Sanofi will pay Regeneron $1 billion up front and as much as $7 billion in development, regulatory and commercial milestones to co-develop four long-acting antibodies aimed at the type II inflammation pathway, the two companies announced on October 2, 2026.

The expanded agreement covers Regeneron-invented candidates targeting interleukin-13, an IL-4xIL-13 bispecific, interleukin-4, and IL-4 receptor alpha. The lead asset, REGN20423, is a long-acting IL-13 monoclonal antibody now in a phase I study for atopic dermatitis. Three additional antibodies are slated to enter clinical studies in 2027.

What does the deal change for dermatologists?

REGN20423 targets the IL-13 arm of the same type II inflammation cascade that has made Dupixent (dupilumab) a cornerstone of moderate-to-severe atopic dermatitis care. The candidate's long-acting design could, if it advances, reduce dosing frequency relative to current pathway agents, though durability claims must await phase II and III readouts.

Regeneron also retains an option to fold lunsekimig — Sanofi's investigational TSLP-and-IL-13 bispecific nanobody — into the collaboration once that program's phase III work in chronic obstructive pulmonary disease reads out. Lunsekimig has not been positioned for skin indications in the announcement.

What else does the agreement settle?

The two companies used the announcement to resolve prior collaboration-related litigation. Terms of the settlement were not disclosed. Regeneron will lead research and development under the new arrangement; Sanofi will run global commercialization. Development costs and future profits will be shared equally. The existing Dupixent profit-sharing structure remains unchanged.

How does Dupixent frame the new pipeline?

The expansion builds on a more than 20-year alliance that has driven Dupixent to the number-one new-to-brand prescription share across all of its U.S. approved indications. More than 1.5 million patients are now receiving the drug across nine approved diseases, including three of direct dermatologic relevance:

• Moderate-to-severe atopic dermatitis
• Prurigo nodularis
• Bullous pemphigoid

Other Dupixent approvals span severe chronic rhinosinusitis with nasal polyposis, severe asthma, eosinophilic esophagitis, chronic obstructive pulmonary disease, chronic spontaneous urticaria, and allergic fungal rhinosinusitis.

What is Dupixent doing commercially?

Sanofi reported €9.3 billion in Dupixent sales during the first half of 2026, up 28.6% year over year. Second-quarter revenue reached €5.2 billion, a 37.6% jump and the first quarter in which the drug crossed the €5 billion threshold. Sanofi is guiding to roughly €25 billion in annual Dupixent sales by 2030.

What to watch next

Phase I safety and pharmacokinetic data for REGN20423 will set the pace for the rest of the four-antibody package, and the 2027 phase I starts for the IL-4, IL-4xIL-13 bispecific, and IL-4Rα programs will land as dermatology competitors — including topical and oral IL-23 and JAK inhibitors — work to defend share in atopic dermatitis and adjacent indications. Whether any of the new candidates eventually displaces Dupilumab or extends into the prurigo nodularis and bullous pemphigoid labels remains the central clinical question for the dermatology community.