Sanofi and Regeneron expand immunology alliance with $8bn deal

Four next-generation long-acting antibodies targeting IL-13, IL-4 and IL-4Rα join the partnership that produced Dupixent, with Regeneron receiving $1bn upfront.

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Sanofi and Regeneron have expanded their two-decade antibody collaboration, adding four Regeneron-invented long-acting antibodies to their joint portfolio in a deal that sees Regeneron receive a $1 billion upfront payment and become eligible for up to a further $7 billion in development, regulatory and commercial milestones.

The agreement, announced on 1 October 2026, brings into the alliance REGN20423, a clinical-stage monoclonal antibody targeting interleukin-13 (IL-13), alongside a long-acting IL-4xIL-13 bispecific antibody and two preclinical candidates targeting IL-4 and IL-4 receptor alpha (IL-4Rα). REGN20423 is currently in a Phase 1 study in atopic dermatitis; the remaining three are expected to enter clinical studies in 2027. Development and commercialisation costs, as well as future profits, will be split equally between the two companies. Regeneron will lead research and development, while Sanofi will manage global commercial operations.

The strategic logic

The expansion follows the extraordinary commercial trajectory of Dupixent (dupilumab), the IL-4/IL-13 dual-pathway inhibitor that has become one of the world's most widely prescribed antibody medicines, with more than 1.5 million patients across nine approved indications in over 60 countries. Sanofi reported Dupixent sales exceeding EUR 13 billion in 2025, and the franchise continues to grow as new indications are added. The existing Dupixent profit-sharing arrangements remain unchanged under the new terms.

Sanofi chief executive Belén Garijo described the deal as "a deliberate first step in igniting Sanofi's innovation engine," framing it as an effort to secure the next wave of type 2 inflammation therapies before Dupixent faces biosimilar pressure later this decade. Regeneron president and CEO Leonard Schleifer said the expansion was designed to accelerate promising long-acting candidates toward the kind of global impact Dupixent has achieved.

The agreement also includes an option for Regeneron to bring Sanofi's lunsekimig into the collaboration. Lunsekimig is an investigational bispecific Nanobody targeting TSLP and IL-13, currently in Phase 3 trials for chronic obstructive pulmonary disease; the option is exercisable upon completion of those studies.

The two companies also confirmed they have settled outstanding collaboration-related litigation, removing an overhang that had complicated their relationship in recent years.

Market and competitive context

The type 2 inflammation space is among the most active in biologics development. AstraZeneca's tezepelumab and GlaxoSmithKline's mepolizumab and depemokimab occupy adjacent positions in severe asthma and eosinophilic disease, while Eli Lilly's lebrikizumab and Pfizer's cendakimab compete with Dupixent in atopic dermatitis. The race to develop longer-acting versions of IL-4/IL-13 pathway inhibitors is gathering pace, as extended dosing intervals would represent a meaningful convenience benefit for patients and a commercial differentiator for manufacturers.

Regeneron's long-acting antibody technology, part of its broader VelociSuite platform, is central to the company's pitch: that the next generation of these medicines can improve on Dupixent's already strong clinical profile by extending the time between injections, potentially to monthly or quarterly schedules. Whether that convenience translates into premium pricing or formulary advantage will depend in part on head-to-head data that has not yet been generated.

For Sanofi, the deal reinforces a strategic pivot toward immunology at a time when the company has been streamlining its vaccines and consumer health businesses. With Dupixent now well established and biosimilar entry possible from the early 2030s, securing rights to the next cohort of targets gives Sanofi a path to maintain its position in type 2 inflammation without a competitor acquisition. Investors will be watching the 2027 IND filings and early Phase 1 readouts to assess whether the new candidates can replicate Dupixent's breadth of clinical activity.

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