Sanofi has expanded its antibody collaboration with Regeneron Pharmaceuticals, a Tarrytown, New York-based bio/pharmaceutical company, to add four new drug candidates in an $8-billion deal ($1 billion upfront and $7 billion in potential milestone payments). The expanded collaboration adds to the companies’ existing antibody collaboration, which includes the partnered blockbuster drug, Dupixent (dupilumab), an anti-inflammatory drug approved for multiple indications, which is Sanofi’s top-selling drug.  

Under the expanded license and collaboration agreement, the companies will co-develop and co-commercialize four new long-acting, Regeneron-invented antibodies targeting interleukin-13 (IL-13), IL-4xIL-13 bispecific, interleukin-4 (IL-4), and interleukin-4 receptor alpha (IL-4Rα). IL-13 antibody REGN20423 is a monoclonal antibody currently in a Phase I clinical trial for treating atopic dermatitis (eczema), and the other three antibodies are expected to enter clinical studies in 2027.  

Regeneron will also have the option to include in the collaboration Sanofi’s lunsekimig, an investigational bispecific proprietary Nanobody VHH (variable heavy domain of heavy chain) therapy targeting thymic stromal lymphopoietin (TSLP) and IL-13, exercisable upon completion of Phase III trials for chronic obstructive pulmonary disease. 

Lunsekimig is made of five linked antibody fragments designed to simultaneously block TSLP and IL-13, which drive airway inflammation and can contribute to tissue damage in certain diseases and bind albumin for longer half-life. It is based on Sanofi’s proprietary Nanobody technology, a biologics platform based on single-domain antibody fragments. Sanofi acquired lunsekimig and the Nanobody technology platform from its EUR 3.9-billion ($4.8-billion) acquisition of Ablynx, a Ghent, Belgium-based bio/pharmaceutical company, in 2018.  

Under the agreement, Regeneron will receive an upfront payment of $1 billion from Sanofi, with the potential for development, regulatory, and commercial milestone payments of up to an additional $7 billion. The companies will share development and commercialization costs for the new programs and will split future profits from these potential products 50:50 on a global basis. Regeneron will lead research and development activities, and Sanofi will lead global commercial efforts. The existing profit-sharing agreement regarding Dupixent will not change. 

The deal comes as Dupixent faces near-term biosimilars competition as the companies seek to diversify their pipeline against loss of exclusivity for the drug. Duxipent was Sanofi’s top-selling drug in 2025 with net sales of EUR 15.71 billion ($18.10 billion), representing 36% of its net sales for 2025. The key US compound patent for Dupixent expires in March 2031. In its second-quarter 2026 earnings call, Sanofi said it has a “vigorous defense planned” with expectation to protect Dupixent innovations beyond the US compound patent expiration through a “robust” patent portfolio of issued patents and pending applications with expiration dates from 2031 to 2045.  

Source: Sanofi and Regeneron Pharmaceuticals