Mont-Saint-Guibert, Belgium – December 17, 2021 – Celyad Oncology SA (Euronext & Nasdaq: CYAD), a clinical stage biotechnology company focused on the discovery and development of CAR T (Chimeric Antigen Receptor) cell therapies based on T lymphocytes for the treatment of cancer, today announced that it had received, on December 17, 2021, a transparency notification from Tolefi SA and related persons indicating that they together passively crossed the 20% threshold and holding 18.65% of the rights vote of the company as of December 8, 2021.