A locally waged battle against cystic fibrosis has yielded an experimental drug combination that is giving new hope to families affected by a disease that historically has meant death at an early age. In a clinical trial, Vertex Pharmaceuticals in Cambridge found that a combination of its drug Kalydeco, which won federal regulatory approval only four months ago, and the experimental drug VX-809 substantially improved breathing for some cystic fibrosis patients. “I never dreamed we’d have this day,” said Joe O’Donnell, who has raised about $250 million for the Cystic Fibrosis Foundation over the past 35 years and lost his...