Sanofi pays Regeneron $1 billion upfront for four next-generation Dupixent successors

Sanofi has agreed to pay Regeneron $1 billion upfront to co-develop four early-stage immunology antibodies, in an amended alliance the two companies announced on 1 October 2026 ¹². Regeneron can also earn up to $7 billion in milestone payments ¹².

What the deal covers

All four antibodies were invented at Regeneron and are long-acting. They are aimed at IL-13, IL-4 or a subunit of the IL-4 receptor, the same biology Dupixent acts on ¹. The lead candidate, REGN20423, is a long-acting IL-13 monoclonal antibody that entered a first-in-human trial in May in healthy volunteers and people with eczema ². The other three are preclinical and include an IL-4xIL-13 bispecific; the companies expect them to reach human testing next year ¹².

The division of labour is fixed. Regeneron leads research and development, Sanofi leads commercialisation worldwide, and costs and future profits on the new products are split equally ¹. The existing Dupixent profit-sharing arrangement stays as it is ¹. Regeneron also gains an option to bring Sanofi's lunsekimig, which targets TSLP and IL-13, into the alliance once certain late-stage studies finish; Fierce Biotech reports that the trigger is phase 3 data in chronic obstructive pulmonary disease ¹².

Sanofi's chief executive, Belén Garijo, described the agreement as "a deliberate first step in igniting Sanofi's innovation engine" ². Regeneron's chief executive, Leonard Schleifer, said the alliance "has been one of the most productive in biopharma history" ¹.

What it means for the market

The deal is a defensive move around Sanofi's largest product. Dupixent brought Sanofi 5.2 billion euros ($5.9 billion) in the second quarter, and its US patent on the compound expires in 2031 ². Across both companies, Dupixent net product sales reached $10.9 billion in the first half of 2026 ¹. The companies argue a wider set of patents could protect the franchise until 2045, but some investors remain concerned ¹.

For Sanofi, the payment buys a share of the follow-on pipeline rather than a new mechanism. Fierce Biotech notes that Sanofi's own attempts to build new growth drivers have stalled, and that the search under Garijo led back to Regeneron ². The agreement also closes a difficult period: Regeneron sued Sanofi in 2024 over commercial information in the Dupixent collaboration, and the new deal comes with a settlement of that litigation ².

RBC Capital Markets analyst Brian Abrahams told clients the expanded alliance could ease patent concerns and prepare the ground for further collaborations, licensing agreements or purchases of immunology assets ¹. For competitors, the signal is that the two companies intend to defend the IL-4 and IL-13 space with longer-acting successors. Eczema is already busy: Pfizer's tilrekimig has produced positive Phase 2 results and is moving into later testing in eczema, asthma and COPD ¹.

Caveats

Abrahams cautioned that the four antibodies "are still very early" in development ¹. In his view there is not yet substantial data showing they differ from existing treatments, and he described the eczema field as crowded ¹. Only REGN20423 is in the clinic, and the remaining three candidates are not due to start human trials until next year ¹².