Blueprint, based in Cambridge, has an approved drug called Ayvakit that treats a rare immunological condition.

France's Sanofi has agreed to buy U.S.-based Blueprint Medicines Corporation for up to $9.5 billion to boost its position in rare immunology diseases, in the biggest deal struck by a European healthcare company so far this year,

The pharma giant wants to refreshen its portfolio after some of its internal development programs disappointed in clinical trials.