A Multiplex Microsphere IgG Assay for SARS-CoV-2 Using ACE2-Mediated Inhibition as a Surrogate for Neutralization

Variant-specific antibody profiling for tracking SARS-CoV-2 variant infections in children and adolescents

Monitoring the seroprevalence of SARS-CoV-2 in children and adolescents can provide valuable information for effective SARS-CoV-2 surveillance, and thus guide vaccination strategies. In this study, we quantified antibodies against the spike S1 domains of several SARS-CoV-2 variants (wild-type, Alpha, Delta, and Omicron variants) as well as endemic human coronaviruses (HCoVs) in 1,309 children and adolescents screened between December 2020 and March 2023. Their antibody binding profiles were compared with those of 22 pre-pandemic samples from children and adolescents using an in-house Luminex®-based Corona Array (CA). The primary objectives of this study were to (i) monitor SARS-CoV-2-specific antibodies in children and adolescents, (ii) evaluate whether the S1-specific antibody response can identify the infecting variant of concern (VoC), (iii) estimate the prevalence of silent infections, and (iv) test whether vaccination or infection with SARS-CoV-2 induce HCoV cross-reactive antibodies. Both SARS-CoV-2 infection and vaccination induced a robust antibody response against the S1 domain of WT and VoCs in children and adolescents. Antibodies specific for the S1 domain were able to distinguish between SARS-CoV-2 VoCs in infected children. The serologically identified VoC was typically the predominant VoC at the time of infection. Furthermore, our highly sensitive CA identified more silent SARS-CoV-2 infections than a commercial ELISA (12.1% vs. 6.3%, respectively), and provided insights into the infecting VoC. Seroconversion to endemic HCoVs occurred in early childhood, and vaccination or infection with SARS-CoV-2 did not induce HCoV S1 cross-reactive antibodies. In conclusion, the antibody response to the S1 domain of the spike protein of SARS-CoV-2 is highly specific, providing information about the infecting VoC and revealing clinically silent infections.

A bead-based multiplex assay covering all coronaviruses pathogenic for humans for sensitive and specific surveillance of SARS-CoV-2 humoral immunity

Serological assays measuring antibodies against SARS-CoV-2 are key to describe the epidemiology, pathobiology or induction of immunity after infection or vaccination. Of those, multiplex assays targeting multiple antigens are especially helpful as closely related coronaviruses or other antigens can be analysed simultaneously from small sample volumes, hereby shedding light on patterns in the immune response that would otherwise remain undetected. We established a bead-based 17-plex assay detecting antibodies targeting antigens from all coronaviruses pathogenic for humans: SARS-CoV-2, SARS-CoV, MERS-CoV, HCoV strains 229E, OC43, HKU1, and NL63. The assay was validated against five commercial serological immunoassays, a commercial surrogate virus neutralisation test, and a virus neutralisation assay, all targeting SARS-CoV-2. It was found to be highly versatile as shown by antibody detection from both serum and dried blot spots and as shown in three case studies. First, we followed seroconversion for all four endemic HCoV strains and SARS-CoV-2 in an outbreak study in day-care centres for children. Second, we were able to link a more severe clinical course to a stronger IgG response with this 17-plex-assay, which was IgG1 and IgG3 dominated. Finally, our assay was able to discriminate recent from previous SARS-CoV-2 infections by calculating the IgG/IgM ratio on the N antigen targeting antibodies. In conclusion, due to the comprehensive method comparison, thorough validation, and the proven versatility, our multiplex assay is a valuable tool for studies on coronavirus serology.

Diagnostics and analysis of SARS-CoV-2: current status, recent advances, challenges and perspectives

The disastrous spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has induced severe public healthcare issues and weakened the global economy significantly. Although SARS-CoV-2 infection is not as fatal as the initial outbreak, many infected victims suffer from long COVID. Therefore, rapid and large-scale testing is critical in managing patients and alleviating its transmission. Herein, we review the recent advances in techniques to detect SARS-CoV-2. The sensing principles are detailed together with their application domains and analytical performances. In addition, the advantages and limits of each method are discussed and analyzed. Besides molecular diagnostics and antigen and antibody tests, we also review neutralizing antibodies and emerging SARS-CoV-2 variants. Further, the characteristics of the mutational locations in the different variants with epidemiological features are summarized. Finally, the challenges and possible strategies are prospected to develop new assays to meet different diagnostic needs. Thus, this comprehensive and systematic review of SARS-CoV-2 detection technologies may provide insightful guidance and direction for developing tools for the diagnosis and analysis of SARS-CoV-2 to support public healthcare and effective long-term pandemic management and control.

Development, Validation, and Utilization of a Luminex-Based SARS-CoV-2 Multiplex Serology Assay

SARS-CoV-2 antibody testing is important for seroprevalence studies and for evaluating vaccine immune responses. We developed and validated a Luminex bead-based multiplex serology assay for measuring IgG levels of anti-SARS-CoV-2 antibodies against full-length spike (S), nucleocapsid (N), and receptor-binding domains (RBDs) of wild-type, RBD N501Y mutant, RBD E484K mutant, RBD triple mutant SARS-CoV-2 proteins, Sars-CoV-1, MERS-CoV, and common human coronaviruses, including SARS-CoV-2, OC43, 229E, HKU1, and NL63. Assay cutoff values, sensitivity, and specificity were determined using samples from 160 negative controls and 60 PCR-confirmed, SARS-CoV-2-infected individuals. The assay demonstrated sensitivities of 98.3%, 95%, and 100% and specificities of 100%, 99.4%, and 98.8% for anti-(S), -N, and -RBD, respectively. Results are expressed as IgG antibody concentrations in BAU/mL, using the WHO international standard (NIBSC code 20/136) for anti-SARS-CoV-2 IgG antibodies. When the multiplex assay was performed and compared with singleplex assays, the IgG antibody measurement geometric mean ratios were between 0.895 and 1.122, and no evidence of interference was observed between antigens. Lower and upper IgG concentration limits, based on accuracy (between 80% and 120%), precision (percent relative standard deviation, ≤25%), and sample dilutional linearity (between 75% and 125%), were used to establish the assay range. Precision was established by evaluating 24 individual human serum samples obtained from vaccinated and SARS-CoV-2-infected individuals. The assay provided reproducible, consistent results with typical coefficients of variation of ≤20% for all assays, irrespective of the run, day, or analyst. Results indicate the assay has high sensitivity and specificity and thus is appropriate for use in measuring SARS-CoV-2 IgG antibodies in infected and vaccinated individuals. IMPORTANCE The SARS-CoV-2 pandemic resulted in the development and validation of multiple serology tests with variable performance. While there are multiple SARS-CoV-2 serology tests to detect SARS-CoV-2 antibodies, the focus is usually either on only one antigen at a time or multiple proteins from only one SARS-CoV-2 variant. These tests usually do not evaluate antibodies against viral proteins from different SARS-CoV-2 variants or from other coronaviruses. Here, we evaluated a multiplex serology test based on Luminex technology, where antibodies against multiple domains of SARS-CoV-2 wild type, SARS-CoV-2 mutants, and common coronavirus antibodies are detected simultaneously in a single assay. This Luminex-based multiplex serology assay can enhance our understanding of the immune response to SARS-CoV-2 infection and vaccination.

Importance, Applications and Features of Assays Measuring SARS-CoV-2 Neutralizing Antibodies

More than three years ago, the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) caused the unforeseen COVID-19 pandemic with millions of deaths. In the meantime, SARS-CoV-2 has become endemic and is now part of the repertoire of viruses causing seasonal severe respiratory infections. Due to several factors, among them the development of SARS-CoV-2 immunity through natural infection, vaccination and the current dominance of seemingly less pathogenic strains belonging to the omicron lineage, the COVID-19 situation has stabilized. However, several challenges remain and the possible new occurrence of highly pathogenic variants remains a threat. Here we review the development, features and importance of assays measuring SARS-CoV-2 neutralizing antibodies (NAbs). In particular we focus on in vitro infection assays and molecular interaction assays studying the binding of the receptor binding domain (RBD) with its cognate cellular receptor ACE2. These assays, but not the measurement of SARS-CoV-2-specific antibodies per se, can inform us of whether antibodies produced by convalescent or vaccinated subjects may protect against the infection and thus have the potential to predict the risk of becoming newly infected. This information is extremely important given the fact that a considerable number of subjects, in particular vulnerable persons, respond poorly to the vaccination with the production of neutralizing antibodies. Furthermore, these assays allow to determine and evaluate the virus-neutralizing capacity of antibodies induced by vaccines and administration of plasma-, immunoglobulin preparations, monoclonal antibodies, ACE2 variants or synthetic compounds to be used for therapy of COVID-19 and assist in the preclinical evaluation of vaccines. Both types of assays can be relatively quickly adapted to newly emerging virus variants to inform us about the magnitude of cross-neutralization, which may even allow us to estimate the risk of becoming infected by newly appearing virus variants. Given the paramount importance of the infection and interaction assays we discuss their specific features, possible advantages and disadvantages, technical aspects and not yet fully resolved issues, such as cut-off levels predicting the degree of in vivo protection.

Multiplex Immunoassay Approaches Using Luminex® xMAP® Technology for the Study of COVID-19 Disease

The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has been one of the most severe outbreaks of respiratory illness in history. The clinical symptoms of COVID-19 may be similar to flu, although they can be life-threatening, particularly in the elderly and immunocompromised population. Together with nucleic acid detection, serological testing has been essential for the diagnosis of SARS-CoV-2 infection but has been critically important for studying the epidemiology, serosurveillance, and for vaccine research and development. Multiplexed immunoassay technologies have a particular advantage as they can simultaneously measure multiple analytes from a single sample. xMAP technology is a multiplex analysis platform that can measure up to 500 analytes at the same time from the same sample. It has been shown to be an important tool for studying immune response to the various SARS-CoV-2 antigens, as well as for measuring host protein biomarker levels as prognostic indicators of COVID-19. In this chapter, we describe several key studies where xMAP technology was used for multiplexed analysis of SARS-COV-2 antibody responses and host protein expression in COVID-19 patients.

Detecting SARS-CoV-2 neutralizing immunity: highlighting the potential of split nanoluciferase technology

The coronavirus disease 2019 (COVID-19) pandemic has progressed over 2 years since its onset causing significant health concerns all over the world and is currently curtailed by mass vaccination. Immunity acquired against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be following either infection or vaccination. However, one can never be sure whether the acquired immunity is adequate to protect the individual from subsequent infection because of three important factors: individual variations in humoral response dynamics, waning of protective antibodies over time, and the emergence of immune escape mutants. Therefore, a test that can accurately differentiate the protected from the vulnerable is the need of the hour. The plaque reduction neutralization assay is the conventional gold standard test for estimating the titers of neutralizing antibodies that confer protection. However, it has got several drawbacks, which hinder the practical application of this test for wide-scale usage. Hence, various tests have been developed to detect protective immunity against SARS-CoV-2 that directly or indirectly assess the presence of neutralizing antibodies to SARS-CoV-2 in a lower biosafety setting. In this review, the pros and cons of the currently available assays are elaborated in detail and special focus is put on the scope of the novel split nanoluciferase technology for detecting SARS-CoV-2 neutralizing antibodies.

Magnetofluid-Integrated Multicolor Immunochip for Visual Analysis of Neutralizing Antibodies to SARS-CoV-2 Variants

The global spread of SARS-CoV-2 virus has severely affected human health, life, and work. Vaccine immunization is considered to be an effective means to protect the body from infection. Therefore, timely analysis of the antibody level is helpful to identify people with low immune response or attenuated antibodies so as to carry out targeted and precise vaccine booster immunization. Herein, we develop a magnetofluid-integrated multicolor immunochip, as a sample-to-answer system in a fully enclosed space, for visual analysis of neutralizing antibodies of SARS-CoV-2. Generally, this chip adopts an innovative three-dimensional two-phase system that utilizes mineral oil to block the connection between reagent wells in the vertical direction and provides a wide interface for rapid and nondestructive shuttle of magnetic beads during the immunoassay. In order to obtain visualized signal output, gold nanorods with a size-dependent color effect are used as the colorful chromogenic substrates for evaluation of the antibody level. Using this chip, the neutralizing antibodies were successfully detected in vaccine-immunized volunteers with 83.3% sensitivity and 100% specificity. Furthermore, changes in antibody levels of the same individual over time were also reflected by the multicolor assay. Overall, benefiting from simple operation, airtight safety, and nonrequirement of external equipment, this platform can provide a new point-of-care testing strategy for alleviating the shortage of medical resources and promoting epidemic control in underdeveloped areas.

Simultaneous Measurement of IgM and IgG Antibodies to SARS-CoV-2 Spike, RBD, and Nucleocapsid Multiplexed in a Single Assay on the xMAP INTELLIFLEX DR-SE Flow Analyzer

The multiplex capabilities of the new xMAP INTELLIFLEX DR-SE flow analyzer were explored by modifying a serological assay previously used to characterize the IgG antibody to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The goal was to examine the instrument's performance and to simultaneously measure IgM and IgG antibody responses against multiple SARS-CoV-2 antigens in a single assay. Specific antibodies against the SARS-CoV-2 spike (S), receptor binding domain (RBD), and nucleocapsid (N) proteins were investigated in 310 symptomatic case patients using a fluorescent microsphere immunoassay and simultaneous detection of IgM and IgG. Neutralization potential was studied using the addition of soluble angiotensin-converting enzyme 2 (ACE2) to block antibody binding. A profile extending to 180 days from symptom onset (DFSO) was described for antibodies specific to each viral antigen. Generally, IgM levels peaked and declined rapidly ∼3-4 weeks following infection, whereas S- and RBD-specific IgG plateaued at 80 DFSO. ACE2 more effectively prevented IgM and IgG binding in convalescent cases > 30 DFSO, suggesting those antibodies had greater neutralization potential. This work highlighted the multiplex and multi-analyte potential of the xMAP INTELLIFLEX DR-SE, and provided further evidence for antigen-specific IgM and IgG trajectories in acute and convalescent cases. IMPORTANCE The xMAP INTELLIFLEX DR-SE enabled simultaneous and semi-quantitative detection of both IgM and IgG to three different SARS-CoV-2 antigens in a single assay. The assay format is advantageous for rapid and medium-throughput profiling using a small volume of specimen. The xMAP INTELLIFLEX DR-SE technology demonstrated the potential to include numerous SARS-CoV-2 antigens; future work could incorporate multiple spike protein variants in a single assay. This could be an important feature for assessing the serological response to emerging variants of SARS-CoV-2.

Characterizing Kinetics and Avidity of SARS-CoV-2 Antibody Responses in COVID-19 Greek Patients

In-depth understanding of the immune response provoked by SARS-CoV-2 infection is necessary, as there is a great risk of reinfection and a difficulty in achieving herd immunity due to a decline in both antibody concentration and avidity. Avidity testing, however, could overcome variability in the immune response associated with sex or clinical symptoms, and thus differentiate between recent and past infections. In this context, here, we analyzed SARS-CoV-2 antibody kinetics and avidity in Greek hospitalized (26%) and non-hospitalized (74%) COVID-19 patients (N = 71) in the course of up to 15 months after their infection to improve the accuracy of the serological diagnosis in dating the onset of the infection. The results showed that IgG-S1 levels decline significantly at four months (p = 0.0239) in both groups of patients and are higher in hospitalized ones (up to 2.1-fold, p < 0.001). Additionally, hospitalized patients’ titers drop greatly and are equalized to non-hospitalized ones only at a time-point of twelve to fifteen months. Antibody levels of women in total remain more stable months after infection, compared to men. Furthermore, we examined the differential maturation of IgG avidity after SARS-CoV-2 infection, showing an incomplete maturation of avidity that results in a plateau at four months after infection. We also defined 38.2% avidity (sensitivity: 58.9%, specificity: 90.91%) as an appropriate “cut-off” that could be used to determine the stage of infection before avidity reaches a plateau.

Comparison of the Anti-SARS-CoV-2 Surrogate Neutralization Assays by TECOmedical and DiaPROPH-Med with Samples from Vaccinated and Infected Individuals

Anti-SARS-CoV-2-specific serological responses are a topic of ongoing evaluation studies. In the study presented here, the anti-SARS-CoV-2 surrogate neutralization assays by TECOmedical and DiaPROPH -Med were assessed in a head-to-head comparison with serum samples of individuals after vaccination as well as after previous infection with SARS-CoV-2. In case of discordant results, a cell culture-based neutralization assay was applied as a reference standard. The TECOmedical assay showed sensitivity and specificity of 100% and 61.3%, respectively, the DiaPROPH-Med assay 95.0% and 48.4%, respectively. As a side finding of the study, differences in the likelihood of expressing neutralizing antibodies could be shown for different exposition types. So, 60 of 81 (74.07%) of the samples with only one vaccination showed an expression of neutralizing antibodies in contrast to 85.71% (60 of 70 samples) of the samples with two vaccinations and 100% (40 of 40) of the samples from previously infected individuals. In conclusion, the both assays showed results similar to previous assessments. While the measured diagnostic accuracy of both assays requires further technical improvement of this diagnostic approach, as the calculated specificity values of 61.3% and 48.4%, respectively, appear acceptable for diagnostic use only in populations with a high percentage of positive subjects, but not at expectedly low positivity rates.

Development of a quantitative COVID-19 multiplex assay and its use for serological surveillance in a low SARS-CoV-2 incidence community

A serological COVID-19 Multiplex Assay was developed and validated using serum samples from convalescent patients and those collected prior to the 2020 pandemic. After initial testing of multiple potential antigens, the SARS-CoV-2 nucleocapsid protein (NP) and receptor-binding domain (RBD) of the spike protein were selected for the human COVID-19 Multiplex Assay. A comparison of synthesized and mammalian expressed RBD proteins revealed clear advantages of mammalian expression. Antibodies directed against NP strongly correlated with SARS-CoV-2 virus neutralization assay titers (rsp = 0.726), while anti-RBD correlation was moderate (rsp = 0.436). Pan-Ig, IgG, IgA, and IgM against NP and RBD antigens were evaluated on the validation sample sets. Detection of NP and RBD specific IgG and IgA had outstanding performance (AUC > 0.90) for distinguishing patients from controls, but the dynamic range of the IgG assay was substantially greater. The COVID-19 Multiplex Assay was utilized to identify seroprevalence to SARS-CoV-2 in people living in a low-incidence community in Ithaca, NY. Samples were taken from a cohort of healthy volunteers (n = 332) in early June 2020. Only two volunteers had a positive result on a COVID-19 PCR test performed prior to serum sampling. Serological testing revealed an exposure rate of at least 1.2% (NP) or as high as 5.7% (RBD), higher than the measured incidence rate of 0.16% in the county at that time. This highly sensitive and quantitative assay can be used for monitoring community exposure rates and duration of immune response following both infection and vaccination.

OUP accepted manuscript

BACKGROUND

A protective antibody response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is crucial to decrease morbidity and mortality from severe coronavirus disease 2019 (COVID-19) disease. The effects of preexisting anti-human coronavirus (HCoV) antibodies on the SARS-CoV-2-specific immunoglobulin G (IgG) responses and severity of disease are currently unclear.

METHODS

We profiled anti-spike (S), S1, S2, and receptor-binding domain IgG antibodies against SARS-CoV-2 and 6 HCoVs using a multiplex assay (mPLEX-CoV) with serum samples from SARS-CoV-2 infected (n = 155) and pre-COVID-19 (n = 188) cohorts.

RESULTS

COVID-19 subjects showed significantly increased anti-S SARS-CoV-2 IgG levels that were highly correlated with IgG antibodies against OC43 and HKU1 S proteins. However, OC43 and HKU1 anti-S antibodies in pre-COVID-19 era sera did not cross-react with SARS-CoV-2. Unidirectional cross-reactive antibodies elicited by SARS-CoV-2 infection were distinct from the bidirectional cross-reactive antibodies recognizing homologous strains RaTG13 and SARS-CoV-1. High anti-OC43 and anti-S2 antibody levels were associated with both a rapid anti-SARS-CoV-2 antibody response and increased disease severity. Subjects with increased sequential organ failure assessment (SOFA) scores developed a higher ratio of S2- to S1-reactive antibodies.

CONCLUSIONS

Early and rapid emergence of OC43 S- and S2-reactive IgG after SARS-CoV-2 infection correlates with COVID-19 disease severity.

Kinetics of anti-SARS-CoV-2 IgG antibody levels and potential influential factors in subjects with COVID-19: A 11-month follow-up study

We aim to study kinetics of anti-SARS-CoV-2 IgG antibody levels in subjects with COVID-19 for up to 11 months and the potential influential factors. The study was a prospective longitudinal study. The analyses were based on 77 serum/plasma samples with a mean of 4 samples per participant (range 1 – 18) in 20 participants with at least one positive Polymerase Chain Reaction testing result from 19 March 2020 up to 10 February 2021. Among the subjects (median age 34.5 years, 65% male), IgG level declined with the follow-up time (per month; geometric mean ratio [GMR] 0.73; 95% CI, 0.72 – 0.74). In a small sample of subjects from the general population with COVID-19, IgG levels declined non-linearly from month 2 to 11 with individual heterogeneity in quantity and changing speed and may be associated with gender, race and the loss of smell and taste.

Antibody Responses to Natural SARS-CoV-2 Infection or after COVID-19 Vaccination

The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is the causative agent of the ongoing pandemic of coronavirus disease 2019 (COVID-19). The clinical severity of COVID-19 ranges from asymptomatic to critical disease and, eventually, death in smaller subsets of patients. The first case of COVID-19 was declared at the end of 2019 and it has since spread worldwide and remained a challenge in 2021, with the emergence of variants of concern. In fact, new concerns were the still unclear situation of SARS-CoV-2 immunity during the ongoing pandemic and progress with vaccination. If maintained at sufficiently high levels, the immune response could effectively block reinfection, which might confer long-lived protection. Understanding the protective capacity and the duration of humoral immunity during SARS-CoV-2 infection or after vaccination is critical for managing the pandemic and would also provide more evidence about the efficacy of SARS-CoV-2 vaccines. However, the exact features of antibody responses that govern SARS-CoV-2 infection or after vaccination remain unclear. This review summarizes the main knowledge that we have about the humoral immune response during COVID-19 disease or after vaccination. Such knowledge should help to optimize vaccination strategies and public health decisions.

Antibody Mediated Immunity to SARS-CoV-2 and Human Coronaviruses: Multiplex Beads Assay and Volumetric Absorptive Microsampling to Generate Immune Repertoire Cartography

The COVID-19 pandemic is caused by SARS-CoV-2, a novel zoonotic coronavirus. Emerging evidence indicates that preexisting humoral immunity against other seasonal human coronaviruses (HCoVs) plays a critical role in the specific antibody response to SARS-CoV-2. However, current work to assess the effects of preexisting and cross-reactive anti-HCoVs antibodies has been limited. To address this issue, we have adapted our previously reported multiplex assay to simultaneously and quantitatively measure anti-HCoV antibodies. The full mPlex-CoV panel covers the spike (S) and nucleocapsid (N) proteins of three highly pathogenic HCoVs (SARS-CoV-1, SARS-CoV-2, MERS) and four human seasonal strains (OC43, HKU1, NL63, 229E). Combining this assay with volumetric absorptive microsampling (VAMS), we measured the anti-HCoV IgG, IgA, and IgM antibodies in fingerstick blood samples. The results demonstrate that the mPlex-CoV assay has high specificity and sensitivity. It can detect strain-specific anti-HCoV antibodies down to 0.1 ng/ml with 4 log assay range and with low intra- and inter-assay coefficients of variation (%CV). We also estimate multiple strain HCoVs IgG, IgA and IgM concentration in VAMS samples in three categories of subjects: pre-COVID-19 (n=21), post-COVID-19 convalescents (n=19), and COVID-19 vaccine recipients (n=14). Using metric multidimensional scaling (MDS) analysis, HCoVs IgG concentrations in fingerstick blood samples were well separated between the pre-COVID-19, post-COVID-19 convalescents, and COVID-19 vaccine recipients. In addition, we demonstrate how multi-dimensional scaling analysis can be used to visualize IgG mediated antibody immunity against multiple human coronaviruses. We conclude that the combination of VAMS and the mPlex-Cov assay is well suited to performing remote study sample collection under pandemic conditions to monitor HCoVs antibody responses in population studies.

A Microflow Cytometry-Based Agglutination Immunoassay for Point-of-Care Quantitative Detection of SARS-CoV-2 IgM and IgG

A rapid, sensitive and simple microflow cytometry-based agglutination immunoassay (MCIA) was developed for point-of-care (POC) quantitative detection of SARS-CoV-2 IgM and IgG antibodies. The antibody concentration was determined by using the transit time of beads aggregates. A linear relationship was established between the average transit time and the concentration of SARS-CoV-2 IgM and IgG, respectively. The limit of detection (LOD) of SARS-CoV-2 IgM and IgG by the MCIA measurement are 0.06 mg/L and 0.10 mg/L, respectively. The 10 µL sample consumption, 30 min assay time and the compact setup make this technique suitable for POC quantitative detection of SARS-CoV-2 antibodies.

Towards Quantitative and Standardized Serological and Neutralization Assays for COVID-19

Quantitative and robust serology assays are critical measurements underpinning global COVID-19 response to diagnostic, surveillance, and vaccine development. Here, we report a proof-of-concept approach for the development of quantitative, multiplexed flow cytometry-based serological and neutralization assays. The serology assays test the IgG and IgM against both the full-length spike antigens and the receptor binding domain (RBD) of the spike antigen. Benchmarking against an RBD-specific SARS-CoV IgG reference standard, the anti-SARS-CoV-2 RBD antibody titer was quantified in the range of 37.6 µg/mL to 31.0 ng/mL. The quantitative assays are highly specific with no correlative cross-reactivity with the spike proteins of MERS, SARS1, OC43 and HKU1 viruses. We further demonstrated good correlation between anti-RBD antibody titers and neutralizing antibody titers. The suite of serology and neutralization assays help to improve measurement confidence and are complementary and foundational for clinical and epidemiologic studies.

A flexible, pan-species, multi-antigen platform for the detection and monitoring of SARS-CoV-2-specific antibody responses

The SARS-CoV-2 pandemic and the vaccination effort that is ongoing has created an unmet need for accessible, affordable, flexible and precise platforms for monitoring the induction, specificity and maintenance of virus-specific immune responses. Herein we validate a multiplex (Luminex-based) assay capable of detecting SARS-CoV-2-specific antibodies irrespective of host species, antibody isotype, and specimen type (e.g. plasma, serum, saliva or blood spots). The well-established precision of Luminex-based assays provides the ability to follow changes in antibody levels over time to many antigens, including multiple permutations of the most common SARS-CoV-2 antigens. This platform can easily measure antibodies known to correlate with neutralization activity as well as multiple non-SARS-CoV-2 antigens such as vaccines (e.g. Tetanus toxoid) or those from frequently encountered agents (influenza), which serve as stable reference points for quantifying the changing SARS-specific responses. All of the antigens utilized in our study can be made in-house, many in E. coli using readily available plasmids. Commercially sourced antigens may also be incorporated and newly available antigen variants can be rapidly produced and integrated, making the platform adaptable to the evolving viral strains in this pandemic.