A human immunoglobulin G1 (IgG1) monoclonal antibody directed against the human pro-inflammatory cytokine interleukin-15 (IL-15), with potential anti-inflammatory, immunomodulating and antineoplastic activities. Upon administration, anti-IL-15 monoclonal antibody AMG 714 binds to and neutralizes IL-15, thereby preventing IL-15-mediated pro-inflammatory signaling. By inhibiting IL-15-mediated immune responses, AMG 714 decreases natural killer (NK) cell activation and proliferation, reduces T-cell infiltration, increases T-cell apoptosis, and may prevent the growth of IL-15-driven cancer cells. IL-15 plays a key role in inflammation and is associated with a variety of autoimmune and inflammatory disorders as well as with cell proliferation in certain cancer types, such as T-cell lymphomas. IL-15 is required for the proliferation of certain T-cells and NK cells.