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In a bold stride toward strengthening its grip on the immunology and rare disease market, French pharmaceutical titan Sanofi SA said Monday it has reached an agreement to acquire U.S.-based Blueprint Medicines Corp. for up to $9.5 billion — a deal that’s electrifying the biotech landscape.

The agreement, structured with surgical precision, includes a $129-per-share offer, representing a 27% premium over Blueprint’s last traded price of $101.35. That alone values the Nasdaq-listed company at $9.1 billion, but the final sum could swell with an additional $400 million in milestone-based payouts linked to Blueprint’s experimental immunology drug, Blu-808.

Deal Financed by Cash, Debt — and Strategic Firepower

Sanofi plans to finance the buyout through a mix of cash reserves and new debt, reaffirming its aggressive growth strategy in the highly competitive pharmaceutical sector. The Paris-based firm expects the transaction to close in Q3 2025, pending customary regulatory and shareholder approvals.

Weil Gotshal & Manges LLP is advising Sanofi, with a high-powered team out of New York led by Michael J. Aiello and Sachin Kohli. Blueprint is represented by Goodwin Procter LLP, including a roster of top-tier legal talent: Stuart Cable, Lisa Haddad, Kingsley Taft, and additional partners across healthcare and regulatory law.

Rare Disease Market: A Strategic Prize

Blueprint’s most prized asset is Ayvakit, the only approved treatment for the two most severe forms of systemic mastocytosis, a rare, debilitating blood disorder that causes unpredictable symptoms ranging from nausea to full-blown organ damage. Affecting as few as 1 in 10,000 to 20,000 people globally, systemic mastocytosis is often overlooked — but Sanofi sees its potential as a high-reward niche.

Ayvakit pulled in $479 million in 2024 and an additional $150 million in Q1 of 2025, underscoring its strong commercial momentum.

Also in Blueprint’s pipeline are Blu-808, which could add further depth to Sanofi’s immunology division, and elenestinib, now undergoing rigorous placebo-controlled trials aimed at tackling mastocytosis from a different therapeutic angle.

CEO Hudson: This Deal Delivers on Strategy

Sanofi CEO Paul Hudson was unambiguous in his enthusiasm. “This acquisition is fully aligned with our strategic intent to strengthen our existing therapeutic areas, to bring relevant and differentiated medicines to patients, and to secure attractive returns to our shareholders,” he said.

This deal isn't just about growing a pipeline — it's about owning the rare disease conversation.