RBD-specific Antibodies Research Articles

Detection of Anti-SARS-CoV-2-S1 RBD-Specific Antibodies Prior to and during the Pandemic in 2011-2021 and COVID-19 Observational Study in 2019-2021.

Background: Longitudinal surveys to monitor the seroprevalence are required to support efforts for assessment of the levels of endemic stability in certain countries. We investigated seroprevalence of anti-SARS-CoV-2-S1 receptor-binding domain (RBD)-specific antibodies in the serum samples in 2011–2021, including a cohort study of 2019–2021, to evaluate the vaccination and anti-IgG-SARS-CoV-2–S1 RBD-positive statuses to assess the resistance and severity of COVID-19. Materials and Methods: Anti-SARS-CoV-2-S1 RBD-specific antibodies were assayed in the serum samples (N = 565) randomly selected from various cohorts previously recruited from 2011 to 2021 from the city of Moscow and Moscow Region. Among them there were the participants (N = 310) recruited in 2019–2021 with an endpoint of 30 October 2021 when these participants were interviewed over phone with relevant questionnaire. Results: Obtained data indicated a percentage of 3–6% of SARS-CoV-2-S1 RBD-specific antibodies detected in participants recruited in 2011–2019. The percentage of SARS-CoV-2-S1 RBD-specific antibodies was increased to 16.5% in 2020 and to 46% in 2021. The vaccination rate of 238 respondents of this cohort was 58% from August 2020 to October 2021. In total, 12% of respondents were hospitalized. The morbidity rate in the subgroup of anti-SARS-CoV-2-S1 RBD-positive respondents was 5.4-fold higher than that in the subgroup of vaccinated respondents. Conclusions: A small percentage of SARS-CoV-2-S1 RBD-specific antibodies detected in 2011–2019 indicated possible spreading of coronaviruses during the pre-pandemic period. Collective immunity in Moscow and the Moscow region was able to reach 69% from August 2020 to October 2021 if this rate is added to the rate of not vaccinated SARS-CoV-2-S1 RBD-positive subjects.

Decreased and Heterogeneous Neutralizing Antibody Responses Against RBD of SARS-CoV-2 Variants After mRNA Vaccination

The rapid spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) emerging variants raises concerns about their capacity to evade immune protection provided by natural infection or vaccination. The receptor-binding domain (RBD) of the viral spike protein is the major target of neutralizing antibodies, and viral variants accumulate mutations in this region. In this study, we determined the antibody neutralization capacity against the RBD of SARS-CoV-2 variants Alpha (B.1.1.7), Gamma (P.1), Epsilon (B.1.427), Kappa (B.1.617.1), and Delta (B.1.617.2) in a cohort of healthcare workers naturally infected or receiving COVID-19 mRNA vaccines from Moderna or Pfizer-BioNTech. We show that the five RBD variants displayed an augmented binding to ACE2 compared to the original Wuhan strain. The most significant increase was observed in variants Epsilon and Delta, containing mutation L452R. Using a flow cytometry cell-based assay, we found that SARS-CoV-2-infected subjects presented low levels of RBD-specific neutralizing antibodies against all variants analyzed, except Alpha. However, the neutralizing activity incremented considerably after a subsequent mRNA-vaccine dose, to levels significantly higher than those in naïve individuals receiving two vaccine doses. Importantly, we observed partially impaired neutralizing responses against most variants in fully vaccinated individuals. Variants Gamma and Kappa encompassing RBD E484K/Q mutations presented the highest neutralizing resistance. Furthermore, a wide heterogeneity in the magnitude of RBD-specific neutralizing responses against all tested SARS-CoV-2 variants following both mRNA vaccines was detected. Altogether, our findings provide important knowledge regarding SARS-CoV-2 vaccine-induced immunity, and should be very useful to guide future vaccination regimens and personalized vaccine approaches.

Variances in Humoral Responses to Different Spike Protein Domains After SARS-CoV-2 Vaccination in Lung and Heart Transplant Recipients

PurposeSolid organ transplant recipients are lacking an adequate immune response to SARS-CoV-2 vaccination. Therefore, these patients are still at risk and potentially in need of booster vaccinations. Furthermore, it is important to differentiate between the recipients of distinct organs. The efficacy of SARS-CoV-2 vaccination is usually examined via antibodies specific for the spike protein with assays containing the S1 and receptor-binding-domains (RBD) and rather rarely the S2 domain. To gain information about the humoral response in Tx recipients, it is feasible to compare the immunogenicity of these three domains. To address this, we compared the IgG antibody levels specific for the three spike protein domains in heart (HTx) vs lung (LTx) transplant recipients.MethodsBlood plasma 4-6 weeks after the second dose of SARS-CoV-2 vaccination (85% mRNA) of n=100 LTx and n=40 HTx patients was analysed for S1, S2 and RBD-specific IgG antibodies by Luminex-based multiplex assays. The threshold for positive antibody responses was set separately for each spike domain based on the median MFI + 2σ in an unexposed pre-pandemic control group.ResultsFor all three spike protein domains, HTx patients showed a significantly higher rate of positive IgG responses than the LTx patients (73% vs 43%). The comparison of MFI values for S1-, S2- and RBD-specific IgG further underlines the superior antibody response by HTx patients with higher MFI values for S1 (p = 0.0001, S2 p = 0.008, RBD p < 0.0001). In the LTx cohort, MFI values for S2- (p < 0.0001) as well as for RBD-specific IgG (p < 0.0001) were higher than for S1. The same applies for S2 vs S1 (p < 0.0001) and RBD vs S1 (p = 0.0018) in the HTx cohort. Comparing the MFI of S2 vs RBD, the levels of domain-specific IgG were higher for S2 than RBD in both LTx (p < 0.0001) and HTx patients (p = 0.0914).ConclusionHTx patients exhibit a moderately good IgG response to vaccination while LTx recipients show lower antibody responses. Based on the more efficient antibody production against S2 as opposed to the RBD and especially S1-domain, the S2-specific IgG response should be taken into consideration when evaluating the general immune response and the resulting protection after SARS-CoV-2 vaccination in transplant recipients. Both groups of patients might benefit from booster vaccinations.

MRNA-1273 and BNT162b2 COVID-19 vaccines elicit antibodies with differences in Fc-mediated effector functions.

The successful development of several coronavirus disease 2019 (COVID-19) vaccines has substantially reduced morbidity and mortality in regions of the world where the vaccines have been deployed. However, in the wake of the emergence of viral variants that are able to evade vaccine-induced neutralizing antibodies, real-world vaccine efficacy has begun to show differences across the two approved mRNA platforms, BNT162b2 and mRNA-1273; these findings suggest that subtle variation in immune responses induced by the BNT162b2 and mRNA-1273 vaccines may confer differential protection. Given our emerging appreciation for the importance of additional antibody functions beyond neutralization, we profiled the post-boost binding and functional capacity of humoral immune responses induced by the BNT162b2 and mRNA-1273 vaccines in a cohort of hospital staff. Both vaccines induced robust humoral immune responses to wild-type severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and to variants of concern. However, differences emerged across epitope-specific responses, with higher concentrations of receptor binding domain (RBD)- and N-terminal domain-specific IgA observed in recipients of mRNA-1273. Antibodies eliciting neutrophil phagocytosis and natural killer cell activation were also increased in mRNA-1273 vaccine recipients as compared to BNT162b2 recipients. RBD-specific antibody depletion highlighted the different roles of non-RBD-specific antibody effector functions induced across the mRNA vaccines. These data provide insights into potential differences in protective immunity conferred by these vaccines.

Omicron variant Spike-specific antibody binding and Fc activity are preserved in recipients of mRNA or inactivated COVID-19 vaccines.

The Omicron variant of SARS-CoV-2 has been shown to evade neutralizing antibodies elicited by vaccination or prior infection. Despite the dramatic global spread of the Omicron variant, even among highly vaccinated populations, death rates have not increased concomitantly. These data suggest that immune mechanisms beyond antibody-mediated virus neutralization may protect against severe disease. In addition to neutralizing pathogens, antibodies contribute to control and clearance of infections through Fc-effector mechanisms. Here we probed the ability of vaccine-induced antibodies to drive Fc-effector activity against the Omicron variant using samples from individuals receiving one of three SARS-CoV-2 vaccines. Despite a substantial loss of IgM, IgA, and IgG binding to the Omicron variant Receptor Binding Domain (RBD) in samples from individuals receiving BNT162b2, mRNA-1273, and CoronaVac vaccines, stable binding was maintained against the full-length Omicron Spike protein. Compromised RBD binding IgG was accompanied by a loss of cross RBD-specific antibody Fcγ receptor (FcγR) binding in samples from individuals who received the CoronaVac vaccine, but RBD-specific FcγR2a and FcγR3a binding was preserved in recipients of mRNA vaccines. Conversely, Spike protein-specific antibodies exhibited persistent but reduced binding to FcγRs across all three vaccines, though higher binding was observed in samples from recipients of mRNA vaccines. This was associated with preservation of FcγR2a and FcγR3a binding antibodies and maintenance of Spike protein-specific antibody-dependent natural killer cell activating antibodies. Thus, despite the loss of Omicron neutralization, vaccine-induced Spike protein-specific antibodies continue to drive Fc-effector functions, suggesting a capacity for extra-neutralizing antibodies to contribute to disease control.

Neutralization or enhancement of SARS-CoV-2 infection by a monoclonal antibody targeting a specific epitope in the spike receptor-binding domain

Neutralizing antibodies (NAbs) are believed to be promising prophylactic and therapeutic treatment against the coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Here, we reported two mouse monoclonal antibodies 7 Eb-4G and 1Ba–3H that specifically recognized the receptor-binding domain (RBD) of SARS-CoV-2 spike (S) protein without exhibiting cross-reactivity with the S proteins of SARS-CoV and MERS-CoV. The binding epitopes of 7 Eb-4G and 1Ba–3H were respectively located in the regions of residues 457–476 and 477–496 in the S protein. Only 1Ba–3H exhibited the neutralizing activity for preventing the pseudotyped lentivirus from binding to the angiotensin-converting enzyme 2 (ACE2)-transfected HEK293T cells. The competitive ELISA further showed that 1Ba–3H interfered with the binding between RBD and ACE2. Epitope mapping experiments demonstrated that a single alanine replacement at residues 480, 482, 484, 485, and 488–491 in the RBD abrogated 1Ba–3H binding. 1Ba–3H exhibited the neutralizing activity against the wild-type, Alpha, Delta, and Epsilon variants of SARS-CoV-2, but lost the neutralizing activity against Gamma variant in the plaque reduction assay. On the contrary, 1Ba–3H enhanced the cellular infection of Gamma variant in a dose-dependent manner. Our findings suggest that the antibody-dependent enhancement of infection mediated by the RBD-specific antibody for different SARS-CoV-2 variants must be considered while developing the NAb.

Lack of Induction of RBD-Specific Neutralizing Antibodies despite Repeated Heterologous SARS-CoV-2 Vaccination Leading to Seroconversion and Establishment of T Cell-Specific Memory in a Patient in Remission of Multiple Myeloma.

Background: Prophylactic vaccination against infectious diseases may induce a state of long-term protection in the otherwise healthy host. However, the situation is less predictable in immunocompromised patients and may require adjustment of vaccination schedules and/or basic therapy. Methods: A patient in full remission of multiple myeloma since the last three years and on long-term maintenance therapy with pomalidomide, a drug inhibiting angiogenesis and myeloma cell growth, was vaccinated twice with Comirnaty followed by two vaccinations with Vaxzevria. Seroconversion and SARS-CoV-2-specific cellular responses were monitored. Results: No signs of seroconversion or T cellular memory were observed after the first “full immunization” with Comirnaty. Consequently, long-term-maintenance therapy with Pomalidomide was stopped and two additional shots of Vaxzevria were administered after which the patient seroconverted with Spike(S)-protein specific antibody levels reaching 49 BAU/mL, mild S-peptide pool-specific T cell proliferation, effector cytokine production (IL-2, IL-13), and T cellular activation with increased numbers of CD3+CD4+CD25+ T cells as compared to vaccinated and non-vaccinated control subjects. However, despite suspension of immunosuppression and administration of in total four consecutive heterologous SARS-CoV-2 vaccine shots, the patient did not develop neutralizing RBD-specific antibodies. Conclusions: Despite immunomonitoring-based adjustment of vaccination and/or therapy schedules vaccination success, with clear correlates of protection, the development of RBD-specific antibodies could not be achieved in the immunocompromised patient with current SARS-CoV-2 vaccines. Thus, our report emphasizes the need for improved active and passive immunization strategies for SARS-CoV-2 infections.

Randomized, Double Blind, Placebo Controlled, Clinical Trial to Study Ashwagandha Administration in Participants Vaccinated Against COVID-19 on Safety, Immunogenicity, and Protection With COVID-19 Vaccine-A Study Protocol.

IntroductionVaccines have emerged as the most effective tool in the fight against COVID-19. Governments all over the world have rolled out the COVID-19 vaccine program for their populations. Oxford-AstraZeneca COVID-19 vaccine (COVISHIELD™) is widely used in India. A large number of Indian people have been consuming various traditional medicines in the hope of better protection against COVID-19 infection. Several studies have reported immunological benefits of Withania somnifera (Ashwagandha) and its potential as a vaccine adjuvant. We propose to study the safety, immunogenicity and clinical protection offered by a 6-month regimen of Ashwagandha in participants who volunteer to be vaccinated against COVID-19 (COVISHIELDTM) in the ongoing national program of vaccination.Methods and AnalysisWe designed a prospective, randomized, double-blind, parallel-group, placebo-controlled, two-arm, exploratory study on healthy volunteers receiving the COVISHIELDTM vaccine. The administration of Ashwagandha will begin within 7 days of the first or second dose of COVISHIELDTM. Primary outcome measure is immunogenicity as measured by SARS-CoV-2 spike (S1) and RBD-specific IgG antibody titres. Secondary outcome measures are safety, protective immune response and quality of life measures. All adverse events will be monitored at each time throughout the study. Participants will be tracked on a daily basis with a user-friendly mobile phone application. Following power calculation 600 participants will be recruited per arm to demonstrate superiority by a margin of 7% with 80% power. Study duration is 28 weeks with interim analysis at the end of 12 weeks.Ethics and DisseminationEthics approval was obtained through the Central and Institutional Ethics Committees. Participant recruitment commenced in December 2021. Results will be presented in conferences and published in preprints followed by peer-reviewed medical journals.Clinical Trial Registration[www.ClinicalTrials.gov], identifier [CTRI/2021/06/034496].

The human ACE-2 receptor binding domain of SARS-CoV-2 express on the viral surface of the Newcastle disease virus as a non-replicating viral vector vaccine candidate.

Since the SARS-CoV-2 infection was identified in December 2019, SARS-CoV-2 infection has rapidly spread worldwide and has become a significant pandemic disease. In addition, human death and serious health problem caused by SARS-CoV-2 infection, the socio-economic impact has been very serious. Here, we describe the development of the viral vector vaccine, which is the receptor-binding domain (RBD) of SARS-CoV-2 expressed on the surface of Newcastle disease virus (LVP-K1-RBD19). The RBD protein concentrations on the viral surface were measured by the sandwich ELISA method. 106.7 TCID50/ml of LVP-K1-RBD19 has a 0.17 μg of RBD protein. Optical density (OD) values of mouse sera inoculated with 10 μg of RBD protein expressed on the surface of LVP-K1-RBD19 generated 1.78-fold higher RBD-specific antibody titers than mice inoculated with 10 μg RBD protein with alum at 28 dpi. Moreover, mice inoculated with 10 μg of RBD protein expressed on the surface of LVP-K1-RBD19 virus showed more than 80% neutralization at 1:256 against the SARS-CoV-2 pseudovirus. These results demonstrated that inactivated LVP-K1-RBD19 virus produces neutralizing antibodies against SARS-CoV-2 in a short period and could be elect protective immunity in humans and LVP-K1-RBD19 will be a good candidate for the COVID-19 vaccine.

Development and multi-center clinical trials of an up-converting phosphor technology-based point-of-care (UPT-POCT) assay for rapid COVID-19 diagnosis and prediction of protective effects

BackgroundQuantitative point-of-care testing assay for detecting antibodies is critical to COVID-19 control. In this study, we established an up-conversion phosphor technology-based point-of-care testing (UPT-POCT), a lateral flow assay, for rapid COVID-19 diagnosis, as well as prediction of seral neutralizing antibody (NAb) activity and protective effects.MethodsUPT-POCT was developed targeting total antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 spike protein. Using ELISA as a contrast method, we evaluated the quantitation accuracy with NAb and serum samples. Cutoff for serum samples was determined through 70 healthy and 140 COVID-19 patients. We evaluated the cross-reactions with antibodies against other viruses. Then, we performed multi-center clinical trials of UPT-POCT, including 782 patients with 387 clinically confirmed COVID-19 cases. Furthermore, RBD-specific antibody levels were detected using UPT-POCT and microneutralization assay for samples from both patients and vaccinees. Specifically, the antibodies of recovered patients with recurrent positive (RP) reverse transcriptase-polymerase chain reaction test results were discussed.ResultsThe ratios of signal intensities between the test and control bands on the lateral flow strip, namely, T/C ratios, was defined as the results of UPT-POCT. T/C ratios had excellent correlations with concentrations of NAb, as well as OD values of ELISA for serum samples. The sensitivity and specificity of UPT-POCT were 89.15% and 99.75% for 782 cases in seven hospitals in China, respectively. We evaluated RBD-specific antibodies for 528 seral samples from 213 recovered and 99 RP COVID-19 patients, along with 35 seral samples from inactivated SARS-CoV-2 vaccinees, and we discovered that the total RBD-specific antibody level indicated by T/C ratios of UPT-POCT was significantly related to the NAb titers in both COVID-19 patients (r = 0.9404, n = 527; ρ = 0.6836, n = 528) and the vaccinees (r = 0.9063, ρ = 0.7642, n = 35), and it was highly relevant to the protection rate against RP (r = 0.9886, n = 312).ConclusionThis study reveals that the UPT-POCT for quantitative detection of total RBD-specific antibody could be employed as a surrogate method for rapid COVID-19 diagnosis and prediction of protective effects.

RBD-specific antibody responses after two doses of BBIBP-CorV (Sinopharm, Beijing CNBG) vaccine

BackgroundLimited information is available on the effectiveness of the BBIBP-CorV (Sinopharm, Beijing CNBG) vaccine, especially in the elderly, despite the fact that it is approved in more than 50 countries.MethodsRBD-specific antibody titres, as a rapidly available and highly predictive surrogate marker, were measured after two doses of the BBIBP-CorV vaccine in 450 subjects. Results were analyzed in a multivariable model accounting for age, sex and time since the administration of the second dose of the vaccine.ResultsSex and time since the second dose had little association with the antibody titres. Age, however, was highly relevant: measurable antibody levels were present in about 90% of individuals below the age of 50, but antibody production after BBIBP-CorV vaccination was strongly reduced with increasing age. A large number of elderly subjects, reaching 25% at 60 years, and up to 50% at ages over 80, were found not to produce any protective antibody.ConclusionsRBD-specific antibody titre, as a correlate of protection for COVID-19 disease susceptibility, should help to evaluate the effectiveness of the BBIBP-CorV vaccine. Results suggest that proper measures should be undertaken to prevent a potential outbreak of COVID-19 in BBIBP-CorV vaccinated but eventually unprotected elderly individuals.

SARS-CoV-2 mRNA vaccine induces robust specific and cross-reactive IgG and unequal neutralizing antibodies in naive and previously infected people

Understanding vaccine-mediated protection against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is critical to overcoming the global coronavirus disease 2019 (COVID-19) pandemic. We investigate mRNA-vaccine-induced antibody responses against the reference strain, seven variants, and seasonal coronaviruses in 168 healthy individuals at three time points: before vaccination, after the first dose, and after the second dose. Following complete vaccination, both naive and previously infected individuals developed comparably robust SARS-CoV-2 spike antibodies and variable levels of cross-reactive antibodies to seasonal coronaviruses. However, the strength and frequency of SARS-CoV-2 neutralizing antibodies in naive individuals were lower than in previously infected individuals. After the first vaccine dose, one-third of previously infected individuals lacked neutralizing antibodies; this was improved to one-fifth after the second dose. In all individuals, neutralizing antibody responses against the Alpha and Delta variants were weaker than against the reference strain. Our findings support future tailored vaccination strategies against emerging SARS-CoV-2 variants as mRNA-vaccine-induced neutralizing antibodies are highly variable among individuals.

Neutralizing Activity and SARS-CoV-2 Vaccine mRNA Persistence in Serum and Breastmilk After BNT162b2 Vaccination in Lactating Women.

BackgroundThere is limited information on the functional neutralizing capabilities of breastmilk SARS-CoV-2-specific antibodies and the potential adulteration of breastmilk with vaccine mRNA after SARS-CoV-2 mRNA vaccination.MethodsWe conducted a prospective cohort study of lactating healthcare workers who received the BNT162b2 vaccine and their infants. The presence of SARS-CoV-2 neutralizing antibodies, antibody isotypes (IgG, IgA, IgM) and intact mRNA in serum and breastmilk was evaluated at multiple time points using a surrogate neutralizing assay, ELISA, and PCR, over a 6 week period of the two-dose vaccination given 21 days apart.ResultsThirty-five lactating mothers, median age 34 years (IQR 32-36), were included. All had detectable neutralizing antibodies in the serum immediately before dose 2, with significant increase in neutralizing antibody levels 7 days after this dose [median 168.4 IU/ml (IQR 100.7-288.5) compared to 2753.0 IU/ml (IQR 1627.0-4712.0), p <0.001]. Through the two vaccine doses, all mothers had detectable IgG1, IgA and IgM isotypes in their serum, with a notable increase in all three antibody isotypes after dose 2, especially IgG1 levels. Neutralizing antibodies were detected in majority of breastmilk samples a week after dose 2 [median 13.4 IU/ml (IQR 7.0-28.7)], with persistence of these antibodies up to 3 weeks after. Post the second vaccine dose, all (35/35, 100%) mothers had detectable breastmilk SARS-CoV-2 spike RBD-specific IgG1 and IgA antibody and 32/35 (88.6%) mothers with IgM. Transient, low intact vaccine mRNA levels was detected in 20/74 (27%) serum samples from 21 mothers, and 5/309 (2%) breastmilk samples from 4 mothers within 1 weeks of vaccine dose. Five infants, median age 8 months (IQR 7-16), were also recruited - none had detectable neutralizing antibodies or vaccine mRNA in their serum.ConclusionMajority of lactating mothers had detectable SARS-CoV-2 antibody isotypes and neutralizing antibodies in serum and breastmilk, especially after dose 2 of BNT162b2 vaccination. Transient, low levels of vaccine mRNA were detected in the serum of vaccinated mothers with occasional transfer to their breastmilk, but we did not detect evidence of infant sensitization. Importantly, the presence of breastmilk neutralising antibodies likely provides a foundation for passive immunisation of the breastmilk-fed infant.

Identification of immunodominant epitopes on nucleocapsid and spike proteins of the SARS-CoV-2 in Iranian COVID-19 patients.

Given the emergence of SARS-CoV-2 virus as a life-threatening pandemic, identification of immunodominant epitopes of the viral structural proteins, particularly the nucleocapsid (NP) protein and receptor binding domain (RBD) of spike protein, is important to determine targets for immunotherapy and diagnosis. In this study, epitope screening was performed using a panel of overlapping peptides spanning the entire sequences of the RBD and NP proteins of SARS-CoV-2 in the sera from 66 COVID-19 patients and 23 healthy subjects by enzyme-linked immunosorbent assay (ELISA). Our results showed that while reactivity of patients' sera with reduced recombinant RBD protein was significantly lower than the native form of RBD (p<0.001), no significant differences were observed for reactivity of patients' sera with reduced and non-reduced NP protein. Pepscan analysis revealed weak to moderate reactivity towards different RBD peptide pools, which was more focused on peptides encompassing aa 181-223 of RBD. NP peptides, however, displayed strong reactivity with a single peptide covering aa 151-170. These findings were confirmed by peptide depletion experiments using both ELISA and Western blotting. Altogether, our data suggest involvement of mostly conformational disulfide bond-dependent immunodominant epitopes in RBD-specific antibody response, while the IgG response to NP is dominated by linear epitopes. Identification of dominant immunogenic epitopes in NP and RBD of SARS-CoV-2 could provide important information for the development of passive and active immunotherapy as well as diagnostic tools for the control of COVID-19 infection.

Design and Immunological Properties of the Novel Subunit Virus-like Vaccine against SARS-CoV-2.

The COVID-19 pandemic is ongoing, and the need for safe and effective vaccines to prevent infection and to control spread of the virus remains urgent. Here, we report the development of a SARS-CoV-2 subunit vaccine candidate (Betuvax-CoV-2) based on RBD and SD1 domains of the spike (S) protein fused to a human IgG1 Fc fragment. The antigen is adsorbed on betulin adjuvant, forming spherical particles with a size of 100–180 nm, mimicking the size of viral particles. Here we confirm the potent immunostimulatory activity of betulin adjuvant, and demonstrate that two immunizations of mice with Betuvax-CoV-2 elicited high titers of RBD-specific antibodies. The candidate vaccine was also effective in stimulating a neutralizing antibody response and T cell immunity. The results indicate that Betuvax-CoV-2 has good potential for further development as an effective vaccine against SARS-CoV-2.

A Highly Conserved Peptide Vaccine Candidate Activates Both Humoral and Cellular Immunity Against SARS-CoV-2 Variant Strains.

Facing the imminent need for vaccine candidates with cross-protection against globally circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mutants, we present a conserved antigenic peptide RBD9.1 with both T-cell and B-cell epitopes. RBD9.1 can be recognized by coronavirus disease 2019 (COVID-19) convalescent serum, particularly for those with high neutralizing potency. Immunization with RBD9.1 can successfully induce the production of the receptor-binding domain (RBD)-specific antibodies in Balb/c mice. Importantly, the immunized sera exhibit sustained neutralizing efficacy against multiple dominant SARS-CoV-2 variant strains, including B.1.617.2 that carries a point mutation (SL452R) within the sequence of RBD9.1. Specifically, SY451 and SY454 are identified as the key amino acids for the binding of the induced RBD-specific antibodies to RBD9.1. Furthermore, we have confirmed that the RBD9.1 antigenic peptide can induce a S448-456 (NYNYLYRLF)-specific CD8+ T-cell response. Both RBD9.1-specific B cells and the S448-456-specific T cells can still be activated more than 3 months post the last immunization. This study provides a potential vaccine candidate that can generate long-term protective efficacy over SARS-CoV-2 variants, with the unique functional mechanism of activating both humoral and cellular immunity.

Maternal-Fetal Immunologic Response to SARS-CoV-2 Infection in a Symptomatic Vulnerable Population: A Prospective Cohort.

Coronavirus disease 2019 (COVID-19) disproportionally affects pregnant women and their newborn; however, little is known about variables that modulate maternal-fetal immune response to infection. We prospectively studied socioeconomic, biologic, and clinical factors affecting humoral immunity in 87 unvaccinated pregnant women hospitalized in Buenos Aires for symptoms consistent with COVID-19. The number of days between symptom onset and childbirth predicted maternal and newborn virus spike protein receptor binding domain (RBD)-specific immunoglobulin G (IgG). These findings suggest newborns may benefit less when mothers deliver soon after COVID-19 infection. Similarly, a longer time between symptom onset and birth predicted higher in utero transfer of maternal IgG and its concentration in cord blood. Older gestational age at birth was associated with lower maternal to cord blood IgG ratio. Of women with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, 87% developed RBD-specific IgA responses in breast milk within 96 hours of childbirth. IgA was not significantly associated with time from infection but correlated with maternal serum IgG and placental transfer. These results demonstrate the combined role of biologic, clinical, and socioeconomic variables associated with maternal RBD-specific antibodies and supports early vaccination strategies for COVID-19 in socioeconomically vulnerable pregnant women. NCT04362956.

Life Sciences Discovery and Technology Highlights

Life Sciences Discovery and Technology Highlights

Production and Characterization of Nucleocapsid and RBD Cocktail Antigens of SARS-CoV-2 in Nicotiana benthamiana Plant as a Vaccine Candidate against COVID-19.

The COVID-19 pandemic has put global public health at high risk, rapidly spreading around the world. Although several COVID-19 vaccines are available for mass immunization, the world still urgently needs highly effective, reliable, cost-effective, and safe SARS-CoV-2 coronavirus vaccines, as well as antiviral and therapeutic drugs, to control the COVID-19 pandemic given the emerging variant strains of the virus. Recently, we successfully produced receptor-binding domain (RBD) variants in the Nicotiana benthamiana plant as promising vaccine candidates against COVID-19 and demonstrated that mice immunized with these antigens elicited a high titer of RBD-specific antibodies with potent neutralizing activity against SARS-CoV-2. In this study, we engineered the nucleocapsid (N) protein and co-expressed it with RBD of SARS-CoV-2 in Nicotiana benthamiana plant to produce an antigen cocktail. The purification yields were about 22 or 24 mg of pure protein/kg of plant biomass for N or N+RBD antigens, respectively. The purified plant produced N protein was recognized by N protein-specific monoclonal and polyclonal antibodies demonstrating specific reactivity of mAb to plant-produced N protein. In this study, for the first time, we report the co-expression of RBD with N protein to produce a cocktail antigen of SARS-CoV-2, which elicited high-titer antibodies with potent neutralizing activity against SARS-CoV-2. Thus, obtained data support that a plant-produced antigen cocktail, developed in this study, is a promising vaccine candidate against COVID-19.

Immunogenic Properties of the DNA Construct Encoding the Receptor-Binding Domain of the SARS-CoV-2 Spike Protein.

—The development of preventive vaccines became the first order task in the COVID-19 pandemic caused by SARS-CoV-2. This paper reports the construction of the pVAX-RBD plasmid containing the Receptor-Binding Domain (RBD) of the S protein and a unique signal sequence 176 which promotes target protein secretion into the extracellular space thereby increasing the efficiency of humoral immune response activation. A polyglucine-spermidine conjugate (PGS) was used to deliver pVAX-RBD into the cells. The comparative immunogenicity study of the naked pVAX-RBD and pVAX-RBD enclosed in the PGS envelope showed that the latter was more efficient in inducing an immune response in the immunized mice. In particular, RBD-specific antibody titers were shown in ELISA to be no higher than 1 : 1000 in the animals from the pVAX-RBD group and 1 : 42 000, in the pVAX-RBD-PGS group. The pVAX-RBD‒PGS construct effectively induced cellular immune response. Using ELISpot, it has been demonstrated that splenocytes obtained from the immunized animals effectively produced INF-γ in response to stimulation with the S protein-derived peptide pool. The results suggest that the polyglucine-spermidine conjugate-enveloped pVAX-RBD construct may be considered as a promising DNA vaccine against COVID-19.