On Feb. 16, 2016, Sanofi-aventis announced it would acquired Genzyme for $74 a share in cash or $21.1 billion, and a tradable contingent value right (CVR) whose value will depend on Genzyme’s experimental multiple sclerosis drug Lemtrada and production of two other medicines. The CVR CVR ran through 2020.

The deal announced comes nine months after Sanofi Chief Executive Chris Viehbacher first put the idea to Genzyme’s Henri Termeer and gives Sanofi a new platform in rare diseases.

The deal’s announcement, which confirmed what sources with knowledge of the talks told Reuters, marks the second-biggest acquisition in biotech history after Roche’s $46.8 billion purchase of Genentech in 2009.  It initially offered $69 per share in cash in August, but was rebuffed by Genzyme.