Human coronaviruses activate and hijack the host transcription factor HSF1 to enhance viral replication.

Organisms respond to proteotoxic-stress by activating the heat-shock response, a cellular defense mechanism regulated by a family of heat-shock factors (HSFs); among six human HSFs, HSF1 acts as a proteostasis guardian regulating severe stress-driven transcriptional responses. Herein we show that human coronaviruses (HCoV), both low-pathogenic seasonal-HCoVs and highly-pathogenic SARS-CoV-2 variants, are potent inducers of HSF1, promoting HSF1 serine-326 phosphorylation and triggering a powerful and distinct HSF1-driven transcriptional-translational response in infected cells. Despite the coronavirus-mediated shut-down of the host translational machinery, selected HSF1-target gene products, including HSP70, HSPA6 and AIRAP, are highly expressed in HCoV-infected cells. Using silencing experiments and a direct HSF1 small-molecule inhibitor we show that, intriguingly, HCoV-mediated activation of the HSF1-pathway, rather than representing a host defense response to infection, is hijacked by the pathogen and is essential for efficient progeny particles production. The results open new scenarios for the search of innovative antiviral strategies against coronavirus infections.

An Interesting Case of Coronavirus NL63 Encephalitis Diagnosed in a 14-Year-Old Immunocompetent Female: A Case Report and Literature Review.

Human coronavirus NL63 (HCoV-NL63) belongs to the human coronavirus family but is distinct from other common coronaviruses such as HCoV-043, HCoV-229E, and SARS-CoV-1 and SARS-CoV-2 viruses. It causes a mild upper respiratory tract infection, affecting children and adults. The usual symptoms associated with the HCoV-NL63 infection are vomiting, a runny nose, and a sore throat. In vivo, HCoV-NL63 showed neurotropism as it can be detected in the CSF, through which it disseminates into the brain and the spinal column. Herein, we describe the case of a 14-year-old female patient who initially presented with disorientation and a drop in consciousness level and was admitted as a case of encephalitis to the pediatric intensive care unit.

Structural basis for the inhibition of the HCoV-NL63 main protease Mpro by X77.

Human coronaviruses are a group of pathogens that primarily cause respiratory and intestinal diseases. Infection can easily cause respiratory symptoms, as well as a variety of serious complications. There are several types of human coronaviruses, such as SARS-CoV, MERS-CoV, HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, and SARS-CoV-2. The prevalence of COVID-19 has led to a growing focus on drug research against human coronaviruses. The main protease (Mpro) from human coronaviruses is a relatively conserved that controls viral replication. X77 was discovered to have extremely high inhibitory activity against SARS-CoV-2 Mpro through the use of computer-simulated docking. In this paper, we have resolved the crystal structure of the HCoV-NL63 Mpro complexed with X77 and analyzed their interaction in detail. This data provides essential information for solving their binding modes and their structural determinants. Then, we compared the binding modes of X77 with SARS-CoV-2 Mpro and HCoV-NL63 Mpro in detail. This study illustrates the structural basis of HCoV-NL63 Mpro binding to the inhibitor X77. The structural insights derived from this study will inform the development of new drugs with broad-spectrum resistance to human coronaviruses.

Influenza-like illness symptoms due to endemic human coronavirus reinfections are not influenced by the length of the interval separating reinfections.

After 3 years of its introduction to humans, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been declared as endemic. Little is known about the severity of the disease manifestation that future infections may cause, especially when reinfections occur after humoral immunity from a previous infection or vaccination has waned. Such knowledge could inform policymakers regarding the frequency of vaccination. Reinfections by endemic human coronaviruses (HCoVs) can serve as a model system for SARS-CoV-2 endemicity. We monitored 44 immunocompetent male adults with blood sampling every 6 months (for 17 years), for the frequency of HCoV (re-)infections, using rises in N-antibodies of HCoV-NL63, HCoV-29E, HCoV-OC43, and HCoV-HKU1 as markers of infection. Disease associations during (re-)infections were examined by comparison of self-reporting records of influenza-like illness (ILI) symptoms, every 6 months, by all participants. During 8,549 follow-up months, we found 364 infections by any HCoV with a median of eight infections per person. Symptoms more frequently reported during HCoV infection were cough, sore throat, and myalgia. Two hundred fifty-one of the 364 infections were species-specific HCoV-reinfections, with a median interval of 3.58 (interquartile range 1.92-5.67) years. The length of the interval between reinfections-being either short or long-had no influence on the frequency of reporting ILI symptoms. All HCoV-NL63, HCoV-229E, HCoV-OC43, and HCoV-HKU1 (re-)infections are associated with the reporting of ILIs. Importantly, in immunocompetent males, these symptoms are not influenced by the length of the interval between reinfections. IMPORTANCE: Little is known about the disease following human coronavirus (HCoV) reinfection occurring years after the previous infection, once humoral immunity has waned. We monitored endemic HCoV reinfection in immunocompetent male adults for up to 17 years. We found no influence of reinfection interval length in the disease manifestation, suggesting that immunocompetent male adults are adequately protected against future HCoV infections.

Endemic Human Coronavirus-Specific Nasal Immunoglobulin A and Serum Immunoglobulin G Dynamics in Lower Respiratory Tract Infections.

Endemic human coronaviruses (HCoV) NL63, 229E, OC43, and HKU1 cause respiratory infection. Following infection, a virus-specific serum antibody rise is usually observed, coinciding with recovery. In some cases, an infection is not accompanied by an immunoglobulin G (IgG) antibody rise in serum in the first month after HCoV infection, even though the infection has cleared in that month and the patient has recovered. We investigated the possible role of nasal immunoglobulin A (IgA). We measured spike (S) and nucleocapsid (N)-specific nasal IgA during and after an HCoV lower respiratory tract infection (LRTI) and compared the IgA responses between subjects with and without a significant IgG rise in serum (IgG responders (n = 31) and IgG non-responders (n = 14)). We found that most IgG responders also exhibited significant nasal IgA rise in the first month after the infection, whereas such an IgA rise was lacking in most IgG non-responders. Interestingly, the serum IgG non-responders presented with a significantly higher nasal IgA when they entered this study than during the acute phase of the LRTI. Our data suggest that nasal IgA could be part of a fast acute response to endemic HCoV infection and may play a role in clearing the infection.

The FDA-approved drug nitazoxanide is a potent inhibitor of human seasonal coronaviruses acting at postentry level: effect on the viral spike glycoprotein.

Coronaviridae is recognized as one of the most rapidly evolving virus family as a consequence of the high genomic nucleotide substitution rates and recombination. The family comprises a large number of enveloped, positive-sense single-stranded RNA viruses, causing an array of diseases of varying severity in animals and humans. To date, seven human coronaviruses (HCoV) have been identified, namely HCoV-229E, HCoV-NL63, HCoV-OC43 and HCoV-HKU1, which are globally circulating in the human population (seasonal HCoV, sHCoV), and the highly pathogenic SARS-CoV, MERS-CoV and SARS-CoV-2. Seasonal HCoV are estimated to contribute to 15-30% of common cold cases in humans; although diseases are generally self-limiting, sHCoV can sometimes cause severe lower respiratory infections and life-threatening diseases in a subset of patients. No specific treatment is presently available for sHCoV infections. Herein we show that the anti-infective drug nitazoxanide has a potent antiviral activity against three human endemic coronaviruses, the Alpha-coronaviruses HCoV-229E and HCoV-NL63, and the Beta-coronavirus HCoV-OC43 in cell culture with IC50 ranging between 0.05 and 0.15 µg/mL and high selectivity indexes. We found that nitazoxanide does not affect HCoV adsorption, entry or uncoating, but acts at postentry level and interferes with the spike glycoprotein maturation, hampering its terminal glycosylation at an endoglycosidase H-sensitive stage. Altogether the results indicate that nitazoxanide, due to its broad-spectrum anti-coronavirus activity, may represent a readily available useful tool in the treatment of seasonal coronavirus infections.

Prime editor-mediated functional reshaping of ACE2 prevents the entry of multiple human coronaviruses, including SARS-CoV-2 variants.

The spike protein of SARS-CoV-2 hijacks the host angiotensin converting enzyme 2 (ACE2) to meditate its entry and is the primary target for vaccine development. Nevertheless, SARS-CoV-2 keeps evolving and the latest Omicron subvariants BQ.1 and XBB have gained exceptional immune evasion potential through mutations in their spike proteins, leading to sharply reduced efficacy of current spike-focused vaccines and therapeutics. Compared with the fast-evolving spike protein, targeting host ACE2 offers an alternative antiviral strategy that is more resistant to viral evolution and can even provide broad prevention against SARS-CoV and HCoV-NL63. Here, we use prime editor (PE) to precisely edit ACE2 at structurally selected sites. We demonstrated that residue changes at Q24/D30/K31 and/or K353 of ACE2 could completely ablate the binding of tested viruses while maintaining its physiological role in host angiotensin II conversion. PE-mediated ACE2 editing at these sites suppressed the entry of pseudotyped SARS-CoV-2 major variants of concern and even SARS-CoV or HCoV-NL63. Moreover, it significantly inhibited the replication of the Delta variant live virus. Our work investigated the unexplored application potential of prime editing in high-risk infectious disease control and demonstrated that such gene editing-based host factor reshaping strategy can provide broad-spectrum antiviral activity and a high barrier to viral escape or resistance.

Surveillance of endemic coronaviruses during the COVID-19 pandemic in Iran, 2021-2022.

Background: Human coronaviruses (HCoVs) 229E, OC43, HKU1, and NL63 are common viruses that continuously circulate in the human population. Previous studies showed the circulation of HCoVs during the cold months in Iran. We studied the circulation of HCoVs during coronavirus disease 2019 (COVID-19) pandemic to find the impact of pandemic on the circulation of these viruses. Methods: As a cross-sectional survey conducted during 2021 to 2022, of all throat swabs sent to Iran National Influenza Center from patients with severe acute respiratory infection, 590 samples were selected to test for HCoVs using one-step real-time RT-PCR. Results: Overall, 28 out of 590 (4.7%) tested samples were found to be positive for at least one HCoVs. HCoV-OC43 was the most common (14/590 or 2.4%), followed by HCoV-HKU1 (12/590 or 2%) and HCoV-229E (4/590 or 0.6%), while HCoV-NL63 was not detected. HCoVs were detected in patients of all ages and throughout the study period with peaks in the cold months of the year. Conclusions: Our multicenter survey provides insight into the low circulation of HCoVs during the COVID-19 pandemic in Iran in 2021/2022. Hygiene habits and social distancing measures might have important role in decreasing of HCoVs transmission. We believe that surveillance studies are needed to track the pattern of HCoVs distributions and detect changes in the epidemiology of such viruses to set out strategies in order to timely control the future outbreaks of HCoVs throughout the nation.

SARS-CoV-2 Is More Efficient than HCoV-NL63 in Infecting a Small Subpopulation of ACE2+ Human Respiratory Epithelial Cells.

Human coronavirus (HCoV)-NL63 is an important contributor to upper and lower respiratory tract infections, mainly in children, while severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of COVID-19, can cause lower respiratory tract infections, and more severe, respiratory and systemic disease, which leads to fatal consequences in many cases. Using microscopy, immunohistochemistry (IHC), virus-binding assay, reverse transcriptase qPCR (RT-qPCR) assay, and flow cytometry, we compared the characteristics of the susceptibility, replication dynamics, and morphogenesis of HCoV-NL63 and SARS-CoV-2 in monolayer cultures of primary human respiratory epithelial cells (HRECs). Less than 10% HRECs expressed ACE2, and SARS-CoV-2 seemed much more efficient than HCoV-NL63 at infecting the very small proportion of HRECs expressing the ACE2 receptors. Furthermore, SARS-CoV-2 replicated more efficiently than HCoV-NL63 in HREC, which correlates with the cumulative evidence of the differences in their transmissibility.

Molecular mechanisms of human coronavirus NL63 infection and replication.

Human coronavirus NL63 (HCoV-NL63) is spread globally, causing upper and lower respiratory tract infections mainly in young children. HCoV-NL63 shares a host receptor (ACE2) with severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2 but, unlike them, HCoV-NL63 primarily develops into self-limiting mild to moderate respiratory disease. Although with different efficiency, both HCoV-NL63 and SARS-like CoVs infect ciliated respiratory cells using ACE2 as receptor for binding and cell entry. Working with SARS-like CoVs require access to BSL-3 facilities, while HCoV-NL63 research can be performed at BSL-2 laboratories. Thus, HCoV-NL63 could be used as a safer surrogate for comparative studies on receptor dynamics, infectivity and virus replication, disease mechanism, and potential therapeutic interventions against SARS-like CoVs. This prompted us to review the current knowledge on the infection mechanism and replication of HCoV-NL63. Specifically, after a brief overview on the taxonomy, genomic organization and virus structure, this review compiles the current HCoV-NL63-related research in virus entry and replication mechanism, including virus attachment, endocytosis, genome translation, and replication and transcription. Furthermore, we reviewed cumulative knowledge on the susceptibility of different cells to HCoV-NL63 infection in vitro, which is essential for successful virus isolation and propagation, and contribute to address different scientific questions from basic science to the development and assessment of diagnostic tools, and antiviral therapies. Finally, we discussed different antiviral strategies that have been explored to suppress replication of HCoV-NL63, and other related human coronaviruses, by either targeting the virus or enhancing host antiviral mechanisms.

Mouse models susceptible to HCoV-229E and HCoV-NL63 and cross protection from challenge with SARS-CoV-2.

Human coronavirus 229E (HCoV-229E) and NL63 (HCoV-NL63) are endemic causes of upper respiratory infections such as the "common cold" but may occasionally cause severe lower respiratory tract disease in the elderly and immunocompromised patients. There are no approved antiviral drugs or vaccines for these common cold coronaviruses (CCCoV). The recent emergence of COVID-19 and the possible cross-reactive antibody and T cell responses between these CCCoV and SARS-CoV-2 emphasize the need to develop experimental animal models for CCCoV. Mice are an ideal experimental animal model for such studies, but are resistant to HCoV-229E and HCoV-NL63 infections. Here, we generated 229E and NL63 mouse models by exogenous delivery of their receptors, human hAPN and hACE2 using replication-deficient adenoviruses (Ad5-hAPN and Ad5-hACE2), respectively. Ad5-hAPN- and Ad5-hACE2-sensitized IFNAR-/- and STAT1-/- mice developed pneumonia characterized by inflammatory cell infiltration with virus clearance occurring 7 d post infection. Ad5-hAPN- and Ad5-hACE2-sensitized mice generated virus-specific T cells and neutralizing antibodies after 229E or NL63 infection, respectively. Remdesivir and a vaccine candidate targeting spike protein of 229E and NL63 accelerated viral clearance of virus in these mice. 229E- and NL63-infected mice were partially protected from SARS-CoV-2 infection, likely mediated by cross-reactive T cell responses. Ad5-hAPN- and Ad5-hACE2-transduced mice are useful for studying pathogenesis and immune responses induced by HCoV-229E and HCoV-NL63 infections and for validation of broadly protective vaccines, antibodies, and therapeutics against human respiratory coronaviruses including SARS-CoV-2.

Low pre-existing endemic human coronavirus (HCoV-NL63)-specific T cell frequencies are associated with impaired SARS-CoV-2-specific T cell responses in people living with HIV.

Background: Understanding how HIV affects SARS-CoV-2 immunity is crucial for managing COVID-19 in sub-Saharan populations due to frequent coinfections. Our previous research showed that unsuppressed HIV is associated with weaker immune responses to SARS-CoV-2, but the underlying mechanisms are unclear. We investigated how pre-existing T cell immunity against an endemic human coronavirus HCoV-NL63 impacts SARS-CoV-2 T cell responses in people living with HIV (PLWH) compared to uninfected individuals, and how HIV-related T cell dysfunction influences responses to SARS-CoV-2 variants. Methods: We used flow cytometry to measure T cell responses following PBMC stimulation with peptide pools representing beta, delta, wild-type, and HCoV-NL63 spike proteins. Luminex bead assay was used to measure circulating plasma chemokine and cytokine levels. ELISA and MSD V-PLEX COVID-19 Serology and ACE2 Neutralization assays were used to measure humoral responses. Results: Regardless of HIV status, we found a strong positive correlation between responses to HCoV-NL63 and SARS-CoV-2. However, PLWH exhibited weaker CD4+ T cell responses to both HCoV-NL63 and SARS-CoV-2 than HIV-uninfected individuals. PLWH also had higher proportions of functionally exhausted (PD-1high) CD4+ T cells producing fewer proinflammatory cytokines (IFNγ and TNFα) and had elevated plasma IL-2 and IL-12(p70) levels compared to HIV-uninfected individuals. HIV status didn't significantly affect IgG antibody levels against SARS-CoV-2 antigens or ACE2 binding inhibition activity. Conclusion: Our results indicate that the decrease in SARS-CoV-2 specific T cell responses in PLWH may be attributable to reduced frequencies of pre-existing cross-reactive responses. However, HIV infection minimally affected the quality and magnitude of humoral responses, and this could explain why the risk of severe COVID-19 in PLWH is highly heterogeneous.

Severe coronavirus HCoV-NL63 pneumonia in a patient receiving blinatumomab with secondary antibody deficiency in COVID-19 times.

Introduction: Human coronavirus NL63 (HCoV-NL63) is one of four common human respiratory coronaviruses. It causes lower respiratory tract infections in young children, elderly and immunosuppressed people, which could result in fatal outcomes. In this time of pandemic, we want to highlight the importance of other coronaviruses infection besides SARS-CoV-2, especially in a patient with underlying conditions like acute lymphoblastic leukemia, receiving immunosuppressive therapy that could result in humoral secondary immunodeficiencies. Case report: We present the case of a 44-year-old Colombian man with acute lymphoblastic leukemia who developed HCoV-NL63 pulmonary infection after the first month of treatment with blinatumomab complicated with severe secondary hypogammaglobulinemia. HCoV-NL63 was detected by multiplex PCR, and HCoV-NL63 viral pneumonia was diagnosed. Hypogammaglobulinemia was studied by determining serum immunoglobulins levels and protein electrophoresis. The treatment consisted of supportive therapy and replacement with intravenous immunoglobulins. After therapy, the patient improved his oxygenation, and the infection was resolved in a few days. Conclusions: This case highlights the relevance of other coronaviruses infections besides SARS-CoV-2 in patients receiving immunosuppressive therapy who develop secondary antibody deficiency, and the importance of replacement therapy with intravenous immunoglobulins at early stage of infection with HCoV-NL63.

Broad-Spectrum Small-Molecule Inhibitors of the SARS-CoV-2 Spike-ACE2 Protein-Protein Interaction from a Chemical Space of Privileged Protein Binders.

Therapeutically useful small-molecule inhibitors (SMIs) of protein−protein interactions (PPIs) initiating the cell attachment and entry of viruses could provide novel alternative antivirals that act via mechanisms similar to that of neutralizing antibodies but retain the advantages of small-molecule drugs such as oral bioavailability and low likelihood of immunogenicity. From screening our library, which is focused around the chemical space of organic dyes to provide good protein binders, we have identified several promising SMIs of the SARS-CoV-2 spike­ACE2 interaction, which is needed for the attachment and cell entry of this coronavirus behind the COVID-19 pandemic. They included organic dyes, such as Congo red, direct violet 1, and Evans blue, which seem to be promiscuous PPI inhibitors, as well as novel drug-like compounds (e.g., DRI-C23041). Here, we show that in addition to the original SARS-CoV-2 strain, these SMIs also inhibit this PPI for variants of concern including delta (B.1.617.2) and omicron (B.1.1.529) as well as HCoV-NL63 with low- or even sub-micromolar activity. They also concentration-dependently inhibited SARS-CoV-2-S expressing pseudovirus entry into hACE2-expressing cells with low micromolar activity (IC50 < 10 µM) both for the original strain and the delta variant. DRI-C23041 showed good therapeutic (selectivity) index, i.e., separation between activity and cytotoxicity (TI > 100). Specificities and activities require further optimization; nevertheless, these results provide a promising starting point toward novel broad-spectrum small-molecule antivirals that act via blocking the interaction between the spike proteins of coronaviruses and their ACE2 receptor initiating cellular entry.

Structural insights into the binding of SARS-CoV-2, SARS-CoV, and hCoV-NL63 spike receptor-binding domain to horse ACE2.

Severe acute respiratory syndrome coronavirus (SARS-CoV), SARS-CoV-2, and human coronavirus (hCoV)-NL63 utilize ACE2 as the functional receptor for cell entry, which leads to zoonotic infection. Horses (Equus caballus) attracted our attention because the spike protein receptor-binding domains (RBDs) of SARS-CoV-2 and SARS-CoV-2-related coronaviruses bind equine ACE2 (eACE2) with high affinity. Here we show that eACE2 binds the RBDs of these three coronaviruses and also SARS-CoV-2 variants but with lower affinities compared with human ACE2 (hACE2). Structural analysis and mutation assays indicated that eACE2-H41 accounts for the lower binding affinity of eACE2 to the RBDs of SARS-CoV-2 variants (Alpha, Beta, and Gamma), SARS-CoV, and hCoV-NL63. Pseudovirus infection assays showed that the SARS-CoV-2 Delta strain (B.1.617.2) displayed a significantly increased infection efficiency in eACE2-expressing HeLa cells. Our results reveal the molecular basis of eACE2 binding to the RBDs of SARS-CoV, SARS-CoV-2, and hCoV-NL63, which provides insights into the potential animal transmission of these ACE2-dependent coronaviruses.

Human Air-Liquid-Interface Organotypic Airway Cultures Express Significantly More ACE2 Receptor Protein and Are More Susceptible to HCoV-NL63 Infection than Monolayer Cultures of Primary Respiratory Epithelial Cells.

Human coronavirus NL63 (HCoV-NL63) is commonly associated with mild respiratory tract infections in infants, being that the respiratory epithelial cells are the main target for infection and initial replication of this virus. Standard immortalized cells are highly permissive to HCoV-NL63, and they are routinely used for isolation and propagation of the virus from clinical specimens. However, these cell lines are not the natural cell target of the virus and lack sufficient complexity to mimic the natural infection process in vivo. This study comparatively evaluated the differences on the susceptibility to HCoV-NL63 infection and virus replication efficiency of submerged monolayer cultures of LLC-MK2 and primary human respiratory epithelial cells (HRECs) and organotypic airway cultures of respiratory cells (ALI-HRECs). Productive viral infection and growth kinetics were assessed by morphologic examination of cytopathic effects, immunofluorescence, reverse transcription quantitative real-time PCR, and flow cytometry. Results from this study showed higher susceptibility to HCoV-NL63 infection and replication in LLC-MK2 cells followed by ALI-HRECs, with very low susceptibility and no significant virus replication in HRECs. This susceptibility was associated with the expression levels of angiontensin-converting enzyme 2 (ACE2) receptor protein in LLC-MK2, ALI-HRECs, and HRECs, respectively. Remarkably, organotypic ALI-HREC cultures expressed significantly more ACE2 receptor protein and were more susceptible to HCoV-NL63 infection than monolayer cultures of HREC. The ACE2 receptor is, therefore, a critical factor for susceptibility to HCoV-NL63 infection and replication, as is the type of culture used during infection studies. IMPORTANCE HCoV-NL63 is widespread globally, accounting for a significant number of respiratory infections in children and adults. HCoV-NL63 gains entrance into respiratory epithelial cells via the ACE2 receptor, the same cell receptor used by severe acute respiratory syndrome coronavirus (SARS-CoV) and SARS-CoV-2. Thus, HCoV-NL63 has been suggested as safe surrogate for studying disease mechanisms and therapeutic interventions against SARS-like CoVs, while working under BSL-2 conditions. The present study not only showed the critical role of ACE2 for effective HCoV-NL63 infection and replication, but also shed light on the need of more refined and complex in vitro organotypic models that recapitulate the proxy of air-liquid respiratory epithelia cell composition, structure, and functionality. These cultures have broaden virological studies toward improving our understanding of how coronaviruses cause disease and transmission not just within humans but also in animal populations.

TiO2 Nanostructures That Reduce the Infectivity of Human Respiratory Viruses Including SARS-CoV-2.

The rapid emergence and global spread of the COVID-19 causing Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) and its subsequent mutated strains has caused unprecedented health, economic, and social devastation. Respiratory viruses such as SARS-CoV-2 can be transmitted through both direct and indirect channels, including aerosol respiratory droplets, contamination of inanimate surfaces (fomites), and direct person-to-person contact. Current methods of virus inactivation on surfaces include chemicals and biocides, and while effective, continuous and repetitive cleaning of all surfaces is not always viable. Recent work in the field of biomaterials engineering has established the antibacterial effects of hydrothermally synthesized TiO2 nanostructured surfaces against both Gram-negative and -positive bacteria. The current study investigates the effectiveness of said TiO2 nanostructured surfaces against two enveloped human coronaviruses, SARS-CoV-2 and HCoV-NL63, and nonenveloped HRV-16 for surface-based inactivation. Results show that structured surfaces reduced infectious viral loads of SARS-CoV-2 (5 log), HCoV-NL63 (3 log), and HRV-16 (4 log) after 5 h, compared to nonstructured and tissue culture plastic control surfaces. Interestingly, infectious virus remained present on control tissue culture plastic after 7 h exposure. These encouraging results establish the potential use of nanostructured surfaces to reduce the transmission and spread of both enveloped and nonenveloped respiratory viruses, by reducing their infectious period on a surface. The dual antiviral and antibacterial properties of these surfaces support their potential application in a wide variety of settings such as hospitals and healthcare environments, public transport and community hubs.

Atypical Antibody Dynamics During Human Coronavirus HKU1 Infections.

Human coronavirus HKU1 (HCoV-HKU1) is one of the four endemic coronaviruses. It has been suggested that there is a difference in incidence, with PCR-confirmed HCoV-NL63 and HCoV-OC43 infections occurring more commonly, whereas HCoV-HKU1 is the least seen. Lower incidence of HCoV-HKU1 infection has also been observed in serological studies. The current study aimed to investigate antibody dynamics during PCR-confirmed HCoV-HKU1 infections using serum collected during infection and 1 month later. We expressed a new HCoV-HKU1 antigen consisting of both the linker and carboxy-terminal domain of the viral nucleocapsid protein and implemented it in ELISA. We also applied a spike-based Luminex assay on serum samples from PCR-confirmed infections by the four endemic HCoVs. At least half of HCoV-HKU1-infected subjects consistently showed no antibody rise via either assay, and some subjects even exhibited substantial antibody decline. Investigation of self-reported symptoms revealed that HCoV-HKU1-infected subjects rated their illness milder than subjects infected by other HCoVs. In conclusion, HCoV-HKU1 infections reported in this study displayed atypical antibody dynamics and milder symptoms when compared to the other endemic HCoVs.

A Novel Method to Reduce ELISA Serial Dilution Assay Workload Applied to SARS-CoV-2 and Seasonal HCoVs.

Assays using ELISA measurements on serially diluted serum samples have been heavily used to measure serum reactivity to SARS-CoV-2 antigens and are widely used in virology and elsewhere in biology. We test a method using Bayesian hierarchical modelling to reduce the workload of these assays and measure reactivity of SARS-CoV-2 and HCoV antigens to human serum samples collected before and during the COVID-19 pandemic. Inflection titers for SARS-CoV-2 full-length spike protein (S1S2), spike protein receptor-binding domain (RBD), and nucleoprotein (N) inferred from 3 spread-out dilutions correlated with those inferred from 8 consecutive dilutions with an R2 value of 0.97 or higher. We confirm existing findings showing a small proportion of pre-pandemic human serum samples contain cross-reactive antibodies to SARS-CoV-2 S1S2 and N, and that SARS-CoV-2 infection increases serum reactivity to the beta-HCoVs OC43 and HKU1 S1S2. In serial dilution assays, large savings in resources and/or increases in throughput can be achieved by reducing the number of dilutions measured and using Bayesian hierarchical modelling to infer inflection or endpoint titers. We have released software for conducting these types of analysis.