He Jiankui grew up brilliant but poor in a rural part of China’s Hunan province. Though his family couldn’t afford to buy him textbooks, Jiankui surged ahead in school, ending up a physics major at the University of Science and Technology in Hefei, China, and a doctoral student at Rice University in Houston. Branching off to biotechnology, Jiankui joined Stanford bioengineer Stephen Quake at a company that commercialized gene-sequencing technology. In 2012, Jiankui launched a similar company in China and soon became a millionaire. By 2018, Jiankui began to consider the field of genetic editing, specifically editing human embryos for genetic diseases. He was, however, against the idea of using gene editing for some kinds of enhancement, such as IQ.

In 2017, Jiankui wrote to Doudna, who invited him to a small conference in Berkeley. George Church, one of the speakers, discussed a variant of the CCR5 gene that could make a person less receptive to the AIDS-causing HIV virus. Church’s work resonated with Jiankui, who had been editing the gene in monkey and nonviable human embryos.

Jiankui now wanted to enable AIDS-affected couples to have babies who were protected from HIV. Back in China, he recruited 20 couples in which the husband was HIV positive and the wife HIV negative.