9 DECEMBER 2016 • VOL 354 ISSUE 6317 1211 SCIENCE sciencemag.org P H O T O : S T E V E G S C H M E IS S N E R / S C IE N C E P H O T O L IB R A R Y A n experimental cancer therapy is facing its biggest setback yet, after an unexpected complication killed seven people over about a year, five of them in a single clinical trial. The company, Seattle, Washington–based Juno Therapeutics, has its mos...