Sanofi and Regeneron, the partners behind Dupixent, have expanded their immunology alliance in a deal worth up to $8 billion. Sanofi will pay Regeneron $1 billion upfront, with up to $7 billion more tied to development, regulatory and commercial milestones, to jointly develop a new generation of long-acting antibodies aimed at the same biology that made Dupixent one of the world’s best-selling medicines.
What the deal covers
The expansion adds four experimental antibodies discovered by Regeneron:
- a long-acting IL-13 antibody (REGN20423), already in Phase 1 for atopic dermatitis;
- an IL-4 x IL-13 bispecific, which blocks both signals with one molecule;
- an IL-4 antibody; and
- an IL-4 receptor alpha antibody, the same target as Dupixent.
The three that are not yet in human trials are expected to enter the clinic in 2027. The companies will split development and commercialization costs and share profits 50/50, with Regeneron leading research and development and Sanofi handling global commercialization. Sanofi’s own bispecific, lunsekimig, which targets TSLP and IL-13, could optionally be added to the alliance once it completes Phase 3 testing in COPD.
Why Dupixent matters so much
Launched in 2017, Dupixent (dupilumab) generated $18.3 billion in sales in 2025, up 25% on the year before. It works by blocking the shared receptor for two immune messengers, IL-4 and IL-13, that drive what is known as type 2 inflammation. That one mechanism turned out to underlie a long list of conditions: Dupixent is approved for atopic dermatitis (eczema), asthma, chronic sinusitis with nasal polyps, eosinophilic esophagitis, prurigo nodularis, COPD and chronic hives, among others.
The patent clock
Dupixent’s key patent protection runs out in 2031, after which cheaper biosimilar copies can be expected. For both companies, and especially Regeneron, replacing that revenue is the central strategic challenge of the decade. The new deal is the clearest statement yet of the plan: rather than find an entirely new blockbuster, build better versions of the same idea.
What “long-acting” would change
Dupixent is typically injected every two weeks. Antibodies can be engineered to stay in the bloodstream much longer, by modifying the part of the molecule that controls how quickly the body recycles it. A long-acting version could mean injections every few months instead of 26 times a year. For patients with a lifelong condition, especially children, that is a meaningful improvement — and for the companies, a new product with fresh patents that could move patients over before biosimilars arrive.
Why four shots on goal
The four candidates split Dupixent’s mechanism in different ways. Blocking IL-13 alone has proved effective in eczema, as rival drugs have shown, while IL-4 matters more in some other allergic diseases. A bispecific against both, or a longer-lasting receptor antibody, would aim to match Dupixent’s breadth. Developing several in parallel lets the partners see which approach works best in which disease, rather than betting on one.
What type 2 inflammation is
The immune system has several modes of attack. Type 2 responses evolved to deal with parasites, but in many people they misfire against harmless triggers such as pollen, foods or the skin’s own surface. IL-4 and IL-13 are the main messengers of that response: they drive the itch and barrier damage of eczema, the mucus and airway narrowing of asthma, and the swelling behind nasal polyps. Because the same two signals sit behind so many allergic conditions, a drug that blocks them can work across the skin, lungs, nose and gut — which is why Dupixent’s list of approvals keeps growing, and why its successors are aimed at exactly the same targets.
The competition
They are not alone. Lilly’s Ebglyss (lebrikizumab), an IL-13 antibody for eczema, can be given monthly for maintenance, and several biotechs are developing extended half-life antibodies against the same targets designed for dosing every three to six months. Oral drugs, including JAK inhibitors, compete at the more severe end. Dupixent’s dominance rests on its safety record and breadth of approvals; any successor will have to match that while offering real convenience.
A repaired relationship
The announcement also settled litigation Regeneron filed in 2024 over transparency in how Dupixent is commercialized. Regeneron chief executive Leonard Schleifer called the alliance “one of the most productive in biopharma history,” and the new deal suggests both sides see more value in extending it than in fighting.
The caveats
The candidates are early: one is in Phase 1 and three have not been tested in people. Analysts at Citi called the deal “a step in the right direction” but cautioned that such early-stage assets may not reach the market before Dupixent’s patent expires. Drug development typically takes the better part of a decade, and most candidates fail along the way. As with all such deals, most of the headline $8 billion is contingent on success.
What it means for patients
Nothing changes in the near term; Dupixent remains available and its expanding list of approvals continues. Over the longer run, the deal points to a future of less frequent injections for people with eczema, asthma and related conditions, and eventually lower-cost biosimilars of Dupixent itself. This is business news, not investment or medical advice.