Having already brought one of the most successful drugs in the world to market, Sanofi and Regeneron are broadening their pipeline horizon – the companies have agreed to expand their partnership that will see the two work together on four new antibodies in a deal rising to $8bn.
Sanofi and Regeneron have been working together for more than two decades, marking one of the longest and most successful pharma pair-ups in the industry. The zenith of the alliance has been their inflammatory drug Dupixent (dupilumab), a product that reached $18.3bn in global sales in 2025. Now, the two companies are seeking new drugs that will make the same impact.
Under the expanded license and collaboration agreement, the companies will co-develop and co-commercialise four new long-acting antibodies discovered by Regeneron. The four assets target interleukin-13 (IL-13), an IL-4xIL-13 bispecific, an interleukin-4 (IL-4) and an interleukin-4 receptor alpha (IL-4Rα).
As per the deal, Sanofi will pay $1bn upfront to Regeneron, with development, regulatory, and commercial milestones adding a potential further $7bn. Development and commercialisation costs for the new programmes will be shared between the French drugmaker and US biotech, with profits from any drugs approved via the partnership split evenly. Regeneron will lead research and development activities, and Sanofi will lead global commercial efforts.
REGN20423, an IL-13 antibody, is currently in a Phase I clinical study for atopic dermatitis (AD), and the other three antibodies are expected to enter clinical studies in 2027. Regeneron will also have the option to include in the collaboration Sanofi’s lunsekimig, an investigational bispecific nanobody therapy targeting TSLP and IL-13, which will be exercisable upon completion of its Phase III studies for chronic obstructive pulmonary disease (COPD).
Shares rise, but analysts guarded
The alliance double-down quells concerns that recent legal proceedings would rumble on. In 2024, Regeneron sued Sanofi alleging lack of transparency in Dupixent’s commercialisation. In announcing the expanded partnership, the companies said that they have now settled the litigation.
Dupixent sales have consistently grown each year since its initial approval in 2017, with several indication expansions also arriving in that time. While 2025 sales grew 25% to reach $18.3bn, investors have been wary given the drug’s patents begin to expire in 2031. The license expansion with Regeneron, which will help advance immunology pipeline assets, therefore eases investor concern.
Shares in Paris-listed Sanofi rose 2.7% at market open on 1 October compared to market close on 30 September. The big pharma company has a market cap of €87.5bn.
Citi analysts called the deal “a step in the right direction”, though caveated that the expansion “was largely expected”. The team added that assets are early in development and, as such, may not reach the market before Dupixent loses exclusivity.
It does mark a first triumph for Sanofi’s new CEO Belén Garijo, who replaced six-year helmsman Paul Hudson in April this year.
Regeneron’s CEO, Leonard Schleifer, said: “The Regeneron-Sanofi alliance has been one of the most productive in biopharma history. “By expanding our alliance, we are positioning promising new long-acting antibodies for the kind of rapid, global impact that our shared work on Dupixent has already achieved.”
