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International audience; Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in young children. Currently, there is no RSV vaccine or universally accessible antiviral treatment available. Addressing the urgent need for new antiviral agents, we have investigated the capacity of a non-coding single-stranded oligonucleotide (ssON) to inhibit RSV infection. By utilizing a GFP-expressing RSV, we demonstrate that the ssON significantly reduced the proportion of RSV infected A549 cells (lung epithelial cells). Furthermore, we show that ssON’s antiviral activity was length dependent and that both RNA and DNA of this class of oligonucleotides have antiviral activity. We reveal that ssON inhibited RSV infection by competing with the virus for binding to the cellular receptor nucleolin in vitro . Additionally, using a recombinant RSV that expresses luciferase we show that ssON effectively blocked RSV infection in mice. Treatment with ssON in vivo resulted in the upregulation of RSV-induced interferon stimulated genes (ISGs) such as Stat1 , Stat2 , Cxcl10 , and Ccl2. This study highlights the possibility of using oligonucleotides as therapeutic agents against RSV infection. We demonstrate that the mechanism of action of ssON is the inhibition of viral entry in vitro , likely through the binding of the receptor, nucleolin and that ssON treatment against RSV infection in vivo additionally results in the upregulation of ISGs.

Respiratory syncytial virus (RSV) is the leading cause of acute lower respiratory tract infections in young children. Currently, there is no RSV vaccine or universally accessible antiviral treatment available. Addressing the urgent need for new antiviral agents, we have investigated the capacity of a non-coding single-stranded oligonucleotide (ssON) to inhibit RSV infection. By utilizing a GFP-expressing RSV, we demonstrate that the ssON significantly reduced the proportion of RSV infected A549 cells (lung epithelial cells). Furthermore, we show that ssON´s antiviral activity was length dependent and that both RNA and DNA of this class of oligonucleotides have antiviral activity. We reveal that ssON inhibited RSV infection by competing with the virus for binding to the cellular receptor nucleolin in vitro. Additionally, using a recombinant RSV that expresses luciferase we show that ssON effectively blocked RSV infection in mice. Treatment with ssON in vivo resulted in the upregulation of RSV-induced interferon stimulated genes (ISGs) such as Stat1, Stat2, Cxcl10 and Ccl2. This study highlights the possibility of using oligonucleotides as therapeutic agents against RSV infection. We demonstrate that the mechanism of action of ssON is the inhibition of viral entry in vitro, likely through the binding of the receptor, nucleolin and that ssON treatment against RSV infection in vivo additionallyresults in the upregulation of ISGs.

Numerous inflammatory skin disorders display a high prevalence of itch. The Mas-related G protein coupled receptor X2 (MRGPRX2) has been shown to modulate itch by inducing non-IgE-mediated mast cell degranulation and the release of endogenous inducers of pruritus. Various substances collectively known as basic secretagogues, which include inflammatory peptides and certain drugs, can trigger MRGPRX2 and thereby induce pseudo-allergic reactions characterized by histamine and protease release as well as inflammation. Here, we investigated the capacity of an immunomodulatory single-stranded oligonucleotide (ssON) to modulate IgE-independent mast cell degranulation and, more specifically, its ability to inhibit the basic secretagogues compound 48/80 (C48/80)-and LL-37 in vitro and in vivo. We examined the effect of ssON on MRGPRX2 activation in vitro by measuring degranulation in a human mast cell line (LAD2) and calcium influx in MRGPRX2-transfected HEK293 cells. To determine the effect of ssON on itch, we performed behavioral studies in established mouse models and collected skin biopsies for histological analysis. Additionally, with the use of a rosacea mouse model and RT-qPCR, we investigated the effect on ssON on LL-37-induced inflammation. We reveal that both mast cell degranulation and calcium influx in MRGPRX2 transfected HEK293 cells, induced by the antimicrobial peptide LL-37 and the basic secretagogue C48/80, are effectively inhibited by ssON in a dose-dependent manner. Further, ssON demonstrates a capability to inhibit LL-37 and C48/80 activation in vivo in two mouse models. We show that intradermal injection of ssON in mice is able to block itch induced via C48/80 in a dose-dependent manner. Histological staining revealed that ssON inhibits acute mast cell degranulation in murine skin treated with C48/80. Lastly, we show that ssON treatment ameliorates LL-37-induced inflammation in a rosacea mouse model. Since there is a need for new therapeutics targeting non-IgE-mediated activation of mast cells, ssON could be used as a prospective drug candidate to resolve itch and inflammation in certain dermatoses

As the first line of defense, the innate immune system is exceptionally efficacious against invading pathogens but must be tightly regulated to avoid immune-related pathogenesis. Accordingly, the innate immune system recognizes highly conserved components associated with infections and damaged cells using a limited number of pattern-recognition receptors (PRRs), which are differentially expressed across cell types. Importantly, tissue damage and viral infections can induce the release and production of nucleic acids, which can be sensed by nucleic-acid sensing Toll-like-receptors (TLRs), a subset of PRRs located in cellular endosomes that encompass the receptors TLR3,7,8 or 9. It is imperative that these receptors can differentiate “self” nucleic acids from “non-self” in order to avoid autoimmune reactions. However, increasing data has shown that over-active signaling from these receptors can contribute to TLR-mediated inflammatory and auto-immune consequences. Previously, a 35 bases long single-stranded oligonucleotide (ssON) was revealed to inhibit TLR3 activation in dendritic cells (DCs). Hence, the research presented in this thesis aims to harness the capacity of certain immunosuppressive oligonucleotides to modulate the innate immune response to inflammation and viral infection. In Paper I we demonstrated that ssON inhibits certain receptor-mediated endocytosis, thereby preventing activation from TLR3/4/7 signaling endosomes Additionally, ssON modulated TLR3-mediated activation in vivo in the skin. Therefore, in Paper II, we further assessed ssON’s effect on prominent symptoms of inflammatory skin disorders. We demonstrated that ssON inhibits non-IgE-mediated degranulation of mast cells induced by certain ligands of the pseudo-allergic receptor MRGPRX2, thereby alleviating the respective downstream itch and inflammation. There is currently an urgent need to develop new broad-spectrum antivirals against acute respiratory tract infections, which at present remain the deadliest communicable diseases. Since ssON inhibits clathrin-mediated and caveolin-dependent endocytosis, which are cellular entry pathways utilized by many viruses, we investigated ssON’s potential as an anti-viral agent against two major respiratory viruses. In Paper III we aimed to assess the effect of ssON on influenza A virus (IAV) infection. We demonstrated that ssON inhibits the infection of IAV, and more specifically the pandemic H1N1, in vitro in DCs and reduces viral load and disease in murine models of IAV infection. In Paper IV we aimed to assess the anti-viral capacity of ssON on respiratory syncytial virus (RSV) infection. We discovered that ssON acts as an efficient antiviral agent against RSV in vitro, seemingly by competing with the virus for binding to the entry receptor nucleolin. Additionally, ssON inhibits viral infection in vivo in a murine model of RSV infection, and the combination of ssON treatment and RSV infection leads to an upregulation of immune-related genes in the lungs, which most likely aid in viral clearance. In summary, the research presented in this thesis uncovers novel immunomodulatory functions of synthetic, noncoding ssONs to modulate the innate immune responses in the context pseudo- allergic itch and inflammation as well as in IAV and RSV infection. Furthermore, these studies unveil prospective therapeutic possibilities for ssON as an antiviral agent or as a treatment for certain inflammatory dermatoses.

The initiation of an immune response is dependent on the activation and maturation of dendritic cells after sensing pathogen associated molecular patterns by pattern recognition receptors. However, the response needs to be balanced as excessive pro-inflammatory cytokine production in response to viral or stress-induced pattern recognition receptor signaling has been associated with severe influenza A virus (IAV) infection. Here, we use an inhibitor of Toll-like receptor (TLR)3, a single-stranded oligonucleotide (ssON) with the capacity to inhibit certain endocytic routes, or a TLR3 agonist (synthetic double-stranded RNA PolyI:C), to evaluate modulation of innate responses during H1N1 IAV infection. Since IAV utilizes cellular endocytic machinery for viral entry, we also assessed ssON's capacity to affect IAV infection. We first show that IAV infected human monocyte-derived dendritic cells (MoDC) were unable to up-regulate the co-stimulatory molecules CD80 and CD86 required for T cell activation. Exogenous TLR3 stimulation did not overcome the IAV-mediated inhibition of co-stimulatory molecule expression in MoDC. However, TLR3 stimulation using PolyI:C led to an augmented pro-inflammatory cytokine response. We reveal that ssON effectively inhibited PolyI:C-mediated pro-inflammatory cytokine production in MoDC, notably, ssON treatment maintained an interferon response induced by IAV infection. Accordingly, RNAseq analyses revealed robust up-regulation of interferon-stimulated genes in IAV cultures treated with ssON. We next measured reduced IAV production in MoDC treated with ssON and found a length requirement for its anti-viral activity, which overlapped with its capacity to inhibit uptake of PolyI:C. Hence, in cases wherein an overreacting TLR3 activation contributes to IAV pathogenesis, ssON can reduce this signaling pathway. Furthermore, concomitant treatment with ssON and IAV infection in mice resulted in maintained weight and reduced viral load in the lungs. Therefore, extracellular ssON provides a mechanism for immune regulation of TLR3-mediated responses and suppression of IAV infection in vitro and in vivo in mice. QC 20210126