Mouse Anti-SARS-CoV-2 NP Monoclonal antibody, clone F27D

Author summary The world is facing an unprecedented challenge with communities and economies affected by the growing pandemic of coronavirus disease 2019 (COVID-19). Currently, there is no vaccine or effective drugs have been approved to treat or prevent COVID-19. The development of antibody response to SARS-CoV-2, the virus that causes COVID-19, started to be reported but remained largely elusive. Understanding the adaptive responses where the body makes antibodies that specifically bind to the SARS-CoV-2 among COVID-19 patients provides fundamental information for developing effective treatment and preventive vaccine. In this study, we not only successively analyzed the specificity and magnitude of antibody responses using four SARS-CoV-2 related antigens, but also monitored the neutralization potency of the convalescent sera from COVID-19 patients at the time point of hospital discharge and follow-up visit. Our results indicated that most patients generated humoral responses against nucleoprotein and three spike protein-related antigens with their distinct kinetics profiles. Additionally, most convalescent sera had the varying extents of neutralization activities against SARS-CoV-2. Of note, we identified that IgA antibody responses specific to S1 and ECD were strongly correlated with neutralization activities in non-severe patients, but not in severe patients. Furthermore, we identified a significant reduction of neutralizing activities of the convalescent sera within one month. Our data provide a collective basis of serological testing, antibody-based intervention, and vaccine design of COVID-19. There is an urgent need for effective treatment and preventive vaccine to contain this devastating global pandemic, which requires a comprehensive understanding of humoral responses specific to SARS-CoV-2 during the disease progression and convalescent phase of COVID-19 patients. We continuously monitored the serum IgM and IgG responses specific to four SARS-CoV-2 related antigens, including the nucleoprotein (NP), receptor binding domain (RBD), S1 protein, and ectodomain (ECD) of the spike protein among non-severe and severe COVID-19 patients for seven weeks since disease onset. Most patients generated humoral responses against NP and spike protein-related antigens but with their distinct kinetics profiles. Combined detection of NP and ECD antigens as detecting antigen synergistically improved the sensitivity of the serological assay, compared to that of using NP or RBD as detection antigen. 80.7% of convalescent sera from COVID-19 patients revealed that the varying extents of neutralization activities against SARS-CoV-2. S1-specific and ECD-specific IgA responses were strongly correlated with the neutralization activities in non-severe patients, but not in severe patients. Moreover, the neutralizing activities of the convalescent sera were shown to significantly decline during the period between 21 days to 28 days after hospital discharge, accompanied by a substantial drop in RBD-specific IgA response. Our data provide evidence that are crucial for serological testing, antibody-based intervention, and vaccine design of COVID-19.

Background Coronavirus disease 2019 (COVID-19) causes severe community and nosocomial outbreaks. Comprehensive data for serial respiratory viral load and serum antibody responses from patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not yet available. Nasopharyngeal and throat swabs are usually obtained for serial viral load monitoring of respiratory infections but gathering these specimens can cause discomfort for patients and put health-care workers at risk. We aimed to ascertain the serial respiratory viral load of SARS-CoV-2 in posterior oropharyngeal (deep throat) saliva samples from patients with COVID-19, and serum antibody responses. Methods We did a cohort study at two hospitals in Hong Kong. We included patients with laboratory-confirmed COVID-19. We obtained samples of blood, urine, posterior oropharyngeal saliva, and rectal swabs. Serial viral load was ascertained by reverse transcriptase quantitative PCR (RT-qPCR). Antibody levels against the SARS-CoV-2 internal nucleoprotein (NP) and surface spike protein receptor binding domain (RBD) were measured using EIA. Whole-genome sequencing was done to identify possible mutations arising during infection. Findings Between Jan 22,2020, and Feb 12,2020,30 patients were screened for inclusion, of whom 23 were included (median age 62 years [range 37-75]). The median viral load in posterior oropharyngeal saliva or other respiratory specimens at presentation was 5.2 log 10 copies per mL (IQR 4.1-7.0). Salivary viral load was highest during the first week after symptom onset and subsequently declined with time (slope -0.15, 95% CI -0.19 to -0.11; R-2=0.71). In one patient, viral RNA was detected 25 days after symptom onset. Older age was correlated with higher viral load (Spearman's p=0.48,95% CI 0.074-0.75; p=0.020). For 16 patients with serum samples available 14 days or longer after symptom onset, rates of seropositivity were 94% for anti-NP IgG (n=15), 88% for anti-NP IgM (n=14), 100% for anti-RBD IgG (n=16), and 94% for anti-RBD IgM (n=15). Anti-SARS-CoV-2-NP or anti-SARS-CoV-2-RBD IgG levels correlated with virus neutralisation titre (R-2 >0.9). No genome mutations were detected on serial samples. Interpretation Posterior oropharyngeal saliva samples are a non-invasive specimen more acceptable to patients and health-care workers. Unlike severe acute respiratory syndrome, patients with COVID-19 had the highest viral load near presentation, which could account for the fast-spreading nature of this epidemic. This finding emphasises the importance of stringent infection control and early use of potent antiviral agents, alone or in combination, for high-risk individuals. Serological assay can complement RT-qPCR for diagnosis. Copyright (C) 2020 Elsevier Ltd. All rights reserved.