Zilebesiran, an RNA Interference Therapeutic Agent for Hypertension.

BACKGROUND: Angiotensinogen is the sole precursor of angiotensin peptides and has a key role in the pathogenesis of hypertension. Zilebesiran, an investigational RNA interference therapeutic agent with a prolonged duration of action, inhibits hepatic angiotensinogen synthesis. METHODS: In this phase 1 study, patients with hypertension were randomly assigned in a 2:1 ratio to receive either a single ascending subcutaneous dose of zilebesiran (10, 25, 50, 100, 200, 400, or 800 mg) or placebo and were followed for 24 weeks (Part A). Part B assessed the effect of the 800-mg dose of zilebesiran on blood pressure under low- or high-salt diet conditions, and Part E the effect of that dose when coadministered with irbesartan. End points included safety, pharmacokinetic and pharmacodynamic characteristics, and the change from baseline in systolic and diastolic blood pressure, as measured by 24-hour ambulatory blood-pressure monitoring. RESULTS: Of 107 patients enrolled, 5 had mild, transient injection-site reactions. There were no reports of hypotension, hyperkalemia, or worsening of renal function resulting in medical intervention. In Part A, patients receiving zilebesiran had decreases in serum angiotensinogen levels that were correlated with the administered dose (r = -0.56 at week 8; 95% confidence interval, -0.69 to -0.39). Single doses of zilebesiran (≥200 mg) were associated with decreases in systolic blood pressure (>10 mm Hg) and diastolic blood pressure (>5 mm Hg) by week 8; these changes were consistent throughout the diurnal cycle and were sustained at 24 weeks. Results from Parts B and E were consistent with attenuation of the effect on blood pressure by a high-salt diet and with an augmented effect through coadministration with irbesartan, respectively. CONCLUSIONS: Dose-dependent decreases in serum angiotensinogen levels and 24-hour ambulatory blood pressure were sustained for up to 24 weeks after a single subcutaneous dose of zilebesiran of 200 mg or more; mild injection-site reactions were observed. (Funded by Alnylam Pharmaceuticals; ClinicalTrials.gov number, NCT03934307; EudraCT number, 2019-000129-39.).

Blood pressure-independent renoprotective effects of small interference RNA targeting liver angiotensinogen in experimental diabetes.

BACKGROUND AND PURPOSE: Small interfering RNA (siRNA) targeting liver angiotensinogen lowers blood pressure, but its effects in hypertensive diabetes are unknown. EXPERIMENTAL APPROACH: To address this, TGR (mRen2)27 rats (angiotensin II-dependent hypertension model) were made diabetic with streptozotocin over 18 weeks and treated with either vehicle, angiotensinogen siRNA, the AT1 antagonist valsartan, the ACE inhibitor captopril, valsartan + siRNA or valsartan + captopril for the final 3 weeks. Mean arterial pressure (MAP) was measured via radiotelemetry. KEY RESULTS: MAP before treatment was 153 ± 2 mmHg. Diabetes resulted in albuminuria, accompanied by glomerulosclerosis and podocyte effacement, without a change in glomerular filtration rate. All treatments lowered MAP and cardiac hypertrophy, and the largest drop in MAP was observed with siRNA + valsartan. Treatment with siRNA lowered circulating angiotensinogen by >99%, and the lowest circulating angiotensin II and aldosterone levels occurred in the dual treatment groups. Angiotensinogen siRNA did not affect renal angiotensinogen mRNA expression, confirming its liver-specificity. Furthermore, only siRNA with or without valsartan lowered renal angiotensin I. All treatments lowered renal angiotensin II and the reduction was largest (>95%) in the siRNA + valsartan group. All treatments identically lowered albuminuria, whereas only siRNA with or without valsartan restored podocyte foot processes and reduced glomerulosclerosis. CONCLUSION AND IMPLICATIONS: Angiotensinogen siRNA exerts renoprotection in diabetic TGR (mRen2)27 rats and this relies, at least in part, on the suppression of renal angiotensin II formation from liver-derived angiotensinogen. Clinical trials should now address whether this is also beneficial in human diabetic kidney disease.

Conventional Vasopressor and Vasopressor-Sparing Strategies to Counteract the Blood Pressure-Lowering Effect of Small Interfering RNA Targeting Angiotensinogen.

Background A single dose of small interfering RNA (siRNA) targeting liver angiotensinogen eliminates hepatic angiotensinogen and lowers blood pressure. Angiotensinogen elimination raises concerns for clinical application because an angiotensin rise is needed to maintain perfusion pressure during hypovolemia. Here, we investigated whether conventional vasopressors can raise arterial pressure after angiotensinogen depletion. Methods and Results Spontaneously hypertensive rats on a low-salt diet were treated with siRNA (10 mg/kg fortnightly) for 4 weeks, supplemented during the final 2 weeks with fludrocortisone (6 mg/kg per day), the α-adrenergic agonist midodrine (4 mg/kg per day), or a high-salt diet (all groups n=6-7). Pressor responsiveness to angiotensin II and norepinephrine was assessed before and after siRNA administration. Blood pressure was measured via radiotelemetry. Depletion of liver angiotensinogen by siRNA lowered plasma angiotensinogen concentrations by 99.2±0.1% and mean arterial pressure by 19 mm Hg. siRNA-mediated blood pressure lowering was rapidly reversed by intravenous angiotensin II or norepinephrine, or gradually reversed by fludrocortisone or high salt intake. Midodrine had no effect. Unexpectedly, fludrocortisone partially restored plasma angiotensinogen concentrations in siRNA-treated rats, and nearly abolished plasma renin concentrations. To investigate whether this angiotensinogen originated from nonhepatic sources, fludrocortisone was administered to mice lacking hepatic angiotensinogen. Fludrocortisone did not increase angiotensinogen in these mice, implying that the rise in angiotensinogen in the siRNA-treated rats must have depended on the liver, most likely reflecting diminished cleavage by renin. Conclusions Intact pressor responsiveness to conventional vasopressors provides pharmacological means to regulate the blood pressure-lowering effect of angiotensinogen siRNA and may support future therapeutic implementation of siRNA.

Renoprotective Effects of Small Interfering RNA Targeting Liver Angiotensinogen in Experimental Chronic Kidney Disease.

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No evidence for brain renin-angiotensin system activation during DOCA-salt hypertension.

Brain renin-angiotensin system (RAS) activation is thought to mediate deoxycorticosterone acetate (DOCA)-salt hypertension, an animal model for human primary hyperaldosteronism. Here, we determined whether brainstem angiotensin II is generated from locally synthesized angiotensinogen and mediates DOCA-salt hypertension. To this end, chronic DOCA-salt-hypertensive rats were treated with liver-directed siRNA targeted to angiotensinogen, the angiotensin II type 1 receptor antagonist valsartan, or the mineralocorticoid receptor antagonist spironolactone (n = 6-8/group). We quantified circulating angiotensinogen and renin by enzyme-kinetic assay, tissue angiotensinogen by Western blotting, and angiotensin metabolites by LC-MS/MS. In rats without DOCA-salt, circulating angiotensin II was detected in all rats, whereas brainstem angiotensin II was detected in 5 out of 7 rats. DOCA-salt increased mean arterial pressure by 19 ± 1 mmHg and suppressed circulating renin and angiotensin II by >90%, while brainstem angiotensin II became undetectable in 5 out of 7 rats (<6 fmol/g). Gene silencing of liver angiotensinogen using siRNA lowered circulating angiotensinogen by 97 ± 0.3%, and made brainstem angiotensin II undetectable in all rats (P<0.05 vs. non-DOCA-salt), although brainstem angiotensinogen remained intact. As expected for this model, neither siRNA nor valsartan attenuated the hypertensive response to DOCA-salt, whereas spironolactone normalized blood pressure and restored brain angiotensin II together with circulating renin and angiotensin II. In conclusion, despite local synthesis of angiotensinogen in the brain, brain angiotensin II depended on circulating angiotensinogen. That DOCA-salt suppressed circulating and brain angiotensin II in parallel, while spironolactone simultaneously increased brain angiotensin II and lowered blood pressure, indicates that DOCA-salt hypertension is not mediated by brain RAS activation.

Strong and Sustained Antihypertensive Effect of Small Interfering RNA Targeting Liver Angiotensinogen.

Small interfering RNAs (siRNAs) targeting hepatic angiotensinogen ( Agt) may provide long-lasting antihypertensive effects, but the optimal approach remains unclear. Here, we assessed the efficacy of a novel AGT siRNA in spontaneously hypertensive rats. Rats were treated with vehicle, siRNA (10 mg/kg fortnightly; subcutaneous), valsartan (31 mg/kg per day; oral), captopril (100 mg/kg per day; oral), valsartan+siRNA, or captopril+valsartan for 4 weeks (all groups, n=8). Mean arterial pressure (recorded via radiotelemetry) was lowered the most by valsartan+siRNA (-68±4 mm Hg), followed by captopril+valsartan (-54±4 mm Hg), captopril (-23±2 mm Hg), siRNA (-14±2 mm Hg), and valsartan (-10±2 mm Hg). siRNA and captopril monotherapies improved cardiac hypertrophy equally, but less than the dual therapies, which also lowered NT-proBNP (N-terminal pro-B-type natriuretic peptide). Glomerular filtration rate, urinary NGAL (neutrophil gelatinase-associated lipocalin), and albuminuria were unaffected by treatment. siRNA lowered circulating AGT by 97.9±1.0%, and by 99.8±0.1% in combination with valsartan. Although siRNA greatly reduced renal Ang (angiotensin) I, only valsartan+siRNA suppressed circulating and renal Ang II. This coincided with decreased renal sodium hydrogen exchanger type 3 and phosphorylated sodium chloride cotransporter abundances. Renin and plasma K+ increased with every treatment, but especially during valsartan+siRNA; no effects on aldosterone were observed. Collectively, these data indicate that Ang II elimination requires >99% suppression of circulating AGT. Maximal blockade of the renin-angiotensin system, achieved by valsartan+siRNA, yielded the greatest reduction in blood pressure and cardiac hypertrophy, whereas AGT lowering alone was as effective as conventional renin-angiotensin system inhibitors. Given its stable and sustained efficacy, lasting weeks, RNA interference may offer a unique approach to improving therapy adherence and treating hypertension.

Preclinical Development of a Subcutaneous ALAS1 RNAi Therapeutic for Treatment of Hepatic Porphyrias Using Circulating RNA Quantification.

The acute hepatic porphyrias are caused by inherited enzymatic deficiencies in the heme biosynthesis pathway. Induction of the first enzyme 5-aminolevulinic acid synthase 1 (ALAS1) by triggers such as fasting or drug exposure can lead to accumulation of neurotoxic heme intermediates that cause disease symptoms. We have demonstrated that hepatic ALAS1 silencing using siRNA in a lipid nanoparticle effectively prevents and treats induced attacks in a mouse model of acute intermittent porphyria. Herein, we report the development of ALN-AS1, an investigational GalNAc-conjugated RNAi therapeutic targeting ALAS1. One challenge in advancing ALN-AS1 to patients is the inability to detect liver ALAS1 mRNA in the absence of liver biopsies. We here describe a less invasive circulating extracellular RNA detection assay to monitor RNAi drug activity in serum and urine. A striking correlation in ALAS1 mRNA was observed across liver, serum, and urine in both rodents and nonhuman primates (NHPs) following treatment with ALN-AS1. Moreover, in donor-matched human urine and serum, we demonstrate a notable correspondence in ALAS1 levels, minimal interday assay variability, low interpatient variability from serial sample collections, and the ability to distinguish between healthy volunteers and porphyria patients with induced ALAS1 levels. The collective data highlight the potential utility of this assay in the clinical development of ALN-AS1, and in broadening our understanding of acute hepatic porphyrias disease pathophysiology.

An RNAi therapeutic targeting antithrombin to rebalance the coagulation system and promote hemostasis in hemophilia.

Hemophilia A and B are inherited bleeding disorders characterized by deficiencies in procoagulant factor VIII (FVIII) or factor IX (FIX), respectively. There remains a substantial unmet medical need in hemophilia, especially in patients with inhibitory antibodies against replacement factor therapy, for novel and improved therapeutic agents that can be used prophylactically to provide effective hemostasis. Guided by reports suggesting that co-inheritance of prothrombotic mutations may ameliorate the clinical phenotype in hemophilia, we developed an RNA interference (RNAi) therapeutic (ALN-AT3) targeting antithrombin (AT) as a means to promote hemostasis in hemophilia. When administered subcutaneously, ALN-AT3 showed potent, dose-dependent, and durable reduction of AT levels in wild-type mice, mice with hemophilia A, and nonhuman primates (NHPs). In NHPs, a 50% reduction in AT levels was achieved with weekly dosing at approximately 0.125 mg/kg, and a near-complete reduction in AT levels was achieved with weekly dosing at 1.5 mg/kg. Treatment with ALN-AT3 promoted hemostasis in mouse models of hemophilia and led to improved thrombin generation in an NHP model of hemophilia A with anti-factor VIII inhibitors. This investigational compound is currently in phase 1 clinical testing in subjects with hemophilia A or B.

Interleukin-21 enhances rituximab activity in a cynomolgus monkey model of B cell depletion and in mouse B cell lymphoma models.

Rituximab, a monoclonal antibody targeting CD20 on B cells, is currently used to treat many subtypes of B cell lymphomas. However, treatment is not curative and response rates are variable. Recombinant interleukin-21 (rIL-21) is a cytokine that enhances immune effector function and affects both primary and transformed B cell differentiation. We hypothesized that the combination of rIL-21 plus rituximab would be a more efficacious treatment for B cell malignancies than rituximab alone. We cultured human and cynomolgus monkey NK cells with rIL-21 and found that their activity was increased and proteins associated with antibody dependent cytotoxicity were up-regulated. Studies in cynomolgus monkeys modeled the effects of rIL-21 on rituximab activity against CD20 B cells. In these studies, rIL-21 activated innate immune effectors, increased ADCC and mobilized B cells into peripheral blood. When rIL-21 was combined with rituximab, deeper and more durable B cell depletion was observed. In another series of experiments, IL-21 was shown to have direct antiproliferative activity against a subset of human lymphoma cell lines, and combination of murine IL-21 with rituximab yielded significant survival benefits over either agent alone in xenogeneic mouse tumor models of disseminated lymphoma. Therefore, our results do suggest that the therapeutic efficacy of rituximab may be improved when used in combination with rIL-21.

Lipid nanoparticles improve activity of single-stranded siRNA and gapmer antisense oligonucleotides in animals.

We evaluated the abilities of an antisense oligonucleotide (ASO), a small interfering RNA (siRNA), and a single-stranded siRNA (ss-siRNA) to inhibit expression from the PTEN gene in mice when formulated identically with lipid nanoparticles (LNPs). Significantly greater reductions in levels of PTEN mRNA were observed for LNP-formulated agents compared to unformulated drugs when gene silencing was evaluated after a single dose in the livers of mice. An unformulated ss-siRNA modified with a metabolically stable phosphate mimic 5'-(E)-vinylphosphonate showed dose-dependent reduction of PTEN mRNA in mice, albeit at doses significantly higher than those observed for formulated ss-siRNA. These results demonstrate that LNPs can be used to deliver functional antisense and ss-siRNA therapeutics to the liver, indicating that progress in the field of siRNA delivery is transferable to other classes of nucleic acid-based drugs.

Psychosocial analysis of HIV/AIDS-related stigma in South Africa.

Eleven well-educated students from a university in South Africa, all actively involved in the field of HIV/AIDS, were interviewed through a free-associative-narrative method. This study sought to explore students' perceptions of HIV/AIDS in an attempt to assess whether stigma may occur. To the authors' knowledge, no similar studies exploring HIV/AIDS-related stigma have been done on young adults in South Africa who are actively involved with, and highly educated on, issues around HIV/AIDS. Through their representations, the participants tend to "other" the epidemic and thus distance themselves from a sense of threat. Many of the discourses in which the participants invest also fit into existing power relations, reinforcing some of the most prevalent forms of oppression in South Africa. In line with psychosocial understandings of HIV/AIDS stigma, the results indicate that this "atypical" group of students possess stigmatizing tendencies toward the epidemic and those infected. The findings have both theoretical and practical implications for conceptualizing and challenging HIV/AIDS stigma.

Interleukin-29 uses a type 1 interferon-like program to promote antiviral responses in human hepatocytes.

Interleukin-28A (IL-28A), IL-28B and IL-29 are a family of class II cytokines that stimulate antiviral responses through a heterodimeric receptor that is distinct from the type I interferon (IFN) receptor. To better understand how this newly described family of cytokines regulates the antiviral state, we compared various cellular responses elicited by IL-29 and IFN-alpha. Here we show that these cytokines stimulate similar patterns of signal transducer and activator of transcription 1 (STAT-1), -2, -3, and -5 phosphorylation and nearly identical patterns of gene expression when analyzed in two distinct cell types by microarray analysis. Interestingly, the IL-29 receptor is preferentially expressed on primary hepatocytes within normal liver and pegylated forms of IL-29 and IFN-alpha induced equivalent 2'5' oligoadenylate synthetase (OAS) and MX1 gene expression in this cell type. Pegylated IL-29 also produced a significant reduction in human hepatitis B and hepatitis C viral load in vitro and reduced the cytopathic effect caused by the fully replicating flavivirus, West Nile virus. In conclusion, IL-29 and IFN-alpha stimulate identical antiviral responses despite their utilization of different receptors. This fact, combined with significant receptor expression in hepatitis virus-infected livers, suggests that IL-29 may have therapeutic value against chronic viral hepatitis in human patients.

Interleukin 31, a cytokine produced by activated T cells, induces dermatitis in mice.

T cell-derived cytokines are important in the development of an effective immune response, but when dysregulated they can promote disease. Here we identify a four-helix bundle cytokine we have called interleukin 31 (IL-31), which is preferentially produced by T helper type 2 cells. IL-31 signals through a receptor composed of IL-31 receptor A and oncostatin M receptor. Expression of IL-31 receptor A and oncostatin M receptor mRNA was induced in activated monocytes, whereas epithelial cells expressed both mRNAs constitutively. Transgenic mice overexpressing IL-31 developed severe pruritus, alopecia and skin lesions. Furthermore, IL-31 receptor expression was increased in diseased tissues derived from an animal model of airway hypersensitivity. These data indicate that IL-31 may be involved in promoting the dermatitis and epithelial responses that characterize allergic and non-allergic diseases.

Cutting edge: IL-21 is a switch factor for the production of IgG1 and IgG3 by human B cells.

IL-21 is a cytokine that regulates the activation of T and NK cells and promotes the proliferation of B cells activated via CD40. In this study, we show that rIL-21 strongly induces the production of all IgG isotypes by purified CD19(+) human spleen or peripheral blood B cells stimulated with anti-CD40 mAb. Moreover, it was found to specifically induce the production of IgG(1) and IgG(3) by CD40-activated CD19(+)CD27(-) naive human B cells. Although stimulation of CD19(+) B cells via CD40 alone induced gamma 1 and gamma 3 germline transcripts, as well as the expression of activation-induced cytidine deaminase, only stimulation with both anti-CD40 mAb and rIL-21 resulted in the production of S gamma/S mu switch circular DNA. These results show that IL-21, in addition to promoting growth and differentiation of committed B cells, is a specific switch factor for the production of IgG(1) and IgG(3).

Cytokine-receptor pairing: accelerating discovery of cytokine function.

Over the past decade, advances in both gene discovery and ligand-receptor pairing techniques have led to the recognition that systematic pairing of 'orphan' database-derived cytokines and/or cytokine receptors with their cognate partners can lead to a marked acceleration in the elucidation of biological function. The sometimes-restricted tissue distribution of the receptor, coupled with the highly specific bioactivity of the corresponding ligand, can direct investigators rapidly towards regulatory function and site-of-action studies. The power of cytokine-receptor pairing to accelerate the understanding of function will be illustrated, citing several examples of candidate drug discoveries. Several of these discoveries, resulting from cytokine-receptor pairings, are at present advancing towards human clinical evaluation.

Cytokine requirements for the growth and development of mouse NK cells in vitro.

Natural killer (NK) cells arise from immature progenitors present in fetal tissues and adult bone marrow, but the factors responsible for driving the proliferation and differentiation of these progenitors are poorly understood. Mouse NK cells had previously been thought not to express interleukin (IL)-2Ralpha chains, but we show here that immature and mature mouse NK cells express IL-2Ralpha chain mRNA and that low levels of IL-2Ralpha chains can be detected on the surface of immature and mature NK cells provided they are cultured in the absence of IL-2. Despite their potential expression of high-affinity IL-2 receptors, immature NK cells only proliferate if IL-2 is present at extremely high concentrations. Surprisingly, IL-15 can also only support the growth of immature NK cells at high, presumably nonphysiological concentrations. Although NK cells express mRNA for the high-affinity IL-15Ralpha chain, they also express a variety of alternately spliced transcripts whose protein products could potentially disrupt signaling through IL-15 receptors. The requirement for high concentrations of IL-2 and IL-15 suggests that if these cytokines play any role in the proliferative expansion of NK cells in vivo, they act indirectly via other cells or in cooperation with other factors. In support of the latter possibility, we report that the recently described cytokine IL-21 can markedly enhance the proliferation of immature (and mature) NK cells in the presence of doses of IL-2 and IL-15 that by themselves have little growth-promoting activity.

IL-21 in synergy with IL-15 or IL-18 enhances IFN-gamma production in human NK and T cells.

NK and T cell-derived IFN-gamma is a key cytokine that stimulates innate immune responses and directs adaptive T cell response toward Th1 type. IL-15, IL-18, and IL-21 have significant roles as activators of NK and T cell functions. We have previously shown that IL-15 and IL-21 induce the expression of IFN-gamma, T-bet, IL-12R beta 2, and IL-18R genes both in NK and T cells. Now we have studied the effect of IL-15, IL-18, and IL-21 on IFN-gamma gene expression in more detail in human NK and T cells. IL-15 clearly activated IFN-gamma mRNA expression and protein production in both cell types. IL-18 and IL-21 enhanced IL-15-induced IFN-gamma gene expression. IL-18 or IL-21 alone induced a modest expression of the IFN-gamma gene but a combination of IL-21 and IL-18 efficiently up-regulated IFN-gamma production. We also show that IL-15 activated the binding of STAT1, STAT3, STAT4, and STAT5 to the regulatory sites of the IFN-gamma gene. Similarly, IL-21 induced the binding of STAT1, STAT3, and STAT4 to these elements. IL-15- and IL-21-induced STAT1 and STAT4 activation was verified by immunoprecipitation with anti-phosphotyrosine Abs followed by Western blotting with anti-STAT1 and anti-STAT4 Abs. IL-18 was not able to induce the binding of STATs to IFN-gamma gene regulatory sites. IL-18, however, activated the binding of NF-kappa B to the IFN-gamma promoter NF-kappa B site. Our results suggest that both IL-15 and IL-21 have an important role in activating the NK cell-associated innate immune response.

IL-28, IL-29 and their class II cytokine receptor IL-28R.

Cytokines play a critical role in modulating the innate and adaptive immune systems. Here, we have identified from the human genomic sequence a family of three cytokines, designated interleukin 28A (IL-28A), IL-28B and IL-29, that are distantly related to type I interferons (IFNs) and the IL-10 family. We found that like type I IFNs, IL-28 and IL-29 were induced by viral infection and showed antiviral activity. However, IL-28 and IL-29 interacted with a heterodimeric class II cytokine receptor that consisted of IL-10 receptor beta (IL-10Rbeta) and an orphan class II receptor chain, designated IL-28Ralpha. This newly described cytokine family may serve as an alternative to type I IFNs in providing immunity to viral infection.

Human IL-21 and IL-4 bind to partially overlapping epitopes of common gamma-chain.

Interleukin 21 (IL-21) is a recently identified novel cytokine that plays an important role in the regulation of B, T, and NK cell functions. Its effects depend on binding to and signaling through an IL-21 receptor complex consisting of the IL-21 receptor (IL-21R) and the common gamma-chain (gamma(c)). In this study using biosensor technique, the ligand-binding properties of IL-21R and gamma(c), which are presently poorly understood on a molecular level, were analyzed employing recombinant ectodomains of IL-21R and gamma(c). The formation of a binary complex between IL-21 and immobilized IL-21R (K(D) 70pM), gamma(c) and immobilized IL-21 (K(D) 160 microM) and a ternary complex between gamma(c) and IL-21 saturated immobilized IL-21R (K(D) 160nM) could be analyzed. The gamma(c) residues involved in IL-21 binding were defined by alanine-scanning mutational analysis. The epitope comprises gamma(c) residues N44, Y103, N128, L161, E162, and L208. It is not identical but partially overlapping with the previously established gamma(c) epitope for IL-4 binding. These results open the way to understand the molecular recognition mechanism in the IL-21 receptor system and also the promiscuous binding properties of gamma(c).

IL-21 up-regulates the expression of genes associated with innate immunity and Th1 response.

IL-21 is a recently characterized T cell-derived cytokine that regulates NK and T cell function. IL-21R shares the common gamma-chain (gamma(c)) with the receptors for IL-2, IL-4, IL-7, IL-9, and IL-15. Despite the same gamma(c), these cytokines have different effects on diverse cells. In this study, we have studied IL-15- and IL-21-induced gene expression in human primary NK and T cells and the NK-92 cell line. Both IL-15 and IL-21 rapidly induced mRNA synthesis for IFN-gamma, T-bet, IL-2Ralpha, IL-12Rbeta2, IL-18R, and myeloid differentiation factor 88 (MyD88), the genes that are important in activating innate immunity and Th1 response. IL-15 induced STAT5 DNA binding to the IL-2Ralpha IFN-gamma-activated sequence (GAS), MyD88 GAS, and c-cis-inducible elements, whereas IL-21 induced STAT3 DNA binding to MyD88 GAS and c-sis-inducible elements. IL-21-induced STAT3 activation was verified by immunoprecipitation and Western blotting with anti-phosphotyrosine Ab. In addition, pretreatment of NK-92 cells with IL-15 or IL-21 strongly enhanced IL-12-induced STAT4 DNA binding to IL-2Ralpha GAS. The induction of IFN-gamma, T-bet, IL-12Rbeta2, and IL-18R gene expression in NK cells, along with STAT3 activation, suggests that IL-21 is involved in the activation of innate immune responses. Moreover, the enhanced transcription of these genes in T cells establishes a significant role for IL-21 also in the Th1 response.