The worms arrived in hamster guts already knowing their job—migration to the small intestine, decades-long survival, the careful dance of parasitic coexistence. What they didn’t know was that their makers had quietly rewritten a crucial instruction into their genome: produce an antibody. Make it. Secrete it. Let it slip into the bloodstream of the animal that hosts you. Then, perhaps, save a life. This is not science fiction. On 3 June, researchers at Washington University School of Medicine...