This past spring, a biotech company announced the first use of a new gene-editing technology in people to fix an errant gene that causes a severe immune disorder. In June, a baby born with a life-threatening metabolic disorder was allowed to leave the hospital after a six-month sprint by scientists to create a bespoke treatment for him. And increasingly, a generation of “bubble babies” born without immune defenses are nearing their teenage years after receiving a one-time experimental gene therapy in early childhood.