NAb Titers Research Articles

Characterization of anti-AAV2 neutralizing antibody levels in sheep prior to and following intravitreal AAV2.7m8 injection

AbstractGene augmentation therapy is a promising treatment for incurable, blinding inherited retinal diseases, and intravitreal delivery is being studied as a safe alternative to subretinal injections. Adeno-Associated Viruses (AAV) are commonly-used vectors for ocular gene augmentation therapy. Naturally occurring pre-operative exposure and infection with AAV could result in presence of neutralizing antibodies (NAB’s) in patients’ serum, and may affect the safety and efficacy of treatment. Our aim was to characterize the humoral response against AAV pre- and post-intravitreal delivery of AAV2.7m8 vectors in a naturally-occurring sheep model of CNGA3 achromatopsia. Serial serum neutralization assays were performed to screen sheep for pre-exiting anti-AAV2 NAB’s, and to assess the effect of intravitreal AAV2.7m8 injection on post-operative NAB titers and intraocular inflammation in sheep. The effect of viral dose and transgene type were also assessed. Serological screening revealed pre-operative seropositivity in 21.4% of animals, with age being a risk factor for the presence of anti-AAV2 NAB’s. NAB titers increased following intravitreal AAV administration in the majority of sheep. There was no significant difference in the degree of post-operative serum neutralization between pre-operatively seronegative sheep and those with pre-existing antibodies. However, only sheep with pre-existing antibodies presented with signs of post-operative inflammation. We conclude that pre-existing anti-AAV2 NAB’s do not affect the level of post-operative NAB titers; however, they increase the risk of post-operative ocular inflammation. Our results could have implications for the management of AAV-mediated ocular gene therapies, a technology being increasingly studied and used in patients.

Long term T cell response and safety of a tetravalent dengue vaccine in healthy children

As robust cellular responses are important for protection against dengue, this phase 2 study evaluated the kinetics and phenotype of T cell responses induced by TAK-003, a live-attenuated tetravalent dengue vaccine, in 4–16-year-old living in dengue-endemic countries (NCT02948829). Two hundred participants received TAK-003 on Days 1 and 90. Interferon-gamma (IFN-γ) enzyme-linked immunospot assay [ELISPOT] and intracellular cytokine staining were used to analyze T cell response and functionality, using peptide pools representing non-structural (NS) proteins NS3 and NS5 matching DENV-1, -2, -3, and -4 and DENV-2 NS1. One month after the second TAK-003 dose (Day 120), IFN-γ ELISPOT T cell response rates against any peptide pool were 97.1% (95% CI: 93.4% to 99.1%), and similar for baseline dengue seropositive (96.0%) and seronegative (98.6%) participants. IFN-γ ELISPOT T cell response rates at Day 120 were 79.8%, 90.2%, 77.3%, and 74.0%, against DENV-1, -2, -3, and -4, respectively, and remained elevated through 3 years post-vaccination. Multifunctional CD4 and CD8 T cell responses against DENV-2 NS peptides were observed, independent of baseline serostatus: CD8 T cells typically secreted IFN-γ and TNF-α whereas CD4 T cells secreted ≥ 2 of IFN-γ, IL-2 and TNF-α cytokines. NAb titers and seropositivity rates remained substantially elevated through 3 years post-vaccination. Overall, TAK-003 was well tolerated and elicited durable T cell responses against all four DENV serotypes irrespective of baseline serostatus in children and adolescents aged 4–16 years living in dengue-endemic countries. TAK-003-elicited CD4 and CD8 T cells were multifunctional and persisted up to 3 years post-vaccination.

Spike and nucleocapsid antibody dynamics following SARS-CoV-2 infection and vaccination: Implications for sourcing COVID-19 convalescent plasma from routinely collected blood donations.

COVID-19 convalescent plasma (CCP) remains a treatment option for immunocompromised patients; however, the current FDA qualification threshold of ≥200 BAU/mL of spike antibody appears to be relatively low. We evaluated the levels of binding (bAb) and neutralizing antibodies (nAb) on serial samples from repeat blood donors who were vaccinated and/or infected to inform criteria for qualifying CCP from routinely collected plasma components. Donors were categorized into four groups: (1) infected, then vaccinated, (2) vaccinated then infected during the delta, or (3) omicron waves, (4) vaccinated without infection. IgG Spike and total Nuclecapsid bAb were measured, along with S variants and nAb titers using reporter viral particle neutralization. Mean S IgG bAb peaks after infection alone were lower than after primary and booster vaccinations, and higher after delta and omicron infection in previously vaccinated donors. Half-lives for S IgG ranged from 34 to 66 days after first infection/vaccination events and up to 108 days after second events. The levels of S IgG bAb and nAb were similar across different variants, except for omicron, which were lower. Better correlations of nAb with bAb were observed at higher levels (hybrid immunity) than at the current FDA CCP qualifying threshold. Routine plasma donations from donors with hybrid immunity had high S bAb and potent neutralizing activity for 3-6 months after infection. In donations with high (>4000 BAU/mL) S IgG, >95% had high nAb titers (>500) against ancestral and variant S, regardless of COVID-19 symptoms. These findings provide the basis for test-based criteria for qualifying CCP from routine blood donations.

Ad5-nCoV boosted vaccine and reinfection-induced memory T/B cell responses and humoral immunity to SARS-CoV-2: based on two prospective cohorts

Here, we regularly followed SARS-CoV-2 infected cohorts to investigate the combined effects of neutralizing antibodies (NAbs) and B and T cell profiles during the convalescent period. Ten participants infected with SARS-CoV-2 in December 2022 were selected to assess the effects of an inhaled adenovirus type 5 vectored COVID-19 vaccine (Ad5-nCoV) booster on B cells and humoral immunity. To evaluate T cell responses, eight primary and 20 reinfection participants were included. Blood samples from all 38 participants were collected at 1-, 2-, and 6-months post-infection. The assays included single B cell technology, activation-induced marker (AIM) assays, and pseudovirus neutralization. In the first cohort, eighteen monoclonal antibodies (mAbs) with neutralizing activity from memory B cells (MBC) against SARS-CoV-2 mutants were obtained by high throughput single-B-cell cloning method, which lasted from 1- month to 6- month post infection. The overall number of mAbs from MBC in the inhaled Ad5-nCoV-boosted immunization group was higher than that in the non-boosted immunization group at 2-, and 6-months post-infection. In the second cohort, circulating T follicular helper cells (cTfh) and AIM + CD4 + T cells increased over time in the reinfection group (P < 0.05). The serum NAb levels against XBB.1.22, EG.5.1, and JN.1 in the primary infection group tended to increase from the post 1-month to 2-month infection (P < 0.05). In both cohorts, serum NAb titers showed significant immune escape, while cTfh and AIM + CD4 + T cells in the second cohort essentially showed no immune escape to new strains (including XBB, EG.5) during the six-month follow-up period. AIM + CD4 + T cells against BA.5 and EG.5 were strongly negatively correlated with the time to viral clearance in the reinfected group after months of 6M infection. The broader significance of this study was to comprehensively assess the ability of the SARS-CoV-2 boosted immunization and reinfection-induced generation of T/B cell immune memories in preventing reinfection.

B-043 Q-nab™ Igg kit: verification and validation of a novel cell-free quantitative neutralizing antibody assay

Abstract Background As the world exits the COVID-19 pandemic era, it is very important to assess population-level and individual seroprotectivity against multiple circulating and emerging SARS-CoV-2 strains, especially in vulnerable populations. Current serological measurements for neutralizing antibodies (NAbs) are either done using complex and time-intensive pseudovirus- or micro-neutralization assays or as a high throughput competitive ELISA assay. These assays, by design, cannot be multiplexed to measure NAb titers against multiple strains and suffer from a limited dynamic range. The Q-NAb IgG Tests, which rely on blocking the non-neutralizing antibodies (NNAbs) using a novel fusion protein, were developed and validated to quantitatively measure NAb titer against the SARS-CoV-2 strains used to develop the first two mRNA vaccines viz. ancestral and BA.4/5 strains. Methods The Q-NAb assay measures the NAb titer in a sample by first sequestering the NNAbs using the fusion protein (made by covalently coupling SARS-CoV-2 BA.4/5 RBD and h-ACE2 protein) thereby enriching the NAbs in the sample. Variant-specific NAbs are then detected using an indirect ELISA where the wells are coated with the variant RBD and yield a signal that is directly proportional to the concentration of NAb. Clinical samples from subjects that have either had a SARS-CoV-2 infection (N=27), taken the initial vaccine series (N=123) and/or the bivalent booster (N=151) and pre-pandemic samples (N=29) were commercially sourced. Q-NAb NAb titers were measured using the ancestral and BA.4/5 kits and were compared against corresponding MN50 values using both parametric and non-parametric models. Single-site precision, low-end sensitivity, dilutional linearity, and interference screening of Q-NAb IgG Kits were evaluated in accordance with appropriate CLSI guidelines. Traceability and total uncertainty of the Q-NAb IgG Kits (Ancestral and BA.4/5) to WHO International Standard 21/340 and 21/338 respectively was established using a calibration hierarchy adapted from ISO 17511:2020. Results Both the ancestral and BA.4/5 Q-NAb IgG Test Kits correlated with MN50 titers with a Spearman correlation coefficient of 0.90 and 0.89 respectively. The total uncertainty in traceability of calibration to WHO International standards 21/340 and 21/338 was found to be less than 10% for both tests. Single site precision across the assay range for BA.4/5 kit was found to be 6-10% with a limit of quantitation of 312 IU/mL. Assays exhibited dilutional linearity across their respective dynamic range and had no significant interference from common endogenous and exogenous substances. Conclusions We have successfully validated the novel Q-NAb IgG neutralization assay platform as individual assays for measuring neutralizing titers against ancestral and BA.4/5 SARS-CoV-2 strains. The assays have expanded dynamic range, excellent analytical performance and correlation to accepted gold-standard microneutralization assays. Both assays are calibrated and traceable to WHO international standards, thereby enabling the compilation and comparison of data from multiple clinical cohorts run across multiple laboratories. The design of the Q-NAb IgG Test kit makes it amenable to multiplexing (for example, on an MSD platform) to assess neutralization titers against multiple variants at the same time. Such a multiplexed platform can be used to assess vaccine efficacy and seroprotection against multiple variants including emerging variants.

Immuno-persistence after the fourth and fifth doses of inactivated polio vaccines in school-aged children

ObjectivesThis study aimed to assess the long-term persistence of neutralizing antibodies (nAb) titres and seroprotection proportions after the fourth and fifth doses of inactivated polio vaccine (IPV). MethodsSerum samples from 299 children in Hong Kong were collected and used to estimate the persistence of nAb titres and seroprotection proportions by neutralisation test. ResultsThe mean nAb titres against poliovirus types 1, 2, and 3 (PV1, PV2, and PV3) 1 month after receiving the fourth dose of IPV at 19 months of age were 2068 (95% credible interval, 1517–2864); 4705 (3439–6436); and 2758 (1894–4086); respectively, but declined substantially in 4 years to 268 (222–325), 751 (630–900), and 411 (323–521), respectively. Administration of the fifth dose of IPV restored nAb titres among children aged 6 to 7 years, and the decline in nAb titres was slightly slower with the estimated mean titres of 355 (272–462), 538 (427–681), and 548 (378–786) against PV1, PV2, and PV3 at 4 years post the fifth dose. We estimated that the proportion of children who were seroprotected against PV1, PV2, and PV3 would drop below 90%: (i) 8.2, 10.8, and 8.7 years after the fourth dose; and (ii) 11.6, 11.2, and 11.0 years after the fifth dose. DiscussionThe results revealed the immuno-persistence after the fourth and fifth doses of IPV and highlighted the importance of completing immunization series to ensure high vaccination coverage, particularly among children in the developing countries affected by the COVID-19 pandemic.

Enhancing Omicron Sublineage Neutralization: Insights From Bivalent and Monovalent COVID-19 Booster Vaccines and Recent SARS-CoV-2 Omicron Variant Infections.

Omicron variants have rapidly diversified into sublineages with mutations that enhance immune evasion, posing challenges for vaccination and antibody responses. This study aimed to compare serum cross-neutralizing antibody responses against various SARS-CoV-2 Omicron sublineages (BA.1, BA.5, XBB.1.17.1, FK.1.1, and JN.1) in recipients of monovalent COVID-19 boosters, bivalent booster recipients, and individuals who had recovered from Omicron BA.5 infections. We conducted a micro-neutralization assay on serum samples from monovalent BNT162b2 booster recipients (N = 54), bivalent BNT162b2 booster recipients (N = 24), and SARS-CoV-2 Omicron BA.5-recovered individuals (N = 13). The history of SARS-CoV-2 Omicron infection was assessed using ELISA against the SARS-CoV-2 NP protein. Bivalent booster recipients exhibited significantly enhanced neutralization efficacy against Omicron sublineages compared to those who had received monovalent booster vaccinations. Omicron BA.5-recovered individuals displayed similar neutralizing antibodies (NAbs) to the bivalent booster recipients. Despite the improved neutralization in bivalent recipients and BA.5-recovered individuals, there were limitations in neutralization against the recently emerged Omicron subvariants: XBB.1.17.1 FK.1.1, and JN.1. In both monovalent and bivalent booster recipients, a history of Omicron breakthrough infection was associated with relatively higher geometric mean titers of NAbs against Omicron BA.1, BA.5, and XBB.1.17.1 variants. This study underscores the intricate interplay between vaccination strategies, immune imprinting, and the dynamic landscape of SARS-CoV-2 variants. Although bivalent boosters enhance neutralization, addressing the challenge of emerging sublineages like XBB.1.17.1, FK.1.1, and JN.1 may necessitate the development of tailored vaccines, underscoring the need for ongoing adaptation to effectively combat this highly mutable virus.

Continuous Treatment with IncobotulinumtoxinA Despite Presence of BoNT/A Neutralizing Antibodies: Immunological Hypothesis and a Case Report.

Botulinum Neurotoxin A (BoNT/A) is a bacterial protein that has proven to be a valuable pharmaceutical in therapeutic indications and aesthetic medicine. One major concern is the formation of neutralizing antibodies (nAbs) to the core BoNT/A protein. These can interfere with the therapy, resulting in partial or complete antibody (Ab)-mediated secondary non-response (SNR) or immunoresistance. If titers of nAbs reach a level high enough that all injected BoNT/A molecules are neutralized, immunoresistance occurs. Studies have shown that continuation of treatment of neurology patients who had developed Ab-mediated partial SNR against complexing protein-containing (CPC-) BoNT/A was in some cases successful if patients were switched to complexing protein-free (CPF-) incobotulinumtoxinA (INCO). This seems to contradict the layperson's basic immunological understanding that repeated injection with the same antigen BoNT/A should lead to an increase in antigen-specific antibody titers. As such, we strive to explain how immunological memory works in general, and based on this, we propose a working hypothesis for this paradoxical phenomenon observed in some, but not all, neurology patients with immunoresistance. A critical factor is the presence of potentially immune-stimulatory components in CPC-BoNT/A products that can act as immunologic adjuvants and activate not only naïve, but also memory B lymphocyte responses. Furthermore, we propose that continuous injection of a BoN/TA formulation with low immunogenicity, e.g., INCO, may be a viable option for aesthetic patients with existing nAbs. These concepts are supported by a real-world case example of a patient with immunoresistance whose nAb levels declined with corresponding resumption of clinical response despite regular INCO injections.

Immunogenicity and Safety of Omicron-Containing Multivalent COVID-19 Vaccines in Unvaccinated and Previously Vaccinated Adults.

The SARS-CoV-2 evolution trajectory remains uncertain, and the antigenic characteristics of future variants are highly unpredictable. We report the immunogenicity and safety of multivalent COVID-19 vaccines, SCTV01E and SCTV01E-1, against Omicron BA.5. This phase 2 trial randomized 400 adults into two cohorts, 160 unvaccinated (3 doses) and 240 previously vaccinated (2 doses) individuals to receive 30 µg SCTV01E-1 or 30 µg SCTV01E (1:1) between 4 November and 28 November 2022. Among the unvaccinated cohort, day 42 geometric mean fold rises (GMFRs) of neutralizing antibodies (nAb) against Omicron BA.5 were reported to be 12.8× and 20.5× over day 0 for SCTV01E-1 and SCTV01E, respectively. On day 178, both vaccines increased geometric mean titers (GMTs) of nAb against BA.5 following the booster dose compared to pre-booster levels on D150. Similar frequencies of solicited [6.2% (5/81) and 7.6% (6/79)] and unsolicited [11.1% (9/81) and 10.1% (8/79)] adverse events (AEs) were reported in SCTV01E-1 and SCTV01E groups, respectively. Grade 3 or more AEs were < 2% in both vaccine groups [SCTV01E-1: 1.2% (1/81), SCTV01E: 1.3% (1/79)]. In the previously vaccinated cohort, similar GMFRs were reported on day 28 (SCTV01E-1: 9.4× and SCTV01E: 8.7×) over baseline (D0). On day 148, both vaccines showed increased nAb levels with similar GMFRs over D120. Comparable incidences of solicited [13.2% (16/121) and 10.9% (13/119)] and unsolicited [17.4% (21/121) and 10.9% (13/119)] AEs were reported in SCTV01E-1 and SCTV01E groups, respectively. Numerically identical ≥ grade 3 AEs [SCTV01E-1: 1.7% (2/121) and SCTV01E: 1.7% (2/119)] were reported. This trial demonstrates the effectiveness of updated multivalent vaccines with acceptable safety profiles.

Assessment of twelve echovirus virus-neutralisation assays in Europe: recommendations for harmonisation of non-polio enterovirus sero-surveillance studies

Non-polio enteroviruses (NPEV) cause significant disease worldwide. Population-based sero-surveillance, by measuring antibodies against specific NPEV types, provides additional information on past circulation and the prediction for future upsurges. Virus neutralisation assays (VNA), the current method of choice for measuring NPEV type specific antibodies, are not entirely standardised. Via the European Non-Polio Enterovirus Network, we organised a VNA quality assessment in which twelve laboratories participated. We provided five echovirus (E) types (E1, E18, E30 G2, E30 G6 and E6) and intravenous immunoglobulins (IVIG) as a sample for the NPEV VNA quality assessment. Differences in VNA protocols and neutralising Ab (nAb) titres were found between the participating laboratories with geometric coefficients of variation ranging from 10.3–62.9 %. Mixed-effects regression analysis indicated a small but significant effect of type of cell line used. Harmonisation of cell line passage number, however, did not improve variation between laboratories. Calibration by making use of a reference sample, reduced variation between laboratories but differences in nAb titres remained higher than two log2 dilution steps. In conclusion, sero-surveillance data from different laboratories should be compared with caution and standardised protocols are needed.

Antibody Persistence and Risk of COVID-19 Infection: Insights from Modeling.

In this post hoc exploratory study of the APHP-COVIBOOST trial (NCT05124171), we used statistical modeling to describe the evolution of neutralizing antibody (nAb) titers over time, asses its impact on SARS-CoV-2 infection, and explore potential differences between three booster vaccine formulations (D614, B.1.351, and BNT162b2). Antibody titers were measured for 208 adult participants at day 28, 3 months, and 6 months using a microneutralization assay against different Omicron subvariants. We developed four specific Bayesian statistical models based on a core model, accounting for vaccine-specific antibody decline, boosting of nAb for breakthrough infection, and risk of infection according to nAb levels. The model findings were cross-verified using another validated microneutralization assay. The decrease in nAb titers was significantly lower for the B.1.351 vaccine than for the other booster formulations. An inverse relationship was found between risk of infection upon exposure and nAb levels. With Omicron BA.1 data, these results translated into a positive relative vaccine efficacy against any infection over 6 months for the B.1.351 vaccine compared to the BNT162b2 (31%) and D614 (21%) vaccines. Risk of infection decreased with increasing nAb titers for all vaccines. Statistical models predicted significantly better antibody persistence for the B.1.351 booster formulation compared to the other evaluated vaccines.

Immune Response after Vaccination against Tick-Borne Encephalitis Virus (TBEV) in Horses.

(1) Background: Horses infected by a tick-borne encephalitis virus (TBEV) can develop clinically apparent infections. In humans, vaccination is the most effective preventive measure, while a vaccine is not available for horses. The objective of this study was to describe the immune response in horses after a TBEV vaccination with a human vaccine. (2) Materials and Methods: Seven healthy horses were randomised to a treatment or a control group in a stratified fashion based on TBEV-IgG concentrations on day -4. The treatment group (n = 4) was intramuscularly vaccinated using an inactivated human TBEV vaccine on days 0 and 28; the control group (n = 3) did not receive an injection. A clinical examination and blood sampling were performed on day -4, 0, 2, 4, 6, 8, 10, 14, 28, 30, 32, 34, 36, 38, 43, 56, 84, and 373. A linear mixed model analysis was used to compare IgG and IgM concentrations, neutralising antibody (nAb) titres, leucocyte count, serum amyloid A (SAA), and fibrinogen and globulin concentrations between the groups and time points. (3) Results: The clinical examination was normal in all horses at all time points. There were no significant changes in SAA, globulin, and fibrinogen concentrations and leucocyte count between the groups or time points (all p > 0.05). There was no significant increase in IgG, IgM, or nAb titres in the control group over time (all p > 0.05). In the vaccination group, there was a significant increase in IgG concentration and nAb titres after the second vaccination (p < 0.0001). There was no significant increase in IgM antibodies after the TBEV vaccination (all p > 0.05). One horse in the vaccination group had an IgM concentration above the laboratory reference on day 10. (4) Conclusions: The human TBEV vaccine did not have side effects when used in healthy horses in this study. A significant rise in TBEV-specific IgG antibodies and nAbs after the second vaccination was observed. However, IgG and nAb titres have been shown to decrease within 1 year after vaccination. The results of this study indicate that a vaccination with a human vaccine only induces a mild rise in IgM antibodies and only in previously naive horses. With no significant changes to inflammatory parameters in the vaccinated horses, it remains unclear whether vaccination with the human vaccine leads to protective immunity.

Evaluation of Vaccine Strategies among Healthcare Workers during COVID-19 Omicron Outbreak in Taiwan.

This study aimed to assess the reactogenicity and immunogenicity of various SARS-CoV-2 vaccines and compare their protective effects against COVID-19 among healthcare workers (HCWs) during the Omicron outbreak in Taiwan. Conducted from March 2021 to July 2023, this prospective observational study included healthy HCWs without prior COVID-19 immunization. Participants chose between adenovirus-vectored (AstraZeneca), mRNA (Moderna, BioNTech-Pfizer), and protein-based (Medigen, Novavax) vaccines. Blood samples were taken at multiple points to measure neutralizing antibody (nAb) titers, and adverse events (AEs) were recorded via questionnaires. Of 710 HCWs, 668 (94.1%) completed three doses, and 290 (40.8%) received a fourth dose during the Omicron outbreak. AEs were more common with AstraZeneca and Moderna vaccines, while Medigen caused fewer AEs. Initial nAb titers were highest with Moderna but waned over time regardless of the vaccine. Booster doses significantly increased nAb titers, with the highest levels observed in Moderna BA1 recipients. The fourth dose significantly reduced COVID-19 incidence, with Moderna BA1 being the most effective. Regular booster doses, especially with mRNA and adjuvant-protein vaccines, effectively enhance nAb levels and reduce infection rates, providing critical protection for frontline HCWs during variant outbreaks.

Omicron COVID-19 immune correlates analysis of a third dose of mRNA-1273 in the COVE trial

In the phase 3 Coronavirus Efficacy (COVE) trial (NCT04470427), post-dose two Ancestral Spike-specific binding (bAb) and neutralizing (nAb) antibodies were shown to be correlates of risk (CoR) and of protection against Ancestral-lineage COVID-19 in SARS-CoV-2 naive participants. In the SARS-CoV-2 Omicron era, Omicron subvariants with varying degrees of immune escape now dominate, seropositivity rates are high, and booster doses are administered, raising questions on whether and how these developments affect the bAb and nAb correlates. To address these questions, we assess post-boost BA.1 Spike-specific bAbs and nAbs as CoRs and as correlates of booster efficacy in COVE. For naive individuals, bAbs and nAbs inversely correlate with Omicron COVID-19: hazard ratios (HR) per 10-fold marker increase (95% confidence interval) are 0.16 (0.03, 0.79) and 0.31 (0.10, 0.96), respectively. In non-naive individuals the analogous results are similar: 0.15 (0.04, 0.63) and 0.28 (0.07, 1.08). For naive individuals, three vs two-dose booster efficacy correlates with predicted nAb titer at exposure, with estimates -8% (-126%, 48%), 50% (25%, 67%), and 74% (49%, 87%), at 56, 251, and 891 Arbitrary Units/ml. These results support the continued use of antibody as a surrogate endpoint.

CoronaVac-vaccinated kidney transplant recipients with hybrid immunity have strong neutralizing responses against Omicron and Mu variants of SARS-CoV-2.

Neutralizing antibody (nAb) responses against SARS-CoV-2 variants after inactivated virus vaccine (CoronaVac) in kidney transplant recipients (KTRs) with or without SARS-CoV-2 infection history remains unclear. We aimed to evaluate the neutralizing antibody responses against emerging SARS-CoV-2 variants after two doses of CoronaVac in these patients. 22.2% of participants had hybrid immunity. Anti-spike IgG antibodies were evidenced in 44% of the patients. nAbs against B.1.111, Mu, and Omicron were detected in 28.5%, 17.9%, and 21.4% of naïve KTRs, respectively. Furthermore, nearly 100% of KTRs with hybrid immunity had nAbs against the variants evaluated. Thus, a significant proportion of infection-naïve KTRs had no detectable nAb titers against Mu and Omicron variants after two doses of the CoronaVac vaccine. However, the nAb titers were significantly higher in patients with hybrid immunity, and it was no association between the immunosuppressive regimen and the seropositivity rate of anti-SARS-CoV-2 neutralizing antibodies. Therefore, hybrid KTRs are protected against COVID-19 by emerging variants able to escape from vaccine-elicited nAbs such as Mu and Omicron.

Safety and immunogenicity of an mRNA-based RSV vaccine in Japanese older adults aged ≥60 years: A phase 1, randomized, observer-blind, placebo-controlled trial

BackgroundRespiratory syncytial virus (RSV) represents a global health concern, including in older adults. This study assessed the safety and immunogenicity of mRNA-1345, an investigational mRNA RSV vaccine, in adults aged ≥60 years of Japanese descent. MethodsIn this phase 1, randomized, observer-blind, placebo-controlled study, participants were randomized to receive one injection of mRNA-1345 100 μg or placebo. Solicited local and systemic adverse reactions (ARs) were collected within 7 days following injection. Unsolicited adverse events (AEs) were collected up to 28 days after injection; AEs of special interest, medically attended AEs, and serious AEs were collected through end of study. Immunogenicity was assessed at baseline and months 1, 2, 3, and 6 following injection. ResultsTwenty-five adults of Japanese descent aged ≥60 years received one injection of mRNA-1345 100 μg (n = 21) or placebo (n = 4). mRNA-1345 was well-tolerated; the most common local and systemic solicited ARs were injection site pain, and fatigue and myalgia, respectively, which were generally mild to moderate and transient. No serious AEs were reported. Neutralizing (nAb) and binding (bAb) antibodies were detectable at baseline, consistent with prior RSV exposure. mRNA-1345 boosted RSV nAb titers and preF bAb concentrations 1 month post-injection (geometric mean fold rise: RSV-A nAb, 11.2; RSV-B nAb, 6.6; preF bAb, 9.1). Titers among mRNA-1345 recipients remained above baseline through 6 months. ConclusionsmRNA-1345 100 μg was well-tolerated among older adults of Japanese descent and induced nAbs and bAbs which were durable through 6 months, supporting its continued development. Trial registrationClinicalTrials.gov, NCT04528719.

Neutralization and Stability of JN.1-derived LB.1, KP.2.3, KP.3 and KP.3.1.1 Subvariants.

During the summer of 2024, COVID-19 cases surged globally, driven by variants derived from JN.1 subvariants of SARS-CoV-2 that feature new mutations, particularly in the N-terminal domain (NTD) of the spike protein. In this study, we report on the neutralizing antibody (nAb) escape, infectivity, fusion, and stability of these subvariants-LB.1, KP.2.3, KP.3, and KP.3.1.1. Our findings demonstrate that all of these subvariants are highly evasive of nAbs elicited by the bivalent mRNA vaccine, the XBB.1.5 monovalent mumps virus-based vaccine, or from infections during the BA.2.86/JN.1 wave. This reduction in nAb titers is primarily driven by a single serine deletion (DelS31) in the NTD of the spike, leading to a distinct antigenic profile compared to the parental JN.1 and other variants. We also found that the DelS31 mutation decreases pseudovirus infectivity in CaLu-3 cells, which correlates with impaired cell-cell fusion. Additionally, the spike protein of DelS31 variants appears more conformationally stable, as indicated by reduced S1 shedding both with and without stimulation by soluble ACE2, and increased resistance to elevated temperatures. Molecular modeling suggests that the DelS31 mutation induces a conformational change that stabilizes the NTD and strengthens the NTD-Receptor-Binding Domain (RBD) interaction, thus favoring the down conformation of RBD and reducing accessibility to both the ACE2 receptor and certain nAbs. Additionally, the DelS31 mutation introduces an N-linked glycan modification at N30, which shields the underlying NTD region from antibody recognition. Our data highlight the critical role of NTD mutations in the spike protein for nAb evasion, stability, and viral infectivity, and suggest consideration of updating COVID-19 vaccines with antigens containing DelS31.

Assessment of Anti-spike and Neutralizing Antibody Response Against SARS-CoV-2 after Covishield and CovaxinTM Vaccination

ABSTRACT Introduction: This study was conducted to determine total and neutralizing antibody (nAb) titer in individuals at an interval of 2 and 6 months after primary vaccination and after 1 month after administration of booster dose. Materials and Methods: A serum sample was collected from 72 volunteers who were vaccinated with either the Covishield or CovaxinTM vaccine for quantitative estimation of human anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike immunoglobulin G (IgG) antibodies and nAb. nAb against SARS-CoV-2 was detected by GenScript (New Jersey, USA) and was quantitatively estimated by in-house developed enzyme-linked immunosorbent assay (ELISA). Results: Out of 72 study participants, 62.5% and 37.5% were male and female, respectively, and were in the age group of 21–83 years. About 94.44% of study volunteers were vaccinated with the CovishieldTM vaccine. Diabetes mellitus and hypertension were observed in 7.5% of volunteers. The average time interval between two doses of study vaccination was 37 days. Sixty-seven (93.18%), 50 (69.3%), and 69 (96.8%) (N = 72) volunteers elicited good nAb response at the end of 2 months, 6 months, and 1 month post-booster dose vaccination, respectively. Conclusion: Rapid nAb reaction to Spike protein development correlates with viral immunity for Covishield vaccine recipients. Due to the availability of limited data for the CovaxinTM vaccine, we are unable to compare the effectiveness of the two vaccinations, and we are also unable to analyze the vaccine’s efficacy.

A nucleoside-modified mRNA vaccine forming rabies virus-like particle elicits strong cellular and humoral immune responses against rabies virus infection in mice

ABSTRACT Rabies is a lethal zoonotic disease that threatens human health. As the only viral surface protein, the rabies virus (RABV) glycoprotein (G) induces main neutralizing antibody (Nab) responses; however, Nab titre is closely correlated with the conformation of G. Virus-like particles (VLP) formed by the co-expression of RABV G and matrix protein (M) improve retention and antigen presentation, inducing broad, durable immune responses. RABV nucleoprotein (N) can elicit humoral and cellular immune responses. Hence, we developed a series of nucleoside-modified RABV mRNA vaccines encoding wild-type G, soluble trimeric RABV G formed by an artificial trimer motif (tG-MTQ), membrane-anchored prefusion-stabilized G (preG). Furthermore, we also developed RABV VLP mRNA vaccine co-expressing preG and M to generate VLPs, and VLP/N mRNA vaccine co-expressing preG, M, and N. The RABV mRNA vaccines induced higher humoral and cellular responses than inactivated rabies vaccine, and completely protected mice against intracerebral challenge. Additionally, the IgG and Nab titres in RABV preG, VLP and VLP/N mRNA groups were significantly higher than those in G and tG-MTQ groups. A single administration of VLP or VLP/N mRNA vaccines elicited protective Nab responses, the Nab titres were significantly higher than that in inactivated rabies vaccine group at day 7. Moreover, RABV VLP and VLP/N mRNA vaccines showed superior capacities to elicit potent germinal centre, long-lived plasma cell and memory B cell responses, which linked to high titre and durable Nab responses. In summary, our data demonstrated that RABV VLP and VLP/N mRNA vaccines could be promising candidates against rabies.

Enhanced D614G and Omicron Variants Antibody Persistence in Infants at 2 Months of Age Following Maternal mRNA Booster Vaccination During Pregnancy or Postpartum

Background: Following maternal COVID-19 vaccination, the persistence of antibodies in sera and breast milk for mothers and infants is not well characterized. We sought to describe the persistence of antibodies through 2 months after delivery in maternal and infant serum and breast milk following maternal COVID-19 mRNA vaccination and to examine differences by receipt of booster dose during pregnancy or postpartum. Methods: This is a prospective cohort study with enrollment from July 2021 to January 2022 at 9 US academic sites. Pregnant or postpartum participants and their infants were enrolled after COVID-19 mRNA monovalent vaccination during pregnancy (primary 2-dose series) with booster (third dose) vaccination during pregnancy or within 2 months post-partum. SARS-CoV-2–binding and functional antibody responses at delivery and 2 months after delivery in mothers and infants were measured by spike and receptor-binding domain immunoglobulin (Ig) G, pseudovirus and live neutralizing antibody (nAb) titers to ancestral and Omicron BA.1 and BA.5 strains. Breast milk spike and receptor-binding domain IgG and IgA titers were also measured. Results: A total of 237 maternal/infant dyads were included (110 primary series during pregnancy, 99 pregnancy booster and 28 postpartum booster). A pregnancy booster resulted in 2.2-4.7-fold higher IgG and nAb at delivery and 2 months for both mothers and infants compared to the primary series alone (P &lt; 0.001 for all comparisons). While infant IgG and nAb titers decreased by 2 months of age, the proportion of infants with detectable nAb at 2 months was greater in infants of mothers boosted during pregnancy compared with primary series for all variants (D614G: 99% vs. 56%; BA.1: 56% vs. 4% and BA.5: 57% vs. 9%; P &lt; 0.001 for all comparisons). Breast milk spike IgA and IgG were present in 64%-100% and 100% of participants, respectively, and those boosted during pregnancy or postpartum had 3.1-4.6-fold higher levels of breast milk antibodies at 2 months compared to primary series during pregnancy (P &lt; 0.001). Conclusions: mRNA COVID-19 monovalent booster vaccination during pregnancy results in significantly higher maternal and infant serum–binding IgG and nAb titers compared to a primary 2-dose series, including against Omicron variants, through 2 months of age. Breast milk antibodies following maternal vaccination during pregnancy or postpartum may provide additional protection during early infancy.