After 16-h activation with IL-12, IL-15 and IL-18, a marked reduction in the number of viable NK cells was documented, while the dose of IL-2 used in combination with 1 ng/mL of IL-15 during the maintenance/expansion phase (from day 1 to day 7) was critical to the recovery and anti-tumor activity of NK cells. The gene discussed is IL15; the disease is neoplasm.