The EPO published international patent application EP3969475A1 filed by Chugai Seiyaku Kabushiki Kaisha for an anti-C1S (complement component 1s) antibody. The application claims priority to IPC classifications covering antibody proteins (C07K 16/18), neurological indications (A61P 25/28), nucleotide sequences (C12N 15/13), and immunological compositions (A61K 39/00). The application designates all 31 EU/EEA states plus Switzerland, Turkey, and other EPC contracting states.

Pharmaceutical companies and biotechnology firms developing complement system therapeutics or neurological treatments should review this publication for freedom-to-operate considerations. Competitors in the C1S antibody space should assess potential overlap with their own development programs. The publication date of March 25, 2026 marks the start of the nine-month opposition period during which third parties may file observations.