nick leslie, the bluebird bio ceo.famously started by mark zuckerberg in a harvard dorm room, is perhaps considered by boston's tech community, the one that got away. facebook quietly returned to cambridge in 2013 to open an engineering office. today, more than ever, the company is taking advantage of town.p talent in the kendall square in cambridge is the heart of boston's tech community. west coast software giants have taken note, establishing a presence here. >> facebook is always looking for an opportunity to hire the best talent. we came here because boston is a town of talented senior engineers and great universities. caroline: ryan mac helped open the office nine years after facebook was formed. has grown, employing about 100 engineers, tackling their toughest challenges. most of what we are working on in boston is infrastructure. two thirds are working on the technology that is the underpinning for the products that people see on a regular basis. caroline: he breaks it down into four pillars. storage, security,