A SARS-CoV-2 surrogate virus neutralization test based on antibody-mediated blockage of ACE2-spike protein-protein interaction

Neutralizing antibodies against SARS-CoV-2 of vaccinated healthcare workers in Taiwan

BACKGROUND

Vaccination is one of the best ways to control the SARS-CoV-2 outbreak. In Taiwan, healthcare workers were prioritized for vaccination, but the effectiveness of these vaccines for them remains unclear. Thus, it's essential to examine their neutralizing antibodies after prime-boost vaccinations.

METHODS

In this prospective observational study, 514 healthcare workers from Chang Gung Memorial hospitals in Taiwan were included between 19 March 2021 and 21 August 2021. The two doses of COVID-19 vaccines were either a match or a mixing of AZD1222 and mRNA-1273, e.g. AZD1222 + AZD1222 (n = 406), mRNA-1273 + mRNA-1273 (n = 62), and AZD1222 + mRNA-1273 (n = 46). Blood specimens were drawn after two doses of vaccines, defined as post-vaccine days [median 34.00 days and interquartile range (IQR) 29.00-42.00 days], and examined for the neutralizing antibodies via SARS-CoV-2 neutralization kits. The results were analyzed as a percentage of inhibition based on the negative control.

RESULTS

After 2 vaccination doses, subjects with AZD1222 + mRNA-1273 (median 97.15%, IQR 96.06-98.06%) and mRNA-1273 + mRNA-1273 (median 97.47%, IQR 96.75-97.89%) exhibited higher neutralizing antibodies than those receiving AZD1222 + AZD1222 vaccines (median 71.28%, IQR 49.39-89.70%) (the percentage was referred to inhibition of surrogate virus). The post-vaccination days negatively impacted the neutralizing antibodies, except for the mRNA-1273 + mRNA-1273 group. The presence of fever, headache, and myalgia after the second dosage was reflected in the higher neutralizing antibodies (median of no fever 76.00% vs. fever 97.00%, p < 0.0001; median of no headache 76.00% vs. headache 95.00%, p < 0.0001; median of no myalgia 75.50% vs. myalgia 96.00%, p < 0.0001). The subjects with underlying diseases, including hypertension and cancer showed lower neutralizing antibodies (median of no hypertension 81.00% vs. hypertension 56.00%, p = 0.0029; median of no cancer 81.00% vs. cancer 56.00%, p = 0.0143).

CONCLUSION

Heterologous prime-boost vaccines (AZD1222 + mRNA-1273) and two doses of mRNA vaccines are recommended. For future directions, we need to investigate the effectiveness of the vaccination against new SARS-CoV-2 variants.

Sensitively detecting antigen of SARS-CoV-2 by a homogeneous immunoassay based on ortho-touch reaction and graphene oxide (GO) quenched acridine esterification chemiluminescence

In this study, a homogeneous immunoassay based on ortho-touch reaction and graphene oxide (GO) quenched acridine esterification chemiluminescence is developed for sensitive detection of SARS-CoV-2 antigen. The sensitivity and specificity of this method was further evaluated with viral protein, virus strains and clinical samples. Benefiting from strong chemiluminescence signal and good quenching performance of GO, this method allows enhanced signal-to-background ratio, and the limit of detection is down to 0.02 ng/ml of viral protein or equivalently 200 copies/ml of virus strains. In clinical evaluations, our approach demonstrated a high level of agreement with digital RT-PCR, achieving a positive coincidence rate of 90.87 %, a negative coincidence rate of 99.77 %, and an overall concordance of 96.53 %, while showing no cross-reactivity with other prevalent viruses. This method offers a promising, sensitive, rapid, and cost-effective platform for early SARS-CoV-2 diagnosis. Moreover, it can potentially be adapted for detecting other pathogens.

Comparative assessment of four virus neutralization assays for detection of SARS-CoV-2 neutralizing antibodies

Neutralizing antibodies (NAbs) targeting receptor-binding domain (RBD) or spike of SARS-CoV-2 play an important role in blocking virus entry to the host cells and detecting their levels is critical for the assessment of humoral protective immune response following vaccination or recovery from SARS-CoV-2 infection. Here, we compared the performance of four virus neutralization tests to measure neutralizing antibodies in various sample types. We analyzed 25 serum samples obtained from mice or rabbits immunized with different vaccine platforms, and also 11 mouse anti-RBD monoclonal antibodies (MAbs) using surrogate virus neutralization test (SVNT), pseudovirus neutralization test (PVNT), conventional virus neutralization test (CVNT), and one-step or two-step inhibition flowcytometry virus neutralization test (IFVNT). All four VNTs showed significant correlations with each other, though PVNT and CVNT displayed significantly lower limit of detection (LoD) compared to the other two assays. In conclusion, our findings indicate that all four VNT assays give valid and accurate results and could be employed to determine the level of SARS-CoV-2 neutralizing monoclonal and polyclonal antibodies.

Comparison of Three Commercial ELISA Kits for Detection of Antibodies Against SARS-CoV-2 in Serum Samples from Different Animal Species

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the coronavirus disease 19 (COVID-19) pandemic, significantly impacting global health, economies, and social stability. In February 2020, the first cases of SARS-CoV-2 infections in animals were documented, highlighting the potential risks posed by regular human-animal interactions in facilitating viral transmission. In consequence, it is essential to validate surveillance methods for SARS-CoV-2 in animals. In the present study, 101 sera from different animal species (36 cats, 41 dogs, 4 ferrets, 10 wild boar, 6 domestic goats, and 4 lions) were tested using three different ELISA kits to evaluate humoral responses against SARS-CoV-2. ELISA results were compared and correlated with a pseudovirus neutralization test (pVNT), considered as the reference assay. ELISA-1, targeting the receptor binding domain (RBD) neutralizing antibodies (nAbs) of SARS-CoV-2, exhibited the highest diagnostic performance, and proved to be a reliable tool for initial screenings in high-throughput animal studies. In contrast, ELISA-2 (also targeting RBD nAbs) and ELISA-3 (targeting nucleoprotein antibodies) demonstrated lower sensitivity for detecting seropositive animals.

Temporal correlations between RBD-ACE2 blocking and binding antibodies to SARS-CoV-2 variants in CoronaVac-vaccinated individuals and their persistence in COVID-19 patients

Antibodies play a crucial role in protection against SARS-CoV-2. Understanding the correlation between binding and functional antibodies is essential to determine whether binding antibody levels can reliably predict neutralizing activity. We assessed antibody responses in 111 individuals vaccinated with the inactivated vaccine CoronaVac and 111 COVID-19 patients in Thailand. Plasma levels of ACE2-blocking antibodies targeting the receptor-binding domain (RBD) of SARS-Co-V2 variants were measured before vaccination and at 14 and 28 days after the second dose using a multiplex surrogate virus neutralization test. Anti-spike and anti-nucleocapsid antibodies were quantified by electrochemiluminescence immunoassay, and anti-RBD IgG by ELISA. After vaccination, blocking, anti-spike, and IgG antibody levels increased but declined rapidly within a month, whereas antibody levels in COVID-19 patients increased and persisted. Blocking and anti-spike antibody correlated at day 14 post-vaccination but not at day 28. In COVID-19 patients, correlations were moderate at day 14, and stronger at day 28. Correlations were weaker for Omicron subvariants than for the ancestral strain and non-Omicron variants. The weak correlation between blocking and anti-RBD IgG suggests binding antibodies might not predict neutralizing activity. These findings highlight the temporal nature of CoronaVac-induced immunity and the need for booster doses and variant-adapted vaccine.

Critical role of ferroptosis in viral infection and host responses

Ferroptosis is an iron-dependent form of programmed cell death that plays a crucial role in regulating intracellular redox homeostasis and lipid metabolism, and in combating viral infections. Viruses have persistently evolved and adapted synergistically with their hosts over a long period and, to some extent, have been able to utilize ferroptosis to promote viral replication. Herein, we summarize the characteristics, mechanisms, and regulatory networks of ferroptosis and provide an overview of the key regulatory steps of ferroptosis involved in viral infection, together with the changes in host indicators and key regulatory signaling pathways. This study intends to deepen our understanding of the critical role of ferroptosis in viral infection, which will be meaningful for further revealing the mechanisms underlying the occurrence and progression of virus diseases, as well as for the future exploration of anti-viral strategies.

Transcriptomic analysis after SARS-CoV-2 mRNA vaccination reveals a specific gene signature in low-responder hemodialysis patients

Introduction

Individuals with comorbidities, such as chronic kidney disease and hemodialysis patients (HDP), are particularly susceptible to severe COVID-19 and to its complications. Furthermore, their immune response to vaccines is impaired, requiring tailored vaccination strategies. In this study, we investigated through transcriptomic profiling the immune response heterogeneity of HDP vaccinated with two doses of mRNA BNT162b2 vaccine.

Methods

Transcriptomic analyses were conducted in peripheral blood mononuclear cells (PBMC) collected from HDP and healthy controls (HC) before and 7 days after each dose. The HDP were stratified into high- and low-responders based on their humoral response after the second dose.

Results

Significant differences in gene expression related to B cell abundance and regulation, CD4 T cell proliferation, and inflammation pathways were observed at baseline and day 7 between HDP-low responders and HC, while the HDP high-responders displayed an intermediate expression profile for these genes.

Discussion

Results were consistent with the known immunologic alterations occurring in HDP cohorts related to lymphopenia, chronic inflammation, and dysregulated proliferation of CD4+. Our analyses identified an early transcriptional signature correlated with a diminished immune response in HDP low-responders, highlighting the importance of conducting a characterization of immunocompromised cohorts.

Convalescent plasma for the treatment of patients with COVID-19: the Singapore experience and lessons learnt

INTRODUCTION

We report Singapore's convalescent plasma (CP) programme during the first year of the COVID-19 pandemic. Based on historical data and its potential therapeutic promise, CP was offered as an experimental treatment option for severe or high-risk COVID-19 patients when established therapeutics were lacking.

METHODS

The CP programme was implemented under monitored expanded access approved by Singapore's Ministry of Health. CP donors were primarily selected based on specific antibody titres, while suitable recipients were chosen based on risk factors and disease severity. Operational protocols and logistical considerations are discussed in-depth.

RESULTS

Between April 2020 and September 2020, the CP donor programme successfully collected 33 plasma units from 27 qualified donors. Seven patients received CP treatment under this programme. Six of the seven recipients of CP survived for more than 28 days post-transfusion and were discharged alive. Given the availability of other validated therapeutic options, the CP programme was officially suspended in September 2021.

CONCLUSION

This study provides a comprehensive overview of the intricacies of Singapore's CP programme, from its operational challenges to the observed clinical outcomes, while highlighting the potential benefits and complexities of CP as a therapeutic option. Successful implementation of the CP programme requires robust collaboration across multidisciplinary teams. Access to serological tests was crucial for donor selection. Both the selection of CP with high neutralising antibodies and careful selection of appropriate recipients are key aspects to optimise the therapeutic success of CP. A meticulous approach is warranted if CP were to be used in future pandemics.

Use of a Multiplex Immunoassay Platform to Investigate Multifaceted Antibody Responses in SARS-CoV-2 Vaccinees with and Without Prior Infection

The emergence of COVID-19 necessitated the rapid development of vaccines. While highly effective at reducing severe disease and death, breakthrough infections remain a problem as the virus continues to mutate. To help address this issue, we show the utility of a multiplex immunoassay in measuring multiple aspects of the antibody response generated by SARS-CoV-2 vaccines. We use a multiplex immunoassay platform to measure spike-specific IgG concentration, avidity, and receptor-binding inhibition. In addition, we correlate results from an ACE-2 receptor-binding inhibition assay with corresponding data from a SARS-CoV-2 microneutralization assay to establish this inhibitory assay as a potential predictor of virus neutralization. We studied these antibody responses in SARS-CoV-2-naïve and -convalescent vaccinees. Our results showed increased IgG concentrations, avidity, and inhibition following vaccination in both groups. We were also able to differentiate the immune response between the two groups using the multiplex immunoassay platform to look at antibody diversity. The receptor-binding inhibition assay has strong correlations with a cell-based pseudovirus neutralization assay as well as with WT SARS-CoV-2 Washington and Delta variant PRNT50 assays. This suggests that the inhibition assay may be able to simultaneously predict virus neutralization of different SARS-CoV-2 variants. Overall, we show that the developed custom multiplex immunoassay with several experimental variations is a powerful tool in assessing multiple aspects of the SARS-CoV-2 antibody response in vaccinated individuals.

A live attenuated SARS-CoV-2 vaccine constructed by dual inactivation of NSP16 and ORF3a

BACKGROUND

Live attenuated vaccines against SARS-CoV-2 activate all phases of host immunity resembling a natural infection and they block viral transmission more efficiently than existing vaccines in human use. In our prior work, we characterised an attenuated SARS-CoV-2 variant, designated d16, which harbours a D130A mutation in the NSP16 protein, inactivating its 2'-O-methyltransferase function. The d16 variant has demonstrated an ability to induce both mucosal and sterilising immunity in animal models. However, further investigation is required to identify any additional modifications to d16 that could mitigate concerns regarding potential virulence reversion and the suboptimal regulation of the proinflammatory response.

METHODS

Mutations were introduced into molecular clone of SARS-CoV-2 and live attenuated virus was recovered from cultured cells. Virological, biochemical and immunological assays were performed in vitro and in two animal models to access the protective efficacies of the candidate vaccine strain.

FINDINGS

Here we describe evaluation of a derivative of d16. We further modified the d16 variant by inverting the open reading frame of the ORF3a accessory protein, resulting in the d16i3a strain. This modification is anticipated to enhance safety and reduce pathogenicity. d16i3a appeared to be further attenuated in hamsters and transgenic mice compared to d16. Intranasal vaccination with d16i3a stimulated humoural, cell-mediated and mucosal immune responses, conferring sterilising protection against SARS-CoV-2 Delta and Omicron variants in animals. A version of d16i3a expressing the XBB.1.16 spike protein further expanded the vaccine's protection spectrum against circulating variants. Notably, this version has demonstrated efficacy as a booster in hamsters, providing protection against Omicron subvariants and achieving inhibition of viral transmission.

INTERPRETATION

Our work established a platform for generating safe and effective live attenuated vaccines by dual inactivation of NSP16 and ORF3a of SARS-CoV-2.

FUNDING

This work was supported by National Key Research and Development Program of China (2021YFC0866100, 2023YFC3041600, and 2023YFE0203400), Hong Kong Health and Medical Research Fund (COVID190114, CID-HKU1-9, and 23220712), Hong Kong Research Grants Council (C7142-20GF and T11-709/21-N), Hong Kong Innovation and Technology Commission grant (MHP/128/22), Guangzhou Laboratory (EKPG22-01) and Health@InnoHK (CVVT). Funding sources had no role in the writing of the manuscript or the decision to submit it for publication.

Detection of SARS-CoV-2- specific antibodies in domestic cats using different ELISA tests

The emergence of SARS-CoV-2 raised concerns about the potential for interspecies transmission, particularly among domestic animals. We evaluated the seroprevalence of SARS-CoV-2 antibodies in domestic cats from various sites in North America. A total of 216 serum samples collected between December 2019 and February 2022, were analyzed using four different enzyme-linked immunosorbent assays (ELISAs), including a commercial surrogate virus neutralization test (sVNT), a commercial double antigen test (dN ELISA), and two in-house developed indirect ELISAS based on receptor-binding domain (RBD iELISA) and the nucleocapsid (N iELISA) proteins, respectively. Seropositive samples in the commercial ELISAs were subject to virus neutralization test (cVNT) employing the Wuhan-like USA-WA1/2020 SARS-CoV-2 isolate. Our findings revealed that, 6 % (12/216) of the cat serum samples tested positive by the sVNT, while 4 % (9/216) tested positive for the dN-ELISA. Interestingly, the N iELISA showed a higher seroprevalence, with 31 % of the samples testing positive, possibly due to cross-reactive antibodies against the N protein of other coronavirus commonly found in cats. There was a high concordance between sVNT, cVNT, and RBD iELISA. Among positive sVNT cat serum samples, 75 % (9/12) exhibited neutralizing titers with all samples also being positive by RBD iELISA. Notably, the RBD iELISA and sVNT demonstrated high sensitivity and specificity in detecting SARS-CoV-2 antibodies (100 and 79 %; 100 and 90 %, respectively). In conclusion, our study provides important insights into the seroprevalence of SARS-CoV-2 antibodies in domestic cats, highlighting the potential for interspecies transmission and the need for continued monitoring of SARS-CoV-2 in animal populations.

Evaluation of SARS-CoV-2 antibody detection methods for wild Cervidae

Wildlife surveillance programs often use serological data to monitor exposure to pathogens. Diagnostic sensitivity and specificity of a serological assay quantify the true positive and negative rates of the diagnostic assay, respectively. However, an assay's accuracy can be affected by wild animals' pathogen exposure history and quality of the sample collected, requiring separate estimates of an assay's detection ability for wild-sampled animals where an animal's true disease status is unknown (referred to hereafter as sampling sensitivity and specificity). We assessed the sampling sensitivity and specificity of a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) surrogate virus neutralization test (sVNT) and conventional virus neutralization tests (cVNT) to detect antibodies for ancestral and Omicron B.1.1.529 variants of SARS-CoV-2 in wild white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus). We studied the influence of sample collection method using paired blood samples collected in serum separator tubes and on Nobuto strips from the same animal. Mean estimates of sampling sensitivity and specificity ranged from 0.21-0.95 and 0.94-1.00, respectively, varying by sample collection method, host species, and SARS-CoV-2 variant targeted by the assay. Broadly, sampling sensitivity was estimated to be higher for 1) sera collected in tubes, 2) detecting pre-Omicron SARS-CoV-2 variants, and 3) sVNT relative to cVNT assays. Sampling specificity tended to be high for all tests. We augmented our study with SARS-CoV-2 spike protein sequences derived from sampling locations and times coincident with white-tailed deer captures, finding common amino acid mutations relative to the sVNT Omicron antigen variant. The mutations may indicate that the SARS-CoV-2 variants circulating in cervids from 2021 through 2024 may be better adapted to cervid hosts and more closely related to variants that circulated in humans prior to Omicron variants. We conclude our study with an inter-test comparison of sVNT results, revealing that 40 % inhibition is an optimal threshold for test positivity when testing deer sera for responses to Omicron variant B.1.1.529, compared to the 30 % inhibition recommended for ancestral variants.

Memory B cell proliferation drives differences in neutralising responses between ChAdOx1 and BNT162b2 SARS-CoV-2 vaccines

Introduction

Vaccination against COVID-19 has been pivotal in reducing the global burden of the disease. However, Phase III trial results and observational studies underscore differences in efficacy across vaccine technologies and dosing regimens. Notably, mRNA vaccines have exhibited superior effectiveness compared to Adenovirus (AdV) vaccines, especially with extended dosing intervals.

Methods

Using in-host mechanistic modelling, this study elucidates these variations and unravels the biological mechanisms shaping the immune responses at the cellular level. We used data on the change in memory B cells, plasmablasts, and antibody titres after the second dose of a COVID-19 vaccine for Australian healthcare workers. Alongside this dataset, we constructed a kinetic model of humoral immunity which jointly captured the dynamics of multiple immune markers, and integrated hierarchical effects into this kinetics model, including age, dosing schedule, and vaccine type.

Results

Our analysis estimated that mRNA vaccines induced 2.1 times higher memory B cell proliferation than AdV vaccines after adjusting for age, interval between doses and priming dose. Additionally, extending the duration between the second vaccine dose and priming dose beyond 28 days boosted neutralising antibody production per plasmablast concentration by 30%. We also found that antibody responses after the second dose were more persistent when mRNA vaccines were used over AdV vaccines and for longer dosing regimens.

Discussion

Reconstructing in-host kinetics in response to vaccination could help optimise vaccine dosing regimens, improve vaccine efficacy in different population groups, and inform the design of future vaccines for enhanced protection against emerging pathogens.

Clinical Significance of Neutralizing Antibodies in COVID-19: Implications for Disease Prognosis

The pathogenesis of COVID-19 highlights a complex relationship between disease severity and neutralizing antibodies (NAbs). We aimed to investigate the relationships among the total NAb (tNAb) levels, the presence of potential neutralization antibodies (pNAbs), and the clinical outcomes of COVID-19 patients. Patients aged ≥18 years diagnosed between October 2021 and September 2022 were grouped by symptom severity. Blood samples were taken at two time points and data on demographics, epidemiology, and vaccination were recorded. The tNAbs and pNAbs were measured by an enhanced chemiluminescence assay and a surrogate virus neutralization test, respectively. The tNAbs of 68 and the pNAbs of 52 patients were analyzed. Twenty-six (38.2%) patients had severe infection. The 28-day mortality rate was 16.2% (n = 11). The tNAb levels in the control blood samples (CBSs) were significantly higher than those of the admission blood samples (ABSs) (p < 0.001). The statistical analysis showed no relationship between disease severity and pNAbs. Vaccinated patients had significantly higher tNAbs in the ABSs and CBSs (p < 0.001 and p < 0.001, respectively). The presence of pNAbs in the ABSs was correlated with a lower 28-day mortality (p = 0.026) and a milder disease course (p = 0.041). Although these findings support a correlation between tNAbs and disease severity and mortality, their presence seems to be unrelated to favorable clinical outcomes.

Serological Assays Reveal No Evidence of Natural SARS-CoV-2 Infection in US Cattle

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to pose a significant threat to public health. Notably, SARS-CoV-2 demonstrates the capacity to infect various non-human animal species, including both captive and free-living animals. Earlier experimental studies revealed low susceptibility of domestic cattle (Bos taurus) to ancestral B.1 lineage; however, recent experimental findings indicate greater permissiveness of cattle to SARS-CoV-2 Delta variant. While some studies detected evidence of SARS-CoV-2 infection in cattle in Italy, Germany, India, and Nigeria, currently, there is no evidence of SARS-CoV-2 infections in US cattle. We have investigated over 600 samples, including pre-pandemic and pandemic cattle sera collected from Pennsylvania for the presence of SARS-CoV-2 antibodies. Since serological tests have inherent problems of false positives and negatives, we conducted a comprehensive assessment of multiple serological assays. As there are no known SARS-CoV-2 positive cattle serum samples, we used hyperimmune serum raised in cattle with SARS-CoV-2-spike receptor binding domain (RBD) as positive control for the test validation. We found that pseudovirus neutralization assays with a luciferase reporter system can produce false positive results, and care must be taken to interpret serological diagnosis using these assays. We found no serological evidence of natural SARS-CoV-2 infection or transmission among cattle in the US. This study underscores the importance of robust evaluation when employing serological assays for SARS-CoV-2 detection in cattle populations.

Longitudinal immunogenicity cohort study of SARS-CoV-2 mRNA vaccines across individuals with different immunocompromising conditions: heterogeneity in the immune response and crucial role of Omicron-adapted booster doses

BACKGROUND

Individuals with primary and secondary immunodeficiencies, being more susceptible to infections, are a priority for vaccination. Here, we determined and compared in a longitudinal study the immune response elicited by SARS-CoV-2 vaccination across different groups of individuals who are immunocompromised.

METHODS

In the PatoVac_COV longitudinal prospective single-centre study, the spike-specific B cell and antibody responses to SARS-CoV-2 mRNA vaccination were compared across 5 different groups of individuals with haematological malignancies, hematopoietic stem cell (HCT) or solid organ transplantation (SOT), undergoing haemodialysis, and people living with HIV (PLWH), for a total of 585 participants. Data from participants who were immunocompromised were compared to a group of 123 participants who were immunocompetent. Blood samples were collected before and after each vaccine administration, up to 2 years.

FINDINGS

A different immune responsiveness was observed after the first two vaccine doses, with haematological, haemodialysis, and SOT participants showing reduced responsiveness compared to HCT and PLWH, and relative to the comparison group. Spike-specific B cell response was both slower and lower in all groups except in PLWH when compared to participants who were immunocompetent. However, the first booster dose enhanced both the B and the antibody responses in all groups, that persisted up to 2 years after the first vaccine administration. The administration of Omicron-adapted booster vaccines promoted a primary BA.2 RBD-specific B cell response, especially in participants who were immunocompromised. Despite repeated vaccinations, a subset of persistent low-responders, especially among SOT, was identified.

INTERPRETATION

Our study highlights the heterogeneous immune response across individuals with different pathologies, the pivotal role of the first booster dose, the primary activation of Omicron-specific B cells elicited by updated variant-adapted vaccines and the persistence of low-responders despite multiple vaccine administrations. These aspects have a clinical relevance for planning vaccination schedules tailored for individuals with different immunocompromising conditions.

FUNDING

This work was supported by funds from the Department of Medical Biotechnologies of the University of Siena, and from EU within the NextGenerationEU-MUR PNRR Tuscany Health Ecosystem (Project no ECS00000017-THE).

SARS-CoV-2 IgG antibodies in COVID-19 convalescent plasma and conventional plasma units

BACKGROUND

The Association for the Advancement of Blood and Biotherapies guidelines recommend the use of high-titer COVID-19 convalescent plasma (CCP) for patients with SARS-CoV-2 at high risk of disease progression, including those who are immunocompromised. We hypothesized that conventional plasma units have comparable neutralizing antibody levels to CCP.

STUDY DESIGN AND METHODS

Conventional plasma and CCP units were obtained from blood suppliers. Quantitatively measured antibodies to SARS-CoV-2 were assessed using the MesoScale Discovery multiplex electrochemiluminescence immunoassay. Binding antibody distributions were compared with Wilcoxon rank-sum tests. SARS-CoV-2 neutralizing antibodies were analyzed using the GeneScript ELISA-based neutralization assay. The proportion of conventional and CCP units with a percent signal inhibition of ≥80% (as defined by the United States Food and Drug Administration for CCP in 2021) and exact binomial confidence intervals (CIs) were calculated.

RESULTS

Among 218 conventional plasma units and 74 CCP units collected between September 2023 and July 2024, the distribution of total antibody binding levels largely overlapped between conventional plasma and CCP, though statistically significant differences in median nucleocapsid and spike Omicron variant concentrations were observed. Median percent signal neutralization was 97.5% (range 3.4%-98.6%) among conventional plasma units and 97.7% (range 95.4%-98.6%) among CCP units. For conventional plasma, 95.0% (95% CI = 91.2%-97.5%) met the neutralization antibody threshold for high-titer CCP. For CCP, 100% (95% CI = 95.1%-100.0%) met the neutralization threshold for high-titer CCP.

CONCLUSION

Conventional plasma units demonstrate similar median antibody concentration to CCP units. In countries or regions where licensed CCP is unavailable and titers are unknown, transfusion of multiple conventional plasma units may be of clinical utility.

A Live-Cell Imaging-Based Fluorescent SARS-CoV-2 Neutralization Assay by Antibody-Mediated Blockage of Receptor Binding Domain-ACE2 Interaction

Neutralization assays have become an important tool since the beginning of the COVID-19 pandemic for testing vaccine responses and therapeutic antibodies as well as for monitoring humoral immunity to SARS-CoV-2 in epidemiological studies. The spike glycoprotein (S) present on the viral surface contains a receptor binding domain (RBD) that recognizes the angiotensin-converting enzyme 2 receptor (ACE2) in host cells, allowing virus entry. The gold standard for determining SARS-CoV-2 neutralizing antibodies is the plaque reduction neutralization test (PRNT), which relies on live-virus replication performed exclusively in biosafety level 3 (BSL-3) laboratories. Here, we report the development of a surrogate live-cell imaging-based fluorescent SARS-CoV-2 neutralization assay, applicable to BSL-1 or BSL-2 laboratories, by antibody-mediated blockage of the interaction between recombinant RBD with overexpressed ACE2 receptor in a genetically modified HEK 293T stable cell line. Our approach was able to detect neutralizing antibodies both in COVID-19-positive human serum samples and polyclonal equine formulations against SARS-CoV-2. This new cell-based surrogate neutralization assay represents a virus-free fluorescence imaging alternative to the reported approaches, which can be used to detect antibody-neutralizing capabilities toward SARS-CoV-2. This assay could also be extrapolated in the future to other established and emergent viral agents.

Adjuvanted subunit intranasal vaccine reduces SARS-CoV-2 onward transmission in hamsters

Introduction

Most COVID-19 vaccine trials have focused on recipient protection, not protection of their contacts, a critical need. As a subunit intranasal COVID-19 vaccine reduced nasopharyngeal virus more than did an intramuscular (IM) vaccine, we hypothesized that this vaccine might reduce onward transmission to others.

Methods

We vaccinated hamsters with either the IM-administrated licensed mRNA vaccine twice or one dose of mRNA IM followed by adjuvanted subunit intranasal vaccine. 24 hours after SARS-CoV-2 challenge, these animals were housed with naïve recipients in a contactless chamber that allows airborne transmission.

Results

Onward airborne transmission was profoundly blocked: the donor and recipients of the intranasal vaccine-boosted group had lower oral and lung viral loads (VL), which correlated with mucosal ACE2 inhibition activity. Notably, in this head-to-head comparison of COVID-19 booster vaccines on SARS-CoV-2 onward transmission, we found that statistically significant viral reduction in the lung tissues and oral swabs was observed only in the intranasal S1 nanoparticle vaccine-boosted group, but not in the systemic mRNA vaccine-boosted group, suggesting the superior protection of this intranasal vaccine, which could act as an attractive vaccine booster candidate to complement the current licensed systemic vaccines.

Discussion

Overall, our study strongly supports the use of the intranasal vaccine as a boost to protect not only the vaccinated person, but also people exposed to the vaccinated person, a key public health goal.

Mucosal vaccination against SARS-CoV-2 using recombinant influenza viruses delivering self-assembling nanoparticles

Recombinant influenza viruses are promising vectors that can bolster antibody and resident lymphocyte responses within mucosal sites. This study evaluates recombinant influenza viruses with SARS-CoV-2 RBD genes in eliciting mucosal and systemic responses. Using reverse genetics, we generated replication-competent recombinant influenza viruses carrying heterologous RBD genes in monomeric, trimeric, or ferritin-based nanoparticle forms. Following intranasal immunisation, mice developed potent serological anti-RBD responses, with ferritin nanoparticles superseding monomeric or trimeric RBD responses. While parenteral and mucosal immunisation elicited robust anti-RBD IgG in serum, mucosal immunisation seeded respiratory IgA, RBD-specific lung-resident memory and germinal centre (GC) B cells. In animals with prior intramuscular vaccination, intranasal boosting with recombinant influenza vectors augmented mucosal IgG, IgA, GC and memory B cells, and SARS-CoV-2 lung neutralising titres. Recall of RBD-specific memory B cells via antigen re-exposure in the lung increased antibody-secreting cells in the lung-draining lymph nodes, with maintenance of lung GC B cells. Recombinant influenza-based vaccines effectively deliver highly immunogenic self-assembling nanoparticles, generating antibodies and B cells in the respiratory mucosa. This strategy provides a tractable pathway to augment lung-localised responses against recurrent respiratory viral infections.

Viral Burden and Illness Severity During Acute SARS-CoV-2 Infection Predict Persistent Long COVID Symptoms

Background

Long COVID is a common complication of infection with severe acute respiratory syndrome coronavirus 2, but the prevalence and predictors of the condition remain poorly characterized.

Methods

We prospectively studied adults (≥18 years) with acute coronavirus disease 2019 (COVID-19) presenting to an urban safety net hospital and associated clinics between July 2020 and December 2022. Logistic regression models were used to evaluate the association between baseline demographic, clinical, and laboratory characteristics with long COVID status, defined as symptoms persisting at least 9 months after acute disease. Among unrecovered participants, we describe the prevalence of individual symptoms.

Results

We enrolled 222 participants, 162 (73%) of whom had known recovery status by 9 months. Median age was 54 years, half (55%) were female, and the majority of participants (78%) had at least 1 comorbidity at the time of COVID-19 diagnosis. Based on acute illness characteristics, the adjusted odds ratio for long COVID was 3.0 (95% confidence interval [CI], 1.1-8.0) among those with detectable nucleocapsid antigen and 3.6 (95% CI, 1.2-11) for those who required supplemental oxygen. Of the 41% of participants with symptoms persisting at least 9 months, central nervous system and psychological symptoms were most commonly reported, with 57% reporting functional limitations due to their persistent symptoms.

Conclusions

The strong association with initial disease suggests a decreasing prevalence of long COVID as acute illnesses become milder. However, many contemporary patients still experience high viral burden with extended viral replication, even after vaccination. Our findings highlight the importance of properly characterizing long COVID as viral evolution shifts acute disease presentation.

COVID-19 vaccination and cerebral small vessel disease progression-A prospective cohort study

OBJECTIVES

The association between SARS-CoV-2 spike protein and cerebrovascular diseases raised a concern of cerebrovascular safety of COVID-19 vaccines. We aimed to determine the risk of radiologic cerebral small vessel disease (cSVD) progression with BNT162b2 and CoronaVac.

METHODS

In this community-based prospective cohort study, community-dwelling subjects underwent brain magnetic resonance imaging (MRI) before and 4 months after vaccination with BNT162b2 or CoronaVac. Unvaccinated subjects received serial brain MRI over a comparable interval. The primary outcome was progression of a composite of six standard cSVD biomarkers. We compared the risk of cSVD progression between vaccinated and unvaccinated subjects and identified predictors of primary outcome within each vaccine subgroup.

RESULTS

Of the 415 subjects recruited, 190 received BNT162b2, 152 received CoronaVac, and 73 remained unvaccinated. A total of 60 (14.4%) had COVID-19 infection before follow-up MRI, and 109 (26.3%) developed the primary outcome. Neither BNT162b2 (adjusted odds ratio [aOR] 0.61, 95% confidence interval [CI] 0.30-1.26, P = 0.179) nor CoronaVac (aOR 0.71, 95% CI 0.34-1.47, P = 0.349) was associated with cSVD progression. Among the BNT162b2 recipients, a higher surrogate virus neutralization test was associated (aOR 0.97, 95% CI 0.95-0.99, P = 0.002) with a lower risk of cSVD progression.

CONCLUSIONS

BNT162b2 and CoronaVac did not increase cSVD burden in community-dwelling citizens. The association between surrogate virus neutralization test and cSVD progression among BNT162b2 recipients requires further investigation.

Viral Mimetic Bacterial Outer Membrane Vesicles for Targeting Angiotensin-Converting Enzyme 2

Purpose

Outer membrane vesicles (OMVs) derived from Gram-negative bacteria naturally serve as a heterologous nano-engineering platform, functioning as effective multi-use nanovesicles for diagnostics, vaccines, and treatments against pathogens. To apply refined OMVs for human theranostic applications, we developed naturally exposed receptor-binding domain (RBD) OMVs grafted with antigen 43 as a minimal modular system targeting angiotensin-converting enzyme 2 (ACE2).

Methods

We constructed E. coli-derived OMVs using the antigen 43 autotransporter system to display RBD referred to as viral mimetic Ag43β700_RBD OMVs. Based on this, Ag43β700_RBD protein were expressed onto Escherichia coli (E. coli) membrane. Artificial viral mimetic Ag43β700_RBD OMVs were fabricated by self-assembly through membrane disruption of the Ag43β700_RBD E. coli using a chemical detergent mainly containing lysozyme. Through serial centrifugation to purify fabricated OMVs, spherical Ag43β700_RBD OMVs with an average diameter of 218 nm were obtained. The confirmation of the RBD expressed on OMVs was performed using trypsin treatment.

Results

Our viral mimetic Ag43β700_RBD OMVs had an impact on the theranostic studies: (i) angiotensin-converting enzyme 2 blockade assay, (ii) enzyme-linked immunosorbent assay for the OMVs, and (iii) intracellular uptake and neutralization assay. As serodiagnostic surrogates, Ag43β700_RBD OMVs were applied to ACE2 blockade and OMVs-ELISA assay to quantify neutralization antibodies (nAbs). They reduced the robust immune response in vitro, especially IL-6 and IL-1β. Experiments in mice, Ag43β700_RBD OMVs was successfully proven to be safe and effective; they produced a detectable level of nAbs with 39-58% neutralisation and reduced viral titres in the lungs and brain without weight loss.

Conclusion

The developed viral mimetic Ag43β700_RBD OMVs may therefore be applied as a nanovesicle-theranostic platform for further emerging infectious disease-related diagnosis, vaccination, and treatment.

Integration of DNA-Decorated Hapten in Emergency Immunoassays for Antibody and Small-Molecule Detection: A Review

DNA-decorated hapten (DDH)-based immunoassays have emerged, demonstrating supreme advantages in sensing applications because of their excellent sensitivity, specificity, and reliability. DDH combines both a recognition element (hapten) and a signal transduction element (DNA portion) with its highly programmable DNA structure enabling the trigger of signal transduction following a recognition event, thereby introducing a novel signal transduction mechanism to immunoassays. In this review, we provide a critical overview of recent research in the DDH-based immunoassays, which are designed to detect specific small molecules and antibodies. On the basis of the following events after binding of antibodies to DDH, the reported studies involved with DDH-based immunoassays can be categorized into three groups: (i) DDH-based immunoassay based on DNA conformational switches induced by antibody binding, (ii) DDH-based immunoassay based on co-localization of nucleic acids induced by antibody binding, and (iii) DDH-based immunoassay based on antibody steric hindrance. We also focus on several fundamental elements of DDH-based immunoassays, including the designed DNA structure, principles of signal transformation, and platform of DDH-based immunoassays. Then, the representative applications of DDH-based immunoassays in areas such as food safety, medical diagnostics, and environmental monitoring as well as the challenges and perspectives of DDH-based immunoassays are also explored.

Tracking Immunity: An Increased Number of COVID-19 Boosters Increases the Longevity of Anti-RBD and Anti-RBD-Neutralizing Antibodies

BACKGROUND/OBJECTIVES

Since the World Health Organization declared COVID-19 a pandemic in March 2020, the virus has caused multiple waves of infection globally. Arizona State University (ASU), the largest four-year university in the United States, offers a uniquely diverse setting for assessing immunity within a large community. This study aimed to test our hypothesis that an increased number of exposures to SARS-CoV-2 RBD through vaccination/boosters/infection will increase SARS-CoV-2 antibody seroprevalence by increasing the longevity of anti-RBD and anti-RBD-neutralizing antibodies.

METHODS

A serosurvey was conducted at ASU from 30 January to 3 February 2023. Participants completed questionnaires about demographics, respiratory infection history, symptoms, and COVID-19 vaccination status. Blood samples were analyzed for anti-receptor binding domain (RBD) IgG and anti-nucleocapsid (NC) antibodies, offering a comprehensive view of immunity from both natural infection and vaccination.

RESULTS

The seroprevalence of anti-RBD IgG antibodies was 96.2% (95% CI: 94.8-97.2%), and 64.9% (95% CI: 61.9-67.8%) of participants had anti-NC antibodies. Anti-RBD IgG levels correlated strongly with neutralizing antibody levels, and participants who received more vaccine doses showed higher levels of both anti-RBD IgG and neutralizing antibodies. Increasing the number of exposures through vaccination and/or infection resulted in higher and long-lasting antibodies.

CONCLUSIONS

The high levels of anti-RBD antibodies observed reflect substantial vaccine uptake within this population. Ongoing vaccination efforts, especially as new variants emerge, are essential to maintaining protective antibody levels. These findings underscore the importance of sustained public health initiatives to support broad-based immunity and protection.

Dynamic modeling of antibody repertoire reshaping in response to viral infections

For decades, research has largely focused on the generation of high-affinity, antigen-specific antibodies during viral infections. This emphasis has made it challenging for immunologists to systematically evaluate the mechanisms initiating humoral immunity in specific immune responses. In this study, we employ ordinary differential equations (ODE) to investigate the dynamic reshaping of the entire antibody repertoire in response to viral infections. Our findings demonstrate that the host's antibody atlas undergoes significant restructuring during these infections by the selective expansion of antibody pools with strong binding activity. The simulation results indicate that the ELISA (Enzyme-Linked Immunosorbent Assay) outcomes do not directly reflect the levels of specific neutralizing antibodies, but rather represent a quantitative response of the reshaped antibody repertoire following infection. Our model transcends traditional theories of immune memory, providing an explanation for the sustained presence of specific antibodies in the human body in long term. Additionally, our model extends to explore the mechanistic basis of the original antigenic sin, providing practical applications of our framework. One important application of this model is that it indicates that antibodies with a faster forward binding rate are more effective in preventing and treating associated viral infections compared to those with higher binding affinity.

Humoral Immunity Profiling to Pandemic and Bat-Derived Coronavirus Variants: A Geographical Comparison

Dynamic pathogen exposure may impact the immunological response to SARS-CoV-2 (SCV2). One potential explanation for the lack of severe SCV2-related morbidity and mortality in Southeast Asia is prior exposure to related betacoronaviruses. Recent discoveries of SCV2-related betacoronaviruses from horseshoe bats (Rhinolophus sinicus) in Thailand, Laos, and Cambodia suggest the potential for bat-to-human spillover exposures in the region. In this work, serum antibodies to protein constructs from SCV2 and a representative bat coronavirus isolated in Cambodia (RshSTT182) are measured in pre-pandemic Cambodian human sera using ELISA assays. Of 293 Cambodian samples tested (N = 131 with acute malaria, n = 162 with acute undifferentiated febrile illness), 32 (10.9%) are seropositive for SCV2 based on established Spike and receptor-binding domain (RBD) cutoffs. Within SCV2 seropositive samples, 16 (50%) have higher antibody levels to antigens from the representative virus RshSTT182 versus SCV2 antigens; competitive binding ELISA assays demonstrate inhibition of reactivity to SCV2 Spike after pre-incubation with RshSTT182 Spike. Surrogate virus neutralization tests demonstrate that 8/30 (26.7%) SCV2 ELISA positive pre-pandemic Cambodian samples have neutralizing activity against SCV2, while 14/30 (46.7%) have activity against other SCV2-related betacoronaviruses. These data suggest that exposure to related betacoronaviruses may elicit cross-reactive immunity to SCV2 prior to the global pandemic.

Automated and virus variant-programmable surrogate test qualitatively compares to the gold standard SARS-CoV-2 neutralization assay

The ongoing emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants underscores the need for rapid, adaptable, high-throughput testing. However, assays for neutralizing antibodies, which are a good measure of viral protection, usually require cell culture and either infectious SARS-CoV-2 or pseudotyped viral particles. To circumvent the challenges of cell-based assays, SARS-CoV-2 surrogate virus neutralization tests (sVNTs) measure inhibition of the binding of the spike (S) protein receptor binding domain (RBD) to its receptor, human angiotensin-converting enzyme 2 (hACE2) by neutralizing antibodies. Here we tested a prototype automated microfluidic cartridge-based sVNT platform using SARS-CoV-2 wild-type (WT) and B.1.617.2 (Delta) variant RBDs. This sVNT showed a high correlation with cell-based neutralization assays for biospecimens collected post-COVID-19 vaccination and post-SARS-CoV-2 infection as well as for pre-pandemic SARS-CoV-2 negative sera. Thus, this assay, which takes less than 80 min, is a relatively simple, safe, and accurate alternative to traditional VNTs.

Evaluation of a surrogate virus neutralization assay for detecting neutralizing antibodies against SARS-CoV-2 in an African population

The global resurgence of coronaviruses and the move to incorporate COVID-19 vaccines into the expanded program for immunization have warranted for a high-throughput and low-cost assay to measure and quantify mounted neutralizing antibodies as an indicator for protection against SARS-CoV-2. Hence, we evaluated the surrogate-virus-neutralization-assay (sVNT) as an alternative assay to the pseudo-virus neutralization assay (pVNT). The sVNT was used to measure neutralizing antibodies among 119 infected and/or vaccinated blood samples, against wild-type SARS-CoV-2 (WT) and the Omicron-variant with reference to the pVNT. Four different cut-offs were assessed for suitability in distinguishing neutralizers: the manufacturer (>30%), literature-based (>50%) and (>80%), and population-based (>27.69%). The obtained data was analyzed using "R" through its integrated development environments; JAMOV and R-Studio. Using the WT strain, only the population-based cut-off was able to differentiate neutralizers from non-neutralizers beyond chance, with an area under the curve (AUC) of 0.833 (95%CI, 0.505-1.0; P = .049). Applying the population-based cut-off, improved the sensitivity to 100% from 91.4% obtained from the manufacturer cut-off (P = .002). However, the specificity remained low (67%). The negative-predictive-value also improved to 100% vs 16.4% (P = .006), but there was no difference in the positive-predictive-value (99.1% vs 99.1%) (P = .340). When we used the Omicron-variant, the sVNT titers were not able to predict the neutralizers and non-neutralizers with reference to pVNT (AUC of 0.649) (P = .221). The sVNT assay is a potential alternative for screening individuals harboring potent neutralizing antibody with high sensitivity, although we recommend continuous improvement of the assay in line with the viral mutations. Further, we recommend that individual users establish a population-based cut-off while using the sVNT assay.

Longitudinal Study of SARS-CoV-2 Vaccinations and Infections in Patients with Gastrointestinal Cancer: Stabilizing Immune Responses and Neutralizing Emerging Variants with Variant-Adapted Antigen Exposures

This longitudinal study examined how active gastrointestinal (GI) cancer types affect immune responses to SARS-CoV-2, focusing on the ability to neutralize the Omicron variants. Patients with GI cancer (n = 168) were categorized into those with hepatocellular carcinoma, hepatic metastatic GI cancer, non-hepatic metastatic GI cancer, and two control groups of patients with and without underlying liver diseases. Humoral and cellular immune responses were evaluated before and after Omicron antigen exposures. In the pre-Omicron era, humoral SARS-CoV-2 immunity decreased after three antigen contacts without further antigen exposure. While Omicron neutralization was significantly lower than wildtype neutralization (p < 0.01), Omicron infections were yet mild to moderate. Additional Omicron exposures improved IgG levels (p < 0.01) and Omicron neutralization (p < 0.01). However, this effect was significantly less intense in patients with active GI cancer, particularly in patients with pancreaticobiliary neoplasms (PBN; p = 0.04), with underlying immunodeficiency (p = 0.05), and/or under conventional chemotherapy (p = 0.05). Pre-Omicron SARS-CoV-2 immunity prevented severe clinical courses of infections with Omicron variants in patients with GI cancer. However, in patients with PBN, with underlying immunodeficiency, and/or under conventional chemotherapy initial contacts with Omicron antigens triggered only reduced immune responses. Thus, subgroups could be identified for whom booster vaccinations are of special clinical significance.

mRNA vaccines encoding membrane-anchored RBDs of SARS-CoV-2 mutants induce strong humoral responses and can overcome immune imprinting

We investigated mRNA vaccines encoding a membrane-anchored receptor-binding domain (RBD), each a fusion of a variant RBD, the transmembrane (TM) and cytoplasmic tail fragments of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. In naive mice, RBD-TM mRNA vaccines against SARS-CoV-2 variants induced strong humoral responses against the target RBD. Multiplex surrogate viral neutralization (sVNT) assays revealed broad neutralizing activity against a range of variant RBDs. In the setting of a heterologous boost, against the background of exposure to ancestral whole-spike vaccines, sVNT studies suggested that BA.1 and BA.5 RBD-TM vaccines had the potential to overcome the detrimental effects of immune imprinting. A subsequent heterologous boost study using XBB.1.5 booster vaccines was evaluated using both sVNT and authentic virus neutralization. Geometric mean XBB.1.5 neutralization values after third-dose RBD-TM or whole-spike XBB.1.5 booster vaccines were compared with those after a third dose of ancestral spike booster vaccine. Fold-improvement over ancestral vaccine was just 1.3 for the whole-spike XBB.1.5 vaccine, similar to data published using human serum samples. In contrast, the fold-improvement achieved by the RBD-TM XBB.1.5 vaccine was 16.3, indicating that the RBD-TM vaccine induced the production of antibodies that neutralize the XBB.1.5 variant despite previous exposure to ancestral spike protein.

Antibody Avidity Maturation Following Booster Vaccination with an Intranasal Adenovirus Salnavac Vaccine

BACKGROUND

The COVID-19 pandemic has led to the rapid development of new vaccines and methods of testing vaccine-induced immunity. Despite the extensive research that has been conducted on the level of specific antibodies, less attention has been paid to studying the avidity of these antibodies. The avidity of serum antibodies is associated with a vaccine showing high effectiveness and reflects the process of affinity maturation. In the context of vaccines against SARS-CoV-2, only a limited number of studies have investigated the avidity of antibodies, often solely focusing on the wild-type virus following vaccination. This study provides new insights into the avidity of serum antibodies following adenovirus-based boosters. We focused on the effects of an intranasal Salnavac booster, which is compared, using a single analytical platform, to an intramuscular Sputnik V.

METHODS

The avidity of RBD-specific IgGs and IgAs was investigated through ELISA using urea and biolayer interferometry.

RESULTS

The results demonstrated the similar avidities of serum antibodies, which were induced by both vaccines for six months post-booster. However, an increase in antibody avidity was observed for the wild-type and Delta variants, but not for the BA.4/5 variant.

CONCLUSIONS

Collectively, our data provide the insights into antibody avidity maturation after the adenovirus-based vaccines against SARS-CoV-2.

Constructing the cGAMP-Aluminum Nanoparticles as a Vaccine Adjuvant-Delivery System (VADS) for Developing the Efficient Pulmonary COVID-19 Subunit Vaccines

The cGAMP-aluminum nanoparticles (CAN) are engineered as a vaccine adjuvant-delivery system to carry mixed RBD (receptor-binding domain) of the original severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its new variant for developing bivalent pulmonary coronavirus disease 2019 (COVID-19) vaccines (biRBD-CAN). High phosphophilicity/adsorptivity made intrapulmonary CAN instantly form the pulmonary ingredient-coated CAN (piCAN) to possess biomimetic features enhancing biocompatibility. In vitro biRBD-CAN sparked APCs (antigen-presenting cells) to mature and make extra reactive oxygen species, engendered lysosome escape effects and enhanced proteasome activities. Through activating the intracellular stimulator of interferon genes (STING) and nucleotide-binding domain and leucine-rich repeat and pyrin domain containing proteins 3 (NALP3) inflammasome pathways to exert synergy between cGAMP and AN, biRBD-CAN stimulated APCs to secret cytokines favoring mixed Th1/Th2 immunoresponses. Mice bearing twice intrapulmonary biRBD-CAN produced high levels of mucosal antibodies, the long-lasting systemic antibodies, and potent cytotoxic T lymphocytes which efficiently erased cells displaying cognate epitopes. Notably, biRBD-CAN existed in mouse lungs and different lymph nodes for at least 48 h, unveiling their sustained immunostimulatory activity as the main mechanism underlying the long-lasting immunity and memory. Hamsters bearing twice intrapulmonary biRBD-CAN developed high resistance to pseudoviral challenges performed using different recombinant strains including the ones with distinct SARS-CoV-2-spike mutations. Thus, biRBD-CAN as a broad-spectrum pulmonary COVID-19 vaccine candidate may provide a tool for controlling the emerging SARS-CoV-2 variants.

Safety and immunogenicity of CoronaVac in healthy adults: A prospective observational multicenter real-world study in Henan Province, China

Vaccination has emerged as the primar approach for managing the COVID-19 pandemic. Despite certain clinical trials reporting the safety and immunogenicity of CoronaVac, additional multicenter real-world studies are still necessary. In this study, we recruited 506 healthy volunteers who were not infected with COVID-19 or vaccinated. Each participant provided peripheral blood samples three times: prior to the first dose of vaccine, prior to the second dose, and 8 weeks following the second dose. Ultimately, 388 participants completed the entire follow-up process. No serious adverse events were observed among any of the participants. Within 1 week of vaccination, 13.4% of participants experienced systemic adverse reactions, with fatigue (5.93%) and dizziness (3.35%) being the most frequent. Although some clinical indicators, including creatinine, significantly changed after vaccination (p < 0.05), the mean of all altered indicators remained within the normal range. The positive rates of neutralizing antibodies (NAb), IgG, and IgM were 12.3%, 18.85%, and 5.24% prior to the second dose, respectively; and 57.99%, 86.34%, and 2.32% at 8 weeks following the second dose, respectively. Additionally, seven indicators, such as sex, age, and BMI, were significantly correlated with NAb (p < 0.05). Finally, a prediction model was developed based on age, monocytes, and alanine aminotransferase (ALT) with an AUC value of 87.56% in the train set and 80.71% in the test set. This study demonstrated that safety and immunogenicity of CoronaVac were good. The prediction model based on the baseline clinical characteristics prior to vaccination can help to develop more suitable vaccination strategies.

Serological evidence of sarbecovirus exposure along Sunda pangolin trafficking pathways

BACKGROUND

Early in the coronavirus disease 2019 (COVID-19) pandemic, Sunda pangolins (Manis javanica) involved in the illegal wildlife trade in mainland China were identified as hosts of severe acute respiratory syndrome-related coronaviruses (SARSr-CoVs). Although it is unconfirmed whether pangolins or other traded wildlife served as intermediate hosts for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the trafficking of pangolins presents a clear risk for transmission of viruses with zoonotic and epizootic potential regardless. We have investigated the origins of pangolin carcasses seized in Hong Kong and have evaluated their potential exposure to SARSr-CoVs, other coronaviruses, and paramyxoviruses, aiming to address a gap in our knowledge with regard to the role of wildlife trade in the maintenance and emergence of pathogens with zoonotic and epizootic potential.

RESULTS

Using a combination of virological and wildlife forensics tools, we investigated 89 Sunda pangolin carcasses seized by Hong Kong authorities during anti-smuggling operations in the territory conducted in 2013 (n = 1) and 2018 (n = 88). Swabs, organ tissues, blood, and other body fluids were collected during post-mortem examination. Two enzyme-linked immunosorbent assays (ELISAs), which employ a double-antigen sandwich format, were used to detect antibodies reactive against SARSr-CoVs. One individual was found to be seropositive with support from both methods, while five individuals exhibited a putatively seropositive result from one ELISA method. Polymerase chain reaction (PCR) screening for coronavirus and paramyxovirus ribonucleic acid (RNA) did not yield any positives. Based on genomic data, the seropositive individual was determined to have likely originated from Java, while the putatively seropositive individuals were determined to have originated from populations in Borneo, Java, and Singapore/Sumatra.

CONCLUSIONS

While the role of pangolins in the evolution and ecology of SARS-CoV-2 is uncertain, our results suggest susceptibility and potential exposure of pangolins to SARSr-CoVs, occurring naturally or associated with the illegal trafficking of these animals. Complex dynamics between natural populations, traded individuals, and pathogen susceptibility complicate conclusions about the role of pangolins, as well as other host species, in the ecology of SARSr-CoVs and potentially zoonotic viruses with risk of future emergence.

A Novel Cell- and Virus-Free SARS-CoV-2 Neutralizing Antibody ELISA Based on Site-Specific Labeling Technology

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to the global spread of coronavirus disease 2019 (COVID-19), creating an urgent need for updated methods to evaluate immune responses to vaccines and therapeutic strategies. In this study, we introduce a novel cell-free, virus-free SARS-CoV-2 neutralizing antibody ELISA (NAb-ELISA), which is based on competitive inhibition of the receptor binding domain (RBD) of spike protein binding to the angiotensin-converting enzyme 2 (ACE2) receptor. In this method, site-specific biotinylated hACE2-Fc-Avi recombinant protein is immobilized onto a 96-well plate for capture, and the RBD-Fc-vHRP recombinant proteins serve as detection probes. Evaluation of sera from wild type (WT) or Delta RBD-immunized mice using the NAb-ELISA and pseudovirus neutralization tests (pVNTs) demonstrated strong correlations between assays (R2 = 0.91 and 0.90 for the WT and Delta groups, respectively). Additionally, the NAb-ELISA successfully detected cross-neutralizing activity in sera, though with slightly lower correlation to pVNT (R2 = 0.70-0.83). By employing NAb-ELISA instead of an indirect ELISA for hybridoma screening, five monoclonal antibodies (mAbs) with neutralizing activities against WT, Delta, and BA.2 pseudoviruses were obtained. This assay offers a straightforward, rapid, and safe approach to characterizing vaccine-induced antibody responses and mAb neutralization activity. Notably, the NAb-ELISA platform can be quickly adapted to assess neutralizing antibody responses against emerging mutant strains, addressing the rapid mutation of the virus.

A statistically established reference value determined for the Vaxarray Coronavirus (CoV) seroassay to characterize vaccination and natural infection

Serological diagnostic tests are available that measure antibody levels against SARS-CoV-2 antigens. We utilized the Vaxarray Coronavirus (CoV) seroassay, which measures SARS-CoV-2 IgG antibodies against the full-length spike protein (FLS), receptor binding domain (RBD), and S2 extracellular domain (ECD). Previous serological studies have used reference values that have not been validated and require many samples. Here, we show statistically established reference values determined using the upper tail of the Student t-distribution method. The target population was any personnel age 18 years and older working on a U.S. Navy ship, and vaccinated with Wuhan variant. The relative fluorescence mean (RFM) reference values for the full-length spike protein, RBD, and S2 ECD were 17,731, 13,990 and 9096, respectively. By using generalized non-parametric regression and reference values for the RBD spike protein and S2 ECD of SARS-CoV-2, this study was able to distinguish vaccine-mediated immune responses from natural infections. We provide the method and statistical code as a resource to determine future reference values for other serological assays.

FoldMark: Protecting Protein Generative Models with Watermarking

Protein structure is key to understanding protein function and is essential for progress in bioengineering, drug discovery, and molecular biology. Recently, with the incorporation of generative AI, the power and accuracy of computational protein structure prediction/design have been improved significantly. However, ethical concerns such as copyright protection and harmful content generation (biosecurity) pose challenges to the wide implementation of protein generative models. Here, we investigate whether it is possible to embed watermarks into protein generative models and their outputs for copyright authentication and the tracking of generated structures. As a proof of concept, we propose a two-stage method FoldMark as a generalized watermarking strategy for protein generative models. FoldMark first pretrain watermark encoder and decoder, which can minorly adjust protein structures to embed user-specific information and faithfully recover the information from the encoded structure. In the second step, protein generative models are fine-tuned with Low-Rank Adaptation modules with watermark as condition to preserve generation quality while learning to generate watermarked structures with high recovery rates. Extensive experiments are conducted on open-source protein structure prediction models (e.g., ESMFold and MultiFlow) and de novo structure design models (e.g., FrameDiff and FoldFlow) and we demonstrate that our method is effective across all these generative models. Meanwhile, our watermarking framework only exerts a negligible impact on the original protein structure quality and is robust under potential post-processing and adaptive attacks.

Neutralizing antibodies and safety of a COVID-19 vaccine against SARS-CoV-2 wild-type and Omicron variants in solid cancer patients

OBJECTIVE

The aim of this study was to assess the seroconversion rate and percent inhibition of neutralizing antibodies against the wild-type and Omicron variants of SARS-CoV-2 in patients with solid cancer who received two COVID-19 vaccine doses by comparing chemotherapy and nonchemotherapy groups.

METHODS

This prospective cohort study enrolled 115 cancer patients from Maharaj Nakorn Chiang Mai Hospital, Sriphat Medical Center, Faculty of Medicine, Chiang Mai University, and Chiang Mai Klaimor Hospital, Chiang Mai, Thailand, between August 2021 and February 2022, with data from 91 patients who received two COVID-19 vaccine doses analyzed. Participants received vaccines as part of their personal vaccination programs, including various mRNA and non-mRNA vaccine combinations. Blood samples were collected at baseline, on day 28, and at 6 months post-second dose to assess neutralizing antibodies. The primary outcome was the seroconversion rate against the wild-type and Omicron variants on day 28. Secondary outcomes included seroconversion at 6 months, factors associated with seroconversion, and safety.

RESULTS

Among the participants, 45% were receiving chemotherapy. On day 28, seroconversion rates were 77% and 62% for the wild-type and Omicron variants, respectively. Chemotherapy did not significantly affect seroconversion rates (p = 0.789 for wild type, p = 0.597 for Omicron). The vaccine type administered was positively correlated with seroconversion, with an adjusted odds ratio (95% confidence interval) of 25.86 (1.39-478.06) for the wild type and 17.38 (3.65-82.66) for the Omicron variant with the primary heterologous vaccine regimen. Grades 1 and 2 adverse events were observed in 34.0% and 19.7% of participants, respectively.

CONCLUSIONS

Despite the lower seroconversion rate against the Omicron variant, no significant difference was observed between the chemotherapy and nonchemotherapy groups. COVID-19 vaccinations demonstrated good tolerability in this cohort. These findings highlight the importance of vaccine safety and immunogenicity in cancer patients and can inform tailored vaccination strategies for this vulnerable population.

STAR LIGHT Study: XBB.1.5 COVID-19 mRNA Vaccines Boost Systemic but Not Mucosal Immunity Against the SARS-CoV-2 JN.1 Variant in Patients with Chronic Liver Disease

BACKGROUND

Patients with chronic liver disease (CLD) have impaired vaccine immunogenicity and an excess risk of severe COVID-19. While variant-adapted COVID-19 mRNA vaccines are recommended for vulnerable individuals, their efficacy in patients with CLD has not been studied.

METHODS

We present the first evaluation of XBB.1.5 COVID-19 vaccine immunogenicity against the SARS-CoV-2 JN.1 variant in patients with CLD. Serum anti-receptor binding domain (RBD) IgG, neutralization, and saliva anti-RBD IgG and IgA against wild-type SARS-CoV-2 (WT) and the XBB.1.5, EG.5.1, BA.2.86, and JN.1 variants were quantified before and 2-4 weeks following a fourth dose of XBB.1.5 mRNA vaccines.

RESULTS

Vaccination boosted anti-RBD IgG and neutralization against all tested variants including JN.1 (each p < 0.001). Following immunization, neutralization was lower against JN.1 compared to WT, XBB.1.5, and EG.5.1 (p < 0.001, p < 0.001, and p < 0.01, respectively). Vaccination reduced neutralization failure rates against BA.2.86 and JN.1 (each p < 0.05). The evasion of vaccine-induced antibodies by the tested variants was low, indicated by the positive correlation between anti-RBD IgG and neutralization. At mucosal sites, vaccination boosted anti-RBD IgG (each p < 0.01) but failed to induce infection-blocking IgA (each p > 0.05).

CONCLUSION

XBB.1.5 vaccines protect CLD patients against recent SARS-CoV-2 variants, but developing vaccines with optimized mucosal immunogenicity is required to prevent SARS-CoV-2 transmission and recurrent seasonal COVID-19 outbreaks.

Repeated COVID-19 mRNA-based vaccination contributes to SARS-CoV-2 neutralizing antibody responses in the mucosa

To prevent infection by respiratory viruses and consequently limit virus circulation, vaccines need to promote mucosal immunity. The extent to which the currently used messenger RNA (mRNA)-based COVID-19 vaccines induce mucosal immunity remains poorly characterized. We evaluated mucosal neutralizing antibody responses in a cohort of 183 individuals. Participants were sampled at several time points after primary adenovirus vector-based or mRNA-based COVID-19 vaccination and after mRNA-based booster vaccinations. Our findings revealed that repeated vaccination with mRNA boosters promoted severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) neutralizing antibodies in nasal secretions. Nasal and serum neutralizing antibody titers of both IgG and IgA isotypes correlated to one another. We investigated the source of these mucosal antibodies in a mouse model wherein mice received repeated mRNA vaccines for SARS-CoV-2. These experiments indicated that neutralizing antibody-producing cells reside in the spleen and bone marrow, whereas no proof of tissue homing to the respiratory mucosa was observed, despite the detection of mucosal antibodies. Serum transfer experiments confirmed that circulating antibodies were able to migrate to the respiratory mucosa. Collectively, these results demonstrate that, especially upon repeated vaccination, the currently used COVID-19 mRNA vaccines can elicit mucosal neutralizing antibodies and that vaccination might also stimulate mucosal immunity induced by previous SARS-CoV-2 infection. Moreover, migration of circulating antibodies to the respiratory mucosa might be a main mechanism. These findings advance our understanding of mRNA vaccine-induced immunity and have implications for the design of vaccine strategies to combat respiratory infections.

Interferon-mediated NK cell activation is associated with limited neutralization breadth during SARS-CoV-2 infection

Best known for their ability to kill infected or malignant cells, natural killer (NK) cells are also underappreciated regulators of the antibody response to viral infection. In mice, NK cells can kill T follicular helper (Tfh) cells, decreasing somatic hypermutation and vaccine responses. Although human NK cell activation correlates with poor vaccine response, the mechanisms of human NK cell regulation of adaptive immunity are poorly understood. We found that in human ancestral SARS-CoV-2 infection, broad neutralizers, who were capable of neutralizing Alpha, Beta, and Delta, had fewer NK cells that expressed inhibitory and immaturity markers whereas NK cells from narrow neutralizers were highly activated and expressed interferon-stimulated genes (ISGs). ISG-mediated activation in NK cells from healthy donors increased cytotoxicity and functional responses to induced Tfh-like cells. This work reveals that NK cell activation and dysregulated inflammation may play a role in poor antibody response to SARS-CoV-2 and opens exciting avenues for designing improved vaccines and adjuvants to target emerging pathogens.

Inflammasome-Driven Fatal Acute-on-Chronic Liver Failure Triggered by Mild COVID-19

Inflammasome is linked to many inflammatory diseases, including COVID-19 and autoimmune liver diseases. While severe COVID-19 was reported to exacerbate liver failure, we report a fatal acute-on-chronic liver failure (ACLF) in a stable primary biliary cholangitis-autoimmune hepatitis overlap syndrome patient triggered by a mild COVID-19 infection. Postmortem liver biopsy showed sparse SARS-CoV-2-infected macrophages with extensive ASC (apoptosis-associated speck-like protein containing a CARD) speck-positive hepatocytes, correlating with elevated circulating ASC specks and inflammatory cytokines, and depleted blood monocyte subsets, indicating widespread liver inflammasome activation. This first report of a fatal inflammatory cascade in an autoimmune liver disease triggered by a mild remote viral infection hopes to elucidate a less-described pathophysiology of ACLF that could prompt consideration of new diagnostic and therapeutic options.

Impact of Lipid Tail Length on the Organ Selectivity of mRNA-Lipid Nanoparticles

The delivery of mRNA molecules to organs beyond the liver is valuable for therapeutic applications. Functionalized lipid nanoparticles (LNPs) using exogenous mechanisms can regulate in vivo mRNA expression profiles from hepatocytes to extrahepatic tissues but lead to process complexity and cost escalation. Here, we report that mRNA expression gradually shifts from the liver to the spleen in an ionizable lipid tail length-dependent manner. Remarkably, this simple chemical strategy held true even when different ionizable lipid head structures were employed. As a potential mechanism underlying this discovery, our data suggest that 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) is enriched on the surface of mRNA/LNPs with short-tail lipids. This feature limits their interaction with biological components, avoiding their rapid hepatic clearance. We also show that spleen-targeting LNPs loaded with SARS-CoV-2 receptor-binding domain (RBD) mRNA can efficiently induce immune responses and neutralize activity following intramuscular vaccination priming and boosting.

The Influence of Initial Immunosuppression on the Kinetics of Humoral Response after SARS-CoV-2 Vaccination in Patients Undergoing Kidney Transplantation

Background: The effect of initial immunosuppressive therapy on the kinetics of the SARS-CoV-2 vaccine-induced humoral response is unknown. Here, we compared the kinetics of SARS-CoV-2 vaccine-induced humoral response in chronic kidney disease patients undergoing kidney transplantation (KTRs) and compared to patients remaining on dialysis during the Omicron circulation. Methods: This prospective, non-randomized, real-world study included 113 KTRs and 108 patients on dialysis. Those with previous COVID-19 or negative IgG at screening were excluded. Blood samples were collected to assess SARS-CoV-2 IgG titers and neutralizing antibodies at months (M) 1, 3, 6, and 12. Results: Seroreversion occurred in one KTR and in three patients on dialysis. KTRs had lower IgG titers over time (M1: 10,809.3 ± 12,621.7 vs. 15,267.8 ± 16,096.2 AU/mL; M3: 12,215.5 ± 12,885.8 vs. 15,016.2 ± 15,346.1 AU/mL; M6: 12,540.4 ± 13,010.7 vs. 18,503.5 ± 14,581.0 AU/mL; p = 0.005), but neutralizing antibodies were similar (M1: 94.0 vs. 90.3%; M3: 92.9 vs. 90.5%; M6: 99.0 vs. 95.5%; M12: 98.9 vs. 97.5%; p = 0.812). During follow-up, KTRs received more vaccines (141 vs. 73; p < 0.001) and contracted more COVID-19 (32.7% vs. 14.8%; p = 0.002). Conclusions: Compared to patients on dialysis, KTRs had lower SARS-CoV-2 IgG titers and similar rates of seroreversion and neutralizing antibodies over time. Although KTRs received more boosters, they had a higher incidence of COVID-19.

Multiparametric analysis of the specific immune response against SARS-CoV-2

BACKGROUND

SARS-CoV-2, which causes COVID-19, has killed more than 7 million people worldwide. Understanding the development of postinfectious and postvaccination immune responses is necessary for effective treatment and the introduction of appropriate antipandemic measures.

OBJECTIVES

We analysed humoral and cell-mediated anti-SARS-CoV-2 immune responses to spike (S), nucleocapsid (N), membrane (M), and open reading frame (O) proteins in individuals collected up to 1.5 years after COVID-19 onset and evaluated immune memory.

METHODS

Peripheral blood mononuclear cells and serum were collected from patients after COVID-19. Sampling was performed in two rounds: 3-6 months after infection and after another year. Most of the patients were vaccinated between samplings. SARS-CoV-2-seronegative donors served as controls. ELISpot assays were used to detect SARS-CoV-2-specific T and B cells using peptide pools (S, NMO) or recombinant proteins (rS, rN), respectively. A CEF peptide pool consisting of selected viral epitopes was applied to assess the antiviral T-cell response. SARS-CoV-2-specific antibodies were detected via ELISA and a surrogate virus neutralisation assay.

RESULTS

We confirmed that SARS-CoV-2 infection induces the establishment of long-term memory IgG+ B cells and memory T cells. We also found that vaccination enhanced the levels of anti-S memory B and T cells. Multivariate comparison also revealed the benefit of repeated vaccination. Interestingly, the T-cell response to CEF was lower in patients than in controls.

CONCLUSION

This study supports the importance of repeated vaccination for enhancing immunity and suggests a possible long-term perturbation of the overall antiviral immune response caused by SARS-CoV-2 infection.

Liquid-metal-based microfluidic nanoplasmonic platform for point-of-care naked-eye antibody detection

Despite high sensitivity of nanoparticle-on-mirror cavities, a crucial branch of plasmonic nanomaterials, complex preparation and readout processes limit their extensive application in biosensing. Alternatively, liquid metals (LMs) combining fluidity and excellent plasmonic characteristics have become potential candidates for constructing plasmonic nanostructures. Herein, we propose a microfluidic-integration strategy to construct LM-based immunoassay platform, enabling LM-based nanoplasmonic sensors to be used for point-of-care (POC) clinical biomarker detection. Flowable LM is introduced onto protein-coated Au nanoparticle monolayer to form a "mirror-on-nanoparticle" nanostructure, simplifying the fabrication process in the conventional nanoparticle-on-mirror cavities. When antibodies were captured by antigens coated on the Au nanoparticle monolayer, devices respond both thickness and refractive index change of biomolecular layers, outputting naked-eye readable signals with high sensitivity (limit of detection: ∼ 604 fM) and a broad dynamic range (6 orders). This new assay, which generates quantitative results in 30 min, allows for high-throughput, smartphone-based detection of SARS-CoV-2 antibodies against multiple variants in clinical serum or blood samples. These results establish an advanced avenue for POC testing with LM materials, and demonstrate its potential to facilitate diagnostics, surveillance and prevalence studies for various infectious diseases.

Characterisation of the antibody-mediated selective pressure driving intra-host evolution of SARS-CoV-2 in prolonged infection

Neutralising antibodies against the SARS-CoV-2 spike (S) protein are major determinants of protective immunity, though insufficient antibody responses may cause the emergence of escape mutants. We studied the humoral immune response causing intra-host evolution in a B-cell depleted, haemato-oncologic patient experiencing clinically severe, prolonged SARS-CoV-2 infection with a virus of lineage B.1.177.81. Following bamlanivimab treatment at an early stage of infection, the patient developed a bamlanivimab-resistant mutation, S:S494P. After five weeks of apparent genetic stability, the emergence of additional substitutions and deletions within the N-terminal domain (NTD) and the receptor binding domain (RBD) of S was observed. Notably, the composition and frequency of escape mutations changed in a short period with an unprecedented dynamic. The triple mutant S:Delta141-4 E484K S494P became dominant until virus elimination. Routine serology revealed no evidence of an antibody response in the patient. A detailed analysis of the variant-specific immune response by pseudotyped virus neutralisation test, surrogate virus neutralisation test, and immunoglobulin-capture enzyme immunoassay showed that the onset of an IgM-dominated antibody response coincided with the appearance of escape mutations. The formation of neutralising antibodies against S:Delta141-4 E484K S494P correlated with virus elimination. One year later, the patient experienced clinically mild re-infection with Omicron BA.1.18, which was treated with sotrovimab and resulted in an increase in Omicron-reactive antibodies. In conclusion, the onset of an IgM-dominated endogenous immune response in an immunocompromised patient coincided with the appearance of additional mutations in the NTD and RBD of S in a bamlanivimab-resistant virus. Although virus elimination was ultimately achieved, this humoral immune response escaped detection by routine diagnosis and created a situation temporarily favouring the rapid emergence of various antibody escape mutants with known epidemiological relevance.

Immunogenicity of Abdala COVID-19 vaccine in Vietnamese people after primary and booster vaccinations: A prospective observational study in Vietnam

OBJECTIVES

We studied the immunogenicity after primary and booster vaccinations of the Abdala COVID-19 vaccine, a receptor-binding domain protein subunit vaccine, in Vietnamese people by determining the level of neutralization and cross-neutralization activities against the ancestral SARS-CoV-2 and its variants and SARS-CoV-1.

METHODS

We performed a prospective observational study, enrolling adults aged 19-59 years in Dong Thap province, southern Vietnam, and collected blood samples from baseline until 4 weeks after the booster dose. We measured anti-nucleocapsid, anti-spike, and neutralizing antibodies against SARS-CoV-2 and assessed the cross-neutralization against 14 SARS-CoV-2 variants and SARS-CoV-1. Complementary antibody data came from Vietnamese health care workers fully vaccinated with ChAdOx1-S.

RESULTS

After primary vaccination, anti-spike antibody and neutralizing antibodies were detectable in 98.4% and 87% of 251 study participants, respectively, with neutralizing antibody titers similar to that induced by ChAdOx1-S vaccine. Antibody responses after a homologous (Abdala COVID-19) or heterologous (messenger RNA BNT162b2) booster could neutralize 14 SARS-CoV-2 variants (including Omicron) and SARS-CoV-1.

CONCLUSIONS

Abdala COVID-19 vaccine is immunogenic in Vietnamese people. Enhanced antibody response after a booster dose could cross-neutralize 14 SARS-CoV-2 variants and SARS-CoV-1. Our results have added to the growing body of knowledge about the contribution of protein subunit vaccine platforms to pandemic control.

Studying the Humoral Response against SARS-CoV-2 in Cuban COVID-19 Recovered Patients

Understanding the immune response generated by SARS-CoV-2 is critical for assessing efficient therapeutic protocols and gaining insights into the durability of protective immunity. The current work was aimed at studying the specific humoral responses against SARS-CoV-2 in Cuban COVID-19 convalescents. We developed suitable tools and methods based on ELISA methodology, for supporting this evaluation. Here, we describe the development of an ELISA for the quantification of anti-RBD IgG titers in a large number of samples and a similar test in the presence of NH4SCN as chaotropic agent for estimating the RBD specific antibody avidity. Additionally, a simple and rapid ELISA based on antibody-mediated blockage of the binding RBD-ACE2 was implemented for detecting, as a surrogate of conventional test, the levels of anti-RBD inhibitory antibodies in convalescent sera. In a cohort of 273 unvaccinated convalescents, we identified higher anti-RBD IgG titer (1 : 1,330, p  < 0.0001) and higher levels of inhibitory antibodies blocking RBD-ACE2 binding (1 : 216, p  < 0.05) among those who had recovered from severe illness. Our results suggest that disease severity, and not demographic features such as age, sex, and skin color, is the main determinant of the magnitude and neutralizing ability of the anti-RBD antibody response. An additional paired longitudinal assessment in 14 symptomatic convalescents revealed a decline in the antiviral antibody response and the persistence of neutralizing antibodies for at least 4 months after the onset of symptoms. Overall, SARS-CoV-2 infection elicits different levels of antibody response according to disease severity that declines over time and can be monitored using our homemade serological assays.