Single chain recombinant human IL-15 (sch rhIL-15), hetIL-15, and several IL-15:IL-15Rα fusion proteins (Figure 2) have been produced and tested in preclinical models (mice and monkeys) to determine the pharmacokinetics, the bioavailability and the bioactivity of these agents, in order to advance to clinical trials for cancer immunotherapy. The gene discussed is IL15; the disease is cancer.