Mechanistic and structural insight into the functional dichotomy between IL-2 and IL-15.

Interleukin 15 (IL-15) and IL-2 have distinct immunological functions even though both signal through the receptor subunit IL-2Rß and the common γ-chain (γ(c)). Here we found that in the structure of the IL-15-IL-15Rα-IL-2Rß-γ(c) quaternary complex, IL-15 binds to IL-2Rß and γ(c) in a heterodimer nearly indistinguishable from that of the IL-2-IL-2Rα-IL-2Rß-γ(c) complex, despite their different receptor-binding chemistries. IL-15Rα substantially increased the affinity of IL-15 for IL-2Rß, and this allostery was required for IL-15 trans signaling. Consistent with their identical IL-2Rß-γ(c) dimer geometries, IL-2 and IL-15 showed similar signaling properties in lymphocytes, with any differences resulting from disparate receptor affinities. Thus, IL-15 and IL-2 induced similar signals, and the cytokine specificity of IL-2Rα versus IL-15Rα determined cellular responsiveness. Our results provide new insights for the development of specific immunotherapeutics based on IL-15 or IL-2.

[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.

Combination Cancer Immunotherapy with Dendritic Cell Vaccine and Nanoparticles Loaded with Interleukin-15 and Anti-beta-catenin siRNA Significantly Inhibits Cancer Growth and Induces Anti-Tumor Immune Response.

PURPOSE: The invention and application of new immunotherapeutic methods can compensate for the inefficiency of conventional cancer treatment approaches, partly due to the inhibitory microenvironment of the tumor. In this study, we tried to inhibit the growth of cancer cells and induce anti-tumor immune responses by silencing the expression of the ß-catenin in the tumor microenvironment and transmitting interleukin (IL)-15 cytokine to provide optimal conditions for the dendritic cell (DC) vaccine. METHODS: For this purpose, we used folic acid (FA)-conjugated SPION-carboxymethyl dextran (CMD) chitosan (C) nanoparticles (NPs) to deliver anti-ß-catenin siRNA and IL-15 to cancer cells. RESULTS: The results showed that the codelivery of ß-catenin siRNA and IL-15 significantly reduced the growth of cancer cells and increased the immune response. The treatment also considerably stimulated the performance of the DC vaccine in triggering anti-tumor immunity, which inhibited tumor development and increased survival in mice in two different cancer models. CONCLUSIONS: These findings suggest that the use of new nanocarriers such as SPION-C-CMD-FA could be an effective way to use as a novel combination therapy consisting of ß-catenin siRNA, IL-15, and DC vaccine to treat cancer.

IL-15Rα membrane anchorage in either cis or trans is required for stabilization of IL-15 and optimal signaling.

Interleukin (IL)-15 plays an important role in the communication between immune cells. It delivers its signal through different modes involving three receptor chains: IL-15Rα, IL-2Rß and IL-2Rγc. The combination of the different chains result in the formation of IL-15Rα/IL-2Rß/γc trimeric or IL-2Rß/γc dimeric receptors. In this study, we have investigated the role of the IL-15Rα chain in stabilizing the cytokine in the IL-2Rß/γc dimeric receptor. By analyzing the key amino acid residues of IL-15 facing IL-2Rß, we provide evidence of differential interfaces in the presence or in the absence of membrane-anchored IL-15Rα. Moreover, we found that the anchorage of IL-15Rα to the cell surface regardless its mode of presentation - i.e. cis or trans - is crucial for complete signaling. These observations show how the cells can finely modulate the intensity of cytokine signaling through the quality and the level of expression of the receptor chains.

A method for making alignments of related protein sequences that share very little similarity; shark interleukin 2 as an example.

An optimized alignment of related protein sequences helps to see their important shared features and to deduce their phylogenetic relationships. At low levels of sequence similarity, there are no suitable computer programs for making the best possible alignment. This review summarizes some guidelines for how in such instances, nevertheless, insightful alignments can be made. The method involves, basically, the understanding of molecular family features at both the protein and intron-exon level, and the collection of many related sequences so that gradual differences may be observed. The method is exemplified by identifying and aligning interleukin 2 (IL-2) and related sequences in Elasmobranchii (sharks/rays) and coelacanth, as other authors have expressed difficulty with their identification. From the point of general immunology, it is interesting that the unusual long "leader" sequence of IL-15, already known in other species, is even more impressively conserved in cartilaginous fish. Furthermore, sequence comparisons suggest that IL-2 in cartilaginous fish has lost its ability to bind an IL-2Rα/15Rα receptor chain, which would prohibit the existence of a mechanism for regulatory T cell regulation identical to mammals.

Phase I study protocol: NKTR-255 as monotherapy or combined with daratumumab or rituximab in hematologic malignancies.

NKTR-255 is an investigational polyethylene glycol-modified recombinant human IL-15 (rhIL-15) receptor agonist, designed to improve the immunotherapeutic and anti-cancer benefit observed with rhIL-15 while circumventing the toxicities associated with this therapy. In preclinical studies, NKTR-255 has demonstrated enhanced proliferation and function of CD8+ T cells and natural killer cells, as well as enhanced anti-tumor activity and survival both as monotherapy and in combination with monoclonal antibodies in multiple cancer models. Here, we describe the rationale and design of the first-in-human Phase I, dose-escalation and dose-expansion study of NKTR-255 alone and in combination with daratumumab or rituximab in adults with relapsed/refractory multiple myeloma or non-Hodgkin's lymphoma that will determine the maximum tolerated dose and recommended Phase II dose for NKTR-255.

Lay abstract Interleukin-15 (IL-15) is a protein that helps the body's natural immune system to defend itself against infections and diseases like cancer. This article discusses a clinical trial in patients with multiple myeloma or non-Hodgkin's lymphoma that evaluates a new investigational medicine, NKTR-255, a polymer-modified form of IL-15 that has been engineered to improve its ability to provide a sustained anti-tumor immune response. The trial will explore different doses of NKTR-255 to determine patient side effects and to find the highest acceptable dose that patients can tolerate. Based on this, a dose will be chosen that offers an optimal balance between having a positive anti-cancer effect and minimizing side effects. This dose will be tested further in patients who have had different treatments in the past. If the side effects are acceptable, this dose will be tested in a new trial in a large number of patients. Clinical Trial Registration: NCT04136756 (ClinicalTrials.gov).

A Chimeric IL-15/IL-15Rα Molecule Expressed on NFκB-Activated Dendritic Cells Supports Their Capability to Activate Natural Killer Cells.

Natural killer (NK) cells, members of the innate immune system, play an important role in the rejection of HLA class I negative tumor cells. Hence, a therapeutic vaccine, which can activate NK cells in addition to cells of the adaptive immune system might induce a more comprehensive cellular response, which could lead to increased tumor elimination. Dendritic cells (DCs) are capable of activating and expanding NK cells, especially when the NFκB pathway is activated in the DCs thereby leading to the secretion of the cytokine IL-12. Another prominent NK cell activator is IL-15, which can be bound by the IL-15 receptor alpha-chain (IL-15Rα) to be transpresented to the NK cells. However, monocyte-derived DCs do neither secrete IL-15, nor express the IL-15Rα. Hence, we designed a chimeric protein consisting of IL-15 and the IL-15Rα. Upon mRNA electroporation, the fusion protein was detectable on the surface of the DCs, and increased the potential of NFκB-activated, IL-12-producing DC to activate NK cells in an autologous cell culture system with ex vivo-generated cells from healthy donors. These data show that a chimeric IL-15/IL-15Rα molecule can be expressed by monocyte-derived DCs, is trafficked to the cell surface, and is functional regarding the activation of NK cells. These data represent an initial proof-of-concept for an additional possibility of further improving cellular DC-based immunotherapies of cancer.

Role of interleukin-15 in cardiovascular diseases.

Interleukin (IL)-15 is a recently identified cytokine, which belongs to the interleukin-2(IL-2) family, and plays an important role in innate and adaptive immunoreaction. Given the fact that the structure of IL-15 is partially similar to IL-2, they share some common biological effects, including immunoregulation. IL-2 was proven to protect cardiac function in mouse myocardial infarction models. Cardiovascular diseases (CVDs) dominate the cause of mortality worldwide. Besides atherosclerosis, inflammation is also widely involved in the pathogenesis of many CVDs including hypertension, heart failure (HF) and aneurysm. IL-15, as a pro-inflammatory cytokine, is up-regulated in some cardiovascular diseases, such as myocardial infarction and atherosclerosis. The current understanding of IL-15, including its signal pathway and cellular function, was described. Furthermore, IL-15 has a protective effect in myocardial infarction and myocarditis by decreasing cardiomyocyte death and improving heart function. The inhibited effect of IL-15 in ductus arteriosus (DA) should be focused on. IL-15 promoted atherogenesis. IL-15 may be a good target in treatment of cardiovascular diabetology. Finally, future research direction of IL-15 deserves attention. Since IL-15 plays several roles in CVDs, understanding the role of the IL-15/IL-15R system may provide a scientific basis for the development of new approaches that use IL-15 for the treatment of CVDs.

Treatment with native heterodimeric IL-15 increases cytotoxic lymphocytes and reduces SHIV RNA in lymph nodes.

B cell follicles in secondary lymphoid tissues represent an immune privileged sanctuary for AIDS viruses, in part because cytotoxic CD8+ T cells are mostly excluded from entering the follicles that harbor infected T follicular helper (TFH) cells. We studied the effects of native heterodimeric IL-15 (hetIL-15) treatment on uninfected rhesus macaques and on macaques that had spontaneously controlled SHIV infection to low levels of chronic viremia. hetIL-15 increased effector CD8+ T lymphocytes with high granzyme B content in blood, mucosal sites and lymph nodes, including virus-specific MHC-peptide tetramer+ CD8+ cells in LN. Following hetIL-15 treatment, multiplexed quantitative image analysis (histo-cytometry) of LN revealed increased numbers of granzyme B+ T cells in B cell follicles and SHIV RNA was decreased in plasma and in LN. Based on these properties, hetIL-15 shows promise as a potential component in combination immunotherapy regimens to target AIDS virus sanctuaries and reduce long-term viral reservoirs in HIV-1 infected individuals. TRIAL REGISTRATION: ClinicalTrials.gov NCT02452268.

Characterisation of IL-15 and IL-2Rß in grass carp: IL-15 upregulates cytokines and transcription factors of type 1 immune response and NK cell activation.

Interleukin (IL) -15 belongs to the common cytokine receptor γ chain (γC) family and has diverse functions in regulating the development, proliferation and activation of NK and T cells. It activates a hetero-trimeric receptor complex consisting of IL-2Rα, IL-2Rß and a common γ chain (γC). In this study, the full-length cDNA sequences of IL-15 and IL-2Rß were identified in grass carp (Ctenopharyngodon idella, Ci) and their expression profiles analysed. The CiIL-15 and CiIL-2Rß were shown to be broadly expressed in tissues, with the highest levels detected in the spleen. Moreover, the CiIL-15 and CiIL-2Rß were modulated in primary head kidney leucocytes (HKLs) and splenocytes by immunostimulants and cytokines, and in the head kidney and spleen of fish after infection of Flavobacterium columnare and grass carp reovirus. The bioactivity of bacteria derived recombinant CiIL-15 protein was evaluated in the primary leucocytes. The CiIL-15 was shown to induce signature genes of type 1 immune response (IFN-γ and T-bet) and NK cell activation (perforin and Eomesa), whilst exhibiting inhibitory effects on the genes involved in the type 2 immune response (IL-4/13, IL-10 and Gata3). Our data suggest that IL-15 is a key regulator in promoting the type 1 immune response and NK cell activation in fish.

MiR-122 is involved in immune response by regulating Interleukin-15 in the orange-spotted grouper (Epinephelus coioides).

Epinephelus coioides is an important economic culture marine fish and is susceptible to various pathogenic diseases. Increasingly evidences showed that miRNAs participated in the regulation of the cell proliferation, differentiation and immune response. MiR-122 has been reported to play an essential role in immune response by triggering an inflammatory reaction. However, the function of miR-122 in response to bacterial infection is unclear in Epinephelus coioides. Herein, we report that miR-122 is involved in response to Aeromonas hydrophila infection of grouper spleen cells (GS). IL-15, IL-6 and IL-1ß are inhibited in overexpression miR-122 GS cells, while induced in silence miR-122 GS cells. In addition, IL-15 is predicted to be the target gene of miR-122, which is further confirmed by LUC. Taken together, we propose that miR-122 regulates the immune response to bacterial infection by triggering IL-15.

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.

Molecular recognition of IL-8, IL-10, IL-12, and IL-15 in biological fluids using phthalocyanine-based stochastic sensors.

Two stochastic sensors based on the modification of graphite paste with the complexes formed by phthalocyanine (PhCN) with Ni and Cu were designed and used for molecular recognition of IL-8, IL-10, IL-12, and IL-15. The four interleukins were recognized according to their signatures-called toff (qualitative parameter) from the diagrams obtained after measurements. The limit of determination for IL-8 was 1 × 10-4µg mL-1 when both stochastic sensors were used; for IL-10, the determination limit was 4.5 × 10-4µg mL-1 for the Ni complex-based sensor, and 4.5 × 10-7µg mL-1 for the Cu complex-based sensor, respectively; for IL-12, the determination limit was 5 × 10-4µg mL-1 for the Ni complex-based sensor, and 5 × 10-7µg mL-1 for the Cu complex-based sensor, respectively; while for IL-15, the determination limit was 5 × 10-5µg/mL for the Ni complex-based sensor, and 5 × 10-5µg/mL for the Cu complex-based sensor, respectively. The stochastic method used was validated using the following biological fluids: nasal lavage, saliva, serum, and whole blood. Graphical abstract ᅟ.

A novel self-cleavable tag Zbasic-∆I-CM and its application in the soluble expression of recombinant human interleukin-15 in Escherichia coli.

Soluble expression of recombinant therapeutic proteins in Escherichia coli (E. coli) has been a challenging task in biopharmaceutical development. In this study, a novel self-cleavable tag Zbasic-intein has been constructed for the soluble expression and purification of a recombinant cytokine, human interleukin-15 (IL-15). We screened several solubilizing tags fused with the self-cleavable Mycobacterium tuberculosis recA mini-intein ∆I-CM and demonstrated that Zbasic tag can significantly improve the solubility of the product with correspondent to the intein activity. The fusion protein "Zbasic-∆I-CM-IL-15" was expressed with high solubility and easily enriched by the cost-effective cation-exchange chromatography. The self-cleavage of the fusion tag Zbasic-∆I-CM was then induced by a pH shift, with an activation energy of 7.48 kcal/mol. The mature IL-15 with natural N-terminus was released and further purified by hydrophobic interaction and anion-exchange chromatography. High-resolution reverse-phase high-performance liquid chromatography and mass spectrometry analysis confirmed that the product was of high purity and correct mass. With a CTLL-2 cell proliferation-based assay, the EC50 was evaluated to be of about 0.126 ng/mL, similar to the product in clinical trials. By avoiding the time-consuming denaturing-refolding steps in previously reported processes, the current method is efficient and cost-effective. The novel tag Zbasic-∆I-CM can be potentially applied to large-scale manufacturing of recombinant human cytokines as well as other mammalian-sourced proteins in E. coli.

Purification of inclusion bodies using PEG precipitation under denaturing conditions to produce recombinant therapeutic proteins from Escherichia coli.

It has been documented that the purification of inclusion bodies from Escherichia coli by size exclusion chromatography (SEC) may benefit subsequent refolding and recovery of recombinant proteins. However, loading volume and the high cost of the column limits its application in large-scale manufacturing of biopharmaceutical proteins. We report a novel process using polyethylene glycol (PEG) precipitation under denaturing conditions to replace SEC for rapid purification of inclusion bodies containing recombinant therapeutic proteins. Using recombinant human interleukin 15 (rhIL-15) as an example, inclusion bodies of rhIL-15 were solubilized in 7 M guanidine hydrochloride, and rhIL-15 was precipitated by the addition of PEG 6000. A final concentration of 5% (w/v) PEG 6000 was found to be optimal to precipitate target proteins and enhance recovery and purity. Compared to the previously reported S-200 size exclusion purification method, PEG precipitation was easier to scale up and achieved the same protein yields and quality of the product. PEG precipitation also reduced manufacturing time by about 50 and 95% of material costs. After refolding and further purification, the rhIL-15 product was highly pure and demonstrated a comparable bioactivity with a rhIL-15 reference standard. Our studies demonstrated that PEG precipitation of inclusion bodies under denaturing conditions holds significant potential as a manufacturing process for biopharmaceuticals from E. coli protein expression systems.

The level of FoxO1 and IL-15 in skeletal muscle, serum and synovial fluid in people with knee osteoarthritis: a case control study.

UNLABELLED: The molecular regulation of muscle function in knee osteoarthritis is unclear. Elevated muscle atrophy regulation marker expression was associated with reduced muscle strength in knee osteoarthritis. The level of protein expression appears to be different between muscle, knee joint and serum, suggesting that inflammation is regulated differently within these tissues. INTRODUCTION: Impaired muscle function is common in knee osteoarthritis (OA). Numerous biochemical molecules have been implicated in the development of OA; however, these have only been identified in the joint and serum. We compared the expression of interleukin-15 (IL-15) and Forkhead box protein-O1 (FoxO1) in muscle of patients with knee OA and asymptomatic individuals and examined whether IL-15 was also present in the joint and serum. METHODS: Muscle and blood samples were collected from 19 patients with knee OA and 10 age-matched asymptomatic individuals. Synovial fluid and muscle biopsies were collected from the OA group during knee replacement surgery. IL-15 and FoxO1 were measured in the skeletal muscle. IL-15 abundance was also analysed in the serum of both groups and synovial fluid from the OA group. Knee extensor strength was measured and correlated with IL-15 and FoxO1 in the muscle. RESULTS: FoxO1 protein expression was higher (p = 0.04), whereas IL-15 expression was lower (p = 0.02) in the muscle of the OA group. Strength was also lower in the OA group and was inversely correlated with FoxO1 expression. No correlation was found between IL-15 in the joint, muscle or serum. CONCLUSION: Skeletal muscle, particularly the quadriceps, is affected in people with knee OA where elevated FoxO1 protein expression was associated with reduced muscle strength. While IL-15 protein expression in the muscle was lower in the knee OA group, no correlation was found between the expression of IL-15 protein in the muscle, joint and serum, which suggests that inflammation is regulated differently within these tissues. Australian Clinical Trials Registry (ACTR) number: ACTRN12613000467730 ( http://www.anzctr.org.au/TrialSearch.aspx?searchTxt=ACTRN12613000467730&isBasic=True ).

Recombinant human heterodimeric IL-15 complex displays extensive and reproducible N- and O-linked glycosylation.

Human interleukin 15 (IL-15) circulates in blood as a stable molecular complex with the soluble IL-15 receptor alpha (sIL-15Rα). This heterodimeric IL-15:sIL-15Rα complex (hetIL-15) shows therapeutic potential by promoting the growth, mobilization and activation of lymphocytes and is currently evaluated in clinical trials. Favorable pharmacokinetic properties are associated with the heterodimeric formation and the glycosylation of hetIL-15, which, however, remains largely uncharacterized. We report the site-specific N- and O-glycosylation of two clinically relevant large-scale preparations of HEK293-derived recombinant human hetIL-15. Intact IL-15 and sIL-15Rα and derived glycans and glycopeptides were separately profiled using multiple LC-MS/MS strategies. IL-15 Asn79 and sIL-15Rα Asn107 carried the same repertoire of biosynthetically-related N-glycans covering mostly α1-6-core-fucosylated and ß-GlcNAc-terminating complex-type structures. The two potential IL-15 N-glycosylation sites (Asn71 and Asn112) located at the IL-2 receptor interface were unoccupied. Mass analysis of intact IL-15 confirmed its N-glycosylation and suggested that Asn79-glycosylation partially prevents Asn77-deamidation. IL-15 contained no O-glycans, whereas sIL-15Rα was heavily O-glycosylated with partially sialylated core 1 and 2-type mono- to hexasaccharides on Thr2, Thr81, Thr86, Thr156, Ser158, and Ser160. The sialoglycans displayed α2-3- and α2-6-NeuAc-type sialylation. Non-human, potentially immunogenic glycoepitopes (e.g. N-glycolylneuraminic acid and α-galactosylation) were not displayed by hetIL-15. Highly reproducible glycosylation of IL-15 and sIL-15Rα of two batches of hetIL-15 demonstrated consistent manufacturing and purification. In conclusion, we document the heterogeneous and reproducible N- and O-glycosylation of large-scale preparations of the therapeutic candidate hetIL-15. Site-specific mapping of these molecular features is important to evaluate the consistent large-scale production and clinical efficacy of hetIL-15.

Molecular characterization of interleukin 15 mRNA from rohu, Labeo rohita (Hamilton): Its prominent role during parasitic infection as indicated from infection studies.

Interleukin 15 (IL-15) is an important cytokine of fish immune system. Sequence characterization of IL-15 from rohu, Labeo rohita revealed a mRNA sequence of 1064 bp with coding sequence of 567 bp and signal peptide of 16 amino acids. There are four characteristic sequence features viz., presence of four out-of-frame AUG initiation codons, four highly conserved cysteine residues, constitutive expression in all tissues and evolutionary similarity. The ontogeny study revealed maternal transfer of this molecule and higher expression up to 3 h post-fertilization in fertilized embryos. Its expression was down-regulated in anterior and posterior kidneys, intestine and liver tissues of rohu infected with Aeromonas hydrophila. Mild up-regulation in liver and higher expression in spleen was noticed in rohu stimulated with poly I:C (poly ionosinic:cytidylic), whereas down-regulation was observed in intestine and kidney tissues. However, a consistent higher expression was noticed in kidney and skin tissues during Argulus siamensis infection. Therefore, rohu IL-15 might possess more defensive role during early development and parasitic infection.

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.

Soluble IL-15/IL-15Rα complexes in human serum.

In this issue of Blood, Bergamaschi and colleagues demonstrate that effectively all circulating IL-15 found in the serum of humans and mice is associated with the soluble IL-15Rα.(1)