CD172a antibody, clone P84, recognizes CD172a, also known as single regulatory protein α (SIRPα) (signal regulatory protein alpha) or Src homology 2 domain-containing phosphatase substrate-1 (SHP-1), a type I transmembrane glycoprotein with three Ig-like extracellular domains and two cytoplasmic immunoreceptor tyrosine-based inhibition motifs (ITIMs)1. SIRPα is expressed predominantly in myeloid cells2 - including monocytes, macrophages, and dendritic cells (DCs) - and neuronal cells3. The extracellular ligand for SIRPα, CD47 (or integrin-associated protein [IAP])4, is expressed in most cell types5. In macrophages, ligation of SIRPα by CD47 inhibits macrophage phagocytosis of self cells6,7. SIRPα also negatively regulates DC-mediated T cell activation and DC maturation8-10. CD47 is also upregulated on tumor cells, inhibiting the phagocytosis of tumor cells by macrophages11. Therapeutics targeting the CD47-SIRPα interaction, including antibodies and fusion proteins, are currently under preclinical and clinical study for various malignancies as a monotherapy or in combination with other therapeutics12.