Mont-Saint-Guibert, Belgium, September 12, 2023, 10:01 p.m. CET – regulated information – Celyad Oncology SA (Euronext: CYAD) (“Celyad Oncology” or the “Company”), announced today, in accordance with article 14 of the Belgian law of May 2, 2007 relating to the publication of significant participations in issuers whose shares are admitted to trading on a regulated market (the “Transparency Law”), have received a transparency notification dated September 8, 2023 of Tolefi SA and related persons indicating that they have together crossed the 20% threshold, holding 6,568,978 shares, or 22.74% of the voting rights of the Company as of September 4, 2023.