Interferon Induction Research Articles

N6-methyladenosine is required for efficient RNA synthesis of Ebola virus and other haemorrhagic fever viruses

ABSTRACT N6-methyladenosine (m6A) is one of the most abundant modifications of cellular RNA, where it serves various functions. m6A methylation of many viral RNA species has also been described; however, little is known about the m6A epitranscriptome of haemorrhagic fever-causing viruses like Ebola virus (EBOV). Here, we analysed the importance of the methyltransferase METTL3 for the life cycle of this virus. We found that METTL3 interacts with the EBOV nucleoprotein and the transcriptional activator VP30 to support viral RNA synthesis, and that METTL3 is recruited into EBOV inclusions bodies, where viral RNA synthesis occurs. Analysis of the m6A methylation pattern of EBOV mRNAs showed that they are methylated by METTL3. Further studies revealed that METTL3 interaction with the viral nucleoprotein, as well as its importance for RNA synthesis and protein expression, is also observed for other haemorrhagic fever viruses such as Junín virus (JUNV) and Crimean-Congo haemorrhagic fever virus (CCHFV). The negative effects on viral RNA synthesis due to loss of m6A methylation are independent of innate immune sensing, as METTL3 knockout did not affect type I interferon induction in response to viral RNA synthesis or infection. Our results suggest a novel function for m6A that is conserved among diverse haemorrhagic fever-causing viruses (i.e. EBOV, JUNV and CCHFV), making METTL3 a promising target for broadly-acting antivirals.

Basal and immune-responsive transcript expression of two Atlantic salmon interferon regulatory factor 2 (irf2) paralogues.

Atlantic salmon (Salmo salar) is one of the most economically important aquaculture species globally. However, disease has become a prevalent threat to this industry. A thorough understanding of the genes and molecular pathways involved in the immune responses of Atlantic salmon is imperative for selective breeding of disease-resistant broodstock, as well as developing new diets and vaccines to mitigate the impact of disease. Members of the interferon regulatory factor (IRF) family of transcription factors play roles in the induction of interferons and other cytokines involved in host immune responses to intracellular and parasitic pathogens. IRF family members also play diverse roles in other biological processes, such as stress response, reproduction and development. The current study focused on one member of the IRF family: interferon regulatory factor 2 (irf2). As previously shown, due to the genome duplication that occurred ∼80 million years ago in the salmonid lineage, there are two irf2 paralogues in the Atlantic salmon genome. In silico analyses at the cDNA and deduced amino acid levels were conducted followed by phylogenetic tree construction with IRF2 amino acid sequences from various ray-finned fishes, cartilaginous fish and tetrapods. qPCR was then used to analyze paralogue-specific irf2 constitutive expression across 17 adult tissues, as well as responses to the viral mimic pIC (i.e., synthetic double-stranded RNA analog) in cultured macrophage-like cells (in vitro) and to infection with the Gram-negative bacterium Moritella viscosa in skin samples (in vivo). The qPCR studies showed sex- and paralogue-specific differences in expression across tissues. For example, expression of both paralogues was higher in ovary than in testes; expression (considering both sexes together) was highest for irf2-1 in gonad and for irf2-2 in hindgut. Both irf2 paralogues were responsive to pIC stimulation, but varied in their induction level, with irf2-1 having an overall stronger response than irf2-2. Only one paralogue, irf2-2, was significantly responsive to M. viscosa infection. Differences in irf2-1 and irf2-2 transcript expression levels constitutively across tissues, and in response to pIC and M. viscosa, may suggest neo- or subfunctionalization of the duplicated genes. This novel information expands current knowledge and provides insight into how genome duplication events may impact host regulation of important immune markers.

Identification of an effective fraction from Ampelopsis Radix with anti-dengue virus activities in vitro and in vivo.

Dengue virus (DENV) infection is a global public health issue without effective therapeutic interventions. Chinese medicine with heat-clearing and detoxifying properties has been frequently used in the treatment of viral infection. Ampelopsis Radix (AR) is a traditional Chinese medicine for clearing heat and detoxification that has been widely used in the prevention and treatment of infectious diseases. However, no studies on the effects of AR against viral infection have been reported, thus far. To explore the anti-DENV activities of the fraction (AR-1) obtained from AR both in vitro and in vivo. The chemical composition of AR-1 was identified by liquid chromatography-tandem MS (LC‒MS/MS). The antiviral activities of AR-1 were studied in baby hamster kidney fibroblast BHK-21cells, ICR suckling mice and induction of interferon α/β (IFN-α/β) and IFN-γ R-/- (AG129) mice. Based on LC‒MS/MS analysis, 60 compounds (including flavonoids, phenols, anthraquinones, alkaloids and other types) were tentatively characterized from AR-1. AR-1 inhibited the cytopathic effect, the production of progeny virus and the synthesis of viral RNA and proteins by blocking DENV-2 binding to BHK-21cells. Moreover, AR-1 significantly attenuated weight loss, decreased clinical scores and prolonged the survival of DENV-infected ICR suckling mice. Critically, the viral load in blood, brain and kidney tissues and the pathological changes in brain were remarkably alleviated after AR-1 treatment. Further study on AG129 mice showed that AR-1 obviously improved the clinical manifestations and survival rate, reduced viremia, attenuated gastric distension and relieved the pathological lesions caused by DENV. In summary, this is the first report that AR-1 exhibits anti-DENV effects both in vitro and in vivo, which suggests that AR-1 may be developed as a therapeutic candidate against DENV infection.

Poly(I:C) Induces Distinct Liver Cell Type-Specific Responses in Hepatitis B Virus-Transgenic Mice In Vitro, but Fails to Induce These Signals In Vivo.

Immunopathology in hepatitis B virus (HBV) infection is driven by innate and adaptive immunity. Whether the hepatitis B surface antigen (HBsAg) affects hepatic antiviral signalling was investigated in HBV-transgenic mouse models that either accumulate (Alb/HBs, Tg[Alb1HBV]Bri44), lack (Tg1.4HBV-s-mut3) or secrete (Tg1.4HBV-s-rec (F1, Tg1.4HBV-s-mut × Alb/HBs) the HBsAg. Herein, the responsiveness of TLR3 and RIG-I in primary parenchymal and non-parenchymal liver cells was determined in vitro and in vivo. Cell type-specific and mouse strain-dependent interferon, cytokine and chemokine expression were observed by LEGENDplex™ and validated by quantitative PCR. In vitro, the hepatocytes, liver sinusoidal endothelial cells and Kupffer cells of Tg1.4HBV-s-rec mice showed poly(I:C) susceptibilities similar to the wild-type controls, while in the remaining leucocyte fraction the interferon, cytokine and chemokine induction was reduced. On the contrary, poly(I:C)-injected 1.4TgHBV-s-rec mice showed suppressed interferon, cytokine and chemokine levels in hepatocytes but increased levels in the leucocyte fraction. Thus, we concluded that liver cells of Tg1.4HBV-s-rec mice, which produce HBV particles and release the HBsAg, responded to exogenous TLR3/RIG-I stimuli in vitro but exhibited a tolerogenic environment in vivo.

A single, oral dose of the TLR7 agonist JNJ-64794964 induces transcriptomic and phenotypic changes in peripheral immune cells in healthy adults.

Chronic hepatitis B (CHB) is responsible for major disease burden worldwide. However, the number of available therapies is limited; cure remains an elusive goal. JNJ-64794964 (JNJ-4964) is an oral toll-like receptor-7 (TLR7) agonist being evaluated for the treatment of CHB. Here, we investigated the capacity of JNJ-4964 to induce transcriptomic and immune cell changes in peripheral blood in healthy volunteers. Peripheral blood was collected in the JNJ-4964 first-in-human phase 1 trial at multiple time points to assess transcriptomics and changes in frequency and phenotype of peripheral-blood mononuclear cells. Correlation of changes to JNJ-4964 exposure (Cmax) and changes in cytokine levels (C-X-C motif chemokine ligand 10 [CXCL10] and interferon alpha [IFN-α]) were evaluated. Fifty-nine genes, mainly interferon-stimulated genes, were up-regulated between 6hours and 5days after JNJ-4964 administration. JNJ-4964 increased frequencies of CD69, CD134, CD137, and/or CD253-expressing natural killer (NK) cells, indicative of NK cell activation. These changes correlated with Cmax, increase of CXCL10, and induction of IFN-α and were observed at IFN-α levels that are associated with no/acceptable flu-like adverse events. JNJ-4964 administration resulted in increased frequencies of CD86-expressing B cells, indicative of B-cell activation. These changes were predominantly observed at high IFN-α levels, which are associated with flu-like adverse events. JNJ-4964 administration led to changes in transcriptional profiles and immune cell activation phenotype, particularly for NK cells and B cells. Together, these changes could represent a set of biomarkers for the characterization of the immune response in CHB patients receiving TLR7 agonists.

Expression of L1 retrotransposons in granulocytes from patients with active systemic lupus erythematosus

BackgroundPatients with systemic lupus erythematosus (SLE) have autoantibodies against the L1-encoded open-reading frame 1 protein (ORF1p). Here, we report (i) which immune cells ORF1p emanates from, (ii) which L1 loci are transcriptionally active, (iii) whether the cells express L1-dependent interferon and interferon-stimulated genes, and (iv) the effect of inhibition of L1 ORF2p by reverse transcriptase inhibitors.ResultsL1 ORF1p was detected by flow cytometry primarily in SLE CD66b+CD15+ regular and low-density granulocytes, but much less in other immune cell lineages. The amount of ORF1p was higher in neutrophils from patients with SLE disease activity index (SLEDAI) > 6 (p = 0.011) compared to patients with inactive disease, SLEDAI < 4. Patient neutrophils transcribed seven to twelve human-specific L1 loci (L1Hs), but only 3 that are full-length and with an intact ORF1. Besides serving as a source of detectable ORF1p, the most abundant transcript encoded a truncated ORF2p reverse transcriptase predicted to remain cytosolic, while the two other encoded an intact full-length ORF2p. A number of genes encoding proteins that influence L1 transcription positively or negatively were altered in patients, particularly those with active disease, compared to healthy controls. Components of nucleic acid sensing and interferon induction were also altered. SLE neutrophils also expressed type I interferon-inducible genes and interferon β, which were substantially reduced after treatment of the cells with drugs known to inhibit ORF2p reverse transcriptase activity.ConclusionsWe identified L1Hs loci that are transcriptionally active in SLE neutrophils, and a reduction in the epigenetic silencing mechanisms that normally counteract L1 transcription. SLE neutrophils contained L1-encoded ORF1p protein, as well as activation of the type I interferon system, which was inhibited by treatment with reverse transcriptase inhibitors. Our findings will enable a deeper analysis of L1 dysregulation and its potential role in SLE pathogenesis.

Metagenomics-enabled reverse-genetics assembly and characterization of myotis bat morbillivirus.

Morbilliviruses are among the most contagious viral pathogens of mammals. Although previous metagenomic surveys have identified morbillivirus sequences in bats, full-length morbilliviruses from bats are limited. Here we characterize the myotis bat morbillivirus (MBaMV) from a bat surveillance programme in Brazil, whose full genome was recently published. We demonstrate that the fusion and receptor binding protein of MBaMV utilize bat CD150 and not human CD150, as an entry receptor in a mammalian cell line. Using reverse genetics, we produced a clone of MBaMV that infected Vero cells expressing bat CD150. Electron microscopy of MBaMV-infected cells revealed budding of pleomorphic virions, a characteristic morbillivirus feature. MBaMV replication reached 103-105 plaque-forming units ml-1 in human epithelial cell lines and was dependent on nectin-4. Infection of human macrophages also occurred, albeit 2-10-fold less efficiently than measles virus. Importantly, MBaMV is restricted by cross-neutralizing human sera elicited by measles, mumps and rubella vaccination and is inhibited by orally bioavailable polymerase inhibitors in vitro. MBaMV-encoded P/V genes did not antagonize human interferon induction. Finally, we show that MBaMV does not cause disease in Jamaican fruit bats. We conclude that, while zoonotic spillover into humans may theoretically be plausible, MBaMV replication would probably be controlled by the human immune system.

Interferon Regulatory Factor 7-mediated induction of interferon-α is required for survival from alphavirus encephalomyelitis

Abstract Alphaviruses are a group of arthropod-borne viruses that have the capacity to cause encephalomyelitis, which is inflammation of the brain and spinal cord due to the immune response to viral infection, and can result in fever, headache, and neurologic disease such as cognitive impairment, seizures, ataxia, and paralysis. Neurons are the primary target cells of Sindbis virus (SINV), the prototypic alphavirus; however, due to the indispensable nature of neurons, mechanisms of viral clearance from the central nervous system (CNS) during recovery cannot depend on immune-mediated killing of infected neurons and is therefore specialized. We have previously shown that interferon (IFN) regulatory factor (IRF) 7, a transcription factor important for amplification of type I IFN (mainly IFNα), is required for survival from infection with SINV. Mice deficient in IRF7 succumb to infection – despite local production of IFNβ – while wild type (WT) mice recover. Treatment of Irf7−/−mice with IFNα rescues the WT phenotype, suggesting that IRF7-mediated induction of IFNα and subsequent downstream signaling is required for survival from SINV infection. Additionally, Ifnb−/−mice do not phenocopy Irf7−/−mice, further suggesting that IFNα is required for survival while IFNβ is dispensable despite usage of the same receptor. Interestingly, Ifnb−/−mice have similar viral titers to Irf7−/−mice, implying that the protective effects of IFNα are independent from restriction of viral replication. These findings show subtype-specific differences in protection by type I IFN and can inform treatment options for alphavirus-induced encephalomyelitis. These works have been funded by the U.S. National Institutes of Health (R01 NS087539 and T32 AI007417).

IFIH1 deficiency causing neonatal herpes simplex virus encephalitis and recurrent retinitis

Homozygous loss-of-function variants in Interferon induced with helicase C domain 1 (IFIH1) leads to immunodeficiency with early onset recurrent and severe viral respiratory infections (Immunodeficiency 95; MIM 619773). Severe respiratory infections with RNA viruses such as rhinovirus and respiratory syncytial virus (RSV) are most characteristic of IFIH1 deficiency. IFIH1 encodes melanoma differentiation-associated protein 5 (MDA5), an intracellular sensor of mainly long double-stranded RNA (ds-RNA), a viral replication intermediate. When activated, MDA5 triggers antiviral pathways including increased transcription of Type 1-interferon. The antiviral role of MDA5 is best described for positive (+) RNA viruses such as Picornavirus family which produce long ds-RNA as a replication intermediate. We present a patient with neonatal herpes simplex virus (HSV) encephalitis and recurrent retinitis with homozygous variant of unknown significance (VUS) in IFIH1, c.2062A>G (p.Lys688Glu).Patient is a 10-year-old male, born of consanguineous parents from the United Arab Emirates. Past medical history is notable for neonatal HSV encephalitis, grade 3 intraventricular hemorrhage, cerebral palsy, epilepsy, optic atrophy and recurrent HSV retinitis. Patient has no additional history of severe or recurrent infections. No family history of recurrent or severe infections, malignancy, autoimmunity or autoinflammation.Immune evaluation demonstrated anemia with elevated mean corpuscular volume and mild elevation of platelets and monocytes. Patient had normal lymphocyte subsets, normal T and B cell subset distributions, protective vaccine titers and normal immunoglobins apart from mildly elevated immunoglobulin G. An Invitae primary immunodeficiency panel demonstrated homozygous VUS in IFIH1, c.2062A>G (p.Lys688Glu). This variant is not found in gnomAD or ClinVar and has a Combined Annotation Dependent Depletion score of 22.6. Functional testing demonstrated decreased interferon induction after stimulation with intracellular RNA, intracellular DNA and agonists of both Toll-like receptor 7 and 9. These findings are consistent with MDA5 deficiency given decreased interferon response with known MDA5 agonists.In summary, we describe a patient with recurrent and severe infections with a DNA virus and no known infections with respiratory RNA viruses. Both DNA and RNA viruses produce long ds-RNA as replication intermediates, an MDA5 agonist. This patient highlights the anti-viral role of MDA5 for both DNA and RNA viruses.

Uncovering alterations in the murine interferon response due to dsRNA mycovirus during Aspergillus fumigatus infection

Abstract Aspergillus fumigatus is a mold that causes an array of diseases, the most severe form being invasive aspergillosis which occurs in highly immunocompromised individuals. We demonstrated that tissue-resident alveolar macrophages are critical for maintaining host resistance against Aspergillus fumigatus due to their role in the early type I/III interferon response. Specifically, CD11c-Cre x Mavs fl/flmice have a decreased interferon response and survival outcomes when challenged with A. fumigatus, which can be functionally restored via adoptive transfer of wild-type SiglecF +alveolar macrophages. Why alveolar macrophages are potent inducers of the type I/III interferon response after Aspergillus fumigatus challenge remains elusive. Here, we demonstrate that TGF-beta metabolically programs alveolar macrophages to be potent interferon inducers via enhanced dependency on oxidative phosphorylation and peroxisome biogenesis. The type I/III interferon responses were partially related to the inability of alveolar macrophages to recognize mycoviral double-stranded RNA (dsRNA). Aspergillus fumigatus strains infected with polymycovirus 1 (PmV1) are shown to induce a robust type I/III interferon responses both in vitro and in vivo. Critically, Mda5/MAVS-dependent interferon response can still be induced in a fungal dsRNA independent manner, which warrant further explorations. In this study we identified key metabolic traits of alveolar macrophages which enable robust Mda5/MAVS signaling necessary for initiating the Aspergillus fumigatus induced interferon response, which maintains host resistance against this ubiquitous mold, through both fungal dsRNA-dependent and -independent mechanisms.

The IFN-stimulated gene IFI27 counteracts innate immune responses after viral infections by interfering with RIG-I signaling.

The recognition of viral nucleic acids by host pattern recognition receptors (PRRs) is critical for initiating innate immune responses against viral infections. These innate immune responses are mediated by the induction of interferons (IFNs), IFN-stimulated genes (ISGs) and pro-inflammatory cytokines. However, regulatory mechanisms are critical to avoid excessive or long-lasting innate immune responses that may cause detrimental hyperinflammation. Here, we identified a novel regulatory function of the ISG, IFN alpha inducible protein 27 (IFI27) in counteracting the innate immune responses triggered by cytoplasmic RNA recognition and binding. Our model systems included three unrelated viral infections caused by Influenza A virus (IAV), Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2), and Sendai virus (SeV), and transfection with an analog of double-stranded (ds) RNA. Furthermore, we found that IFI27 has a positive effect on IAV and SARS-CoV-2 replication, most likely due to its ability to counteract host-induced antiviral responses, including in vivo. We also show that IFI27 interacts with nucleic acids and PRR retinoic acid-inducible gene I (RIG-I), being the interaction of IFI27 with RIG-I most likely mediated through RNA binding. Interestingly, our results indicate that interaction of IFI27 with RIG-I impairs RIG-I activation, providing a molecular mechanism for the effect of IFI27 on modulating innate immune responses. Our study identifies a molecular mechanism that may explain the effect of IFI27 in counterbalancing innate immune responses to RNA viral infections and preventing excessive innate immune responses. Therefore, this study will have important implications in drug design to control viral infections and viral-induced pathology.

Inborn Error of STAT2-Dependent IFN-I Immunity in a Patient Presented with Hemophagocytic Lymphohistiocytosis and Multisystem Inflammatory Syndrome in Children.

Human inborn errors of immunity (IEI) affecting the type I interferon (IFN-I) induction pathway have been associated with predisposition to severe viral infections. Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening systemic hyperinflammatory syndrome that has been increasingly associated with inborn errors of IFN-I-mediated innate immunity. Here is reported a novel case of complete deficiency of STAT2 in a 3-year-old child that presented with typical features of HLH after mumps, measles, and rubella vaccination at the age of 12months. Due to the life-threatening risk of viral infection, she received SARS-CoV-2 mRNA vaccination. Unfortunately, she developed multisystem inflammatory syndrome in children (MIS-C) after SARS-CoV-2 infection, 4months after the last dose. Functional studies showed an impaired IFN-I-induced response and a defective IFNα expression at later stages of STAT2 pathway induction. These results suggest a possible more complex mechanism for hyperinflammatory reactions in this type of patients involving a possible defect in the IFN-I production. Understanding the cellular and molecular links between IFN-I-induced signaling and hyperinflammatory syndromes can be critical for the diagnosis and tailored management of these patients with predisposition to severe viral infection.

The HDAC inhibitor domatinostat induces type I interferon α in Merkel cell carcinoma by HES1 repression

BackgroundClass I selective histone deacetylase inhibitors (HDACi) have been previously demonstrated to not only increase major histocompatibility complex class I surface expression in Merkel cell carcinoma (MCC) cells by restoring the antigen processing and presentation machinery, but also exert anti-tumoral effect by inducing apoptosis. Both phenomena could be due to induction of type I interferons (IFN), as has been described for HDACi. However, the mechanism of IFN induction under HDACi is not fully understood because the expression of IFNs is regulated by both activating and inhibitory signaling pathways. Our own preliminary observations suggest that this may be caused by suppression of HES1.MethodsThe effect of the class I selective HDACi domatinostat and IFNα on cell viability and the apoptosis of MCPyV-positive (WaGa, MKL-1) and -negative (UM-MCC 34) MCC cell lines, as well as, primary fibroblasts were assessed by colorimetric methods or measuring mitochondrial membrane potential and intracellular caspase-3/7, respectively. Next, the impact of domatinostat on IFNA and HES1 mRNA expression was measured by RT-qPCR; intracellular IFNα production was detected by flow cytometry. To confirm that the expression of IFNα induced by HDACi was due to the suppression of HES1, it was silenced by RNA interference and then mRNA expression of IFNA and IFN-stimulated genes was assessed.ResultsOur studies show that the previously reported reduction in viability of MCC cell lines after inhibition of HDAC by domatinostat is accompanied by an increase in IFNα expression, both of mRNA and at the protein level. We confirmed that treatment of MCC cells with external IFNα inhibited their proliferation and induced apoptosis. Re-analysis of existing single-cell RNA sequencing data indicated that induction of IFNα by domatinostat occurs through repression of HES1, a transcriptional inhibitor of IFNA; this was confirmed by RT-qPCR. Finally, siRNA-mediated silencing of HES1 in the MCC cell line WaGa not only increased mRNA expression of IFNA and IFN-stimulated genes but also decreased cell viability.ConclusionOur results demonstrate that the direct anti-tumor effect of HDACi domatinostat on MCC cells is at least in part mediated via decreased HES1 expression allowing the induction of IFNα, which in turn causes apoptosis.

Borrelia burgdorferi Engages Mammalian Type I IFN Responses via the cGAS-STING Pathway.

Borrelia burgdorferi, the etiologic agent of Lyme disease, is a spirochete that modulates numerous host pathways to cause a chronic, multisystem inflammatory disease in humans. B. burgdorferi infection can lead to Lyme carditis, neurologic complications, and arthritis because of the ability of specific borrelial strains to disseminate, invade, and drive inflammation. B. burgdorferi elicits type I IFN (IFN-I) responses in mammalian cells and tissues that are associated with the development of severe arthritis or other Lyme-related complications. However, the innate immune sensors and signaling pathways controlling IFN-I induction remain unclear. In this study, we examined whether intracellular nucleic acid sensing is required for the induction of IFN-I to B. burgdorferi. Using fluorescence microscopy, we show that B. burgdorferi associates with mouse and human cells in culture, and we document that internalized spirochetes colocalize with the pattern recognition receptor cyclic GMP-AMP synthase (cGAS). Moreover, we report that IFN-I responses in mouse macrophages and murine embryonic fibroblasts are significantly attenuated in the absence of cGAS or its adaptor stimulator of IFN genes (STING), which function to sense and respond to intracellular DNA. Longitudinal invivo tracking of bioluminescent B. burgdorferi revealed similar dissemination kinetics and borrelial load in C57BL/6J wild-type, cGAS-deficient, or STING-deficient mice. However, infection-associated tibiotarsal joint pathology and inflammation were modestly reduced in cGAS-deficient compared with wild-type mice. Collectively, these results indicate that the cGAS-STING pathway is a critical mediator of mammalian IFN-I signaling and innate immune responses to B. burgdorferi.

Oncolytic Rodent Protoparvoviruses Evade a TLR- and RLR-Independent Antiviral Response in Transformed Cells.

The oncolytic rodent protoparvoviruses (PVs) minute virus of mice (MVMp) and H-1 parvovirus (H-1PV) are promising cancer viro-immunotherapy candidates capable of both exhibiting direct oncolytic activities and inducing anticancer immune responses (AIRs). Type-I interferon (IFN) production is instrumental for the activation of an efficient AIR. The present study aims at characterizing the molecular mechanisms underlying PV modulation of IFN induction in host cells. MVMp and H-1PV triggered IFN production in semi-permissive normal mouse embryonic fibroblasts (MEFs) and human peripheral blood mononuclear cells (PBMCs), but not in permissive transformed/tumor cells. IFN production triggered by MVMp in primary MEFs required PV replication and was independent of the pattern recognition receptors (PRRs) Toll-like (TLR) and RIG-like (RLR) receptors. PV infection of (semi-)permissive cells, whether transformed or not, led to nuclear translocation of the transcription factors NFĸB and IRF3, hallmarks of PRR signaling activation. Further evidence showed that PV replication in (semi-)permissive cells resulted in nuclear accumulation of dsRNAs capable of activating mitochondrial antiviral signaling (MAVS)-dependent cytosolic RLR signaling upon transfection into naïve cells. This PRR signaling was aborted in PV-infected neoplastic cells, in which no IFN production was detected. Furthermore, MEF immortalization was sufficient to strongly reduce PV-induced IFN production. Pre-infection of transformed/tumor but not of normal cells with MVMp or H-1PV prevented IFN production by classical RLR ligands. Altogether, our data indicate that natural rodent PVs regulate the antiviral innate immune machinery in infected host cells through a complex mechanism. In particular, while rodent PV replication in (semi-)permissive cells engages a TLR-/RLR-independent PRR pathway, in transformed/tumor cells this process is arrested prior to IFN production. This virus-triggered evasion mechanism involves a viral factor(s), which exert(s) an inhibitory action on IFN production, particularly in transformed/tumor cells. These findings pave the way for the development of second-generation PVs that are defective in this evasion mechanism and therefore endowed with increased immunostimulatory potential through their ability to induce IFN production in infected tumor cells.

Maximal interferon induction by influenza lacking NS1 is infrequent owing to requirements for replication and export.

Influenza A virus exhibits high rates of replicative failure due to a variety of genetic defects. Most influenza virions cannot, when acting as individual particles, complete the entire viral life cycle. Nevertheless influenza is incredibly successful in the suppression of innate immune detection and the production of interferons, remaining undetected in >99% of cells in tissue-culture models of infection. Notably, the same variation that leads to replication failure can, by chance, inactivate the major innate immune antagonist in influenza A virus, NS1. What explains the observed rarity of interferon production in spite of the frequent loss of this, critical, antagonist? By studying how genetic and phenotypic variation in a viral population lacking NS1 correlates with interferon production, we have built a model of the "worst-case" failure from an improved understanding of the steps at which NS1 acts in the viral life cycle to prevent the triggering of an innate immune response. In doing so, we find that NS1 prevents the detection of de novo innate immune ligands, defective viral genomes, and viral export from the nucleus, although only generation of de novo ligands appears absolutely required for enhanced detection of virus in the absence of NS1. Due to this, the highest frequency of interferon production we observe (97% of infected cells) requires a high level of replication in the presence of defective viral genomes with NS1 bearing an inactivating mutation that does not impact its partner encoded on the same segment, NEP. This is incredibly unlikely to occur given the standard variation found within a viral population, and would generally require direct, artificial, intervention to achieve at an appreciable rate. Thus from our study, we procure at least a partial explanation for the seeming contradiction between high rates of replicative failure and the rarity of the interferon response to influenza infection.

Zebrafish MARCH7 negatively regulates IFN antiviral response by degrading TBK1

Membrane-associated RING-CH-type finger (MARCH) proteins have been reported to regulate type I IFN production during host antiviral innate immunity. The present study reported the zebrafish MARCH family member, MARCH7, as a negative regulator in virus-triggered type I IFN induction via targeting TANK-binding kinase 1 (TBK1) for degradation. As an IFN-stimulated gene (ISG), we discovered that MARCH7 was significantly induced by spring viremia of carp virus (SVCV) or poly(I:C) stimulation. Ectopic expression of MARCH7 reduced the activity of IFN promoter and dampened the cellular antiviral responses triggered by SVCV and grass carp reovirus (GCRV), which concomitantly accelerated the viral replication. Accordingly, the knockdown of MARCH7 by siRNA transfection significantly promoted the transcription of ISG genes and inhibited SVCV replication. Mechanistically, we found that MARCH7 interacted with TBK1 and degraded it via K48-linked ubiquitination. Further characterization of truncated mutants of MARCH7 and TBK1 confirmed that the C-terminal RING of MARCH7 is essential in the MARCH7-mediated degradation of TBK1 and the negative regulation of IFN antiviral response. This study reveals a molecular mechanism by which zebrafish MARCH7 negatively regulates the IFN response by targeting TBK1 for protein degradation, providing new insights into the essential role of MARCH7 in antiviral innate immunity.

Abstract 3095: Development of a novel ADAR1 inhibitor as a potent immunomodulator for the treatment of solid tumors

Abstract Background: Adenosine deaminase, RNA specific (ADAR1), catalyzes the hydrolytic deamination of adenosine (A) to inosine (I) in double-stranded (ds) RNAs. There are 2 isoforms of ADAR1 (p110 in the nucleus; p150 in cytoplasm) and both modify self dsRNA in coding and non-coding regions​. The ADAR1 p150 isoform is expressed from an interferon (IFN)-response promoter and has a Z-DNA/Z-RNA binding domain at the N-terminus. ADAR1 p150 edits 3′-untranslated region dsRNAs comprising of inverted Alu repeats and thereby suppresses MDA5-MAVS-IFN signaling. ADAR1 is commonly overexpressed in multiple myeloma, breast, lung, liver, skin and esophageal cancer where it promotes cancer progression. Inhibition of ADAR1 has promising anti-tumor efficacy as monotherapy and in combination with checkpoint inhibitors, radiotherapy and chemotherapeutic modalities. Herein, we outline the discovery of a potential first-in-class ADAR1 inhibitor for cancer immunotherapy. Methods: AVA-ADR-001 was identified through a high throughput p110 knockout cell-based assay. The ability of AVA-ADR-001 to induce interferons was confirmed in various cell lines like A549 p110 KO, HCT116 and B16F10. Finally, the anti-tumor efficacy of AVA-ADR-001 was evaluated in B16F10 syngeneic melanoma mice model as monotherapy and in combination with anti-PD-1. Results: We have identified a first-in-class small molecule inhibitor of ADAR1, which shows significant IFN response in vitro in an MDA5 dependent manner. In vitro binding studies have confirmed direct binding of AVA-ADR-001 with the Zα domain of ADAR1 thus confirming its selectivity to the p150 isoform. AVA-ADR-001 demonstrates micromolar EC50 and anti-tumor efficacy against B16F10 melanoma syngeneic mouse model. 100 µg of AVA-ADR-001 treatment resulted in 45% tumor growth inhibition (TGI), 1.5x superior to Anti-PD1 treatment. Combining AVA-ADR-001 with Anti-PD1 demonstrated a synergistic effect 2x superior to Anti-PD1 alone. Additionally, several interferon stimulated genes like IFIH1, IFN-β and CXCL-10 were significantly upregulated in the tumor samples of the AVA-ADR-001 monotherapy and combination groups. Conclusions: To our knowledge no selective small molecule inhibitors of ADAR1 have been reported so far and AVA-ADR-001 is the first disclosure of such an inhibitor. AVA-ADR-001 is a potent and selective first-in-class ADAR1 inhibitor which has shown significant IFN induction in various cancer cell lines and in vivo in the tumor microenvironment resulting in substantial tumor growth inhibition as monotherapy and synergistically in combination with Anti-PD1. Considering the immune-suppressive and pro-metastatic role of ADAR1, AVA-ADR-001 serves as a promising starting point for novel ADAR1 inhibitors as therapeutic modalities in cancer immunotherapy. Keywords: Cancer immunotherapy, small molecule inhibitors, ADAR1, innate immunity Citation Format: Aditya Kulkarni, Avijit Goswami, Sandeep Goyal, Kawaljit Singh, Princy Khurana, Ishani Ghoshal. Development of a novel ADAR1 inhibitor as a potent immunomodulator for the treatment of solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3095.

Abstract 793: Mechanism of interferon induction by cannabidiol (CBD) and analogues in lung cancer cells

Abstract CBD, an FDA approved drug for epilepsy, may have therapeutic potential for other diseases and is currently being tested for efficacy in cancer-related clinical trials. As the literature about CBD, especially in vitro reports, is often contradictory, increasing our understanding of its specific action on a molecular level will allow to determine whether CBD can become a useful therapy or exacerbates specific cancers in a context-dependent manner. Due to its relative lipophilicity, CBD is challenging to dispense at therapeutic concentrations; therefore, one goal is to identify cannabinoid congeners with greater efficacy and reduced drug delivery challenges. We recently showed that CBD activates interferons as a mechanism of inhibiting SARS-CoV-2 replication in lung carcinoma cells. As factors produced by the innate immune system, interferons have been implicated in both pro-survival and growth arrest and apoptosis signaling in cancer. Here we show that CBD induces interferon production and interferon stimulated genes (ISGs) through a mechanism involving NRF2 and MAVS in lung carcinoma cells. We also show that CBDV, which differs from CBD by 2 fewer aliphatic tail carbons, has limited potency, suggesting that CBD specifically interacts with one or more cellular proteins rather than having a non-specific effect. We also identified other CBD-related cannabinoids that are more effective at inducing ISGs. Taken together, these results characterize a novel mechanism by which CBD activates the innate immune system in lung cancer cells and identify related cannabinoids that have possible therapeutic potential in cancer treatment. Citation Format: Leticia Stock, Lydia Robinson-Mailman, Long C. Nguyen, Shao-Nong Chen, Guido F. Pauli, Marsha R. Rosner. Mechanism of interferon induction by cannabidiol (CBD) and analogues in lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 793.

The anti-immune dengue subgenomic flaviviral RNA is present in vesicles in mosquito saliva and is associated with increased infectivity.

Mosquito transmission of dengue viruses to humans starts with infection of skin resident cells at the biting site. There is great interest in identifying transmission-enhancing factors in mosquito saliva in order to counteract them. Here we report the discovery of high levels of the anti-immune subgenomic flaviviral RNA (sfRNA) in dengue virus 2-infected mosquito saliva. We established that sfRNA is present in saliva using three different methods: northern blot, RT-qPCR and RNA sequencing. We next show that salivary sfRNA is protected in detergent-sensitive compartments, likely extracellular vesicles. In support of this hypothesis, we visualized viral RNAs in vesicles in mosquito saliva and noted a marked enrichment of signal from 3'UTR sequences, which is consistent with the presence of sfRNA. Furthermore, we show that incubation with mosquito saliva containing higher sfRNA levels results in higher virus infectivity in a human hepatoma cell line and human primary dermal fibroblasts. Transfection of 3'UTR RNA prior to DENV2 infection inhibited type I and III interferon induction and signaling, and enhanced viral replication. Therefore, we posit that sfRNA present in salivary extracellular vesicles is delivered to cells at the biting site to inhibit innate immunity and enhance dengue virus transmission.