CD45

Class

Radioimmunotherapy (iodine-131-labeled anti-CD45 monoclonal antibody, BC8/apamistamab)

CD45 is a transmembrane protein tyrosine phosphatase expressed on essentially all nucleated blood cells derived from the bone marrow, including normal lymphocytes and myeloid cells as well as most leukemic and lymphoma cells. Because its expression is so broad and consistent across this cell lineage, CD45 is useful less as a signaling target to be blocked or activated and more as a landmark for directing therapy to hematopoietic tissue. In radioimmunotherapy, a monoclonal antibody against CD45 is chemically linked to a radioactive isotope, iodine-131, which emits ionizing radiation capable of damaging DNA and killing nearby cells. When infused, the antibody circulates and binds CD45-bearing cells throughout the bone marrow, spleen, and blood, delivering localized radiation to that compartment. This approach is used in the context of preparing patients with leukemia or related blood cancers for hematopoietic stem cell transplantation: the radiation helps eliminate residual malignant cells and existing marrow function, creating space and reducing disease burden before donor stem cells are infused. The broad rationale for choosing CD45 over a lineage-restricted marker is that it captures malignant cells across many blood cancer subtypes without requiring separate lineage-specific targeting, while its restriction to hematopoietic cells limits radiation exposure to unrelated tissues compared with untargeted whole-body irradiation.