No pulmonary metastasis in C57BL/6 mice injected with IL-15Rα–transfected MC38 cells. Micro-MR images of lungs of C57/BL6 mice injected with parental or IL-15Rα–transfected (high or moderate expression) MC38 cells are shown. Parental MC38 cells formed fatal pulmonary metastases and almost filled the lungs of all of the injected mice (n = 11) (left). In contrast, no visible metastatic masses were observed in lungs of all mice (n = 6) injected with IL-15Rα⁺MC38 (images were taken at 28 days after injection; T indicates tumor).