Regulation of IL-21 signaling by suppressor of cytokine signaling-1 (SOCS1) in CD8(+) T lymphocytes

LncRNA MIAT suppresses inflammation in LPS-induced J774A.1 macrophages by promoting autophagy through miR-30a-5p/SOCS1 axi

Accumulated data implicate that long noncoding RNA (lncRNA) plays a pivotal role in rheumatoid arthritis (RA), potentially serving as a competitive endogenous RNA (ceRNA) for microRNAs (miRNAs). The lncRNA myocardial infarction-associated transcript (MIAT) has been demonstrated to regulate inflammation. However, the role of MIAT in the inflammation of RA remains inadequately explored. This study aims to elucidate MIAT's role in the inflammation of lipopolysaccharide (LPS)-induced macrophages and to uncover the underlying molecular mechanisms. We observed heightened MIAT expression in LPS-induced J774A.1 cells and collagen-induced arthritis mouse models, in contrast to the expression pattern of miR-30a-5p. Silencing MIAT resulted in increased expression of the inflammatory cytokines IL-1β and TNF-α. Simultaneously, MIAT interference significantly impeded macrophage autophagy, evidenced by decreased expression of autophagy-related markers LC3-II and Beclin-1, alongside increased levels of p62 in LPS-induced J774A.1 cells. Notably, MIAT functioned as a ceRNA, sponging miR-30a-5p and exerting a negative regulatory influence on its expression. SOCS1 emerged as a target of miR-30a-5p, modulated by MIAT. Mechanistically, inhibiting miR-30a-5p reversed the impact of MIAT deficiency in promoting LPS-induced inflammation, while SOCS1 knockdown countered the cytokine inhibitory effect induced by silencing miR-30a-5p. In summary, this study indicates that lncRNA MIAT suppresses inflammation in LPS-induced J774A.1 macrophages by stimulating autophagy through the miR-30a-5p/SOCS1 axis. This suggests that MIAT holds promise as a potential therapeutic target for RA inflammation.

SOCS1 is a critical checkpoint in immune homeostasis, inflammation and tumor immunity

The Suppressor of Cytokine Signaling (SOCS) family proteins are important negative regulators of cytokine signaling. SOCS1 is the prototypical member of the SOCS family and functions in a classic negative-feedback loop to inhibit signaling in response to interferon, interleukin-12 and interleukin-2 family cytokines. These cytokines have a critical role in orchestrating our immune defence against viral pathogens and cancer. The ability of SOCS1 to limit cytokine signaling positions it as an important immune checkpoint, as evidenced by the detection of detrimental SOCS1 variants in patients with cytokine-driven inflammatory and autoimmune disease. SOCS1 has also emerged as a key checkpoint that restricts anti-tumor immunity, playing both a tumor intrinsic role and impacting the ability of various immune cells to mount an effective anti-tumor response. In this review, we describe the mechanism of SOCS1 action, focusing on the role of SOCS1 in autoimmunity and cancer, and discuss the potential for new SOCS1-directed cancer therapies that could be used to enhance adoptive immunotherapy and immune checkpoint blockade.

SOCS1 expression in cancer cells: potential roles in promoting antitumor immunity

Suppressor of cytokine signaling 1 (SOCS1) is a potent regulator immune cell responses and a proven tumor suppressor. Inhibition of SOCS1 in T cells can boost antitumor immunity, whereas its loss in tumor cells increases tumor aggressivity. Investigations into the tumor suppression mechanisms so far focused on tumor cell-intrinsic functions of SOCS1. However, it is possible that SOCS1 expression in tumor cells also regulate antitumor immune responses in a cell-extrinsic manner via direct and indirect mechanisms. Here, we discuss the evidence supporting the latter, and its implications for antitumor immunity.

Inflammatory Cytokines That Enhance Antigen Responsiveness of Naïve CD8+ T Lymphocytes Modulate Chromatin Accessibility of Genes Impacted by Antigen Stimulation

Naïve CD8⁺ T lymphocytes exposed to certain inflammatory cytokines undergo proliferation and display increased sensitivity to antigens. Such 'cytokine priming' can promote the activation of potentially autoreactive and antitumor CD8⁺ T cells by weak tissue antigens and tumor antigens. To elucidate the molecular mechanisms of cytokine priming, naïve PMEL-1 TCR transgenic CD8⁺ T lymphocytes were stimulated with IL-15 and IL-21, and chromatin accessibility was assessed using the assay for transposase-accessible chromatin (ATAC) sequencing. PMEL-1 cells stimulated by the cognate antigenic peptide mgp100_25-33 served as controls. Cytokine-primed cells showed a limited number of opening and closing chromatin accessibility peaks compared to antigen-stimulated cells. However, the ATACseq peaks in cytokine-primed cells substantially overlapped with those of antigen-stimulated cells and mapped to several genes implicated in T cell signaling, activation, effector differentiation, negative regulation and exhaustion. Nonetheless, the expression of most of these genes was remarkably different between cytokine-primed and antigen-stimulated cells. In addition, cytokine priming impacted the expression of several genes following antigen stimulation in a synergistic or antagonistic manner. Our findings indicate that chromatin accessibility changes in cytokine-primed naïve CD8⁺ T cells not only underlie their increased antigen responsiveness but may also enhance their functional fitness by reducing exhaustion without compromising regulatory controls.

Interferons limit autoantigen-specific CD8+ T-cell expansion in the non-obese diabetic mouse

Interferon gamma (IFNγ) is a proinflammatory cytokine implicated in autoimmune diseases. However, deficiency or neutralization of IFNγ is ineffective in reducing disease. We characterize islet antigen-specific T cells in non-obese diabetic (NOD) mice lacking all three IFN receptor genes. Diabetes is minimally affected, but at 125 days of age, antigen-specific CD8⁺ T cells, quantified using major histocompatibility complex class I tetramers, are present in 10-fold greater numbers in Ifngr-mutant NOD mice. T cells from Ifngr-mutant mice have increased proliferative responses to interleukin-2 (IL-2). They also have reduced phosphorylated STAT1 and its target gene, suppressor of cytokine signaling 1 (SOCS-1). IFNγ controls the expansion of antigen-specific CD8⁺ T cells by mechanisms which include increased SOCS-1 expression that regulates IL-2 signaling. The expanded CD8⁺ T cells are likely to contribute to normal diabetes progression despite reduced inflammation in Ifngr-mutant mice.

SOCS Proteins in Immunity, Inflammatory Diseases, and Immune-Related Cancer

Cytokine signaling represents one of the cornerstones of the immune system, mediating the complex responses required to facilitate appropriate immune cell development and function that supports robust immunity. It is crucial that these signals be tightly regulated, with dysregulation underpinning immune defects, including excessive inflammation, as well as contributing to various immune-related malignancies. A specialized family of proteins called suppressors of cytokine signaling (SOCS) participate in negative feedback regulation of cytokine signaling, ensuring it is appropriately restrained. The eight SOCS proteins identified regulate cytokine and other signaling pathways in unique ways. SOCS1–3 and CISH are most closely involved in the regulation of immune-related signaling, influencing processes such polarization of lymphocytes and the activation of myeloid cells by controlling signaling downstream of essential cytokines such as IL-4, IL-6, and IFN-γ. SOCS protein perturbation disrupts these processes resulting in the development of inflammatory and autoimmune conditions as well as malignancies. As a consequence, SOCS proteins are garnering increased interest as a unique avenue to treat these disorders.

IL-21 regulates SOCS1 expression in autoreactive CD8+ T cells but is not required for acquisition of CTL activity in the islets of non-obese diabetic mice

In type 1 diabetes, maturation of activated autoreactive CD8⁺ T cells to fully armed effector cytotoxic T lymphocytes (CTL) occurs within the islet. At present the signals required for the maturation process are poorly defined. Cytokines could potentially provide the necessary "third signal" required to generate fully mature CTL capable of killing insulin-producing β-cells. To determine whether autoreactive CTL within islets respond to cytokines we generated non-obese diabetic (NOD) mice with a reporter for cytokine signalling. These mice express a reporter gene, hCD4, under the control of the endogenous regulatory elements for suppressor of cytokine signalling (SOCS)1, which is itself regulated by pro-inflammatory cytokines. In NOD mice, the hCD4 reporter was expressed in infiltrated islets and the expression level was positively correlated with the frequency of infiltrating CD45⁺ cells. SOCS1 reporter expression was induced in transferred β-cell-specific CD8⁺ 8.3T cells upon migration from pancreatic draining lymph nodes into islets. To determine which cytokines induced SOCS1 promoter activity in islets, we examined hCD4 reporter expression and CTL maturation in the absence of the cytokine receptors IFNAR1 or IL-21R. We show that IFNAR1 deficiency does not confer protection from diabetes in 8.3 TCR transgenic mice, nor is IFNAR1 signalling required for SOCS1 reporter upregulation or CTL maturation in islets. In contrast, IL-21R-deficient 8.3 mice have reduced diabetes incidence and reduced SOCS1 reporter activity in islet CTLs. However IL-21R deficiency did not affect islet CD8⁺ T cell proliferation or expression of granzyme B or IFNγ. Together these data indicate that autoreactive CD8⁺ T cells respond to IL-21 and not type I IFNs in the islets of NOD mice, but neither IFNAR1 nor IL-21R are required for islet intrinsic CTL maturation.

Adoptive Transfer of Interleukin-21-stimulated Human CD8+ T Memory Stem Cells Efficiently Inhibits Tumor Growth

Memory stem T (T_SCM) cells, a new subset of memory T cells with self-renewal and multipotent capacities, are considered as a promising candidates for adoptive cellular therapy. However, the low proportion of human T_SCM cells in total CD8⁺ T cells limits their utility. Here, we aimed to induce human CD8⁺ T_SCM cells by stimulating naive precursors with interleukin-21 (IL-21). We found that IL-21 promoted the generation of T_SCM cells, described as CD45RA⁺CD45RO⁻CD62L⁺CCR7⁺CD122⁺CD95⁺ cells, with a higher efficiency than that observed with other common γ-chain cytokines. Upon adoptive transfer into an A375 melanoma mouse model, these lymphocytes mediated much stronger antitumor responses. Further mechanistic analysis revealed that IL-21 activated the Janus kinase signal transducer and activator of transcription 3 pathway by upregulating signal transducer and activator of transcription 3 phosphorylation and consequently promoting the expression of T-bet and suppressor of cytokine signaling 1, but decreasing the expression of eomesodermin and GATA binding protein 3. Our findings provide novel insights into the generation of human CD8⁺ T_SCM cells and reveal a novel potential clinical application of IL-21.

Increased Binding of Specificity Protein 1 to the IL21R Promoter in B Cells Results in Enhanced B Cell Responses in Rheumatoid Arthritis

B cells are implicated in rheumatoid arthritis (RA) based on the presence of autoantibodies and the therapeutic response to B cell depletion. IL-21 has a significant role in B cell development and function. Here we assess B cell responses to IL-21 and the mechanisms responsible for altered IL-21R expression in RA. Flow cytometry of PBMC and cultured B cells was used to quantify protein and mRNA levels of IL-21R, IL-21 signaling through pSTAT3, specificity protein 1 (SP1) and to determine cytokine production (IL-6) and maturation status of B cells in RA and healthy control subjects. SP1 binding to the IL21R promoter region in B cells was assessed with ChIP-qPCR. We demonstrate an increase in IL-21R expression in total and memory B cells from RA subjects, which correlated with responsiveness to IL-21 stimulation. Stimulation of naïve RA B cells with IL-21 and CD40L resulted in an increase in differentiation into plasmablasts and an increase in IL-6 production in comparison to healthy controls, which was dose dependent on IL-21 stimulation. IL-21R expression on memory B cells in RA synovial fluid was comparable to peripheral blood making our study pertinent to understanding B cell responses in the joint and site of inflammation. We identified an increase in SP1 protein and mRNA in RA B cells and demonstrate an increase in binding of SP1 to the IL21R promoter region, which suggests a mechanism by which IL-21R expression is enhanced on B cells in RA. Taken together, our results indicate a mechanism by which IL-21 enhances B cell development and function in RA through an SP1 mediated increase in IL-21R expression on B cells.

Negative Regulation of Cytokine Signaling in Immunity

Cytokines are key modulators of immunity. Most cytokines use the Janus kinase and signal transducers and activators of transcription (JAK-STAT) pathway to promote gene transcriptional regulation, but their signals must be attenuated by multiple mechanisms. These include the suppressors of cytokine signaling (SOCS) family of proteins, which represent a main negative regulation mechanism for the JAK-STAT pathway. Cytokine-inducible Src homology 2 (SH2)-containing protein (CIS), SOCS1, and SOCS3 proteins regulate cytokine signals that control the polarization of CD4+ T cells and the maturation of CD8+ T cells. SOCS proteins also regulate innate immune cells and are involved in tumorigenesis. This review summarizes recent progress on CIS, SOCS1, and SOCS3 in T cells and tumor immunity.

Absence of Grail promotes CD8+ T cell anti-tumour activity

T-cell tolerance is a major obstacle to successful cancer immunotherapy; thus, developing strategies to break immune tolerance is a high priority. Here we show that expression of the E3 ubiquitin ligase Grail is upregulated in CD8+ T cells that have infiltrated into transplanted lymphoma tumours, and Grail deficiency confers long-term tumour control. Importantly, therapeutic transfer of Grail-deficient CD8+ T cells is sufficient to repress established tumours. Mechanistically, loss of Grail enhances anti-tumour reactivity and functionality of CD8+ T cells. In addition, Grail-deficient CD8+ T cells have increased IL-21 receptor (IL-21R) expression and hyperresponsiveness to IL-21 signalling as Grail promotes IL-21R ubiquitination and degradation. Moreover, CD8+ T cells isolated from lymphoma patients express higher levels of Grail and lower levels of IL-21R, compared with CD8+ T cells from normal donors. Our data demonstrate that Grail is a crucial factor controlling CD8+ T-cell function and is a potential target to improve cytotoxic T-cell activity.Grail is an E3 ubiquitin ligase that inhibits T-cell receptor signalling in CD4+ T cells. Here the authors show Grail also limits IL-21 receptor expression and function in CD8+ T cells, is overactive in these cells in patients with lymphoma, and promotes tumour development in a lymphoma transplant mouse model.

Suppressors of cytokine signaling: Potential immune checkpoint molecules for cancer immunotherapy

Inhibition of immune checkpoint molecules, PD‐1 and CTLA4, has been shown to be a promising cancer treatment. PD‐1 and CTLA4 inhibit TCR and co‐stimulatory signals. The third T cell activation signal represents the signals from the cytokine receptors. The cytokine interferon‐γ (IFNγ) plays an important role in anti‐tumor immunity by activating cytotoxic T cells (CTLs). Most cytokines use the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and the suppressors of cytokine signaling (SOCS) family of proteins are major negative regulators of the JAK/STAT pathway. Among SOCS proteins, CIS, SOCS1, and SOCS3 proteins can be considered the third immunocheckpoint molecules since they regulate cytokine signals that control the polarization of CD4⁺ T cells and the maturation of CD8⁺ T cells. This review summarizes recent progress on CIS, SOCS1, and SOCS3 in terms of their anti‐tumor immunity and potential applications.

SOCS1: Regulator of T Cells in Autoimmunity and Cancer

SOCS1 is a negative feedback regulator of cytokine and growth factor receptor signaling, and plays an indispensable role in attenuating interferon gamma signaling. Studies on SOCS1-deficient mice have established a crucial role for SOCS1 in regulating CD8⁺ T cell homeostasis. In the thymus, SOCS1 prevents thymocytes that had failed positive selection from surviving and expanding, ensures negative selection and prevents inappropriate developmental skewing toward the CD8 lineage. In the periphery, SOCS1 not only controls production of T cell stimulatory cytokines but also attenuates the sensitivity of CD8⁺ T cells to synergistic cytokine stimulation and antigen non-specific activation. As cytokine stimulation of CD8⁺ T lymphocytes increases their sensitivity to low affinity TCR ligands, SOCS1 likely contributes to peripheral T cell tolerance by putting brakes on aberrant T cell activation driven by inflammatory cytokines. In addition, SOCS1 is critical to maintain the stability of T regulatory cells and control their plasticity to become pathogenic Th17 and Th1 cells under the harmful influence of inflammatory cytokines. SOCS1 also regulates T cell activation by dendritic cells via modulating their generation, maturation, antigen presentation, costimulatory signaling, and cytokine production. The above control mechanisms of SOCS1 on T cells, T regulatory cells and dendritic cells collectively contribute to immunological tolerance and prevent autoimmune manifestation. On other hand, silencing SOCS1 in dendritic cells or CD8⁺ T cells stimulates efficient antitumor immunity. Thus, even though SOCS1 is not a cell surface checkpoint inhibitor, its regulatory functions on T cell responses qualify SOCS1as a "non-classical" checkpoint blocker. SOCS1 also functions as a tumor suppressor in cancer cells by regulating oncogenic signal transduction pathways. The loss of SOCS1 expression observed in many tumors may have an impact on classical checkpoint pathways. The potential to exploit SOCS1 to treat inflammatory/autoimmune diseases and elicit antitumor immunity is discussed.

NLRC5 elicits antitumor immunity by enhancing processing and presentation of tumor antigens to CD8(+) T lymphocytes

Cancers can escape immunesurveillance by diminishing the expression of MHC class-I molecules (MHC-I) and components of the antigen-processing machinery (APM). Developing new approaches to reverse these defects could boost the efforts to restore antitumor immunity. Recent studies have shown that the expression of MHC-I and antigen-processing molecules is transcriptionally regulated by NOD-like receptor CARD domain containing 5 (NLRC5). To investigate whether NLRC5 could be used to improve tumor immunogenicity, we established stable lines of B16-F10 melanoma cells expressing NLRC5 (B16-5), the T cell co-stimulatory molecule CD80 (B16-CD80) or both (B16-5/80). Cells harboring NLRC5 constitutively expressed MHC-I and LMP2, LMP7 and TAP1 genes of the APM. The B16-5 cells efficiently presented the melanoma antigenic peptide gp100_25–33 to Pmel-1 TCR transgenic CD8⁺ T cells and induced their proliferation. In the presence of CD80, B16-5 cells stimulated Pmel-1 cells even without the addition of gp100 peptide, indicating that NLRC5 facilitated the processing and presentation of endogenous tumor antigen. Upon subcutaneous implantation, B16-5 cells showed markedly reduced tumor growth in C57BL/6 hosts but not in immunodeficient hosts, indicating that the NLRC5-expressing tumor cells elicited antitumor immunity. Following intravenous injection, B16-5 and B16-5/80 cells formed fewer lung tumor foci compared to control cells. In mice depleted of CD8⁺ T cells, B16-5 cells formed large subcutaneous and lung tumors. Finally, immunization with irradiated B16-5 cells conferred protection against challenge by parental B16 cells. Collectively, our findings indicate that NLRC5 could be exploited to restore tumor immunogenicity and to stimulate protective antitumor immunity.

Regulation of effector and memory CD8(+) T cell function by inflammatory cytokines

Cells communicate with each other through the production and secretion of cytokines, which are integral to the host response to infection. Once recognized by specific cytokine receptors expressed on the cell surface, these exogenous signals direct the biological function of a cell in order to adapt to their microenvironment. CD8(+) T cells are critical immune cells that play an important role in the control and elimination of intracellular pathogens. Current findings have demonstrated that cytokines influence all aspects of the CD8(+) T cell response to infection or immunization. The cytokine milieu induced at the time of activation impacts the overall magnitude and function of the effector CD8(+) T cell response and the generation of functional memory CD8(+) T cells. This review will focus on the impact of inflammatory cytokines on different aspects of CD8(+) T cell biology.

IL-21: a pleiotropic cytokine with potential applications in oncology

Interleukin- (IL-) 21 is a pleiotropic cytokine that regulates the activity of both innate and specific immunity. Indeed, it costimulates T and natural killer (NK) cell proliferation and function and regulates B cell survival and differentiation and the function of dendritic cells. In addition, IL-21 exerts divergent effects on different lymphoid cell leukemia and lymphomas, as it may support cell proliferation or on the contrary induce growth arrest or apoptosis of the neoplastic lymphoid cells. Several preclinical studies showed that IL-21 has antitumor activity in different tumor models, through mechanism involving the activation of NK and T or B cell responses. Moreover, IL-21's antitumor activity can be potentiated by its combination with other immune-enhancing molecules, monoclonal antibodies recognizing tumor antigens, chemotherapy, or molecular targeted agents. Clinical phase I-II studies of IL-21 in cancer patients showed immune stimulatory properties, acceptable toxicity profile, and antitumor effects in a fraction of patients. In view of its tolerability, IL-21 is also suitable for combinational therapeutic regimens with other agents. This review will summarize the biological functions of IL-21, and address its role in lymphoid malignancies and preclinical and clinical studies of cancer immunotherapy.

SOCS1 hypermethylation mediated by DNMT1 is associated with lipopolysaccharide-induced inflammatory cytokines in macrophages

Macrophages activation which releases the pro-inflammatory cytokines is an essential event in the process of inflammation. SOCS1 has been shown to act as a negative regulator of cytokine signals and plays a key role in the suppression of tissue injury and inflammatory diseases. DNA methylation mediated by specific DNA methyltransferases1 (DNMT1) which contributes to the epigenetic silencing of multiple genes. SOCS1 promoter hypermethylation is by far the best categorized epigenetic change in tumors. Our study with a view to investigate whether the loss of SOCS1 due to SOCS1 promoter methylation was involved in the course of inflammatory cytokines released from lipopolysaccharide (LPS)-stimulated macrophages. Here, we found that treatment of LPS-induced RAW264.7 macrophage cells with the DNA methylation inhibitor 5-aza-2'-deoxycytidine (5-azadC) reduced aberrant promoter hypermethylation of SOCS1 and prevented the loss of the expression of SOCS1 in macrophages which secret inflammatory cytokines. Knockdown of DNMT1 gene not only attenuated the SOCS1 gene promoter methylation but also up-regulated the expression of SOCS1 in activated RAW264.7 cells. Furthermore, silencing of DNMT1 prevented the activation of JAK2/STAT3 pathway in LPS-induced RAW264.7 cells. These studies demonstrated that DNMT1-mediated SOCS1 hypermethylation caused the loss of SOCS1 expression results in negative regulation of activation of the JAK2/STAT3 pathway, and enhanced the release of LPS-induced pro-inflammatory cytokines such as TNF-α and IL-6 in macrophages.

SOCS1 prevents potentially skin-reactive cytotoxic T lymphocytes from gaining the ability to cause inflammatory lesions

Suppressor of cytokine signaling 1 (SOCS1) is a critical regulator of T lymphocyte homeostasis. SOCS1-deficient mice accumulate CD8(+) T cells, which display a memory-like phenotype and proliferate strongly to IL-15. Socs1(-/-) mice develop inflammatory skin lesions, however, the underlying mechanisms are not well understood. In order to investigate the role of SOCS1 in regulating CD8(+) T cells potentially reactive to tissue antigens (Ags) of the skin, we generated Socs1(-/-) mice expressing MHC-I-restricted Pmel-1 transgenic TCR specific to the melanoma-derived gp100 Ag, which is also expressed by normal melanocytes. Socs1(-/-) Pmel-1 cells express increased levels of memory markers CD44, Ly6C, CD122, and CD62L, and show downregulation of TCR and upregulation of CD5, suggesting in vivo TCR stimulation. However, stimulation of Socs1(-/-)Pmel-1 cells with gp100-derived peptide induced only marginal proliferation in vitro despite eliciting strong effector functions, which was associated with elevated Blimp-1 induction. Following adoptive transfer to Rag1(-/-) mice, Socs1(-/-)Pmel-1 cells underwent lymphopenia-induced proliferation and caused severe skin pathology characterized by inflammatory lesions in ears, muzzle, extremities, and eyes. These findings underscore the importance of SOCS1 in regulating potentially skin-reactive cytotoxic T lymphocytes, which could get activated under conditions that promote Ag-nonspecific, cytokine-driven proliferation.

Selective reduction of post-selection CD8 thymocyte proliferation in IL-15Rα deficient mice

Peripheral CD8⁺ T cells are defective in both IL-15 and IL-15Rα knock-out (KO) mice; however, whether IL-15/IL-15Rα deficiency has a similar effect on CD8 single-positive (SP) thymocytes remains unclear. In this study, we investigated whether the absence of IL-15 transpresentation in IL-15Rα KO mice results in a defect in thymic CD8 single positive (SP) TCR^hi thymocytes. Comparison of CD8SP TCR^hi thymocytes from IL-15Rα KO mice with their wild type (WT) counterparts by flow cytometry showed a significant reduction in the percentage of CD69⁻ CD8SP TCR^hi thymocytes, which represent thymic premigrants. In addition, analysis of in vivo 5-bromo-2-deoxyuridine (BrdU) incorporation demonstrated that premigrant expansion of CD8SP TCR^hi thymocytes was reduced in IL-15Rα KO mice. The presence of IL-15 transpresentation-dependent expansion in CD8SP TCR^hi thymocytes was assessed by culturing total thymocytes in IL-15Rα-Fc fusion protein-pre-bound plates that were pre-incubated with IL-15 to mimic IL-15 transpresentation in vitro. The results demonstrated that CD8SP thymocytes selectively outgrew other thymic subsets. The contribution of the newly divided CD8SP thymocytes to the peripheral CD8⁺ T cell pool was examined using double labeling with intrathymically injected FITC and intravenously injected BrdU. A marked decrease in FITC⁺ BrdU⁺ CD8⁺ T cells was observed in the IL-15Rα KO lymph nodes. Through these experiments, we identified an IL-15 transpresentation-dependent proliferation process selective for the mature CD8SP premigrant subpopulation. Importantly, this process may contribute to the maintenance of the normal peripheral CD8⁺ T cell pool.

Enhanced anti-tumor activity of interferon-alpha in SOCS1-deficient mice is mediated by CD4⁺ and CD8⁺ T cells

Interferon-alpha (IFN-α) is an immunomodulatory cytokine that is used clinically for the treatment of melanoma in the adjuvant setting. The cellular actions of IFN-α are regulated by the suppressors of cytokine signaling (SOCS) family of proteins. We hypothesized that the anti-tumor activity of exogenous IFN-α would be enhanced in SOCS1-deficient mice. SOCS1-deficient (SOCS1(-/-)) or control (SOCS1(+/+)) mice on an IFN-γ(-/-) C57BL/6 background bearing intraperitoneal (i.p.) JB/MS murine melanoma cells were treated for 30 days with i.p. injections of IFN-A/D or PBS (vehicle). Log-rank Kaplan-Meier survival curves were used to evaluate survival. Tumor-bearing control SOCS1(+/+) mice receiving IFN-A/D had significantly enhanced survival versus PBS-treated mice (P = 0.0048). The anti-tumor effects of IFN-A/D therapy were significantly enhanced in tumor-bearing SOCS1(-/-) mice; 75% of these mice survived tumor challenge, whereas PBS-treated SOCS1(-/-) mice all died at 13-16 days (P = 0.00038). Antibody (Ab) depletion of CD8(+) T cells abrogated the anti-tumor effects of IFN-A/D in SOCS1(-/-) mice as compared with mice receiving a control antibody (P = 0.0021). CD4(+) T-cell depletion from SOCS1(-/-) mice also inhibited the effects of IFN-A/D (P = 0.0003). IFN-A/D did not alter expression of CD80 or CD86 on splenocytes of SOCS1(+/+) or SOCS1(-/-) mice, or the proportion of T regulatory cells or myeloid-derived suppressor cells in SOCS1(+/+) or SOCS1(-/-) mice. An analysis of T-cell function did reveal increased proliferation of SOCS1-deficient splenocytes at baseline and in response to mitogenic stimuli. These data suggest that modulation of SOCS1 function in T-cell subsets could enhance the anti-tumor effects of IFN-α in the setting of melanoma.

Regulation of cytokine-driven functional differentiation of CD8 T cells by suppressor of cytokine signaling 1 controls autoimmunity and preserves their proliferative capacity toward foreign antigens

We have previously shown that naive CD8 T cells exposed to IL-7 or IL-15 in the presence of IL-21 undergo Ag-independent proliferation with concomitant increase in TCR sensitivity. In this study, we examined whether CD8 T cells that accumulate in suppressor of cytokine signaling 1 (SOCS1)-deficient mice because of increased IL-15 signaling in vivo would respond to an autoantigen expressed at a very low level using a mouse model of autoimmune diabetes. In this model, P14 TCR transgenic CD8 T cells (P14 cells) adoptively transferred to rat insulin promoter-glycoprotein (RIP-GP) mice, which express the cognate Ag in the islets, do not induce diabetes unless the donor cells are stimulated by exogenous Ag. Surprisingly, SOCS1-deficient P14 cells, which expanded robustly following IL-15 stimulation, proliferated poorly in response to Ag and failed to cause diabetes in RIP-GP mice. SOCS1-deficient CD8 T cells expressing a polyclonal TCR repertoire also showed defective expansion following in vivo Ag stimulation. Notwithstanding the Ag-specific proliferation defect, SOCS1-null P14 cells produced IFN-gamma and displayed potent cytolytic activity upon Ag stimulation, suggesting that SOCS1-null CD8 T cells underwent cytokine-driven functional differentiation that selectively compromised their proliferative response to Ag but not to cytokines. Cytokine-driven homeostatic expansion in lymphopenic RIP-GP mice allowed SOCS1-null, but not wild-type, P14 cells to exert their pathogenic potential even without Ag stimulation. These findings suggest that by attenuating cytokine-driven proliferation and functional differentiation, SOCS1 not only controls the pathogenicity of autoreactive cells but also preserves the ability of CD8 T cells to proliferate in response to Ags.

Increased generation of CD8 single positive cells in SOCS1-deficient thymus does not proportionately increase their export

Mice lacking suppressor of cytokine signaling 1 (SOCS1) accumulate CD8(+) T lymphocytes in the thymus and in the periphery. Whereas IL-7 and IL-15 promote the generation of CD8 single positive (SP) thymocytes, IL-15 drives the expansion of CD8 T cells in the periphery. Here, we investigated whether increased production of CD8 SP thymocytes is accompanied by their increased export in SOCS1-deficient mice. In vivo labeling with bromodeoxyuridine showed increased cycling of CD8 SP thymocytes in SOCS1-deficient mice. However, SOCS1-deficient thymi contained increased proportion of CD24(lo)CD69(lo) SP thymocytes as well as increased expression of Qa-2 in both CD4 and CD8 SP compartments. Analysis of recent thymic emigrants (RTE) following intrathymic labeling with fluorescein isothiocyanate revealed less efficient export of CD8 RTEs from SOCS1-deficient thymi and comparable CD4:CD8 ratio among RTEs in SOCS1-null and control mice. These findings show that the rate of export of CD8 SP thymocytes is not proportional to their generation in SOCS1-deficient thymi and suggest the existence of homeostatic mechanisms controlling the egress of CD8 T cells.

SOCS1 links cytokine signaling to p53 and senescence

SOCS1 is lost in many human tumors, but its tumor suppression activities are not well understood. We report that SOCS1 is required for transcriptional activity, DNA binding, and serine 15 phosphorylation of p53 in the context of STAT5 signaling. In agreement, inactivation of SOCS1 disabled p53-dependent senescence in response to oncogenic STAT5A and radiation-induced apoptosis in T cells. In addition, SOCS1 was sufficient to induce p53-dependent senescence in fibroblasts. The mechanism of activation of p53 by SOCS1 involved a direct interaction between the SH2 domain of SOCS1 and the N-terminal transactivation domain of p53, while the C-terminal domain of SOCS1 containing the SOCS Box mediated interaction with the DNA damage-regulated kinases ATM/ATR. Also, SOCS1 colocalized with ATM at DNA damage foci induced by oncogenic STAT5A. Collectively, these results add another component to the p53 and DNA damage networks and reveal a mechanism by which SOCS1 functions as a tumor suppressor.

Immune modulation with interleukin-21

Interleukin 21 (IL-21) is produced by activated CD4(+) T cells. The IL-21R shares the common receptor gamma-chain with IL-2, IL-4, IL-7, IL-9, and IL-15, is widely expressed on immune cells, and mediates a variety of effects on the immune system. IL-21 enhances the proliferation, antigen-induced activation, clonal expansion, IFN-gamma production, and cytotoxicity of NK cells and T cells. The antitumor actions of IL-21 have been variously attributed to NK cell and CD8(+) T cell cytotoxicity, CD4(+) T cell help, NKT cells, and the antiangiogenic properties induced by IFN-gamma secretion. In clinical trials IL-21 has been well tolerated and induces a unique pattern of immune activation. IL-21 is therefore an excellent candidate for use in immune therapy.

Suppressors of cytokine signaling (SOCS) in T cell differentiation, maturation, and function

Cytokines are key modulators of T cell biology, but their influence can be attenuated by suppressors of cytokine signaling (SOCS), a family of proteins consisting of eight members, SOCS1-7 and CIS. SOCS proteins regulate cytokine signals that control the polarization of CD4(+) T cells into Th1, Th2, Th17, and T regulatory cell lineages, the maturation of CD8(+) T cells from naïve to "stem-cell memory" (Tscm), central memory (Tcm), and effector memory (Tem) states, and the activation of these lymphocytes. Understanding how SOCS family members regulate T cell maturation, differentiation, and function might prove critical in improving adoptive immunotherapy for cancer and therapies aimed at treating autoimmune and infectious diseases.

SOCS-1 binding to tyrosine 441 of IFN-gamma receptor subunit 1 contributes to the attenuation of IFN-gamma signaling in vivo

Suppressor of cytokine signaling (SOCS)-1 is a critical inhibitor of IFN-gamma signal transduction in vivo, but the precise biochemical mechanism of action of SOCS-1 is unclear. Studies in vitro have shown that SOCS-1 binds to Jaks and inhibits their catalytic activity, but recent studies indicate SOCS-1 may act in a similar manner to SOCS-3 by firstly interacting with cytokine receptors and then inhibiting Jak activity. Here, we have generated mice, termed Ifngr1(441F), in which a putative SOCS-1 binding site, tyrosine 441 (Y441), on the IFN-gamma receptor subunit 1 (IFNGR1) is mutated. We confirm that SOCS-1 binds to IFNGR1 in wild-type but not mutant cells. Mutation of Y441 results in impaired negative regulation of IFN-gamma signaling. IFN-gamma-induced STAT1 activation is prolonged in Ifngr1(441F) cells, but not to the extent seen in cells completely lacking SOCS-1, suggesting that SOCS-1 maintains activity to modulate IFN-gamma signaling via other mechanisms. Despite this, we show that hypersensitivity to IFN-gamma results in enhanced innate tumor protection in Ifngr1(441F) mice in vivo, and unregulated expression of an IFN-gamma-dependent chemokine, monokine-induced by IFN-gamma. Collectively, these data indicate that Y441 contributes to the regulation of signaling through IFNGR1 via the recruitment of SOCS-1 to the receptor.

IRF4 is essential for IL-21-mediated induction, amplification, and stabilization of the Th17 phenotype

Differentiation of murine T-helper (Th) 17 cells is induced by antigenic stimulation and the sequential action of the cytokines IL-6, IL-21, and IL-23, along with TGFbeta. Current dogma proposes that IL-6 induces IL-21, which, in a STAT3-dependent manner, amplifies its own transcription, contributes to IL-17 production, and, moreover, promotes the expression of the IL-23 receptor. This, in turn, prepares cells for IL-23-mediated stabilization of the Th17 phenotype. Here we demonstrate that these effects of IL-21 on Th17 differentiation are completely dependent on IFN regulatory factor 4 (IRF4). After culturing in the presence of IL-21 plus TGFbeta, IRF4-deficient (Irf4(-/-)) Th cells showed a profound intrinsic defect in IL-17 production and in the autocrine IL-21 loop. Likewise, the levels of IL-23 receptor and the lineage-specific orphan nuclear receptors RORalpha and RORgammat were diminished, whereas the T regulatory (Treg) transcription factor forkhead box P3 (Foxp3) was strongly up-regulated, consistent with the reciprocal relationship between Th17 and Treg development. Despite this loss of IL-21 functions, IL-21-induced STAT3 activation was unimpaired and induced normal Socs3 expression. Forced expression of Foxp3 in WT cells inhibited IL-21-mediated IL-17 production, suggesting that the increase in Foxp3 contributes to the Irf4(-/-) phenotype. Additionally, the low levels of RORalpha and RORgammat are also partially responsible, because simultaneous overexpression of both proteins restored IL-17 production in Irf4(-/-) cells to some extent. These data highlight IRF4 as a decisive factor during the IL-21-mediated steps of Th17 development by influencing the balance of Foxp3, RORalpha, and RORgammat.

Interleukin-21 signaling: functions in cancer and autoimmunity

Interleukin-21 (IL-21) is a cytokine with structural and sequence homology to IL-2 and IL-15, yet possesses several biological properties distinct from these cytokines. IL-21 is produced mainly by activated CD4(+) T cells and natural killer T cells and mediates its activity by binding to the IL-21 receptor (IL-21R), consisting of an IL-21-specific alpha chain (IL-21Ralpha; JAK/STAT) that heterodimerizes with the common gamma chain (CD132). Intracellular signaling occurs through the Janus-activated kinase/signal transducer and activator of transcription pathways. Physiologic expression of IL-21R is restricted to lymphoid tissues and peripheral blood mononuclear cells; however, other tissues such as epithelium, synovium, or transformed cells can acquire expression of both components of IL-21R heterodimer. IL-21 has complex activities on a wide variety of cell types, leading to enhancement of adaptive T-cell immunity, antibody production, activation of natural killer cell subtypes, and opposition to suppressive effects mediated by regulatory T cells. Functionally, these activities promote immune responses and point to a physiologic role of IL-21 in autoimmunity and immune enhancement. Therapeutic manipulation of IL-21 activity may allow improved immunotherapy for cancer as well as insights into autoimmune disease. Recently conducted phase 1 trials in metastatic melanoma and renal cell carcinoma have shown that recombinant IL-21 has a favorable safety profile and support its continued investigation as a potential anticancer drug.

Perturbed thymopoiesis in vitro in the absence of suppressor of cytokine signalling 1 and 3

Cytokine signals are central to the differentiation of thymocytes and their stepwise progression through defined developmental stages. The intensity and duration of cytokine signals are regulated by the suppressor of cytokine signalling (SOCS) proteins. A clear role for SOCS1 during the later stages of thymopoiesis has been established, but little is known about its role during early thymopoiesis, nor the function of its closest relative, SOCS3. Here, we find that both SOCS1 and SOCS3 are expressed during early thymopoiesis, with expression coincident during the double negative (DN)2 and DN3 stages. We examined thymocyte differentiation in vitro by co-culture of SOCS-deficient bone marrow cells with OP9 cells expressing the Notch ligand Delta-like1 (OP9-DL1). Cells lacking SOCS1 were retarded at the DN3:DN4 transition and appeared unable to differentiate into double positive (DP) thymocytes. Cells lacking both SOCS1 and SOCS3 were more severely affected, and displayed an earlier block in T cell differentiation at DN2, the stage at which expression of SOCS1 and SOCS3 coincides. This indicates that, in addition to their specific roles, SOCS1 and SOCS3 share overlapping roles during thymopoiesis. This is the first demonstration of functional redundancy within the SOCS family, and has uncovered a vital role for SOCS1 and SOCS3 during two important checkpoints in early T cell development.

Measurement of interleukin-21

This unit describes three procedures for measurement of interleukin-21 (IL-21). The first employs the use of an antibody sandwich ELISA. An alternative procedure measures proliferative responses of T cells to a combination of IL-21 and IL-15 using CFSE. Finally, a method to assess IL-21-induced tyrosine phosphorylation of Stat3 in splenic CD8(+) T cells using a flow cytometry-based analysis is described.

IL-21 induces in vivo immune activation of NK cells and CD8(+) T cells in patients with metastatic melanoma and renal cell carcinoma

PURPOSE

Human interleukin-21 (IL-21) is a class I cytokine previously reported in clinical studies on immune responsive cancers. Here we report the effects of systemic IL-21 therapy on the immune system in two phase 1 trials with this novel cytokine.

EXPERIMENTAL DESIGN

Recombinant IL-21 was administered by intravenous bolus injection at dose levels from 1 to 100 microg/kg using two planned treatment regimens: thrice weekly for 6 weeks (3/week); or once daily for five consecutive days followed by nine dose-free days (5 + 9). The following biomarkers were studied in peripheral blood mononuclear cells (PBMC) during treatment: phosphorylation of STAT3, alterations in the composition of leukocyte subsets, ex vivo cytotoxicity, expression of effector molecules in enriched CD8(+) T cells and CD56(+) NK cells by quantitative RT-PCR, and gene array profiling of CD8(+) T cells.

RESULTS

Effects of IL-21 were observed at all dose levels. In the 5 + 9 regimen IL-21 induced a dose dependent decrease in circulating NK cells and T cells followed by a return to baseline in resting periods. In both CD8(+) T cells and CD56(+) NK cells we found up-regulation of perforin and granzyme B mRNA. In addition, full transcriptome analysis of CD8(+) T cells displayed changes in several transcripts associated with increased cell cycle progression, cellular motility, and immune activation. Finally, cytotoxicity assays showed that IL-21 enhanced the ability of NK cells to kill sensitive targets ex vivo.

CONCLUSIONS

IL-21 was biologically active at all dose levels administered with evidence of in vivo NK cell and CD8(+) T cell activation.

SOCS1 downregulation in dendritic cells promotes memory T-cell responses

SOCS1-1 is crucial for control of immune cell cytokine expression, including those cytokines known to enable memory T-cell formation and homeostasis. In this study, we found that immunization with SOCS1-downregulated bone marrow-derived dendritic cells generated increased antigen-specific CD8(+) T memory cells and antigen-specific responses, as measured by ELISPOT, CTL assays, serum ELISAs, and T-cell proliferation assays. Bone marrow-derived dendritic cells in which SOCS1 was downregulated expressed increased levels of surface IL-15Ra and thymic leukemia (TL) antigen, both of which support memory cell development. This work supports a crucial role for SOCS1 in regulation of dendritic cell-directed generation of memory T-cell responses.

Role of IL-21 in immune-regulation and tumor immunotherapy

IL-21, the most recently discovered member of the IL-2 cytokine family, is an attractive subject for research due to its involvement in experimental models of autoimmunity, its ability to down-regulate IgE production, and its anti-tumor properties. Its interest for cancer immunotherapy stems from its physiological immune-enhancing functions. These include regulation of T, B and NK cell proliferation, survival, differentiation, and effector functions. IL-21's functional activities partially overlap those of IL-2. Both cytokines display similar structural features and use the common gamma-chain receptor and its downstream signaling pathways. Besides its activities on normal lymphoid cells, IL-21 is an in vitro growth factor for myeloma and acute-T cell leukemia cells, whereas it induces the apoptosis of B-CLL (chronic lymphocytic leukemia) cells. These findings indicate that the IL-21/IL-21R system exerts opposite functions in different lymphoid neoplasias, and suggest its employment in B-CLL therapy. Since IL-2, but not IL-21, is specifically required for the development of regulatory T (Treg) cell immune-suppressive functions, IL-21 may be a new tool for cancer immunotherapy. It is, in fact, a powerful anti-tumor agent in a variety of murine experimental tumor models through its activation of specific or innate immune responses against neoplastic cells. The preliminary data from phase-I clinical studies suggest that the use of IL-21 is feasible and may result in immune-enhancing effects.