Protective humoral and cellular immune responses to SARS-CoV-2 persist up to 1 year after recovery

Dynamics of SARS-CoV-2 antibodies after natural infection: insights from a study on Pasteur Institute of Tunis employees

This study aimed to assess the kinetics of antibodies against the SARS-CoV-2, following natural infection in a cohort of employees of the Institut Pasteur de Tunis (IPT) and to assess the risk of reinfection over a 12-months follow-up period. A prospective study was conducted among an open cohort of IPT employees with confirmed SARS-CoV-2 infection that were recruited between September 2020 and March 2021. Sera samples were taken at 1, 3, 6, 9 and 12 months after confirmation of COVID-19 infection and tested for SARS-CoV-2-specific immunoglobulin G (IgG) antibodies to the spike (S-RBD) protein (IgG anti-S-RBD) and for neutralizing antibodies. Participants who had an initial decline of IgG anti-S-RBD and neutralizing antibodies followed by a subsequent rise in antibody titers as well as those who tested positive for SARS-CoV-2 by RT-PCR after at least 60 days of follow up were considered as reinfected. In total, 137 individuals were included with a mean age of 44.7 ± 12.3 years and a sex-ratio (Male/Female) of 0.33. Nearly all participants (92.7%) were symptomatic, and 2.2% required hospitalization. Among the 70 participants with three or more prospective blood samples, 32.8% were reinfected among whom 11 (47.8%) reported COVID-19 like symptoms. Up to 12 months of follow up, 100% and 42.9% of participants had detectable IgG anti-S-RBD and neutralizing antibodies, respectively. This study showed that humoral immune response following COVID-19 infection may persist up to 12 months after infection despite the potential risk for reinfection that is mainly explained by the emergence of new variants.

Natural and hybrid immunity after SARS-CoV-2 infection in children and adolescents

PURPOSE

In contrast to adults, immune protection against SARS-CoV-2 in children and adolescents with natural or hybrid immunity is still poorly understood. The aim of this study was to analyze different immune compartments in different age groups and whether humoral immune reactions correlate with a cellular immune response.

METHODS

72 children and adolescents with a preceding SARS-CoV-2 infection were recruited. 37 were vaccinated with an RNA vaccine (BNT162b2). Humoral immunity was analyzed 3-26 months (median 10 months) after infection by measuring Spike protein (S), nucleocapsid (NCP), and neutralizing antibodies (nAB). Cellular immunity was analyzed using a SARS-CoV-2-specific interferon-γ release assay (IGRA).

RESULTS

All children and adolescents had S antibodies; titers were higher in those with hybrid immunity (14,900 BAU/ml vs. 2118 BAU/ml). NCP antibodies were detectable in > 90%. Neutralizing antibodies (nAB) were more frequently detected (90%) with higher titers (1914 RLU) in adolescents with hybrid immunity than in children with natural immunity (62.5%, 476 RLU). Children with natural immunity were less likely to have reactive IGRAs (43.8%) than adolescents with hybrid immunity (85%). The amount of interferon-γ released by T cells was comparable in natural and hybrid immunity.

CONCLUSION

Spike antibodies are the most reliable markers to monitor an immune reaction against SARS-CoV-2. High antibody titers of spike antibodies and nAB correlated with cellular immunity, a phenomenon found only in adolescents with hybrid immunity. Hybrid immunity is associated with markedly higher antibody titers and a higher probability of a cellular immune response than a natural immunity.

Hybrid immunity from severe acute respiratory syndrome coronavirus 2 infection and vaccination in Canadian adults: A cohort study

Background

Few national-level studies have evaluated the impact of 'hybrid' immunity (vaccination coupled with recovery from infection) from the Omicron variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Methods

From May 2020 to December 2022, we conducted serial assessments (each of ~4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots (DBSs) to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels.

Results

Spike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than 6 months earlier, spike levels fell notably and continuously for the 9-month post-vaccination. In contrast, among adults infected within 6 months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than 6 months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% confidence interval 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the coronavirus disease 2019 (COVID-19) weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity.

Conclusions

Strategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected DBSs are a practicable biological surveillance platform.

Funding

Funding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michael's Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.

Heterotypic immunity from prior SARS-CoV-2 infection but not COVID-19 vaccination associates with lower endemic coronavirus incidence

Immune responses from prior severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and COVID-19 vaccination mitigate disease severity, but they do not fully prevent subsequent infections, especially from genetically divergent strains. We examined the incidence of and immune differences against human endemic coronaviruses (eCoVs) as a proxy for response against future genetically heterologous coronaviruses (CoVs). We assessed differences in symptomatic eCoV and non-CoV respiratory disease incidence among those with known prior SARS-CoV-2 infection or previous COVID-19 vaccination but no documented SARS-CoV-2 infection or neither exposure. Retrospective cohort analyses suggest that prior SARS-CoV-2 infection, but not previous COVID-19 vaccination alone, associates with a lower incidence of subsequent symptomatic eCoV infection. There was no difference in non-CoV incidence, implying that the observed difference was eCoV specific. In a second cohort where both cellular and humoral immunity were measured, those with prior SARS-CoV-2 spike protein exposure had lower eCoV-directed neutralizing antibodies, suggesting that neutralization is not responsible for the observed decreased eCoV disease. The three groups had similar cellular responses against the eCoV spike protein and nucleocapsid antigens. However, CD8+ T cell responses to the nonstructural eCoV proteins nsp12 and nsp13 were higher in individuals with previous SARS-CoV-2 infection as compared with the other groups. This association between prior SARS-CoV-2 infection and decreased incidence of eCoV disease may therefore be due to a boost in CD8+ T cell responses against eCoV nsp12 and nsp13, suggesting that incorporation of nonstructural viral antigens in a future pan-CoV vaccine may improve vaccine efficacy.

[Impact of systemic therapies on SARS-CoV-2 antibody seroprevalence in patients with immune-mediated diseases]

OBJECTIVE

To determine the seroprevalence of SARS-CoV-2 in patients with immune-mediated inflammatory diseases (IMID) treated with biologic (bDMARDs) or synthetic targeted disease-modifying antirheumatic drugs (tsDMARDs).

METHODS

An observational, descriptive, prospective and cross-sectional study of analytical prevalence analysis was conducted in patients with IMID with bDMARDs or tsDMARDs. Seroprevalence was compared by measuring immunoglobulinG (IgG) against SARS-CoV-2 between October/2020 and May/2021.

RESULTS

A total of 550 IMID's patients were studied, all of them on treatment with bDMARDs or tsDMARDs. The seroprevalence of the total patient group was 16% (88/550). Patients receiving therapy with tumor necrosis factor alpha inhibitors (TNFi) had a higher seroprevalence compared to other biologic and synthetic targeted therapies (OR: 1.792 [95%CI: 1.088-2.951]; P=.021). The influence on seroprevalence of concomitant use with b/tsDMARDs of conventional synthetic DMARDs (csDMARDs) was also analyzed. A lower seroprevalence was demonstrated in the group of patients treated with TNFi and methotrexate together, compared with those on TNFi monotherapy, 10.1 vs 24.1% (OR: 0.355 [95%CI: 0.165-0.764]; P=.006). No significant differences were found with the other DMARDs. Regarding IMIDs, no differences in seroprevalence were identified between the different disease groups.

CONCLUSION

Patients on treatment with TNFα inhibitors have better humoral response compared to the other b/tsDMARDs. However, when associated with methotrexate the seroprevalence decreases significantly.

Longitudinal Analysis of Humoral and Cellular Immune Response up to 6 Months after SARS-CoV-2 BA.5/BF.7/XBB Breakthrough Infection and BA.5/BF.7-XBB Reinfection

The rapid mutation of SARS-CoV-2 has led to multiple rounds of large-scale breakthrough infection and reinfection worldwide. However, the dynamic changes of humoral and cellular immunity responses to several subvariants after infection remain unclear. In our study, a 6-month longitudinal immune response evaluation was conducted on 118 sera and 50 PBMC samples from 49 healthy individuals who experienced BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection. By studying antibody response, memory B cell, and IFN-γ secreting CD4+/CD8+ T cell response to several SARS-CoV-2 variants, we observed that each component of immune response exhibited distinct kinetics. Either BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection induces relatively high level of binding and neutralizing antibody titers against Omicron subvariants at an early time point, which rapidly decreases over time. Most of the individuals at 6 months post-breakthrough infection completely lost their neutralizing activities against BQ.1.1, CH.1.1, BA.2.86, JN.1 and XBB subvariants. Individuals with BA.5/BF.7-XBB reinfection exhibit immune imprinting shifting and recall pre-existing BA.5/BF.7 neutralization antibodies. In the BA.5 breakthrough infection group, the frequency of BA.5 and XBB.1.16-RBD specific memory B cells, resting memory B cells, and intermediate memory B cells gradually increased over time. On the other hand, the frequency of IFN-γ secreting CD4+/CD8+ T cells induced by WT/BA.5/XBB.1.16 spike trimer remains stable over time. Overall, our research indicates that individuals with breakthrough infection have rapidly declining antibody levels but have a relatively stable cellular immunity that can provide some degree of protection from future exposure to new antigens.

Enhanced aerobic granular sludge with micro-electric field for sulfamethoxazole degradation: Efficiency, mechanism, and microbial community

In this study, an aerobic granular sludge electrochemical system (AGES) was established by applying the micro-electric field to an aerobic granular sludge (AGS) reactor for the degradation of sulfamethoxazole (SMZ). Under the stimulation of the micro-electric field, the granulation of sludge was improved and the degradation rate of SMZ was enhanced. The features of granular sludge were characterized by scanning electron microscopy and X-ray diffraction. The optimal degradation rate of SMZ (88%) was obtained at the voltage of 3 V and the effective electrode area of 800 mm2. The results of kinetics analyses revealed that the degradation of SMZ by AGES can be fitted with the second-order kinetic equation, showing a degradation rate constant (k) of 0.001 L mol-1·min-1. The degradation products of SMZ in the AGES system were detected by LC-MS and their possible degradation routes were elucidated. The micro-electric field in the AGES system played a selective role in microbes' enrichment and growth, changing the diversity of the microbial community. Pseudomonas, Tolumonas, and Acidovorax were the dominant bacteria in the AGES system, which is accountable for the abatement of SMZ and nutrients. This work provides a green means for improving AGS and paves the way for applying the AGS process to real-world wastewater treatment.

Immunization-induced antigen archiving enhances local memory CD8+ T cell responses following an unrelated viral infection

Antigens from viruses or immunizations can persist or are archived in lymph node stromal cells such as lymphatic endothelial cells (LEC) and fibroblastic reticular cells (FRC). Here, we find that, during the time frame of antigen archiving, LEC apoptosis caused by a second, but unrelated, innate immune stimulus such as vaccina viral infection or CpG DNA administration resulted in cross-presentation of archived antigens and boosted memory CD8 + T cells specific to the archived antigen. In contrast to "bystander" activation associated with unrelated infections, the memory CD8 + T cells specific to the archived antigen from the immunization were significantly higher than memory CD8 + T cells of a different antigen specificity. Finally, the boosted memory CD8 + T cells resulted in increased protection against Listeria monocytogenes expressing the antigen from the immunization, but only for the duration that the antigen was archived. These findings outline an important mechanism by which lymph node stromal cell archived antigens, in addition to bystander activation, can augment memory CD8 + T cell responses during repeated inflammatory insults.

SARS-CoV-2-Specific Immune Responses in Vaccination and Infection during the Pandemic in 2020-2022

To gain insight into how immunity develops against SARS-CoV-2 from 2020 to 2022, we analyzed the immune response of a small group of university staff and students who were either infected or vaccinated. We investigated the levels of receptor-binding domain (RBD)-specific and nucleocapsid (N)-specific IgG and IgA antibodies in serum and saliva samples taken early (around 10 days after infection or vaccination) and later (around 1 month later), as well as N-specific T-cell responses. One patient who had been infected in 2020 developed serum RBD and N-specific IgG antibodies, but declined eight months later, then mRNA vaccination in 2021 produced a higher level of anti-RBD IgG than natural infection. In the vaccination of naïve individuals, vaccines induced anti-RBD IgG, but it declined after six months. A third vaccination boosted the IgG level again, albeit to a lower level than after the second. In 2022, when the Omicron variant became dominant, familial transmission occurred among vaccinated people. In infected individuals, the levels of serum anti-RBD IgG antibodies increased later, while anti-N IgG peaked earlier. The N-specific activated T cells expressing IFN γ or CD107a were detected only early. Although SARS-CoV-2-specific salivary IgA was undetectable, two individuals showed a temporary peak in RBD- and N-specific IgA antibodies in their saliva on the second day after infection. Our study, despite having a small sample size, revealed that SARS-CoV-2 infection triggers the expected immune responses against acute viral infections. Moreover, our findings suggest that the temporary mucosal immune responses induced early during infection may provide better protection than the currently available intramuscular vaccines.

Comparing population-level humoral and cellular immunity to SARS-Cov-2 in Bangalore, India

Two types of immunity, humoral and cellular, offer protection against COVID. Humoral protection, contributed by circulating neutralizing antibodies, can provide immediate protection but decays more quickly than cellular immunity and can lose effectiveness in the face of mutation and drift in the SARS-CoV-2 spike protein. Therefore, population-level seroprevalence surveys used to estimate population-level immunity may underestimate the degree to which a population is protected against COVID. In early 2021, before India began its vaccination campaign, we tested for humoral and cellular immunity to SARS-Cov-2 in representative samples of slum and non-slum populations in Bangalore, India. We found that 29.7% of samples (unweighted) had IgG antibodies to the spike protein and 15.5% had neutralizing antibodies, but at up to 46% showed evidence of cellular immunity. We also find that prevalence of cellular immunity is significantly higher in slums than in non-slums. These findings suggest (1) that a significantly larger proportion of the population in Bangalore, India, had cellular immunity to SARS-CoV-2 than had humoral immunity, as measured by serological surveys, and (2) that low socio-economic status communities display higher frequency of cellular immunity, likely because of greater exposure to infection due to population density.

PeptiVAX: A new adaptable peptides-delivery platform for development of CTL-based, SARS-CoV-2 vaccines

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) posed a threat to public health and the global economy, necessitating the development of various vaccination strategies. Mutations in the SPIKE protein gene, a crucial component of mRNA and adenovirus-based vaccines, raised concerns about vaccine efficacy, prompting the need for rapid vaccine updates. To address this, we leveraged PeptiCRAd, an oncolytic vaccine based on tumor antigen decorated oncolytic adenoviruses, creating a vaccine platform called PeptiVAX. First, we identified multiple CD8 T-cell epitopes from highly conserved regions across coronaviruses, expanding the range of T-cell responses to non-SPIKE proteins. We designed short segments containing the predicted epitopes presented by common HLA-Is in the global population. Testing the immunogenicity, we characterized T-cell responses to candidate peptides in peripheral blood mononuclear cells (PBMCs) from pre-pandemic healthy donors and ICU patients. As a proof of concept in mice, we selected a peptide with epitopes predicted to bind to murine MHC-I haplotypes. Our technology successfully elicited peptide-specific T-cell responses, unaffected by the use of unarmed adenoviral vectors or adeno-based vaccines encoding SPIKE. In conclusion, PeptiVAX represents a fast and adaptable SARS-CoV-2 vaccine delivery system that broadens T-cell responses beyond the SPIKE protein, offering potential benefits for vaccine effectiveness.

Post-pandemic memory T cell response to SARS-CoV-2 is durable, broadly targeted, and cross-reactive to the hypermutated BA.2.86 variant

Ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evolution has given rise to recombinant Omicron lineages that dominate globally (XBB.1), as well as the emergence of hypermutated variants (BA.2.86). In this context, durable and cross-reactive T cell immune memory is critical for continued protection against severe COVID-19. We examined T cell responses to SARS-CoV-2 approximately 1.5 years since Omicron first emerged. We describe sustained CD4+ and CD8+ spike-specific T cell memory responses in healthcare workers in South Africa (n = 39) who were vaccinated and experienced at least one SARS-CoV-2 infection. Spike-specific T cells are highly cross-reactive with all Omicron variants tested, including BA.2.86. Abundant nucleocapsid and membrane-specific T cells are detectable in most participants. The bulk of SARS-CoV-2-specific T cell responses have an early-differentiated phenotype, explaining their persistent nature. Overall, hybrid immunity leads to the accumulation of spike and non-spike T cells evident 3.5 years after the start of the pandemic, with preserved recognition of highly mutated SARS-CoV-2 variants.

Immune response to SARS-CoV-2 variants after immunization with different vaccines in Mexico

There is limited information on the antibody responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in subjects from developing countries with populations having a high incidence of co-morbidities. Here, we analysed the immunogenicity of homologous schemes using the ChAdOx1-S, Sputnik V, or BNT162b2 vaccines and the effect of a booster dose with ChAdOx1-S in middle-aged adults who were seropositive or seronegative to the SARS-CoV-2 spike protein before vaccination. The study was conducted post-vaccination with a follow-up of 4 months for antibody titre using enzyme-linked immunosorbent assay (ELISA) and pseudovirus (PV) neutralization assays (PNAs). All three vaccines elicited a superior IgG anti-receptor-binding domain (RBD) and neutralization response against the Alpha and Delta variants when administered to individuals with a previous infection by SARS-CoV-2. The booster dose spiked the neutralization activity among individuals with and without a prior SARS-CoV-2 infection. The ChAdOx1-S vaccine induced weaker antibody responses in infection-naive subjects. A follow-up of 4 months post-vaccination showed a drop in antibody titre, with about 20% of the infection-naive and 100% of SARS-CoV-2 pre-exposed participants with detectable neutralization capacity against Alpha pseudovirus (Alpha-PV) and Delta PV (Delta-PV). Our observations support the use of different vaccines in a country with high seroprevalence at the vaccination time.

Results of phase 2 randomized multi-center study to evaluate the safety and efficacy of infusion of memory T cells as adoptive therapy in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia and/or lymphopenia (RELEASE NCT04578210)

BACKGROUND AIMS

There are currently no effective anti-viral treatments for coronavirus disease 2019 (COVID-19)-hospitalized patients with hypoxemia. Lymphopenia is a biomarker of disease severity usually present in patients who are hospitalized. Approaches to increasing lymphocytes exerting an anti-viral effect must be considered to treat these patients. Following our phase 1 study, we performed a phase 2 randomized multicenter clinical trial in which we evaluated the efficacy of the infusion of allogeneic off-the-shelf CD45RA- memory T cells containing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells from convalescent donors plus the standard of care (SoC) versus just the SoC treatment.

METHODS

Eighty-four patients were enrolled in three Spanish centers. The patients were randomized into the infusion of 1 × 106/kg CD45RA- memory T cells or the SoC. We selected four unvaccinated donors based on the expression of interferon gamma SARS-CoV-2-specific response within the CD45RA- memory T cells and the most frequent human leukocyte antigen typing in the Spanish population.

RESULTS

We analyzed data from 81 patients. The primary outcome for recovery, defined as the proportion of participants in each group with normalization of fever, oxygen saturation sustained for at least 24 hours and lymphopenia recovery through day 14 or at discharge, was met for the experimental arm. We also observed faster lymphocyte recovery in the experimental group. We did not observe any treatment-related adverse events.

CONCLUSIONS

Adoptive cell therapy with off-the-shelf CD45RA- memory T cells containing SAR-CoV-2-specific T cells is safe, effective and accelerates lymphocyte recovery of patients with COVID-19 pneumonia and/or lymphopenia.

TRIAL REGISTRATION

NCT04578210.

Immune response and severity of Omicron BA.5 reinfection among individuals previously infected with different SARS-CoV-2 variants

Introduction

COVID-19 continues to spread worldwide, with an increasing number of individuals experiencing reinfection after recovering from their primary infection. However, the nature and progression of this infection remain poorly understood. We aimed to investigate the immune response, severity and outcomes of Omicron BA.5 reinfection among individuals previously infected with different SARS-CoV-2 variants.

Methods

We enrolled 432 COVID-19 cases who had experienced prior infection with the ancestral SARS-CoV-2 virus, Delta variant or Omicron BA.2 variant between January 2020 and May 2022 in Guangzhou, China. All cases underwent follow-up from March to April, 2023 through telephone questionnaires and clinical visits. Nasal lavage fluid and peripheral blood were collected to assess anti-RBD IgA, anti-RBD IgG and virus-specific IFN-γ secreting T cells.

Results

Our study shows that 73.1%, 56.7% and 12.5% of individuals with a prior infection of the ancestral virus, Delta or Omicron BA.2 variant experienced reinfection with the BA.5 variant, respectively. Fever, cough and sore throat were the most common symptoms of BA.5 reinfection, with most improving within one week and none progressing to a critical condition. Compared with individuals without reinfection, reinfected patients with a prior Delta infection exhibited elevated levels of nasal anti-RBD IgA, serum anti-RBD IgG and IFN-γ secreting T cells, whereas there was no noticeable change in reinfected individuals with a prior BA.2 infection.

Conclusion

These results suggest that BA.5 reinfection is common but severe outcomes are relatively rare. Reinfection with a novel SARS-CoV-2 variant different from the prior infection may induce a more robust immune protection, which should be taken into account during vaccine development.

B cell responses to SARS-CoV-2

This chapter provides an overview of B cell responses in COVID-19, highlighting the structure of SARS-CoV-2 and its impact on B cell immunity. It explores the production and maturation of SARS-CoV-2-specific B cells, with a focus on the two distinct phases of the humoral immune response: the extrafollicular (EF) phase and the germinal center (GC) phase. Furthermore, the interplay between B cells, follicular T helper cells, CD4+ T cells, and plasma cells is discussed, emphasizing their collaborative role in mounting an effective humoral immune response against SARS-CoV-2. The concept of immunological memory is explored, highlighting the roles of plasma cells and B memory cells in providing long-term protection. The chapter delves into the antibody response during SARS-CoV-2 infection, categorizing the types of antibodies generated. This includes a detailed analysis of neutralizing antibodies, such as those directed against the receptor-binding domain (RBD) and the N-terminal domain (NTD), as well as non-neutralizing antibodies. The role of mucosal antibodies, cross-reactive antibodies, and auto-reactive antibodies is also discussed. Factors influencing the dynamics of anti-SARS-CoV-2 antibodies are examined, including the duration and strength of the humoral response. Additionally, the chapter highlights the impact of the Omicron variant on humoral immune responses and its implications for vaccine efficacy and antibody-mediated protection.

Robust memory humoral immune response to SARS-CoV-2 in the tonsils of adults and children

Background

Adaptive humoral immunity against SARS-CoV-2 has mainly been evaluated in peripheral blood. Human secondary lymphoid tissues (such as tonsils) contain large numbers of plasma cells that secrete immunoglobulins at mucosal sites. Yet, the role of mucosal memory immunity induced by vaccines or natural infection against SARS-CoV-2 and its variants is not fully understood.

Methods

Tonsillar mononuclear cells (TMNCs) from adults (n=10) and children (n=11) were isolated and stimulated using positive SARS-CoV-2 nasal swabs. We used endpoint enzyme-linked immunosorbent assays (ELISAs) for the measurement of anti-S1, -RBD, and -N IgG antibody levels and a pseudovirus microneutralization assay to assess neutralizing antibodies (nAbs) in paired serum and supernatants from stimulated TMNCs.

Results

Strong systemic humoral response in previously SARS-CoV-2 infected and vaccinated adults and children was observed in accordance with the reported history of the participants. Interestingly, we found a significant increase in anti-RBD IgG (305 and 834 folds) and anti-S1 IgG (475 and 443 folds) in the stimulated TMNCs from adults and children, respectively, compared to unstimulated cells. Consistently, the stimulated TMNCs secreted higher levels of nAbs against the ancestral Wuhan strain and the Omicron BA.1 variant compared to unstimulated cells by several folds. This increase was seen in all participants including children with no known history of infection, suggesting that these participants might have been previously exposed to SARS-CoV-2 and that not all asymptomatic cases necessarily could be detected by serum antibodies. Furthermore, nAb levels against both strains were significantly correlated in adults (r=0.8788; p = 0.0008) and children (r = 0.7521; p = 0.0076), and they strongly correlated with S1 and RBD-specific IgG antibodies.

Conclusion

Our results provide evidence for persistent mucosal humoral memory in tonsils from previously infected and/or vaccinated adults and children against recent and old variants upon re-exposure. They also highlight the importance of targeting mucosal sites with vaccines to help control infection at the primary sites and prevent potential breakthrough infections.

Persistence of SARS-CoV-2-antibodies against N, S and RBD after natural infection

Background and Objectives

Coronavirus disease 2019 (COVID-19) pandemic has affected most countries in the world. Monitoring the humoral immune responses during the natural course of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) infection and the duration of them provide useful information for the development of vaccination strategies against this virus and its emerging variants. The importance of the antibody response especially neutralizing antibodies in long-term immunity to SARS-CoV-2 is significant.

Materials and Methods

The present study is a cross-sectional study of sero-epidemiological type that has been proposed to compare the persistence of Immunoglobulin G (IgG) against N (nucleocapsid), S (spike) and RBD (receptor-binding domain) proteins in the community after the time of primary disease. A total of 652 serum samples were collected from hospital staff working in COVID wards, as well as a number of community members with different occupations, among those with positive antibody titers, 86 participated in the resampling test before vaccination.

Results

There was no association between antibody titer and disease severity (p>0.05). A significant decrease in Ab levels was observed in the paired second samples. The highest rate of decrease was related to anti-N, then anti-RBD and anti-S IgG levels, respectively. There is a significant relationship between the initial antibody titer and its reduction over time (p-value <0.05).

Conclusion

Our data revealed that humoral immunity following natural infection of SARS-CoV-2 is detectable for at least 4 months, regardless of disease severity. The most decrease in antibody titer over time was related to anti-N IgG levels.

Nasopharyngeal Viral Load Is the Major Driver of Incident Antibody Immune Response to SARS-CoV-2 Infection

Background

Virologic determinants of seroconversion to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were defined in a post hoc analysis of prospectively studied vaccine- and infection-naïve individuals at high risk for coronavirus disease 2019 (COVID-19).

Methods

This phase 3 COVID-19 prevention trial (NCT04452318) with casirivimab and imdevimab was conducted in July 2020-February 2021, before widespread vaccine availability. Placebo-treated participants who were uninfected (SARS-CoV-2 quantitative reverse transcription polymerase chain reaction [RT-qPCR] negative) and seronegative were assessed weekly for 28 days (efficacy assessment period [EAP]) for COVID-19 symptoms and SARS-CoV-2 infection by RT-qPCR of nasopharyngeal swab samples and for serostatus by antinucleocapsid immunoglobulin (Ig) G. Regression-based modeling, including causal mediation analysis, estimated the effects of viral load on seroconversion.

Results

Of 157/1069 (14.7%) uninfected and seronegative (for antispike IgG, antispike IgA, and antinucleocapsid IgG) participants who became infected during the EAP, 105 (65%) seroconverted. The mean (SD) maximum viral load of seroconverters was 7.23 (1.68) log10 copies/mL vs 4.8 (2.2) log10 copies/mL in those who remained seronegative; viral loads of ∼6.0 log10 copies/mL better predicted seroconversion. The mean of the maximum viral load was 7.11 log10 copies/mL in symptomatic participants vs 5.58 log10 copies/mL in asymptomatic participants. The mean duration of detectable viral load was longer in seroconverted vs seronegative participants: 3.24 vs 1.63 weeks.

Conclusions

Maximum SARS-CoV-2 viral load is a major driver of seroconversion and symptomatic COVID-19, with high viral loads (∼6.0 log10 copies/mL) better predicting seroconversion. Serology underestimates infection rates, incidence, and prevalence of SARS-CoV-2 infection.

Persistence of T-Cell Immunity Responses against SARS-CoV-2 for over 12 Months Post COVID-19 Infection in Unvaccinated Individuals with No Detectable IgG Antibodies

BACKGROUND

Immune response to SARS-CoV-2 is crucial for preventing reinfection or reducing disease severity. T-cells' long-term protection, elicited either by COVID-19 vaccines or natural infection, has been extensively studied thus far; however, it is still attracting considerable scientific interest. The aim of the present epidemiological study was to define the levels of T-cellular immunity response in a specific group of unvaccinated individuals from the general population with a prior confirmed COVID-19 infection and no measurable levels of IgG antibodies.

METHODS

We performed a retrospective descriptive analysis of data collected from the medical records of consecutive unvaccinated individuals recovered from COVID-19, who had proceeded to a large private medical center in the Attica region from September 2021 to September 2022 in order to be examined on their own initiative for SARS-CoV-2 T-cell immunity response. The analysis of T-cell responses was divided into three time periods post infection: Group A: up to 6 months; Group B: 6-12 months; Group C: >12 months. The SARS-CoV-2 T-cell response was estimated against spike (S) and nucleocapsid (N) structural proteins by performing the T-SPOT. COVID test methodology. SARS-CoV-2 IgG antibody levels were measured by the SARS-CoV-2 IgG II Quant assay (Abbott Diagnostics).

RESULTS

A total of 182 subjects were retrospectively included in the study, 85 females (46.7%) and 97 (53.3%) males, ranging from 19 to 91 years old (mean 50.84 ± 17.2 years). Among them, 59 (32.4%) had been infected within the previous 6 months from the examination date (Group A), 69 (37.9%) had been infected within a time period > 6 months and <1 year (Group B) and 54 (29.7%) had been infected within a time period longer than 1 year from the examination date (Group C). Among the three groups, a positive T-cell reaction against the S antigen was reported in 47/58 (81%) of Group A, 61/69 (88.4%) of Group B and 40/54 (74.1%) of Group C (chi square, p = 0.27). T-cell reaction against the N antigen was present in 45/58 (77.6%) of Group A, 61/69 (88.4%) of Group B and 36/54 (66.7%) of Group C (chi square, p = 0.02). The median Spot-Forming Cells (SFC) count for the S antigen was 18 (range from 0-160) in Group A, 19 (range from 0-130) in Group B and 17 (range from 0-160) in Group C (Kruskal-Wallis test, p = 0.11; pairwise comparisons: groups A-B, p = 0.95; groups A-C, p = 0.89; groups B-C, p = 0.11). The median SFCs count for the N antigen was 14.5 (ranging from 0 to 116) for Group A, 24 (ranging from 0-168) in Group B and 16 (ranging from 0-112) for Group C (Kruskal-Wallis test, p = 0.01; pairwise comparisons: groups A-B, p = 0.02; groups A-C, p = 0.97; groups B-C, p = 0.03).

CONCLUSIONS

Our data suggest that protective adaptive T-cellular immunity following natural infection by SARS-CoV-2 may persist for over 12 months, despite the undetectable humoral element.

Convalescent Adaptive Immunity Is Highly Heterogenous after SARS-CoV-2 Infection

The optimal detection strategies for effective convalescent immunity after SARS-CoV-2 infection and vaccination remain unclear. The objective of this study was to characterize convalescent immunity targeting the SARS-CoV-2 spike protein using a multiparametric approach. At the beginning of the pandemic, we recruited 30 unvaccinated convalescent donors who had previously been infected with COVID-19 and 7 unexposed asymptomatic controls. Peripheral blood mononuclear cells (PBMCs) were obtained from leukapheresis cones. The humoral immune response was assessed by measuring serum anti-SARS-CoV-2 spike S1 subunit IgG via semiquantitative ELISA, and T-cell immunity against S1 and S2 subunits were studied via IFN-γ enzyme-linked immunosorbent spot (ELISpot) and flow cytometric (FC) activation-induced marker (AIM) assays and the assessment of cytotoxic CD8+ T-cell function (in the subset of HLA-A2-positive patients). No single immunoassay was sufficient in identifying anti-spike convalescent immunity among all patients. There was no consistent correlation between adaptive humoral and cellular anti-spike responses. Our data indicate that the magnitude of anti-spike convalescent humoral and cellular immunity is highly heterogeneous and highlights the need for using multiple assays to comprehensively measure SARS-CoV-2 convalescent immunity. These observations might have implications for COVID-19 surveillance, and the determination of optimal vaccination strategies for emerging variants. Further studies are needed to determine the optimal assessment of adaptive humoral and cellular immunity following SARS-CoV-2 infection, especially in the context of emerging variants and unclear vaccination schedules.

SARS-CoV-2-specific antibody and T-cell immunity in convalescents after infection wave in Beijing in late 2022

OBJECTIVES

To evaluate SARS-CoV-2-specific antibody and T-cell responses in convalescents 5 months after infection wave in Beijing from December 2022 to January 2023 to prevent reinfection and severe disease.

METHODS

Convalescents and uninfected individuals vaccinated with different doses were enrolled to assess the IFNγ T-cell responses against SARS-CoV-2 prototype strain, BF.7, BQ.1, and XBB. Neutralizing antibodies against prototype strain, BF.7, BA.5, and XBB and immunoglobulin G antibody were further analyzed.

RESULTS

In convalescents, the IFNγ T-cell response was significantly higher than that of uninfected individuals (all P < 0.001), and the T-cell response against XBB had no significant difference from that of SARS-CoV-2 prototype strain and BF.7 and BQ.1 (all P > 0.05). The seropositive rates of IgG antibodies were 100% (303/303) with a median concentration of 90.52 (95% CI, 82.52-99.37). The neutralizing antibodies titers of convalescents against BF.7 and BA.5 were higher than that against the prototype strain (both P < 0.001), while XBB.1.5 was lower (P < 0.001). T-cell response, IgG and neutralizing antibodies had no significant difference in convalescents vaccinated with different doses (all P > 0.05).

CONCLUSIONS

The immunities may have some protective effect against possible future outbreaks and severe diseases of COVID-19.

Heterotypic responses against nsp12/nsp13 from prior SARS-CoV-2 infection associates with lower subsequent endemic coronavirus incidence

Immune responses from prior SARS-CoV-2 infection and COVID-19 vaccination do not prevent re-infections and may not protect against future novel coronaviruses (CoVs). We examined the incidence of and immune differences against human endemic CoVs (eCoV) as a proxy for response against future emerging CoVs. Assessment was among those with known SARS-CoV-2 infection, COVID-19 vaccination but no documented SARS-CoV-2 infection, or neither exposure. Retrospective cohort analyses suggest that prior SARS-CoV-2 infection, but not COVID-19 vaccination alone, protects against subsequent symptomatic eCoV infection. CD8+ T cell responses to the non-structural eCoV proteins, nsp12 and nsp13, were significantly higher in individuals with previous SARS-CoV-2 infection as compared to the other groups. The three groups had similar cellular responses against the eCoV spike and nucleocapsid, and those with prior spike exposure had lower eCoV-directed neutralizing antibodies. Incorporation of non-structural viral antigens in a future pan-CoV vaccine may improve protection against future heterologous CoV infections.

Vaccine-induced antigen archiving enhances local memory CD8+ T cell responses following an unrelated viral infection

Viral and vaccine antigens persist or are archived in lymph node stromal cells (LNSC) such as lymphatic endothelial cells (LEC) and fibroblastic reticular cells (FRC). Here, we find that, during the time frame of antigen archiving, LEC apoptosis caused by a second, but unrelated, innate immune stimulus such as vaccina viral infection or CpG DNA administration boosted memory CD8+ T cells specific to the archived antigen. In contrast to "bystander" activation associated with unrelated infections, the memory CD8+ T cells specific to the vaccine archived antigen were significantly higher than memory CD8+ T cells of a different antigen specificity. Finally, the boosted memory CD8+ T cells resulted in increased protection against Listeria monocytogenes expressing the vaccine antigen, but only for the duration that the vaccine antigen was archived. These findings outline a novel mechanism by which LNSC archived antigens, in addition to bystander activation, can augment memory CD8+ T cell responses during repeated inflammatory insults.

Convalescent Adaptive Immunity is Highly Heterogenous after SARS-CoV-2 Infection

Optimal detection strategies for effective convalescent immunity after SARS-CoV-2 infection and vaccination remain unclear. The objective of this study was to characterize convalescent immunity targeting the SARS-CoV-2 spike protein using a multiparametric approach. At the beginning of the pandemic, between April 23, 2020, to May 11, 2020, we recruited 30 COVID-19 unvaccinated convalescent donors and 7 unexposed asymptomatic donors. Peripheral blood mononuclear cells (PBMCs) were obtained from leukapheresis cones. The humoral immune response was assessed by measuring serum anti-SARS-CoV-2 spike S1 subunit IgG semiquantitative ELISA and T cell immunity against S1 and S2 subunits were studied by IFN-γ Enzyme-Linked Immune absorbent Spot (ELISpot), flow cytometric (FC) activation-induced marker (AIM) assays and the assessment of cytotoxic CD8+ T-cell function (in the subset of HLA-A2 positive patients). No single immunoassay was sufficient in identifying anti-spike convalescent immunity among all patients. There was no consistent correlation between adaptive humoral and cellular anti-spike responses. Our data indicate that the magnitude of anti-spike convalescent humoral and cellular immunity is highly heterogeneous and highlights the need for using multiple assays to comprehensively measure SARS-CoV-2 convalescent immunity. These observations might have implications for COVID-19 surveillance, and optimal vaccination strategies for emerging variants. Further studies are needed to determine the optimal assessment of adaptive humoral and cellular immunity following SARSCoV-2 infection, especially in the context of emerging variants and unclear vaccination schedules.

The Burden of COVID-19 in the Immunocompromised Patient: Implications for Vaccination and Needs for the Future

Approximately 3% of US adults are immunocompromised and less capable of fighting infections such as SARS-CoV-2 (the causative agent of COVID-19). Individuals may be immunocompromised for reasons related to an underlying medical condition or to immunomodulatory therapies that alter the immune response. In general, vaccination with mRNA-based vaccines is effective at reducing COVID-19-associated hospitalization and death among immunocompromised populations, particularly after 3 or more doses. However, the immunocompromised population is heterogeneous, with COVID-19 vaccine-elicited immune responses and risk for severe COVID-19 existing on a continuum. Therefore, understanding the impact of vaccination and the complexity of immune responses across heterogeneous immunocompromised individuals is essential for guiding effective vaccination regimens including additional (booster) doses. In this article, we provide an overview of the immunocompromised population and the burden of disease attributable to COVID-19, while discussing key opportunities and challenges of vaccinating immunocompromised individuals.

Hydroxychloroquine reduces T cells activation recall antigen responses

BACKGROUND

In the context of the current COVID-19 pandemic, there is still limited information about how people suffering from autoimmune diseases respond to the different COVID vaccines. The fact that they are taking an immunosuppressant or other drugs that aim to decrease the immune system activities, such as hydroxychloroquine (HCQ), could also impact their ability to respond to a COVID vaccine and vaccines in general.

METHODS

Heathy donors were given 200mg of HCQ daily for 6-weeks to assess HCQs impact on the systemic T cells and humoral immune response. Peripheral blood mononuclear cells (PBMC) and plasma were obtained at baseline and 6-weeks after starting daily HCQ. Flow cytometry assays were designed to determine changes in T cell activation and T cell responses. Bead array multiplex were used to analyse antibodies and cytokine levels before and after HCQ intake.

RESULTS

As anticipated, HCQ treatment decreased ex vivo T cell activation. We observed a decrease in CD4+CD161- expressing CCR5 (p = 0.015) and CD69 (p = 0.004) as well as in CD8+CCR5+ (p = 0.003), CD8+CD161+CCR5+ (p = 0.002) and CD8+CD161+CD95+ (p = 0.004). Additionally, HCQ decreased the proportion of Th17 expressing CD29 (p = 0.019), a subset associated with persistent inflammation. The proportion of T regulatory cells expressing the inhibitory molecule TIGIT was also reduced by HCQ (p = 0.003). As well, T cells from people on HCQ were less responsive to activation and cytokine production following stimulation with recall antigens and memory T cells were less likely to produce both IFNγ and TNFα following stimulation.

CONCLUSION

This study shows HCQ is associated with lower T cell activation and decreased T cell cytokine production. While this study was not performed with the intent of looking at COVID vaccine response, it does provide important information about the changes in immune response that may occur in patient taking HCQ as a treatment for their autoimmune disease.

Long-term evaluation of the seroprevalence of SARS-CoV-2 IgG and IgM antibodies in recovered patients: a meta-analysis

Estimating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) -specific immunoglobulin G (IgG) immunoglobulin M (IgM) antibodies are increasingly important for tracking the spread of infection and defining herd immunity barrier and individual immunization levels in the ongoing coronavirus disease 2019 (COVID-19) pandemic. Therefore, we conducted the present systematic review and meta-analysis to evaluate the seroprevalence of SARS-CoV-2 IgM and IgG antibodies of recovered COVID-19 patients in long-term follow-up studies. A systematic search of the MEDLINE, Embase, COVID-19 Primer, PubMed, CNKI, and the Public Health England library databases was conducted. Twenty-fourth eligible studies were included. Meta-analysis showed that 27% (95%CI: 0.04-0.49) and 66% (95%CI:0.47-0.85) were seropositive for SARS-CoV-2 IgM and IgG, respectively, while in long-term 12 months following up studies, the seroprevalences of IgM antibody (17%) decreased and IgG antibody (75%) was higher than 6 months follow-up patients. However, due to the limited number of relevant studies, the high level of heterogeneity, and the large gap in studies conducted, the findings of our study may not accurately reflect the true seroprevalence status of SARS-CoV-2 infection. Nevertheless, sequential vaccination or booster immunization is considered to be a necessary long-term strategy to sustain the fight against the pandemic.

Durability and extent of protection of SARS-CoV-2 antibodies among patients with COVID-19 in Metro Manila, Philippines

Introduction

Information on the magnitude and durability of humoral immunity against COVID-19 among specific populations can guide policies on vaccination, return from isolation and physical distancing measures. The study determined the durability of SARS-CoV-2 antibodies after an initial infection among Filipinos in Metro Manila, Philippines, and the extent of protection SARS-CoV-2 antibodies confer against reinfection.

Methods

We conducted a cohort study to monitor the antibody levels of patients diagnosed with COVID-19. Receptor-binding domain (RBD)-specific antibodies were measured at Days 21, 90, 180, 270 and 360. Antibody levels were reported as geometric mean titers (GMT) with geometric standard deviation (GSD). Differences in GMT were tested using Friedman test and Kruskal Wallis test, with Bonferroni multiple comparisons procedure. Adjusted hazard ratios on the development of probable reinfection were estimated using Cox proportional models.

Results

There were 307 study participants included in the study, with 13 dropouts. Study participants received SARS-CoV-2 vaccines at varying times, with 278 participants (90.5%) fully vaccinated by the end of study. The GMT of the study cohort increased over time, from 19.7 U/mL (GSD 11) at Day 21; to 284.5 U/mL (GSD 9.6) at Day 90; 1,061 U/mL (GSD 5.3) at Day 180; 2,003 U/mL (GSD 6.7) at Day 270; and 8,403 U/mL (GSD 3.1) at Day 360. The increase was statistically significant from Day 21 to Day 90 (p<0.0001), Day 90 to Day 180 (p=0.0005), and Day 270 to Day 360 (p<0.0001). Participants with more severe initial infection demonstrated significantly higher antibody levels compared to those with milder infection at Day 21. Sixty-four patients had probable COVID-19 reinfection (incidence of 20.8%, 95% CI 16.4, 25.8%). The GMT of these 64 patients was 411.8 U/mL (GSD 6.9) prior to the occurrence of the probable reinfection. Majority (87.5%) were fully vaccinated. Antibody titers significantly affected the risk of developing reinfection, with adjusted hazard ratio of 0.994, 95% CI 0.992-0.996, p<0.001.

Conclusion

Antibody levels against SARS-CoV-2 increased over a one-year follow-up. Higher antibody levels were observed among those with more severe initial infection and those vaccinated. Higher antibody levels are associated with a lower risk of probable reinfection.

Potentiating the Cross-Reactive IFN-γ T Cell and Polyfunctional T Cell Responses by Heterologous GX-19N DNA Booster in Mice Primed with Either a COVID-19 mRNA Vaccine or Inactivated Vaccine

Waning vaccine-induced immunity, coupled with the emergence of SARS-CoV-2 variants, has inspired the widespread implementation of COVID-19 booster vaccinations. Here, we evaluated the potential of the GX-19N DNA vaccine as a heterologous booster to enhance the protective immune response to SARS-CoV-2 in mice primed with either an inactivated virus particle (VP) or an mRNA vaccine. We found that in the VP-primed condition, GX-19N enhanced the response of both vaccine-specific antibodies and cross-reactive T Cells to the SARS-CoV-2 variant of concern (VOC), compared to the homologous VP vaccine prime-boost. Under the mRNA-primed condition, GX-19N induced higher vaccine-induced T Cell responses but lower antibody responses than the homologous mRNA vaccine prime-boost. Furthermore, the heterologous GX-19N boost induced higher S-specific polyfunctional CD4⁺ and CD8⁺ T cell responses than the homologous VP or mRNA prime-boost vaccinations. Our results provide new insights into booster vaccination strategies for the management of novel COVID-19 variants.

One-Year Temporal Changes in Long COVID Prevalence and Characteristics: A Systematic Review and Meta-Analysis

OBJECTIVES

This study aimed to explore the 1-year temporal change in prevalence, variety, and potential risk factors of long COVID symptoms and to further predict the prognostic trends of long COVID.

METHODS

We searched electronic databases for related studies published from January 2020 to February 2022 and conducted 1-group meta-analysis and locally weighted regression to explore the monthly temporal change in the prevalence of each long COVID symptom in 1-year follow-up period.

RESULTS

A total of 137 studies were included in meta-analysis, including 134 093 participants. The temporal change of any long COVID symptom showed a steep decrease initially (from 92% at acute phase to 55% at 1-month follow-up), followed by stabilization at approximately 50% during 1-year follow-up. Six months or more after the acute phase, the odds ratio of population characteristic-related factors increased, such as female (from 1.62 to 1.82), whereas the odds ratio value of acute phase-related factors (severe or critical cases and hospitalization) decreased. As for specific symptoms, approximately two-thirds of the symptoms did not significantly reduce during the 1-year follow-up, and the neuropsychiatric symptoms showed a higher long-term prevalence (approximately 25%) and longer persistence than physical symptoms.

CONCLUSIONS

The temporal changes in the prevalence and characteristics speculate that long COVID may persist longer than expected. In particular, we should pay more attention to neuropsychiatric symptoms and other symptoms for which there is no significant downward trend in prevalence. The influence of acute phase-related factors for long COVID gradually decreases over time, whereas the influence of population characteristic-related factors gradually increases.

A longitudinal seroepidemiology study to evaluate antibody response to SARS-CoV-2 virus infection and vaccination in children in Calgary, Canada from July 2020 to April 2022: Alberta COVID-19 Childhood Cohort (AB3C) Study

BACKGROUND

Measurement of SARS-CoV-2 antibody seropositivity is important to accurately understand exposure to infection and/or vaccination in specific populations. This study aimed to estimate the serologic response to SARS-CoV-2 virus infection and vaccination in children in Calgary, Alberta over a two-year period.

METHODS

Children with or without prior SARS-CoV-2 infections, were enrolled in Calgary, Canada in 2020. Venous blood was sampled 4 times from July 2020 to April 2022 for SARS-CoV-2 nucleocapsid and spike antibodies. Demographic and clinical information was obtained including SARS-CoV-2 testing results and vaccination records.

RESULTS

1035 children were enrolled and 88.9% completed all 4 visits; median age 9 years (IQR: 5,13); 519 (50.1%) female; and 815 (78.7%) Caucasian. Before enrolment, 118 (11.4%) had confirmed or probable SARS-CoV-2. By April 2022, 39.5% of previously uninfected participants had a SARS-CoV-2 infection. Nucleocapsid antibody seropositivity declined to 16.4% of all infected children after more than 200 days post diagnosis. Spike antibodies remained elevated in 93.6% of unvaccinated infected children after more than 200 days post diagnosis. By April 2022, 408 (95.6%) children 12 years and older had received 2 or more vaccine doses, and 241 (61.6%) 5 to 11 year-old children had received 2 vaccine doses. At that time, all 685 vaccinated children had spike antibodies, compared with 94/176 (53.4%) of unvaccinated children.

CONCLUSIONS

In our population, after the first peak of Omicron variant infections and introduction of COVID-19 vaccines for children, all vaccinated children, but just over one-half of unvaccinated children, had SARS-CoV-2 spike antibodies indicating infection and/or vaccination, highlighting the benefit of vaccination. It is not yet known whether a high proportion of seropositivity at the present time predicts sustained population-level protection against future SARS-CoV-2 transmission, infection or severe COVID-19 outcomes in children.

Comparison and monitoring of antibody response in convalescent and healthy vaccinated individuals against RBD and PCS of SARS-CoV-2 spike protein

The prevalence of SARS-CoV-2 as a global health threat has called for population-wide vaccination to curb COVID-19. Hence, the World Health Organization (WHO) has approved several platforms of SARS-CoV-2 vaccines for emergency use. Therefore, a more comprehensive study on the immune response induced by vaccines in diverse individuals is still required. Here, we expressed a local variant of SARS-CoV-2 receptor-binding domain (RBD) and protease cleavage site (PCS), playing a vital role in binding and fusion in Rosetta (DE3). We then characterized it through SDS-PAGE analysis and western blotting. Moreover, we compared and monitored ChAdOx1 nCoV-19 vaccination-induced antibody response in convalescent and healthy vaccinated individuals after the first and second vaccine doses through serologic assay against RBD and PCS, which have not yet been compared. We investigated a cohort of 100 sera samples; based on our parameters, 25 serum samples were selected as convalescent samples and 25 serum samples as healthy samples for comparison. These findings demonstrate that most of the convalescent sera show more reactivity with PCS (80%) than with RBD (56%). Interestingly, IgG antibody response against PCS was more significant in both pre- and post-vaccination in convalescent individuals than in healthy individuals. Indeed, anti-RBD antibody titers were most significant in pre-vaccination and post-first vaccination in convalescent individuals than in healthy individuals and not in pre-vaccination and post-second vaccination. Besides monitoring IgG antibody response against COVID-19, these findings could shed light on the progress, assessment, and efficacy evaluation of SARS-CoV-2 vaccines.Communicated by Ramaswamy H. Sarma.

Tocilizumab-treated convalescent COVID-19 patients retain the cross-neutralization potential against SARS-CoV-2 variants

Although tocilizumab treatment in severe and critical coronavirus disease 2019 (COVID-19) patients has proven its efficacy at the clinical level, there is little evidence supporting the effect of short-term use of interleukin-6 receptor blocking therapy on the B cell sub-populations and the cross-neutralization of SARS-CoV-2 variants in convalescent COVID-19 patients. We performed immunological profiling of 69 tocilizumab-treated and non-treated convalescent COVID-19 patients in total. We observed that SARS-CoV-2-specific IgG1 titers depended on disease severity but not on tocilizumab treatment. The plasma of both treated and non-treated patients infected with the ancestral variant exhibit strong neutralizing activity against the ancestral virus and the Alpha, Beta, and Delta variants of SARS-CoV-2, whereas the Gamma and Omicron viruses were less sensitive to seroneutralization. Overall, we observed that, despite the clinical benefits of short-term tocilizumab therapy in modifying the cytokine storm associated with COVID-19 infections, there were no modifications in the robustness of B cell and IgG responses to Spike antigens.

T Cell Responses Correlate with Self-Reported Disease Severity and Neutralizing Antibody Responses Predict Protection against SARS-CoV-2 Breakthrough Infection

OBJECTIVES

The objective of this prospective study was to investigate the role of adaptive immunity in response to SARS-CoV-2 vaccines.

DESIGN AND METHODS

A cohort of 677 vaccinated individuals participated in a comprehensive survey of their vaccination status and associated side effects, and donated blood to evaluate their adaptive immune responses by neutralizing antibody (NAb) and T cell responses. The cohort then completed a follow-up survey to investigate the occurrence of breakthrough infections.

RESULTS

NAb levels were the highest in participants vaccinated with Moderna, followed by Pfizer and Johnson & Johnson. NAb levels decreased with time after vaccination with Pfizer and Johnson & Johnson. T cell responses showed no significant difference among the different vaccines and remained stable up to 10 months after the study period for all vaccine types. In multivariate analyses, NAb responses (<95 U/mL) predicted breakthrough infection, whereas previous infection, the type of vaccine, and T cell responses did not. T cell responses to viral epitopes (<0.120 IU/mL) showed a significant association with the self-reported severity of COVID-19 disease.

CONCLUSION

This study provides evidence that NAb responses to SARS-CoV-2 vaccination correlate with protection against infection, whereas the T cell memory responses may contribute to protection against severe disease but not against infection.

Donor selection for adoptive cell therapy with CD45RA- memory T cells for patients with coronavirus disease 2019, and dexamethasone and interleukin-15 effects on the phenotype, proliferation and interferon gamma release

BACKGROUND AIMS

We have previously demonstrated the safety and feasibility of adoptive cell therapy with CD45RA- memory T cells containing severe acute respiratory syndrome coronavirus 2-specific T cells for patients with coronavirus disease 2019 from an unvaccinated donor who was chosen based on human leukocyte antigen compatibility and cellular response. In this study, we examined the durability of cellular and humoral immunity within CD45RA- memory T cells and the effect of dexamethasone, the current standard of care treatment, and interleukin-15, a cytokine critically involved in T-cell maintenance and survival.

METHODS

We performed a longitudinal analysis from previously severe acute respiratory syndrome coronavirus 2-infected and infection-naïve individuals covering 21 months from infection and 10 months after full vaccination with the BNT162b2 Pfizer/BioNTech vaccine.

RESULTS

We observed that cellular responses are maintained over time. Humoral responses increased after vaccination but were gradually lost. In addition, dexamethasone did not alter cell functionality or proliferation of CD45RA- T cells, and interleukin-15 increased the memory T-cell activation state, regulatory T cell expression, and interferon gamma release.

CONCLUSIONS

Our results suggest that the best donors for adoptive cell therapy would be recovered individuals and 2 months after vaccination, although further studies with larger cohorts would be needed to confirm this finding. Dexamethasone did not affect the characteristics of the memory T cells at a concentration used in the clinical practice and IL-15 showed a positive effect on SARS-CoV-2-specific CD45RA- T cells.

Dynamics of Different Classes and Subclasses of Antibody Responses to Severe Acute Respiratory Syndrome Coronavirus 2 Variants after Coronavirus Disease 2019 and CoronaVac Vaccination in Thailand

The humoral immune response plays a key role in protecting the population from SARS-CoV-2 transmission. Patients who recovered from COVID-19 as well as fully vaccinated individuals have elevated levels of antibodies. The dynamic levels of the classes and subclasses of antibody responses to new variants that occur in different populations remain unclear. We prospectively recruited 60 participants, including COVID-19 patients and CoronaVac-vaccinated individuals, in Thailand from May to August 2021. Plasma samples were collected on day 0, day 14, and day 28 to determine the dynamic levels of the classes and subclasses of plasma antibodies against the receptor-binding domain (RBD) in the spike protein (S) of four SARS-CoV-2 strains (Wuhan, Alpha, Delta, and Omicron) via enzyme-linked immunosorbent assay. Our results indicated that the patients with SARS-CoV-2 infections had broader class and subclass profiles as well as higher levels of anti-S RBD antibodies to the Wuhan, Alpha, and Delta strains than did the CoronaVac-vaccinated individuals. The median antibody levels increased and subsequently declined in a month in the COVID-19 patients and in the vaccinated group. Correlations of the classes and subclasses of antibodies were observed in the COVID-19 patients but not in the vaccinated individuals. The levels of all of the anti-S RBD antibodies against the Omicron variant were low in the patients and in the vaccinated individuals. Our study revealed distinct antibody profiles between the two cohorts, suggesting different pathways of immune activation. This could have an impact on protection from infections by new variants of concern (VOC). IMPORTANCE The antibody responses to new SARS-CoV-2 variants that occur in different populations remain unclear. In this study, we recruited 60 participants, including COVID-19 patients and CoronaVac-vaccinated individuals, in Thailand and determined the dynamic levels of the IgG, IgA, IgM, and IgG subclasses of antibodies against the spike protein (S) of four SARS-CoV-2 strains. Our results showed that the patients with SARS-CoV-2 infections had broader profiles and higher levels of antibodies to the Wuhan, Alpha, and Delta strains than did the CoronaVac-vaccinated individuals. The antibody levels of both groups increased and subsequently decreased within 1 month. Higher and functional correlations of these antibodies were observed in the COVID-19 patients. The levels of all anti-S RBD antibodies against the Omicron variant were low in patients and vaccinated individuals. Our study revealed distinct antibody responses between the two groups, suggesting different pathways of immune response, which may have an impact on protection from infections by new SARS-CoV-2 variants.

Immunosuppressive treatments selectively affect the humoral and cellular response to SARS-CoV-2 in vaccinated patients with vasculitis

OBJECTIVES

To analyse humoral and cellular immune response to mRNA COVID-19 vaccines in patients with GCA.

METHODS

Consecutive patients with a diagnosis of GCA receiving two doses of BNT162b2 vaccine were assessed at baseline and 3 weeks from the second vaccine dose. Healthy subjects (n = 51) were included as controls (HC). Humoral response was assessed with Spike-specific IgG antibody response (S-IgG) and neutralizing antibodies (NtAb). Specific T cell response was assessed by enzyme linked immunosorbent spot (ELISpot).

RESULTS

Of 56 included patients with GCA, 44 were eligible after exclusion of previous evidence of COVID-19 and incomplete follow-up. A significant proportion of patients with GCA (91%) demonstrated antibody (S-IgG) response, but this was significantly lower than HCs (100%); P < 0.0001. Neutralizing activity was not detected in 16% of patients with GCA. Antibody titres (S-IgG and NtAb) were significantly lower compared with HCs. Humoral response (S-IgG and NtAb) was significantly hampered by treatment with MTX. Cellular response was lacking in 30% of patients with GCA (vs 0% in HCs; P < 0.0001). Cellular response was significantly influenced by the levels of baseline peripheral T-lymphocytes and by glucocorticoid treatment. Treatment with tocilizumab did not affect any level of the immune response elicited by vaccination.

CONCLUSIONS

Although patients with GCA apparently achieve a robust antibody seroconversion, there is a significant impairment of the neutralizing activity. MTX significantly reduced all levels of the humoral response. Up to one-third of patients do not develop a cellular immune protection in response to COVID-19 vaccination.

Multimodal characterization of antigen-specific CD8 + T cells across SARS-CoV-2 vaccination and infection

The human immune response to SARS-CoV-2 antigen after infection or vaccination is defined by the durable production of antibodies and T cells. Population-based monitoring typically focuses on antibody titer, but there is a need for improved characterization and quantification of T cell responses. Here, we utilize multimodal sequencing technologies to perform a longitudinal analysis of circulating human leukocytes collected before and after BNT162b2 immunization. Our data reveal distinct subpopulations of CD8 + T cells which reliably appear 28 days after prime vaccination (7 days post boost). Using a suite of cross-modality integration tools, we define their transcriptome, accessible chromatin landscape, and immunophenotype, and identify unique biomarkers within each modality. By leveraging DNA-oligo-tagged peptide-MHC multimers and T cell receptor sequencing, we demonstrate that this vaccine-induced population is SARS-CoV-2 antigen-specific and capable of rapid clonal expansion. Moreover, we also identify these CD8 + populations in scRNA-seq datasets from COVID-19 patients and find that their relative frequency and differentiation outcomes are predictive of subsequent clinical outcomes. Our work contributes to our understanding of T cell immunity, and highlights the potential for integrative and multimodal analysis to characterize rare cell populations.

Persistence of IgG COVID-19 antibodies: A longitudinal analysis

Background and aim

The kinetics of antibody production in response to coronavirus disease 2019 (COVID-19) infection is not well-defined yet. This study aimed to evaluate the antibody responses to SARS-CoV-2 and its dynamics during 9-months in a cohort of patients infected during the first phase of the pandemic. As a secondary aim, it was intended to evaluate the factors associated with different concentrations of IgG antibodies.

Methods

A prospective cohort study was conducted from June 2020 to January 2021. This study recruited a convenience sample of adult individuals who where recently diagnosed with COVID-19 and were living in mainland Portugal. A total of 1,695 blood samples were collected from 585 recovered COVID-19 patients up to 9 months after SARS-CoV-2 acute infection. A blood sample was collected at baseline and three, 6 and 9 months after SARS-CoV-2 acute infection to assess the concentration of IgG antibody against SARS-CoV-2.

Results

The positivity rate of IgG reached 77.7% in the first 3 months after symptom onset. The IgG persists at all subsequent follow-up time-points, which was 87.7 and 89.2% in the 6th and 9th months after symptom onset, respectively. Three distinct kinetics of antibody response were found within the 9 months after infection. Kinetic 1 (K1) was characterized by a constant low IgG antibody concentration kinetic (group size: 65.2%); kinetic 2 (K2), composed by constant moderate IgG kinetic (group size: 27.5%) and kinetic 3 (K3) characterized by higher IgG kinetic (group size: 7.3%). People with ≥56 years old (OR: 3.33; CI 95%: [1.64; 6.67]; p-value: 0.001) and symptomatic COVID-19 (OR: 2.08; CI 95%: [1.08; 4.00]; p-value: 0.031) had higher odds of a "Moderate IgG kinetic." No significant association were found regarding the "Higher IgG kinetic."

Conclusion

Our results demonstrate a lasting anti-spike (anti-S) IgG antibody response at least 9 months after infection in the majority of patients with COVID-19. Younger participants with asymptomatic disease have lower IgG antibody positivity and possibly more susceptible to reinfection. This information contributes to expanding knowledge of SARS-CoV-2 immune response and has direct implications in the adoption of preventive strategies and public health policies.

Neutralizing antibodies and T-cell responses to inactivated SARS-CoV-2 vaccine in COVID-19 convalescents one and a half years after infection

Vaccines have been considered the most promising solution for ending the coronavirus disease 2019 (COVID-19) pandemic. Information regarding neutralizing antibodies (NAbs) and T-cell immune response in inactivated SARS-CoV-2 vaccine-immunized COVID-19 convalescent patients were either only available for a short time after illness recovered or not available at all (T-cell immunity). We evaluated SARS-CoV-2 NAbs and cellular immune responses to the SARS-CoV-2 inactivated vaccine in convalescent patients who recovered from infection for about one and a half years. We found that compared to before vaccination, SARS-CoV-2 NAbs and specific T-cell responses were significantly boosted by the inactivated vaccine in convalescent patients, which confirmed the pre-existing adaptive immunity in SARS-CoV-2 infected people. We observed that NAbs and IFN-γ-secreting T-cell response elicited by a single vaccine dose in subjects with prior COVID-19 infection were higher than after two doses of vaccine in SARS-CoV-2 naïve subjects. Both humoral and cellular immune responses elicited by one and two doses of inactivated vaccine were comparable in COVID-19-recovered persons. In conclusion, inactivated COVID-19 vaccine induced robust NAbs and T-cell responses to SARS-CoV-2 in COVID-19 convalescent patients and immune responses after one dose were equal to that after receiving two doses, which highlighted that robust humoral and cellular immune response can be reactivated by the inactivated vaccine in SARS-CoV-2 convalescent patients.

Cellular and humoral responses after second and third SARS-CoV-2 vaccinations in patients with autoimmune diseases treated with rituximab: specific T cell immunity remains longer and plays a protective role against SARS-CoV-2 reinfections

Background

Humoral and cellular immune responses are known to be crucial for patients to recover from COVID-19 and to protect them against SARS-CoV-2 reinfection once infected or vaccinated.

Objectives

This study aimed to investigate humoral and T cell responses to SARS-CoV-2 vaccination in patients with autoimmune diseases after the second and third vaccine doses while on rituximab and their potential protective role against reinfection.

Methods

Ten COVID-19-naïve patients were included. Three time points were used for monitoring cellular and humoral responses: pre-vaccine to exclude virus exposure (time point 1) and post-second and post-third vaccine (time points 2 and 3). Specific IgG antibodies were monitored by Luminex and T cells against SARS-CoV-2 spike-protein by ELISpot and CoVITEST. All episodes of symptomatic COVID-19 were recorded.

Results

Nine patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis and one with an undifferentiated autoimmune disease were included. Nine patients received mRNA vaccines. The last rituximab infusion was administered for a mean (SD) of 15 (10) weeks before the first vaccine and six patients were CD19-B cell-depleted. After a mean (SD) of 19 (10) and 16 (2) days from the second and third vaccine dose, IgG anti-SARS-CoV-2 antibodies were detected in six (60%) and eight (80%) patients, respectively. All patients developed specific T cell responses by ELISpot and CoVITEST in time points 2 and 3. Previous B cell depletion correlated with anti-SARS-CoV-2 IgG levels. Nine (90%) patients developed mild COVID-19 after a median of 7 months of the third dose.

Conclusion

Rituximab in patients with autoimmune diseases reduces humoral responses but does not avoid the development of T cell responses to SARS-CoV-2 vaccination, which remain present after a booster dose. A steady cellular immunity appears to be protective against subsequent reinfections.

SARS-CoV-2 antibodies persist up to 12 months after natural infection in healthy employees working in non-medical contact-intensive professions

OBJECTIVES

This study aimed to evaluate dynamics of antibody levels after exposure to SARS-CoV-2 for 12 months in Dutch non-vaccinated hairdressers and hospitality staff.

METHODS

In this prospective cohort study, blood samples were collected every 3 months for 1 year and analyzed using a qualitative total antibody enzyme-linked immunosorbent assay (ELISA) and a quantitative immunoglobulin (Ig)G antibody ELISA. Participants completed questionnaires, providing information on demographics, health, and work. Differences in antibody levels were evaluated using Mann-Whitney U and Wilcoxon signed-rank tests. Beta coefficients (β) and 95% confidence intervals (CIs) were calculated using linear regression.

RESULTS

Ninety-five of 497 participants (19.1%) had ≥1 seropositive measurement before their last visit using the qualitative ELISA. Only 2.1% (2/95) seroreverted during follow-up. Of 95 participants, 82 (86.3%) tested IgG seropositive in the quantitative ELISA too. IgG antibody levels significantly decreased in the first months (P <0.01) but remained detectable for up to 12 months in all participants. Older age (β, 10-years increment: 24.6, 95% CI: 5.7-43.5) and higher body mass index (β, 5kg/m² increment: 40.0, 95% CI: 2.9-77.2) were significantly associated with a higher peak of antibody levels.

CONCLUSION

In this cohort, SARS-CoV-2 antibodies persisted for up to 1 year after initial seropositivity, suggesting long-term natural immunity.

Persistent memory despite rapid contraction of circulating T Cell responses to SARS-CoV-2 mRNA vaccination

Introduction

While antibodies raised by SARS-CoV-2 mRNA vaccines have had compromised efficacy to prevent breakthrough infections due to both limited durability and spike sequence variation, the vaccines have remained highly protective against severe illness. This protection is mediated through cellular immunity, particularly CD8+ T cells, and lasts at least a few months. Although several studies have documented rapidly waning levels of vaccine-elicited antibodies, the kinetics of T cell responses have not been well defined.

Methods

Interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISpot) assay and intracellular cytokine staining (ICS) were utilized to assess cellular immune responses (in isolated CD8+ T cells or whole peripheral blood mononuclear cells, PBMCs) to pooled peptides spanning spike. ELISA was performed to quantitate serum antibodies against the spike receptor binding domain (RBD).

Results

In two persons receiving primary vaccination, tightly serially evaluated frequencies of anti-spike CD8+ T cells using ELISpot assays revealed strikingly short-lived responses, peaking after about 10 days and becoming undetectable by about 20 days after each dose. This pattern was also observed in cross-sectional analyses of persons after the first and second doses during primary vaccination with mRNA vaccines. In contrast, cross-sectional analysis of COVID-19-recovered persons using the same assay showed persisting responses in most persons through 45 days after symptom onset. Cross-sectional analysis using IFN-γ ICS of PBMCs from persons 13 to 235 days after mRNA vaccination also demonstrated undetectable CD8+ T cells against spike soon after vaccination, and extended the observation to include CD4+ T cells. However, ICS analyses of the same PBMCs after culturing with the mRNA-1273 vaccine in vitro showed CD4+ and CD8+ T cell responses that were readily detectable in most persons out to 235 days after vaccination.

Discussion

Overall, we find that detection of spike-targeted responses from mRNA vaccines using typical IFN-γ assays is remarkably transient, which may be a function of the mRNA vaccine platform and an intrinsic property of the spike protein as an immune target. However, robust memory, as demonstrated by capacity for rapid expansion of T cells responding to spike, is maintained at least several months after vaccination. This is consistent with the clinical observation of vaccine protection from severe illness lasting months. The level of such memory responsiveness required for clinical protection remains to be defined.

High titers of neutralizing antibodies in the blood fail to eliminate SARS-CoV-2 viral RNA in the upper respiratory tract

Retest-positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA, as a unique phenomenon among discharged individuals, has been demonstrated to be safe in the community. Still, the underlying mechanism of viral lingering is less investigated. In this study, first, we find that the frequency of viral RNA-positive retesting differs among variants. Higher ratios of viral RNA-positive retest were more frequently observed among Delta (61.41%, 514 of 837 cases) and Omicron (39.53%, 119 of 301 cases) infections than among ancestral viral infection (7.27%, 21 of 289 cases). Second, the tissues where viral RNA reoccurred were altered. Delta RNA reoccurred mainly in the upper respiratory tract (90%), but ancestral virus RNA reoccurred mainly in the gastrointestinal tract (71%). Third, vaccination did not reduce the frequency of viral RNA-positive retests, despite high concentrations of viral-specific antibodies in the blood. Finally, 37 of 55 (67.27%) Delta-infected patients receiving neutralizing antibody therapy become viral RNA retest positive when high concentrations of neutralizing antibodies still patrol in the blood. Altogether, our findings suggest that the presentence of high titers of neutralizing antibodies in the blood is incompetent in clearing residual viral RNA in the upper respiratory tract.

SARS-CoV-2 spike RBD-specific IgA and IgG antibodies in breast milk after vaccination with the protein subunit vaccine Abdala

Background

COVID-19 vaccines that trigger a strong secretory antibody response in breast milk may achieve effective passive protection of vulnerable newborns and breastfed infants of immunized mothers. The aim of this work was to investigate the presence of SARS-CoV-2 spike RBD-specific IgA and IgG antibodies in breast milk, 5 and 9 weeks after vaccination with 3 doses of the protein subunit vaccine Abdala, compared to those found in breast milk from COVID-19-recovered women, collected at least 40 days after the infection.

Methods

SARS-CoV-2 spike RBD-specific IgA and IgG antibodies were semi-quantified by indirect ELISA, using a homemade standard generated by pooling twenty breast milk samples with high absorbance values according to preliminary data. The validity of the standard curves was proved following the European Medicines Agency Guideline. Two breast milk samples from 2 unvaccinated women who had not been infected with COVID-19 were included as negative controls. Potentially neutralizing antibodies was assessed by a SARS-CoV-2 surrogate virus neutralization test.

Results

High levels of anti-RBD IgA antibodies were detected in breast milk samples 9 weeks after vaccination and anti-RBD IgG antibodies rise from the fifth to the ninth week. In the post-COVID-19 time that was evaluated, the IgG-type response was notably higher compared to both post-vaccination periods. Neutralizing antibody titers were similar in breast milk from vaccinated and COVID-19 recovered women.

Conclusions

This is the first report about the immune response in breast milk after the administration of a COVID-19 protein subunit vaccine, which could provide analogous protection to that conferred by SARS-CoV-2 infection. This implies a potential passive immunity that breastfed infants receive from their mothers vaccinated with Abdala.

High antibody levels and reduced cellular response in children up to one year after SARS-CoV-2 infection

The COVID-19 course and immunity differ in children and adults. We analyzed immune response dynamics in 28 families up to 12 months after mild or asymptomatic infection. Unlike adults, the initial response is plasmablast-driven in children. Four months after infection, children show an enhanced specific antibody response and lower but detectable spike 1 protein (S1)-specific B and T cell responses than their parents. While specific antibodies decline, neutralizing antibody activity and breadth increase in both groups. The frequencies of S1-specific B and T cell responses remain stable. However, in children, one year after infection, an increase in the S1-specific IgA class switch and the expression of CD27 on S1-specific B cells and T cell maturation are observed. These results, together with the enhanced neutralizing potential and breadth of the specific antibodies, suggest a progressive maturation of the S1-specific immune response. Hence, the immune response in children persists over 12 months but dynamically changes in quality, with progressive neutralizing, breadth, and memory maturation. This implies a benefit for booster vaccination in children to consolidate memory formation.

Antibody Levels Poorly Reflect on the Frequency of Memory B Cells Generated following SARS-CoV-2, Seasonal Influenza, or EBV Infection

The scope of immune monitoring is to define the existence, magnitude, and quality of immune mechanisms operational in a host. In clinical trials and praxis, the assessment of humoral immunity is commonly confined to measurements of serum antibody reactivity without accounting for the memory B cell potential. Relying on fundamentally different mechanisms, however, passive immunity conveyed by pre-existing antibodies needs to be distinguished from active B cell memory. Here, we tested whether, in healthy human individuals, the antibody titers to SARS-CoV-2, seasonal influenza, or Epstein-Barr virus antigens correlated with the frequency of recirculating memory B cells reactive with the respective antigens. Weak correlations were found. The data suggest that the assessment of humoral immunity by measurement of antibody levels does not reflect on memory B cell frequencies and thus an individual's potential to engage in an anamnestic antibody response against the same or an antigenically related virus. Direct monitoring of the antigen-reactive memory B cell compartment is both required and feasible towards that goal.

Association of Alleles of Human Leukocyte Antigen Class II Genes and Severity of COVID-19 in Patients of the 'Red Zone' of the Endocrinology Research Center, Moscow, Russia

The aim of this study was to assess the correlations of clinical features of patients with moderate and severe courses of COVID-19, comorbidity (endocrine, autoimmune, cardiovascular, oncological, and pulmonary diseases), and alleles of the HLA class II system genes. One hundred COVID-19 patients hospitalized in the Endocrinology Research Centre, Moscow, Russia, were analyzed for age, gender, smoking, comorbidity, and invasive mechanical ventilation. Computer tomography was used to assess the severity of the disease. HLA-DRB1, HLA-DQA1, and HLA-DQB1 alleles were identified in samples from 100 patients and samples from 327 randomly selected individuals collected in the prepandemic period (control group). There was no association of gender, age, weight, body mass index, smoking, and comorbidity with the severity of COVID-19. Allele DQB1*06:02-8 was more common in patients (p < 0.00005), and DQB1*06:01 and DQB1*05:03 were more common in the control group (p < 0.00005, and p = 0.0011, respectively). DQB1*06:02-8 can probably be considered as predisposing to moderate and severe COVID-19, and DQB1*06:01 can be considered as protective. No association of these alleles with comorbidity was found. Our results suggest that carriers of predisposing alleles, with cardiovascular and non-autoimmune endocrine diseases, should take more stringent preventive measures, and if infected, a more aggressive COVID-19 treatment strategy should be used.

Development and Evaluation of a Rapid Neutralizing Antibody Assay for COVID-19 Vaccination

SARS-CoV-2 neutralizing antibodies have excellent application prospects in the prevention and treatment of COVID-19. This study established a competitive colloidal gold immunochromatography assay (GICA) to detect neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in postvaccination serum. The sensitivity, stability, and specificity of GICA were evaluated using neutralizing antibody solution reference material and positive serum. The consistency and correlation between GICA, pseudovirus neutralization (PN) assay, and ELISA were compared. Consistency analysis of serum neutralizing antibody and specific IgG antibody titers was conducted, and changes in neutralizing antibodies and specific IgG antibodies in serum after inoculation with the homologous booster inactivated vaccine and recombinant vaccine were noted. The sensitivity of the reagent was 20.66 IU/L, and the specificity was 100%. There was a strong consistency and correlation between GICA and PN (κ = 0.886, n = 165; r = 0.918, P < 0.001). The correlation coefficient of serum anti-RBD antibody and specific IgG antibody titers was 0.5253 (P < 0.001). The specific IgG antibody titers in serum after (W4) inoculation with homologous booster inactivated vaccine were 10.80 (S/CO).The anti-RBD antibody titers were 28.33. The anti-RBD omicron variant (B.1.1.529) antibody titers were 11.67. After inoculation with the recombinant vaccine, the specific IgG antibody titers in the serum of W4 were 10.68. The serum anti-RBD antibody titers of W4 were 103.30. The serum anti-RBD omicron variant (B.1.1.529) antibody titers of W4 were 56.67. Therefore, vaccination of the third dose of the homologous booster inactivated vaccine and recombinant vaccine can enhance the level of neutralizing antibodies against the omicron variant (B.1.1.529). This study demonstrates that a GICA kit for neutralizing antibodies against the RBD of SARS-CoV-2 can be used for COVID-19 vaccine evaluation. Changes in titers enable long-term monitoring of a population's immunity and guide interventions when their immunity declines.