Determination of neutralising anti-SARS-CoV-2 antibody half-life in COVID-19 convalescent donors

Persistent IgG1 clones dominate and personalize the plasma antibody repertoire

Antibodies play a pivotal role in the immune defense and long-term immunity. Yet, while several studies have highlighted the persistence of antigen-specific antibody responses, it is unclear whether this stems from the continuous production of the same clones or recurrent activation of B cells generating new clones. To examine the stability of the human antibody repertoire, we monitored the concentrations of the most abundant IgG1 clones in plasma samples of 11 healthy donors at nine sampling points over a year. During this year, each donor received three doses of a COVID-19 vaccine. Notwithstanding these vaccinations, the concentrations of the most abundant IgG1 clones remained constant. Given the 2- to 3-week half-life of IgG1 molecules in blood, our data suggest that these clones are associated with long-term immunity and do not undergo somatic hypermutation which would imply short-lived plasma cells. Overall, our data suggest that most of the abundant IgG1 clones in plasma are persistently produced by long-lived plasma cells.

Modeling SARS-CoV-2 Infection Dynamics: Insights into Viral Clearance and Immune Synergy

Understanding the mechanisms of interaction between SARS-CoV-2 infection and the immune system is crucial for developing effective treatment strategies against COVID-19. In this paper, a mathematical model is formulated to investigate the interactions among SARS-CoV-2 infection, cellular immunity, and humoral immunity. Clinical data from eight asymptomatic or mild COVID-19 patients in Munich are used to fit the model, and the dynamics of natural killer (NK) cells, cytotoxic T lymphocytes (CTLs), B cells, and antibodies are further explored using the average of the best-fitting parameter values. Subsequently, the impact of NK cells, CTLs, B cells, and antibodies on SARS-CoV-2 infection is numerically investigated. The results indicate that (i) the synergy of NK cells, CTLs, and antibodies leads to a rapid decrease in the viral load during SARS-CoV-2 infection; (ii) antibodies play a crucial role compared to other immune mechanisms, and enhancing B cell stimulation may be more effective in clearing the virus from the lungs; (iii) in terms of cytotoxic effects, CTLs are stronger and more sustained than NK cells. Furthermore, the existence and local stability of the model's equilibria are fully classified, and complex dynamics of the model are further investigated using bifurcation theory, revealing multistability phenomena, including multiple attractors and periodic solutions. These findings suggest potential uncertainty and diversity in SARS-CoV-2 infection outcomes.

SARS-CoV-2 evolution on a dynamic immune landscape

Since the onset of the pandemic, many SARS-CoV-2 variants have emerged, exhibiting substantial evolution in the virus' spike protein1, the main target of neutralizing antibodies2. A plausible hypothesis proposes that the virus evolves to evade antibody-mediated neutralization (vaccine- or infection-induced) to maximize its ability to infect an immunologically experienced population1,3. Because viral infection induces neutralizing antibodies, viral evolution may thus navigate on a dynamic immune landscape that is shaped by local infection history. Here we developed a comprehensive mechanistic model, incorporating deep mutational scanning data4,5, antibody pharmacokinetics and regional genomic surveillance data, to predict the variant-specific relative number of susceptible individuals over time. We show that this quantity precisely matched historical variant dynamics, predicted future variant dynamics and explained global differences in variant dynamics. Our work strongly suggests that the ongoing pandemic continues to shape variant-specific population immunity, which determines a variant's ability to transmit, thus defining variant fitness. The model can be applied to any region by utilizing local genomic surveillance data, allows contextualizing risk assessment of variants and provides information for vaccine design.

COVID-19 mRNA vaccination responses in individuals with sickle cell disease: an ASH RC Sickle Cell Research Network Study

ABSTRACT

Children and adults with sickle cell disease (SCD) have increases in morbidity and mortality with COVID-19 infections. The American Society of Hematology Research Collaborative Sickle Cell Disease Research Network performed a prospective COVID-19 vaccine study to assess antibody responses and analyze whether messenger RNA (mRNA) vaccination precipitated any adverse effects unique to individuals with SCD. Forty-one participants received 2 doses of the Pfizer-BioNTech vaccine and provided baseline blood samples before vaccination and 2 months after the initial vaccination for analysis of immunoglobulin G (IgG) reactivity against the receptor binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 spike protein. Six-month IgG reactivity against the viral RBD was also available in 37 patients. Postvaccination reactogenicity was common and similar to the general population. There were no fevers that required inpatient admission. Vaso-occlusive pain within 2 to 3 days of first or second vaccination was reported by 5 participants (12%) including 4 (10%) who sought medical care. Twenty-seven participants (66%) were seropositive at baseline, and all 14 initially seronegative participants (34%) converted to seropositive after vaccination. Overall, mRNA vaccination had a good risk-benefit profile in individuals with SCD. This mRNA vaccine study also marks the first evaluation of vaccine safety and antibody response in very young children with SCD. This trial was registered at www.ClinicalTrials.gov as #NCT05139992.

Molecular and Serological Studies on Potential SARS-CoV-2 Infection among 43 Lemurs under Human Care-Evidence for Past Infection in at Least One Individual

In the setting of the recent COVID-19 pandemic, transmission of SARS-CoV-2 to animals has been reported in both domestic and wild animals and is a matter of concern. Given the genetic and functional similarities to humans, non-human primates merit particular attention. In the case of lemurs, generally considered endangered, they are believed to be susceptible to SARS-CoV-2 infection. We have conducted a study for evidence of SARS-CoV-2 infection among the 43 lemurs of Mundomar, a zoological park in Benidorm, Spain. They belong to two endangered lemur species, 23 black-and-white ruffed lemurs (Varecia variegata) and 20 ring-tailed lemurs (Lemur catta). Health assessments conducted in 2022 and 2023 included molecular analyses for SARS-CoV-2 RNA of oral and rectal swabs using two different RT-qPCR assays, always with negative results for SARS-CoV-2 in all animals. The assessment also included serological testing for antibodies against the receptor-binding domain (RBD) of the spike protein (S) of SARS-CoV-2, which again yielded negative results in all animals except one black-and-white ruffed lemur, supporting prior infection of that animal with SARS-CoV-2. Our data, while not indicating a high susceptibility of lemurs to SARS-CoV-2 infection, show that they can be infected, adding to the existing information body on potential ways for SARS-CoV-2 virus spreading in zoos, highlighting the need for animal surveillance for the virus.

Infant rhesus macaques immunized against SARS-CoV-2 are protected against heterologous virus challenge 1 year later

The U.S. Food and Drug Administration only gave emergency use authorization of the BNT162b2 and mRNA-1273 SARS-CoV-2 vaccines for infants 6 months and older in June 2022. Yet questions regarding the durability of vaccine efficacy, especially against emerging variants, in this age group remain. We demonstrated previously that a two-dose regimen of stabilized prefusion Washington SARS-CoV-2 S-2P spike (S) protein encoded by mRNA encapsulated in lipid nanoparticles (mRNA-LNP) or purified S-2P mixed with 3M-052, a synthetic Toll-like receptor (TLR) 7/8 agonist, in a squalene emulsion (Protein+3M-052-SE) was safe and immunogenic in infant rhesus macaques. Here, we demonstrate that broadly neutralizing and spike-binding antibodies against variants of concern (VOCs), as well as T cell responses, persisted for 12 months. At 1 year, corresponding to human toddler age, we challenged vaccinated rhesus macaques and age-matched nonvaccinated controls intranasally and intratracheally with a high dose of heterologous SARS-CoV-2 B.1.617.2 (Delta). Seven of eight control rhesus macaques exhibited severe interstitial pneumonia and high virus replication in the upper and lower respiratory tract. In contrast, vaccinated rhesus macaques had faster viral clearance with mild to no pneumonia. Neutralizing and binding antibody responses to the B.1.617.2 variant at the day of challenge correlated with lung pathology and reduced virus replication. Overall, the Protein+3M-052-SE vaccine provided superior protection to the mRNA-LNP vaccine, emphasizing opportunities for optimization of current vaccine platforms. The observed efficacy of both vaccines 1 year after vaccination supports the implementation of an early-life SARS-CoV-2 vaccine.

Long-term durability of immune responses to the BNT162b2 and mRNA-1273 vaccines based on dosage, age and sex

The lipid nanoparticle (LNP)-formulated mRNA vaccines BNT162b2 and mRNA-1273 are a widely adopted multi vaccination public health strategy to manage the COVID-19 pandemic. Clinical trial data has described the immunogenicity of the vaccine, albeit within a limited study time frame. Here, we use a within-host mathematical model for LNP-formulated mRNA vaccines, informed by available clinical trial data from 2020 to September 2021, to project a longer term understanding of immunity as a function of vaccine type, dosage amount, age, and sex. We estimate that two standard doses of either mRNA-1273 or BNT162b2, with dosage times separated by the company-mandated intervals, results in individuals losing more than 99% humoral immunity relative to peak immunity by 8 months following the second dose. We predict that within an 8 month period following dose two (corresponding to the original CDC time-frame for administration of a third dose), there exists a period of time longer than 1 month where an individual has lost more than 99% humoral immunity relative to peak immunity, regardless of which vaccine was administered. We further find that age has a strong influence in maintaining humoral immunity; by 8 months following dose two we predict that individuals aged 18-55 have a four-fold humoral advantage compared to aged 56-70 and 70+ individuals. We find that sex has little effect on the immune response and long-term IgG counts. Finally, we find that humoral immunity generated from two low doses of mRNA-1273 decays at a substantially slower rate relative to peak immunity gained compared to two standard doses of either mRNA-1273 or BNT162b2. Our predictions highlight the importance of the recommended third booster dose in order to maintain elevated levels of antibodies.

Self-collection of capillary blood and saliva to determine COVID-19 vaccine immunogenicity in patients with immune-mediated inflammatory diseases and health professionals

Introduction

Being able to independently determine vaccine induced antibody responses by minimal-invasive methods is of great interest to enable a flexible and effective vaccination strategy. This study aimed to evaluate (1) the accuracy, feasibility, usability and acceptability of capillary blood and saliva self-sampling to determine SARS-CoV-2 antibody responses in patients with immune-mediated inflammatory diseases (IMIDs) and health professionals (HP).

Methods

IMID patients and HP having received two doses of SARS-CoV-2 vaccines, self-collected capillary blood (Tasso+) and saliva samples. Capillary samples were considered interchangeable with venous blood if three criteria were met: Spearman's correlation coefficient (r) > 0.8, non-significant Wilcoxon signed-rank test (i.e., p > 0.05), and a small bias or 95% of tests within 10% difference through Bland-Altman. Participants completed a survey to investigate self-sampling usability (system usability scale; SUS) and acceptability (net promoter score; NPS). Study personnel monitored correct self-sampling completion and recorded protocol deviations.

Results

60 participants (30 IMID patients and 30 HP) were analyzed. We observed interchangeability for capillary samples with an accuracy of 98.3/100% for Anti-SARS-CoV-2 IgG/IgA antibodies, respectively. Fifty-eight capillary blood samples and all 60 saliva samples were successfully collected within the first attempt. Usability of both self-sampling procedures was rated as excellent, with significantly higher saliva ratings (p < 0.001). Capillary self-sampling was perceived as significantly (p < 0.001) less painful compared to traditional venous blood collection. Participants reported a NPS for capillary and saliva self-sampling of +68% and +63%, respectively. The majority of both groups (73%) preferred capillary self-sampling over professional venous blood collection.

Conclusion

Our results indicate that capillary self-sampling is accurate, feasible and preferred over conventional venous blood collection. Implementation could enable easy access, flexible vaccination monitoring, potentially leading to a better protection of vulnerable patient groups. Self-collection of saliva is feasible and safe however more work is needed to determine its application in clinical practice.

Recent advances in point of care testing for COVID-19 detection

The World Health Organizations declaration of the COVID-19 pandemic was a milestone for the scientific community. The high transmission rate and the huge number of deaths, along with the lack of knowledge about the virus and the evolution of the disease, stimulated a relentless search for diagnostic tests, treatments, and vaccines. The main challenges were the differential diagnosis of COVID-19 and the development of specific, rapid, and sensitive tests that could reach all people. RT-PCR remains the gold standard for diagnosing COVID-19. However, new methods, such as other molecular techniques and immunoassays emerged. Also, the need for accessible tests with quick results boosted the development of point of care tests (POCT) that are fast, and automated, with high precision and accuracy. This assay reduces the dependence on laboratory conditions and mass testing of the population, dispersing the pressure regarding screening and detection. This review summarizes the advances in the diagnostic field since the pandemic started, emphasizing various laboratory techniques for detecting COVID-19. We reviewed the main existing diagnostic methods, as well as POCT under development, starting with RT-PCR detection, but also exploring other nucleic acid techniques, such as digital PCR, loop-mediated isothermal amplification-based assay (RT-LAMP), clustered regularly interspaced short palindromic repeats (CRISPR), and next-generation sequencing (NGS), and immunoassay tests, and nanoparticle-based biosensors, developed as portable instruments for the rapid standard diagnosis of COVID-19.

Heterogenous humoral and cellular immune responses with distinct trajectories post-SARS-CoV-2 infection in a population-based cohort

To better understand the development of SARS-CoV-2-specific immunity over time, a detailed evaluation of humoral and cellular responses is required. Here, we characterize anti-Spike (S) IgA and IgG in a representative population-based cohort of 431 SARS-CoV-2-infected individuals up to 217 days after diagnosis, demonstrating that 85% develop and maintain anti-S responses. In a subsample of 64 participants, we further assess anti-Nucleocapsid (N) IgG, neutralizing antibody activity, and T cell responses to Membrane (M), N, and S proteins. In contrast to S-specific antibody responses, anti-N IgG levels decline substantially over time and neutralizing activity toward Delta and Omicron variants is low to non-existent within just weeks of Wildtype SARS-CoV-2 infection. Virus-specific T cells are detectable in most participants, albeit more variable than antibody responses. Cluster analyses of the co-evolution of antibody and T cell responses within individuals identify five distinct trajectories characterized by specific immune patterns and clinical factors. These findings demonstrate the relevant heterogeneity in humoral and cellular immunity to SARS-CoV-2 while also identifying consistent patterns where antibody and T cell responses may work in a compensatory manner to provide protection.

The persistence of the immune response to SARS-CoV-2 after recovery from infection is an indicator for subsequent protection against infection. Here the authors follow recovered patients and measure antibody and T cell responses and find that these two parts of the immune response may have different longevity.

Analysis of 52 240 source plasma donors of convalescent COVID-19 plasma: Sex, ethnicity, and age association with initial antibody levels and rate of dissipation

Background

COVID‐19 convalescent plasma (CCP) was approved under emergency authorization to treat critically ill patients with COVID‐19 in the United States in 2020. We explored the demographics of donors contributing plasma for a hyperimmune, plasma‐derived therapy to evaluate factors that may be associated with anti‐SARS‐CoV‐2 antibody response variability and, subsequently, antibody titers.

Study Design

An electronic search of CCP donors was performed across 282 US plasma donation centers. Donations were screened for nucleocapsid protein‐binding‐IgG using the Abbott SARS‐CoV‐2 IgG assay.

Results

Overall, 52 240 donors donated 418 046 units of CCP. Donors were of various ethnicities: 43% Caucasian, 34% Hispanic, 17% African American, 2% Native American, 1% Asian, and 3% other. Females had higher initial mean anti‐SARS‐CoV‐2 antibody titers but an overall faster rate of decline (P < .0001). Initial antibody titers increased with age: individuals aged 55 to 66 years had elevated anti‐SARS‐CoV‐2 titers for longer periods compared with other ages (P = .0004). African American donors had the lowest initial antibody titers but a slower rate of decline (P < .0001), while Caucasian (P = .0088) and Hispanic (P = .0193) groups had the fastest rates of decline. Most donor antibody levels decreased below the inclusion criteria (≥1.50) within 30 to 100 days of first donation, but donation frequency did not appear to be associated with rate of decline.

Conclusion

Several factors may be associated with anti‐SARS‐CoV‐2 antibody response including donor age and sex. Evaluating these factors during development of future hyperimmune globulin products may help generation of therapies with optimal efficacy.

Longitudinal comparison of automated SARS-CoV-2 serology assays in assessing virus neutralization capacity in COVID-19 convalescent sera

CONTEXT.–

Serological tests on automated immunology analyzers are increasingly used to monitor the acquired immunity against SARS-CoV-2. The heterogeneity of assays raises concerns about their diagnostic performance and comparability.

OBJECTIVE.–

To test sera from formerly infected individuals for SARS-Cov-2 antibodies utilizing six automated serology assays and a pseudoneutralization test (PNT).

DESIGN.–

Six SARS-CoV-2 serology assays were utilized to assess 954 samples collected during a 12 months period from 315 COVID-19 convalescents. The tests determined either antibodies against the viral nucleocapsid (anti-NC) or spike protein (anti-S). Two assays did not distinguish between antibody classes whereas the others selectively measured immunoglubulins G (IgG) antibodies. PNT was used to detect the presence of neutralizing antibodies.

RESULTS.–

Comparison of qualitative results showed only slight to moderate concordance between the assays (Cohen's kappa < 0.57). Significant correlations (P < .001) were observed between the antibody titers from all quantitative assays. However, titer changes were not detected equally. A total anti-S assay measured an increase in 128 out of 172 cases (74%) of a suitable subset, whereas all IgG anti-S tests reported decreases in at least 118 (69%). Regarding the PNT results, diagnostic sensitivities ≥89% were achieved with PPVs ≥93%. In contrast, specificity changed substantially over time varying from 20 to 100%.

CONCLUSIONS.–

Comparability of serological SARS-CoV-2 antibody tests is rather poor. Due to different diagnostic specificities, the tested assays were not equally capable of capturing changes in antibody titers. However, with thoroughly validated cut-offs, IgG-selective anti-S assays are a reliable surrogate test for SARS-CoV-2 neutralizing antibodies in former COVID-19 patients.

Modelling the concentration of anti-SARS-CoV-2 immunoglobulin G in intravenous immunoglobulin product batches

Background

Plasma-derived intravenous immunoglobulin (IVIg) products contain a dynamic spectrum of immunoglobulin (Ig) G reactivities reflective of the donor population from which they are derived. We sought to model the concentration of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG which could be expected in future plasma pool and final-product batches of CSL Behring’s immunoglobulin product Privigen.

Study design and methods

Data was extracted from accessible databases, including the incidence of coronavirus disease 2019 and SARS-CoV-2 vaccination status, antibody titre in convalescent and vaccinated groups and antibody half-life. Together, these parameters were used to create an integrated mathematical model that could be used to predict anti-SARS-CoV-2 antibody levels in future IVIg preparations.

Results

We predict that anti-SARS-CoV-2 IgG concentration will peak in batches produced in mid-October 2021, containing levels in the vicinity of 190-fold that of the mean convalescent (unvaccinated) plasma concentration. An elevated concentration (approximately 35-fold convalescent plasma) is anticipated to be retained in batches produced well into 2022. Measurement of several Privigen batches using the Phadia^™ EliA^™ SARS-CoV-2-Sp1 IgG binding assay confirmed the early phase of this model.

Conclusion

The work presented in this paper may have important implications for physicians and patients who use Privigen for indicated diseases.