Definition

A long-acting form of the cytokine interleukin (IL)-15 and a fusion protein complex composed of a mutated form of IL-15, with an asparagine to aspartic acid substitution at amino acid 72 (N72D) (IL-15N72D), complexed with a soluble IL-15 receptor alpha (IL-15 Ralpha; IL-15Ra) Fc domain (IL-15Ra-sFc) (IL-15N72D/IL-15Ra-sFc), with potential antineoplastic activity. Upon administration, IL-15(N72D)/IL-15Ra-sFc fusion protein complex FL115 targets and binds to the IL-2/IL-15 receptor beta-common gamma chain (IL-2Rbetagamma) receptor on natural killer (NK) and CD8+ T lymphocytes, which activates and increases the levels of NK cells and memory CD8+(CD44high) 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. By coupling IL-15 to IL-15Ra-sFc, this agent has a prolonged drug half-life and shows an increased ability to bind IL-2Rbetagamma, which enhances its immune stimulatory activity as compared to IL-15 alone.