IL-2 Family Cytokines and their Receptors-- Biology of the IL-21 system

National Heart, Lung, And Blood Institute

Investigators

Linked publications & trials

Abstract

IL-2 and related cytokine systems are studied to clarify the immune response in normal, neoplastic, immunodeficient, and other disease states. Following activation by antigen, the magnitude and duration of the T-cell immune response is determined by the amount of IL-2 produced, levels of receptors expressed, and time course of each event. The IL-2 receptor contains three chains, IL-2Ra, IL-2Rb, and gc. Dr. Leonard cloned IL-2Ra in 1984, the lab co-discovered IL-2Rb in 1986 and then reported in 1993 that mutation of the gc chain results in X-linked severe combined immunodeficiency (XSCID, which has a T-B+NK- phenotype) in humans. We reported in 1995 that mutations of the gc-associated kinase, JAK3, result in an autosomal recessive form of SCID that phenocopies XSCID and in 1998 that T-B+NK+ SCID results from mutations in the IL7R gene. Based on work in our lab and others, gc was previously shown to be shared by the receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. We previously cloned the IL-21 receptor, generated IL-21 transgenic and Il21r knockout mice, elucidated mechanisms of IL-21 signaling, showed with Dan Littman that IL-21 can promote differentiation of Th17 cells (important in Crohn's disease and psoriasis), and regulate immunoglobulin production. We showed IL-21 serves key roles in autoimmune disease, including in mouse models of lupus, type 1 diabetes, and uveitis, and indicated potential for IL-21 as an anti-tumor agent. We previously showed a role for IL-21 in the development of T follicular helper cells and that IL-21 signaling is required for CD8 T cell survival and memory cell formation in response to vaccinia. We previously found that IL-21 promotes the pathogenic response to pneumonia virus of mice (PVM), a virus related to human respiratory syncytial virus, and that infection of Il21r-deficient mice with PVM induced fewer neutrophils and CD8, CD4, and gamma-delta T cell numbers in the lungs than in WT mice, indicating that IL-21 mediates the inflammatory response to PVM and that inhibiting IL-21 may be a mechanism for treating select viral infections. We previously showed that IL-21 induces IL-10 and with Tom Tedder that IL-21 could expand regulatory B cells (Breg cells) that produce IL-10 (B10 cells). Previously, we demonstrated that IL-21 regulated the Prdm1 gene (encoding BLIMP1) via a response element that depends on STAT3 and IRF4, leading to our finding that in contrast to its ability to cooperate with PU.1 in B cells to act via ETS-IRF composite elements (EICEs), IRF4 cooperates with BATF/JUN family proteins to act via AP1-IRF composite elements (AICEs) in T cells and some B cells. We showed critical regulation of important genes via these AICEs and cooperative binding of IRF4, BATF, and JUN family proteins, with diminished IRF4 binding in Batf-deficient cells and BATF binding in Irf4-deficient cells. IL-21 broadly acts on T- and B-cells, but its actions in innate immunity are poorly understood. Previously, we showed IL-21 induces apoptosis of conventional dendritic cells (cDCs) via STAT3 and BIM, and this was inhibited by GM-CSF. Importantly, the canonical pathway for IL-1 production requires TLR-mediated NF-kB-dependent Il1b gene induction, followed by caspase-mediated processing of pro-IL-1. We also previously showed that IL-21 induces IL-1 production in cDCs via a STAT3-dependent but NF-kB-independent pathway. STAT3-dependent IL-1 expression in cDCs partially explains the IL-21-mediated pathologic response occurring during infection with PVM. We also previously showed that IL-1 receptor signaling is critical for the development of autoimmune uveitis, a process we showed was dependent on IL-21. Mechanistically, IL-21 activates several STAT proteins. Besides signaling via STAT3, STAT1 is also important, and we had found that Tbx21 (encoding Tbet) and Ifng are differentially regulated by these STATs, with opposing actions of STAT1 and STAT3 on IFN- expression in CD4(+) T cells during chronic LCMV infection, and moreover, concordant actions of IL-21 related to IFNG and TBX21 expression was found using CD4 T cells from patients with hyper-IgE syndrome, a disease caused by STAT3 mutations, as well as in cells from STAT1 gain-of-function patients. Thus, STAT1 vs. STAT3 activation can fine-tune the actions of IL-21. We also previously found opposing roles for IL-21 and IL-2 in Th9 differentiation and contributed to studies showing that IL-21 with IFNg and IL-4 can govern TBET and CD11c expression in TLR-activated B cells, and that IL-21 signaling in B cells but not T cells is essential for the development of collagen-induced arthritis in mice. Moreover, over the year, we collaborated with Brian Annex related the loss of IL-21 receptor activation in hypoxic endothelial cells impairing perfusion recovery after hindlimb ischemia and showed there is increased endothelial IL-21 receptor in peripheral artery disease. We previously reported an interplay between IL-21 and type I IFN that regulates neutrophil-dependent responses to S. aureus and showed IL-2 and IL-21 differentially influence CD8+ T cell differentiation; IL-2 drives terminal differentiation to cells poorly effective against tumors, whereas IL-21 promotes stem cell memory T cells (TSCM) and antitumor responses. IL-2 promoted effector-like metabolism and aerobic glycolysis, inducing lactate dehydrogenase (LDH) and lactate production, whereas IL-21 maintained a more quiescent state. LDH inhibition rewired IL-2-induced effects, promoting pyruvate entry into the tricarboxylic acid cycle and inhibiting terminal effector and exhaustion programs, including mRNA expression of NR4A family nuclear receptors, as well as Prdm1 and Xbp1. Deleting Ldha prevented development of cells with antitumor effector function, but transient LDH inhibition increased memory cells that exhibited antitumor efficacy after adoptive transfer. Moreover, combining LDH inhibition with IL-21 increased TSCM cells, with greater antitumor responses and host survival, showing LDH modulates cytokine-mediated T cell differentiation, with translational potential of transiently inhibiting LDH during adoptive T cell-based immunotherapy. In the current year, we investigated the effect of cytokines on the cytolytic activity of exosomes derived from NK cells. Extracellular vesicles (EVs) derived from NK cells (NK-EVs), including exosomes, possess cytotoxic capacity against tumor cells, but their characteristics and regulation by cytokines had not been studied. We found that EVs from human NK-92 cells stimulated with IL-15 + IL-21 had enhanced cytotoxic capacity. Granzyme B and H were induced by by IL-15 + IL-21 stimulation in NK-EVs, but they were not required for the cytotoxic capacity. However, mass spectrometry analyses showed CD226 (DNAM-1) was induced by IL-15+IL-21 and blocking antibodies to CD226 reduced the cytolytic activity of NK-EVs. We also showed that NK-EVs are taken up by micropinocytosis. Thus, we elucidated novel properties of NK-EVs. We also are collaboratively working on IL-21 mimetics. Overall, we elucidated the biology and mechanisms of action by IL-21, expanding our knowledge of normal and pathological immune cell function, with relevance to autoimmunity and cancer, as well as to the basic control of T-cell and B-cell actions. We also contributed to a study showing that proliferation, together with increased apoptosis, causes T-cell lymphopenia in endogenous Cushings patients. IL-21 was decreased in high-dose glucocorticoid environments, and adding IL-21 could reverse apoptotic effects of glucocorticoid therapy. Thus, administering IL-21 in patients receiving long-term, high-dose glucocorticoid therapy potentially could be beneficial.