Infection kinetics, syncytia formation, and inflammatory biomarkers as predictive indicators for the pathogenicity of SARS-CoV-2 Variants of Concern in Calu-3 cells

The ongoing COVID-19 pandemic has led to the emergence of new SARS-CoV-2 variants as a result of continued host-virus interaction and viral genome mutations. These variants have been associated with varying levels of transmissibility and disease severity. We investigated the phenotypic profiles of six SARS-CoV-2 variants (WT, D614G, Alpha, Beta, Delta, and Omicron) in Calu-3 cells, a human lung epithelial cell line. In our model demonstrated that all variants, except for Omicron, had higher efficiency in virus entry compared to the wild-type. The Delta variant had the greatest phenotypic advantage in terms of early infection kinetics and marked syncytia formation, which could facilitate cell-to-cell spreading, while the Omicron variant displayed slower replication and fewer syncytia formation. We also identified the Delta variant as the strongest inducer of inflammatory biomarkers, including pro-inflammatory cytokines/chemokines (IP-10/CXCL10, TNF-α, and IL-6), anti-inflammatory cytokine (IL-1RA), and growth factors (FGF-2 and VEGF-A), while these inflammatory mediators were not significantly elevated with Omicron infection. These findings are consistent with the observations that there was a generally more pronounced inflammatory response and angiogenesis activity within the lungs of COVID-19 patients as well as more severe symptoms and higher mortality rate during the Delta wave, as compared to less severe symptoms and lower mortality observed during the current Omicron wave in Thailand. Our findings suggest that early infectivity kinetics, enhanced syncytia formation, and specific inflammatory mediator production may serve as predictive indicators for the virulence potential of future SARS-CoV-2 variants.

Unveiling the Antiviral Properties of Panduratin A through SARS-CoV-2 Infection Modeling in Cardiomyocytes

Establishing a drug-screening platform is critical for the discovery of potential antiviral agents against SARS-CoV-2. In this study, we developed a platform based on human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to investigate SARS-CoV-2 infectivity, with the aim of evaluating potential antiviral agents for anti-SARS-CoV-2 activity and cardiotoxicity. Cultured myocytes of iPSC-CMs and immortalized human cardiomyocyte cell line (AC-16) were primarily characterized for the expression of cardiac markers and host receptors of SARS-CoV-2. An infectivity model for the wild-type SARS-CoV-2 strain was then established. Infection modeling involved inoculating cells with SARS-CoV-2 at varying multiplicities of infection (MOIs) and then quantifying infection using immunofluorescence and plaque assays. Only iPSC-CMs, not AC16 cells, expressed angiotensin-converting enzyme 2 (ACE-2), and quantitative assays confirmed the dose-dependent infection of iPSC-CMs by SARS-CoV-2, unlike the uninfectable AC16 cells lacking the expression of ACE2. Cytotoxicity was evaluated using MTT assays across a concentration range. An assessment of the plant-derived compound panduratin A (panA) showed cytotoxicity at higher doses (50% cytotoxic concentration (CC50) 10.09 μM) but promising antiviral activity against SARS-CoV-2 (50% inhibition concentration (IC50) 0.8-1.6 μM), suppressing infection at concentrations 10 times lower than its CC50. Plaque assays also showed decreased viral production following panA treatment. Overall, by modeling cardiac-specific infectivity, this iPSC-cardiomyocyte platform enables the reliable quantitative screening of compound cytotoxicity alongside antiviral efficacy. By combining disease pathogenesis and pharmacology, this system can facilitate the evaluation of potential novel therapeutics, such as panA, for drug discovery applications.

Immunogenicity and protective efficacy of SARS-CoV-2 mRNA vaccine encoding secreted non-stabilized spike in female mice

Establishment of an mRNA vaccine platform in low- and middle-income countries (LMICs) is important to enhance vaccine accessibility and ensure future pandemic preparedness. Here, we describe the preclinical studies of "ChulaCov19", a SARS-CoV-2 mRNA encoding prefusion-unstabilized ectodomain spike protein encapsulated in lipid nanoparticles (LNP). In female BALB/c mice, ChulaCov19 at 0.2, 1, 10, and 30 μg elicits robust neutralizing antibody (NAb) and T cell responses in a dose-dependent relationship. The geometric mean titers (GMTs) of NAb against wild-type (WT, Wuhan-Hu1) virus are 1,280, 11,762, 54,047, and 62,084, respectively. Higher doses induce better cross-NAb against Delta (B.1.617.2) and Omicron (BA.1 and BA.4/5) variants. This elicited immunogenicity is significantly higher than those induced by homologous CoronaVac or AZD1222 vaccination. In a heterologous prime-boost study, ChulaCov19 booster dose generates a 7-fold increase of NAb against Wuhan-Hu1 WT virus and also significantly increases NAb response against Omicron (BA.1 and BA.4/5) when compared to homologous CoronaVac or AZD1222 vaccination. Challenge studies show that ChulaCov19 protects human-ACE-2-expressing female mice from COVID-19 symptoms, prevents viremia and significantly reduces tissue viral load. Moreover, anamnestic NAb response is undetectable in challenge animals. ChulaCov19 is therefore a promising mRNA vaccine candidate either as a primary or boost vaccination and has entered clinical development.

Preclinical evaluation of immunogenicity, efficacy and safety of a recombinant plant-based SARS-CoV-2 RBD vaccine formulated with 3M-052-Alum adjuvant

Cost-effective, and accessible vaccines are needed for mass immunization to control the ongoing coronavirus disease 2019 (COVID-19), especially in low- and middle-income countries (LMIC).A plant-based vaccine is an attractive technology platform since the recombinant proteins can be easily produced at large scale and low cost. For the recombinant subunit-based vaccines, effective adjuvants are crucial to enhance the magnitude and breadth of immune responses elicited by the vaccine. In this study, we report a preclinical evaluation of the immunogenicity, efficacy and safety of a recombinant plant-based SARS-CoV-2 RBD vaccine formulated with 3M-052 (TLR7/8 agonist)-Alum adjuvant. This vaccine formulation, named Baiya SARS-CoV-2 Vax 2, induced significant levels of RBD-specific IgG and neutralizing antibody responses in mice. A viral challenge study using humanized K18-hACE2 mice has shown that animals vaccinated with two doses of Baiya SARS-CoV-2 Vax 2 established immune protection against SARS-CoV-2. A study in nonhuman primates (cynomolgus monkeys) indicated that immunization with two doses of Baiya SARS-CoV-2 Vax 2 was safe, well tolerated, and induced neutralizing antibodies against the prototype virus and other viral variants (Alpha, Beta, Gamma, Delta, and Omicron subvariants). The toxicity of Baiya SARS-CoV-2 Vax 2 was further investigated in Jcl:SD rats, which demonstrated that a single dose and repeated doses of Baiya SARS-CoV-2 Vax 2 were well tolerated and no mortality or unanticipated findings were observed. Overall, these preclinical findings support further clinical development of Baiya SARS-CoV-2 Vax 2.

Immunogenicity and efficacy of recombinant subunit SARS-CoV-2 vaccine candidate in the Syrian hamster model

SARS-CoV-2 causes devastating impact on the human population and has become a major public health concern. The frequent emergence of SARS-CoV-2 variants of concern urges the development of safe and efficacious vaccine against SARS-CoV-2 variants. We developed a candidate vaccine Baiya SARS-CoV-2 Vax 1, based on SARS-CoV-2 receptor-binding domain (RBD) by fusing with the Fc region of human IgG. The RBD-Fc fusion was produced in Nicotiana benthamiana. Previously, we reported that this plant-produced vaccine is effective in inducing immune response in both mice and non-human primates. Here, the efficacy of our vaccine candidate was tested in Syrian hamster challenge model. Hamsters immunized with two intramuscular doses of Baiya SARS-CoV-2 Vax 1 induced neutralizing antibodies against SARS-CoV-2 and protected from SARS-CoV-2 challenge with reduced viral load in the lungs. These preliminary results demonstrate the ability of plant-produced subunit vaccine Baiya SARS-CoV-2 Vax 1 to provide protection against SARS-CoV-2 infection in hamsters.

Systematic exploration of SARS-CoV-2 adaptation to Vero E6, Vero E6/TMPRSS2, and Calu-3 cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread globally, and scientists around the world are currently studying the virus intensively in order to fight against the on-going pandemic of the virus. To do so, SARS-CoV-2 is typically grown in the lab to generate viral stocks for various kinds of experimental investigations. However, accumulating evidence suggests that such viruses often undergo cell culture adaptation. Here, we systematically explored cell culture adaptation of two SARS-CoV-2 variants, namely the B.1.36.16 variant and the AY.30 variant, a sub lineage of the B.1.617.2 (Delta) variant, propagated in three different cell lines, including Vero E6, Vero E6/TMPRSS2, and Calu-3 cells. Our analyses detected numerous potential cell culture adaptation changes scattering across the entire virus genome, many of which could be found in naturally circulating isolates. Notable ones included mutations around the spike glycoprotein's multibasic cleavage site, and the Omicron-defining H655Y mutation on the spike glycoprotein, as well as mutations in the nucleocapsid protein's linker region, all of which were found to be Vero E6-specific. Our analyses also identified deletion mutations on the non-structural protein 1 and membrane glycoprotein as potential Calu-3-specific adaptation changes. S848C mutation on the non-structural protein 3, located to the protein's papain-like protease domain, was also identified as a potential adaptation change, found in viruses propagated in all three cell lines. Our results highlight SARS-CoV-2 high adaptability, emphasise the need to deep-sequence cultured viral samples when used in intricate and sensitive biological experiments, and illustrate the power of experimental evolutionary study in shedding lights on the virus evolutionary landscape.

Dynamics of Neutralizing Antibodies and Binding Antibodies to Domains of SARS-CoV-2 Spike Protein in COVID-19 Survivors

Neutralizing antibody level is used to predict immune protection against SARS-CoV-2 infection. Spike protein of SARS-CoV-2 is a major target for virus-neutralizing antibody. A number of neutralizing epitopes were mapped on receptor binding domain (RBD) and N-terminal domain (NTD) of S1 subunit of the spike. Anti-SARS-CoV-2 antibody usually decreases over time after recovery. Level of neutralizing antibody and binding antibody to several domains from COVID-19 recovered patients was observed longitudinally in this study. Sequentially collected serum samples from 35 patients demonstrated both similar and different trends of neutralizing antibodies versus binding antibodies to each domain. Twenty-three individuals showed similarly decreasing pattern of neutralizing titer, binding antibodies to RBD, NTD, fusion protein (S2), and nucleocapsid (NP). Interestingly, eight individuals had stably high neutralizing titer (≥320) for 3-12 months, whereas their binding antibodies to RBD, NTD, and NP rapidly decreased. Moreover, their binding antibodies to S2 were stable over time similar to the persistence of neutralizing antibody levels. The long-lasting antibody to S2 suggested an anamnestic response to cross-reactive epitopes from previous infections with other related coronaviruses. These data indicate a difference in kinetics and longevity of antibodies to various domains and epitopes of the SARS-CoV-2 proteins. A better understanding in this difference may help improve vaccine design to induce long-lasting immunity to COVID-19.

A recombinant subunit vaccine candidate produced in plants elicits neutralizing antibodies against SARS-CoV-2 variants in macaques

Since the outbreak of the coronavirus disease (COVID) pandemic in 2019, the development of effective vaccines to combat the infection has been accelerated. With the recent emergence of highly transmissible severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOC), there are concerns regarding the immune escape from vaccine-induced immunity. Hence an effective vaccine against VOC with a potent immune response is required. Our previous study confirmed that the two doses of the plant-produced receptor-binding domain (RBD) of SARS-CoV-2 fused with the Fc region of human IgG1, namely Baiya SARS-CoV-2 Vax 1, showed high immunogenicity in mice and monkeys. Here, we aimed to evaluate the immunogenicity of a three-dose intramuscular injection of Baiya SARS-CoV-2 Vax 1 on days 0, 21, and 133 in cynomolgus monkeys. At 14 days after immunization, blood samples were collected to determine RBD-specific antibody titer, neutralizing antibody, and pseudovirus neutralizing antibody titers. Immunized monkeys developed significantly high levels of antigen-specific antibodies against SARS-CoV-2 compared to the control group. Interestingly, the sera collected from immunized monkeys also showed a neutralizing antibody response against the SARS-CoV-2 VOCs; Alpha, Beta, Gamma, Delta, and Omicron. These findings demonstrate that a three-dose regimen of Baiya SARS-CoV-2 Vax 1 vaccine elicits neutralizing immune response against SARS-CoV-2 variants.

Receptor binding domain proteins of SARS-CoV-2 variants produced in Nicotiana benthamiana elicit neutralizing antibodies against variants of concern

The constantly emerging severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) variants of concerns (VOCs) with mutations in the receptor-binding domain (RBD) spread rapidly and has become a severe public health problem worldwide. Effective vaccines and optimized booster vaccination strategies are thus highly required. Here, the gene encoding six different RBD (Alpha, Beta, Gamma, Kappa, Delta, and Epsilon variants) along with the Fc fragment of human IgG1 (RBD-Fc) was cloned into plant expression vector and produced in Nicotiana benthamiana by transient expression. Further, the immunogenicity of plant-produced variant RBD-Fc fusion proteins were tested in cynomolgus monkeys. Each group of cynomolgus monkeys was immunized three times intramuscularly with variant RBD-Fc vaccines at Day 0, 21, 42, and neutralizing antibody responses were evaluated against ancestral (Wuhan), Alpha, Beta, Gamma, and Delta variants. The results showed that three doses of the RBD-Fc vaccine significantly enhanced the immune response against all tested SARS-CoV-2 variants. In particular, the vaccines based on Delta and Epsilon mutant RBD elicit broadly neutralizing antibodies against ancestral (Wuhan), Alpha, and Delta SARS-CoV-2 variants whereas Beta and Gamma RBD-Fc vaccines elicit neutralizing antibodies against their respective SARS-CoV-2 strains. The Delta and Epsilon RBD-Fc based vaccines displayed cross-reactive immunogenicity and might be applied as a booster vaccine to induce broadly neutralizing antibodies. These proof-of-concept results will be helpful for the development of plant-derived RBD-Fc-based vaccines against SARS-CoV-2 and its variants.

A circular mRNA vaccine prototype producing VFLIP-X spike confers a broad neutralization of SARS-CoV-2 variants by mouse sera

Next-generation COVID-19 vaccines are critical due to the ongoing evolution of SARS-CoV-2 virus and rapid waning duration of the neutralizing antibody response against current vaccines. The mRNA vaccines mRNA-1273 and BNT162b2 were developed using linear transcripts encoding the prefusion-stabilized trimers (S-2P) of the wildtype spike, which have shown a reduced neutralizing activity against the variants of concern B.1.617.2 and B.1.1.529. Recently, a new version of spike trimer, termed VFLIP (five (V) prolines, Flexibly-Linked, Inter-Protomer disulfide) was developed. Based on the original amino acid sequence of the wildtype spike, VFLIP was genetically engineered by using five proline substitutions, a flexible cleavage site amino acid linker, and an inter-protomer disulfide bond. It has been suggested to possess native-like glycosylation, and greater pre-fusion trimeric stability as opposed to S-2P. Here, we report that the spike protein VFLIP-X, containing six rationally substituted amino acids to reflect emerging variants (K417N, L452R, T478K, E484K, N501Y and D614G), offers a promising candidate for a next-generation SARS-CoV-2 vaccine. Mice immunized by a circular mRNA (circRNA) vaccine prototype producing VFLIP-X had detectable neutralizing antibody titers for up to 7 weeks post-boost against SARS-CoV-2 variants of concern (VOCs) and variants of interest (VOIs). In addition, a balance in TH1 and TH2 responses was achieved by immunization with VFLIP-X. Our results indicate that the VFLIP-X delivered by circRNA induces humoral and cellular immune responses, as well as broad neutralizing activity against SARS-CoV-2 variants.

Preclinical evaluation of a plant-derived SARS-CoV-2 subunit vaccine: Protective efficacy, immunogenicity, safety, and toxicity

Coronavirus disease 2019 (COVID-19) is an acute respiratory illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The prevention of SARS-CoV-2 transmission has become a global priority. Previously, we showed that a protein subunit vaccine that was developed based on the fusion of the SARS-CoV-2 receptor-binding domain (RBD) to the Fc portion of human IgG1 (RBD-Fc), produced in Nicotiana benthamiana, and adjuvanted with alum, namely, Baiya SARS-CoV-2 Vax 1, induced potent immunological responses in both mice and cynomolgus monkeys. Hence, this study evaluated the protective efficacy, safety, and toxicity of Baiya SARS-CoV-2 Vax 1 in K18-hACE2 mice, monkeys and Wistar rats. Two doses of vaccine were administered three weeks apart on Days 0 and 21. The administration of the vaccine to K18-hACE2 mice reduced viral loads in the lungs and brains of the vaccinated animals and protected the mice against challenge with SARS-CoV-2. In monkeys, the results of safety pharmacology tests, general clinical observations, and a core battery of studies of three vital systems, namely, the central nervous, cardiovascular, and respiratory systems, did not reveal any safety concerns. The toxicology study of the vaccine in rats showed no vaccine-related pathological changes, and all the animals remained healthy under the conditions of this study. Furthermore, the vaccine did not cause any abnormal toxicity in rats and was clinically tolerated even at the highest tested concentration. In addition, general health status, body temperature, local toxicity at the administration site, hematology, and blood chemistry parameters were also monitored. Overall, this work presents the results of the first systematic study of the safety profile of a plant-derived vaccine, Baiya SARS-CoV-2 Vax 1; this approach can be considered a viable strategy for the development of vaccines against COVID-19.

Detectable Duration of Viable SARS-CoV-2, Total and Subgenomic SARS-CoV-2 RNA in Noncritically Ill COVID-19 Patients: a Prospective Cohort Study

Determination of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infectivity is important in guiding the infection control and differentiating between reinfection and persistent viral RNA. Although viral culture is the gold standard to determine viral infectivity, the method is not practical. We studied the kinetics of SARS-CoV-2 total RNAs and subgenomic RNAs (sgRNAs) and their potential role as surrogate markers of viral infectivity. The kinetics of SARS-CoV-2 sgRNAs compared to those of the culture and total RNA shedding in a prospective cohort of patients diagnosed with coronavirus disease 2019 (COVID-19) were investigated. A total of 260 nasopharyngeal swabs from 36 patients were collected every other day after entering the study until the day of viral total RNA clearance, as measured by reverse transcription PCR (RT-PCR). Time to cessation of viral shedding was in order from shortest to longest: by viral culture, sgRNA RT-PCR, and total RNA RT-PCR. The median time (interquartile range) to negativity of viral culture, subgenomic N transcript, and N gene were 7 (5 to 9), 11 (9 to 16), and 18 (13 to 21) days, respectively (P < 0.001). Further analysis identified the receipt of steroid as the factors associated with longer duration of viral infectivity (hazard ratio, 3.28; 95% confidence interval, 1.02 to 10.61; P = 0.047). We propose the potential role of the detection of SARS-CoV-2 subgenomic RNA as the surrogate marker of viral infectivity. Patients with negative subgenomic N RNA RT-PCR could be considered for ending isolation. IMPORTANCE Our study, combined with existing evidence, suggests the feasibility of the use of subgenomic RNA RT-PCR as a surrogate marker for SARS-CoV-2 infectivity. The kinetics of SARS-CoV-2 subgenomic RNA should be further investigated in immunocompromised patients.

Synergistic anti-SARS-CoV-2 activity of repurposed anti-parasitic drug combinations

BACKGROUND

COVID-19 pandemic has claimed millions of lives and devastated the health service system, livelihood, and economy in many countries worldwide. Despite the vaccination programs in many countries, the spread of the pandemic continues, and effective treatment is still urgently needed. Although some antiviral drugs have been shown to be effective, they are not widely available. Repurposing of anti-parasitic drugs with in vitro anti-SARS-CoV-2 activity is a promising approach being tested in many clinical trials. Combination of these drugs is a plausible way to enhance their effectiveness.

METHODS

The in vitro anti-SARS-CoV-2 activity of combinations of niclosamide, ivermectin and chloroquine were evaluated in Vero E6 and lung epithelial cells, Calu-3.

RESULTS

All the two-drug combinations showed higher potency resulting in up to 4-fold reduction in the half maximal inhibitory concentration (IC₅₀) values compared to individual drugs. Among these combinations, niclosamide-ivermectin achieved the highest inhibitory level of over 99%. Combination synergy analysis showed niclosamide-ivermectin combination to have the best synergy score with a mean Loewe synergy score of 4.28 and a peak synergy score of 24.6 in Vero E6 cells and a mean Loewe synergy score of 3.82 and a peak synergy score of 10.86 in Calu-3 cells.

CONCLUSIONS

The present study demonstrated the benefit of drug combinations on anti-SARS-CoV-2 activity. Niclosamide and ivermectin showed the best synergistic profile and should be further tested in clinical trials.

Virus MIP-composites for SARS-CoV-2 detection in the aquatic environment

SARS-CoV-2 is the virus responsible for causing the global COVID-19 pandemic. Identifying the presence of this virus in the environment could potentially improve the effectiveness of disease control measures. Environmental SARS-CoV-2 monitoring may become increasingly demanded in areas where the available testing methods are ineffective. In this study, we present an electrochemical polymer composites biosensor for measuring SARS-CoV-2 whole-virus particles in the environment. The sensitized layer was prepared from molecularly imprinted polymer (MIP) composites of inactivated SARS-CoV-2. Testing demonstrated increased sensor signaling with SARS-CoV-2 specifically, while lower responses were observed to the negative controls, H5N1 influenza A virus and non-imprinted polymers (NIPs). This sensor detected SARS-CoV-2 at concentrations as low as 0.1 fM in buffer and samples prepared from reservoir water with a 3 log-scale linearity.

Target Enrichment Metagenomics Reveals Human Pegivirus-1 in Pediatric Hematopoietic Stem Cell Transplantation Recipients

Human pegivirus-1 (HPgV-1) is a lymphotropic human virus, typically considered nonpathogenic, but its infection can sometimes cause persistent viremia both in immunocompetent and immunosuppressed individuals. In a viral discovery research program in hematopoietic stem cell transplant (HSCT) pediatric patients, HPgV-1 was detected in 3 out of 14 patients (21.4%) using a target enrichment next-generation sequencing method, and the presence of the viruses was confirmed by agent-specific qRT-PCR assays. For the first time in this patient cohort, complete genomes of HPgV-1 were acquired and characterized. Phylogenetic analyses indicated that two patients had HPgV-1 genotype 2 and one had HPgV-1 genotype 3. Intra-host genomic variations were described and discussed. Our results highlight the necessity to screen HSCT patients and blood and stem cell donors to reduce the potential risk of HPgV-1 transmission.

SARS-CoV-2 neutralizing antibodies decline over one year and patients with severe COVID-19 pneumonia display a unique cytokine profile

OBJECTIVES

As coronavirus disease 2019 (COVID-19) rages on worldwide, there is an urgent need to characterize immune correlates of protection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and to identify immune determinants of COVID-19 severity.

METHODS

This study examined the longitudinal profiles of neutralizing antibody (NAb) titers in hospitalized COVID-19 patients clinically diagnosed with mild symptoms, pneumonia, or severe pneumonia, up to 12 months after illness onset, using live-virus neutralization. Multiplex, correlation, and network analyses were used to characterize serum-derived inflammatory cytokine profiles in all severity groups.

RESULTS

Peak NAb titers correlated with disease severity, and NAb titers declined over the course of 12 months regardless of severity. Multiplex analyses revealed that IP-10, IL-6, IL-7, and VEGF-α were significantly elevated in severe pneumonia cases compared to those with mild symptoms and pneumonia cases. Correlation and network analyses further suggested that cytokine network formation was distinct in different COVID-19 severity groups.

CONCLUSIONS

The study findings inform on the long-term kinetics of naturally acquired serological immunity against SARS-CoV-2 and highlight the importance of identifying key cytokine networks for potential therapeutic immunomodulation.

Anti-SARS-CoV-2 Activity of Extracellular Vesicle Inhibitors: Screening, Validation, and Combination with Remdesivir

The coronavirus disease 2019 (COVID-19) pandemic severely impacts health, economy, and society worldwide. Antiviral drugs against SARS-CoV-2 are urgently needed to cope with this global crisis. It has been found that the biogenesis and release mechanisms of viruses share a common pathway with extracellular vesicles (EVs). We hypothesized that small molecule inhibitors of EV biogenesis/release could exert an anti-SARS-CoV-2 effect. Here, we screened 17 existing EV inhibitors and found that calpeptin, a cysteine proteinase inhibitor, exhibited the most potent anti-SARS-CoV-2 activity with no apparent cytotoxicity. Calpeptin demonstrated the dose-dependent inhibition against SARS-CoV-2 viral nucleoprotein expression in the infected cells with a half-maximal inhibitory concentration (IC50) of 1.44 µM in Vero-E6 and 26.92 µM in Calu-3 cells, respectively. Moreover, calpeptin inhibited the production of infectious virions with the lower IC50 of 0.6 µM in Vero E6 cells and 10.12 µM in Calu-3 cells. Interestingly, a combination of calpeptin and remdesivir, the FDA-approved antiviral drug against SARS-CoV-2 viral replication, significantly enhanced the anti-SARS-CoV-2 effects compared to monotherapy. This study discovered calpeptin as a promising candidate for anti-SARS-CoV-2 drug development. Further preclinical and clinical studies are warranted to elucidate the therapeutic efficacy of calpeptin and remdesivir combination in COVID-19.

Immunogenicity Studies of Plant-Produced SARS-CoV-2 Receptor Binding Domain-Based Subunit Vaccine Candidate with Different Adjuvant Formulations

Due to the rapid transmission of the coronavirus disease 2019 (COVID-19) causing serious public health problems and economic burden, the development of effective vaccines is a high priority for controlling the virus spread. Our group has previously demonstrated that the plant-produced receptor-binding domain (RBD) of SARS-CoV-2 fused with Fc of human IgG was capable of eliciting potent neutralizing antibody and cellular immune responses in animal studies, and the immunogenicity could be improved by the addition of an alum adjuvant. Here, we performed a head-to-head comparison of different commercially available adjuvants, including aluminum hydroxide gel (alum), AddaVax (MF59), monophosphoryl lipid A from Salmonella minnesota R595 (mPLA-SM), and polyinosinic-polycytidylic acid (poly(I:C)), in mice by combining them with plant-produced RBD-Fc, and the differences in the immunogenicity of RBD-Fc with different adjuvants were evaluated. The specific antibody responses in terms of total IgG, IgG1, and IgG2a subtypes and neutralizing antibodies, as well as vaccine-specific T-lymphocyte responses, induced by the different tested adjuvants were compared. We observed that all adjuvants tested here induced a high level of total IgG and neutralizing antibodies, but mPLA-SM and poly (I:C) showed the induction of a balanced IgG1 and IgG2a (Th2/Th1) immune response. Further, poly (I:C) significantly increased the frequency of IFN-γ-expressing cells compared with control, whereas no significant difference was observed between the adjuvanted groups. This data revealed the adjuvants' role in enhancing the immune response of RBD-Fc vaccination and the immune profiles elicited by different adjuvants, which could prove helpful for the rational development of next-generation SARS-CoV-2 RBD-Fc subunit vaccines. However, additional research is essential to further investigate the efficacy and safety of this vaccine formulation before clinical trials.

Plant-Produced Receptor-Binding Domain of SARS-CoV-2 Elicits Potent Neutralizing Responses in Mice and Non-human Primates

The emergence of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected global public health and economy. Despite the substantial efforts, only few vaccines are currently approved and some are in the different stages of clinical trials. As the disease rapidly spreads, an affordable and effective vaccine is urgently needed. In this study, we investigated the immunogenicity of plant-produced receptor-binding domain (RBD) of SARS-CoV-2 in order to use as a subunit vaccine. In this regard, RBD of SARS-CoV-2 was fused with Fc fragment of human IgG1 and transiently expressed in Nicotiana benthamiana by agroinfiltration. The plant-produced RBD-Fc fusion protein was purified from the crude extract by using protein A affinity column chromatography. Two intramuscular administration of plant-produced RBD-Fc protein formulated with alum as an adjuvant have elicited high neutralization titers in immunized mice and cynomolgus monkeys. Further it has induced a mixed Th1/Th2 immune responses and vaccine-specific T-lymphocyte responses which was confirmed by interferon-gamma (IFN-γ) enzyme-linked immunospot assay. Altogether, our results demonstrated that the plant-produced SARS-CoV-2 RBD has the potential to be used as an effective vaccine candidate against SARS-CoV-2. To our knowledge, this is the first report demonstrating the immunogenicity of plant-produced SARS-CoV-2 RBD protein in mice and non-human primates.

Anti-SARS-CoV-2 Activity of Andrographis paniculata Extract and Its Major Component Andrographolide in Human Lung Epithelial Cells and Cytotoxicity Evaluation in Major Organ Cell Representatives

The coronaviruses disease 2019 (COVID-19) caused by a novel coronavirus (SARS-CoV-2) has become a major health problem, affecting more than 50 million people with over one million deaths globally. Effective antivirals are still lacking. Here, we optimized a high-content imaging platform and the plaque assay for viral output study using the legitimate model of human lung epithelial cells, Calu-3, to determine the anti-SARS-CoV-2 activity of Andrographis paniculata extract and its major component, andrographolide. SARS-CoV-2 at 25TCID50 was able to reach the maximal infectivity of 95% in Calu-3 cells. Postinfection treatment of A. paniculata and andrographolide in SARS-CoV-2-infected Calu-3 cells significantly inhibited the production of infectious virions with an IC50 of 0.036 μg/mL and 0.034 μM, respectively, as determined by the plaque assay. The cytotoxicity profile developed over the cell line representatives of major organs, including liver (HepG2 and imHC), kidney (HK-2), intestine (Caco-2), lung (Calu-3), and brain (SH-SY5Y), showed a CC50 of >100 μg/mL for A. paniculata extract and 13.2-81.5 μM for andrographolide, respectively, corresponding to a selectivity index of over 380. In conclusion, this study provided experimental evidence in favor of A. paniculata and andrographolide for further development as a monotherapy or in combination with other effective drugs against SARS-CoV-2 infection.

Anti-SARS-CoV-2 Activity of Andrographis paniculata Extract and Its Major Component Andrographolide in Human Lung Epithelial Cells and Cytotoxicity Evaluation in Major Organ Cell Representatives

The coronaviruses disease 2019 (COVID-19) caused by a novel coronavirus (SARS-CoV-2) has become a major health problem, affecting more than 50 million people with over one million deaths globally. Effective antivirals are still lacking. Here, we optimized a high-content imaging platform and the plaque assay for viral output study using the legitimate model of human lung epithelial cells, Calu-3, to determine the anti-SARS-CoV-2 activity of Andrographis paniculata extract and its major component, andrographolide. SARS-CoV-2 at 25TCID₅₀ was able to reach the maximal infectivity of 95% in Calu-3 cells. Postinfection treatment of A. paniculata and andrographolide in SARS-CoV-2-infected Calu-3 cells significantly inhibited the production of infectious virions with an IC₅₀ of 0.036 μg/mL and 0.034 μM, respectively, as determined by the plaque assay. The cytotoxicity profile developed over the cell line representatives of major organs, including liver (HepG2 and imHC), kidney (HK-2), intestine (Caco-2), lung (Calu-3), and brain (SH-SY5Y), showed a CC₅₀ of >100 μg/mL for A. paniculata extract and 13.2-81.5 μM for andrographolide, respectively, corresponding to a selectivity index of over 380. In conclusion, this study provided experimental evidence in favor of A. paniculata and andrographolide for further development as a monotherapy or in combination with other effective drugs against SARS-CoV-2 infection.

Rapid and Efficient Cell-to-Cell Transmission of Avian Influenza H5N1 Virus in MDCK Cells Is Achieved by Trogocytosis

Viruses have developed direct cell-to-cell transfer strategies to enter target cells without being released to escape host immune responses and antiviral treatments. These strategies are more rapid and efficient than transmission through indirect mechanisms of viral infection between cells. Here, we demonstrate that an H5N1 influenza virus can spread via direct cell-to-cell transfer in Madin-Darby canine kidney (MDCK) cells. We compared cell-to-cell transmission of the H5N1 virus to that of a human influenza H1N1 virus. The H5N1 virus has been found to spread to recipient cells faster than the human influenza H1N1 virus. Additionally, we showed that plasma membrane exchange (trogocytosis) occurs between co-cultured infected donor cells and uninfected recipient cells early point, allowing the intercellular transfer of viral material to recipient cells. Notably, the H5N1 virus induced higher trogocytosis levels than the H1N1 virus, which could explain the faster cell-to-cell transmission rate of H5N1. Importantly, this phenomenon was also observed in A549 human lung epithelial cells, which are representative cells in the natural infection site. Altogether, our results provide evidence demonstrating that trogocytosis could be the additional mechanism utilized by the H5N1 virus for rapid and efficient cell-to-cell transmission.

Development of Plant-Produced Recombinant ACE2-Fc Fusion Protein as a Potential Therapeutic Agent Against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease (COVID-19) which has recently emerged as a potential threat to global public health. SARS-CoV-2 is the third known human coronavirus that has huge impact on the human population after SARS-CoV and MERS-CoV. Although some vaccines and therapeutic drugs are currently in clinical trials, none of them are approved for commercial use yet. As with SARS-CoV, SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) as the cell entry receptor to enter into the host cell. In this study, we have transiently produced human ACE2 fused with the Fc region of human IgG1 in Nicotiana benthamiana and the in vitro neutralization efficacy of the plant-produced ACE2-Fc fusion protein was assessed. The recombinant ACE2-Fc fusion protein was expressed in N. benthamiana at 100 μg/g leaf fresh weight on day 6 post-infiltration. The recombinant fusion protein showed potent binding to receptor binding domain (RBD) of SARS-CoV-2. Importantly, the plant-produced fusion protein exhibited potent anti-SARS-CoV-2 activity in vitro. Treatment with ACE2-Fc fusion protein after viral infection dramatically inhibit SARS-CoV-2 infectivity in Vero cells with an IC50 value of 0.84 μg/ml. Moreover, treatment with ACE2-Fc fusion protein at the pre-entry stage suppressed SARS-CoV-2 infection with an IC50 of 94.66 μg/ml. These findings put a spotlight on the plant-produced ACE2-Fc fusion protein as a potential therapeutic candidate against SARS-CoV-2.

Colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) as a visual diagnostic platform for the detection of the emerging coronavirus SARS-CoV-2

RT-LAMP to detect SARS-CoV-2: in a positive sample, RT-LAMP leads to a color change from pink to yellow.

Rapid production of SARS-CoV-2 receptor binding domain (RBD) and spike specific monoclonal antibody CR3022 in Nicotiana benthamiana

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for the ongoing global outbreak of coronavirus disease (COVID-19) which is a significant threat to global public health. The rapid spread of COVID-19 necessitates the development of cost-effective technology platforms for the production of vaccines, drugs, and protein reagents for appropriate disease diagnosis and treatment. In this study, we explored the possibility of producing the receptor binding domain (RBD) of SARS-CoV-2 and an anti-SARS-CoV monoclonal antibody (mAb) CR3022 in Nicotiana benthamiana. Both RBD and mAb CR3022 were transiently produced with the highest expression level of 8 μg/g and 130 μg/g leaf fresh weight respectively at 3 days post-infiltration. The plant-produced RBD exhibited specific binding to the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2). Furthermore, the plant-produced mAb CR3022 binds to SARS-CoV-2, but fails to neutralize the virus in vitro. This is the first report showing the production of anti-SARS-CoV-2 RBD and mAb CR3022 in plants. Overall these findings provide a proof-of-concept for using plants as an expression system for the production of SARS-CoV-2 antigens and antibodies or similar other diagnostic reagents against SARS-CoV-2 rapidly, especially during epidemic or pandemic situation.

Rapid production of SARS-CoV-2 receptor binding domain (RBD) and spike specific monoclonal antibody CR3022 in Nicotiana benthamiana

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for the ongoing global outbreak of coronavirus disease (COVID-19) which is a significant threat to global public health. The rapid spread of COVID-19 necessitates the development of cost-effective technology platforms for the production of vaccines, drugs, and protein reagents for appropriate disease diagnosis and treatment. In this study, we explored the possibility of producing the receptor binding domain (RBD) of SARS-CoV-2 and an anti-SARS-CoV monoclonal antibody (mAb) CR3022 in Nicotiana benthamiana. Both RBD and mAb CR3022 were transiently produced with the highest expression level of 8 μg/g and 130 μg/g leaf fresh weight respectively at 3 days post-infiltration. The plant-produced RBD exhibited specific binding to the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2). Furthermore, the plant-produced mAb CR3022 binds to SARS-CoV-2, but fails to neutralize the virus in vitro. This is the first report showing the production of anti-SARS-CoV-2 RBD and mAb CR3022 in plants. Overall these findings provide a proof-of-concept for using plants as an expression system for the production of SARS-CoV-2 antigens and antibodies or similar other diagnostic reagents against SARS-CoV-2 rapidly, especially during epidemic or pandemic situation.

Trogocytosis with monocytes associated with increased α2,3 sialic acid expression on B cells during H5N1 influenza virus infection

The immunopathogenesis of H5N1 virus has been studied intensively since it caused cross-species infection and induced high mortality to human. We previously observed the interaction between monocytes and B cells, which increased the susceptibility of B cell to H5N1 virus infection after a co-culture. Levels of α2,3 sialic acid (avian flu receptor) were also significantly increased on B cell surface in this co-culture model with unclear explanation. In this study, we aimed to determine the possible mechanism that responded for this increase in α2,3 sialic acid on B cells. Acquisition of α2,3 SA by B cells via cell contact-dependent trogocytosis was proposed. Results showed that the lack of α2,3 SA was detected on B cell surface, and B cells acquired membrane-bound α2,3 SA molecules from monocytes in H5N1-infected co-cultures. Occurrence of membrane exchange mainly relied on H5N1 infection and cell-cell contact as opposed to a mock infection and transwell. The increase in α2,3 SA on B cell surface mediated by trogocytosis was associated with the enhanced susceptibility to H5N1 infection. These observations thus provide the evidence that H5N1 influenza virus may utilize trogocytosis to expand its cell tropism and spread to immune cells despite the lack of avian flu receptor.

Monoclonal Antibodies B38 and H4 Produced in Nicotiana benthamiana Neutralize SARS-CoV-2 in vitro

The ongoing coronavirus disease 2019 (COVID-19) outbreak caused by novel zoonotic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was initially reported in Wuhan city, Hubei Province of China, in late December 2019. The rapid global spread of the virus calls for the urgent development of vaccines or therapeutics for human applications to combat the coronavirus infection. Monoclonal antibodies (mAbs) have been utilized as effective therapeutics for treating various infectious diseases. In the present study, we evaluated the feasibility of plant expression system for the rapid production of recently identified therapeutically suitable human anti-SARS-CoV-2 mAbs B38 and H4. Transient co-expression of heavy-chain and light-chain sequences of both the antibodies by using plant expression geminiviral vector resulted in rapid accumulation of assembled mAbs in Nicotiana benthamiana leaves within 4 days post-infiltration. Furthermore, both the mAbs were purified from the plant crude extracts with single-step protein A affinity column chromatography. The expression level of mAb B38 and H4 was estimated to be 4 and 35 μg/g leaf fresh weight, respectively. Both plant-produced mAbs demonstrated specific binding to receptor binding domain (RBD) of SARS-CoV-2 and exhibited efficient virus neutralization activity in vitro. To the best of our knowledge, this is the first report of functional anti-SARS-CoV-2 mAbs produced in plants, which demonstrates the ability of using a plant expression system as a suitable platform for the production of effective, safe, and affordable SARS-CoV-2 mAbs to fight against the spread of this highly infectious pathogen.