SIRPA and neoplasm: CD47 on tumor cells binds to Signal-Regulatory Protein alpha (SIRPα) on macrophages, sequentially inhibits phagocytosis of macrophages, and attenuates the presentation of tumor antigens to T cells, thereby impairing both macrophage-mediated and cytotoxic CD8 T cell-mediated anti-tumor effects 15,16,18.