Regeneron, Sanofi Expand Alliance with $1 Billion Upfront, 4 Antibodies

Regeneron Pharmaceuticals and Sanofi announced Oct. 1, 2026, an expansion of their long-standing antibody collaboration, adding 4 next-generation, long-acting antibodies targeting interleukin-13 (IL-13), an IL-4xIL-13 bispecific, IL-4 and IL-4 receptor alpha (IL-4Rα).¹ Under the expanded agreement, Regeneron will receive a $1 billion upfront payment from Sanofi, with the potential for up to an additional $7 billion in development, regulatory, and commercial milestone payments.¹

"The Regeneron-Sanofi alliance has been one of the most productive in biopharma history. This agreement builds on that foundation to bring the next generation of immunology medicines to patients even faster," said Leonard S. Schleifer, MD, PhD, board co-chair, president, and CEO of Regeneron, in a company press release.¹ "By expanding our alliance, we are positioning promising new long-acting antibodies for the kind of rapid, global impact that our shared work on Dupixent has already achieved."

What assets are being added to the alliance?

The IL-13 antibody REGN20423 is currently in a phase 1 clinical trial for atopic dermatitis, and the other 3 new antibodies are expected to enter clinical studies in 2027.¹^,² IL-4 and IL-13 are established as central drivers of the type 2 inflammation underlying dupilumab’s (Dupixent) approved indications, and the newly added antibodies target the same biology in longer-acting formats.¹^,³ Regeneron will also have the option to add Sanofi's lunsekimig, an investigational bispecific Nanobody single variable domain on a heavy chain (VHH) therapy targeting thymic stromal lymphopoietin and IL-13, to the collaboration once lunsekimig's phase 3 trials for chronic obstructive pulmonary disease are complete.¹

What are the financial terms, and how will the work be divided?

Beyond the $1 billion upfront payment, Regeneron is eligible for up to $7 billion in additional milestones, putting the deal's total potential value at up to $8 billion.¹ The companies will equally share development and commercialization costs for the new programs and split future profits 50:50 on a global basis.¹ Regeneron will lead research and development, while Sanofi will lead global commercial efforts.¹ The existing dupilumab profit-sharing arrangement is unchanged.¹

"This is a deliberate first step in igniting Sanofi's innovation engine. Our longstanding alliance with Regeneron has transformed the treatment landscape for millions of patients living with diseases driven by type 2 inflammation and created one of the world's leading immunology businesses," said Belén Garijo, MD, PhD, CEO, Sanofi, in the release.¹ "By deepening our collaboration, we will make rapid progress in creating the next generation of meaningful therapies for patients with immune-mediated diseases, while contributing to Sanofi's long-term future."

How does this build on the companies' dupilumab alliance?

Regeneron and Sanofi's clinical and commercial alliance dates to 2003 and has produced multiple approved medicines, most notably dupilumab, which more than 1.5 million people currently use across 9 indications in more than 60 countries, according to the companies.¹

"By combining Regeneron's world-class scientific discovery and antibody development expertise with Sanofi's global capabilities and reach, we hope to once again deliver the next wave of innovation in immunology," said George D. Yancopoulos, MD, PhD, board co-chair, president, and chief scientific officer, Regeneron, and a principal inventor of dupilumab, in the release.¹ The companies also said they have settled their prior collaboration-related litigation.¹

What are the limitations?

REGN20423 has only reached phase 1 testing, and the other 3 new antibodies have not yet entered clinical trials, so none has yet demonstrated safety or efficacy in patients. The $7 billion milestone figure represents a cumulative ceiling tied to development, regulatory, and sales progress that may not be fully realized. Regeneron's option on lunsekimig depends on that drug's ongoing phase 3 trials succeeding and being completed, an outcome that is not yet known.

References

1. Regeneron Pharmaceuticals. Regeneron and Sanofi expand global alliance with multiple next-generation, long-acting immunology antibodies. Press release. Published October 1, 2026. Accessed October 1, 2026. https://investor.regeneron.com/news-releases/news-release-details/regeneron-and-sanofi-expand-global-alliance-multiple-next
2. First-in-human trial to assess REGN20423 in healthy adult participants and adult participants with atopic dermatitis (AURA-AD). ClinicalTrials.gov; NCT07527923. Updated September 25, 2026. Accessed October 1, 2026. https://clinicaltrials.gov/study/NCT07527923
3. McCann MR, Kosloski MP, Xu C, Davis JD, Kamal MA. Dupilumab: mechanism of action, clinical, and translational science. Clin Transl Sci. 2024;17(8):e13899. doi:10.1111/cts.13899