NK cells traffic to and accumulate within tumor sites. (A) Trafficking of C57BL/6 luc⁺ NK cells to A20 tumor implanted subcutaneously in Balb/c recipients. Red circles indicate tumor site and size; control groups received NK cells without tumor implantation. ROI quantification indicates photons/s/area and correlates with the number of NK cells within the site. Mice received PBS (left) or recombinant human IL-2 5 × 10⁴ units intraperitoneally every second day (right). One mouse representative of each group is shown. (B) Quantification of NK-cell accumulation by BLI in the group receiving no IL-2. NK-cells accumulate in proportion to tumor growth. Each line represents an individual mouse. Results are representative of 5 individual experiments with up to 5 mice per group. (C) NK-cell homing and accumulation on day 14 within tumor-bearing Balb/c mice receiving standard-dose (1 × 10⁶) freshly isolated C57BL/6 NK; standard-dose NK in combination with high-dose IL-2 (5 × 10⁵ units daily for 14 days); high-dose NK cells (6 × 10⁶) stimulated ex vivo in IL-2 for 5 days; or intratumoral standard-dose NK. Unless stated otherwise all groups received standard-dose IL-2 5 × 10⁴ units every second day. NK cells were derived from luciferase-transgenic animals. Three mice from each group are shown (left panel) and BLI is quantified (right panel). ANOVA P = .18 for differences in BLI between the different groups. (D). Survival of animals in (C); P = .88. Results are representative of 2 experiments containing 5 mice in each group.