PRF1 and neoplasm: Consistent with the increase in intercellular IL-15, the density of tumor-infiltrating CD8+ T lymphocytes was greater in Lv-mIL-15-transfected LLC tumors than in control LLC tumors (Fig. 5E); moreover, the effector functions of these tumor-infiltrating CD8+ T cells were also enhanced, as evidenced by the increased proportion of perforin-positive and Ki-67-positive T cells compared to that in control LLC tumors (Fig. 5F).