Advances in Neutralization Assays for SARS‐CoV‐2

Advancements in nanoparticle-based vaccine development against Japanese encephalitis virus: a systematic review

Vaccination remains the sole effective strategy for combating Japanese encephalitis (JE). Both inactivated and live attenuated vaccines exhibit robust immunogenicity. However, the production of these conventional vaccine modalities necessitates extensive cultivation of the pathogen, incurring substantial costs and presenting significant biosafety risks. Moreover, the administration of live pathogens poses potential hazards for individuals or animals with compromised immune systems or other health vulnerabilities. Subsequently, ongoing research endeavors are focused on the development of next-generation JE vaccines utilizing nanoparticle (NP) platforms. This systematic review seeks to aggregate the research findings pertaining to NP-based vaccine development against JE. A thorough literature search was conducted across established English-language databases for research articles on JE NP vaccine development published between 2000 and 2023. A total of twenty-eight published studies were selected for detailed analysis in this review. Of these, 16 studies (57.14%) concentrated on virus-like particles (VLPs) employing various structural proteins. Other approaches, including sub-viral particles (SVPs), biopolymers, and both synthetic and inorganic NP platforms, were utilized to a lesser extent. The results of these investigations indicated that, despite variations in the usage of adjuvants, dosages, NP types, antigenic proteins, and animal models employed across different studies, the candidate NP vaccines developed were capable of eliciting enhanced humoral and cellular adaptive immune responses, providing effective protection (70-100%) for immunized mice against lethal challenges posed by virulent Japanese encephalitis virus (JEV). In conclusion, prospective next-generation JE vaccines for humans and animals may emerge from these candidate formulations following further evaluation in subsequent vaccine development phases.

An Improved Theileria parva Sporozoite Seroneutralization Assay for the Identification of East Coast Fever Immune Correlates

BACKGROUND

Immune correlates of protection are ideal tools to predict treatment or vaccine efficacy. However, the accuracy of the immune correlate and the capability to robustly predict the outcome of a vaccine candidate are determined by the performance of the in vitro immunoassay used. Several Theileria parva sporozoite seroneutralization assays have previously been used to assess antibody functional activities; however, a common limitation has been the need for fresh material, target cells and sporozoites, and operator-to-operator bias. An improved assay represents a positive step toward overcoming challenges associated with variability and it might provide a more reliable means of establishing an immune correlate with protection after sub-unit vaccine administration.

METHODS

Herein, we describe key improvements, among them, (1) the use of frozen parasites and target cells to avoid batch-to-batch variations and (2) the development of a new assay read-out based on the detection of infected cells through flow cytometry, instead of the use of Giemsa staining and microscopic evaluation, in order to improve the reproducibility of the results.

RESULTS

The improved seroneutralization assay is not only able to detect the individual neutralizing capacity of antibodies; it also detects the additive effect of antibody combinations.

CONCLUSIONS

This effect is described for the first time in Theileria parva and is of great interest for new antigen discovery and/or the epitope discovery of already known antigens like p67, opening a new avenue for the identification of ECF immune correlates of protection and the in vitro down-selection of new Theileria parva vaccine candidates, thereby contributing to reducing the use of animals in challenge experiments.

Optimization of Cellular Transduction by the HIV-Based Pseudovirus Platform with Pan-Coronavirus Spike Proteins

Over the past three years, new SARS-CoV-2 variants have continuously emerged, evolving to a point where an immune response against the original vaccine no longer provided optimal protection against these new strains. During this time, high-throughput neutralization assays based on pseudoviruses have become a valuable tool for assessing the efficacy of new vaccines, screening updated vaccine candidates against emerging variants, and testing the efficacy of new therapeutics such as monoclonal antibodies. Lentiviral vectors derived from HIV-1 are popular for developing pseudo and chimeric viruses due to their ease of use, stability, and long-term transgene expression. However, the HIV-based platform has lower transduction rates for pseudotyping coronavirus spike proteins than other pseudovirus platforms, necessitating more optimized methods. As the SARS-CoV-2 virus evolved, we produced over 18 variants of the spike protein for pseudotyping with an HIV-based vector, optimizing experimental parameters for their production and transduction. In this article, we present key parameters that were assessed to improve such technology, including (a) the timing and method of collection of pseudovirus supernatant; (b) the timing of host cell transduction; (c) cell culture media replenishment after pseudovirus adsorption; and (d) the centrifugation (spinoculation) parameters of the host cell+ pseudovirus mix, towards improved transduction. Additionally, we found that, for some pseudoviruses, the addition of a cationic polymer (polybrene) to the culture medium improved the transduction process. These findings were applicable across variant spike pseudoviruses that include not only SARS-CoV-2 variants, but also SARS, MERS, Alpha Coronavirus (NL-63), and bat-like coronaviruses. In summary, we present improvements in transduction efficiency, which can broaden the dynamic range of the pseudovirus titration and neutralization assays.

Novel Competitive ELISA Utilizing Trimeric Spike Protein of SARS-CoV-2, Could Identify More Than RBD-RBM Specific Neutralizing Antibodies in Hybrid Sera

Since the initiation of the COVID-19 pandemic, there has been a need for the development of diagnostic methods to determine the factors implicated in mounting an immune response against the virus. The most promising indicator has been suggested to be neutralizing antibodies (nAbs), which mainly block the interaction between the Spike protein (S) of SARS-CoV-2 and the host entry receptor ACE2. In this study, we aimed to develop and optimize conditions of a competitive ELISA to measure serum neutralizing titer, using a recombinant trimeric Spike protein modified to have six additional proline residues (S(6P)-HexaPro) and h-ACE2. The results of our surrogate Virus Neutralizing Assay (sVNA) were compared against the commercial sVNT (cPass, Nanjing GenScript Biotech Co., Nanjing City, China), using serially diluted sera from vaccinees, and a high correlation of ID50-90 titer values was observed between the two assays. Interestingly, when we tested and compared the neutralizing activity of sera from eleven fully vaccinated individuals who subsequently contracted COVID-19 (hybrid sera), we recorded a moderate correlation between the two assays, while higher sera neutralizing titers were measured with sVNA. Our data indicated that the sVNA, as a more biologically relevant model assay that paired the trimeric S(6P) with ACE2, instead of the isolated RBD-ACE2 pairing cPass test, could identify nAbs other than the RBD-RBM specific ones.

Exploring immune evasion of SARS-CoV-2 variants using a pseudotyped system

In the United States, coronavirus disease 2019 (COVID-19) cases have consistently been linked to the prevailing variant XBB.1.5 of SARS-CoV-2 since late 2022. A system has been developed for producing and infecting cells with a pseudovirus (PsV) of SARS-CoV-2 to investigate the infection in a Biosafety Level 2 (BSL-2) laboratory. This system utilizes a lentiviral vector carrying ZsGreen1 and Firefly luciferase (Fluc) dual reporter genes, facilitating the analysis of experimental results. In addition, we have created a panel of PsV variants that depict both previous and presently circulating mutations found in circulating SARS-CoV-2 strains. A series of PsVs includes the prototype SARS-CoV-2, Delta B.1.617.2, BA.5, XBB.1, and XBB.1.5. To facilitate the study of infections caused by different variants of SARS-CoV-2 PsV, we have developed a HEK-293T cell line expressing mCherry and human angiotensin converting enzyme 2 (ACE2). To validate whether different SARS-CoV-2 PsV variants can be used for neutralization assays, we employed serum from rats immunized with the PF-D-Trimer protein vaccine to investigate its inhibitory effect on the infectivity of various SARS-CoV-2 PsV variants. According to our observations, the XBB variant, particularly XBB.1.5, exhibits stronger immune evasion capabilities than the prototype SARS-CoV-2, Delta B.1.617.2, and BA.5 PsV variants. Hence, utilizing the neutralization test, this study has the capability to forecast the effectiveness in preventing future SARS-CoV-2 variants infections.

The Nucleocapsid Protein of SARS-CoV-2, Combined with ODN-39M, Is a Potential Component for an Intranasal Bivalent Vaccine with Broader Functionality

Despite the rapid development of vaccines against COVID-19, they have important limitations, such as safety issues, the scope of their efficacy, and the induction of mucosal immunity. The present study proposes a potential component for a new generation of vaccines. The recombinant nucleocapsid (N) protein from the SARS-CoV-2 Delta variant was combined with the ODN-39M, a synthetic 39 mer unmethylated cytosine-phosphate-guanine oligodeoxynucleotide (CpG ODN), used as an adjuvant. The evaluation of its immunogenicity in Balb/C mice revealed that only administration by intranasal route induced a systemic cross-reactive, cell-mediated immunity (CMI). In turn, this combination was able to induce anti-N IgA in the lungs, which, along with the specific IgG in sera and CMI in the spleen, was cross-reactive against the nucleocapsid protein of SARS-CoV-1. Furthermore, the nasal administration of the N + ODN-39M preparation, combined with RBD Delta protein, enhanced the local and systemic immune response against RBD, with a neutralizing capacity. Results make the N + ODN-39M preparation a suitable component for a future intranasal vaccine with broader functionality against Sarbecoviruses.

A comprehensive review on immunogen and immune-response proteins of SARS-CoV-2 and their applications in prevention, diagnosis, and treatment of COVID-19

Exposure to severe acute respiratory syndrome-corona virus-2 (SARS-CoV-2) prompts humoral immune responses in the human body. As the auxiliary diagnosis of a current infection, the existence of viral proteins can be checked from specific antibodies (Abs) induced by immunogenic viral proteins. For people with a weakened immune system, Ab treatment can help neutralize viral antigens to resist and treat the disease. On the other hand, highly immunogenic viral proteins can serve as effective markers for detecting prior infections. Additionally, the identification of viral particles or the presence of antibodies may help establish an immune defense against the virus. These immunogenic proteins rather than SARS-CoV-2 can be given to uninfected people as a vaccination to improve their coping ability against COVID-19 through the generation of memory plasma cells. In this work, we review immunogenic and immune-response proteins derived from SARS-CoV-2 with regard to their classification, origin, and diverse applications (e.g., prevention (vaccine development), diagnostic testing, and treatment (via neutralizing Abs)). Finally, advanced immunization strategies against COVID-19 are discussed along with the contemporary circumstances and future challenges.

SARS-CoV-2 antibodies and their neutralizing capacity against live virus in human milk after COVID-19 infection and vaccination: prospective cohort studies

BACKGROUND

There is limited understanding of the impact of coronavirus disease 2019 (COVID-19) infection and vaccination type and interval on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) human milk antibodies and their neutralizing capacity.

OBJECTIVES

These cohort studies aimed to determine the presence of antibodies and live virus neutralizing capacity in milk from females infected with COVID-19, unexposed milk bank donors, and vaccinated females and examine impacts of vaccine interval and type.

METHODS

Milk was collected from participants infected with COVID-19 during pregnancy or lactation (Cohort-1) and milk bank donors (Cohort-2) from March 2020-July 2021 at 3 sequential 4-wk intervals and COVID-19 vaccinated participants with varying dose intervals (Cohort-3) (January-October 2021). Cohort-1 and Cohort-3 were recruited from Sinai Health (patients) and through social media. Cohort-2 included Ontario Milk Bank donors. Milk was examined for SARS-CoV-2 antibodies and live virus neutralization.

RESULTS

Of females with COVID-19, 53% (Cohort-1, n = 55) had anti-SARS-CoV-2 IgA antibodies in ≥1 milk sample. IgA+ samples (40%) were more likely neutralizing than IgA- samples (odds ratio [OR]: 2.18; 95% confidence interval [CI]: 1.03, 4.60; P = 0.04); however, 25% of IgA- samples were neutralizing. Both IgA positivity and neutralization decreased ∼6 mo after symptom onset (0-100 compared with 201+ d: IgA OR: 14.30; 95% CI: 1.08, 189.89; P = 0.04; neutralizing OR: 4.30; 95% CI: 1.55, 11.89; P = 0.005). Among milk bank donors (Cohort-2, n = 373), 4.3% had IgA antibodies; 23% of IgA+ samples were neutralizing. Vaccination (Cohort-3, n = 60) with mRNA-1273 and shorter vaccine intervals (3 to <6 wk) resulted in higher IgA and IgG than BNT162b2 (P < 0.04) and longer intervals (6 to <16 wk) (P≤0.02), respectively. Neutralizing capacity increased postvaccination (P = 0.04) but was not associated with antibody positivity.

CONCLUSIONS

SARS-CoV-2 infection and vaccination (type and interval) impacted milk antibodies; however, antibody presence did not consistently predict live virus neutralization. Although human milk is unequivocally the best way to nourish infants, guidance on protection to infants following maternal infection/vaccination may require more nuanced messaging. This study was registered at clinicaltrials.gov as NCT04453969 and NCT04453982.

Quantitative and Standardized Pseudovirus Neutralization Assay for COVID-19

COVID-19 is a global pandemic caused by the highly infectious SARS-CoV-2 virus. Efforts to combat SARS-CoV-2 infection include mass vaccination and development of monoclonal and convalescent plasma therapeutics that require precise measurements of correlative, functional neutralizing antibodies that prevent virus infection. Developing rapid, safe, easy-to-use, and high-quality neutralization assays are essential for the success of the massive effort. Here, we developed a vesicular stomatitis virus-based neutralization assay that was capable of quantifying varying degrees of neutralization in patient serum samples. This assay has two detection readouts, flow cytometry and live cell imaging. The two readout methods produced consistent values of all 50% neutralization titers, further enhancing measurement confidence on the assay. Moreover, the use of available reference standards such as the World Health Organization International Standard (NIBSC code 20/136) enables quantification and standardization of the pseudovirus neutralization assay with neutralizing antibody titers measured in International Units/mL. Quantitative and standardized neutralization assays are critical for reliable efficacy evaluation and comparison of numerous vaccines and therapeutics.

Clinical and laboratory considerations: determining an antibody-based composite correlate of risk for reinfection with SARS-CoV-2 or severe COVID-19

Much of the global population now has some level of adaptive immunity to SARS-CoV-2 induced by exposure to the virus (natural infection), vaccination, or a combination of both (hybrid immunity). Key questions that subsequently arise relate to the duration and the level of protection an individual might expect based on their infection and vaccination history. A multi-component composite correlate of risk (CoR) could inform individuals and stakeholders about protection and aid decision making. This perspective evaluates the various elements that need to be accommodated in the development of an antibody-based composite CoR for reinfection with SARS-CoV-2 or development of severe COVID-19, including variation in exposure dose, transmission route, viral genetic variation, patient factors, and vaccination status. We provide an overview of antibody dynamics to aid exploration of the specifics of SARS-CoV-2 antibody testing. We further discuss anti-SARS-CoV-2 immunoassays, sample matrices, testing formats, frequency of sampling and the optimal time point for such sampling. While the development of a composite CoR is challenging, we provide our recommendations for each of these key areas and highlight areas that require further work to be undertaken.

Performance of a Point-of-Care Fluorescence Immunoassay Test to Measure the Anti-Severe Acute Respiratory Syndrome Corona Virus 2 Spike, Receptor Binding Domain Antibody Level

Quantitative determination of anti-SARS-CoV2-S-RBD is necessary for the evaluation of vaccination effectiveness. The surrogate viral neutralization test (SVNT) is approved for measuring anti-SARS-CoV2-S-RBD, but a point-of-care platform is needed to simplify anti-SARS-CoV-2-S-RBD measurement. We aimed to evaluate the performance of a rapid fluorescent immunoassay-based kit, FastBio-RBDTM, compared to the SVNT. During April-September 2021, we enrolled two groups of subjects, convalescent subjects and subjects without a COVID-19 history. The subjects were tested for the anti-SARS-CoV2-S-RBD antibody using FastBio-RBDTM and the GenScript-cPASSTM SVNT. We measured the correlation coefficient and conducted an ROC analysis to determine the best cut-off value of anti-SARS-CoV2-S-RBD against the SVNT percent inhibition levels of 30% and 60%. We included 109 subjects. Anti-SARS-CoV-2-S-RBD strongly correlated to SVNT % inhibition with an R value of 0.866 (p < 0.0001). The ROC analysis showed that the anti-SARS-CoV-2-S-RBD of 6.71 AU/mL had 95.7% sensitivity and 87.5% specificity to detect a percentage inhibition of 30%. The anti-SARS-CoV-2-S-RBD of 59.76 AU/mL had a sensitivity of 88.1% and specificity of 97.0% to detect a percentage inhibition of 60%. FastBio-RBDTM could determine the presence and level of anti-SARS-CoV-2-S-RBD with good sensitivity and specificity. It has the potential to be deployed in health facilities with limited resources.

Pseudotyping Improves the Yield of Functional SARS-CoV-2 Virus-like Particles (VLPs) as Tools for Vaccine and Therapeutic Development

Virus-like particles (VLPs) have been proposed as an attractive tool in SARS-CoV-2 vaccine development, both as (1) a vaccine candidate with high immunogenicity and low reactogenicity and (2) a substitute for live virus in functional and neutralization assays. Though multiple SARS-CoV-2 VLP designs have already been explored in Sf9 insect cells, a key parameter ensuring VLPs are a viable platform is the VLP spike yield (i.e., spike protein content in VLP), which has largely been unreported. In this study, we show that the common strategy of producing SARS-CoV-2 VLPs by expressing spike protein in combination with the native coronavirus membrane and/or envelope protein forms VLPs, but at a critically low spike yield (~0.04-0.08 mg/L). In contrast, fusing the spike ectodomain to the influenza HA transmembrane domain and cytoplasmic tail and co-expressing M1 increased VLP spike yield to ~0.4 mg/L. More importantly, this increased yield translated to a greater VLP spike antigen density (~96 spike monomers/VLP) that more closely resembles that of native SARS-CoV-2 virus (~72-144 Spike monomers/virion). Pseudotyping further allowed for production of functional alpha (B.1.1.7), beta (B.1.351), delta (B.1.617.2), and omicron (B.1.1.529) SARS-CoV-2 VLPs that bound to the target ACE2 receptor. Finally, we demonstrated the utility of pseudotyped VLPs to test neutralizing antibody activity using a simple, acellular ELISA-based assay performed at biosafety level 1 (BSL-1). Taken together, this study highlights the advantage of pseudotyping over native SARS-CoV-2 VLP designs in achieving higher VLP spike yield and demonstrates the usefulness of pseudotyped VLPs as a surrogate for live virus in vaccine and therapeutic development against SARS-CoV-2 variants.

Quantifying neutralising antibody responses against SARS-CoV-2 in dried blood spots (DBS) and paired sera

The ongoing SARS-CoV-2 pandemic was initially managed by non-pharmaceutical interventions such as diagnostic testing, isolation of positive cases, physical distancing and lockdowns. The advent of vaccines has provided crucial protection against SARS-CoV-2. Neutralising antibody (nAb) responses are a key correlate of protection, and therefore measuring nAb responses is essential for monitoring vaccine efficacy. Fingerstick dried blood spots (DBS) are ideal for use in large-scale sero-surveillance because they are inexpensive, offer the option of self-collection and can be transported and stored at ambient temperatures. Such advantages also make DBS appealing to use in resource-limited settings and in potential future pandemics. In this study, nAb responses in sera, venous blood and fingerstick blood stored on filter paper were measured. Samples were collected from SARS-CoV-2 acutely infected individuals, SARS-CoV-2 convalescent individuals and SARS-CoV-2 vaccinated individuals. Good agreement was observed between the nAb responses measured in eluted DBS and paired sera. Stability of nAb responses was also observed in sera stored on filter paper at room temperature for 28 days. Overall, this study provides support for the use of filter paper as a viable sample collection method to study nAb responses.

Development of a Cell-Based SARS-CoV-2 Pseudovirus Neutralization Assay Using Imaging and Flow Cytometry Analysis

COVID-19 is an ongoing, global pandemic caused by the novel, highly infectious SARS-CoV-2 virus. Efforts to mitigate the effects of SARS-CoV-2, such as mass vaccination and development of monoclonal therapeutics, require precise measurements of correlative, functional neutralizing antibodies that block virus infection. The development of rapid, safe, and easy-to-use neutralization assays is essential for faster diagnosis and treatment. Here, we developed a vesicular stomatitis virus (VSV)-based neutralization assay with two readout methods, imaging and flow cytometry, that were capable of quantifying varying degrees of neutralization in patient serum samples. We tested two different spike-pseudoviruses and conducted a time-course assay at multiple multiplicities of infection (MOIs) to optimize the assay workflow. The results of this assay correlate with the results of previously developed serology and surrogate neutralization assays. The two pseudovirus readout methods produced similar values of 50% neutralization titer values. Harvest-free in situ readouts for live-cell imaging and high-throughput analysis results for flow cytometry can provide unique capabilities for fast evaluation of neutralization, which is critical for the mitigation of future pandemics.

Humoral response after a BNT162b2 heterologous third dose of COVID-19 vaccine following two doses of BBIBP-CorV among healthcare personnel in Peru

Background

The inactivated virus vaccine, BBIBP-CorV, was principally distributed across low- and middle-income countries as primary vaccination strategy to prevent poor COVID-19 outcomes. Limited information is available regarding its effect on heterologous boosting. We aim to evaluate the immunogenicity and reactogenicity of a third booster dose of BNT162b2 following a double BBIBP-CorV regime.

Methods

We conducted a cross-sectional study among healthcare providers from several healthcare facilities of the Seguro Social de Salud del Perú - ESSALUD. We included participants two-dose BBIBP-CorV vaccinated who presented a three-dose vaccination card at least 21 days passed since the vaccinees received their third dose and were willing to provide written informed consent. Antibodies were determined using LIAISON® SARS-CoV-2 TrimericS IgG (DiaSorin Inc., Stillwater, USA). Factors potentially associated with immunogenicity, and adverse events, were considered. We used a multivariable fractional polynomial modeling approach to estimate the association between anti-SARS-CoV-2 IgG antibodies' geometric mean (GM) ratios and related predictors.

Results

We included 595 subjects receiving a third dose with a median (IQR) age of 46 [37], [54], from which 40% reported previous SARS-CoV-2 infection. The overall geometric mean (IQR) of anti-SARS-CoV-2 IgG antibodies was 8,410 (5,115 - 13,000) BAU/mL. Prior SARS-CoV-2 history and full/part-time in-person working modality were significantly associated with greater GM. Conversely, time from boosting to IgG measure was associated with lower GM levels. We found 81% of reactogenicity in the study population; younger age and being a nurse were associated with a lower incidence of adverse events.

Conclusions

Among healthcare providers, a booster dose of BNT162b2 following a full BBIBP-CorV regime provided high humoral immune protection. Thus, SARS-CoV-2 previous exposure and working in person displayed as determinants that increase anti-SARS-CoV-2 IgG antibodies.

Genotype-phenotype landscapes for immune-pathogen coevolution

Our immune systems constantly coevolve with the pathogens that challenge them, as pathogens adapt to evade our defense responses, with our immune repertoires shifting in turn. These coevolutionary dynamics take place across a vast and high-dimensional landscape of potential pathogen and immune receptor sequence variants. Mapping the relationship between these genotypes and the phenotypes that determine immune-pathogen interactions is crucial for understanding, predicting, and controlling disease. Here, we review recent developments applying high-throughput methods to create large libraries of immune receptor and pathogen protein sequence variants and measure relevant phenotypes. We describe several approaches that probe different regions of the high-dimensional sequence space and comment on how combinations of these methods may offer novel insight into immune-pathogen coevolution.

A Systematic Review and Meta-Analysis Comparing the Diagnostic Accuracy Tests of COVID-19

In this paper, we present a systematic review and meta-analysis that aims to evaluate the reliability of coronavirus disease diagnostic tests in 2019 (COVID-19). This article seeks to describe the scientific discoveries made because of diagnostic tests conducted in recent years during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Between 2020 and 2021, searches for published papers on the COVID-19 diagnostic were made in the PubMed database. Ninety-nine scientific articles that satisfied the requirements were analyzed and included in the meta-analysis, and the specificity and sensitivity of the diagnostic accuracy were assessed. When compared to serological tests such as the enzyme-linked immunosorbent assay (ELISA), chemiluminescence immunoassay (CLIA), lateral flow immunoassay (LFIA), and chemiluminescent microparticle immunoassay (CMIA), molecular tests such as reverse transcription polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), and clustered regularly interspaced short palindromic repeats (CRISPR) performed better in terms of sensitivity and specificity. Additionally, the area under the curve restricted to the false-positive rates (AUC_FPR) of 0.984 obtained by the antiviral neutralization bioassay (ANB) diagnostic test revealed significant potential for the identification of COVID-19. It has been established that the various diagnostic tests have been effectively adapted for the detection of SARS-CoV-2; nevertheless, their performance still must be enhanced to contain potential COVID-19 outbreaks, which will also help contain potential infectious agent outbreaks in the future.

Evaluation of S- and M-Proteins Expressed in Escherichia coli and HEK Cells for Serological Detection of Antibodies in Response to SARS-CoV-2 Infections and mRNA-Based Vaccinations

This study investigated the IgG and IgA antibody response against recombinant S1 and receptor binding domains (RBD) of the spike (S-) protein and the membrane (M-) protein using a set of 115 serum samples collected from patients infected with SARS-CoV-2 in Germany before April 2021 using protein and peptide ELISA. As S1- and RBD-proteins expressed in Escherichia coli provided poor sensitivities in ELISA, they were replaced by proteins expressed in HEK cells. The RBD-ELISA provided a sensitivity of 90.6% (N = 85) for samples collected from patients with confirmed SARS-CoV-2 infections more than 14 days after symptom onset or a positive PCR test. In population-based controls, the specificity was 97.9% (N = 94). In contrast, the sensitivities were only 41.2% and 72.6% for M- and N-proteins, respectively, while the specificities were 88.5% and 100%, respectively. Considering also 20 samples collected during the first two weeks of symptom onset or PCR confirmation, the sensitivity of RBD- and N-protein ELISA decreased to 82.6% and 72.6%, respectively. The combination of two data sets, i.e., N- and RBD-, N- and M-, or RBD- and M-proteins increased the sensitivity to 85.8%, 77.9%, and 87.8%, respectively. Peptide mapping mostly confirmed epitopes previously reported for S1- and M-proteins, but they were only recognized by a few samples already tested positive in the corresponding protein ELISA indicating that peptide-based assays will not improve the diagnostic sensitivity.

Antibody correlates of protection from SARS-CoV-2 reinfection prior to vaccination: A nested case-control within the SIREN study

OBJECTIVES

To investigate serological differences between SARS-CoV-2 reinfection cases and contemporary controls, to identify antibody correlates of protection against reinfection.

METHODS

We performed a case-control study, comparing reinfection cases with singly infected individuals pre-vaccination, matched by gender, age, region and timing of first infection. Serum samples were tested for anti-SARS-CoV-2 spike (anti-S), anti-SARS-CoV-2 nucleocapsid (anti-N), live virus microneutralisation (LV-N) and pseudovirus microneutralisation (PV-N). Results were analysed using fixed effect linear regression and fitted into conditional logistic regression models.

RESULTS

We identified 23 cases and 92 controls. First infections occurred before November 2020; reinfections occurred before February 2021, pre-vaccination. Anti-S levels, LV-N and PV-N titres were significantly lower among cases; no difference was found for anti-N levels. Increasing anti-S levels were associated with reduced risk of reinfection (OR 0·63, CI 0·47-0·85), but no association for anti-N levels (OR 0·88, CI 0·73-1·05). Titres >40 were correlated with protection against reinfection for LV-N Wuhan (OR 0·02, CI 0·001-0·31) and LV-N Alpha (OR 0·07, CI 0·009-0·62). For PV-N, titres >100 were associated with protection against Wuhan (OR 0·14, CI 0·03-0·64) and Alpha (0·06, CI 0·008-0·40).

CONCLUSIONS

Before vaccination, protection against SARS-CoV-2 reinfection was directly correlated with anti-S levels, PV-N and LV-N titres, but not with anti-N levels. Detectable LV-N titres were sufficient for protection, whilst PV-N titres >100 were required for a protective effect.

TRIAL REGISTRATION NUMBER

ISRCTN11041050.

The Bovine Seminal Plasma Protein PDC-109 Possesses Pan-Antiviral Activity

Mammalian seminal plasma contains a multitude of bioactive components, including lipids, glucose, mineral elements, metabolites, proteins, cytokines, and growth factors, with various functions during insemination and fertilization. The seminal plasma protein PDC-109 is one of the major soluble components of the bovine ejaculate and is crucially important for sperm motility, capacitation, and acrosome reaction. A hitherto underappreciated function of seminal plasma is its anti-microbial and antiviral activity, which may limit the sexual transmission of infectious diseases during intercourse. We have recently discovered that PDC-109 inhibits the membrane fusion activity of influenza virus particles and significantly impairs viral infections at micromolar concentrations. Here we investigated whether the antiviral activity of PDC-109 is restricted to Influenza or if other mammalian viruses are similarly affected. We focused on Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), the etiological agent of the Coronavirus Disease 19 (COVID-19), thoroughly assessing PDC-109 inhibition with SARS-CoV-2 Spike (S)-pseudotyped reporter virus particles, but also live-virus infections. Consistent with our previous publications, we found significant virus inhibition, albeit accompanied by substantial cytotoxicity. However, using time-of-addition experiments we discovered a treatment regimen that enables virus suppression without affecting cell viability. We furthermore demonstrated that PDC-109 is also able to impair infections mediated by the VSV glycoprotein (VSVg), thus indicating a broad pan-antiviral activity against multiple virus species and families.

Leveraging South African HIV research to define SARS-CoV-2 immunity triggered by sequential variants of concern

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19), has shifted our paradigms about B cell immunity and the goals of vaccination for respiratory viruses. The development of population immunity, through responses directed to highly immunogenic regions of this virus, has been a strong driving force in the emergence of progressively mutated variants. This review highlights how the strength of the existing global virology and immunology networks built for HIV vaccine research enabled rapid adaptation of techniques, assays, and skill sets, to expeditiously respond to the SARS-CoV-2 pandemic. Allying real-time genomic surveillance to immunological platforms enabled the characterization of immune responses elicited by infection with distinct variants, in sequential epidemic waves, as well as studies of vaccination and hybrid immunity (combination of infection- and vaccination-induced immunity). These studies have shown that consecutive variants of concern have steadily diminished the ability of vaccines to prevent infection, but that increasing levels of hybrid immunity result in higher frequencies of cross-reactive responses. Ultimately, this rapid pivot from HIV to SARS-CoV-2 enabled a depth of understanding of the SARS-CoV-2 antigenic vulnerabilities as population immunity expanded and diversified, providing key insights for future responses to the SARS-CoV-2 pandemic.

Japanese Knotweed Rhizome Bark Extract Inhibits Live SARS-CoV-2 In Vitro

Coronavirus disease 2019 (COVID-19), a viral infectious respiratory disease, is caused by highly contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is responsible for the ongoing COVID-19 pandemic. Since very few drugs are known to be effective against SARS-CoV-2, there is a general need for new therapeutics, including plant-based drugs, for the prophylaxis and treatment of infections. In the current study, the activity of a 70% ethanolic(aq) extract of the rhizome bark of Japanese knotweed, an invasive alien plant species, was tested for the first time against the wild-type SARS-CoV-2 virus using a specific and robust virus neutralization test (VNT) on Vero-E6 cells, which best mimics the mechanism of real virus−host interaction. A statistically significant antiviral effect against SARS-CoV-2 (p-value < 0.05) was observed for the 50.8 µg mL−1 extract solution in cell medium. A suitable extract preparation was described to avoid loss of polyphenols throughout filtration of the extract, which was dissolved in cell medium containing fetal bovine serum (FBS). The significance of the differences between the sums of the test and control groups in the incidence of cytopathic effects (CPE) was determined using the one-way ANOVA test. A dose−response relationship was observed, with the cytotoxic effect occurring at higher concentrations of the extract (≥101.6 µg mL−1). The obtained results suggest possible use of this plant material for the production of various products (e.g., packaging, hygiene products, biodisinfectants, etc.) that would be useful against the spread of and for self-protection against COVID-19.

Serum peptidome profiles immune response of COVID-19 Vaccine administration

Background

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused significant loss of life and property. In response to the serious pandemic, recently developed vaccines against SARS-CoV-2 have been administrated to the public. Nevertheless, the research on human immunization response against COVID-19 vaccines is insufficient. Although much information associated with vaccine efficacy, safety and immunogenicity has been reported by pharmaceutical companies based on laboratory studies and clinical trials, vaccine evaluation needs to be extended further to better understand the effect of COVID-19 vaccines on human beings.

Methods

We performed a comparative peptidome analysis on serum samples from 95 participants collected at four time points before and after receiving CoronaVac. The collected serum samples were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to profile the serum peptides, and also subjected to humoral and cellular immune response analyses to obtain typical immunogenicity information.

Results

Significant difference in serum peptidome profiles by MALDI-TOF MS was observed after vaccination. By supervised statistical analysis, a total of 13 serum MALDI-TOF MS feature peaks were obtained on day 28 and day 42 of vaccination. The feature peaks were identified as component C1q receptor, CD59 glycoprotein, mannose-binding protein C, platelet basic protein, CD99 antigen, Leucine-rich alpha-2-glycoprotein, integral membrane protein 2B, platelet factor 4 and hemoglobin subunits. Combining with immunogenicity analysis, the study provided evidence for the humoral and cellular immune responses activated by CoronaVac. Furthermore, we found that it is possible to distinguish neutralizing antibody (NAbs)-positive from NAbs-negative individuals after complete vaccination using the serum peptidome profiles by MALDI-TOF MS together with machine learning methods, including random forest (RF), partial least squares-discriminant analysis (PLS-DA), linear support vector machine (SVM) and logistic regression (LR).

Conclusions

The study shows the promise of MALDI-TOF MS-based serum peptidome analysis for the assessment of immune responses activated by COVID-19 vaccination, and discovered a panel of serum peptides biomarkers for COVID-19 vaccination and for NAbs generation. The method developed in this study can help not only in the development of new vaccines, but also in the post-marketing evaluation of developed vaccines.

Neutralizing antibody responses in healthcare personnel after three doses of mRNA BNT162b2 vaccine and association with baseline characteristics and past SARS-CoV-2 infection

Aim

To estimate neutralizing antibody (NAb) immunity against SARS-CoV-2 in 739 healthcare personnel (HCP) vaccinated with three doses of BNT162b2 mRNA vaccine.

Methods

Serum samples were collected at 3, 6, and 9 months after the second vaccine dose and at 7–55 days after the third dose. Samples were tested for NAbs against SARS-CoV-2 receptor binding domain.

Results

The mean inhibition rates at 3, 6, and 9 months after the second dose were 86.33%, 73.38%, and 61.18%, and increased to 95.57% after the booster dose. Younger HCP and HCP with past SARS-CoV-2 infection had higher inhibition rates while there was an inverse correlation between NAb levels and comorbidities or tobacco use (p-values < 0.001). Increased NAb titers were also noticed in women (p-value = 0.033), especially at the end of the 9-month study period.

Conclusion

NAb levels increased considerably after a booster mRNA vaccine dose. Host factors and past SARS-CoV-2 infection influence NAb titers.

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.

Homogeneous surrogate virus neutralization assay to rapidly assess neutralization activity of anti-SARS-CoV-2 antibodies

The COVID-19 pandemic triggered the development of numerous diagnostic tools to monitor infection and to determine immune response. Although assays to measure binding antibodies against SARS-CoV-2 are widely available, more specific tests measuring neutralization activities of antibodies are immediately needed to quantify the extent and duration of protection that results from infection or vaccination. We previously developed a 'Serological Assay based on a Tri-part split-NanoLuc® (SATiN)' to detect antibodies that bind to the spike (S) protein of SARS-CoV-2. Here, we expand on our previous work and describe a reconfigured version of the SATiN assay, called Neutralization SATiN (Neu-SATiN), which measures neutralization activity of antibodies directly from convalescent or vaccinated sera. The results obtained with our assay and other neutralization assays are comparable but with significantly shorter preparation and run time for Neu-SATiN. As the assay is modular, we further demonstrate that Neu-SATiN enables rapid assessment of the effectiveness of vaccines and level of protection against existing SARS-CoV-2 variants of concern and can therefore be readily adapted for emerging variants.

Effectiveness of the third dose of BNT162b2 vaccine on neutralizing Omicron variant in the Japanese population

Introduction

The vaccine against SARS-CoV-2 provides humoral immunity to fight COVID-19; however, the acquired immunity gradually declines. Booster vaccination restores reduced humoral immunity; however, its effect on newly emerging variants, such as the Omicron variant, is a concern. As the waves of COVID-19 cases and vaccine programs differ between countries, it is necessary to know the domestic effect of the booster.

Methods

Serum samples were obtained from healthcare workers (20–69 years old) in the Pfizer BNT162b2 vaccine program at the Toyama University Hospital 6 months after the second dose (6mA2D, n = 648) and 2 weeks after the third dose (2wA3D, n = 565). The anti-SARS-CoV-2 antibody level was measured, and neutralization against the wild-type and variants (Delta and Omicron) was evaluated using pseudotyped viruses. Data on booster-related events were collected using questionnaires.

Results

The median anti-SARS-CoV-2 antibody was >30.9-fold elevated after the booster (6mA2D, 710.0 U/mL [interquartile range (IQR): 443.0–1068.0 U/mL]; 2wA3D, 21927 U/mL [IQR: 15321.0–>25000.0 U/mL]). Median neutralizing activity using 100-fold sera against wild-type-, Delta-, and Omicron-derived variants was elevated from 84.6%, 36.2%, and 31.2% at 6mA2D to >99.9%, 99.1%, and 94.6% at 2wA3D, respectively. The anti-SARS-CoV-2 antibody levels were significantly elevated in individuals with fever ≥37.5 °C, general fatigue, and myalgia, local swelling, and local hardness.

Conclusion

The booster effect, especially against the Omicron variant, was observed in the Japanese population. These findings contribute to the precise understanding of the efficacy and side effects of the booster and the promotion of vaccine campaigns.

Antigenic characterization of influenza and SARS-CoV-2 viruses

Antigenic characterization of emerging and re-emerging viruses is necessary for the prevention of and response to outbreaks, evaluation of infection mechanisms, understanding of virus evolution, and selection of strains for vaccine development. Primary analytic methods, including enzyme-linked immunosorbent/lectin assays, hemagglutination inhibition, neuraminidase inhibition, micro-neutralization assays, and antigenic cartography, have been widely used in the field of influenza research. These techniques have been improved upon over time for increased analytical capacity, and some have been mobilized for the rapid characterization of the SARS-CoV-2 virus as well as its variants, facilitating the development of highly effective vaccines within 1 year of the initially reported outbreak. While great strides have been made for evaluating the antigenic properties of these viruses, multiple challenges prevent efficient vaccine strain selection and accurate assessment. For influenza, these barriers include the requirement for a large virus quantity to perform the assays, more than what can typically be provided by the clinical samples alone, cell- or egg-adapted mutations that can cause antigenic mismatch between the vaccine strain and circulating viruses, and up to a 6-month duration of vaccine development after vaccine strain selection, which allows viruses to continue evolving with potential for antigenic drift and, thus, antigenic mismatch between the vaccine strain and the emerging epidemic strain. SARS-CoV-2 characterization has faced similar challenges with the additional barrier of the need for facilities with high biosafety levels due to its infectious nature. In this study, we review the primary analytic methods used for antigenic characterization of influenza and SARS-CoV-2 and discuss the barriers of these methods and current developments for addressing these challenges.

Optimization of SARS-CoV-2 Pseudovirion Production in Lentivirus Backbone With a Novel Liposomal System

Due to the fast mutating nature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the development of novel therapeutics, vaccines, and evaluating the efficacies of existing one’s against the mutated strains is critical for containing the virus. Pseudotyped SARS-CoV-2 viruses are proven to be instrumental in evaluating the efficiencies of therapeutics, owing to their ease in application and safety when compared to handling the live virus. However, a comprehensive protocol that includes selecting transfection reagents, validating different packaging systems for high-throughput screening of neutralizing antibodies, is still a requisite. To this end, we designed and synthesized amide linker-based cationic lipids with varying hydrophilic head groups from dimethyl (Lipo-DME) to methyl, ethylhydroxyl (Lipo-MeOH), and diethylhydroxyl (Lipo-DOH) keeping the hydrophobic tail, stearic acid, as constant. Among the liposomal formulations of these lipids, Lipo-DOH was found to be superior in delivering plasmids and demonstrated comparable transfection efficiencies with commercial standard Lipofectamine 3000. We further used Lipo-DOH for lentivirus and SARS-CoV-2 pseudovirion preparation. For comparing different lentivirus packaging systems, we optimized conditions using Addgene and BEI systems and found that the BEI lenti plasmid system was found to be efficient in making lentiviruses using Lipo-DOH. Using the optimized transfection reagent and the lentivirus system, we developed a robust protocol for the generation of SARS-CoV-2 pseudovirions and characterized their infectivity in human ACE2 expressing HEK-293T cells and neutralizing properties in IgG against spike protein of SARS-CoV-2 positive human sera from individuals recovered from COVID-19.

Vaccine Candidate Against COVID-19 Based on Structurally Modified Plant Virus as an Adjuvant

A recombinant vaccine candidate has been developed based on the major coronaviruses’ antigen (S protein) fragments and a novel adjuvant—spherical particles (SPs) formed during tobacco mosaic virus thermal remodeling. The receptor-binding domain and the highly conserved antigenic fragments of the S2 protein subunit were chosen for the design of recombinant coronavirus antigens. The set of three antigens (Co1, CoF, and PE) was developed and used to create a vaccine candidate composed of antigens and SPs (SPs + 3AG). Recognition of SPs + 3AG compositions by commercially available antibodies against spike proteins of SARS-CoV and SARS-CoV-2 was confirmed. The immunogenicity testing of these compositions in a mouse model showed that SPs improved immune response to the CoF and PE antigens. Total IgG titers against both proteins were 9–16 times higher than those to SPs. Neutralizing activity against SARS-CoV-2 in serum samples collected from hamsters immunized with the SPs + 3AG was demonstrated.

Enzyme-Linked Immunosorbent Assay: An Adaptable Methodology to Study SARS-CoV-2 Humoral and Cellular Immune Responses

The Enzyme-Linked Immunosorbent Assay is a versatile technique, which can be used for several applications. It has enormously contributed to the study of infectious diseases. This review highlights how this methodology supported the science conducted in COVID-19 pandemics, allowing scientists to better understand the immune response against SARS-CoV-2. ELISA can be modified to assess the functionality of antibodies, as avidity and neutralization, respectively by the standardization of avidity-ELISA and surrogate-neutralization methods. Cellular immunity can also be studied using this assay. Products secreted by cells, like proteins and cytokines, can be studied by ELISA or its derivative Enzyme-linked immunospot (ELISpot) assay. ELISA and ELISA-based methods aided the area of immunology against infectious diseases and is still relevant, for example, as a promising approach to study the differences between natural and vaccine-induced immune responses against SARS-CoV-2.

Commercial immunoassays for detection of anti-SARS-CoV-2 spike and RBD antibodies: urgent call for validation against new and highly mutated variants

Measuring the level of protection conferred by anti-SARS-CoV-2 (trimeric) spike or RBD (receptor binding domain) antibodies (especially total and IgG) is a suitable and reliable approach for predicting biological protection against the risk of infection and severe coronavirus disease 2019 (COVID-19) illness. Nonetheless, SARS-CoV-2 has undergone a broad process of recombination since the identification of the prototype lineage in 2019, introducing a huge number of mutations in its genome and generating a vast array of variants of interest (VoI) and concern (VoC). Many of such variants developed several mutations in spike protein and RBD, with the new Omicron (B.1.1.529) clade displaying over 30 changes, 15 of which concentrated in the RBD. Besides their impact on virus biology, as well as on the risk of detection failure with some molecular techniques (i.e., S gene dropout), recent evidence suggests that these mutations may also jeopardize the reliability of currently available commercial immunoassays for detecting anti-SARS-CoV-2 antibodies. The antigen (either spike or RBD) and epitopes of the prototype SARS-CoV-2 coated in some immunoassays may no longer reflect the sequence of circulating variants. On the other hand, anti-SARS-CoV-2 antibodies elicited by highly mutated SARS-CoV-2 variants may no longer be efficiently recognized by the currently available commercial immunoassays. Therefore, beside the compelling need to regularly re-evaluate and revalidate all commercially available immunoassays against live virus neutralization assays based on emerging VoCs or VoIs, diagnostic companies may also consider to redevelop their methods, replacing former SARS-CoV-2 antigens and epitopes with those of the new variants.

Two rapid SARS-CoV-2 disposable devices for semi-quantitative S-RBD antibody levels determination compared with CLIA and ELISA assays at different protective thresholds

BACKGROUND AND AIMS

Performance of two disposable devices for identifying subjects with low anti-SARS-CoV-2 protection was compared with that of automated enzyme-linked immunosorbent (ELISA) and chemiluminescent (CLIA) assay.

MATERIALS AND METHODS

In July 2021, 123 healthcare workers (HCW), twice vaccinated by BNT162b2/Comirnaty mRNA (BioNTech-Pfizer), underwent Ab iRapid COVID-19 Quant "Neutralizing" Self-test (iRapid Self-test) and "Neutralizing" Professional-use (iRapid pro) (DIESSE, Diagnostica Senese, Siena, Italy). Simultaneously, serum Ab were determined by Maglumi 2000 plus (anti S-RBD CLIA assay, Snibe Diagnostics, Shenzhen, China) and SARS-CoV-2 "Neutralizing" Ab Chorus ELISA (DIESSE, Siena, Italy). Results were evaluated against two "protective-thresholds", 90 kBAU/L and 506 kBAU/L.

RESULTS

HCW mean age, 46.2 (±12.6) years; 26 (20.5%), males, 101 (79.5%), females. The mean time interval (and standard deviation) between the first vaccine dose and Ab determination was 129.5 (±36.4) days and was neither gender (p = 0.879) nor age (p = 0.341) related. With Maglumi, 114 (89.7%) and 43 (33.8%) HCW presented Ab ≥ 90 kBAU/L and Ab ≥ 506 kBAU/L, respectively; with Chorus, 96 (75.6%) presented Ab values ≥506 kBAU/L. CLIA and ELISA agreement was 56.7%. At 90 kBAU/L, iRapid self-test and Pro sensitivities were 98.2% (95% CI: 92.7-99.8), specificity 69.2% (95% CI: 38.6-90.9%) and 76.9% (46.2-95%), respectively. At 506 kBAU/L, iRapid sensitivities were 58.1-91.6%, and specificities, 89-96.6%. On evaluating Ab at <4 and ≥4 months, protective titers had decreased.

CONCLUSIONS

iRapid semi-quantitative devices had very good overall agreements of 95.1% and 95.9% for detecting individuals with low anti-SARS-CoV-2 protection.

Ad26.COV2.S breakthrough infections induce high titers of neutralizing antibodies against Omicron and other SARS-CoV-2 variants of concern

The Janssen (Johnson & Johnson) Ad26.COV2.S non-replicating viral vector vaccine has been widely deployed for COVID-19 vaccination programs in resource-limited settings. Here we confirm that neutralizing and binding antibody responses to Ad26.COV2.S vaccination are stable for 6 months post-vaccination, when tested against multiple SARS-CoV-2 variants. Secondly, using longitudinal samples from individuals who experienced clinically mild breakthrough infections 4 to 5 months after vaccination, we show dramatically boosted binding antibodies, Fc effector function, and neutralization. These high titer responses are of similar magnitude to humoral immune responses measured in convalescent donors who had been hospitalized with severe illness, and are cross-reactive against diverse SARS-CoV-2 variants, including the neutralization-resistant Omicron (B.1.1.529) variant that currently dominates global infections, as well as SARS-CoV-1. These data have implications for population immunity in areas where the Ad26.COV2.S vaccine has been widely deployed, but where ongoing infections continue to occur at high levels.

SARS-CoV-2 Antibody Neutralization Assay Platforms Based on Epitopes Sources: Live Virus, Pseudovirus, and Recombinant S Glycoprotein RBD

The high virulent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that emerged in China at the end of 2019 has generated novel coronavirus disease, coronavirus disease 2019 (COVID-19), causing a pandemic worldwide. Every country has made great efforts to struggle against SARS-CoV-2 infection, including massive vaccination, immunological patients’ surveillance, and the utilization of convalescence plasma for COVID-19 therapy. These efforts are associated with the attempts to increase the titers of SARS-CoV-2 neutralizing Abs (nAbs) generated either after infection or vaccination that represent the body’s immune status. As there is no standard therapy for COVID-19 yet, virus eradication will mainly depend on these nAbs contents in the body. Therefore, serological nAbs neutralization assays become a requirement for researchers and clinicians to measure nAbs titers. Different platforms have been developed to evaluate nAbs titers utilizing various epitopes sources, including neutralization assays based on the live virus, pseudovirus, and neutralization assays utilizing recombinant SARS-CoV-2 S glycoprotein receptor binding site, receptor-binding domain. As a standard neutralization assay, the plaque reduction neutralization test (PRNT) requires isolation and propagation of live pathogenic SARS-CoV-2 virus conducted in a BSL-3 containment. Hence, other surrogate neutralization assays relevant to the PRNT play important alternatives that offer better safety besides facilitating high throughput analyses. This review discusses the current neutralization assay platforms used to evaluate nAbs, their techniques, advantages, and limitations.

Neutralizing antibody titers six months after Comirnaty vaccination: kinetics and comparison with SARS-CoV-2 immunoassays

OBJECTIVES

mRNA vaccines, including Comirnaty (BNT162b2 mRNA, BioNTech-Pfizer), elicit high IgG and neutralizing antibody (NAb) responses after the second dose, but the progressive decrease in serum antibodies against SARS-CoV-2 following vaccination have raised questions concerning long-term immunity, decreased antibody levels being associated with breakthrough infections after vaccination, prompting the consideration of booster doses.

METHODS

A total number of 189 Padua University-Hospital healthcare workers (HCW) who had received a second vaccine dose were asked to collect serum samples for determining Ab at 12 (t₁₂) and 28 (t₂₈) days, and 6 months (t_6m) after their first Comirnaty/BNT162b2 inoculation. Ab titers were measured with plaque reduction neutralization test (PRNT), and three chemiluminescent immunoassays, targeting the receptor binding domain (RBD), the trimeric Spike protein (trimeric-S), and surrogate viral neutralization tests (sVNT).

RESULTS

The median percentages (interquartile range) for decrease in antibodies values 6 months after the first dose were 86.8% (67.1-92.8%) for S-RBD IgG, 82% (58.6-89.3%) for trimeric-S, 70.4% (34.5-86.4%) for VNT-Nab, 75% (50-87.5%) for PRNT₅₀ and 75% (50-93.7%) for PRNT₉₀. At 6 months, neither PRNT titers nor VNT-Nab and S-RBD IgG bAb levels correlated with age (p=0.078) or gender (p=0.938), while they were correlated with previous infection (p<0.001).

CONCLUSIONS

After 6 months, a method-independent reduction of around 90% in anti-SARS-CoV-2 antibodies was detected, while no significant differences were found between values of males and females aged between 24 and 65 years without compromised health status. Further efforts to improve analytical harmonization and standardization are needed.

SARS-CoV-2 neutralizing antibodies after one or two doses of Comirnaty (BNT162b2, BioNTech/Pfizer): Kinetics and comparison with chemiluminescent assays

BACKGROUND

Studies evaluating neutralizing antibody (NAb) after BNT162b2 vaccine are scarce. We therefore compared NAb using the plaque reduction neutralization test (PRNT) in vaccinated subjects, with those from five chemiluminescent (CLIA) assays, two targeting ACE and S-RBD interaction.

METHODS

Sera from 174 completely Comirnaty/BNT162b2 vaccinated healthcare workers (HCW) were evaluated at t₁₂ and t₂₈. NAb titers at low (PRNT₅₀) or high (PRNT₉₀) stringency were compared with: Liaison SARS-CoV-2 Trimeric-S IgG, Elecsys S-RBD Ab, Maglumi SARS-CoV-2 S-RBD IgG and SARS-CoV-2 Nab; iFlash 2019-nCoV NAb.

RESULTS

Neither PRNT₅₀ nor PRNT₉₀ correlated with age (range, 24-65 years); no significant differences were found for gender. PRNT₅₀ and PRNT₉₀ seropositive titers (≥1:20) were 43 (24.7%) and 15 (8.6%) at t₁₂ and 167 (95.9%) and 149 (85.6%) at t₂₈. CLIA results at t₂₈ were uncorrelated with age, apart from Elecsys S-RBD Ab (r = -0.164, p = 0.046). Gender differences were found for Maglumi SARS-CoV-2 S-RBD IgG (p = 0.037) and Maglumi NAb (p = 0.046). Considering PRNT₅₀ at thresholds of 1:20 (or 1:40) and 1:160 (or 1:320), corresponding to different immune protective levels, CLIA cut-offs have been identified.

CONCLUSIONS

Comirnaty/BNT162b2 elicits strong NAb production, especially 28 days after first inoculum. Differences in correlation between Nab titers and circulating antibodies measured by 5 immunoassays have been found, being stronger the correlation for Maglumi Nab.