On 28 July 2026, Suzhou Ribo Life Science Co., Ltd. (Ribo Life Science) disclosed that the European Medicines Agency has authorised the initiation of ORBIT-XI-AF, a Phase 2b multi-regional clinical trial evaluating vortosiran (RBD4059) for stroke prevention in patients with atrial fibrillation (SPAF).

Vortosiran is described as the world’s first and most advanced small interfering RNA therapy targeting coagulation Factor XI. Developed via the company’s proprietary RiboGalSTAR™ liver-targeting platform, the GalNAc-conjugated siRNA selectively suppresses FXI synthesis, inhibiting the intrinsic coagulation pathway to deliver antithrombotic activity.

Human genetic data cited in the announcement indicate that naturally reduced FXI levels are linked to lower thrombotic risk without a corresponding rise in spontaneous bleeding, positioning FXI inhibition as a potentially safer anticoagulation strategy relative to current therapies.

The EMA’s green light marks a pivotal milestone in Ribo Life Science’s global development programme for next-generation anticoagulants, enabling advancement of vortosiran into the next stage of clinical evaluation.

The company cautions that vortosiran may not ultimately achieve successful development or commercialisation.