IL2 and leukemia: Indeed, the use of a low IL-2 concentration (10 U/mL, protocol A) with IL-15 or of IL-15 alone (protocol D) resulted in a low recovery of NK cells displaying high anti-leukemia lytic levels assessed against the THP-1 cell line, whereas a higher concentration of IL-2 combined with IL-15 was associated with a progressively enhanced cellular recovery but a decreased cytolytic activity of NK cells.