Transgene expression knock-down in recombinant Modified Vaccinia virus Ankara vectors improves genetic stability and sustained transgene maintenance across multiple passages.

Modified vaccinia virus Ankara is a versatile vaccine vector, well suited for transgene delivery, with an excellent safety profile. However, certain transgenes render recombinant MVA (rMVA) genetically unstable, leading to the accumulation of mutated rMVA with impaired transgene expression. This represents a major challenge for upscaling and manufacturing of rMVA vaccines. To prevent transgene-mediated negative selection, the continuous avian cell line AGE1.CR pIX (CR pIX) was modified to suppress transgene expression during rMVA generation and amplification. This was achieved by constitutively expressing a tetracycline repressor (TetR) together with a rat-derived shRNA in engineered CR pIX PRO suppressor cells targeting an operator element (tetO) and 3' untranslated sequence motif on a chimeric poxviral promoter and the transgene mRNA, respectively. This cell line was instrumental in generating two rMVA (isolate CR19) expressing a Macaca fascicularis papillomavirus type 3 (MfPV3) E1E2E6E7 artificially-fused polyprotein following recombination-mediated integration of the coding sequences into the DelIII (CR19 M-DelIII) or TK locus (CR19 M-TK), respectively. Characterization of rMVA on parental CR pIX or engineered CR pIX PRO suppressor cells revealed enhanced replication kinetics, higher virus titers and a focus morphology equaling wild-type MVA, when transgene expression was suppressed. Serially passaging both rMVA ten times on parental CR pIX cells and tracking E1E2E6E7 expression by flow cytometry revealed a rapid loss of transgene product after only few passages. PCR analysis and next-generation sequencing demonstrated that rMVA accumulated mutations within the E1E2E6E7 open reading frame (CR19 M-TK) or deletions of the whole transgene cassette (CR19 M-DelIII). In contrast, CR pIX PRO suppressor cells preserved robust transgene expression for up to 10 passages, however, rMVAs were more stable when E1E2E6E7 was integrated into the TK as compared to the DelIII locus. In conclusion, sustained knock-down of transgene expression in CR pIX PRO suppressor cells facilitates the generation, propagation and large-scale manufacturing of rMVA with transgenes hampering viral replication.

Relevance of Host Cell Surface Glycan Structure for Cell Specificity of Influenza A Viruses.

Influenza A viruses (IAVs) initiate infection via binding of the viral hemagglutinin (HA) to sialylated glycans on host cells. HA's receptor specificity towards individual glycans is well studied and clearly critical for virus infection, but the contribution of the highly heterogeneous and complex glycocalyx to virus-cell adhesion remains elusive. Here, we use two complementary methods, glycan arrays and single-virus force spectroscopy (SVFS), to compare influenza virus receptor specificity with virus binding to live cells. Unexpectedly, we found that HA's receptor binding preference does not necessarily reflect virus-cell specificity. We propose SVFS as a tool to elucidate the cell binding preference of IAVs, thereby including the complex environment of sialylated receptors within the plasma membrane of living cells.

Expression, purification and crystallization of CLK1 kinase - A potential target for antiviral therapy.

Cdc-like kinase 1 (CLK1) is a dual-specificity kinase capable of autophosphorylation on tyrosine residues and Ser/Thr phosphorylation of its substrates. CLK1 belongs to the CLK kinase family that regulates alternative splicing through phosphorylation of serine-arginine rich (SR) proteins. Recent studies have demonstrated that CLK1 has an important role in the replication of influenza A and chikungunya viruses. Furthermore, CLK1 was found to be relevant for the replication of HIV-1 and the West Nile virus, making CLK1 an interesting cellular candidate for the development of a host-directed antiviral therapy that might be efficient for treatment of newly emerging viruses. We describe here our attempts and detailed procedures to obtain the recombinant kinase domain of CLK1 in suitable amounts for crystallization in complex with specific inhibitors. The key solution for the reproducibility of crystals resides in devising and refining expression and purification protocols leading to homogeneous protein. Co-expression of CLK1 with λ-phosphatase and careful purification has yielded crystals of CLK1 complexed with the KH-CB19 inhibitor that diffracted to 1.65 Å. These results paved the path to the screening of more structures of CLK1 complexed compounds, leading to further optimization of their inhibitory activity. Moreover, since kinases are desired targets in numerous pathologies, the approach we report here, the co-expression of kinases with λ-phosphatase, previously used in other kinases, can be adopted as a general protocol in numerous kinase targets for obtaining reproducible and homogenic non-phosphorylated (inactive) forms suitable for biochemical and structural studies thus facilitating the development of novel inhibitors.

Regulation of influenza A virus mRNA splicing by CLK1.

Influenza A virus carries eight negative single-stranded RNAs and uses spliced mRNAs to increase the number of proteins produced from them. Several genome-wide screens for essential host factors for influenza A virus replication revealed a necessity for splicing and splicing-related factors, including Cdc-like kinase 1 (CLK1). This CLK family kinase plays a role in alternative splicing regulation through phosphorylation of serine-arginine rich (SR) proteins. To examine the influence that modulation of splicing regulation has on influenza infection, we analyzed the effect of CLK1 knockdown and inhibition. CLK1 knockdown in A549 cells reduced influenza A/WSN/33 virus replication and increased the level of splicing of segment 7, which encodes the viral M1 and M2 proteins. CLK1-/- mice infected with influenza A/England/195/2009 (H1N1pdm09) virus supported lower levels of virus replication than wild-type mice. Screening of newly developed CLK inhibitors revealed several compounds that have an effect on the level of splicing of influenza A gene segment M in different models and decrease influenza A/WSN/33 virus replication in A549 cells. The promising inhibitor KH-CB19, an indole-based enaminonitrile with unique binding mode for CLK1, and its even more selective analogue NIH39 showed high specificity towards CLK1 and had a similar effect on influenza mRNA splicing regulation. Taken together, our findings indicate that targeting host factors that regulate splicing of influenza mRNAs may represent a novel therapeutic approach.

Model-based analysis of influenza A virus replication in genetically engineered cell lines elucidates the impact of host cell factors on key kinetic parameters of virus growth.

The best measure to limit spread of contagious diseases caused by influenza A viruses (IAVs) is annual vaccination. The growing global demand for low-cost vaccines requires the establishment of high-yield production processes. One possible option to address this challenge is the engineering of novel vaccine producer cell lines by manipulating gene expression of host cell factors relevant for virus replication. To support detailed characterization of engineered cell lines, we fitted an ordinary differential equation (ODE)-based model of intracellular IAV replication previously established by our group to experimental data obtained from infection studies in human A549 cells. Model predictions indicate that steps of viral RNA synthesis, their regulation and particle assembly and virus budding are promising targets for cell line engineering. The importance of these steps was confirmed in four of five single gene overexpression cell lines (SGOs) that showed small, but reproducible changes in early dynamics of RNA synthesis and virus release. Model-based analysis suggests, however, that overexpression of the selected host cell factors negatively influences specific RNA synthesis rates. Still, virus yield was rescued by an increase in the virus release rate. Based on parameter estimations obtained for SGOs, we predicted that there is a potential benefit associated with overexpressing multiple host cell genes in one cell line, which was validated experimentally. Overall, this model-based study on IAV replication in engineered cell lines provides a step forward in the dynamic and quantitative characterization of IAV-host cell interactions. Furthermore, it suggests targets for gene editing and indicates that overexpression of multiple host cell factors may be beneficial for the design of novel producer cell lines.

Efficient influenza A virus production in high cell density using the novel porcine suspension cell line PBG.PK2.1.

Seasonal and pandemic influenza respiratory infections are still a major public health issue. Vaccination is the most efficient way to prevent influenza infection. One option to produce influenza vaccines is cell-culture based virus propagation. Different host cell lines, such as MDCK, Vero, AGE1.CR or PER.C6 cells have been shown to be a good substrate for influenza virus production. With respect to the ease of scale-up, suspension cells should be preferred over adherent cells. Ideally, they should replicate different influenza virus strains with high cell-specific yields. Evaluation of new cell lines and further development of processes is of considerable interest, as this increases the number of options regarding the design of manufacturing processes, flexibility of vaccine production and efficiency. Here, PBG.PK2.1, a new mammalian cell line that was developed by ProBioGen AG (Germany) for virus production is presented. The cells derived from immortal porcine kidney cells were previously adapted to growth in suspension in a chemically-defined medium. Influenza virus production was improved after virus adaptation to PBG.PK2.1 cells and optimization of infection conditions, namely multiplicity of infection and trypsin concentration. Hemagglutinin titers up to 3.24 log10(HA units/100 µL) were obtained in fed-batch mode in bioreactors (700 mL working volume). Evaluation of virus propagation in high cell density culture using a hollow-fiber based system (ATF2) demonstrated promising performance: Cell concentrations of up to 50 × 106 cells/mL with viabilities exceeding 95%, and a maximum HA titer of 3.93 log10(HA units/100 µL). Analysis of glycosylation of the viral HA antigen expressed showed clear differences compared to HA produced in MDCK or Vero cell lines. With an average cell-specific productivity of 5000 virions/cell, we believe that PBG.PK2.1 cells are a very promising candidate to be considered for next-generation influenza virus vaccine production.

RNAi-based small molecule repositioning reveals clinically approved urea-based kinase inhibitors as broadly active antivirals.

Influenza viruses (IVs) tend to rapidly develop resistance to virus-directed vaccines and common antivirals targeting pathogen determinants, but novel host-directed approaches might preclude resistance development. To identify the most promising cellular targets for a host-directed approach against influenza, we performed a comparative small interfering RNA (siRNA) loss-of-function screen of IV replication in A549 cells. Analysis of four different IV strains including a highly pathogenic avian H5N1 strain, an influenza B virus (IBV) and two human influenza A viruses (IAVs) revealed 133 genes required by all four IV strains. According to gene enrichment analyses, these strain-independent host genes were particularly enriched for nucleocytoplasmic trafficking. In addition, 360 strain-specific genes were identified with distinct patterns of usage for IAVs versus IBV and human versus avian IVs. The strain-independent host genes served to define 43 experimental and otherwise clinically approved drugs, targeting reportedly fourteen of the encoded host factors. Amongst the approved drugs, the urea-based kinase inhibitors (UBKIs) regorafenib and sorafenib exhibited a superior therapeutic window of high IV antiviral activity and low cytotoxicity. Both UBKIs appeared to block a cell signaling pathway involved in IV replication after internalization, yet prior to vRNP uncoating. Interestingly, both compounds were active also against unrelated viruses including cowpox virus (CPXV), hantavirus (HTV), herpes simplex virus 1 (HSV1) and vesicular stomatitis virus (VSV) and showed antiviral efficacy in human primary respiratory cells. An in vitro resistance development analysis for regorafenib failed to detect IV resistance development against this drug. Taken together, the otherwise clinically approved UBKIs regorafenib and sorafenib possess high and broad-spectrum antiviral activity along with substantial robustness against resistance development and thus constitute attractive host-directed drug candidates against a range of viral infections including influenza.

Long-Term Culture of Distal Airway Epithelial Cells Allows Differentiation Towards Alveolar Epithelial Cells Suited for Influenza Virus Studies.

As the target organ for numerous pathogens, the lung epithelium exerts critical functions in health and disease. However, research in this area has been hampered by the quiescence of the alveolar epithelium under standard culture conditions. Here, we used human distal airway epithelial cells (DAECs) to generate alveolar epithelial cells. Long-term, robust growth of human DAECs was achieved using co-culture with feeder cells and supplementation with epidermal growth factor (EGF), Rho-associated protein kinase inhibitor Y27632, and the Notch pathway inhibitor dibenzazepine (DBZ). Removal of feeders and priming with DBZ and a cocktail of lung maturation factors prevented the spontaneous differentiation into airway club cells and instead induced differentiation to alveolar epithelial cells. We successfully transferred this approach to chicken distal airway cells, thus generating a zoonotic infection model that enables studies on influenza A virus replication. These cells are also amenable for gene knockdown using RNAi technology, indicating the suitability of the model for mechanistic studies into lung function and disease.

ALPK1- and TIFA-Dependent Innate Immune Response Triggered by the Helicobacter pylori Type IV Secretion System.

Activation of transcription factor NF-κB is a hallmark of infection with the gastric pathogen Helicobacter pylori, associated with inflammation and carcinogenesis. Genome-wide RNAi screening revealed numerous host factors involved in H. pylori-, but not IL-1ß- and TNF-α-dependent NF-κB regulation. Pathway analysis including CRISPR/Cas9-knockout and recombinant protein technology, immunofluorescence microscopy, immunoblotting, mass spectrometry, and mutant H. pylori strains identified the H. pylori metabolite D-glycero-ß-D-manno-heptose 1,7-bisphosphate (ßHBP) as a cagPAI type IV secretion system (T4SS)-dependent effector of NF-κB activation in infected cells. Upon pathogen-host cell contact, TIFA forms large complexes (TIFAsomes) including interacting host factors, such as TRAF2. NF-κB activation, TIFA phosphorylation, and TIFAsome formation depend on a functional ALPK1 kinase, highlighting the ALPK1-TIFA axis as a core innate immune pathway. ALPK1-TIFA-mediated NF-κB activation was independent of CagA protein translocation, indicating that CagA translocation and HBP delivery to host cells are distinct features of the pathogen's T4SS.

Quantitative Proteomic Approach Identifies Vpr Binding Protein as Novel Host Factor Supporting Influenza A Virus Infections in Human Cells.

Influenza A virus (IAV) infections are a major cause for respiratory disease in humans, which affects all age groups and contributes substantially to global morbidity and mortality. IAV have a large natural host reservoir in avian species. However, many avian IAV strains lack adaptation to other hosts and hardly propagate in humans. While seasonal or pandemic IAV strains replicate efficiently in permissive human cells, many avian IAV cause abortive nonproductive infections in these hosts despite successful cell entry. However, the precise reasons for these differential outcomes are poorly defined. We hypothesized that the distinct course of an IAV infection with a given virus strain is determined by the differential interplay between specific host and viral factors. By using Spike-in SILAC mass spectrometry-based quantitative proteomics we characterized sets of cellular factors whose abundance is specifically up- or downregulated in the course of permissive versus nonpermissive IAV infection, respectively. This approach allowed for the definition and quantitative comparison of about 3500 proteins in human lung epithelial cells in response to seasonal or low-pathogenic avian H3N2 IAV. Many identified proteins were similarly regulated by both virus strains, but also 16 candidates with distinct changes in permissive versus nonpermissive infection were found. RNAi-mediated knockdown of these differentially regulated host factors identified Vpr binding protein (VprBP) as proviral host factor because its downregulation inhibited efficient propagation of seasonal IAV whereas overexpression increased viral replication of both seasonal and avian IAV. These results not only show that there are similar differences in the overall changes during permissive and nonpermissive influenza virus infections, but also provide a basis to evaluate VprBP as novel anti-IAV drug target.

A human genome-wide loss-of-function screen identifies effective chikungunya antiviral drugs.

Chikungunya virus (CHIKV) is a globally spreading alphavirus against which there is no commercially available vaccine or therapy. Here we use a genome-wide siRNA screen to identify 156 proviral and 41 antiviral host factors affecting CHIKV replication. We analyse the cellular pathways in which human proviral genes are involved and identify druggable targets. Twenty-one small-molecule inhibitors, some of which are FDA approved, targeting six proviral factors or pathways, have high antiviral activity in vitro, with low toxicity. Three identified inhibitors have prophylactic antiviral effects in mouse models of chikungunya infection. Two of them, the calmodulin inhibitor pimozide and the fatty acid synthesis inhibitor TOFA, have a therapeutic effect in vivo when combined. These results demonstrate the value of loss-of-function screening and pathway analysis for the rational identification of small molecules with therapeutic potential and pave the way for the development of new, host-directed, antiviral agents.

Genetic characterization of an adapted pandemic 2009 H1N1 influenza virus that reveals improved replication rates in human lung epithelial cells.

The 2009 influenza pandemic originated from a swine-origin H1N1 virus, which, although less pathogenic than anticipated, may acquire additional virulence-associated mutations in the future. To estimate the potential risk, we sequentially passaged the isolate A/Hamburg/04/2009 in A549 human lung epithelial cells. After passage 6, we observed a 100-fold increased replication rate. High-throughput sequencing of viral gene segments identified five dominant mutations, whose contribution to the enhanced growth was analyzed by reverse genetics. The increased replication rate was pinpointed to two mutations within the hemagglutinin (HA) gene segment (HA1 D130E, HA2 I91L), near the receptor binding site and the stem domain. The adapted virus also replicated more efficiently in mice in vivo. Enhanced replication rate correlated with increased fusion pH of the HA protein and a decrease in receptor affinity. Our data might be relevant for surveillance of pre-pandemic strains and development of high titer cell culture strains for vaccine production.

Meta- and Orthogonal Integration of Influenza "OMICs" Data Defines a Role for UBR4 in Virus Budding.

Several systems-level datasets designed to dissect host-pathogen interactions during influenza A infection have been reported. However, apparent discordance among these data has hampered their full utility toward advancing mechanistic and therapeutic knowledge. To collectively reconcile these datasets, we performed a meta-analysis of data from eight published RNAi screens and integrated these data with three protein interaction datasets, including one generated within the context of this study. Further integration of these data with global virus-host interaction analyses revealed a functionally validated biochemical landscape of the influenza-host interface, which can be queried through a simplified and customizable web portal (http://www.metascape.org/IAV). Follow-up studies revealed that the putative ubiquitin ligase UBR4 associates with the viral M2 protein and promotes apical transport of viral proteins. Taken together, the integrative analysis of influenza OMICs datasets illuminates a viral-host network of high-confidence human proteins that are essential for influenza A virus replication.

Dynamin-mediated lipid acquisition is essential for Chlamydia trachomatis development.

Chlamydia trachomatis is an obligate intracellular pathogen responsible for a high burden of human disease. Here, a loss-of-function screen using a set of lentivirally transduced shRNAs identified 14 human host cell factors that modulate C. trachomatis infectivity. Notably, knockdown of dynamin, a host GTPase, decreased C. trachomatis infectivity. Dynamin functions in multiple cytoplasmic locations, including vesicle formation at the plasma membrane and the trans-Golgi network. However, its role in C. trachomatis infection remains unclear. Here we report that dynamin is essential for homotypic fusion of C. trachomatis inclusions but not for C. trachomatis internalization into the host cell. Further, dynamin activity is necessary for lipid transport into C. trachomatis inclusions and for normal re-differentiation from reticulate to elementary bodies. Fragmentation of the Golgi apparatus is proposed to be an important strategy used by C. trachomatis for efficient lipid acquisition and replication within the host. Here we show that a subset of C. trachomatis-infected cells displayed Golgi fragmentation, which was concurrent with increased mitotic accumulation. Golgi fragmentation was dispensable for dynamin-mediated lipid acquisition into C. trachomatis inclusions, irrespective of the cell cycle phase. Thus, our study reveals a critical role of dynamin in host-derived lipid acquisition for C. trachomatis development.

Evidence for a crucial role of a host non-coding RNA in influenza A virus replication.

A growing body of evidence suggests the non-protein coding human genome is of vital importance for human cell function. Besides small RNAs, the diverse class of long non-coding RNAs (lncRNAs) recently came into focus. However, their relevance for infection, a major evolutionary driving force, remains elusive. Using two commercially available microarray systems, namely NCode™ and Sureprint™ G3, we identified differential expression of 42 ncRNAs during influenza A virus (IAV) infection in human lung epithelial cells. This included several classes of lncRNAs, including large intergenic ncRNAs (lincRNAs). As analyzed by qRT-PCR, expression of one lincRNA, which we termed virus inducible lincRNA (VIN), is induced by several IAV strains (H1N1, H3N2, H7N7) as well as vesicular stomatitis virus. However, we did not observe an induction of VIN by influenza B virus, treatment with RNA mimics, or IFNß. Thus, VIN expression seems to be a specific response to certain viral infections. RNA fractionation and RNA-FISH experiments revealed that VIN is localized to the host cell nucleus. Most importantly, we show that abolition of VIN by RNA interference restricts IAV replication and viral protein synthesis, highlighting the relevance of this lincRNA for productive IAV infection. Our observations suggest that viral pathogens interfere with the non-coding portion of the human genome, thereby guaranteeing their successful propagation, and that the expression of VIN correlates with their virulence. Consequently, our study provides a novel approach for understanding virus pathogenesis in greater detail, which will enable future design of new antiviral strategies targeting the host's non-protein coding genome.

RORγt⁺ innate lymphoid cells acquire a proinflammatory program upon engagement of the activating receptor NKp44.

RORγt⁺ innate lymphoid cells (ILCs) are crucial players of innate immune responses and represent a major source of interleukin-22 (IL-22), which has an important role in mucosal homeostasis. The signals required by RORγt⁺ ILCs to express IL-22 and other cytokines have been elucidated only partially. Here we showed that RORγt⁺ ILCs can directly sense the environment by the engagement of the activating receptor NKp44. NKp44 triggering in RORγt⁺ ILCs selectively activated a coordinated proinflammatory program, including tumor necrosis factor (TNF), whereas cytokine stimulation preferentially induced IL-22 expression. However, combined engagement of NKp44 and cytokine receptors resulted in a strong synergistic effect. These data support the concept that NKp44⁺ RORγt⁺ ILCs can be activated without cytokines and are able to switch between IL-22 or TNF production, depending on the triggering stimulus.

Cigarette smoke extract induces prolonged endoplasmic reticulum stress and autophagic cell death in human umbilical vein endothelial cells.

AIMS: Consumption of cigarette smoke (CS) is a well-known risk factor for early atherosclerosis; yet, the underlying mechanisms of smoking-associated atherosclerosis are poorly understood. Based on the previous results indicating that CS-induced endothelial cell death neither shows typical features of apoptosis nor of necrosis, we investigated the role of autophagy in CS extract (CSE)-induced cell death of human umbilical vein endothelial cells (HUVECs). METHODS AND RESULTS: Here, we demonstrate that overexpression of the classical apoptosis inhibitor BCL-XL had no protective effect on CSE-induced cell death, whereas the autophagy inhibitor 3-methyladenin and an shRNAi-mediated knockdown of the autophagy mediator ATG5 significantly delayed cell death. Our results indicate that CSE induces an excess accumulation of misfolded proteins in the endoplasmic reticulum (ER) and consequently the onset of the unfolded protein response. We provide evidence that the ER-resident kinase PERK is a major transducer of ER stress leading to phosphorylation of eIF2α and attenuation of protein synthesis. Finally, we show that prolonged ER stress in cells subjected to CS is followed by activation of an autophagic programme. CSE-induced autophagy is characterized by an increase in LC3 II/I ratio and activation ATG12. The autophagic signalling pathway via energy depletion and consequent activation AMP-activated protein kinase could be excluded. CONCLUSION: Our results confirm and extend previous findings reporting on the induction of autophagy by CSE in the lung. We show that protein damage caused by CSE activates autophagy, ultimately resulting in necrotic death of HUVECs. Via this mechanism, cigarette smoking may contribute to the deterioration of vascular endothelial function and the initiation of atherosclerosis.

Autophagy-independent function of MAP-LC3 during intracellular propagation of Chlamydia trachomatis.

Microtubule-associated protein 1 (MAP1) light chain 3 (LC3) has proven useful as autophagosomal marker in studies on the interaction between pathogens and the host autophagic machinery. However, the function of LC3 is known to extend above and beyond its role in autophagosome formation. We previously reported that intrinsic LC3 is associated with the intracellular Chlamydia trachomatis inclusion in human epithelial cells. Here we show that LC3, most likely the cytoplasmic nonlipidated form, interacts with the C. trachomatis inclusion as a microtubule-associated protein rather than an autophagosome-associated component. In contrast, N-terminally GFP-tagged LC3 exclusively targets autophagosomes rather than chlamydial inclusions. Immunofluorescence analysis revealed an association of LC3 and MAP1 subunits A and B with the inclusion as early as 18 h post infection. Inclusion-bound LC3 was connected with the microtubular network. Depolymerization of the microtubular architecture disrupted the association of LC3/MAP1s with the inclusion. Furthermore, siRNA-mediated silencing of the MAP1 and LC3 proteins revealed their essential function in the intracellular growth of C. trachomatis. Interestingly, defective autophagy remarkably enhanced chlamydial growth, suggesting a suppressive effect of the autophagic machinery on bacterial development. However, depletion of LC3 in autophagy-deficient cells noticeably reduced chlamydial propagation. Thus, our findings demonstrate a new function for LC3, distinct from autophagy, in intracellular bacterial pathogenesis.

Genome-wide RNAi screen for viral replication in mammalian cell culture.

Influenza infections are considered a global threat to public health and cause seasonal epidemics and recurring pandemics. High mutation rates facilitate the generation of viral escape mutants rendering vaccines and drugs directed against virus-encoded targets ineffective. One alternative approach that could prevent viral escape is the targeting of host cell determinants that are temporarily dispensable for the host but crucial for virus replication. Here, we report a genome-wide RNAi screening approach in mammalian cell culture system that led us to the identification of several host cell genes influencing influenza A virus replication. Interestingly, the majority of the identified host gene products are indispensable for viral replication of a broad range of influenza viruses ranging from the highly pathogenic avian H5N1 strain to the current pandemic swine-origin H1N1 strain. Our results provide a new approach to explore virus-host interactions and to identify promising antiviral targets.

Pulmonary gene silencing in transgenic EGFP mice using aerosolised chitosan/siRNA nanoparticles.

PURPOSE: This work describes the production and application of an aerosolised formulation of chitosan nanoparticles for improved pulmonary siRNA delivery and gene silencing in mice. METHODS: Aerosolised chitosan/siRNA nanoparticles were pneumatically formed using a nebulising catheter and sized by laser diffraction. In vitro silencing of aerosolised and non-aerosolised formulations was evaluated in an EGFP endogenous-expressing H1299 cell line by flow cytometry. Non-invasive intratracheal insertion of the catheter was used to study nanoparticle deposition by histological detection of Cy3-labeled siRNA and gene silencing in transgenic EGFP mouse lungs using a flow cytometric method. RESULTS: Flow cytometric analysis demonstrated minimal alteration in gene silencing efficiency before (68%) and after (62%) aerosolisation in EGFP-expressing H1299 cells. Intratracheal catheter administration in mice resulted in nanoparticle deposition throughout the entire lung in both alveoli and bronchiolar regions using low amounts of siRNA. Transgenic EGFP mice dosed with the aerosolised nanoparticle formulation showed significant EGFP gene silencing (68% reduction compared to mismatch group). CONCLUSIONS: This work provides a technology platform for effective pulmonary delivery and gene silencing of RNAi therapeutics with potential use in preclinical studies of respiratory disease treatment.