(A) Survival of IL-15 Tg mice following injection with MC38 cells. (A) Survival curve describing MC-38–injected IL-15 Tg mice. Two million MC38 cells,²³  a murine colon carcinoma cell line, were injected via the tail vain into C57BL/6 mice or IL-15 Tg mice¹¹  (n = 7), and their survival was monitored over 8 months. (B) MC38 cells formed lung metastases in the IL-15 Tg mouse following the NK-cell depletion. Anti-asialo GM1 antibody was injected into IL-15 Tg mice every 3 days (from day -9 to day 45) to deplete NK cells, which were occasionally monitored by analyzing the peripheral blood cells from mice by flow cytometry. Micro-MR (magnetic resonance) images were collected using a 1.5-Tesla superconductive magnet unit (Signa LX, WI). The arrows indicate the location of metastatic MC38 tumor masses in the lungs of an NK-depleted IL-15 Tg mouse.