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 α (sIL-15Rα). Here, we show efficient production of this noncovalently linked but stable heterodimer in clonal human HEK293 cells and release of the processed IL-15·sIL-15Rα heterodimer in the medium. Purification of the IL-15 and sIL-15Rα polypeptides allowed identification of the proteolytic cleavage site of IL-15Rα and characterization of multiple glycosylation sites. Administration of the IL-15·sIL-15Rα 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. Background: IL-15 acts in vivo in association with IL-15Rα, as a heterodimeric cytokine. Results: Authentically processed and glycosylated IL-15·sIL-15Rα heterodimer was purified from human cells and characterized by sequencing and functional studies. Conclusion: IL-15 heterodimer shows favorable in vivo properties compared with monomeric IL-15. Significance: Characterization and availability of the IL-15 heterodimer is important for functional studies and clinical applications.