Aflatoxin B1 and Epstein-Barr virus-induced CCL22 expression stimulates B cell infection.

Epstein-Barr Virus (EBV) infects more than 90% of the adult population worldwide. EBV infection is associated with Burkitt lymphoma (BL) though alone is not sufficient to induce carcinogenesis implying the involvement of co-factors. BL is endemic in African regions faced with mycotoxins exposure. Exposure to mycotoxins and oncogenic viruses has been shown to increase cancer risks partly through the deregulation of the immune response. A recent transcriptome profiling of B cells exposed to aflatoxin B1 (AFB1) revealed an upregulation of the Chemokine ligand 22 (CCL22) expression although the underlying mechanisms were not investigated. Here, we tested whether mycotoxins and EBV exposure may together contribute to endemic BL (eBL) carcinogenesis via immunomodulatory mechanisms involving CCL22. Our results revealed that B cells exposure to AFB1 and EBV synergistically stimulated CCL22 secretion via the activation of Nuclear Factor-kappa B pathway. By expressing EBV latent genes in B cells, we revealed that elevated levels of CCL22 result not only from the expression of the latent membrane protein LMP1 as previously reported but also from the expression of other viral latent genes. Importantly, CCL22 overexpression resulting from AFB1-exposure in vitro increased EBV infection through the activation of phosphoinositide-3-kinase pathway. Moreover, inhibiting CCL22 in vitro and in humanized mice in vivo limited EBV infection and decreased viral genes expression, supporting the notion that CCL22 overexpression plays an important role in B cell infection. These findings unravel new mechanisms that may underpin eBL development and identify novel pathways that can be targeted in drug development.

Do NSm Virulence Factors in the Bunyavirales Viral Order Originate from Gn Gene Duplication?

One-third of the nine WHO shortlisted pathogens prioritized for research and development in public health emergencies belong to the Bunyavirales order. Several Bunyavirales species carry an NSm protein that acts as a virulence factor. We predicted the structures of these NSm proteins and unexpectedly found that in two families, their cytosolic domain was inferred to have a similar fold to that of the cytosolic domain of the viral envelope-forming glycoprotein N (Gncyto) encoded on the same genome fragment. We show that although the sequence identity between the NSmcyto and the Gncyto domains is low, the conservation of the two zinc finger-forming CysCysHisCys motifs explains the predicted structural conservation. Importantly, our predictions provide a first glimpse into the long-unknown structure of NSm. Also, these predictions suggest that NSm is the result of a gene duplication event in the Bunyavirales Nairoviridae and Peribunyaviridae families and that such events may be common in the recent evolutionary history of RNA viruses.

Low-density hepatitis C virus infectious particles are protected from oxidation by secreted cellular proteins.

IMPORTANCE: Assessments of viral stability on surfaces or in body fluids under different environmental conditions and/or temperatures are often performed, as they are key to understanding the routes and parameters of viral transmission and to providing clues on the epidemiology of infections. However, for most viruses, the mechanisms of inactivation vs stability of viral particles remain poorly defined. Although they are structurally diverse, with different compositions, sizes, and shapes, enveloped viruses are generally less stable than non-enveloped viruses, pointing out the role of envelopes themselves in virus lability. In this report, we investigated the properties of hepatitis C virus (HCV) particles with regards to their stability. We found that, compared to alternative enveloped viruses such as Dengue virus (DENV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), hepatitis delta virus (HDV), and Crimean-Congo hemorrhagic fever virus (CCHFV) that infect the liver, HCV particles are intrinsically labile. We determined the mechanisms that drastically alter their specific infectivity through oxidation of their lipids, and we highlighted that they are protected from lipid oxidation by secreted cellular proteins, which can protect their membrane fusion capacity and overall infectivity.

Engineering B cells with customized therapeutic responses using a synthetic circuit.

The expansion of genetic engineering has brought a new dimension for synthetic immunology. Immune cells are perfect candidates because of their ability to patrol the body, interact with many cell types, proliferate upon activation, and differentiate in memory cells. This study aimed at implementing a new synthetic circuit in B cells, allowing the expression of therapeutic molecules in a temporally and spatially restricted manner that is induced by the presence of specific antigens. This should enhance endogenous B cell functions in terms of recognition and effector properties. We developed a synthetic circuit encoding a sensor (a membrane-anchored B cell receptor targeting a model antigen), a transducer (a minimal promoter induced by the activated sensor), and effector molecules. We isolated a 734-bp-long fragment of the NR4A1 promoter, specifically activated by the sensor signaling cascade in a fully reversible manner. We demonstrate full antigen-specific circuit activation as its recognition by the sensor induced the activation of the NR4A1 promoter and the expression of the effector. Overall, such novel synthetic circuits offer huge possibilities for the treatment of many pathologies, as they are completely programmable; thus, the signal-specific sensors and effector molecules can be adapted to each disease.

Molecular and serological evidence of Crimean-Congo hemorrhagic fever orthonairovirus prevalence in livestock and ticks in Cameroon.

Introduction: Despite a high fatality rate in humans, little is known about the occurrence of Crimean-Congo hemorrhagic fever virus (CCHFV) in Cameroon. Hence, this pioneer study was started with the aim of determining the prevalence of CCHFV in domestic ruminants and its potential vector ticks in Cameroon. Methods: A cross-sectional study was carried out in two livestock markets of Yaoundé to collect blood and ticks from cattle, sheep, and goats. CCHFV-specific antibodies were detected in the plasma using a commercial ELISA assay and confirmed using a modified seroneutralization test. Ticks were screened for the presence of orthonairoviruses by amplification of a fragment of the L segment using RT-PCR. Phylogeny was used to infer the genetic evolution of the virus. Results: Overall, 756 plasma samples were collected from 441 cattle, 168 goats, and 147 sheep. The seroprevalence of CCHFV was 61.77% for all animals, with the highest rate found in cattle (433/441, 98.18%) followed by sheep (23/147, 15.65%), and goats (11/168, 6.55%), (p-value < 0.0001). The highest seroprevalence rate was found in cattle from the Far North region (100%). Overall, 1500 ticks of the Rhipicephalus (773/1500, 51.53%), Amblyomma (341/1500, 22.73%), and Hyalomma (386/1500, 25.73%) genera were screened. CCHFV was identified in one Hyalomma truncatum pool collected from cattle. Phylogenetic analysis of the L segment classified this CCHFV strain within the African genotype III. Conclusion: These seroprevalence results call for additional epidemiological studies on CCHFV, especially among at-risk human and animal populations in high-risk areas of the country.

Hepatitis D virus interferes with hepatitis B virus RNA production via interferon-dependent and -independent mechanisms.

BACKGROUND & AIMS: Chronic coinfection with HBV and HDV leads to the most aggressive form of chronic viral hepatitis. Herein, we aimed to elucidate the molecular mechanisms underlying the widely reported observation that HDV interferes with HBV in most coinfected patients. METHODS: Patient liver tissues, primary human hepatocytes, HepaRG cells and human liver chimeric mice were used to analyze the effect of HDV on HBV using virological and RNA-sequencing analyses, as well as RNA synthesis, stability and association assays. RESULTS: Transcriptomic analyses in cell culture and mouse models of coinfection enabled us to define an HDV-induced signature, mainly composed of interferon (IFN)-stimulated genes (ISGs). We also provide evidence that ISGs are upregulated in chronically HDV/HBV-coinfected patients but not in cells that only express HDV antigen (HDAg). Inhibition of the hepatocyte IFN response partially rescued the levels of HBV parameters. We observed less HBV RNA synthesis upon HDV infection or HDV protein expression. Additionally, HDV infection or expression of HDAg alone specifically accelerated the decay of HBV RNA, and HDAg was associated with HBV RNAs. On the contrary, HDAg expression did not affect other viruses such as HCV or SARS-CoV-2. CONCLUSIONS: Our data indicate that HDV interferes with HBV through both IFN-dependent and IFN-independent mechanisms. Specifically, we uncover a new viral interference mechanism in which proteins of a satellite virus affect the RNA production of its helper virus. Exploiting these findings could pave the way to the development of new therapeutic strategies against HBV. IMPACT AND IMPLICATIONS: Although the molecular mechanisms remained unexplored, it has long been known that despite its dependency, HDV decreases HBV viremia in patients. Herein, using in vitro and in vivo models, we showed that HDV interferes with HBV through both IFN-dependent and IFN-independent mechanisms affecting HBV RNA metabolism, and we defined the HDV-induced modulation signature. The mechanisms we uncovered could pave the way for the development of new therapeutic strategies against HBV by mimicking and/or increasing the effect of HDAg on HBV RNA. Additionally, the HDV-induced modulation signature could potentially be correlated with responsiveness to IFN-α treatment, thereby helping to guide management of HBV/HDV-coinfected patients.

Crimean-Congo hemorrhagic fever: a growing threat to Europe.

Tick-borne infectious diseases are increasing, driven by geographic expansion of ticks. Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus of the family Nairoviridae that poses serious threat to public health. CCHFV can cause severe forms of hemorrhagic fever with high case fatality rates (CFR) (10-40%) and can be transmitted from human to human. Until a few years ago, no cases of CCHF had been reported in western Europe. However, high seropositivity rates in wildlife and detection of multiple strains of CCHFV in ticks in Spain suggest that CCHFV enzootic cycle has been established in some areas of southwestern Europe. As far as CCHFV-associated morbidity and mortality are concerned, there are no approved therapeutic options or US/EU licensed vaccines for treatment. Here we discuss some eco-epidemiological aspects as well as public health and socio-economic impacts associated with CCHFV circulation and outbreaks. We also emphasize that it has become essential to identify key inter-species transmission processes of this group of pathogens, to understand basic molecular mechanisms of their replication, and to define their pathogenic potentials.

Partout dans le monde, les maladies infectieuses transmises par les tiques sont en augmentation, en raison de l'expansion géographique de ces dernières. Le virus de la fièvre hémorragique de Crimée-Congo (CCHFV) est un virus de la famille des Nairoviridae transmis par les tiques et constitue une menace importante pour la santé publique. Il est responsable de graves fièvres hémorragiques associées à des taux de létalité élevés (10­40%), une transmission d'homme à homme possible et une absence d'options thérapeutiques approuvées ou de vaccins homologués en Espagne et dans l'Union européenne. Jusqu'à il y a quelques années, aucun cas de CCHFV n'avait été signalé en Europe occidentale. Cependant, les taux élevés de séroprévalence chez les animaux sauvages et la détection de multiples souches du CCHFV chez des tiques en Espagne suggèrent que le cycle enzootique du CCHFV s'est déjà établi dans certaines régions du sud-ouest de l'Europe. Outre la morbidité et la mortalité associées à la FHCC, il n'existe pas d'options thérapeutiques approuvées ni de vaccins homologués aux États-Unis et dans l'UE pour son traitement. Nous discutons ici des aspects éco-épidémiologiques ainsi que des impacts socio-économiques et de santé publique associés à la circulation et aux foyers du FHCC. Nous soulignons également qu'il est maintenant devenu essentiel d'identifier les principaux processus de transmission inter-espèces de ce groupe d'agents pathogènes, de comprendre les mécanismes moléculaires de leur réplication et de définir leur potentiel pathogène.

Nup98 Is Subverted from Annulate Lamellae by Hepatitis C Virus Core Protein to Foster Viral Assembly.

Nup98, an essential component of the nuclear pore that also participates in annulate lamella pore structures localized in the cytosol, is involved in hepatitis C virus (HCV) assembly. Here, we combined confocal microscopy and biochemical assays to study the interplay between Nup98, core (i.e., the HCV capsid protein), and viral genomes. Our results show that in HCV-infected cells, core protein is necessary and sufficient to induce relocalization of Nup98 from annulate lamellae to lipid droplet-apposed areas in which core/NS5A and HCV genomic RNA [(+)RNA] are clustered to promote viral assembly. Furthermore, we found that Nup98 interacts with HCV RNA and that upon Nup98 downregulation, the viral (+)RNA genome was specifically excluded from areas that contain active translating ribosomes and the core and NS5A proteins. Altogether, these results indicate that Nup98 is recruited by HCV core from annulate lamellae to viral assembly sites to locally increase the concentration of (+)RNA genome, which may favor its encapsidation into nascent virions. IMPORTANCE Nup98 is an essential component of the nuclear pore that also participates in annulate lamella pore structures localized in the cytosol. Nup98 is involved in HCV assembly, though its role remains elusive. Here, we show that Nup98 is retrieved from annulate lamellae during HCV infection. We demonstrate that Nup98 interacts with viral genome within infected cells and that these interactions are essential to maintain viral (+)RNAs in subcellular regions promoting viral replication, assembly, and translation. Importantly, we also show that HCV core nucleocapsid protein is the viral component responsible for the retrieval of Nup98 protein from annulate lamellae, hence allowing an enrichment of Nup98 complexed with viral (+)RNAs in core protein-containing areas. Altogether, our results indicate that Nup98 is recruited from annulate lamellae to viral assembly sites by HCV core protein to promote viral assembly, which highlights a novel virus-induced subversion mechanism of nuclear pore complex components.

Efficient adoptive transfer of autologous modified B cells: a new humanized platform mouse model for testing B cells reprogramming therapies.

Here, we report a novel experimental setup to perform adoptive transfer of gene-edited B cells using humanized immune system mice by infusing autologous HIS mouse-derived human B cells "educated" in a murine context and thus rendered tolerant to the host. The present approach presents two advantages over the conventional humanized PBMC mouse models: (i) it circumvents the risk of xenogeneic graft-versus-host reaction and (ii) it mimics more closely human immune responses, thus favoring clinical translation. We show that the frequencies and numbers of transduced B cells in recipient's spleens one week post-transfer are within the range of the size of the pre-immune B cell population specific for a given protein antigen in the mouse. They are also compatible with the B cell numbers required to elicit a sizeable immune response upon immunization. Altogether, our findings pave the way for future studies aiming at assessing therapeutic interventions involving B cell reprogramming for instance by an antibody transgene in a "humanized" hematopoietic setting.

Hepatitis C virus core protein uses triacylglycerols to fold onto the endoplasmic reticulum membrane.

Lipid droplets (LDs) are involved in viral infections, but exactly how remains unclear. Here, we study the hepatitis C virus (HCV) whose core capsid protein binds to LDs but is also involved in the assembly of virions at the endoplasmic reticulum (ER) bilayer. We found that the amphipathic helix-containing domain of core, D2, senses triglycerides (TGs) rather than LDs per se. In the absence of LDs, D2 can bind to the ER membrane but only if TG molecules are present in the bilayer. Accordingly, the pharmacological inhibition of the diacylglycerol O-acyltransferase enzymes, mediating TG synthesis in the ER, inhibits D2 association with the bilayer. We found that TG molecules enable D2 to fold into alpha helices. Sequence analysis reveals that D2 resembles the apoE lipid-binding region. Our data support that TG in LDs promotes the folding of core, which subsequently relocalizes to contiguous ER regions. During this motion, core may carry TG molecules to these regions where HCV lipoviroparticles likely assemble. Consistent with this model, the inhibition of Arf1/COPI, which decreases LD surface accessibility to proteins and ER-LD material exchange, severely impedes the assembly of virions. Altogether, our data uncover a critical function of TG in the folding of core and HCV replication and reveals, more broadly, how TG accumulation in the ER may provoke the binding of soluble amphipathic helix-containing proteins to the ER bilayer.

Structural basis of synergistic neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies.

Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread tick-borne zoonotic virus, with a 30% case fatality rate in humans. Structural information is lacking in regard to the CCHFV membrane fusion glycoprotein Gc­the main target of the host neutralizing antibody response­as well as antibody­mediated neutralization mechanisms. We describe the structure of prefusion Gc bound to the antigen-binding fragments (Fabs) of two neutralizing antibodies that display synergy when combined, as well as the structure of trimeric, postfusion Gc. The structures show the two Fabs acting in concert to block membrane fusion, with one targeting the fusion loops and the other blocking Gc trimer formation. The structures also revealed the neutralization mechanism of previously reported antibodies against CCHFV, providing the molecular underpinnings essential for developing CCHFV­specific medical countermeasures for epidemic preparedness.

Baboon Envelope Pseudotyped "Nanoblades" Carrying Cas9/gRNA Complexes Allow Efficient Genome Editing in Human T, B, and CD34+ Cells and Knock-in of AAV6-Encoded Donor DNA in CD34+ Cells.

Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into human blood cells can be challenging. Here, we have utilized "nanoblades," a new technology that delivers a genomic cleaving agent into cells. These are modified murine leukemia virus (MLV) or HIV-derived virus-like particle (VLP), in which the viral structural protein Gag has been fused to Cas9. These VLPs are thus loaded with Cas9 protein complexed with the guide RNAs. Highly efficient gene editing was obtained in cell lines, IPS and primary mouse and human cells. Here, we showed that nanoblades were remarkably efficient for entry into human T, B, and hematopoietic stem and progenitor cells (HSPCs) thanks to their surface co-pseudotyping with baboon retroviral and VSV-G envelope glycoproteins. A brief incubation of human T and B cells with nanoblades incorporating two gRNAs resulted in 40 and 15% edited deletion in the Wiskott-Aldrich syndrome (WAS) gene locus, respectively. CD34+ cells (HSPCs) treated with the same nanoblades allowed 30-40% exon 1 drop-out in the WAS gene locus. Importantly, no toxicity was detected upon nanoblade-mediated gene editing of these blood cells. Finally, we also treated HSPCs with nanoblades in combination with a donor-encoding rAAV6 vector resulting in up to 40% of stable expression cassette knock-in into the WAS gene locus. Summarizing, this new technology is simple to implement, shows high flexibility for different targets including primary immune cells of human and murine origin, is relatively inexpensive and therefore gives important prospects for basic and clinical translation in the area of gene therapy.

Immunogenicity and efficacy of          heterologous ChAdOx1-BNT162b2 vaccination.

Following severe adverse reactions to the AstraZeneca ChAdOx1-S-nCoV-19 vaccine1,2, European health authorities recommended that patients under the age of 55 years who received one dose of ChAdOx1-S-nCoV-19 receive a second dose of the Pfizer BNT162b2 vaccine as a booster. However, the effectiveness and the immunogenicity of this vaccination regimen have not been formally tested. Here we show that the heterologous ChAdOx1-S-nCoV-19 and BNT162b2 combination confers better protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection than the homologous BNT162b2 and BNT162b2 combination in a real-world observational study of healthcare workers (n = 13,121). To understand the underlying mechanism, we conducted a longitudinal survey of the anti-spike immunity conferred by each vaccine combination. Both combinations induced strong anti-spike antibody responses, but sera from heterologous vaccinated individuals displayed a stronger neutralizing activity regardless of the SARS-CoV-2 variant. This enhanced neutralizing potential correlated with increased frequencies of switched and activated memory B cells that recognize the SARS-CoV-2 receptor binding domain. The ChAdOx1-S-nCoV-19 vaccine induced a weaker IgG response but a stronger T cell response than the BNT162b2 vaccine after the priming dose, which could explain the complementarity of both vaccines when used in combination. The heterologous vaccination regimen could therefore be particularly suitable for immunocompromised individuals.

Exploiting B Cell Transfer for Cancer Therapy: Engineered B Cells to Eradicate Tumors.

Nowadays, cancers still represent a significant health burden, accounting for around 10 million deaths per year, due to ageing populations and inefficient treatments for some refractory cancers. Immunotherapy strategies that modulate the patient's immune system have emerged as good treatment options. Among them, the adoptive transfer of B cells selected ex vivo showed promising results, with a reduction in tumor growth in several cancer mouse models, often associated with antitumoral immune responses. Aside from the benefits of their intrinsic properties, including antigen presentation, antibody secretion, homing and long-term persistence, B cells can be modified prior to reinfusion to increase their therapeutic role. For instance, B cells have been modified mainly to boost their immuno-stimulatory activation potential by forcing the expression of costimulatory ligands using defined culture conditions or gene insertion. Moreover, tumor-specific antigen presentation by infused B cells has been increased by ex vivo antigen loading (peptides, RNA, DNA, virus) or by the sorting/ engineering of B cells with a B cell receptor specific to tumor antigens. Editing of the BCR also rewires B cell specificity toward tumor antigens, and may trigger, upon antigen recognition, the secretion of antitumor antibodies by differentiated plasma cells that can then be recognized by other immune components or cells involved in tumor clearance by antibody-dependent cell cytotoxicity or complement-dependent cytotoxicity for example. With the expansion of gene editing methodologies, new strategies to reprogram immune cells with whole synthetic circuits are being explored: modified B cells can sense disease-specific biomarkers and, in response, trigger the expression of therapeutic molecules, such as molecules that counteract the tumoral immunosuppressive microenvironment. Such strategies remain in their infancy for implementation in B cells, but are likely to expand in the coming years.

Report of One-Year Prospective Surveillance of SARS-CoV-2 in Dogs and Cats in France with Various Exposure Risks: Confirmation of a Low Prevalence of Shedding, Detection and Complete Sequencing of an Alpha Variant in a Cat.

Despite the probable zoonotic origin of SARS-CoV-2, only limited research efforts have been made to understand the role of companion animals in SARS-CoV-2 epidemiology. According to recent serological prevalence studies, human-to-companion animal transmission is quite frequent, which led us to consider that the risk of SARS-CoV-2 transmission from animal to human, albeit negligible in the present context, may have been underestimated. In this study, we provide the results of a prospective survey that was conducted to evaluate the SARS-CoV-2 isolation rate by qRT-PCR in dogs and cats with different exposure risks and clinical statuses. From April 2020 to April 2021, we analyzed 367 samples and investigated the presence of SARS-CoV-2 RNA using qRT-PCR. Only four animals tested positive, all of them being cats. Three cats were asymptomatic and one presented a coryza-like syndrome. We describe in detail the infection in two cats and the associated clinical characteristics. Importantly, we obtained SARS-CoV-2 genomes from one infected animal and characterized them as Alpha variants. This represents the first identification of the SARS-CoV-2 Alpha variant in an infected animal in France.

Evidence for long-term association of virion-delivered HBV core protein with cccDNA independently of viral protein production.

BACKGROUND & AIMS: HBV persists in the nucleus of infected hepatocytes as a covalently closed circular DNA (cccDNA) episome that constitutes the template for viral RNA and protein synthesis. Both HBx and HBc (core) viral proteins associate with cccDNA but, while HBx is required for viral transcription, the role of HBc is still unclear. The aim of this study was to determine if HBc derived from incoming nucleocapsid can associate with cccDNA before the onset of viral transcription and protein production. METHODS: Chromatin immunoprecipitation assays were performed in native conditions. In addition, differentiated HepaRG (dHepaRG) cells infected with HBx-deficient HBV were used to investigate if HBc delivered by incoming virions can associate with cccDNA. RESULTS: Our results indicate that HBc can associate with cccDNA in the absence of viral transcription and de novo protein synthesis. In dHepaRG cells, this association is stable for at least 6 weeks. CONCLUSION: These results suggest that virion-delivered HBc may participate at an early stage of cccDNA formation and/or transcription. LAY SUMMARY: The hepatitis B virus genome is released into the nucleoplasm of infected cells after disassembly of the viral nucleocapsids at the nuclear membrane. Herein, we show for the first time that virion-delivered hepatitis B core protein, a component of the viral capsid, can stably associate with integrated viral DNA.

HDV-Like Viruses.

Hepatitis delta virus (HDV) is a defective human virus that lacks the ability to produce its own envelope proteins and is thus dependent on the presence of a helper virus, which provides its surface proteins to produce infectious particles. Hepatitis B virus (HBV) was so far thought to be the only helper virus described to be associated with HDV. However, recent studies showed that divergent HDV-like viruses could be detected in fishes, birds, amphibians, and invertebrates, without evidence of any HBV-like agent supporting infection. Another recent study demonstrated that HDV can be transmitted and propagated in experimental infections ex vivo and in vivo by different enveloped viruses unrelated to HBV, including hepatitis C virus (HCV) and flaviviruses such as Dengue and West Nile virus. All this new evidence, in addition to the identification of novel virus species within a large range of hosts in absence of HBV, suggests that deltaviruses may take advantage of a large spectrum of helper viruses and raises questions about HDV origins and evolution.

A fusion peptide in preS1 and the human protein disulfide isomerase ERp57 are involved in hepatitis B virus membrane fusion process.

Cell entry of enveloped viruses relies on the fusion between the viral and plasma or endosomal membranes, through a mechanism that is triggered by a cellular signal. Here we used a combination of computational and experimental approaches to unravel the main determinants of hepatitis B virus (HBV) membrane fusion process. We discovered that ERp57 is a host factor critically involved in triggering HBV fusion and infection. Then, through modeling approaches, we uncovered a putative allosteric cross-strand disulfide (CSD) bond in the HBV S glycoprotein and we demonstrate that its stabilization could prevent membrane fusion. Finally, we identified and characterized a potential fusion peptide in the preS1 domain of the HBV L glycoprotein. These results underscore a membrane fusion mechanism that could be triggered by ERp57, allowing a thiol/disulfide exchange reaction to occur and regulate isomerization of a critical CSD, which ultimately leads to the exposition of the fusion peptide.

Host Cell Restriction Factors of Bunyaviruses and Viral Countermeasures.

The Bunyavirales order comprises more than 500 viruses (generally defined as bunyaviruses) classified into 12 families. Some of these are highly pathogenic viruses infecting different hosts, including humans, mammals, reptiles, arthropods, birds, and/or plants. Host cell sensing of infection activates the innate immune system that aims at inhibiting viral replication and propagation. Upon recognition of pathogen-associated molecular patterns (PAMPs) by cellular pattern recognition receptors (PRRs), numerous signaling cascades are activated, leading to the production of interferons (IFNs). IFNs act in an autocrine and paracrine manner to establish an antiviral state by inducing the expression of hundreds of IFN-stimulated genes (ISGs). Some of these ISGs are known to restrict bunyavirus infection. Along with other constitutively expressed host cellular factors with antiviral activity, these proteins (hereafter referred to as "restriction factors") target different steps of the viral cycle, including viral entry, genome transcription and replication, and virion egress. In reaction to this, bunyaviruses have developed strategies to circumvent this antiviral response, by avoiding cellular recognition of PAMPs, inhibiting IFN production or interfering with the IFN-mediated response. Herein, we review the current knowledge on host cellular factors that were shown to restrict infections by bunyaviruses. Moreover, we focus on the strategies developed by bunyaviruses in order to escape the antiviral state developed by the infected cells.

Massive clonal expansion of polycytotoxic skin and blood CD8+ T cells in patients with toxic epidermal necrolysis.

Toxic epidermal necrolysis (TEN) is a life-threatening cutaneous adverse drug reaction. To better understand why skin symptoms are so severe, we conducted a prospective immunophenotyping study on skin and blood. Mass cytometry results confirmed that effector memory polycytotoxic CD8+ T cells (CTLs) are the main leucocytes in TEN blisters at the acute phase. Deep T cell receptor (TCR) repertoire sequencing identified massive expansion of unique CDR3 clonotypes in blister cells. The same clones were highly expanded in patient's blood, and the degree of their expansion showed significant correlation with disease severity. By transducing α and ß chains of the expanded clonotypes into a TCR-defective cell line, we confirmed that those cells were drug specific. Collectively, these results suggest that the relative clonal expansion and phenotype of skin-recruited CTLs condition the clinical presentation of cutaneous adverse drug reactions.