To further evaluate the migratory potential of macrophages in vivo in response to CD47 blockade and irradiation, we labeled macrophages within the irradiated tumor through local injection of FITC-ferumoxytol, a fluorescently-tagged iron oxide nanoparticle that is preferentially phagocytosed by macrophages38 (Fig. 6b and Extended Data Fig. 9d). Here, CD47 is linked to neoplasm.