[Screening of small molecule inhibitors of IL-15Rα using molecular docking and surface plasmon resonance technology].

The study aims to explore the active molecules of traditional Chinese medicine that specifically bind to interleukin-15 receptor α (IL-15Rα) using molecular docking and surface plasmon resonance (SPR) technology. AutoDock molecular docking software was used to perform simulated docking of more than 3 000 compounds from 48 traditional Chinese medicines at IL-15Rα and screen the specific binding compounds. Then Biocore T200 biomolecular interaction analysis system of SPR was used to confirm the binding specificity of the selected target compounds. Finally, the biological effects of the target compounds on IL-15Rα were verified by cell biological experiments. The results showed that neoprzewaquinone A (Neo) possessed the highest specific binding affinity among the active molecules from traditional Chinese medicine, and the dissociation constant (KD) value was (0.62 ± 0.20) µmol/L. The results of cell experiment showed that Neo significantly inhibited the proliferation of Mo7e cells induced by IL-15, and the IC50 was 1.075 µmol/L, approximately 1/120 of the IC50 of Cefazolin (IL-15 specific antagonist). These results suggest that Neo is a specific inhibitor of IL-15Rα and may be a potential active drug for the treatment of diseases related to the dysfunction of the IL-15Rα signaling.

Mechanistic and Structural Insights on the IL-15 System through Molecular Dynamics Simulations.

Interleukin 15 (IL-15), a four-helix bundle cytokine, is involved in a plethora of different cellular functions and, particularly, plays a key role in the development and activation of immune responses. IL-15 forms receptor complexes by binding with IL-2Rß- and common γ(γc)-signaling subunits, which are shared with other members of the cytokines family (IL-2 for IL-2Rß- and all other γc- cytokines for γc). The specificity of IL-15 is brought by the non-signaling α-subunit, IL-15Rα. Here we present the results of molecular dynamics simulations carried out on four relevant forms of IL-15: its monomer, IL-15 interacting individually with IL-15Rα (IL-15/IL-15Rα), with IL-2Rß/γc subunits (IL-15/IL-2Rß/γc) or with its three receptors simultaneously (IL-15/IL-15Rα/IL-2Rß/γc). Through the analyses of the various trajectories, new insights on the structural features of the interfaces are highlighted, according to the considered form. The comparison of the results with the experimental data, available from X-ray crystallography, allows, in particular, the rationalization of the importance of IL-15 key residues (e.g. Asp8, Lys10, Glu64). Furthermore, the pivotal role of water molecules in the stabilization of the various protein-protein interfaces and their H-bonds networks are underlined for each of the considered complexes.

Discovery of a novel IL-15 based protein with improved developability and efficacy for cancer immunotherapy.

Interleukin-15 (IL-15) can promote both innate and adaptive immune reactions by stimulating CD8+/CD4+ T cells and natural killer cells (NK) while showing no effect in activating T-regulatory (Treg) cells or inducing activation-associated death among effector T cells and NK cells. Thus, IL-15 is considered as one of the most promising molecules for antitumor immune therapy. To improve the drug-like properties of natural IL-15, we create an IL-15-based molecule, named P22339, with the following characteristics: 1) building a complex of IL-15 and the Sushi domain of IL-15 receptor α chain to enhance the agonist activity of IL-15 via transpresentation; 2) through a rational structure-based design, creating a disulfide bond linking the IL-15/Sushi domain complex with an IgG1 Fc to augment its half-life. P22339 demonstrates excellent developability, pharmacokinetic and pharmacodynamic properties as well as antitumor efficacy in both in vitro assessments and in vivo studies. It significantly suppresses tumor growth and metastasis in rodent models, and activates T effector cells and NK cells in cynomolgus monkey. Overall, these data suggest that P22339 has a great potential for cancer immunotherapy.

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.

Paracrine and transpresentation functions of IL-15 are mediated by diverse splice versions of IL-15Rα in human monocytes and dendritic cells.

BACKGROUND: IL-15 can either be transpresented by IL-15Rα or be secreted. RESULTS: New N- and C-terminal splice versions of human IL-15Rα determine whether IL-15 is secreted or stays bound to the cell membrane. CONCLUSION: IL-15Rα isoforms determine the mode of action of IL-15. SIGNIFICANCE: IL-15Rα isoforms may modify immune response outcomes in humans. Species-specific differences of post-translational modifications suggested the existence of human IL-15Rα isoforms. We identified eight new isoforms that are predicted to modify the intracellular C termini of IL-15Rα, and another N-terminal exon "Ex2A" that was consistently present in all but one of the C-terminal isoforms. Ex2A encodes a 49-amino acid domain that allowed the transfer of IL-15/IL-15Rα complex to the cell surface but prevented its cleavage from cell membranes and its secretion thus facilitating the transpresentation of IL-15 as part of the immunological synapse. The Ex2A domain also affected the O-glycosylation of IL-15Rα that explained the species-specific differences. The Ex2A domain appeared to be removed from major IL-15Rα species during protein maturation, but both Ex2A and IL-15Rα appeared on the surface of monocytic cells upon activation. The membrane-associated form of the only C-terminal isoform that lacked Ex2A (IC3) was retained inside the cell, but soluble IL-15/IL-15Rα complexes were readily released from cells that expressed IL-15/IL-15Rα-IC3 thus limiting this IL-15/IL-15Rα isoform to act as a secreted molecule. These data suggest that splice versions of IL-15Rα determine the range of IL-15 activities.

Design and characterization of a protein superagonist of IL-15 fused with IL-15Rα and a high-affinity T cell receptor.

To avoid high systemic doses, strategies involving antigen-specific delivery of cytokine via linked antibodies or antibody fragments have been used. Targeting cancer-associated peptides presented by major histocompatibility complex (MHC) molecules (pepMHC) increases the number of potential target antigens and takes advantage of cross-presentation on tumor stroma and in draining lymph nodes. Here, we use a soluble, high-affinity single-chain T cell receptor Vα-Vß (scTv), to deliver cytokines to intracellular tumor-associated antigens presented as pepMHC. As typical wild-type T cell receptors (TCRs) exhibit low affinity (K(d) = 1-100 µM or more), we used an engineered TCR, m33, that binds its antigenic peptide SIYRYYGL (SIY) bound to the murine class I major histocompatability complex protein H2-K(b) (SIY/K(b) ) with nanomolar affinity (K(d) = 30 nM). We generated constructs consisting of m33 scTv fused to murine interleukin 2 (IL-2), interleukin 15 (IL-15), or IL-15/IL-15Rα (IL-15 linked to IL-15Rα sushi domain, called "superfusion"). The fusions were purified with good yields and bound specifically to SIY/K(b) with high affinity. Proper cytokine folding and binding were confirmed, and the fusions were capable of stimulating proliferation of cytokine-dependent cells, both when added directly and when presented in trans, bound to cells with the target pepMHC. The m33 superfusion was particularly potent and stable and represents a promising design for targeted antitumor immunomodulation.

Liver gene transfer of interkeukin-15 constructs that become part of circulating high density lipoproteins for immunotherapy.

Apolipoprotein A-I (Apo A-I) is a major component of high density lipoproteins (HDL) that transport cholesterol in circulation. We have constructed an expression plasmid encoding a chimeric molecule encompassing interleukin-15 (IL-15) and Apo A-I (pApo-hIL15) that was tested by hydrodynamic injections into mice and was co-administered with a plasmid encoding the sushi domain of IL-15Rα (pSushi) in order to enhance IL-15 trans-presentation and thereby bioactivity. The pharmacokinetics of the Apo A-I chimeric protein were much longer than non-stabilized IL-15 and its bioactivity was enhanced in combination with IL-15Rα Sushi. Importantly, the APO-IL-15 fusion protein was incorporated in part into circulating HDL. Liver gene transfer of these constructs increased NK and memory-phenotype CD8 lymphocyte numbers in peripheral blood, spleen and liver as a result of proliferation documented by CFSE dilution and BrdU incorporation. Moreover, the gene transfer procedure partly rescued the NK and memory T-cell deficiency observed in IL-15Rα(-/-) mice. pApo-hIL15+ pSushi gene transfer to the liver showed a modest therapeutic activity against subcutaneously transplanted MC38 colon carcinoma tumors, that was more evident when tumors were set up as liver metastases. The improved pharmacokinetic profile and the strong biological activity of APO-IL-15 fusion protein holds promise for further development in combination with other immunotherapies.

Non-random distribution of interleukin receptors on the cell surface.

Spatial organization of cell surface proteins plays a key role in the process of transmembrane signalling. Receptor clustering and changes in their cell surface distribution are often determining factors in the final outcome of ligand-receptor interactions. There are several techniques for assessing the distribution of protein molecules. Fluorescence resonance energy transfer (FRET) is an excellent tool for determining distance relationships of cell surface molecules. However, it does not provide information on the distribution of molecular clusters. Different kinds of microscopies fill this gap. The evaluation of the images provided by the listed techniques is often questionable. Herein we show the applicability of Ripley's K(t) function as a tool for analyzing the cell surface receptor patterns (Y. Nakamura, et al., Nature 1994, 369, 330-333). We have implemented an effective image processing algorithm for fast localization of gold labels on biological samples. We investigated spatial organization of Interleukin-2R alpha and -15R alpha (IL-2R alpha and IL-15R alpha) on a human CD4+leukaemia T-cell line, Kit225 FT7.10 by using transmission electron microscopy (TEM). TEM analysis showed co-clustering of the two types of alpha-chains even on the few-hundred-nanometer scale. The analysis of our data may contribute to our understanding the action of the IL-2/IL-15 receptor system in T-cell function.

The IL-15 receptor {alpha} chain cytoplasmic domain is critical for normal IL-15Ralpha function but is not required for trans-presentation.

IL-15 is critical for natural killer (NK)-cell development and function and for memory CD8(+) T-cell homeostasis. The IL-15 receptor consists of IL-15Ralpha, IL-2Rbeta, and the common cytokine receptor gamma chain (gamma(c)). IL-15Ralpha is known to "trans-present" IL-15 to an IL-2Rbeta/gamma(c) heterodimeric receptor on responding cells to initiate signaling. To investigate the importance of the IL-15Ralpha cytoplasmic domain, we generated a chimeric receptor consisting of the extracellular domain of IL-15Ralpha and intracellular domain of IL-2Ralpha (IL-15Ralpha(ext)/IL-2Ralpha(int)) and examined its function in 32D cells, in knock-in (KI) mice, and in adoptive-transfer experiments. The chimeric protein exhibited decreased cell-surface expression, and KI mice exhibited diminished NK, NKT, and CD8(+) T-cell development and defects in T-cell functional responses. However, 32D cells expressing the chimeric receptor had less IL-15-induced proliferation than wild-type (WT) transfectants with similar levels of IL-15Ralpha expression, indicating a signaling role for the IL-15Ralpha cytoplasmic domain beyond its effect on expression, and demonstrating that the IL-2Ralpha and IL-15Ralpha cytoplasmic domains are functionally distinct. Interestingly, adoptive-transfer experiments indicated that the chimeric IL-15Ralpha(ext)/IL-2Ralpha(int) receptor still supports trans-presentation. These experiments collectively indicate that IL-15Ralpha can act in cis in addition to acting in trans to present IL-15 to responding cells.

The exon-3-encoded domain of IL-15ralpha contributes to IL-15 high-affinity binding and is crucial for the IL-15 antagonistic effect of soluble IL-15Ralpha.

We previously showed that a natural soluble form of interleukin-15 (IL-15) Ralpha corresponding to the full-length ectodomain of IL-15Ralpha behaved as a potent antagonist of IL-15 action through IL-15Ralpha/beta/gamma, whereas a recombinant soluble IL-15Ralpha sushi domain did not, but instead acted as an agonist of IL-15 action through IL-15Rbeta/gamma. In order to determine precisely the molecular basis governing these antagonistic versus agonistic actions, we compared the binding properties and biological effects of recombinant soluble IL-15Ralpha (sIL-15Ralpha) species containing the sushi domain and different remaining parts of the ectodomain. We first demonstrate that the exon-3-encoded domain and, more particularly, its N-terminal 13-amino-acid (aa) peptide are important, in addition to the adjacent exon-2-encoded sushi domain, for the stabilization of the high-affinity IL-15.IL-15Ralpha complex by slowing down its dissociation rate and by contributing to about 10-20% of the free energy of interaction. We next show that all sushi-containing sIL-15Ralpha are agonists on IL-15Rbeta/gamma, coordinately increasing IL-15 binding and IL-15-induced proliferation. Their agonistic potencies are proportional to their respective affinities for IL-15. We then show that the antagonistic effect of sIL-15Ralpha in the context of IL-15Ralpha/beta/gamma is due to the 13-aa peptide that creates a sterical constraint impeding the binding of the sIL-15Ralpha.IL-15 complex to the membrane-anchored IL-15Ralpha/beta/gamma. In the frame of the soluble IL-15Ralpha sushi domain-IL-15 fusion protein that contains the 13-aa peptide, this constraint is alleviated as a result of a conformational effect due to the covalent linking of the 13-aa peptide to the N-terminus of IL-15. The soluble IL-15Ralpha sushi domain-IL-15 fusion protein is therefore able to bind and activate both the IL-15Rbeta/gamma and the IL-15Ralpha/beta/gamma receptors.

The soluble alpha chain of interleukin-15 receptor: a proinflammatory molecule associated with tumor progression in head and neck cancer.

Interleukin (IL)-15 is a proinflammatory cytokine, as it induces the production of inflammatory cytokines [IL-6, tumor necrosis factor alpha (TNFalpha), IL-17, etc.]. A correlation between high intratumoral IL-15 concentrations and poor clinical outcome in lung and head and neck cancer patients has been recently reported. The purpose of this study was to investigate the role of the soluble alpha chain of IL-15 receptor (sIL-15Ralpha), a natural regulator of IL-15, in head and neck cancer. Fifty-three newly diagnosed untreated head and neck cancer patients were included in this study. Quantification of sIL-15Ralpha was performed with a newly developed RIA. Increased serum sIL-15Ralpha concentrations were found in head and neck cancer patients and were closely correlated with poor clinical outcome both in terms of locoregional control and survival even on multivariate analysis. sIL-15Ralpha was mainly produced by tumor cells via proteolytic cleavage of IL-15Ralpha mediated by ADAM-17. A correlation was observed between ADAM-17 expression in tumor cells and serum sIL-15Ralpha concentrations. Surprisingly, sIL-15Ralpha did not act in vitro as an IL-15 antagonist but rather as an enhancer of IL-15-induced proinflammatory cytokines (IL-6, TNFalpha, and IL-17) that may promote tumor progression. This new tumor evasion mechanism based on amplification of the intratumoral inflammatory reaction is probably not restricted to head and neck cancer, as other tumors have been shown to release sIL-15Ralpha. Overall, these results support for the first time an original protumor role of sIL-15Ralpha in cancer.

Elucidation of the interleukin-15 binding site on its alpha receptor by NMR.

The cytokine interleukin-15 (IL-15) signals through the formation of a quaternary receptor complex composed of an IL-15-specific alpha receptor, together with beta and gammac receptors that are shared with interleukin-2 (IL-2). The initiating step in the formation of this signaling complex is the interaction between IL-15 and IL-15Ralpha, which is a single sushi domain bearing strong structural homology to one of the two sushi domains of IL-2Ralpha. The crystal structure of the IL2-Ralpha/IL-2 complex has been determined, however little is known about the analogous IL-15Ralpha/IL-15 binding interaction. Here we show that recombinant IL-15 can be overexpressed as a stable complex in the presence of its high affinity receptor, IL-15Ralpha. We find that this complex is 10-fold more active than IL-15 alone in stimulating proliferation and survival of memory phenotype CD8 T cells. To probe the ligand/receptor interface, we used solution NMR to map chemical shifts on 15N-labeled IL-15Ralpha in complex with unlabeled IL-15. Our results predict that the binding surface on IL-15Ralpha involves strands C and D, similar to IL-2Ralpha. The interface, as predicted here, leaves open the possibility of trans-presentation of IL-15 by IL-15Ralpha on an opposing cell.

Crystal structure of the IL-15-IL-15Ralpha complex, a cytokine-receptor unit presented in trans.

Interleukin 15 (IL-15) and IL-2, which promote the survival of memory CD8(+) T cells and regulatory T cells, respectively, bind receptor complexes that share beta- and gamma-signaling subunits. Receptor specificity is provided by unique, nonsignaling alpha-subunits. Whereas IL-2 receptor-alpha (IL-2Ralpha) is expressed together in cis with the beta- and gamma-subunits on T cells and B cells, IL-15Ralpha is expressed in trans on antigen-presenting cells. Here we present a 1.85-A crystal structure of the human IL-15-IL-15Ralpha complex. The structure provides insight into the molecular basis of the specificity of cytokine recognition and emphasizes the importance of water in generating this very high-affinity complex. Despite very low IL-15-IL-2 sequence homology and distinct receptor architecture, the topologies of the IL-15-IL-15Ralpha and IL-2-IL-2Ralpha complexes are very similar. Our data raise the possibility that IL-2, like IL-15, might be capable of being presented in trans in the context of its unique receptor alpha-chain.