In a human organoid-based mechanistic investigation, researchers revealed how an immunosuppressive drug, antithymocyte globulin (ATG), induces injury to blood vessels in the liver. According to the study, ATG first triggers rapid clotting through a complement activation system and later causes inflammation by activating the TGF-β pathway. This discovery explains why some patients experience severe liver-related side effects following organ transplantation, and the research may aid in the development of safer immunosuppressive regimens.