Characterization and Favorable in Vivo Properties of Heterodimeric Soluble IL-15•IL-15Rα Cytokine Compared to IL-15 Monomer

Interleukin-15 (IL-15), a 114-amino acid cytokine related to IL-2, regulates immune homeostasis and the fate of many lymphocyte subsets. We reported that, in the blood of mice and humans, IL-15 is present as a heterodimer associated with soluble IL-15 receptor alpha (sIL-15R alpha). Here, we show efficient production of this noncovalently linked but stable heterodimer in clonal human HEK293 cells and release of the processed IL-15 center dot sIL-15R alpha heterodimer in the medium. Purification of the IL-15 and sIL-15R alpha polypeptides allowed identification of the proteolytic cleavage site of IL-15R alpha and characterization of multiple glycosylation sites. Administration of the IL-15 center dot sIL-15R alpha heterodimer reconstituted from purified subunits resulted in sustained plasma IL-15 levels and in robust expansion of NK and T cells in mice, demonstrating pharmacokinetics and in vivo bioactivity superior to single chain IL-15. These identified properties of heterodimeric IL-15 provide a strong rationale for the evaluation of this molecule for clinical applications.