A human fusion protein consisting of the cytokine interleukin (IL)-15 and the high-affinity binding sushi+ domain of IL-15 receptor alpha (IL-15Ra), with potential antineoplastic activities. Upon administration, nanrilkefusp alfa activates and increases the levels of natural killer (NK) cells and memory CD8+ T-cells. The memory T-cells enhance the secretion of the cytokine interferon-gamma (IFN-g), which further potentiates the immune response against tumor cells. This may increase tumor cell killing and decrease tumor cell proliferation. IL-15 regulates CD8+ T and NK cell development, activation and proliferation. Nanrilkefusp alfa is more potent than unmodified IL-15 and does not require endogenous IL-15Ra for its action.