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Since the early 2000’, regulation agencies have encouraged viral vaccine manufacturers to implement in-process and real-time monitoring tools in production processes. Even if more assays have been recently developed, none of the novel viral particle quantification technologies can monitor virus levels and their secretion kinetics within production vessels. Vaccine manufacturers still rely on offline cell-based infectivity assays and antigen amount quantification to monitor their processes. The present study describes the development of the first automated biosensor for at-line monitoring of influenza virus production. It involves coupling a fetuin-based SPRi quantitative biosensor with an automated sampler of culture broth and a consecutive clarification setup via an acoustic filter. The SPRi response of different viral strains produced in two distinct cell production platforms was qualified. We demonstrated that fetuin-based quantitative SPRi is a robust, potency-indicating, and universal analytical technology for quantifying bioactive influenza virus particles. It was validated with both purified and complex matrices. Finally, an influenza viral production kinetic was monitoredonlinefor three days. This novel online tool enabled the access in real-time to total bioactive viral particles from early production phases (8hpi).

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first identified in late 2019, has caused a worldwide pandemic with unprecedented economic and societal impact. Currently, several vaccines are available, and multitudes of antiviral treatments have been proposed and tested. Although many of the vaccines show high clinical efficacy, they are not equally accessible worldwide. Additionally, due to the continuous emergence of new virus variants, and generally short duration of immunity, the development of safe and effective antiviral treatments remains of the utmost importance. Since the emergence of SARS-CoV-2, substantial efforts have been undertaken to repurpose existing and approved drugs for accelerated clinical testing and potential emergency use authorizations. However, drug-repurposing using high throughput screenings in cellular assays, often identify hits that later prove ineffective in clinical studies. Our approach was to evaluate the activity of compounds that have either been tested clinically or already undergone extensive preclinical profiling, using a standardized in vitro model of human nasal epithelium. Secondly, we evaluated drug combinations using sub-maximal doses of each active single compound. Here, we report the antiviral effects of 95 single compounds and 30 combinations. The data show that selected drug combinations including 10 μM of molnupiravir, a viral RNA-dependent RNA polymerase (RdRp) inhibitor, effectively inhibit SARS-CoV-2 replication. This indicates that such combinations are worthy of further evaluation as potential treatment strategies against coronavirus disease 2019 (COVID-19).

Human metapneumovirus (HMPV) is a major pediatric respiratory pathogen for which there is currently no specific treatment or licensed vaccine. Different strategies have been evaluated to prevent this infection, including the use of live-attenuated vaccines (LAVs). However, further development of LAV approaches is often hampered by the lack of highly efficient and scalable cell-based production systems that support worldwide vaccine production. In this context, avian cell lines cultivated in suspension are currently competing with traditional cell platforms used for viral vaccine manufacturing. We investigated whether the DuckCelt®-T17 avian cell line (Vaxxel) we previously described as an efficient production system for several influenza strains could also be used to produce a new HMPV LAV candidate (Metavac®), an engineered SH gene-deleted mutant of the A1/C-85473 strain of HMPV. To that end, we characterized the operational parameters of multiplicity of infection (MOI), cell density, and trypsin addition to achieve optimal production of the LAV Metavac® in the DuckCelt®-T17 cell line platform. We demonstrated that the DuckCelt®-T17 cell line is permissive and is well adapted to the production of the wild-type A1/C-85473 HMPV and the Metavac® vaccine candidate. Moreover, our results confirmed that the LAV candidate produced in DuckCelt®-T17 cells conserves its advantageous replication properties in LLC-MK2 and 3D-reconstituted human airway epithelium models, as well as its capacity to induce efficient neutralizing antibodies in a mouse model. Our results suggest that the DuckCelt®-T17 avian cell line is a very promising platform for scalable in-suspension serum-free production of the HMPV-based LAV candidate Metavac®.

Influenza A viruses (IAV) are known to modulate and "hijack" several cellular host mechanisms, including gene splicing and RNA maturation machineries. These modulations alter host cellular responses and enable an optimal expression of viral products throughout infection. The interplay between the host protein p53 and IAV, in particular through the viral nonstructural protein NS1, has been shown to be supportive for IAV replication. However, it remains unknown whether alternatively spliced isoforms of p53, known to modulate p53 transcriptional activity, are affected by IAV infection and contribute to IAV replication. Using a TP53 minigene, which mimics intron 9 alternative splicing, we have shown here that the NS1 protein of IAV changes the expression pattern of p53 isoforms. Our results demonstrate that CPSF4 (cellular protein cleavage and polyadenylation specificity factor 4) independently and the interaction between NS1 and CPSF4 modulate the alternative splicing of TP53 transcripts, which may result in the differential activation of p53-responsive genes. Finally, we report that CPSF4 and most likely beta and gamma spliced p53 isoforms affect both viral replication and IAV-associated type I interferon secretion. All together, our data show that cellular p53 and CPSF4 factors, both interacting with viral NS1, have a crucial role during IAV replication that allows IAV to interact with and alter the expression of alternatively spliced p53 isoforms in order to regulate the cellular innate response, especially via type I interferon secretion, and perform efficient viral replication.IMPORTANCE Influenza A viruses (IAV) constitute a major public health issue, causing illness and death in high-risk populations during seasonal epidemics or pandemics. IAV are known to modulate cellular pathways to promote their replication and avoid immune restriction via the targeting of several cellular proteins. One of these proteins, p53, is a master regulator involved in a large panel of biological processes, including cell cycle arrest, apoptosis, or senescence. This "cellular gatekeeper" is also involved in the control of viral infections, and viruses have developed a wide diversity of mechanisms to modulate/hijack p53 functions to achieve an optimal replication in their hosts. Our group and others have previously shown that p53 activity is finely modulated by different multilevel mechanisms during IAV infection. Here, we characterized IAV nonstructural protein NS1 and the cellular factor CPSF4 as major partners involved in the IAV-induced modulation of the TP53 alternative splicing that was associated with a strong modulation of p53 activity and notably the p53-mediated antiviral response.

Influenza A viruses (IAV) are known to modulate and “hijack” several cellular host mechanisms, including gene splicing and RNA maturation machineries. These modulations alter host cellular responses and enable an optimal expression of viral products throughout infection. The interplay between the host protein p53 and IAV, in particular through the viral nonstructural protein NS1, has been shown to be supportive for IAV replication. However, it remains unknown whether alternatively spliced isoforms of p53, known to modulate p53 transcriptional activity, are affected by IAV infection and contribute to IAV replication. Using a TP53 minigene, which mimics intron 9 alternative splicing, we have shown here that the NS1 protein of IAV changes the expression pattern of p53 isoforms. Our results demonstrate that CPSF4 (cellular protein cleavage and polyadenylation specificity factor 4) independently and the interaction between NS1 and CPSF4 modulate the alternative splicing of TP53 transcripts, which may result in the differential activation of p53-responsive genes. Finally, we report that CPSF4 and most likely beta and gamma spliced p53 isoforms affect both viral replication and IAV-associated type I interferon secretion. All together, our data show that cellular p53 and CPSF4 factors, both interacting with viral NS1, have a crucial role during IAV replication that allows IAV to interact with and alter the expression of alternatively spliced p53 isoforms in order to regulate the cellular innate response, especially via type I interferon secretion, and perform efficient viral replication. IMPORTANCE Influenza A viruses (IAV) constitute a major public health issue, causing illness and death in high-risk populations during seasonal epidemics or pandemics. IAV are known to modulate cellular pathways to promote their replication and avoid immune restriction via the targeting of several cellular proteins. One of these proteins, p53, is a master regulator involved in a large panel of biological processes, including cell cycle arrest, apoptosis, or senescence. This “cellular gatekeeper” is also involved in the control of viral infections, and viruses have developed a wide diversity of mechanisms to modulate/hijack p53 functions to achieve an optimal replication in their hosts. Our group and others have previously shown that p53 activity is finely modulated by different multilevel mechanisms during IAV infection. Here, we characterized IAV nonstructural protein NS1 and the cellular factor CPSF4 as major partners involved in the IAV-induced modulation of the TP53 alternative splicing that was associated with a strong modulation of p53 activity and notably the p53-mediated antiviral response.

Summary In the current COVID-19 pandemic context, proposing and validating effective treatments represents a major challenge. However, the scarcity of biologically relevant pre-clinical models of SARS-CoV-2 infection imposes a significant barrier for scientific and medical progress, including the rapid transition of potentially effective treatments to the clinical setting. We use reconstituted human airway epithelia to isolate and then characterize the viral infection kinetics, tissue-level remodeling of the cellular ultrastructure, and transcriptional early immune signatures induced by SARS-CoV-2 in a physiologically relevant model. Our results emphasize distinctive transcriptional immune signatures between nasal and bronchial HAE, both in terms of kinetics and intensity, hence suggesting putative intrinsic differences in the early response to SARS-CoV-2 infection. Most important, we provide evidence in human-derived tissues on the antiviral efficacy of remdesivir monotherapy and explore the potential of the remdesivir-diltiazem combination as an option worthy of further investigation to respond to the still-unmet COVID-19 medical need., Graphical Abstract, Highlights We use reconstituted human airway epithelia to characterize SARS-CoV-2 infection kinetics SARS-CoV-2 induces characteristic remodeling of the respiratory epithelium cellular ultrastructure SARS-CoV-2 induces differential early immune responses in nasal and bronchial HAE We evaluate the antiviral activity of remdesivir and remdesivir-diltiazem in both Vero E6 and HAE models, Pizzorno et al. report the characterization of SARS-CoV-2 infection, tissue-level remodeling of cellular ultrastructure, and transcriptional immune signatures using a model of reconstituted human airway epithelia. This model was advantageously used to evaluate the antiviral activity of remdesivir or a combination of remdesivir-diltiazem against SARS-CoV-2.