Bluebird Bio Inc. became the latest in a spate of gene therapy firms to disclose restructuring plans, as the company aims to save $160 million over the next two years, saying goodbye to about a third of its workforce. It’s the other shoe to drop after Cambridge, Mass.-based Bluebird rattled Wall Street with phraseology in the firm’s fourth-quarter earnings report March 4 that expressed “substantial doubt” regarding whether operations could go on.