Jiankui’s process involved taking sperm from the father, washing the cells to rid them of the HIV virus, and then injecting the sperm into the mother’s eggs. This was probably enough to ensure that the resulting fertilized eggs were free of HIV. But his goal was to guarantee that the children would never later be infected. So he injected the fertilized eggs with CRISPR-Cas9 that targeted the CCR5 gene. They were allowed to grow for five or so days in a Petri dish until they were an early-stage embryo more than two hundred cells large, and then their DNA was sequenced to see if the edits had
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