SAR445399 (Sanofi)

SAR445399 is an investigational **monoclonal antibody** developed by **Sanofi** that targets **interleukin-1 receptor accessory protein**, also known as **IL-1R3** or **IL1RAP**. By antagonizing this common co-receptor, the antibody is designed to inhibit signaling across multiple IL-1 family pathways, notably **IL-1**, **IL-33**, and **IL-36**, thereby suppressing inflammatory responses implicated in neutrophilic and immune-mediated skin disease. The program is being developed for **moderate to severe hidradenitis suppurativa**, where it is in **Phase 2** clinical evaluation as a subcutaneous injectable solution, and Sanofi has also described proof-of-mechanism data showing reduced experimentally induced skin inflammation consistent with multi-cytokine pathway blockade.