Neutrophils are required for NK cell development in mice and humans,414 and patients with chronic neutropenia have increased frequencies of CD56bright NK cells and lack mature CD56dim NK cells.415 Neutrophils have an anti-tumor effect mediated by TNF-related apoptosis-inducing ligand (TRAIL), which can induce apoptosis in leukemic cells416 (Fig. 7b). This evidence concerns the gene TNFSF10 and neoplasm.