CD33 and neoplasm: In hematologic diseases, where tumor cells are readily accessible for carrier molecules and single cells are the main cause of tumor manifestations, the isotope bismuth-213 (τ1⁄2= 46 min) and the 9.9-day half-life radionuclide 225Ac were used to couple to the CD33-binding antibody lintuzumab (HuM195), and leukemia-inhibitory activity was reported [81,82,83].