Sanofi and Regeneron have broadened their long-running antibody alliance by adding four new long-acting immunology programs tied to IL-4/IL-13 biology, in a deal worth up to $8 billion. Sanofi will pay Regeneron $1 billion upfront, with the remaining amount available through development, regulatory and commercial milestones, and the companies will share costs and profits on a 50:50 basis. Regeneron is set to lead research and development while Sanofi handles global commercialization. The expanded portfolio includes assets such as REGN20423, an investigational long-acting IL-13 monoclonal antibody in Phase I testing in atopic dermatitis, along with additional long-acting IL-4 and IL-4 receptor alpha candidates and IL-4xIL-13 bispecific approaches. The company-level signal is that late-stage differentiation around blockbuster Dupixent’s targets continues to motivate major alliance expansion and platform investment, especially as patent timelines approach. For competitors, the move reinforces that long-acting formulations and next-generation target engagement remain a key battleground in immunology. (Selected items cover the alliance expansion and deal economics.)