispr-Cas9, to disable the gene, called CCR5, which creates a protein that makes H.I.V., the virus that causes AIDS, infects people's cells.
Dr He said that with the help of H.I.V./AIDS organization in China, he recruited eight couples in which he had H.I.V. and the woman does not. One pair turned out, and another achieved a "chemical pregnancy," a pregnancy that does not immediately get into the uterus after the embryo.
After regulating the genes of CCR5, he said he used in vitro fertilization to create embryos that were resistant to H.V. The goal, he said, is to create babies that would not be vulnerable to H.V. infection.
Many scientists have noted that there are other, simpler ways to protect newborns from the infected parent, especially the infected father, from getting H.I.V. Editing embryos should be used only to prevent or treat severe medical conditions that can not be solved otherwise, they say.
But Dr. He pointed out that the parents of the twins, especially the HI-positive father, considered the procedure as a way to regain their cause of living.
"I feel proud because they have lost the hope of life," said Dr. He. "But with this protection, he sent a message that he would work hard, earn money and take care of his two daughters and his wife for this life."
The scientists also opposed the suggestion that Dr. He did not inform his colleagues, his university, or his parents about what exactly he was doing. For example, while the consent form given to potential parents mentioned the arrangement of the genes in the text, it initially described the research as a "project to develop a vaccine against AIDS".