PDCD1 and hematologic disorder: In contrast, in Cord Blood (CB), PD-1 expression on NK cells is independent of HCMV infection and moreover PD-1+ NK cells are characterized by a more immature CD56dimKIR+/−NKG2A+/−CD57−NCRs+ phenotype [21] Interestingly, the expansion of PD-1+ NK cell subsets has been observed in patients with hematologic malignancies, certain solid tumors (including OC) [15], or chronic viral infections [23–31].