Minimal Determinants for Lifelong Antiviral Antibody Responses in Mice from a Single Exposure to Virus-like Immunogens at Low Doses

The durability of an antibody (Ab) response is highly important for antiviral vaccines. However, due to the complex compositions of natural virions, the molecular determinants of Ab durability from viral infection or inactivated viral vaccines have been incompletely understood. Here we used a reductionist system of liposome-based virus-like structures to examine the durability of Abs from primary immune responses in mice. This system allowed us to independently vary fundamental viral attributes and to do so without additional adjuvants to model natural viruses. We show that a single injection of protein antigens (Ags) orderly displayed on a virion-sized liposome is sufficient to induce a long-lived neutralizing Ab (nAb) response. The introduction of internal nucleic acids dramatically modulates the magnitude of Ab responses without an alteration of the long-term kinetic trends. These Abs are characterized by very slow off-rates of ~0.0005 s-1, which emerged as early as day 5 after injection and these off-rates are comparable to that of affinity-matured monoclonal Abs. A single injection of these structures at doses as low as 100 ng led to lifelong nAb production in mice. Thus, a minimal virus-like immunogen can give rise to potent and long-lasting antiviral Abs in a primary response in mice without live infection. This has important implications for understanding both live viral infection and for optimizing vaccine design.

Hybrid immunity and SARS-CoV-2 antibodies: results of the HEROES-RECOVER prospective cohort study

BACKGROUND

There are limited data on whether hybrid immunity differs by count and order of immunity-conferring events (SARS-CoV-2 infection or COVID-19 vaccination). From a cohort of health care personnel, first responders, and other frontline workers in six US states, we examined heterogeneity of the effect of hybrid immunity on SARS-CoV-2 antibody levels.

METHODS

Exposures included event-count (sum of infections and vaccine doses) and event-order, categorized into seven permutations of vaccination and/or infection. Outcome was level of serum binding antibodies against receptor binding domain (RBD) of the ancestral SARS-CoV-2 spike protein (total RBD-binding Ig), measured by enzyme-linked immunosorbent assay. Mean antibody levels were examined up to 365 days after each of the 1st-7th events.

RESULTS

Analysis included 5,793 participants measured from August 7, 2020 to April 15, 2023. Hybrid immunity from infection before one or two vaccine doses elicited modestly superior antibody responses after the 2nd and 3rd events (compared to infections or vaccine-doses alone). This superiority was not evident after the 4th and 5th events (additional doses). Among adults infected before vaccination, adjusted geometric mean ratios (95% CI) of anti-RBD early response (versus vaccinated-only) were 1.23 (1.14-1.33), 1.09 (1.03-1.14), 0.87 (0.81-0.94), and 0.99 (0.85-1.15) after the 2nd-5th events, respectively. Post-vaccination infections elicited superior responses: adjusted geometric mean ratios (95% CI) of anti-RBD early response (versus vaccinated-only) were: 0.93 (0.75-1.17), 1.11 (1.06-1.16), 1.17 (1.11-1.24), and 1.20 (1.07-1.34) after the 2nd-5th events, respectively.

CONCLUSIONS AND RELEVANCE

Findings reflecting heterogeneity in antibody levels by permutations of infection and vaccination history could inform COVID-19 vaccination policy.

The 6-Month Antibody Durability of Heterologous Convidecia Plus CoronaVac and Homologous CoronaVac Immunizations in People Aged 18-59 Years and over 60 Years Based on Two Randomized Controlled Trials in China

Previous reports have shown that heterologous boosting with the AD5-vectored COVID-19 vaccine Convidecia based on a primary series of two doses of inactivated vaccine induces increasing immune responses. However, the immune persistence until 6 months after the heterologous prime-boost immunization was limited. Participants were from two single-center, randomized, controlled, observer-blinded trials, which involved individuals of 18-59 years of age and over 60 years of age. Eligible participants who previously primed with one dose or two doses of CoronaVac were stratified and randomly assigned to inoculate a booster dose of Convidecia or CoronaVac. Neutralizing antibodies against a live SARS-CoV-2 prototype virus and Delta and Omicron (B.1.1.529) variants, pseudovirus neutralizing antibodies against Omicron BA.4/5 variants, and anti-SARS-CoV-2 RBD antibodies at month 6 were detected, and the fold decreases and rate difference were calculated by comparing the levels of antibodies at month 6 with the peak levels at month 1. The neutralizing antibody titers against prototype SARS-CoV-2, RBD-specific IgG antibodies, and the Delta variant in the heterologous regimen of the CoronaVac plus Convidecia groups were significantly higher than those of the homologous prime-boost groups. In three-dose regimen groups, the geometric mean titers (GMTs) of neutralizing antibodies against prototype SARS-CoV-2 were 30.6 (95% CI: 25.1; 37.2) in the heterologous boosting group versus 6.9 (95% CI: 5.6; 8.6) in the homologous boosting group (p < 0.001) at month 6 in participants aged 18-59 years, and in the two-dose regimen, the neutralizing antibody GMTs were 8.5 (95% CI: 6.2; 11.7) and 2.7 (2.3 to 3.1) (heterologous regimen group versus CoronaVac regimen group, p < 0.001). Participants aged over 60 years had similar levels of neutralizing antibodies against the prototype, with GMTs of 49.1 (38.0 to 63.6) in the group receiving two doses of CoronaVac plus one dose of Convidecia versus 9.4 (7.7 to 11.4) in the group receiving three doses of CoronaVac (p < 0.001) and 11.6 (8.4 to 16.0) in the group receiving one dose of CoronaVac and one dose of Convidecia versus 3.3 (2.7 to 4.0) in the group receiving two doses of CoronaVac (p < 0.001). Compared with day 14, over sixfold decreases in neutralizing antibody GMTs were observed in the heterologous groups of the three- or two-dose regimen groups of younger and elderly participants, while in the homologous regimen groups, the GMTs of neutralizing antibodies decreased about fivefold in the two age groups. The heterologous prime-boost regimen with two doses of CoronaVac and one dose of Convidecia was persistently more immunogenic than the regimen of the homologous prime-boost with three doses of CoronaVac.

Natural killer cells and BNT162b2 mRNA vaccine reactogenicity and durability

Introduction

Natural killer (NK) cells can both amplify and regulate immune responses to vaccination. Studies in humans and animals have observed NK cell activation within days after mRNA vaccination. In this study, we sought to determine if baseline NK cell frequencies, phenotype, or function correlate with antibody responses or inflammatory side effects induced by the Pfizer-BioNTech COVID-19 vaccine (BNT162b2).

Methods

We analyzed serum and peripheral blood mononuclear cells (PBMCs) from 188 participants in the Prospective Assessment of SARS-CoV-2 Seroconversion study, an observational study evaluating immune responses in healthcare workers. Baseline serum samples and PBMCs were collected from all participants prior to any SARS-CoV-2 infection or vaccination. Spike-specific IgG antibodies were quantified at one and six months post-vaccination by microsphere-based multiplex immunoassay. NK cell frequencies and phenotypes were assessed on pre-vaccination PBMCs from all participants by multi-color flow cytometry, and on a subset of participants at time points after the 1st and 2nd doses of BNT162b2. Inflammatory side effects were assessed by structured symptom questionnaires, and baseline NK cell functionality was quantified by an in vitro killing assay on participants that reported high or low post-vaccination symptom scores.

Results

Key observations include: 1) circulating NK cells exhibit evidence of activation in the week following vaccination, 2) individuals with high symptom scores after 1st vaccination had higher pre-vaccination NK cytotoxicity indices, 3) high pre-vaccination NK cell numbers were associated with lower spike-specific IgG levels six months after two BNT162b2 doses, and 4) expression of the inhibitory marker NKG2A on immature NK cells was associated with higher antibody responses 1 and 6 months post-vaccination.

Discussion

These results suggest that NK cell activation by BNT162b2 vaccination may contribute to vaccine-induced inflammatory symptoms and reduce durability of vaccine-induced antibody responses.

A 1-year longitudinal study on COVID-19 convalescents reveals persistence of anti-SARS-CoV-2 humoral and cellular immunity

The immune memory of over 400 million COVID-19 convalescents is not completely understood. In this integrated study, we recorded the post-acute sequelae symptoms and tested the immune memories, including circulating antibodies, memory B cell, and memory CD4 or CD8 T cell responses of a cohort of 65 COVID-19 patients over 1-year after infection. Our data show that 48% of them still have one or more sequelae symptoms and all of them maintain at least one of the immune components. The chances of having sequelae symptoms or having better immune memory are associated with peak disease severity. We did four-time points sampling per subject to precisely understand the kinetics of durability of SARS-CoV-2 circulating antibodies. We found that the RBD IgG levels likely reach a stable plateau at around 6 months, albeit it is waning at the first 6 months after infection. At 1-year after infection, more than 90% of the convalescents generated memory CD4 or CD8 T memory responses, preferably against the SARS-CoV-2 M peptide pool. The convalescents also have polyfunctional and central memory T cells that could provide rapid and efficient response to SARS-CoV-2 re-infection. Based on this information, we assessed the immune protection against the Omicron variant and concluded that convalescents should still induce effective T cell immunity against the Omicron. By studying the circulating antibodies and memory B or T cell responses to SARS-CoV-2 in an integrated manner, our study provides insight into the understanding of protective immunity against diseases caused by secondary SARS-CoV-2 infection.

SARS-CoV-2 Spike-Binding Antibody Longevity and Protection from Reinfection with Antigenically Similar SARS-CoV-2 Variants

The PARIS (Protection Associated with Rapid Immunity to SARS-CoV-2) cohort follows health care workers with and without documented coronavirus disease 2019 (COVID-19) since April 2020. We report our findings regarding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike-binding antibody stability and protection from infection in the pre-variant era. We analyzed data from 400 health care workers (150 seropositive and 250 seronegative at enrollment) for a median of 84 days. The SARS-CoV-2 spike-binding antibody titers were highly variable with antibody levels decreasing over the first 3 months, followed by a relative stabilization. We found that both more advanced age (>40 years) and female sex were associated with higher antibody levels (1.6-fold and 1.4-fold increases, respectively). Only six percent of the initially seropositive participants “seroreverted.” We documented a total of 11 new SARS-CoV-2 infections (10 naive participants and 1 previously infected participant without detectable antibodies; P < 0.01), indicating that spike antibodies limit the risk of reinfection. These observations, however, only apply to SARS-CoV-2 variants antigenically similar to the ancestral SARS-CoV-2 ones. In conclusion, SARS-CoV-2 antibody titers mounted upon infection are stable over several months and provide protection from infection with antigenically similar viruses.

Pre-existing SARS-CoV-2 immunity influences potency, breadth, and durability of the humoral response to SARS-CoV-2 vaccination

The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic highlights the importance of determining the breadth and durability of humoral immunity to SARS-CoV-2 mRNA vaccination. Herein, we characterize the humoral response in 27 naive and 40 recovered vaccinees. SARS-CoV-2-specific antibody and memory B cell (MBC) responses are durable up to 6 months, although antibody half-lives are shorter for naive recipients. The magnitude of the humoral responses to vaccination strongly correlates with responses to initial SARS-CoV-2 infection. Neutralization titers are lower against SARS-CoV-2 variants in both recovered and naive vaccinees, with titers more reduced in naive recipients. While the receptor-binding domain (RBD) is the main neutralizing target of circulating antibodies, Moderna-vaccinated naives show a lesser reliance on RBDs, with >25% neutralization remaining after depletion of RBD-binding antibodies. Overall, we observe that vaccination induces higher peak titers and improves durability in recovered compared with naive vaccinees. These findings have broad implications for current vaccine strategies deployed against the SARS-CoV-2 pandemic.

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Single vaccine dose effectively boosts B cell responses in recovered subjects

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SARS-CoV-2-specific MBCs remain activated and increase over time in naive subjects

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Antibody response to vaccination is broader and more durable in recovered versus naive subjects

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Naive vaccinees have higher proportion of non-RBD-specific neutralizing antibodies

Safety of Multiple Vaccinations and Durability of Vaccine-Induced Antibodies in an Italian Military Cohort 5 Years after Immunization

We previously examined the safety and immunogenicity of multiple vaccines administered to a military cohort, divided into two groups, the first composed of students at military schools, thus operating inside the national borders for at least 3 years, and the other formed of soldiers periodically engaged in a 9-month-long mission abroad (Lebanon). In the current study, we analyzed 112 individuals of this cohort, 50 pertaining to the first group and 62 to the second group, in order to examine the possible late appearance of side effects and to calculate the half-life of the induced antibodies. Moreover, the possible involvement of B-cell polyclonal activation as a pathogenetic mechanism for long term antibody persistence has even been explored. No late side effects, as far as autoimmunity and/or lymphoproliferation appearance, have been noticed. The long duration of the vaccine induced anti-HAV antibodies has been confirmed, whereas the antibodies induced by tetravalent meningococcal polysaccharide vaccine have been found to persist above the threshold for putative protection for a longer time, and anti-tetanus, diphtheria, and polio 1 and 3 for a shorter time than previously estimated. No signs of polyclonal B-cell activation have been found, as a possible mechanism to understand the long antibody persistence.