Or that would be the case if He had limited his work to instances in which the editing was successful. He claims that a pair of twins were born following the editing procedure (other couples tried but have not yet brought a baby to term). But the AP showed data obtained from He to a number of scientists, who indicated at least one of the twins born was a mosaic—editing took place after the embryo started cell divisions, making that individual a patchwork of edited and unedited cells.

"In that child, there really was almost nothing to be gained in terms of protection against HIV, and yet you're exposing that child to all the unknown safety risks," Kiran Musunuru of the University of Pennsylvania told the AP. Harvard's George Church suggested that the "main emphasis was on testing editing rather than avoiding this disease." That's consistent with He's video, linked above, in which he describes the need for this editing for treating incurable genetic diseases—something that doesn't describe this work.