Neutralization of SARS-CoV-2 requires antibodies against conformational receptor-binding domain epitopes

Immuno-μSARS2 Chip: A Peptide-Based Microarray to Assess COVID-19 Prognosis Based on Immunological Fingerprints

A multiplexed microarray chip (Immuno-μSARS2) aiming at providing information on the prognosis of the COVID-19 has been developed. The diagnostic technology records information related to the profile of the immunological response of patients infected by the SARS-CoV-2 virus. The diagnostic technology delivers information on the avidity of the sera against 28 different peptide epitopes and 7 proteins printed on a 25 mm2 area of a glass slide. The peptide epitopes (12-15 mer) derived from structural proteins (Spike and Nucleocapsid) have been rationally designed, synthesized, and used to develop Immuno-μSARS2 as a multiplexed and high-throughput fluorescent microarray platform. The analysis of 755 human serum samples (321 from PCR+ patients; 288 from PCR- patients; 115 from prepandemic individuals and classified as hospitalized, admitted to intensive-care unit (ICU), and exitus) from three independent cohorts has shown that the chips perform with a 98% specificity and 91% sensitivity identifying RT-PCR+ patients. Computational analysis utilized to correlate the immunological signatures of the samples analyzed indicate significant prediction rates against exitus conditions with 82% accuracy, ICU admissions with 80% accuracy, and 73% accuracy over hospitalization requirement compared to asymptomatic patients' fingerprints. The miniaturized microarray chip allows simultaneous determination of 96 samples (24 samples/slide) in 90 min and requires only 10 μL of sera. The diagnostic approach presented for the first time here could have a great value in assisting clinicians in decision-making based on the information provided by the Immuno-μSARS2 regarding progression of the disease and could be easily implemented in diagnostics of other infectious diseases.

Fusion protein-based COVID-19 vaccines exemplified by a chimeric vaccine based on a single fusion protein (W-PreS-O)

In this article we discuss characteristics of fusion protein-based SARS-CoV-2 vaccines. We focus on recombinant vaccine antigens comprising fusion proteins consisting of combinations of SARS-CoV-2-derived antigens or peptides or combinations of SARS-CoV-2 antigens/peptides with SARS-CoV-2-unrelated proteins/peptides. These fusion proteins are made to increase the immunogenicity of the vaccine antigens and/or to enable special targeting of the immune system. The protein-based vaccine approach is exemplified solely in a proof of concept study by using W-PreS-O, a chimeric vaccine based on a single fusion protein (W-PreS-O), combining RBDs from Wuhan hu-1 wild-type and Omicron BA.1 with the hepatitis B virus (HBV)-derived PreS surface antigen adsorbed to aluminum hydroxide. The W-PreS-O vaccine was evaluated in Syrian hamsters which were immunized three times at three-week intervals with W-PreS-O or with aluminum hydroxide (placebo) before they were infected with Omicron BA.1. Neutralizing antibody (nAB) titers, weight, lung symptoms, and viral loads, as measured using RT-PCR in the upper and lower respiratory tracts, were determined. In addition, infectious virus titers from the lungs were measured using a plaque-forming assay. We found that W-PreS-O-vaccinated hamsters developed robust nABs against Omicron BA.1, showed almost no development of pneumonia, and had significantly reduced infectious virus titers in the lungs. Importantly, the viral loads in the nasal cavities of W-PreS-O-vaccinated hamsters were close to or above the PCR cycle threshold considered to be non-infectious. The data of our proof-of-concept study provides compelling evidence that the W-PreS-O vaccine has protective effect against Omicron BA.1 in a Syrian hamster in vivo infection model and thus support the promising results obtained also for other fusion protein-based SARS-CoV-2 vaccines.

Characterization of monoclonal antibodies targeting SARS-CoV-2 spike glycoprotein: Reactivity against Delta and Omicron BA.1 variants

The cross-species transmissibility of SARS-CoV-2 infection has necessitated development of specific reagents for detecting infection in various animal species. The spike glycoprotein of SARS-CoV-2, which is involved in viral entry, is a highly immunogenic protein. To develop assays targeting this protein, we generated eight monoclonal antibodies (mAbs) against the S1 and seven against the S1/S2 protein (ectodomain) of SARS CoV-2. Based on neutralization capability and reactivity profile observed in ELISA, the mAbs generated against the S1/S2 antigen exhibited a broader spectrum of epitope specificity than those produced against the S1 domain alone. The full-length ectodomain induced antibodies that could neutralize the two most important variants of the virus encountered during the pandemic, namely Delta and Omicron. The availability of these reagents could greatly enhance the development of precise diagnostics for detecting COVID-19 infections in various host species and contribute to the advancement of mAb-based therapeutics.

Intranasal Self-Adjuvanted Lipopeptide Vaccines Elicit High Antibody Titers and Strong Cellular Responses against SARS-CoV-2

Despite concerted efforts to tackle the COVID-19 pandemic, the persistent transmission of SARS-CoV-2 demands continued research into novel vaccination strategies to combat the virus. In light of this, intranasally administered peptide vaccines, particularly those conjugated to an immune adjuvant to afford so-called "self-adjuvanted vaccines", remain underexplored. Here, we describe the synthesis and immunological evaluation of self-adjuvanting peptide vaccines derived from epitopes of the spike glycoprotein of SARS-CoV-2 covalently fused to the potent adjuvant, Pam2Cys, that targets toll-like receptor 2 (TLR2). When administered intranasally, these vaccines elicited a strong antigen-specific CD4+ and CD8+ T-cell response in the lungs as well as high titers of IgG and IgA specific to the native spike protein of SARS-CoV-2. Unfortunately, serum and lung fluid from mice immunized with these vaccines failed to inhibit viral entry in spike-expressing pseudovirus assays. Following this, we designed and synthesized fusion vaccines composed of the T-cell epitope discovered in this work, covalently fused to epitopes of the receptor-binding domain of the spike protein reported to be neutralizing. While antibodies elicited against these fusion vaccines were not neutralizing, the T-cell epitope retained its ability to stimulate strong antigen-specific CD4+ lymphocyte responses within the lungs. Given the Spike(883-909) region is still completely conserved in SARS-CoV-2 variants of concern and variants of interest, we envision the self-adjuvanting vaccine platform reported here may inform future vaccine efforts.

Differential decline of SARS-CoV-2-specific antibody levels, innate and adaptive immune cells, and shift of Th1/inflammatory to Th2 serum cytokine levels long after first COVID-19

BACKGROUND

SARS-CoV-2 has triggered a pandemic and contributes to long-lasting morbidity. Several studies have investigated immediate cellular and humoral immune responses during acute infection. However, little is known about long-term effects of COVID-19 on the immune system.

METHODS

We performed a longitudinal investigation of cellular and humoral immune parameters in 106 non-vaccinated subjects ten weeks (10 w) and ten months (10 m) after their first SARS-CoV-2 infection. Peripheral blood immune cells were analyzed by multiparametric flow cytometry, serum cytokines were examined by multiplex technology. Antibodies specific for the Spike protein (S), the receptor-binding domain (RBD) and the nucleocapsid protein (NC) were determined. All parameters measured 10 w and 10 m after infection were compared with those of a matched, noninfected control group (n = 98).

RESULTS

Whole blood flow cytometric analyses revealed that 10 m after COVID-19, convalescent patients compared to controls had reduced absolute granulocyte, monocyte, and lymphocyte counts, involving T, B, and NK cells, in particular CD3+CD45RA+CD62L+CD31+ recent thymic emigrant T cells and non-class-switched CD19+IgD+CD27+ memory B cells. Cellular changes were associated with a reversal from Th1- to Th2-dominated serum cytokine patterns. Strong declines of NC- and S-specific antibody levels were associated with younger age (by 10.3 years, p < .01) and fewer CD3-CD56+ NK and CD19+CD27+ B memory cells. Changes of T-cell subsets at 10 m such as normalization of effector and Treg numbers, decline of RTE, and increase of central memory T cell numbers were independent of antibody decline pattern.

CONCLUSIONS

COVID-19 causes long-term reduction of innate and adaptive immune cells which is associated with a Th2 serum cytokine profile. This may provide an immunological mechanism for long-term sequelae after COVID-19.

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.

MultiTEP-Based Vaccines Targeting SARS-CoV-2 Spike Protein IgG Epitopes Elicit Robust Binding Antibody Titers with Limited Virus-Neutralizing Activity

Within the last two decades, SARS-CoV-2 was the third zoonotic severe acute respiratory betacoronavirus (sarbecovirus) to infect humans, following SARS and MERS. The disruptions caused by the pandemic underscore the need for a universal vaccine against respiratory betacoronaviruses. Our group previously developed the universal platform for vaccine development, MultiTEP, which has been utilized in this study to generate a range of SARS-CoV-2 epitope vaccine candidates. We prepared and characterized 18 vaccines incorporating small peptide fragments from SARS-CoV-2 Spike protein fused with the MultiTEP sequence using overlapping PCR. Wild-type mice were immunized intramuscularly with the immunogen formulated in AdvaxCpG adjuvant. Serum antibodies were detected by ELISA, surrogate neutralization, and pseudovirus neutralization assays. Finally, the most promising vaccine candidate was administered to three non-human primates. All vaccines generated high titers of spike-binding IgG antibodies. However, only three vaccines generated antibodies that blocked RBD binding to the ACE2 receptor in a surrogate virus neutralization assay. However, none of the vaccines induced antibodies able to neutralize pseudotype viruses, including after the administration of the lead vaccine to NHPs. MultiTEP-based COVID-19 vaccines elicited robust, IgG-binding responses against the Spike protein in mice and non-human primates, but these antibodies were not neutralizing, underscoring the need to refine this approach further.

Immunogenicity of Covishield vaccine in patients with autoimmune rheumatic diseases

Introduction

The Coronavirus disease 2019 (COVID-19) pandemic has been the biggest threat to humankind during the last 3 years. It has caused the loss of more than 6.9 million precious lives across the world. The only method by which the massacre could be stopped was by mass vaccination or mass immunization. The patients suffering from autoimmune rheumatic disorders (AIRDs) and treated with immunosuppressants were the high-priority candidates for vaccination. However, the data regarding the efficacy of COVID-19 vaccines in this group of patients are very less. Hence, this study was planned to study the immunogenicity of Covishield in patients with AIRDs attending the rheumatology OPD at DMCH, Ludhiana.

Materials and Methods

It was a prospective cohort study and was planned by the Department of Biochemistry and Department of Clinical Immunology and Rheumatology at Dayanand Medical College and Hospital, Ludhiana. Fifty patients with AIRDs attending the DMCH rheumatology OPD and 52 age and sex-matched healthy controls who had received two doses of Covishield vaccine were included in this study. Patients having any other immunosuppressive conditions like uncontrolled diabetes, hepatitis, malignancy or HIV were excluded. Patients who had suffered from previous laboratory-confirmed COVID-19 infection (by RT-PCR) were also excluded. Blood samples were collected following all aseptic precautions from patients and controls on the 28th day after administration of a second dose of Covishield vaccine and total antibodies to the severe acute respiratory syndrome coronavirus 2 spike (S) protein receptor binding domain was measured using Elecsys Anti-SARS-CoV-2 S kit from Roche.

Results

It was observed that no significant difference was there in antibody titre between cases and controls (6213 ± 4418 vs. 8331 ± 7979, P = 0.1022). It was also observed that no statistically significant difference in antibody titre in cases without prednisolone and those taking treatment with prednisolone was found (P = 0.7058). A similar observation was found in terms of methotrexate also (P = 0.457). No significant difference in antibody titres was there when compared with controls (for prednisolone, P = 0.169, for methotrexate, P = 0.078). We found that only the patients receiving mycophenolate mofetil showed a statistically significant decrease in antibody titre in comparison to healthy controls (P = 0.03). Our study showed no statistically significant difference in antibody titres between patients suffering from different AIRDs.

Conclusion

Our study supplements the fact that patients with AIRDs in India can receive Covishield as the primary vaccine against COVID-19 without concerns regarding decreased immunogenicity or increased adverse effects.

The coevolution of Covid-19 and host immunity

The dynamic of the virus-host interaction is subject to constant evolution, which makes it difficult to predict when the SARS-CoV-2 pandemic will become endemic. Vaccines in conjunction with efforts around masking and social distancing have reduced SARS-CoV-2 infection rates, however, there are still significant challenges to contend with before the pandemic shifts to endemic, such as the coronavirus acquiring mutations that allow the virus to dodge the immunity acquired by hosts. SARS-CoV-2 variants deploy convergent evolutionary mechanisms to sharpen their ability to impede the host’s innate immune response. The continued emergence of variants and sub-variants poses a significant hurdle to reaching endemicity. This underscores the importance of continued public health measures to control SARS-CoV-2 transmission and the need to develop better second-generation vaccines and effective treatments that would tackle current and future variants. We hypothesize that the hosts’ immunity to the virus is also evolving, which is likely to abet the process of reaching endemicity.

Flow Cytometry-Based Measurement of Antibodies Specific for Cell Surface-Expressed Folded SARS-CoV-2 Receptor-Binding Domains

BACKGROUND

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has now become endemic and is currently one of the important respiratory virus infections regularly affecting mankind. The assessment of immunity against SARS-CoV-2 and its variants is important for guiding active and passive immunization and SARS-CoV-2-specific treatment strategies.

METHODS

We here devised a novel flow cytometry-based diagnostic platform for the assessment of immunity against cell-bound virus antigens. This platform is based on a collection of HEK-293T cell lines which, as exemplified in our study, stably express the receptor-binding domains (RBDs) of the SARS-CoV-2 S-proteins of eight major SARS-CoV-2 variants, ranging from Wuhan-Hu-1 to Omicron.

RESULTS

RBD-expressing cell lines stably display comparable levels of RBD on the surface of HEK-293T cells, as shown with anti-FLAG-tag antibodies directed against a N-terminally introduced 3x-FLAG sequence while the functionality of RBD was proven by ACE2 binding. We exemplify the usefulness and specificity of the cell-based test by direct binding of IgG and IgA antibodies of SARS-CoV-2-exposed and/or vaccinated individuals in which the assay shows a wide linear performance range both at very low and very high serum antibody concentrations. In another application, i.e., antibody adsorption studies, the test proved to be a powerful tool for measuring the ratios of individual variant-specific antibodies.

CONCLUSION

We have established a toolbox for measuring SARS-CoV-2-specific immunity against cell-bound virus antigens, which may be considered as an important addition to the armamentarium of SARS-CoV-2-specific diagnostic tests, allowing flexible and quick adaptation to new variants of concern.

Humoral Immune Response to SARS-CoV-2 Spike Protein Receptor-Binding Motif Linear Epitopes

The worldwide spread of SARS-CoV-2 has led to a significant economic and social burden on a global scale. Even though the pandemic has concluded, apprehension remains regarding the emergence of highly transmissible variants capable of evading immunity induced by either vaccination or prior infection. The success of viral penetration is due to the specific amino acid residues of the receptor-binding motif (RBM) involved in viral attachment. This region interacts with the cellular receptor ACE2, triggering a neutralizing antibody (nAb) response. In this study, we evaluated serum immunogenicity from individuals who received either a single dose or a combination of different vaccines against the original SARS-CoV-2 strain and a mutated linear RBM. Despite a modest antibody response to wild-type SARS-CoV-2 RBM, the Omicron variants exhibit four mutations in the RBM (S477N, T478K, E484A, and F486V) that result in even lower antibody titers. The primary immune responses observed were directed toward IgA and IgG. While nAbs typically target the RBD, our investigation has unveiled reduced seroreactivity within the RBD's crucial subregion, the RBM. This deficiency may have implications for the generation of protective nAbs. An evaluation of S1WT and S2WT RBM peptides binding to nAbs using microscale thermophoresis revealed a higher affinity (35 nM) for the S2WT sequence (GSTPCNGVEGFNCYF), which includes the FNCY patch. Our findings suggest that the linear RBM of SARS-CoV-2 is not an immunodominant region in vaccinated individuals. Comprehending the intricate dynamics of the humoral response, its interplay with viral evolution, and host genetics is crucial for formulating effective vaccination strategies, targeting not only SARS-CoV-2 but also anticipating potential future coronaviruses.

Usefulness of receptor binding domain protein-based serodiagnosis of COVID-19

Objectives

This study evaluated the performance of recombinant receptor binding domain (RBD) protein-based enzyme-linked immunosorbent assays (RBD-ELISAs) for detecting anti-SARS-CoV-2 immunoglobulin (Ig) G and IgM antibodies.

Methods

In this study, 705 sera from SARS-CoV-2-infected individuals and 315 sera from healthy individuals were analyzed.

Results

The RBD-ELISA IgG exhibited high specificity (99.1%) and moderate sensitivity (48.0%), with an overall diagnostic accuracy of 73.5%. RBD-ELISA IgM demonstrated specificity at 94.6% and sensitivity at 51.1%, with an accuracy of 72.8%. Both assays displayed improved performance when analyzing samples collected 15-21 days post-symptom onset, achieving sensitivity and accuracy exceeding 88% and 90%, respectively. Combining RBD-ELISA IgG and IgM in parallel analysis enhanced sensitivity to 98.6% and accuracy to 96.2%. Comparing these RBD-ELISAs with commercially available tests, the study found overlapping sensitivity and similar specificity values. Notably, the combined RBD-ELISA IgG and IgM showed superior performance. Cross-reactivity analysis revealed low false-positive rates (4.4% for IgG, 3.7% for IgM), primarily with viral infections.

Conclusion

This research underscores the potential of RBD-based ELISAs for COVID-19 diagnosis, especially when assessing samples collected 15-21 days post-symptom onset and utilizing a parallel testing approach. The RBD protein's immunogenicity and specificity make it a valuable tool for serodiagnosis, offering an alternative to polymerase chain reaction-based methods, particularly in resource-limited settings.

Natural human Bet v 1-specific IgG antibodies recognize non-conformational epitopes whereas IgE reacts with conformational epitopes

BACKGROUND

The nature of epitopes on Bet v 1 recognized by natural IgG antibodies of birch pollen allergic patients and birch pollen-exposed but non-sensitized subjects has not been studied in detail.

OBJECTIVE

To investigate IgE and IgG recognition of Bet v 1 and to study the effects of natural Bet v 1-specific IgG antibodies on IgE recognition of Bet v 1 and Bet v 1-induced basophil activation.

METHODS

Sera from birch pollen allergic patients (BPA, n = 76), allergic patients without birch pollen allergy (NBPA, n = 40) and non-allergic individuals (NA, n = 48) were tested for IgE, IgG as well as IgG1 and IgG4 reactivity to folded recombinant Bet v 1, two unfolded recombinant Bet v 1 fragments comprising the N-terminal (F1) and C-terminal half of Bet v 1 (F2) and unfolded peptides spanning the corresponding sequences of Bet v 1 and the apple allergen Mal d 1 by ELISA or micro-array analysis. The ability of Bet v 1-specific serum antibodies from non-allergic subjects to inhibit allergic patients IgE or IgG binding to rBet v 1 or to unfolded Bet v 1-derivatives was assessed by competition ELISAs. Furthermore, the ability of serum antibodies from allergic and non-allergic subjects to modulate Bet v 1-induced basophil activation was investigated using rat basophilic leukaemia cells expressing the human FcεRI which had been loaded with IgE from BPA patients.

RESULTS

IgE antibodies from BPA patients react almost exclusively with conformational epitopes whereas IgG, IgG1 and IgG4 antibodies from BPA, NBPA and NA subjects recognize mainly unfolded and sequential epitopes. IgG competition studies show that IgG specific for unfolded/sequential Bet v 1 epitopes is not inhibited by folded Bet v 1 and hence the latter seem to represent cryptic epitopes. IgG reactivity to Bet v 1 peptides did not correlate with IgG reactivity to the corresponding Mal d 1 peptides and therefore does not seem to be a result of primary sensitization to PR10 allergen-containing food. Natural Bet v 1-specific IgG antibodies inhibited IgE binding to Bet v 1 only poorly and could even enhance Bet v 1-specific basophil activation.

CONCLUSION

IgE and IgG antibodies from BPA patients and birch pollen-exposed non-sensitized subjects recognize different epitopes. These findings explain why natural allergen-specific IgG do not protect against allergic symptoms and suggest that allergen-specific IgE and IgG have different clonal origin.

The impact of Bacillus Calmette-Guérin vaccination on antibody response after COVID-19 vaccination

Earlier studies showed that BCG vaccination improves antibody responses of subsequent vaccinations. Similarly, in older volunteers we found an increased IgG receptor-binding domain (RBD) concentration after SARS-CoV-2 infection if they were recently vaccinated with BCG. This study aims to assess the effect of BCG on the serum antibody concentrations induced by COVID-19 vaccination in a population of adults older than 60 years. Serum was collected from 1,555 participants of the BCG-CORONA-ELDERLY trial a year after BCG or placebo, and we analyzed the anti-SARS-CoV-2 antibody concentrations using a fluorescent-microsphere-based multiplex immunoassay. Individuals who received the full primary COVID-19 vaccination series before serum collection and did not test positive for SARS-CoV-2 between inclusion and serum collection were included in analyses (n = 945). We found that BCG vaccination before first COVID-19 vaccine (median 347 days [IQR 329-359]) did not significantly impact the IgG RBD concentration after COVID-19 vaccination in an older European population.

SARS-CoV-2 specific immune responses in overweight and obese COVID-19 patients

Obesity is a known risk factor for severe respiratory tract infections. In this prospective study, we assessed the impact of being obese or overweight on longitudinal SARS-CoV-2 humoral and cellular responses up to 18 months after infection. 274 patients provided blood samples at regular time intervals up to 18 months including obese (BMI ≥30, n=32), overweight (BMI 25-29.9, n=103) and normal body weight (BMI 18.5-24.9, n=134) SARS-CoV-2 patients. We determined SARS-CoV-2 spike-specific IgG, IgA, IgM levels by ELISA and neutralising antibody titres by neutralisation assay. RBD- and spike-specific memory B cells were investigated by ELISpot, spike- and non-spike-specific IFN-γ, IL-2 and IFN-γ/IL-2 secreting T cells by FluoroSpot and T cell receptor (TCR) sequencing was performed. Higher BMI correlated with increased COVID-19 severity. Humoral and cellular responses were stronger in overweight and obese patients than normal weight patients and associated with higher spike-specific IgG binding titres relative to neutralising antibody titres. Linear regression models demonstrated that BMI, age and COVID-19 severity correlated independently with higher SARS-CoV-2 immune responses. We found an increased proportion of unique SARS-CoV-2 specific T cell clonotypes after infection in overweight and obese patients. COVID-19 vaccination boosted humoral and cellular responses irrespective of BMI, although stronger immune boosting was observed in normal weight patients. Overall, our results highlight more severe disease and an over-reactivity of the immune system in overweight and obese patients after SARS-CoV-2 infection, underscoring the importance of recognizing overweight/obese individuals as a risk group for prioritisation for COVID-19 vaccination.

Kinetics and ability of binding antibody and surrogate virus neutralization tests to predict neutralizing antibodies against the SARS-CoV-2 Omicron variant following BNT162b2 booster administration

OBJECTIVES

To assess the long-term humoral immunity induced by booster administration, as well as the ability of binding antibody and surrogate virus neutralization tests (sVNT) to predict neutralizing antibodies (NAbs) against the SARS-CoV-2 Omicron variant.

METHODS

A total of 269 sera samples were analyzed from 64 healthcare workers who had received a homologous booster dose of BNT162b2. Neutralizing antibodies assessed by sVNT and anti-RBD IgG measured with the sCOVG assay (Siemens Healthineers®) were analyzed at five timepoints; before and up to 6 months following the booster. Antibody titers were correlated with neutralizing antibodies against the Omicron BA.1 variant obtained by pseudovirus neutralization test (pVNT) as a reference method.

RESULTS

While Wild-type sVNT percentage of inhibition (POI) remained above 98.6% throughout the follow-up period after booster administration, anti-RBD IgG and NAbs assessed by Omicron BA.1 pVNT showed respectively a 3.4-fold and 13.3-fold decrease after 6 months compared to the peak reached at day 14. NAbs assessed by Omicron sVNT followed a steady decline until reaching a POI of 53.4%. Anti-RBD IgG and Omicron sVNT assays were strongly correlated (r=0.90) and performed similarly to predict the presence of neutralizing antibodies with Omicron pVNT (area under the ROC: 0.82 for both assays). In addition, new adapted cut-off values of anti-RBD IgG (>1,276 BAU/mL) and Omicron sVNT (POI>46.6%) were found to be better predictors of neutralizing activity.

CONCLUSIONS

This study showed a significant drop in humoral immunity 6 months after booster administration. Anti-RBD IgG and Omicron sVNT assays were highly correlated and could predict neutralizing activity with moderate performance.

Molecular Evolutionary Analyses of the Spike Protein Gene and Spike Protein in the SARS-CoV-2 Omicron Subvariants

To better understand the evolution of the SARS-CoV-2 Omicron subvariants, we performed molecular evolutionary analyses of the spike (S) protein gene/S protein using advanced bioinformatics technologies. First, time-scaled phylogenetic analysis estimated that a common ancestor of the Wuhan, Alpha, Beta, Delta variants, and Omicron variants/subvariants diverged in May 2020. After that, a common ancestor of the Omicron variant generated various Omicron subvariants over one year. Furthermore, a chimeric virus between the BM.1.1.1 and BJ.1 subvariants, known as XBB, diverged in July 2021, leading to the emergence of the prevalent subvariants XBB.1.5 and XBB.1.16. Next, similarity plot (SimPlot) data estimated that the recombination point (breakpoint) corresponded to nucleotide position 1373. As a result, XBB.1.5 subvariants had the 5' nucleotide side from the breakpoint as a strain with a BJ.1 sequence and the 3' nucleotide side as a strain with a BM.1.1.1 sequence. Genome network data showed that Omicron subvariants were genetically linked with the common ancestors of the Wuhan and Delta variants, resulting in many amino acid mutations. Selective pressure analysis estimated that the prevalent subvariants, XBB.1.5 and XBB.1.16, had specific amino acid mutations, such as V445P, G446S, N460K, and F486P, located in the RBD when compared with the BA.4 and BA.5 subvariants. Moreover, some representative immunogenicity-associated amino acid mutations, including L452R, F486V, R493Q, and V490S, were also found in these subvariants. These substitutions were involved in the conformational epitopes, implying that these mutations affect immunogenicity and vaccine evasion. Furthermore, these mutations were identified as positive selection sites. These results suggest that the S gene/S protein Omicron subvariants rapidly evolved, and mutations observed in the conformational epitopes may reduce the effectiveness of the current vaccine, including bivalent vaccines such as mRNA vaccines containing the BA.4/BA.5 subvariants.

Detection of Antibodies against Endemic and SARS-CoV-2 Coronaviruses with Short Peptide Epitopes

(1) Background: Coronavirus proteins are quite conserved amongst endemic strains (eCoV) and SARS-CoV-2. We aimed to evaluate whether peptide epitopes might serve as useful diagnostic biomarkers to stratify previous infections and COVID-19. (2) Methods: Peptide epitopes were identified at an amino acid resolution that applied a novel statistical approach to generate data sets of potential antibody binding peptides. (3) Results: Data sets from more than 120 COVID-19 or eCoV-infected patients, as well as vaccinated persons, have been used to generate data sets that have been used to search in silico for potential epitopes in proteins of SARS-CoV-2 and eCoV. Peptide epitopes were validated with >300 serum samples in synthetic peptide micro arrays and epitopes specific for different viruses, in addition to the identified cross reactive epitopes. (4) Conclusions: Most patients develop antibodies against non-structural proteins, which are useful general markers for recent infections. However, there are differences in the epitope patterns of COVID-19, and eCoV, and the S-protein vaccine, which can only be explained by a high degree of cross-reactivity between the viruses, a pre-existing immune response against some epitopes, and even an alternate processing of the vaccine proteins.

An Overview of the Conventional and Novel Methods Employed for SARS-CoV-2 Neutralizing Antibody Measurement

SARS-CoV-2 is the etiological agent of the coronavirus disease-19 (COVID-19) and is responsible for the pandemic that started in 2020. The virus enters the host cell through the interaction of its spike glycoprotein with the angiotensin converting enzyme-2 (ACE2) on the host cell's surface. Antibodies present an important role during the infection and pathogenesis due to many reasons, including the neutralization of viruses by binding to different spike epitopes. Therefore, measuring the neutralizing antibody titers in the whole population is important for COVID-19's epidemiology. Different methods are described in the literature, and some have been used to validate the main vaccines used worldwide. In this review, we discuss the main methods used to quantify neutralizing antibody titers, their advantages and limitations, as well as new approaches to determineACE2/spike blockage by antibodies.

Antisera Produced Using an E. coli-Expressed SARS-CoV-2 RBD and Complemented with a Minimal Dose of Mammalian-Cell-Expressed S1 Subunit of the Spike Protein Exhibits Improved Neutralization

E. coli-expressed proteins could provide a rapid, cost-effective, and safe antigen for subunit vaccines, provided we can produce them in a properly folded form inducing neutralizing antibodies. Here, we use an E. coli-expressed SARS-CoV-2 receptor-binding domain (RBD) of the spike protein as a model to examine whether it yields neutralizing antisera with effects comparable to those generated by the S1 subunit of the spike protein (S1 or S1 subunit, thereafter) expressed in mammalian cells. We immunized 5-week-old Jcl-ICR female mice by injecting RBD (30 µg) and S1 subunit (5 µg) according to four schemes: two injections 8 weeks apart with RBD (RBD/RBD), two injections with S1 (S1/S1), one injection with RBD, and the second one with S1 (RBD/S1), and vice versa (S1/RBD). Ten weeks after the first injection (two weeks after the second injection), all combinations induced a strong immune response with IgG titer > 10⁵ (S1/RBD < S1/S1 < RBD/S1 < RBD/RBD). In addition, the neutralization effect of the antisera ranked as S1/RBD~RBD/S1 (80%) > S1/S1 (56%) > RBD/RBD (42%). These results indicate that two injections with E. coli-expressed RBD, or mammalian-cell-produced spike S1 subunit alone, can provide some protection against SARS-CoV-2, but a mixed injection scheme yields significantly higher protection.

CIDP: Analysis of Immunomarkers During COVID-19 mRNA-Vaccination and IVIg-Immunomodulation: An Exploratory Study

Availability of COVID-19 mRNA vaccine for patients with chronic inflammatory demyelinating polyneuropathy (CIDP) treated with intravenous immunoglobulin (IVIg) raises the question of whether COVID-19 mRNA vaccine influences disease activity or IVIg-mediated immunomodulation in CIDP. In this exploratory study, blood samples of CIDP patients on IVIg treatment were longitudinally analyzed before and after vaccination with a COVID-19 mRNA vaccine. A total of 44 samples of eleven patients were characterized at four timepoints by ELISA and flow cytometry in terms of immunomarkers for disease activity and IVIg-immunomodulation. Apart from a significantly lower expression of CD32b on naïve B cells after vaccination, no significant alteration of immunomarkers for CIDP or IVIg-mediated immunomodulation was observed. Our exploratory study suggests that COVID-19 mRNA vaccine does not have a relevant impact on immune activity in CIDP. In addition, immunomodulatory effects of IVIg in CIDP are not altered by COVID-19 mRNA vaccine. This study was registered in the German clinical trial register (DRKS00025759). Overview over the study design. Blood samples of CIDP patients on recurrent IVIg treatment and vaccination with a COVID-19 mRNA vaccine were obtained at four timepoints for cytokine ELISA and flow cytometry, to assess key cytokines and cellular immunomarkers for disease activity and IVIg-immunomodulation in CIDP.

Milk Allergen Micro-Array (MAMA) for Refined Detection of Cow's-Milk-Specific IgE Sensitization

BACKGROUND

Immunoglobulin-E(IgE)-mediated hypersensitivity to cow's milk allergens is a frequent cause of severe and life-threatening anaphylactic reactions. Besides case histories and controlled food challenges, the detection of the IgE antibodies specific to cow's milk allergens is important for the diagnosis of cow-milk-specific IgE sensitization. Cow´s milk allergen molecules provide useful information for the refined detection of cow-milk-specific IgE sensitization.

METHODS

A micro-array based on ImmunoCAP ISAC technology was developed and designated milk allergen micro-array (MAMA), containing a complete panel of purified natural and recombinant cow's milk allergens (caseins, α-lactalbumin, β-lactoglobulin, bovine serum albumin-BSA and lactoferrin), recombinant BSA fragments, and α-casein-, α-lactalbumin- and β-lactoglobulin-derived synthetic peptides. Sera from 80 children with confirmed symptoms related to cow's milk intake (without anaphylaxis: n = 39; anaphylaxis with a Sampson grade of 1-3: n = 21; and anaphylaxis with a Sampson grade of 4-5: n = 20) were studied. The alterations in the specific IgE levels were analyzed in a subgroup of eleven patients, i.e., five who did not and six who did acquire natural tolerance.

RESULTS

The use of MAMA allowed a component-resolved diagnosis of IgE sensitization in each of the children suffering from cow's-milk-related anaphylaxis according to Sampson grades 1-5 requiring only 20-30 microliters of serum. IgE sensitization to caseins and casein-derived peptides was found in each of the children with Sampson grades of 4-5. Among the grade 1-3 patients, nine patients showed negative reactivity to caseins but showed IgE reactivity to alpha-lactalbumin (n = 7) or beta-lactoglobulin (n = 2). For certain children, an IgE sensitization to cryptic peptide epitopes without detectable allergen-specific IgE was found. Twenty-four children with cow-milk-specific anaphylaxis showed additional IgE sensitizations to BSA, but they were all sensitized to either caseins, alpha-lactalbumin, or beta-lactoglobulin. A total of 17 of the 39 children without anaphylaxis lacked specific IgE reactivity to any of the tested components. The children developing tolerance showed a reduction in allergen and/or peptide-specific IgE levels, whereas those remaining sensitive did not.

CONCLUSIONS

The use of MAMA allows for the detection, using only a few microliters of serum, of IgE sensitization to multiple cow's milk allergens and allergen-derived peptides in cow-milk-allergic children with cow-milk-related anaphylaxis.

The SpACE-CCM: A facile and versatile cell culture medium-based biosensor for detection of SARS-CoV-2 spike-ACE2 interaction

The COVID-19 pandemic is an ongoing global public health threat. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, and binding of the SARS-CoV-2 spike to its receptor, angiotensin-converting enzyme 2 (ACE2), on host cells is critical for viral infection. Here, we developed a luminescent biosensor that readily detects interactions of the spike receptor-binding domain (RBD) and ACE2 in cell culture medium ('SpACE-CCM'), which was based on bimolecular complementation of the split nanoluciferase-fused spike RBD and ectodomain of ACE2 and further engineered to be efficiently secreted from cells by adding a heterologous secretory signal peptide (SSP). Screening of various SSPs identified 'interferon-α+alanine-aspartate' as the SSP that induced the highest activity. The SpACE-CCM biosensor was validated by observing a marked reduction of the activity caused by interaction-defective mutations or in the presence of neutralizing antibodies, recombinant decoy proteins, or peptides. Importantly, the SpACE-CCM biosensor responded well in assay-validating conditions compared with conventional cell lysate-based NanoLuc Binary Technology, indicating its advantage. We further demonstrated the biosensor's versatility by quantitatively detecting neutralizing activity in blood samples from COVID-19 patients and vaccinated individuals, discovering a small molecule interfering with the spike RBD-ACE2 interaction through high-throughput screening, and assessing the cross-reactivity of neutralizing antibodies against SARS-CoV-2 variants. Because the SpACE-CCM is a facile and rapid one-step reaction biosensor that aptly recapitulates the native spike-ACE2 interaction, it would be advantageous in many experimental and clinical applications associated with this interaction.

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

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

Dissection of Antibody Responses of Gam-COVID-Vac-Vaccinated Subjects Suggests Involvement of Epitopes Outside RBD in SARS-CoV-2 Neutralization

Millions of people have been vaccinated with Gam-COVID-Vac but fine specificities of induced antibodies have not been fully studied. Plasma from 12 naïve and 10 coronavirus disease 2019 (COVID-19) convalescent subjects was obtained before and after two immunizations with Gam-COVID-Vac. Antibody reactivity in the plasma samples (n = 44) was studied on a panel of micro-arrayed recombinant folded and unfolded severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins and 46 peptides spanning the spike protein (S) and by immunoglobulin G (IgG) subclass enzyme-linked immunosorbent assay (ELISA). The ability of Gam-COVID-Vac-induced antibodies to inhibit binding of the receptor-binding domain (RBD) to its receptor angiotensin converting enzyme 2 (ACE2) was investigated in a molecular interaction assay (MIA). The virus-neutralizing capacity of antibodies was studied by the pseudo-typed virus neutralization test (pVNT) for Wuhan-Hu-1 and Omicron. We found that Gam-COVID-Vac vaccination induced significant increases of IgG1 but not of other IgG subclasses against folded S, spike protein subunit 1 (S1), spike protein subunit 2 (S2), and RBD in a comparable manner in naïve and convalescent subjects. Virus neutralization was highly correlated with vaccination-induced antibodies specific for folded RBD and a novel peptide (i.e., peptide 12). Peptide 12 was located close to RBD in the N-terminal part of S1 and may potentially be involved in the transition of the pre- to post-fusion conformation of the spike protein. In summary, Gam-COVID-Vac vaccination induced S-specific IgG1 antibodies in naive and convalescent subjects in a comparable manner. Besides the antibodies specific for RBD, the antibodies induced against a peptide close to the N-terminus of RBD were also associated with virus-neutralization.

Recent developments in the immunopathology of COVID-19

There has been an important change in the clinical characteristics and immune profile of Coronavirus disease 2019 (COVID-19) patients during the pandemic thanks to the extensive vaccination programs. Here, we highlight recent studies on COVID-19, from the clinical and immunological characteristics to the protective and risk factors for severity and mortality of COVID-19. The efficacy of the COVID-19 vaccines and potential allergic reactions after administration are also discussed. The occurrence of new variants of concerns such as Omicron BA.2, BA.4, and BA.5 and the global administration of COVID-19 vaccines have changed the clinical scenario of COVID-19. Multisystem inflammatory syndrome in children (MIS-C) may cause severe and heterogeneous disease but with a lower mortality rate. Perturbations in immunity of T cells, B cells, and mast cells, as well as autoantibodies and metabolic reprogramming may contribute to the long-term symptoms of COVID-19. There is conflicting evidence about whether atopic diseases, such as allergic asthma and rhinitis, are associated with a lower susceptibility and better outcomes of COVID-19. At the beginning of pandemic, the European Academy of Allergy and Clinical Immunology (EAACI) developed guidelines that provided timely information for the management of allergic diseases and preventive measures to reduce transmission in the allergic clinics. The global distribution of COVID-19 vaccines and emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants with reduced pathogenic potential dramatically decreased the morbidity, severity, and mortality of COVID-19. Nevertheless, breakthrough infection remains a challenge for disease control. Hypersensitivity reactions (HSR) to COVID-19 vaccines are low compared to other vaccines, and these were addressed in EAACI statements that provided indications for the management of allergic reactions, including anaphylaxis to COVID-19 vaccines. We have gained a depth knowledge and experience in the over 2 years since the start of the pandemic, and yet a full eradication of SARS-CoV-2 is not on the horizon. Novel strategies are warranted to prevent severe disease in high-risk groups, the development of MIS-C and long COVID-19.

Therapeutic Phage Display-Derived Single-Domain Antibodies for Pandemic Preparedness

Driven by necessity, the COVID-19 pandemic caused by SARS-CoV-2 has accelerated the development and implementation of new vaccine platforms and other viral therapeutics. Among these is the therapeutic use of antibodies including single-domain antibodies, in particular the camelid variable heavy-chain fragment (VHH). Such therapies can provide a critical interim intervention when vaccines have not yet been developed for an emerging virus. It is evident that an increasing number of different viruses are emerging and causing epidemics and pandemics with increasing frequency. It is therefore imperative that we capitalize on the experience and knowledge gained from combatting COVID-19 to be better prepared for the next pandemic.

Immunodominant antibody responses directed to SARS-CoV-2 hotspot mutation sites and risk of immune escape

Introduction

Considering the likely need for the development of novel effective vaccines adapted to emerging relevant CoV-2 variants, the increasing knowledge of epitope recognition profile among convalescents and afterwards vaccinated with identification of immunodominant regions may provide important information.

Methods

We used an RBD peptide microarray to identify IgG and IgA binding regions in serum of 71 COVID-19 convalescents and 18 vaccinated individuals.

Results

We found a set of immunodominant RBD antibody epitopes, each recognized by more than 30% of the tested cohort, that differ among the two different groups and are within conserved regions among betacoronavirus. Of those, only one peptide, P44 (S415-429), recognized by 68% of convalescents, presented IgG and IgA antibody reactivity that positively correlated with nAb titers, suggesting that this is a relevant RBD region and a potential target of IgG/IgA neutralizing activity.

Discussion

This peptide is localized within the area of contact with ACE-2 and harbors the mutation hotspot site K417 present in gamma (K417T), beta (K417N), and omicron (K417N) variants of concern. The epitope profile of vaccinated individuals differed from convalescents, with a more diverse repertoire of immunodominant peptides, recognized by more than 30% of the cohort. Noteworthy, immunodominant regions of recognition by vaccinated coincide with mutation sites at Omicron BA.1, an important variant emerging after massive vaccination. Together, our data show that immune pressure induced by dominant antibody responses may favor hotspot mutation sites and the selection of variants capable of evading humoral response.

Advances in SARS-CoV-2 receptor-binding domain-based COVID-19 vaccines

INTRODUCTION

The Coronavirus Disease 2019 (COVID-19) pandemic has caused devastating human and economic costs. Vaccination is an important step in controlling the pandemic. Severe acute respiratory coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19, infects cells by binding a cellular receptor through the receptor-binding domain (RBD) within the S1 subunit of the spike (S) protein. Viral entry and membrane fusion are mediated by the S2 subunit.

AREAS COVERED

SARS-CoV-2 S protein, particularly RBD, serves as an important target for vaccines. Here we review the structure and function of SARS-CoV-2 S protein and its RBD, summarize current COVID-19 vaccines targeting the RBD, and outline potential strategies for improving RBD-based vaccines. Overall, this review provides important information that will facilitate rational design and development of safer and more effective COVID-19 vaccines.

EXPERT OPINION

The S protein of SARS-CoV-2 harbors numerous mutations, mostly in the RBD, resulting in multiple variant strains. Although many COVID-19 vaccines targeting the RBD of original virus strain (and previous variants) can prevent infection of these strains, their ability against recent dominant variants, particularly Omicron and its offspring, is significantly reduced. Collective efforts are needed to develop effective broad-spectrum vaccines to control current and future variants that have pandemic potential.

A six-month study of anti-SARS-CoV-2 BNT162b2 mRNA vaccination: A comparative analysis of essential trace elements and anti-RBD IgG sera levels

BACKGROUND

Although essential trace elements (ETEs) play pivotal roles in life-supporting biochemical processes, their function in innate and adaptive immunity has not been fully elucidated, particularly during immunization. Furthermore, the association between anti-SARS-CoV-2 specific IgG antibodies and ETE levels with vaccine responsiveness has not been investigated.

METHODS

The present study explored the status of ETEs (Mn, Cu, Zn, and Se) in sera of healthy women before and after vaccination with the anti-SARS-CoV-2 BNT162b2 mRNA vaccine in a follow-up period of six months. The main aim was to explore links between ETE levels and IgG antibodies produced against Spike glycoprotein's Receptor-Binding Domain (RBD).

RESULTS

A recombinant protein of SARS-CoV-2 comprising the receptor binding domain was successfully expressed in HEK-293 T cells. The purified protein was suitable for producing a sensitive antibody detection assay for human serum and monitored seropositivity, indicating a transient response with peak anti-SARS-CoV-2 IgG levels 2 months after vaccination. In parallel to increasing antibody titers, serum concentrations of Cu, Mn, and Se were not affected by vaccination, and concentrations remained relatively constant at the different sampling times during the 6-month observation period. Total serum Zn concentrations were slightly elevated when compared between the first and last sampling dates. Overall, no consistent effects of vaccination on any of the three trace elements analyzed in our study were observed.

CONCLUSION

Vaccination of adult healthy female volunteers with an mRNA vaccine was not associated with consistent changes in serum trace element concentrations over a six-month observation period.

The Spike Mutants Website: A Worldwide Used Resource against SARS-CoV-2

A large number of SARS-CoV-2 mutations in a short period of time has driven scientific research related to vaccines, new drugs, and antibodies to combat the new variants of the virus. Herein, we present a web portal containing the structural information, the tridimensional coordinates, and the molecular dynamics trajectories of the SARS-CoV-2 spike protein and its main variants. The Spike Mutants website can serve as a rapid online tool for investigating the impact of novel mutations on virus fitness. Taking into account the high variability of SARS-CoV-2, this application can help the scientific community when prioritizing molecules for experimental assays, thus, accelerating the identification of promising drug candidates for COVID-19 treatment. Below we describe the main features of the platform and illustrate the possible applications for speeding up the drug discovery process and hypothesize new effective strategies to overcome the recurrent mutations in SARS-CoV-2 genome.

Comparison of the immunogenicity of five COVID-19 vaccines in Sri Lanka

To determine the antibody responses elicited by different vaccines against SARS-CoV-2, we compared antibody responses in individuals 3 months post-vaccination in those who had received different vaccines in Sri Lanka. Abs to the receptor binding domain (RBD) of the ancestral (wild type) virus (WT) as well as to variants of concern (VoCs), and ACE2 blocking Abs, were assessed in individuals vaccinated with Moderna (n = 225), Sputnik V (n = 128) or Sputnik light (n = 184) and the results were compared with previously reported data on Sinopharm and AZD1222 vaccinees. A total of 99.5% of Moderna, >94% of AZD1222 or Sputnik V and >70% of Sputnik light, >60% of Sinopharm vaccine recipients, had a positive response to ACE2 blocking antibodies. The ACE2 blocking antibody levels were highest to lowest was Moderna > Sputnik V/AZD1222 (had equal levels) > Sputnik light > Sinopharm. All Moderna recipients had antibodies to the RBD of WT, alpha and beta, while positivity rates for delta variant was 80%. The positivity rates for Sputnik V vaccinees for the WT and VoCs were higher than for AZD1222 vaccinees while those who received Sinopharm had the lowest positivity rates (<16.7%). The total antibodies to the RBD were highest for the Sputnik V and AZD1222 vaccinees. The Moderna vaccine elicited the highest ACE2 blocking antibody levels followed by Sputnik V/AZD1222, while those who received Sinopharm had the lowest levels. These findings highlight the need for further studies to understand the effects on clinical outcomes.

New insights into human immune memory from SARS-CoV-2 infection and vaccination

Since early 2020, the world has been embroiled in an ongoing viral pandemic with SARS-CoV-2 and emerging variants resulting in mass morbidity and an estimated 6 million deaths globally. The scientific community pivoted rapidly, providing unique and innovative means to identify infected individuals, technologies to evaluate immune responses to infection and vaccination, and new therapeutic strategies to treat infected individuals. Never before has immunology been so critically at the forefront of combatting a global pandemic. It has now become evident that not just antibody responses, but formation and durability of immune memory cells following vaccination are associated with protection against severe disease from SARS-CoV-2 infection. Furthermore, the emergence of variants of concern (VoC) highlight the need for immunological markers to quantify the protective capacity of Wuhan-based vaccines. Thus, harnessing and modulating the immune response is key to successful vaccination and treatment of disease. We here review the latest knowledge about immune memory generation and durability following natural infection and vaccination, and provide insights into the attributes of immune memory that may protect from emerging variants.

Vaccine based on folded receptor binding domain-PreS fusion protein with potential to induce sterilizing immunity to SARS-CoV-2 variants

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the ongoing global COVID-19 pandemic. One possibility to control the pandemic is to induce sterilizing immunity through the induction and maintenance of neutralizing antibodies preventing SARS-CoV-2 from entering human cells to replicate in.

METHODS

We report the construction and in vitro and in vivo characterization of a SARS-CoV-2 subunit vaccine (PreS-RBD) based on a structurally folded recombinant fusion protein consisting of two SARS-CoV-2 Spike protein receptor-binding domains (RBD) fused to the N- and C-terminus of hepatitis B virus (HBV) surface antigen PreS to enable the two unrelated proteins serving as immunologic carriers for each other.

RESULTS

PreS-RBD, but not RBD alone, induced a robust and uniform RBD-specific IgG response in rabbits. Currently available genetic SARS-CoV-2 vaccines induce mainly transient IgG1 responses in vaccinated subjects whereas the PreS-RBD vaccine induced RBD-specific IgG antibodies consisting of an early IgG1 and sustained IgG4 antibody response in a SARS-CoV-2 naive subject. PreS-RBD-specific IgG antibodies were detected in serum and mucosal secretions, reacted with SARS-CoV-2 variants, including the omicron variant of concern and the HBV receptor-binding sites on PreS of currently known HBV genotypes. PreS-RBD-specific antibodies of the immunized subject more potently inhibited the interaction of RBD with its human receptor ACE2 and their virus-neutralizing titers (VNTs) were higher than median VNTs in a random sample of healthy subjects fully immunized with registered SARS-CoV-2 vaccines or in COVID-19 convalescent subjects.

CONCLUSION

The PreS-RBD vaccine has the potential to serve as a combination vaccine for inducing sterilizing immunity against SARS-CoV-2 and HBV by stopping viral replication through the inhibition of cellular virus entry.

Combined assessment of S- and N-specific IL-2 and IL-13 secretion and CD69 neo-expression for discrimination of post-infection and post-vaccination cellular SARS-CoV-2-specific immune response

BACKGROUND

Antibody-based tests are available for measuring SARS-CoV-2-specific immune responses but fast T-cell assays remain scarce. Robust T cell-based tests are needed to differentiate specific cellular immune responses after infection from those after vaccination.

METHODS

One hundred seventeen individuals (COVID-19 convalescent patients: n = 40; SARS-CoV-2 vaccinees: n = 41; healthy controls: n = 36) were evaluated for SARS-CoV-2-specific cellular immune responses (proliferation, Th1, Th2, Th17, and inflammatory cytokines, activation-induced marker [AIM] expression) by incubating purified peripheral blood mononuclear cells (PBMC) or whole blood (WB) with SARS-CoV-2 peptides (S, N, or M), vaccine antigens (tetanus toxoid, tick borne encephalitis virus) or polyclonal stimuli (Staphylococcal enterotoxin, phytohemagglutinin).

RESULTS

N-peptide mix stimulation of WB identified the combination of IL-2 and IL-13 secretion as superior to IFN-γ secretion to discriminate between COVID-19-convalescent patients and healthy controls (p < .0001). Comparable results were obtained with M- or S-peptides, the latter almost comparably recalled IL-2, IFN-γ, and IL-13 responses in WB of vaccinees. Analysis 10 months as opposed to 10 weeks after COVID-19, but not allergic disease status, positively correlated with IL-13 recall responses. WB cytokine responses correlated with cytokine and proliferation responses of PBMC. Antigen-induced neo-expression of the C-type lectin CD69 on CD4⁺ (p < .0001) and CD8⁺ (p = .0002) T cells informed best about the SARS-CoV-2 exposure status with additional benefit coming from CD25 upregulation.

CONCLUSION

Along with N- and S-peptide-induced IL-2 and CD69 neo-expression, we suggest to include the type 2 cytokine IL-13 as T-cellular recall marker for SARS-CoV-2 specific T-cellular immune responses after infection and vaccination.

Characterization and Utilization of Disulfide-Bonded SARS-CoV-2 Receptor Binding Domain of Spike Protein Synthesized by Wheat Germ Cell-Free Production System

The spike protein (SP) of SARS-CoV-2 is an important target for COVID-19 therapeutics and vaccines as it binds to the ACE2 receptor and enables viral infection. Rapid production and functional characterization of properly folded SP is of the utmost importance for studying the immunogenicity and receptor-binding activity of this protein considering the emergence of highly infectious viral variants. In this study, we attempted to express the receptor-binding region (RBD) of SARS-CoV-2 SP containing disulfide bonds using the wheat germ cell-free protein synthesis system. By adding protein disulfide isomerase (PDI) and endoplasmic reticulum oxidase (ERO1α) to the translational reaction mixture, we succeeded in synthesizing a functionally intact RBD protein that can interact with ACE2. Using this RBD protein, we have developed a high-throughput AlphaScreen assay to evaluate the RBD–ACE2 interaction, which can be applied for drug screening and mutation analysis. Thus, our method sheds new light on the structural and functional properties of SARS-CoV-2 SP and has the potential to contribute to the development of new COVID-19 therapeutics.

A Moderated Mediation Model Explaining the Relationship Between Risk-Group Membership, Threat Perception, Knowledge, and Adherence to COVID-19 Behavioral Measures

Background

COVID-19 is a threat to individual and global health, thus, reducing the disease's spread is of significant importance. However, adherence to behavioral measures against the spread of COVID-19 is not universal, even within vulnerable populations who are at higher risk of exposure to the virus or severe COVID-19 infection. Therefore, this study investigates how risk-group membership relates to adherence to COVID-19 behavioral measures, whether perceived threat of COVID-19 is a mechanism explaining this relationship, and whether knowledge about COVID-19 moderates these effects.

Methods

We conducted a web-based survey (N = 4,096) representative of the adult population in Germany with regard to gender, age (18 to 74), and province. Therein, we assessed risk group membership with two indicators (risk of exposure to COVID-19 and risk of severe COVID-19 infection), perceived COVID-19 threat with the Perceived Coronavirus Threat Questionnaire, knowledge about COVID-19 with a knowledge test; and adherence to six behavioral measures to protect against the spread of COVID-19 (e.g., keeping distance, using mouth-nose protection, and following contact restrictions). We used moderated mediation models to test whether perceived threat mediates the relationship between risk-group membership and adherence and whether knowledge about COVID-19 moderates this relationship.

Results

We found that risk group members had more perceived COVID-19 threat and that knowledge about COVID-19 increased perceived threat. Moreover, risk group membership had a positive direct effect on adherence to most behavioral measures and risk group members with less knowledge about COVID-19 violated measures more frequently. Risk-group membership also had positive indirect effects on adherence via perceived COVID-19 threat. The moderated indirect effects of threat indicate that threat led to more adherence when knowledge was low, but lost relevance as knowledge increased.

Conclusion

The results may help to evaluate disease-regulation measures and to combat the pandemic more effectively. For example, increasing COVID-19 knowledge in the general population could increase adherence to COVID-19 behavioral measures. However, policy makers should be mindful that this could also have negative mental health implications as knowledge increases perceived COVID-19 threat.

The kinetics and predictors of anti-SARS-CoV-2 antibodies up to eight months after symptomatic COVID-19: a Czech cross-sectional study

The presence of neutralizing SARS‐CoV‐2‐specific antibodies indicates protection against (re)infection, however, the knowledge of their long‐term kinetics is limited. This study analyzed the presence of COVID‐19‐induced antibodies in unvaccinated healthcare workers (HCWs) over the period of 1–8 months post symptom onset (SO) and explored the determinants of persisting immunoglobulin (Ig) seropositivity. Six hundred sixty‐two HCWs were interviewed for anamnestic data and tested for IgG targeting the spike protein (S1 and S2) and IgM targeting the receptor‐binding domain. A Cox regression model was used to explore potential predictors of seropositivity with respect to the time lapse between SO and serology testing. 82.9% and 44.7% of HCWs demonstrated IgG and IgM seropositivity, respectively, with a mean interval of 83 days between SARS‐CoV‐2 detection and serology testing. On average, HCWs reported seven symptoms in the acute phase lasting 20 days. IgG seropositivity rates among HCWs decreased gradually to 80%, 50%, and 35% at 3, 6, and 8 months after SO, while IgM seropositivity fell rapidly to 60%, 15%, and 0% over the same time intervals. The number of symptoms was the only predictor of persisting IgG seropositivity (odds ratio [OR] 1.096, 95% confidence interval [CI] 1.003–1.199, p = 0.043) and symptom duration a predictor of IgM seropositivity (OR 1.011, 95% CI 1.004–1.017, p = 0.002). Infection‐induced anti‐SARS‐CoV‐2 IgG rates drop to a third in seropositive participants over the course of 8 months. Symptom count and duration in the acute phase of COVID‐19 are both relevant to the subsequent kinetics of antibody responses.

60% and 35% of subjects maintain IgG seropositivity 6‐ and 8‐month post COVID‐19.

Characteristics of the acute phase of COVID‐19 are relevant for antibody responses.

The number of symptoms of acute COVID‐19 predicts persisting IgG seropositivity.

Symptom duration predicts persisting IgM seropositivity.

Anamnestic data may serve as simple predictors of seropositivity post COVID‐19.

Evaluation of a commercial ELISA as alternative to plaque reduction neutralization test to detect neutralizing antibodies against SARS-CoV-2

High-throughput detection of neutralizing antibodies against SARS-CoV-2 presents a valuable tool for vaccine trials or investigations of population immunity. We evaluate the performance of the first commercial surrogate virus neutralization test (sVNT, GenScript Biotech) against SARS-CoV-2 plaque reduction neutralization test (PRNT) in convalescent and vaccinated individuals. We compare it to five other ELISAs, two of which are designed to detect neutralizing antibodies. In 491 pre-vaccination serum samples, sVNT missed 23.6% of PRNT-positive samples when using the manufacturer-recommended cutoff of 30% binding inhibition. Introducing an equivocal area between 15 and 35% maximized sensitivity and specificity against PRNT to 72.8–93.1% and 73.5–97.6%, respectively. The overall diagnostic performance of the other ELISAs for neutralizing antibodies was below that of sVNT. Vaccinated individuals exhibited higher antibody titers by PRNT (median 119.8, IQR 56.7–160) and binding inhibition by sVNT (median 95.7, IQR 88.1–96.8) than convalescent patients (median 49.1, IQR 20–62; median 52.9, IQR 31.2–76.2). GenScript sVNT is suitable to screen for SARS-CoV-2-neutralizing antibodies; however, to obtain accurate results, confirmatory testing by PRNT in a equivocal area is required. This equivocal area may require adaptation for use in vaccinated individuals, due to higher antibody titers.

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.

Interdependencies of cellular and humoral immune responses in heterologous and homologous SARS-CoV-2 vaccination

Background

Homologous and heterologous SARS‐CoV‐2 vaccinations yield different spike protein‐directed humoral and cellular immune responses. This study aimed to explore their currently unknown interdependencies.

Methods

COV‐ADAPT is a prospective, observational cohort study of 417 healthcare workers who received vaccination with homologous ChAdOx1 nCoV‐19, homologous BNT162b2 or with heterologous ChAdOx1 nCoV‐19/BNT162b2. We assessed humoral (anti‐spike‐RBD‐IgG, neutralizing antibodies, and avidity) and cellular (spike‐induced T‐cell interferon‐γ release) immune responses in blood samples up to 2 weeks before (T1) and 2–12 weeks following secondary immunization (T2).

Results

Initial vaccination with ChAdOx1 nCoV‐19 resulted in lower anti‐spike‐RBD‐IgG compared with BNT162b2 (70 ± 114 vs. 226 ± 279 BAU/ml, p < .01) at T1. Booster vaccination with BNT162b2 proved superior to ChAdOx1 nCoV‐19 at T2 (anti‐spike‐RBD‐IgG: ChAdOx1 nCoV‐19/BNT162b2 2387 ± 1627 and homologous BNT162b2 3202 ± 2184 vs. homologous ChAdOx1 nCoV‐19 413 ± 461 BAU/ml, both p < .001; spike‐induced T‐cell interferon‐γ release: ChAdOx1 nCoV‐19/BNT162b2 5069 ± 6733 and homologous BNT162b2 4880 ± 7570 vs. homologous ChAdOx1 nCoV‐19 1152 ± 2243 mIU/ml, both p < .001). No significant differences were detected between BNT162b2‐boostered groups at T2. For ChAdOx1 nCoV‐19, no booster effect on T‐cell activation could be observed. We found associations between anti‐spike‐RBD‐IgG levels (ChAdOx1 nCoV‐19/BNT162b2 and homologous BNT162b2) and T‐cell responses (homologous ChAdOx1 nCoV‐19 and ChAdOx1 nCoV‐19/BNT162b2) from T1 to T2. Additionally, anti‐spike‐RBD‐IgG and T‐cell response were linked at both time points (all groups combined). All regimes yielded neutralizing antibodies and increased antibody avidity at T2.

Conclusions

Interdependencies between humoral and cellular immune responses differ between common SARS‐CoV‐2 vaccination regimes. T‐cell activation is unlikely to compensate for poor humoral responses.

Identification of Chicken CD44 as a Novel B Lymphocyte Receptor for Infectious Bursal Disease Virus

Infectious bursal disease virus (IBDV), which targets bursa B lymphocytes, causes severe immunosuppressive disease in chickens, inducing huge economic losses for the poultry industry. To date, the functional receptor for IBDV binding and entry into host cells remains unclear. This study used mass spectrometry to screen host proteins of chicken bursal lymphocytes interacting with VP2. The chicken transmembrane protein cluster of differentiation 44 (chCD44) was identified and evaluated for its interaction with IBDV VP2, the major capsid protein. Overexpression and knockdown experiments showed that chCD44 promotes replication of IBDV. Furthermore, soluble chCD44 and the anti-chCD44 antibody blocked virus binding. The results of receptor reconstitution indicated that chCD44 overexpression conferred viral binding capability in non-permissive cells. More important, although we found that IBDV could not replicate in the chCD44-overexpressed non-permissive cells, the virus could enter non-permissive cells using chCD44. Our finding reveals that chCD44 is a cellular receptor for IBDV, facilitating virus binding and entry in target cells by interacting with the IBDV VP2 protein. IMPORTANCE IBDV causes severe immunosuppressive disease in chickens, inducing huge economic losses for the poultry industry. However, the specific mechanism of IBDV invading host cells of IBDV was not very clear. This study shed light on which cellular protein component IBDV is used to bind and/or enter B lymphocytes. The results of our study revealed that chCD44 could promote both the binding and entry ability of IBDV in B lymphocytes, acting as a cellular receptor for IBDV. Besides, this is the first report about chicken CD44 function in viral replication. Our study impacts the understanding of the IBDV binding and entry process and sets the stage for further elucidation of the infection mechanism of IBDV.

Characterization of the antibody response to SARS-CoV-2 in a mildly affected pediatric population

BACKGROUND

While children usually experience a mild course of COVID-19, and a severe disease is more common in adults, the features, specificities, and functionality of the SARS-CoV-2-specific antibody response in the pediatric population are of interest.

METHODS

We performed a detailed analysis of IgG antibodies specific for SARS-CoV-2-derived antigens S and RBD by ELISA in 26 SARS-CoV-2 seropositive schoolchildren with mild or asymptomatic disease course, and in an equally sized, age- and gender-matched control group. Furthermore, a detailed mapping of IgG reactivity to a panel of microarrayed SARS-CoV-2 proteins and S-derived peptides was performed by microarray technology. The capacity of the antibody response to block RBD-ACE2 binding and virus neutralization were assessed. Results were compared with those obtained in an adult COVID-19 convalescent population.

RESULTS

After mild COVID-19, anti-S and RBD-specific IgG antibodies were developed by 100% and 84.6% of pediatric subjects, respectively. No difference was observed in regards to symptoms and gender. Mounted antibodies recognized conformational epitopes of the spike protein and were capable to neutralize the virus up to a titer of ≥80 and to inhibit the ACE2-RBD interaction by up to 65%. SARS-CoV-2-specific IgG responses in children were comparable to mildly affected adult patients.

CONCLUSION

SARS-CoV-2 asymptomatic and mildly affected pediatric patients develop a SARS-CoV-2-specific antibody response, which is comparable regarding antigen, epitope recognition, and the ability to inhibit the RBD-ACE2 interaction to that observed in adult patients after mild COVID-19.