Sanofi Pays Regeneron $1 Billion Upfront to Expand Dupixent Alliance in Deal Worth Up to $8 Billion

SNY and REGN expanded their immunology alliance on October 1, with Sanofi paying Regeneron $1 billion upfront and up to an additional $7 billion in development, regulatory and commercial milestones, putting the headline value at up to $8 billion. The deal adds four new long-acting, Regeneron-invented antibodies targeting IL-13, an IL-4xIL-13 bispecific, IL-4 and the IL-4 receptor alpha. The lead program, REGN20423, is in a Phase 1 trial for atopic dermatitis, and the other three are expected to enter clinical studies in 2027.

The companies will share development and commercialization costs and split future profits from the new programs 50:50 globally, with Regeneron leading research and development and Sanofi leading commercialization. The existing Dupixent profit-sharing arrangement does not change, Regeneron gains an option to join Sanofi's lunsekimig after its Phase 3 trials in COPD, and the partners settled their prior collaboration-related litigation.

Reuters described the agreement as an early win for new Sanofi CEO Belén Garijo, who told investors in July that Sanofi needed to rebuild trust with Regeneron, according to BioPharma Dive. It addresses investors' biggest worry, Dupixent's loss of patent protection in 2031; the drug had $18.3 billion in global sales in 2025, according to Pharmaceutical Technology. Sanofi shares rose about 2% in early Paris trading. Not everyone sees it as enough: Citi called it a step in the right direction but noted the assets are early and may not reach market before Dupixent loses exclusivity, and Reuters Breakingviews argued that Sanofi's fix requires an extra shot of M&A.

What to watch: early data from REGN20423, the 2027 clinical starts for the other three antibodies, and whether Garijo follows with further deals.