Sanofi Pays Regeneron $1 Billion Upfront to Expand Alliance in Search of Dupixent’s Successors

What happened

Sanofi and Regeneron Pharmaceuticals expanded their long-standing alliance on Oct. 1 to develop a new generation of immune-system drugs designed to follow Dupixent, the companies’ top-selling medicine. According to BioPharma Dive, Regeneron will receive a $1 billion upfront payment and is eligible for up to $7 billion in additional milestone payments.

The partners will co-develop and co-commercialize four long-acting antibodies invented by Regeneron. Regeneron will lead research and development, and Sanofi will lead global commercial efforts.

Deal details

• Upfront: $1 billion to Regeneron.
• Milestones: Up to $7 billion.
• Economics: Costs and future profits from the new products will be shared evenly. The existing profit-sharing arrangement for Dupixent is unchanged.
• Option: Regeneron gained an option to add Sanofi’s experimental drug lunsekimig, exercisable after certain late-stage studies. Lunsekimig is being studied in respiratory illnesses driven by chronic inflammation.

The four antibodies target interleukins, specifically IL-13, IL-4 or an IL-4 subunit, the same type of target that Dupixent hits. The most advanced, REGN20423, is in an early-stage clinical trial for eczema. The other three are expected to enter human testing next year.

“The Regeneron-Sanofi alliance has been one of the most productive in biopharma history,” said Regeneron chief executive Leonard Schleifer.

Why it matters for the sector

Dupixent, first approved in 2017 for eczema, has since been cleared for asthma, chronic obstructive pulmonary disease and several chronic skin, throat and nose conditions. BioPharma Dive reported that it generated $10.9 billion in net product sales in the first half of 2026 and is the top earner for both companies.

Key patents on Dupixent face expiration over the next five years, although the companies say a patent thicket could protect the drug until 2045. Building successor products that hit the same biology with longer dosing intervals is a common lifecycle strategy for blockbuster biologics. A long-acting version could reduce injection frequency and help retain patients if biosimilar competition eventually arrives.

The deal is also one of the largest pharma partnerships of the year by upfront payment. BioSpace, in its weekly review published Oct. 7, listed it among a rush of early October deals that included Shionogi’s $2 billion IntraBio buyout and Novartis’s licensing agreement with Abogen.

Expanding an existing alliance rather than signing with a new partner can reduce execution risk. Sanofi and Regeneron already share commercial infrastructure for Dupixent, and the new antibodies would likely be sold to the same specialists, including dermatologists, allergists and pulmonologists.

For Regeneron, the upfront payment funds its research leadership on the new programs while preserving half of their economics. For Sanofi, the agreement secures a role in the next generation of type 2 inflammation therapies, an area central to its immunology franchise.

Immunology has become one of the most competitive areas in pharma, with multiple companies developing long-acting antibodies and oral drugs aimed at the same inflammatory pathways. Successor products need to show clear advantages, such as less frequent dosing or broader efficacy, to displace an established brand.

The $1 billion upfront payment is notable because it is being paid between existing partners for programs that are mostly preclinical. That reflects the value both companies place on extending the Dupixent franchise and on Regeneron’s antibody discovery capabilities, which produced the original drug.

What to watch

• Clinical data from REGN20423 in eczema.
• Entry of the three other antibodies into human testing next year.
• Late-stage results for lunsekimig, which will determine whether Regeneron exercises its option.
• Dupixent sales trends and any developments in patent challenges.

Sources: BioPharma Dive, BioSpace

Type 2 Inflammation, Explained

The immune system uses several distinct styles of response. One of them, often called type 2 inflammation, evolved in part to fight parasites, but it also drives many allergic and inflammatory conditions. Two signaling proteins, interleukin-4 and interleukin-13, are central to this response.

When overactive, type 2 signaling can contribute to itching and skin barrier damage in eczema, airway inflammation and mucus production in asthma, nasal polyps and swelling of the esophagus in eosinophilic esophagitis. Dupixent works by blocking a receptor component shared by IL-4 and IL-13 signaling, which is why a single drug has proven useful across several conditions with this common biology.

Why the successors target the same pathway

Because the biology has already been validated in many patients, new antibodies that hit IL-4, IL-13 or a receptor subunit start with a well-understood mechanism. The goal is not necessarily a new way of treating disease, but an improved version of an established one.

What Makes an Antibody “Long-Acting”

Antibodies naturally remain in the bloodstream for weeks. Engineers can extend that further, often by modifying the Fc region so that the antibody is recycled more efficiently by cells rather than broken down. Longer persistence can allow injections every few months instead of every few weeks.

For patients managing a chronic condition, fewer injections can be meaningful. For the companies, a long-acting successor can be a reason for patients and physicians to stay within the franchise when biosimilars eventually appear.

How a 50-50 Co-Development Deal Typically Operates

1. Shared budgets. The partners agree on development plans and split the costs evenly.
2. Defined leadership. One partner leads research and development, the other leads commercialization, as in this alliance.
3. Joint committees. Steering groups with representatives from both companies make major decisions, such as which indications to pursue.
4. Profit sharing. Once products launch, profits are divided according to the agreed split.
5. Milestones. Payments between partners can reward the inventing company as programs advance.

Questions Readers Ask

What is a patent thicket?

A dense layer of overlapping patents covering a drug’s formulation, manufacturing, uses and other aspects beyond the original compound. It can make it harder for competitors to launch copies even after the main patent expires, though patents can be challenged.

What is a biosimilar?

A biologic medicine highly similar to an approved reference product, with no clinically meaningful differences in safety or effectiveness, which can typically launch once relevant patents and exclusivities end.

Why pay $1 billion for mostly preclinical programs?

The payment reflects confidence in the underlying biology and in the inventing partner’s track record, plus the strategic value of protecting a very large franchise. Readers should consult a financial professional before making investment decisions.

This article is for general information only and is not medical or investment advice. Patients should consult their own physicians.