Characterization of Monoclonal Antibodies to Measure Cell Surface Protein Levels of Human Interferon-Lambda Receptor 1

Type III interferons (IFN-lambdas, IFN-λs) are important antiviral cytokines that can also modulate immune responses by acting through a heterodimeric receptor composed of the specific and limited expressed IFN-λR1 chain and the ubiquitous IL-10R2 chain, which is shared with IL-10 family cytokines. Conflicting data have been reported regarding which cells express the IFN-λR1 subunit and directly respond to IFN-λs. This is, in part, owing to transcript levels of the IFN-λR1 gene, IFNLR1, not always correlating with cell surface protein levels. In this study, we tested a panel of novel monoclonal antibodies (mAbs) that specifically recognize human IFN-λR1. Initially, antigen specificity was confirmed by enzyme-linked immunosorbent assay (ELISA), from which a subset of antibodies was selected for additional flow cytometry and neutralization assays. We further characterized two antibodies based on their strong ELISA binding activity (HLR1 and HLR14) and found only HLR14 could reliably detect cell surface IFN-λR1 protein on a variety of cell lines by flow cytometry. HLR14 could also detect IFN-λR1 protein on certain primary human blood cells, including plasmacytoid dendritic cells and B cells from peripheral blood. Availability of the HLR14 mAb will enable the quantification of IFN-λR1 protein levels on cells and better characterization of the cell specificity of the IFN-λ response.

The Interferon-Lambda Family Celebrates 20 Years of Scientific Discovery

It has now been 20 years since the original discovery of the interferon λ (IFN-λ) family (Kotenko et al., 2003; Sheppard et al., 2003) and 10 years since the subsequent discovery of IFN-λ4 (Prokunina-Olsson et al., 2013). The IFN-λ family (type III IFNs) includes 4 members: IFN-λ1, 2, 3, and 4, and all 4 of these proteins signal through the same heterodimeric receptor complex: IFN-λR1 plus IL-10R2. Throughout the past 20 years, much has been learned about the IFN-λ family and the important role of these cytokines in antiviral responses against viruses such as hepatitis C virus, influenza A virus, and SARS-CoV-2. This special issue of the Journal of Interferon & Cytokine Research (JICR) features a group of new reports that highlight recent developments regarding various aspects of IFN-λ-mediated responses. Many of these reports were first presented during the Interferon Lambda 2022 Satellite Meeting after the "Cytokines 2022" meeting in Hawaii. These articles underscore the fact that our understanding of the IFN-λ family continues to evolve and remains a critical subject area for additional future research.

Impact of Baloxavir Resistance-Associated Substitutions on Influenza Virus Growth and Drug Susceptibility

Baloxavir marboxil (baloxavir) is a recently FDA-approved influenza virus polymerase acidic (PA) endonuclease inhibitor. Several PA substitutions have been demonstrated to confer reduced susceptibility to baloxavir; however, their impacts on measurements of antiviral drug susceptibility and replication capacity when present as a fraction of the viral population have not been established. We generated recombinant A/California/04/09 (H1N1)-like viruses (IAV) with PA I38L, I38T, or E199D substitutions and B/Victoria/504/2000-like virus (IBV) with PA I38T. These substitutions reduced baloxavir susceptibility by 15.3-, 72.3-, 5.4-, and 54.5-fold, respectively, when tested in normal human bronchial epithelial (NHBE) cells. We then assessed the replication kinetics, polymerase activity, and baloxavir susceptibility of the wild-type:mutant (WT:MUT) virus mixtures in NHBE cells. The percentage of MUT relative to WT virus necessary to detect reduced baloxavir susceptibility in phenotypic assays ranged from 10% (IBV I38T) to 92% (IAV E199D). While I38T did not alter IAV replication kinetics or polymerase activity, IAV PA I38L and E199D MUTs and the IBV PA I38T MUT exhibited reduced replication levels and significantly altered polymerase activity. Differences in replication were detectable when the MUTs comprised ≥90%, ≥90%, or ≥75% of the population, respectively. Droplet digital PCR (ddPCR) and next-generation sequencing (NGS) analyses showed that WT viruses generally outcompeted the respective MUTs after multiple replication cycles and serial passaging in NHBE cells when initial mixtures contained ≥50% of the WT viruses; however, we also identified potential compensatory substitutions (IAV PA D394N and IBV PA E329G) that emerged and appeared to improve the replication capacity of baloxavir-resistant virus in cell culture. IMPORTANCE Baloxavir marboxil, an influenza virus polymerase acidic endonuclease inhibitor, represents a recently approved new class of influenza antivirals. Treatment-emergent resistance to baloxavir has been observed in clinical trials, and the potential spread of resistant variants could diminish baloxavir effectiveness. Here, we report the impact of the proportion of drug-resistant subpopulations on the ability to detect resistance in clinical isolates and the impact of substitutions on viral replication of mixtures containing both drug-sensitive and drug-resistant variants. We also show that ddPCR and NGS methods can be successfully used for detection of resistant subpopulations in clinical isolates and to quantify their relative abundance. Taken together, our data shed light on the potential impact of baloxavir-resistant I38T/L and E199D substitutions on baloxavir susceptibility and other biological properties of influenza virus and the ability to detect resistance in phenotypic and genotypic assays.

Comparison of the Antiviral Activity of Remdesivir, Chloroquine, and Interferon-β as Single or Dual Agents Against the Human Beta-Coronavirus OC43

The human beta-coronavirus strain, OC43, provides a useful model for testing the antiviral activity of various agents. We compared the activity of several antiviral drugs against OC43, including remdesivir, chloroquine, interferon (IFN)-β, IFN-λ1, and IFN-λ4, in two distinct cell types: human colorectal carcinoma cell line (HCT-8 cells) and normal human bronchial epithelial (NHBE) cells. We also tested whether these agents mediate additive, synergistic, or antagonistic activity against OC43 infection when used in combination. When used as single agents, remdesivir exhibited stronger antiviral activity than chloroquine, and IFN-β exhibited stronger activity than IFN-λ1 or IFN-λ4 against OC43 in both HCT-8 and NHBE cells. Anakinra (IL-1 inhibitor) and tocilizumab (IL-6 inhibitor) did not mediate any antiviral activity. The combination of IFN-β plus chloroquine or remdesivir resulted in higher synergy scores and higher expression of IFN-stimulated genes than did IFN-β alone. In contrast, the combination of remdesivir plus chloroquine resulted in an antagonistic interaction in NHBE cells. Our findings indicate that the combined use of IFN-β plus remdesivir or chloroquine induces maximal antiviral activity against human coronavirus strain OC43 in primary human respiratory epithelial cells. Furthermore, our experimental OC43 virus infection model provides an excellent method for evaluating the biological activity of antiviral drugs.

Identification of a pharmacological approach to reduce ACE2 expression and development of an in vitro COVID-19 viral entry model

Because of rapid emergence and circulation of the SARS-CoV-2 variants, especially Omicron which shows increased transmissibility and resistant to antibodies, there is an urgent need to develop novel therapeutic drugs to treat COVID-19. In this study we developed an in vitro cellular model to explore the regulation of ACE2 expression and its correlation with ACE2-mediated viral entry. We examined ACE2 expression in a variety of human cell lines, some of which are commonly used to study SARS-CoV-2. Using the developed model, we identified a number of inhibitors which reduced ACE2 protein expression. The greatest reduction of ACE2 expression was observed when CK869, an inhibitor of the actin-related protein 2/3 (ARP2/3) complex, was combined with 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), an inhibitor of sodium-hydrogen exchangers (NHEs), after treatment for 24 h. Using pseudotyped lentivirus expressing the SARS-CoV-2 full-length spike protein, we found that ACE2-dependent viral entry was inhibited in CK869 + EIPA-treated Calu-3 and MDA-MB-468 cells. This study provides an in vitro model that can be used for the screening of novel therapeutic candidates that may be warranted for further pre-clinical and clinical studies on COVID-19 countermeasures.

Effect of Fatty Acid Composition in Polysorbate 80 on the Stability of Therapeutic Protein Formulations

Purpose

Polysorbate excipients are commonly used as surfactants to stabilize therapeutic proteins in formulations. Degradation of polysorbates could lead to particle formation and instability of the drug formulation. We investigated how the fatty acid composition of polysorbate 80 impacts the degradation profile, particle formation, and product stability under stress conditions.

Methods

Two polysorbate 80-containing therapeutic protein formulations were reformulated with either Polysorbate 80 NF synthesized from a fatty acid mixture that contains mainly oleic acid (≥58%) or a version of polysorbate 80 synthesized with high oleic acid (>98%). Stress conditions, including high temperature and esterase spiking, were applied and changes to both the polysorbate and the therapeutic protein product were investigated for stability, purity, innate immune response and biological activity.

Results

The addition of esterase and storage at 37°C led to significant hydrolysis of the polysorbate and increases in sub-visible particle formation for both polysorbates tested. The fatty acid composition of polysorbate 80 did not directly alter the stability profile of either therapeutic protein as measured by size exclusion chromatography, or significantly impact innate immune response or biological activity. However, formulations with Polysorbate 80 NF showed greater propensity for sub-visible particle formation under stress conditions.

Conclusions

These results suggest that composition of fatty acids in polysorbate 80 may be a promoter for sub-visible particulate formation under the stress conditions tested but may not impact protein aggregation or biological activity.

The ELISA Detectability and Potency of Pegfilgrastim Decrease in Physiological Conditions: Key Roles for Aggregation and Individual Variability

PEGylated recombinant human granulocyte colony stimulating factor (pegfilgrastim) is used clinically to accelerate immune reconstitution following chemotherapy and is being pursued for biosimilar development. One challenge to overcome in pegfilgrastim biosimilar development is establishing pharmacokinetic (PK) similarity, which is partly due to the degree of PK variability. We herein report that commercially available G-CSF and PEG ELISA detection kits have different capacities to detect pegfilgrastim aggregates that rapidly form in vitro in physiological conditions. These aggregates can be observed using SDS-PAGE, size-exclusion chromatography, dynamic light scattering, and real-time NMR analysis and are associated with decreased bioactivity as reflected by reduced drug-induced cellular proliferation and STAT3 phosphorylation. Furthermore, individual variability in the stability and detectability of pegfilgrastim in human sera is also observed. Pegfilgrastim levels display marked subject variability in sera from healthy donors incubated at 37 °C. The stability patterns of pegfilgrastim closely match the stability patterns of filgrastim, consistent with a key role for pegfilgrastim's G-CSF moiety in driving formation of inactive aggregates. Taken together, our results indicate that individual variability and ELISA specificity for inactive aggregates are key factors to consider when designing and interpreting studies involving the measurement of serum pegfilgrastim concentrations.

Influenza A virus hemagglutinin mutations associated with use of neuraminidase inhibitors correlate with decreased inhibition by anti-influenza antibodies

Background

Vaccination and the use of neuraminidase inhibitors (NAIs) are currently the front lines of defense against seasonal influenza. The activity of influenza vaccines and antivirals drugs such as the NAIs can be affected by mutations in the influenza hemagglutinin (HA) protein. Numerous HA substitutions have been identified in nonclinical NAI resistance-selection experiments as well as in clinical specimens from NAI treatment or surveillance studies. These mutations are listed in the prescribing information (package inserts) for FDA-approved NAIs, including oseltamivir, zanamivir, and peramivir.

Methods

NAI treatment-emergent H1 HA mutations were mapped onto the H1N1 HA1 trimeric crystal structure and most of them localized to the HA antigenic sites predicted to be important for anti-influenza immunity. Recombinant A/California/04/09 (H1N1)-like viruses carrying HA V152I, G155E, S162 N, S183P, and D222G mutations were generated. We then evaluated the impact of these mutations on the immune reactivity and replication potential of the recombinant viruses in a human respiratory epithelial cell line, Calu− 3.

Results

We found that the G155E and D222G mutations significantly increased viral titers ~ 13-fold compared to the wild-type virus. The hemagglutination and microneutralization activity of goat and ferret antisera, monoclonal antibodies, and human serum samples raised against pandemic A(H1N1)pdm09 viruses was ~ 100-fold lower against mutants carrying G155E or D222G compared to the wild-type virus.

Conclusions

Although the mechanism by which HA mutations emerge during NAI treatment is uncertain, some NAI treatment-emergent HA mutations correlate with decreased immunity to influenza virus.

Effect of influenza H1N1 neuraminidase V116A and I117V mutations on NA activity and sensitivity to NA inhibitors

Neuraminidase inhibitors (NAIs) play a key role in the management of influenza. Given the limited number of FDA-approved anti-influenza drugs, evaluation of potential drug-resistant variants is of high priority. Two NA mutations, V116A and I117V, are found in ∼0.6% of human, avian, and swine N1 isolates. Using the A/California/04/09-like (CA/04, H1N1) background, we examined the impact of V116A and I117V NA mutations on NAI susceptibility, substrate specificity, and replicative capacity in normal human bronchial (NHBE) cells and a human respiratory epithelial cell line (Calu-3). We compared the impact of V116A and I117V on the functional properties of NA and compared these mutations with that of previously reported NAI-resistant mutations, E119A, H275Y, and N295S. All NA mutations were genetically stable. None of the viruses carrying NA mutations grew to significantly lower titers than CA/04 in Calu-3 cells. In contrast, V116A, I117V, E119A, and N295S substitutions resulted in significantly lower viral titers (1.2 logs) than the parental CA/04 virus in NHBE cells. V116A conferred reduced sensitivity to oseltamivir and zanamivir (13.7-fold). When MUNANA, 3'SL, and 6'SL substrates were applied, we observed that V116A reduced binding ability for all substrates (13.9-fold) and I117V led to the significantly decreased affinity for MUNANA and 6'SL (4.2-fold). Neither mutation altered the catalytic efficiency (k_cat/K_M) in catalyzing 3'SL, but the efficiency in catalyzing MUNANA and 6'SL was significantly decreased: only ∼34.7% compared to the wild-type NA. The efficiencies of NAs with E119A, H275Y, and N295S mutations to catalyze all substrates were ∼19.4% of the CA/04 NA. Our study demonstrates the direct effect of drug-resistant mutations located inside or adjacent to the NA active site on NA substrate specificity.

Identification and quantification of defective virus genomes in high throughput sequencing data using DVG-profiler, a novel post-sequence alignment processing algorithm

Most viruses are known to spontaneously generate defective viral genomes (DVG) due to errors during replication. These DVGs are subgenomic and contain deletions that render them unable to complete a full replication cycle in the absence of a co-infecting, non-defective helper virus. DVGs, especially of the copyback type, frequently observed with paramyxoviruses, have been recognized to be important triggers of the antiviral innate immune response. DVGs have therefore gained interest for their potential to alter the attenuation and immunogenicity of vaccines. To investigate this potential, accurate identification and quantification of DVGs is essential. Conventional methods, such as RT-PCR, are labor intensive and will only detect primer sequence-specific species. High throughput sequencing (HTS) is much better suited for this undertaking. Here, we present an HTS-based algorithm called DVG-profiler to identify and quantify all DVG sequences in an HTS data set generated from a virus preparation. DVG-profiler identifies DVG breakpoints relative to a reference genome and reports the directionality of each segment from within the same read. The specificity and sensitivity of the algorithm was assessed using both in silico data sets as well as HTS data obtained from parainfluenza virus 5, Sendai virus and mumps virus preparations. HTS data from the latter were also compared with conventional RT-PCR data and with data obtained using an alternative algorithm. The data presented here demonstrate the high specificity, sensitivity, and robustness of DVG-profiler. This algorithm was implemented within an open source cloud-based computing environment for analyzing HTS data. DVG-profiler might prove valuable not only in basic virus research but also in monitoring live attenuated vaccines for DVG content and to assure vaccine lot to lot consistency.

Meeting Overview: Interferon Lambda-Disease Impact and Therapeutic Potential

A meeting entitled, "Interferon Lambda: Disease Impact and Translational Potential," was held on the campus of the National Institutes of Health in Bethesda, Maryland, on October 25-26, 2018. To our knowledge, this was the first meeting that focused exclusively on interferon lambda (IFN-λ). The meeting's purpose was to enhance interdisciplinary communication and promote new collaborations. The gathering brought together an international group of scientists from a wide range of disciplines. Sessions included: IFN-λ Biology, Therapy and Genetic Variation; IFN-λ and Hepatitis C Virus Infection; IFN-λ in Other Infections; and IFN-λ-Hepatic Fibrosis and Cancer. The next meeting on IFN-λ is planned for 2020.

A comparison of interferon gene expression induced by influenza A virus infection of human airway epithelial cells from two different donors

Influenza is an acute respiratory disease that can cause local annual epidemics and worldwide pandemics of different morbidity and mortality. Our understanding of host factors that modulate the frequency and severity of influenza virus infections is less than complete. In this study, we examined the inter-individual variations in the innate immune responses to H1N1 and H3N2 influenza A viruses (IAV) using primary cultures of normal human bronchial epithelial (NHBE) cells derived from two different donors (D1 and D2). Although IAV replication kinetics were similar in cultures derived from these two donors, the levels of type III interferons (IFNs) were significantly higher in D1 cells compared to D2 cells (˜31-fold↑ in D1 cells versus D2 cells; P < 0.05). The levels of IFN-λ1 protein at individual time points as well as the total amounts of IFN-λ1 secreted over 72 h were also significantly higher in D1 than in D2 NHBE cells (0.7-7.7-fold↑, P < 0.05). The relative levels of IFN-stimulated gene (ISG) expression also differed significantly between D1 and D2 cells. Our data indicate that donor-specific differences can result in significant differences in IFN and ISG induction by human airway epithelium.

The use of plant lectins to regulate H1N1 influenza A virus receptor binding activity

We applied an in vitro selection approach using two different plant lectins that bind to α2,3- or α2,6-linked sialic acids to determine which genetic changes of the A/California/04/09 (H1N1) virus alter hemagglutinin (HA) receptor binding toward α2,3- or α2,6-linked glycans. Consecutive passages of the A/California/04/09 virus with or without lectins in human lung epithelial Calu-3 cells led to development of three HA1 amino acid substitutions, N129D, G155E, and S183P, and one mutation in the neuraminidase (NA), G201E. The S183P mutation significantly increased binding to several α2,6 SA-linked glycans, including YDS, 6'SL(N), and 6-Su-6'SLN, compared to the wild-type virus (↑3.6-fold, P < 0.05). Two other HA1 mutations, N129D and G155E, were sufficient to significantly increase binding to α2,6-linked glycans, 6'SLN and 6-Su-6'SLN, compared to S183P (↑4.1-fold, P < 0.05). These HA1 mutations also increased binding affinity for 3'SLN glycan compared to the wild-type virus as measured by Biacore surface plasmon resonance method. In addition, the HA1 N129D and HA1 G155E substitutions were identified as antigenic mutations. Furthermore, the G201E mutation in NA reduced the NA enzyme activity (↓2.3-fold). These findings demonstrate that the A/California/04/09 (H1N1) virus can acquire enhanced receptor affinity for both α2,3- and α2,6-linked sialic receptors under lectin-induced selective pressure. Such changes in binding affinity are conferred by selection of beneficial HA1 mutations that affect receptor specificity, antigenicity, and/or functional compatibility with the NA protein.

IFN-λ4 Attenuates Antiviral Responses by Enhancing Negative Regulation of IFN Signaling

Type III IFNs are important mediators of antiviral immunity. IFN-λ4 is a unique type III IFN because it is produced only in individuals who carry a dG allele of a genetic variant rs368234815-dG/TT. Counterintuitively, those individuals who can produce IFN-λ4, an antiviral cytokine, are also less likely to clear hepatitis C virus infection. In this study, we searched for unique functional properties of IFN-λ4 that might explain its negative effect on hepatitis C virus clearance. We used fresh primary human hepatocytes (PHHs) treated with recombinant type III IFNs or infected with Sendai virus to model acute viral infection and subsequently validated our findings in HepG2 cell line models. Endogenous IFN-λ4 protein was detectable only in Sendai virus-infected PHHs from individuals with the dG allele, where it was poorly secreted but highly functional, even at concentrations < 50 pg/ml. IFN-λ4 acted faster than other type III IFNs in inducing antiviral genes, as well as negative regulators of the IFN response, such as USP18 and SOCS1 Transient treatment of PHHs with IFN-λ4, but not IFN-λ3, caused a strong and sustained induction of SOCS1 and refractoriness to further stimulation with IFN-λ3. Our results suggest unique functional properties of IFN-λ4 that can be important in viral clearance and other clinical conditions.

Generation and characterization of interferon-lambda 1-resistant H1N1 influenza A viruses

Influenza A viruses pose a constant potential threat to human health. In view of the innate antiviral activity of interferons (IFNs) and their potential use as anti-influenza agents, it is important to know whether viral resistance to these antiviral proteins can arise. To examine the likelihood of emergence of IFN-λ1-resistant H1N1 variants, we serially passaged the A/California/04/09 (H1N1) strain in a human lung epithelial cell line (Calu-3) in the presence of increasing concentrations of recombinant IFN-λ1 protein. To monitor changes associated with adaptation of this virus to growth in Calu-3 cells, we also passaged the wild-type virus in the absence of IFN-λ1. Under IFN-λ1 selective pressure, the parental virus developed two neuraminidase (NA) mutations, S79L and K331N, which significantly reduced NA enzyme activity (↓1.4-fold) and sensitivity to IFN-λ1 (↓˃20-fold), respectively. These changes were not associated with a reduction in viral replication levels. Mutants carrying either K331N alone or S79L and K331N together induced weaker phosphorylation of IFN regulatory factor 3 (IRF3), and, as a consequence, much lower expression of the IFN genes (IFNB1, IFNL1 and IFNL2/3) and proteins (IFN-λ1 and IFN-λ2/3). The lower levels of IFN expression correlated with weaker induction of tyrosine-phosphorylated STAT1 and reduced RIG-I protein levels. Our findings demonstrate that influenza viruses can develop increased resistance to the antiviral activity of type III interferons.

Influenza virus NS1 protein mutations at position 171 impact innate interferon responses by respiratory epithelial cells

The influenza virus NS1 protein interacts with a wide range of proteins to suppress the host cell immune response and facilitate virus replication. The amino acid sequence of the 2009 pandemic virus NS1 protein differed from sequences of earlier related viruses. The functional impact of these differences has not been fully defined. Therefore, we made mutations to the NS1 protein based on these sequence differences, and assessed the impact of these changes on host cell interferon (IFN) responses. We found that viruses with mutations at position 171 replicated efficiently but did not induce expression of interferon genes as effectively as wild-type viruses in A459 lung epithelial cells. The decreased ability of these NS1 mutant viruses to induce IFN gene and protein expression correlated with decreased activation of STAT1 and lower levels of IFN-stimulated gene (ISG) expression. These findings demonstrate that mutations at position 171 in the NS1 protein result in decreased expression of IFN and ISGs by A549 cells. Consequently, these viruses may be more virulent than the parental strains that do not contain mutations at position 171 in the NS1 protein.

Innate IFNs and pro-inflammatory cytokines in local control of Respiratory Syncytial Virus infection of respiratory epithelial cells

The host innate response contributes to the severity of disease caused by Respiratory Syncytial Virus (RSV). The primary target of RSV is the airway epithelium. The host becomes infected by inhaling droplets containing viral particles, which then infect small foci of cells. Infected cells then express types I and III interferons (IFN) and pro-inflammatory cytokines to alert neighboring epithelial and myeloid cells of danger. Despite their inherent differences, A549 (carcinoma, type II alveolar epithelium) and BEAS-2B (transformed bronchial epithelium) cells are often used interchangeably to study RSV-epithelial interactions. We compared these two cell lines by infecting them with low MOIs of RSV expressing GFP (rgRSV). We measured expression of types I and III IFNs, interferon stimulated genes (ISGs), pro-inflammatory cytokines and signaling intermediaries. We found that BEAS-2B cells contained rgRSV within foci of ~10–15 cells, but all A549 cells were infected by 48h. Both cell lines highly expressed IFN-β, IFN-λ1 and -λ2, but expression was greater in the A549s. Despite lower levels of IFN expression, BEAS-2Bs expressed higher levels of most classic antiviral ISGs (ISG15, MX1, PKR) and critical TLRs, RLRs and IFN receptors. In contrast, A549 cells expressed higher levels of NF-kB associated genes (CCL2, CCL5, CXCL8). Our data suggests that a balance between expression of NF-kB genes and ISGs may determine local control of RSV infection by respiratory epithelial cells.

The Interleukin-13 Receptor-α1 Chain Is Essential for Induction of the Alternative Macrophage Activation Pathway by IL-13 but Not IL-4

Macrophages coexpress both the interleukin (IL)-2Rγ chain (γ(c)) and IL-13Rα1. These receptor chains can heterodimerize with IL-4Rα to form type I or type II IL-4 receptor complexes, respectively. We used macrophages derived from Il2rg and Il13ra1 knockout (KO) mice to evaluate the requirements for these receptor chains for induction of the alternative macrophage activation (AMA) pathway by IL-4 and IL-13. Absence of γ(c) significantly decreased activation of STAT6 by IL-4 but not IL-13. However, although activation of STAT6 by IL-4 was markedly reduced in γ(c) KO macrophages, it was not abolished, indicating that IL-4 can still signal through type II IL-4 receptors via the IL-13Rα1 chain. IL-13 failed to activate STAT6 in macrophages derived from Il13ra1 KO mice; however, these cells remained fully responsive to IL-4. The inability of IL-13 but not IL-4 to signal in Il13ra1(-/-) macrophages correlated with the inability of IL-13 but not IL-4 to induce expression of genes such as Arg1, Retnla and Ccl11 that are characteristically expressed by alternatively activated macrophages. In addition, IL-13 but not IL-4 failed to induce membrane fusion and giant cell formation by Il13ra1 KO macrophages. These findings demonstrate that the IL-13Rα1 chain is essential for induction of the AMA pathway by IL-13 but not IL-4.

In vitro anti-influenza A activity of interferon (IFN)-λ1 combined with IFN-β or oseltamivir carboxylate

Influenza viruses, which can cross species barriers and adapt to new hosts, pose a constant potential threat to human health. The influenza pandemic of 2009 highlighted the rapidity with which an influenza virus can spread worldwide. Currently available antivirals have a number of limitations against influenza, and novel antiviral strategies, including novel drugs and drug combinations, are urgently needed. Here, we evaluated the in vitro effects of interferon (IFN)-β, IFN-λ1, oseltamivir carboxylate (a neuraminidase (NA) inhibitor), and combinations of these agents against two seasonal (i.e., H1N1 and H3N2) influenza A viruses. We observed that A/California/04/09 (H1N1) and A/Panama/2007/99 (H3N2) isolates were equally sensitive to the antiviral activity of IFN-β and oseltamivir carboxylate in A549 and Calu-3 cells. In contrast, IFN-λ1 exhibited substantially lower protective potential against the H1N1 strain (64-1030-fold ↓, P<0.05), and was ineffective against H3N2 virus in both cell lines. Three dimensional analysis of drug-drug interactions revealed that IFN-λ1 interacted with IFN-β and oseltamivir carboxylate in an additive or synergistic manner, respectively, to inhibit influenza A virus replication in human airway epithelial cells. Overall, the present study demonstrated that anti-influenza agents with different mechanisms of action (e.g., a NA inhibitor combined with IFN-λ1) exerted a significantly greater (P<0.05) synergistic effect compared to co-treatment with drugs that target the same signaling pathway (i.e., IFN-β plus IFN-λ1) in vitro. Our findings provide support for the combined use of interferon plus oseltamivir as a potential means for treating influenza infections.

mTORC1-dependent metabolic reprogramming is a prerequisite for NK cell effector function

The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cellular metabolism and also has fundamental roles in controlling immune responses. Emerging evidence suggests that these two functions of mTORC1 are integrally linked. However, little is known regarding mTORC1 function in controlling the metabolism and function of NK cells, lymphocytes that play key roles in antiviral and antitumor immunity. This study investigated the hypothesis that mTORC1-controlled metabolism underpins normal NK cell proinflammatory function. We demonstrate that mTORC1 is robustly stimulated in NK cells activated in vivo and in vitro. This mTORC1 activity is required for the production of the key NK cell effector molecules IFN-γ, which is important in delivering antimicrobial and immunoregulatory functions, and granzyme B, a critical component of NK cell cytotoxic granules. The data reveal that NK cells undergo dramatic metabolic reprogramming upon activation, upregulating rates of glucose uptake and glycolysis, and that mTORC1 activity is essential for attaining this elevated glycolytic state. Directly limiting the rate of glycolysis is sufficient to inhibit IFN-γ production and granzyme B expression. This study provides the highly novel insight that mTORC1-mediated metabolic reprogramming of NK cells is a prerequisite for the acquisition of normal effector functions.

An essential role for IFN-β in the induction of IFN-stimulated gene expression by LPS in macrophages

TLR agonists such as LPS and poly(I:C) induce expression of type I IFNs, such as IFN-α and -β, by macrophages. To examine the role of IFN-β in the induction of ISGs by LPS, we compared the ability of LPS to induce ISGF3 activity and ISG expression in bone marrow-derived macrophages from WT and Ifnb1(-/-) mice. We found that LPS treatment activated ISGF3 and induced expression of ISGs such as Oas1, Mx1, Ddx58 (RIG-I), and Ifih1 (MDA5) in WT macrophages, but not in macrophages derived from Ifnb1(-/-) mice or Ifnar1(-/-) mice. The inability of LPS to induce activation of ISGF3 and ISG expression in Ifnb1(-/-) macrophages correlated with the failure of LPS to induce activation of STAT1 and -2 in these cells. Consistent with these findings, LPS treatment also failed to induce ISG expression in bone marrow-derived macrophages from Stat2 KO mice. Although activation of ISGF3 and induction of ISG expression by LPS was abrogated in Ifnb1(-/-) and Ifnar1(-/-) macrophages, activation of NF-κB and induction of NF-κB-responsive genes, such as Tnf (TNF-α) and Il1b (IL-1β), were not affected by deletion of either the IFN-β or IFN-αR1 genes. These findings demonstrate that induction of ISGF3 activity and ISG expression by LPS is critically dependent on intermediate production of IFN-β and autocrine signaling through type I IFN receptors.

IFN-λ4: the paradoxical new member of the interferon lambda family

Interferons (IFNs) are generally considered antiviral cytokines, yet the newly discovered IFN-λ4 is linked with the failure to clear hepatitis C virus (HCV) infection either spontaneously or in response to treatment. IFN-λ4 can be generated only by individuals who carry the IFNL4-ΔG allele (rs368234815), which is the strongest known host factor for predicting clearance of HCV. The ancestral IFNL4-ΔG allele is the major variant in Africans while the minor variant in Asians, suggesting very strong negative genetic selection for this allele-most likely driven by an infectious agent other than HCV. IFN-λ4 most closely resembles IFN-λ3, but these proteins share only 29% amino-acid identity, and, in contrast to IFN-λ3, IFN-λ4 is only weakly secreted. Nevertheless, IFN-λ4 signals through the IFN-λ receptor complex and induces expression of IFN-stimulated genes via the Janus kinase-signal transducer and activator of transcription signaling pathway. Although the IFNL4-ΔG variant is strongly associated with the failure to clear HCV infection, HCV-infected patients who carry this allele have lower baseline HCV RNA levels in the absence of treatment. Resolving the paradoxical functions of IFN-λ4, which appears to induce antiviral activity yet impair effective clearance of HCV, may yield critical new insights into the immunologic response to HCV infection and IFN biology.

Interferon-lambda (IFN-λ) induces signal transduction and gene expression in human hepatocytes, but not in lymphocytes or monocytes

This study compared the ability of IFN-α and IFN-λ to induce signal transduction and gene expression in primary human hepatocytes, PBLs, and monocytes. IFN-α drug products are widely used to treat chronic HCV infection; however, IFN-α therapy often induces hematologic toxicities as a result of the broad expression of IFNARs on many cell types, including most leukocytes. rIFN-λ1 is currently being tested as a potential alternative to IFN-α for treating chronic HCV. Although IFN-λ has been shown to be active on hepatoma cell lines, such as HepG2 and Huh-7, its ability to induce responses in primary human hepatocytes or leukocytes has not been examined. We found that IFN-λ induces activation of Jak/STAT signaling in mouse and human hepatocytes, and the ability of IFN-λ to induce STAT activation correlates with induction of numerous ISGs. Although the magnitude of ISG expression induced by IFN-λ in hepatocytes was generally lower than that induced by IFN-α, the repertoire of regulated genes was quite similar. Our findings demonstrate that although IFN-α and IFN-λ signal through distinct receptors, they induce expression of a common set of ISGs in hepatocytes. However, unlike IFN-α, IFN-λ did not induce STAT activation or ISG expression by purified lymphocytes or monocytes. This important functional difference may provide a clinical advantage for IFN-λ as a treatment for chronic HCV infection, as it is less likely to induce the leukopenias that are often associated with IFN-α therapy.

A variant upstream of IFNL3 (IL28B) creating a new interferon gene IFNL4 is associated with impaired clearance of hepatitis C virus

Chronic infection with hepatitis C virus (HCV) is a common cause of liver cirrhosis and cancer. We performed RNA sequencing in primary human hepatocytes activated with synthetic double-stranded RNA to mimic HCV infection. Upstream of IFNL3 (IL28B) on chromosome 19q13.13, we discovered a new transiently induced region that harbors a dinucleotide variant ss469415590 (TT or ΔG), which is in high linkage disequilibrium with rs12979860, a genetic marker strongly associated with HCV clearance. ss469415590[ΔG] is a frameshift variant that creates a novel gene, designated IFNL4, encoding the interferon-λ4 protein (IFNL4), which is moderately similar to IFNL3. Compared to rs12979860, ss469415590 is more strongly associated with HCV clearance in individuals of African ancestry, although it provides comparable information in Europeans and Asians. Transient overexpression of IFNL4 in a hepatoma cell line induced STAT1 and STAT2 phosphorylation and the expression of interferon-stimulated genes. Our findings provide new insights into the genetic regulation of HCV clearance and its clinical management.

Distinct and overlapping genomic profiles and antiviral effects of Interferon-λ and -α on HCV-infected and noninfected hepatoma cells

Recently, several SNPs in the region of the IL28B (IFN-λ) gene have been associated with spontaneous clearance of hepatitis C virus (HCV) and enhanced cure rates for IFN-alfa-based therapies, suggesting a potential correlation between IFN-λ and the ability to clear HCV. To understand the mechanism of IFN-λ's as compared to IFN-α's antiviral activity, we performed a comprehensive analysis of their anti-HCV effects, whole genome transcriptome profiling with validation, and signalling of IFN-α and IFN-λ using J6/JFH-1 and Huh7.5 cells in vitro. IFN-λ and IFN-α exhibited comparable anti-HCV activity and gene expression profiles in Huh7.5 cells. While the majority of genes induced by IFN-α and IFN-λ were similar, IFN-λ exhibits profound, but delayed kinetics of IFN-stimulated genes (ISG) induction, while IFN-α induced more rapid induction of ISGs. Furthermore, the increased induction of ISG expression by IFN-λ correlated with up-regulation of IFN-λ receptor (IL-28RA) expression and more prolonged activation of the Jak-STAT signalling pathway. The findings from our comparative analysis of IFN-α and IFN-λ in HCV-infected and noninfected cells support the clinical use of IFN-λ as a potential alternative to IFN-α in the treatment of chronic hepatitis C.

Type III IFNs are produced by and stimulate human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDC) are rare cells found in peripheral blood and lymphoid tissues. pDC are considered to be "professional" type I IFN-producing cells and produce 10- to 100-fold more IFN-α than other cell types in response to enveloped viruses or synthetic TLR7 and TLR9 agonists. In this study, purified pDC were found to express high levels of IFN-λ receptor mRNA, as well as cell-surface IFN-λ receptor. We have developed intracellular flow cytometry assays using Abs to IFN-λ1/3 or -λ2 to assess the expression of IFN-λ proteins by pDC. We observed that a subset of human pDC expresses only intracellular IFN-α, whereas another subset produces both IFN-α and IFN-λ after stimulation with virus or the TLR9 agonist, CpG A; the cells that coexpressed IFN-α and IFN-λ were the cells with the highest levels of IFN-α expression. Ab cross-linking of CD4 or CD303 molecules on pDC inhibited both HSV-induced IFN-λ and IFN-α production. Like the production of IFN-α, the HSV-induced IFN-λ production in pDC was mediated through TLR9 and independent of virus replication. Exogenous IFN-λ treatment of pDC resulted in increased virus-induced expression of both IFN-α and IFN-λ. In addition, both exogenous IFN-λ and -α inhibited dexamethasone-induced apoptosis of pDC. We conclude that pDC are major producers of IFN-λ1 and -λ2 in response to viral stimulation and also express functional receptors for this cytokine. Thus, IFN-λ can serve as an autocrine signal to strengthen the antiviral response of pDC by increasing IFN-α and IFN-λ production, resulting in prolonged pDC survival.

IL-4 engagement of the type I IL-4 receptor complex enhances mouse eosinophil migration to eotaxin-1 in vitro

Background

Previous work from our laboratory demonstrated that IL-4Rα expression on a myeloid cell type was responsible for enhancement of Th2-driven eosinophilic inflammation in a mouse model of allergic lung inflammation. Subsequently, we have shown that IL-4 signaling through type I IL-4 receptors on monocytes/macrophages strongly induced activation of the IRS-2 pathway and a subset of genes characteristic of alternatively activated macrophages. The direct effect(s) of IL-4 and IL-13 on mouse eosinophils are not clear. The goal of this study was determine the effect of IL-4 and IL-13 on mouse eosinophil function.

Methods

Standard Transwell chemotaxis assay was used to assay migration of mouse eosinophils and signal transduction was assessed by Western blotting.

Results

Here we determined that (i) mouse eosinophils express both type I and type II IL-4 receptors, (ii) in contrast to human eosinophils, mouse eosinophils do not chemotax to IL-4 or IL-13 although (iii) pre-treatment with IL-4 but not IL-13 enhanced migration to eotaxin-1. This IL-4-mediated enhancement was dependent on type I IL-4 receptor expression: γC-deficient eosinophils did not show enhancement of migratory capacity when pre-treated with IL-4. In addition, mouse eosinophils responded to IL-4 with the robust tyrosine phosphorylation of STAT6 and IRS-2, while IL-13-induced responses were considerably weaker.

Conclusions

The presence of IL-4 in combination with eotaxin-1 in the allergic inflammatory milieu could potentiate infiltration of eosinophils into the lungs. Therapies that block IL-4 and chemokine receptors on eosinophils might be more effective clinically in reducing eosinophilic lung inflammation.

Interferon-lambda and therapy for chronic hepatitis C virus infection

Interferon (IFN)-α, a type-I IFN, is widely used to treat chronic hepatitis C virus infection, but the broad expression of IFN-α receptors often leads to adverse reactions in many organs. Here, we examine IFN-λ, a type-III IFN, as a therapeutic alternative to IFN-α. Like IFN-α, IFN-λ also induces antiviral activity in hepatocytes, but might induce fewer adverse reactions because its receptor is largely restricted to cells of epithelial origin. We also discuss the recent discovery of single nucleotide polymorphisms (SNPs) near the human IFN-λ3 gene, IL28B, that correlate strongly with the ability to achieve a sustained virological response to therapy with pegylated IFN-α plus ribavirin in patients with chronic hepatitis C.

Interferon-lambda: a new addition to an old family

The discovery and initial description of the interferon-lambda (IFN-lambda) family in early 2003 opened an exciting new chapter in the field of IFN research. There are 3 IFN-lambda genes that encode 3 distinct but highly related proteins denoted IFN-lambda1, -lambda2, and -lambda3. These proteins are also known as interleukin-29 (IL-29), IL-28A, and IL-28B, respectively. Collectively, these 3 cytokines comprise the type III subset of IFNs. They are distinct from both type I and type II IFNs for a number of reasons, including the fact that they signal through a heterodimeric receptor complex that is different from the receptors used by type I or type II IFNs. Although type I IFNs (IFN-alpha/beta) and type III IFNs (IFN-lambda) signal via distinct receptor complexes, they activate the same intracellular signaling pathway and many of the same biological activities, including antiviral activity, in a wide variety of target cells. Consistent with their antiviral activity, expression of the IFN-lambda genes and their corresponding proteins is inducible by infection with many types of viruses. Therefore, expression of the type III IFNs (IFN-lambdas) and their primary biological activity are very similar to the type I IFNs. However, unlike IFN-alpha receptors which are broadly expressed on most cell types, including leukocytes, IFN-lambda receptors are largely restricted to cells of epithelial origin. The potential clinical importance of IFN-lambda as a novel antiviral therapeutic agent is already apparent. In addition, preclinical studies by several groups indicate that IFN-lambda may also be useful as a potential therapeutic agent for other clinical indications, including certain types of cancer.

A novel role for IL-22R1 as a driver of inflammation

The interleukin (IL)-22R1 chain of the heterodimeric IL-22 receptor is not expressed on normal leukocytes, but this receptor is expressed on T cells from anaplastic lymphoma kinase-positive (ALK(+)) anaplastic large cell lymphoma (ALCL) patients. To investigate the consequences of aberrant expression of this receptor on lymphocytes, we generated transgenic mice that express IL-22R1 on lymphocytes. The health of these animals progressively deteriorated at 8 to 12 weeks of age, as they displayed respiratory distress, rough coat and sluggish movement, and subsequent lethality due to multiorgan inflammation. The IL-22R1 transgenic animals developed neutrophilia that correlated with increased levels of circulating IL-17 and granulocyte colony-stimulating factor. In addition, these mice had increased serum IL-22 levels, suggesting that T cells expressing IL-22R1 generate IL-22 in a positive autoregulatory loop. As a result of the mouse model findings, we analyzed circulating cytokine levels in ALK(+)ALCL patients and detected elevated levels of IL-22, IL-17, and IL-8 in untreated patient samples. Importantly, IL-22 and IL-17 were undetectable in all patients who were in complete remission after chemotherapy. This study documents a previously unknown role of IL-22R1 in inflammation and identifies the involvement of IL-22R1/IL-22 in ALK(+)ALCL.

Interleukin-26: an IL-10-related cytokine produced by Th17 cells

IL-26 is classified as a member of the IL-10 cytokine family because it has limited sequence homology to IL-10 and the IL-10-related cytokines. The human IL-26 gene, IL26, is located on chromosome 12q15 between the genes for two other important class-2 cytokines, IFNG (IFN-γ) and IL22 (IL-22). IL-26 is often co-expressed with IL-22 by activated T cells, especially Th17 cells. It signals through a heterodimeric receptor complex composed of the IL-20R1 and IL-10R2 chains. IL-26 receptors are primarily expressed on non-hematopoietic cell types, particularly epithelial cells. Signaling through IL-26 receptor complexes results in the activation of STAT1 and STAT3 with subsequent induction of IL-26-responsive genes. The biological functions of IL-26 have only begun to be defined.

An overview of cytokines and cytokine antagonists as therapeutic agents

Cytokine-based therapies have the potential to provide novel treatments for cancer, autoimmune diseases, and many types of infectious disease. However, to date, the full clinical potential of cytokines as drugs has been limited by a number of factors. To discuss these limitations and explore ways to overcome them, the FDA partnered with the New York Academy of Sciences in March 2009 to host a two-day forum to discuss more effective ways to harness the clinical potential of cytokines and cytokine antagonists as therapeutic agents. The first day was focused primarily on the use of recombinant cytokines as therapeutic agents for treatment of human diseases. The second day focused largely on the use of cytokine antagonists as therapeutic agents for treatment of human diseases. This issue of the Annals includes more than a dozen papers that summarize much of the information that was presented during this very informative two-day conference.

Resistance to IFN-alpha-induced apoptosis is linked to a loss of STAT2

Type I IFNs (IFN-alpha/beta) are pleitropic cytokines widely used in the treatment of certain malignancies, hepatitis B and C, and multiple sclerosis. IFN resistance is a challenging clinical problem to overcome. Hence, understanding the molecular mechanism by which IFN immunotherapy ceases to be effective is of translational importance. In this study, we report that continuous IFN-alpha stimulation of the human Jurkat variant H123 led to resistance to type I IFN-induced apoptosis due to a loss of signal transducers and activators of transcription 2 (STAT2) expression. The apoptotic effects of IFN-alpha were hampered as STAT2-deficient cells were defective in activating the mitochondrial-dependent death pathway and ISGF3-mediated gene activation. Reconstitution of STAT2 restored the apoptotic effects of IFN-alpha as measured by the loss of mitochondrial membrane potential, cytochrome c release from mitochondria, caspase activation, and ultimately cell death. Nuclear localization of STAT2 was a critical event as retention of tyrosine-phosphorylated STAT2 in the cytosol was not sufficient to activate apoptosis. Furthermore, silencing STAT2 gene expression in Saos2 and A375S.2 tumor cell lines significantly reduced the apoptotic capacity of IFN-alpha. Altogether, we show that STAT2 is a critical mediator in the activation of type I IFN-induced apoptosis. More importantly, defects in the expression or nuclear localization of STAT2 could lessen the efficacy of type I IFN immunotherapy.

IFN-gamma down-regulates Secretoglobin 3A1 gene expression

STAT1 mediates Interferon (IFN)-dependent positive and negative regulation of inflammatory gene expression in lung. In this study, we examined the effect of IFN-gamma on the expression of SCGB3A1 which is thought to play crucial roles in inflammation and epithelial cell differentiation in lung. We found that expression of SCGB3A1 was down-regulated by IFN-gamma in a time- and dose-dependent manner in the murine transformed Clara Cells (mtCC) line. IFN-gamma induced the phosphorylation of STAT1, which binds to a STAT-binding element (SBE) in the SCGB3A1 gene promoter, leading to decreased transcriptional activation of this gene.

Oncostatin M regulates secretoglobin 3A1 and 3A2 expression in a bidirectional manner

Secretoglobin (SCGB) 3A1 and 3A2 are members of the small molecular weight secretoglobin gene superfamily. SCGB3A1 is a tumor suppressor gene, whereas SCGB3A2 has anti-inflammatory properties. Both genes are mainly expressed in the lung and trachea in mice. Whether the expression and/or function of these two genes are related is not known. Here we show that the expression of SCGB3A1 and SCGB3A2 are bidirectionally regulated by oncostatin M (OSM) when examined in a mouse transformed Clara cell line (mtCC); SCGB3A1 is up-regulated by OSM, while SCGB3A2 is down-regulated in a time- and dose-dependent manner. OSM-activated STAT3/5, through binding to the STAT-binding element located at -201 to -209 bp in the mouse Scgb3a1 gene promoter, and the extracellular signal-regulated kinase (ERK)- and p38-mitogen-activated protein kinase (MAPK) pathways are responsible for the OSM-induced up-regulation of SCGB3A1 expression. On the other hand, the -113 to -273 bp region in the Scgb3a2 promoter appears to be responsible for the OSM induced down-regulation of the gene. No significant differences in the levels or patterns of specific DNA-binding proteins were found in the -113 to -273 bp region as determined by electrophoretic mobility shift assays. Neither the ERK- nor p38-MAPK pathways were involved in the OSM-induced reduction of Scgb3a2 promoter activity. These results suggest that OSM-induced suppression of SCGB3A2 expression is an indirect effect of OSM. Expression of the Clara cell marker, CYP2F2, was markedly decreased upon OSM treatment in parallel with the decrease of SCGB3A2 expression in mtCC cells. The differential regulation of Scgb3a1 and Scgb3a2 gene expression by OSM may explain the unique functions of these genes in the lung.

Tuning sensitivity to IL-4 and IL-13: differential expression of IL-4Ralpha, IL-13Ralpha1, and gammac regulates relative cytokine sensitivity

Interleukin (IL)-4 and -13 are related cytokines sharing functional receptors. IL-4 signals through the type I (IL-4Rα/common γ-chain [γc]) and the type II (IL-4Rα/-13Rα1) IL-4 receptors, whereas IL-13 utilizes only the type II receptor. In this study, we show that mouse bone marrow–derived macrophages and human and mouse monocytes showed a much greater sensitivity to IL-4 than to IL-13. Lack of functional γc made these cells poorly responsive to IL-4, while retaining full responsiveness to IL-13. In mouse peritoneal macrophages, IL-4 potency exceeds that of IL-13, but lack of γc had only a modest effect on IL-4 signaling. In contrast, IL-13 stimulated greater responses than IL-4 in fibroblasts. Using levels of receptor chain expression and known binding affinities, we modeled the assemblage of functional type I and II receptor complexes. The differential expression of IL-4Rα, IL-13Rα1, and γc accounted for the distinct IL-4–IL-13 sensitivities of the various cell types. These findings provide an explanation for IL-13's principal function as an “effector” cytokine and IL-4's principal role as an “immunoregulatory” cytokine.

IFNalpha and IFNlambda differ in their antiproliferative effects and duration of JAK/STAT signaling activity

Interferon (IFN)lambda, also known as IL-28A, IL-28B or IL-29, is a new type III IFN, which like type I IFN(alpha/beta), activates common elements of the JAK/STAT signaling pathway and exhibits antiproliferative activity. Currently, IFNalpha is used in the treatment of certain forms of cancer, but its antitumor effects are limited and associated with high toxicity. In this study, we determined whether IFNlambda induced the same level of cell growth inhibition relative to IFNalpha. To this effect HaCaT cells, which are typically growth inhibited by IFNalpha, underwent apoptosis in response to IFNlambda. Next, in contrast to IFNalpha stimulation, IFNlambda prolonged the duration of activated STAT1 and STAT2. Furthermore, the kinetics of IFN-stimulated genes was different as IFNlambda induced a delayed but stronger induction of IFN-responsive genes. Components of the JAK/STAT pathway remained essential for the antiproliferative effects of IFNalpha and IFNlambda. IFNlambda-induced persistence of STAT activation required de novo protein synthesis and was in part due to a delay in STAT2 inactivation. Thus our data demonstrate that the duration of IFNlambda signaling is different from that of IFNalpha, and that IFNlambda could be a suitable cytokine to evaluate for cancer therapy.