Several cytokines and chemokines, such as interleukin (IL) 2 [1, 2], interferon (IFN) α [3], IL12 [4–8], IL15 [9–12], and chemokine platelet factor 4 (PF4) [13–15], are very effective for inhibiting tumor growth via immunomodulatory mechanisms in mouse models, and dozens of either active or completed clinical trials utilize cytokines alone or as an adjuvant for treating cancer [16]. The gene discussed is IL15; the disease is cancer.