IL-15 enhanced the in vivo antitumor activity of tumor-reactive CD8+ T cells25 26 and prolonged the survival of mice in several tumor models including colon carcinoma, prostatic cancer, melanoma, breast, myeloma and pancreatic models.22 24 27–33 Recent studies have investigated the mechanism by which IL-15 induces lymphocyte entry into tumors and increases their cytotoxicity.27 This evidence concerns the gene IL15 and prostate cancer.