Neutralizing Antibody Titers Research Articles

Foot-and-mouth disease virus antigenic landscape and reduced immunogenicity elucidated in atomic detail

Unlike most other picornaviruses, foot-and-mouth disease (FMD) intact virions (146S) dissociate easily into small pentameric subunits (12S). This causes a dramatically decreased immunogenicity by a mechanism that remains elusive. Here, we present the high-resolution structures of 12S (3.2 Å) and its immune complex of a single-domain antibody (VHH) targeting the particle interior (3.2 Å), as well as two 146S-specific VHHs complexed to distinct sites on the 146S capsid surface (3.6 Å and 2.9 Å). The antigenic landscape of 146S is depicted using 13 known FMD virus-antibody complexes. Comparison of the immunogenicity of 146S and 12S in pigs, focusing on the resulting antigenic sites and incorporating structural analysis, reveals that dissociation of 146S leads to structural alteration and destruction of multiple epitopes, resulting in significant differences in antibody profiles/lineages induced by 12S and 146S. Furthermore, 146S generates higher synergistic neutralizing antibody titers compared to 12S, whereas both particles induce similar total FMD virus specific antibody titers. This study can guide the structure-based rational design of novel multivalent and broad-spectrum recombinant vaccines for protection against FMD.

Persistence of West Nile Virus circulation in North-East region of India: A prospective facility-based study spanning over a decade.

To understand the distribution and presence of West Nile (WN) among the acute encephalitis syndrome (AES) patients, a prospective facility-based study was conducted over 13 years (2007-2019). During the period, 8957 patients hospitalized with AES in northeastern India were tested for the evidence of WN virus infection by IgM ELISA followed by Plaque reduction neutralization test (PRNT). Of the samples tested 324 (3.62%) were found positive for WN IgM antibodies and 73 paired sera showed a fourfold rise in neutralizing antibody titre by PRNT. The study establishes WN as a noteworthy cause of encephalitis in an erstwhile endemic area for Japanese encephalitis (JE). Therefore, it is important that WN is recognized as an important acute encephalitis syndrome (AES) causing aetiology in this region and the National centre for vector borne disease control (NCVBDC) guidelines for detection of AES may be modified accordingly. Thus, inclusion of WN in routine diagnosis, along with establishment of an integrative surveillance network with one-health approach will be important.

Truncated VZV gE Induces High-Titer Neutralizing Antibodies in Mice.

Backgrounds: A contemporary public health challenge is the increase in the prevalence rates of herpes zoster (HZ) worldwide. Methods: In this work, the gE gene structure was analyzed using bioinformatics techniques, and three plasmids of varying lengths, tgE537, tgE200, and tgE350, were expressed in Chinese hamster ovary (CHO) cells. These proteins were used to immunize BALB/c mice with Al/CpG adjuvant; ELISPOT and FCM were used to evaluate cellular immunity; and ELISA, VZV microneutralization, and FAMA assays were performed to detect antibody titers. Results: Target protein concentrations of 1.8 mg/mL for tgE537, 0.15 mg/mL for tgE200 and 0.65 mg/mL for tgE350 were effectively produced. The ability of the three protein segments to stimulate CD4+ and CD8+ T cells, as well as to cause lymphocytes to secrete IFN-γ and IL-4, did not significantly differ from one another. Both tgE537 and tgE350 were capable of generating VZV-specific antibodies and neutralizing antibodies, while tgE350 had the highest neutralizing antibody titer (4388). There was no equivalent humoral immune response induced by tgE200. Conclusions: The results of this investigation provide the groundwork for the creation of HZ recombinant vaccines using truncated proteins as antigens.

Mechanism of modified mRNA structure in COVID-19 vaccines for inducing neutralizing antibodies

The development of SARS-CoV-2 mRNA vaccines is closely linked to advancements in mRNA manufacturing technology. Structural modifications, such as replacing uridine with 1-methylpseudouridine (1mψ), enhance translation efficiency and help the mRNA evade immune detection. Lipid nanoparticles (LNPs) serve as an effective delivery system. Vaccines like BNT162b2 and mRNA-1273 target the receptor-binding domain (RBD) of the spike (S) protein, prompting B cells to produce neutralizing antibodies that block the RBD from binding to the Angiotensin-Converting Enzyme 2 (ACE2) receptor, preventing infection. These vaccines also stimulate adaptive immune responses by activating CD4+ and CD8+ T cells, with mRNA functioning as an endogenous antigen. Antigen-presenting cells (APCs) present the vaccine antigens via major histocompatibility complex (MHC) class I and II pathways, with CD8+ T cells recognizing MHC class I and destroying infected cells, while CD4+ T cells recognize MHC class II and assist in B cell maturation and antibody production. While mRNA vaccines have proven effective in neutralizing SARS-CoV-2, challenges remain, including the decline in neutralizing antibody titers over time and the emergence of new viral variants.

Preparation of bovine coronavirus virus-like particles and its immunogenicity in mice and cattle

The widespread prevalence of bovine coronavirus (BCoV) disease worldwide has impacted the livestock industry economically. No effective vaccine is available in China. In this study, we produced BCoV virus-like particles (VLPs) containing E, M, N, S, and hemagglutinin-esterase (HE) proteins using a baculovirus expression system. Five recombinant baculoviruses were co-infected with Sf9 cells, and the VLPs were assembled and characterized. Mice and cattle were immunized by VLPs mixed with MF59 and CpG 55.2 adjuvants. Two doses of the VLPs/MF59/CpG vaccine were administered in mice and cattle. The immune effect of the VLPs/MF59/CpG vaccine was measured using indirect ELISA and neutralization assays. After immunization, the serum IgG-specific antibody titer against S protein and neutralization antibody titer increased to 1:1.28 × 104 (p < 0.01) and 1:128 (p < 0.01) in mice, respectively. Interestingly, the high IgG antibody and neutralizing antibody titers were maintained for seven days in mice. In addition, the serum IgG-specific antibody titer against S proteins and neutralization antibody titer increased to 1:1.024 × 105 and 1:512 (p < 0.05) in cattle, respectively. The high IgG antibody and neutralizing antibody titers were maintained for 21 days in cattle. Notably, BCoV VLPs group interferon-gamma (IFN-γ) lymphocytes in spleens were significantly increased (p < 0.01). These findings suggest that BCoV VLPs induced strong cellular and humoral immune responses in mice and cattle. These findings suggest that BCoV VLPs could serve as a potent immunogen for vaccine development.

Neutralizing antibody titers after COVID-19 vaccination

BackgroundMonitoring COVID-19 and evaluating the effectiveness of prevention and control strategies are considered critical priorities in public health. As a result, the administration of COVID-19 vaccines has been widely approved around the world. In the current study, we investigated the level of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) neutralizing antibody (NAb) among individuals who received different COVID-19 vaccines. MethodsThis cross-sectional study recorded demographical data and clinical characteristics of 168 individuals who received COVID-19 vaccines from 2021 to 2022. Vaccination data of participants, including type and times of vaccine and any complications and symptoms after vaccination, were also recorded. SARS-CoV-2 NAb level was assessed by performing an ELISA test, and all data was analyzed using SPSS version 21. The significant level was set at 0.05. ResultsThe mean age of the participants was 40.4 ± 16 years, and 109 were females. About 18.4% of participants had the underlying diseases, of which thyroid diseases were the most frequent. The mean SARS-CoV-2 NAb level was 31.6 ± 39.78 ng/ml. Sinopharm was the common vaccine in our population, and AstraZeneca represented a high level of Nab 47.18 ng/ml. Among the participants, 96 had mild to severe complications after vaccination, with the most complaining of arm pain. Significant differences of NAb levele were observed only between types of vaccine and gender (P<0.05). ConclusionDue to our findings, all employed vaccines demonstrated efficacy in generating NAb. The levels of Nab were different among genders, age groups, and different types of vaccine receivers.

Immunogenicity analysis based on VP1 and VP2 proteins of bovine enterovirus

Bovine enterovirus (BEV) infection manifests as a spectrum of clinical signs affecting the respiratory, gastrointestinal, and reproductive systems in cattle. Outbreaks of this disease results in large economic losses to the bovine industry worldwide. Currently there are no efficacious vaccines and medicines to prevent BEV infection. In the present study, reverse transcription-polymerase chain reaction was used to amplify the VP1 and VP2 genes of BEV, enabling the synthesis of a chimeric recombinant protein which contained partial sequences from both proteins. Subsequently, the emulsified purified proteins with Freund’s adjuvant were used for triple-fold immunization of 4-week-old Institute of Cancer Research (ICR) mice. The mice were subsequently subjected to a challenge assay which elicited an immune response that was characterized by elevated titers of BEV-specific neutralizing antibodies. Notably, the results showed that the purification of pET32a-VP1 and pET32a-VP2 proteins markedly curtailed virus excretion and mitigated the histopathological damage usually associated with BEV infections. These were observed in the small intestines, kidneys and brain in infected animals. It also alleviated clinical symptoms such as hypothermia and weight loss. In summary, this study offers a theoretical and practical basis for BEV vaccine development.

New Engineered-Chimeric Botulinum Neurotoxin Mutant Acts as an Effective Bivalent Vaccine Against Botulinum Neurotoxin Serotype A and E.

Botulinum neurotoxins (BoNTs), including serotypes A and E, are potent biotoxins known to cause human poisoning. In addition to the critical protective antigen found in the full BoNT molecule, the receptor binding domain (Hc domain), BoNTs also harbour another essential protective antigen-the light chain-translocation domain (L-HN domain). Leveraging these pivotal protective antigens, we genetically engineered a series of inactivated chimeric molecules incorporating L-HN and Hc domains of BoNT/A and E. The structure of these chimeric molecules, mirror BoNT/A and E, but are devoid of enzyme activity. Experimental findings demonstrated that a lead candidate mEL-HN-mAHc harnessing the inactivated protease LCHN/E with the mutated gangliosides binding site Hc/A (mE-mA) elicited robust immune protection against BoNT/A and E simultaneously in a mouse model, requiring low immune dosages and minimal immunisations. Moreover, mE-mA exhibited high protective efficacy against BoNT/A and E in guinea pigs and New Zealand white rabbits, resulting in elevated neutralising antibody titres. Furthermore, mE-mA proved to be a more stable and safer vaccine compared to formaldehyde-inactivated toxoid. Our data underscore the genetically engineered mE-mA as a highly effective bivalent vaccine against BoNT/A and E, paving the way for the development of polyvalent vaccines against biotoxins.

Bison, Elk, and Other Captive Wildlife Species Humoral Immune Responses against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, has been found to infect various domestic and wild animal species. In this study, convenience serum samples from 575 bison, 180 elk, and 147 samples from various wildlife species collected between 2020 and 2023 from several regions in the United States were analyzed for the presence of SARS-CoV-2-specific antibodies. Two commercial ELISA assays based on the inhibition of the SARS-CoV-2 receptor-binding domain (sVNT) or the nucleocapsid protein (N-ELISA) of SARS-CoV-2 were used. Positive samples from the sVNT were additionally evaluated using a conventional virus neutralization test (VNT). Our results indicated that 1.2% of bison, 2.2% of elk, and 4.1% of the other wildlife species serum samples were seropositive in the sVNT, whereas 4.2% of bison, 3.3% of elk, and 1.4% of the other captive wildlife species serum samples tested positive by the N-ELISA. Among the sVNT serum samples, two samples from bison, one sample from elk, and five serum samples from other wildlife species (one cheetah, one gorilla, two lions, and one hippopotamus) had neutralizing antibody titers in the VNT, indicating these species are susceptible to SARS-CoV-2 infection. These findings highlight the importance of broad surveillance efforts for the effective monitoring of SARS-CoV-2 in non-human hosts.

Isolation and genetic characterization of canine adenovirus type 2 variant from raccoon dog (Nyctereutes procynoide koresis) in Republic of Korea

Canine adenovirus type 2 (CAV-2) is a common causative agent of respiratory disease in canines. There have been no reports of CAV-2 variants isolated from raccoon dogs. This study aims to investigate the biological and genetic characteristics of a novel Korean CAV-2 variant. Madin-Darby canine kidney cells were used to isolate the CAV-2 variant from 45 fecal swab samples. Diagnostic tools such as the cytopathic effect (CPE) assay, electron microscopy, polymerase chain reaction, and immunofluorescence and hemagglutination assays were used to confirm the presence of the CAV-2 isolate. A cross-virus neutralization assay was performed to verify the novelty of this CAV variant. Genetic analysis was performed using nucleotide sequences obtained through next-generation sequencing. The isolate was confirmed to be a CAV-2 variant based on the aforementioned methods and designated CAV2232. The number of bases in the fiber and E3 genes of CAV2232 were 1,626 and 414, respectively. Phylogenetic analysis of the fiber and E3 genes confirmed that CAV2232 was classified into a different clade from the known CAV-1 and CAV-2 strains. Mice inoculated with the CAV2232 vaccine developed high virus neutralization antibody titers of 1,024 (210) against CAV2232, while mice inoculated with CAV-1 and CAV-2 vaccines had low virus neutralization antibody titers of 12.9 (23.7) and 6.5 (22.7), respectively, against CAV2232. CAV2232 isolated from wild raccoon dog feces was classified as a novel CAV-2 variant. CAV2232 may therefore be used as an antigen for new vaccine development and serological investigations.

Evaluation of Tembusu virus single-round infectious particle as vaccine vector in chickens

Orthoflaviviruses are single-stranded RNA viruses characterized by highly efficient self-amplification of RNA in host cells, which makes them attractive vehicles for vaccines. Numerous preclinical and clinical studies have demonstrated the efficacy and safety of orthoflavivirus replicon vectors for vaccine development. In this study, we constructed Tembusu virus (TMUV) replicon-based single-round infectious particles (SRIPs) as vaccine development platform. To evaluate the potential of TMUV SRIPs as vaccines, we generated SRIPs that express the heterologous Fowl adenovirus 4 (FAdV-4) fiber2 protein and fiber2 head domain, named TMUVRP-fiber2 and TMUVRP-fiber2H, respectively. To assess the immunogenicity of the TMUV SRIPs, SPF chicks were intramuscularly inoculated twice. Our results showed that the TMUVRP-fiber2 vaccines elicited high levels of neutralizing antibodies. Challenge experiments showed that TMUVRP-fiber2 provided full protection against virulent FAdV-4 and significantly reduced viral shedding. Moreover, the immunogenicity of TMUVRP-fiber2H was significantly lower than that of TMUVRP-fiber2, which was reflected in the neutralizing antibody titer, survival rate, and virus shedding after challenge. Therefore, our results suggested that TMUV SRIPs are a promising novel platform for the development of vaccines for existing and emerging poultry diseases.

Comparison of Waning Antibody Responses After Natural Monkeypox Virus Infection and Mpox Vaccination Beyond 6 Months in South Korea

Abstract Natural Monkeypox virus infection induced significantly higher neutralizing antibody titers than Jynneos vaccination, with similar antibody decay rates beyond 6 months. Jynneos recipients with prior smallpox vaccination showed antibody levels comparable to mpox convalescents.

Neutralizing Antibody Immune Correlates for a Recombinant Protein Vaccine in the COVAIL Trial.

For COVAIL recipients of a COVID-19 Sanofi booster vaccine, neutralizing antibody titers were assessed as a correlate of risk (CoR) of COVID-19. Peak and exposure-proximal titers were inverse CoRs with covariate-adjusted hazard ratios (95% confidence intervals) 0.30 (0.11, 0.78) and 0.25 (0.07, 0.85) per 10-fold increase in weighted average titer.

Immunostimulatory/Immunodynamic model of mRNA-1273 to guide pediatric vaccine dose selection.

COVID-19 vaccines, including mRNA-1273, have been rapidly developed and deployed. Establishing the optimal dose is crucial for developing a safe and effective vaccine. Modeling and simulation have the potential to play a key role in guiding the selection and development of the vaccine dose. In this context, we have developed an immunostimulatory/immunodynamic (IS/ID) model to quantitatively characterize the neutralizing antibody titers elicited by mRNA-1273 obtained from three clinical studies. The developed model was used to predict the optimal vaccine dose for future pediatric trials. A 25-μg primary vaccine series was predicted to meet non-inferiority criteria in young children (aged 2-5 years) and infants (aged 6-23 months). The geometric mean titers and geometric mean ratios for this dose level predicted using the IS/ID model a priori matched those observed in the pediatric clinical study. These findings demonstrate that IS/ID models represent a novel approach to guide data-driven clinical dose selection of vaccines.

Variant-specific neutralising antibodies levels induced by the PHH-1 V SARS-CoV-2 vaccine (Bimervax®) by HIPRA

SARS-CoV-2 virus variants continue to emerge at an alarming rate due to spontaneous genetic mutations, particularly in the spike protein receptor-binding domain (RBD) portion, which render the virus more likely to escape immunity. So far, the immunity obtained through global primary and/or booster immunisation campaigns has been sufficient to protect the population from new emerging variants of the Omicron lineage. The current approach to update vaccines' antigen composition to new variants to boost immunity may not be sustainable in the long term. It might also be potentially redundant if the mutations are giving rise to variants which induce milder infections and existing vaccines, such as Bimervax®, are still sufficiently protective, as Covid is slowly becoming a seasonal illness. Through measuring neutralising antibody titres in sera from subjects boosted with Bimervax®, we have demonstrated the ability of Bimervax® to induce immune responses against a variety of SARS-CoV-2 variants, ranging from earlier variants inducing more serious infections to more recent variants which have been found to produce milder infections.

Time-course analysis of antibody and cytokine response after the third SARS-CoV-2 vaccine dose

The widespread administration of an additional dose of the SARS-CoV-2 vaccine has been promoted across adult populations, demonstrating a robust immune response against COVID-19. Longitudinal studies provide crucial data on the durability of immune response after the third vaccination. This study aims to explore the antibody response, neutralizing activity, and cytokine response against the SARS-CoV-2 ancestral strain (wild-type) and its variants during the timeline before and after the administration of the third vaccine dose. Anti-spike antibody titers and neutralizing antibodies blocking ACE2 binding to spike antigens were measured in 62 study participants at baseline, and on days 7, 21, and 180 post-vaccination. Cytokine levels were assessed at the same points except for day 180, with an additional measurement on day 3 post-vaccination. The analysis revealed no substantial variation in anti-spike antibody titer against the SARS-CoV-2 ancestral strain between the pre-vaccination phase and three days following the third dose. However, a significant nine-fold increase in these titers was observed by day 7, maintained until day 21. Although a decrease was observed by day 180, all participants still had detectable antibody levels. A similar trend was noted for neutralizing antibodies, with a four-fold rise by day 7 post-vaccination. At day 180, a diminution of neutralizing antibody titers was evident for both wild-type and all variants, including Omicron subvariant. A transient increase in cytokine activity, notably involving components of the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway, such as CXCL10 and IL-10, was observed within three days after the third dose. This study underscores a distinct amplification of humoral immune response seven days following the third SARS-CoV-2 vaccine dose and observes a decline in neutralizing antibody titers 180 days following the third dose, thus indicating the temporal humoral effectiveness of booster vaccination. A short-term cytokine surge, notably involving the JAK/STAT pathway, highlights the dynamic immune modulation post-vaccination.

Bats generate lower affinity but higher diversity antibody responses than those of mice, but pathogen-binding capacity increases if protein is restricted in their diet.

Bats are reservoirs of many zoonotic viruses that are fatal in humans but do not cause disease in bats. Moreover, bats generate low neutralizing antibody titers in response to experimental viral infection, although more robust antibody responses have been observed in wild-caught bats during times of food stress. Here, we compared the antibody titers and B cell receptor (BCR) diversity of Jamaican fruit bats (Artibeus jamaicensis; JFBs) and BALB/c mice generated in response to T-dependent and T-independent antigens. We then manipulated the diet of JFBs and challenged them with H18N11 influenza A-like virus or a replication incompetent Nipah virus VSV (Nipah-riVSV). Under standard housing conditions, JFBs generated a lower avidity antibody response and possessed more BCR mRNA diversity compared to BALB/c mice. However, withholding protein from JFBs improved serum neutralization in response to Nipah-riVSV and improved serum antibody titers specific to H18 but reduced BCR mRNA diversity.

Enhanced production of recombinant coxsackievirus A16 using a serum-free HEK293A suspension culture system for bivalent enterovirus vaccine development

Coxsackievirus A16 (CVA16) is one of the primary pathogens that causes hand, foot, and mouth disease (HFMD) in young children. In previous studies, CVA16 vaccine development has encountered several challenges, such as inefficient replication of the CVA16 virus in present culture systems, the induction of only mild neutralizing antibody titers, and neutralizing antibodies induced by certain vaccine candidates that are unable to protect against CVA16 viral challenge. In this study, we constructed a DNA-launched CVA16 infectious clone (CVA16ic) based on the genomic sequence of the CVA16 N5079 strain to minimize interference from viral quasispecies. The biochemical properties of this CVA16ic strain were similar to those of its parental strain. Serum-free HEK293A suspension cells, which produced higher virus titers than Vero cells, were demonstrated to improve CVA16 production yields. In addition, our study showed that inactivated EV-A71 antigens could enhance the immunogenicity of inactivated CVA16 mature/full particles (F-particles), suggesting that a bivalent CVA16 and EV-A71 vaccine may be an effective strategy for CVA16 vaccine development. These findings are expected to provide novel strategies and accelerate the development of bivalent HFMD vaccines.

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.

From bench to clinic: the development of VLA1553/IXCHIQ, a live-attenuated chikungunya vaccine.

Over the past 20 years, over 5 million cases of chikungunya, a mosquito-transmitted viral disease, have been reported in over 110 countries. Until recently, preventative strategies for chikungunya were largely ineffective, relying on vector control and individual avoidance of mosquito bites. This review outlines the preclinical and clinical efficacy and safety data that led to the approval of VLA1553 (IXCHIQ®), a live-attenuated vaccine against chikungunya disease. It also describes the innovative development pathway of VLA1553, based on an immunological surrogate of protection, and discusses ongoing and future post-licensure studies. In mice and non-human primate models, VLA1553 elicited high titres of neutralizing antibodies, conferred protection against wild-type chikungunya virus challenge and raised no safety concerns. A Phase 1 clinical trial of VLA1553 demonstrated 100% seroconversion among 120 healthy participants, with sustained neutralizing antibody titres after 12 months. These results and determination of a surrogate marker of protection led to advancement of VLA1553 directly into Phase 3 clinical development, as agreed with the US Food and Drug Administration (FDA) and the European Medicines Agency. The pivotal Phase 3 trial met its primary immunogenicity endpoint, achieving seroprotective levels based on immuno-bridging in baseline seronegative participants 28 days post-vaccination. These findings enabled submission of a Biologics License Application to the FDA for accelerated approval of VLA1553 in the US for adults aged ≥18 years. Ongoing and planned studies will confirm the clinical efficacy/effectiveness and safety of VLA1553 in adults and younger individuals, and will generate data in chikungunya endemic countries that have the highest unmet need. VLA1553 is the first vaccine approved for the prevention of chikungunya disease in adults, following accelerated development based on a serological surrogate marker of protection. VLA1553 adds to strategies to reduce the spread and burden of chikungunya in endemic populations and travellers.