CD226 and pachyonychia congenita: In particular, we observed a large fraction of immature NKG2A+ CD57- NK cells displaying a strong downregulation of the main activating NK cell receptors (such as NKp30, DNAM-1, and CD16) in low-grade PC patients vs. a most mature KIR+ CD57+ NK cell fraction showing an up-regulation/induction of the immune checkpoint PD-1 in high-grade PC patients.