Paris and New York, October 1, 2026 — French pharmaceutical company Sanofi and U.S.-based biotechnology company Regeneron Pharmaceuticals have expanded their long-standing immunology partnership in a new agreement that could be worth up to $8 billion.
Under the expanded collaboration, Sanofi will pay Regeneron $1 billion upfront. Regeneron could receive an additional $7 billion in development, regulatory and commercial milestone payments if the new medicines reach specified stages of development and commercialization.
The agreement adds four next-generation, long-acting antibody programs to the companies' existing alliance, which previously produced the widely used immunology medicine Dupixent.
Four New Antibody Programs Added
The expanded agreement covers four Regeneron-developed antibody candidates targeting biological pathways involved in type 2 inflammation and immune-mediated diseases.
One of the candidates, REGN20423, is a long-acting interleukin-13 antibody currently being evaluated in a Phase 1 clinical trial for atopic dermatitis.
The collaboration also includes a long-acting IL-4xIL-13 bispecific antibody and two additional preclinical antibody candidates targeting IL-4 and IL-4 receptor alpha.
The companies said the other three antibody programs are expected to enter clinical studies in 2027.
Companies Will Share Costs and Future Profits
Under the new agreement, Sanofi and Regeneron will equally share development and commercialization costs for the newly added programs.
They will also share future global profits from the new medicines equally.
Regeneron will lead research and development activities, while Sanofi will take the lead in global commercial activities.
The structure is designed to combine Regeneron's antibody research capabilities with Sanofi's international development and commercial infrastructure.
Deal Builds on More Than 20 Years of Collaboration
Sanofi and Regeneron have worked together for more than two decades. Their collaboration produced Dupixent, also known by its generic name dupilumab.
Dupixent is an antibody medicine that targets signaling pathways involving interleukin-4 and interleukin-13, which are involved in type 2 inflammation.
The medicine has been developed and approved for multiple inflammatory and allergic conditions in different markets.
According to the companies, more than 1.5 million people are currently receiving Dupixent across nine indications.
Dupixent Agreement Remains Separate
The new agreement does not change the existing economic arrangement for Dupixent.
Sanofi and Regeneron will continue their existing collaboration on the medicine while using the expanded agreement to develop the next generation of long-acting immunology therapies.
This distinction allows the companies to maintain their established business while creating a separate framework for the newly added antibody programs.
Potential Addition of Another Investigational Medicine
The agreement also gives Regeneron an option to include Sanofi's investigational medicine lunsekimig in the expanded collaboration.
Lunsekimig is an experimental bispecific therapy targeting TSLP and IL-13 and is being studied for chronic obstructive pulmonary disease, commonly known as COPD.
The option can be exercised after the completion of the relevant Phase 3 studies.
Because lunsekimig remains investigational, its future development and regulatory status will depend on clinical results and decisions by health authorities.
New Medicines Still Require Clinical Development
The newly added antibody programs are at different stages of development. REGN20423 is already in a Phase 1 study, while the other three programs are earlier in development.
Medicines in clinical development must pass multiple stages of testing before they can potentially receive regulatory approval.
Phase 1 studies generally focus on initial safety and dosing information. Later-stage trials are designed to provide broader evidence about safety and effectiveness in specific patient populations.
As a result, the potential milestone payments described in the agreement are dependent on future development, regulatory and commercial achievements.
Previous Litigation Resolved
The expanded partnership also resolves previous legal disputes between Sanofi and Regeneron concerning their collaboration.
The companies have agreed on new terms for the expanded relationship and will move forward with a revised framework for the additional antibody programs.
The resolution removes a legal dispute that had affected the companies' relationship while preserving their existing collaboration around Dupixent.
Why Long-Acting Antibodies Matter
Long-acting antibody medicines are being developed with the goal of maintaining therapeutic activity for longer periods between doses.
For patients with chronic diseases, treatments that can potentially require less frequent administration could affect how therapies are delivered if they ultimately demonstrate appropriate safety and effectiveness.
However, the new Sanofi-Regeneron candidates are still at different stages of clinical development, and their eventual dosing schedules, effectiveness and regulatory status cannot yet be determined.
Sanofi Expands Its Immunology Pipeline
The agreement comes as Sanofi continues to build its immunology and inflammation business around established products and new research programs.
The company has been investing in biological therapies designed to address diseases involving immune-system pathways.
Expanding the partnership with Regeneron gives Sanofi access to additional antibody candidates while allowing Regeneron to use Sanofi's global commercial infrastructure for potential future products.
Regeneron Adds New Commercial Opportunities
For Regeneron, the agreement creates additional opportunities to develop and commercialize antibody candidates through a long-established international partnership.
The company will receive $1 billion immediately under the new agreement and could receive up to another $7 billion if the programs achieve the specified milestones.
The milestone structure means the full potential value of the agreement depends on future clinical, regulatory and commercial performance rather than representing an immediate $8 billion payment.
Global Immunology Market Continues to Expand
Immunology has become one of the major areas of investment in the global pharmaceutical industry as researchers develop targeted biological therapies for chronic inflammatory diseases.
Companies are increasingly focusing on specific immune pathways rather than relying only on broad immune suppression.
The Sanofi-Regeneron agreement reflects that wider industry trend, with the new programs targeting specific biological pathways involved in immune-mediated diseases.
What Comes Next
The immediate focus will be on advancing the four newly added antibody programs through clinical development.
REGN20423 is already being studied in patients with atopic dermatitis, while the remaining three candidates are expected to enter clinical studies in 2027.
Future clinical results will determine whether the programs can progress through later stages of development and potentially reach regulatory review.
For Sanofi and Regeneron, the expanded agreement creates a new development pipeline alongside their established Dupixent partnership.
The companies' latest deal therefore combines a $1 billion upfront payment, potential milestone payments of up to $7 billion and an equal profit-sharing structure as they work on the next generation of long-acting immunology antibodies.
Journalist: Vijay Singh