Penny stocks -- companies whose shares are trading for $5 or less -- look cheap for a reason: They have encountered severe issues, and the market has little faith that they will turn things around. That's the situation in which Bluebird Bio (BLUE -3.24%), a biotech focused on gene editing, finds itself. The company has made tremendous progress and has proven innovative abilities, but still faces severe headwinds. On the bright side, buying shares today would translate to outsized returns in the long run if ...