PDCD1 and neoplasm: Another group of glioma tracers evaluates immune system components in the tumor microenvironment by targeting immune cell infiltration and activation markers, such as CD8+ lymphocytes (389), its co-stimulatory molecule, OX40 (390), a marker of tumor-associated myeloid cells, CD11b (391, 392), a phagocytosis checkpoint molecule, CD47 (393), and lymphocyte checkpoint molecule/ligand, PD-1/PD-L1 (378, 394).