The role of IL-21 in immunity and cancer

Mechanism involved in interleukin-21-induced phagocytosis in human monocytes and macrophages

The interleukin (IL)-21/IL-21 receptor (R) is a promising system to be exploited for the development of therapeutic strategies. Although the biological activities of IL-21 and its cell signalling events have been largely studied in immunocytes, its interaction with human monocytes and macrophages have been neglected. Previously, we reported that IL-21 enhances Fc gamma receptor (FcRγ)-mediated phagocytosis in human monocytes and in human monocyte-derived macrophages (HMDM) and identified Syk as a novel molecular target of IL-21. Here, we elucidate further how IL-21 promotes phagocytosis in these cells. Unlike its ability to enhance phagocytosis of opsonized sheep red blood cells (SRBCs), IL-21 did not promote phagocytosis of Escherichia coli and zymosan by monocytes and did not alter the cell surface expression of CD16, CD32 and CD64. In HMDM, IL-21 was found to enhance phagocytosis of zymosan. In addition, we found that IL-21 activates p38, protein kinase B (Akt), signal transducer and activator of transcription (STAT)-1 and STAT-3 in monocytes and HMDM. Using a pharmacological approach, we demonstrate that IL-21 enhances phagocytosis by activating some mitogen-activated protein kinases (MAPKs) and phosphoinositide 3-kinase (PI3K)-Akt and Janus kinase (JAK)-STAT pathways. These results obtained in human monocytes and macrophages have to be considered for a better exploitation of the IL-21/IL-21R system for therapeutic purposes.

Distinct gene expression patterns correlate with developmental and functional traits of iNKT subsets

Invariant natural killer T (iNKT) cells comprise a subpopulation of innate lymphocytes developing in thymus. A new model proposes subdividing murine iNKT cells into iNKT1, 2 and 17 cells. Here, we use transcriptome analyses of iNKT1, 2 and 17 subsets isolated from BALB/c and C57BL/6 thymi to identify candidate genes that may affect iNKT cell development, migration or function. We show that Fcɛr1γ is involved in generation of iNKT1 cells and that SerpinB1 modulates frequency of iNKT17 cells. Moreover, a considerable proportion of iNKT17 cells express IL-4 and IL-17 simultaneously. The results presented not only validate the usefulness of the iNKT1/2/17-concept but also provide new insights into iNKT cell biology.

Highly efficient IL-21 and feeder cell-driven ex vivo expansion of human NK cells with therapeutic activity in a xenograft mouse model of melanoma

Natural killer (NK) cells are promising antitumor effector cells, but the generation of sufficient NK cell numbers for adoptive immunotherapy remains challenging. Therefore, we developed a method for highly efficient ex vivo expansion of human NK cells. Ex vivo expansion of NK cells in medium containing IL-2 and irradiated clinical-grade feeder cells (EBV-LCL) induced a 22-fold NK cell expansion after one week that was significantly increased to 53-fold by IL-21. Repeated stimulation with irradiated EBV-LCL and IL-2 and addition of IL-21 at the initiation of the culture allowed sustained NK cell proliferation with 10¹¹-fold NK cell expansion after 6 weeks. Compared to naive NK cells, expanded NK cells upregulated TRAIL, NKG2D, and DNAM-1, had superior cytotoxicity against tumor cell lines in vitro and produced more IFNγ and TNF-α upon PMA/Iono stimulation. Most importantly, adoptive transfer of NK cells expanded using feeder cells, IL-2 and IL-21 led to significant inhibition of tumor growth in a melanoma xenograft mouse model, which was greater than with NK cells activated with IL-2 alone. Intriguingly, adoptively transferred NK cells maintained their enhanced production of IFNγ and TNF-α upon ex vivo restimulation, although they rapidly lost their capacity to degranulate and mediate tumor cytotoxicity after the in vivo transfer. In conclusion, we developed a protocol for ex vivo NK cell expansion that results in outstanding cell yields. The expanded NK cells possess potent antitumor activity in vitro and in vivo and could be utilized at high numbers for adoptive immunotherapy in the clinic.

[Th9 cells: a new population of helper T cells]

Th9 cells are CD4 T helper cells characterized by their ability to produce IL-9 and IL-21. These cells are obtained from naive CD4(+) T cells cultured in the presence of TGF-β and IL-4. Thus their differentiation results from the balance between the signaling pathways induced by IL-4 in one hand and the one induced by TGF-β in the other hand. These cells are inflammatory cells and were first described in the context of atopic and autoimmune diseases in which they have a pathogenic role. They are also involved in the defense against parasite infections. Recently, some reports defined Th9 anticancer properties through their cytokine secretion. Indeed, their high secretion of IL-9 and IL-21 in the tumor bed contributes to their anticancer functions. These cytokines trigger the activation of dendritic cells, mast cells, natural killer cells, and CD8 T cells to mount an antitumor immune response.

Emerging nanotechnologies for cancer immunotherapy

Founded on the growing insight into the complex cancer-immune system interactions, adjuvant immunotherapies are rapidly emerging and being adapted for the treatment of various human malignancies. Immune checkpoint inhibitors, for example, have already shown clinical success. Nevertheless, many approaches are not optimized, require frequent administration, are associated with systemic toxicities and only show modest efficacy as monotherapies. Nanotechnology can potentially enhance the efficacy of such immunotherapies by improving the delivery, retention and release of immunostimulatory agents and biologicals in targeted cell populations and tissues. This review presents the current status and emerging trends in such nanotechnology-based cancer immunotherapies including the role of nanoparticles as carriers of immunomodulators, nanoparticles-based cancer vaccines, and depots for sustained immunostimulation. Also highlighted are key translational challenges and opportunities in this rapidly growing field.

Advances of the interleukin-21 signaling pathway in immunity and angiogenesis

Interleukin-21 (IL-21) and its receptor (IL-21R) are broadly expressed on human B cells, activated T cells and other myeloid cells. IL-21 cooperates with IL-6 and transforming growth factor-β to regulate T-cell differentiation. IL-21-mediated human B cell and dendritic cells differentiation requires signal transducer and activator of transcription 3 (STAT3), and also induces B-cell apoptosis dependents on the Toll-like receptor signal. Recently, in vitro and in vivo experiments showed that IL-21/IL-21R regulate angiogenesis through STAT3. IL-21 signaling pathways are complex due to its cooperation with other transcriptional factors, such as interferon regulatory factor 4 and granulocyte-macrophage colony-stimulating factor. The Janus kinase-STAT pathway has been the most extensively studied. With the increase in the understanding of IL-21 biology in the context of each specific disease or pathological condition, IL-21 could be a new therapeutic target for immune-related disease.

Regulation of Memory T Cells by Interleukin-23

Interleukin-23 (IL-23), a member of the IL-12 family of cytokines, is a heterodimeric cytokine. It is composed of subunits p40 (shared with IL-12) and p19 (an IL-12 p35-related subunit) and is secreted by several types of immune cells, such as natural killer cells and dendritic cells. The IL-23 receptor is composed of the subunit IL-12Rβ1 and the IL-23-specific subunit IL-23R. The binding of IL-23 to its specific cell surface receptor regulates a number of functions, including proliferation and differentiation of cells and secretion of cell factors. Memory T cells are a subset of T cells that secrete numerous important cell factors, and they function in the immune response to infection and diseases like cancer, autoimmune disease and bronchial asthma. IL-23R is expressed on the surface of memory T cells, which suggests that it can specifically regulate memory T cell function. IL-23 has been widely used as a clinical indicator in immune-related diseases and shows potential for use in disease treatment. Here we review the current progress in the study of the role of IL-23 in the regulation of memory T cells.

Interleukin-21 induces migration and invasion of fibroblast-like synoviocytes from patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial fibroblast hyperplasia and bone erosion. Fibroblast-like synoviocytes (FLS) play a pivotal role in RA pathogenesis through aggressive migration and matrix invasion, and certain proinflammatory cytokines may affect synoviocyte invasion. Whether interleukin (IL)-21 influences this process remains controversial. Here, we evaluated the potential regulatory effect of IL-21 on the migration, invasion and matrix metalloproteinase (MMP) expression in RA-FLS. We found that IL-21 promoted the migration, invasion and MMP (MMP-2, MMP-3, MMP-9, MMP-13) production in RA-FLS. Moreover, IL-21 induced activation of the phosphoinositide 3-kinase (PI3K), signal transducer and activator of transcription-3 (STAT-3) and extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) pathways, and blockage of these pathways [PI3K/protein kinase B (AKT) inhibitor LY294002, STAT-3 inhibitor STA-21 and ERK1/2 inhibitor PD98059] attenuated IL-21-induced migration and secretion of MMP-3 and MMP-9. In conclusion, our results suggest that IL-21 promotes migration and invasion of RA-FLS. Therefore, therapeutic strategies targeting IL-21 might be effective for the treatment of RA.

The good and the bad faces of STAT1 in solid tumours

Signal transducer and activator of transcription (STAT) 1 is part of the Janus kinase (JAK)/STAT signalling cascade and is best known for its essential role in mediating responses to all types of interferons (IFN). STAT1 regulates a variety of cellular processes, such as antimicrobial activities, cell proliferation and cell death. It exerts important immune modulatory activities both in the innate and the adaptive arm of the immune system. Based on studies in mice and data from human patients, STAT1 is generally considered a tumour suppressor but there is growing evidence that it can also act as a tumour promoter. This review aims at contrasting the two faces of STAT1 in tumourigenesis and providing an overview on the current knowledge of the underlying mechanisms or pathways.