PRF1 and neoplasm: Importantly, in HNSCC, tumour-infiltrating NK cells often occupy the CD56bright/CD16dim subset; these showed an immature phenotype predominantly characterized by the decreased expression of DX5, CD27lowCD11blow, increased NKG2A and lower levels of Siglec-7, NKG2D and natural cytotoxicity receptors, such as NKp30, NKp44, NKp46, perforin, granzyme B and CD16.