The primary objective of the dose finding phase is to determine the maximum tolerated, minimum efficacious dose (MTD/MED) of a interleukin-15 (IL-15) super agonist complex (ALT-803) when given once weekly for 4 weeks in the outpatient setting. The study will follow a standard 3+3 design of dose escalation for toxicity with an added feature of stopping early if efficacy is confirmed. There are six dose levels of ALT-803 for to determine the MTD/MED: 1, 3, 6, 10, 20, and 30 mcg/kg.