TNFSF13 and myeloid sarcoma: Development of atacicept, a soluble fusion protein decoy receptor (incorporating the ligand-binding domain of the transmembrane activator and cyclophilin ligand activator (TACI, also known as TNFRSF13B)), designed to block two B-cell cytokines B-cell activating factor of the TNF family (BAFF, also known as BLyS, TNFSF13B) and a proliferation-induced ligand (APRIL, TNFSF13), unexpectedly led to severe adverse events and exacerbated symptoms and lesions when tested in clinical trials in MS patients15.