Blandine Monel

Bio: Blandine Monel is an academic researcher from Pasteur Institute. The author has contributed to research in topics: Viral replication & Virus. The author has an hindex of 7, co-authored 12 publications receiving 348 citations. Previous affiliations of Blandine Monel include Centre national de la recherche scientifique.

Syncytia formation by SARS-CoV-2-infected cells.

Abstract: Severe cases of COVID-19 are associated with extensive lung damage and the presence of infected multinucleated syncytial pneumocytes. The viral and cellular mechanisms regulating the formation of these syncytia are not well understood. Here, we show that SARS-CoV-2-infected cells express the Spike protein (S) at their surface and fuse with ACE2-positive neighboring cells. Expression of S without any other viral proteins triggers syncytia formation. Interferon-induced transmembrane proteins (IFITMs), a family of restriction factors that block the entry of many viruses, inhibit S-mediated fusion, with IFITM1 being more active than IFITM2 and IFITM3. On the contrary, the TMPRSS2 serine protease, which is known to enhance infectivity of cell-free virions, processes both S and ACE2 and increases syncytia formation by accelerating the fusion process. TMPRSS2 thwarts the antiviral effect of IFITMs. Our results show that SARS-CoV-2 pathological effects are modulated by cellular proteins that either inhibit or facilitate syncytia formation.

Syncytia formation by SARS-CoV-2 infected cells

Abstract: Severe cases of COVID-19 are associated with extensive lung damage and the presence of infected multinucleated syncytial pneumocytes. The viral and cellular mechanisms regulating the formation of these syncytia are not well understood. Here, we show that SARS-CoV-2 infected cells express the viral Spike protein (S) at their surface and fuse with ACE2-positive neighbouring cells. Expression of S without any other viral proteins triggers syncytia formation. Type-I interferon (IFN)-induced transmembrane proteins (IFITMs), a family of restriction factors that block the entry of many viruses, inhibit S-mediated fusion, with IFITM1 being more active than IFITM2 and IFITM3. On the contrary, the TMPRSS2 serine protease, which is known to enhance infectivity of cell-free virions, processes both S and ACE2 and increases syncytia formation by accelerating the fusion process. TMPRSS2 thwarts the antiviral effect of IFITMs. Our results show that the pathological effects of SARS-CoV-2 are modulated by cellular proteins that either inhibit or facilitate syncytia formation.

Drug-induced phospholipidosis confounds drug repurposing for SARS-CoV-2.

Abstract: Repurposing drugs as treatments for COVID-19, the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has drawn much attention. Beginning with sigma receptor ligands and expanding to other drugs from screening in the field, we became concerned that phospholipidosis was a shared mechanism underlying the antiviral activity of many repurposed drugs. For all of the 23 cationic amphiphilic drugs we tested, including hydroxychloroquine, azithromycin, amiodarone, and four others already in clinical trials, phospholipidosis was monotonically correlated with antiviral efficacy. Conversely, drugs active against the same targets that did not induce phospholipidosis were not antiviral. Phospholipidosis depends on the physicochemical properties of drugs and does not reflect specific target-based activities-rather, it may be considered a toxic confound in early drug discovery. Early detection of phospholipidosis could eliminate these artifacts, enabling a focus on molecules with therapeutic potential.

Zika virus induces massive cytoplasmic vacuolization and paraptosis-like death in infected cells.

Abstract: The cytopathic effects of Zika virus (ZIKV) are poorly characterized. Innate immunity controls ZIKV infection and disease in most infected patients through mechanisms that remain to be understood. Here, we studied the morphological cellular changes induced by ZIKV and addressed the role of interferon‐induced transmembrane proteins (IFITM), a family of broad‐spectrum antiviral factors, during viral replication. We report that ZIKV induces massive vacuolization followed by “implosive” cell death in human epithelial cells, primary skin fibroblasts and astrocytes, a phenomenon which is exacerbated when IFITM3 levels are low. It is reminiscent of paraptosis, a caspase‐independent, non‐apoptotic form of cell death associated with the formation of large cytoplasmic vacuoles. We further show that ZIKV‐induced vacuoles are derived from the endoplasmic reticulum (ER) and dependent on the PI3K/Akt signaling axis. Inhibiting the Sec61 ER translocon in ZIKV‐infected cells blocked vacuole formation and viral production. Our results provide mechanistic insight behind the ZIKV‐induced cytopathic effect and indicate that IFITM3, by acting as a gatekeeper for incoming virus, restricts virus takeover of the ER and subsequent cell death.

Remodeling of the Core Leads HIV-1 Preintegration Complex into the Nucleus of Human Lymphocytes.

Abstract: Retroviral replication proceeds through obligate integration of the viral DNA into the host genome. In particular, for the HIV-1 genome to enter the nucleus, it must be led through the nuclear pore complex (NPC). During the HIV-1 cytoplasmic journey, the viral core acts as a shell to protect the viral genetic material from antiviral sensors and ensure an adequate environment for reverse transcription. However, the relatively narrow size of the nuclear pore channel requires that the HIV-1 core is reshaped into a structure that fits the pore. On the other hand, the organization of the viral CA proteins that remain associated with the preintegration complex (PIC) during and after nuclear translocation is still enigmatic. In this study, we analyzed the progressive organizational changes of viral CA proteins within the cytoplasm and the nucleus by immunogold labeling. Furthermore, we set up a novel technology, HIV-1 ANCHOR, which enables the specific detection of the retrotranscribed DNA by fluorescence microscopy, thereby offering the opportunity to uncover the architecture of the potential HIV-1 PIC. Thus, we combined the immunoelectron microscopy and ANCHOR technologies to reveal the presence of DNA- and CA-positive complexes by correlated light and electron microscopy (CLEM). During and after nuclear translocation, HIV-1 appears as a complex of viral DNA decorated by multiple viral CA proteins remodeled in a pearl necklace-like shape. Thus, we could describe how CA proteins are reshaped around the viral DNA to permit the entrance of the HIV-1 in the nucleus. This particular CA protein complex composed of the integrase and the retrotranscribed DNA leads the HIV-1 genome inside the host nucleus. Our findings contribute to the understanding of the early steps of HIV-1 infection and provide new insights into the organization of HIV-1 CA proteins during and after viral nuclear entry. Of note, we are now able to visualize the viral DNA in viral complexes, opening up new perspectives for future studies on virus's fate in the cell nucleus.IMPORTANCE How the reverse-transcribed genome reaches the host nucleus remains a main open question related to the infectious cycle of HIV-1. The HIV-1 core has a size of ∼100 nm, largely exceeding that of the NPC channel (∼39 nm). Thus, a rearrangement of the viral CA protein organization is required to achieve an effective nuclear translocation. The mechanism of this process remains undefined due to the lack of a technology capable of visualizing potential CA subcomplexes in association with the viral DNA in the nucleus of HIV-1-infected cells. By the means of state-of-the-art technologies (HIV-1 ANCHOR system combined with CLEM), our study shows that remodeled viral complexes retain multiple CA proteins but not an intact core or only a single CA monomer. These viral CA complexes associated with the retrotranscribed DNA can be observed inside the nucleus, and they represent a potential PIC. Thus, our study shed light on critical early steps characterizing HIV-1 infection, thereby revealing novel, therapeutically exploitable points of intervention. Furthermore, we developed and provided a powerful tool enabling direct, specific, and high-resolution visualization of intracellular and intranuclear HIV-1 subviral structures.

Reduced sensitivity of SARS-CoV-2 variant Delta to antibody neutralization.

Abstract: The SARS-CoV-2 B.1.617 lineage was identified in October 2020 in India1–5. Since then, it has become dominant in some regions of India and in the UK, and has spread to many other countries6. The lineage includes three main subtypes (B1.617.1, B.1.617.2 and B.1.617.3), which contain diverse mutations in the N-terminal domain (NTD) and the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein that may increase the immune evasion potential of these variants. B.1.617.2—also termed the Delta variant—is believed to spread faster than other variants. Here we isolated an infectious strain of the Delta variant from an individual with COVID-19 who had returned to France from India. We examined the sensitivity of this strain to monoclonal antibodies and to antibodies present in sera from individuals who had recovered from COVID-19 (hereafter referred to as convalescent individuals) or who had received a COVID-19 vaccine, and then compared this strain with other strains of SARS-CoV-2. The Delta variant was resistant to neutralization by some anti-NTD and anti-RBD monoclonal antibodies, including bamlanivimab, and these antibodies showed impaired binding to the spike protein. Sera collected from convalescent individuals up to 12 months after the onset of symptoms were fourfold less potent against the Delta variant relative to the Alpha variant (B.1.1.7). Sera from individuals who had received one dose of the Pfizer or the AstraZeneca vaccine had a barely discernible inhibitory effect on the Delta variant. Administration of two doses of the vaccine generated a neutralizing response in 95% of individuals, with titres three- to fivefold lower against the Delta variant than against the Alpha variant. Thus, the spread of the Delta variant is associated with an escape from antibodies that target non-RBD and RBD epitopes of the spike protein. The SARS-CoV-2 Delta variant partially evades neutralization by several monoclonal antibodies and by sera from individuals who have had COVID-19, but two doses of anti-COVID-19 vaccines still generate a strong neutralizing response.

SARS-CoV-2 B.1.617.2 Delta variant replication and immune evasion.

Abstract: The B.1.617.2 (Delta) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in the state of Maharashtra in late 2020 and spread throughout India, outcompeting pre-existing lineages including B.1.617.1 (Kappa) and B.1.1.7 (Alpha)1. In vitro, B.1.617.2 is sixfold less sensitive to serum neutralizing antibodies from recovered individuals, and eightfold less sensitive to vaccine-elicited antibodies, compared with wild-type Wuhan-1 bearing D614G. Serum neutralizing titres against B.1.617.2 were lower in ChAdOx1 vaccinees than in BNT162b2 vaccinees. B.1.617.2 spike pseudotyped viruses exhibited compromised sensitivity to monoclonal antibodies to the receptor-binding domain and the amino-terminal domain. B.1.617.2 demonstrated higher replication efficiency than B.1.1.7 in both airway organoid and human airway epithelial systems, associated with B.1.617.2 spike being in a predominantly cleaved state compared with B.1.1.7 spike. The B.1.617.2 spike protein was able to mediate highly efficient syncytium formation that was less sensitive to inhibition by neutralizing antibody, compared with that of wild-type spike. We also observed that B.1.617.2 had higher replication and spike-mediated entry than B.1.617.1, potentially explaining the B.1.617.2 dominance. In an analysis of more than 130 SARS-CoV-2-infected health care workers across three centres in India during a period of mixed lineage circulation, we observed reduced ChAdOx1 vaccine effectiveness against B.1.617.2 relative to non-B.1.617.2, with the caveat of possible residual confounding. Compromised vaccine efficacy against the highly fit and immune-evasive B.1.617.2 Delta variant warrants continued infection control measures in the post-vaccination era.

IgA dominates the early neutralizing antibody response to SARS-CoV-2.

Abstract: Humoral immune responses are typically characterized by primary IgM antibody responses followed by secondary antibody responses associated with immune memory and comprised of of IgG, IgA and IgE. Here we measured acute humoral responses to SARS-CoV-2, including the frequency of antibody-secreting cells and the presence of SARS-CoV-2-specific neutralizing antibodies in the serum, saliva and broncho-alveolar fluid of 159 patients with COVID-19. Early SARS-CoV-2-specific humoral responses were dominated by IgA antibodies. Peripheral expansion of IgA plasmablasts with mucosal-homing potential was detected shortly after the onset of symptoms and peaked during the third week of the disease. The virus-specific antibody responses included IgG, IgM and IgA, but IgA contributed to virus neutralization to a greater extent compared with IgG. Specific IgA serum concentrations decreased notably one month after the onset of symptoms, but neutralizing IgA remained detectable in saliva for a longer time (days 49 to 73 post symptoms). These results represent a critical observation given the emerging information as to the types of antibodies associated with optimal protection against re-infection, and whether vaccine regimens should consider targeting a potent but potentially short-lived IgA response.

Sensitivity of infectious SARS-CoV-2 B.1.1.7 and B.1.351 variants to neutralizing antibodies.

Abstract: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.7 and B.1.351 variants were first identified in the United Kingdom and South Africa, respectively, and have since spread to many countries. These variants harboring diverse mutations in the gene encoding the spike protein raise important concerns about their immune evasion potential. Here, we isolated infectious B.1.1.7 and B.1.351 strains from acutely infected individuals. We examined sensitivity of the two variants to SARS-CoV-2 antibodies present in sera and nasal swabs from individuals infected with previously circulating strains or who were recently vaccinated, in comparison with a D614G reference virus. We utilized a new rapid neutralization assay, based on reporter cells that become positive for GFP after overnight infection. Sera from 58 convalescent individuals collected up to 9 months after symptoms, similarly neutralized B.1.1.7 and D614G. In contrast, after 9 months, convalescent sera had a mean sixfold reduction in neutralizing titers, and 40% of the samples lacked any activity against B.1.351. Sera from 19 individuals vaccinated twice with Pfizer Cominarty, longitudinally tested up to 6 weeks after vaccination, were similarly potent against B.1.1.7 but less efficacious against B.1.351, when compared to D614G. Neutralizing titers increased after the second vaccine dose, but remained 14-fold lower against B.1.351. In contrast, sera from convalescent or vaccinated individuals similarly bound the three spike proteins in a flow cytometry-based serological assay. Neutralizing antibodies were rarely detected in nasal swabs from vaccinees. Thus, faster-spreading SARS-CoV-2 variants acquired a partial resistance to neutralizing antibodies generated by natural infection or vaccination, which was most frequently detected in individuals with low antibody levels. Our results indicate that B1.351, but not B.1.1.7, may increase the risk of infection in immunized individuals.